development of an ammonia based pcc technology for ... of an ammonia based pcc technology for...

Development of an Ammonia Based PCC Technology for

Australian Conditions

Technical Report NO. 2

Hai Yu, Paul Feron, Leigh Wardhaugh, Graeme Puxty

CSIRO Energy Technology

PO Box 330, Newcastle, NSW 2300, Australia

Lichun Li, Marcel Maeder

Department of Chemistry, University of Newcastle, Callaghan, NSW 2308, Australia

Project Number: 3-0911-0142

Project Start Date: 15/06/2012

Project End date: 30/09/2015

The Report Period: 31/03/2013 - 30/09/2013

Energy Flagship

Development of an Ammonia Based PCC Technology for Australian Conditions-Technical Report No.2

2

Copyright and disclaimer

© 2013 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication

covered by copyright may be reproduced or copied in any form or by any means except with the written

permission of CSIRO.

Important disclaimer

CSIRO advises that the information contained in this publication comprises general statements based on

scientific research. The reader is advised and needs to be aware that such information may be incomplete

or unable to be used in any specific situation. No reliance or actions must therefore be made on that

information without seeking prior expert professional, scientific and technical advice. To the extent

permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for

any consequences, including but not limited to all losses, damages, costs, expenses and any other

compensation, arising directly or indirectly from using this publication (in part or in whole) and any

information or material contained in it.


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Acknowledgement

The authors wish to acknowledge financial assistance provided through both CSIRO Energy Flagship and

Australian National Low Emissions Coal Research and Development (ANLEC R&D). ANLEC R&D is

supported by Australian Coal Association Low Emissions Technology Limited and the Australian

Government through the Clean Energy Initiative. The authors are also grateful to Dr Allen Lowe, Dr

Anthony Callen and Dr Barry Hooper for review of this report and providing comments and suggestions.


4

Contents

1 Executive Summary 7

2 Recent Advancement of Solvent Development for Post-Combustion Capture 9

3 Introduction 15

4 Scope of the Project 18

5 Approaches and Methodologies 21

6 Results and Discussion 33

7 Impact of Research Achievements from This Project 48

8 Status of Milestones 53

9 Conclusions 56

10 Future work 57

List of Figures

Figure 1: Levelised cost of electricity (LCOE) for a new plant with and without CCS; (b) Incremental LCOE

with the amine based CCS. The estimated incremental LCOE with the advanced ammonia based CCS is

also included in (b) to demonstrate the potential benefits from using ammonia based CCS 15

Figure 2: Correlation of kg fitted by CO2 absorption into MEA solution 23

Figure 3: A schematic diagram of the wetted wall column facility 25

Figure 4: A diagram of the wetted wall column with the glass jacket (not to scale) 26

Figure 5: Gas and liquid mass transfer processes in wetted-wall column 27

Figure 6: CO2 absorption flux as a function of log mean of inlet and outlet of (PCO2-PCO2*) 28

Figure 7: Overall gas phase mass transfer coefficient in ammonia and monoethanolamine (MEA) at a

range of CO2 loadings 29

Figure 8: (a) CO2 partial pressure and NH3 concentration at the outlet of the wetted-wall column as a

function of time (NH3=1 wt%, CO2 loading=0.5); (b) NH3 concentration at the outlet of absorber as a

function of time at NH3 concentrations of 0.59–4.12 M and CO2 loading of 0.5 30

Figure 9: Overall mass transfer coefficients of CO2 as a function of promoters in the presence and

absence of 3 M ammonia at the temperature of 288 K. Promoters include Piperazine (PZ), 1 methyl

piperazine (1PZ), 2 methyl piperazine (2PZ), potassium salts of proline, sarcosine and taurine 34

Figure 10: Mass transfer coefficient of CO2 in the mixture of ammonia with amino acid salts as a

function of CO2 loading at the temperature of 288 K 35


5

Figure 11: Mass transfer coefficient of CO2 in the mixture of ammonia with piperazine and its

derivatives as a function of CO2 loading at the temperature of 288 K 35

Figure 12: (a) KG as a function of CO2 loading at different temperatures (283.15 to 298.15 K) and an NH3

concentration of 3 M; (b) Arrhenius plot for second-order rate constant for the forward reaction of NH3

and CO2 at an NH3 concentration of 3 M and CO2 loading verified from 0 to 0.5 36

Figure 13: (a) KG for CO2 in PZ solution at different temperature as a function of PZ concentration; (b)

Arrhenius plot for second-order rate constant for the reaction of PZ with CO2 at PZ concentrations of 0.1

to 0.5 M 37

Figure 14: Comparison of second-order rate constant for the reaction of PZ and CO2 as a function of

temperature 38

Figure 15: (a) KG as a function of NH3 concentration at 288.15 K with and without the addition of 0.3 M

PZ; (b) KG as a function of CO2 loading at 288.15 and 298.15 K and the NH3 concentration of 3 M with

and without the addition of 0.3 M PZ 39

Figure 16: KG as a function of PZ concentration at NH3 concentration of 3 M, CO2 loadings of 0.3 and 0.5

and temperature of 288.15 K 40

Figure 17: Speciation profile as a function of CO2 loading in 3 M NH3/0.3 M PZ at 288.15 K, predicted

results from e-NRTL PZ-NH3-CO2-H2O model in Aspen Plus V8.0 41

Figure 18: Polarity plot of the measured and calculated KG values 42

Figure 19: NH3 loss rate (a) and equilibrium partial pressure (predicted from e-NRTL PZ-NH3-CO2-H2O

model in Aspen Plus V8.0) (b) as a function of NH3 concentration at 288.15 K 43


model in Aspen Plus V8.0) (b) at different temperatures of 283.15–298.15 K as a function of CO2 loading

in 3 M NH3 44


model in Aspen Plus V8.0) (b) of NH3 solutions in the presence and absence of 0.3 M PZ as function of

CO2 loading at 288.15 K and 298.15 K 44


model in Aspen Plus V8.0) (b)as a function of PZ concentration in 3 M NH3 solutions, CO2 loadings of 0.3

and 0.5, 288.15 K 45

Figure 23: Comparison of the predicted equilibrium concentration profiles of NH3 related species in the

presence (dash line) and absence (solid line) of 0.3 M PZ, predicted form e-NRTL PZ-NH3-CO2-H2O model

in Aspen Plus V8.0 45

Figure 24: The predicted equilibrium profiles of NH3, PZ and PZCOO- in 3 M NH3 at CO2 loading of 0.3 as a

function of PZ concentration 46

Figure 25: Schematic flow-sheet of the CO2 absorbers in series 49


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List of Tables

Table 1: Recent development of the near term post combustion CO2 capture technologies .................... 9

Table 2: Summary of screening tests. Absorption temperature = 288 K (15oC) ..................................... 31

Table 3: Summary of solvents tested in the parametric study of CO2 absorption in piperazine and

ammonia blends ................................................................................................................................ 32

Table 4: Comparison of experimental and published values of second-order rate constant for the

reaction of NH3 and CO2 at four different temperatures....................................................................... 37

Table 5: Comparison between the experimental and calculated values of KG ....................................... 42

Table 6: Summary of rate-based model predictions and pilot plant trial results conducted under a

variety of experimental conditions ..................................................................................................... 50


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1 Executive Summary

This research project focuses on the development of the advanced aqueous ammonia based post

combustion capture (PCC) technology for significant reduction of CO2 emission from coal fired power

stations in Australia.

Currently, the commercially available PCC technology is mainly based on alkanol/alkyl amine solutions.

This technology will reduce the power plant efficiency by 25-30% and involve significant

capital/investment costs including the expensive flue gas desulfurization which is not installed in

Australian power plants. As a promising solvent, aqueous ammonia has many advantages over amine-

based capture technologies, including no degradation in the presence of O2, a higher CO2 absorption

capacity than monoethanolamine (MEA), a low regeneration energy. It also has a potential to capture

oxides of nitrogen (NOx) and sulphur dioxide (SO2) from the flue gas of coal-fired power plants, and to

produce value-added chemicals, such as ammonium sulfate and ammonium nitrate, which are commonly

used as fertiliser.

This research project is based on CSIRO PCC pilot plant trials with an aqueous ammonia based liquid

absorbent under real flue gas conditions in an 7M AUD pilot plant at Delta Electricity’s Munmorah power

station and ongoing work in this area. The pilot plant trials have confirmed the technical feasibility of the

process and confirmed some of the expected benefits. The pilot plant trials have also highlighted some of

the issues when using aqueous ammonia in a PCC process. These include a relatively low CO2 absorption

rate and high ammonia loss. These issues currently limit the economical feasibility of the aqueous

ammonia based PCC process.

The strategy of the research proposed here is to extend a number of novel approaches developed

previously by CSIRO to address the issues identified and make the process economically favourable. These

novel approaches to be further explored in this project include promotion of CO2 absorption rate through

the introduction of additives, in particular those stable and environmentally friendly additives, combined

removal of SO2 and CO2 and recovery of ammonia, and absorption under pressure to further enhance CO2

absorption and suppress ammonia loss. In addition, the research project will combine an experimental

and modelling approach to develop a rigorous rate based model for the aqueous ammonia based capture

process which allows for reliable process simulation, optimisation and scale up. The outcomes of this

research project will include the demonstration of the advanced aqueous ammonia based PCC at a CO2

capture rate of at least 10 kg/h with CSIRO’s process development facility in Newcastle. The advanced

technology is expected to achieve a CO2 absorption rate that is comparable with the standard MEA based

solution, limit the power plant efficiency loss below 20%, and achieve the combined removal of SO2 and

recovery of ammonia to produce ammonium sulphate and eliminate additional flue gas desulfurization

and reduce wash water consumption. The combined outcomes will enable the advanced technology to

achieve a significant reduction in incremental levelised cost of electricity compared to state of the art,

advanced amine based PCC technology.


8

This project is planned over a three-year time frame and is divided into 6 stages. This report summaries

the progress of the projects and presents the results obtained in stage 2.

6 promoters were elected in the screening tests on a wetted wall column. The promoters are Piperazine

(PZ), 1 methyl piperazine (1PZ), 2 methyl piperazine (2PZ), and potassium salts of proline, taurine and

sarcosine. Introduction of these 6 promoters except potassium salt of taurine can significantly enhance

CO2 mass transfer in the solvent. The overall gas phase mass transfer coefficients of CO2 in the blends are

significantly higher than those in ammonia alone and also higher than those in promoter alone. Extent of

increase of mass transfer coefficients with introduction of promoters depend on the nature of promoters

and their concentrations. Except the ammonia and taurine mixture, 3 M ammonia mixed with other

promoters can have a mass transfer coefficient more than double of those for ammonia alone at various

CO2 loadings.

A further parametric study of CO2 absorption in the mixture of ammonia and PZ was carried out to

understand the role of piperazine on the CO2 absorption process. The second-order rate constants for the

reactions of CO2 with PZ and NH3, which were determined based on the kinetic results from the wetted

wall column, agree reasonably well with published values. PZ has no catalytic effect on the absorption of

CO2. The enhancement by addition of PZ is due to the fast reaction of CO2 with PZ and PZ carbamate.

However, addition of PZ to aqueous NH3 increases the concentration of free NH3 in the solvent, thereby

increasing NH3 loss.

The milestones of the project for the report period have been achieved and the project is on track to

achieve the milestones which are due on 30 March 2014.


9

2 Recent Advancement of Solvent Development for Post-Combustion Capture

Post combustion capture (PCC) is a process that uses an aqueous absorption liquid incorporating

compounds such as ammonia or amine to capture CO2 from power station flue gases and many other

industrial sources. It is the leading capture technology as a result of the potential benefits, such as,

- It can be retrofitted to existing power plants or integrated with new infrastructure to achieve a

range of CO2 reductions, from partial retrofit to full capture capacity;

- It has a lower technology risk compared with other competing technologies;

- Renewable technologies can be integrated with PCC, for example, low cost solar thermal

collectors can provide the heat required to separate CO2 from solvents;

- PCC can be used to capture CO2 from a range of sources – smelters, kilns and steel works, as well

as coal- and gas-fired power stations.

Currently, the commercially available PCC technology is mainly based on alkanol/alkyl amine solutions. A

study by Dave et al. shows that retrofitting a monoethanolamine (MEA) based PCC plant to the

existing/new mechanical draft water cooled black coal fired plants will reduce the power plant efficiency

by 10 absolute percentage points and involves significant capital investment costs (Dave et al., 2011). The

research work has been intensified in recent years to improve the existing solvents or developed novel

solvents to reduce the capital and running costs of the PCC technologies. The report from Global CCS

institute summaries the status of near term PCC technologies up to Jan 2012 (Global CCS Institute, 2012).

This report presents the recent development of these near term technologies and novel PCC solvents at

early stages. Table 1 summarises the recent development of these near term technologies.

Table 1 Recent development of the near term post combustion CO2 capture technologies

Technology provider Solvent Comments

Fluor Econamine FG Plus Fluor’s Econamine FG PlusSM technology is claimed to

reduce steam consumption by over 30% compared to

‘generic’ MEA technology and has been used in more

than 25 commercial plants for the recovery of CO2

from flue gas at rates from 6 to 1000 metric tons per

day. The flue gas processed was mainly produced by

combustion of natural gas; four units use flue gas from

natural gas steam reformers.

Recently Fluor’s Econamine FG PlusSM technology has

been applied to demonstrate removal of carbon

dioxide from flue gas at E.ON’s Wilhelmshaven coal-


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fired power plant. The Wilhelmshaven carbon capture

pilot plant is designed for capturing 70 metric tons per

day when operating at full capacity. The plant has

been operated since October 2012. Over 1,400 hours

of operation had been achieved by January 2013

(Reddy et al., 2013).

MHI KS-1 sterically hindered

amine solvent

MHI KM-CDR process was employed in the world's

first integrated CCS project for flue gas from a coal-

fired power plant. At Plant Barry, CO2 capture

demonstration test has been successfully being

conducted since June 2011. The CO2 capture facility,

which was built jointly by MHI and Southern

Company, is the world's largest in scale and is able to

capture 500 metric tons per day, with CO2 recovery

efficiency above 90%. (Hirata et al., 2013). The

proprietary KS-1 high-performance solvent for CO2

absorption and desorption was jointly developed by

MHI and the Kansai Electric Power Co., Inc. Compared

with other CO2 capture technologies, the KM CDR

Process uses significantly less energy. MHI claims that

KM-CDR circulation rate is 60% of that for

(unspecified) MEA, regeneration energy is 68% of

MEA, and solvent loss and degradation are 10% of

MEA. MHI is working on process improvements that

are said to have potential to reduce the regeneration

heat requirement to 1860 kJ/kg CO2 from 2790 kJ/kg

CO2(Global CCS Institute, 2012).

Cansolv Cansolv chemical

solvents

As part of a retrofit of SaskPower's Boundary Dam 3

unit, a post combustion carbon dioxide (CO2) capture

facility based on Cansolv chemical solvent will be

installed to capture up to 1 million metric tons per

annum (Mtpa) of CO2 starting early 2014. Captured

CO2 in excess of that to be delivered to oil fields for

enhanced oil recovery will be injected into a deep

saline formation as part of the Aquistore Project .

In addition, Cansolv has recently developed a new

solvent, DC-201. Pilot plant trials showed the new

solvent can achieve a reduction of regeneration

energy consumption by 35% compared to MEA. The

new solvent will be tested in CANSOLV SO2 CO2

Demonstrated Plant in Wales, UK (Just, 2013).

Alstom Power Aqueous ammonia Alstom conducted a number of field tests of chilled


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ammonia process (CAP) and completed the

demonstration project at American Electric Power’s

Mountaineer Plant at end of May 2011 after a 21

month period The results shows the heat

requirement of 2.2 MJ/kg CO2 captured for the chilled

ammonia process (Jönssona and Telikapalli, 2012).

Gassnova awarded Alstom a concept study for a full-

scale CO2 capture plant to be located at Mongstad

near Bergen, Norway. The Alstom test plant recently

commissioned at TCM continues the overall validation

programme for CAP, demonstrating it to be a highly

efficient and cost effective process compared to

alternatives.

Babcock & Wilcox OptiCapTM Babcock & Wilcox Power Generation Group, Inc.

(B&W PGG) completed a three months test campaign

from September 2011 to December 2011 using

OptiCap solvent. The OptiCap solvent has many

benefits including low corrosivity, low regeneration

energy, and an expected high resistance to solvent

degradation. The solvent can reduce the regeneration

energy consumption by 26% compared to 30 wt%

MEA. In addition, it offers the ability to operate the

capture process at elevated pressures due to its

thermal stability, which will have a significant

favourable impact on mechanical compression energy

(Gayheart et al., 2013).

Aker Clean carbon

(ACC)

ACC proprietary

solvents

ACC has been testing its solvent on the CO2

technology Centre Mongstad since 2012. The results

are not available in the public domain at the time of

submission of this report (Andersson et al., 2013).

China Huaneng Clean

Energy Research

Institute(CERI)

Amines based solvents CERI operated one of the largest post combustion CO2

capture plant in the Shanghai Shidongkou No. 2 power

station since Jan 2010. The plant can capture 120,000

metric tons CO2 per annum. The reported capture

cost is US$30–35 per metric ton of CO2, including the

further expense of purifying the captured gas for use

in the food and beverage industry (Tollefson, 2011).

In addition to further development of the near term technologies, intensive research work has been

carried out to develop novel solvents. The focus of these researchers is primarily on increase in absorption

capacity and reduction of energy consumption of the solvents. These novel solvents include ionic liquids,

enzyme catalysed solvents, and phase change solvents.


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Ionic liquids are salts and consist of ions only. These chemicals have a melting point below 100 oC and have

gained a lot of attention as an alternative solvent for CO2 capture because of negligible volatility, high

thermal stability, non flammability, tunability and high CO2 solubility. However, the CO2 solubility is still

too low at post combustion capture conditions to compete with amine based solvents. In addition, the

selectivity of CO2, SO2 and other impurities to the ionic liquids and the toxicity of ionic liquids are not clear

(Ramdin et al., 2012).

Tertiary amine such as methyl diethanolamine (MDEA) or alkali carbonate solution including potassium

carbonate have relatively low heat of absorption with CO2, but these solvents have very low reaction

kinetics with CO2. The reaction of CO2 in these solutions can be promoted by introduction of the enzyme,

carbonic anhydrate (CA) as a catalyst. CA is found in the blood of humans and other mammals. It can

facilitate transfer of CO2 during respiration. Penders-van Elk et al studied the absorption of CO2 in MDEA

and sodium carbonate in the presence and absence of CA. The results suggest that CA can significantly

increase the kinetic of absorption (Penders-van Elk et al., 2013). CO2 solution claims that its enzyme

enabled carbon capture technologies at least one third less expensive than existing carbon capture

technology in terms of energy consumption. The technology can withstand the rigors of industrial

application (CO2 Solutions, 2013).

Phase change solvents refer to solvents which change from one liquid phase to two phases, either liquid-

liquid or liquid-solid during the capture process. French Institute of Petroleum developed a DMXTM process

and employed special solvents which are characterised by the formation of two immiscible phases for

given temperature and CO2 loading conditions. After the rich solvents go through the rich and lean heat

exchanger, the rich solvents become two phases, a water rich phase, with a very high CO2 loading and an

amine rich phase, with a very low CO2 loading. Only the water rich phase goes through the stripper. The

thermodynamic studies and associated process simulations show that the process can achieve a reboiler

duty as low as 2.1 GJ/t CO2 (Raynal et al., 2011). Agar et al. developed the thermomorphic biphasic solvent

(TBS) which exhibits a thermal induced liquid-liquid phase separation behaviour. Due to the limited

aqueous solubility of these lipophilic amines, a thermal induced miscibility gap arises upon modest

heating of the loaded solvents in the temperature range of 60-80oC. In comparison to conventional

alkanolamines such as MEA, the novel TBS system has exhibits several advantages, for instance, (i) high

net CO2 capacity, (ii) low required regeneration temperature, (iii) enhanced solvent regeneration,

(iv)moderate energy consumption and (v) satisfactory chemical stability (Zhang et al., 2013). Researchers

from TNO and SINTEF has investigated the amino acid salt based precipitating system and the preliminary

investigation has established the potential of precipitating amino acids as an energy effective alternative

to alkanol amines (Madan et al., 2013; Sanchez-Fernandez et al., 2013) .

The novel solvents mentioned above are still at the early stage development and have not been tested in

the pilot plant under the real flue gas conditions.


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The recent advancement of the solvent development indicates that the research efforts focus on the

development of the solvents which can significantly reduce the regeneration energy consumption and the

advanced solvents can achieve a heat requirement below 2 GJ/ t CO2.

References

Andersson, V., Wittmeyer, K., Gorset, O., Maree, Y., and Sanden, K. (2013), Operational experience and

initial results from the first test period at CO2 Technology Centre Mongstad, Energy Procedia, 37, 6348-

6356.

Dave, N., Do, T., Palfreyman, D., and Feron, P. H. M. (2011), Impact of liquid absorption process

development on the costs of post-combustion capture in Australian coal-fired power stations, Chemical

Engineering Research & Design, 89, 1625-1638.

Gayheart, J. W., Moorman, S. A., Parsons, T. R., and Poling, C. W. (2013), Babcock & Wilcox Power

Generation Group, Inc.’s RSAT™ process and field demonstration of the OptiCap™ advanced solvent at the

US-DOE's National Carbon Capture Center, Energy Procedia, 37, 1951-1967.

Hirata, T., Nagayasu, H., Kamijo, T., Kubota, Y., Tsujiuchi, T., Yonekawa, T., Wood, P., Ivie Ii, M. A., and

Nick, I. P. E. (2013), Project update of 500 TPD demonstration plant for coal-fired power plant, Energy

Procedia, 37, 6248-6255.

Global CCS Institute (2012), CO2 capture technologies - post combustion capture (PCC).

Jönssona, S., and Telikapalli, V. (2012), Chilled ammonia process installed at the Technology Center

Mongstad, The 11st International Conference on Greenhouse Gas Control Technologies (GHGT-11), Kyoto,

Japan, 18th-22nd November.

Just, P.-E. (2013), Advances in the development of CO2 capture solvents, Energy Procedia, 37, 314-324.

Madan, T., Van Wagener, D. H., Chen, E., and Rochelle, G. T. (2013), Modeling pilot plant results for CO2

stripping using piperazine in two stage flash, Energy Procedia, 37, 386-399.

Penders-van Elk, N. J. M. C., Hamborg, E. S., Huttenhuis, P. J. G., Fradette, S., Carley, J. A., and Versteeg, G.

F. (2013), Kinetics of absorption of carbon dioxide in aqueous amine and carbonate solutions with

carbonic anhydrase, International Journal of Greenhouse Gas Control, 12, 259-268.

Ramdin, M., de Loos, T. W., and Vlugt, T. J. H. (2012), State-of-the-art of CO2 capture with ionic liquids,

Industrial & Engineering Chemistry Research, 51, 8149-8177.

Raynal, L., Alix, P., Bouillon, P.-A., Gomez, A., de Nailly, M. l. F., Jacquin, M., Kittel, J., di Lella, A., Mougin,

P., and Trapy, J. (2011), The DMX™ process: An original solution for lowering the cost of post-combustion

carbon capture, Energy Procedia, 4, 779-786.

Reddy, S., Scherffius, J. R., Yonkoski, J., Radgen, P., and Rode, H. (2013), Initial results from Fluor's CO2

capture demonstration plant using Econamine FG PlusSM technology at E.ON Kraftwerke's Wilhelmshaven

power plant, Energy Procedia, 37, 6216-6225.

Sanchez-Fernandez, E., Mercader, F. d. M., Misiak, K., van der Ham, L., Linders, M., and Goetheer, E.

(2013), New process concepts for CO2 capture based on precipitating amino acids, Energy Procedia, 37,

1160-1171.


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CO2 Solutions. (2013), CO2 solutions says its enzyme technology cuts CCS costs by a third, in Carbon

capture journal, http://www.carboncapturejournal.com/ViewNews.aspx?NewsID=3360, access on 27

November 2013.

Tollefson, J. (2011), Low-cost carbon-capture project sparks interest, Nature, 469, 276-277.

Zhang, J., Qiao, Y., Wang, W., Misch, R., Hussain, K., and Agar, D. W. (2013), Development of an energy-

efficient CO2 capture process using thermomorphic biphasic solvents, Energy Procedia, 37, 1254-1261.


15

3 Introduction

PCC is one of the leading capture technologies for significant reduction of CO2 emission from coal fired

power stations. Currently, the state of the art PCC technology is based on amine solutions, MEA in

particular. A report by US Department of Energy (Ramezan, 2007) shows that the advanced amine

technology will reduce the power plant efficiency by 30% and involve significant capital investment costs

for retrofitting an existing coal fired power station (Conesville unit 5 in Ohio, subcritical, 90% capture). The

incremental levelized cost of electricity (LCOE) is estimated to USD $69/MWh. Recent studies of low CO2

emission technologies for power generation in the Australian context (EPRI, 2010) show that addition of

an advanced amine PCC process (state of the art) and CO2 transport and storage to a new coal fired power

station (pulverised black coal, supercritical, 750 MW sent out) will lead to a decrease in plant efficiency

from 38% to 28.4 % (25.3% decrease) and an increase in LCOE from 77 AUD/MWh to 167 AUD/MWh

(Figure 1 a). As shown in Figure 1b, the significant increase is due to increase in capital (plant cost), fuel,

O&M and CO2 transport and storage. The capital cost increase accounts for almost 60% of the total

incremental LCOE. High capital costs are due to the fact that the new plants have to process more than

33% of coal extra to have the same power output and need to remove a large amount of CO2 from an

even larger amount of flue gas and compress it. This involves an increase in the size of the existing

equipment and introduction of flue gas desulfurization (FGD) unit and CO2 capture and compression

facilities.

Figure 1 (a) Levelised cost of electricity (LCOE) for a new plant with and without CCS; (b) Incremental

LCOE with the amine based CCS. The estimated incremental LCOE with the advanced ammonia based

CCS is also included in (b) to demonstrate the potential benefits from using ammonia based CCS

The advanced amine solvent has poor SOX tolerance which requires a deep cut in SO2 content to levels

below 10 ppm. The cost of building a desulfurization unit is substantial. According to the EPRI report, in a

new plant in Australia in which the bare erected capital cost increase due to CO2 removal and compression

is AUD 888M AUD while capital increase due to clean up costs (installation of FGD) is AUD 90 M AUD

(EPRI, 2010). FGD alone will count for more than 9% of the increased capital costs.

Leve

lised

co

st o

f e

lectr

icity

AU

D/M

Wh

0

20

40

60

80

100

120

140

160

180

Capital

O&M

Fuel

CO2 T&S

Pulverised black coalno CCS, no SOx

Pulverised black coalamine CCS + SOx

(a)

Incre

menta

l le

velis

ed c

ost of ele

ctr

icity

AU

D/M

Wh

0

20

40

60

80

100

Capital

O&M

Fuel

CO2 T&S

Pulverised black coalamine CCS + SOx

Pulverised black coalammonia CCS + SOx

(b)


16

It is clear that to make CCS technologies, and in particular PCC, economically more feasible, the research

focus will be on the reduction of capital costs by using more efficient, smaller and cheaper units and

development of solvents which require low parasitic energy consumption and thus consume less coal and

have less gas to treat which results in a smaller facility, and have less environmental and health effects. In

this context, the current submission is proposed, aiming at the development of advanced aqueous

ammonia based PCC to achieve a significant cost reduction and reduce environmental risks.

Advantages of aqueous ammonia based PCC

Aqueous ammonia is a promising emerging solvent for CO2 capture. Compared to other amines, ammonia,

as one of the most widely produced chemicals in the world, is a low cost solvent, does not degrade in the

presence of O2 and other species present in the flue gas, and is less corrosive. The environmental and

health effects of ammonia are well studied and are more benign than amines. Ammonia has a high CO2

removal capacity and a low regeneration energy. It also has the potential of capturing multiple

components (NOx, SOx, CO2 and Hg) (Ciferno, 2005) and producing value added products such as

ammonium sulphate and ammonium nitrate, which are widely used as fertilisers. This potential is of

particular interest to Australian power stations since desulfurization and DeNOx are not implemented in

Australia. It has been estimated by Powerspan (MacDowell, 2009) that the power plant efficiency loss is

below 20% for an ammonia based capture process. A scoping study by US Department of Energy (Ciferno,

2005) suggested that the incremental cost of electricity using ammonia is less than half of that using

traditional amines. It has to be pointed out that these reports assumed the availability of low temperature

cooling water for solvent and flue gas cooling and recovery of ammonia. In Australia where ambient

temperature is generally high, the energy consumption for production of low temperature cooling water is

expected to be high, thus partially offsetting the energy saving from the solvent regeneration.

CSIRO has identified the aqueous ammonia based technology as a promising low cost technology for

significant reduction of multiple components emissions from coal fired power stations in Australia. CSIRO

and Delta Electricity completed pilot plant trials of the aqueous ammonia based capture technology under

the real flue gas conditions in 7M AUD pilot plant scale research facility at Delta’s Munmorah Power

Station in 2010. The pilot plant trials have confirmed the benefits and technical feasibility of the process

and its potential for application in the Australian power sector. The benefits include high CO2 removal

efficiency (more than 85%) and production of high purity of CO2 (99-100 vol%), and effectiveness of the

combined SO2 removal (more than 95%) and ammonia recovery, high stability of ammonia solvent and

low regeneration energy. Part of the results were published in a number of conferences and journal

papers (Yu, 2011a and 2011b). It is the first time that results from an actual aqueous ammonia plant

operating on real flue gases have been published.

Areas for improvement

The pilot plant trials have identified a number of research opportunities to further develop aqueous

ammonia based capture technologies.


17

Relatively low CO2 absorption rate compared to amine based solvent, which results in 2-3 times

the number of absorbers compared to monoethanolamine (MEA, the benchmark solvent) and

thus higher capital costs.

Relatively high ammonia loss at high CO2 absorption rate. The consumption of wash water is high.

Operating the desorption process in a similar pattern to regular amine processes will result in the

formation of ammonium-bicarbonate solids in the condenser, resulting in blockage.

The available process simulation models were insufficient to support the process optimisation and

scale up.

This limits the economical feasibility of the aqueous ammonia based PCC process. In this research project,

CSIRO will collaborate with the University of Newcastle and Curtin University of Technology (by way of

student exchange or other collaboration), exploring and evaluating novel approaches and concepts to

further advance the aqueous ammonia based PCC process in Australian context.

References

Ciferno J., Philip D., Thomas T., 2005. An economic scoping study for CO2 capture using aqueous ammonia.

Final Report - DOE/NETL.

EPRI, 2010. Australian electricity generation technology costs-reference case 2010.

McLarnon C.R., Duncan J.L., 2009. Testing of ammonia based CO2 capture with multi-pollutant control

technology, Energy Procedia, 1, 1027-1034.

Ramezan M., Skone T.J., Nsakala N.Y., Liljedahl G.N, 2007. Carbon dioxide capture from existing coal-fired

power plants, DOE/NETL-401/110907.

Yu H., Morgan S., Allport A., Do T., Cottrell A., McGregor J., Wardhaugh L., Feron P., 2011a. Results from

trialling aqueous ammonia based post combustion capture in a pilot plant at Munmorah Power Station:

Absorption, Chemical Engineering Research and Design, 89, 1204-1215.

Yu H., Morgan S., Allport A., Do T., Cottrell A., McGregor J., Feron P., 2011b. Results from trialling aqueous

ammonia based post combustion capture in a pilot plant at Munmorah Power Station, Energy Procedia, V

4, 1294-1302, 10th International Conference on Greenhouse Gas Control Technologies.

http://www.sciencedirect.com/science/journal/18766102

http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%2359073%232011%23999959999%233065790%23FLP%23&_cdi=59073&_pubType=J&view=c&_auth=y&_acct=C000056895&_version=1&_urlVersion=0&_userid=2322062&md5=e3ebadcf6a7e0031d7e6c92857901d7b



18

4 Scope of the Project

This research project will further develop a promising aqueous ammonia (NH3) based post combustion

capture (PCC) process to achieve a significant reduction of investment and running cost in the Australian

context and reduce potential environmental risks resulting from the implementation of PCC technologies.

The objectives of the project are:

1. Develop a novel aqueous ammonia based solvent which has fast CO2 absorption rate equivalent to

MEA while maintaining a low regeneration energy requirement.

2. Further advance the combined SO2 removal and ammonia recovery technology to eliminate

additional FGD, reduce the ammonia slip in the exiting flue gas to acceptable levels and produce a

value added fertiliser, i.e. ammonium sulphate.

3. Further develop CSIRO technology (patent application no WO/2010/020017) to enhance CO2

absorption, reduce ammonia loss and cooling water consumption.

4. Develop and validate a rigorous rate based model for the capture process which will guide process

modification to achieve further savings on capture costs.

The research proposed here is to extend a number of novel approaches developed previously by CSIRO to

address the issues identified, achieve the project objectives and thus make the process economically

favourable. The new ideas and approaches include;

Promotion of CO2 absorption rate through addition of promoters. Ammonia has been confirmed as a

high loading capacity solvent and has a theoretically 1:1 ratio with CO2 on a molar basis. It has been

reported in a study by DOE (Ciferno, 2005) that the CO2 carrying capacity in g CO2 per g of ammonia

solution (8 wt.%) circulated is 0.07 as compared with 0.036 g CO2 per g MEA solution (20 wt.%). However,

the CO2 absorption rate is much lower in ammonia than in MEA, as identified by our recent pilot plant

investigation (Yu, 2011a). This is preventing ammonia of achieving its high loading capacity and low

regeneration energy potential.

The CO2 absorption flux within the column can be correlated by NCO2= KGA(PCO2-P*CO2), where NCO2 is CO2

absorption flux, KG mass transfer coefficient, PCO2 partial pressure of CO2 in the flue gas, P*CO2 CO2

equilibrium partial pressure in the solvent and A, effective interfacial surface area. For a given CO2

absorption flux to achieve a typically 85-90% CO2 removal efficiency, KG and (PCO2-P*CO2), need to be high

in order to reduce A, which is directly related to the size of column (capital cost).

Recent studies by CSIRO showed that with introduction of a small amount of additive such as an amino

acid salt which is environmentally friendly, stable and cheap, the CO2 mass transfer coefficients increase

significantly (Yu, 2012). With the introduction of 0.3 M additive to 3 M ammonia, the mass transfer

coefficients increase dramatically compared to ammonia alone. They are comparable with MEA at high

CO2 loadings which are relevant to industrial applications. It is expected that further tests of new additives

and optimisation of the solvent will lead to the development of the novel ammonia based solvent with

high mass transfer coefficients which match and are even high than those for MEA while maintaining its

low regeneration energy.


19

The promotion of CO2 absorption in ammonia is relatively new and the mechanism involved is unknown.

Recently CSIRO has developed a new software tool in Matlab® to model CO2 absorption into aqueous MEA,

PZ, ammonia and binary mixtures of PZ with AMP or ammonia (Puxty, 2011). The tool solves partial

differential and simultaneous equations describing diffusion and chemical reaction automatically derived

from reactions written using chemical notation. It has been demonstrated that by using reactions that are

chemically plausible the mass transfer in binary mixtures can be described by combining the chemical

reactions and their associated parameters determined for single amines. The observed enhanced mass

transfer in binary mixtures can be explained through chemical interactions occurring in the mixture

without need to resort to using additional reactions or unusual transport phenomena (e.g. the shuttle

mechanism). Such a tool in conjunction with a stopped flow reactor at the University of Newcastle will

help elucidate the promotion mechanism (Wang, 2011).

Combined removal of SO2 and recovery of ammonia. This research project also tests a hypothesis that an

integrated approach can be used to achieve the combined removal of SO2 and recovery of ammonia. In

this approach, as described in our publication (Yu, 2011a), the wash water is circulated between the pre-

treatment column (before absorber) and wash column (after absorber). Ammonia recovered from the flue

gas in the wash column is used to capture SO2 in the pre-treatment column. The results from the pilot

plant trials have demonstrated the effectiveness of the approach. More than 95% SO2 in the flue gas and

more than 80% ammonia which slips to flue gas in the absorber can be removed from the gas phase by

the wash water. The removal of SO2 from flue gas by ammonia is the established technology and its

fundamentals have been well documented (Kohl, Nielsen, 1997). Ammonia has a strong affinity for SO2,

thus permitting a compact absorber with a very low liquid-to-gas ratio. The high-purity, high-market value

ammonium sulphate crystals were successfully compacted into a premium granular by-product. The

combined removal of SO2 and ammonia has a potential of reducing or offsetting the cost involved for

removal of SO2 and ammonia with production of saleable ammonium sulphate. The focus of the research

project is to identify conditions under which SO2 and ammonia are selectively removed at high efficiencies

in preference to CO2, understand the mechanism involved for oxidation of sulphite to sulphate, and

explore more efficient methods for separation of ammonium sulphate from the aqueous ammonia

solvent.

Absorption under pressure. This research project will also further develop a new concept developed by

CSIRO. The flue gas is pressurised and absorption of CO2, SO2 and recovery of ammonia can take place

under pressure. The flue gas cooling requirement is provided by the expansion of the flue gas after

pressurisation. It is well known that pressurisation of flue gas will lead to high energy penalties but the

size of absorption columns and ammonia loss as well as energy consumption for production of cooling

water can be reduced significantly. In the Australian context, capital costs are the major contributors to

the capture costs while fuel contribution is relatively small. The proposed high pressure absorption

experiments and the rigorous process model to be developed will allow an evaluation of the feasibility of

the concept and its economic viability.

Development of rate based absorption model. The available process simulation models were insufficient

to support the process optimisation and scale up. The project will develop a rigorous rate based model for

the advanced aqueous ammonia based capture process and validate the model with results from previous

pilot plant trials and from experiments with the CSIRO’s processes development facility. The developed

model will be used to evaluate novel process concepts such as rich solvent recycle in the absorber and

identify approaches to further reduce ammonia loss and energy and water consumption.


20

The research plan has been developed to carry out the proposed research activities. The project is

planned over three year and divided into 6 stages with each stage being approximately 6 months. This

report is the progress report of Stage 2 of the project.

References

Ciferno J., Philip D., Thomas T., 2005. An economic scoping study for CO2 capture using aqueous ammonia.

Final Report - DOE/NETL.

EPRI, 2010. Australian Electricity Generation Technology Costs-Reference Case 2010.

Kohl. A. L, Nielsen R. B., 1997. Gas purification, 5th Ed, Gulf Professional Publishing.

Puxty G., Rowland R., Attalla M., 2011. Describing CO2 mass transfer in amine/ammonia mixtures — No

shuttle mechanism required, Energy Procedia, 4, 1369-1376.

Wang X.G., Conway W., Fernandes D., Lawrance G., Burns R., Puxty G., and Maeder M., 2011. Kinetics of

the reversible reaction of CO2(aq) with ammonia in aqueous solution. Journal of Physical Chemistry, A.

115, 6405–6412.

Yu H., Morgan S., Allport A., Do T., Cottrell A., McGregor J., Wardhaugh L., Feron P., 2011a. Results from

trialling aqueous ammonia based post combustion capture in a pilot plant at Munmorah Power Station:

Absorption, Chemical Engineering Research and Design, 89, 1204-1215.

Yu H., Morgan S., Allport A., Do T., Cottrell A., McGregor J., Feron P., 2011b. Results from trialling aqueous

ammonia based post combustion capture in a pilot plant at Munmorah Power Station, Energy Procedia, V

4, 1294-1302, 10th International Conference on Greenhouse Gas Control Technologies.

Yu H, Xiang Q, Fang M, Qi Y and Feron P., 2012. Promoted CO2 absorption in aqueous ammonia.

Greenhouse Gases: Science and Technology 2, 1-9.


http://www.sciencedirect.com/science?_ob=PublicationURL&_hubEid=1-s2.0-S1876610211X00036&_cid=277910&_pubType=JL&view=c&_auth=y&_acct=C000056895&_version=1&_urlVersion=0&_userid=2322062&md5=80cfe23bb55f99327ca8ff37e26584d4





21

5 Approaches and Methodologies

(1) Choice of promoters

The screening tests were carried out to evaluate the performance of various promoters in the aqueous

ammonia based CO2 capture processes. The preliminary screening tests of a number of promoters showed

that piperazine (PZ), potassium salts of proline and sarcosine have a great potential of promoting CO2

absorption in aqueous ammonia. So these three promoters were selected for further studies. In addition,

we also selected 1 methly piperazine (1PZ), 2 methyl piperazine (2PZ) and potassium taurinate. 1PZ and 2

PZ have the similar properties to piperazine but they have a higher solubility in water than piperazine.

Taurine reacts with CO2 at a slower rate than proline and sarcosine, but it has a lower pKa value than

these two amino acids and even ammonia. In the CO2 absorption process, ammonia or additives will react

with CO2 to form an intermediate –Zwitterion whch will be deprotonated by a base to form a carbamate

ions, as shown in Absorption chemistry and Kinetics Section below. A base with a low pKa will more easily

accept the proton. If the promoter has a lower pKa, the proton released will be taken by ammonia rather

than promoters. As a result, more promoters will be available compared to the case in which an additive

with a higher pKa value is used and the enhancement is expected to be pronounced.

(2) Absorption chemistry and kinetics

Overall rate constant (kov) for CO2 absorption

The reaction of CO2 with primary and secondary amines (RNH2), including NH3, amino acid salt and PZ, can

be described by a Zwitterion mechanism, as shown below:

(R1)

(R2)

Where B represents any base present in the solution; it can be molecule of amine, water or a hydroxide

ion. PZ is a diamine which enables the formation of both single and dicarbamate, as shown by the

following reactions:

(R3)

(R4)

In addition to the above reactions, the reaction of CO2 with a hydroxy ion can also contribute to CO2

absorption.

2

2

k

2 2 2kCO RNH RNH COO

B

B

k

2 kRNH COO B RNHCOO BH

2,PZ

2,PZ

k

2 kCO PZ PZ COO

2,PZCOO

2,PZCOO

k

2 2kCO PZCOO PZ (COO )


22

(R5)

At quasi-steady state, the overall chemical rate of absorption of CO2 by amine (2cor ) is given by:

(1)

When deprotonation is almost instantaneous, as compared to the reverse reaction in Eq. (R2), k-2 << kBCB,

and zwitterion formation is rate-determining. In addition, the concentration of OH– is very small and the

contribution of reaction (R3) to CO2 absorption is negligible. Eq. (1) becomes:

(2)

The overall reaction is of the first order with respect to both CO2 and amine; hence, k2 is the second-order

rate constant15.

Overall gas phase mass transfer coefficient (KG)

The mass transfer taking place in the wetted-wall column can be described as a combination of CO2

diffusion and chemical reaction processes. The CO2 absorption rate of a chemical solvent within a wetted

wall column can be calculated by Eq. (3):

(3)

Where 2COr is the CO2 absorption rate, mmol/s; GK is the overall mass transfer coefficient,

mmol/(s·m2·kPa); 2COP is the partial pressure of CO2 in the flue gas, kPa; 2

*

COP is the CO2 equilibrium

partial pressure in the solvent, kPa; and A is the effective interfacial surface area, m2.

1/KG represents the global resistance, and is related to the gas side resistance (1/kg) and liquid side

resistance (1/kL) by Eq. (4) :

(4)

Gas side mass transfer coefficient (kg)

Pacheco (1998) developed an empirical 2-parameter model, as shown in Eq. 5.

(5)

Where

2

g

Gas

CO

RTk dSh

D ,

dNRe

,

2

Gas

CO

ScD

, ρ is the density of the gas, μ is the dynamic viscosity, d

is the hydraulic diameter of the annulus, which is equal to the gap between the radii of the inner glass

jacket and the central column (d=5.5 mm); h is the height of the central column (h=10.32 mm), and N is

the mean gas velocity. 2

Gas

COD is the CO2 diffusion constant in gas phase, which can be calculated using the

following equation (Gilliland, 1934):

OHk

2 3CO OH HCO

2 2

2 2 2

CO RNH

CO CO ov COOH OH2 2 2 B B

C Cr k C C k C

1/ k (k / k )(1/ k C )

2 2 2 2CO ov CO 2 CO RNHr k C k C C

2 2 2

*

CO G CO COr K A(P P )

G g L

1 1 1

K k k

dSh (Re Sc )

h


23

2

Gas

COD =

1

5 1.5 2

A B

1 1

23 3A B

1 14.36 10 T ( )

M M

P[( ) ( ) ]

(6)

Where, T is the temperature, K; Mi is the mass weight of i (A or B), g/mol; νi is the molecular volume of i at

the normal boiling point ( A and B are equal to 34 and 31.2, respectively. ), cm3/mol; and P is the total

pressure, kPa.

We adopted the same approach to determine the parameters for calculation of kg. The absorption

temperature was 10–40 °C, the flow rate of CO2 and N2 gas mixture was 1.5–7 L/min, and CO2 partial

pressure in the gas mixture was up to 5 kPa. The results for kg are fitted in Figure 2 and the value of the

parameters for the calculation of kg were determined, with α equal to 1.44 and β equal to 1.17.

Re.Sc.d/h

2 4 6 8

Sh

0

2

4

6

8

10

12

14

16

18

y=1.44x1.17

R2=0.9543

Figure 2 Correlation of kg fitted by CO2 absorption into MEA solution

Liquid side mass transfer coefficient (kL)

If the pseudo first-order regime applies to the reaction of CO2 with ammonia or PZ, kL can be calculated

by:

(7)

When CO2 is absorbed in the PZ/NH3 blended solutions, PZ, piperazine carbamate (PZCOO–) and NH3 can

react with CO2 to form carbamates. The reaction rate constant for the reaction of PZCOO– with CO2

(k2,PZCOO-) was assumed to equal to one quarter of

2,PZk (Dang and Rochelle, 2001). Based on the pseudo

first order assumption, kL in PZ and NH3 blended solutions was calculated according to Eq. (8):

2

2

ov CO

L

CO

k Dk

H


24

(8)

Physical properties of aqueous NH3 solutions, such as Henry’s Law constant, 2COH , and diffusion constant

for CO2, 2COD , are required for the calculation of kL. Henry’s Law constants for CO2 in loaded NH3 solutions

and loaded mixtures of NH3 and PZ are not available in the literature; we assume it is equal to that of pure

water, considering the low concentration of additives and NH3 in the solution. The correlation for the

calculation of Henry’s law constant of CO2 in water is estimated from Eq. (9) (Versteeg et al., 1996):

2COH =

2044

6 T2.82 10 e

(9)

The diffusion constant of CO2 in both loaded NH3 solutions and loaded NH3 and PZ blended solutions is

determined from the Stokes–Einstein equation, (Eq. (10)) (Derks and Versteeg, 2009):

(10)

The viscosities of NH3 solutions and NH3 and PZ blended solutions were measured by an AMVn automated

microviscometer from Anton Paar, with viscosity ranging from 0.3 to 2500 m·Pa·s. The measurement is

based on the “rolling ball” principle. The sample to be measured is introduced into a glass capillary in

which a steel ball rolls. The visicoty of the liquid can be determined by measuring the rolling time of the

steel ball. The diameters of the capillary and ball used in the measurements are 1.6 mm and 1.5 mm with

viscosity measure range of 0.3–10 m·Pa·s. The viscosities of PZ solutions were taken from Qin et al. (2010).

The diffusion constant of CO2 (m2/s) in pure water was calculated with the correlations given by Versteeg

and Swaaij (1988).

2

2

H O

COD =2119

6 T2.35 10 e

(11)

(3) Wetted wall column facility for measurement of overall gas phase mass transfer coefficient (KG) and

ammonia loss

The screening tests were carried out on a wetted wall column facility. KG and ammonia loss rate were

obtained from these tests. The KG values are used to assess the CO2 absorption kinetics in the solvents.

Figure 3 shows a schematic diagram of the wetted wall column facility. It consists of a gas mixing system

for producing a gas mixture of N2 and CO2, a water bath for controlling absorption temperature, a solvent

reservoir, a wetted wall column for gas liquid contact, an ammonia scrubber for removal of ammonia in

the gas phase and gas analysers for measurement of CO2 and ammonia concentration in the flue gas.

3 32

2 2

2,NH NH 2,PZ PZov CO 2,PZCOO PZCOO

L

CO CO

k C k C k Ck Dk

H H

2

3 2

2 2 3

H ONH H O 0.8

CO CO NHD D ( )


25

The key part of the facility is the wetted wall column for gas-liquid contact. Figure 4 show a diagram of the

wetted wall column with the glass jacket. The column was made from a stainless-steel tube and was

10.32 cm in height and 1.27 cm in diameter with a known surface area of 41 cm2. The solvent stored in a

solvent reservoir was pumped through the inside of the column and overflowed through a number of

holes at the top of the column and fell along the outside surface of the column. The liquid flow rates for

the solvent were controlled at 100–120 ml/min by a rotameter to enable the formation of a thin and

ripple free film on the surface of the column. A K-type thermocouple (±1°C) was used to measure the

temperature of the liquid inside the column. A glass gasket was used to enclose the reaction chamber and

had an inside diameter of 2.32 cm and outside diameter of 4.24 cm. The flow rate of N2 and CO2 were

controlled by mass flow controllers and the gas was well mixed and bubbled through a saturator which

was placed in the water bath. The gas mixture of CO2 and N2 was introduced from the bottom of the

column and moved upwards, passing the outer column surface before being exhausted from the top. The

CO2 mass transfer procedure is illustrated in Figure 5.

Figure 3 A schematic diagram of the wetted wall column facility


26

Figure 4 A diagram of the wetted wall column with the glass jacket (not to scale)

Thermocouple

Solvent in

Solvent out Gas in

Gas out

Liquid film

Column

Glass jacket

Cooling water out

Cooling water in


27

Figure 5 Gas and liquid mass transfer processes in wetted-wall column

Since ammonia itself is volatile and will inevitably slip to the gas during the wetted wall column

experiments, an ammonia scrubber which contained concentrated phosphoric acid solution was used to

remove ammonia in the gas. This prevented ammonia from dissolving in the water which condensed in

the cooler before the gas entered the Horiba gas analyser and avoided the absorption of CO2 in the

ammonia solution in the cooler. The total gas flow rate used was 5 L/min for each measurement. The

temperature was varied from 283.15 to 298.15 K. One litre of aqueous solution was used in each

measurement to ensure the CO2 loading in a solution changed less than 0.01 (mol CO2/mol NH3) during

the absorption process.

The amount of CO2 absorbed from the gas flow into the liquid film was determined by measuring the CO2

content of the gas entering and exiting the column. This, in conjunction with knowledge of the contact

surface area of the liquid film with the gas allowed determination of the CO2 absorption flux (mmol s-1m-2).

2 2 2

*

CO G CO COr / A K (P P ) (12)

Four to six inlet CO2 partial pressures were used, varying from 0 to 10 kPa. Plotting 2COr / A vs

2 2CO CO(P P *) gave a linear curve, and its slope was KG. The log mean of inlet and outlet values of

2 2CO CO(P P *) was used. For fresh solutions,2

*

COP 0 , while for CO2 loaded ammonia solutions with

additives, the equilibrium pressure was assumed to equal that for ammonia at the same concentration

and CO2 loading in the absence of additives. It has been found that for the conditions studied, the values

of the equilibrium pressures for the solvents investigated affected the y-intercept of the CO2r vs A


28

2 2CO CO(P P *) plot, but had little effect on the value of slope. Figure 6 shows some examples of how KG

was obtained. As shown in Figure 6, KG of CO2 in 3 M aqueous ammonia at the CO2 loading of 0.3 and 15oC

is 0.33 mmol/(kPa m2 s) while Kg of CO2 in 30% MEA at the CO2 loading of 0.3 and 40oC is 1.45 mmol/(kPa

m2 s).

PCO2

- PCO2

*, kPa

0 1 2 3 4 5 6

CO

2 a

bsorp

tion flu

x, m

mo

l/(m

2 s

)

0

2

4

6

8

10

3 M NH3, CO2 loading = 0.3, 15oC

30% MEA, CO2 loading = 0.3, 40oC

y=0.33x+0.03

y=1.45x+0.04

Figure 6 CO2 absorption flux as a function of log mean of inlet and outlet of (PCO2-PCO2*)

Figure 7 shows the mass transfer coefficients of CO2 in 3 M (5 wt%) aqueous ammonia solution and 5 M

(30 wt%) MEA solution at the absorption temperature of 15 oC and 40oC, respectively. Figure also includes

the mass transfer coefficients obtained from pilot plant studies and shows good agreement between

results obtained from the pilot plant and wetted wall column for the ammonia solvent. This suggests that

the mass transfer coefficients obtained from the wetted wall column can be used to estimate those in

large-scale packed columns, at least under the conditions reported here.


29

CO2 loading

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Ove

rall

gas p

ha

se m

ass tra

nsfe

r co

effic

ien

t

(m

mo

l s

-1 k

Pa

-1 m

-2)

0.0

0.5

1.0

1.5

2.0

2.5

4-5 wt% NH3 at 15-20oC, Pilot plant

3 M NH3 at 15oC, WWC

30 wt% MEA at 40oC, WWC

Figure 7 Overall gas phase mass transfer coefficient (KG)in ammonia and monoethanolamine (MEA) at a

range of CO2 loadings

The ammonia concentration in the gas at the outlet of the WWC was measured by a FTIR Analyzer DX4000

from Gasmet technologies. Since the ammonia measurement range on FTIR is up to 15,000ppm, a dilution

gas, N2 was mixed with the gas leaving the WWC to reduce the ammonia concentration below 15,000ppm.

The actual ammonia concentration (or loss rate) can be calculated based on the flow rates of dilution gas

and the gas mixture from the WWC. Figure 8(a) shows the CO2 partial pressure and NH3 concentration at

the outlet of the wetted-wall column as a function of time, at the NH3 concentration of 1 wt% and CO2

loading of 0.5. The inlet of CO2 partial pressure was varied from 2–20 kPa. As can be seen from Figure 8(a),

at different CO2 partial pressures, the NH3 concentration in the gas phase remained essentially constant

during the test. This suggests that CO2 partial pressure has little influence on NH3 loss in the wetted-wall

column, in which the composition of the liquid does not change in the short period of measurement time.

Figure 8(b) shows NH3 concentration versus time at the outlet of the wetted-wall column, at a CO2 loading

of 0.5 and various NH3 concentrations. During the measurement, the CO2 partial pressure was varied as

per Figure 8(a). The results in Figure 8(b) further shows that the NH3 concentration at the outlet of the

wetted wall column is determined by the solvent, and that the results from the wetted wall columns can

be used to understand the relationship between NH3 loss and operating conditions.


30

Time (s)

0 200 400 600 800

CO

2 p

art

ial p

ressu

re (

kP

a)

0

5

10

15

20

25

Am

mo

nia

co

nce

ntr

atio

n (

pp

m)

0

200

400

600

800

1000

1200(a)

NH3

CO2

Time (s)

0 200 400 600 800

Am

mo

nia

Co

nce

ntr

atio

n (

pp

m)

0

1000

2000

3000

4000

5000

6000

7000

8000(b)

4.12 M

2.94 M

1.76 M

0.59 M

Figure 8 (a) CO2 partial pressure and NH3 concentration at the outlet of the wetted-wall column as a

function of time (NH3=1 wt%, CO2 loading=0.5); (b) NH3 concentration at the outlet of absorber as a

function of time at NH3 concentrations of 0.59–4.12 M and CO2 loading of 0.5

Thermodynamic model for PZ-NH3-CO2-H2O

In order to describe the thermodynamics in PZ-NH3-CO2-H2O system, the e-NRTL (electrolyte Non-Random

Two-Liquid) models of both NH3-CO2-H2O and PZ-CO2-H2O, available in Aspen Plus V8.0 (Aspentech 2012a

and b), were combined together to calculate the speciation distribution and vapour-liquid equilibrium

(VLE). In the combined model, the binary interaction parameters between NH3 and PZ were unavailable

and were assumed to be zero. Sensitivity analysis showed that the results for the speciation distribution

and VLE changed with variation of binary interaction parameters between NH3 and PZ, but the change is

small. There are no published experimental results available to validate the combined model. However,

the thermodynamic models for both NH3-CO2-H2O and PZ-CO2-H2O have been validated with extensive

experimental results. We believe the combined model is sufficient to provide the information on VLE and

speciation that is used in this work to help understand the role of PZ in CO2 absorption and NH3 loss.

(4) Experimental conditions

The tests include a screening test of 6 promoters and a parametric test of piperzaine and ammonia blends.

The objective of the screening test is to investigate the effect of promoter concentration and CO2 loading

on the mass transfer coefficient of CO2 in the blends. The test will facilitate the development of an

aqueous ammonia based solvent which has improved absorption kinetics. The parametric test of

piperazine and ammonia blends aims at obtaining the insights into the role of piperazine in absorption

rate and ammonia loss. To our knowledge, there is little research available in the open literature reporting

the mass transfer of CO2 in the CO2 loaded NH3 and PZ solutions and ammonia loss. The detailed

understanding will help elucidate the role of other promoters in the blended solvents.

Table 2 summarise the experimental conditions for screening tests. The concentrations for promoters in

the mixture are chosen depending on the solubility of the promoters and the relationship between the


31

concentration of promoters in the blended solutions and mass transfer coefficients. For example,

piperazine has a low solubility in water so we only test its concentration up to 0. 5M.

Table 2 Summary of screening tests. Absorption temperature = 288 K (15oC)

Solvent Conditions

Promoter alone PZ: 0-0.5 M; 1PZ: 0-3M; 2PZ: 0-3M

Tau: 0-2M; Sar:1-3M; Pro:1:3M

Promoter and ammonia mixture with

and without CO2

NH3: 3M;

PZ: 0.3 M; 1PZ: 3M: 2PZ: 1.5M

Tau: 2M; Sar: 3M; Pro: 2M

CO2 loading: 0-0.5

PZ: piperazine; 1PZ: 1 methyl piperazine; 2PZ: 2 methyl piperazine

Tau: Potassium taurinate; Sar: potassium sarcosinate: Pro: potassium prolinate

In the parametric study of CO2 absorption in PZ/ammonia blends, we tested ammonia alone, piperazine

alone, and CO2 loaded blends. Table 3 lists the solvents tested.


32

Table 3 Summary of solvents tested in the parametric study of CO2 absorption in piperazine and

ammonia blends

Temperature

(K)

Solvents

3NHC (M) PZC (M) CO2 loading

(mol CO2/mol NH3)

283.15 3 0 0, 0.1, 0.2, 0.3, 0.5

288.15 3 0, 0.3 0, 0.1, 0.2, 0.3, 0.5

293.15 3 0 0, 0.1, 0.2, 0.3, 0.5

298.15 3 0, 0.3 0, 0.1, 0.2, 0.3, 0.5

288.15 1, 2, 4 0 0

288.15 0.59 0 0.3, 0.5, 0.7

288.15 1.76 0 0.5

288.15 2.94 0 0.5

288.15 4.12 0 0.5

283.15 0 0.1, 0.2, 0.3, 0.5 0

288.15 0 0.1, 0.2, 0.3, 0.5 0

293.15 0 0.1, 0.2, 0.3, 0.5 0

298.15 0 0.1, 0.2, 0.3, 0.5 0

288.15 3 0.1, 0.2, 0.5 0.3

288.15 3 0.1, 0.2, 0.5 0.5

References

Aspentech, 2012a. Rate-based model of the CO2 capture process by NH3 using Aspen Plus, V8.0

documentation .

Aspentech, 2012b, Rate-based model of the CO2 capture process by PZ using Aspen Plus, V8.0

documentation.

Dang H.Y., Rochelle G.T. 2001. CO2 absorption rate and solubility in Monoethanolamine /Piperazine

/Water. M.S. Thesis, The University of Texas at Austin, Texas.

Derks, P.W.J., Versteeg, G.F. 2009. Kinetics of absorption of carbon dioxide in aqueous ammonia solutions.

International Greenhouse Gas Control Technologies. 9 (1), 1139–1146.

Gilliland, E. R. 1934. Diffusion coefficients in gaseous systems. Industrial & Engineering Chemistry. 26,

681–685.

Pacheco, M.A. 1998. Mass transfer, kinetics and rate-based modelling of reactive absorption. Doctoral

Dissertation , The University of Texas, Texas.

Qin, F., Wanga, S., Hartono, A., Svendsen, H.F. 2010. Kinetics of CO2 absorption in aqueous ammonia

solution. International Journal of Greenhouse Gas Control. 4, 729–738.

Versteeg, G., Dijck, L., Swaaij, W. 1996. On the kinetics between CO2 and Alkanolamines both in Aqueous

and Nonaqueous Solutions. An overview. Chemical Engineering Communications. 144, 113–158.

Versteeg, G., Swaaij, W. 1988. Solubility and diffussivity of acid gases (CO2, N2O) in aqueous

alkanolamines solutions. Journal of Chemical & Engineering Data. 33, 29–34.

http://pubs.acs.org/doi/abs/10.1021/ie50294a020


33

6 Results and Discussion

6.1 Screening tests

Figure 9 show the overall mass transfer coefficients of CO2 as a function of promoter concentration in the

presence and absence of 3 M ammonia at the temperature of 288 K.

As shown in Figure 9, introduction of these 6 promoters can significantly enhance CO2 mass transfer in the

solvent. The mass transfer coefficients of CO2 in the blends are significantly higher than those in ammonia

alone and higher than those in promoter alone. The extent of increase of mass transfer coefficients with

introduction of promoters depends on the nature of promoters and their concentrations. it is expected

that each promoter has its own optimum conditions when mixing with ammonia in order to achieve the

highest CO2 absorption kinetics.

Figure 9 Overall gas phase mass transfer coefficients of CO2 as a function of promoters in the presence and absence of 3 M ammonia at the temperature of 288

K. Promoters include Piperazine (PZ), 1 methyl piperazine (1PZ), 2 methyl piperazine (2PZ), potassium salts of proline, sarcosine and taurine

1PZ concentration, M

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Overa

ll gas p

hase m

ass tra

nsfe

r co

effic

ient

(mm

ol s

-1 k

Pa

-1 m

-2)

0.0

0.5

1.0

1.5

2.0

2.5

1PZ alone

1PZ + 3M NH3

PZ concentration, M

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Ove

rall

ga

s p

ha

se

ma

ss tra

nsfe

r co

effic

ien

t

(mm

ol s

-1 k

Pa

-1 m

-2)

0.0

0.5

1.0

1.5

2.0

2.5

PZ alone

PZ + 3M NH3

2PZ concentration, M

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Ove

rall

ga

s p

ha

se

ma

ss tra

nsfe

r co

effic

ien

t

(mm

ol s

-1 k

Pa

-1 m

-2)

0.0

0.5

1.0

1.5

2.0

2.5

2PZ alone

2PZ + 3M NH3

Taurine concentration, M

0.0 0.5 1.0 1.5 2.0

Overa

ll gas p

hase m

ass tra

nsfe

r co

effic

ient

(mm

ol s

-1 k

Pa

-1 m

-2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Taurine alone

Taurine + 3M NH3

Sarcosine concentration, M

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Overa

ll gas p

hase m

ass tra

nsfe

r co

effic

ient

(mm

ol s

-1 k

Pa

-1 m

-2)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Sarcosine alone

Sarcosine + 3M NH3

Proline concentration, M

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Ove

rall

ga

s p

ha

se

ma

ss tra

nsfe

r co

effic

ien

t

(mm

ol s

-1 k

Pa

-1 m

-2)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Proline alone

Proline + 3M NH3

Development of an Ammonia Based PCC Technology for Australian Conditions-Technical Report

No.2

35

CO2 loading (mol CO

2/mol(NH

3+amino acid salts))

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Ove

rall

gas p

ha

se m

ass tra

nsfe

r co

effic

ien

t

K

G(m

mol/m

2 s

kP

a)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

2M Proline+3M NH3

2M Taurine+3M NH3

3M Sarcosine+3M NH3

5M MEA, 40oC

3M NH3, 15oC

Figure 10 Mass transfer coefficient of CO2 in the mixture of ammonia with amino acid salts as a

function of CO2 loading at the temperature of 288 K

CO2 loading (mol CO

2/mol(NH

3+amino acid salts))

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Overa

ll gas p

hase m

ass tra

nsfe

r coe

ffic

ien

t

K

G(m

mol/m

2 s

kP

a)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.3M PZ+3M NH3

2M 1PZ+3M NH3

1.5M 2PZ+3M NH3

5M MEA, 40oC

3M NH3, 15oC

Figure 11 Mass transfer coefficient of CO2 in the mixture of ammonia with piperazine and its

derivatives as a function of CO2 loading at the temperature of 288 K


No.2

36

Figures 10 and 11 show the overall gas phase mass transfer coefficient in ammonia blended with

promoters at a range of CO2 loadings and the temperature of 288 K. For comparison purpose,

overall gas phase mass transfer coefficients in ammonia alone and MEA are included. Except the

ammonia and taurine mixture, ammonia mixed with other promoters can achieve a mass transfer

coefficient more than double of those for ammonia alone.

6.2 Parametric study of CO2 absorption in PZ and ammonia mixture

Overall gas phase mass transfer coefficient (KG) for CO2 in aqueous NH3 alone and PZ alone

Figure 12 (a) shows KG for CO2 in aqueous NH3 as a function of CO2 loading at an NH3 concentration

of 3 M and temperatures of 283.15–298.15 K. The second order rate constants 32,NHk for the

reaction of CO2 with NH3 were calculated from Eq. (2) and Eq. (7). The temperature dependence of

32,NHk at different temperatures was used to fit the Arrhenius equation, as shown in Figure 12(b).

The Arrhenius expression obtained from experimental results can be expressed by Eq. (13):

3

9

2,NH

34193k 1.1451 10 exp( )

RT

(13)

CO2 loading (mol CO

2/mol NH

3)

0.0 0.1 0.2 0.3 0.4 0.5

KG (

mm

ol. s

-1 k

Pa

-1 m

-2)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

283.15K

288.15K

293.15K

298.15K

1/T (1/K)

0.00335 0.00340 0.00345 0.00350 0.00355

ln K

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

(b)

Figure 12 (a) KG as a function of CO2 loading at different temperatures (283.15 to 298.15 K) and an

NH3 concentration of 3 M; (b) Arrhenius plot for second-order rate constant for the forward

reaction of NH3 and CO2 at an NH3 concentration of 3 M and CO2 loading verified from 0 to 0.5

Table 4 shows the comparison of the second-order rate constant for the forward reaction of NH3 and

CO2 obtained in this study with literature values. The results from this study are in a reasonable


No.2

37

agreement with literature, and fall between those from Pinsent (1956) and Puxty (2010) and are

close to those from Derks (2009).

Table 4 Comparison of experimental and published values of second-order rate constant for the

reaction of NH3 and CO2 at four different temperatures

Temperature

(K)

32,NHk (L·mol-1·s-1)

This work Puxty (2010) Pinsent (1956) Derks (2009)

283.15 563 915 155 700

288.15 725±56 1437 223 -

293.15 925±136 2217 313 1400

298.15 1170±94 3369 440 -

Figure 13 (a) KG for CO2 in PZ solution at different temperature as a function of PZ concentration;

(b) Arrhenius plot for second-order rate constant for the reaction of PZ with CO2 at PZ

concentrations of 0.1 to 0.5 M

1/T (1/K)

0.00335 0.00340 0.00345 0.00350 0.00355

ln K

7

8

9

10

11

12

(b)

PZ concentration (M)

0.1 0.2 0.3 0.4 0.5 0.6

KG (

mm

ol·m

-2·s

-1·k

Pa

-1)

0.8

1.0

1.2

1.4

1.6

1.8

2.0

283.15K

288.15K

293.15K

298.15K

(a)


No.2

38

Figure 13(a) illustrates KG for CO2 in PZ solution as a function of PZ concentration at temperatures

ranging from 283.15–298.15 K and (b) the Arrhenius plot for the second order rate constant for the

reaction of PZ with CO2. The Arrhenius expression for PZ and CO2 is given below as:

8

2,PZ

20139k 1.63 10 exp( )

RT

(14)

Temperature (K)

282 284 286 288 290 292 294 296 298 300

K2

,PZ (

m3·K

mol-1

·s-1

)

0

10000

20000

30000

40000

50000

60000

Bougie (2009)

Bishnoi (2000)

Sun (2005)

Zhang (2001)

This work

Figure 14 Comparison of second-order rate constant for the reaction of PZ and CO2 as a function of

temperature

Figure 14 compares the rate constant between this study and published values. As illustrated in

Figure 14, the second-order rate constants obtained in this work show good agreement with the

results obtained from Bougie (2009), Bishnoi (2000), and Zhang (2001). The results from Sun et al.

(2005) are much lower. This might be because that the CO2 absorption in their investigation did not

fall in the pseudo-first-order reaction regime and PZ depletion occurred at gas-liquid interface. The

good agreement with published values of kinetics results for both NH3 and PZ suggests that our

experimental results are reliable and the assumptions are reasonable. The results obtained from

individual solvents can help develop a better understanding of CO2 absorption in a mixture of NH3

and PZ with and without loaded CO2.

http://www.sciencedirect.com/science/article/pii/S0009250909000542


No.2

39

6.3 KG for CO2 in a mixture of NH3 and PZ

Figure 15(a) shows KG of CO2 in aqueous NH3 as a function of NH3 concentration in the absence and

presence of 0.3 M PZ. At all NH3 concentrations studied, addition of 0.3 M PZ to the aqueous NH3

solution significantly increases the mass transfer coefficient, while an increase in NH3 concentration

in solutions only leads to a marginal increase in mass transfer coefficient. The promotion of CO2

absorption by PZ is also observed in the CO2-loaded NH3 solutions. Figure 15(b) shows the effect of

the addition of PZ on KG in 3 M aqueous NH3 solutions at various CO2 loadings and two absorption

temperatures. Under all CO2 loadings studied, addition of 0.3 M PZ significantly increases the mass

transfer coefficients. The extent of increase falls as more CO2 is added to solution. Figure 15 also

shows that, as in the case of CO2 absorption in NH3 alone or PZ alone, KG in a mixture of NH3 and PZ

with or without loaded CO2 only increases slightly as the temperature rises. We further investigated

the promotion effect of PZ by examining the effect of PZ concentration on the CO2 mass transfer

coefficients in a mixture of NH3 and PZ at two CO2 loadings. As shown in Figure 16, raising the PZ

concentration greatly increases the mass transfer coefficient of CO2: particularly at PZ

concentrations below 0.3 M. As the concentration of PZ rises, the extent of increase in KG is smaller

in the solution with higher CO2 loading.

Figure 15(a) KG as a function of NH3 concentration at 288.15 K with and without the addition of 0.3

M PZ; (b) KG as a function of CO2 loading at 288.15 and 298.15 K and the NH3 concentration of 3 M

with and without the addition of 0.3 M PZ

NH3 concentration (M)

0 1 2 3 4

KG (

mm

ol·s

-1·k

Pa

-1 m

-2)

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

(a)

NH3

NH3+PZ

CO2 loading(mol CO

2/mol NH

3)

0.0 0.1 0.2 0.3 0.4 0.5

KG (

mm

ol·

s-1

· kP

a-1

m-2

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

(b)

NH3, 288.15 K

NH3, 298.15 K

NH3+PZ, 288.15 K

NH3+PZ, 298.15 K


No.2

40


0.0 0.1 0.2 0.3 0.4 0.5

KG (

mm

ol·

s-1

· kP

a-1

· m-2

)

0.2

0.4

0.6

0.8

1.0

1.2

1.4

3 M NH3, loading = 0.5

3 M NH3, Loading = 0.3

Figure 16 KG as a function of PZ concentration at NH3 concentration of 3 M, CO2 loadings of 0.3 and

0.5 and temperature of 288.15 K

The reactions of CO2 with a mixture of NH3 and PZ are quite complicated, in particular if the mixture

is loaded with CO2. In this work, we adopt a simplified approach to describe the CO2 absorption in

this mixture. We assume that there is no catalytic effect of PZ on the CO2 absorption in aqueous NH3

and that the reaction of CO2 with the mixture of NH3 and PZ is a simple combination of the reactions

of CO2 with NH3, PZ and other species that could react with CO2.


No.2

41

CO2 loading

0.0 0.1 0.2 0.3 0.4 0.5

Concentr

ation (

M)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

NH3

NH4

+

NH2COO-

HCO3

-

CO2 loading

0.0 0.1 0.2 0.3 0.4 0.5

Concentr

ation (

mol.L

-1)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

PZ

PZCOO-

PZ(COO-)2

PZH+

HPZ

Figure 17 Speciation profile as a function of CO2 loading in 3 M NH3/0.3 M PZ at 288.15 K,

predicted results from e-NRTL PZ-NH3-CO2-H2O model in Aspen Plus V8.0

Figure 17 shows the modelled speciation as a function of CO2 loading in the mixture of 3 M NH3/0.3

M PZ at 288.15 K, obtained from the e-NRTL model of PZ-NH3-CO2-H2O system in Aspen Plus V8.0. As

CO2 loading increases, the PZ concentration drops dramatically, while the concentration of PZCOO–

increases initially at CO2 loadings below 0.2. Even at a CO2 loading of 0.5, there is still some free

PZCOO– available. PZCOO– can react with CO2 at a fast rate. Dang and Rochelle (2001) investigated

the CO2 absorption rate in MEA/PZ/H2O solutions and reported that PZCOO– contributes more than

40% of the total CO2 absorption in solutions with high CO2 loadings. Similarly, our results indicate

that PZCOO– plays an important role in the reaction of CO2 with PZ promoted, CO2 loaded NH3

solutions. The reaction of CO2 with PZCOO– should also be considered. The comparison of KG,CO2

between calculated results and the results obtained from experimental measurements is listed in

Table 5 and plotted in Figure 18 . The calculated KG,CO2 was determined from Eq. (3), with kg

calculated from Eq. (5).


No.2

42

Table 5 Comparison between the experimental and calculated values of KG

Solutions KG experimental

(mmol·s-1·m-2·kPa-1)

KG calculated

(mmol·s-1·m-2·kPa-1)

Deviation

(%)

1 M, 0.3 PZ 1.4305 1.4872 3.96

2 M, 0.3 PZ 1.4839 1.5267 2.88

3 M, 0.3 PZ 1.6899 1.5649 7.39

4 M, 0.3 PZ 1.6568 1.6017 3.32

3M, 0.1, 0.3 PZ 1.198145 1.4057

14.76

3M, 0.2, 0.3 PZ 0.966849 1.1454

15.59

3M, 0.3, 0.3 PZ 0.785865 1.0304

23.73

3M, 0.5, 0.3 PZ 0.505827 0.6785

25.45

3M, 0.3, 0.1 PZ 0.597449 0.6488

7.91

3M, 0.3, 0.2 PZ 0.721394 0.9222

21.77

3M, 0.3, 0.5 PZ 1.04631 1.1897

12.05

3M, 0.5, 0.1 PZ 0.372417 0.3317

12.27

3M, 0.5, 0.2 PZ 0.450618 0.4642

2.93

3M, 0.5, 0.5 PZ 0.65323 0.7733

15.53

Figure 18 Polarity plot of the measured and calculated KG values

Experimental KG, mmol s

-1 kPa

-1 m

-2

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Calc

ula

ted K

G, m

mo

l s

-1 k

Pa

-1 m

-2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8


No.2

43

The calculated results show reasonably good agreement with the experimental results, particularly,

for the mixture of NH3 and PZ in the absence of CO2. This indicates that the simplified mechanism for

the absorption of CO2 in a mixture of NH3 and PZ is reasonable. PZ has no catalytic effect on the

absorption of CO2. The promotion effect is due to the reaction constant for the reaction of PZ and

NH3 being much larger than that for the reaction of NH3 with CO2. This can explain the enhancement

effect of PZ and NH3 concentration on the mass transfer coefficient, as shown in Figures. 5 and 6. In

the CO2 loaded solution, PZ concentration is very slow but PZCOO–is present in large quantity;

therefore, the promotion is mainly due to the reaction of PZCOO– with CO2. Table 5 shows relatively

large discrepancy for the CO2 loaded solutions. This could be due to possible inaccuracies in the

determination of the rate constant for the reaction of PZCOO– and CO2, and the concentration of

PZCOO–.

6.4 NH3 loss

We investigated a range of parameters, including temperature, CO2 loading, NH3 concentration, and

PZ concentration; the results are shown in Figures 19–22. As expected, greater NH3 concentrations

and absorption temperatures, and lower CO2 loading, increase NH3 loss. The addition of PZ to the

NH3 also increases NH3 loss in a mixture of PZ and NH3 with and without CO2.


1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

NH

3 lo

ss r

ate

(m

mo

l·s

-1)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

(a)


1.0 1.5 2.0 2.5 3.0 3.5 4.0

P*

(kP

a)

0

1

2

3

4

5

6

(b)

Figure 19 NH3 loss rate (a) and equilibrium partial pressure (predicted from e-NRTL PZ-NH3-CO2-

H2O model in Aspen Plus V8.0) (b) as a function of NH3 concentration at 288.15 K


No.2

44

CO2 loading (mol/L CO

2/ mol/L NH

3)

0.0 0.1 0.2 0.3 0.4 0.5

NH

3 lo

ss r

ate

(m

mo

l·s

-1)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

283.15 K

288.15 K

293.15 K

298.15 K

(a)

CO2 loading (mol/L CO

2/ mol/L NH

3)

0.0 0.1 0.2 0.3 0.4 0.5

P*

(pK

a)

0

1

2

3

4

5

6

7

283.15 K

288.15 K

293.15 K

298.15 K

(b)


H2O model in Aspen Plus V8.0) (b) at different temperatures of 283.15–298.15 K as a function of

CO2 loading in 3 M NH3

CO2 loading

0.0 0.1 0.2 0.3 0.4 0.5

N N

H3 (

mm

ol·s

-1)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

(a)

NH3, 288.15 K

NH3, 298.15 K

NH3+PZ, 298.15 K

NH3+PZ, 288.15 K

CO2 loading

0.0 0.1 0.2 0.3 0.4 0.5

P*

(kP

a)

1

2

3

4

5

6

(b)

NH3, 288.15 K

NH3+PZ, 298.15K

NH3+PZ, 288.15 K

NH3, 198.15 K


H2O model in Aspen Plus V8.0) (b) of NH3 solutions in the presence and absence of 0.3 M PZ as

function of CO2 loading at 288.15 K and 298.15 K


No.2

45


H2O model in Aspen Plus V8.0) (b)as a function of PZ concentration in 3 M NH3 solutions, CO2

loadings of 0.3 and 0.5, 288.15 K

Figures 19-22 also shows the predicted NH3 partial pressure, modelled from e-NRTL PZ-NH3-CO2-H2O

model in Aspen Plus V8.0. The higher the equilibrium partial pressure, the higher the NH3 loss. The

partial pressure of NH3 increases with addition of PZ. This is due to the greater availability of free

NH3. Figure 23 compares the predicted profiles of NH3-related species in the presence and absence

of 0.3 M PZ.

Figure 23 Comparison of the predicted equilibrium concentration profiles of NH3 related species in

the presence (dash line) and absence (solid line) of 0.3 M PZ, predicted form e-NRTL PZ-NH3-CO2-

H2O model in Aspen Plus V8.0


0.0 0.1 0.2 0.3 0.4 0.5

NN

H3 (

mm

ol.s

-1)

0.01

0.02

0.03

0.04

0.05

0.06

3 M NH3, CO

2 loading = 0.5

3 M NH3, CO

2 Loading= 0.3

(a)


0.0 0.1 0.2 0.3 0.4 0.5

P*

(kP

a)

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3 M NH3, CO

2 loading = 0.5

3 M NH3, CO

2 loading = 0.3

(b)

CO2 loading (mol CO

2/mol NH

3)

0.0 0.1 0.2 0.3 0.4 0.5

Co

nce

ntr

atio

n (

mo

l.L

-1)

0

1

2

3

NH3

NH4+

NH2COO

-

HCO3

-


No.2

46

The presence of PZ increases the concentration of free NH3 under all CO2 loadings modelled (except

zero CO2 loading) in NH3/PZ mixtures. Figure 24 shows the predicted speciation profiles of several

species in NH3/PZ solutions as a function of PZ concentration at NH3 concentrations of 3 M and a CO2

loading of 0.3. The free NH3 concentration increases as PZ concentration rises.

PZ Concentration (M)

0.0 0.1 0.2 0.3 0.4 0.5

Co

nce

ntr

atio

n (

M)

0.0

0.5

1.0

1.5

NH3

PZ

PZCOO-

3 M NH3, CO2 Loading = 0.3

Figure 24 The predicted equilibrium profiles of NH3, PZ and PZCOO- in 3 M NH3 at CO2 loading of 0.3

as a function of PZ concentration

References

Bougie F., Julien Lauzon-Gauthier J., Iliuta M.C. 2009. Acceleration of the reaction of carbon dioxide

into aqueous 2-amino-2-hydroxymethyl-1,3-propanediol solutions by piperazine addition. Chemical

Engineering Science. 64, 2011–2019.

Bishnoi B. Rochelle, T.R. 2000. Absorption of carbon dioxide into aqueous piperazine: reaction

kinetics, mass transfer and solubility. Chemical Engineering Science. 55, 5531–5543.

Dang H.Y., Rochelle G.T. 2001. CO2 absorption rate and solubility in Monoethanolamine /Piperazine

/Water. M.S. Thesis, The University of Texas at Austin, Texas.






No.2

47

Derks, P.W.J., Versteeg, G.F. 2009. Kinetics of absorption of carbon dioxide in aqueous ammonia

solutions. International Greenhouse Gas Control Technologies. 9 (1), 1139–1146.

Pinsent, B., Pearson, L., and Roughton, F.1956. The kinetics of combination of carbon dioxide with

ammonia. Transactions of the Faraday Society. 52, 1594.

Puxty, G., Rowland, R., Attalla, M. 2010. Comparison of the rate of CO2 absorption into aqueous

ammonia and monoethanolamine. Chemical Engineering Science. 65, 915–922.

Sun, W., Yong, C., Li, M. 2005. Kinetics of the absorption of carbon dioxide into mixed aqueous

solutions of 2-amino-2-methyl-l-propanol and piperazine. Chemical Engineering Science. 60, 503–

516.

Zhang, X., Zhang, C., Qin, S., Zheng, Z. 2001. A Kinetics study on the absorption of carbon dioxide into

a mixed aqueous solution of methyldiethanolamine and piperazine. Industrial & Engineering

Chemistry Research. 40 (17), 3785–3791.


No.2

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7 Impact of Research Achievements from This Project

Summary of results obtained from this project

This project focuses on the development of the advanced aqueous ammonia based post combustion

capture (PCC) technology for significant reduction of CO2 emission from coal fired power stations in

Australia. The project started from June 2012 and is expected to complete by September 2015. In

the last 12 months the project has been focusing on the development of a rate based model for CO2

absorption in aqueous ammonia and identification of promoters which can significantly enhance CO2

absorption rate in the aqueous ammonia based solvent. The project so far has generated the

following key results.

(1) Development of a rate-based model for CO2 absorption in aqueous ammonia in a packed

column

A rigorous rate-based model for CO2 absorption using aqueous ammonia in a packed column has

been developed and used to simulate results from a recent pilot plant trial of an aqueous

ammonia-based post-combustion capture process at the Munmorah Power Station, New South

Wales, Australia. The model is based on the RateSep module, a rate-based absorption and stripping

unit operation model in Aspen Plus, and uses the available thermodynamic, kinetic and transport

property models for the NH3-CO2-H2O system to predict the performance of CO2 capture. The

thermodynamic and transport property models satisfactorily predict experimental results from the

published literature. The modeling results from the rate-based model also agree reasonably well

with pilot plant results, including CO2 absorption rate, NH3 loss rate, temperature profiles and mass

transfer coefficients in the absorber. Table 6 shows the summary of rate-based model predictions

and pilot plant trial results conducted under a variety of experimental conditions. The flow-sheet for

the rate-based absorber model is shown in Figure 25. The two absorbers are operated in series. The

flue gas containing CO2 is introduced into the bottom of Absorber 1, and the lean solvent to the top

of Absorber 2. Since aqueous ammonia is used to remove SO2 in the pretreatment column, the flue

gas at the inlet of the absorber contains a certain amount of ammonia and water. One cooler is used


No.2

49

between the two absorbers in order to reduce the temperature of the semi-rich solvent that leaves

Absorber 2. The detailed description of the model and experimental results can be found in the first

technical report of this project.

Figure 25 Schematic flow-sheet of the CO2 absorbers in series


50

Table 6 Summary of rate-based model predictions and pilot plant trial results conducted under a variety of experimental conditions

Test ID 30 31 31R 31B 32 32A 32B 33 34 34R1 34R2 36 35B 35 39 38

NH3 weight percentage, wt% 4.91 4.08 4.21 3.80 3.56 4.19 3.98 4.24 4.37 4.37 4.00 4.97 5.82 4.96 4.49 1.92

CO2 loading of lean solvent 0.240 0.240 0.229 0.250 0.245 0.261 0.220 0.206 0.219 0.232 0.223 0.407 0.358 0.315 0.284 0.220

Flue gas flow rate, kg/hr 646 646 632 750 780 760 821 817 906 915 916 799 799 799 898 912

CO2 volume concentration in flue gas, vol% 8.624 9.395 9.765 7.583 8.849 10.784 8.050 7.989 10.090 9.446 9.446 9.810 9.370 8.007 10.131 11.660

NH3 volume concentration in flue gas, vol % 0.521 0.433 0.473 0.211 0.422 0.091 0.071 0.089 0.252 0.275 0.275 0.028 0.134 0.083 0.237 0.079

H2O volume concentration in flue gas, vol % 2.213 3.217 3.043 1.391 2.550 1.347 1.438 1.421 1.583 1.561 1.561 1.214 1.821 1.434 1.475 1.648

Liquid flow rate, L/min 134 134 134 134 134 134 134 100 67 67 67 134 134 134 134 134

CO2 weight percentage, wt% 3.04 2.53 2.50 2.45 2.23 2.82 2.22 2.28 2.50 2.61 2.27 5.30 5.39 4.00 3.26 1.08

H2O weight percentage, wt% 92.06 93.39 93.30 93.75 94.17 92.98 93.88 93.52 93.10 92.99 93.73 89.70 88.81 91.00 92.24 97.02

Absorber 1 gas inlet temperature, oC 21.81 27.99 30.02 16.61 22.05 16.90 17.68 17.02 18.01 17.52 18.60 12.58 18.26 17.16 16.24 18.08

Absorber 2 liquid inlet temperature, oC 23.89 26.98 32.28 16.38 25.77 16.85 17.03 15.52 15.19 15.48 15.61 14.47 19.89 16.39 16.27 17.10

Cooler outlet temperature, oC 23.10 26.65 31.41 15.27 25.00 15.79 15.90 14.73 14.06 14.99 15.02 13.78 18.90 15.12 15.41 16.19

Exp. CO2 loading(semi-richa), mol CO2/ mol NH3 0.265 0.275 0.257 0.281 0.283 0.303 0.256 0.266 0.300 0.312 0.312 0.436 0.361 0.354 0.326 0.322

Pred. CO2 loading(semi-rich) , mol CO2/ mol NH3 0.274 0.269 0.258 0.280 0.279 0.299 0.254 0.251 0.301 0.305 0.303 0.439 0.385 0.335 0.319 0.320

Exp. CO2 loading (richb) , mol CO2/ mol NH3 0.296 0.345 0.319 0.332 0.365 0.364 0.320 0.340 0.374 0.398 0.389 0.459 0.432 0.390 0.375 0.399

Pred. CO2 loading(rich) , mol CO2/ mol NH3 0.315 0.336 0.331 0.331 0.350 0.365 0.312 0.320 0.404 0.403 0.405 0.483 0.430 0.379 0.379 0.430

Exp.CO2 absorption rate (abs1, gas analysis)c, kg/hr 32.2 59.1 55.2 38.3 44.5 49.2 46.8 51.4 34.4 33.2 31.5 29.5 35.7 42.8 47.2 43.3

Exp. CO2 absorption rate (abs1, liquid analysis)d, kg/hr 37.3 47.0 44.9 42.8 54.1 42.2 45.0 43.1 39.6 32.9 31.4 27.9 35.7 38.6 43.8 35.6

Pred. CO2 absorption rate (abs1, equilibrium), kg/hr 76.3 76.3 81.3 86.6 57.2 78.2 83.4 66.9 66.2 67.0 64.9 59.0 67.2 85.1 66.5 83.6

Pred. CO2 absorption rate (abs1, rate-based), kg/hr 28.9 52.6 56.9 38.0 49.0 54.5 42.9 40.3 43.8 41.6 40.1 45.2 50.9 41.7 53.3 43.6

Exp.CO2 absorption rate (overall, gas analysis)c, kg/hr 66.6 79.6 77.7 68.2 72.1 87.8 80.5 85.9 78.3 74.4 70.0 60.4 70.6 81.2 85.6 74.9

Exp. CO2 absorption rate (overall, liquid analysis)d, kg/hr 64.5 78.5 69.6 65.7 77.6 74.7 70.5 72.0 76.6 70.4 67.1 57.2 70.0 65.7 80.8 76.4

Pred. CO2 absorption rate (overall, equilibrium), kg/hr 83.3 83.3 90.3 91.8 78.7 99.3 113.3 91.8 91.0 107.5 102.8 97.4 98.4 106.8 89.3 120.6

Pred. CO2 absorption rate (overall, rate-based), kg/hr 70.9 76.3 80.1 61.0 77.1 87.8 69.7 66.5 78.4 73.6 71.9 74.3 80.4 67.3 88.8 80.1

Exp. absorber 1outlet NH3 concentratione, ppm 19463 16708 28030 9173 12783 10574 11930 11546 8453 10245 7885 5482 7918 8299 10071 3756

Pred. absorber 1outlet NH3 concentration, ppm 18641 18798 25834 8994 14348 9342 10754 11020 8523 8825 8051 4379 9895 9072 8881 3827

a Absorber 2 liquid outlet;

b Absorber 1 liquid outlet;

c Gas analysis using a Gasmet

TM Analyzer;

d Liquid analysis by solvent samples CO2 loading titration;

e NH3 concentration on the top of Absorber 1, before the washing colum

45

(2) Development of aqueous ammonia based solvents which absorb CO2 as least 2 times as fast as the

solvent based on aqueous ammonia alone.

The project has identified several promoters which can significantly enhance CO2 absorption rate in

the aqueous ammonia based solvent. These promotes include piperazine, its derivatives and several

amino acid salts including proline and sarcosine. As shown in Figures 10 and 11, except the ammonia

and taurine mixture, ammonia mixed with other promoters can achieve a mass transfer coefficient more

than double of those for ammonia alone. It is expected that further optimisation of the solvent

formulation will lead to the development of an aqueous ammonia based solvent which can achieve a CO2

absorption rate that can match the standard MEA based solvent. The detailed description of the approach

and methodology and experimental results can be found in the second technical report of this project.

Impact of research achievements from this project

Our previous research including pilot plant trials have identified a number of research opportunities to

further develop aqueous ammonia based capture technologies.

Relatively low CO2 absorption rate compared to amine based solvent, which results in 2-3 times

the number of absorbers compared to monoethanolamine (MEA, the benchmark solvent) and

thus higher capital costs.

Relatively high ammonia loss at high CO2 absorption rate. The consumption of wash water is high.

Operating the desorption process in a similar pattern to regular amine processes will result in the

formation of ammonium-bicarbonate solids in the condenser, resulting in blockage.

The available process simulation models were insufficient to support the process optimisation and

scale up.

This limits the economical feasibility of the aqueous ammonia based PCC process. This research project

will develop a rate based process model and explores and evaluate novel approaches and concepts to

further advance the aqueous ammonia based PCC process which can achieve a significant cost reduction

and reduce environmental risks in Australian context.

As presented above, a rigorous rate-based model for CO2 absorption using aqueous ammonia in a packed

column has been developed and validated with results from the pilot plant trial of an aqueous

ammonia-based post-combustion capture process at the Munmorah Power Station, New South Wales,

Australia. The previous modelling work in the literature used the equilibrium based model and can only

assess the energy consumption of the process. The availability of the rate based model allows more

reliable estimation of size of the absorber and capital costs of the capture process. The rate based model

can also support the process optimisation and evaluate the new process configuration to achieve the cost

reduction.

As shown in Figure 1, addition of an advanced amine PCC process and CO2 transport and storage to a new

coal fired power station will lead to an increase in LCOE from 77 AUD/MWh to 167 AUD/MWh. The

significant increase is due to increase in plant cost, fuel, O&M and CO2 transport and storage. The capital

cost increase accounts for almost 60% of the total incremental LCOE. The absorber column is the most

expensive capital item and accounts for more than 30% of the total capital costs. As shown in Figure 10,


52

the mass transfer coefficients of CO2 in the unpromoted ammonia solution are significantly lower than

those in MEA. CO2 capture based on the unpromoted ammonia solution will require more than double the

number of absorbers used in the MEA based solvents. It is expected that the increase in capital cost will

be much larger than the cost reduction from use of aqueous ammonia and the process based on the

unpromoted ammonia is less competitive compared to the MEA based process, at least in Australia.

The project has led to the identification of a number of promoters which can significantly enhance CO2

absorption rate in the aqueous ammonia based solvent. Aqueous ammonia mixed with these promoters

can achieve a mass transfer coefficient more than double of those in ammonia alone. The significance of

this result is that the absorber size and the related capital cost can be reduced with the advanced aqueous

ammonia solvent. It is expected that further optimisation of the solvent formulation will lead to the

development of an aqueous ammonia based solvent which can achieve a CO2 absorption rate that can

match the standard MEA based solvent. In other words, the capital cost related to the absorber used in

the aqueous ammonia based process can be competitive to that for the standard MEA based solvent while

the benefits associates with aqueous ammonia can be maintained. It should been pointed out that the

project is still ongoing and the impact of promoters on the ammonia loss and energy consumption will be

evaluated in the following steps to allow an overall evaluation of the new solvent developed in this

project.


53

8 Status of Milestones

Date Due Description ANLEC Funding ($)

Status

15/06/2012 Contract signing $ 212,630 Complete 30/03/2013 Completion of recruitment of PhD students and

research project officer Delivery of a progress report approved by ANLEC R&D which shows the following: (1) Results have been generated from wetted wall column screening experiments and promoters for stopped flow reactor experiments have been identified. (2) The framework for the rate based model has been established and the comparison between the modelling work and pilot plant results has been made. (3) Analytic methods for gas and liquid analysis have been established.

$ 68,042 Complete

30/09/2013 Completion of experiments for screening promoters and optimisation of solvent formulation on wetted wall column Delivery of a progress and technical report approved by ANLEC R&D which includes: (1) Status of the research activities and milestone (2) Approaches and methodologies used in the screening experiments (3) Results obtained (4) Evidence that the following has been achieved:

a. The new aqueous ammonia based solvent can absorb CO2 as least 2 times as fast as the solvent based on aqueous ammonia alone

Delivery of an industry report approved by ANLEC R&D which includes a description of: (1) Recent advancement of solvent development for post combustion capture including aqueous ammonia around the world (2)Results from this research project (3) The impact of research achievements from this project on the advancement of aqueous ammonia based PCC processes for application in Australia

$ 68,042 Complete This report

31/03/2014 Completion of experiments on stopped flow reactor Delivery of a progress and technical report approved by ANLEC R&D which includes: (1) Status of the research activities and milestones (2) Approaches and methodologies used in the stopped flow reactor experiments (3) Results from stopped flow reactor experiments and discussion

$ 59,537 Ongoing 10% complete

30/09/2014 Completion of process modelling for elucidation of promotion mechanism and completion of SO2 and NH3 absorption experiments

$ 59,537 Not yet started


54

Delivery of a progress and technical report approved by ANLEC R&D which includes: (1) Status of the research activities and milestone (2) Approaches and methodologies used in the process modelling and SO2 and NH3 absorption experiments (3) Results obtained (4) Evidence that the following has been achieved:

a. Develop a novel aqueous ammonia based solvent which can achieve a CO2 absorption rate that can match the standard MEA based solvent

b. Develop a rigorous rate based model for the aqueous ammonia based CO2 capture process and validate the model with results from previous pilot plant trials

c. Achieve the combined removal of SO2 and recovery of ammonia and eliminate additional flue gas desulfurization. This includes:

Identification and validation of experimental conditions under which SO2 in the flue gas is selectively removed in preference to CO2 by ammonia (flue gas pre-treatment). More than 90% of SO2 will be removed in the pre-treatment stage in which CO2 removal is negligible.

Ammonia in the flue gas can be reduced to an acceptable level by SO2 solution (flue gas post-treatment).

Delivery of an industry report approved by ANLEC R&D which includes a description of: (1) Recent advancement of solvent development for post combustion capture including aqueous ammonia (2) Summary of results obtained from this research project (3) Impact of the research achievements from this project on the advancement of aqueous ammonia based PCC processes for application in Australia

31/03/2015 Completion of high pressure experiments. Delivery of a progress and technical report approved by ANLEC R&D which includes: (1) Status of the research activities and milestone (2) Approaches and methodologies used in the high pressure experiments (3) Results obtained

$ 59,537 Ongoing 10% complete

31/08/2015 Submit Draft of Final Report to ANLEC R&D for review $ 68,042 Not yet started

30/09/2015 Completion of process modification, evaluation and demonstration of advanced ammonia technology; Completion of development of rigorous process development and delivery of scale up design. Final Report submitted as acceptable to ANLEC R&D

$ 255,157 Not yet started


55

Delivery of an industry report which includes a description of: (1) Recent advancement of solvent development for post combustion capture including aqueous ammonia (2) Summary of results obtained from this research project (3) Impact of the research achievements from this project on the advancement of aqueous ammonia based PCC processes for application in Australia (4) Evaluation of technical and economic feasibility for application of the improved process developed from this project


56

9 Conclusions

The project has made a good progress and has completed the milestones listed in the reporting period.

The screening tests have been carried out to investigate the effect of 6 promoters on the mass transfer

coefficients of CO2 in aqueous ammonia using a wetted wall column. The promoters include Piperazine

(PZ), 1 methyl piperazine, 2 methyl piperazine, and potassium salts of proline, taurine and sarcosine.

Introduction of these 6 promoters except potassium salt of taurine can significantly enhance CO2 mass

transfer in the solvent. The mass transfer coefficients of CO2 in the blends are significantly higher than

those in ammonia alone and also higher than those in promoter alone. The extent of increase of mass

transfer coefficients with introduction of promoters depend on the nature of promoters and their

concentrations. Except the ammonia and taurine mixture, 3 M ammonia mixed with other promoters can

have a mass transfer coefficient more than double of those for ammonia alone at various CO2 loadings. It

is expected that further optimisation of the solvent formulation to be carried out in the following steps

can lead to the development of aqueous ammonia based solvents which can match MEA in terms of CO2

absorption kinetics.

A parametric study of CO2 absorption in the mixture of ammonia and PZ has shown that PZ has no

catalytic effect on the absorption of CO2.The mechanism of the reaction of CO2 with the NH3/PZ mixture is

the simple combination of the individual reactions of NH3 and PZ with CO2. The enhancement by addition

of PZ is due to the fast reaction of CO2 with PZ and PZ carbamate. However, addition of PZ to aqueous NH3

increases the concentration of free NH3 in the solvent, thereby increasing NH3 loss. Reduction of ammonia

loss will be achieved through the process modification and solvent formulation to be carried out in the

following steps.


57

10 Future work

In the next 6 months, we will follow the plan specified in the proposal and carry out the following work

Validation of the rate based model using the previous pilot plant results. The focus is on the CO2

regeneration in the stripper.

Stopped flow kinetic study of the reaction of CO2 with ammonia in the presence of selected

promoters to understand the promotion mechanism for CO2 absorption in aqueous ammonia by

promoters.

Conducting the SO2 and NH3 absorption experiments

Process modelling of the combined removal of SO2 and CO2 using aqueous ammonia

Further optimisation of the solvent formulation to develop aqueous ammonia based solvents

which can match MEA in terms of CO2 absorption kinetics.

development of an ammonia based pcc technology for ... of an ammonia based pcc technology for...

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