May-2021

Getting the most out of syngas

Optimise production and effectively remove CO2 from syngas with the right separation equipment.

CLAUDIA VON SCALA and NATALIA MOLCHANOVA
Sulzer Chemtech

Article Summary

Carbon dioxide (CO2) removal is one of the most common activities that producers and users of synthetic gas (syngas) need to perform to obtain suitable feed for downstream processes. By utilising advanced separation column internals, including the latest column packings, businesses can maximise efficiency, throughput, and CO2 capture while also supporting environmental goals.

Syngas is a key product and ingredient for a wide range of applications within the manufacturing and processing sectors, including petrochemical and ammonia production. However, the levels of CO2 in this mixture may need to be adjusted and businesses often process this gas in order to reduce CO2 concentrations.

In a number of industrial applications, it is more advantageous to adjust the ratio of hydrogen versus carbon in syngas via shift reactions to utilise pure hydrogen in their processes. In some other cases, CO2 is removed from syngas to increase efficiency and chemical conversion in downstream activities as well as to prevent catalyst poisoning or corrosion. Carbon capture can also help to reduce the environmental impact of different manufacturing activities.

How to feed the system
In all cases, businesses need to select advanced and robust solutions that can minimise both the concentration of CO2 in syngas and energy consumption while maximising throughput and yield. When it comes to separation, column packing and internals play a key role in the overall efficiency of the process.

One of the first elements to look at is how the syngas feed enters the separation unit. Conventional feed inlets release the gas from a singular opening and hardly separate the vapour and liquid phases using gravitational forces only. Businesses can improve their separation performance by adopting a radial system, such as a tangential vapour horn or a Shell Schoepentoeter, which divides the feed into a series of discrete horizontal streams, using a number of vanes (see Figure 1). This can be installed in new facilities or retrofitted in existing units.

Thanks to these innovative designs, it is possible to dissipate the kinetic energy and momentum of the stream, reducing the likelihood of liquid entrainment. In addition, the vapour horn can provide the feed with centrifugal acceleration that promotes the liquid-vapour separation process, even under high loads. The Shell Schoepentoeter can also decrease the momentum of the feed, performing a first stage separation of liquid from the vapour, and achieving an even vapour distribution across the vessel’s cross section.

Succeeding in CO2 removal
New and existing CO2 removal units for syngas should also leverage the latest generation of packing solutions, such as Sulzer’s fourth-generation NeXRing random packing. Replacing conventional second-generation random packings with the latest components can increase column capacity by 25-35% while maintaining, or increasing, separation efficiency and product quality.

Upgrades in the design are one of the main reasons for these substantial improvements. These changes have allowed manufacturers to increase the uniformity of their bed distribution as well as the system’s wettability, strength, and durability. Furthermore, newer generation random packing can maximise the interfacial area between gas and liquid, as well as liquid flow rate.

Case study: CO2 removal
A large chemical company, specialised in the production of nitrogen based chemicals and mineral fertilizers, wanted to increase the capacity of its CO2 removal unit to boost the production of technical ammonia from 1500 tons/day (1361 tonnes/day) to 1900 tons/day (1724 tonnes per day). After assessing the system, Sulzer suggested the replacement of the second-generation random packing in the absorber and regenerator with NeXRing as well as upgrading to a Shell Schoepentoeter feed inlet device. In addition, the existing sieve trays were replaced with fixed valve trays, which would allow the manufacturer to increase column capacity, while also increasing the separation efficiency and lowering the pressure drop per theoretical stage.

These upgrades helped to boost the capacity of the plant’s CO2 removal system by 27%. It was also possible to decrease the overall pressure drop by 10% in the absorber and by 50% in the regenerator. Furthermore, the manufacturer was able to increase separation performance by reducing the concentration of CO2 at the outlet by 30%. As a result, an intensification of the ammonia synthesis process was achieved, increasing the overall output.

In addition, considerable reductions in pressure drop within the regenerator allowed the plant to reduce the temperature at the bottom of the column by 4°C. This led to a more energy efficient process and greatly reduced the risk of thermal degradation of the solvent. As a result, the plant can now reuse most of this solvent, as it is reintroduced into the CO2 removal loop and then used in subsequent separation processes, optimising the raw material consumption.

Conclusion
The effective removal of CO2 from syngas is required to enable a number of downstream activities for manufacturers. By utilising state-of-the-art separation equipment, companies can maximise their throughput and process efficiency, optimising the volume of CO2 removed as well as syngas recovery rates. A separation specialist, such as Sulzer, can help to identify the best technology for an intended application. Sulzer’s teams have been supporting industries in a variety of sectors with effective column internals and packings. These have been key to boosting CO2 removal strategies, ultimately enhancing competitiveness in increasingly challenging markets.