Research On Straw Torrefaction Technology Based On Low Temperature Heating

Biomass energy has the characteristics of reproducibility,abundant reserves and clean combustion,but the shortcomings of biomass energy such as high water content,low energy density,easy corrosion and excessive dispersion restrict the use of biomass energy.Biomass thermal conversion technology is the most widely used biomass utilization technology.At present,it is more inclined to concentrate the biomass of a region for treatment,which not only consumes expensive transportation costs,but also the biomass processing device has a large area and a complicated structure.This paper proposes a distributed torrefaction technology model.By divideing a large-scale biomass treatment device into many small devices,which greatly improves energy efficiency and saves costs,and biochar with excellent fuel properties can also be obtained.First,the analysis of the solid product were done at different temperatures and times.With the increase in torrefaction temperature and holding time,the color of biochar is gradually deepened,the content of fixed carbon,C,higher heating value and the energy density increases,the moisture decreases,and the grindability increases,the fuel properties of biochar are enhanced,but the mass and energy yield are reduced.Second,through the isothermal thermogravimetric experiment,it was found that the increase of torrefaction temperature and time will promote the decomposition of straw,and the torrefaction temperature has a greater impact on straw than holding time.Through non-isothermal thermogravimetric and infrared analysis experiments,it was found that torrefaction will promote evaporation of mositure in the straw,a large amount of hemicellulose and cellulose are decomposed,and lignin is also degraded.The higher the torrefaction temperature,the more decomposition of the three components of straw.The higher the decomposition rate of biomass with a smaller heating rate,the faster the decomposition is when the atmosphere is air,and the particle size reduces the decomposition resistance.A kinetic model was obtained by the Coats-Redfem method to calculate the kinetic parameters before and after the torrefaction of straw,as well as the kinetic parameters of the heating rate,atmosphere and particle size.Finally,through gas-phase product analysis,the gas products of straw during torrefaction can be divided into non-condensable gases,acids,aldehydes,esters,furans,phenols,etc.These substances are mainly CO2,acetic acid,furfural,ethyl acetate,3-methylfuran and dimethoxyphenol,etc.,the increase in temperature and time will promote the increase in the content of condensable gas products.Temperature also promotes the conversion of acids to esters.Oligosaccharides and dehydrated sugars produced by biomass pyrolysis continue to decompose to form acids and aldehydes.Methanol is derived from the methoxy decomposition of lignin,and methanol and CO react to form CO2 and H2.Formaldehyde is unstable and generates CO and H2.The formation of furan originates from decarboxylated pyromucic acid,which is derived from the oxidation of furfural.Phenols come from the degradation of lignin?It was found that the distributed torrefaction model proposed in this paper can obtain biochar fuel with excellent properties.Torrefaction consumes hemicellulose in biomass,while degrading cellulose and lignin.The rate of temperature rise,atmosphere,and particle size all affect the pyrolysis results.In the torrefaction process,a large amount of condensable gas products will be produced,which will promote the pressure increase in the torrefaction device.At the same time,the gas products are toxic,flammable and explosive.It is recommended that the gas condensation device be used to collect the gas after completing the torrefaction to reduce the pressure in the device,and finally take out the biochar.