Ammonia Technology

Topsøe ammonia technology

Topsøe ammonia technology – processes for today and the future Our ammonia experience For more than 60 years, Topsøe has been one of the main suppliers of catalysts and technology for the ammonia industry. By introduction of new catalysts, new equipment design and extensive process optimisation studies, Topsøe has contributed significantly to the development of efficient ammonia production technology. Today, approximately 50% of new ammonia plants use Topsøe technology.

Why choose Topsøe ammonia technology?

Our integrated approach of research-based catalysts and technologies ensures a fundamental understanding of the ammonia process, reinforced by decades of industrial experience as well as a full range of catalysts and technologies for ammonia production. Topsøe’s ammonia experience is unmatched as a result of more than 60 years of industrial experience with plant operations throughout the world. Topsøe can offer our clients a reliable and optimised catalyst and technology solution.

Grassroot units – tailor made solutions

The Topsøe low-energy ammonia process is adjusted according to the specific project requirements. In the design of new plants, investment cost is often the deciding factor. However, in some parts of the world feedstock prices are very high, which means that the optimum design may change from client to client. Topsøe’s approach ensures that an optimum design is achieved for each individual project in terms of minimising investment cost and operating cost. Furthermore, Topsøe has led the trend towards plant economy of scale, resulting in lower investment per ton of ammonia, and we have developed designs for plants with capacities up to 5,000 MTPD.

Alternative feedstocks and plant integration

In addition to the design of ammonia plants based on natural gas feedstock, Topsøe also has extensive experience in designing ammonia synthesis loops based on alternative feedstocks such as synthesis gas from gasification of coal, residual refinery products and hydrogen containing waste streams from other petrochemical plants. Topsøe’s ammonia plants can be integrated with production of petrochemicals such as methanol or DME, thus achieving a lower relative investment cost. Poly-production capabilities ensure lower sensitivity to market prices and enable the client to switch to producing a more valuable product. Methanol and DME synthesis are both in-house technologies of Topsøe.

Revamp options

Topsøe has always emphasised the importance of continuous optimisation of operating plants. In many cases this has led to revamp projects based on detailed optimisation studies. Our flexible and project-specific approach ensures that a revamp project is performed efficiently based on the client’s requirements.

Depending on the type and size of the revamp project, Topsøe will provide a scope of supply ranging from basic process design to complete equipment supply. Topsøe has extensive experience with revamp of proprietary as well as out-of-house plant designs with regard to lowering energy consumption, increasing capacity and flexibility of feedstocks.

The Topsøe approach

The Topsøe approach to a revamp project is to divide the project into a study phase followed by an engineering and implementation phase. Based on the objective of the revamp, which is defined in close collaboration with the client, the study will establish with reasonable accuracy the possible capacity increase and/or energy savings obtainable, and the capital expenditures required for materialising these benefits, thus creating a sound basis for the client’s decision. Topsøe’s involvement in the implementation of the revamp scheme can be tailored to the needs of the client.

The Topsøe ammonia process Topsøe continuously develops and optimises equipment, catalysts and processes for ammonia production, ensuring our clients state-of-the-art operations.

Our specialised equipment

Topsøe’s research programme has made many improvements in the process technology and development of specialised equipment for critical processing steps. Such equipment includes:

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tubular reformers secondary reformer burners Haldor Topsøe Exchange Reformer (HTER) waste heat boilers ammonia converters

Our ammonia process

Topsøe’s low-energy ammonia process scheme is optimised for the actual project conditions by selection of process features and by adjusting the process parameters. Topsøe’s ammonia plant designs are characterised by the extensive integration between process sections and the steam and power system. A new Topsøe ammonia plant will typically consist of the following main process steps:

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feed purification steam reforming CO conversion CO2 removal methanation ammonia synthesis

Our catalyst

Our catalysts and processes are developed in close collaboration between research, engineering and production, with a detailed R&D programme for the catalysts used in every step of the ammonia process, from feed purification to ammonia synthesis.

Figure 1: The ammonia proces

Feed purification

In plants using the steam reforming process it is imperative to remove sulphur efficiently from the hydrocarbon feed in order to prevent poisoning of the nickel-based reforming catalyst in the primary reformer and other downstream catalysts. Chlorine is also a poison for several catalysts, particularly copper-containing catalysts such as the low temperature shift catalyst, and it can further cause corrosion in piping and equipment. Therefore it is essential to remove both sulphur and chlorine present in the feedstock in the feed purification section. The feed purification section usually consists of units for hydrogenation, sulphur absorption and optionally chlorine absorption. All of these catalytic units are based on Topsøe’s range of feed purification catalysts.

Steam reforming

Steam reforming is a well established process for the manufacture of hydrogen and synthesis gases. The feedstock to steam reformers may be natural gas, refinery off-gases, LPG, naphtha or any mixture of these feedstocks. Topsøe’s steam reforming range Topsøe’s range of steam reforming processes includes several technologies:

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prereforming tubular reforming heat exchange reforming secondary reforming

Topsøe’s state of the art low-energy ammonia process will always include a tubular reformer and an air-blown secondary reformer. However, depending on the specific conditions such as natural gas composition, plant capacity and requirements to steam export, it may be beneficial to introduce prereforming and/or heat exchange reforming as well.

Prereforming Prereforming is used for low-temperature steam reforming of hydrocarbon feedstocks ranging from natural gas to heavy naphtha. The prereformer is located upstream the primary (tubular) reformer where it converts all higher hydrocarbons into methane. The prereformer predigests the feed and ensures easier and consistent feed for the primary reformer, resulting in savings in the investment cost as the primary reformer can be designed for milder operating conditions. Furthermore, the prereformer catalyst will pick-up any traces of sulphur and will consequently increase the lifetime of the downstream catalysts in the tubular reformer and the CO conversion section. Tubular reforming Steam reforming is used in the production of synthesis gas from feedstocks such as natural gas, refinery off-gases, LPG or naphtha. Topsøe’s fundamental knowledge of steam reforming reactions and the complex interaction between heat transfer and reaction kinetics has resulted in the development of superior steam reforming technologies and catalysts. Topsøe’s reforming designs are based on the side-fired furnace concept, which ensures optimum use of high alloy tube materials. Accurate temperature control ensures long lifetime of the reformer tubes. A range of catalysts designed for the reforming processes provide optimal plant performance. Topsøe has licensed more than 250 side-fired reformers all over the world.

Heat exchange reforming (HTER) The HTER (Haldor Topsøe Exchange Reformer) is a relatively new feature, initially developed for use in synthesis gas plants. In ammonia plants this unit is operated in parallel with the primary reformer. The advantage of the HTER is that it reduces the size of the primary reformer and at the same time it reduces the HP steam production.

Typically up to around 20% of the natural gas feed can in this way by-pass the primary reformer.

Therefore, the HTER is found to be particularly well suited in large capacity plants (especially stand-alone ammonia plants not requiring a large steam export to a urea plant) as well as in revamp scenarios where the reforming section is the bottleneck.

Secondary reforming In ammonia plants the methane reforming reaction from the primary reformer is continued in the secondary reformer. The addition of air in the secondary reformer provides oxygen for the combustion of the leftover methane. Furthermore, the nitrogen for the ammonia is introduced to the process.

The principle of the HTER is that reaction heat is provided 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 are adjusted independently of the primary reformer in order to get the optimum performance of the overall reforming unit.

The first reference for an HTER has been in successful operation in a synthesis gas producing plant in South Africa since 2003. The HTER concept is also widely used in the design of high capacity hydrogen plants.

Figure 2 illustrates a Computational Fluid Dynamics (CFD) profile of a CTS burner, illustrating the maintenance of low temperatures at the vessel walls and an efficient gas circulation pattern, thereby producing optimal mixing and minimising reactor damage.

Figure 3 illustrates a Computational Fluid Dynamics (CFD) model of a Topsøe-designed ring-type burner. The Topsøe nozzle does not experience impingement of hot gas back-flow and therefore is able to operate for much longer periods without need for repair or replacement compared to burners of conventional design.

Topsøe burner technology A critical parameter for satisfactory secondary or autothermal reformer performance is efficient mixing of the process gas and air or oxygen. Uneven mixing can result in large temperature variations above and into the catalyst bed, causing variations in the degree of methane reforming achieved and often yielding a poor overall approach to reforming equilibrium, even with a highly active secondary reforming catalyst.

Topsøe has done extensive research to optimise the burner design to eliminate the problems described above, and offers two special burners. For air-blown secondary reformers in ammonia plants, we offer a ring-type burner with a specialised nozzle shape that eliminates back-flow of hot gas onto the nozzles themselves, thereby reducing mechanical wear and damage to the burner.

The efficiency of gas mixing is primarily a function of the burner design. In addition to causing inefficient gas mixing, a poorly designed burner can damage the vessel walls, refractory or even the burner itself due to impingement of hot gas and/or flame in these areas.

In autothermal and oxygen-blown secondary reformers, the enriched air or oxygen is typically supplied at high pressures, thereby allowing for the possibility of a higher pressure drop across the reactor burner. For these services, Topsøe offers the CTS burner.

Feeding the world About 60% of the ammonia used for the world’s fertiliser production is produced with Topsøe’s catalysts and technology. Without the use of fertiliser, we would only be able to feed half of the world’s population of 6.3 billion.

CO conversion

Methanation

The performance of the CO conversion section strongly affects the overall plant energy efficiency, as unconverted CO will consume H2 and form CH4 in the methanator, reducing the feedstock efficiency and increasing the inert gas level in the synthesis loop.

The carbon monoxide and carbon dioxide content in the feed is normally reduced to less than 5 ppm before the feed passes to the ammonia synthesis converter.

The CO conversion in a Topsøe ammonia plant normally consists of a two-step process: a high temperature shift (HTS) and a low temperature shift (LTS). The process reacts water with CO and forms CO2 and hydrogen.

CO2 removal

The removal of CO2 is a non-catalytic process and has as such not been a focus area for Topsøe with respect to process development. In order to ensure that the optimum CO2 process is chosen for each individual project, Topsøe maintains close contact with all relevant suppliers of CO2 removal technology, and in-depth studies are performed regularly to optimise the integration of each technology into the Topsøe ammonia process schemes. Topsøe’s knowledge of the integration options ensures that the correct technology is selected for each individual project, taking both the technical and economical aspects into consideration. Topsøe has arrangements so that we can include the CO2 removal technology with our technology supply.

In order to ensure that the feed is free from carbon oxides, it passes through the methanator, which removes any traces of carbon dioxide and unconverted carbon monoxide from the shift section.

Cold shots

Ammonia synthesis

Topsøe’s ammonia synthesis technology is based on radial flow converters where the synthesis of ammonia from hydrogen and nitrogen takes place. Topsøe pioneered radial flow converters with the installation of the first radial flow converters in the 1960’s. Since then continuous development has resulted in a comprehensive portfolio of radial flow converter designs to meet the multifaceted requirements in the industry. Today Topsøe offers three radial flow converters adapted to client needs and plant requirements for the most efficient plant operation. Selection of the optimal converter depends on the clients’ objectives such as investments cost, energy consumption, steam production or possible reuse of an existing pressure shell. Benefits Topsøe’s converter types offer a number of benefits:

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100% radial flow through the catalyst beds to obtain low pressure and high conversion with a small size catalyst particle indirect cooling of the gas in the heat exchangers between the catalyst beds instead of quenching to avoid dilution of the converted gas total converter feed flow passes through all beds fully utilising the total installed catalyst volume stable operation with great flexibility in operating range simple temperature control

Main gas inlet Gas outlet

Inlet gas interbed heat exchager Figure 4: S-300 converter

The Topsøe S-200 converter The Topsøe S-200 ammonia converter is a two-bed radial flow converter with indirect cooling between the catalyst beds. Since the introduction of the S-200 ammonia converter in 1976, this converter type has been used in more ammonia plants than any other converter design. Two versions of the S-200 converter are available: The first has a built-in-feed-effluent heat exchanger (lower heat exchanger) below the second catalyst bed allowing the heat of the reaction to be used for preheating the boiler feed water downstream the ammonia converter. The second version is designed without a lower heat exchanger, meaning that the outlet gas from the second bed will go directly to a boiler for production of highpressure steam. The Topsøe S-300 converter Topsøe’s S-300 converter is the newest development in Topsøe’s ammonia converter portfolio and the recommended converter selection for all new plants.

The three catalyst beds offer a higher conversion of ammonia or alternatively a reduced catalyst volume compared to the S-200 converter, thus ensuring increased production or lower investment cost. The S-300 basket design has been well received by the industry, and since the first reference for the S-300 basket was sold in 1999, more than 30 plant owners have selected the S-300 basket technology. The Topsøe 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. The two converter configurations can be used 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.

Less makes more – producing ammonia 1958: 2010:

3,3 GJ to produce 2000 tonnes ammonia pr. day 1,7 GJ to produce 2000 tonnes ammonia pr. day

1.1 MM ton reduction in CO2 emission pr. year It takes energy to produce ammonia. With more efficient Topsøe catalysts and processes, we have reduced the energy required to produce 1 ton of ammonia with 50%, which also means that we have reduced the CO2 emissions substantially.

Committed to a better future

The Topsøe approach to quality

Continued improvement

Each ammonia process scheme is custom-designed based on detailed technical reviews and dialogue with our clients to ensure an optimal design to meet or exceed the required performance and specifications.

Extensive collaboration between Topsøe’s engineering disciplines, Research and Development and industrial feedback ensures fast implementation of new ideas and design features for constant improvement of our technology.

Topsøe’s product portfolio includes catalyst, licensing of technology, engineering of processing units and technical service. Proprietary knowledge in these areas makes Topsøe a valuable business partner for our clients.

We offer our clients a wide range of services through individualised service agreements. Topsøe has at its disposal a full range of resources to diagnose the most complex problems. Combined with our skilled and experienced process, mechanical and instrument engineering departments, this forms the basis for our advisory services and operational assistance. Topsøe’s unique business model integrates all aspects from fundamental knowledge to practical implementation to achieve optimum industrial efficiency. By choosing Topsøe’s ammonia technology, clients will have a competent and reliable partner for today and for the future.

Corporate PR 08.2010.2

Haldor Topsøe A/S - Nymøllevej 55 - 2800 Kgs. Lyngby - Denmark Tel. +45 4527 2000 - Fax. +45 4527 2999 - www.topsoe.com

The information and recommendations have been prepared by Topsøe specialists having a thorough knowledge of the catalysts. However, any operation instructions should be considered to be of a general nature and we cannot assume any liability for upsets or damage of the customer’s plants or personnel. Nothing herein is to be construed as recommending any practice or any product in violation of any patent, law or regulation.