Pressurized Water scrubberJunaid Maqsood (2012-ag-3661)M.Sc. (Hons.) Agricultural EngineeringWater scrubber:It is an instrument that is used to upgrade a raw biogas of low grade to a high grade fuel. A low grade fuel has lower percentage of Methane (CH4 55-65 % & CO2 35-45 %). And high grade fuel has high percentage of methane (CH4 > 90 % and < 10 % other gases). Objectives:It is used to upgrade a low grade raw biogas, to remove CO2 from raw biogas, to remove H2S from raw biogas, to remove water vapors from raw biogas, to increased thermal efficiency, to Storage space increase for upgrade biogas, to higher specific output from engine.
Raw biogas:Biogas is a mixture of gasses which is produced as a result of breakdown of organic matter by the process of anaerobic fermentation. Raw biogas has Composition• Methane (CH4) 40-75% Water (H2O) 0-10%• Carbon dioxide (CO2) 25-55% Hydrogen sulfide(H2S) 1-3% • Ammonia (NH3) 0-1% Nitrogen (N2) 0-5% • Oxygen (O2) 0-1% Hydrogen (H2) 0-1%So large amount of carbon dioxide, hydrogen sulphide and water vapors in raw biogas creates some problems.Problems: Due to CO2: CO2 is non- combustible gas due to which it reduced the thermal efficiency of raw gas and it also lowers the power output from the engine. CO2 takes up space when biogas is compressed and stored in cylinder. As compressed gas undergoes expansion during engine running CO2 can also cause freezing problem at valve and metering point. Due to H2S: The traces of H2S present in raw biogas produces H2SO4 due to which it corroded the internals of pipes, fittings and etc.Water vapors: Moisture present in raw biogas causes corrosion and decreases heating value of the fuel.
Design of pressurized water scrubber:Packed bed scrubber is consists of three parts, which are Top section: a liquid inlet and distributor is present at top of scrubber column.Middle section: this section consists of packing or filling. This packing provides a larger area of contact between the liquid and gas.
Bottom section: gas inlet and distributing space is present at the bottom of cylindrical column.Methodology of pressurized water scrubber:Biogas is produced from biogas unit is compressed and stored in storage tanks. This low grade biogas from storage tank is transferred to water scrubber column from bottom. Water is pumped from water tank and enter into column from top section through a pump. CO2 and H2S are physically absorbed in water at high pressures and by releasing the pressure with very little change in temperature it can be regenerated. Thus the absorption process is a counter-current one.
The dissolved CO2 and H2S in water are collected from the bottom of the tower and upgrade gas is collected from top section. This upgrade biogas is then compressed and Stored in cascade for further use with high efficiency.