Research On Mobile Biomass Pyrolysis System Hydrodynamics And Its Key Equipments Development

Mobile pyrolysis units can go deep into the areas of concentrated biomass and convert the low density raw materials into liquid products with higher energy density,which can significantly improve the economic benefit of bio-energy technology.In this paper,the dividing wall type fluidized bed(DWFB)is chosen as the reaction unit to enhance internal heat transfer.The fluidization characteristic inside the annular region is firstly simulated using CFD approach.Hot state test is also carried out to reveal the mechanism of heat transfer inside DWFB.The best heat supply scheme of the reaction system is determined based on theoretical calculation,and its operability analysis is carried out.A novel dual pneumatic biomass powder conveying method is also came up in this paper to achieve a constant and steady raw material feeding.The effects of gas path and structure parameters on feeding are investigated.Then,the characteristic of biomass feeding in the dense phase of the fluidized bed is studied to obtain the key factors that influence the feeding rate under fluidized bed condition.Lastly,the key equipments of a mobile pyrolysis unit are developed based on the current conclusions.Major conclusions and novelties of this paper are listed as follow:(1)The influences of drag model,parameters and boundary conditions on simulation result are studied.Then,the optimal combination of drag model,restitution coefficient and specularity coefficient is selected according to the comparison of simulation and cold test results.(2)Based on the selected model with its parameters,the numerical simulation is further carried out to learn the effects of initial bed height,particle diameter and gas velocity on the fluidization inside the annular region.By comparing the results with that of a cylindrical fluidized bed,it is found that the shape of cross-section of the channel has a significant impact on particle velocity distribution.(3)The hot state test results show that the bed height has a remarkable influence on the heat transfer inside DWFB while the effect of particle is not so obvious.Then,the heat transfer model is established based on "packet renewal theory".The results of numerical calculation show that the heat transfer mainly occurs in the dense phase of the fluidized bed,packet contact time plays an important role in the heat transfer,the overall heat transfer coefficient increases with the increase in Reynolds number.(4)The optimal connection scheme of DWFB and the external heat exchanger(EHE)used for heat supply and energy recovery is determined as well as the temperature regulation method based on theoretical calculation.The calculation results show that DWFB has a higher heat transfer efficiency compared with the same size gas-to-gas heat exchanger,the heat transfer coefficient increases with the increase in cold fluid mass flowrate.Also,the linear relationship between the temperature in reaction region and cold fluid mass flowrate in bypass line is observed which validates the feasibility of the temperature regulation method in this study.(5)The biomass feeding experiment is conducted to test dual pneumatic conveying method proposed in this study.It is shown that using injection and fluidizing gas will benefit the gas efficiency and the conveying stability respectively.The structure parameters of the injection pipe have remarkable impact on feeding rate.The opening ratio of the gas distributor has positive effect on the feeding rate while has negative effect on the conveying stability.(6)The structure parameters of the injection pipe are innovatively integrated into the Ergun equation to establish the gas-to-solid flow model inside the pressure chamber.The model is found to have an error within ±150%.(7)The experiment of biomass feeding inside the dense phase of the fluidized bed is carried out to investigate the effect of gas velocity,particle diameter and opening ratio of the gas distributor on feeding rate.It is indicated that the bed voidage is anothor key factor that influence the feeding except the pressure drop of the bed.(8)The model of three phases flow including gas,bed material and biomass is presented.Also,the"stepwise testing" method is proposed to solve the model.The modeling results show that the biomass particle velocity plays an important role in biomass feeding.(9)Key equipments of a mobile pyrolysis system are developed.First,an double pipe fluidized bed reactor is designed which includes a spiral-plate heat exchanger to improve the energy efficiency.Then,a new dual pneumatic type feeder is designed which has an injection pipe and gas distributor inside the pressure chamber to improve both the efficiency and stability.A hybrid type pyrolytic vapor condenser is also developed which contains two-stage direct contact condensation and has cooling pipe inside the shell to ensure a compact structure.