Small installations can also be installed at home. As an aside, I will say that producing biogas with your own hands is not some kind of new invention. Even in ancient times, biogas was actively produced at home in China. This country is still the leader in the number of biogas installations. But here how to make a biogas plant with your own hands, what is needed for this, how much it will cost - I will try to tell you all this in this and subsequent articles.
Preliminary calculation of a biogas plant
Before you start purchasing or independently assembling a biogas plant, you must adequately assess the availability of raw materials, their type, quality and the possibility of uninterrupted supply. Not every raw material is suitable for producing biogas. Raw materials that are not suitable:
- raw materials with high lignin content;
- raw materials that contain sawdust from coniferous trees (with the presence of resins)
- with humidity exceeding 94%
- rotting manure, as well as raw materials containing mold or synthetic detergents.
If the raw material is suitable for processing, then you can begin to determine the volume of the bioreactor. The total volume of raw materials for the mesophilic mode (biomass temperature ranges from 25-40 degrees, the most common mode) does not exceed 2/3 of the reactor volume. The daily dose is no more than 10% of the total loaded raw materials.
Any raw material is characterized by three important parameters:
- density;
- ash content;
- humidity.
The last two parameters are determined from statistical tables. The raw material is diluted with water to achieve 80-92% humidity. The ratio of the amount of water and raw materials can vary from 1:3 to 2:1. This is done to give the substrate the required fluidity. Those. to ensure the passage of the substrate through the pipes and the possibility of mixing it. For small biogas plants, the density of the substrate can be taken equal to the density of water.
Let's try to determine the volume of the reactor using an example.
Let's say a farm has 10 heads of cattle, 20 pigs and 35 chickens. The following excrement is produced per day: 55 kg from 1 cattle, 4.5 kg from 1 pig and 0.17 kg from chicken. The volume of daily waste will be: 10x55+20x4.5+0.17x35 = 550+90+5.95 =645.95 kg. Let's round up to 646 kg. The moisture content of pig and cattle excrement is 86%, and that of chicken droppings is 75%. To achieve 85% moisture in chicken manure, you need to add 3.9 liters of water (about 4 kg).
It turns out that the daily dose of raw material loading will be about 650 kg. Full reactor load: OS=10x0.65=6.5 tons, and reactor volume OR=1.5x6.5=9.75 m³. Those. we will need a reactor with a volume of 10 m³.
Biogas yield calculation
Table for calculating biogas yield depending on the type of raw material.
| Raw material type | Gas output, m³ per 1 kg of dry matter | Gas output m³ per 1 ton at humidity 85% |
| Cattle manure | 0,25-0,34 | 38-51,5 |
| Pig manure | 0,34-0,58 | 51,5-88 |
| Bird droppings | 0,31-0,62 | 47-94 |
| Horse dung | 0,2-0,3 | 30,3-45,5 |
| Sheep manure | 0,3-0,62 | 45,5-94 |
If we take the same example, then multiplying the weight of each type of raw material by the corresponding tabular data and summing up all three components, we obtain a biogas yield of approximately 27-36.5 m³ per day.
In order to get an idea of the required amount of biogas, I will say that the average family of 4 people will need 1.8-3.6 m³ for cooking. To heat a room of 100 m² – 20 m³ of biogas per day.
Reactor installation and fabrication
A metal tank, a plastic container can be used as a reactor, or it can be built from brick or concrete. Some sources say that the preferred shape is a cylinder, but in square structures built from stone or brick, cracks form due to the pressure of the raw materials. Regardless of the shape, material and installation location, the reactor must:
- be water- and gas-tight. Mixing of air and gas should not occur in the reactor. There must be a gasket made of sealed material between the cover and the body;
- be thermally insulated;
- withstand all loads (gas pressure, weight, etc.);
- have a hatch for carrying out repair work.
Installation and selection of the reactor shape is carried out individually for each farm.
Manufacturing theme DIY biogas plant very extensive. Therefore, in this article I will focus on this. In the next article we will talk about choosing the remaining elements of a biogas plant, prices and where it can be purchased.
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 a clear 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 mainly build small ones for small farms. Let's explain why this is so:
Does it make sense to produce biofuel 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.
Another video from the domestic Kulibin
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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 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 that work on the same principle can be assembled on your own from available materials and parts.
This video shows a small installation that allows you to produce biogas from manure. Livestock waste products (100 kg/day) are loaded into the bioreactor.
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What is biogas and how is it formed?
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.
How to build a bioreactor on your own?
To begin with, I would like to indicate what kind of structure can be built:
Scheme of the simplest biogas plant, assembled on your own. Its design does not provide for heating and a mixing device. Legend: 1 - reactor (digester) for processing manure; 2 - hopper for loading raw materials; 3 - entrance hatch; 4 - water seal; 5 - pipe for unloading mining; 6 - pipe for biogas removal
To obtain free biofuel on the site, you must select a place to build a reinforced concrete tank that will serve as a bioreactor. 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.
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.
Organic waste is fed into a sealed bioreactor container buried in the ground, which contributes to the release of biogas during the fermentation process.
If there is a small amount of waste, the reinforced concrete tank can be replaced with a metal container, for example, a barrel. P
When choosing a metal container, pay attention to the presence of welds and their strength. 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.
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.
Similar temperature control systems are installed in hot water boilers, so they can be purchased in stores specializing in the sale of gas equipment.
Scheme of organizing biogas production at home. 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.
Correct gas removal from the bioreactor
The gas produced during the fermentation of organic matter is removed through a special hole provided in the design of the upper part of the lid, which tightly closes the tank. To eliminate the possibility of biogas mixing with air, it is necessary to ensure its removal through a water seal (hydraulic seal).
You can control the pressure of the gas mixture inside the bioreactor using the lid, which should rise when there is excess gas, that is, play the role of a release valve. You can use a regular weight as a counterweight. If the pressure is normal, then the exhaust gas will flow through the outlet pipe into the gas tank, being cleaned in water along the way.
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.
P.S. And remember, just by changing your consumption, we are changing the world together! ©
Biogas is a gas produced by the fermentation of biomass. In this way you can get hydrogen or methane. We are interested in methane as an alternative to natural gas. Methane is colorless and odorless and is highly flammable. Considering that the raw materials for producing biogas are literally under your feet, the cost of such gas is significantly less than natural gas, and you can save a lot on this. Here are the numbers from Wikipedia “From a ton of cattle manure, 50-65 m³ of biogas is obtained with a methane content of 60%, 150-500 m³ of biogas from various types of plants with a methane content of up to 70%. The maximum amount of biogas is 1300 m³ with a methane content of up to 87% can be obtained from fat.", "In practice, 300 to 500 liters of biogas are obtained from 1 kg of dry matter."
Tools and materials:
-Plastic container 750 liters;
-Plastic container 500 liters;
-Plumbing pipes and adapters;
-Cement for PVC pipes;
-Epoxy adhesive;
-Knife;
-Hacksaw;
-Hammer;
- Open-end wrenches;
-Gas fittings (details in step 7);
Step one: a little more theory
Some time ago, the master made a prototype of a biogas plant.
And he was bombarded with questions and requests to help with the assembly. As a result, even the state authorities became interested in the installation (the master lives in India).
The next step the master had to do a more complete installation. Let's consider what it is.
-The installation consists of a storage tank in which organic material is stored, and microorganisms process it and release gas.
-The gas thus obtained is collected in a reservoir known as a gas header. In the floating type model, this tank floats in suspension and moves up and down depending on the amount of gas stored in it
-The guide pipe helps the gas collector tank to move up and down inside the storage tank.
-Waste is fed through a supply pipe inside the storage tank.
-The completely recycled suspension flows through the outlet pipe. It can be collected, diluted and used as plant fertilizer.
-From the gas manifold, gas is supplied through a pipe to consumer appliances (gas stoves, water heaters, generators)
Step two: choosing a container
To select a container, you need to consider how much waste can be collected per day. According to the master, there is a rule where 5 kg of waste requires a container of 1000 liters. For a master it is approximately 3.5 - 4 kg. This means the capacity needed is 700-800 liters. As a result, the master purchased a capacity of 750 liters.
Installation with a floating type of gas manifold, which means you need to select a container such that gas losses are minimal. A 500 liter tank was suitable for these purposes. This 500 liter container will move inside the 750 liter container. The distance between the walls of the two containers is about 5 cm on each side. Containers need to be selected that will be resistant to sunlight and aggressive environments.
Step Three: Preparing the Tank
Cuts the top off the smaller tank. First, he makes a hole with a knife, then saws it with a hacksaw blade along the cut line.
The top part of the 750 liter container also needs to be cut off. The diameter of the cut part is the lid of the smaller tank + 4 cm.
Step four: supply pipe
An inlet pipe must be installed at the bottom of the larger tank. Biofuel will be poured inside through it. The pipe has a diameter of 120 mm. Cuts a hole in the barrel. Installs the knee. The connection is secured on both sides with cold welding epoxy glue.
Step five: pipe for draining the suspension
To collect the suspension, a pipe with a diameter of 50 mm and a length of 300 mm is installed in the upper part of a larger tank.
Step six: guides
As you already understood, a smaller one will “float” freely inside a large container. As the internal tank fills with gas, it will heat up and vice versa. To allow it to move freely up and down, the master makes four guides. In the “ears” he makes cutouts for a 32 mm pipe. Secures the pipe as shown in the photo. Pipe length 32 cm.
4 guides made of 40 mm pipes are also attached to the inner container.
Step seven: gas fittings
The gas supply is divided into three sections: from the gas manifold to the pipe, from the pipe to the cylinder, from the cylinder to the gas stove.
The master needs three 2.5 m pipes with threaded ends, 2 taps, sealing gaskets, threaded adapters, FUM tape and brackets for fastening.
To install the gas fittings, the master makes a hole in the upper part (formerly the lower part, i.e. the 500 liter cylinder is turned upside down) in the center. Installs the fittings, seals the joint with epoxy.
Step Eight: Assembly
Now you need to place the container on a flat, hard surface. The installation location should be as sunny as possible. The distance between the installation and the kitchen should be minimal.
Installs smaller diameter tubes inside the guide tubes. The pipe for draining excess suspension is extended.
Extends the inlet pipe. The connection is fixed using cement for PVC pipes.
Installs a gas accumulator inside a large tank. Orients it along the guides.
Step nine: first launch
For the initial start-up of a biogas plant of this volume, about 80 kg of cow manure is needed. Manure is diluted with 300 liters of non-chlorinated water. The master also adds a special additive to accelerate the growth of bacteria. The supplement consists of concentrated juice of sugar cane, coconut and palm trees. Apparently it's something like yeast. Fills this mass through the inlet pipe. After filling, the inlet pipe must be washed and a plug installed.
After a couple of days, the gas accumulator will begin to rise. This began the process of gas formation. As soon as the storage tank is full, the resulting gas must be vented. The first gas contains many impurities, and there was air in the storage tank.
Step ten: fuel
The process of gas formation has started and now we need to figure out what can and cannot be used as fuel.
So, the following are suitable for fuel: rotten vegetables, peelings of vegetables and fruits, unusable dairy products, overcooked butter, chopped weeds, waste from livestock and poultry, etc. A lot of unusable plant and animal waste can be used in the installation. The pieces need to be crushed as finely as possible. This will speed up the recycling process.
Do not use: onion and garlic peelings, eggshells, bones, fibrous materials.
Now let's look at the question of the amount of loaded fuel. As already mentioned, such a capacity requires 3.5 - 4 kg of fuel. Fuel processing takes from 30 to 50 days, depending on the type of fuel. Every day adding 4 kg of fuel, within 30 days about 750 g of gas will be produced from it daily. Overfilling the unit will lead to excess fuel, acidity and lack of bacteria. The master reminds that according to the rules, 5 kg of fuel is needed daily per 1000 liters of volume.
Step Eleven: Plunger
To make loading fuel easier, the master made a plunger.
Required mandatory materials:
- two containers;
- connecting pipes;
- valves;
- gas filter;
- means of ensuring tightness (glue, resin, sealant, etc.);
Desirable:
- stirrer with electric motor;
- temperature sensor;
- pressure meter;
The sequence below is suitable for the southern regions. For operation under any conditions, a reactor heating system should be added, which will ensure heating of the vessel to 40 degrees Celsius and increase thermal insulation, for example, by enclosing the structure with a greenhouse. It is advisable to cover the greenhouse with black film. It is also advisable to add a condensate drainage device to the pipeline.
Creating a simple biogas plant:
- Create a storage container. We select a tank where the resulting biogas will be stored. The reservoir is fixed with a valve and equipped with a pressure gauge. If gas consumption is constant, then there is no need for a gas tank.
- Insulate the structure inside the pit.
- Install pipes. Lay pipes into the pit for loading raw materials and unloading compost humus. An inlet and outlet hole are made in the reactor tank. The reactor is placed in a pit. Pipes are connected to the holes. The pipes are tightly secured using glue or other suitable means. Pipe diameters less than 30 cm will contribute to their clogging. The loading location should be chosen on the sunny side.
- Install the hatch. The rector, equipped with a hatch, makes repair and maintenance work more convenient. The hatch and reactor vessel should be sealed with rubber. You can also install temperature, pressure and raw material level sensors.
- Select a container for the bioreactor. The selected container must be durable - since fermentation releases a large amount of energy; have good thermal insulation; be air and waterproof. Egg-shaped vessels are best suited. If building such a reactor is problematic, then a cylindrical vessel with rounded edges would be a good alternative. Square-shaped containers are less efficient because hardened biomass will accumulate in the corners, making fermentation difficult.
- Prepare the pit.
- Select a location for mounting the future installation. It is advisable to choose a place far enough from the house and so that you can dig a hole. Placing it inside a pit allows you to significantly save on thermal insulation, using cheap materials like clay.
- Check the tightness of the resulting structure.
- Start the system.
- Add raw materials. We wait about two weeks until all the necessary processes take place. A necessary condition for gas combustion is to get rid of carbon dioxide. A regular filter from a hardware store will do for this. A homemade filter is made from a 30 cm long piece of gas pipe filled with dry wood and metal shavings.
Composition and types
Biogas is a gas obtained as a result of a three-phase biochemical process on biomass, taking place in sealed conditions.
The process of biomass decomposition is sequential: first it is exposed to hydrolytic bacteria, then acid-forming bacteria and finally methane-forming bacteria. The material for microorganisms at each stage is the product of the activity of the previous stage.
At the output, the approximate composition of biogas looks like this:
- methane (50 to 70%);
- carbon dioxide (30 to 40%);
- hydrogen sulfide (~2%);
- hydrogen (~1%);
- ammonia (~1%);
The accuracy of the proportions is affected by the raw materials used and gas production technology. Methane has the potential for combustion; the higher its percentage, the better.
Ancient cultures dating back more than three thousand years (India, Persia or Assyria) have experience using flammable swamp gas. The scientific basis was formed much later. The chemical formula of methane CH 4 was discovered by scientist John Dalton, and the presence of methane in swamp gas was discovered by Humphry Davy. The Second World War played a major role in the development of the alternative energy industry, requiring the warring parties to have a huge need for energy resources.
The USSR's possession of huge reserves of oil and natural gas led to a lack of demand for other energy production technologies; the study of biogas was mainly a subject of interest to academic science. At the moment, the situation has changed so much that, in addition to the industrial production of various types of fuel, anyone can create a biogas plant for their own purposes.
Installation device – a set of equipment designed to produce biogas from organic raw materials.
Based on the type of raw material supplied, the following types of biogas plants are distinguished:
- with portioned feeding;
- with continuous feed;
Biogas plants with a constant supply of raw materials are more efficient.
By type of raw material processing:
- No automatic stirring raw materials and maintaining the required temperature - complexes with minimal equipment, suitable for small farms (Diagram 1).
- With automatic stirring, but without maintaining the required temperature - also serves small farms, more efficiently than the previous type.
- With support for the required temperature, but without automatic mixing.
- With automatic mixing of raw materials and temperature support.
Principle of operation
The process of converting organic raw materials into biogas is called fermentation. The raw materials are loaded into a special container that provides reliable protection of the biomass from oxygen. An event that occurs without the intervention of oxygen is called anaerobic.
Under the influence of special bacteria, fermentation begins to occur in an anaerobic environment. As fermentation progresses, the raw material becomes covered with a crust, which must be destroyed regularly. Destruction is carried out by thorough mixing.
It is necessary to mix the contents at least twice a day, without violating the tightness of the process. In addition to removing the crust, stirring allows you to evenly distribute acidity and temperature inside the organic mass. As a result of these manipulations, biogas is produced.
The resulting gas is collected in a gas tank and from there it is delivered to the consumer through pipes. Biofertilizers obtained after processing the feedstock can be used as a food additive for animals or added to the soil. This fertilizer is called compost humus.
The biogas plant includes the following elements:
- homogenization tank;
- reactor;
- stirrers;
- storage tank (gas-holder);
- heating and water mixing complex;
- gas complex;
- pump complex;
- separator;
- control sensors;
- Instrumentation and automation with visualization;
- safety system;
An example of an industrial-type biogas plant is shown in Diagram 2.
Raw materials used
The decomposition of any animal or plant matter will release flammable gas to varying degrees. Mixtures of various compositions are well suited for raw materials: manure, straw, grass, various wastes, etc. The chemical reaction requires a humidity of 70%, so the raw material must be diluted with water.
The presence of cleaning agents, chlorine, and washing powders in organic biomass is unacceptable, as they interfere with chemical reactions and can damage the reactor. Also not suitable for the reactor are raw materials with sawdust from coniferous trees (containing resins), with a high proportion of lignin and exceeding the moisture threshold of 94%.
Vegetable. Plant raw materials are excellent for biogas production. Fresh grass gives the maximum fuel yield - about 250 m 3 of gas with a methane share of 70% is obtained from a ton of raw material. Corn silage is slightly smaller - 220 m3. Beet tops – 180 m3.
Almost any plant, hay or algae can be used as biomass. The disadvantage of application is the length of the production cycle. The process of obtaining biogas takes up to two months. The raw materials must be finely ground.
Animal. Waste from processing plants, dairy plants, slaughterhouses, etc. Suitable for biogas plant. The maximum fuel yield is provided by animal fats - 1500 m 3 of biogas with a methane share of 87%. The main disadvantage is shortage. Animal raw materials must also be ground.
Excrement. The main advantage of manure is its cheapness and easy availability. Disadvantage – the quantity and quality of biogas is lower than from other types of raw materials. Horse and cow excrement can be processed immediately. The production cycle will take approximately two weeks and will produce an output of 60 m3 with 60% methane content.
Chicken manure and pig manure cannot be used directly because they are toxic. To start the fermentation process, they must be mixed with silage. Human waste products can also be used, but sewage is not suitable since the fecal content is low.
Schemes of work
Scheme 1 – biogas plant without automatic mixing of raw materials:
Scheme 2 – industrial biogas plant:
