Study On The Optimal Operation Key Technology Of Direct Air Cooling Power Plant

In China, direct air cooling (DAC) unit develops rapidly in the region of coal-rich and water-poor. But in operation, there are many problems such as higher back pressure, poor vacuum leakage performance, hot air recirculation, radiator fouling and freeze, which influence seriously safe and economic operation of DAC unit. Take domestic 300MW DAC unit as an example, the operation performance was analyzed, and the key technologies and solution scheme of summer operation and anti-freeze were approached.The simple calculation method of air cooling condenser (ACC) off-design performance was brought forward, and condenser pressure target value and off-design performance curves were obtained, which was satisfied with the data provided by manufacturer. Fouling thermoresistance and cleaning coefficient of tube outside were calculated, and the tendency of cleaning coefficient with time and optimum cleaning period were obtained. Differential relationship equation between condenser pressure and its influencing factors were derived, and the main factor influencing condenser pressure was found. The optimal rotate speed of fan was calculated also. Based on VB 6.0 software, performance calculation program of ACC is written.Seven different types of spray cooling systems were designed, and numerical analysis model of spray cooling system was established. The influence of system structure, nozzle type, cooling mode on the performance of spray cooling system was analyzed, and the results show that the important factors of influencing heat exchange are nozzle number and vertical dimension from radiator. The cooling performance of direct evaporation mode is better than that of adiabatic humidification mode, and spray system D with spiral nozzle is the best option.Numerical analysis model of environmental wind influence was built, and the relationship between heat exchange efficiency of ACC and wind direction & speed was obtained. The influence of installing windbreak net down along windbreak wall was simulated, and the temperature and speed field with or without windbreak net were compared. The influence of opening ratio and net height were approached. The results show that air flow and heat transfer rate of air cooling unit with windbreak net are both increased, and the higher wind speed is, the more increment is. For 6m/s crosswind, the optimal opening ratio and height of windbreak net are 15% and 12m. For 6m/s wind from boiler side, the optimal opening ratio and height of windbreak net are 28% and 7m.The method of monitoring radiator freeze status was brought forward based on finned tube wall temperature. The acceptable minimum limit of steam flow (AMLSF) is calculated, and the relation between AMLSF and environment temperature was obtained. Tube frozen coefficient and economic back pressure of anti-freeze were calculated also. The model of diagnosing ACC freeze was built based on fuzzy neural network, and the diagnose software was developed, which was proven to be feasible.Take domestic 300MW DAC unit as an example, the optimal operation and guide system was exploited based on MS Dotnet 2.0 + Fortran V4.0 + J2EE 2.0. The system was proven to be reliable by operation practice.