Ammonia Production can be More Smart, Safe & Profitable
Merethe Kjul Hoffmann
Technology Marketing Manager, MSc
Haldor Topsoe

This article talks about brand new technology for the production of ammonia, primarily for fertilizer.

The ammonia and fertilizer industries are changing as the drive for smart industrial solutions that exploit feedstocks in an optimal way continues to intensify. Natural resources must be utilized in the best possible way to secure profitability and reduce environmental impact, but advances have been scarce in the very mature ammonia production technology. Nonetheless, a new solution based on SynCOR™ synthesis gas technology widely used in the gas-toliquids industry offers the ammonia industry an opportunity to produce ammonia in a smarter, safer and more profitable way - with significantly reduced environmental impact.

The new solution is based on autothermal reforming for the production of syngas in ammonia plants and thereby challenges conventional tubular reforming. The technology brings significant benefits in large-scale applications, most notably an extremely low steam-to-carbon ratio of 0.6 and capacities above 6,000 MTPD in single-train plants. This enables ammonia and urea producers to gain significant economies of scale that cannot be achieved with conventional technology.

Figure 1: Simplified process sheet of Topsoe's SynCOR Ammonia™ plant

Catalyst induced a technology shift

Conventional ammonia plants use a high temperature shift followed by a low temperature shift. A standard high temperature shift uses an iron/chromiumbased catalyst, which demands a minimum operating steam-to-carbon ratio of 2.6. That changed with Topsoe's introduction of the first commercial iron-free high temperature shift catalyst (SK-501 Flex™). This catalyst is based on promoted zinc aluminum spinel, which can operate at very low steam-to-carbon ratios at typical high temperature shift conditions, but without the risk of mechanical integrity or by-products associated with iron/chromium catalysts. The zinc aluminum catalyst opens up new possibilities for ammonia producers, as they can reduce their plants’ steam-to-carbon ratio significantly with Topsoe’s SynCOR Ammonia™ process.

This solution may be a new opportunity in ammonia production, but the technology is well-proven in other industrial applications, especially within gas-to-liquids. SynCOR Ammonia™ is based on stand-alone autothermal reforming by oxygen and uses well-known and industrially proven process steps and equipment. Today, the combined industrial operation of SynCOR™ units exceeds 70 years, and the technology has demonstrated availability factors greater than 99% as an average over operating periods longer than five years.

Due to the introduction of the new shift catalyst, the operating conditions are quite different from the conditions in conventional ammonia plants. With only 0.6 steam-to-carbon ratio, the shift section is limited by the low water content to perform the shift reaction, to achieve an acceptable CO slip, and at the same time minimize the formation of by-products.

Figure 2: Comparison between steam methane reformer (SMR) vs. SynCOR Ammonia™

However, an efficient solution to deal with this low water content, is the introduction of a second shift operated at medium to high temperature in combination with recirculation of steam from the process condensate stripper. Depending on the specific requirement, the second shift catalyst can be SK-501 Flex™ or a copper-based catalyst.

After the shift section, by-products are condensed out together with process condensate. The solution reduces the well-known problem of especially methanol entering the CO2 removal section in conventional process layouts. The process condensate and washing water, which contains the shift by-products, flows to a process condensate stripper that strips off practically all shift by-products.

The stripper steam containing the shift byproducts is recycled to the inlet of the high temperature shift section.

Less and smaller equipment reduce cost

From a cost perspective, it is critically important to stay within commercially available standard sizes for equipment and piping, no matter the size of the plant. Exceeding standards limits the number of possible vendors and increases cost.

SynCOR Ammonia™ operates at a steamto- carbon ratio of 0.6, which reduces steam throughput by 80% compared to conventional plants. In combination with an inert-free ammonia synthesis, this makes it possible to significantly reduce the size of piping and equipment throughout the plant. It also enables the use of a single ammonia converter operating at single pressure.

The process uses a standard commercial CO2 removal unit. However, the CO2 absorber is relatively smaller than for conventional design because nitrogen is added further downstream.

After the CO2 removal section, remaining CO2 and H2O is removed in a synthesis gas drier unit. Then CH4, Ar and CO is removed in a nitrogen wash, in which N2 is admitted to the synthesis gas to adjust the hydrogen-to-nitrogen ratio to the level required by the ammonia synthesis. The result is an inert-free synthesis gas, which makes methanation, purge gas ammonia wash, and hydrogen recovery units obsolete and significantly reduces sizes of high-pressure equipment and piping. Furthermore, less power for recycling compressors is needed. The simplified process scheme translates directly into CAPEX and OPEX savings.

The inert-free synthesis loop uses a single S-300 ammonia converter in a standard, well-proven Topsoe ammonia synthesis loop with single pressure level. The required converter size is already referenced.

Figure 1 shows the main process steps, and table 1 provides a comparison of the main differences between a conventional plant and SynCOR Ammonia™.

Economies of scale

The scaling exponent relating to the CAPEX cost of a plant has huge impact on economies of scale and Total Cost of Ownership in the plant's lifetime. SynCOR™ has a very advantageous scaling exponent in comparison with conventional tubular steam reforming and is referenced within the full capacity range to above 6,000 MTPD ammonia. Tubular steam reforming is beyond reference above 3,500 MTPD. See figure 2 for a comparison.

The SynCOR™ technology is competitive from well inside the conventional tubular steam reforming capacities and becomes the preferred choice at large capacities because of its referenced single line capacity above 3,500 MTPD and significant economies of scale.

Production cost in large-scale single train plants is reduced by a combination of attractive scaling exponent, reduced steam throughput, inert-free ammonia synthesis, and reduced sizes of piping and equipment. Due to the differences in scaling exponents and CAPEX cost, SynCOR Ammonia™ becomes increasingly competitive the higher the capacity and the result can be two-digit savings per ton in production cost.

Environment and Safety

SynCOR Ammonia™ significantly improves environmental impact, personal safety and process reliability and has the potential to bring down the number of lost production days.

The overall energy consumption figures for SynCOR Ammonia™ is up to 3% lower than for conventional designs. In addition, electric power for the air separation unit can be obtained from sustainable energy sources, which will reduce CO2 emissions per ton of product considerably. The total reduction of CO2 emissions from natural gas firing and sustainable power sources amount to 30%, when assuming 100% conversion into urea.

Table 1: The Main differences between a conventional SMR based plant and SynCOR Ammonia

NOx emissions are more than 50% lower compared to conventional tubular steam reforming plants.

Another safety benefit is gained from the SK-501 Flex™ catalyst because it is completely free from chromium, most notably the highly toxic hexavalent chromium found in all iron-based high temperature shift catalysts in the market. This helps plants to avoid the potential risk that hexavalent chromium poses to personnel safety and to the environment during product handling, operation and disposal.

Ammonia producers can also achieve cost reductions as well as safety benefits from the high degree of automation in the SynCOR Ammonia™ process. The difference in fieldwork from large scale tubular reforming can be as much as two to three persons in favor of SynCOR™. Automation enables remote operation that can lead to fewer human errors and higher efficiency.

The autothermal reactor itself requires no fieldwork during operation, and, typically, a simple plant walk-through per work shift is all that is needed to perform surface monitoring. Alternatively, camera surveillance can replace this.

SynCOR Ammonia™ incorporates a complete integrated Safety Integrated System (SIS), which guides plant operators and ensures safe operation at all times. The number of Lost Time Incidents is reduced, simply because less people are prone to accidents. Fieldwork is turned into control room work with more time spent proactively optimizing performance. The result is a higher general safety level and a better bottom line.

Key benefits of SynCOR™ in ammonia production
  • Significant economies of scale – single trains at large capacities
  • More than 3% lower operational expenses – 3% lower energy consumption
  • Reduced environmental impact – up to 30% lower CO2 emissions, more than 50% lower NOx emissions, and up to 50% reduction of make-up water consumption
  • Increased safety - high degree of automation reduces manual fieldwork significantly