Bioenergy: Biomass to Energy
Biogas - Anaerobic Process
Anaerobic digestion is a biochemical process where complex organic materials are broken down by various anaerobic microorganisms in the absence of oxygen. This process is comparable to natural occurrences, such as digestion in the stomachs of ruminant animals like cows.
Biogas produced from sources like landfills or digesters primarily consists of methane (CH4), carbon dioxide (CO2), nitrogen (N2), oxygen (O2), hydrogen sulfide (H2S), and water vapor (H2O).
Raw biogas has a low calorific value due to these impurities. Therefore, upgrading biogas is essential for its use as transportation fuel, grid injection, or industrial heating. This ensures it meets the composition and quality standards of LPG and CNG (BNG/RNG).
We provide comprehensive solutions for upgrading and purifying biogas to effectively recover methane, making it suitable for various applications.
BioCNG / BioRNG Installation
A BioCNG installation produces BioCNG and digestate as the final outputs of the anaerobic digestion process.
Feedstock for Anaerobic Digestion
A wide range of biomass types can be used as feedstock for producing BioCNG through anaerobic digestion. These include:
- Animal manure and slurry.
- Agricultural residues and by-products, including those from horticulture, fruits, and vegetables.
- Digestible organic waste from food and agro-industries.
- Organic waste of animal origin.
- By-products from sugar processing, molasses production, fermentation, cereals, edible oil processing, cocoa, tea, and tobacco industries.
- Waste from the baking, confectionery, and beverage industries (alcoholic and non-alcoholic).
- Dedicated energy crops, such as maize and corn.
- Organic fractions of municipal solid waste, including household, commercial, industrial, institutional, and catering wastes of vegetable and animal origin.
- Sewage sludge and external waste from water treatment facilities.
- Residuals from wood processing, furniture manufacturing, pulp, paper, and cardboard production.
- Waste generated by the leather and textile industries.
- Garden and park waste.
This diversity of feedstocks enables flexible and efficient production of BioCNG, promoting sustainable waste management and renewable energy generation.
Processes and Steps to Upgrade and Purify Biogas
- Hydrogen Sulfide (H₂S) Removal
Biogas is initially compressed at 1 bar and introduced into the biogas upgrading system. The first step involves removing hydrogen sulfide (H₂S), which typically constitutes less than 1% of the biogas, though this percentage may vary based on the raw materials used for biogas production. Activated carbon with a catalyst is used to reduce the H₂S content to below 20 ppm. - Moisture Removal
After H₂S removal, moisture (H₂O) is the next component to be extracted. Raw biogas generally contains 5–8% moisture. The biogas is cooled to below 5°C to remove the moisture content, which is essential before proceeding with carbon dioxide (CO₂) removal using VPSA technology. - Gas Analysis
An online gas analyzer is utilized to continuously monitor the biogas composition and the purity of the upgraded gas. Key components analyzed include methane (CH₄), carbon dioxide (CO₂), moisture (H₂O), and hydrogen sulfide (H₂S). NDIR (Non-Dispersive Infrared) and electrochemical methods are employed for accurate analysis. - Carbon Dioxide (CO₂) Removal
The removal of CO₂ is carried out using Vacuum Pressure Swing Adsorption (VPSA) technology. A molecular sieve adsorbs CO₂ to enhance the methane concentration, aiming to achieve natural gas quality. Over time, the adsorber becomes saturated and requires regeneration, which is achieved by lowering the pressure below atmospheric levels to release CO₂. Pressure equalization steps are incorporated to optimize methane recovery. VPSA technology can achieve methane purity levels as high as 98%. - Odorization
Since bio methane is naturally odorless; an odorant is added for safety reasons. Ethyl Mercaptan is commonly used to provide a detectable odor. - CNG Cascade filling
The purified biomethane is compressed to 250 bar and filled into CNG cascades or tube trailers. These are then supplied to industries, hotels, and colleges for applications such as thermal energy generation, power production, and transportation fuel. Vehicles powered by biogas can achieve a CO₂ emissions reduction of 75% to 200% compared to conventional fuels. - Grid Injection
The upgraded bio methane can also be injected into national or regional grid networks. This includes high-pressure gas transmission grids or local low-pressure gas distribution systems.