The constant increase in the cost of traditional energy resources is pushing home craftsmen to create homemade equipment that allows them to produce biogas from waste with their own hands. With this approach to farming, it is possible not only to obtain cheap energy for heating the house and other needs, but also to establish the process of recycling organic waste and obtaining free fertilizers for subsequent application to the soil.
Excess produced biogas, like fertilizers, can be sold at market value to interested consumers, turning into money what is literally “lying under your feet.” Large farmers can afford to buy ready-made biogas production stations assembled in factories. The cost of such equipment is quite high. However, the return on its operation corresponds to the investment made. Less powerful installations operating on the same principle can be assembled on your own from available materials and parts.
What is biogas and how is it formed?
As a result of biomass processing, biogas is obtained
Biogas is classified as an environmentally friendly fuel. According to its characteristics, biogas is in many respects similar to natural gas produced on an industrial scale. The technology for producing biogas can be presented as follows:
- in a special container called a bioreactor, the process of processing biomass takes place with the participation of anaerobic bacteria under airless fermentation conditions for a certain period, the duration of which depends on the volume of loaded raw materials;
- as a result, a mixture of gases is released, consisting of 60% methane, 35% carbon dioxide, 5% other gaseous substances, among which there is a small amount of hydrogen sulfide;
- the resulting gas is constantly removed from the bioreactor and, after purification, is sent for its intended use;
- processed waste, which has become high-quality fertilizers, is periodically removed from the bioreactor and transported to the fields.
Visual diagram of the biofuel production process
In order to establish continuous production of biogas at home, you must own or have access to agricultural and livestock enterprises. It is economically profitable to produce biogas only if there is a source of free supply of manure and other organic waste from animal husbandry.
Gas heating remains the most reliable heating method. You can learn more about autonomous gasification in the following material:
Types of bioreactors
Installations for the production of biogas differ in the type of loading of raw materials, collection of the resulting gas, placement of the reactor relative to the surface of the earth, and material of manufacture. Concrete, brick and steel are the most suitable materials for constructing bioreactors.
Based on the type of loading, a distinction is made between bio-installations, into which a given portion of raw materials is loaded and goes through a processing cycle, and then completely unloaded. Gas production in these installations is unstable, but any type of raw material can be loaded into them. As a rule, they are vertical and take up little space.
A portion of organic waste is loaded into the system of the second type daily and an equal portion of ready-made fermented fertilizers is unloaded. The working mixture always remains in the reactor. The so-called continuous feeding plant consistently produces more biogas and is very popular among farmers. Basically, these reactors are located horizontally and are convenient if there is free space on the site.
The selected type of biogas collection determines the design features of the reactor.
- balloon systems consist of a rubber or plastic heat-resistant cylinder in which a reactor and a gas holder are combined. The advantages of this type of reactor are simplicity of design, loading and unloading of raw materials, ease of cleaning and transportation, and low cost. The disadvantages include a short service life, 2-5 years, and the possibility of damage as a result of external influences. Balloon reactors also include channel-type units, which are widely used in Europe for processing liquid waste and wastewater. This rubber top is effective at high ambient temperatures and there is no risk of damage to the cylinder. The fixed dome design has a completely enclosed reactor and a compensating tank for slurry discharge. Gas accumulates in the dome; when loading the next portion of raw materials, the processed mass is pushed into the compensation tank.
- Biosystems with a floating dome consist of a monolithic bioreactor located underground and a movable gas holder, which floats in a special water pocket or directly in the raw material and rises under the influence of gas pressure. The advantage of a floating dome is ease of operation and the ability to determine gas pressure by the height of the dome. This is an excellent solution for a large farm.
- When choosing an underground or above-surface installation location, you need to take into account the slope of the terrain, which makes it easier to load and unload raw materials, enhanced thermal insulation of underground structures, which protects the biomass from daily temperature fluctuations and makes the fermentation process more stable.
The design can be equipped with additional devices for heating and mixing raw materials.
Is it profitable to make a reactor and use biogas?
The construction of a biogas plant has the following goals:
- production of cheap energy;
- production of easily digestible fertilizers;
- savings on connecting to expensive sewerage;
- recycling of farm waste;
- possible profit from gas sales;
- reducing the intensity of unpleasant odors and improving the environmental situation in the area.
Profitability chart for biogas production and use
To assess the benefits of building a bioreactor, a prudent owner should consider the following aspects:
- the cost of a bio-plant is a long-term investment;
- homemade biogas equipment and installation of a reactor without the involvement of third-party specialists will cost much less, but its efficiency is also lower than that of an expensive factory one;
- To maintain stable gas pressure, the farmer must have access to livestock waste in sufficient quantity and for a long period of time. In the case of high prices for electricity and natural gas or the lack of possibility of gasification, the use of the installation becomes not only profitable, but also necessary;
- for large farms with their own raw material base, a profitable solution would be to include a bioreactor in the system of greenhouses and cattle farms;
- For small farms, efficiency can be increased by installing several small reactors and loading raw materials at different time intervals. This will avoid interruptions in gas supply due to a lack of feedstock.
How to build a bioreactor on your own
The decision to build has been made, now you need to design the installation and calculate the necessary materials, tools and equipment.
Important! Resistance to aggressive acidic and alkaline environments is the main requirement for bioreactor material.
If a metal tank is available, it can be used provided it has a protective coating against corrosion. When choosing a metal container, pay attention to the presence of welds and their strength.
A durable and convenient option is a polymer container. This material does not rot or rust. A barrel with thick hard walls or reinforced will withstand the load perfectly.
The cheapest way is to lay out a container made of brick or stone or concrete blocks. To increase strength, the walls are reinforced and covered inside and outside with a multi-layer waterproofing and gas-tight coating. The plaster must contain additives that provide the specified properties. The best shape to withstand all pressure loads is oval or cylindrical.
At the base of this container there is a hole through which waste raw materials will be removed. This hole must be tightly closed, because the system only works effectively in sealed conditions.
Calculation of necessary tools and materials
To lay out a brick container and install the entire system, you will need the following tools and materials:
- container for mixing cement mortar or concrete mixer;
- drill with mixer attachment;
- crushed stone and sand for constructing a drainage cushion;
- shovel, tape measure, trowel, spatula;
- brick, cement, water, fine sand, reinforcement, plasticizer and other necessary additives;
- welding machine and fasteners for installation of metal pipes and components;
- a water filter and a container with metal shavings for gas purification;
- tire cylinders or standard propane cylinders for gas storage.
The size of the concrete tank is determined from the amount of organic waste that appears daily in a private farmstead or farm. Full operation of the bioreactor is possible if it is filled to two-thirds of the available volume.
Let us determine the volume of the reactor for a small private farm: if there are 5 cows, 10 pigs and 40 chickens, then per day of their life activity a litter of 5 x 55 kg + 10 x 4.5 kg + 40 x 0.17 kg = 275 kg + is formed 45 kg + 6.8 kg = 326.8 kg. To bring chicken manure to the required humidity of 85%, you need to add 5 liters of water. Total weight = 331.8 kg. For processing in 20 days you need: 331.8 kg x 20 = 6636 kg - about 7 cubic meters only for the substrate. This is two thirds of the required volume. To get the result, you need 7x1.5 = 10.5 cubic meters. The resulting value is the required volume of the bioreactor.
Remember that it will not be possible to produce large amounts of biogas in small containers. The yield directly depends on the mass of organic waste processed in the reactor. So, to get 100 cubic meters of biogas, you need to process a ton of organic waste.
Preparing a site for a bioreactor
The organic mixture loaded into the reactor should not contain antiseptics, detergents, chemicals that are harmful to the life of bacteria and slow down the production of biogas.
Important! Biogas is flammable and explosive.
For proper operation of the bioreactor, the same rules must be followed as for any gas installations. If the equipment is sealed and biogas is discharged into the gas tank in a timely manner, then there will be no problems.
If the gas pressure exceeds the norm or poisons if the seal is broken, there is a risk of explosion, so it is recommended to install temperature and pressure sensors in the reactor. Inhaling biogas is also dangerous to human health.
How to ensure biomass activity
You can speed up the fermentation process of biomass by heating it. As a rule, this problem does not arise in the southern regions. The ambient temperature is sufficient for the natural activation of fermentation processes. In regions with harsh climatic conditions in winter, it is generally impossible to operate a biogas production plant without heating. After all, the fermentation process starts at a temperature exceeding 38 degrees Celsius.
There are several ways to organize heating of a biomass tank:
- connect the coil located under the reactor to the heating system;
- install electric heating elements at the base of the container;
- provide direct heating of the tank through the use of electric heating devices.
Bacteria that influence methane production are dormant in the raw materials themselves. Their activity increases at a certain temperature level. The installation of an automated heating system will ensure the normal course of the process. The automation will turn on the heating equipment when the next cold batch enters the bioreactor, and then turn it off when the biomass warms up to the specified temperature level.
Similar temperature control systems are installed in hot water boilers, so they can be purchased in stores specializing in the sale of gas equipment.
The diagram shows the entire cycle, starting from the loading of solid and liquid raw materials, and ending with the removal of biogas to consumers
It is important to note that you can activate biogas production at home by mixing biomass in a reactor. For this purpose, a device is made that is structurally similar to a household mixer. The device can be set in motion by a shaft that is output through a hole located in the lid or walls of the tank.
What special permits are required for the installation and use of biogas
In order to build and operate a bioreactor, as well as use the resulting gas, you need to take care of obtaining the necessary permits at the design stage. Coordination must be completed with the gas service, firefighters and Rostechnadzor. In general, the rules for installation and operation are similar to the rules for using conventional gas equipment. Construction must be carried out strictly in accordance with SNIPs, all pipelines must be yellow and have appropriate markings. Ready-made systems manufactured at the factory cost several times more, but have all the accompanying documents and meet all technical requirements. Manufacturers provide a warranty on equipment and provide maintenance and repair of their products.
A home-made installation for producing biogas can allow you to save on energy costs, which occupy a large share in determining the cost of agricultural products. Reducing production costs will affect the increase in profitability of a farm or private farmstead. Now that you know how to obtain biogas from existing waste, all that remains is to put the idea into practice. Many farmers have long learned to make money from manure.
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 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:
Ecology of consumption. Estate: Is it profitable to produce biofuel at home in small quantities on a private plot? If you have several metal barrels and other iron junk, as well as a lot of free time and you don’t know how to manage it - yes.
Suppose there was no natural gas in your village and there never will be. And even if there is, it costs money. Although it is an order of magnitude cheaper than costly heating with electricity and liquid fuel. The nearest pellet production workshop is a couple of hundred kilometers away, and transport is expensive. It’s becoming more and more difficult to buy firewood every year, and it’s also troublesome to burn with it. Against this background, the idea of obtaining free biogas in your own backyard from weeds, chicken droppings, manure from your favorite pig or the contents of the owner’s outhouse looks very tempting. All you have to do is make a bioreactor! On TV they talk about how thrifty German farmers keep themselves warm with “manure” resources and now they don’t need any “Gazprom”. This is where the saying “takes the film off feces” is true. The Internet is replete with articles and videos on the topic “biogas from biomass” and “do-it-yourself biogas plant.” But we know little about the practical application of the technology: everyone is talking about the production of biogas at home, but few people have seen concrete examples in the village, as well as the legendary Yo-Mobile on the road. Let's try to figure out why this is so and what are the prospects for progressive bioenergy technologies in rural areas.
What is biogas + a little history
Biogas is formed as a result of sequential three-stage decomposition (hydrolysis, acid and methane formation) of biomass by various types of bacteria. The useful combustible component is methane, and hydrogen may also be present.
The process of bacterial decomposition that produces flammable methane
To a greater or lesser extent, flammable gases are formed during the decomposition of any remains of animal and plant origin.
The approximate composition of biogas, the specific proportions of the components depend on the raw materials and technology used
People have long been trying to use this type of natural fuel; medieval chronicles contain references to the fact that residents of the low-lying regions of what is now Germany a millennium ago received biogas from rotting vegetation by immersing leather furs in swamp slurry. In the dark Middle Ages and even the enlightened centuries, the most talented meteorists, who, thanks to a specially selected diet, were able to release and ignite abundant methane flatus in time, aroused the constant delight of the public at cheerful fair performances. Industrial biogas plants began to be built with varying degrees of success in the mid-19th century. In the USSR in the 80s of the last century, a state program for the development of the industry was adopted, but not implemented, although a dozen production facilities were launched. Abroad, the technology for producing biogas is being improved and is being promoted relatively actively; the total number of operating installations is in the tens of thousands. In developed countries (EEC, USA, Canada, Australia) these are highly automated large complexes, in developing countries (China, India) - semi-handicraft biogas plants for homes and small farms.
Percentage of the number of biogas plants in the European Union. It is clearly visible that the technology is actively developing only in Germany, the reason is solid government subsidies and tax incentives
What uses does biogas have?
It is clear that it is used as fuel, since it burns. Heating of industrial and residential buildings, electricity generation, cooking. However, not everything is as simple as they show in the videos scattered on YouTube. Biogas must burn stably in heat-generating installations. To do this, its gas environment parameters must be brought to fairly stringent standards. The methane content must be at least 65% (optimum 90-95%), hydrogen must be absent, water vapor has been removed, carbon dioxide has been removed, the remaining components are inert to high temperatures.
It is impossible to use biogas of “animal dung” origin, not freed from foul-smelling impurities, in residential buildings.
The normalized pressure is 12.5 bar; if the value is less than 8-10 bar, the automation in modern models of heating equipment and kitchen equipment stops the gas supply. It is very important that the characteristics of the gas entering the heat generator are stable. If the pressure jumps beyond the normal limits, the valve will work and you will have to turn it back on manually. It’s bad if you use outdated gas appliances that are not equipped with a gas control system. At best, the boiler burner may fail. The worst case scenario is that the gas will go out, but its supply will not stop. And this is already fraught with tragedy. Let us summarize what has been said: the characteristics of biogas must be brought to the required parameters, and safety precautions must be strictly observed. Simplified technological chain for biogas production. An important stage is separation and gas separation
What raw materials are used to produce biogas
Plant and animal raw materials
- Plant raw materials are excellent for the production of biogas: from fresh grass you can get the maximum fuel yield - up to 250 m3 per ton of raw material, methane content up to 70%. Somewhat less, up to 220 m3 can be obtained from corn silage, up to 180 m3 from beet tops. Any green plants are suitable, algae and hay are good (100 m3 per ton), but it makes sense to use valuable feed for fuel only if there is an obvious excess of it. The yield of methane from the pulp formed during the production of juices, oils and biodiesel is low, but the material is also free. The lack of plant raw materials is a long production cycle, 1.5-2 months. It is possible to obtain biogas from cellulose and other slowly decomposing plant waste, but the efficiency is extremely low, little methane is produced, and the production cycle is very long. In conclusion, we say that plant raw materials must be finely chopped.
- Raw materials of animal origin: traditional horns and hooves, waste from dairies, slaughterhouses and processing plants are also suitable and also in crushed form. The richest “ore” is animal fats; the yield of high-quality biogas with a methane concentration of up to 87% reaches 1500 m3 per ton. However, animal raw materials are in short supply and, as a rule, other uses are found for them.
Flammable gas from excrement
- Manure is cheap and is available in abundance on many farms, but the yield and quality of biogas is significantly lower than from other types. Cow pats and horse apples can be used in their pure form, fermentation begins immediately, biogas yield is 60 m2 per ton of raw material with a low methane content (up to 60%). The production cycle is short, 10-15 days. Pig manure and chicken droppings are toxic - so that beneficial bacteria can develop, it is mixed with plant waste and silage. A big problem is represented by detergent compositions and surfactants, which are used when cleaning livestock buildings. Together with antibiotics, which enter manure in large quantities, they inhibit the bacterial environment and inhibit the formation of methane. It is completely impossible not to use disinfectants, and agricultural enterprises that have invested in the production of gas from manure are forced to seek a compromise between hygiene and control over animal disease, on the one hand, and maintaining the productivity of bioreactors, on the other.
- Human excrement, completely free, is also suitable. But using ordinary sewage is unprofitable, the concentration of feces is too low and the concentration of disinfectants and surfactants is high. Technologists claim that they could be used only if “products” only flow from the toilet into the sewer system, provided that the bowl is flushed with only one liter of water (standard 4/8 l). And without detergents, of course.
Additional requirements for raw materials
A serious problem faced by farms that have installed modern equipment for producing biogas is that the raw material should not contain solid inclusions; a stone, nut, piece of wire or board that accidentally gets into the mass will clog the pipeline and disable an expensive fecal pump or mixer. It must be said that the given data on the maximum gas yield from the raw material correspond to ideal laboratory conditions. To get closer to these figures in real production, a number of conditions must be met: maintain the required temperature, periodically stir finely ground raw materials, add additives that activate fermentation, etc. In a makeshift installation, assembled according to the recommendations of articles on “producing biogas with your own hands,” it is barely possible to achieve 20% of the maximum level, while high-tech installations allow you to achieve values of 60-95%.
Quite objective data on the maximum biogas yield for various types of raw materials
Biogas plant design
Is it profitable to produce biogas?
We have already mentioned that in developed countries large industrial installations are built, while in developing countries they build mainly small ones for small farms. Let's explain why this is so:
Does it make sense to produce biofuels at home?
Is it profitable to produce biofuel at home in small quantities on a private plot? If you have several metal barrels and other iron junk, as well as a lot of free time and you don’t know how to manage it - yes. But the savings, alas, are meager. And investing in high-tech equipment with small volumes of raw materials and methane production does not make sense under any circumstances.
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Without mixing the raw materials and activating the fermentation process, the methane yield will be no more than 20% of the possible one. This means that, in the best case, with 100 kg (hopper loading) of selected grass you can get 5 m3 of gas without taking into account compression. And it will be good if the methane content exceeds 50% and it is not a fact that it will burn in the heat generator. According to the author, raw materials are loaded daily, that is, his production cycle is one day. In fact, the required time is 60 days. The amount of biogas obtained by the inventor, contained in a 50-liter cylinder, which he managed to fill, in frosty weather for a heating boiler with a capacity of 15 kW (a residential building of about 150 m2) is enough for 2 minutes.
Those who are interested in the possibility of producing biogas are advised to carefully study the problem, especially from a financial point of view, and contact specialists with experience in such work with technical questions. Practical information obtained from those farms where bioenergy technologies have already been used for some time will be very valuable. published
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;
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.
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 pit 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.
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.
The main problem of biofertilizer producers is marketing in winter, when plants are dormant. On the world market, the cost of fertilizers of this quality fluctuates around $130 per ton. If you set up a line for packaging concentrates, you can pay for your reactor within two years.
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The issue of methane production is of interest to those owners of private farms who breed poultry or pigs, and also keep cattle. As a rule, such farms produce a significant amount of organic animal waste, which can bring considerable benefits by becoming a source of cheap fuel. The purpose of this material is to tell you how to produce biogas at home using this same waste.
General information about biogas
Home biogas, obtained from various manures and poultry droppings, mostly consists of methane. There it is from 50 to 80%, depending on whose waste was used for production. The same methane that burns in our stoves and boilers, and for which we sometimes pay a lot of money according to the meter readings.
To give an idea of the amount of fuel that can theoretically be produced when keeping animals at home or in the country, we present a table with data on the yield of biogas and the content of pure methane in it:
As you can see from the table, to effectively produce gas from cow dung and silage waste, a fairly large amount of raw material will be needed. It is more profitable to extract fuel from pig manure and turkey droppings.
The remaining share of substances (25-45%) that make up home biogas is carbon dioxide (up to 43%) and hydrogen sulfide (1%). The fuel also contains nitrogen, ammonia and oxygen, but in small quantities. By the way, it is thanks to the release of hydrogen sulfide and ammonia that the manure heap emits such a familiar “pleasant” smell. As for the energy content, 1 m3 of methane can theoretically release up to 25 MJ (6.95 kW) of thermal energy when burned. The specific heat of combustion of biogas depends on the proportion of methane in its composition.
For reference. In practice, it has been verified that heating an insulated house located in the middle zone requires about 45 m3 of biological fuel per 1 m2 of area during the heating season.
Nature arranges it in such a way that biogas from manure is formed spontaneously and regardless of whether we want to receive it or not. A manure heap rots within a year to a year and a half, simply by being in the open air and even at sub-zero temperatures. All this time it releases biogas, but only in small quantities, since the process is extended over time. The cause is hundreds of types of microorganisms found in animal excrement. That is, nothing is needed to start gas evolution; it will happen on its own. But to optimize the process and speed it up, special equipment will be required, which will be discussed further.
Biogas technology
The essence of effective production is to accelerate the natural process of decomposition of organic raw materials. To do this, the bacteria in it need to create the best conditions for reproduction and waste processing. And the first condition is to place the raw material in a closed container - a reactor, otherwise - a biogas generator. The waste is crushed and mixed in a reactor with a calculated amount of clean water until the initial substrate is obtained.
Note. Clean water is necessary to ensure that substances that adversely affect the life of bacteria do not get into the substrate. As a result, the fermentation process can slow down greatly.
An industrial biogas production plant is equipped with substrate heating, means of mixing and control of the acidity of the environment. Stirring is carried out in order to remove hard crust from the surface, which occurs during fermentation and interferes with the release of biogas. The duration of the technological process is at least 15 days, during which time the degree of decomposition reaches 25%. It is believed that the maximum fuel yield occurs up to 33% of biomass decomposition.
The technology provides for daily renewal of the substrate, which ensures intensive production of gas from manure; in industrial installations it amounts to hundreds of cubic meters per day. Part of the waste mass, amounting to about 5% of the total volume, is removed from the reactor, and the same amount of fresh biological raw materials is loaded in its place. The waste material is used as organic fertilizer for fields.
Biogas plant diagram
When producing biogas at home, it is impossible to create such favorable conditions for microorganisms as in industrial production. And first of all, this statement concerns the organization of generator heating. As is known, this requires energy consumption, which leads to a significant increase in the cost of fuel. It is quite possible to control compliance with the slightly alkaline environment inherent in the fermentation process. But how can it be corrected in case of deviations? Costs again.
Owners of private farms who want to produce biogas with their own hands are recommended to make a reactor of a simple design from available materials, and then modernize it according to their capabilities. What need to do:
- hermetically sealed container with a volume of at least 1 m3. Various small tanks and barrels are also suitable, but little fuel will be released from them due to the insufficient amount of raw materials. Such production volumes will not suit you;
- When organizing biogas production at home, you are unlikely to heat the container, but you definitely need to insulate it. Another option is to bury the reactor in the ground, thermally insulating the upper part;
- install a manual stirrer of any design in the reactor, extending the handle through the top cover. The handle passage assembly must be sealed;
- provide pipes for supplying and unloading the substrate, as well as for collecting biogas.
Below is a diagram of a biogas plant located below ground level:
1 – fuel generator (container made of metal, plastic or concrete); 2 — hopper for filling the substrate; 3 – technical hatch; 4 – vessel acting as a water seal; 5 – outlet for unloading waste waste; 6 – biogas sampling pipe.
How to get biogas at home?
The first operation is grinding waste to a fraction whose size is no more than 10 mm. This makes it much easier to prepare the substrate, and it will be easier for bacteria to process the raw materials. The resulting mass is thoroughly mixed with water, its quantity is about 0.7 liters per 1 kg of organic matter. As mentioned above, only clean water should be used. Then a self-made biogas plant is filled with the substrate, after which the reactor is hermetically sealed.
Several times during the day you need to visit the container to mix the contents. On the 5th day, you can check for the presence of gas, and if it appears, periodically pump it out with a compressor into a cylinder. If this is not done in time, the pressure inside the reactor will increase and fermentation will slow down, or even stop altogether. After 15 days, it is necessary to unload part of the substrate and add the same amount of new one. You can find out more by watching the video:
Conclusion
It is likely that the simplest biogas installation will not meet all your needs. But, given the current cost of energy resources, this will already be of considerable help in the household, because you do not have to pay for the raw materials. Over time, being closely involved in production, you will be able to grasp all the features and make the necessary improvements to the installation.