Design And Optimization Of A Small-scale Biomass-fuelled Trigeneration System Integrated Organic Rankine Cycles

With the increasingly energy shortage and environmental deterioration,the development of new energy or renewable energy has become an important way to alleviate this contradiction.As a kind of renewable energy,biomass has the characteristics of large supply and stability,and as a driven power it can meet the requirement of sustainable development well in C hina and even in the world.In this paper,a novel small-scale biomass-fuelled CCHP(Combined cooling heat and power)system installed with ORC(organic Rankine cycle)was proposed,and it was analyzed from the perspective of working fluids selection,t hermodynamic analysis and structure optimization.The research contents and conclusions are as follows:A system structure model was established.Initial parameters were given such as heat load of biomass boiler was 1 MW and biomass fuel was maize straw.Thermodynamic model was established through the structure model and Matlab was used for simulation to reach a series of performance evaluation index.The selection of organic working fluids for this biomass-fuelled CCHP – ORC system was introduced.Under different evaporation temperature,the system using different working fluids was evaluated by performance indicators such as net output power,heating capacity,refrigerating capacity,thermal efficiency,economic efficiency,exergy efficiency,CO2 emissions and sustainable development index SI.The system using PF5050 and HFE7000 has a higher net output power,heating capacity and thermal efficiency,while R141 b has a higher refrigerating capacity.In addition,a comprehensive performance evaluation index was put forward,selecte six parameters for data standardization and use coefficient of variation method to determine the index weight.It was concluded that to the comprehensive evaluation index the optimal working fluid was R245 fa.Select R245 fa as a working fluid and regard evaporation temperature and pinch point temperature as non-independent variable to analyze this CCHP-ORC system.It was concluded that evaporation temperature under different pinch point temperature made a difference on the system while the pinch point temperature has little effects on it.By using the control variable method,with the pinch point temperature of 5 k,analyze the effects of the single variable heat source temperature,evaporation temperature and O RC pump inlet temperature on the system under four kinds of operating modes(only power generation,combined heat and power CHP,combined cooling and power CCP,CCHP).Heat source temperature has little impact on the system.Most indicators are optimal when the evaporation temperature is 409 K,and ORC pump inlet temperature will produce different effects on each index under different operating modes.The ratio of power and heat and cooling can be adjusted by changing evaporation temperature and ORC pump inlet temperature.Under the four operating modes,evaluation index from high to low is CCHP > CCP > C HP > only power generation.In addition,system and environment were combined by CO2 emission and sustainable development index SI,and it was concluded that most exergy loss was produced by biomass boiler,we can optimize the structure of biomass boiler to reduce total exergy loss of the system.Make structure optimization by adding flue gas waste heat recovery,start-stop auxiliary valve and 3-way valve.3-way valve was used to adjust operation strategy in winter and summer.Through the first law of thermodynamics,the second law of thermodynamics and the impact on environment,it showed excellent relative to the non-optimized system.Through the research analysis it was concluded that biomass-fuelled CCHP-ORC system has the characteristics of higher efficiency and flexible adjustable.It has been shown suitable for the hospitals,office buildings,residential area or in remote rural communities and more conducive to business applications.