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SELF-DYNAMIC REACTOR FOR OBTAINING BIOGAS
On average, for heating a building with an area of 40-50 m 2 , a four-burner plate is needed per hour of 3.0-3.5 m 3 biogas. When equipping the local heating system, it is possible to use the widely used automatic heating gas heater AOGV-11, 3-3-U .
The significant factor determining the intensity of gas formation is the temperature of the process. It should not be forgotten that the article "Biogas: Heats, Also Brews" describes an experiment relating to a country with a mild climate. Apparently, for more severe climatic conditions, heating is more necessary, perhaps even in a steady process. And if the preheating is envisaged, then it seems appropriate to use it as an effective regulating factor, due to which it is possible to increase gas formation several times. (On another controlling factor - mixing - let's say further.)
Now, given the combined effect of these factors on the capacity of the plant, we can give some recommendations.
When choosing the size of the fermenter, you can focus on the options given in the previous publication; taking into account the more severe climate, it is worth adding to the installation a heating element, for example in the form of coils. Trial operation will immediately reveal the effect of heating on the performance of the device. To systemize the debugging work it is recommended to create a notebook (not relying on memory) to also record all the changes - as if entered, as well as received. Practice illustrates that every 10 ° of additional biomass heating doubles the gas yield from 1 m 3 of the fermenter.
Here are some data for those who are going to do the design of the installation. From 1 ton of raw material, CO 2 100 m 3 of gas is produced. Its calorific value is approximately 5500-6000 kcal / m 3 . For comparison: household gas is not much more caloric - only 7000 kcal / m 3 .
Now about the biology of the process. Methane-producing bacteria are present in the raw material itself. Their cultures develop in the fermenter for up to three weeks, until the mass begins to release gas. When using the ready-made "starter" from the previous portion from the already operating fermentor, the time of the source of gas production is reduced to about a week.
Methane-producing bacteria are divided into three groups. Psychrophilic effectively work in the range of +5 ... + 20 ° . With a further increase in temperature, mesophilic bacteria develop, their operating range is + 30 ... + 42 ° . And at an even higher temperature, the action of already thermophilic bacteria manifests itself, which operate in a very narrow range: +54 ... + 56 .
An impressive number of questions pertain to the design of the installation, primarily - to create the possibility of periodic refueling of raw materials and mixing of biomass without depressurizing the bell. First of all, it must be said that the continuous production of gas can be obtained by a route of duplication of installations. With duplicated fermentors, when replacing them repeatedly, you can do without complicating the system.
Therefore, the future creator of the biogas plant should be compared, in relation to its capabilities, three schemes: the simplest with periodic refilling; paired protozoa, with alternate refills; with a special device that provides a continuous supply of gas.
Choosing the third scheme, we need to keep in mind that for the fermenter's work not only refueling with raw materials is required, but also waste disposal.
In the latter scheme refueling of raw materials, waste disposal is not equivalent in terms of periodicity. So, waste disposal can be combined with the suspension of the process for cleaning, revision of the system. What touches refueling, then it is done more often is also easier: daily from the bottom is removed 1/10 of capacity, from above is added the same fresh biosyarya.
One of the feasible ways of refueling a fermenter without gas deprivation is based on the so-called principle of communicating vessels. To do this, near the fermentor pit, a small filling capacity is arranged, connected to it by a pipeline located below the liquid level ( Fig. 1 ). The pipeline is made of a piece of ceramic sewer or asbestos cement pipe, which is embedded in the walls of the tanks.
Such a system is in itself a liquid gas shutter. Increase the efficiency of feeding the concentrate with an insert hopper hopper ( Fig. 1a ). Pushing the ditch through the pipeline can also be the simplest mesh piston. At once it is also used as a damper, which prevents self-mixing of biomass between the two tanks.
Much of the need for periodic mixing of biomass. How to perform this operation without depressurization? Not everyone knows about the possibility of its self-mixing. Let's recall the effect of convection: it can be observed in the upper room, when some fluff appears over the heating battery, floats up, falls down at the opposite wall, and again gets carried away by a light stream to the battery. this effect of thermal circulation of the medium is not difficult to obtain also in the fermenter if one places the heating pipes (coil) in its lower part, displacing them to one edge; convection will provide self-agitation. In the gasification process that has already begun, the effect of raising gas bubbles in the zone above the preheater will be added to this.
It is also easy to make a mechanical biomass mixer. It is especially expedient in a place with a mild climate, in which place there is no need to use heating. As practice shows, it is better to provide this in advance. After all, if the system itself goes on heating, then why, at that time, it is asked, to expend energy on mixing. In addition, it is not necessary to stir the mass continuously. You can act this periodically, for example, in the morning also in the evening. It is even necessary to turn this operation into an additional, regulating. To do this, it is enough to monitor the location of the bell: as if only it falls to the lower level (a small gas reserve), it is necessary to mix biomass - the gas emission will immediately increase.
The simplest mixer is easy to make in the form of an impeller with a drive through connections through the same siphon pipeline ( Fig. 2 ). There is no need for continuous rotation in one direction. If the mixer owns radial blades, enough rocking movements. You can also confine yourself to one blade. The common space for their own solutions. As drafts it is better to use non-rotting materials, for example, an insulated electric wire or kapron (chloride) cord, sold in hardware stores as if underwear. There is also the problem of bell stability. Readers who carefully studied the material " Biogas: Also Warms, Also Brews, " already noticed that if the diagrams shown in Figure 1 are implemented without any modification of the structure, then the bell may lose its balance at once, as if it pops up: either it capsizes or jams .
In Figure 3 , the same publication does not inadvertently provide a guiding tube for the bell, but such a setup is more difficult for home production.
Such a bell balancing system is also advantageous in that it can be used as a lifting device in a revision as well as cleaning the fermenter. Taking this into account, it is not difficult to supplement the system with some auxiliary elements: it is better to arrange the blocks on the re-arrow (after all, it is strictly forbidden to raise the bell to work under it - " DO NOT STOP UNDER THE CARGO! "). It is also worthwhile to make the crutch of the "crane" also rotary, but the counterweight to tying as on a warehouse scale. But if in your area of frost does not happen, provide a counterweight in the form of a container filled with water.
The most serious embarrassment on the way of the self-made craft is the production of the bell. Galvanized roofing iron allows you to give it the right shape with simple means, besides it will become light. But the fragility of such material with rapid corrosion in an aggressive environment makes it necessary to look for other options. Therefore, we strongly advise you to take a closer look at the available scrap metal. Old containers, for example, from oil products, being cut off, can be a very suitable semi-finished product, as if in shape (usually with welded spherical bottoms), as well as in the thickness of the sheet material: from 2 to 5 mm .
Apparently, the bell's dimensions will be 2-3 m in the same height. If the "barrel" turns out to be smaller, it is worth considering whether to operate a large bell or take a smaller pair (for example, D = 1.5 m ), at the same time returning to the version of coupled simple plants.
Some readers have the problem of determining the gas pressure. Apparently, they did not take care of the obvious: as if only the bell pops up - the power of the gas pressure reached the value of the mass of the bell. Let us explain this on the sample. With a bell skirt diameter of 2 m, the area of its cross-section will be S = kN 2 = 3.14 X 1 = 3.14 m 2 = 31 400 cm 2 . At a wall thickness of a bell of 5 mm and height of 2 m its authority will make about 500 kg. Let us assume that the actual authority of the bell is 470 kg . Then the bell will float at a gas pressure of 0.15 atm . (In the SI system , the mass M = 470 kg , the power of weight F = 4700 N , the gas pressure p = 4700/31 400 = 0.15 N / cm 2 = 0.15 atm ).
By the measure of lifting the bell, the pressure will not change approximately, its rise will only result from the displacement of the liquid capacity equal to the emerging elements of the bell walls.
Noting the low gas pressure, we observe that it (if necessary) can be increased in a simple way: to install an additional load on the bell, placing it lower, for the chosen balance of the bell.
A few interesting examples for comparison. The gas pressure in the city network is in the range of 200-300 mm of water. Art. , and allowed - up to 600 mm of water. Art . In our system, this pressure should be similar to the limiting one. Naturally, the question begins: is a personal farmstead able to give a sufficient amount of bio-raw materials? Of course not. Our recommendations refer primarily to cooperative livestock farms, which are getting more and more development every day. In addition, the reserves are also considerable in the collective and state farms: another time near the livestock farms a considerable amount of manure is accumulated, which in no way is used at all. Local residents could dispose of it, and then export it to the fields. After all, the raw material from the fermenter practically does not lose its value as a fertilizer. There is a double economic benefit.
In conclusion, we again ask readers to share their experiments in designing also the operation of biogas plants.
Author of the article: Sergey Velichkin