Thermodynamic Performance Potential Of IGCC

Integrated Gasification Combined Cycle(IGCC) is a kind of super clean and high efficiency power generation technology. There are many ways and huge potential to improve the net efficiency of IGCC. The present work explores how much IGCC can benefit from technologies of warm gas desulfurization, Ion Transport Membrane(ITM), and advanced gas turbine. Influences of key gasification parameters on thermodynamic performance of IGCC plants have been analyzed. The main contents and results are presented as follows:1. IGCC integrated with warm gas clean-up(WGCU)Four IGCC systems with different gas clean-up processes based on the model of ZnO-desulfurization are established and compared. Impacts of key parameters of WGD on thermodynamic performance of IGCC plants including desulfurization temperature, oxygen concentration in regeneration stream, and H2S removal efficiency are discussed. It is found that the net efficiency of IGCC with full WGCU increases1.77percentage points compared with IGCC with cold gas clean-up(CGCU), among which the dry ash removal contributes about1percentage point. The net efficiency will increase0.74percentage point when the desulfurization temperature increases from200℃to650℃. However, if the way of steam injection were considered to control the same SFT, the net efficiency increases only0.3percentage point.2. IGCC integrated with ITMThe thermodynamic performance of IGCC with different ways of integration between ITM and gas turbine is discussed. In comparison to IGCC system with cryogenic air separation, the net efficiency of IGCC with full integration of ITM technology experiences an improvement of1.11percentage points, and is higher than that of the IGCC with independent ITM by1.81percentage points. In addition, in view of the full integration IGCC, influences of O2separation rate and the N2reinjection temperature on IGCC net efficiency are evaluated.3. IGCC with advanced gas turbineA quasi-1D turbine cooling model is built and validated. Impacts of turbine cooling techniques such as convection cooling and film cooling, blade material, thermal barrier coating and coolant medium on the thermal performance of GTCC and IGCC are studied.With constant "cooling-material" technology(F class), the efficiency of simple gas turbine cycle and combined cycle increases first and then decreases with the increase of combustor exit temperature. For combined cycle, the maximum efficiency appears on the point where the combustor exit temperature is1700℃and the pressure ratio is about25. With constant combustor exit temperature, the net efficiency of GTCC increases following the improvement of the "cooling-material" technology. When the combustor exit temperature increases, the effect of improving "cooling-material" technology on improving the net efficiency of GTCC becomes more obvious.Taking GE9G as an example, the performance of turbine adopting steam as the coolant medium is discussed. According to results, the net efficiency of IGCC, which adopts9G gas turbine but steam is taken as the coolant of first nozzle, is higher than that of the IGCC with9G gas turbine by0.6percentage point. When the first two stages adopt steam cooling, the IGCC net efficiency can be further improved by1.7percentage points. Additional1.1percentage points of net efficiency improvement can be obtained by taking steam as coolant of whole turbine.The net efficiency of IGCC employing M701G2、9H、M701J gas turbines is higher than that of IGCC employing PG9351FA by2.8、3.3、4.2percentage points respectively. If the "cooling-material" technology of1700℃class gas turbine keeps constant with the M701J, the net efficiency of IGCC with1700℃class gas turbine is higher than that of the M701J-IGCC by0.6percentage point. And if the "cooling-material" technology is improved in order to keep the cooling flow same to the M701J, the net efficiency can be further improved by0.7percentage point. Additional0.3percentage point of net efficiency improvement can be obtained by improving the "cooling-material" technology which can decrease the cooling flow by10%with respect to M701J.4. Influences of gasification on thermodynamic performance of IGCCInfluences of key parameters, including gasification temperature, C conversion, the mass ratio of steam to coal, on thermodynamic performance of IGCC are assessed in view of the air and oxygen blown gasification. Results show that, when the gasification temperature dropped by100℃, the IGCC net efficiency decrease by0.32-0.49and0.67～0.77percentage point respectively for IGCC systems with air and oxygen blown gasification. When the mass ratio of steam to coal increases by0.1, the IGCC net efficiency decreases by0.28～0.36and0.29～0.52percentage point respectively for IGCC systems with air and oxygen blown gasification. When the C conversion efficiency is improved by1percentage point, the IGCC net efficiency can be improved by0.42～0.45and0.41～0.43percentage point respectively for IGCC systems with air-and oxygen gasification.There is an obvious advantage in the view of thermal performance for IGCC systems with pressurized gasification with respect to the atmospheric gasification. The IGCC net efficiency of pressurized oxygen blown gasification is higher than that of atmospheric oxygen gasification by2.6～3.2percentage points, and the IGCC net efficiency of pressurized air blown gasification is higher than that of atmospheric air gasification by3.9-4.2percentage points. For pressurized air blown gasification, an efficiency gap about1.7percentage points can be affected by adopting various ways of compression.5. Calculating the thermodynamic performance potential of IGCCThe net efficiency of IGCC system whose key components include1700℃class gas turbine, dry-feed gasifier, warm gas clean-up and ITM air separation unit can reach54.8%, which is higher than the IGCC system integrated by technologies of F class gas turbine, slurry-feed gasifier, cold gas clean-up and cryogenic air separation unit by9.6percentage points. Another1.5percentage points can be further improved by integrating with syngas recirculation and high gas clean-up.