What is biogas and how to make a biogas plant with your own hands

A thrifty owner dreams of cheap energy resources, efficient waste disposal and obtaining fertilizers. A DIY home biogas plant is an inexpensive way to make your dream come true.

Self-assembly of such equipment will cost a reasonable amount of money, and the gas produced will be a good help in the household: it can be used for cooking, heating the house and other needs.

Let's try to understand the specifics of this equipment, its advantages and disadvantages. And also whether it is possible to build a biogas plant yourself and whether it will be effective.

Description and properties of biogas

Biogas is formed during anaerobic (without air) methane digestion of biomass . The mixture contains up to 55–75% methane, 25–45% carbon dioxide , varying amounts sulfide , nitrogen oxides, ammonia and other compounds.
the components included :

• methane is explosive and extremely flammable, colorless and odorless, its consumer properties are associated with a large release of heat during combustion;
• carbon dioxide (carbon dioxide) when inhaled causes loss of attention and fatigue, reducing the level of oxygen saturation in the blood;
• hydrogen sulfide in the concentration that occurs in the finished product is not subject to explosion, but is toxic to the human body;
• ammonia smells unpleasant, but is rarely produced in installations in dangerous quantities that can damage the mucous membranes of the eyes and respiratory system.

Physical properties:

• energy reserve 5–6.5 kW/h per cubic meter;
• calorific value up to 7500 kcal/m³;
• ignition temperature - 680–750°C;
• pressure in the reactor from 0.05 atm.

The spread of parameters is determined by the different composition of the raw material, the selection of processing technology and climatic conditions during the reaction.

Raw materials for biogas production

A biogas plant for a private home uses a wide variety of agricultural waste as raw materials. The biogas station processes:

• manure of any fraction, bird droppings;
• plant residues - weeds, straw, silage;
• pulp and pulp;
• beer bard;
• substandard grain crops;
• fishery waste;
• molasses of various origins;
• remains of a slaughterhouse;
• fat;
• root vegetables that have lost their nutritional value.

The exact amount of biofuel for each type of feedstock depends on the processing technology.

Extraction methods

The raw materials go through a preparation stage so that the fermentation process is more active and productive.

of manure : natural and self-floating. The first type is taken from under the animal along with the bedding. The self-fusing type is removed from the farm by a stream of water.

Pulp and pulp are crushed parts of vegetables, fruits and root vegetables, from which the juice is squeezed.

Grape pulp

Beet pulp

Beer stillage and molasses, a by-product of breweries and sugar factories, are a valuable food additive, so the feasibility of using them to produce gas is determined by the cost of the product.

Molasses

Beer still

Plant residues are cut or ensiled.

Corn silage

How long is it enough?

The approximate gas yield from different substrates is compiled in a table.

The following table contains data on the amount of raw materials that can be obtained from animals and from one hectare of arable land.

The data presented in the tables cannot serve as the basis for accurate calculations; the indicators are averaged for the industry.

Efficiency

The benefits of biogas are assessed by the advantages of its use and the output of thermal or electrical energy .

Pros and cons of biogas production

Energy is obtained from renewable natural sources

Use a wide range of raw materials

The versatility of biogas to produce heat or electricity

Environmentally friendly processing

Waste disposal and use of waste biomass to increase the fertility of agricultural land and improve soil structure

Production on an industrial scale does not always pay off

The efficiency indicator depends on the amount of methane in the mixture, which can contain 45–75%. On average, when burning 1 m³ of biogas, taking into account losses and generator efficiency, you can get 1.5–2 kW/electricity.

Comparison with other energy sources

In terms of consumer properties, biogas can be compared with other energy sources: natural and liquefied gas, compressed methane.

What can be recycled

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

How much biogas can be obtained from various wastes?

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

Operating principle of a biogas plant

The biochemical principles underlying gas production technology are based on the life activity of three groups of bacteria . Hydrolytic, acid-forming and methane-forming are used .
During multi-level processing, the final product is produced - a gaseous combustible mixture. In practice, two types of biofuel production have become widespread: “dry” and “wet”.

Wet

The method is most widespread, as it is suitable for the production of biofuels from raw materials with a high moisture content . This is how gas is obtained from manure.

The raw materials are saturated with water to 90% humidity. Self-floating manure (removed from farms by water flows) is ready for processing. In industrial installations, the substance is supplied to the reactors by screw conveyors or fecal pumps. The tank is insulated, and the biomass is constantly mixed in it.

As decomposition proceeds, a gas mixture is produced, which is discharged into the storage tank. The sulfur content is reduced by special bacteria that colonize the walls of the tank. After cleaning, the fuel enters the cogeneration department, where electricity is generated by gas piston generators. In other station options, gas is brought by compressors to the required operating pressure and enters the distribution network.

Part of the energy is taken to heat the biomass in the reactor to 41–43°C.

The sediment is removed as it accumulates.

In domestic models, there is no cogeneration system; all gas is used for heat production. Loading and unloading of the reactor is carried out manually.

Dry

Allows you to obtain gas from raw materials with low humidity. Dilution of the substrate with water is not provided, and fermentation occurs at 50% humidity in the reaction zone.

As fermentation proceeds, the liquid fraction is collected in the drainage system and, using circulation pumps, is sprayed over a semi-dry substrate. There is no stirring or turning over, which reduces energy costs for production.

Fermentation takes place at a temperature of 34–37°C. External heating is minimal; heat is released during chemical reactions of organic raw materials.

Both methods can be used when operating a self-built biogas plant.

Use as fertilizer

In addition to producing gas, the bioreactor is useful because the waste is used as a valuable fertilizer, which retains almost all nitrogen and phosphates. When manure is added to the soil, 30–40% of nitrogen is irretrievably lost.

To reduce the loss of nitrogen substances, fresh excrement is added to the soil, but then the released methane damages the root system of plants. After processing the manure, the methane is used for its own needs, and all nutrients are preserved.

After fermentation, potassium and phosphorus pass into a chelated form, which is absorbed by plants by 90%. Generally speaking, 1 ton of fermented manure can replace 70 - 80 tons of regular animal excrement.

Anaerobic processing preserves all the nitrogen present in manure, converting it into ammonium form, which increases the yield of any crop by 20%.

This substance is not dangerous for the root system and can be applied 2 weeks before planting crops in open ground, so that the organic matter has time to be processed by soil aerobic microorganisms.

Before use, the biofertilizer is diluted with water in a ratio of 1:60. Both dry and liquid fractions are suitable for this, which after fermentation also goes into the waste raw material tank.

Per hectare you need from 700 to 1,000 kg/l of undiluted fertilizer. Considering that from one cubic meter of reactor area up to 40 kg of fertilizers are obtained per day, in a month you can provide not only your own plot, but also your neighbor’s, by selling organic matter.

What nutrients can be obtained after manure processing?

The main value of fermented manure as a fertilizer is the presence of humic acids, which, like a shell, retain potassium and phosphorus ions. Oxidizing in air during long-term storage, microelements lose their beneficial qualities, but during anaerobic processing, on the contrary, they gain.

Humates have a positive effect on the physical and chemical composition of the soil. As a result of adding organic matter, even the heaviest soils become more permeable to moisture. In addition, organic matter provides food for soil bacteria. They further process the residues that have not been eaten by anaerobes and release humic acids. As a result of this process, plants receive nutrients that are completely absorbed.

In addition to the main ones - nitrogen, potassium and phosphorus - the biofertilizer contains microelements. But their quantity depends on the source material - plant or animal origin.

Scope of application

The goals of processing differ between large industries and private farms.

For a private home

In private households, as a rule, there is not enough organic waste to provide heating for a residential building. However, the manure of one cow and a couple of pigs is enough to produce gas for heating animal housing and for feed preparation . Gas infrared burners are used for combustion.

The fermented mass is distributed throughout the garden or household plot.

For farming

On a farm, the resulting gas will be enough to heat all the premises with gas boilers , which are safer than burners and can operate around the clock.

The cost of factory installations with an electricity generator approaches 1 million rubles, so they are rarely purchased.

Processing manure into a fermented mass is beneficial for the farmer, as it reduces the cost of delivering the resulting fertilizer to the fields.

For enterprise

Large agricultural enterprises receive raw materials for biogas plants all year round.

The resulting biogas is used to generate electricity and fuel for boiler houses. The waste is granulated and distributed over arable land. Some enterprises produce liquid fertilizers, which are sold in small containers of 5 liters or more.

At the same time as obtaining gas, agricultural holdings are solving the problem of disposing of manure and bird droppings.

Methods for heating a bioreactor

Microorganisms that process the substrate are constantly present in the biomass, but for their intensive reproduction they need a temperature of 38 degrees or higher.

For heating during cold periods, you can use a coil connected to the home heating system or electric heaters. The first method is more economical, so it is used more often.

The biogas plant does not have to be buried in the ground; there are other options for arrangement. An example of the operation of a system assembled from barrels is shown in the video below.

The easiest way to arrange heating from below is to lay a pipe from the heating system, but the efficiency of such a heat exchanger is relatively low. It is better to arrange external heating, ideally steam, so that the biomass does not overheat

DIY biogas station

If there is a lack of experience in building complex engineering systems, they try to adhere to the principle: the simpler the design, the more reliable and durable it is . Instructions for making a biogas production plant with your own hands include several steps :

• design taking into account the amount of available raw materials and productivity;
• selection and preparation of equipment placement;
• procurement of devices, components, assemblies;
• installation of the container;
• connection of auxiliary equipment;
• gas pipeline installation;
• start-up, setup and adjustment.

After a successful start-up, the identified deficiencies are eliminated and the system is put into operation at full load.

Design

Homemade simple biogas plants are not highly efficient due to the fact that the reactions take place in an inappropriate mode.
Based on this, it is assumed that one cubic meter of fermentation tank releases an amount of gas sufficient to heat 10 m² of housing . Thus, to heat a country house with an area of ​​50 m², you will need a 5 m³ tank.

Loading and unloading of raw materials in home installations is carried out simultaneously, approximately once every 15–25 days , depending on consumption. Getting into working mode may take up to 5 days.

During this time, the house is heated by other means or a reservoir of 1–2 m³ is built.

Location

The location for the fermentation tank is selected based on several conditions:

• convenience of delivery of raw materials and waste disposal;
• safe storage of raw materials and waste away from housing;
• minimal costs for connecting utility networks.

The correctly chosen location should be conveniently located taking into account the infrastructure of the site.

Materials for making a bioreactor

The basis of a biogas station in private farms is a bunker . The following is used as a reservoir:

• concrete or brick bunker;
• plastic and fiberglass sealed containers;
• polyethylene, polypropylene and polyvinyl chloride hoses;
• steel barrels, cubes, columns.

Reactor requirements:

• waterproof;
• sufficient strength to withstand the mass of the wet substrate and the current soil pressure;
• ease of maintenance;
• resistance to aggressive environments.

To manufacture the raw material supply system, plastic pipes , which are used in sewers. To drain gas to the gas tank, it is more profitable to use HDPE pipes - they are connected without using gas welding.

Gas collection and removal system

At the highest point of the fermentation bunker, a pipe for exhaust gas is inserted . If possible, the pipe is installed in the air, but protected from the sun. Provide a small 1-2% increase. In this case, the outlet is a refrigerator and condensate settles on the inner walls and flows into the tank.

A branch leading to the gas tank storage is connected to the outlet pipe.

In small stations, gas tanks are made of reinforced polymer film.

Cleansing from impurities

To operate domestic hot water boilers or cookers, purified gas is required.

At home, cleaning and drying is carried out by passing fuel through a container with a water seal . Another way is to use housings from household water filters with silica gel poured into them. The second filter is filled with metal filings or sponges - this is reliable protection against excess sulfur.

Mixing equipment

Factory-made electric mixers with complex gearboxes are rarely used in do-it-yourself biogas plants because of their high price and electricity costs.

Other methods are used:

• mixing by hand;
• periodic switching on of fecal pumps pumping the liquid fraction from the bottom to the surface;
• using a compressor, which pumps gas from under the tank lid into the substrate, the bottom layers move.

There is no need to do round-the-clock mixing; to automate the switching process, pumps, compressors or mixers are connected through timers of suitable power.

Heating and thermal insulation

The fermentation reaction actively occurs at temperatures from 34 to 43°C. None of the known methods for producing biogas can maintain such parameters independently year-round. Even in the southernmost regions, external heating and high-quality insulation .

Heat preservation methods:

• deepening the reactor into the ground while simultaneously insulating the walls;
• insulation of the external bunker with modern materials - polystyrene foam, expanded polystyrene, stone wool, foil foam insulation.

Sometimes the equipment is installed in outbuildings or pavilions made of wood or polycarbonate are erected around the reactors. Heating is carried out by electric heating elements or by starting a boiler, which consumes part of the generated gas.

When the substrate temperature drops below 30°C, fermentation can take up to 30 days or stop completely.

Autonomous gasification - gas holder

In recent years, a solution to the problem of energy supply for a country house has appeared on the market of gas equipment for domestic use. This is autonomous gasification. And first of all, we are talking about installing gas tanks or gas holders. The principle of using a gas tank is to periodically fill its volume with liquefied natural gas. Today there are many companies offering services for delivering LNG by specialized tank trucks and filling the gas into the tank. Depending on the volume, you can forget about its maintenance for 3-6 months, and use household gas appliances to the fullest, without thinking about economical consumption.

Non-conventional energy sources include biogas, which is produced in special installations and used to produce various types of energy used by humans in everyday life (heat, electricity and fuel for cars).

Approximate cost calculation

Before you begin designing an installation, you must carefully calculate all upcoming costs. In some cases - harsh climate, small amount of available raw materials - it is more profitable to refuse construction.

Biogas production costs

A home mini-station will cost about 50 thousand rubles.
The costs of biogas production consist of the cost of equipment, installation and maintenance costs of installations . If purchased raw materials are used, their cost and delivery costs are taken into account.

The installation itself is purchased from a factory or made independently . Factory products are installed, configured and maintained by specialized organizations. For some models you will have to purchase consumables - fermentation activators or bacteria.

During operation, costs consist of electricity costs for mixing the substrate and heating the reactor.

Cost of a ready-made and home-made biogas plant

A farm installation will cost several hundred thousand rubles.
The industry produces biogas plants for farms. The volume of the bioreactor varies from 0.5 to 30 m³ . A ready-made system with a 1m³ , for example, BUG-M, containing all the necessary components, costs about 180 thousand rubles . Installations for farms with a herd of 12 heads of cattle or 1000 heads of poultry will cost 2 million rubles.

Few farms can afford the purchase of such equipment, so they prefer to make the installation themselves.

Home generators can cost from 50 thousand rubles , which allows you to significantly save on the purchase.

Average prices

Currently, biogas plants are manufactured by a number of domestic and foreign companies.

The most popular among various user groups are the following models:

• Mini biogas plant BUG-M, made in Russia. The installation includes equipment with a capacity of 1.0 m3 (100 l) of processed raw materials and an output of the finished product in the form of biogas in a volume of 1.0 m3/day and fertilizer - 100 l/day. The cost of the kit is from 170,000.00 rubles.
• Biogas plant “BioMash-20”, made in Russia.

The volume of processed raw materials is 700.0 kg/day, while the yield of the finished product is:

1. Electrical energy – up to 20.0 kW/hour;
2. Thermal energy – up to 2.4 Gcal/day. This model can be used on livestock farms housing up to 12 heads of cattle, 250 pigs or up to 1200 birds of various species. The cost of a set of equipment is from 2,000,000.00 rubles.

• Biogas complexes of various capacities, Rucons Gobal UG (Germany). All equipment is made of stainless steel and installed in separate technological modules (fermentation, mixing, fermentation, automation and control, etc.). The cost of the kit, depending on performance, is from 2,500,000.00 rubles.

Reactor for a large farm

A simple bioreactor design is suitable for small farms with 1-2 animals. If you own a farm, it is best to install an industrial reactor that can handle large volumes of fuel. It is best to involve special companies involved in developing the project and installing the system.

Membrane bioreactor

Industrial complexes consist of:

• Interim storage tanks;
• Mixing installations;
• Bioreactor;
• A small thermal power plant that provides energy for heating buildings and greenhouses, as well as electricity;
• Containers for fermented manure used as fertilizer.

The most effective option is to build one complex for several neighboring farms. The more biomaterial is processed, the more energy is produced as a result.

Before receiving biogas, industrial installations must be approved by the sanitary and epidemiological station, fire and gas inspection. They are documented; there are special standards for the location of all elements.

Correct gas removal

Biogas from the manure is removed through the top cover of the reactor. It must be tightly closed during the fermentation process. Typically a water seal is used. It controls the pressure in the system; when it increases, the lid rises and the release valve is activated. A weight is used as a counterweight. At the outlet, the gas is purified with water and flows further through the tubes. Purification with water is necessary to remove water vapor from the gas, otherwise it will not burn.

Before biogas can be processed into energy, it must be accumulated. It should be stored in a gas tank:

• It is made in the shape of a dome and installed at the outlet of the reactor.
• Most often it is made of iron and coated with several layers of paint to prevent corrosion.
• In industrial complexes, the gas tank is a separate tank.

Another option for making a gas holder: use a PVC bag. This elastic material stretches as the bag fills. If necessary, it can store large quantities of biogas.

Fireplace for gas heating at home

In terms of equipment costs, gas fireplaces are comparable to their electric or wood-burning counterparts. But gas fuel is much cheaper.

And, unlike firewood, gas heating using a fireplace in a country house means there are no problems with ash. Plus, you don’t have to constantly monitor the operation of the firebox and worry about chopping logs.

Fireplaces that convert gas into thermal energy are used in heating systems because... are not equipped with the devices necessary to service two circuits

According to the type of installation, gas fireplaces are:

• wall;
• island;
• built-in

In terms of their general design and internal contents (burners, automation, design of combustion chambers), they completely replicate gas boilers. In both cases, the technology for connecting to networks is identical. Differences exist only in the principle of heating the premises.

According to the principle of connecting and organizing the heating system, gas fireplaces are similar to floor-standing heating boilers

A hot water boiler is initially designed to heat water, and a regular fireplace is designed to convect air from the body and front screen, behind which fuel combustion occurs.

Legal registration

The installation will have to be coordinated with the SES, gas inspectorate and firefighters. You will need:

• Technological diagram of the installation.
• Layout plan for equipment and components with reference to the installation itself, the installation location of the thermal unit, the location of pipelines and energy mains, and pump connections. The diagram should indicate the lightning rod and access roads.
• If the installation will be located indoors, then a ventilation plan will also be required, which will provide at least an eightfold exchange of all the air in the room.

As we see, we cannot do without bureaucracy here.

Having a source of energy is a sin not to use it

Finally, a little about the performance of the installation. On average, per day a biogas plant produces a volume of gas twice the useful volume of the reservoir. That is, 40 m3 of slurry will produce 80 m3 of gas per day. Approximately 30% will be spent on ensuring the process itself (the main expense item is heating). Those. at the output you will receive 56 m3 of biogas per day. According to statistics, to cover the needs of a family of three and to heat an average-sized house, 10 m3 is required. In net balance you have 46 m3 per day. And this is with a small installation.

Advantages of biodiesel over petroleum diesel

Biodiesel does not pollute the planet.

If we are talking about buying ready-made fuel, then from an economic point of view, ordinary diesel fuel, which is made from oil, will be more profitable, since it is cheaper. If you make biodiesel at home from purchased oil, it is also expensive. The only option when it is profitable to produce biofuel is to have your own oil. If this is not the case, buy regular diesel fuel and heat it with it.

Strengths of using biofuels to heat your home:

• it is much safer to store energy reserves - the ignition temperature is 100 degrees, while ordinary diesel fuel ignites at 60 degrees;
• biodiesel does not pollute nature, minimal sulfur content;
• Biodiesel emits little carbon dioxide.

The fact that it is safer to store biofuels is good, but not everything is ideal here either. After three months, biodiesel begins to break down into its component parts, and this imposes some restrictions.

General characteristics of methane

Methane is a light, colorless, odorless, flammable gas. Distributed in nature as the main component of natural gas and associated petroleum gases. Chemical formula - .

Methane enters the atmosphere as part of volcanic gases, and is also a product of the vital activity of a number of microorganisms. It is found in significant quantities in the form of gas hydrates on the ocean floor and in permafrost. It is one of the most important greenhouse gases.

As a representative of a number of saturated hydrocarbons, it exhibits low chemical activity. Due to its low solubility in water and chemical inertness, methane is considered a low-toxic substance (hazard class IV), but at high concentrations in the air (4.4 - 17%) it is explosive, and a further increase in methane content leads to suffocation from lack of oxygen.

Physical properties

The main physical characteristics of methane at normal atmospheric pressure are given in the table.

How to ensure biomass activity

For proper fermentation of biomass, it is best to heat the mixture. In the southern regions, the air temperature promotes the onset of fermentation. If you live in the north or in the middle zone, you can connect additional heating elements.

To start the process, a temperature of 38 degrees is required. There are several ways to ensure this:

• A coil under the reactor connected to the heating system;
• Heating elements inside the container;
• Direct heating of the container with electric heating devices.

The biological mass already contains bacteria that are needed to produce biogas. They wake up and begin activity when the air temperature rises.

It is best to heat them with automatic heating systems. They turn on when cold mass enters the reactor and automatically turn off when the temperature reaches the desired value. Such systems are installed in water heating boilers; they can be purchased at gas equipment stores.

If you provide heating to 30-40 degrees, then processing will take 12-30 days. It depends on the composition and volume of the mass. When heated to 50 degrees, bacterial activity increases, and processing takes 3-7 days. The disadvantage of such installations is the high cost of maintaining high temperatures. They are comparable to the amount of fuel received, so the system becomes ineffective.

Another way to activate anaerobic bacteria is by stirring the biomass. You can install the shafts in the boiler yourself and move the handle out to stir the mass if necessary. But it is much more convenient to design an automatic system that will mix the mass without your participation.

Insulation layer

After manufacturing the bioreactor, it can be immediately filled with raw materials. The biomass must be covered with film. This is necessary to ensure low gas pressure during the fermentation process.

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Once the dome is made, this ensures that biogas flows efficiently through the system.