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The Revamping of CF Industries #5 NH3 Plant: Application of Casale’s Isothermal Technology and

Clariant’s AmoMax®-10 Catalyst

The CF Industries (CFI) Ammonia Plant No. 5 in Donaldsonville, LA has been in operation for more than 35 years. The plant’s design capacity was 1150 STPD. To improve the ammonia converter

performance CFI opted for revamping both the main and the booster Ammonia converters. The main converter was upgraded from a Casale 4 bed with interchanger and 122-C exchanger to an

Isothermal converter. The second converter which had not been in service was converted to a single bed adiabatic converter. Both converters now combine Casale’s internals with Clariant’s wustite-based catalyst AmoMax®-10. CFI led the project with the goal of achieving a higher converter exit ammonia capacity with improved energy savings. The combined effect of CFI project management

and advanced technology from Casale and Clariant resulted in a successful project. The project was initiated in 2010 and a successful test run certificate was signed by the parties in September 2013.

This discussion illustrates the teamwork between CFI, Casale, and Clariant to implement this project along with outlining the improved converter and synloop performance and production efficiencies

achieved after the project was completed.

Michael Dean CF Industries

Davide Carrara Ammonia Casale

Tim Rembold Clariant Corporation

Introduction

he CFI plant No 5 in Donaldsonville has been in operation for more than 35 years, having an original design capacity of

1,150 STPD (1,043 MTPD). With further modifications and optimizations, the plant capacity reached 1,550 STPD (1,406 MTPD) when the revamping project started. CFI initially requested that Ammonia Casale

perform a revamping study for the synthesis loop in 2010, with the following targets:

Obtain energy saving through installation of advanced synthesis converters;

Increase capacity from 1,550 STPD (1,406 MTPD) to 1,800 STPD (1,633 MTPD).

The results of this study were presented in a report in January 2011. CF elected to install the

T

2072014 AMMONIA TECHNICAL MANUAL

retrofit on the synthesis converters which included the installation, by revamping “in situ” the two existing converters, of new Isothermal and Adiabatic Casale internals (herein called IAC) and the use of Clariant’s wustite-based AmoMax®-10RS catalyst. The plant was restarted in May 2013 after the completion of the revamping activities. Ammonia Converter Retrofit Selection The ammonia conversion in CFI Ammonia 5 plant is performed in two synthesis converters. The first one (called 105-D) had a 4 adiabatic bed Casale layout, and now has been revamped with Casale Isothermal Technology. The second converter (called 1105-D) had a 2 adiabatic bed layout; the reactor had been idled for several years. CF worked with Casale to compare the perfor-mance of the existing 4-bed Casale converter design with new catalyst versus upgrading to the IAC as well as the potential use of magnetite vs. wustite-based AmoMax®-10RS catalyst. The resulting benefit of moving to the IAC was that there was about 1.8 (Molar %) increase in the exit Ammonia concentration of the IAC vs 4-bed. Additionally the use of wustite-based AmoMax®-10RS catalyst resulted in an increase of about 0.6 (Molar %) exit Ammonia concen-tration out of the IAC. The 1105-D counted for a total additional increase of ammonia concen-tration of 2.55 (Molar %), of which the installa-tion of wustite catalyst contributed to about 0.5%. As will be further discussed in later sections of this paper, the converter internals and loop con-figuration were selected primarily because they offered the highest performance advantage with an expected energy saving of 1.058 MMBTU/ST (1.230 GJ/MT) as compared against previous design at End Of Life Condi-tions. The efficiency increase is attributable to the low pressure drop design and, mostly, to the

higher conversion per pass. The two converters show low differential pressure even in the series configuration. The higher conversion is achieved thanks to the optimized temperature profile and full catalyst utilization for reaction (i.e., no dead zones) offered by this design. The use of wustite-based AmoMax®-10RS catalyst also made an important contribution to the start of run (SOR) higher-than-expected efficiency. The actual energy savings proved to be 1.202 MMBTU/ST, (1.398 GJ/MT). Casale Internals Design Overview Both isothermal and adiabatic installed technol-ogies share the common advantages of the well-known Casale layout. The selected configura-tion, namely 2 converters in series (isothermal followed by adiabatic), gives high per-pass con-version. This helps reduce the circulation of the loop and therefore the total pressure drop. An-other factor positively affecting the synthesis loop pressure drop is the single-bed configura-tion of both converters, with the application of Casale Axial-radial technology, which is shown in Figure 1. As will be explained in later sections of this pa-per, the reduced load on the synthesis gas com-pressor recycle wheel helped obtain considera-ble energy saving.

Figure 1 - Axial-radial design for catalytic beds

208 2014AMMONIA TECHNICAL MANUAL

Also the reliability of the converter is enhanced by the improvements developed and introduced by Casale in recent years (e.g. slotted plates, elastic ring seals). Isothermal Converter

As mentioned above, the first of the two converters has an isothermal design. This converter was de-signed with one axial-radial bed directly cooled by plates immersed in the catalyst. This allows a simple mechanical design, which can be installed in a shorter time in the existing converter with respect to multi-bed layouts. The ex-changer plates are ar-ranged radially-in a verti-cal fashion and the cold gas inside the plates flows in parallel with the react-ing gas in the catalyst.

Figure 2 – New isothermal internals of 105-D ammonia converter The converter feed gas is warmed up to react-ing condition inside the plates by exchanging heat from the catalyst exothermic reaction, and is then fed to the catalyst bed. Bed collectors are made with slotted plates, the outer built in panels, the inner in one single piece. (Figure 2).

Isothermal converter concept The Casale Isothermal Ammonia Converter (IAC) replaces the commonly used multiple adi-abatic catalyst bed design and offers higher per-pass conversion. The design is based on the use of cooling plates, directly immersed into the catalyst to continuously remove the heat while

the reaction proceeds. As indicated in Figure 3 below, the converter is designed to precisely fol-low the maximum reaction rate curve, therefore obtaining the maximum achievable conversion per pass.

Figure 3 – Temperature/Conversion chart – adiabatic vs. isothermal converter The design of the internals has been carried out thanks to the advanced modeling software, in-ternally developed by Casale, with the aim of obtaining the optimal reaction path inside the converter. Exchanger plates The use of plates, (Figure 4) for cooling instead of tube-based design eliminates internal size re-strictions (the use of tubes requires the presence of a tube sheet) and simplifies the construction of the internals.

Figure 4 – Detail of exchanger plate


The plates consist of purely radial channels in which the cold feed gas flows while removing the reaction heat from the outside catalyst and reacting gas. The plates ensure a high exchange area, with consequent uniform temperature pro-file across the whole bed. An important feature of the plates is that they are automatically made by laser welding, for the highest mechanical quality and reliability. Converter temperature control The converter performance is optimized by con-trolling two main variables: the inlet tempera-ture of cooling plates and the inlet temperature of the catalyst bed. The plate’s inlet tempera-ture is regulated with 122-C bypass valves. The catalyst inlet temperature is then regulated by mixing the hot gas from the plates with a cold-shot stream of fresh gas. The efficient mixing of control streams is provided by carefully de-signed mixing devices, assuring the uniform conditions of the gas entering the catalyst bed. Reliability of Casale Internals The internals of the converters are designed in order to allow free thermal expansion of all components. The nozzle connections between cartridge and pressure vessel and the connection to the exchanger plates inside the cartridge use expansion joints with internal sleeves, while all the other joints internal to the cartridge use the Casale patented elastic ring seal. In particular, the internal connection between the bottom of the 122-C and the outlet pipe with elastic ring seal, allows for easy and fast maintenance since the 122-C can be removed without cutting welds inside the converter in an inert atmosphere. In-stallation is easy as well and, as per Casale’s well proven design, no welding on existing pressure parts are performed. Moreover the single bed configuration simpli-fies the design while increasing the converter re-liability and the catalyst volume.

Materials selection The exchanger plates consist of AISI 321 stain-less steel. The selected material of construction for the plates is based on proven technology that has been installed in other converters. It should be noted that the operating conditions of the ex-changer plates are milder than the rest of the in-ternals (e.g. collectors) since the cold gas flow-ing inside the plates keeps the metal temperature at lower levels. The rest of the internals have the same design features of all Casale ammonia converters (e.g. CF Medicine Hat Plant No. 1). In general all the internals are constructed from AISI 321 stainless steel, while thin parts like expansion joint bellows are made of Inconel al-loy 600. Adiabatic Converter In addition to the revamping of the first synthe-sis converter, CFI requested that Casale assess the feasibility of revamping the existing addi-tional converter. The second converter had been idled for several years. As a result, this hot walled converter, which has no internal car-tridge, is now retrofitted to a single bed adia-batic with Casale axial-radial internals design (Figure 5). It is in series, after the isothermal converter and it shares with the isothermal con-verter the well-proven features of Casale inter-nals described above.


Figure 5 – New axial-radial adiabatic internals of 1105-D ammonia converter

Feed gas enters the pressure vessel from the bot-tom and then flows from the outer walls inward toward the inner collector. The feed gas then flows into the inner collector of the catalytic bed. The inward axial-radial flow path brings the gas, after reacting, into the central collector, and then exits the vessel from the top.

During the design phase, Casale was requested to minimize modifications on the existing con-verter internals and the synthesis loop. With this approach the external piping configuration was maintained and, thanks to the design of the in-ternals, the inlet colder gas is in contact with the vessel wall as it flows to the outer collector. This reduces the vessel temperature and ensures its reliability. The new design allowed installa-tion of a larger catalyst volume. The simple de-sign provides an easier and quick installation with minimal piping changes. Catalyst Selection Clariant’s Pre-reduced AmoMax®-10RS catalyst was selected by CF for this project based on Casale’s predictions of converter and catalyst

performance and to ensure that catalyst activa-tion could be completed with minimal water make and at lower reduction temperatures to protect both the IAC and adiabatic converter catalyst. Prior to selecting AmoMax®-10RS, the Don-aldsonville site also reviewed the performance of the then 3 year old charge of AmoMax-10 in-stalled at their sister site in Woodward, OK from startup through 3 years of operation. Dur-ing SOR performance testing, CF Woodward achieved 2.04 mol% higher outlet NH3 content, 33 STPD higher production rate with a 175 psi lower pressure when compared to the pre-revamp operation [1]. AmoMax®-10 is based on Fe(1-x)O (wustite) in-stead of Fe3O4 (magnetite) and offers the fol-lowing advantages when compared to all other iron-based ammonia synthesis catalysts, includ-ing those containing cobalt:

mechanical stability, thermal stability, higher resistance to deactivation, lower light-off temperature due to im-

proved low temperature activity. The following AmoMax®-10 data was com-piled through cooperation between Clariant and the University of Queensland [2]. Activity As shown in the Arrhenius plot on the next page, AmoMax®-10 provides higher activity at lower temperatures. This property allows for operation at lower inlet temperatures while providing more conversion per pass due to a more favorable thermodynamic equilibrium at lower temperatures.


Figure 6 – Activity of AmoMax®-10 vs. mag-netite-based catalysts Thermal Stability Thermal stability is very important to ensure the long life of an ammonia synthesis catalyst in the elevated temperature and pressure conditions of commercial ammonia converters. Lab tests were conducted at temperatures, exceeding normal operating conditions (1022°F, 550°C), to compare the thermal stability of commercially available magnetite catalysts with AmoMax®-10. As shown by the results in the figure below, AmoMax®-10 provides higher initial activity and undergoes less deactivation with time on stream. By comparison, the thermal stability of AmoMax®-10 exceeds that of magnetite-2 com-petitor-2 and magnetite-3 competitor-3 and be-haves comparably to magnetite-1 competitor-1. This has been confirmed commercially by stable operation in several references with some on-stream for more than nine years.

Figure 7 - Thermal stability of AmoMax®-10 vs. magnetite catalysts Light-Off Temperature The lower light-off temperature of AmoMax®-10RS, as shown in the figure below, allows for faster start-up of the synthesis loop, which saves both time and energy. During operation of AmoMax®-10, the lower light-off temperature results in a reduced potential for loss of reaction during process upsets.

Figure 8 - Lower light-off temperature of AmoMax®-10RS vs. magnetite catalysts


Casale Catalyst and Converter Predictions and Actual Results The main goals of the revamping were to in-crease plant capacity and realize energy savings. Both targets were successfully reached after the revamp. The information that follows are Casale catalyst and converter revamp predic-tions and actual ammonia converter and catalyst performances. Catalyst Change Comparison End of Run (EOR) Case vs SOR Case Table 1 shows the predicted energy impact of only changing out the old magnetite-based cata-lyst with new magnetite-based catalyst. This ta-ble also shows the effect of the installation of AmoMax®-10RS wustite-based catalyst instead of magnetite in the old converter configuration. Calculations were performed considering actual compressor performance and the average capac-ity achieved at the time this paper was written. BASE CASE

EOR BASE CASE

SOR BASE CASE

SOR

(A) (B) (C)

Production STPD 1,550 1,770 1,770 MTPD 1,406 1,606 1,606

Total ener‐gy consump‐tion

MMBtu/ST 3.358 2.835 2.698

GJ/MT 3.905 3.297 3.138

Total ener‐gy saving

MMBtu/ST ‐ 0.523 0.660

GJ/MT ‐ 0.608 0.756

Table 1 - Catalyst Change Comparison

Case A: calculated with EOR 4-bed Casale converter magnetite-based catalyst performance before revamping. Case B: calculated with SOR 4-bed Casale converter magnetite-based catalyst.

Case C: calculated with SOR 4-bed Casale converter AmoMax®-10RS wustite-based catalyst.

The converters revamping plus AmoMax®-10RS catalyst installation was the selected op-tion.

Converter Change Comparison Old NH3 converter layout vs revamping Table 2 illustrates the energy saving given by the revamping of the NH3 converters plus the installation of AmoMax®-10RS catalyst. The SOR base case using the Casale 4-bed converter with magnetite catalyst has also been included for this comparison. BASE CASE

SOR Rev CASE

SOR Rev CASE

SOR

(B) (D) (E)

Production STPD 1,770 1,770 1,770 MTPD 1,606 1,606 1,606

Total energy consump‐tion

MMBtu/ST 2.835 2.217 2.156

GJ/MT 3.297 2.578 2.507

Total energy Saving

MMBtu/ST 0.523 1.141 1.202 GJ/MT 0.608 1.327 1.398

Table 2 - Converter Change Comparison

Case B: calculated with SOR magnetite based catalyst and old NH3 converter layout..

Case D: calculated with SOR magnetite-based catalyst and revamping of the two NH3 converters. Case E: actual operation with SOR AmoMax®-10RS wustite-based catalyst and revamping of the two NH3 converters. Revamped Converter Performance Table 3 illustrates the catalyst and converter re-vamp results which compare guaranteed ammo-nia converter performance with test run perfor-mance after revamping. The contractual test-run was held in September 2013; further analy-sis was performed on more recent data from March 2014.


Base Case

Predicted

ContractTEST Sept. 14, 2013

TEST RUN

Mar. 14,2014

Case (A) (E)

Production [STPD] 1,550 1,800 1,766 1,817

[MTPD] 1,406 1,633 1,602 1,639

Inerts in 105‐D

[%v/v] 7.30 7.53 7.43 8.46

P out 1105‐D

[psig] 2,106 (1)

1,957 1,860 1,921

NH3 in 105‐D

[%v/v] 2.02 2.83 2.6 2.57

NH3 out 105‐D

[%v/v] 14.4 17.84 18.15 17.9

NH3 out 1105‐D

[%v/v] ‐ 20.25 20.7 20.4

ΔNH3 105‐D

[%v/v] 12.38 15.01 15.55 15.33

ΔNH3 1105‐D

[%v/v] ‐ 2.42 2.55 2.5

Energy Consump‐tion.

[MMb‐tu/ST]

3.358 2.300 2.156 2.231

[GJ/MT] 3.905 2.67 2.507 2.594

Energy Sav‐ing

[MMb‐tu/ST]

‐ 1.058 1.202 1.127

[GJ/MT] ‐ 1.23 1.398 1.311

Table 3 – Converter Performance (1) for Base Case A it refers to outlet pressure of 105-D (1105-D is idled)

The operating data have been analyzed and a model of the converter behavior has been devel-oped. The internally developed software used for the design of the converter internals, has been used to simulate the current behavior of the converter. The following Figure 9 shows, on a xNH3/T graph, the path of the Ammonia Con-version. At the time the analysis was performed, further adjustment of operating condition could be made to allow the isothermal converter to follow a better reaction path.

Figure 9 – Reaction path of isothermal con-verter

Summary of Energy Savings The overall impact of the converter revamp from the EOR to the SOR Test run is as follows:

- Predicted: 1.058 MMBtu/ST - Actual: 1.202 MMBtu/ST of which:

o 0.523 from changing the catalyst with new one.

o 0.618 from the new converters lay-out and internals.

o 0.061 from choosing AmoMax®-10 RS instead on magnetite based cata-lyst.

Project Safety CF Donaldsonville’s commitment to safety along with the collaboration between CF, Casale, Clariant, and various contractors helped ensure a safe and successful project. The following describe some of the key safety procedures implemented during this project:

Casale was instrumental in ensuring that converter retrofit components were in-spected during fabrication and shipped on-time. They coordinated the logistics of the internal component manufacturing schedule, along with coordinating pack-


aging & transportation of material from Italy to Louisiana .

Precautions for the catalyst unloading, mechanical installation, loading, reduc-tion, and startup were discussed by CF, Casale, Clariant, catalyst handlers and various contractors prior to the start of work.

In addition to these items, Casale and Clariant worked with CF to complete the revamp safely in several aspects: Casale helped ensure a safe mechanical installa-tion, catalyst loading, and reduction by complet-ing the following:

Provided an engineering design package with procedures for all the site activities and a list of required manpower and tools.

Reviewed the mechanical installation procedure with CF prior to the turna-round.

Dedicated Casale field engineers super-vised the mechanical installation of the adiabatic and isothermal converters and the loading of the catalyst.

Ensured that the catalyst was safely re-duced by providing 24-hour coverage during the catalyst reduction.

Clariant helped ensure a safe catalyst loading and reduction by completing the following:

Participated in pre-turnaround meetings with the Donaldsonville staff, Casale field engineers, catalyst handlers and various contractors to discuss the safety around loading and reducing AmoMax®-10 RS,

Ensured a safe and successful catalyst loading by providing technical service engineers to work with CF during the loading, in cooperation with Casale field engineers,

Reviewed the reduction procedure and water testing methods with Casale, CF engineering and CF lab staff to ensure

correct analysis was completed and cata-lyst was not damaged during the reduc-tion,

Performed a full walkthrough of the ammonia converter revamp prior to the reduction to ensure water analysis was sampled properly,

Ensured the catalyst was safely reduced by providing 24-hour coverage with Clariant technical service engineers.

Project milestones

CF requests feasibility study: 2010

Delivery of feasibility study: January 2011

Contract signature: July 13, 2011

Issue of Main Engineering documents: November 13, 2011

Casale, CF and Contractors meet to re-view job scope: February 9, 2012

Shipment of 1105-D internals: June 29, 2012 (on site July 31, 2012)

Delivery of 1105-D catalyst: November 26, 2012

Delivery of 105-D internals: February 15, 2013 (on site 18 March 18, 2013)

Delivery of 105-D catalyst: March 1, 2013

Installation of 105-D internals: April 8 to May 9, 2013

Start-up completion: May 28, 2013

Test run: September 14, 2013


Lessons Learned Through collaborative work from CF, Ammonia Casale, and Clariant, the Donaldsonville Am-monia #5 converter revamp project was a suc-cess. All of the field work was completed ac-cording to the schedule ensuring the highest safety for workers. The following safety points are critical to consider when undertaking con-verter revamp projects.

Start Early – Utilizing ground breaking converter and catalyst technologies re-quires significant additional time to qualify and implement.

Multiple planning and logistics meetings related to converter and catalyst change-out took place which were essential to ensure proper communication between all parties. Significant effort was under-taken to be ready for any unforeseen ac-tivities related to the congested area with several contractors at work.

Each of the three parties contributed to writing the catalyst reduction procedure. CF, Casale and Clariant provided con-tinuous support during the reduction. With the new converter design and the new type of catalyst, having this level of on-site support and cooperation was crit-ical to ensure that the reduction was car-ried out safely and successfully.

Close monitoring of the reduction pro-duced a safe startup of the ammonia converter’s at the #5 plant.

Water sampling reviews throughout the reduction process ensured that accurate water make indications could be used to adjust reduction temperature appropri-ately.

The revamp was successful due in large part to the team effort and the continu-ous technical support provided by Casale, Clariant and all participating contractors.

References [1] D. Lawrence, CF Industries, J. Ballard, Süd-Chemie, Francesco Baratto, Ammonia Casale, AICHe Ammonia Safety Symposium Meeting 2011, Paper 3b. [2]1 V. Pattabuthla, A. Grace, Incitec Pivot, S. Bhatia, University of Queensland, J. Richard-son, Süd-Chemie, Nitrogen + Syngas Meeting 2008.

Feasibility Study by Casale

January 2011

Signature of Contract07.13.2011Issue of Main

Engineering documents11.13.2011 Delivery of 105‐D internals

02.15.2013Delivery of 105‐D catalyst

03.01.2013Start up Completion05.28.2013

Contractual Test Run09.14.13


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