Feedstock Evaluation of a Downdraft Biomass Gasifier Coupled with a Tar Removal Mechanism /

Abstract

Feedstock selection and development of biomass gasifier are basic needs for completion of biomass gasification. The producer gas is emitted with ―tar‖ and some other gases which need proper purification before feeding it to gas generators for electricity production. Here, feedstock evaluation of downdraft biomass gasifier is done and a proposed model for tar removal mechanism is suggested at field level. Producer gas from biomass gasification can replace natural gas as source of heating in water heating systems. Residential water heaters consume a significant portion of natural gas energy in a typical home. A hybrid Solar/Syngas water heating system at domestic level is proposed as cost effective and efficient technology to meet challenges in energy sector of Pakistan. Proximate analysis and ultimate analysis for corncobs were done by TGA and True spec elemental analyzer respectively. HHV of corncobs was determined by bomb calorimeter. In present study proximate analysis gives 60.04% VM(Volatile Matter), 6.61% ASH, 29.85% FC (Fixed Carbon) and ultimate analysis gives 45% Carbon, 5.8% Hydrogen, , 48.5% Oxygen. HHV of corncobs was found 17.41 MJ/kg. In conversion process, thermo grams of corncobs and other biomass samples for temperature change from ambient to specified temperature were compared. Most elevated and quickest change was watched for corncobs because of high part of cellulose, hemi-cellulose in corncobs, which is least in lignin. Current reviews were found in great concurrence with consequences of other revealed information. For locally fabricated downdraft biomass gasifier, present modification in throat diameter (8.6 cm) and throat inclination (48°) of downdraft biomass gasifier provides high yield of gas; 1kg of biomass gives 2.5m3 of producer gas. Gas analysis by IMR gas analyzer provided information about presence of 17.6% CO, 14.5% H2, 4.4% CH4 and some % of other gases when 18kg fuel was gasified. Energy conversion efficiency of corncobs based gasifier was found as 74.7% and temperature in gasification process was 700 °C. This experimental data can validate simulation data by other researchers for locally fabricated gasifiers. Heating Value of gas was 5.2 MJ/m3. Also, in non-throated gasifier experiment biomass gasification was done at 700° C and gas analysis was done by GC (Gas Chromatography). This analysis provided information about presence of 54.45% CO, 14.82% H2, 2.56% CH4 and 28.17% other heavy hydrocarbons when 150g biomass sample was gasified. An innovative approach is presented to remove tar maximally using home electric appliance at small scale which can be up graded for larger scales. At small scale flame quality comparison was done with and without electric appliance scrubber. A high blue quality flame was found with electric appliance scrubber that was the indication for removal of tar. Hybrid Solar/Natural Gas water heating system at domestic level provides natural gas savings by using natural gas as on demand heating source. The gas burner firing efficiency was found to be very consistent and recorded about 70±2% for different storage tank temperatures. The energy factor which reflects the overall performance of the system was found 0.52. The total annual delivered energy and consumption was 125therms and 247therms respectively. By including solar part minimum of 125 therms of natural gas are saved for 60°C hot water. Syngas as replacement of natural gas for water heating purpose at domestic level can save conventional fuels. For proposed solar/syngas water heating system, gas supply efficiency was determined as 47% in syngas heating test and total annual consumption and delivered energy was calculated as 129.2 therms and 131.35 therms. Energy Factor was calculated for water heating system as 0.9 following natural gas parametric scenario.