Technology Research On Air Injection From Underground Into Air-cooled Island Of Direct Air-cooled Unit

The exhaust steam of direct air-cooled turbine was condensed into water by air,the heat transfer performance was highly affected by the environmental parameters.If the air temperature decreased1℃, the condenser pressure would reduce about1kPa, the coal consumption of power generation would reduce about2.5g/kWh.Currently, direct air-cooled condenser was arranged on the platform which was inthe air over forty meters above sea level. Because of the high air inlet arrangement,the condenser performance was influenced by environmental conditions. Someproblems, such as, hot air reflow, flow backward, uncleanness of condenser finsurface, high oxygen content of condensed water and equipment freezing in winteret al, would appear. Of which, high exhaust steam pressure in summer and low heattransfer coefficient of heat pipe were particularly prominent.In view of the present problems existing in the operation of air-cooled island,the mode of air injection from underground into air-cooled island was put forward.The advantages of this mode, such as improving the performance of the condenserand reducing the back pressure of the steam turbine, were analyzed. The heattransfer coefficients of condenser under different air velocities against the face werecalculated. The influence of wind temperature, speed and dust deposition oncondenser pressure under two arrangement modes were compared and analyzed. Theresults showed that: when the wind speed was4m/s, compared with condenser ofhigh altitude layout, the mode of air injection from underground into air-cooledisland could reduce the condenser pressure about9~13kPa.The model of air injection from underground into air-cooled island was built,and the numerical simulation of the air flow filed and temperature filed was madewith Fluent software. The ventilation rate of air-cooled condenser was calculated,and the impact of wind speed on the heat transfer efficiency and pressure of directair-cooled condenser under the prevailing wind direction was analyzed. The resultsshowed that: under the influence of environment wind, there was no hot air reflowand flow backward for the mode of air injection from underground into air-cooledisland. When the ambient wind speed increased, the high temperature region scopeof hot air outside of the air-cooled island decreased. When the environmental air temperature was30℃and wind speed was over4m/s, compared with condenser ofhigh altitude layout, the ventilation rate of air injection from underground intoair-cooled island was greater, and the heat transfer efficiency of condenser washigher. When the ambient wind speed exceeded8m/s, the condenser heat transferefficiency of air injection from underground oblique wind tunnel into air-cooledisland was15%~20%higher than that of current ventilation mode.