Case Studies for Various Igcc Parameters Using Blended Coal/biomass with Supercritical Steam Bottom Cycles

Great efforts have been spent to reduce the greenhouse gas (GHG) emissions and improve the efficiency of the Integrated Gasification Combined Cycle (IGCC). This study focuses on investigating two approaches to achieve these goals. First, replace the traditional subcritical Rankine steam cycle of the overall plant with a supercritical steam cycle. Second, add different amounts of biomass as feedstock to reduce carbon footprint as well as the SOx and NOx emissions. The goal of this study is to examine the thermal and economic impact of different design implementations for an IGCC plant. The parametric dichotomies investigated were: radiant cooling vs. syngas quenching, dry-fed vs. slurry-fed gasification (particularly in relation to sour-shift and sweet-shift carbon capture systems), oxygen-blown vs. air-blown gasifiers, lowrank coals vs. high-rank coals, and options for using syngas or alternative fuels for the duct burner in the heat recovery steam generator (HRSG) to raise achieve the desired steam turbine inlet temperature. Employing biomass as a feedstock has the advantage of being carbon neutral or even carbon negative if carbon is captured and sequestered (CCS), whether the goal is to generate chemicals or provide electrical power. However, due to a limited supply of feedstock, biomass plants are usually small, which results in higher capital and production costs. Considering these challenges, it is more economically attractive and less technically challenging to co-gasify biomass wastes with coal. Using the commercial software, Thermoflow®, the case studies were performed on a simulated 250 MW coal IGCC plant located near New Orleans and cofed with biomass from 10% to 50% by weight. The analysis is conducted using lower heating value (LHV) and 2011 USD as the standard. The results show that syngas coolers are more efficient than quench systems (by 5.5 percentage points), but are also more expensive (by $500/kW and 0.6 cents/kW-hr). For the feeding system, dry-fed is more efficient than slurry-fed (by 2.2-2.5 points) and less expensive (by $200/kW and 0.5 cents/kW-hr). Sour-shift CCS is both more efficient (by 3 percentage points) and cheaper (by $600/kW or 1.5 cents/kW-hr) than sweet-shift CCS Natural gas is a better duct burner fuel than syngas (by 1.7 percentage points efficiency, $400/kW capital, and 0.5 cents/kW-hr CoE). Higher-ranked coals are more efficient than lower-ranked coals (2.8 points without biomass, or 1.5 percentage points with biomass), and have lower capital cost (by $600/kW without using biomass, or $400/kW with biomass.) Without biomass, they produce a lower total CoE (by 0.1 cents/kW-hr), but are 0.21 cents/kW-hr more expensive with biomass. Finally, plants with biomass and low-rank coal feedstock are both more efficient and have lower costs than those with pure coal: just 10% biomass seems to increase the efficiency by 0.7 points and reduce costs by $400/kW and 0.3 cents/kW-hr. However, for high-rank coals, this trend is different: efficiency decreases by 0.7 points and CoE increases by 0.1 cents/kW-hr, but capital costs still decrease by about $160/kW. NOMENCLATURE ASU Air Separation Unit RSC Radiant Syngas Cooler CSC Convective Syngas Cooler GT Gas Turbine ST Steam Turbine HRSG Heat Recovery Steam Generator IGCC Integrated Gasification Combined Cycle GHG Greenhouse Gas(es) AGR Acid Gas Removal DA De-aerator DB Duct Burner HP High Pressure (PSI) IP Intermediate Pressure (PSI) BMR Biomass Ratio (biomass/feedstock) (wt%) M.W. Molecular Weight (lbs/lb-mol) R.H. Relative Humidity LHV Lower Heating Value (Btu/lb) HHV Higher Heating Value (Btu/lb) CoE Cost of Electricity ($/kW-hr) O&M Overhead and Maintenance ($)