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    June, 2005

Vol 1 Chapter 13: Development of the sorption enhanced water gas shift process

Rodney J. Allam et al, Air Products plc, UK

Abstract: The CO₂ Capture Project (CCP), working with Air Products and Chemicals and with funding support of the US DOE, has undertaken development of a novel precombustion decarbonization technology referred to as the sorption enhanced water gas shift (SEWGS) process. This technology is particularly attractive for decarbonizing gas turbine fuel, and hence provides opportunities for power generation with minimal CO₂ emissions, high power efficiency and potentially lower cost of capturing CO₂ for storage.

The SEWGS process simultaneously converts syngas containing CO into H₂ and CO₂ and removes the CO₂ from the product hydrogen by adsorption. The system operates as a multi-bed pressure swing adsorption unit, with each bed packed with a mixture of shift catalyst and a high-temperature CO₂ adsorbent. Carbon in the feed gas in the form of CO and CO₂ are removed from the product gas by the CO₂ adsorbent, and after specific PSA process steps, rejected as relatively high-purity CO₂ for recovery. The product hydrogen produced during the feed step contains the excess steam from the reaction and any nitrogen from the syngas generation, and is at high temperature and feed pressure. This hot fuel mixture can be burned in gas turbines with higher turbine efficiency than with natural gas firing and substantially lower NO_x formation.

During a 2-year development program, the key process performance and design issues were studied through a combination of experimental work, simulation and techno-economic evaluation. The experimental program developed and characterized candidate adsorbents in a range of tests including thermogravimetric analysis and the use of a cyclic process test unit. Many potential CO₂ adsorbent materials were screened prior to identification of the leading material, a promoted hydrotalcite (HTC), which showed the highest cyclic capacity for removal of CO₂ under the conditions of interest. Detailed parametric studies were conducted with this material to provide the sizing data for design of full-scale SEWGS units. Proof-of-concept test runs were conducted in the process test unit with a model syngas feed containing CO, H₂ and CO₂, which was fed in breakthrough and cyclic modes to a single bed vessel containing a mixture of catalyst and HTC. These tests demonstrated that the equilibrium limit for conventional reactors was overcome, a substantially decarbonized hydrogen product was produced, and a carbon recovery of over 80% was achieved.

Process designs were developed by APCI for two CCP case studies, a 400 MW combined cycle case and capture from multiple gas turbine drives in an oil-field gas compression system. Flow schemes were developed using autothermal reforming to produce syngas from the natural gas feed. Air blown and oxygen blown autothermal reformer schemes were prepared and overall power generation process performance was determined by ASPEN simulation. Process equipment sizing calculations and SEWGS cost estimates were conducted and passed, along with utility requirements, to CCP-funded cost estimators. The CCP common economic model was used to determine costs of CO₂ capture for the process in each case study and compared with the existing baseline technologies.

Carbon Dioxide Capture for Storage in Deep Geologic Formations – Results from the CO₂ Capture Project Capture and Separation of Carbon Dioxide from Combustion Sources - Volume 1
Edited by: David C. Thomas, Senior Technical Advisor, Advanced Resources International Inc, USA

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