Study On Solid Oxide Fuel Cells Utilizing Biomass As Fuel

Solid oxide fuel cell?SOFC?is an all-solid-state power generation device with solid oxides as electrolyte to directly convert the chemical energy of fuel into electric energy by electrochemical reactions.The prominent feature of SOFC is the wide availability of fuel: Not only can use hydrogen,natural gas,methanol,gasoline and other gaseous or liquid fuels,but also can use coal,biomass and other solid carbonaceous fuels.Biomass has the characteristics of renewable,carbon neutral,widely available and cost efficient.The conventional way of biomass utilization is to burn directly as firewood,with low energy conversion efficiency and high pollutant emission.This paper investigates the feasibility of using biomass directly as SOFC fuel to achieve green power generation,aiming to pave the way for efficient and clean utilization of biomass resources.In this work,the two kinds of biomass,the fruit tree branch and medium density fiberboard?MDF?,were chosen as the research objects.On the basis of systematic characterization of the physicochemical properties of the fruit tree branch,MDF and their pyrolytic biochars,the electrochemical performance and fuel utilization of their direct use as SOFC fuel were studied.The results show that the peak power density?PPD?of the cells with the fruit tree branch fuel at 850? was 157 mW cm^-2,and the fuel utilization was 36.2%,which indicated that the fruit tree branch could directly achieve in situ efficient power generation through SOFC.After loading the steel slag catalyst,the PPD of the fruit tree branch reached 303 mW cm^-2 at 850?,and the fuel utilization was 18.33%.The possible reasons for the decrease in fuel utilization lie in:?i?The pyrolysis-gasification reactions of the fruit tree branch had occurred at a lower temperature below 850?,and?ii?the pyrolysis-gasification rates of the fruit tree branch at 850? exceeded the consumption rate of the cells,resulting in the loss of some gasified fuel without utilization.The solid carbon content of the fruit tree branch was 81.46%,and the total sulfur content was 0.05%.The graphitization degree was low,and the PPD at 850? was 238 mW cm^-2.The discharge process was stable,and the mass specific energy density was 7928.4J g^-1.The absolute fuel utilization of the fruit tree biochar was 49.3%.The yield of pyrolysis of the fruit tree branch was 28%,so the relative fuel utilization of the fruit tree branch was 13.8%,which is 22.4% lower than that of the direct utilization of fruit tree branch.When MDF was directly used as SOFC fuel,the PPD at 850? was83 mW cm^-2,the fuel utilization was 28.72% and the electrical power output per unit mass was 2419.8 J g^-1.After loading the steel slag catalyst,the PPD reached about 220 mW cm^-2 at 850?,which is about 2.6 times that of MDF,indicating that the catalyst significantly accelerated the biomass pyrolysis rate and/or Boudouard gasification rate.However,the decrease of reaction temperature brought by the catalyst and the increase of pyrolysis-gasification reaction rates at the same temperature may lead to the gasification products of MDF not being fully utilized and losing with the tail gas,which eventually led to the decrease of fuel utilization?about 21%?.The solid carbon content of MDF biochar was 58.70%,and the total sulfur content was 0.02%.The ash content was 27.59%,and the graphitization degree was low.The PPD at 850? was 172 mW cm^-2,and the discharge process was more stable.The absolute fuel utilization of MDF biochar was 54.67%.Considering that the MDF pyrolysis yield was30%,so the relative fuel utilization of the MDF biochar was just 16.4%,which is 12.3% lower than that of the direct utilization of MDF.This paper verifies the feasibility of SOFCs using biomass directly as fuel,so we put forward the concept of direct biomass SOFC?DB-SOFC?.In a word,this study provides a theoretical basis for the clean and efficient power generation by directly using the fruit tree branch and abandoned MDF.