Experimental Investigation Of A Compact-Fast Dual Fluidized Bed For Calcium-Looping Biomass Gasification

The CO₂ emission from combustion of fossil fuel is one of the primary factors contributing to global warming.Therefore,it is imperative to develop the renewable energy and CO₂emission reduction technology.Biomass is"zero carbon"fuel,and calcium-looping biomass gasification on dual fluidized bed has promising prospect of application,which can produce high concentration of H₂ syngas with in-situ CO₂ capture and further realize negative CO₂emissions.In this work,a compact fluidized bed is used as the gasifier while a fast fluidized bed is used as the regenerator（or the combustion reactor）.A series of calcium-looping biomass gasification tests are carried out on dual fluidized bed in order to provide sufficient data and experiences supporting for the design and the operation of the pilot plant.Quartz sand and dolomite were used as bed materials and pine wood pellets were used as fuel for the calcium-looping gasification process on a 10 k W_th compact-fast dual fluidized bed system.The results show that the system can operate stably when the biomass flow rate is 2kg/h,the S/B is 0.8,and the temperatures in bubbling fluidized bed,riser and regenerator are 650℃,800℃ and 860℃ respectively,and the solid recirculation flux is 10.0 kg/m²s.The bed height in the bubbling bed is 0.5 m and the pressure drop is around 10 k Pa,and most of the bed materials stay in the bubbling fluidized bed.Comparing to that with quartz sand as the bed materials under the same operating conditions,hydrogen production is obviously enhanced with dolomite.The H₂production is 0.460 Nm³/kg_fuel,increasedby 0.225 Nm³/kg_fuel,and the H₂concentration is 70.88%,increased by a percentage of 38.03.The cold gasification efficiency is 45.93%,and the LHV of the syngas is 13.26 MJ/Nm³.Increase of temperature in the upper riser benefits on the conversion of tar.The tar content at the outlet of the upper riser is 21.18g/Nm³,which is 13.2%lower than that at the outlet of bubbling fluidized bed.In the compact fluidized bed gasifier,the enhancing performances of upper riser on gas production and tar conversion were studied under different temperatures and solid recirculation fluxs.The results show that the increase of temperature can promote the tar conversion.The tar content decreases by 3.77 g/Nm³ when temperature increases from 600℃ to 800℃,and the tar conversion rate increases from 2.8%to 21.8%.When the upper riser operates at 600℃,the H₂concentration increases by 3.11%and the H₂ production by 0.012 Nm³/kg_fuel.The upper riser can also enhance the conversion of tar,especialy when it operates at high temperature（e.g.800℃）,while the tar content decreases by 4.46 g/Nm³,and the production of syngas increases by 0.026 Nm³/kg_fuel.Increase of solid recirculation flux can enhance H₂ production and H₂concentration,and reduce tar content.Uner the temperature of 600℃ in the upper riser,the production increases by 0.021 Nm³/kg _Fuel,and concentration of H₂ increases by 2.82%,while the tar content reduces by 3.4 g/Nm³ and production of syngas increases by 0.012 Nm³/kg _Fuel,under the temperature of 800℃ in the upper riser.The temperature variations in the regenerator under different fuel feeding rates（system load）and solid recirculation flux were studied.The results show that the temperature in the regenerator is sensitive to the fuel rate and the heat distributes between the two reactors are self-balanced.When the solid recirculation flux is constant,the increase of fuel feed rate makes a quick increase of temperature in the regenerator and then the temperature tends to be stable.When the fuel feeding rate is constant,the increase of the solid recirculation fluxs lead the increase of temperature in the regenerator.