Performance assessment of an integrated gasification combined cycle under flexible operation

In this paper a simulation tool (Thermoflex®) has been setup to model an entire Integrated Gasification Combined Cycle (IGCC) on the basis of the report entitled "Cost and Performance of PC and IGCC Plants for a Range of Carbon dioxide Capture" by DOE/NETL [1]. The investigated layout has no water-gas-shift (WGS) reactor and does not allow for any CO2capture. Two gasification islands are included, each of which consists of Air Separation Unit (ASU), GEE radiant-only gasifier, quench and syngas scrubber as well as syngas cleanup. Two advanced GE's F-class gas turbines (2x232 MW), coupled with two heat recovery steam generators and one steam turbine (276 MW) constitute the power block. In the IGCC simulation, the base model of the GE 7F.05 gas turbine has been adapted to burn syngas. Mass and energy balances were carefully computed on design condition to validate the proposed modelling procedure against the IGCC performance data contained in the above mentioned report: The net power output of 622 MW was underestimated by about 5% whereas the net electric efficiency was slightly overpredicted. The off-design behavior of the syngas turbine was then simulated as dependent on ambient temperature and partial load, in preparation for modelling flexible operation of the whole power plant. The variation in IGCC net efficiency and power output was assessed in a load following operational strategy, thus reducing the load factor and varying the number and slope of ramps in a typical day. The IGCC net efficiency goes down from 42.5% to 32.8% when the load is reduced from 100% to 40% of the design rate.