Research On Integration System Coupled By Natural Gas-fired Combined Cooling Heating And Power System And Heat Pump

In order to ensure the energy security and achieve the goal of energy conservation and emission reduction,the energy structure will be adjusted in China;and so the proportion of natural gas consumption will be improved.Combined cooling,heating and power(CCHP)system,as a high-efficiency,environmental friendly and secure energy system,has become the advanced technology in the natural gas efficient utilization and attracted the attention of many researchers and policy-makers;and its performance can be further improved by means of the complementary integration with renewable energy,environmental energy and energy storage system.Heat pump(HP),as a kind of efficient and energy-saving technology,is an effective way to utilize renewable energy and maintain the ecological balance,and is also concerned by various fields.Therefore,it is very significant to study the coupling system integrated with the natural gas-fired CCHP system and heat pump(HP).However,by the review analysis,the existing coupling systems have many problems,i.e.simple parallel operation,low system integration,low efficiency of flue gas heat recovery,low COP in the high-temperature HP and so on.Therefore,to solve the above problems,this study is expected to reveal the new integration mechanism and construct the typical coupling system;then analyze its thermodynamic performances,influence characters and multi-condition performances;and further develop the multi-objective optimization model for the design and operation optimization of typical coupling system.The main contents of this dissertation are presented as follows.Firstly,the fundamental principle of system integration was revealed,which is based on the principle of cascade utilization of physical energy and the reasonable optimization for the temperature potential difference to achieve the appropriate integration.The novel application approach of waste heat from the flue gas was put forward,which can realize the synchronous improvement of the heat exchanger efficiency(waste heat utilization efficiency)and the COP of HP,and provide a new solution idea for multi-energy system integration.Based on the proposed application approach of waste heat,the energy-saving potential of the coupling system integrated with natural gas-fired CCHP and HP was discussed,and so the novel integration mechanism of the coupling system was revealed.Taking the natural gas-fired combined heating and power system and ground source heat pump as an example,thetypical coupling system and reference system were constructed,and the essential differences between the two systems were also described.In order to identify the performances of typical coupling system,the system evaluation criteria were presented,which are the first law of thermodynamics,the second law of thermodynamics and the primary energy saving ratio;and the physical meanings and calculation methods of each evaluation criteria were also explained.Secondly,the thermodynamic calculation and optimization analysis of the typical coupling system were completed by help of the Aspen Plus software.The analysis results indicated that,the total energy efficiency of typical coupling system is 142.2%,about 3.9% higher than that of the reference system;the exergy efficiency of typical coupling system is 22.58%,about 3.7% higher than that of the reference system.Therefore,the proposed typical coupling system can provide a new way for renewable energy and environmental energy application in CCHP system.Based on the method of theoretical calculation and numerical simulation,the exergy characters of the typical coupling system and reference system were analyzed using the "grey box" model.And the exergy losses of the key operating components and their differences between two systems were calculated in order to identify the enegy-saving essence and the key integration parameters.Therefore,the conclusion that the outlet temperature of the HP is the key integration parameter of typical coupling system,was presented.Next,the influence characters of key integration parameter on the system performances were analyzed.Namely,the impact of the outlet temperature of HP on the COP of HP,input and output parameters of system,exergy losses characters of system and system efficiency were studied.And the influence differences of the key integration parameters on two systems were also compared.The performances of typical coupling system in different conditions were studied.Namely,based on the typical operation mode: following the electricity demand and following the heating demand,the performances under different load demand conditions with different outlet temperature of the HP were calculated,which include the device size,primary energy consumption and primary energy saving ratio.The research results can be used as a reference for the feasible evaluation and the selection of operation mode and key integration parameter.Finally,the multi-objective optimization model of typical coupling system was developed.Under the building dynamic load demands,the device size,key integration parameter and system operating strategy can be optimized by help of the geneticalgorithms.And the influence of optimal variables within a certain range on the operation performances of typical coupling system were also analyzed in order to verify the accuracy of the genetic algorithm in the optimization process.In addition,the sensitivity of the electricity and natural gas price to the operating performances were also studied in order to identify how the performance of typical coupling system will change due to the variation of the energy price.The research results can provide the theoretical support for the optimization design and engineering application of typical coupling system.