Biogas is a gas produced by the methane fermentation of biomass. The decomposition of biomass into components occurs under the influence of 3 types of bacteria. In the food chain, subsequent bacteria feed on the waste products of the previous ones. The first type is hydrolytic bacteria, the second is acid-forming, the third is methane-forming. In the production of biogas, not only bacteria of the methanogen class are involved, but all three species.

Composition of biogas

55%-75% methane, 25%-45% CO2, small amounts of H2 and H2S. After purification of biogas from CO2, biomethane is obtained. Biomethane is a complete analogue of natural gas. The only difference is in the origin.

Raw material to receive

Organic waste: manure, grain and molasses post-alcohol stillage, brewer's grains, beet pulp, fecal sludge, fish and slaughterhouse waste (blood, fat, intestines, canyga), grass, household waste, dairy waste - lactose, whey, production waste biodiesel - technical glycerin from the production of biodiesel from rapeseed, waste from the production of juices - fruit pulp, berry, grape pomace, algae, waste from the production of starch and molasses - pulp and syrup, waste from potato processing, the production of chips - peelings, skins, rotten tubers.

The yield of biogas depends on the dry matter content and the type of feedstock used. From a ton of cattle manure, 30-50 m³ of biogas is obtained with a methane content of 60 , 150-500 m3 of biogas from various types of plants with a methane content of up to 70%. The maximum amount of biogas is 1300 m3 with a methane content of up to 87 can be obtained from fat.

In biogas calculations, the concept of dry matter (CB or English TS) or dry residue (CO) is used. Water contained in biomass does not produce gas.

From 1 kg of dry matter, from 300 to 500 liters of biogas are obtained.

To calculate the yield of biogas from a particular raw material, it is necessary to conduct laboratory tests or look at reference data and determine the content of fats, proteins and carbohydrates. When determining the latter, it is important to know the percentage of rapidly degradable (fructose, sugar, sucrose, starch) and difficult to decompose substances (for example, cellulose, hemicellulose, lignin). Having determined the content of the elements, the gas output is calculated for each separately and then summarized.

Previously, when there was no science of biogas and biogas was associated with manure, the concept of "animal unit" was used. Today, when they learned how to get biogas from anything organic, this concept has moved away and has ceased to be used.

In addition to waste, biogas can be produced from specially grown energy crops, such as silage corn or sylph. The gas output can reach up to 500 m3 per ton.

Story

Mankind has learned to use biogas for a long time. In the 2nd millennium BC. primitive biogas plants already existed on the territory of modern Germany. The Alemans, who inhabited the wetlands of the Elbe basin, imagined Dragons in snags in the swamp. They believed that the combustible gas accumulating in the pits in the swamps was the stinking breath of the Dragon. To appease the Dragon, sacrifices and leftover food were thrown into the swamp. People believed that the Dragon comes at night and his breath remains in the pits. The Alemans thought of sewing awnings from leather, covering the swamp with them, diverting gas through leather pipes to their dwelling and burning it for cooking. This is understandable, because it was difficult to find dry firewood, and swamp gas (biogas) perfectly solved this problem.

In the 17th century, Jan Baptist Van Helmont discovered that decaying biomass emits flammable gases. Alessandro Volta in 1776 came to the conclusion that there is a relationship between the amount of decaying biomass and the amount of gas released. In 1808, Sir Humphry Davy discovered methane in biogas.

The first documented biogas plant was built in Bombay, India in 1859. In 1895, biogas was used in the UK for street lighting. In 1930, with the development of microbiology, bacteria involved in the biogas production process were discovered.

Ecology

Biogas production helps prevent methane emissions into the atmosphere. Processed manure is used as a fertilizer in agriculture. This reduces the use of chemical fertilizers, reduces the load on groundwater.

Methane has a 21 times greater greenhouse effect than CO2 and stays in the atmosphere for 12 years. Capturing methane is the best short-term way to prevent global warming.

Production

In total, about 60 varieties of biogas production technologies are currently used or developed in the world. The most common method is anaerobic digestion in metatanks, or anaerobic columns (the term has not been established in Russian). Part of the energy received as a result of biogas utilization is directed to support the process (up to 15-20% in winter). In countries with a hot climate, there is no need to heat the methane tank. Bacteria process biomass into methane at temperatures from 25°C to 70°C.

For the fermentation of some types of raw materials in their pure form, a special two-stage technology is required. For example, bird droppings, distillery stillage, are not processed into biogas in a conventional reactor. For the processing of such raw materials, an additional hydrolysis reactor is required. Such a reactor allows you to control the level of acidity, so bacteria do not die due to an increase in the content of acids or alkalis.

Obtaining biogas is economically justified by processing a constant stream of waste, for example, on livestock farms.

Landfill gas is one of the varieties of biogas. Obtained in landfills from municipal household waste.

Application

Biogas is used as a fuel for the production of: electricity, heat or steam, or as a vehicle fuel. In India, Vietnam, Nepal and other countries, small (single-family) biogas plants are being built. The gas they produce is used for cooking.

Biogas plants can be installed as treatment facilities on farms, poultry farms, distilleries, sugar factories, meat processing plants. A biogas plant can replace a veterinary and sanitary plant. Those. carrion can be disposed of in biogas instead of producing meat and bone meal.

Most of the small biogas plants are located in China - more than 10 million (at the end of the 1990s). They produce about 7 billion m³ of biogas per year, which provides fuel for about 60 million farmers. In India, 3.8 million small biogas plants have been installed since 1981.

At the end of 2006, about 18 million biogas plants were operating in China. Their use makes it possible to replace 10.9 million tons of reference fuel.

Among industrialized countries, the leading place in the production and use of biogas in terms of relative indicators belongs to Denmark - biogas occupies up to 18% in its total energy balance. In absolute terms, in terms of the number of medium and large installations, Germany occupies the leading position - 8,000 thousand units. In Western Europe, at least half of all poultry farms are heated with biogas.

Volvo and Scania make buses with biogas engines. Such buses are actively used in Swiss cities: Bern, Basel, Geneva, Lucerne and Lausanne. According to the forecasts of the Swiss Association of the Gas Industry by 2010, 10% of vehicles in Switzerland will run on biogas.

Gas is widely used both for industry, including chemical (for example, raw materials for plastics production) and in everyday life. In domestic conditions, gas is used for heating residential private and apartment buildings, cooking, heating water, as fuel for cars, etc.

From an environmental point of view, gas is one of the cleanest types of fuel. Compared with other types of fuel, the smallest amount of emissions of harmful substances.

But if we talk about gas, then we automatically mean natural gas extracted from the bowels of the earth.

One day I stumbled upon an article in a newspaper that told how one grandfather assembled a not tricky installation and gets gas from manure. This topic interested me a lot. And I would like to talk about this alternative to natural gas - this is biogas. I think that this topic is quite interesting and useful for ordinary people and especially for farmers.

On the farmstead of any peasant farm, you can use not only the energy of wind, the sun, but also biogas.

Biogas- gaseous fuel, a product of anaerobic microbiological decomposition of organic substances. Gas production technology is an environmentally friendly, waste-free method of processing, recycling and disinfection of various organic wastes of plant and animal origin.

The raw material for biogas production is ordinary manure, leaves, grass, in general, any organic debris: tops, food waste, fallen leaves.

The resulting gas - methane - is the result of the vital activity of methane bacteria. From methane - it is also called marsh or firedamp gas, 90-98% consists of natural gas, which is used in everyday life.

The gas plant is very easy to manufacture. We need the main container, you can weld it yourself or use some kind of ready-made one, it can be anything. On the sides of the tank, you need to install thermal insulation, for using the installation in the cold season. From above we make a couple of hatches. From one of them we attach pipes for venting gas. For an intensive fermentation process and gas evolution, the mixture must be periodically stirred. Therefore, you need to install a mixing device. Further, the gas must be collected and stored or used for its intended purpose. To collect gas, you can use an ordinary car chamber, and then, if there is a compressor, compress and pump it into cylinders.

The principle of operation is quite simple: manure is loaded through one hatch. Inside, this biomass is decomposed by special methane bacteria. To make the process more intensive, the contents must be mixed and preferably heated. For heating, you can install pipes inside which hot water should circulate. The methane released as a result of the vital activity of bacteria through the tubes enters the car chambers, and when a sufficient amount of it accumulates, we compress it with the help of a compressor and pump it into cylinders.

In warm weather or when artificial heating is used, the plant can produce a fairly large amount of gas, about 8 m 3 /day.

It is also possible to obtain gas from household waste from landfills, but chemicals used in everyday life are a problem.

Methane bacteria are found in the intestines of animals and therefore in manure. But in order for them to start working, it is necessary to limit their interaction with oxygen, since it depresses their vital activity. That is why it is necessary to create special installations so that bacteria do not come into contact with air.

In the resulting biogas, the concentration of methane is slightly lower than in natural gas, therefore, when it is burned, it will produce slightly less heat. When burning 1 m 3 of natural gas, 7-7.5 Gcal is released, while with biogas - 6-6.5 Gcal.

This gas is suitable for both heating (we still have general information about heating) and for use in domestic stoves. The cost of biogas is low, and in some cases it is practically zero if everything is made from improvised materials and you keep, for example, a cow.

Waste from gas production is biohumus - an organic fertilizer in which, in the process of decay without access to oxygen, everything from weed seeds rots, and only useful microelements necessary for plants remain.

Abroad, there are even methods for creating artificial gas fields. It looks like this. Since a large proportion of the discarded household waste is organic matter, which can rot and produce biogas. In order for the gas to begin to stand out, it is necessary to deprive the organic matter of interaction with air. Therefore, the waste is rolled up in layers, and the top layer is made of a gas-water-tight material, such as clay. Then wells are drilled and gas is extracted as from natural deposits. And at the same time several problems are being solved, these are waste disposal and energy production.

Under what conditions is biogas produced?

Conditions for obtaining and energy value of biogas

In order to assemble a small-sized plant, it is necessary to know from what raw materials and by what technology biogas can be obtained.

Gas is obtained in the process of decomposition (fermentation) of organic substances without air access (anaerobic process): pet droppings, straw, tops, fallen leaves and other organic waste generated in an individual household. It follows that biogas can be obtained from any household waste that can decompose and ferment in a liquid or wet state.

The process of decomposition (fermentation) takes place in two phases:

1. Decomposition of biomass (hydration);
2. Gasification (biogas release).

These processes take place in a fermenter (anaerobic biogas plant).

The sludge obtained after decomposition in biogas plants increases soil fertility and yield increases by 10-50%. Thus, a valuable fertilizer is obtained.

Biogas consists of a mixture of gases:

• methane-55-75%;
• carbon dioxide-23-33%;
• hydrogen sulfide-7%.

Methane fermentation is a complex organic fermentation process - a bacterial process. The main condition for this process to take place is the presence of heat.

In the process of biomass decomposition, heat is generated, which is sufficient for the process to proceed, in order to retain this heat, the fermenter must be thermally insulated. With a decrease in temperature in the fermenter, the intensity of gas evolution decreases, since microbiological processes in the organic mass slow down. Therefore, reliable thermal insulation of a biogas plant (biofermenter) is one of the most important conditions for its normal operation. When loading manure into the fermenter, it must be mixed with hot water at a temperature of 35-40 ° C. This will help ensure the necessary mode of its operation.

When reloading, heat loss should be kept to a minimum. Biogas Engineering Assistance

For better heating of the fermenter, you can use the "greenhouse effect". To do this, a wooden or light metal frame is installed above the dome and covered with plastic wrap. The best results are achieved when the temperature of the fermented material is 30-32°C and the humidity is 90-95%. In the areas of the middle and northern strip, part of the gas produced must be spent during the cold periods of the year for additional heating of the fermented mass, which complicates the design of biogas plants.

Installations are easy to build in individual farms in the form of special fermenters for fermentation of biomass. The main organic raw material for loading into the fermenter is manure.

At the first loading of cattle manure, the fermentation process should be at least 20 days, pig manure at least 30 days. You can get more gas when loading a mixture of various components compared to loading, for example, cattle manure.

For example, a mixture of cattle manure and poultry manure during processing produces up to 70% of methane in biogas.

After the fermentation process has stabilized, it is necessary to load raw materials every day no more than 10% of the amount of mass processed in the fermenter.

During fermentation, in addition to the production of gas, disinfection of organic substances occurs. Organic waste gets rid of pathogenic microflora, deodorization of unpleasant odors.

The resulting sludge must be periodically unloaded from the fermenter, it is used as a fertilizer.

When the biogas plant is first filled, the gas taken off does not burn, this happens because the first gas received contains a large amount of carbon dioxide, about 60%. Therefore, it must be released into the atmosphere, and after 1-3 days the operation of the biogas plant will stabilize.

Table No. 1 - the amount of gas obtained per day during the fermentation of the excrement of one animal

In terms of the amount of energy released, 1 m 3 of biogas is equivalent to:

• 1.5 kg of coal;
• 0.6 kg of kerosene;
• 2 kWh of electricity;
• 3.5 kg of firewood;
• 12 kg of manure briquettes.

Construction of small biogas plants

Figure 1 - Scheme of the simplest biogas plant with a pyramidal dome: 1 - manure pit; 2 - groove - water seal; 3 - bell for collecting gas; 4, 5 - branch pipe for gas removal; 6 - pressure gauge.

According to Figure 1, pit 1 and dome 3 are equipped with dimensions. The pit is lined with reinforced concrete slabs 10 cm thick, which are plastered with cement mortar and covered with resin for tightness. A bell 3 m high is welded from roofing iron, in the upper part of which biogas will accumulate. To protect against corrosion, the bell is periodically painted with two layers of oil paint. It is even better to pre-cover the bell from the inside with red lead. In the upper part of the bell, a fitting 4 is installed for biogas removal and a manometer 5 for measuring its pressure. The gas outlet pipe 6 can be made from a rubber hose, plastic or metal pipe.

Around the pit - the fermenter, a concrete groove is arranged - a water seal 2. filled with water, into which the lower side of the bell is immersed by 0.5 m.

Figure 2 - Device for condensate removal: 1 - pipeline for gas removal; 2 - U-shaped pipe for condensate; 3 - condensate.

Gas can be supplied, for example, to the stove through metal, plastic or rubber pipes. To prevent the tubes from freezing due to freezing of condensing water in winter, a simple device shown in Figure 2 is used: U - shaped tube 2 is connected to pipeline 1 at the lowest point. The height of its free part must be greater than the biogas pressure (in mm of water column). Condensate 3 drains through the free end of the tube, and there will be no gas leakage.

Figure 3 - Scheme of the simplest biogas plant with a conical dome: 1 - manure pit; 2 - dome (bell); 3 - extended part of the branch pipe; 4 - pipe for gas removal; 5 - groove - water seal.

In the installation shown in Figure 3, pit 1 with a diameter of 4 mm and a depth of 2 m is lined inside with roofing iron, the sheets of which are tightly welded. The inner surface of the welded tank is covered with resin for anti-corrosion protection. On the outer side of the upper edge of the concrete tank, an annular groove 5 up to 1 m deep is arranged, which is filled with water. It freely install the vertical part of the dome 2, closing the tank. Thus, the groove filled with water serves as a water seal. Biogas is collected in the upper part of the dome, from where it is fed through the outlet pipe 3 and further through the pipeline 4 (or hose) to the place of use.

About 12 cubic meters of organic matter (preferably fresh manure) is loaded into the round tank 1, which is filled with the liquid manure fraction (urine) without adding water. A week after filling, the fermenter starts to work. In this installation, the capacity of the fermenter is 12 cubic meters, which makes it possible to build it for 2-3 families whose houses are located nearby. Such an installation can be built in the backyard if the family raises, for example, bulls or contains several cows.

Figure 4 - Schemes of options for the simplest installations: 1 - supply of organic waste; 2 - container for organic waste; 3 - place of gas collection under the dome; 4 - branch pipe for gas removal; 5 - sludge removal; 6 - pressure gauge; 7 - a dome made of polyethylene film; 8 - water seal and; 9 - cargo; 10 - all-glued polyethylene bag.

Structural and technological schemes of the simplest small-sized installations are shown in Figure 4. The arrows indicate the technological movements of the initial organic mass, gas, and sludge. Structurally, the dome can be rigid or made of polyethylene film. A rigid dome can be made with a long cylindrical part for deep immersion in the processed mass, floating (Figure 4, d), or inserted into a hydraulic seal (Figure 4, e). , and. In the latest version, a weight 9 is placed on the film bag so that the bag does not swell too much, and also to form sufficient pressure under the film.

The gas that is collected under the dome or film is supplied through a gas pipeline to the place of use. To avoid a gas explosion, a valve adjusted to a certain pressure can be installed on the outlet pipe. However, the danger of a gas explosion is unlikely, since with a significant increase in gas pressure under the dome, the latter will be raised in the hydraulic seal to a critical height and overturn, releasing gas.

Biogas production can be reduced due to the fact that a crust forms on the surface of organic raw materials in the fermenter during its fermentation. In order for it not to interfere with the release of gas, it is broken by stirring the mass in the fermenter. You can mix not manually, but by attaching a metal fork from below to the dome. The dome rises in a hydraulic seal to a certain height when gas is accumulated and falls as it is used.

Due to the systematic movement of the dome from top to bottom, the forks connected to the dome will break the crust.

High humidity and the presence of hydrogen sulfide (up to 0.5%) contribute to increased corrosion of metal parts of biogas plants. Therefore, the condition of all metal elements of the fermenter is regularly monitored and the places of damage are carefully protected, best of all with red lead in one or two layers, and then painted in two layers with any oil paint.

Figure 5. Scheme of a biogas plant with heating: 1 - fermenter; 2 - wooden shield; 3 - filler neck; 4 - methane tank; 5 - stirrer; 6 - branch pipe for sampling biogas; 7 - heat-insulating layer; 8 - lattice; 9 - drain valve for processed mass; 10 - channel for air supply; 11 - blower.

Biogas plant with heating of the fermented mass with heat , released during the decomposition of manure, in an aerobic fermenter, is shown in Figure 5. It includes a methanetank - a cylindrical metal container with a filler neck 3. a drain valve 9. a mechanical agitator 5 and a biogas extraction pipe 6.

Fermenter 1 can be made rectangular and 3 wooden materials. To unload the treated manure, the juice walls are made removable. The floor of the fermenter is slatted, air is blown through the technological channel 10 from the blower 11. The top of the fermenter is covered with wooden shields 2. To reduce heat loss, the walls and bottom are made with a heat-insulating layer 7.

The setup works like this. Preliminarily prepared liquid manure with a moisture content of 88-92% is poured into the methane tank 4 through the golovin 3, the liquid level is determined by the lower part of the filler neck. Aerobic fermenter 1 through the upper opening part is filled with litter manure or a mixture of manure with loose dry organic filler (straw, sawdust) with a moisture content of 65-69%. When air is supplied through the technological channel in the fermenter, the organic mass begins to decompose and heat is released. It is enough to heat the contents of the methane tank. As a result, biogas is released. It accumulates in the upper part of the methanetank. Through the branch pipe 6 it is used for domestic needs. In the process of fermentation, the manure in the digester is mixed with a stirrer 5.

Such an installation will pay off in a year only due to the disposal of waste in a personal household. Approximate values ​​for biogas consumption are given in table 2.

Table No. 2 - approximate values ​​\u200b\u200bfor biogas consumption

Note: the unit can operate in any climate zone.

Figure 6 - Scheme of an individual biogas plant IBGU-1: 1 - filler neck; 2 - .mixer; 3 - branch pipe, for gas sampling; 4 - heat-insulating layer; 5 - branch pipe with a crane for unloading the processed mass; 6 - thermometer.

Individual biogas plant (IBGU-1) for a family with 2 to 6 cows or 20-60 pigs or 100-300 poultry (Figure 6). The unit can process from 100 to 300 kg of manure daily and produces 100-300 kg of environmentally friendly organic fertilizers and 3-12 m 3 of biogas.

Biogas is a gas obtained as a result of fermentation (fermentation) of organic substances (for example: straw; weeds; animal and human feces; garbage; organic waste from domestic and industrial waste water, etc.) under anaerobic conditions. Biogas production involves different types of microorganisms with a varied number of catabolic functions.

Composition of biogas.

Biogas consists of more than half of methane (CH 4). Methane makes up approximately 60% of biogas. In addition, biogas contains carbon dioxide (CO 2) about 35%, as well as other gases such as water vapor, hydrogen sulfide, carbon monoxide, nitrogen and others. Biogas obtained under different conditions is different in its composition. So biogas from human excrement, manure, slaughter waste contains up to 70% methane, and from plant residues, as a rule, about 55% methane.

Microbiology of biogas.

Biogas fermentation, depending on the microbial species of bacteria involved, can be divided into three stages:

The first is called the start of bacterial fermentation. Various organic bacteria, multiplying, secrete extracellular enzymes, the main role of which is the destruction of complex organic compounds with the hydrolysis formation of simple substances. For example, polysaccharides to monosaccharides; protein into peptides or amino acids; fats into glycerol and fatty acids.

The second stage is called hydrogen. Hydrogen is formed as a result of the activity of acetic acid bacteria. Their main role is to bacterially decompose acetic acid to form carbon dioxide and hydrogen.

The third stage is called methanogenic. It involves a type of bacteria known as methanogens. Their role is to use acetic acid, hydrogen and carbon dioxide to form methane.

Classification and characteristics of raw materials for biogas fermentation.

Almost all natural organic materials can be used as feedstock for biogas fermentation. The main raw materials for the production of biogas are wastewater: sewerage; food, pharmaceutical and chemical industries. In rural areas, this is the waste generated during harvesting. Due to differences in origin, the formation process, chemical composition and structure of biogas are also different.

Sources of raw materials for biogas depending on origin:

1. Agricultural raw materials.

These feedstocks can be divided into nitrogen-rich feedstocks and carbon-rich feedstocks.

Raw materials with a high nitrogen content:

human feces, livestock manure, bird droppings. The carbon-nitrogen ratio is 25:1 or less. Such raw material has been completely digested by the human or animal gastrointestinal tract. As a rule, it contains a large amount of low molecular weight compounds. Water in such raw materials was partially transformed and became part of low molecular weight compounds. This raw material is characterized by easy and fast anaerobic decomposition into biogas. As well as a rich yield of methane.

Raw materials with a high carbon content:

straw and husk. The carbon-nitrogen ratio is 40:1. It has a high content of macromolecular compounds: cellulose, hemicellulose, pectin, lignin, vegetable waxes. Anaerobic decomposition is rather slow. In order to increase the rate of gas production, such materials usually require pre-treatment before fermentation.

2. Urban organic water waste.

Includes human waste, sewage, organic waste, organic industrial wastewater, sludge.

3. Aquatic plants.

Includes water hyacinth, other aquatic plants and algae. Estimated planned load of production capacities is characterized by high dependence on solar energy. They have high returns. Technological organization requires a more careful approach. Anaerobic decomposition is easy. The methane cycle is short. The peculiarity of such raw materials is that without pre-treatment it floats in the reactor. In order to eliminate this, the raw material must be slightly dried or pre-composted within 2 days.

Sources of raw materials for biogas depending on humidity:

1. Solid raw material:

straw, organic waste with a relatively high dry matter content. Their processing takes place according to the method of dry fermentation. Difficulties arise with the removal of a large amount of solid deposits from the reactor. The total amount of feedstock used can be expressed as the sum of solids content (TS) and volatile matter (VS). Volatile substances can be converted to methane. To calculate volatile substances, a raw material sample is loaded into a muffle furnace at a temperature of 530-570°C.

2. Liquid raw material:

fresh faeces, manure, droppings. They contain about 20% dry matter. Additionally, they require the addition of water in an amount of 10% for mixing with solid raw materials during dry fermentation.

3. Organic waste of medium moisture:

bards of alcohol production, wastewater from pulp mills, etc. Such raw materials contain various amounts of proteins, fats and carbohydrates, and are a good raw material for biogas production. For this raw material, devices of the UASB type (Upflow Anaerobic Sludge Blanket - ascending anaerobic process) are used.

Table 1. Information about the debit (formation rate) of biogas for the following conditions: 1) fermentation temperature 30°C; 2) periodic fermentation

Name of fermented waste	Average biogas flow rate during normal gas production (m 3 /m 3 /d)	Biogas output, m 3 /Kg/TS	Biogas flow rate (in % of total biogas production)
			0-15d	25-45d	45-75d	75-135d
dry manure	0,20	0,12	11	33,8	20,9	34,3
Chemical industry water	0,40	0,16	83	17	0	0
Rogulnik (chilim, water chestnut)	0,38	0,20	23	45	32	0
water salad	0,40	0,20	23	62	15	0
Pig manure	0,30	0,22	20	31,8	26	22,2
Dry grass	0,20	0,21	13	11	43	33
Straw	0,35	0,23	9	50	16	25
human excrement	0,53	0,31	45	22	27,3	5,7

Calculation of the process of methane fermentation (fermentation).

The general principles of fermentation engineering calculations are based on increasing the loading of organic raw materials and reducing the duration of the methane cycle.

Calculation of raw materials per cycle.

The loading of raw materials is characterized by: Mass fraction TS (%), mass fraction VS (%), concentration COD (COD - chemical oxygen demand, which means COD - chemical index of oxygen) (Kg / m 3). The concentration depends on the type of fermentation devices. For example, modern industrial wastewater reactors are UASB (upstream anaerobic process). For solid feedstocks, AF (anaerobic filters) are used - typically less than 1%. Industrial waste as a feedstock for biogas is most often highly concentrated and needs to be diluted.

Download speed calculation.

To determine the daily amount of loading of the reactor: concentration COD (Kg/m 3 ·d), TS (Kg/m 3 ·d), VS (Kg/m 3 ·d). These indicators are important indicators for evaluating the effectiveness of biogas. It is necessary to strive to limit the load and at the same time have a high level of gas production.

Calculation of the ratio of reactor volume to gas output.

This indicator is an important indicator for evaluating the efficiency of the reactor. Measured in Kg/m 3 d.

Biogas output per unit mass of fermentation.

This indicator characterizes the current state of biogas production. For example, the volume of the gas collector is 3 m 3 . 10 Kg/TS is served daily. The biogas yield is 3/10 = 0.3 (m 3 /Kg/TS). Depending on the situation, the theoretical gas output or the actual gas output can be used.

The theoretical yield of biogas is determined by the formulas:

Methane production (E):

E = 0.37A + 0.49B + 1.04C.

Carbon dioxide production (D):

D = 0.37A + 0.49B + 0.36C. Where A is the carbohydrate content per gram of fermented material, B is protein, C is fat content

hydraulic volume.

To increase efficiency, it is necessary to reduce the fermentation time. To some extent, there is an association with the loss of fermenting microorganisms. Currently, some efficient reactors have a fermentation time of 12 days or even less. Hydraulic volume is calculated by counting the volume of daily feedstock loading from the day the feedstock loading began and depends on the residence time in the reactor. For example, a fermentation at 35° C., a feed concentration of 8% (total TS), a daily feed volume of 50 m 3 , a reactor fermentation period of 20 days is planned. The hydraulic volume will be: 50 20 \u003d 100 m 3.

Removal of organic contaminants.

Biogas production, like any biochemical production, has waste. Waste from biochemical production can harm the environment in cases of uncontrolled disposal of waste. For example, falling into the river next door. Modern large biogas plants produce thousands and even tens of thousands of kilograms of waste per day. The qualitative composition and ways of waste disposal of large biogas plants are controlled by the laboratories of enterprises and the state environmental service. Small farm biogas plants do not have such control for two reasons: 1) since there is little waste, there will be little harm to the environment. 2) Carrying out a qualitative analysis of waste requires specific laboratory equipment and highly specialized personnel. Small farmers do not have this, and government agencies rightly consider such control to be inappropriate.

An indicator of the level of contamination of waste from biogas reactors is COD (chemical index of oxygen).

The following mathematical relationship is used: COD organic loading rate Kg/m 3 ·d= COD loading concentration (Kg/m 3) / hydraulic storage time (d).

Gas flow rate in the reactor volume (kg/(m 3 d)) = biogas output (m 3 /kg) / COD organic loading rate kg/(m 3 d).

Advantages of biogas power plants:

solid and liquid wastes have a specific smell repelling flies and rodents;

the ability to produce a useful end product - methane, which is a clean and convenient fuel;

in the process of fermentation, weed seeds and some of the pathogens die;

during the fermentation process, nitrogen, phosphorus, potassium and other ingredients of the fertilizer are almost completely preserved, part of the organic nitrogen is converted into ammonia nitrogen, and this increases its value;

the fermentation residue can be used as animal feed;

biogas fermentation does not require the use of oxygen from the air;

anaerobic sludge can be stored for several months without the addition of nutrients, and then when the raw material is loaded, fermentation can quickly start again.

Disadvantages of biogas power plants:

a complex device and requires relatively large investments in construction;

a high level of construction, management and maintenance is required;

the initial anaerobic propagation of fermentation is slow.

Features of the methane fermentation process and process control:

1. Temperature of biogas production.

The temperature for producing biogas can be in a relatively wide temperature range of 4~65°C. With increasing temperature, the rate of biogas production increases, but not linearly. The temperature of 40~55°C is a transition zone for the vital activity of various microorganisms: thermophilic and mesophilic bacteria. The highest rate of anaerobic fermentation occurs in a narrow temperature range of 50~55°C. At a fermentation temperature of 10°C for 90 days, the gas flow rate is 59%, but the same flow rate at a fermentation temperature of 30°C occurs in 27 days.

A sudden change in temperature will have a significant impact on biogas production. The project of a biogas plant must necessarily provide for the control of such a parameter as temperature. Temperature changes of more than 5°C significantly reduce the performance of the biogas reactor. For example, if the temperature in the biogas reactor was 35°C for a long time and then suddenly dropped to 20°C, then the production of the biogas reactor would almost completely stop.

2. Grafting material.

To complete methane fermentation, a certain amount and type of microorganism is usually required. The sediment rich in methane microbes is called graft sediment. Biogas fermentation is widespread in nature, and places with inoculation material are also widespread. These are: sewage sludge, sludge, bottom sediments of manure pits, various sewage sludge, digestive residues, etc. Due to the abundant organic matter and good anaerobic conditions, they form rich microbial communities.

Seeding added for the first time to a new biogas reactor can significantly reduce the stagnation period. In a new biogas reactor, it is necessary to manually feed with inoculum. When using industrial waste as a raw material, special attention is paid to this.

3. Anaerobic environment.

Anaerobic environment is determined by the degree of anaerobicity. Usually, the redox potential is usually denoted by the value of Eh. Under anaerobic conditions, Eh has a negative value. For anaerobic methane bacteria, Eh lies within -300 ~ -350mV. Some bacteria producing facultative acids are able to live normal lives at Eh -100~+100mV.

In order to ensure anaerobic conditions, biogas reactors should be built tightly closed to ensure water tightness and no leakage. For large industrial biogas reactors, the value of Eh is always controlled. For small farm biogas reactors, there is a problem of controlling this value due to the need to purchase expensive and complex equipment.

4. Control of the acidity of the medium (pH) in the biogas reactor.

Methanogens need a pH range within a very narrow range. Average pH=7. Fermentation occurs in the pH range from 6.8 to 7.5. pH control is available for small scale biogas reactors. To do this, many farmers use disposable litmus indicator paper strips. In large enterprises, electronic pH control devices are often used. Under normal circumstances, the balance of methane fermentation is a natural process, usually without pH adjustment. Only in some cases of mismanagement appear massive accumulations of volatile acids, a decrease in pH.

Measures to mitigate the effects of increased pH acidity are:

(1) Replace part of the medium in the biogas reactor, and thereby dilute the content of volatile acids. This will increase the pH.

(2) Add ash or ammonia to raise the pH.

(3) Adjust pH with lime. This measure is especially effective for cases of ultra-high acid levels.

5. Mixing of the medium in a biogas reactor.

In a conventional fermentation tank, fermentation usually separates the medium into four layers: top crust, supernatant, active layer, and sludge layer.

Purpose of mixing:

1) relocation of active bacteria to a new portion of primary raw materials, increasing the contact surface of microbes and raw materials to accelerate the pace of biogas production, increasing the efficiency of using raw materials.

2) avoiding the formation of a thick layer of crust, which creates resistance to the release of biogas. Mixing is especially demanding for such raw materials as: straw, weeds, leaves, etc. In a thick layer of crust, conditions are created for the accumulation of acid, which is unacceptable.

Mixing methods:

1) mechanical mixing by wheels of various types installed inside the working space of the biogas reactor.

2) mixing with biogas taken from the upper part of the bioreactor and supplied to the lower part with excess pressure.

3) agitation by a circulating hydraulic pump.

6. Ratio of carbon to nitrogen.

Efficient fermentation is promoted only by the optimal ratio of nutrients. The main indicator is the ratio of carbon to nitrogen (C:N). The optimal ratio is 25:1. Numerous studies have shown that the optimal ratio limits are 20-30:1, and biogas production is significantly reduced at a ratio of 35:1. Experimental studies have shown that biogas fermentation is possible at a carbon to nitrogen ratio of 6:1.

7. Pressure.

Methane bacteria can adapt to high hydrostatic pressures (about 40 meters or more). But they are very sensitive to pressure changes and because of this there is a need for stable pressure (no sudden pressure drops). Significant pressure changes can occur in cases of: a significant increase in biogas consumption, a relatively fast and large loading of the bioreactor with primary raw materials, or a similar unloading of the reactor from deposits (cleaning).

Ways to stabilize pressure:

2) the supply of fresh primary raw materials and cleaning should be carried out simultaneously and at the same discharge rate;

3) the installation of floating covers on the biogas reactor allows you to maintain a relatively stable pressure.

8. Activators and inhibitors.

Some substances, after adding a small amount, improve the performance of the biogas reactor, such substances are known as activators. While other substances added in small amounts lead to a significant inhibition of processes in the biogas reactor, such substances are called inhibitors.

Many types of activators are known, including some enzymes, inorganic salts, organic and inorganic substances. For example, adding a certain amount of the cellulase enzyme greatly facilitates the production of biogas. The addition of 5 mg/Kg of higher oxides (R 2 O 5) can increase gas production by 17%. The biogas flow rate for primary raw materials from straw and the like can be significantly increased by the addition of ammonium bicarbonate (NH 4 HCO 3). Activators are also activated carbon or peat. Feeding hydrogen into the bioreactor can dramatically increase methane production.

Inhibitors mainly refers to some of the metal ion compounds, salts, fungicides.

Classification of fermentation processes.

Methane fermentation is strictly anaerobic fermentation. Fermentation processes are divided into the following types:

Classification by fermentation temperature.

Can be divided into "natural" temperature fermentation (variable temperature fermentation), in this case the fermentation temperature is about 35°C, and the high temperature fermentation process (about 53°C).

Classification by differentiality.

According to the differential fermentation can be divided into single-stage fermentation, two-stage fermentation and multi-stage fermentation.

1) Single-stage fermentation.

Refers to the most common type of fermentation. This applies to devices in which the production of acids and methane occurs simultaneously. Single-stage fermentation may be less efficient in terms of BOD (Biological Oxygen Demand) than two- and multi-stage fermentations.

2) Two-stage fermentation.

Based on separate fermentation of acids and methanogenic microorganisms. These two types of microbes have different physiology and nutritional requirements, there are significant differences in growth, metabolic characteristics and other aspects. Two-stage fermentation can greatly improve the biogas yield and volatile fatty acid decomposition, shorten the fermentation cycle, bring significant savings in operating costs, effectively remove organic pollution from waste.

3) Multistage fermentation.

It is used for primary raw materials rich in cellulose in the following sequence:

(1) Produce hydrolysis of cellulosic material in the presence of acids and alkalis. Glucose is produced.

(2) Apply the inoculum. This is usually active sludge or wastewater from a biogas reactor.

(3) Create suitable conditions for the production of acidic bacteria (producing volatile acids): pH=5.7 (but not more than 6.0), Eh=-240mV, temperature 22°C. At this stage, such volatile acids are formed: acetic, propionic, butyric, isobutyric.

(4) Create suitable conditions for the production of methane bacteria: pH=7.4-7.5, Eh=-330mV, temperature 36-37°C

Classification by periodicity.

Fermentation technology is classified into batch fermentation, continuous fermentation, semi-continuous fermentation.

1) Periodic fermentation.

Raw materials and grafting material are loaded into the biogas reactor at a time and subjected to fermentation. This method is used when there are difficulties and inconveniences in loading primary raw materials, as well as unloading waste. For example, not crushed straw or large-sized briquettes of organic waste.

2) Continuous fermentation.

This includes cases when, several times a day, raw materials are loaded into the bioreactor and fermentation effluents are removed.

3) Semi-continuous fermentation.

This applies to biogas reactors, for which it is considered normal to add different raw materials from time to time in unequal amounts. Such a technological scheme is most often used by small farms in China and is associated with the peculiarities of agricultural management. works. Biogas reactors for semi-continuous fermentation can have various design differences. These structures are discussed below.

Scheme No. 1. Biogas reactor with a fixed lid.

Design features: combination of a fermentation chamber and a biogas storage facility in one building: raw materials ferment in the lower part; biogas is stored in the upper part.

Operating principle:

Biogas emerges from the liquid and is collected under the cover of the biogas reactor in its dome. The biogas pressure is balanced by the weight of the liquid. The greater the gas pressure, the more liquid leaves the fermentation chamber. The lower the gas pressure, the more liquid enters the fermentation chamber. During the operation of a biogas reactor, there is always liquid and gas inside it. But in different proportions.

Scheme No. 2. Biogas reactor with floating lid.

Scheme No. 3. Biogas reactor with fixed lid and external gas tank.

Design features: 1) instead of a floating cover, it has a separately built gas tank; 2) biogas outlet pressure is constant.

Advantages of Scheme No. 3: 1) ideal for the operation of biogas burners that strictly require a certain pressure rating; 2) with low fermentation activity in the biogas reactor, it is possible to provide a stable and high biogas pressure to the consumer.

Guidelines for the construction of a domestic biogas reactor.

GB/T 4750-2002 Domestic biogas reactors.

GB/T 4751-2002 Quality assurance of domestic biogas reactors.

GB/T 4752-2002 Rules for the construction of domestic biogas reactors.

GB 175 -1999 Portland cement, ordinary Portland cement.

GB 134-1999 Portland slag cement, volcanic tuff cement and fly ash cement.

GB 50203-1998 Masonry construction and acceptance.

JGJ52-1992 Quality Standard for Ordinary Sand Concrete. Test methods.

JGJ53-1992 Quality standard for ordinary crushed stone or gravel concrete. Test methods.

JGJ81 -1985 Mechanical characteristics of ordinary concrete. Test method.

JGJ/T 23-1992 Technical Specification for Rebound Compressive Strength Testing of Concrete.

JGJ70 -90 Mortar. Test method for basic characteristics.

GB 5101-1998 Bricks.

GB 50164-92 Concrete quality control.

Airtight.

The design of the biogas reactor provides an internal pressure of 8000 (or 4000 Pa). The degree of leakage after 24 hours is less than 3%.

Unit of biogas production per reactor volume.

For satisfactory biogas production conditions, it is considered normal when 0.20-0.40 m 3 of biogas is produced per cubic meter of reactor volume.

The normal volume of gas storage is 50% of daily biogas production.

Safety factor not less than K=2,65.

The normal service life is at least 20 years.

Live load 2 kN/m 2 .

The value of the bearing capacity of the foundation structure is at least 50 kPa.

Gas tanks are designed for a pressure of not more than 8000 Pa, and with a floating cover for a pressure of not more than 4000 Pa.

The maximum pressure limit for the pool is not more than 12000 Pa.

The minimum thickness of the arched arch of the reactor is not less than 250 mm.

The maximum loading of the reactor is 90% of its volume.

The design of the reactor provides for the presence of a place under the reactor cover for gas flotation, which is 50% of the daily production of biogas.

The volume of the reactor is 6 m 3 , the gas flow rate is 0.20 m 3 /m 3 /d.

It is possible to build reactors with a volume of 4 m 3 , 8 m 3 , 10 m 3 according to these drawings. For this, it is necessary to use the correction dimensional values ​​indicated in the table in the drawings.

Preparations for the construction of a biogas reactor.

The choice of the type of biogas reactor depends on the quantity and characteristics of the fermented feedstock. In addition, the choice depends on local hydrogeological and climatic conditions and the level of construction technology.

The household biogas reactor should be located near toilets and livestock rooms at a distance of no more than 25 meters. The location of the biogas reactor should be downwind and sunny on solid ground with a low level of groundwater.

To select the design of the biogas reactor, use the building material consumption tables below.

Table3. Material Scale for Precast Concrete Panel Biogas Reactor

		Reactor volume, m 3
		4	6	8	10
	Volume, m 3	1,828	2,148	2,508	2,956
	Cement, kg	523	614	717	845
	Sand, m 3	0,725	0,852	0,995	1,172
	Gravel, m 3	1,579	1,856	2,167	2,553
	Volume, m 3	0,393	0,489	0,551	0,658
	Cement, kg	158	197	222	265
	Sand, m 3	0,371	0,461	0,519	0,620
cement paste	Cement, kg	78	93	103	120
Total amount of material	Cement, kg	759	904	1042	1230
	Sand, m 3	1,096	1,313	1,514	1,792
	Gravel, m 3	1,579	1,856	2,167	2,553

Table4. Material Scale for Precast Concrete Biogas Reactor

		Reactor volume, m 3
		4	6	8	10
	Volume, m 3	1,540	1,840	2,104	2,384
	Cement, kg	471	561	691	789
	Sand, m 3	0,863	0,990	1,120	1,260
	Gravel, m 3	1,413	1,690	1,900	2,170
Plastering of the prefabricated body	Volume, m 3	0,393	0,489	0,551	0,658
	Cement, kg	158	197	222	265
	Sand, m 3	0,371	0,461	0,519	0,620
cement paste	Cement, kg	78	93	103	120
Total amount of material	Cement, kg	707	851	1016	1174
	Sand, m 3	1,234	1,451	1,639	1,880
	Gravel, m 3	1,413	1,690	1,900	2,170
Steel materials	Steel bar diameter 12 mm, kg	14	18,98	20,98	23,00
	Steel reinforcement diameter 6.5 mm, kg	10	13,55	14,00	15,00

Table5. Scale of materials for a biogas reactor made of cast concrete

		Reactor volume, m 3
		4	6	8	10
	Volume, m 3	1,257	1,635	2,017	2,239
	Cement, kg	350	455	561	623
	Sand, m 3	0,622	0,809	0,997	1,107
	Gravel, m 3	0,959	1,250	1,510	1,710
Plastering of the prefabricated body	Volume, m 3	0,277	0,347	0,400	0,508
	Cement, kg	113	142	163	208
	Sand, m 3	0,259	0,324	0,374	0,475
cement paste	Cement, kg	6	7	9	11
Total amount of material	Cement, kg	469	604	733	842
	Sand, m 3	0,881	1,133	1,371	1,582
	Gravel, m 3	0,959	1,250	1,540	1,710

Table6. Symbols on the drawings.

Description	Designation on the drawings
Materials:
Shtruba (trench in the ground)
Symbols:
Link to part drawing. The top number indicates the part number. The lower number indicates the drawing number with the detailed description of the part. If a “-” sign is indicated instead of the lower number, then this indicates that a detailed description of the part is presented in this drawing.
Detail cut. Bold lines indicate the plane of the cut and the direction of view, and the numbers indicate the identification number of the cut.
The arrow indicates the radius. The numbers after the letter R indicate the value of the radius.
Common:
Accordingly, the semi-major axis and the short axis of the ellipsoid
Length

Designs of biogas reactors.

Peculiarities:

The type of design feature of the main pool.

The bottom has a slope from the inlet window to the outlet window. This ensures the formation of a constant moving stream. Drawings No. 1-9 show three types of biogas reactor structures: type A, type B, type C.

Biogas reactor type A: The most simple arrangement. Removal of the liquid substance is provided only through the outlet window by the biogas pressure force inside the fermentation chamber.

Biogas reactor type B: The main basin is equipped with a vertical pipe in the center, through which, during operation, the supply or removal of liquid substance can be carried out, depending on the need. In addition, to form a flow of substance through a vertical pipe, this type of biogas reactor has a reflective (deflector) baffle at the bottom of the main pool.

Type C Biogas Reactor: It has a similar design to the Type B reactor. However, it is equipped with a simple piston hand pump installed in the central vertical pipe, as well as other baffles at the bottom of the main pool. These design features allow you to effectively control the parameters of the main technological processes in the main pool due to the simplicity of express tests. And also use the biogas reactor as a donor of biogas bacteria. In a reactor of this type, diffusion (mixing) of the substrate occurs more completely, which in turn increases the yield of biogas.

Fermentation characteristics:

The process consists in the selection of grafting material; preparation of primary raw materials (adjustment of density with water, adjustment of acidity, introduction of grafting material); fermentation (control of substrate mixing and temperature).

Human feces, livestock manure, bird droppings are used as fermentation material. With a continuous digestion process, relatively stable conditions for the efficient operation of a biogas reactor are created.

Design principles.

Compliance with the "triune" system (biogas, toilet, barn). The biogas reactor is a vertical cylindrical tank. The height of the cylindrical part is H=1 m. The upper part of the tank has an arched vault. The ratio of the height of the vault to the diameter of the cylindrical part f 1 /D=1/5. The bottom has an inclination from the inlet window to the outlet window. Tilt angle 5 degrees.

The design of the tank ensures satisfactory fermentation conditions. The movement of the substrate occurs by gravity. The system operates at full capacity of the tank and controls itself by the residence time of the raw materials by increasing the production of biogas. Biogas reactors types B and C have additional devices for processing the substrate.

The loading of the tank with raw materials may not be complete. This reduces the gas capacity without sacrificing efficiency.

Low cost, easy operation, wide distribution.

Description of building materials.

The material of the walls, bottom, arch of the biogas reactor is concrete.

Square sections, such as a feed channel, can be made of brick. Concrete structures can be made by pouring a concrete mixture, but can be made from precast concrete elements (such as: inlet window cover, bacteria cage, center pipe). The bacteria tank is round in cross section and consists of a broken eggshell placed in a braid.

Sequence of construction operations.

The formwork casting method is as follows. On the ground, the outline of the future biogas reactor is being marked. Soil is removed. The bottom is poured first. A formwork is installed at the bottom for pouring concrete around the ring. The walls are poured using formwork and then the arched vault. Formwork can be steel, wood or brick. Filling is carried out symmetrically and tamping devices are used for strength. Excess flowing concrete is removed with a spatula.

Construction drawings.

Construction is carried out according to drawings No. 1-9.

Drawing 1. Biogas reactor 6 m 3 . Type A:

Drawing 2. Biogas reactor 6 m 3 . Type A:

The construction of biogas reactors from precast concrete slabs is a more advanced construction technology. This technology is more perfect due to the ease of implementation of dimensional accuracy, reducing the time and cost of construction. The main feature of the construction is that the main elements of the reactor (arched roof, walls, channels, covers) are manufactured far from the installation site, then they are transported to the installation site and assembled on site in a large pit. When assembling such a reactor, the focus is on matching the accuracy of the installation horizontally and vertically, as well as the density of butt joints.

Drawing 13. Biogas reactor 6 m 3 . Details of biogas reactor made of reinforced concrete slabs:

Drawing 14. Biogas reactor 6 m 3 . Biogas reactor assembly elements:

Drawing 15. Biogas reactor 6 m 3 . Reinforced concrete reactor assembly elements:

Rising energy prices make us think about the possibility of self-sufficiency. One option is a biogas plant. With its help, biogas is obtained from manure, litter and plant residues, which, after cleaning, can be used for gas appliances (stove, boiler), pumped into cylinders and used as fuel for cars or electric generators. In general, the processing of manure into biogas can provide all the energy needs of a home or farm.

Building a biogas plant is a way to provide energy resources independently

General principles

Biogas is a product that is obtained from the decomposition of organic matter. In the process of decay / fermentation, gases are released, by collecting which you can meet the needs of your own household. The equipment in which this process takes place 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 the decomposition of waste occurs, which is accompanied by gas formation.

There are three modes of 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, a lot of gas is formed, its quality is low.
• Mesophilic. The unit enters this mode at temperatures from +30°C to +40°C. In this case, mesophilic bacteria actively multiply. In this case, more gas is formed, the processing process takes less time - from 10 to 20 days.
• Thermophilic. These bacteria multiply at temperatures above +50°C. The process is the fastest (3-5 days), the gas yield is the largest (under ideal conditions, up to 4.5 liters of gas can be obtained from 1 kg of delivery). Most reference tables for gas yield from processing are given specifically for this mode, so when using other modes, it is worth making a downward adjustment.

The most difficult thing in biogas plants is the thermophilic regime. This requires high-quality thermal insulation of a 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 reloading. The remaining two modes - psychophilic and mesophilic - allow you to add a fresh portion of prepared raw materials daily. But, in the thermophilic mode, a short processing time makes it possible to divide the bioreactor into zones in which its share of raw materials with different loading times will be processed.

Scheme of a biogas plant

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

For mesophilic and thermophilic regimes, a bioreactor heating system is also required to reach the required regimes. For this, gas-fired boilers are usually used. From it, the pipeline system goes to the bioreactor. Usually these are polymer pipes, as they best tolerate being in an aggressive environment.

Another biogas plant needs a system for mixing the substance. During fermentation, a hard crust forms at the top, heavy particles settle down. All this together worsens the process of gas formation. To maintain a homogeneous state of the processed mass, agitators are necessary. They can be mechanical or even manual. 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.

Biogas plant by type of location can be:

• Overhead.
• Semi-submerged.
• Buried.

More expensive to install buried - a large amount of land work is required. But when operating in our conditions, they are better - it is easier to organize insulation, less heating costs.

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, chemicals negatively affect the process. It is desirable to minimize their intake, as they kill the flora that is involved in processing.

Cattle manure is considered ideal, as it contains microorganisms in large quantities. If there are no cows in the farm, when loading the bioreactor, it is desirable to add some of the litter to populate the substrate with the required microflora. Plant residues are pre-crushed, diluted with water. In the bioreactor, vegetable raw materials and excrement are mixed. Such a “refueling” takes longer to process, but at the exit, with the right mode, we have the highest product yield.

Location determination

To minimize the cost of organizing the process, it makes sense to locate a biogas plant near the source of waste - near buildings where birds or animals are kept. It is desirable to develop a design so that loading occurs by gravity. From a cowshed or pigsty, a pipeline can be laid under a slope, through which manure will flow by gravity into the bunker. This greatly simplifies the task of maintaining the reactor, and cleaning up manure too.

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

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

Bioreactor

Quite stringent requirements are imposed on the manure processing tank:

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

What materials can be made

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

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

An excellent option is the capacity of a polymer bioreactor. Plastic is chemically neutral, does not rot, does not rust. Only it is necessary to choose from such materials that endure freezing and heating to sufficiently high temperatures. The walls of the reactor should be thick, preferably reinforced with fiberglass. Such containers are not cheap, but they last a long time.

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

Reactor sizing

The volume of the reactor depends on the selected temperature for processing manure into biogas. Most often, mesophilic is chosen - it is easier to maintain and it implies the possibility of daily additional loading of the reactor. Biogas production after reaching the normal mode (about 2 days) is stable, without bursts and 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 the average data.

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 volume of the tank - gas should accumulate under the ceiling.

For example, the farm has 5 cows, 10 pigs and 40 chickens. As a matter of fact, 5 * 55 kg + 10 * 4.5 kg + 40 * 0.17 kg = 275 kg + 45 kg + 6.8 kg = 326.8 kg are formed. To bring chicken manure to a moisture content of 85%, you need to add a little more than 5 liters of water (that's another 5 kg). The total mass is 331.8 kg. For processing in 20 days it is necessary: ​​331.8 kg * 20 \u003d 6636 kg - about 7 cubes 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 volume of the biogas plant reactor.

Loading and unloading hatches lead directly to 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.

With the buried installation method of the biogas plant, 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 are only open for loading or unloading.

Since the manure may contain large fragments (bedding elements, grass stalks, etc.), small diameter pipes will often become clogged. Therefore, for loading and unloading, they must be 20-30 cm in diameter. They must be installed before the start of work on the insulation of 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 pre-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 desirable to calculate the installation depth of the receiving hopper so that the 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 damper will block it off during the preparation.

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

Collection and disposal of biogas

The removal of biogas from the reactor occurs 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. More pure biogas comes out into it. A shut-off gas valve is installed at the outlet of their bioreactor. The best option is ball.

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 with soap suds. The entire pipeline is assembled from pipes and fittings of the same diameter. No contractions or expansions.

Purification of impurities

The approximate composition of the resulting biogas is as follows:

• 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 have no smell 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 the gas starts to burn worse, it's time to change it).

Gas dehydration can be done in two ways - by making hydraulic seals in the gas pipeline - by inserting curved sections under the hydraulic seals into the pipe, in which condensate will accumulate. The disadvantage of this method is the need for regular emptying of the water seal - with a large amount of collected water, it can block the passage of gas.

The second way is to put a filter with silica gel. The principle is the same as in the water seal - the gas is fed into the silica gel, dried out from under the cover. With this method of drying biogas, silica gel has to be dried periodically. To do this, it needs to be warmed up for some time in the microwave. It heats up, the moisture evaporates. You can fall asleep and use again.

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

Gas holder and compressor

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

To create a stable pressure in the system after the compressor, it is desirable 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 the generated gas;
• equalizes the temperature of the liquid, excluding warmer and colder areas;
• maintains the homogeneity of the substrate, preventing the settling or surfacing of some constituents.

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

The second way is to mix the liquid by passing through it part of the generated gas. To do this, after leaving the metatank, a tee is placed and part of the gas is poured 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 mixing method is to pump the substrate from the lower part with the help of fecal pumps, pour it out at the top. The disadvantage of this method is the dependence on the availability of electricity.

Heating system and thermal insulation

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

What to heat and where to place

Heat is used for best results. The most rational is water heating from the boiler. The boiler can operate on electricity, solid or liquid fuel, it can also be run on the generated biogas. The maximum temperature to which water must be heated is +60°C. Hotter pipes can cause particles to adhere to the surface, resulting in reduced heating efficiency.

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

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

To reduce the possibility of deposition of particles on the heating elements, they are placed in the stirrer zone. Only in this case it is necessary to design everything so that the mixer cannot touch the pipes. It often seems that it is better to place the heaters from below, but practice has shown that due to sediment at the bottom, such heating is inefficient. So it is more rational to place the heaters on the walls of the metatank of the biogas plant.

Water heating methods

According to the way the pipes are located, heating can be external or internal. When located indoors, heating is efficient, but repair and maintenance of heaters is impossible without shutting down and pumping out the system. Therefore, special attention is paid to the selection of materials and the quality of the connections.

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

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

How to insulate

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

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

Of modern materials, you can use high-density extruded polystyrene foam, low-density aerated concrete blocks,. The most technologically advanced in this case is polyurethane foam (PPU), but the services for its application are not cheap. But it turns out seamless thermal insulation, which minimizes heating costs. There is another heat-insulating material - foamed glass. In plates, it is very expensive, but its battle or crumb costs quite a bit, and in terms of characteristics it is almost perfect: it does not absorb moisture, is not afraid of freezing, tolerates static loads well, and has low thermal conductivity.

Biogas production technology. Modern livestock complexes provide high production rates. The applied technological solutions allow to fully comply with the requirements of the current sanitary and hygienic standards in the premises of the complexes themselves.

However, large amounts of liquid manure concentrated in one place create significant environmental problems for the territories 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, the requirements of the legislation on these issues are constantly tightened.

Biocomplex offers a comprehensive solution for the disposal of liquid manure, which includes accelerated processing in modern biogas plants (BGU). In the process of processing, in an accelerated mode, natural processes of decomposition of organic matter proceed 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-generating (cogeneration) installations that produce electrical and thermal energy.

Biogas - combustible gas, formed during anaerobic methane digestion 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 activity of the 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 - hydrolytic bacteria, the second - acid-forming, the third - methane-forming.

Both organic agro-industrial or household waste, and vegetable raw materials can be used as raw materials for the production of biogas.

The most common types of agro-industrial complex waste used for biogas production are:

• pig and cattle manure, poultry droppings;
• leftovers from the feed table of cattle complexes;
• tops of vegetable crops;
• substandard crop of cereals and vegetables, sugar beet, corn;
• pulp and molasses;
• flour, pellet, fine grain, embryos;
• beer grains, malt sprouts, protein sludge;
• waste of starch-treacle production;
• pomace fruit and vegetable;
• serum;
• etc.

Raw material source	Type of raw material	Quantity of raw materials per year, m3 (tons)	Amount of biogas, m3
1 cash cow	Bedless liquid manure
1 fattening pig	Bedless liquid manure
1 fattening bull	Bedding solid manure
1 horse	Bedding solid manure
100 chickens	Dry litter
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 for biogas production 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:

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

The most common way of energy use of biogas is combustion in gas piston engines as part of a mini-CHP, with the production of 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 a number of 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 total biogas yield. In the case of using several substrates that differ in properties, for example, liquid and solid waste, their accumulation, preliminary preparation (separation into fractions, grinding, heating, homogenization, biochemical or biological treatment, etc.) is carried out separately, after which they are either mixed before feed into bioreactors, or are fed in separate streams.

The main structural elements of a typical biogas plant layout are:

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

BGU technological schemes vary depending on the type and number of processed substrates, on the type and quality of the final target products, on one or another “know-how” of the technological solution supplier used, 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 an increase in the overall efficiency of using the working volume of bioreactors.

Feature 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 substrate mixture that has a high content of organic matter, and at the same time can be pumped. This is a substrate with a solids content of 10-12%. The solution is achieved by separating excess moisture using screw separators.

Liquid manure enters the tank from the production facilities, is homogenized with a submersible mixer, and is fed by a submersible pump to the separation shop for screw separators. The liquid fraction is collected 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 loader of the solid raw material is turned on. Alternatively, the liquid fraction can be fed into a solid feeder with a mixing function, and then the finished mixture is fed into the fermenter according to the developed loading program. Inclusions are short. This is done to prevent excessive input of organic substrate into the fermenter, as this can upset the balance of substances and cause destabilization of the process in the fermenter. At the same time, pumps are also switched on, pumping the digestate from the fermenter to the after-fermenter and from the after-fermenter into the digestate accumulator (lagoon), in order to prevent overfilling of the fermenter and after-fermenter.

The digestate masses located in the fermenter and after-fermenter are mixed to ensure an even distribution of bacteria throughout the volume of the containers. For mixing, low-speed mixers of a special design are used.

In the process of finding the substrate in the fermenter, bacteria release up to 80% of the total biogas produced by the biogas plant. The rest of the biogas is released in the conditioner.

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

The accumulation of biogas is carried out in a gas holder, which is formed between the surface of the digestate and the elastic high-strength material covering the fermenter and the fermenter from above. The material has the ability to stretch strongly (without reducing strength), which significantly increases the capacity of the gas tank with the accumulation of biogas. To prevent overfilling of the gas tank and rupture of the material, there is a safety valve.

The biogas then enters the cogeneration plant. A cogeneration plant (CHP) is a unit in which electrical energy is generated by generators driven by gas piston engines running on biogas. Cogenerators running on biogas have structural differences from conventional gas generator engines, since biogas is a very depleted fuel. The electrical energy generated by the generators provides power to the electrical equipment of the biogas plant itself, and everything in excess of this is released to nearby consumers. The energy of the liquid used to cool the cogenerators is the generated thermal energy minus the losses in the boiler devices. The generated thermal energy is partly used to heat fermenters and after-fermenters, and the rest is also sent to nearby consumers. goes to

It is possible to install additional equipment for cleaning biogas to the level of natural gas, however, this equipment is expensive and is used only if the purpose of the biogas plant is not to produce heat and electricity, but to produce fuel for gas piston engines. The proven and most commonly used biogas treatment technologies are water absorption, pressurized carrier adsorption, chemical precipitation and membrane separation.

The energy efficiency of biogas plant operation largely depends both on the chosen technology, materials and design of the main structures, and on the climatic conditions in the area of ​​their location. The average consumption of thermal energy for heating bioreactors in the temperate climate zone is 15-30% of the energy generated by cogenerators (gross).

The overall energy efficiency of a biogas complex with biogas-fired CHP is 75-80% on average. In a situation where all the heat received from a cogeneration plant in the production of electricity cannot be consumed (a common situation due to the lack of external heat consumers), it is discharged 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, operating practices, and the tasks performed by each individual installation.

The process of manure processing is 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 the 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 is applied to the solid fraction, then it will be suitable for long-term storage and transportation over long distances.

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

1. Renewable energy source (RES). Renewable biomass is used to produce biogas.
2. A wide range of raw materials used for biogas production makes it possible to build biogas plants virtually everywhere in areas of concentration of agricultural production and technologically related industries.
3. The versatility of biogas energy use methods both for the production of electrical and / or thermal energy at the place of its formation, and at any facility connected to the gas transmission 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, such as solar and wind power plants.
5. Creation of jobs through the formation of a market chain from biomass suppliers to the operating personnel of energy facilities.
6. Reducing the negative impact on the environment through the processing and neutralization of waste through controlled digestion in biogas reactors. Biogas technologies are one of the main and most rational ways of neutralizing organic waste. Biogas projects help reduce greenhouse gas emissions into the atmosphere.
7. The agrotechnical effect of the use of the mass fermented in biogas reactors on agricultural fields is manifested in improving the structure of soils, regenerating and increasing their fertility due to the introduction of nutrients of organic origin. The development of the market for organic fertilizers, including from the mass processed in biogas reactors, in the future will contribute to the development of the market for environmentally friendly agricultural products and increase its competitiveness.

Estimated unit investment costs

BSU 75 kWel. ~ 9.000 €/kWh.

BSU 150 kWel. ~ 6.500 €/kWh.

BSU 250 kWel. ~ 6.000 €/kWh.

BSU bis 500 kWel. ~ 4.500 €/kWh.

BGU 1 MWtel. ~ 3.500 €/kWh.

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