Research On The Model And Optimization Of Cold-End System In The Large-Scale Coal-Fired Thermal Power Plant

The cold-end system of large-scale coal-fired power unit is a thermal system which consists of condenser, cooling tower and circulating water pump and so on. The cold-end system has a significant influence on the economical efficiency of the power unit by changing the exhaust steam pressure. The optimization of the cold-end system is this:When the external conditions are determined such as the ambient condition and the unit load, the optimal objective function of coal-fired power unit obtains the optimum by changing the run mode of the circulating water pump. The main research content includes the modeling of thermal equipment, the mathematical description of the optimization problem, getting the optimum through the optimization algorithm. The main research results are as following:1、Put forward a method to obtain the Incremental power based the data sample. Constructing an analytical model of the final stage efficiency about the pressure ratio and the specific volume ratio through a data-drive method. Combining the heat balance calculation, the computational model of the exhaust steam enthalpy and the incremental power is constructed.2、Put forward an analytical model to calculate the thermal performance of the wet cooling tower by constructing analytical models for outlet water temperature and inlet air speed separately. Comparing to the traditional method, the analytical model reduces the iterations. Based on the analytical model, put forward a novel couple model for the condenser and the wet cooling tower which is based the heat equilibrium. Comparing to the method which is based on the temperature equilibrium, the model proposed here not only reduces the iteration number but also reduces the complexity. The practical calculation shows that the novel model has the characteristics of good convergence and fast calculating speed.3、For the common modification of two-speed or variable frequency pumps in the thermal power plants, the model of pump power consumption is constructed here according to the characteristic curve of the pump and the pipeline. When the paralleled variable frequency pumps have the different characteristic curves of the pump, an optimization algorithm with the constant flow rate is proposed here, and then the optimal operating parameters are obtained.4、Construct an optimization model for cold-end system with the objective that the on-grid energy is the largest, and an optimization algorithm is put forward here, named grid algorithm. A practical calculation for a 600 MW coal-fired power plant is done here. The best circulating flow rate is obtained according the temperature variation curve of a typical day in summer or winter. And then the energy conservation can be calculated, finally, the economical efficiency can be obtained with the local feed-in tariff.5、Put forward a scheme of separated building the dry and wet cooling tower, which is used to solve the problem that the insufficient performance and poor economical efficiency of the power unit when the temperature is very high in summer. Based on the scheme, the computational model of dry cooling tower is established, and then the calculation model of backpressure is constructed for paralleled dry and wet cooling towers. A 600 MW power plant is chosen as a case study here. It is analyzed that the economical efficiency of parallel operation of dry and wet cooling towers considering the feed-in tariff and water price.