| Combined Cooling,Heating and Power(CCHP)system based on gas turbine is featured by the cascade utilization of energy,and it is widely used due to its characteristics of energy saving,reliability and environmental protection.The CCHP system operators at off-design conditions in most cases,and the dynamic response time of different components is greatly different.Overshoot and shock of the system often take place when the CCHP system is running,and the Primary Energy Efficient Ratio(PER)of the system would decrease.Aiming at those problems,the dynamic model of the CCHP system based on micro-gas turbine was established,and the main works and conclusions were as follows:(1)Key components models of the CCHP system,the PID control and DMC control system were built.The heat and mass transfer in the absorber were described according to a physical model based on Nusselt's film theory;Holman correlation was applied to the calculation of heat transfer coefficients of main components of the absorption chiller;The simulation accuracy of the system increased significantly:the relative error of the steady-state models of micro gas turbine(MGT)and absorption chiller was within 1%under on-design and off-design conditions;For the absorption chiller,the relative error between the dynamic simulation result and paper's result was within 5%.(2)The off-design performance of the steady-state model of the CCHP system were explored,and the effect of the running model of the cooling tower on the system performance was investigated.The result shows that when the output power of the MGT decreased from 76 kW to 25 kW,the PER decreased from 56.9%to 46.9%because of the poor performance of the micro gas turbine.When the ambient temperature increased from 10? to 30?,the efficiency of MGT decreased from 27.16%to 24.06%,and the output power decreased from 84 kW to 66 kW,and the cooling capacity of the absorption chiller increased slightly from 100.5 kW to 101.5 kW.The two cooling tower operation modes presented a negligible difference with regard to their effects on the cooling capacity of the system once energy quality was considered.(3)The dynamic model of a single-effect absorption chiller was developed.A detailed investigation of model performance,including dynamic response,effects of thermal mass,and comparison of two different control strategies was presented.The main conclusions are as follows:The decrease of the cooling water inlet temperature would increase the COP and cooling capacity of the absorption chiller,and increase the possibility of crystallization;The decrease of the chilled water inlet temperature would decrease the COP and cooling capacity of the absorption chiller,and decrease the possibility of crystallization;When the solution mass of generator increased from 1 kg to 20 kg,the response time of the absorption chiller increased from 200 s to 3000 s,and the thermal mass of the generator had a major effect on the time to reach the steady state of the chiller;This chiller exhibited better control performance in the off-design condition when setting the generator solution temperature as the manipulated variable,compared with setting the chilled water outlet temperature as the manipulated variable,and the settling time was 700 s and 1000 s respectively when the chilled water outlet temperature decreased from 14.5? to 14 ?.(4)The dynamic model of the CCHP system was developed.The result showed that the response time was 20 s,300 s,and 1500 s for the MGT,absorption chiller,and user respectively.The dynamic performance of the system was explored when the electrical load and refrigeration load smoothly changed.The maximum temperature difference of the room temperature was 3.6? when the PID controller was used in the system;When the afterburning device and logic control method was added in the system,the maximum temperature difference of the room temperature was 2.7?.The PER of the system in one day was 55.4%,because part of the exhaust gas of the MGT was wasted;Then the thermal storage equipment was arranged near the user,and the exhaust gas of the MGT was all used for exchanging heat with the absorption chiller.In this way,the maximum temperature difference of the room temperature was 1.5? in one day,so the comfort degree was enhanced,and the cooling capacity increased 5 kW,and the PER of the system in one day was 57.6%.The dynamic performance of the system with cooling storage was explored when step disturbance occurred.The result showed that the flowrate of the exhaust gas into the absorption chiller increased from 0.77 kg/s to 0.778 kg/s,and the settling time was about 20 s for the MGT,and the settling time of absorption chiller was about 500 s.(5)The DMC controller was applied to the control of the absorption,and the results showed that when the sampling period was 5 s,the overshoot was 2.7%,and the settling time was 750 s,and when the sampling period was 50 s,the overshoot was zero,and the settling time was 2000 s.For the absorption chiller,the step change of ambient temperature?electrical power or the cooling water inlet temperature would lead to the oscillation of the system when the PID controller was applied,which was not beneficial to the safety of the system,and the system would run smoothly when DMC controller was used.Then DMC controller was used in the CCHP system.The result showed that when the cooling water inlet temperature of the absorber decreased 1?,the overshoot was 19%,and the settling time was 1200 s when the PID controller was used,but the overshoot was only 3%,and the settling time was 1000 s when the DMC controller was used.So stable control performance of the system was realized,and the system had good control performance under various conditions when DMC controller was used in the CCHP system. |
PDF Full Text Request