Decarbonisation Technology - May 2024 Issue

Pre-combustion carbon capture Pre-combustion carbon capture is the easiest route to rapid decarbonisation of the chemical and petrochemical sectors

Stephen B Harrison sbh4 Consulting

T hrough the years 2030 to 2050, it is inevitable that post-combustion carbon dioxide (CO 2 ) capture will be used to decarbonise heavy industry and fossil-fired power generation. Capturing CO 2 after air- fed combustion is expensive since the CO 2 concentration is low, and a huge volume of nitrogen gas must be processed. Pre-combustion CO 2 capture has the benefit of operating at high pressure and often with a high CO 2 concentration. The consequence is that the combined Opex and Capex costs per tonne of CO 2 captured can be only 50% of post- combustion CO 2 capture. Retrofitting CO2 capture to steam methane reformers (SMRs) for refinery hydrogen production represents a cost-effective way to achieve impactful decarbonisation. Additionally, ammonia and ethylene oxide (EO) production must remove CO 2 from the process gases to ensure the chemical reactions and catalyst performance are effective. In these cases, the Capex and Opex costs of CO 2 capture are absorbed into the core process. These applications must represent some of the easiest routes to rapid decarbonisation of the chemical and petrochemical sectors. Putting it into practice at Porthos Air Products will retrofit a CO2 capture facility at its existing Botlek SMR in Rotterdam. The SMR was built in 2011 with a capacity of around 100,000 tonnes of hydrogen per year. The annual CO 2 emissions at this production capacity would be more than 1,000,000 tonnes. The retrofitted CO2 capture, drying, and compression facility is expected to be on-stream in 2026. Retrofitting CO2 capture equipment to an SMR of this size could cost in the order of €100 million. This represents an additional 50% of the original capital cost of the SMR. Steam

is required to operate the CO 2 capture facility, and power is needed to compress the dried pure CO 2 . These represent the main operating costs. Once operational, this will be the largest low- carbon or ‘blue’ hydrogen plant in Europe. The hydrogen from the Botlek SMR will continue to serve ExxonMobil’s Rotterdam refinery and additional customers via Air Products’ hydrogen pipeline and hydrogen liquefier. ExxonMobil aims to achieve net-zero Scope 1 and 2 emissions from its operated assets by 2050. Since Air Products owns and operates the hydrogen production facility, the CO 2 emissions reduction is categorised as Scope 1 for Air Products and Scope 2 for ExxonMobil. This CO 2 capture retrofit with CO2 sequestration in the Porthos scheme will allow Air Products to reduce its CO 2 emissions in the port of Rotterdam by more than half. The Porthos CCS scheme is the first large-scale CO 2 transportation and storage infrastructure scheme in the Netherlands to achieve final investment decision (FID) and regulatory approval. CO 2 will be sequestered 3km beneath the surface of the North Sea in depleted gas fields, which lie about 20km from the coast. When capturing CO 2 from an SMR, the location from which the CO 2 is captured influences the cost (see Figure 1 ). The lowest unit cost is to capture CO 2 from the pre- combustion syngas stream prior to the pressure swing adsorption (PSA) unit (Location A in Figure 1). At this point, the partial pressure of CO 2 is at its highest. On the other hand, the maximum CO 2 recovery rate is capped at 70% because the post-combustion CO 2 from the SMR burners is not captured. To achieve low-carbon hydrogen certification in some markets, such as the EU, capturing CO 2 in the SMR flue gas may be


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