Design and performance analysis of coal-fired fluidized bed for supercritical CO2 power cycle

Abstract

A coal-fired circulating fluidized bed (CFB) boiler for 600 MW power plant is designed to integrate with the supercritical CO2 (SCO2) power cycle in this study. The boiler configuration, heating surface arrangement and regulation analysis were figured out based on the First Law of Thermodynamics and the basic rules of heat transfer. Compared to typical water steam CFB boilers, the SCO2 CFB boiler as a superheater unit in essence contains the simpler configuration with less heating components. More than 40% of heating surfaces for working fluid needs to be arranged in the furnace and external heat exchangers and 80% of the heat absorption of SCO2 comes from such regions of high-temperature heat resource, while only 20% comes from the backpass with the aim to recover flue gas heat. The relative low furnace temperature in CFB boiler (about 900 °C) greatly reduces the stress on the residual flue gas heat extraction and the exhaust flue gas could be cooled to 129 °C by just setting the split SCO2 flow (∼5%) preheater in backpass and doubling the area of air preheater, with which the primary air being heated up to 490 °C. The commonly used working fluid temperature regulation methods such as the spray desuperheating and adjusting external solid circulation were evaluated and proved to be still effective in the SCO2 CFB boiler.