Experimental Study On Separation And Disposal Of Fly Ash From Biomass Boiler And Applications Of Unbuned Carbon

With the continuous expansion of the biomass power industry worldwide,it will surely produce a large amount of biomass ash.At present,most of the biomass ash is mainly used as building materials or as auxiliary materials of chemical fertilizer to return to the field.Due to the changeable ash content and harmful composition,resulting in a series of problems.This paper starts with the problems in the application of biomass ash to building materials and soil improvement in agricultural and forestry vegetation.Using biomass fly ash as raw material to screen for the unburned carbon and the purified fly ash.Ultrasound-assisted filtration was used in the treatment of the purified biomass fly ash,and research was carried on the combustion characteristics and preparation of activated carbon for supercapacitor electrode of unburned carbon.The following work was carried out:(1)For the purified biomass fly ash with the particle size of less than 0.2 mm,ultrasound-assisted leaching of water-soluble ingredients from biomass fly ash was carried out,and the research mainly focused on the influence of ultrasonication time?slurry temperature and liquid-solid mass ratio in the process of ultrasound treatment.Results show that by increasing the ultrasonication time,increasing the ultrasonication temperature,and increasing the liquid-solid ratio moderately have played a certain role in promoting the dissolution of the elements K,Na,Ca,Zn in biomass fly ash.Based on the actual process cost needs,results show that the suitable parameters are as follows:ultrasonication time of 20 min,slurry temperature of 50?,liquid-solid ratio of 3:1.In addition,these three factors also have a certain effect on the leaching process of heavy metal elements in biomass fly ash,however most of the heavy metal elements are distributed in the lattice structure of insoluble minerals,the overall leaching rate has been maintained at a very low level.The leaching rates of heavy metals such as Co,Cr,Ni,and Pb are below 0.1%,0.3%,0.05%,0.1%,it has no obvious effect on the use of fine ash leachate in the production of agricultural fertilizers.After ultrasound-assisted leaching of water-soluble ingredients,the alkali metal elements such as K,Na and Ca etc.have been reduced in different degree,non-metallic elements such as Cl and S also significantly reduced.It can be used as raw materials for industrial building materials after further processing.(2)Unburned carbon of biomass fly ash has the property of biomass charcoal fuel,using as an alternative fuel is one of the feasible ways.Combustion characteristics research was carried out on unburned carbon with the particle size of over 0.3 mm.The analysis results of basic fuel characteristics such as industrial analysis,elemental analysis,and calorific value analysis show that the unburned carbon has a lower volatile content and a higher fixed carbon content.After testing,the calorific value is 21.94 MJ/kg.In addition,the unburned carbon contains a certain amount of K and Ca alkali metal elements,which makes the unburned carbon have certain sulfur self-fixing characteristics when used as a fuel.The thermal analysis of the combustion process of unburned carbon shows that its ignition temperature is about 400?.During the entire combustion process,the volatile combustion stage and the fixed carbon combustion stage combine to form a high and wide weightlessness peak in the temperature range of 350-650?,and then the fuel reaches the burn-out stage at 730?.The test results of SO2 and NO emissions during the combustion of unburned carbon show that the unburned carbon meet the emission standards during the common combustion temperature range of biomass boilers and can be used for industrial applications.Composite fuel is prepared with the ratio of 8:2 of unburned carbon and biomass bark combined with a little binder.Analysis results show that its calorific value is 20.55 MJ/kg,the sulfur and nitrogen emissions in the combustion process have been reduced compared with the combustion process of unburned carbon.The SO2 and NO emissions of the composite fuel still meet the emission standards during the common combustion temperature range of biomass boilers.Thus having a good prospect of industrial application.(3)Unburned carbon of biomass fly ash has undergone the process of combustion and pyrolysis.Compared with biomass raw materials,Unburned carbon has a great change in physical and chemical properties,especially it has a large specific surface area and an abundant pore structure.Activated carbon was prepared by KOH activation method from unburned carbon with particle size over 0.2 mm.When the impregnation ratio is 4.5:1,the specific surface area is 2073 m2·g-1 and the total pore volume is 1.393 cm3·g-1.Its pore size is mainly concentrated in 0.5-0.8 nm and 2-4 nm.It is microporous structure which mainly contributed to the increase in specific surface area.The prepared activated carbon electrode material exhibits good electrochemical performance when applied to supercapacitors,it has high charge and discharge efficiency,and excellent capacitance performance.Among them,activated carbon HYC-3.5 has the best performance.It has as a large specific capacitance as 233 F·g-1 when the current density is 0.1 A·g-1.Through analysis of the micromorphology and microcrystalline structure of HYC-3.5 samples,It is found that it has an abundant pore structure,and it contains a certain amount of graphite microcrystalline structure and multilayer graphite structure.These structures have effects on improving the conductive properties and the electrochemical performance of activated carbon.Finally,by testing its cycling stability,results show that after 5000 cycles,the capacitance retention rate is 93.57%,which shows good electrochemical stability with a low capacitance attenuation.The research results in this article provide alternative technical path and basic theories for solving the problems of biomass fly ash in the application of industrial building materials and agricultural soil improvement,it has a certain guiding significance for providing a high value-added use of biomass fly ash and extending the industrial chain of biomass power generation.