Defining CCS Ready: An Approach to An International Definition

Appendix B: Technology Design Options for a Capture Ready PlantSyngas CleanupOne of the significant areas of potential improvement in IGCC technology is the process ofsyngas cleanup. In order to avoid damaging the turbine, particulate materials and othercontaminants must be removed before the syngas produced by the gasifier is injected intothe gas turbine.Conventional syngas cleanup is generally accomplished by cooling the syngas totemperatures as low as 38ºC or less (the coldest point is usually the syngas desulphurizationusing chemical or physical absorption processes). To humidify syngas before firing andpossibly before shifting, the syngas needs to be re-heated. To avoid these temperaturechanges and thus improve electrical efficiency and cost, less complex syngas cleanup systemswith moderately cooled syngas requirements (“warm gas cleanup”) are being developed.Warm gas cleanup processes may use solid sorbents for the removal of chlorides andsulphur at high temperatures of around 480ºC.Warm gas cleanup is projected to cost about 25 percent less than cold gas cleanup. Whencapital costs are measured on a $/kW basis, they are further reduced as both the steampower output is increased and auxiliary power requirements are lowered. 148 It should benoted that higher temperature syngas cleanup has been pursued for decades, so far withoutsuccess in terms of complete cleanup systems and actual commercial introduction.Oxygen GenerationAir separation provides high-purity oxygen (around 95%) for the gasifier. Currently, this isachieved by using a cryogenic process in which air is cooled to a liquid state and thendistilled. There are, however, new technologies for oxygen generation—as discussed abovein the oxy-fuel combustion sections.Advanced Syngas TurbineTesting shows that hydrogen diluted with nitrogen could be fired in current-vintage F-Classgas turbines. However, achieving significantly higher efficiencies, reduced emissions, andlower costs will require advances in combustor technology, materials, and aerodynamics.R&D strives to increase efficiency by 2% to 5% compared with the conventional combustorF-frame turbines. 148 Coupling the advanced syngas turbine with a low-cost air separationprocess can further increase efficiency gains and reduce cost.Dry Coal Feed PumpNew coal feed pump technology can lead to improvements in gasifier efficiency comparedwith slurry fed gasifiers, as evaporation of the slurry is no longer required. According toNETL an efficiency gain of around 1% can be achieved this way.148 U.S. Department of Energy, National Energy Technology Laboratory (U.S. DOE-NETL). (2008c). Current and futureIGCC technologies (DOE/NETL Publication no. 2008/1337).23 February 2010 95