Study On Optimal Design Cold-End System Of Large Size Coal-Fired Generating Units

Turbine cold-end system possesses dramatic potential in the lowering energy consumption of large size coal-fired generating units. For many years, researchers only focused on the operation optimization of cold-end system, which only works under the condition of no design optimization. This paper begins with large scale coal-fired generating units'earlier stage design, with full consideration of local atmosphere condition, network load distribution, units investment and cost, etc. Designed dereference combined with practical operation situation is made as well, followed by designed calculation of the optimization of cold-end system. It also proposes minimum drainage-anergy-expense method that is different from traditional minimum annual-expense method.The paper deeply researched the calculation about average heat transfer coefficient of condenser, proposed holistic algorithmic for condenser heat transfer coefficient, revised the computational formula on tube bundle arrangement correction for heat transfer coefficient in HEI, and providing empirical value for correction coefficient. The paper analyzed and discussed the calculation for output correction for differing back pressure in large capacity steam turbines, and then converted it to coal consumption increment by differing back pressure for using. The paper deeply analyzed resistance calculation for cold-end system, concluded reasonable formula for condenser water resistance and cooling water pipe resistance and chose the reasonable formula. This paper also calculated water lose volume in periodical feeding system, and formed the foundation for the further reasonable choice of design approach for cold-end system.Minimum annual-expense method adopted in traditional design pursues the maximization of economical benefit from the vies of engineering economy between quality decreasing and value in the process of condensation heat transfer of turbine exhaust (low pressure steam). Minimum drainage-anergy-expense method proposed by the paper takes the principles of thermal economics as reference, as a result makes up the deficiency of thermodynamics and the individual optimization of engineering practice. Otherwise maximized drainage anergy and cost of lowering drainage anergy expense have been accounted comprehensively. The paper also applied the two methods of the cold-end system optimized design of a large600MW direct current ocean water units. The comparasion between the two sets of result shows that:minimum annual-expense method optimized result is double pressure condenser, one machine and three pump(unit element system), cooling multiplying power is fifty-five, the area of Ti's condenser choosing minimum value in the range of standard; but minimum drainage-anergy-expense method result is double pressure condenser, one machine and two pump(expanding unit element system), cooling multiplying power is ninety-five, the area of Ti's condenser choosing maximum value in the range of standard. In a climate of resource shortage and energy conservation, we consider to improving the exergy efficiency in energy utilization is reasonable. This kind of cold-end system program of optimized design is completely practicable.