Research On Combustion And System Performance Of ORC Biomass Briquetting Fuel Chain Furnace

Biomass resources are very rich and the biomass is about1.8trillion tons on the earth. There are about400million tons biomass resources can be developed into energy in China in2013, and with the development of agroforestry, the biomass resources will be more and more. It is estimated that various kinds of biomass alternative fuels will account for more than40%of total global energy consumption. The production capacity of biomass briquette fuel is increasing with the forming technology is more and more mature, and the next hot issues of the biomass briquette fuel are expansioning the application range and inproving the utilization efficiency. In this paper, the biomass briquette fuel heat-conducting oil chain boiler, which is convert the biomass to the electricity, is used as the driving heat source of organic rankine cycle. This boiler can realize the effective utilization of biomass briquette fuel. In order to improve the efficiency of ORC biomass briquette fuel heat-conducting oil chain boiler system, the main contents are studied in this paper are as follows:(1) The reaction mechanisms of water evaporation process, volatile devolatilization and combustion process and fixed carbon combustion process in biomass briquette fuel combustion are analysed according to the thermal test. The two-dimensional mathematical model of combustion process of single particle biomass briquette fuel is established based on the theories and methords of computational fluid dynamics, heat transfer, chemical reaction dynamics. The combustion process of single particle is simulated with this model, and the gas composition and temperature distribution is obtained. The accuracy of this model is verified by comparing the test results with the calculation results. The simulation study of single particle biomass briquette fuel combustion process is the base of the construction of mathematical model in bed of biomass briquette fuel heat-conducting oil chain boiler.(2) The comprehensive mathematical model of bed and furnace in biomass briquette fuel heat-conducting oil chain boiler is developed, the process of flow, heat and mass transfer are simulated with this model. In order to verify the model, the distribution of gas component in bed furnace was measured by chromatographic instrument, and the simulated results are in good agreement with the test results. The influence of secondary air temperature, bed thickness, chain velocity, particle size and air distribution mode on combustion of bed and furnace is studied based on this model. This study provides a theoretical basis for the operation.(3) The mathematical model of thermal properties of biomass briquette fuel heat-conducting oil chain boiler is developed according to the theories of heat transfer, thermodynamics, fluid mechanics and the method of exergy analysis. The influence of heat-conducting oil temperature and flow, secondary air temperature and velocity on the flue gas temperature, thermal efficiency, outlet heat-conducting oil temperature, exergy efficiency of biomass briquette fuel heat-conducting oil chain boiler was studied with this model. The results indicate that the relationship between the factors and the system performance is a complex nonlinear mathematical relationship. In order to improve the performance of chain boiler, the parallel optimization of multi parameters is necessary.(4) By application of mathematical programming theory and ant colony algorithm (ACA), optimization model of biomass briquette fuel heat-conducting oil chain boiler system was suggested, single-objective, multi-objective and exergoeconomic optimization methods were discussed. Optimization design of biomass boiler system was done, the optimization objectives include exhaust temperature, outlet temperature of the heat conduction oil, thermal efficiency and exergy efficiency, annual total cost index, annual net benefit index.The performances of biomass briquette fuel heat-conducting oil chain boiler system were remarkably improved by means of the proposed optimization design method. For example, in a13.95WM biomass briquette fuel heat-conducting oil chain boiler system, the annual total cost came nearly down8.8%and annual net benefit was raised upabout7%after optimized by this method.