| There is much garbage,sludge and biomass in rural areas in our country every year,and their improper disposal cause serious environmental pollutions and wastes of energy resources.As it is unsuitable to build large-scale incineration power plants in the widely separated villages,a promising way of distributed energy system based on co-gasification technology is proposed for the treatment of rural garbage,sludge and biomass.By combining the waste treatments,power generation and cooling/heating all together,the system could meet the aim of energy demand and improve energy utilization in the rurals.In this work,distributed energy systems based on co-gasification of rural garbage,sludge and biomass are simulated using Aspen Plus software,and their performances based on the first and second law are discussed.The adaptability of different prime engines to the distributed energy systems,including micro gas turbine,internal combustion engine or fuel cell,are discussed by adopting an interconnected dual fluidized bed as the gasifier,and single-effect lithium bromide absorptivetyped refrigeration as the cooling subsystem.Firstly,the gasification performance of the interconnected dual fluidized bed is analyzed,then the differences in overall system performance of the three systems,such as power generation,energy utilization efficiency are compared.Secondly,the sensitivity analysis of gasification parameters such as gasification temperature,gasification pressure and mass ratio of different fuel components on the overall performance of energy distributed systems are investigated,also the influence of prime engine parameters on the efficiencies of the distributed energy systems are studied.Thirdly,the exergy analysis of three distributed energy systems based on micro gas turbine,internal combustion engine,fuel cell,respectively,is performed,and exergy destruction and exergy efficiency of each component and each subsystem in the three distributed energy systems are calculated and compared.Methods of improving system efficiencies are discussed.The results show that,the system with fuel cells as the prime engine has the highest power generation efficiency,up to 43.5%,and the system with a mico gas turbine has the lowest power generation efficiency which is 21.9%.The distributed energy system with fuel cells has the highest energy utilization efficiency,equally up to 78%,and those of the distributed energy systems with a micro gas turbine and the internal combustion engine are similar,which is 75%.The gasification temperature of fluidized bed increased by 200℃,the cold gas efficiency decreased by 1%,the steam/reaction material mass ratio increased from 0.6 to 1.1,the cold gas efficiency decreased by 2.8%,the gasification pressure increased from 0.1MPa to 0.6MPa,the cold gas efficiency increased by 0.2%,the increase in the feed ratio of garbage component improves the cold gas efficiency,the feed ratios of sludge and biomass component increase,the cold gas efficiency decrease.For the distributed energy systems based on different prime engines,the power generation efficiency is positively correlated with the feed ratio of garbage component,and negatively correlated with gasification temperature,gasification pressure,steam/reaction material mass ratio.The increase of the feed ratio of sludge component and biomass component also lead to a decrease in the power generation efficiency.The energy utilization efficiency of the energy distributed system is positively correlated with the garbage feed ratio,and negatively correlated with the steam/reaction material mass ratio and sludge feed ratio.For the distributed energy system based on micro gas turbine,the power generation efficiency is positively correlated with the temperature of gas turbine.With the increase of the pressure ratio of compressor,the power generation first increases and then decreases.When the combustion temperature is higher,the optimal pressure ratio corresponding to the highest power generation efficiency increases.The energy utilization efficiency of the distributed energy system is positively correlated with the temperature and negatively correlated with the pressure ratio.For the distributed energy system based on internal combustion engine,the power generation efficiency is mainly affected by the pressure ratio of the internal combustion engine,the pressure ratio is increased from 10 to 20,the power generation efficiency increases by 6%,the energy utilization efficiency in winter decreases by 0.5%,and that in summer increases by1.5%.For the distributed energy system based on fuel cell,the fuel utilization rate increases from 0.6 to 0.85,the power generation efficiency increases by 10%,the average energy utilization efficiency is decreased by 7.5%,the pressure of fuel cell increases from 0.15 MPa to0.4MPa,the power generation efficiency is increased by 9%,and the average energy utilization efficiency is increased by about 1.2%.The energy utilization efficiency is positively correlated with the temperature of fuel cell.From the second law of thermodynamics,the results show that the components with low exergy efficiency that is under 55% all include the evaporator,economizer,heat exchangers in heating and cooling subsystems for the three kinds of distributed energy system.Furthermore,for the three distributed energy systems based on different prime engines,the exergy destruction of power subsystem all accounts for the highest proportion of the total exergy loss,the exergy destruction percentages of the gasification subsystem and the purification system are similar.The exergy destruction of the power subsystem in the distributed energy system based on the internal engine accounts for 66%,the fuel cell system is 58%,and it is 33% for the system based on micro gas turbine.To improve the exergy efficiency and reduce the exergy destruction in th distributed energy system,it can be considered from two aspects: reducing the exergy destruction of the power subsystem and improving the efficiency of heat exchanger. |
PDF Full Text Request