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

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.

Methane in organic synthesis

Methane is widely used to produce many sought-after compounds such as acetylene, methanol or aniline.

Production of acetylene from methane

In laboratory practice, methane dehydrogenation is carried out. The reaction requires high heat:

The following methods are used in industry:

• Electrocracking:

• Oxidative pyrolysis (Sachse process):

This reaction uses the heat of partial combustion of the raw material, due to which the reaction mixture is heated to 1600 ℃.

Producing methanol from methane

Methyl alcohol can be obtained:

• Catalytic oxidation of methane:

• A two-step process in which a methane chloride is first produced, which is then subjected to alkaline hydrolysis:

Obtaining aniline from methane

The aromatic compound aniline is produced in several stages:

1. Methane cracking:
2. Trimerization of acetylene:

3. Nitration of benzene:

4. Reduction of nitrobenzene:

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.

Uniqueness

Our production uses an innovative approach to producing biofuel: first, the raw material (algae biomass) for its production is synthesized, then the oil is pressed, from which biodiesel fuel is produced using proven technology. This fundamentally new approach to producing biofuel from non-food raw materials has a number of advantages compared to the production of bioenergy from vegetable oils. The main advantage of such production is its independence from the yield of oilseeds and their cost (rapeseed and other oils used as the main raw material for the production of biodiesel), the price of which increases with the increase in biofuel production.

Consumer

We plan to work according to the B2B scheme and, ideally, we will sell the full volume of biodiesel production to one interested company. These companies may include companies involved in:

· rail and road transportation

· oil sales

· agro-industrial companies

Organization

The commercial organization ZAO BioEnergoRoss is aimed at producing biodiesel fuel. The management team is also the founders of the organization. The investor will be given a portion of the company's shares corresponding to the invested funds.

Marketing

Goods

produces the main product - biodiesel, and two by-products - glycerin and a food additive for cattle and pigs (algae cake).

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.

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.

How to heat a bioreactor?

The design of the biogas plant assumes its underground location. It is necessary to prepare a hole of the required volume. Its walls can be hermetically reinforced and finished with plastic, polymer rings or concrete.

The intensity of raw material processing depends on tightness. Ideally, you should purchase factory-made polymer rings that have a dry bottom. This is a more expensive solution, but additional sealing can be avoided.

Polymer materials are resistant to humidity and aggressive environments. They do not need to be repaired, and if damaged they can be quickly replaced.

Therefore, the bioreactor needs to be heated, especially in winter. You can install a coil connected to a domestic heating system.

Another way is to install electric heating elements. But, a more economically feasible solution is to connect to the heating system.

The biogas plant does not need to be underground. There are alternative methods. For example, it can be done in a barrel, which will be located in a separate room.

You can also use, for example, a tank. This option will simplify heating, but requires sufficient space.

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.

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.