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Biogas

by | Mar 21, 2022 | Biofuels, Green Energy

Introduction

Biogas consists of hydrocarbons, which are flammable and may generate heat and energy when burned. Biogas forms by a biochemical process in which particular bacteria transform biological wastes into usable biogas. Biogas is the name given to a beneficial gas that comes from a biological process and is mostly composed of methane gas.

The biogas manufacturing process is anaerobic in origin and divided into two phases. The two steps are known as the acid formation phase and the methane formation phase, respectively. The bio-degradable complex biological compounds found in the waste products are acted upon by a group of acid-generating bacteria present in the dung during the acid creation stage. This stage is known as the acid-generating stage because organic acids are the principal products. In the second step, groups of methanogenic bacteria react with organic acids to create methane gas.

The anaerobic digestion part, which is the actual production of biogas and the translation of biogas into electricity, i.e., the cogeneration plant, are the two primary components of a biogas plant.

Biogas may form from various sources, including animal effluents, wastewater treatment plant sludge (OFMSW), agro-industrial waste, and crop residues. The energy yield varies depending on the qualities of the raw material used, in terms of biogas produced and therefore electrical and thermal energy created.

Biogas Mechanism

Anaerobic digestion of organic material in an oxygen-free environment produces biogas, which is a combination of methane, CO2, and minor amounts of other gases. The exact composition of biogas is determined by the type of feedstock used and the process used to produce it, which includes the following basic technologies:

  • Biodigesters: These are sealed systems (e.g., containers or tanks) in which naturally occurring microorganisms break down organic material diluted in water. Before using biogas, contaminants and moisture are normally eliminated.
  • Landfill Gas Recovery Systems: Biogas is produced when municipal solid waste (MSW) decomposes in landfills under anaerobic conditions. Pipes, extraction wells, and compressors induce flow to a central collecting point.
  • Wastewater Treatment Plants: These can recover organic matter, sediments, and nutrients like phosphorus and nitrogen from sewage sludge. Sewage sludge can be used as biogas in an anaerobic digester after additional treatment.

Biogas generally has a methane composition of 45 to 75 percent by volume, with CO2 accounting for most of the rest. The energy content of biogas can vary due to this variance; the lower heating value (LHV) ranges from 16 to 28 megajoules per cubic meter (MJ/m3). It can generate power and heat, as well as cooking fuel.

Biogas generation flow chart

Biogas Potential

Biogas can offer energy in the form most required, whether it’s baseload electric energy and heat, or gas to fuel regions that are more difficult to decarbonize. It can be used to heat houses or fuel heavy goods trucks since it can create renewable energy in the form of the gas continuously.

It can assist companies of any size throughout the world, with the scaling flexibility to construct a facility from two cows’ dung to one recycling 500,000mt of the first world’s food waste or sewage.

The world’s energy potential from currently accessible and sustainably grown/recovered primary feedstocks (livestock manure, food waste, sewage, crop residues, and energy crops) ranges from 10,100 to 14,000 TWh.

This energy can fulfill 6-9 percent of the world’s primary energy demand or 23-32 percent of global coal demand. It can satisfy 16-22 percent of world power demand when converted to electricity. If the energy converts to biomethane, it can replace 993 to 1380 bcm of natural gas, or 26-37 percent of current global natural gas use.

The digestate (or natural fertilizer) leftover from biogas production can replace 5-7 percent of the inorganic fertilizer now in use. It can fertilize 82 million hectares of land, which is the same amount of arable land as Brazil and Indonesia combined. The biogas sector may help supply energy and food security, manage waste, preserve water bodies, restore soil health, enhance air quality, promote health and sanitation, and generate jobs while making these contributions. As the world becomes more urbanized, the health of billions of people depends on cities properly managing trash, and our business is one of the finest ways for doing so, particularly for urban food waste and sewage.

Factor Enhancing the Biogas Production and its Purification

The following are the most important components in the production of biogas:

  • Composition of the sublayers – The feedstock used in the anaerobic fermentation process (digestion) to create biogas should provide a suitable environment for the growth and appropriate metabolic activity of the microorganisms participating in the process.
  • The temperature inside the digester – The selection and management of temperature are crucial for developing the anaerobic digestion process, as it has a significant impact on the quality and amount of biogas produced.
  • Time spent in retention – The hydraulic retention time (HRT) is the mean duration that the anaerobic digestion sublayer stays in contact with biomass in the digester (bacterial mass).
  • The digester’s working pressure – The importance of pressure in the biogas manufacturing process cannot be overstated. Experiments have demonstrated that methane production stops when the functioning methanogenic bacteria’s hydrostatic pressure exceeds 400-500 mm H2O.
  • pH of fermentation medium – All biological activities in anaerobic digestion occur at well-defined pH levels. The appropriate pH for the hydrolytic stage is between 5 and 6, whereas the optimal pH for the methane generation stage is between 6.5 and 8.

In recent years, there has been a lot of study on biogas cleaning and improvement. Water scrubbing, adsorption (physical and chemical), cryogenic separation, membrane technology, biological upgrading, and in-situ upgrading technologies are key biogas upgrading and purification strategies.

To achieve Wobbe Index quality and requirements, CO2 must be removed to raise the density and calorific value of the gas. Some of the current methods are pressure swing adsorption, physical absorption (water and organic solvent scrubbing), chemical absorption, cryogenic separation, membrane separation, and biological methane enrichment.

Cost-Benefit Analysis of Biogas

Alternative energy sources are increasingly becoming a worldwide reality: their utilization allows for both meeting rising energy demand and reducing the environmental effect.

The findings of the economic and financial research and the comparison study demonstrated that biogas plants with a capacity of 250 kW are still a viable home investment.

According to the present incentive law, small plants (with a powerless than 300 kWel) have the best incentive rate. These plants are particularly useful only if the biomass employed is classified as a “biological by-product”; or (ii) constituted for at least 70% of its weight by by-products, which is generally zero-cost biomass.

Another advantage of biogas generation is eliminating environmental challenges, such as manure spreading directly in the soil and other sewage disposal issues.

A biogas plant gives me an economic return on the sale of generated EE (Electric energy) while also (ii) avoiding the hassle of slurry disposal and its associated expenditures. Furthermore, the digestate (a by-product of anaerobic digestion) can be utilized as a fertilizer for main crops, in whole or partial substitution of commercially available chemical fertilizers, lowering farm management expenses.

 

 

Author

  • The author has done a master's in Environmental science and is currently working as chief Environmental Advisor with New Delhi State Government.

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