Research PaperHeat transfer and thermal characteristics analysis of direct air-cooled combined heat and power plants under off-design conditions

- Heat transfer and heat supply characteristics of cold end are modeled.
- Coal consumptions in different modes, temperatures, fans columns are calculated.
- Optimal fans operation columns are proposed under different boundaries.
- Optimal fans mode reduces coal consumption up to 0.86 g/kW h.

The distributed energy systems and efficient utilization of traditional fossil fuel are confronting great opportunities under present energy framework in which coal power dominating and renewable energy emerging gradually. Heating technology, especially cogeneration of heat and power (CHP), has been increasingly concerned and rapidly developed in recent years. It is an effective way for direct air-cooled power units to cope with rigorous complex environmental conditions, decrease coal rate and pollutant emission. This paper analysed the heat transfer characteristics of heating network and air-cooled island and obtained the cold end parameters of steam turbine under off-design condition, which is used to stimulate the operation state combined with relative parameters. The heat transfer characteristics of air-cooled island under different operation mode of air-cooled fans was acquired by introducing heat transfer coefficient; the power consumption of air-cooled island and the net power output were calculated with the relationship between frequency and power, air-cooled based on which the optimal operation and regulation method were determined. The optimized operation mode of both heating system and air-cooled system were determined under different ambient temperature and regulation method. The result showed that a maximum 0.86 g/kW h coal consumption reduction was reached in optimal fans operation mode, which meant the method scientifically supported the development of heating technology and further improved the processes of energy-saving and CO2 reduction.