Minimizing the Energy and Economic Penalty of CCS Power Plants Through Waste Heat Recovery Systems

Abstract

Abstract Implementation of CCS technologies into fossil power plants brings inevitable technical, energy and economic penalty. This penalty increase when low rank coals as lignite are utilized. The efficiency loss results in larger amounts of waste heat rejected into the ambient as it cannot be reasonably utilized within the power cycle. The temperature of the waste heat in some cases is however still sufficient for conversion to electricity by small modular waste heat recovery (WHR) units based on technologies such as Organic Rankine Cycle and absorption power cycle. Three generally considered CCS technologies were modelled – oxyfuel combustion and ammonia scrubbing based post-combustion (subcritical power plant with fuel drying) and pre-combustion (IGCC with Rectisol method for CO2 separation), for which the WHR options have been analyzed. Systems with WHR improve plant efficiency, but also flexibility due to decoupling waste heat streams from the main steam cycle. Results are presented for scenarios of 250 MWe coal fired power plants, applied to central European conditions. The efficiency increase in the case of an IGCC-CCS plant is up to 4.2 percentage points, followed by oxyfuel with 1.3 percentage points while effectiveness in post-combustion is minimal, 0.1 percentage points. The economic effect is positive in all CCS plants, allowing for improvements in the LCOE by up to 6.3%.