Abstract
Many Indian ammonia plants struggle with high feedstock prices. In order to survive in the competition from new plants in areas with low gas cost, many plant owners of existing plants have decided to revamp their plants to reduce the energy consumption and/or increase the capacity. New developments are needed in order to fulfil these needs of the market. This paper will highlight some of the developments made that are suitable to be implemented in revamp jobs. Furthermore, these developments are also important for design of new very large capacity ammonia plants, and process schemes for a 4000 and a 5000 MTPD ammonia plants will be covered, including an attractive option,
which has been in full-scale commercial operation since January 2003, the proprietary and patented Haldor Topsøe Exchange Reformer (HTER).
1 Introduction 

A number of developments made by Topsøe will be described, which is relevant for both revamp projects and new plants. In the following paper some of the revamp projects undertaken by Topsøe in India will be introduced, and also a novel feature, the HTER (Haldor Topsøe Exchange Reformer) implemented in the industry in a synthesis gas plant in South Africa, will be mentioned. Furthermore, process schemes to be used for very large ammonia plant capacities in the order of 4000 to 5000 MTPD will be presented

2 Latest developments in ammonia process technology


Latest New advanced technology relevant for new plants or revamp projects is available including new process concepts, improved or new equipment designs, and more effective catalysts, and new knowledge about the limits acceptable in operation of various units. The extent to which advanced technology can be applied to a specific project varies depending upon the specific situation. 

2.1 Current scheme
The Topsøe low energy ammonia process shown in Figure 1 features a well-proven concept – desulphurisation, primary and secondary reforming, two-step shift conversion, carbon dioxide removal, methanation, compression, ammonia synthesis, and product recovery. The process layout is identical to the scheme proposed for decades, but the performance has significantly improved due to improvements in catalysts and new developments in equipment designs.
3 New developments
Two main areas have significant impact on the performance and cost of an ammonia plant – the reforming section and the ammonia synthesis section. The following items will be covered in this paper: – High flux primary reformer with prereformer – HTER-p (Haldor Topsøe Exchange Reformer) – S-300 and S-50 converters In particular the design and performance of the side-fired primary reformer has been
significantly improved. This has been possible due to the availability of better tube materials with higher strength. Better tube materials permit a reduction in tube wall thickness, thus reducing the level of thermal stress in the tube wall, which again will give potentials for increased lifetime of the tubes. Very high heat flux can be accepted in a modern type reformer, and with a prereformer in front of the reformer the acceptable heat flux can be increased even further.
Figure 2. Prereformer unit
3.1 Prereforming
Adiabatic prereforming can be used for steam reforming of feedstocks ranging from
natural gas to heavy naphtha. In the prereformer all higher hydrocarbons are converted into a mixture of carbon oxides, hydrogen and methane. When a prereformer is S-removal Prereformer High flux reformer Fuel
Steam Hydrocarbon feed Fuel gas channel
To heat recovery Latest developments in ammonia production technology 4 / 20
installed as shown in Figure 2, the primary reformer has to reform methane only, and at the same time at sulphur free conditions, because the prereforming catalyst will pick up any sulphur components in the feed quantitatively. The sulphur free operation is one of the reasons for allowing a much higher heat flux in the reformer. The prereformed feed can be reheated to 650°C befor e entering the primary reformer. This will result in reduced firing in the primary reformer, and thereby a reduced fuel consumption. When the hot flue gas is used to reheat the reformer feed, the amount of heat available for HP steam production is reduced. This will overall result in a reduced HP steam production in the ammonia plant. In general, the reformer size can be reduced up to 25% in a natural gas based plant by incorporating a prereformer.
3.2 HTER-p
Figure 3. HTER-p
Another feature that can be used to reduce the size of the primary reformer, and at the same time reduce the HP steam production, is the HTER-p (Haldor Topsøe Exchange Reformer). Please see Figure 3. This is a new feature, initially developed for use in synthesis gas plants. In ammonia plants this unit is operated in parallel with the primary reformer, and that is why the name is HTER-p. Tubular reformer Secondary reformer
Process steam HTER-p Process air Desulp.
natural gas Latest developments in ammonia production technology 5 / 20
The HTER-p is heated by the exit gas from the secondary reformer, and thereby the waste heat normally used for HP steam production can be used for the reforming process down to typically 750–850°C, depending upon actual requirements. Operating conditions in the HTER-p are adjusted independently of the primary reformer in order to get the optimum performance of the overall reforming unit. Typically up to around 20% of the natural gas feed can in this way by-pass the primary reformer. 3.3 S- 350 ammonia synthesis loop
In the ammonia synthesis section, the 3-bed radial flow converter – the S-300 – has been developed and commercialised as an improved version of the work horse - the S- 200. A highly efficient combination of the S-300 converter and the one-bed S-50 converter – the S-350 synthesis loop – has been developed, which is applicable for new plants as well as for revamp jobs. Figure 4. S-350 ammonia synthesis loop  Figure 4 above describes a typical Topsøe ammonia synthesis loop. Latest developments in ammonia production technology 6 / 20
As can be seen, the loop comprises two ammonia converters, i.e. a S-300 followed by a S-50 converter. The S-50 converter is a single bed radial flow converter, which is added downstream of the main converter to increase the ammonia conversion, and at the same time to improve the steam generation. By having two converters, the heat of reaction after the last bed in the first converter can be utilised for boiling or superheating of HP steam, and the two converter configuration can be used as a mean to close the overall plant steam balance, if the waste heat available for boiler feed water preheat and boiling of steam is not in balance. 4 Recent revamp experience including the S-50 converter The new features mentioned above can be implemented in new plants as well as in revamp projects. Please below find a list of some of the revamp projects done by Topsøe in India recently: – IFFCO, Kalol, natural gas-based plant started up in 1975 designed by Kellogg – RCF, Trombay V natural gas-based plant started up in 1980, designed by Topsøe – IFFCO, Phulpur I, naphtha-based plant started up in 1980 designed by Kellogg – IFFCO, Aonla I, natural gas-based plant started up in 1988 designed by Topsøe – IFFCO, Aonla II, mixed feed-based plant started up in 1996 designed by Topsøe – IFFCO, Phulpur II, naphtha-based plant started up in 1997 designed by Topsøe – NFL, Vijaipur I, natural gas-based plant started up in 1987 designed by Topsøe
A few of these projects will be mentioned below as examples of revamp projects where some of the developments have been introduced. For details about the other revamp projects, please see ref (1) and ref (2). 4.1 Energy conservation projects
 4.1.1 IFFCO, Kalol
The project for IFFCO, Kalol is an energy saving project. The plant has actually been revamped by Topsøe earlier, where a prereformer was installed to process naphtha feed. However, this time the revamp concerns energy saving, and it was decided by IFFCO to implement the energy saving project in two phases, in order to get immediate benefits. The following revamp options have been installed in a phased manner:
Phase I
 – New LTS guard, inlet separator and BFW preheaters.
– Revamping of the existing CO2 removal system to a two-stage aMDEA process - including new LP, HP flash vessels, a new absorber, and a recycle MDEA
compressor. Latest developments in ammonia production technology 7 / 20
Figure 5. Layout of synthesis loop in M.W. Kellogg-designed plant with S-50 converter
Phase II
– Installation of a S-50 radial flow converter with internal electric start-up heater and lower heat exchanger, and MP waste heat boiler in the loop in series with the existing converter
– Drying of make-up gas and synthesis loop re-piping
– Replacement of HP and LP rotors in synthesis gas compressor with kick-back
cooler for synthesis gas compressor recycle stage
– Installation of a new boiler feed water coil in the waste heat section of the primary reformer
– Modification of ID fan turbine
4.1.2 S-50 converter – Kalol plant
The original ammonia synthesis loop contains an existing ammonia converter unit with built-in feed/effluent exchanger. After the revamp, the exit gas from the existing converter is sent direct to the new S-50 converter at a temperature of approx. 325°C. After the S-50 converter a new MP steam boiler is installed. See Figure 5. As the inlet temperature to the S-50 converter is lower than the required inlet temperature to the catalyst bed, an S-50 converter with a lower heat exchanger is applied. Latest developments in ammonia production technology 8 / 20 The S-50 converter consists of a full opening closure pressure
vessel and a converter basket. The converter basket consists of a catalyst bed and a feed/effluent heat exchanger (lower heat exchanger). See Figure 6 for details.
The main part of the gas is introduced into the converter through the main inlet in the top of the converter (A) and passes downwards through the outer annulus between the basket and the pressure shell, keeping the latter cooled. It passes to the shell side of the feed-effluent exchanger, where it is heated to reaction temperature by heat exchange with the converter effluent leaving the catalyst bed. The remaining part of the gas, the cold shot gas, is introduced through the inlet in the bottom of the converter (B). It mixes with the main inlet gas having passed the shell side of the heat exchanger, and the mixed gas passes to the top of the converter through the transfer pipe in the centre of the catalyst
bed. The amount of cold shot gas determines the inlet temperature to the catalyst bed. Figure 6. S-50 converter with lower heat exchanger At the top of the converter the gas passes to the inlet panels of the catalyst bed and through the catalyst bed in radial inward direction to the annulus between the bed and
the central transfer pipe. The effluent from the catalyst bed passes the tube side of the heat exchanger, thereby heating the feed gas to the reaction temperature, and flows to the converter outlet (C). The project was started in November 2003. Most of the new equipment was installed while the plant was running. The major modification was to install the new absorber and the flash vessels. During the normal turn around in March/April 2005, phase I of the project were implemented, and the final installation was done in particular with the
stripper arrangement and reboilers. In the turn around during May 2006, the phase II
items were installed in only 21 days. After commissioning of the new items the plant has been started up, and the test run was successfully passed by the end of 2006. Latest developments in ammonia production technology 9 / 20 4.1.3 IFFCO, Kalol energy saving and payback period The total reduction in energy is about 10%. Simple payback time period is 4.8 years. 4.2 RCF, Trombay V
The project for RCF, Trombay V is an energy saving project. The plant is more than 25 years old, and RCF decided to revamp the plant by incorporating a number of new features. The revamp project is fairly extensive, and the following revamp features have been incorporated: – Modification of primary reformer to single row catalyst tubes and addition of one more section in each chamber – Installation of combustion air preheater in reformer convection section in lieu of the BFW preheater
– Replacement of reformer burners by forced draught type
– Installation of new reforming catalyst
– Installation of new BFW preheater and separator downstream LT guard
– Installation of convection section in existing fired steam superheater with
provision for feed gas preheating and combustion air preheating
– Replacement of burners in the fired steam superheater by forced draught type
– Installation of new 5-stage flash vessel (CO2 removal) with ejectors and
mechanical steam compressor (not yet commissioned)
– Installation of hydraulic turbine with generator on rich solution (not yet
commissioned)
– Replacement of packing in CO2 removal columns
– Installation of DMW preheater OH regenerator
– Installation of additional gas/gas heat exchanger (E 311 B)
– Replacement of existing process condensate stripping system by new MP
stripping system
– Installation of additional process condensate pumps
– Spare HP BFW pump (P 701 A) to be driven by LP steam condensing turbine (not
yet commissioned)
– Modification of process air compressor
– New synthesis gas compressor and turbine drive (not yet commissioned)
– Installation of S-50 converter downstream existing converter
– Installation of new loop boiler downstream new S-50 converter
– Replacement of existing cold flare by two hot flares, one for process gas and one
for ammonia vapour
– New ammonia booster compressor, K 451 (not yet commissioned)
– New water cooler, E 503
Latest developments in ammonia production technology 10 / 20
The RCF, Trombay V revamp project started in March, 2004. Most of the options have been implemented during a long turnaround lasting for 12 weeks during May, June and July 2006. Only the new synthesis gas compressor with driver and the mechanical steam compressor are not yet started. These remaining items will be taken into operation after the scheduled turn around in April 2007. Especially the modifications of the reformer have been very interesting. The old type “snake row” reformer has been converted to straight row, and a new section has been added to each of the chambers. Furthermore, the selfinspirating burners have been replaced by forced draft burners along with combustion air preheating. Also the fired steam heater has been extensively revamped, and a new convection section has been added in order to save energy. This section comprises natural gas preheating and combustion air preheating.
4.2.1 RCF, Trombay V energy saving and payback period The total reduction in energy saving is approx. 19% due to implementation of the energy saving measures. Simple payback period is about 4.4 years. 5 Experience with installation of HTER (Haldor Topsøe Exchange Reformer) 5.1 Industrial experience The first HTER has already been in successful operation for more than 4 years in a synthesis gas plant in South Africa, with Sasol Synfuels and seven more are currently in the engineering design phase. The HTER was installed to increase the reforming capacity of the plant. The revamped unit was ready for operation and start up in January 2003. Only 5 years had passed since the first basic ideas were exchanged about the project. During this period of time, the project went through pre-feasibility and feasibility studies including material screenings, etc., basic and detailed engineering as well as construction and commissioning. This remarkable achievement was possible only through a committed effort from the involved parties, Sasol Synfuels, Sasol Technology and Topsøe. Details of the industrial experience are given in ref (3). Figure
7 shows a picture of the HTER internals being lifted after arrival to the site.
Latest developments in ammonia production technology 11 / 20 Figure 7. HTER internal being installed Figure 8 shows the layout of the reforming section after revamp. Since the initial startup, no unforeseen stops were related to the HTER, and the HTER has been in continuous operation with the exception of planned shut-downs. This has led to a high availability factor (97%). Figure 8. Layout of reforming section revamped with HTER Product flow rate 133% Latest developments in ammonia production technology 12 / 20 During the test-run, it was shown that the predicted capacity increase and conversion of the revamped unit was reached – in fact, there was some additional capacity in the unit compared to the expected figures of a 33% capacity increase. Likewise, the
pressure drops were found to be stable and well within the anticipated values.
Four years of operating experience with the revamped unit has proven the viability of the HTER revamp concept. The operational benefit was achieved as anticipated, and Sasol and Topsøe are jointly in the process of studying how future capacity expansions can be made with this proven technology.
6 Use of the HTER technology in ammonia plants In the reference plant with Sasol Synfuels, the HTER is placed downstream of an ATR, but the HTER is equally well suited to be located after a secondary reformer or even after a stand-alone tubular reformer. The technology is thus generally interesting in many business areas such as hydrogen production, methanol production, GTL/CTL
and ammonia production.