Methane enrichment of biogas produced from floral waste: A potential energy source for rural India

Abstract

ABSTRACTBiogas has emerged as a clean and cheap energy source with additional advantages like waste disposal solution and an alternative for fossil fuels. Raw biogas contains methane between 50% and 70% and carbon dioxide between 30% and 50%, along with traces of hydrogen sulfide and moisture. Presence of contaminants like carbon dioxide and hydrogen sulfide in biogas restricts its applications in India for cooking and lighting purpose or at the place of its generation. Thus, for making biogas as a transportable fuel or for other widespread applications, removal of contaminants from biogas becomes a necessary step. Small-scale biogas plants seldom use purification and scrubbing systems because of cost considerations and inadequate knowledge of purification techniques. The present experimental work uses floral waste with alkaline pretreatment as an input substrate, for biogas production in Deenbandhu-type fixed-dome biogas plant, used in rural parts of India. The experimental investigation focuses on methane enrichment of biogas by removal of contaminants like carbon dioxide, hydrogen sulfide, and moisture from biogas, using chemical absorption technique. Packed column reactors arranged in series facilitate biogas purification and scrubbing process at around atmospheric pressure and temperature. The materials used for filling the purification columns include steel wool, silica gel, and different aqueous alkaline solutions of sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2), sodium carbonate (Na2CO3), and monoethanolamine (MEA). A pedal-operated compressor pressurizes raw biogas and forces it through a series of packed chemical absorption columns for the removal of contaminants. Content analysis of purified biogas and raw biogas contents has been done using gas chromatography. The analysis of purified biogas samples 1 and 2 shows methane enrichment up to 96.91% and 94.16% and the carbon dioxide removal efficiency of 99.85% and 98.86% while hydrogen sulfide removal efficiency of 87.5% and 62.5% for samples 1 and 2, respectively. Purification results for biogas show the potential of the purified gas for applications like running stationery engines or use as a vehicular fuel. The purification and scrubbing technique used in the present work uses low-cost commercial chemicals, and the purification columns comprise 4-in-diameter polyvinyl chloride pipes. Use of the technique on a large scale by common people can further raise the potential of biogas as an energy source with a high heating value for widespread applications. Using floral waste from temples as an input substrate provides an energy-efficient solution for soil and water pollution, arising due to the disposal of the waste into the soil or nearby water resources like a river.