Biogas digester construction manual

The biogas plant construction download page is divided into two sections. The Home section has smaller family sized units and the Village section has larger or community sized construction plans.

Basic Small Scale Drum Plan 1. Biogas Digesters in India K. Biogas Digester: What is a biogas digester and how to build it? Module for a decentral autonomous energy supply, , Culhane. The feedstock inlet pipe and toilet pipe, if installed must be placed in position when the round-wall is cm high.

To reduce the risk of blockages, the inlet pipe s must be placed as vertical as practically possible. Exactly to the opposite of the main feedstock inlet pipe, a 60 cm wide opening must be left in the round-wall that serves as a manhole. The digested slurry will flow to the outlet tank through this opening. Additional inlet pipes should be placed as close as possible to the main feedstock inlet pipe with a maximum distance of 45 degrees from the inlet-center-manhole line.

When the round-wall has reached the correct height, the inside must be plastered with a smooth layer of cement mortar with mix of cement-sand. Dome Construction When the round wall of the digester is complete, the dome is then constructed.

Before filling the pit with earth to make the mould for dome, backside of the round wall should be filled with proper compacted back-fill. If this is not done, the pressure of earth for the mould can lead to cracks in the round-wall. The dome is constructed using a mould or cast technique. This can be accomplished by constructing a timber frame then placing the earth-cast atop for proper arch design. Once the dome is cast, the timber frame and earth will be removed through the outlet chamber manhole.

Photos 8. The vertical pipe should remain in place as the mould is constructed. The guide can be manufactured from an iron rod with a loop at one end to ride on the vertical pole of the biogas plant and the other end bent to seat flush to the top of the digester wall.

The mould is shaped rotating the guide around the central vertical pipe. The top of the round-wall must be clean when the guide is in use. Photo 8.

It is important that the earth of the mould is well compacted. If the earth is further compressed after casting the dome, by its own weight and that of the concrete, it can lead to cracks in the dome. When the earth mould has the exact shape of the guide, a thin layer of fine sand is spread on the mould-top by gently patting it on the surface.

The sand layer will prevent the earth from adhering to the cast. The earth used for the mould needs to be damp to prevent dry earth from soaking up water from freshly casted concrete. The casting must be done as quickly as possible and without interruptions as this will negatively affect the quality of the cast.

A constant, adequate supply of concrete mix: 1 cement, 3 sand, 3 gravel — must be made for the mason. No concrete older than 30 minutes should be used.

Special care should be taken to maintain the thickness of the dome while casting, i. An alternative to concrete cast construction technique is the use of baked clay brick in corbel- arch construction.

The compression of the brick and mortar in a spherical shape will support the dome. The clay brick dome will have a near-uniform thickness compared to the cast-concrete dome that thins towards the center. A continuous application of mortar along the sand mould is necessary as the bricks are placed. The brick dome should be placed continuously and use a mortar mix of cement to sand. Once the bricks for the dome have all been placed, the exterior is covered with cement to sand plaster.

During the casting, the concrete has to be protected against strong sunlight by covering it with wetted burlap, jute bags or straw mats. This protection has to be left in place for at least one week. The day after the casting, the turret must be made. The turret is made with brick, 36 cm square and 50 cm tall. The turret is plastered with concrete. Any delays during dome construction can lead to leakage between main gas pipe and dome.

After the dome has cured for approximately one week, the timbers and earth of the mould can be removed through the manhole. When all earth is removed, the inside of the dome has to be thoroughly cleaned with a stiff brush and clean water.

When a layer of plaster is applied, the work must be executed with great care and without interruptions. The performance of the biogas plant is dependent on the gas tightness of the dome. If the top cover will be prone to erosion due to wind and rain proper protection with gravel, circular wall, or straw matting should be applied. Outlet Chamber Construction The Outlet Chamber excavation and manhole is completed concurrently with the digester vessel and the manhole shares a common foundation with the digester vessel.

The manhole of the Outlet Chamber is near the digester wall. The earth behind the manhole and under the outlet floor must be well compacted to prevent cracks in Outlet Chamber walls. Photo 9. The inside dimensions of the outlet can be found on the drawing under A, B and D. It is important to use the prescribed dimensions as they determine the useful capacity of the gasholder. For the same reason the outlet floor and the top of the walls must be level. The walls will be vertical and finished with a smooth layer of cement plaster mix: 1 part cement, 3 parts sand.

Outside of the walls must be supported with sufficient compacted earth up to the overflow level to avoid cracks. The Outlet Chamber walls should slightly higher elevation than the surrounding ground to reduce chances of surface water entering the outlet during the rainy season. It should be easy to make the additional concrete at this time and the slabs will be well cured before they are placed on the outlet.

The slabs must be 8 cm 3" thick with proper reinforcement re-bar 3 cm 1" from the bottom side. The number of slabs should be designed that they can be handled by four men without great difficulty. Installing re-bar loop handles on the slabs may be useful for the occasional handling of the slabs. When preparing the slab casts use a smoothed, clean sand base and lumber for the frame. Special care must be taken for the placement of the concrete to prevent small holes that can expose the steel reinforcement to corrosive vapor from the slurry in the Outlet Chamber which will cause corrosion and ultimately lead to the slab collapse.

If holes form in the slab these should be filled with plaster layer. The Outlet cover slabs are essential to protect people and animals from falling inside and to avoid excessive evaporation of the slurry in dry season. This can be constructed with or without a mixing device.

Installation of a mixing device is preferable because not only it makes plant operation easier but it also improves the quality of mix.

When a mixer is installed, it has to be firmly attached to the structure, easy to operate, effective in the mixing process and the steel parts in contact with the feedstock should be galvanized. The top of the structure should not be more than one meter above ground level and both inside and outside of the tank must be covered with a smooth layer of plaster Mix: cement, sand.

The finished bottom of the Inlet Tank must be at least 5 cm above the Outlet Chamber overflow level. The position of the inlet pipe must be such that a pole or rod can be inserted through it to the digester vessel without obstructions. This will allow the operator to clear blockages in the inlet pipe.

For the same reason the inlet pipe must be without bends. Even if a mixing device is not installed, the inlet pit should be round in shape as this is a more economical use of material and easier for hand mixing. Photo The toilet inlet pipe should enter the digester tank no more than 45 degrees from the centerline of the main inlet pipe. Additionally, the toilet pan level should be at least 25 cm above the outlet overflow level. Lay-out of Pipeline The gas pipe conveying the gas from the plant to point of user is vulnerable to damages by people, domestic animals and rodents.

Therefore, only light quality galvanized iron pipe should be used which must be, where possible, buried 30 cm 1 foot below ground level. Fittings in the pipeline must be sealed with zinc putty, Teflon tape or jute and paint. Any other sealing agent, like grease, paint only, soap etc. The use of fittings, especially unions, should be kept to a minimum to reduce the risk of leakage.

No fittings should be placed between the main gas valve and the dome gas pipe. The pipe size, inside diameter should be between. Pipe size is determined by the size of the digester, amount of gas produced and amount of gas required in the house. Outlet 7. Main Gas Pipe and Turret 8. Main Gas Valve 9. Pipeline Water Outlet Water Trap or Drain Pressure Gauge Gas Tap Gas Stove with rubber hose pipe Gas Lamp Optional Slurry pit s.

You guys are awesome! Can I please get a personal email address so that I can contact u later? Cut the top off at a 2. This biogas Plant Construction manual writing by T. Culhane publish publish in www. 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. 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. In the fermenter, heated to approx. 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. 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 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. 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 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. 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.