Many household owners are concerned about how to reduce costs for home heating, cooking and electricity supply. Some of them have already built biogas plants with their own hands and have partially or completely isolated themselves from energy suppliers. It turns out that getting almost free fuel in a private household is not very difficult.
What is biogas and how can it be used?
Owners of homestead farms know: by putting any plant material, bird droppings and manure in a heap, over time you can obtain valuable organic fertilizer. But few of them know that biomass does not decompose on its own, but under the influence of various bacteria.
By processing the biological substrate, these tiny microorganisms release waste products, including a gas mixture. Most of it (about 70%) is methane - the same gas that burns in the burners of household stoves and heating boilers.
The idea of using such eco-fuels for various economic needs is not new. Devices for its extraction were used in ancient China. Soviet innovators also explored the possibility of using biogas in the 60s of the last century. But the technology experienced a real revival in the early 2000s. Currently, biogas plants are actively used in Europe and the USA for heating homes and other needs.
How does a biogas plant work?
The operating principle of the biogas production device is quite simple:
- Biomass diluted with water is loaded into a sealed container, where it begins to “ferment” and release gases;
- the contents of the tank are regularly updated - the raw materials processed by bacteria are drained and fresh ones are added (on average about 5-10% daily);
- The gas accumulated in the upper part of the tank is supplied through a special tube to the gas collector, and then to household appliances.
Diagram of a biogas plant.
What raw materials are suitable for bioreactor?
Installations for producing biogas are profitable only where there is a daily replenishment of fresh organic matter - manure or droppings of livestock and poultry. You can also add chopped grass, tops, leaves and household waste (in particular, vegetable peelings) into the bioreactor.
The efficiency of the installation largely depends on the type of raw material being loaded. It has been proven that, with the same mass, the highest biogas yield is obtained from pig manure and turkey droppings. In turn, cow excrement and silage waste produce less gas for the same load.
Use of bio-raw materials for home heating.
What cannot be used in a biogas plant?
There are factors that can significantly reduce the activity of anaerobic bacteria, or even completely stop the process of biogas production. Raw materials containing:
- antibiotics;
- mold;
- synthetic detergents, solvents and other “chemicals”;
- resins (including sawdust from coniferous trees).
It is ineffective to use already rotting manure - only fresh or pre-dried waste can be loaded. Also, the raw materials should not be allowed to become waterlogged - an indicator of 95% is already considered critical. However, a small amount of clean water still needs to be added to the biomass in order to facilitate its loading and speed up the fermentation process. Manure and waste are diluted to the consistency of thin semolina porridge.
Biogas plant for home
Today, industry is already producing installations for producing biogas on an industrial scale. Their acquisition and installation is expensive; such equipment in private households pays for itself no sooner than in 7-10 years, provided that large volumes of organic matter are used for processing. Experience shows that, if desired, a skilled owner can build a small biogas plant for a private home with his own hands, and from the most affordable materials.
Preparing the processing bunker
First of all, you will need a hermetically sealed cylindrical container. You can, of course, use large pots or boils, but their small volume will not allow achieving sufficient gas production. Therefore, for these purposes, plastic barrels with a volume of 1 m³ to 10 m³ are most often used.
You can make one yourself. PVC sheets are commercially available; with sufficient strength and resistance to aggressive environments, they can be easily welded into the structure of the desired configuration. A metal barrel of sufficient volume can also be used as a bunker. True, you will have to carry out anti-corrosion measures - cover it inside and outside with moisture-resistant paint. If the tank is made of stainless steel, this is not necessary.
Gas exhaust system
The gas outlet pipe is mounted in the upper part of the barrel (usually in the lid) - this is where it accumulates, according to the laws of physics. Through a connected pipe, biogas is supplied to the water seal, then to the storage tank (optionally, using a compressor into a cylinder) and to household appliances. It is also recommended to install a release valve next to the gas outlet - if the pressure inside the tank becomes too high, it will release excess gas.
Raw material supply and unloading system
To ensure continuous production of the gas mixture, the bacteria in the substrate must be constantly (daily) “fed”, that is, fresh manure or other organic matter must be added. In turn, already processed raw materials from the bunker must be removed so that they do not take up useful space in the bioreactor.
To do this, two holes are made in the barrel - one (for unloading) almost near the bottom, the other (for loading) higher. Pipes with a diameter of at least 300 mm are welded (soldered, glued) into them. The loading pipeline is directed upward and equipped with a funnel, and the drain is arranged so that it is convenient to collect the processed slurry (it can later be used as fertilizer). The joints are sealed.
Heating system
Thermal insulation of the bunker.
If the bioreactor is installed outdoors or in an unheated room (which is necessary for safety reasons), then it must be provided with thermal insulation and heating of the substrate. The first condition is achieved by “wrapping” the barrel with any insulating material or by deepening it into the ground.
As for heating, you can consider a variety of options. Some craftsmen install pipes inside through which water circulates from the heating system and install them along the walls of the barrel in the form of a coil. Others place the reactor in a larger tank with water inside, heated by electric heaters. The first option is more convenient and much more economical.
To optimize the operation of the reactor, it is necessary to maintain the temperature of its contents at a certain level (at least 38⁰C). But if it rises above 55⁰C, then the gas-forming bacteria will simply “cook” and the fermentation process will stop.
Mixing system
As practice shows, in designs, a manual stirrer of any configuration significantly increases the efficiency of the bioreactor. The axis to which the “mixer” blades are welded (screwed) is removed through the barrel lid. The gate handle is then placed on it, and the hole is carefully sealed. However, home craftsmen do not always equip fermenters with such devices.
Biogas production
After the installation is ready, biomass diluted with water in a ratio of approximately 2:3 is loaded into it. Large waste must be crushed - the maximum fraction size should not exceed 10 mm. Then the lid is closed - all you have to do is wait for the mixture to begin to “ferment” and release biogas. Under optimal conditions, the first supply of fuel is observed several days after loading.
The fact that the gas has “started” can be judged by the characteristic gurgling sound in the water seal. At the same time, the barrel should be checked for leaks. This is done using a regular soap solution - it is applied to all joints and observed to see if bubbles appear.
The first update of bio-raw materials should be carried out in about two weeks. After the biomass is poured into the funnel, the same volume of waste organic matter will pour out of the outlet pipe. Then this procedure is performed daily or every two days.
How long does the resulting biogas last?
In a small farm, a biogas plant will not be an absolute alternative to natural gas and other available energy sources. For example, using a device with a capacity of 1 m³, you can only get fuel for a couple of hours of cooking for a small family.
But with a 5 m³ bioreactor it is already possible to heat a room with an area of 50 m², but its operation will need to be maintained by daily loading of raw materials weighing at least 300 kg. To do this, you need to have about ten pigs, five cows and a couple of dozen chickens on the farm.
Craftsmen who have managed to independently make working biogas plants share videos with master classes on the Internet:
Of course, DIY biogas is not for everyone. First, you must be the owner of a private home. A homemade installation has dimensions and installation options for which the apartment conditions are absolutely not suitable. Secondly, at home it is possible only if there is a large amount of organic waste. And thirdly, perhaps most importantly, you need knowledge.
There is no point in inventing an installation - everything has already been invented a long time ago. But in order to implement a ready-made idea using ready-made drawings, this must be understood. A tool, ingenuity, understanding and awareness of the design of the device, and also a desire that will allow you not to deviate from the intended goal - this is all very important.
Let's summarize:
- Place. Only private courtyards with areas up to 10 m2 free from buildings and trees. It is also worth considering such options when it is possible in the future to construct a building of a commercial or even residential type above the installation itself.
- Material. Stainless steel, brick, concrete, pipes (metal and/or plastic) - these are the basics. Let's add tools to this list: welding equipment, concrete mixers, metal-cutting tools.
- Raw materials. The main source of biogas can only be organic matter - manure, plant waste, slaughterhouse waste. Each type of raw material produces its own amount of biogas of a certain quality. In any case, there must be enough raw materials to increase profitability.
- Understanding and awareness of the idea. It’s possible without this: invited, paid, received – why understanding? But even the most primitive installation designed for small-scale biogas production is expensive, and the whole point is to get everything you need based on your own strength. So here you have to be a bearer of the unspoken title of “folk craftsman”.
Many European farmers have long switched to this alternative type of fuel. The payback period for a biogenerator is 3-5 years, it all depends on the scale of consumption. For example, Danish owners of mini-farms, with livestock numbers of only 50-100 heads, manage to produce biogas with their own installations, which fully satisfies the needs of both the residential building and the farm itself. Comfort at home and on the farm, thanks to their own biogas, is perceived as something ordinary.
How it works
In the entire biological installation, almost every element is important:
- A reservoir is a container in which fermentation of biomass occurs due to the action of bacteria. The tank, of different sizes and made of different materials, serves as a kind of pan. It would be more correct to call it a bioreactor. This complex structure must not only accommodate biomass for fermentation, but also have such qualities as reliability and durability. A biogas production plant is not a reusable building. You need to do it once and only improve the design, otherwise profitability will drop below zero.
- Connecting elements that must not bleed gas. Methane is an explosive gas and an accidental spark can lead to disastrous consequences.
- Raw material mass mixing system. It is quite difficult to make in artisanal conditions, but highly desirable. Regular mixing improves productivity.
- Reactor insulation system. Reliable and high-quality insulation allows you to maintain the required temperature inside the reactor. Bacteria can survive at low temperatures, but they are not viable. And although the temperature inside will always be above zero, it must be able to be maintained and controlled.
- Gas holder is a container for temporary (until consumption) gas storage. In artisanal conditions it is represented by a steel tank.
- Filtration system or filtration system. It is advisable to clean the gas resulting from fermentation from CO2.
The raw materials entering the bioreactor begin to ferment. The gas released is not pure. It contains a proportion of methane (up to 80-90%), carbon dioxide (up to 20-30%), hydrogen (up to 5-10%). Periodic stirring promotes the frequency of gas release. The gas enters the gas tank, then through the filtration system, and then to the consumed unit (boiler, furnace, etc.).
Basic moments
Biogas can be obtained at home in different volumes and different qualities. This is influenced by several factors:
- Quantity of raw materials. For continuous operation of the bioreactor, biomass must be periodically fed inside. The feeding frequency depends on the size of the reactor. High performance is achieved by filling the container to 75%. A lower figure reduces production efficiency, as does a load above 75%.
- Origin of raw materials. Manure or corn pulp - the difference is significant. Usually they start from the presence of one or another type of raw material. For example, a huge amount of high-quality methane can be obtained from animal fats - up to 1500 m3 from a ton of raw materials. At the same time, the methane content will also be the maximum possible - up to 90%. The production of biogas from algae has lower figures - up to 250-300 m3 per ton.
- Frequency of raw material supply. Fermentation must be completed almost completely, the released water must be drained, unfermented residues must be disposed of, and only then can a new supply of a certain amount be possible. In artisanal conditions, this process is quite difficult to control. Industrial installations are more progressive and the entire process is controlled automatically.
- Combination of raw materials. Some types of biomass can complement each other, acting as catalysts for chemical processes inside the reactor. Some, on the contrary, are able to slow down the reaction. For example, grain stillage in combination with manure gives good results as a result of the combination. Whereas fats are not combined with almost any other type of raw material.
The table shows the volume of gas produced (in m3) from one ton of raw material:
How to use
Biogas can be used at home based on its quantity and quality. Usually this is heating of outbuildings or a residential building. For small volumes of gas there may be only enough to heat water, but in this case the profitability of the installation needs to be reconsidered. Some craftsmen have pushed their designs to enormous levels of productivity and completely forgotten about the consumption of government electricity and natural gas.
In any case, through an installation for producing biogas, several positive aspects are realized both for the gas consumer and for all of humanity as a whole:
- transition to low-cost production,
- saving money,
- partial waste disposal,
- preventing global warming.
Humanity has made a giant leap forward, learning to control nature and everyday life. Biogas, as an alternative fuel and form of energy, has now become possible to obtain at home. Of course, the high cost of the equipment is somewhat daunting, but payback calculations show that a bioreactor at home is a profitable and expedient solution.
Owners of private houses located in regions with limited access to traditional fuels should definitely turn their attention to modern biogas plants. Such units make it possible to obtain biogas from a variety of organic waste and use it for personal needs, including heating residential premises.
Gas can be obtained from almost any biomass - waste from the livestock industry, food production, agriculture, foliage, etc. At the same time, you can build such an installation with your own hands.
Both homogeneous raw materials and mixtures of various biomass are suitable for producing biogas. A biogas plant is a volumetric sealed structure equipped with devices for supplying raw materials, heating biomass, mixing components, discharging the resulting biogas into a gas collector and, of course, protecting the structure.
In the reactor, under the influence of anaerobic bacteria, rapid decomposition of biomass occurs. During the fermentation of organic raw materials, biogas is released. Approximately 70% of the composition of such gas is represented by methane, the remaining part is carbon dioxide.
Biogas is characterized by excellent calorific value; it has no distinct odor or color. In terms of its properties, biogas is practically in no way inferior to more traditional natural gas.
In developed countries, additional installations are used to purify biogas from carbon dioxide. If you wish, you can buy the same installation and obtain pure biomethane.
Biogas plants on silos. 1 Silo pits. 2 Biomass loading system. 3 Reactor. 4 Post-fermentation reactor. 5 Substrater. 6 Heating system. 7 Power plant. 8 Automation and control system. 9 Gas pipeline system
Comparison of biogas with more traditional fuels
On average, one cow or other animal weighing half a ton is capable of producing enough manure per day to produce approximately 1.5 m3 of biogas. Daily manure from one average pig can be processed into 0.2 m3 of biogas, and a rabbit or chicken into 0.01-0.02 m3 of fuel.
For comparison: 1 m3 of biogas from manure provides approximately the same amount of thermal energy as 3.5 kg of firewood, 1-2 kg of coal, 9-10 kW/h of electricity.
The simplest recipe for a mixture for producing biogas includes the following components:
- cow manure - about 1500 kg;
- rotted leaves or other organic waste – 3500 kg;
- water – 65-75% of the total mass of the previous components. The water must first be heated to about 35 degrees.
This amount of biomass will be enough to produce biogas for six months of operation with moderate consumption. On average, biogas begins to be released within 1.5-2 weeks after the mixture is loaded into the installation.
Gas can be used to heat a home and a variety of commercial and domestic buildings.
Design of a typical biogas plant
The main components of a complete biogas system are:
- reactor;
- humus supply system;
- stirrers;
- automated biomass heating system;
- gas holder;
- separator;
- protective part.
A household installation will have a somewhat simplified design, however, for a complete understanding, you are invited to read the description of all the listed elements.
Reactor
This part of the installation is usually assembled from stainless steel or concrete. Externally, the reactor looks like a large sealed container, on top of which is a dome, usually spherical in shape.
Currently, the most popular are reactors with a collapsible design, made using innovative technologies. Such a reactor can be easily assembled with your own hands with minimal time investment. If necessary, it can be easily disassembled and transported to another location.
Steel is convenient because you can easily create holes in it to connect other elements of the system. Concrete is superior to steel in terms of strength and durability.
Biomass feeding system
This part of the installation includes a hopper for receiving waste, a supply pipeline for water supply and a screw pump designed to send humus to the reactor.
A front loader is used to load the dry component into the hopper. At home, you can cope with this task without a loader, using various improvised means, for example, shovels.
In the hopper the mixture is moistened to a semi-liquid state. After reaching the desired level of moisture, the screw transfers the semi-liquid mass to the lower compartment of the reactor.
Stirrers
Fermentation of humus in the reactor should occur evenly. This is one of the most important conditions for ensuring intensive release of biogas from the mixture. It is to achieve the most uniform fermentation process of the mixture that the design of a typical biogas plant includes mixers with electric drives.
There are submersible and inclined type mixers. Submersible mechanisms can be lowered into the biomass to the required depth to ensure intensive and uniform mixing of the substrate. Usually such mixers are placed on a mast.
Installation of inclined mixers is carried out on the side surfaces of the reactor. An electric motor is responsible for rotating the screw in the fermenter.
Automated heating system
To successfully produce biogas, the temperature inside the system must be maintained at +35-+40 degrees. For this purpose, automated heating systems are included in the design.
The heat source in this case is a hot water boiler; in some situations, electric heating units are used.
Biogas is collected in this structural element. Most often, the gas holder is placed on the roof of the reactor.
The production of modern gas tanks is usually carried out using polyvinyl chloride, a material that is resistant to sunlight and various adverse natural phenomena.
In some situations, instead of a regular gas tank, special bags are used. Also, these devices allow you to temporarily increase the volume of the produced biogas.
To make a gas holder bag, a special polyvinyl chloride with elastic properties is used, which can inflate as the volume of biogas increases.
This part of the system is responsible for drying waste humus and obtaining, if necessary, high-quality fertilizers.
The simplest separator consists of a screw and a separator chamber. The chamber is made in the form of a sieve. This allows the biomass to be separated into a solid component and a liquid part.
The dried humus is sent to the shipping compartment. The system directs the liquid part back to the receiving chamber. Here the liquid is used to moisten the new feedstock.
The simplest DIY biogas plant
A household biogas installation will have a somewhat simplified design, but its manufacture should be approached with maximum responsibility.
First step. Dig a hole. At its core, a biogas plant is a large pit with a special finish. The most important and at the same time difficult part of manufacturing the system in question is the correct preparation of the walls of the bioreactor and its base.
The pit must be sealed. Strengthen the base and walls with plastic or concrete. Instead, you can purchase ready-made polymer rings with a solid bottom. Such devices make it possible to ensure the necessary tightness of the system. The material will retain its original characteristics for many years, and if necessary, you can easily replace the old ring with a new one.
Second step. Install a gas drainage system. This will save you from the need to purchase and install agitators, due to which the time and money spent on assembling the installation will be significantly reduced.
The simplest version of a gas drainage system is vertically fixed sewer pipes made of polyvinyl chloride with many holes throughout the body.
Select pipes of such length that their upper edges rise slightly above the upper level of the loaded humus.
Third step. Cover the outer layer of the substrate with film insulation. Thanks to the film, conditions will be created for the accumulation of biogas under the dome under conditions of slight excess pressure.
Fourth step. Install the dome and mount the gas exhaust pipe at its highest point.
Gas consumption should be regular. Otherwise, the dome over the biomass container may simply explode. In summer, gas is formed more intensively than in winter. To solve the latter problem, purchase and install suitable heaters.
Procedure and conditions for successful use of a biogas plant
Thus, it is not difficult to assemble a simple biogas plant yourself. However, for its successful operation, you must remember and follow a few simple rules.
One of the most important requirements is that the loaded organic mass should not contain any substances that can have a negative impact on the life of anaerobic microorganisms. Prohibited inclusions include various types of solvents, antibacterial drugs and other similar substances.
A number of inorganic substances can also lead to a deterioration in the functioning of bacteria. In view of this, it is prohibited, for example, to dilute humus with water remaining after washing clothes or washing a car.
Remember: a biogas installation is a potentially explosive unit, so follow all safety regulations relevant for the operation of any gas equipment.
Thus, even manure and, in principle, almost everything that you previously tried your best to get rid of, can be useful on the farm. You just need to properly build a home biogas installation, and very soon your home will be warm. Follow the recommendations received, and you will no longer have to spend enormous sums on heating.
Good luck!
The modern world is built on ever-increasing consumption, so mineral and raw material resources are being depleted especially quickly. At the same time, millions of tons of foul-smelling manure accumulate annually on numerous livestock farms, and considerable resources are spent on its disposal. Humans are also keeping up with the production of biological waste. Fortunately, a technology has been developed that allows us to simultaneously solve these problems: using biowaste (primarily manure) as a raw material, producing environmentally friendly renewable fuel - biogas. The use of such innovative technologies has given rise to a new promising industry - bioenergy.
What is biogas
Biogas is a volatile gaseous substance that is colorless and completely odorless. It consists of 50-70 percent methane, up to 30 percent of it is carbon dioxide CO2 and another 1-2 percent are gaseous substances - impurities (when purified from them, the purest biomethane is obtained).
The qualitative physical and chemical characteristics of this substance are close to those of ordinary high-quality natural gas. According to research by scientists, biogas has very high calorific properties: for example, the heat released when burning one cubic meter of this natural fuel is equivalent to the heat from one and a half kilograms of coal.
The release of biogas occurs due to the vital activity of a special type of bacteria - anaerobic, while mesophilic bacteria are activated when the environment is heated to 30-40 degrees Celsius, and thermophilic bacteria multiply at higher temperatures - up to +50 degrees.
Under the influence of their enzymes, organic raw materials decompose with the release of biological gas.
Raw materials for biogas
Not all organic waste is suitable for processing into biogas. For example, manure from poultry and pig farms cannot be used in its pure form, because it has a high level of toxicity. To obtain biogas from them, it is necessary to add diluents to such waste: silage mass, green grass mass, as well as cow manure. The last component is the most suitable raw material for producing environmentally friendly fuel, since cows eat only plant foods. However, it must also be monitored for the content of heavy metal impurities, chemical components, and surfactants, which in principle should not be present in the raw material. A very important point is control over antibiotics and disinfectants. Their presence in manure can prevent the process of decomposition of the raw material mass and the formation of volatile gas.
Additional Information. It is impossible to do without disinfectants completely, because otherwise mold begins to form on the biomass under the influence of high temperatures. You should also monitor and promptly clean the manure from mechanical impurities (nails, bolts, stones, etc.), which can quickly damage biogas equipment. The humidity of the raw materials used to produce biogas must be at least 80-90%.
Mechanism of gas formation
In order for biogas to begin to be released from organic raw materials during airless fermentation (scientifically called anaerobic fermentation), appropriate conditions are required: a sealed container and elevated temperature. If done correctly, the gas produced rises to the top where it is selected for use, and what solids remain is an excellent bio-organic agricultural fertilizer, rich in nitrogen and phosphorus, but free of harmful microorganisms. Temperature conditions are very important for proper and complete processes.
The full cycle of converting manure into environmental fuel ranges from 12 days to a month, it depends on the composition of the raw materials. From one liter of useful reactor volume, about two liters of biogas are produced. If you use more advanced modernized installations, the biofuel production process is accelerated to 3 days, and biogas production increases to 4.5-5 liters.
People began to study and use the technology of producing biofuel from organic natural sources since the end of the 18th century, and in the former USSR the first device for producing biogas was developed back in the 40s of the last century. Nowadays, these technologies are becoming increasingly important and popular.
Advantages and disadvantages of biogas
Biogas as an energy source has undeniable advantages:
- it serves to improve the environmental situation in those areas where it is widely used, since along with reducing the use of polluting fuel, there is a very effective destruction of biowaste and disinfection of wastewater, i.e. biogas equipment acts as a cleaning station;
- the raw materials for the production of this organic fuel are renewable and practically free - as long as animals on farms receive food, they will produce biomass, and, therefore, fuel for biogas plants;
- the acquisition and use of equipment is economically profitable - once purchased, a biogas production plant will no longer require any investments, and it is simply and cheaply maintained; Thus, a biogas plant for use on a farm begins to pay for itself within three years after launch; there is no need to build utilities and energy transmission lines, the costs of launching a biological station are reduced by 20 percent;
- there is no need to install utilities such as power lines and gas pipelines;
- biogas production at the station using local organic raw materials is a waste-free enterprise, as opposed to enterprises using traditional energy sources (gas pipelines, boiler houses, etc.), waste does not pollute the environment and does not require storage space;
- when using biogas, a certain amount of carbon dioxide and sulfur are released into the atmosphere, however, these amounts are minimal compared to the same natural gas and are absorbed by green spaces during respiration, therefore the contribution of bioethanol to the greenhouse effect is minimal;
- Compared to other alternative energy sources, biogas production is always stable; a person can control the activity and productivity of installations for its production (unlike, for example, solar panels), collecting several installations into one or, conversely, splitting them into separate sections to reduce risk accidents;
- in exhaust gases when using biofuels, the content of carbon monoxide is reduced by 25 percent, and nitrogen oxides by 15;
- in addition to manure, you can also use some types of plants to obtain biomass for fuel, for example, sorghum will help improve soil condition;
- When bioethanol is added to gasoline, its octane number increases, and the fuel itself becomes more detonation-resistant, and its auto-ignition temperature decreases significantly.
Biogas– not an ideal fuel, it and the technology for its production are also not without drawbacks:
- the speed of processing organic raw materials in equipment for the production of biogas is a weak point in the technology compared to traditional sources of energy;
- Bioethanol has a lower calorific value than petroleum fuel - it releases 30 percent less energy;
- the process is quite unstable; to maintain it, a large amount of enzymes of a certain quality is required (for example, a change in the diet of cows greatly affects the quality of manure);
- unscrupulous producers of biomass for processing stations can significantly deplete the soil with increased seeding, this disrupts the ecological balance of the territory;
- pipes and containers with biogas may become depressurized, which will lead to a sharp decrease in the quality of biofuel.
Where is biogas used?
First of all, this ecological biofuel is used to meet the household needs of the population, as a replacement for natural gas, for heating and cooking. Enterprises can use biogas to launch a closed production cycle: its use in gas turbines is especially effective. With proper adjustment and complete combination of such a turbine with a biofuel production plant, its cost competes with the cheapest nuclear energy.
The efficiency of biogas use is very easy to calculate. For example, from one unit of cattle you can get up to 40 kilograms of manure, from which one and a half cubic meters of biogas is produced, sufficient to generate 3 kilowatts/hours of electricity.
Having determined the household's electricity needs, it is possible to determine what type of biogas plant to use. With a small number of cows, it is best to produce biogas at home using a simple low-power biogas plant.
If the farm is very large, and it constantly generates a large amount of biowaste, it is beneficial to install an automated industrial-type biogas system.
Note! When designing and setting up, you will need the help of qualified specialists.
Biogas plant design
Any biological installation consists of the following main parts:
- a bioreactor where the biodecomposition of the manure mixture occurs;
- organic fuel supply system;
- unit for stirring biological masses;
- devices for creating and maintaining the required temperature level;
- tanks for placing the resulting biogas in them (gas holders);
- containers for placing the resulting solid fractions there.
This is a complete list of elements for industrial automated installations, while a biogas installation for a private home is much more simply designed.
The bioreactor must be completely sealed, i.e. access of oxygen is unacceptable. This can be a metal container in the form of a cylinder installed on the surface of the soil; former fuel tanks with a capacity of 50 cubic meters are well suited for these purposes. Ready-made dismountable bioreactors are quickly installed/dismantled and easily moved to a new location.
If a small biogas station is planned, then it is advisable to place the reactor underground and make it in the form of a brick or concrete tank, as well as metal or PVC barrels. You can place such a bioenergy reactor indoors, but it is necessary to ensure constant air ventilation.
Bunkers for the preparation of biological raw materials are a necessary element of the system, because before entering the reactor, it must be prepared: crushed into particles up to 0.7 millimeters and soaked in water to bring the moisture content of the raw material to 90 percent.
Raw material supply systems consist of a raw material receiver, a water supply system and a pump for supplying the prepared mass to the reactor.
If the bioreactor is made underground, the container for raw materials is placed on the surface so that the prepared substrate flows into the reactor independently under the influence of gravity. It is also possible to place the raw material receiver at the top of the bunker, in which case it is necessary to use a pump.
The waste outlet hole is located closer to the bottom, opposite the raw material entrance. The receiver for solid fractions is made in the form of a rectangular box, into which an outlet tube leads. When a new portion of the prepared bio-substrate enters the bioreactor, a batch of solid waste of the same volume is fed into the receiver. They are subsequently used on farms as excellent biofertilizers.
The resulting biogas is stored in gas holders, which are usually placed on top of the reactor and have a cone or dome shape. Gas tanks are made of iron and painted with oil paint in several layers (this helps to avoid corrosive destruction). In large industrial bioinstallations, biogas containers are made in the form of separate tanks connected to the reactor.
To give the resulting gas flammable properties, it is necessary to rid it of water vapor. The biofuel is piped through a water tank (hydraulic seal), after which it can be supplied through plastic pipes directly for consumption.
Sometimes you can find special bag-shaped gas holders made of PVC. They are located in close proximity to the installation. As the bags are filled with biogas, they open and their volume increases enough to accept all the produced gas.
For effective biofermentation processes to occur, constant stirring of the substrate is necessary. To prevent the formation of a crust on the surface of the biomass and slow down the fermentation processes, it is necessary to constantly actively mix it. To do this, submersible or inclined stirrers are mounted on the side of the reactor in the form of a mixer for mechanical mixing of the mass. For small stations they are manual, for industrial ones they are automatically controlled.
The temperature necessary for the vital activity of anaerobic bacteria is maintained using automated heating systems (for stationary reactors); they begin heating when the heat drops below normal and automatically turn off when normal temperature is reached. You can also use boiler systems, electric heaters, or install a special heater in the bottom of the container with raw materials. At the same time, it is necessary to reduce heat loss from the bioreactor; to do this, it is wrapped in a layer of glass wool or other thermal insulation is provided, for example, from polystyrene foam.
Do-it-yourself biogas
For private homes, the use of biogas is now very important - from practically free manure you can get gas for domestic needs and heating your home and farm. Your own biogas installation is a guarantee against power outages and rising gas prices, as well as an excellent way to recycle biowaste, as well as unnecessary paper.
For construction for the first time, it is most logical to use simple schemes; such structures will be more reliable and will last longer. In the future, the installation can be supplemented with more complex parts. For a house with an area of 50 square meters, a sufficient amount of gas is obtained with a fermentation tank volume of 5 cubic meters. To ensure the constant temperature required for proper fermentation, a heating pipe can be used.
At the first stage of construction, they dig a trench for the bioreactor, the walls of which must be strengthened and sealed with plastic, concrete mixture or polymer rings (preferably they have a solid bottom - they will have to be replaced periodically as they are used).
The second stage consists of installing gas drainage in the form of polymer pipes with numerous holes. During installation, it should be taken into account that the tops of the pipes must exceed the planned filling depth of the reactor. The diameter of the outlet pipes should be no more than 7-8 centimeters.
The next stage is isolation. After this, you can fill the reactor with the prepared substrate, after which it is wrapped in film to increase the pressure.
At the fourth stage, the domes and the outlet pipe are installed, which is placed at the highest point of the dome and connects the reactor to the gas tank. The gas holder can be lined with brick, a stainless steel mesh is mounted on top and covered with plaster.
A hatch is placed in the upper part of the gas holder, which closes hermetically; a gas pipe with a valve for equalizing pressure is removed from it.
Important! The resulting gas must be removed and consumed constantly, since its long-term storage in the free part of the bioreactor can provoke an explosion from high pressure. It is necessary to provide a water seal so that the biogas does not mix with air.
To heat the biomass, you can install a coil coming from the heating system of the house - this is much more economically profitable than using electric heaters. External heating can be provided using steam; this will prevent overheating of raw materials above normal.
In general, a do-it-yourself biogas plant is not such a complex structure, but when arranging it, you need to pay attention to the smallest details in order to avoid fires and destruction.
Additional Information. The construction of even the simplest biological installation must be formalized with the appropriate documents, you must have a technological diagram and equipment installation map, you must obtain approval from the Sanitary and Epidemiological Station, fire and gas services.
Nowadays, the use of alternative energy sources is gaining momentum. Among them, the bioenergy sub-sector is very promising - the production of biogas from organic waste such as manure and silage. Biogas production stations (industrial or small home) can solve the problems of waste disposal, obtaining environmental fuel and heat, as well as high-quality agricultural fertilizers.
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The technology is not new. It began to develop back in the 18th century, when Jan Helmont, a chemist, discovered that manure emits gases that are flammable.
His research was continued by Alessandro Volta and Humphrey Davy, who found methane in the gas mixture. At the end of the 19th century in England, biogas from manure was used in street lamps. In the mid-20th century, bacteria were discovered that produce methane and its precursors.
The fact is that three groups of microorganisms alternately work in manure, feeding on the waste products of previous bacteria. The first to start working are acetogenic bacteria, which dissolve carbohydrates, proteins and fats in the slurry.
After processing the nutrient supply by anaerobic microorganisms, methane, water and carbon dioxide are formed. Due to the presence of water, biogas at this stage is not able to burn - it needs purification, so it is passed through treatment facilities.
What is biomethane
The gas obtained as a result of the decomposition of manure biomass is an analogue of natural gas. It is almost 2 times lighter than air, so it always rises. This explains the artificial production technology: free space is left at the top so that the substance can be released and accumulate, from where it is then pumped out for use for one’s own needs.
Methane greatly influences the greenhouse effect - much more than carbon dioxide - 21 times. Therefore, manure processing technology is not only an economical, but also an environmentally friendly way to dispose of animal waste.
Biomethane is used for the following needs:
- cooking;
- in internal combustion engines of automobiles;
- for heating a private house.
Biogas produces a large amount of heat. 1 cubic meter is equivalent to burning 1.5 kg of coal.
How is biomethane produced?
It can be obtained not only from manure, but also algae, plant matter, fat and other animal waste, and residues from the processing of raw materials from fish shops. Depending on the quality of the source material and its energy capacity, the final yield of the gas mixture depends.
The minimum amount of gas obtained is 50 cubic meters per ton of cattle manure. Maximum - 1,300 cubic meters after processing animal fat. The methane content is up to 90%.
One type of biological gas is landfill gas. It is formed during the decomposition of garbage in suburban landfills. The West already has equipment that processes waste from the population and turns it into fuel. As a type of business, it has unlimited resources.
Its raw material base includes:
- food industry;
- livestock farming;
- poultry farming;
- fisheries and processing plants;
- dairies;
- production of alcoholic and low-alcohol drinks.
Any industry is forced to dispose of its waste - it is expensive and unprofitable. At home, with the help of a small homemade installation, you can solve several problems at once: free heating of the house, fertilizing the land with high-quality nutrients left over from manure processing, freeing up space and eliminating odors.
Biofuel production technology
All bacteria that take part in the formation of biogas are anaerobic, that is, they do not need oxygen to function. To do this, completely sealed fermentation containers are constructed, the outlet pipes of which also do not allow air from the outside to pass through.
After pouring the raw liquid into the tank and raising the temperature to the required value, the bacteria begin to work. Methane begins to be released, which rises from the surface of the slurry. It is sent to special pillows or tanks, after which it is filtered and ends up in gas cylinders.
The liquid waste from bacteria accumulates at the bottom, from where it is periodically pumped out and also sent for storage. After this, a new portion of manure is pumped into the tank.
Temperature regime of bacteria functioning
To process manure into biogas, it is necessary to create suitable conditions for bacteria to work. some of them are activated at temperatures above 30 degrees - mesophilic. At the same time, the process is slower and the first product can be obtained after 2 weeks.
Thermophilic bacteria work at temperatures from 50 to 70 degrees. The time required to obtain biogas from manure is reduced to 3 days. In this case, the waste is a fermented sludge that is used in the fields as fertilizer for agricultural crops. There are no pathogenic microorganisms, helminths and weeds in the sludge, as they die when exposed to high temperatures.
There is a special type of thermophilic bacteria that can survive in an environment heated to 90 degrees. They are added to raw materials to speed up the fermentation process.
A decrease in temperature leads to a decrease in the activity of thermophilic or mesophilic bacteria. In private households, mesophylls are more often used, since they do not require special heating of the liquid and gas production is cheaper. Subsequently, when the first batch of gas is received, it can be used to heat the reactor with thermophilic microorganisms.
Important! Methanogens do not tolerate sudden changes in temperature, so in winter they must be kept warm at all times.
How to prepare raw materials for pouring into the reactor
To produce biogas from manure, there is no need to specially introduce microorganisms into the liquid, because they are already found in animal excrement. You just need to maintain the temperature and add a new manure solution in time. It must be prepared correctly.
The humidity of the solution should be 90% (the consistency of liquid sour cream), Therefore, dry types of excrement are first filled with water - rabbit droppings, horse droppings, sheep droppings, goat droppings. Pig manure in its pure form does not need to be diluted, as it contains a lot of urine.
The next step is to break down the manure solids. The finer the fraction, the better the bacteria will process the mixture and the more gas will be released. For this purpose, the installations use a stirrer that is constantly running. It reduces the risk of a hard crust forming on the surface of the liquid.
Those types of manure that have the highest acidity are suitable for biogas production. They are also called cold - pork and cow. A decrease in acidity stops the activity of microorganisms, so it is necessary to monitor at the beginning how long it takes for them to completely process the volume of the tank. Then add the next dose.
Gas purification technology
When processing manure into biogas, the following is obtained:
- 70% methane;
- 30% carbon dioxide;
- 1% impurities of hydrogen sulfide and other volatile compounds.
In order for biogas to become suitable for use on the farm, it must be cleaned of impurities. To remove hydrogen sulfide, special filters are used. The fact is that volatile hydrogen sulfide compounds, dissolving in water, form acid. It contributes to the appearance of rust on the walls of pipes or tanks if they are made of metal.
- The resulting gas is compressed under a pressure of 9–11 atmospheres.
- It is fed into a reservoir of water, where impurities are dissolved in the liquid.
On an industrial scale, lime or activated carbon, as well as special filters, are used for cleaning.
How to reduce moisture content
There are several ways to get rid of water impurities in gas yourself. One of them is the principle of a moonshine still. The cold pipe directs the gas upward. The liquid condenses and flows down. To do this, the pipe is laid underground, where the temperature naturally decreases. As it rises, the temperature also rises, and the dried gas enters the storage facility.
The second option is a water seal. After exiting, the gas enters a container with water and is cleaned of impurities there. This method is called one-stage, when biogas is immediately cleaned from all volatile substances and moisture using water.
Water seal principle
What installations are used to produce biogas?
If the installation is planned to be located near a farm, then the best option would be a collapsible structure that can be easily transported to another location. The main element of the installation is a bioreactor into which raw materials are poured and the fermentation process occurs. Large enterprises use tanks volume 50 cubic meters.
In private farms, underground reservoirs are built as a bioreactor. They are laid out of brick in a prepared hole and coated with cement. Concrete increases the safety of the structure and prevents air from entering. The volume depends on how much raw material is obtained from domestic animals per day.
Surface systems are also popular at home. If desired, the installation can be disassembled and moved to another location, unlike a stationary underground reactor. Plastic, metal or polyvinyl chloride barrels are used as tanks.
By type of control there are:
- automatic stations in which the filling and pumping out of waste raw materials is carried out without human intervention;
- mechanical, where the entire process is controlled manually.
Using a pump, you can facilitate the emptying of the tank into which the waste after fermentation falls. Some craftsmen use pumps to pump gas from cushions (for example, car inner tubes) into a treatment facility.
Scheme of a homemade installation for producing biogas from manure
Before constructing a biogas plant on your site, you need to become familiar with the potential hazards that could cause the reactor to explode. The main condition is the absence of oxygen.
Methane is an explosive gas and can ignite, but to do so it must be heated above 500 degrees. If biogas mixes with air, overpressure will arise, which will rupture the reactor. Concrete may crack and will not be suitable for further use.
Video: Biogas from bird droppings
To prevent the pressure from tearing off the lid, use a counterweight, a protective gasket between the lid and the tank. The container is not completely filled - there should be at least 10% volume for gas release. Better - 20%.
So, to make a bioreactor with all the accessories on your site, you need to:
- It is good to choose a place so that it is located away from housing (you never know).
- Calculate the estimated amount of manure that animals produce daily. How to count - read below.
- Decide where to lay the loading and unloading pipes, as well as a pipe for condensing moisture in the resulting gas.
- Decide on the location of the waste tank (fertilizer by default).
- Dig a pit based on calculations of the amount of raw materials.
- Select a container that will serve as a reservoir for manure and install it in the pit. If a concrete reactor is planned, then the bottom of the pit is filled with concrete, the walls are lined with bricks and plastered with concrete mortar. After this, you need to give it time to dry.
- The connections between the reactor and the pipes are also sealed at the stage of laying the tank.
- Equip a hatch for inspection of the reactor. A sealed gasket is placed between it.
If the climate is cold, then before concreting or installing a plastic tank, consider ways to heat it. These can be heating devices or tape used in “warm floor” technology.
At the end of the work, check the reactor for leaks.
Gas quantity calculation
From one ton of manure you can get approximately 100 cubic meters of gas. Question: How much litter do pets produce per day?
- chicken – 165 g per day;
- cow – 35 kg;
- goat – 1 kg;
- horse – 15 kg;
- sheep – 1 kg;
- pig – 5 kg.
Multiply these figures by the number of heads and you get the daily dose of excrement to be processed.
More gas comes from cows and pigs. If you add energetically powerful plants such as corn, beet tops, and millet to the mixture, the amount of biogas will increase. Marsh plants and algae have great potential.
The highest is for waste from meat processing plants. If there are such farms nearby, then we can cooperate and install one reactor for everyone. The payback period for a bioreactor is 1–2 years.
Biomass waste after gas production
After processing manure in a reactor, the by-product is biosludge. During anaerobic processing of waste, bacteria dissolve about 30% of organic matter. The rest is released unchanged.
The liquid substance is also a by-product of methane fermentation and is also used in agriculture for root feeding.
Carbon dioxide is a waste fraction that biogas producers strive to remove. But if you dissolve it in water, then this liquid can also be beneficial.
Full utilization of biogas plant products
In order to completely utilize the products obtained after processing manure, it is necessary to maintain a greenhouse. Firstly, organic fertilizer can be used for year-round cultivation of vegetables, the yield of which will be stable.
Secondly, carbon dioxide is used as fertilizing - root or foliar, and its output is about 30%. Plants absorb carbon dioxide from the air and at the same time grow better and gain green mass. If you consult with specialists in this field, they will help you install equipment that converts carbon dioxide from liquid form into a volatile substance.
Video: Biogas in 2 days
The fact is that to maintain a livestock farm, the energy resources obtained can be a lot, especially in the summer, when heating the barn or pigsty is not needed.
Therefore, it is recommended to engage in another profitable activity - an environmentally friendly greenhouse. Remaining products can be stored in refrigerated rooms - using the same energy. Refrigeration or any other equipment can run on electricity generated by a gas battery.
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%. If you look at it in general, then 1 ton of fermented manure can replace 70 - 80 tons of ordinary 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.
Sludge storage methods
It is best to store fermented manure dry. This makes it more convenient to pack and transport. The dry substance loses less useful properties and can be stored closed. Although such fertilizer does not deteriorate at all over the course of a year, it must then be sealed in a bag or container.
Liquid forms must be stored in closed containers with a tight-fitting lid to prevent nitrogen from escaping.
How to store manure on the plot for fertilizing the garden: the best ways