Comparative performance assessment of IGCC and USC plants integrated with CO2 capture systems

In recent years coal-fired power plants have increased their role in the global energy scenario and in this framework global warming issues require a sustainable use of coal and great efforts for greenhouse gas reduction, addressing R&D projects towards solutions with low environmental impact. With this aim, this paper reports on a comparative performance assessment of two power generation technologies: an Ultra Super Critical (USC) steam plant and an Integrated Gasification Combined Cycle (IGCC) plant. Performances were assessed referring to typical USC and IGCC large-size plants (400-500 MW), fuelled with a low sulphur coal and integrated with CO2 capture systems. The study is based on simulation models specifically developed through Aspen-Plus and Gate-Cycle commercial software. The USC plant is integrated with a SNOX section that removes simultaneously sulphur and nitrogen oxides and requires lower absorption energy compared to traditional FGD systems, allowing preheating of boiler inlet air and producing no process waste. The USC plant is also integrated with a low temperature CO2 capture section based on a chemical absorption process with an aqueous solution of MEA, and CO2 conditioning and compression sections. The IGCC plant is based on a Texaco entrained bed gasifier equipped with pre-combustion systems for acid gas removal and integrated with a 3-pressure level combined cycle. Fed by a water-coal slurry and a high purity oxygen, the gasifier produces a high temperature syngas that feeds the combined cycle. The IGCC is integrated with a syngas conditioning section, composed of radiant and convective coolers to produce a high pressure saturated steam that increases CC power, of a water gas shift section and a low temperature CO2 capture system based on a physical absorption process. The performance assessment of USC and IGCC plants was performed by varying the main operating parameters of both power section and gas conditioning and purification sections, with particular attention to the influence of SNOX parameters on both gas purification and the CO2 removal process. For both plants an in-depth analysis of performance penalization due to the CO2 capture systems was carried out, evaluating the influence of CO2 removal technology and efficiency