Experimental Study And Simulation Of Wet Biomass Gasification Under Anoxic Environment In Highland Condition

The farmer in Tibet almost completely depends on the traditional biomass for cooking and space heating.Due to high altitude and anoxic environment in Tibet,the combustion time is long and the combustion efficiency is low.It also has a certain negative impact on the fragile ecological environment of Tibet Plateau which is China's ecological security barrier.Gasification can convert biomass into syngas,which is clean and efficient.In terms of improving the quality of life of Tibetan farmers and herders,burning syngas is cleaner than burning biomass directly.In addition,gasification requires lower oxygen concentration than combustion,therefore it is considered as a viable option for biomass in Tibet.In this paper,we aim to explore the gasification of wet biomass under the low-pressure and anoxic environment in Tibet.?1?Based on the statistics data,we estimated the quantity of biomass resource combing with the parameters including residue to rroduct ratio and conversion factor,and so on,emissions from its combustion and gasification and analyzed its distribution in Tibet with environmental pollutant emission factor.The main conclusions are as follows:The acquirable quantity of crop straw and animal dung was 7.27×10⁶ t mainly distributed in Qamdo.Compared to the household combustion,the reduction of SO₂was 72%with household-level gasification and 97%with village-level gasification,and the NO_x reduction was 79%with household-level gasification,96%with village-level gasification and 72%with gasification-combustion.It showed that gasification had great application potential in Tibet.?2?Physical and chemical properties of typical wet biomass?Tibetan medicinal residues and fresh yak dung?collected in Tibet were analyzed.The thermogravimetric experiments of wet biomass were conducted in nitrogen and air atmosphere,respectively.The activation energy were calculated with three methods?Coast-Redfern,Doyle and DAEM methods?.The results demonstrate that the content of alkali metals such as K and Ca in yak manure was very rich,while the content of heavy metals such as Cu and Zn was extremely low.The content of K was 13.02 mg/kg,which was about6-26 times that of common cattle manure;the main pyrolysis and gasification process were divided into three stages.For the yak dung,the activation energy estimated by Doyle method of each stage for pyrolysis were around 97.74,112.01 and 141.50 kJ/mol.Doyle method showed a better fit between simulated data and experimental data.?3?The tube furnace gasification system was built to analyze the effects of gasification temperature,moisture content and altitude on the distribution of gasification products.When the temperature is 1000°C,the humidity is 13.5%and the pressure is 1 atm,the best gasification performance of yak dung was achieved:the LHV is 6.53 MJ/Nm³,the syngas yield is 1.29 Nm³/kg,and the tar yield is 0.39 g/Nm³.The higher moisture coupling the lower pressure tends to promote the formation of a richer yak coke structure.?4?A one-dimensional steady-state kinetic model was developed using Aspen plus for the simulation of a fixed-bed gasifier in highland condition under anoxic environment.The effects of gasification temperature,moisture,gasification pressure,equivalent ratio?ER?and oxygen concentration,gas composition and low heating value were studied,and the optimal optimization of suction fixed bed in high altitude and low pressure environment in Lhasa was obtained.The optimal gasification process parameters were as follows:gasification temperature:1000°C,raw material moisture content:20%,oxygen concentration 44%.Under this condition,the lower heating value of syngas was about 6.44 MJ/Nm³.The model was applied to a self-designed fixed-bed gasifier,and the gas composition and LHV of the yak dung were predicted.