Study On The Tar Formation In Gasification Of Corn Straw In Fluidized Bed

Excessive consumption of fossil fuels and its negative global effects have resulted in increasing interest in biomass energy.Gasification is an attractive avenue for the thermochemical transformation of clean energy,but tar becomes one of the factors restricting gasification efficiency in the biomass gasification.Tar is a viscous liquid at room temperature,in addition to fouling and eroding process equipment,its formation wastes 5-15%of the effective energy from biomass gasification.Reducing tar content of gasification plays an active role in improving gasification efficiency and prolonging equipment life.Therefore,the influence of operating parameters on the change of tar content and the mechanism of component transfer in gasification of corn stalk in the internal circulating fluidized bed were studied in detail.Firstly,taking the actual gasifier of a power plant as the prototype,the internal circulating fluidized bed gasifier is designed and built,calculating and designing the fan,steam generator,screw feeder,air plate,furnace,etc.Then,commissioning experiment and thermal operation debugging were carried out on the experiment bench.In this process,the resistance characteristics of ventilation board,the height of the bed material,feeding rate and other parameters were tested,and ignition and thermal operation were carried out.After repeated experiments,the operation performance of the test bench was mastered,and the experiment bench was confirmed to be fully qualified for biomass gasification test.This work uses compressed corn straw as raw material,and studies the influence of different factors on biomass gasification products.The experimental results showed that when the bed material was coal ash residue and air was used as the gasification agent,an increase in temperature,the CO2 and CH4 contents reduced,whereas the H2 and CO contents increased respectively.When the mixing proportion of dolomite increased,the gasification reaction was enhanced,the H2 and CO contents were significantly increased,the CO2 and CH4 contents were slightly reduced.When the gasification agent was air-steam and the temperature was maintained at 700?,with the gradual increased in the amount of steam supplied to the gasifier,the CO2 and H2 contents gradually increased,the CO and CH4 contents gradually decreased,The collected tar components were analyzed by GC-MS,and the results evaluated.The experimental results showed that with an increase in temperature,the content of tar decreased from 6.2 g/Nm3 at 700? to 2.02 g/Nm3 at 900?,the proportions of class 1 and class 3 tars decrease,whereas those of class 4 and class 5 tars increase significantly;the concentrations of tar compounds(such as the benzene,indene)increased,whereas those of the toluene,phenol,methylnaphthalene decreased.With the increase of the equivalent ratio from 0.21 to 0.34,the tar content decreases,the proportion of class 1,class 2 and class 3 tars tar decreases,and the proportion of PAHs increases.The concentrations of indene and phenanthrene increased from 0.148%and 0.087%respectively to 0.232%and 0.223%as the equivalent ratio is increased from 0.21 to 0.34.The phenol content shows a tendency of first increase and then decrease.Besides,with the gradual addition of steam,the tar content decreased to 2.86 g/Nm3,and all classes of tar also showed different change rules.The concentration of tar compounds(such as acenaphthene and fluorene)increased,and the concentration of methylnaphthalene decreased,but the trend of decrease was not obvious.And catalyst also played a crucial role in tar reduction.In this paper,a targeted study on biomass gasification tar was carried out,the formating regulations of gasification tar were summarized,and the optimal operating conditions for controlling tar content and improving gasification efficiency were proposed,which provided a theoretical basis for biomass gasification coupled power generation.