Study On Off-design Operation Performance Of Cold-end System And Operation Optimization Of Air-cooled Unit With Indirect Surface System

Because of excellent water-saving performance and lower economic backpressure compared to direct air-cooling units,indirect air-cooling units has been widely used in north China in recent years where is rich in coal resources,but lack of water resources.However,the indirect air-cooling system eventually exchanges heat with air,the backpressure is greatly fluctuated due to environmental factors,and the heat rate is still much higher than that of the wet-cooling unit of the same level.Therefore,researching on off-design operation characteristic of cold-end system and operation optimization of air-cooled unit with indirect surface systemt are of great significance to improving operation economy,promoting energy conservation and emission reduction.The main work of this paper includes the following aspects:Adopting the commercial software EBSILON,the steam turbine model was added on the basis of the condenser and air-cooling tower model,and a overall calculation model of the cold-end system was established.There were 1040 kinds of working conditions were calculated and the variation of outlet water temperature of air-cooling tower was obtained.The influence of different ambient temperature,circulating water flow and steam turbine unit load on backpressure was analyzed quantitatively,which provided reference for forecasting the performance of indirect air-cooling system.A numerical model for the variable conditions of an indirect air-cooling systerm was established,and the influence of various factors on the flow and heat transfer of the air-cooling tower is revealed.Which including the following,the influence of the ambient wind speed on heat dissipation and outlet water temperature of air-cooling tower was studied;the influence of different operation regulation of air cooling-tower on the thermal characteristics of the air-cooling tower,including the change of the flow field and the thermal characteristics inside and outside the air cooling-tower when the radiators closed in different locations and different blinds opening angle.A calculation model of operation optimization of iderect air-cooling unit’s cold-end system based on economic value of coal and electricity price was proposed,the optimal operation mode of cold-end system with different steam turbineload and ambient temperature under certain electricity price and coal price is obtained,the effect of the two changes on the optimal operation of cold-end system was analyzed.The optimal operation mode of cold-end system is affected by the combined effect of electricity price and standard coal price.In case of the electricity price is high,coal price is low,it is better to run with less circulating water flow to reduce the circulating water pump power costs and increase the electricity saling revenue.In case of the electricity price is low,coal price is high,it is better to run with more circulating water flow to reduce coal consumption costs.