Do-it-yourself biogas plant. Self-production of biogas How to make a biogas plant for your home

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It is not easy for farms to dispose of manure. It is produced in excess, and a lot of money has to be spent on removal and disposal. In small private farms, manure is actively used as a free and effective fertilizer. It turns out that there is another way to usefully use this raw material, which makes it possible to obtain natural gas.

Many farms are already producing biogas from manure, using environmentally friendly technology that allows them to obtain a valuable product. Biomethane from manure is of high quality, which is why it is used in many countries.

What is biogas

Biogas from manure is an environmentally friendly fuel. According to its characteristics, it is close to natural gas, which is extracted from the bowels of the earth industrially.

Biogas can be an alternative to conventional fuel, because it is made from the waste of animals and birds, which can be found in abundance in any agriculture. With proper processing of raw materials, you can obtain colorless biogas without a characteristic odor, which contains at least 70% methane.

Biogas has good characteristics. One cubic meter of such fuel from manure produces the same amount of heat as one and a half kg of coal.

Process Benefits

Manure was processed to produce biogas back in Soviet times. Today, many countries are engaged in this type of industry, as it is profitable, easy and does not pose a threat to the environment.

Such alternative biogas does not require labor-intensive extraction of raw materials for production, the process of its creation is relatively cheap, and no toxic substances are released into the environment.

Of course, manure can be used simply as fertilizer if there are only a few cows on the farm. It is much more difficult for large farmers with hundreds of heads of livestock, because every year they have to get rid of several tons of manure.

In order for manure to become a high-quality fertilizer, it must be stored at a controlled temperature. But this requires extra expenses, so most farmers simply collect it in a certain place and then transport it to arable land.

If stored improperly, manure loses almost half of the nitrogen compounds in it and most of the phosphorus, so its performance becomes much worse. Methane gas is continuously released into the atmosphere from manure, which worsens the environmental situation.

The latest technologies for producing biomethane make it possible to process raw materials in such a way that the resulting biogas does not have a toxic effect on the environment. Biogas releases an incredible amount of energy when burned, and heated manure, after its use, becomes a very valuable anaerobic fertilizer.

Biogas technology

Biogas can be produced using bacteria, which do not require oxygen to function. Therefore, to produce biogas, it is necessary to build sealed containers in which the fermentation of raw materials will occur. The exhaust pipes are designed in containers in such a way that air from the external environment is not able to leak inside.

First, the reservoir is filled with liquid raw materials and the temperature is raised to the required level so that the world organisms begin to work. Methane rises up from liquid manure and accumulates in special tanks in which it undergoes a filtration stage. Then it is collected in gas cylinders. Used masses of manure accumulate at the bottom of containers, from where they are periodically removed and stored in other places. After pumping out the waste liquid, new manure is supplied to the tank.

Temperature regime of bacteria functioning

Methane can be released from manure only when a suitable temperature regime is created for it. Manure contains different bacteria that are activated and release biogas at different temperatures and at different speeds:

• Mesophilic bacteria. They start working if the ambient temperature rises above 30 degrees. Biogas is produced very slowly - the products can be collected after half a month.
• Thermophilic bacteria. To activate them, a temperature of 50-65 degrees is required. Biogas can be collected in just three days. Of particular value is sludge - manure waste after strong heating. This is a useful fertilizer and, most importantly, harmless - any helminths, weed seeds, pathogenic microorganisms are destroyed when heated.
• There is also another type of thermophilic bacteria that survive when heated to a temperature of 90 degrees. They are additionally included in manure so that fermentation occurs faster.

As temperatures drop, all types of bacteria become less active. In a small farm, mesophylls are usually used, because in this case additional heating is not required. Further, primary biogas can be used to artificially heat manure and activate thermophilic bacteria.

The disadvantage of storing raw materials is that they should not be subject to temperature fluctuations. Therefore, in winter, it is necessary to take care of a warm room for storing manure.

Preparation of raw materials for pouring into the reactor

As a rule, there is no need to further enrich manure with microorganisms, since they are already contained in it. All that needs to be done is to properly prepare the manure solution, monitor the temperature and change the raw materials in the bioreactor on time.

The moisture content of the raw materials should be at least 90% (the consistency of liquid sour cream). Therefore, before use, dry droppings (goats, sheep, horses, rabbits) are mixed with water. There is no need to dilute pig manure due to its high urine content.

It is also important that the manure is homogeneous and free of solid particles. The amount of biogas produced at the outlet depends on the fineness of the fractions. For this reason, a constantly running mixer is installed inside the equipment, destroying the hard crust on the surface of the raw material and preventing the release of methane.

Highly acidic waste (pig and cow manure) is best suited for the process. When the acidity level decreases, the bacteria slow down their work, so it is important to find out for the first time how long it takes to completely process one portion of the manure solution, and only then refill it.

The resulting product contains about seventy percent methane, one percent impurities (hydrogen sulfide and some volatile elements) and just under thirty percent carbon dioxide.

It can be used as fuel only after purification from impurities. Hydrogen sulfide compounds are removed using special filters. This must be done for the reason that such a substance, forming an acid with water, accelerates the corrosion processes of metals, pipes, tanks and the entire biogas plant, if it is metal.

Carbon dioxide also needs to be removed from the fuel, but this takes a lot of time:

• First of all, biogas is compressed under high pressure.
• Water is sent into the container, in which the impurity will dissolve.

If biogas is produced on a large scale, then purification is carried out with lime, activated carbon and special filters.

Reducing moisture content

At this stage, the purification of raw materials is carried out in different ways.

The first method is similar to the operation of a moonshine still. Biogas is directed upward through cold tubes. The water turns into condensate and flows down the tube, while the methane is sent to a reservoir for further storage.

Another way is to use a water seal. The resulting biogas is mixed with water, where all impurities remain. This method requires less time for cleaning, since water gets rid of both excess liquid and unnecessary elements.

For the manufacture of an installation near farms, a design that can subsequently be easily disassembled and moved to another area is best suited. The main equipment of the entire installation is a bioreactor - a container for pouring manure and fermenting it. Large enterprises use tanks of 50 cubic meters.

Small private farms use an underground reservoir instead of tanks. It is laid out with bricks in a dug hole. For tightness and strength, everything is fixed with cement mass. The volume depends on the amount of manure produced daily.

For above-ground installation, tanks made of plastic, metal or polyvinyl chloride can be used.

Installations can be either automated (in which the entire process occurs without human intervention) or mechanical (you must pump out, add raw materials, take in biogas, monitor pressure and temperature yourself).

On a small farm, it is advisable to use electric pumps, mixers, and grinders, which will prevent the appearance of crusts on the surface of manure and clean the structure of waste.

The most important rule is the absence of oxygen in the reactor. If present, an explosion may occur.

To prevent the reactor lid from being blown off by high pressure, counterweights and protective gaskets between the tanks and lids are needed.

The reservoir should never be completely full. It is advisable to leave a fifth of its volume unfilled.

At the site before installation, the equipment must:

• choose the right location (preferably as far as possible from a residential building)
• calculate the daily volumes of manure produced
• select a location for pipes (shipping, loading, condensing)
• find a place for manure waste
• dig a pit
• purchase a container for the tank and secure it to the bottom of the pit
• seal all joints
• construct a hatch for inspecting the reactor (be sure to place a gasket between the hatch and the reactor)

If the installation takes place in a cold climate, then you should definitely consider ways to heat it.

The final stage of construction is checking the equipment for leaks.

Gas quantity calculation

On average, a ton of manure will provide the owner with hundreds of cubic meters of biogas. In order to calculate the amount of biogas produced, it is necessary to multiply the daily mass of manure from each livestock by the number of animals.

Naturally, different animals and birds produce different amounts of manure:

• poultry (primarily chickens) – 150-170 g per day
• cow - 34-36 kg
• goat – 900 – 1100 g
• horse – 14-16 kg
• sheep – 900 – 1100 g
• pig – 4-6 kg

Pig and cow manure provides more fuel. The amount of biogas released can be increased by adding millet, beet tops, marsh plants, algae or corn to the mixture (the presence of chlorophyll in biomass improves methane release).

Biomass waste after gas production

The sludge formed after heating manure is used throughout agriculture in the form of fertilizers.

The carbon dioxide produced is usually purified, but when it is dissolved in water, a useful liquid is obtained.

Full utilization of biogas plant products

With rational use of manure, there may be no waste at all after the formation of biogas. For example, carbon dioxide is used as a fertilizer for vegetable crops.

The sludge is also used for root feeding.

Therefore, if you have a small installation for the production of biogas, it will be useful to install a biogreenhouse, which, due to fertilizers and the resulting energy, can operate all year round.

Farms need fuel for heating systems, generating electricity and other daily needs. Since energy prices are steadily rising year after year, every home or small business owner has at least once thought about how to produce biogas at home.

Biogas plants are increasingly being used on farms, allowing them to save money on heating

A biogas plant for a private home allows you to organize the production of biogas right in your yard, which solves the fuel problem. Since a significant percentage of village residents have skills in working with welding and plumbing tools, the question of self-manufacturing a gas production plant seems logical. This way you can save not only on work, but also on materials if you use improvised means.

What is biogas and how is it formed: obtaining and production

Biogas is a substance formed during the fermentation of organic waste, which contains methane in sufficient quantities to be used as fuel. When burned, biogas releases heat, which is enough to heat a house or refuel a car. the source of energy is manure, which is easily accessible and cheap or even free if we are talking about a livestock enterprise or a large private farm.

Biogas is an environmentally friendly biofuel that you can produce with your own hands; biological gas is related to natural gas. The gas is produced by processing waste by anaerobic bacteria. Fermentation takes place in an airless container called a bioreactor. The rate of biogas production depends on the amount of waste loaded into the biogenerator. Under the influence of bacteria, a mixture of methane and carbon dioxide with some admixtures of other gaseous substances is released from the raw material. The resulting gas is removed from the bioreactor, purified and used for its own needs. The processed raw materials upon completion of the process become fertilizer, which is used to improve soil fertility. Producing biogas is beneficial for livestock enterprises that have access to free manure and other organic waste.

Benefits of burning fuel from manure (farm fertilizer) for heating: electricity from methane

The advantages of biogas as a fuel include:

• Efficient and environmentally friendly waste recycling
• Availability of raw materials for gas production in rural areas
• Possibility to organize a closed cycle of waste-free production of gas and fertilizers from manure
• Non-exhaustible, self-replenishing source of raw materials

How to build a bioreactor (installation) with your own hands

Biogas plants that produce gas from manure can be easily assembled with your own hands on your own site. Before assembling a bioreactor for processing manure, it is worth drawing drawings and carefully studying all the nuances, because a container containing a large amount of explosive gas can be a source of great danger if it is used incorrectly or if there are errors in the design of the installation.

Biogas production scheme

The capacity of the bioreactor is calculated based on the amount of raw material that is used to produce methane. In order for operating conditions to be optimal, the reactor capacity is filled with waste to at least two-thirds. For these purposes, a deep pit is used. To ensure high tightness, the walls of the pit are reinforced with concrete or reinforced with plastic, and sometimes concrete rings are installed in the pit. The surface of the walls is treated with moisture-proofing solutions. Tightness is a necessary condition for efficient operation of the installation. The better the container is insulated, the higher the quality and quantity. In addition, waste breakdown products are poisonous and, if leaked, can be harmful to health.

A stirrer is installed in the waste container. It is responsible for mixing waste during fermentation, preventing uneven distribution of raw materials and the formation of a crust. Following the mixer, a drainage structure is installed in the manure, which facilitates the removal of gas into the storage tank and prevents leakage. It is necessary to remove the gas for safety reasons, as well as to improve the quality of the fertilizers remaining in the reactor after processing. A hole is made in the bottom of the reactor for. The hole is equipped with a tight lid so that the equipment remains sealed.

How to ensure active fermentation of biomass at home using a generator and other equipment: waste processing, composition and extraction

In order for the processing process in a bioreactor to proceed faster, heating is necessary. The ambient temperature is sufficient for manure processing to occur without outside help. But under unfavorable weather conditions, in the winter, a mini-biogas plant needs an additional heat source, otherwise gas production becomes impossible. For bacteria to convert waste into gas, the temperature in the reactor must be above 38 degrees Celsius. It is not difficult to obtain biogas with your own hands; the main thing is to know certain manufacturing rules.

The container is heated using a coil, which is located under the reactor, or by installing electric heaters to directly heat the reservoir. , which process waste into gas, are already in the raw materials. To activate microorganisms and start the process of biogas production, the temperature in the container must be sufficient for fermentation. To make it easier to control compliance with temperature conditions, automatic heating is connected to the reactor. It heats the container when fuel is loaded into it to the desired temperature and turns off the heating when the desired mark on the thermometer is reached. A temperature control device for, which is easy to find in a gas equipment store, can handle the role of an automatic heater.

Temperature control module. It can be purchased at any hardware store

Correct gas removal from the bioreactor: drawings, use of technology

To easily remove the formed gas from the tank, biogas plants are equipped with a number of devices:

1. Vertically arranged plastic pipes with a large number of holes to facilitate the separation of gas from the raw material. The top of the pipe should protrude above the waste mass, allowing gas to escape freely.
2. A film laid over the container and creating a kind of greenhouse effect. It maintains the desired temperature inside the container and also prevents gas from mixing with air.
   

   Sometimes the container is covered with a dome made of concrete or other material. To prevent such a dome from flying away under the pressure of the resulting gas, it is carefully attached to the structure and tied with cables.

3. A gas exhaust pipe is placed at the top of the reactor. The pipe is equipped with a tight locking mechanism so as not to violate the tightness of the structure. The newly released biogas, entering the outlet pipe, is saturated with water vapor and contains many impurities. occurs by condensation: when cooled to ambient temperature, water settles in the form of condensation on the walls of the pipe. To avoid corrosion, the discharge pipe is installed in such a way as to facilitate the removal of condensate through the separator.
4. To remove hydrogen sulfide impurities from biogas, a filter made of specially treated activated carbon is installed on its way to the storage facility, in which the mixture is oxidized into sulfur and deposited in the sorbent.

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A self-assembled biogas plant, processing manure into biogas at home, significantly reduces heating and electricity costs. Such an installation will reduce the cost of providing a private home with heat, reduce the cost of farm products, thereby increasing the profitability of the farm. – the ability to turn waste into a source of energy and an alternative to natural gas. Biogas is environmentally friendly and modern.

Biogas production technology. Modern livestock breeding complexes ensure high production indicators. The technological solutions used make it possible to fully comply with the requirements of current sanitary and hygienic standards in the premises of the complexes themselves.

However, large quantities of liquid manure concentrated in one place create significant problems for the ecology of the areas adjacent to the complex. For example, fresh pig manure and droppings are classified as hazard class 3 waste. Environmental issues are under the control of supervisory authorities, and legislative requirements on these issues are constantly becoming more stringent.

Biocomplex offers a comprehensive solution for the disposal of liquid manure, which includes accelerated processing in modern biogas plants (BGU). During the processing process, natural processes of decomposition of organic matter occur in an accelerated mode with the release of gas including: methane, CO2, sulfur, etc. Only the resulting gas is not released into the atmosphere, causing a greenhouse effect, but is sent to special gas generator (cogeneration) units that generate electrical and thermal energy.

Biogas - flammable gas, formed during anaerobic methane fermentation of biomass and consisting mainly of methane (55-75%), carbon dioxide (25-45%) and impurities of hydrogen sulfide, ammonia, nitrogen oxides and others (less than 1%).

The decomposition of biomass occurs as a result of chemical and physical processes and the symbiotic life activity of 3 main groups of bacteria, while the metabolic products of some groups of bacteria are food products of other groups, in a certain sequence.

The first group is hydrolytic bacteria, the second is acid-forming, the third is methane-forming.

Both organic agro-industrial or household waste and plant raw materials can be used as raw materials for biogas production.

The most common types of agricultural waste used for biogas production are:

• pig and cattle manure, poultry litter;
• residues from the feeding table of cattle complexes;
• vegetable tops;
• substandard harvest of cereals and vegetables, sugar beets, corn;
• pulp and molasses;
• flour, spent grain, small grain, germ;
• brewer's grain, malt sprouts, protein sludge;
• waste from starch and syrup production;
• fruit and vegetable pomace;
• serum;
• etc.

Source of raw materials	Type of raw material	Amount of raw materials per year, m3 (tons)	Amount of biogas, m3
1 milk cow	Unlittered liquid manure
1 fattening pig	Unlittered liquid manure
1 fattening bull	Litter solid manure
1 horse	Litter solid manure
100 chickens	Dry droppings
1 ha of arable land	Fresh corn silage
1 ha of arable land	Sugar beet
1 ha of arable land	Fresh grain silage
1 ha of arable land	Fresh grass silage

The number of substrates (types of waste) used to produce biogas within one biogas plant (BGU) can vary from one to ten or more.

Biogas projects in the agro-industrial sector can be created according to one of the following options:

• biogas production from waste from a separate enterprise (for example, manure from a livestock farm, bagasse from a sugar factory, stillage from a distillery);
• biogas production based on waste from different enterprises, with the project linked to a separate enterprise or a separately located centralized biogas plant;
• biogas production with the primary use of energy plants at separately located biogas plants.

The most common method of energy use of biogas is combustion in gas piston engines as part of mini-CHP, producing electricity and heat.

Exist various options for technological schemes of biogas stations- depending on the types and number of types of substrates used. The use of preliminary preparation, in some cases, makes it possible to achieve an increase in the rate and degree of decomposition of raw materials in bioreactors, and, consequently, an increase in the overall yield of biogas. In the case of using several substrates with different properties, for example, liquid and solid waste, their accumulation and preliminary preparation (separation into fractions, grinding, heating, homogenization, biochemical or biological treatment, etc.) is carried out separately, after which they are either mixed before supplied to bioreactors, or supplied in separate streams.

The main structural elements of a typical biogas plant are:

• system for receiving and preliminary preparation of substrates;
• substrate transportation system within the installation;
• bioreactors (fermenters) with a mixing system;
• bioreactor heating system;
• system for removal and purification of biogas from hydrogen sulfide and moisture impurities;
• storage tanks for fermented mass and biogas;
• system for software control and automation of technological processes.

Technological schemes of biogas plants vary depending on the type and number of processed substrates, the type and quality of the final target products, the particular know-how used by the company providing the technological solution, and a number of other factors. The most common today are schemes with single-stage fermentation of several types of substrates, one of which is usually manure.

With the development of biogas technologies, the technical solutions used are becoming more complex towards two-stage schemes, which in some cases is justified by the technological need for efficient processing of certain types of substrates and increasing the overall efficiency of using the working volume of bioreactors.

Features of biogas production is that it can be produced by methane bacteria only from absolutely dry organic substances. Therefore, the task of the first stage of production is to create a mixture of substrate that has a high content of organic substances, and at the same time can be pumped. This is a substrate with a dry matter content of 10-12%. The solution is achieved by releasing excess moisture using screw separators.

Liquid manure comes from the production premises into a tank, is homogenized using a submersible mixer, and is supplied by a submersible pump to the separation workshop into auger separators. The liquid fraction accumulates in a separate tank. The solid fraction is loaded into the solid raw material feeder.

In accordance with the schedule for loading the substrate into the fermenter, according to the developed program, the pump is periodically turned on, supplying the liquid fraction to the fermenter and at the same time the solid raw material loader is turned on. As an option, the liquid fraction can be fed into a solid raw material loader that has a mixing function, and then the finished mixture is fed into the fermenter according to the developed loading program. The inclusions are short-lived. This is done to prevent excessive intake of organic substrate into the fermenter, since this can upset the balance of substances and cause destabilization of the process in the fermenter. At the same time, pumps are also turned on, pumping digestate from the fermenter to the fermenter and from the fermenter to the digestate storage tank (lagoon) to prevent overflow of the fermenter and fermenter.

The digestate masses located in the fermenter and fermenter are mixed to ensure uniform distribution of bacteria throughout the entire volume of the containers. Low-speed mixers of a special design are used for mixing.

While the substrate is in the fermenter, bacteria release up to 80% of the total biogas produced by the biogas plant. The remaining part of the biogas is released in the digester.

An important role in ensuring a stable amount of biogas released is played by the temperature of the liquid inside the fermenter and fermenter. As a rule, the process proceeds in mesophilic mode with a temperature of 41-43ᴼС. Maintaining a stable temperature is achieved by using special tubular heaters inside fermenters and fermenters, as well as reliable thermal insulation of walls and pipelines. The biogas coming out of the digestate has a high sulfur content. Biogas is purified from sulfur using special bacteria that colonize the surface of the insulation laid on a wooden beam vault inside the fermenters and fermenters.

Biogas is accumulated in a gas holder, which is formed between the surface of the digestate and the elastic, high-strength material covering the fermenter and fermenter on top. The material has the ability to greatly stretch (without reducing strength), which, when biogas accumulates, significantly increases the capacity of the gas holder. To prevent the gas tank from overflowing and material rupture, there is a safety valve.

Next, the biogas enters the cogeneration plant. A cogeneration unit (CGU) is a unit in which electrical energy is generated by generators driven by gas piston engines running on biogas. Cogenerators running on biogas have design differences from conventional gas generator engines, since biogas is a highly depleted fuel. The electrical energy generated by the generators provides power to the electrical equipment of the BSU itself, and everything beyond this is supplied to nearby consumers. The energy of the liquid used to cool cogenerators is the generated thermal energy minus losses in boiler devices. The generated thermal energy is partially used to heat fermenters and fermenters, and the remaining part is also sent to nearby consumers. enters

It is possible to install additional equipment to purify biogas to the level of natural gas, however, this is expensive equipment and is used only if the purpose of the biogas plant is not the production of thermal and electrical energy, but the production of fuel for gas piston engines. The proven and most commonly used biogas purification technologies are aqueous absorption, pressurized adsorption, chemical precipitation and membrane separation.

The energy efficiency of biogas power plants largely depends on the chosen technology, materials and design of the main structures, as well as on the climatic conditions in the area where they are located. The average consumption of thermal energy for heating bioreactors in a temperate climate zone is 15-30% of the energy generated by cogenerators (gross).

The overall energy efficiency of a biogas complex with a biogas-fired thermal power plant averages 75-80%. In a situation where all the heat received from a cogeneration station during the production of electricity cannot be consumed (a common situation due to the lack of external heat consumers), it is released into the atmosphere. In this case, the energy efficiency of a biogas thermal power plant is only 35% of the total biogas energy.

The main performance indicators of biogas plants can vary significantly, which is largely determined by the substrates used, the adopted technological regulations, operational practices, and the tasks performed by each individual plant.

The manure processing process takes no more than 40 days. The digestate obtained as a result of processing is odorless and is an excellent organic fertilizer, in which the highest degree of mineralization of nutrients absorbed by plants has been achieved.

Digestate is usually separated into liquid and solid fractions using screw separators. The liquid fraction is sent to lagoons, where it is accumulated until the period of application to the soil. The solid fraction is also used as fertilizer. If additional drying, granulation and packaging are applied to the solid fraction, it will be suitable for long-term storage and transportation over long distances.

Production and energy use of biogas has a number of advantages justified and confirmed by world practice, namely:

1. Renewable energy source (RES). Renewable biomass is used to produce biogas.
2. The wide range of raw materials used for the production of biogas allows the construction of biogas plants virtually everywhere in areas where agricultural production and technologically related industries are concentrated.
3. The versatility of the methods of energy use of biogas, both for the production of electrical and/or thermal energy at the place of its formation, and at any facility connected to the gas transportation network (in the case of supplying purified biogas to this network), as well as as motor fuel for cars.
4. The stability of electricity production from biogas throughout the year makes it possible to cover peak loads in the network, including in the case of using unstable renewable energy sources, for example, solar and wind power plants.
5. Creation of jobs through the formation of a market chain from biomass suppliers to operating personnel of energy facilities.
6. Reducing the negative impact on the environment through recycling and neutralization of waste through controlled fermentation in biogas reactors. Biogas technologies are one of the main and most rational ways to neutralize organic waste. Biogas production projects reduce greenhouse gas emissions into the atmosphere.
7. The agrotechnical effect of using mass fermented in biogas reactors on agricultural fields is manifested in improving soil structure, regeneration and increasing their fertility due to the introduction of nutrients of organic origin. The development of the market for organic fertilizers, including those from mass processed in biogas reactors, will in the future contribute to the development of the market for environmentally friendly agricultural products and increase its competitiveness.

Estimated unit investment costs

BGU 75 kWel. ~ 9.000 €/kWel.

BGU 150 kWel. ~ 6.500 €/kWel.

BGU 250 kWel. ~ 6.000 €/kWel.

BGU bis 500 kWel. ~ 4.500 €/kWel.

BGU 1 MWel. ~ 3.500 €/kWel.

The generated electrical and thermal energy can satisfy not only the needs of the complex, but also the adjacent infrastructure. Moreover, the raw materials for biogas plants are free, which ensures high economic efficiency after the payback period (4-7 years). The cost of energy generated at biogas power plants does not increase over time, but, on the contrary, decreases.

A biogas plant is a special unit that allows you to process agricultural and food industry waste into biological fertilizers and biological gas.

The use of such an installation allows you to quickly get rid of various types of manure (including bird droppings), process plant residues (overwintered silage, tops of food crops, etc.) and efficiently dispose of organic waste from slaughterhouses and poultry farms. The time it takes to obtain biological waste and gas depends on the density of the processed materials and their quantity.

Such installations are most widespread in countries such as Germany and Holland. In recent years, a huge number of Chinese farms and food production plants have also been equipped with biogas plants of their own production.

Construction of a biogas plant. It should be said that biogas plants have a very simple design. Modern models of such installations have a sufficient degree of automation and require minimal human control. So, a modern biogas plant consists of:

• A transition container into which raw materials enter at the very beginning of processing for heating.
• Mixers for grinding large particles of grass and manure.
• A gas container (gas holder), in which the resulting gas is stored, is necessary to maintain reserves and pressure in the system.
• Bioreactor is the most important part of a biogas plant, in which fermentation of raw materials occurs and gas is produced.
• Gas system, a set of pipes and hoses for supplying and discharging the resulting gas.
• Separators sort processed raw materials into solid and liquid fertilizers.
• Pumps for pumping raw materials and water.
• Devices for measuring and monitoring the pressure in the reactor and the temperature of the heating liquid.
• A cogeneration station serves to distribute the resulting gas.
• Emergency burners for bleeding excess gas from the reactor and gas tank are necessary to maintain a given pressure.

At first glance, it seems that the design of a biogas plant is too complex and confusing, and it includes expensive units and components. However, in reality this is far from the case. Most of the components have menacing names, but in fact they are based on everyday objects. In any case, similar designs have been used by people all over the world for many years, which means that the principle of operation of the installation can be understood without any difficulty.

Operating principle of a biogas plant. Before moving on to a detailed examination of the operating principle of a biogas plant, it should be said that this device appeared solely due to the processes of fermentation and decomposition. As you know, any organic substance (over time and under appropriate conditions) breaks down into simple chemical substances, one of which is biogas. It is on the principles of fermentation and decay that any biogas plant is created, and additional components and assemblies have auxiliary or controlling functions.

Stages of operation of a biogas plant.

• 1. Delivery of processed products and waste to the installation. If the waste is liquid, it is advisable to deliver it to the reactor using specialized pumps. More solid waste can be delivered to the reactor manually or by means of a conveyor belt. In some cases, it is advisable to heat the waste in order to increase its rate of fermentation and decay in the bioreactor. To heat the waste, a transition tank is used, in which the processed products are brought to the required temperature.
• 2. Processing in a reactor. After the transition tank, the prepared (and heated!) waste enters the reactor. A high-quality bioreactor is a hermetic structure made of especially strong steel or concrete with a special anti-acid coating. Without fail, the reactor must have ideal thermal and gas insulation. Even the slightest entry of air or decrease in temperature will stop the process of fermentation and decay. The reactor is heated using hot water tubes. The system is autonomous. The water is heated using the produced biogas. The reactor operates without access to oxygen, in a completely closed environment. Several times a day, using a pump, you can add new portions of the processed substance to it. The optimal temperature regime for the reactor is about 40 degrees Celsius. If the temperature is lower, the fermentation process will slow down significantly. If you increase the temperature, rapid evaporation of water will occur, which will not allow the waste to completely disintegrate. In order to speed up the fermentation process, a special mixer is used. This device mixes the substance in the reactor after a certain period of time.
• 3. Output of the finished product. After a certain time (from several hours to several days), the first results of fermentation appear. These are biogas and biological fertilizers. As a result, the resulting biogas ends up in a gas holder (gas storage tank). The gas pressure in the gas tanks is regulated using valves. In case of excessive pressure, emergency burners will be activated, which will simply burn off excess gas, thereby stabilizing the pressure. The resulting biogas needs to be dried. Only after this can it be used like ordinary natural gas. Separately, it should be said that to maintain the operation of a biogas plant, about 15% of the gas produced is required. In turn, biological fertilizers end up in a specially prepared tank with a separator. There is a division into solid (vermicompost) and liquid fertilizers. Vermicompost makes up only about 5% of the total amount of fertilizer received. Actually, fertilizers can immediately be used for their intended purpose. They do not require additional processing. Moreover, in Europe there are entire production lines that package the resulting biological fertilizers in plastic containers. Trading such fertilizers is a fairly profitable business. The operation of the biogas plant is continuous. To put it simply, new portions of processed material are constantly entering the reactor, and gas and biological fertilizers are also constantly entering the gas holder and separator tank.

Operation and installation of a biogas plant. Installation of a biogas plant is strictly individual. You can’t just bring and assemble all the components. It is necessary to carry out a whole series of preparatory work, dig several large pits, and carry out high-quality insulation of the reactor. It is necessary to take into account all the individual characteristics of a farm or enterprise, and make the biogas plant relevant for specific tasks. One person can monitor the biogas plant, since the processing process is fully automated. Operation of the installation does not require large expenses. With good care and timely maintenance, the annual cost of maintaining such an installation will not exceed 5% of its original cost.

Advantages of using a biogas plant. A biogas plant is a truly magical device that allows you to obtain truly necessary things from industrial waste and manure. In particular, you can get:

• Biogas
• Biological fertilizers
• Electrical and thermal energy
• Fuel for cars.

In order to convert biogas into electrical and thermal energy, it is necessary to equip the installation with additional units. This increases the cost of the installation itself, but allows you to achieve significant autonomy from utilities and significantly reduce bills. If the car is equipped with gas equipment, then it can be refueled with gas produced by a biogas plant. Naturally, biological gas will require additional purification, which will filter out carbon dioxide. After this, the car will be able to drive on gas produced by the biogas plant. This helps to save significantly on the purchase of gasoline, which is very profitable at current fuel prices.

Who needs a biogas plant?

As mentioned above, a biogas plant is a technically complex device that requires professional installation and timely maintenance.

Therefore, a small farmer whose farm consists of a dozen cows and several hectares of land definitely does not need such equipment. He simply does not have enough manure and other fertilizers to make the biogas plant work around the clock and generate significant income. And it’s a completely different matter if we talk about a large farm, poultry farm or meat processing plant. These industries generate hundreds of kilograms of various waste every day, which simply has nowhere to go. For them, purchasing a biogas plant is almost the only way to solve the problem of waste disposal, and at the same time receive free gas, electricity and biological fertilizers.

As practice shows, such biogas systems begin to pay for themselves within 2 years after installation. Considering that the average service life of an installation is 25 years, it is not difficult to calculate the profit that such equipment will bring.

Rising energy prices make us think about the possibility of providing ourselves with them ourselves. One option is a biogas plant. With its help, biogas is obtained from manure, droppings and plant residues, which, after purification, can be used for gas appliances (stoves, boilers), pumped into cylinders and used as fuel for cars or electric generators. In general, processing manure into biogas can meet all the energy needs of a home or farm.

Construction of a biogas plant is a way to independently provide energy resources

General principles

Biogas is a product that is obtained from the decomposition of organic substances. During the process of rotting/fermentation, gases are released, collecting which you can meet the needs of your own household. The equipment in which this process occurs is called a “biogas plant”.

The process of biogas formation occurs due to the vital activity of various kinds of bacteria that are contained in the waste itself. But in order for them to actively “work”, they need to create certain conditions: humidity and temperature. To create them, a biogas plant is being built. This is a complex of devices, the basis of which is a bioreactor, in which waste decomposition occurs, which is accompanied by gas formation.

There are three modes for processing manure into biogas:

• Psychophilic mode. The temperature in the biogas plant is from +5°C to +20°C. Under such conditions, the decomposition process is slow, much gas is formed, and its quality is low.
• Mesophilic. The unit enters this mode at temperatures from +30°C to +40°C. In this case, mesophilic bacteria actively reproduce. In this case, more gas is formed, the processing process takes less time - from 10 to 20 days.
• Thermophilic. These bacteria multiply at temperatures from +50°C. The process goes the fastest (3-5 days), the gas output is the largest (under ideal conditions, with 1 kg of delivery you can get up to 4.5 liters of gas). Most reference tables for gas yield from processing are given specifically for this mode, so when using other modes it is worth making a smaller adjustment.

The most difficult thing to implement in biogas plants is the thermophilic mode. This requires high-quality thermal insulation of the biogas plant, heating and a temperature control system. But at the output we get the maximum amount of biogas. Another feature of thermophilic processing is the impossibility of additional loading. The remaining two modes - psychophilic and mesophilic - allow you to add a fresh portion of prepared raw materials daily. But, in the thermophilic mode, the short processing time makes it possible to divide the bioreactor into zones in which their share of raw materials will be processed with different loading times.

Biogas plant diagram

The basis of a biogas plant is a bioreactor or bunker. The fermentation process occurs in it, and the resulting gas accumulates in it. There is also a loading and unloading hopper; the generated gas is discharged through a pipe inserted into the upper part. Next comes the gas treatment system - cleaning it and increasing the pressure in the gas pipeline to working pressure.

For mesophilic and thermophilic modes, a bioreactor heating system is also required to reach the required modes. For this purpose, gas boilers running on produced fuel are usually used. From it, a pipeline system goes to the bioreactor. Usually these are polymer pipes, since they best withstand being in an aggressive environment.

A biogas plant also needs a system for mixing the substance. During fermentation, a hard crust forms at the top, and heavy particles settle down. All this together worsens the process of gas formation. Mixers are needed to maintain a homogeneous state of the processed mass. They can be mechanical or even manual. They can be started by timer or manually. It all depends on how the biogas plant is made. An automated system is more expensive to install, but requires a minimum of attention during operation.

According to the type of location, a biogas plant can be:

• Overground.
• Semi-recessed.
• Recessed.

Recessed ones are more expensive to install - a large amount of excavation work is required. But when used in our conditions, they are better - it is easier to organize insulation, and the heating costs are lower.

What can be recycled

A biogas plant is essentially omnivorous - any organic matter can be processed. Any manure and urine, plant residues are suitable. Detergents, antibiotics, and chemicals negatively affect the process. It is advisable to minimize their intake, as they kill the flora that processes them.

Cattle manure is considered ideal, since it contains large quantities of microorganisms. If there are no cows on the farm, when loading the bioreactor, it is advisable to add some of the manure to populate the substrate with the required microflora. Plant residues are pre-crushed and diluted with water. Plant materials and excrement are mixed in a bioreactor. This “filling” takes longer to process, but at the end of the day, under the correct mode, we have the highest product yield.

Location determination

To minimize the costs of organizing the process, it makes sense to locate the biogas plant close to the source of waste - near buildings where poultry or animals are kept. It is advisable to develop the design so that loading occurs by gravity. From a barn or pigsty, you can lay a pipeline at a slope through which manure will flow by gravity into the bunker. This greatly simplifies the task of maintaining the reactor, and also removing manure.

It is most advisable to locate the biogas plant so that waste from the farm can flow by gravity

Typically, buildings with animals are located at some distance from a residential building. Therefore, the generated gas will need to be transferred to consumers. But laying one gas pipe is cheaper and easier than organizing a line for transporting and loading manure.

Bioreactor

There are quite strict requirements for manure processing tanks:

All these requirements for the construction of a biogas plant must be met, as they ensure safety and create normal conditions for processing manure into biogas.

What materials can it be made from?

Resistance to aggressive environments is the main requirement for materials from which containers can be made. The substrate in the bioreactor can be acidic or alkaline. Accordingly, the material from which the container is made must tolerate various environments well.

Not many materials meet these requests. The first thing that comes to mind is metal. It is durable and can be used to make containers of any shape. The good thing is that you can use a ready-made container - some old tank. In this case, the construction of a biogas plant will take very little time. The disadvantage of metal is that it reacts with chemically active substances and begins to collapse. To neutralize this disadvantage, the metal is coated with a protective coating.

An excellent option is a bioreactor container made of polymer. Plastic is chemically neutral, does not rot, does not rust. You just need to choose from materials that can withstand freezing and heating to fairly high temperatures. The reactor walls should be thick, preferably glass fiber reinforced. Such containers are not cheap, but they last a long time.

A cheaper option is a biogas plant with a container made of bricks, concrete blocks, or stone. In order for the masonry to withstand high loads, it is necessary to reinforce the masonry (in every 3-5 rows, depending on the thickness of the wall and the material). After completing the wall construction process, to ensure water and gas impermeability, subsequent multi-layer treatment of the walls is necessary both inside and outside. The walls are plastered with a cement-sand composition with additives (additives) that provide the required properties.

Reactor sizing

The reactor volume depends on the selected temperature for processing manure into biogas. Most often, mesophilic is chosen - it is easier to maintain and it allows for the possibility of daily reloading of the reactor. Biogas production after reaching normal mode (about 2 days) is stable, without surges or dips (when normal conditions are created). In this case, it makes sense to calculate the volume of the biogas plant depending on the amount of manure generated on the farm per day. Everything is easily calculated based on average statistical data.

The decomposition of manure at mesophilic temperatures takes from 10 to 20 days. Accordingly, the volume is calculated by multiplying by 10 or 20. When calculating, it is necessary to take into account the amount of water that is necessary to bring the substrate to an ideal state - its humidity should be 85-90%. The found volume is increased by 50%, since the maximum load should not exceed 2/3 of the tank volume - gas should accumulate under the ceiling.

For example, there are 5 cows, 10 pigs and 40 chickens on a farm. The result is 5 * 55 kg + 10 * 4.5 kg + 40 * 0.17 kg = 275 kg + 45 kg + 6.8 kg = 326.8 kg. To bring chicken manure to 85% humidity, you need to add a little more than 5 liters of water (that’s another 5 kg). The total weight is 331.8 kg. For processing in 20 days you need: 331.8 kg * 20 = 6636 kg - about 7 cubic meters only for the substrate. We multiply the found figure by 1.5 (increase by 50%), we get 10.5 cubic meters. This will be the calculated value of the reactor volume of the biogas plant.

Loading and unloading hatches lead directly into the bioreactor tank. In order for the substrate to be evenly distributed over the entire area, they are made at opposite ends of the container.

When installing a biogas plant in-depth, the loading and unloading pipes approach the body at an acute angle. Moreover, the lower end of the pipe should be below the liquid level in the reactor. This prevents air from entering the container. Also, rotary or shut-off valves are installed on the pipes, which are closed in the normal position. They open only during loading or unloading.

Since manure may contain large fragments (litter elements, grass stems, etc.), small diameter pipes will often become clogged. Therefore, for loading and unloading, they must have a diameter of 20-30 cm. They must be installed before the start of work on insulating the biogas plant, but after the container is installed in place.

The most convenient mode of operation of a biogas plant is with regular loading and unloading of the substrate. This operation can be performed once a day or once every two days. Manure and other components are preliminarily collected in a storage tank, where they are brought to the required state - crushed, if necessary, moistened and mixed. For convenience, this container may have a mechanical stirrer. The prepared substrate is poured into the receiving hatch. If you place the receiving container in the sun, the substrate will be preheated, which will reduce the cost of maintaining the required temperature.

It is advisable to calculate the installation depth of the receiving hopper so that waste flows into it by gravity. The same applies to unloading into the bioreactor. The best case is if the prepared substrate moves by gravity. And a shutter will fence it off during preparation.

To ensure the tightness of the biogas plant, the hatches on the receiving hopper and in the unloading area must have a sealing rubber seal. The less air there is in the container, the cleaner the gas will be at the outlet.

Collection and removal of biogas

Biogas is removed from the reactor through a pipe, one end of which is under the roof, the other is usually lowered into a water seal. This is a container with water into which the resulting biogas is discharged. There is a second pipe in the water seal - it is located above the liquid level. Cleaner biogas comes out into it. A gas shut-off valve is installed at the outlet of their bioreactor. The best option is a ball one.

What materials can be used for the gas transmission system? Galvanized metal pipes and gas pipes made of HDPE or PPR. They must ensure tightness; seams and joints are checked using soap foam. The entire pipeline is assembled from pipes and fittings of the same diameter. No contractions or expansions.

Cleansing from impurities

The approximate composition of the resulting biogas is:

• methane - up to 60%;
• carbon dioxide - 35%;
• other gaseous substances (including hydrogen sulfide, which gives the gas an unpleasant odor) - 5%.

In order for biogas to be odorless and burn well, it is necessary to remove carbon dioxide, hydrogen sulfide, and water vapor from it. Carbon dioxide is removed in a water seal if slaked lime is added to the bottom of the installation. Such a bookmark will have to be changed periodically (as soon as the gas starts to burn worse, it’s time to change it).

Gas drying can be done in two ways - by making water seals in the gas pipeline - by inserting curved sections into the pipe under the water seals, in which condensate will accumulate. The disadvantage of this method is the need to regularly empty the water seal - if there is a large amount of collected water, it can block the passage of gas.

The second way is to install a filter with silica gel. The principle is the same as in a water seal - the gas is supplied to the silica gel, and dried out from under the lid. With this method of drying biogas, the silica gel must be dried periodically. To do this, you need to warm it up in the microwave for some time. It heats up and the moisture evaporates. You can fill it up and use it again.

To remove hydrogen sulfide, a filter loaded with metal shavings is used. You can load old metal scourers into the container. Purification occurs in exactly the same way: gas is supplied to the lower part of the container filled with metal. As it passes, it is cleared of hydrogen sulfide, collected in the upper free part of the filter, from where it is discharged through another pipe/hose.

Gas tank and compressor

The purified biogas enters a storage tank - a gas holder. This can be a sealed plastic bag or plastic container. The main condition is gas tightness; shape and material do not matter. The gas holder stores a supply of biogas. From it, with the help of a compressor, gas under a certain pressure (set by the compressor) is supplied to the consumer - to the gas stove or boiler. This gas can also be used to generate electricity using a generator.

To create stable pressure in the system after the compressor, it is advisable to install a receiver - a small device for leveling pressure surges.

Mixing devices

In order for the biogas plant to operate normally, it is necessary to regularly mix the liquid in the bioreactor. This simple process solves many problems:

• mixes a fresh portion of the load with a colony of bacteria;
• promotes the release of produced gas;
• equalizes the temperature of the liquid, excluding warmer and colder areas;
• maintains the homogeneity of the substrate, preventing the settling or floating of some components.

Typically, a small homemade biogas plant has mechanical agitators that are driven by muscle power. In large-volume systems, the agitators can be driven by motors that are activated by a timer.

The second method is to stir the liquid by passing some of the generated gas through it. To do this, after exiting the metatank, a tee is installed and part of the gas flows into the lower part of the reactor, where it exits through a tube with holes. This part of the gas cannot be considered a consumption, since it still enters the system again and, as a result, ends up in the gas tank.

The third method of mixing is to use fecal pumps to pump the substrate from the lower part and pour it at the top. The disadvantage of this method is its dependence on the availability of electricity.

Heating system and thermal insulation

Without heating the processed liquid, psychophilic bacteria will multiply. The processing process in this case will take 30 days, and the gas output will be small. In the summer, if there is thermal insulation and preheating of the load, it is possible to reach temperatures of up to 40 degrees, when the development of mesophilic bacteria begins, but in winter such an installation is practically inoperative - the processes proceed very sluggishly. At temperatures below +5°C they practically freeze.

What to heat and where to place it

For best results, use heating. The most rational is water heating from a boiler. The boiler can run on electricity, solid or liquid fuel, and you can also run it on the produced biogas. The maximum temperature to which water needs to be heated is +60°C. Hotter pipes can cause particles to stick to the surface, reducing heating efficiency.

You can also use direct heating - insert heating elements, but firstly, it is difficult to organize mixing, secondly, the substrate will stick to the surface, reducing heat transfer, the heating elements will quickly burn out

A biogas plant can be heated using standard heating radiators, simply pipes twisted into a coil, or welded registers. It is better to use polymer pipes - metal-plastic or polypropylene. Corrugated stainless steel pipes are also suitable; they are easier to install, especially in cylindrical vertical bioreactors, but the corrugated surface provokes sediment sticking, which is not very good for heat transfer.

To reduce the possibility of particles settling on the heating elements, they are located in the stirrer area. Only in this case everything must be designed so that the mixer cannot touch the pipes. It often seems that it is better to place the heaters at the bottom, but practice has shown that due to sediment on the bottom, such heating is ineffective. So it is more rational to place heaters on the walls of the metatank of a biogas plant.

Water heating methods

Depending on the method of pipe arrangement, heating can be external or internal. When installed internally, heating is effective, but repair and maintenance of heaters is impossible without stopping and pumping out the system. Therefore, special attention is paid to the selection of materials and the quality of connections.

Heating increases the productivity of the biogas plant and reduces the processing time of raw materials

When the heaters are located externally, more heat is required (the cost of heating the contents of a biogas plant is much higher), since a lot of heat is spent heating the walls. But the system is always available for repair, and heating is more uniform, since the environment is heated from the walls. Another advantage of this solution is that stirrers cannot damage the heating system.

How to insulate

First, a leveling layer of sand is poured onto the bottom of the pit, then a heat-insulating layer. It can be clay mixed with straw and expanded clay, slag. All these components can be mixed and poured in separate layers. They are leveled to the horizon and the capacity of the biogas plant is installed.

The sides of the bioreactor can be insulated with modern materials or with classic old-fashioned methods. One of the old-fashioned methods is coating with clay and straw. Apply in several layers.

Modern materials include high-density extruded polystyrene foam, low-density aerated concrete blocks, etc. The most technologically advanced in this case is polyurethane foam (PPU), but the services for its application are not cheap. But the result is seamless thermal insulation, which minimizes heating costs. There is another heat-insulating material - foam glass. It is very expensive in slabs, but its chips or crumbs cost very little, and in terms of characteristics it is almost ideal: it does not absorb moisture, is not afraid of freezing, tolerates static loads well, and has low thermal conductivity.