CCS on Offshore Oil and Gas Installation - Design of Post-Combustion Capture System and Steam Cycle

Abstract

Most of the released CO2 on offshore oil and gas installation originates from the gas turbines that power the installations. For certain offshore installations, CO2 capture and storage (CCS) could be an alternative to decrease the CO2 emissions. When opting for a chemical absorption CO2 capture system, a heat source for the stripper reboiler is needed. Since most offshore installations are powered by simple cycle GTs, there is typically no steam available that could be used for stripper reboiler heat. A compact steam bottoming cycle could, in addition to providing the reboiler steam, partly or fully provide power from a steam turbine generator to the equipment in the CCS system, including CO2 compressors, pumps, and flue gas booster fan. Three different steam cycle configurations were designed, modeled, and simulated. The design of the post-combustion CO2 capture system is also presented but the main focus in the paper is on the steam cycle design. In addition to the energy and mass balance results, a weight assessment of the major equipment was done with the objective to come up with a simplified weight relationship for changes in the oil and gas installation size in terms of changes in total mass flow from the gas turbines. A steam cycle with a back-pressure steam turbine was ultimately selected. The back-pressure option was able to provide all necessary steam and power (with some margin) to the CO2 capture and compression system.