Pneumatic Conveying Characteristics Of Mobile Biomass Fast Pyrolysis Equipment

With the advantages of compact structure,high heat transfer efficiency and self-heating,mobile biomass fast pyrolysis equipment can make full use of pyrolysis by-products-non-condensable gas-to achieve efficient in-situ conversion of biomass energy.However,the current mobile pyrolysis equipment mainly suffers from pneumatic conveying problems such as discontinuous and unstable biomass pneumatic feeding,non-uniform particle diffusion,mixing,fluidization and heat transfer in fluidized bed reactor with pneumatic feed,which restrict the promotion and application of pyrolysis technology.Therefore,this paper aims to solve the pneumatic conveying problem of mobile biomass fast pyrolysis equipment,investigates the influence of feeding parameters on the feeding characteristics of pneumatic feeder,studies the influence of pneumatic feeding on fluidization and heat transfer characteristics of fluidized bed reactor,develops a set of biomass pneumatic feeding-pyrolysis reaction equipment with continuous feeding,uniform fluidization and sufficient heat transfer,and conducts experimental verification.The main conclusions of this paper are as follows:(1)Both injection and disturbance gas can improve feeding rate of pneumatic feeder,but their feeding mechanisms are fundamentally different: injection gas carries particles through drag force,while disturbance gas pushes particles by gas static pressure;disturbance gas produces disturbance and homogenization,weakening or even eliminating particle aggregation and bridging in the pressure bin;injection gas and disturbance gas complement each other,and reasonable regulation of the flow ratio of the two gases(4/12-8/8)can promote the continuity and stability of pneumatic conveying;the prediction model of pneumatic feeding rate(R2 = 0.942)is established to provide a theoretical basis for the design and research of pneumatic feeder for biomass particles.(2)The pneumatic feeding mechanisms of injection gas and fluidizing gas are different in the fluidized bed reactor: injection gas brings biomass particles into the fluidized bed through drag force,while fluidizing gas provides pneumatic feeding space through fluidization and enhances the mixing of different particles in the bed;injection gas and fluidizing gas have complementary effects,and reasonable regulation of the flow ratio of the two gases(1.89-2.6)can improve pneumatic feeding;The mathematical regression model of pneumatic feeding rate(R2 = 0.928)is developed to predict and guide the pneumatic feeding of fluidized bed reactor.(3)The combination of feed gas and fluidizing gas promotes fluidization of the bed and provides pneumatic feeding space for biomass particles;the feed particles collide with the bed particles to promote particle diffusion,mixing and co-fluidization within the bed;the feed gas and feed particles interact with each other to promote the particles to penetrate deeper into the bed and also accelerate their departure from the bed;the pneumatic feeding dynamic model of the fluidized bed reactor is constructed:particle interaction,diffusion,mixing and co-fluidization.(4)The annular fluidized bed reactor is divided into fixed bed and fluidized bed heating stages to achieve rapid and uniform heating;the total heat transfer coefficient of the fluidized bed reactor is affected by the pneumatic feed,resulting in the delay of heating;biomass particles pneumatically fed,firstly,collide with the bed particles for heat transfer,and then,under the fluidization,particles enter the bed for secondary backmixing,resulting in more uniform heating,more stable temperature field and faster reaching pyrolysis temperature.(5)The mobile biomass fast pyrolysis liquefaction process is optimized with compact equipment structure,high heat transfer efficiency and self heating;the development of double bin conical pneumatic feeder,based on double bin and double pneumatic design,combined with multi-stage laser photosensitive sensing system,realizes the continuous and stable pneumatic conveying of biomass;an annular fluidized bed reactor is developed,in which the fixed bed heat transfer zone and the fluidized bed reaction zone are nested in the same axis,the heating mode of combining the wall and carrier gas is used,and the pyrolysis non condensable gas is introduced as the alternative gas to realize self heating;The gas substitution rate of the mobile pyrolysis equipment is 76.1%,and the optimal pyrolysis oil yield is 64.8%,which is about 21% higher than that of fixed pyrolysis equipment,thus verifying the importance of the pneumatic conveying characteristics to the mobile pyrolysis equipment.