| BCHP is a cogeneration system that can accomplish the production of cooling, heating, and power at the same time by making use of both the electrical and "waste" heat output form gas turbine unit. In contrast to the conventional systems, it can use energy resources more efficiently, creating opportunities for reduction in both purchased energy costs and in environmental impact.BCHP has developed quite well in the developed countries, such as in Japan and the United States. But because of the situation in our country, BCHP is still a new field in the country and its application is not as good as expected. So it's very important for us to pay much attention to the investigation into BCHP. Just under this background, a large hospital in Huangpu district is selected for carrying out the study of the BCHP's operational process in this paper. Much attention will also be placed on the BCHP system's optimal economical performance when the load varies.First the constitution of the BCHP system is discussed in this paper, which includes a gas turbine or gas engine, a heat recovery steam generator, water heaters, and double-effect LiBr absorption chillers driven by the waste heat of the exhaust from the gas turbine. Furthermore the running conditions of the BCHP are analyzed in detail in this paper and come to the conclusion that the performance of the BCHP is not good because the actual load is much lower than the designed figure (lower than 40 percent of the designed figure).Under varied conditions the operation parameters are described by the fitting functions that are obtained using MATLAB. On this basis, mathematical model under varied conditions is established, which includes GT model, HRSG model, LiBr chiller model and water heater model. Then a series of program is made by VB, which offers a platform for establishing the objective function and its solution.The analysis of the optimal operational strategy under varied conditions is carried out in Chapter 5, which includes non-constraint optimization and constraint optimization. The optimization models are established based on the objective functions of exergy efficiency and gross profit separately and the variants of the functions are electric load rate, the rate of the steam used in cooling and the inlet temperature of GT. So some useful conclusions can be attained by the calculation of the objective function using the MATLAB optimal toolbox.The improvement of the BCHP is held out in Chapter 6 in this paper. The gross program is held out that the inlet temperature of GT is cooled to the best working conditions by the nozzles. The program has several advantages including less investment, simplicity and feasibility. Furthermore, it can satisfy the requirement of optimal operation and raise the operation efficiency and benefit.According to the optimization results, the exergy efficiency of the BCHP is the highest when the cooling load is temperate and the inlet temperature of GT is low (below 10 degrees centigrade).When the electrical load rate is not less than 0.8, the operation of the system will attain a benefit. Meanwhile, when the electrical load rate reduces, the extreme points of the exergetic efficiency and gross profit will raise up with the inlet temperature of GT rising. The efficiency of GT has the most important influence on the exergy efficiency of the system. In various kinds of working conditions, fuel cost is between 70 percent and 80 percent of the total cost. So the benefit of BCHP is low mainly because of the high price of fuel. |
