Biogas Plant Construction and Working Stages

The secret to understanding the most common biogas plant construction and working stages, is explained here for he most common AD plant type.

By far the most common biogas plants are those based upon one single anaerobic digestion tank, and they are often known as “Continuous Stirred Tank Reactors” (CSTRS).

They are often called single stage biogas plants, which can be confusing, because to the onlooker there would seem to be many more tanks and “stages”.

Tanks are added to increase the amount of biogas produced, and for other uses.

Just remember that for making biogas it is the number of stages in which the methane making bugs grow to make the biogas, that count.

We will now provide an explanation of the way a biogas plant works, in 5 “steps”:

Step 1 – Feeding The Bacteria That Make Biogas

Organic input materials such as silage, foodstuff remnants, fats or sludge, are fed into the biogas plant as what is called “substrate” – that’s food for the biogas making bugs, to you and me!

Renewable resources such as corn, beet, or grass, can serve as feed both for animals such as cows and pigs as well as for the micro-organisms in the biogas plant.

Not only those foods work, so do farm wastes such as manure, dung, and chicken litter, plus increasingly biogas is being made from supermarket and household food waste.

Step 2 – Fermentation in the Large Tank (Digester Tank)- where the bacteria make the biogas.

In the fermenter, heated to approx. 38-40 °C, the substrate is decomposed by the micro organisms under exclusion of light and oxygen. The final product of this fermentation process is biogas with methane as the main ingredient. But, at the same time some other unwanted compounds form a small part of the biogas. Pure biogas is just methane alone. But the raw biogas that emerges can be bad smelling from corrosive hydrogen sulphide. Carbon dioxide is also produced and a percentage is contained in the biogas.

Step 3 – Fermentation Residues Storage Tank

Once the substrate has been fermented, it is pumped to the fermentation residues end storage tank and is retrieved from there for making useful products.

The residues, are called “digestate” and these comprise both a fibrous solid part and a liquid part, and these can be utilised as high quality fertiliser, and a soil conditioner respectively. The advantage of digestate is that it has a lower viscosity than farmyard manure, and it therefore penetrates into the ground more quickly than liquid manure slurry. Furthermore, the fermentation residue usually has a higher fertiliser value than manure, and is less odorous.

Further treating the fibrous part, by leaving it to mature in wind-rows, and subsequently using it as dry fertiliser is also common.

Step 4 – Using the Biogas

The biogas part of the output is usually stored in the plastic roof of the tank. From there it is most often burned in a combined heat and power ( CHP ) plant to generate electricity and heat.

The electric power is fed directly into the power grid.

The heat generated can be utilized to heat buildings, to dry firewood, or to dry harvest products such as grain.

At an increasing number of biogas plants the quality of the raw biogas is upgraded to purify it. The carbon dioxide, hydrogen sulphide, and other impurities are removed, and it is compressed and used as a clean renewable transport fuel.

Step 5 – Delivery of Biogas to Users

The biogas power which is not used in running the biogas plant, is exported as either a supply to the national grid or to gas filling stations.

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Build a Biogas Plant – Biogas Plant Construction Resources Available Online

Biogas Plant Construction Manual

A biogas plant construction and working well is an anaerobic digester of organic material for the purposes of treating waste and concurrently generating biogas fuel.

The treated waste is a nutrient-rich, nitrogen-rich fertilizer while the biogas is mostly methane gas with inert gases including carbon dioxide and nitrogen. Biogas plants are a preferred alternative to burning dried animal dung as a fuel and can be used for the treatment of human waste. Other feedstock which can be used includes plant material, non-meat or grease food-wastes, and most types of animal dung.

Over a million biogas plants have been constructed in the developing world for treatment of organic wastes, alternative energy supply to direct burning in the home, and overall improvement of human health and the environment. Many factors for selection of feedstock and site location must be researched before deciding to install a biogas plant.

Successful construction of the biogas plant requires a proper design and adherence to follow correct construction methods. The success or failure of any biogas plant primarily depends upon the quality of construction work.

The following instructions are based on the step-by-step instructions from the Government of Nepal Biogas Support Program Gobar Gas and Agricultural Equipment Development Company of Nepal has developed the design for model 2047 biogas plant.

This biogas plant model has become prolific across Asia and is known as a fixed-dome plant. The advantages of the fixed dome plant include the simplicity of design, few moving parts, low cost to construct and low maintenance.

The disadvantages when compared to a floating-dome digester are primarily the inability to store gas for use on demand; gas from the fixed dome digester must be used as generated or expelled to avoid damaging the digester. April 2011 United States Forces – Afghanistan Page 1 of 24 1. via Construction Manual

How to Build a Medium Sized Biogas Plant