Study On Combustion Characteristics Of Mixed Fuel Of Semi-coke And Biomass

In order to reduce coal consumption and improve the utilization rate of biomass,blending biomass is a suitable solution for coal-fired boilers.Compared with conventional coal burning in boilers,blue charcoal has higher fixed carbon content,higher calorific value,lower ash and sulfur content,less pollutants produced in the combustion process,and has obvious price advantage.Biomass as a fuel has low carbon characteristics,low calorific value and low utilization rate.Therefore,the mixed combustion of orchid charcoal and biomass can complement each other,improve the fuel characteristics,and have potential environmental and economic benefits.In this paper,three kinds of blue charcoal and two kinds of biomass were mixed to prepare molding fuel,and the combustion characteristics,pollutant emission and ash melting characteristics of fuel were studied.The main work is as follows:(1)The combustion process of three kinds of blue charcoal(Fugu semi-coke,Datong semi-coke,Inner Mongolia semi-coke)and two kinds of biomass(wheat straw,corn straw)and their mixtures were studied by using a comprehensive thermal analyzer under different conditions.The experimental results show that the semi-coke combustion process can be divided into two stages,and the main reaction is concentrated in the fixed carbon combustion stage in the later stage of combustion;Biomass combustion can be divided into three stages.The main combustion stage is volatilization combustion in the middle stage;The combustion process of blended fuel is divided into three stages,which are affected by the mixture of semi-coke and biomass.The ignition temperature of biomass is 195-259 ℃ lower than that of orchid charcoal,and the characteristic indexes of biomass are much higher than that of orchid charcoal.The combustion performance of five kinds of original samples is wheat straw,corn stalk,Fugu semi-coke,Datong semi-coke and Baotou semi-coke in descending order.In a certain range,With the increase of biomass mixing ratio,the combustion characteristic temperature of semi-coke decreases and the comprehensive combustion characteristic index increases.The ignition temperature of the blended fuel is close to that of the straw,and changes little with the mixing ratio.When the corn stalk mixing ratio is 30%-40%,the ignition characteristic index is 1.1-1.7 times of the original sample,and the comprehensive combustion characteristic index is 1.5-1.9 times of the original sample.With the increase of the proportion of straw mixed in the semi-coke,the heat release rate of combustion reaction becomes lower,so we should pay attention to the mixing proportion.When the mixing proportion of corn stalk is about 30%,the comprehensive combustion performance of the fuel is the best.In order to solve the problem of high ignition temperature of semi-coke,in addition to mixing biomass with low ignition point,combustion accelerants can also be added.The combustion condition can be improved by adding combustion-supporting agent to the mixture of semi-coke and corn stalk,and the first stage activation energy of the mixture can be effectively improved by adding manganese dioxide to advance the reaction.(2)The emission of sulfur and nitrogen oxides was studied in a fixed bed system because of the unclear emission of semi-coke blended fuel.At 900℃,the precipitation amount of sulfur oxides from the original sample of semi-coke was 0,and the sulfur fixation rates of wheat straw and corn straw were 99.93%and 95.21%.When the mixture of semi-coke and corn stalks was mixed in a certain proportion,no sulfur was precipitated when the proportion of com stalks was low,but only a small amount of sulfur was precipitated when the ratio reached 6:4,both of which were higher than the sulfur fixation rate of corn stalks,indicating that the sulfur fixation effect of corn stalks was better when the ratio of corn stalks in the fuel was 20-30%The nitrogen precipitation curve of the original sample of straw had two peaks,and the nitrogen precipitation curve of the blue carbon was a peak and a flat stage.The results showed that the nitrogen oxide emissions of the five samples were wheat straw,Datong semi-coke,corn stalk,Baotou semi-coke and Fugu semi-coke,and the nitrogen release rates were 0.07%,0.06%,0.05%,0.03%and 0.007%respectively.When the semi-coke and corn straw were mixed in a certain proportion,the sulfur fixation rate of the mixed fuel was between the two original samples,and the effect of the semi-coke 1 mixed with corn straw was better.The nitrogen precipitation rates of the mixed fuels were all around 0.04%,but showed a linear relationship with the proportion change,indicating that the mixed combustion of corn straw and semi-coke was not a simple physical mixing.With the increase of temperature,the sulfur precipitation of wheat straw and corn straw samples increased significantly,and the emission time increased.A small amount of sulfur was precipitated from Baotou semi-coke,but no sulfur was precipitated from Fugu semi-coke and Datong semi-coke.At this point,the previously selected corn stalks were mixed with Fugu semi-coke,and no sulfur was precipitated out,indicating that the blending of Fugu semi-coke and corn stalks had good self-fixing sulfur properties.The NO precipitation curve of the original sample tended to transition to a single peak value,while that of the mixture tended to change to a single peak value,and both the precipitation rate and the precipitation time decreased.The NO precipitation rate of the sample was always less than 0.02%,and the increase of temperature had a decreasing trend on the NOx precipitation.(3)In order to study the corrosion of mixed fuel ash sample at high temperature,the ash fusion tester was used to measure the fuel,and the composition of the ash sample was calculated and analyzed.The fusion performance of the ash sample of corn straw is lower than that of semi-coke.The characteristic temperature and curve trend of the three kinds of mixed fuels are similar with little difference,which are all between corn straw and Fugu semi-coke.This indicates that the mixing ratio has a certain linear relationship with the ash melting point.After adding combustion-supporting agent,ash melting point decreased with a small amount of additives,and increased with the increase of metering.However,the ash fusion performance of the fuel still needs to be improved.In conclusion,the mixed fuel of semi-coke and biomass straw has the advantages of high calorific value,high combustion efficiency,low pollutant emission and moderate ash melting point,which provides some reference value and practical significance for the improvement and clean utilization of the mixed fuel of semi-coke land biomass.