Biogas from hay and grass. Biogas plant: recycling organic waste for good. Raw material supply and unloading system

The modern world is built on ever-increasing consumption, so mineral and raw material resources are being depleted especially quickly. At the same time, millions of tons of foul-smelling manure accumulate annually on numerous livestock farms, and considerable resources are spent on its disposal. Humans are also keeping up with the production of biological waste. Fortunately, a technology has been developed that allows us to simultaneously solve these problems: using biowaste (primarily manure) as a raw material, producing environmentally friendly renewable fuel - biogas. The use of such innovative technologies has given rise to a new promising industry - bioenergy.

What is biogas

Biogas is a volatile gaseous substance that is colorless and completely odorless. It consists of 50-70 percent methane, up to 30 percent of it is carbon dioxide CO2 and another 1-2 percent are gaseous substances - impurities (when purified from them, the purest biomethane is obtained).

The qualitative physical and chemical characteristics of this substance are close to those of ordinary high-quality natural gas. According to research by scientists, biogas has very high calorific properties: for example, the heat released when burning one cubic meter of this natural fuel is equivalent to the heat from one and a half kilograms of coal.

The release of biogas occurs due to the vital activity of a special type of bacteria - anaerobic, while mesophilic bacteria are activated when the environment is heated to 30-40 degrees Celsius, and thermophilic bacteria multiply at higher temperatures - up to +50 degrees.

Under the influence of their enzymes, organic raw materials decompose with the release of biological gas.

Raw materials for biogas

Not all organic waste is suitable for processing into biogas. For example, manure from poultry and pig farms cannot be used in its pure form, because it has a high level of toxicity. To obtain biogas from them, it is necessary to add diluents to such waste: silage mass, green grass mass, as well as cow manure. The last component is the most suitable raw material for producing environmentally friendly fuel, since cows eat only plant foods. However, it must also be monitored for the content of heavy metal impurities, chemical components, and surfactants, which in principle should not be present in the raw material. A very important point is control over antibiotics and disinfectants. Their presence in manure can prevent the process of decomposition of the raw material mass and the formation of volatile gas.

Additional Information. It is impossible to do without disinfectants completely, because otherwise mold begins to form on the biomass under the influence of high temperatures. You should also monitor and promptly clean the manure from mechanical impurities (nails, bolts, stones, etc.), which can quickly damage biogas equipment. The humidity of the raw materials used to produce biogas must be at least 80-90%.

Mechanism of gas formation

In order for biogas to begin to be released from organic raw materials during airless fermentation (scientifically called anaerobic fermentation), appropriate conditions are required: a sealed container and elevated temperature. If done correctly, the gas produced rises to the top where it is selected for use, and what solids remain is an excellent bio-organic agricultural fertilizer, rich in nitrogen and phosphorus, but free of harmful microorganisms. Temperature conditions are very important for proper and complete processes.

The full cycle of converting manure into environmental fuel ranges from 12 days to a month, it depends on the composition of the raw materials. From one liter of useful reactor volume, about two liters of biogas are produced. If you use more advanced modernized installations, the biofuel production process is accelerated to 3 days, and biogas production increases to 4.5-5 liters.

People began to study and use the technology of producing biofuel from organic natural sources since the end of the 18th century, and in the former USSR the first device for producing biogas was developed back in the 40s of the last century. Nowadays, these technologies are becoming increasingly important and popular.

Advantages and disadvantages of biogas

Biogas as an energy source has undeniable advantages:

• it serves to improve the environmental situation in those areas where it is widely used, since along with reducing the use of polluting fuel, there is a very effective destruction of biowaste and disinfection of wastewater, i.e. biogas equipment acts as a cleaning station;
• the raw materials for the production of this organic fuel are renewable and practically free - as long as animals on farms receive food, they will produce biomass, and, therefore, fuel for biogas plants;
• the acquisition and use of equipment is economically profitable - once purchased, a biogas production plant will no longer require any investments, and it is simply and cheaply maintained; Thus, a biogas plant for use on a farm begins to pay for itself within three years after launch; there is no need to build utilities and energy transmission lines, the costs of launching a biological station are reduced by 20 percent;
• there is no need to install utilities such as power lines and gas pipelines;
• biogas production at the station using local organic raw materials is a waste-free enterprise, as opposed to enterprises using traditional energy sources (gas pipelines, boiler houses, etc.), waste does not pollute the environment and does not require storage space;
• when using biogas, a certain amount of carbon dioxide and sulfur are released into the atmosphere, however, these amounts are minimal compared to the same natural gas and are absorbed by green spaces during respiration, therefore the contribution of bioethanol to the greenhouse effect is minimal;
• Compared to other alternative energy sources, biogas production is always stable; a person can control the activity and productivity of installations for its production (unlike, for example, solar panels), collecting several installations into one or, conversely, splitting them into separate sections to reduce risk accidents;
• in exhaust gases when using biofuels, the content of carbon monoxide is reduced by 25 percent, and nitrogen oxides by 15;
• in addition to manure, you can also use some types of plants to obtain biomass for fuel, for example, sorghum will help improve soil condition;
• When bioethanol is added to gasoline, its octane number increases, and the fuel itself becomes more detonation-resistant, and its auto-ignition temperature decreases significantly.

Biogas– not an ideal fuel, it and the technology for its production are also not without drawbacks:

• the speed of processing organic raw materials in equipment for the production of biogas is a weak point in the technology compared to traditional sources of energy;
• Bioethanol has a lower calorific value than petroleum fuel - it releases 30 percent less energy;
• the process is quite unstable; to maintain it, a large amount of enzymes of a certain quality is required (for example, a change in the diet of cows greatly affects the quality of manure);
• unscrupulous producers of biomass for processing stations can significantly deplete the soil with increased seeding, this disrupts the ecological balance of the territory;
• pipes and containers with biogas may become depressurized, which will lead to a sharp decrease in the quality of biofuel.

Where is biogas used?

First of all, this ecological biofuel is used to meet the household needs of the population, as a replacement for natural gas, for heating and cooking. Enterprises can use biogas to launch a closed production cycle: its use in gas turbines is especially effective. With proper adjustment and complete combination of such a turbine with a biofuel production plant, its cost competes with the cheapest nuclear energy.

The efficiency of biogas use is very easy to calculate. For example, from one unit of cattle you can get up to 40 kilograms of manure, from which one and a half cubic meters of biogas is produced, sufficient to generate 3 kilowatts/hours of electricity.

Having determined the household's electricity needs, it is possible to determine what type of biogas plant to use. With a small number of cows, it is best to produce biogas at home using a simple low-power biogas plant.

If the farm is very large, and it constantly generates a large amount of biowaste, it is beneficial to install an automated industrial-type biogas system.

Note! When designing and setting up, you will need the help of qualified specialists.

Biogas plant design

Any biological installation consists of the following main parts:

• a bioreactor where the biodecomposition of the manure mixture occurs;
• organic fuel supply system;
• unit for stirring biological masses;
• devices for creating and maintaining the required temperature level;
• tanks for placing the resulting biogas in them (gas holders);

• containers for placing the resulting solid fractions there.

This is a complete list of elements for industrial automated installations, while a biogas installation for a private home is much more simply designed.

The bioreactor must be completely sealed, i.e. access of oxygen is unacceptable. This can be a metal container in the form of a cylinder installed on the surface of the soil; former fuel tanks with a capacity of 50 cubic meters are well suited for these purposes. Ready-made dismountable bioreactors are quickly installed/dismantled and easily moved to a new location.

If a small biogas station is planned, then it is advisable to place the reactor underground and make it in the form of a brick or concrete tank, as well as metal or PVC barrels. You can place such a bioenergy reactor indoors, but it is necessary to ensure constant air ventilation.

Bunkers for the preparation of biological raw materials are a necessary element of the system, because before entering the reactor, it must be prepared: crushed into particles up to 0.7 millimeters and soaked in water to bring the moisture content of the raw material to 90 percent.

Raw material supply systems consist of a raw material receiver, a water supply system and a pump for supplying the prepared mass to the reactor.

If the bioreactor is made underground, the container for raw materials is placed on the surface so that the prepared substrate flows into the reactor independently under the influence of gravity. It is also possible to place the raw material receiver at the top of the bunker, in which case it is necessary to use a pump.

The waste outlet hole is located closer to the bottom, opposite the raw material entrance. The receiver for solid fractions is made in the form of a rectangular box, into which an outlet tube leads. When a new portion of the prepared bio-substrate enters the bioreactor, a batch of solid waste of the same volume is fed into the receiver. They are subsequently used on farms as excellent biofertilizers.

The resulting biogas is stored in gas holders, which are usually placed on top of the reactor and have a cone or dome shape. Gas tanks are made of iron and painted with oil paint in several layers (this helps to avoid corrosive destruction). In large industrial bioinstallations, biogas containers are made in the form of separate tanks connected to the reactor.

To give the resulting gas flammable properties, it is necessary to rid it of water vapor. The biofuel is piped through a water tank (hydraulic seal), after which it can be supplied through plastic pipes directly for consumption.

Sometimes you can find special bag-shaped gas holders made of PVC. They are located in close proximity to the installation. As the bags are filled with biogas, they open and their volume increases enough to accept all the produced gas.

For effective biofermentation processes to occur, constant stirring of the substrate is necessary. To prevent the formation of a crust on the surface of the biomass and slow down the fermentation processes, it is necessary to constantly actively mix it. To do this, submersible or inclined stirrers are mounted on the side of the reactor in the form of a mixer for mechanical mixing of the mass. For small stations they are manual, for industrial ones they are automatically controlled.

The temperature necessary for the vital activity of anaerobic bacteria is maintained using automated heating systems (for stationary reactors); they begin heating when the heat drops below normal and automatically turn off when normal temperature is reached. You can also use boiler systems, electric heaters, or install a special heater in the bottom of the container with raw materials. At the same time, it is necessary to reduce heat loss from the bioreactor; to do this, it is wrapped in a layer of glass wool or other thermal insulation is provided, for example, from polystyrene foam.

Do-it-yourself biogas

For private homes, the use of biogas is now very important - from practically free manure you can get gas for domestic needs and heating your home and farm. Your own biogas installation is a guarantee against power outages and rising gas prices, as well as an excellent way to recycle biowaste, as well as unnecessary paper.

For construction for the first time, it is most logical to use simple schemes; such structures will be more reliable and will last longer. In the future, the installation can be supplemented with more complex parts. For a house with an area of ​​50 square meters, a sufficient amount of gas is obtained with a fermentation tank volume of 5 cubic meters. To ensure the constant temperature required for proper fermentation, a heating pipe can be used.

At the first stage of construction, they dig a trench for the bioreactor, the walls of which must be strengthened and sealed with plastic, concrete mixture or polymer rings (preferably they have a solid bottom - they will have to be replaced periodically as they are used).

The second stage consists of installing gas drainage in the form of polymer pipes with numerous holes. During installation, it should be taken into account that the tops of the pipes must exceed the planned filling depth of the reactor. The diameter of the outlet pipes should be no more than 7-8 centimeters.

The next stage is isolation. After this, you can fill the reactor with the prepared substrate, after which it is wrapped in film to increase the pressure.

At the fourth stage, the domes and the outlet pipe are installed, which is placed at the highest point of the dome and connects the reactor to the gas tank. The gas holder can be lined with brick, a stainless steel mesh is mounted on top and covered with plaster.

A hatch is placed in the upper part of the gas holder, which closes hermetically, and a gas pipe with a pressure equalization valve is removed from it.

Important! The resulting gas must be removed and consumed constantly, since its long-term storage in the free part of the bioreactor can provoke an explosion from high pressure. It is necessary to provide a water seal so that the biogas does not mix with air.

To heat the biomass, you can install a coil coming from the heating system of the house - this is much more economically profitable than using electric heaters. External heating can be provided using steam; this will prevent overheating of raw materials above normal.

In general, a do-it-yourself biogas plant is not such a complex structure, but when arranging it, you need to pay attention to the smallest details in order to avoid fires and destruction.

Additional Information. The construction of even the simplest biological installation must be formalized with the appropriate documents, you must have a technological diagram and equipment installation map, you must obtain approval from the Sanitary and Epidemiological Station, fire and gas services.

Nowadays, the use of alternative energy sources is gaining momentum. Among them, the bioenergy sub-sector is very promising - the production of biogas from organic waste such as manure and silage. Biogas production stations (industrial or small home) can solve the problems of waste disposal, obtaining environmental fuel and heat, as well as high-quality agricultural fertilizers.

Video

For owners of large farms, the issue of manure, bird droppings, and animal remains is an acute issue. To solve the problem, you can use special installations designed to produce biogas. They are easy to make at home and can be used for a long period with a high yield of a ready-to-use product.

What is biogas?

Biogas is a substance obtained from natural raw materials in the form of biomass (manure, bird droppings) due to its fermentation. Various bacteria are involved in this process, each of which feeds on the waste products of the previous ones. The following microorganisms are identified that take an active part in the biogas production process:

• hydrolytic;
• acid-forming;
• methane-forming.

The technology for producing biogas from finished biomass involves stimulating natural processes. Bacteria in manure should be provided with optimal conditions for rapid reproduction and efficient processing of substances. To do this, biological raw materials are placed in a tank sealed from oxygen.

After this, a group of anaerobic microbes comes into action. They allow the conversion of phosphorus, potassium and nitrogen-containing compounds into pure forms. As a result of processing, not only biogas is formed, but also quality approvals. They are ideal for agricultural needs and are more efficient than traditional manure.

Environmental value of biogas production

Thanks to the efficient processing of biological waste, valuable fuel is obtained. Establishing this process helps prevent methane emissions into the atmosphere, which have a negative impact on the environment. This compound stimulates the greenhouse effect 21 times stronger than carbon dioxide. Methane can persist in the atmosphere for 12 years.

To prevent global warming, which is a global problem, it is necessary to limit the entry and distribution of this substance into the environment. The resulting waste from the recycling process is a high quality endorsement. Its use makes it possible to reduce the volume of chemical compounds used. Synthetically produced fertilizers pollute groundwater and have a negative impact on the environment.

What affects the productivity of the production process?

With the correct organization of the production process for the production of biogas, from 1 cubic. m of organic raw materials yield about 2-3 cubic meters. m of pure product. Its effectiveness is influenced by many factors:

• ambient temperature;
• acidity level of organic raw materials;
• environmental humidity;
• the amount of phosphorus, nitrogen and carbon in the initial biological mass;
• particle size of manure or droppings;
• the presence of substances that slow down the processing process;
• inclusion of stimulating additives in the biomass;
• substrate supply frequency.

List of raw materials used for biogas production

Biogas can be produced not only from manure or bird droppings. Other raw materials can be used to produce environmentally friendly fuel:

• grain stillage;
• juice waste;
• beet pulp;
• waste from fish or meat production;
• spent grain;
• waste from dairies;
• fecal sludge;
• household waste of organic origin;
• waste from the production of biodiesel from rapeseed.

Composition of biological gas

The composition of biogas after passing through is as follows:

• 50-87% methane;
• 13-50% carbon dioxide;
• impurities of hydrogen and hydrogen sulfide.

After purifying the product from impurities, biomethane is obtained. It is an analogue, but has a different nature of origin. To improve the quality of the fuel, the content of methane in its composition, which is the main source of energy, is normalized.

When calculating the volume of gases produced, the ambient temperature is taken into account. When it increases, the yield of the product increases and its calorie content decreases. The characteristics of biogas are negatively affected by increased air humidity.

Scope of biogas application

Biogas production plays a significant role not only in preserving the environment, but also provides the national economy with fuel. It is characterized by a wide range of applications:

• used as a raw material for the production of electricity, automobile fuel;
• to meet the energy needs of small or medium-sized enterprises;
• Biogas plants play the role of treatment facilities, which makes it possible to solve.

Biogas production technology

To produce biogas, actions should be taken to speed up the process of natural breakdown of organic matter. Before being placed in a sealed container with a limited supply of oxygen, natural raw materials are thoroughly crushed and mixed with a certain amount of water.

As a result, the original substrate is obtained. The presence of water in its composition is necessary to prevent negative effects on bacteria that can occur when substances enter from the environment. Without the liquid component, the fermentation process slows down significantly and reduces the efficiency of the entire bioinstallation.

Industrial-type equipment for processing organic raw materials is additionally equipped with:

• a device for heating the substrate;
• equipment for mixing raw materials;
• devices for monitoring the acidity of the environment.

These devices significantly increase the efficiency of bioreactors. Stirring removes the hard crust from the surface of the biomass, which increases the amount of gas released. The duration of processing of organic mass is about 15 days. During this time, it decomposes only by 25%. The maximum amount of natural gas is released when the degree of breakdown of the substrate reaches 33%.

The technology for producing biological gas involves daily renewal of the substrate. To do this, 5% of the mass is removed from the bioreactor, and a new portion of raw materials is placed in its place. The spent product is used as an endorsement.

Biogas production technology at home

Biogas production at home occurs according to the following scheme:

1. The biological mass is crushed. It is necessary to obtain particles whose size does not exceed 10 mm.
2. The resulting mass is thoroughly mixed with water. For 1 kg of raw materials you need approximately 700 ml of liquid component. The water used must be potable and free of impurities.
3. The entire tank is filled with the resulting substrate, after which it is hermetically sealed.
4. It is advisable to thoroughly mix the substrate several times a day, which will increase the efficiency of its processing.
5. On the 5th day of the production process, the presence of biogas is checked and it is gradually pumped into prepared cylinders using a compressor. Periodic removal of gaseous products is mandatory. Their accumulation leads to an increase in pressure inside the tank, which negatively affects the process of breakdown of biological mass.
6. On the 15th day of production, part of the substrate is removed and a fresh portion of biological material is loaded.

To determine the required volume of the reactor for biomass processing, the amount of manure produced during the day should be calculated. The type of raw materials used and the temperature conditions that will be maintained in the installation must be taken into account. The tank used should be filled to 85-90% of its volume. The remaining 10% is necessary for the accumulation of the resulting biological gas.

The duration of the processing cycle must be taken into account. When maintaining a temperature of +35°C, it is 12 days. We must not forget that the raw materials used are diluted with water before being sent to the reactor. Therefore, its quantity is taken into account before calculating the volume of the tank.

Diagram of a simple biological installation

To produce biogas at home, it is necessary to create optimal conditions for microorganisms that will break down biological mass. First of all, it is advisable to organize heating of the generator, which will entail additional costs.

• The volume of the container for storing waste must be at least 1 cubic meter. m;
• it is necessary to use a hermetically sealed container;
• insulation of the biomass tank is a prerequisite for its effective operation;
• the tank can be deepened into the ground. Thermal insulation is installed only in its upper part;
• A hand mixer is installed in the container. Its handle is brought out through a sealed unit;
• nozzles are provided for loading/unloading raw materials and biogas intake.

Underground reactor manufacturing technology

To produce biogas, you can install the simplest installation, deepening it into the ground. The manufacturing technology of such a tank is as follows:

1. Dig a pit of the required size. Its walls are filled with expanded clay concrete, which is additionally reinforced.
2. Holes are left on the opposite walls of the bunker. They install pipes with a certain slope in order to pump raw materials and extract waste material.
3. An outlet pipeline with a diameter of 70 mm is installed almost near the very bottom. Its other end is installed in a tank into which waste sludge will be pumped out. It is recommended to make it rectangular.
4. The pipeline for supplying raw materials is placed at a height of 0.5 m relative to the bottom. Its recommended diameter is 30-35 mm. The top of the pipe is placed into a separate tank to receive prepared raw materials.
5. The upper part of the bioreactor should have a dome or cone shape. It can be made from ordinary roofing iron or other metal sheets. It is allowed to make a tank lid using a brick tub. To strengthen its structure, the surface is additionally plastered with the installation of reinforcing mesh.
6. I make a hatch on top of the tank lid, which should be hermetically closed. A gas outlet pipeline is also routed through it. Additionally, a pressure relief valve is installed.
7. To mix the substrate, several plastic pipes are installed in the tank. They must be immersed in biomass. Many holes are made in the pipes, which allows the raw materials to be mixed using moving gas bubbles.

Biogas yield calculation

The yield of biological gas depends on the content of dry matter in the raw material and its type:

• from 1 ton of cattle manure, 50-60 cubic meters are obtained. m of product with a methane content of 60%;
• from 1 ton of plant waste, 200-500 cubic meters are obtained. m of biogas with a methane concentration of 70%;
• from 1 ton of fat 1300 cubic meters are obtained. m of gas with a methane concentration of 87%.

To determine production efficiency, laboratory tests are carried out on the raw materials used. Its composition is calculated, which affects the quality characteristics of biogas.

Introduction

Production of biogas from digesters and agricultural biogas plants

Biogas storage systems

Biogas composition

Preparation of biogas for use

Main directions and world leaders in the use of biogas

Conclusion

List of used literature

Introduction

In the global practice of gas supply, sufficient experience has been accumulated in the use of renewable energy sources, including biomass energy. The most promising gaseous fuel is biogas, the interest in the use of which in recent years has not only not waned, but continues to increase. Biogases mean methane-containing gases that are formed during the anaerobic decomposition of organic biomass. Depending on the source of production, biogases are divided into three main types:

Digester gas produced at municipal sewage treatment plants (BG STP);

Biogas produced in biogas plants (BGU) during the fermentation of agricultural waste (BG Agricultural Production);

Landfill gas produced at landfills containing organic components (BG MSW).

In my work, I examined the technologies for producing these gases, their composition, methods of preparing biogas for use, namely methods of purification from ballast substances. Biogas has a wide range of uses, which I briefly discussed in this work.

Production of biogas from digesters and agricultural biogas plants

According to technical design, biogas plants are divided into three systems: accumulative, periodic, continuous.

Accumulative systems provide for fermentation in reactors, which also serve as a storage place for fermented manure (substrate) until it is unloaded. The initial substrate is continuously fed into the tank until it is filled. The fermented substrate is unloaded once or twice a year during the period of applying fertilizers to the soil. In this case, part of the fermented sludge is specially left in the reactor and serves as seed material for the subsequent fermentation cycle. The storage volume combined with the bioreactor is calculated for the total volume of manure removed from the complex during the inter-sowing period. Such systems require large amounts of storage and are used very rarely.

A periodic biogas production system involves a one-time loading of the initial substrate into the reactor, supply of seed material there, and unloading of the fermented product. Such a system is characterized by a rather high labor intensity, very uneven gas output and requires at least two reactors, a reservoir for accumulating the initial manure and storing the fermented substrate.

With a continuous scheme, the initial substrate is continuously or at certain intervals (1-10 times a day) loaded into the fermentation chamber, from where the same amount of fermented sediment is simultaneously removed. To intensify the fermentation process, various additives can be added to the bioreactor, increasing not only the reaction rate, but also the yield and quality of gas. Modern biogas plants are usually designed for a continuous process and are made of steel, concrete, plastics, and brick. For thermal insulation, fiberglass, glass wool, and cellular plastic are used.

Based on daily productivity, existing biogas systems and installations can be divided into 3 types:

small - up to 50 m 3 /day;

medium – up to 500 m 3 /day;

large - up to 30 thousand m 3 / day.

Digester and agricultural biogas plants have no fundamental differences, with the exception of the substrate used. The technological diagram of a biogas agricultural installation is shown in Fig. 1.

According to this scheme, manure from the livestock building (1) enters the storage tank (2), then it is loaded into the digester tank - a tank for anaerobic digestion (4) using a fecal pump (3). The biogas generated during the fermentation process enters the gas tank (5) and then to the consumer. To heat the manure to the fermentation temperature and maintain the thermal regime in the digester, a heat exchanger (6) is used, through which hot water flows, heated in the boiler (7). The fermented manure is unloaded. in the manure storage facility (8).

Fig.1. Generalized scheme of biogas production (agricultural biogas

The bioreactor has thermal insulation, which should stably maintain the fermentation temperature and be quickly replaced if it fails. The bioreactor is heated by placing heat exchangers around the perimeter of the walls in the form of a spiral of pipes through which hot water circulates with an initial temperature of 60-70 °C. Such a low temperature of the coolant is adopted to avoid the death of methane-producing microorganisms and the sticking of substrate particles on the heat exchange surface, which can lead to deterioration of heat transfer. The bioreactor also has devices for constant mixing of manure. The flow of manure into the digester is regulated so that the fermentation process proceeds evenly.

During fermentation, microflora develops in manure, which consistently destroys organic substances to acids, and the latter, under the influence of syntrophic and methane-forming bacteria, are converted into gaseous products - methane and carbon dioxide.

Digesters provide all the necessary process parameters - temperature (33-37º C), concentration of organic substances, acidity (6.8-7.4), etc. The growth of methane biocenosis cells is also determined by the C:N ratio, and its optimal value is 30 :1. Some substances contained in the starting substrate can inhibit methane fermentation (Table 1). For example, chicken manure often inhibits methane fermentation by excess NH3.

Table 1

Methane fermentation inhibitors

Biogas produced at solid waste landfills

The process of uncontrolled gas formation at landfills of household and other waste containing a large proportion of organic components can be considered as a process of producing methane-containing gas in an accumulative system; the duration of the process until the complete decomposition of the organic part is much longer than in metatanks.

In domestic practice, biogas recycling systems at solid waste landfills have not yet become widespread, therefore, when further considering the design features of biogas collection and transportation systems, foreign experience will be taken into account. A schematic diagram of one of such systems at a solid waste landfill is shown in Fig. 2. The system consists of two main parts: a gas collection network, which is under vacuum, and a distribution network of biogas consumers, which is under excess low or (less often) medium pressure.

Rice. 2. Construction of a degassing system for solid waste landfills

Below are definitions of the most important elements of the gas collection system at the landfill, shown in Fig. 2, and requirements for individual elements of the system.

Gas collectors are pipelines laid in the thickness of the waste, in which a vacuum is created. As a rule, they are performed either vertically in the form of gas wells, or horizontally in the form of perforated pipelines, but in practice other forms are also used (reservoirs, gravel or crushed stone chambers, etc.).

Prefabricated gas pipelines mean gas pipelines that are under vacuum and lead to part of the prefabricated collectors. To compensate for drawdowns, they have a flexible connection to the gas manifold; instrumentation (for measuring pressure) and fittings for gas sampling are located in the connection unit.

Collecting gas pipelines are combined at a gas collection point. The gas collection point can be made in the form of a pipe, tank, etc. and is located at the lowest point in order to ensure the collection and removal of falling condensate. Instrumentation and automation devices are located at the gas collection point.

A condensate removal system is a device on a gas pipeline for collecting and discharging condensate at the lowest point of the pipeline system. In the vacuum zone, condensate is discharged through siphons, in the area of ​​excess pressure - through adjustable condensate drains. Condensate can also be removed both in the underpressure zone and in the overpressure zone using a cooling device.

The suction pipeline is the straight section of the pipeline in front of the injection device; instrumentation and automation devices are also provided here.

Pressure devices (fan, blower, etc.) are used to create a vacuum necessary for transporting gas from a disposal body or to create excess pressure when transporting gas to the place of use (to a flare unit, to a recovery system, etc.).

The compressor unit serves to increase the excess gas pressure.

Blower devices are located in the engine room. Traditional structures are containers, metal enclosures, or small buildings (garages, block structures, etc.). In large installations, gas injection devices are located in the machine room; sometimes they can be placed in open areas under a canopy.

In this article: history of the use of biogas; biogas composition; how to increase the methane content in biogas; temperature conditions when producing biogas from organic substrate; types of biogas plants; the shape and location of the bioreactor, as well as a number of other important points in creating a bioreactor installation with your own hands.

Among the important components of our lives, energy resources are of great importance, prices for which are rising almost every month. Each winter season makes a hole in family budgets, forcing them to incur heating costs, and therefore, fuel for heating boilers and furnaces. But what should we do, because electricity, gas, coal or firewood cost money, and the more remote our homes are from major energy highways, the more expensive their heating will be. Meanwhile, alternative heating, independent of any suppliers and tariffs, can be built on biogas, the production of which does not require geological exploration, well drilling, or expensive pumping equipment.

Biogas can be obtained practically at home, while incurring minimal, quickly recouping costs - you will find a lot of information on this issue in our article.

Biogas heating - history

Interest in flammable gas formed in swamps during the warm season of the year arose among our distant ancestors - advanced cultures of India, China, Persia and Assyria experimented with biogas over 3 thousand years ago. In the same ancient times, in tribal Europe, the Alemanni Swabians noticed that the gas released in the swamps burned well - they used it to heat their huts, supplying gas to them through leather pipes and burning them in the hearths. The Swabians considered biogas to be the “breath of dragons,” which they believed lived in swamps.

Centuries and millennia later, biogas experienced its second discovery - in the 17th and 18th centuries, two European scientists immediately paid attention to it. The famous chemist of his time, Jan Baptista van Helmont, established that the decomposition of any biomass produces a flammable gas, and the famous physicist and chemist Alessandro Volta established a direct relationship between the amount of biomass in which decomposition processes take place and the amount of biogas released. In 1804, the English chemist John Dalton discovered the formula for methane, and four years later the Englishman Humphry Davy discovered it as part of swamp gas.

Left: Jan Baptista van Helmont. Right: Alessandro Volta

Interest in the practical use of biogas arose with the development of gas street lighting - at the end of the 19th century, the streets of one district of the English city of Exeter were illuminated with gas obtained from a sewage collector.

In the 20th century, energy demands caused by World War II forced Europeans to look for alternative energy sources. Biogas plants, in which gas was produced from manure, spread in Germany and France, and partly in Eastern Europe. However, after the victory of the countries of the anti-Hitler coalition, biogas was forgotten - electricity, natural gas and petroleum products completely covered the needs of industries and the population.

In the USSR, the technology for producing biogas was considered mainly from an academic point of view and was not considered to be in any demand.

Today, the attitude towards alternative energy sources has changed dramatically - they have become interesting, since the cost of conventional energy resources increases from year to year. At its core, biogas is a real way to avoid tariffs and costs for classical energy sources, to obtain your own source of fuel, for any purpose and in sufficient quantities.

The largest number of biogas plants have been created and operated in China: 40 million plants of medium and low power, the volume of methane produced is about 27 billion m3 per year.

Biogas - what is it?

This is a gas mixture consisting mainly of methane (content from 50 to 85%), carbon dioxide (content from 15 to 50%) and other gases in much smaller percentages. Biogas is produced by a team of three species of bacteria that feed on biomass - hydrolysis bacteria, which produce food for acid-forming bacteria, which in turn provide food for methane-producing bacteria, which form biogas.

Fermentation of the original organic material (for example, manure), the product of which will be biogas, takes place without access to an external atmosphere and is called anaerobic. Another product of such fermentation, called compost humus, is well known to rural residents who use it to fertilize fields and vegetable gardens, but the biogas and thermal energy produced in compost heaps are usually not used - and in vain!

What factors determine the yield of biogas with a higher methane content?

First of all, it depends on the temperature. The higher the temperature of their environment, the higher the activity of bacteria fermenting organic matter; at sub-zero temperatures, fermentation slows down or stops completely. For this reason, biogas production is most common in countries in Africa and Asia, located in the subtropics and tropics. In the Russian climate, obtaining biogas and completely switching to it as an alternative fuel will require thermal insulation of the bioreactor and the introduction of warm water into the mass of organic matter when the temperature of the external atmosphere drops below zero.

Organic material placed in a bioreactor must be biodegradable; a significant amount of water must be introduced into it - up to 90% of the mass of organic matter. An important point will be the neutrality of the organic environment, the absence in its composition of components that prevent the development of bacteria, such as cleaning and detergents, and any antibiotics. Biogas can be obtained from almost any waste of economic and plant origin, wastewater, manure, etc.

The process of anaerobic fermentation of organic matter works best when the pH value is in the range of 6.8-8.0 - high acidity will slow down the formation of biogas, as the bacteria will be busy consuming acids and producing carbon dioxide, which neutralizes the acidity.

The ratio of nitrogen and carbon in the bioreactor must be calculated as 1 to 30 - in this case, the bacteria will receive the amount of carbon dioxide they need, and the methane content in the biogas will be the highest.

The best yield of biogas with a sufficiently high methane content is achieved if the temperature in the fermentable organic matter is in the range of 32-35 ° C; at lower and higher values, the content of carbon dioxide in the biogas increases and its quality decreases. Bacteria that produce methane are divided into three groups: psychrophilic, effective at temperatures from +5 to +20 ° C; mesophilic, their temperature range is from +30 to +42 °C; thermophilic, operating in the mode from +54 to +56 °C. For the biogas consumer, mesophilic and thermophilic bacteria, which ferment organic matter with a higher gas yield, are of greatest interest.

Mesophilic fermentation is less sensitive to changes in temperature by a couple of degrees from the optimal temperature range and requires less energy to heat organic material in the bioreactor. Its disadvantages, compared to thermophilic fermentation, are lower gas yield, longer period of complete processing of the organic substrate (about 25 days), the resulting decomposed organic material may contain harmful flora, since the low temperature in the bioreactor does not ensure 100% sterility.

Raising and maintaining the intra-reactor temperature at a level acceptable for thermophilic bacteria will ensure the greatest yield of biogas, complete fermentation of organic matter will take place in 12 days, the decomposition products of the organic substrate are completely sterile. Negative characteristics: going beyond the temperature range acceptable for thermophilic bacteria by 2 degrees will reduce the gas yield; high need for heating, as a result - significant energy costs.

The contents of the bioreactor must be stirred twice a day, otherwise a crust will form on its surface, creating a barrier to biogas. In addition to eliminating it, stirring allows you to equalize the temperature and acidity level inside the organic mass.

In continuous cycle bioreactors, the highest biogas yield occurs with the simultaneous unloading of organic matter that has undergone fermentation and the loading of new organic matter in an amount equal to the unloaded volume. In small bioreactors, which are usually used in dacha farms, every day it is necessary to extract and add organic matter in a volume approximately equal to 5% of the internal volume of the fermentation chamber.

The yield of biogas directly depends on the type of organic substrate placed in the bioreactor (the average data per kg of dry substrate weight is given below):

• horse manure produces 0.27 m 3 of biogas, methane content 57%;
• cattle manure produces 0.3 m 3 of biogas, methane content 65%;
• fresh cattle manure produces 0.05 m 3 of biogas with 68% methane content;
• chicken droppings - 0.5 m 3, the methane content in it will be 60%;
• pork manure - 0.57 m 3, the share of methane will be 70%;
• sheep manure - 0.6 m 3 with a methane content of 70%;
• wheat straw - 0.27 m 3, with 58% methane content;
• corn straw - 0.45 m 3, methane content 58%;
• grass - 0.55 m 3, with 70% methane content;
• tree foliage - 0.27 m 3, methane share 58%;
• fat - 1.3 m 3, methane content 88%.

Biogas plants

These devices consist of the following main elements - a reactor, an organic loading hopper, a biogas outlet, and a fermented organic matter unloading hopper.

According to the type of design, biogas plants are of the following types:

• without heating and without stirring the fermented organic matter in the reactor;
• without heating, but with stirring of the organic mass;
• with heating and stirring;
• with heating, stirring and devices that allow you to control and manage the fermentation process.

The first type of biogas plant is suitable for a small farm and is designed for psychrophilic bacteria: the internal volume of the bioreactor is 1-10 m 3 (processing 50-200 kg of manure per day), minimal equipment, the resulting biogas is not stored - it immediately goes to the household appliances that consume it. This installation can only be used in southern regions; it is designed for an internal temperature of 5-20 ° C. Removal of fermented organic matter is carried out simultaneously with the loading of a new batch; the shipment is carried out into a container, the volume of which must be equal to or greater than the internal volume of the bioreactor. The contents of the container are stored in it until introduced into the fertilized soil.

The design of the second type is also designed for small farms, its productivity is slightly higher than the biogas plants of the first type - the equipment includes a mixing device with a manual or mechanical drive.

The third type of biogas plants is equipped, in addition to the mixing device, with forced heating of the bioreactor; the hot water boiler runs on alternative fuel produced by the biogas plant. Methane production in such installations is carried out by mesophilic and thermophilic bacteria, depending on the heating intensity and temperature level in the reactor.

Schematic diagram of a biogas plant: 1 - substrate heating; 2 - filler neck; 3 — bioreactor capacity; 4 - hand mixer; 5 — container for collecting condensate; 6 - gas valve; 7 - tank for processed mass; 8 - safety valve; 9 - filter; 10 - gas boiler; 11 - gas valve; 12 - gas consumers; 13 - water seal

The last type of biogas plants is the most complex and is designed for several consumers of biogas; the design of the plants includes an electric contact pressure gauge, a safety valve, a hot water boiler, a compressor (pneumatic mixing of organic matter), a receiver, a gas tank, a gas reducer, and an outlet for loading biogas into transport. These installations operate continuously, allow the setting of any of three temperature conditions thanks to precisely adjustable heating, and biogas selection is carried out automatically.

DIY biogas plant

The calorific value of biogas produced in biogas plants is approximately 5,500 kcal/m3, which is slightly lower than the calorific value of natural gas (7,000 kcal/m3). To heat 50 m 2 of a residential building and use a gas stove with four burners for an hour, an average of 4 m 3 of biogas will be required.

Industrial biogas production plants offered on the Russian market cost from 200,000 rubles. — despite their apparently high cost, it is worth noting that these installations are precisely calculated according to the volume of loaded organic substrate and are covered by manufacturer’s warranties.

If you want to create a biogas plant yourself, then further information is for you!

Bioreactor form

The best shape for it would be oval (egg-shaped), but building such a reactor is extremely difficult. A cylindrical bioreactor, the upper and lower parts of which are made in the form of a cone or semicircle, will be easier to design. Square or rectangular reactors made of brick or concrete will be ineffective, because cracks will form in the corners over time caused by the pressure of the substrate, and hardened organic fragments will also accumulate in them, interfering with the fermentation process.

Steel bioreactor tanks are airtight, resistant to high pressure, and are not that difficult to build. Their disadvantage is their poor resistance to rust; they require a protective coating, for example, resin, to be applied to the inner walls. The outside of the steel bioreactor must be thoroughly cleaned and painted in two layers.

Bioreactor containers made of concrete, brick or stone must be carefully coated on the inside with a layer of resin that can ensure their effective water and gas impermeability, withstand temperatures of about 60 ° C, and the aggression of hydrogen sulfide and organic acids. In addition to resin, to protect the internal surfaces of the reactor, you can use paraffin, diluted with 4% motor oil (new) or kerosene and heated to 120-150 ° C - the surfaces of the bioreactor must be heated with a burner before applying a paraffin layer on them.

When creating a bioreactor, you can use plastic containers that are not susceptible to rust, but only hard ones with sufficiently strong walls. Soft plastic can only be used in the warm season, because with the onset of cold weather it will be difficult to attach insulation to it, and its walls are not strong enough. Plastic bioreactors can only be used for psychrophilic fermentation of organic matter.

Bioreactor location

Its placement is planned depending on the free space on the site, the distance from residential buildings, the location of waste and animals, etc. Planning a ground-based, fully or partially submerged bioreactor depends on the groundwater level, the convenience of entering and exiting the organic substrate into the container reactor. It would be optimal to place the reactor vessel below ground level - savings are achieved on equipment for introducing an organic substrate, and thermal insulation is significantly increased, to ensure which inexpensive materials (straw, clay) can be used.

Bioreactor equipment

The reactor tank must be equipped with a hatch, which can be used to carry out repair and maintenance work. It is necessary to lay a rubber gasket or a layer of sealant between the bioreactor body and the hatch cover. It is optional, but extremely convenient, to equip the bioreactor with a sensor for temperature, internal pressure and organic substrate level.

Bioreactor thermal insulation

Its absence will not allow the biogas plant to be operated all year round, only in warm weather. To insulate a buried or semi-buried bioreactor, clay, straw, dry manure and slag are used. The insulation is laid in layers - when installing a buried reactor, the pit is covered with a layer of PVC film, which prevents direct contact of the heat-insulating material with the soil. Before installing the bioreactor, straw is poured onto the bottom of the pit, a layer of clay is placed on top of it, then the bioreactor is placed. After this, all free areas between the reactor tank and the pit lined with PVC film are filled with straw almost to the end of the tank, and a 300 mm layer of clay mixed with slag is poured on top.

Loading and unloading organic substrate

The diameter of the pipes for loading into and unloading from the bioreactor must be at least 300 mm, otherwise they will clog. In order to maintain anaerobic conditions inside the reactor, each of them should be equipped with screw or half-turn valves. The volume of the bunker for supplying organic matter, depending on the type of biogas plant, should be equal to the daily volume of input raw materials. The feed hopper should be located on the sunny side of the bioreactor, as this will increase the temperature in the introduced organic substrate, accelerating the fermentation processes. If the biogas plant is connected directly to the farm, then the bunker should be placed under its structure so that the organic substrate enters it under the influence of gravity.

The pipelines for loading and unloading the organic substrate should be located on opposite sides of the bioreactor - in this case, the input raw materials will be distributed evenly, and the fermented organic matter will be easily extracted under the influence of gravitational forces and the mass of the fresh substrate. Holes and installation of the pipeline for loading and unloading organic matter should be completed before installing the bioreactor at the installation site and before placing layers of thermal insulation on it. The tightness of the internal volume of the bioreactor is achieved by the fact that the pipe entries are located at an acute angle, while the liquid level inside the reactor is higher than the pipe entry points - a hydraulic seal blocks the access of air.

The easiest way to introduce new and remove fermented organic material is by the overflow principle, i.e., raising the level of organic matter inside the reactor when introducing a new portion will remove the substrate through the unloading pipe in a volume equal to the volume of the introduced material.

If quick loading of organic matter is necessary, and the efficiency of introducing material by gravity is low due to imperfections in the relief, installation of pumps will be required. There are two methods: dry, in which the pump is installed inside the loading pipe and the organic matter, entering the pump through a vertical pipe, is pumped by it; wet, in which the pump is installed in the loading hopper, its drive is carried out by a motor, also installed in the hopper (in an impenetrable housing) or through a shaft, while the motor is installed outside the hopper.

How to collect biogas

This system includes a gas pipeline that distributes gas to consumers, shut-off valves, condensate collection tanks, a safety valve, a receiver, a compressor, a gas filter, a gas tank and gas consumption devices. Installation of the system is carried out only after the bioreactor is completely installed at its location.

The outlet for collecting biogas is located at the highest point of the reactor; the following are connected in series to it: a sealed container for collecting condensate; safety valve and water seal - a container with water, the gas pipeline entry into which is made below the water level, the outlet - above (the gas pipeline pipe in front of the water seal should be bent so that water does not penetrate into the reactor), which will not allow gas to move in the opposite direction.

Biogas formed during the fermentation of an organic substrate contains a significant amount of water vapor, which forms condensate along the walls of the gas pipeline and, in some cases, blocks the flow of gas to consumers. Since it is difficult to build a gas pipeline in such a way that there is a slope along its entire length towards the reactor, where condensate would flow, it is necessary to install water seals in the form of containers with water in each of its low sections. During operation of a biogas plant, it is periodically necessary to remove some of the water from them, otherwise its level will completely block the flow of gas.

The gas pipeline must be built with pipes of the same diameter and the same type, all valves and elements of the system must also have the same diameter. Steel pipes with a diameter of 12 to 18 mm are suitable for biogas plants of low and medium power; the flow rate of biogas supplied through pipes of these diameters should not exceed 1 m 3 / h (at a flow rate of 0.5 m 3 / h, the use of pipes with a diameter of 12 mm for lengths over 60 m). The same condition applies when using plastic pipes in a gas pipeline; in addition, these pipes must be laid 250 mm below ground level, since their plastic is sensitive to sunlight and loses strength under the influence of solar radiation.

When laying a gas pipeline, it is necessary to carefully ensure that there are no leaks and that the joints are gas-tight - the check is carried out with a soap solution.

Gas filter

Biogas contains a small amount of hydrogen sulfide, the combination of which with water creates an acid that actively corrodes the metal - for this reason, unfiltered biogas cannot be used for internal combustion engines. Meanwhile, hydrogen sulfide can be removed from gas with a simple filter - a 300 mm piece of gas pipe filled with a dry mixture of metal and wood shavings. After every 2,000 m 3 of biogas passed through such a filter, it is necessary to extract its contents and keep it in open air for about an hour - the shavings will be completely cleared of sulfur and can be reused.

Shut-off fittings and valves

A main gas valve is installed in the immediate vicinity of the bioreactor; a valve should be inserted into the gas pipeline to release biogas at a pressure of more than 0.5 kg/cm 2 . The best valves for a gas system are chrome-plated ball valves; you cannot use valves designed for plumbing systems in a gas system. The installation of a ball valve on each gas consumer is mandatory.

Mechanical stirring

For small-volume bioreactors, manually driven mixers are best suited - they are simple in design and do not require any special conditions during operation. A mechanically driven mixer is designed like this - a horizontal or vertical shaft placed inside the reactor along its central axis, with blades attached to it, which, when rotated, move masses of organic matter rich in bacteria from the area where the fermented substrate is unloaded to the place where a fresh portion is loaded. Be careful - the mixer should rotate only in the direction of mixing from the unloading area to the loading area; the movement of methane-producing bacteria from the mature substrate to the newly received one will accelerate the maturation of organic matter and the production of biogas with a high methane content.

How often should the organic substrate be mixed in the bioreactor? It is necessary to determine the frequency by observation, focusing on the yield of biogas - excessively frequent stirring will disrupt fermentation, since it will interfere with the activity of bacteria, in addition, it will cause the release of unprocessed organic matter. On average, the time interval between stirrings should be from 4 to 6 hours.

Heating of organic substrate in a bioreactor

Without heating, the reactor can only produce biogas in psychrophilic mode, resulting in less gas produced and poorer fertilizer quality than in higher temperature mesophilic and thermophilic operating modes. The substrate can be heated in two ways: steam heating; combining organics with hot water or heating using a heat exchanger in which hot water circulates (without mixing with organic material).

A serious disadvantage of steam heating (direct heating) is the need to include a steam generation system in the biogas plant, which includes a system for purifying water from the salt present in it. A steam generation plant is only beneficial for really large installations that process large volumes of substrate, for example wastewater. In addition, heating with steam will not allow you to accurately control the heating temperature of organic matter; as a result, it may overheat.

Heat exchangers located inside or outside the bioreactor plant indirectly heat the organic matter inside the reactor. You should immediately discard the option of heating through the floor (foundation), since the accumulation of solid sediment at the bottom of the bioreactor prevents it. The best option would be to insert a heat exchanger inside the reactor, but the material that forms it must be strong enough and successfully withstand the pressure of organic matter when mixing it. A larger area heat exchanger will heat organic matter better and more uniformly, thereby improving the fermentation process. External heating, while less efficient due to heat loss from the walls, is attractive because nothing inside the bioreactor will interfere with the movement of the substrate.

The optimal temperature in the heat exchanger should be about 60 °C; the heat exchangers themselves are made in the form of radiator sections, coils, and parallel welded pipes. Maintaining the coolant temperature at 60 °C will reduce the threat of suspended particles sticking to the walls of the heat exchanger, the accumulation of which will significantly reduce heat transfer. The optimal location for the heat exchanger is near the mixing blades; in this case, the threat of sedimentation of organic particles on its surface is minimal.

The heating pipeline of the bioreactor is designed and equipped similarly to a conventional heating system, i.e., the conditions for returning cooled water to the lowest point of the system must be met, and air release valves are required at its highest points. The temperature of the organic mass inside the bioreactor is controlled by a thermometer, which the reactor should be equipped with.

Gas tanks for collecting biogas

With constant gas consumption, there is no need for them, unless they can be used to equalize the gas pressure, which will significantly improve the combustion process. For low-capacity bioreactor plants, large-volume automobile chambers that can be connected in parallel are suitable as gas holders.

More serious gas tanks, steel or plastic, are selected for a specific bioreactor installation - in the best case, the gas tank should accommodate the volume of biogas produced daily. The required capacity of a gas tank depends on its type and the pressure for which it is designed; as a rule, its volume is 1/5...1/3 of the internal volume of the bioreactor.

Steel gas tank. There are three types of steel gas tanks: low pressure, from 0.01 to 0.05 kg/cm2; average, from 8 to 10 kg/cm2; high, up to 200 kg/cm 2. It is not practical to use low-pressure steel gas tanks; it is better to replace them with plastic gas tanks - they are expensive and are only applicable if there is a significant distance between the biogas plant and consumer devices. Low pressure gas tanks are used mainly to equalize the difference between the daily biogas output and its actual consumption.

Biogas is pumped into medium- and high-pressure steel gas tanks by a compressor; they are used only in medium- and large-capacity bioreactors.

Gas tanks must be equipped with the following control and measuring devices: safety valve, water seal, pressure reducer and pressure gauge. Steel gas tanks must be grounded!

Video on the topic

Biogas is produced in special, corrosion-resistant cylindrical sealed tanks, also called fermenters. The fermentation process takes place in such containers. But before entering the fermenter, the raw materials are loaded into a receiver container. Here it is mixed with water until smooth, using a special pump. Next, the prepared raw material is introduced into the fermenters from the receiver tank. It should be noted that the mixing process does not stop and continues until there is nothing left in the receiver container. After it is empty, the pump stops automatically. After the fermentation process begins, biogas begins to be released, which flows through special pipes into a gas holder located nearby.

Figure 5. Generalized diagram of a biogas plant

Figure 6 shows a diagram of the installation for producing biogas. Organic waste, usually liquid manure, enters receiver-heat exchanger 1, where it is heated by heated sludge supplied through a heat exchanger pipe by pump 9 from digester 3, and diluted with hot water.

Figure 6. Installation diagram for biogas production

Additional dilution of wastewater with hot water and heating to the required temperature is carried out in apparatus 2. Field waste is also supplied here to create the required C/N ratio. The biogas generated in the digester 3 is partially burned in the water heater 4, and the combustion products are discharged through the pipe 5. The rest of the biogas passes through the cleaning device 6, is compressed by the compressor 7 and enters the gas tank 8. The sludge from the apparatus 1 enters the heat exchanger 10, where additionally cooling, it heats up cold water. Sludge is a disinfected, highly effective natural fertilizer that can replace 3-4 tons of mineral fertilizer such as nitrophoska.

2.2 Biogas storage systems

Typically, biogas comes out of the reactors unevenly and with low pressure (no more than 5 kPa). This pressure, taking into account the hydraulic losses of the gas transmission network, is not enough for the normal operation of gas-using equipment. In addition, the peaks of biogas production and consumption do not coincide in time. The simplest solution for eliminating excess biogas is to burn it in a flare, but this results in irreversible loss of energy. A more expensive, but ultimately economically justified way to level out the unevenness of gas production and consumption is the use of gas holders of various types. Conventionally, all gas tanks can be divided into “direct” and “indirect”. “Direct” gas tanks constantly contain a certain volume of gas, injected during periods of decline in consumption and withdrawn at peak load. “Indirect” gas tanks provide for the accumulation not of the gas itself, but of the energy of an intermediate coolant (water or air), heated by the combustion products of the burned gas, i.e. thermal energy is accumulated in the form of a heated coolant.

Biogas, depending on its quantity and the direction of subsequent use, can be stored under different pressures; accordingly, gas storage facilities are called gas holders of low (not higher than 5 kPa), medium (from 5 kPa to 0.3 MPa) and high (from 0.3 to 1. 8 MPa) pressure. Low-pressure gas tanks are designed to store gas at a slightly fluctuating gas pressure and a significantly varying volume, therefore they are sometimes called gas storage facilities of constant pressure and variable volume (provided by the mobility of the structures). Gas tanks of medium and high pressure, on the contrary, are arranged according to the principle of constant volume, but changing pressure. In the practice of using biogas plants, low-pressure gas tanks are most often used.

The capacity of high-pressure gas tanks can vary from several liters (cylinders) to tens of thousands of cubic meters (stationary gas storage facilities). Storage of biogas in cylinders is used, as a rule, in the case of using gas as fuel for vehicles. The main advantages of high and medium pressure gas tanks are their small dimensions with significant volumes of stored gas and the absence of moving parts, but the disadvantage is the need for additional equipment: a compressor unit to create medium or high pressure and a pressure regulator to reduce the gas pressure in front of the burner devices of gas-using units.