Research On The Heating Value And The Release Mechanism Of Inorganic Components Of Biochars

The use of fossil fuels has brought about global changes and environmental pollution.The development and utilization of renewable clean energy has become the most urgent issue today.Biomass is a renewable energy source,and biomass pyrolysis technology can produce higher heating value biochar to make it a substitute for fossil fuels.However,the energy density of biochar and the release of nitrogen,sulfur,phosphorus,alkali metals and alkaline earth metals during combustion are not fully understood,which limits the application of biochar.In this study,a slow pyrolysis method was used to prepare rice husks,corn stalks,rice straws,corn cobs,pinus sylvestris wood chips,white pine wood chips,bamboo willow,ginkgo leaves,sycamore leaves and waste mushroom sticks under different cracking temperatures.Ten kinds of biochar samples focused on the calorific value prediction equation of biochar and the mechanism of inorganic component release and conversion during combustion,and discussed the possibility and advantages of biochar replacing fossil fuels.The main research contents and results are as follows:(1)The industrial analysis of biochar was carried out using the national standard method,the elemental composition of biochar was analyzed using an element analyzer,and the mass yield,energy yield,fixed carbon yield of various biochars were evaluated based on industrial analysis data Indicators,based on elemental analysis data,biochar was analyzed for elemental composition of C,H,O,and O/C and H/C atomic ratios.The results;show,that the ash,fixed carbon and carbon content of different biochars are significantly different.The pyrolysis temperature has a great influence on the analysis components,content and element composition of the biochar industry.The biochar,produced at high temperature has better fuel characteristics.(2)The national standard method was used to measure the higher heating value(HHV)of 10 types of biochar The stepwise multivariate linear and nonlinear regression methods were used to establish the elementary analysis-based biochar HHV prediction equation:HHV=32.9C+162.7H-16.20-954.4S+1.408,the R2 value of this equation is 0.997,the average absolute error(AAE)and the average deviation error(ABE)are 1.12%and 0.05%of the actual measured value,respectively;the biochar HHV prediction equation based on industrial analysis is established:HHV=-30.3FC2+ 65.2Ash2+55.4FC-48.5Ash+9.591,the R2 value of the equation is 0.982,AAE and ABE are 2.59%and 0.08%,respectively.The data of related literatures are used to verify the predicted values of these two equations,which indicates that the predicted equations have high prediction.accuracy.(3)The release and conversion of alkali metals/alkaline earth metals(AAEMs)during the combustion of five kinds of biochar were studied.Based on the weight measurement of combustion residual ash and inductively coupled plasma emission spectrometry analysis method,the element mass balance method was used to quantify the release of AAEMs during the combustion of biochar.The X-ray diffraction and X-ray fluorescence spectroscopic analysis methods were used to qualitatively analyze the existence form and ash composition of AAEMs in ash at different combustion temperatures.The results show that during the combustion process of the five biochars below 1000℃,30-80 wt.%of AAEMs are released into the gas phase,and there are significant differences between different elements and different samples.The release of AAEMs depends to a great extent on the content and associated form of AAEMs in biochar and the combustion temperature.The SiO2 in the biochar ash can effectively capture the AAEMs released during the combustion process,thereby reducing the alkali load in the combustion gas.AAEMs mainly exist in the form of oxides,chlorides and other salts in biochar ash at low temperature,and decompose as the reaction temperature increases,and react with SiO2 and Al2O3 to form insoluble silicate or aluminosilicate.Oxygen bomb-ion chromatography method was used to analyze the conversion rate of N and P in five kinds of biochar and the release mechanism of Cl and S.Two coal standard materials were added as a control.The results showed that the conversion of N in biochar to nitrogen oxidation The ratio of the substance released into the gas phase is 35-60%,and the conversion rate of P release is 8-50%.