introduction · web viewso 2 react with calcium carbonate in sea water to form calcium sulphate and...

Climate Change and Air Quality, Department of Environmental Affairs

Private Bag X447, Pretoria 0001

Tel: +27 12 399 9203 E-mail: [email protected]

Technical Evaluation of Sulphur Dioxide Emission

Limit for Existing Plants: Subcategory 1.1

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Table of contents

1 Introduction......................................................................................................................1

2 Legal Provisions.................................................................................................................1

3 Sulphur Dioxide Abatement Technologies........................................................................3

3.1 Limestone Lime Gypsum Technologies......................................................................3

3.2 Sea Water Scrubbing..................................................................................................5

3.3 Ammonia Scrubbing...................................................................................................5

3.4 Lime and Magnesium Enhanced Lime (MEL) Technologies.......................................5

3.5 Regenerable FGD Technologies.................................................................................5

3.6 Discussions.................................................................................................................5

4 Implications of the Amendments......................................................................................6

5 Conclusion.........................................................................................................................7

References................................................................................................................................8

Annexure A: FGD Cost and Resource Requirements................................................................9

Annexure B: Emission Inventory Estimation...........................................................................10

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1 Introduction

Sulphur dioxide is formed by combustion of sulphur containing material. The industrial

processes in South Africa that generate significant amount of SO2 are the combustion of

fossil fuels, smelting and converting of sulphides ores. These processes are listed activity in

terms of Section 21 of NEM: AQA. The SO2 emission limits for power plants are 3500

mg/Nm3 for existing plants and 500 mg/Nm3 for new plants. The existing facilities are

expected to comply with 500 mg/Nm3 from the year 2020. The major industrial sources of

SO2 in South Africa are Power Generation, Petroleum Industry, Metallurgy and Chemical

Industry. Figure 1 shows the contribution of various industrial sectors to SO2 emissions

based on National Atmospheric Emissions Inventory System (NAEIS) 2017 reports.

Figure 1: The contribution of various industrial sectors to SO2 emissions (DEA: NAIES, 2017)

2 Legal Provisions

Section 24 of the Constitution provides for the right for South African citizens to an

environment, and therefore air, that is not harmful to their health and well-being. To ensure

that this right is fulfilled, the South African Government promulgated the National

Environmental Management: Air Quality Act, 2004 (Act 39 of 2004), which was further

amended in 2014 and hereafter referred to as the AQA.

The Minister published list of activities which result in atmospheric emissions which have

or may have a significant detrimental effect on the environment, including health, social

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conditions, economic conditions, ecological conditions or cultural heritage published

under Government Notice No. 248, Gazette No. 33064 dated 31 March 2010, in terms of

section 21(1) (b) of the National Environmental Management: Air Quality Act, 2004 (Act

No. 39 of 2004). The list was amended under Government Notice No. 893, Gazette

No.37054 dated 22 November 2013.

The notice contain Minimum Emissions Standards (MES) which identify pollutants and

the associated emission limit values for any person undertaking listed activity or

activities. Coal fired boilers with net heat input of 50MW are expected to comply with

SO2 standard of 500 mg/Nm3 from the 1st April 2020.

To meet the MES a person undertaking a listed activity or activities might be required to

develop a pollution prevention strategy that consider Replace, Reduce, Recycle and

Treatment philosophy. These philosophies are summarized as follows:

• Replace

This philosophy involves a complete change in technology to mitigate air pollution.

Cleaner Production (New plants) initiatives are typical example that has the

opportunity to “replace” technology or raw material. The facility may use different

source of fuel or redesign the plant to the MES.

• Reduce

This philosophy involves process optimization and efficiency improvement programs

that improve production whilst reducing pollution.

• Recycle

Recycling and reuse of pollutants can also help to mitigate air pollution. This can be

done through process optimization and efficiency improvement as well.

• Treatment

This option is applicable if all other approach cannot be implemented. Various

abatement technologies (old plants) are available to treat various air pollutants.

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South Africa is developing country which has mainly old production plants with old

technologies. It is generally difficult to retrofit cleaner technologies in these plants without

incurring insurmountable costs. Consequently, existing plants are forced to consider tail gas

treatment of pollutants in order to comply with the MES.

3 Sulphur Dioxide Abatement Technologies

Sulphur content of coal used in power plants in South Africa ranges between 0.8% and 2%.

During the combustion process upto 90% of the sulphur is oxidized to sulphur dioxide. Flue

Gas Desulphurization (FGD) technology is used to recover SO2 from the flue gas in the form

of pure SO2 or sulphur compounds including acids. They FGD can be classified into three

categories namely dry, wet FGD and re-generable FGD. In the wet FGD processes, acidic flue

gas reacts with alkaline solution or slurry in an absorber. The most common absorbent is

calcium carbonate (limestone); however water is also needed to convert SO2 into high

quality gypsum. This technology has an efficiency of up to 98%. In dry FGD, dry sorbent is

injected in the flue gas system or the absorber thus converting SO2 into calcium sulphide.

The dry sorbent injection has efficiency between 50% and 60% (Clean Coal Centre, 2013).

There are other dry FGD that use a more expensive hydrated lime sorbent which can

achieve up to 98% reduction.

Various desulphurization agents can be used to remove SO2 from flue gas using the

following technologies:

Limestone gypsum process

Sea water scrubbing

Ammonia scrubbing

Wellman-lord process

Regenerable process

3.1 Limestone Lime Gypsum Technologies

Considerable interest has been shown on limestone gypsum technology and it has been

used worldwide. The process is classified into wet and dry (semi-dry) FGD. The wet FGD

uses calcium oxide or carbonate and the dry FGD uses calcium hydroxide based scrubber to

absorb SO2 and form gypsum. The reactions showing how SO2 is captured are shown below.

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Dry FGD

CaCO3 + SO2 = CaSO3 + CO2 (1)

Wet FGD

The SO2 absorbed in the atomized slurry reacts with lime to form calcium sulfite (CaSO3) in

the following reaction:

CaO+ SO2 + 1/2 H2O = CaSO3. 1/2 H2O (2)

Ca(OH)2 + SO2 = CaSO3 + H2O (3)

Gypsum production

CaSO3 + 1/2O2 + 2H2O = CaSO4.2H2O (4)

Dry FGD produces a large volume of waste, which does not have many uses due to its

properties, i.e., permeability, soluble products, etc whilst wet FGD can produce commercial-

grade gypsum. Dry FGD can achieve SO2 removal efficiency of up to 94%. Wet FGD were

reported to have higher efficiency of about 97% (Singleton, 2010).

Figure 1 Flue Gas Desulphurization (ESKOM)

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3.2 Sea Water Scrubbing

SO2 react with calcium carbonate in sea water to form calcium sulphate and CO2. An

absorber is used to bring sea water and flue gas into contact where SO2 is completely

dissolves. The removal efficiency of this process is up to 98% (Siagi and Mbarawa, 2008).

This technology does not produce any effluent because the absorber effluent is discharged

into the sea.

3.3 Ammonia Scrubbing

Aqueous ammonia is used as the scrubbing agent to react with SO2 in the flue gas to form

ammonium sulphate. This process can achieve the removal efficiency of 93% (Siagi and

Mbarawa, 2008).

3.4 Lime and Magnesium Enhanced Lime (MEL) Technologies

In lime process, slaked lime is used to react with SO2. This slurry is more reactive than

limestone but more expensive (EPA, 2000). MEL is lime containing calcium hydroxide

[Ca(OH)2] and magnesium hydroxide [Mg(OH)2] (Siagi and Mbarawa, 2008). In addition to

CaO reaction, the SO2 gas will react with both calcium hydroxide and magnesium hydroxide.

The MEL can operate a pH 6 thus improving reagent utilization. It can also achieve high SO 2

removal efficiency in smaller towers that limestone scrubbers

3.5 Regenerable FGD Technologies

Regenerable FGD technologies are used mainly to recover SO2 which will be used in other

process like sulphuric acid process. Regenerable FGD technologies include four wet

regenerable processes (sodium sulfite, magnesium oxide, sodium carbonate, Wellman-lord

process and amine) and one dry regenerable process (activated carbon).

3.6 Discussions

The South Africa’s power generation sector is dominated by old plants which are located

inland. The viable option for these plants is tail gas treatment technology which can be

retrofitted to the existing power generating units. These plants operate units ranging from

100 MW to 800MW. The total installed capacity ranges from 940 MW to 4800 MW. The

large design capacity is a limiting factor for some abatement technologies. Another limiting

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is the availability of sorbent agent. Hydrated lime or slaked lime is considerable expensive

compared to limestone which occurs naturally. There are other wet FGD (Airborne

Process™, NeuStream® technology and SkyMine®) (IEA Clean Coal Centre, 2013) that use

sodium based sorbent which are more expensive for large scale operations and have not jet

being proven commercially in large scale for coal fired power plants. Semi dry FDGs include

Novel Integrated Desulphurisation (NID™), Enhanced All-Dry (EAD™) Scrubber and

VersaMAPS™ system that use hydrated or slacked lime. Dry sorbent injection technology

has been used in a number of installations however the efficiency is considerable low (50% –

60%). The favourable option for most existing plant to achieve 500 mg/Nm3 limit is

limestone based wet FGD.

4 Implications of the Amendments

To meet the 500 mg/Nm3 2020 emission limits, the existing facilities must install wet FGD.

These rules out the options of other technologies specifically dry FGD. By adjusting the limit

to 1000 mg/Nm3, other technologies can be used. It is important to note that currently

power stations around the world are using wet and dry FGD to control SO2 emissions.

However, wet limestone based FGD is commonly used for large installations.

Table 1 shows the implications of different SO2 emission limit in terms of the resources

requirements and the emissions. If all power plants have to install FGD to reduce SO2

emissions, the amount of water required equates to 100 billion litres per annum which as a

water scarce country may not afford. The limestone required for the FGD is 4.43 million tons

per annum. The proposed new limit and the suspension clause imply that only four coal

fired plants will need FGDs as opposed to fifteen. The water and limestone requirement is

now 38 billion litres per annum and 1.9 million tons per annum respectively as opposed to

100 billion litres per annum and 4.43 million tons per annum that is required when having to

comply with 500 mg/Nm3. The expected SO2 emission reduction of 79% in power generation

sector is now 58% (refer to Annexure A and B for calculations).

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Table 1: The resources and emissions for different SO2 limits

Resources Required Wet FGD

500 mg/Nm3

std

Alternative technology

1000 mg/Nm3

std

Water (l/a) 100 billion 38 billion1

Limestone (t/a) 4.43 million 1.9 million1

SO2 79% reduction 59% reduction

CO2 2 million t/a 0.8 million1 t/a

Costs (ZAR) 165 billion 61 billion1

1 The figure is based on the assumption that four power generation facilities will use Wet FGD. The values of CO2 and

Limestone are based on stoichiometry.

Both dry and wet limestone FGDs release CO2 as the by-product. The high limit of SO2

means less limestone will be used thus less CO2 will be emitted. The relaxed emission limit

has positive impact on climate change compared to a stricter limit. Therefore, to meet the

1000 mg/Nm3 less CO2 will be emitted. The FGDs that does not use limestone has minimal

impact on climate change.

If all power stations were to install limestone based FGD, the expected CO2 emissions are 2

million tons per annum. The proposed 1000 mg/Nm3 will require only four power stations to

install wet FGD with the expected CO2 emissions of 0.8 million tons per annum. This is over

50% reduction in CO2 emissions.

If all power plants have to install FGD to reduce SO2 emissions, they will need approximately

R165 Billions. The proposed amendments imply that only four power generation facilities

will need FGDs which lowers the costs from R165 billion to R61 billion.

5 Conclusion

South Africa does not have a SO2 challenges in the ambient atmosphere and thus could not

justify the cost of limestone based wet FGD and the required resources. The lenient 1000

mg/Nm3 will allow for more cost effective technologies to be considered. The 1000 mg/Nm3

limit means the expected reductions of 79% in power generation sector is now 58%

(assuming that all coal fired power plant comply with the 1000 mg/Nm3 standard). The

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biggest challenge in South Africa is PM. All the efforts and investments should be focused on

PM.

References

Z.O. Siagi, M. Mbarawa, An Overview of SO2 Emissions Reduction Techniques, South African

Institution of Mechanical Engineering, 24 (1), 2008

T.C. Singleton, The Decision to install Flue Gas Desulphurisation on Medupi Power Station:

Identification of Environmental Criteria Contributing to the Decision Making Process,

University of Witwatersrand Thesis, 2010

C.L. Stephen, P.R. Godana, A. Moganelwa, C. S. van Heerdren, J. Bore, Y. Singh, E. Patel S.

Stefan, Implementation of De-SOx Technologies in an Eskom Context & the Medupi FGD

Plant Retrofit Project, Eskom Holdings SOC

Controlling SO2 Emissions: A Review of Technologies, USA Environmental Protection Agency, 2000

R. Inglesi-Lotz, J. Blignaut, Estimating the opportunity cost of water for the Kusile and

Medupi coal-fired electricity power plants in South Africa, Journal of Energy in Southern

Africa, Vol 23 No 4, 2012

Annual Energy Outlook 2014, US Energy Information Administration, 2013 (Presentation)

Advances in multi-pollutant control, IEA Clean Coal Centre, 2013

Department of Environmental Affairs: National Atmospheric Emission Inventory System,

2017

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Annexure A: FGD Cost and Resource Requirements

The cost of FGD was based on the US Energy Information Administration capex of R3,47

million /MW.

The chemical equation below was used to calculate the limestone, gypsum and CO2

emissions expected by reducing SO2 emissions.

(A1)

The Department of Energy FGD water consumption of 0.25 m3/MWh (Inglesi-Lotz and

Blignaut, 2012) was used to estimate water consumption.

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Annexure B: Emission Inventory Estimation

Methodology to estimate the percentage reduction of SO2 emissions

The baseline inventory was obtained from National Atmospheric Emission Inventory System

(NAEIS). The inventory used was from the 2017 NAEIS reporting period.

Two scenarios were considered i.e. 500 mg/Nm3 and 1000 mg/Nm3 limits

i. 500 mg/Nm3 limit scenario

This scenarios is based on all power generating units complying with the 500

mg/Nm3. If the unit is already achieving 500 mg/Nm3, the emission would then

remain constant.

ii. 1000 mg/Nm3 limit scenario

This scenarios is based on all power generating units complying with the 1000

mg/Nm3. If the unit is already achieving 1000 mg/Nm3, the emission would then

remain constant.

The emissions for 2020 limit and the 1000 mg/Nm3 limit scenarios where evaluated using

the emissions reduction factors which are based on the ratio of the limits and the current

unit performance. The expression for the reduction factor (x) is shown in Equation A2-A3.

M 2020=xM current∵QC 2020=xQCcurrent (A2)

where

M is the mass flowrate

x is the reduction factor

Q is the volumetric flowrate inside the stack

C is the SO2 concentration inside the stack

Assuming Q is constant for the baseline and the two scenarios. The purpose of each

scenario is to evaluate emissions at different concentrations.

x=C2020Ccurrent (A3)

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Table B1: Emission inventory for 500 mg/Nm3 and 1000 mg/Nm3

Baseline 500 100 Percentage reduction

SO2

(kg/annum)

SO2

(kg/annum)

SO2

(kg/annum) 500 1000

2242731723 471505425,7

934304418,

8 78,97% 58,34%

Table B2: Detailed emission inventory for 500 mg/Nm3 and 1000 mg/Nm3

Source NameSO2

(kg/annum)

Current

performance

(mg/Nm3)

500 SO2

(kg/annum)

1000 SO2

(kg/annum)

Eskom Port Rex Power Station 78,88 500 78,88 78,88

Eskom Lethabo Power Station 30942859 2000 7735714,75 15471429,5

Eskom Lethabo Power Station 32345784 2000 8086446 16172892



Eskom Lethabo Power Station 34299950 2000 8574987,5 17149975


Eskom Matimba Power Station 85073147 3500 12153306,71 24306613,43




Eskom Matimba Power Station 81498410 3500 11642630 23285260

Eskom Matimba Power Station 77076125 3500 11010875 22021750

11

Eskom Medupi Power Station 31218000 3500 4459714,286 8919428,571

Eskom Medupi Power Station 41645000 3500 5949285,714 11898571,43

Eskom Medupi Power Station 0 3500 0 0

Eskom Camden Power Station 31543000 2000 7885750 15771500




Eskom Grootvlei Power Station 21265757 2500 4253151,4 8506302,8

Eskom Grootvlei Power Station 9848570 2500 1969714 3939428

Eskom Majuba Power Station 37213000 2000 9303250 18606500






Eskom Tutuka Power Station 33412000 2100 7955238,095 15910476,19






Eskom Arnot Power Station 16202205,67 2000 4050551,418 8101102,835

12






Eskom Duvha Power Station 27731000 3500 3961571,429 7923142,857





Eskom Hendrina Power Station 38643725,11 2000 9660931,278 19321862,56

Eskom Hendrina Power Station 64857026,35 2000 16214256,59 32428513,18

Eskom Kendal Power Station 42437000 2500 8487400 16974800






Eskom Komati Power Station 11180400 1500 3726800 7453600




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Eskom Komati Power Station 1500 0 0

Eskom Kriel Power Station 37552000 3500 5364571,429 10729142,86

Eskom Kriel Power Station 80227000 3500 11461000 22922000

Eskom Matla Power Station 90685498,79 2000 22671374,7 45342749,4

Eskom Matla Power Station 2000 0 0

Eskom Matla Power Station 34412991 2000 8603247,75 17206495,5

Eskom Matla Power Station 35909047 2000 8977261,75 17954523,5

Eskom Matla Power Station 19469020 2000 4867255 9734510

Eskom Kusile 251000 500 251000 251000

Eskom Acacia Power Station 85,72 500 85,72 85,72

Eskom Gourikwa Power Station 99 500 99 99





Kelvin Power Pty Ltd 804710,56 500 804710,56 804710,56






City of tshwane - Pretoria West 2239,41 500 2239,41 2239,41

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Power Station

Eskom Ankerlig Power Station 2128 500 2128 2128









Total 2242731723 471505425,7 934304418,8

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