BIOGAS

What is biogas?

Biogas is produced when organic matter decomposes in an anaerobic environment (without oxygen). It is a mixture of methane (CH4) and carbon dioxide (CO2) with trace elements of other gases including hydrogen sulphide (H2S). 

A biogas system is best described as a giant anaerobic microbiome consisting of diverse groups of bacteria as well as their ancient cousins,archaea. Billions of anaerobic microorganisms work to break down organic material into simpler and simpler molecules until  eventually the methanogens produce methane gas.

A skilled operator feeds the biogas reactor with organic waste and controls the temperature and acidity levels inside the biogas digester.  The aim is to maintain consistent gas quality, maximising methane production and minimising hydrogen sulphide. 

After the raw biogas is produced it is saturated and needs some basic treatment to be used as a fuel. Water vapour and H2S must be removed to acceptable levels for the intended final application: heating or power. Where the gas is to be used for transport fuel or to be injected into a natural gas pipeline it needs further upgrading to biomethane, the primary source of renewable natural gas.

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what is biomethane?

Biomethane is purified biogas produced by removing CO2 and impurities using a variety of proven gas separation processes. This high value renewable energy source offers a climate friendly way of substituting fossil fuel natural gas.  Its high methane concentration, usually 85-95%, is matched to the natural gas specification in each country.  Biomethane is often referred to as ‘green gas’ or ‘renewable natural gas’ because it is 100% renewable.

Biomethane may be compressed and sold as vehicle fuel or injected to natural gas pipelines to directly replace fossil fuel natural gas.  Compressed Biomethane Gas (CBG) is a direct substitute for Compressed Natural Gas (CNG) which is sold as “NGV” natural gas vehicle fuel in Thailand.  Produced from agricultural waste, biomethane is a second generation biofuel. With its large agricultural sector, Southeast Asia has an enormous potential to supply biomethane but current government support and policies are focused on encouraging production of first generation biofuels.

 

Biogas systems

There are many types of biogas system, each one with certain niches where they are most suited. In-ground “covered lagoon” and “above ground tanks” are often used to describe systems, but these are very superficial attributes which do not actually describe the process. There are many poorly designed cover lagoon and many poorly designed tank systems. In Southeast Asia, due to the high ambient temperatures and the rural location of most projects, in ground lagoon systems are generally the best technical and economic solution.  However not all inground systems are built the same. It is important to ensure that the design is suitable for the type of substrate to be digested. 

Biogas equipment suppliers and clients often focus on achieving the highest CH4 concentration in the biogas but this can be a mistake.  Often to achieve a higher CH4 concentration substrate bypasses the biogas plant, or is pretreated in an acidification step.  Both of these scenarios reduce total CH4 production, which is usually not desirable for project economics.

Asia Biogas has gained a wealth of experience in the construction and operation of cost-effective and reliable covered lagoon biogas systems.  Our design team and directors also have experience in designing and commissioning tank-based solutions.  We are pleased to share this knowledge with our clients.

 

waste sources

In Southeast Asia agricultural and agro-industrial waste is an abundant and excellent organic substrate for biogas production.  Biogas in Asia is therefore overwhelmingly a ‘second generation biofuel’ i.e. produced from waste.  In Europe biogas is often a ‘first generation biofuel’ i.e. produced from so-called energy crops such as maize.  As a second generation biofuel, the biogas we produce in Southeast Asia is a premium product, with far greater postiive environmental and social impacts.

Biogas project in Krabi, Thailand

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