Study On Multi-process Exergy Characteristics Of Solid Fuel

Chemical exergy can measure the quality and economy of fuel,as well as its environmental and ecological effects.In the analysis and evaluation of fuel energy quality,economy,environmental effect,ecological impact,reaction device,conversion process and utilization system,the determination of chemical trace is the premise and the first step.Theoretic inference algorithm based on thermodynamic model,empirical correction method based on reaction heat.The first method is mainly based on the single process thermodynamic model,focusing on the reaction of the theoretical combustion process of fuel,usually ignoring the diffusion of the physical diffusion process of ash.The second method usually multiplies a correction factor determined by the element composition before the reaction heat(high or low calorific value),and usually ignores the effect of ash content on the fuel.In view of the multi-process characteristics of biomass,this paper first establishes a chemical model consisting of separation,reaction and diffusion processes.Then the calorific values of graphite and benzoic acid are measured by oxygen bomb calorimeter.When the pressure in oxygen bomb is 2~2.5 MPa,the calorific errors can be controlled within-1.01%~0.15% and-0.18%~0.09%,respectively.Therefore,the calorific values of graphite and benzoic acid can be measured by oxygen bomb calorimeter.The values are reasonable and accurate.On this basis,the constructed chemical rake model is introduced to verify the chemical rake of graphite and benzoic acid.When the pressure of oxygen bomb is between 2 and 2.5 MPa,the chemical rake error can be controlled within-1.04%~0.22% and-0.15%~0.12% respectively.Therefore,it is feasible to calculate biomass chemistry by using this chemical model.For the multi-process thermodynamic process of material testing,taking the internal pressure of oxygen bomb as an example,the proportion of reaction is 96.09% and 96.64% respectively,and the sum proportion of the other two processes is 3.91% and 3.36% respectively.Based on the data of 128 biomass(64 woody biomass,28 rice husk biomass,24 straw biomass and 12 wheat straw biomass),chemical charcoal model was constructed.The separation charcoal,reaction charcoal,diffusion charcoal and chemical charcoal of 128 biomass were calculated and compared with Szargut empirical formula.The error ranges are-2.83%~3.57%,-3.24%~1.51%,-2.07%~1.94%,respectively.-1.81%~0.29%.The chemical model constructed above needs to know the elemental quality of biomass and the specific composition and content of ash,so it is particularly complicated to determine the chemical properties of biomass accurately.Based on 128 kinds of biomass data,the multi-process characteristics of four kinds of biomass(wood,rice husk,straw,wheat straw)are analyzed and utilized.Four kinds of empirical formulas were obtained by linear regression,which greatly simplified the calculation formulas of chemical furnaces.The errors of single simplified ash items were the lowest,which are-0.77%~2.02%,-0.20%~0.30%,-0.66%~0.90%,-0.24%~0.17%.The second was to estimate chemical furnaces by using single variable biomass high calorific value,with errors of-1.96%~3.12%,-1.14%~1.47%,-1.69%~1.79%,-0.52%~0.71%.The calculation formulas of simplified chemical furnaces with high calorific value,moisture and ash content have errors of-1.78%~1.56%,-2.57%~1.37%,-3.99%~1.51%,-0.66%~0.45%.Estimating chemical uses with single variable low calorific value has errors of-4.88%~4.49%,-3.39%~1.79%,-2.68%~1.77%,-0.33%~0.24%.The biggest error is that all variables of biomass composition are considered,and the error distribution is dispersed.The proportion under 5% was 87.5%,78.6%,83.3% and 100% respectively.