Effect of Steam and Catalyst with Lignite Feedstock on the Performance of Downdraft Gasifier

Abstract

India is facing a shortcoming in rural electrification. It is because of non-feasible and/or expensive process to establish grid connection in some interior area of India. There is an emerging need for a reliable and sustainable energy source. The increase in the energy need of the society has driven the researchers from all around the World to find new sustainable, reliable and renewable source of energy. The gasification of the carbonaceous material has potential to face this surge in the energy need of the rural area. Gasification is one of the suitable technologies for off-grid rural electrification. Carbonaceous fuel such as lignite has very limited scope of its usage to very few technologies due to its high moisture content and ash content. Hence it is required to find the technology that can meet all these challenges and also provide sustainable and reliable energy sources. The gasification of lignite has a promising potential to meet all the major challenges. Pollutants such as tar and particulate matter (PM) restrict usage of gasification technology in electricity generation. This tar and particulates can be reduced by gasification along with catalyst and steam. A 10 kWe pilot scale downdraft gasifier was used for the experimentation. The present work shows the lignite gasification with steam as a gasifying medium. The feed stock chosen for the study were lignite and mixture of lignite and 7 % MgCO3 catalyst. Lignite size taken for experiment was in the range of 22-25 mm. The steam flow rate was varied from 0.49 kg/h to 2.6 kg/h . The calorific value obtained for the producer gas for steam gasification and catalytic steam gasification were found in the range of 5.1 - 5.89 MJ/ kg and 5.89-6.65 MJ/kg. The cold gas efficiency for steam gasification and catalytic steam gasification were in the range of 62.21 - 75.29 % and 79.19 - 86.14 % respectively. The tar yield for steam gasification and catalytic steam gasification were fund in the range of 516.2 to 115.9 mgN m -3 and 472.96 - 105 mg/Nm3. The particulate yield for steam gasification and catalytic steam gasification were found in the range of 92 - 27.38 mg/Nm3 and 72.1 - 22 mg/Nm3 respectively. The optimum calorific value for both the cases study were obtained for 1.6 kg/h of steam flow rate. The optimum H2 yield for steam gasification and catalytic steam gasification was obtained at 32.56 % and 34.73 % respectively. The H2 was produced on the cost of CO which was obtained in the range of 10.12 - 7.38 % and 12 - 7.47 % for steam and catalytic steam gasification respectively. The optimum steam to biomass ratio (SBR) was calculated as 2.55 and 2.51 for steam gasification and catalytic steam gasification respectively. There was no clinker found by adding steam with lignite which was dominating in lignite gasification. The optimum cost of electricity was found to be 10.78 and 10.03 Rs./kWh for steam gasification and catalytic steam gasification respectively.