Research On Modeling And Energy-Saving Optimization Of Cold End System In Thermal Power Units

Thermal power generation is predominant in the power supply structure of our country. Traditional thermal power units have great potentiality in saving energy and reducing consumption. Cold end system is an important auxiliary system, and its working condition has great effects on safety and economic operation. As a result, to do research on subsystems of cold end system, improve their operating characteristics, make sure condenser in the optimum vacuum, and optimize operation of cold end system, is an important way for thermal power units to reduce consumption, save energy, and improve thermal economy. Centered in the modeling, energy conservation, and optimization of cold end system, the thesis strived to build accurate models for subsystems of cold end system, and determine useful plans for energy saving and optimization of cold end systemon the basis of intensive theory analysis.The modeling of cold end system was carried out surrounded by its four subsystems, which are condenser, cooling tower, the end of lower pressure cylinder, and circulating water pump. As for condenser, a novel method for thermal performance calculation on condenser based on the theory of effectiveness of heat exchanger was proposed. The method solves prolems caused by complicated calculation on overall heat transfer coefficient and constant enthalpy difference asuumption in traditional method, and improves the precision of varying condition calculation on condenser pressure through introducing data in design condition as the reflection of condenser's nature property. As far as cooling tower, the thesis proposed an algorithm for variable calculation on cooling tower, and solves some troublesome problems when solving the nonlinear equation, such as the determination of initial value, position of real value and end condition for iteration, and so on. Both outlet water temperature and inlet air speed of cooling tower are with great importance to the thermal calculation of cooling tower. The thesis got the characteristics of real value, and supplied methods for their calculation based on the principle of enthalpy difference motive force. To the end of lower pressure cylinder, the thesis set up architecture of multi-objective energy saving for thermal power units on the basis of power characteristic to back pressure of steam turbine. It has three subsystems, vacuum protection system, optimum vacuum system, and load demand response system. They take separately charge of safe operation, economic operation and load response of power units. During the research on operation characteristic of circulating water pumps, the thesis established the model of lift and flow for variable speed pump, and gave rise to its mathematical description and solution method. And then models in different pumps' connection modes between consumed power and flow rate was established. Their mathematical description and solution method were also givenThere were three main lines in the energy saving and optimization of cold end system, one is to establish target value evaluation system for performance parameters of cold end system, the second is to determine the optimum operating mode of circulating water pumps based on the optimum vacuum of condenser, and the last one is constant vacuum optimization. First of all, the thesis proposed a conception called target value of parameters, and then set up a three-level index system for cold end system. Afterwards, target values of all index parameters are determined to be compared with their actual values so as to monitor whether equipments of cold end system are in normal operation, and finally optimize operating modes of subsystems. Secondly, inlet cooling water temperature are different when circulating water pumps are in different operating modes, so the thesis came up an idea to determine optimum vacuum on the assumption of equal environmental condition. In this process, a conception called net income power of cold end system was proposed. And then the thesis succeeded in determining inlet cooling water temperature in different operating modes of circulating water pumps, introduced the method to optimize the operation of circulating water pumps based on optimum vacuum, analyzed the process of operation optimization of constant speed pump and its energy saving effect. And finally the thesis concluded that the operation optimization of variable speed pump is a constrained, continuous, and nonlinear optimization propostion, the solution of which could result in its constant optimized vacuum.