Jan-2025

Topsoe low-carbon SynCOR Ammonia process (NARTC 2025)

Topsoe pioneered advanced autothermal reforming (ATR) during the 1990s and successfully commercialised plants operating at a low steam-to-carbon (S/C) ATR technology in 2002, known as Topsoe’s SynCOR™ technology.

Henrik Rasmussen and Johan Malan
Topsoe Inc

Article Summary

SynCOR removes the limitations that other technologies have in reaching the optimal syngas composition. This advanced technology provides plant owners with a huge leap towards economies of scale in combination with a significant reduction in operational expenditure (Opex). It ensures high reliability and an on-stream performance of 99.5%, with lower requirements for operators and reduced maintenance.
Topsoe has licensed four large-scale gas-to-liquids (GTL) sites globally, several of which comprise two production units per plant. Each unit produces syngas equivalent to more than 6,000 metric tons per day (MTPD) of ammonia at a low S/C ratio of 0.6. These plants have been in successful operation for more than 150 accumulative operating years.

Topsoe’s large-scale SynCOR Ammonia™ plant has a capacity of 6,000 MTPD and is based on industrially proven equipment sizes and catalysts in both the frontend and backend ammonia loop in a single train configuration. The technology reduces the energy consumption gap for ammonia production by 10%, approaching the minimum theoretical levels.

With the large production capacity comes a reduced capital expenditure (Capex) per ton of ammonia produced. This technology scales more efficiently than steam methane reforming (SMR)-based plants, having a lower scaling exponent. From a Capex perspective, both plant types can be considered for lower capacities. However, SynCOR Ammonia becomes increasingly competitive compared to conventional SMR plants as production capacity increases, and it clearly becomes the preferred choice at large capacities. Where oxygen is available over the fence, the technology is preferred even at very low capacities.

Detailed studies have shown the following additional advantages of SynCOR Ammonia plants:
- More than 3% lower Opex.
- Up to 50% make-up water savings, which is especially important in areas where water is a scarce resource.
- An average availability above 99% of the SynCOR reforming unit.
- More than 99% carbon dioxide (CO₂) capture, which is up to 50% higher than an SMR-based plant.

The SynCOR Ammonia unit has a significantly reduced physical footprint due to the elimination of the tubular reforming unit (SMR) and the use of a single-stage ATR for the entire steam reforming conversion. Figure 1 shows how small the SynCOR reactor is, even though its capacity corresponds to 6,000 MTPD of ammonia. Figure 2 shows the larger footprint of a tubular SMR and a secondary reformer with a capacity of 1,500 MTPD. In comparison, the plot sizes of the SynCOR unit and the secondary reformer are very similar and correspond to less than 5% of the plot size of the SMR.

The most significant operating difference between a conventional SMR-based plant and a SynCOR Ammonia plant is their S/C ratios. Conventional SMR-based plants operate at an S/C ratio of around 3, while SynCOR Ammonia plants operate at an S/C ratio of around 0.6. Consequently, steam throughput is decreased by 80%, resulting in much lower water consumption.

SynCOR Ammonia plants also benefit from an inert-free ammonia synthesis, with the required nitrogen admitted just upstream of the ammonia synthesis section. In contrast, conventional ammonia plants introduce nitrogen in the secondary reforming reactor.

These features enable significantly reduced pipe and equipment sizes for the SynCOR Ammonia plants, not only in the front end (reforming, shift, and CO₂ removal sections) but also in the back end (ammonia synthesis section), resulting in reduced Capex.

The design of the inert-free ammonia synthesis loop provides another huge advantage. Where other large-scale designs require multiple pressure levels and multiple reactors in the ammonia synthesis section, SynCOR Ammonia uses a single S-300 ammonia converter in a standard, well-proven Topsoe ammonia synthesis loop with a single pressure level. The required ammonia converter size is already well-referenced industrially, with ammonia converters having a catalyst volume above 150 m³.

For comparison, an inert-free 6,000 MTPD ammonia synthesis loop in a SynCOR Ammonia plant will require less than 150 m³ of catalyst volume.

In summary, the most important factors enabling the significant benefits from economies of scale of SynCOR Ammonia are:
• Attractive scaling factor for single trains.
• Operation at 0.6 S/C ratio.
• 80% reduced steam throughput.
• Inert-free ammonia synthesis loop.
• Reduced piping and equipment sizes.
• Reduced energy consumption.
• Single ammonia converter at a single pressure.
• Opex savings of around 3%.
• Able to capture more than 99% of the CO₂ as precombustion CO₂.

The decrease in production cost resulting from economies of scale is illustrated in Figure 3 for a conventional SMR-based plant and SynCOR Ammonia.

The SynCOR reactor design consists of a Topsoe proprietary burner, a combustion chamber, target tiles, a fixed catalyst bed, a catalyst bed support, a refractory lining, and a reactor pressure shell, as illustrated in Figure 4.

SynCOR Ammonia is designed with two high-temperature shift reactors in series, a nitrogen wash to remove the carbon monoxide (CO), and the recycling of shift byproducts. The process layout has numerous benefits, such as close to zero byproduct formation and elimination of the methanation step, purge gas recovery, ammonia absorption, and hydrogen recovery, resulting in a reduced need for compressor/recycle power and significantly reduced sizes of high- pressure equipment and piping.

A standard high-temperature shift uses an iron-chromium (Fe/Cr)-based catalyst that cannot operate at an S/C ratio below 2.6. To overcome this limitation, Topsoe invented SK-501 Flex, an Fe and Cr-free catalyst. This catalyst was installed in the first plant 10 years ago and is now in successful operation in more than two dozen plants. To date, none of the SK-501 Flex catalyst has ever needed to be replaced.

Figure 5 shows the main process steps for the new SynCOR Ammonia plant, and Table 1 provides a comparison of the main differences between a conventional ammonia plant and SynCOR Ammonia.

The nitrogen wash removes both the slip of CO from the shift section and the methane slip from the reforming section. The off-gas from the nitrogen wash can be used as fuel without any further treatment. This design generates an inert-free synthesis gas, which results in a higher ammonia conversion per pass in the ammonia synthesis converter.

The CO₂ removal unit in a SynCOR Ammonia plant can be a standard commercial amine solution. The CO₂ absorber is smaller than for conventional design because no nitrogen is added to the synthesis gas.

In the Topsoe low-carbon ammonia process, more than 99% of the CO₂ from natural gas is captured in the CO₂ removal unit and cleaned up to meet the required purity needed for carbon capture, utilisation, and storage (CCUS). This amount of CO₂ capture is up to 50% higher than what can be achieved in an SMR-based design without the use of post-combustion CO₂ capture, which is uneconomic (see Table 1).

Today, Topsoe’s SynCOR technology is by far the preferred technology for the production of low-carbon hydrogen and ammonia in the world. To date, seven low-carbon hydrogen or low-carbon ammonia units are already in construction using SynCOR technology, and many more units are in the pipeline to help decarbonise the world.

This short article originally appeared in the 2025 NARTC Newspaper, which you can VIEW HERE