Pathway for Advanced Architectures of Oxy-pulverized Coal Power Plants: Minimization of the Global System Exergy Losses
Résumé
The objective of this paper is to assess the improvement potential as well as heat integration opportunities of the oxy- pulverized coal power plant by means of the mapping exergy destruction sources on a conventional architecture as a first step towards an integrated, highly efficient system with optimized operating conditions and advanced architecture. On the basis of a first generation oxy-fired power plant, composed by conventional cryogenic ASU and CPU, a standard pulverized-coal boiler with supercritical steam cycle, the whole system is modeled at elementary equipment level. Operating conditions and current state-of-the-art design are considered in order to set a base-case for the identification of the exergy destruction.
The exergy analysis reveals the location and the magnitude of the losses. Main losses occur in the boiler, steam generation, turbines, distillation unit, compression steps of the ASU and CPU, gas quality control system, and in the regenerative heater. According to this assessment, a novel architecture is investigated. Compression heat integration, bypass regenerative heater with improved heat exchange, preheating of the oxygen flow with the bypass flow surplus heat and reheat of the cold depolluted flue gas in a regenerative heater are implemented. Important reduction in exergy destruction is reported and the exergy efficiency of the integrated power plant increases from 36.4% to 39.6% (considering CO2 as a product), which corresponds to an overall exergy destruction diminution of 16%. The resulting net plant energy efficiency is 36.1%LHV, which is a 3.5%-pts increase compared to the base-case oxy-fired power plant, reducing the energy penalty down to 7.9%-pts when compared to the reference air-fired unit without CCS.