One of the main advantages of IGCC technology is that it is the only form of power generation that is compatible with pre-combustion carbon capture. Part 2 of this paper will thus focus on analyzing pre-combustion CCS, utilizing both sour-shift and sweet-shift processes and comparing them to each other and to the results of post-combustion CCS from Part 1. Pre-combustion CCS plants are smaller than post-combustion ones, and usually require 25% less energy for CCS due to their compact size for processing fuel flow only under higher pressure (450 psi), versus processing the combusted gases at near-atmospheric pressure. For pre-combustion CCS, sour-shift appears to be superior both economically and thermally to sweet-shift in the current study. Sour-shift is always cheaper, (by a difference of about $600/kW and $0.02-$0.03/kW-hr), easier to implement, and also 2–3 percentage points more efficient.
Adding biomass to the system always reduces the emissions and can even make a plant carbon-negative with as little as 10% biomass by weight. In addition, the efficiency will improve (0.7 points) and power output will also improve (∼1%–3% more) for up to 10% biomass ratio (BMR) for the right kind of biomass that has been properly pretreated. Beyond 10% BMR, however, the efficiency begins to drop due to the rising pretreatment costs, but the system itself still remains more efficient than from using coal alone (between 0.2–0.3 points on average). The economic difference is fairly marginal, but the trend is inversely proportional to the efficiency, with CoE decreasing by 0.5 cents/kW-hr from 0%–10% BMR and rising 2.5 cents/kW-hr from 10%–50% BMR. Finally, the CO2 removal cost for sour-shift is around $20/ton, whereas sweet-shift’s cost is around $30/ton, which is much cheaper than that of post-combustion CCS from Part 1: about $60-$70/ton.