Technology. Description
The block diagram of typical biogas installation
Distinctive features of our installations
System of preparation of raw material
Reactor
System of heating of the reactor
System of hashing of mass in the reactor
System of the heat insulation of the reactor
Gas-holder
Gas system
System of drainage of the processed raw material
Automatics of control of biogas installation
Algorithms of operation of biogas installation
The schema parallel and the series connection of reactors for escalating power of biogas installation
Mesophilic and thermophilic duties of biogas installation
The block diagram of typical biogas installation
Basis of each biogas installation is the reactor. The reactor represents a tight thermos in which the given constant temperature is supported. For support of temperature the system of preheating and system of a heat insulation of a reactor is used. The block of automatics operates all of it. Also for normal passing response the system of hashing of raw material which also is controlled by the block of automatics is used.
For feeding in a reactor of a feed stock the system of preparation of raw material serves.
For buffering produced gas and stabilization of its pressure the gas-holder is used.
The gas system serves for dehydration of produced gas, the check of pressure of gas, systems of the emergency waste interception of gas and the prevention of reverse motion.
The system of drainage is applied to drainage of the waste raw material (ready biofertilizings).
Distinctive features of our installations
We have analysed all constructions of biogas installations which are applied in the world. After that we have developed philosophy on which it is possible to create biogas installations for small economies of the rather poor countries, such, as the CIS countries. The construction of our installations bases on maximal utilization of standard details and the units manufactured practically in any country of the world. We have chosen for our construction of a detail from the modern synthetics which provide reagent resistance, small weight, a good heat insulation. On the dimension of reactors of installations of our construction, they fall into to small and average installations. But owing to an opportunity of simple scaling, on the basis of our construction it is possible to set even large installations, and to increase volumes and powers gradually, in process of accumulation of resorts.
System of preparation of raw material
The system of preparation of raw material serves for deluting initial organic mass by water for maintenance of necessary dampness and temperature of raw material, and also for pumping raw material in a reactor. Engineering problems solved by development of such unit is an even hashing an original stock, maintenance of temperature of an intermixture in the given limits, irrespective of environment temperature, pumping in a reactor of strictly fixed portion of raw material with maintenance of leakproofness of a reactor and a persistence of pressure of gas on a yield.
In the constructions we offer 2 expedients of the solution of these problems: pumping intermixtures from system of preparation by gravity, or by means of the special fecal pump.
The first expedient most simple and cheap, but it becomes complicated with propagation of volume of a reactor. Its essence is reduced to that the container for preparation of raw material settles down above a reactor on the calculated quantity, and the prepared raw material is filled in a reactor of its own accord. It is especially convenient to apply this method when a topography where biogas installation is located promotes it}, and it is not necessary to build too high stockade. The volume of container for preparation of raw material is routinely equal 5-10 % of volume of a reactor. With propagation of volume the loading on a construction of a stockade that demands its complication and rise in price grows.
The second expedient – classical. Complexities consist that cheap fecal pumps have no cutting knifes and consequently can easily get littered. And sanitation of the pump and a submitting tract of fecal matters manually – a problem not from the most pleasant. Cost of the good fecal pump is comparable to cost of the most small biogas installation. Therefore application of the fecal pump is meaningful for average biogas installations.
The screw feed of raw material is meaningful only for greater installations and consequently by us it is not applied.
Reactor
The reactor of biogas installation represents a tight thermos. Reactors of large biogas installations usually make of concrete which then warm various expedients. The basic minus of the given construction is a capital structure of a specific construction. It cannot be moved, dismantled lost-free. Accordingly, it cannot be sold without sale of the ground area, the bank reluctantly accepts it in the mortgage at handing over of credits. The structure of such reactor occupies the significant time.
Reactors of small installations usually make of a metal leaf. Often use reservoirs was in the use. A minus is major weight, the high price and low rust resistance.
In our construction we have applied containers from the modern synthetics. They have small weight, high rust resistance. Them easily to install, dismantle, interface to input and target tubes. They do not require corrosion protection. Biogas installation on the basis of such reactor can be easily dismantled and installed on a new place and consequently it can be sold or exposed in the mortgage.
System of heating of the reactor
The temperature of raw material in a reactor should be supported at a level, optimal for functioning conforming anaerobic bacteria. Response – exothermic, but at environment temperature the raw material is essential to demanded temperature of reaction is necessary to preheat. Complexity consists that preheating should be even, and the temperature should be kept in the given limits. It is the most rational to use energy of combustion of the biogas produced by installation for preheating a reactor.
In large installations biogas is usually processed in an electricity in cogenegation installations (the generator on the basis of an internal combustion engine). The cooling system of the engine allocates heat in special capacity. And further through heat exchangers in this capacity warmly moves for preheating a reactor, and also for interior needs of the owner of biogas installation. In this case warmly is simply a by-product of the cogeneration installation producing an electricity.
Small and average biogas installations do not produce so much biogas to load standard cogeneration installation. Therefore for their heating apply standard gas boilers, same, as well as to heating rooms. Only tubes with hot water pass through a reactor. This construction not too complex, but nevertheless has no economic sense for small biogas installations.
For each biogas installation it is necessary to provide an initial warming up that response has begun and has become to be produced biogas. If to start installation in a warm season at temperature of an ambient air from above 20°C approximately in a week response will begin, the mass in a reactor will start to be warmed up itself, biogas will start to precipitate out. In a cold season such start is impossible. Therefore for start it is necessary or an exterior radiant of gas, or system of electropreheating. And if gas will be in most cases inaccessible to use an electricity almost always probably. And for small installations the system of electropreheating is represented is single rational. It is not too expensive, is easily controlled and at a good heat insulation of a reactor there will be no the expensive on stream.
System of hashing of mass in the reactor
The raw material in a reactor during passing response tends to be divided into fractions. At the bottom of a reactor the insoluble residue, more light parts, carried away by blisters of gas accumulates, rise upward and form a crust. All this essentially slows down reaction rate.
That response proceeded evenly and efficiently, the mass inside of a reactor is necessary for mixing from time to time. Also mixing improves uniformity of warmup of raw material.
But hashing of reactive mass inside of a tight reactor – not trivial problem. Details of an mixer should be made of a rust-proof material. The driving of an mixer should be or inside of a reactor, or it is necessary to apply a high-quality adapter coupling. It is possible to apply also hydraulic or air hashing. From all four expedients and reliable for small installations application of the mixer which are being inside of a reactor is obtained by the cheapest. Special adapter couplings are not a standard product, therefore their application in small and average biogas installations expediently at their serial discharge. For air mixing it is necessary quality fire and the explosion-proof compressor. For a hydraulic mixing the quality powerful fecal pump which expensively enough costs is necessary. Therefore last two expedients are more expedient for applying in large installations.
We while apply the two first expedient of hashing.
System of the heat insulation of the reactor
The reactor as it is specified above, represents a thermos. If the heat insulation will be more quality made, the above will be efficiency of a reactor, the less energies will be spent for maintenance of necessary temperature. The heat insulation is especially important at exploitation of biogas installation in winter requirements.
The theoretical thermos has hollow walls, inside of which empty space. Really to produce it is impossible, but the philosophy of a heat insulation consists in this: besides interior power wall of a reactor the exterior tight wall with the reflecting bed guided inside is made. Between walls – hollow, or porous filler.
Gas-holder
The gas-holder is a container in which the produced biogas collects. Also the gas-holder in biogas installation carries out function of the stabilizer of pressure of gas and the buffer at a batch of a reactor and drainage of fertilizings.
The reactor which is closed from above by a special rubber membrane serves in large biogas installations by a gas-holder. Displacement volume of such gas-holder not so major, but at large biogas installations is not present irregularity in consumption of gas as all gas at once is processed in an electricity.
In small and average biogas installations consumption of biogas is unpredictable, therefore it is desirable, that displacement volume of a gas-holder corresponded even one or two-hour production of biogas by installation. Also it is desirable, that displacement volume of a gas-holder more than twice exceeded volume one time batches or plum of raw material. To small and average biogas installations usually apply wet and dry seal gas-holders. The dish gasholder has apparently greater cost and complexity on stream, than dry, made of the modern synthetics.
Gas system
The biogas produced by biogas installation, does not move directly to the consumer, and passes through some special devices as which it is possible to term as gas system of biogas installation.
First of all, biogas is necessary for passing through a back pressure valve which provides flow of gas only in one direction – from a reactor to the consumer. The most simple back pressure valve – fluid, similar to what we apply, fermenting house wine. This back pressure valve can be blanket for several reactors, providing simultaneously independence of their gas systems, and at the same time equality of pressures in operating duties.
For the check of pressure of gas the pressure gage is installed. Also an obligatory and major device is the safety valve which pits in an atmosphere biogas at excess of admissible pressure. Such safety valve too easier and most cheaply to make fluid, as well as a back pressure valve. Only it is necessary to fill in a fluid non-freezing and not evaporating, phylum “Antifreeze”.
Generally, methane – the basic constituent of biogas – more all destroys an ozonosphere of the Earth and consequently exhausts of methane in an atmosphere from the point of view of ecology are very undesirable. Therefore the biogas which has been elapsed through a safety valve, usually burn in a flare. The Flare is a burner on which the spark for burning during the moment of operation of a safety valve moves, and fire is supported, while the safety valve is open. That is the mechanism of activity precisely same, as well as in the modern gas boilers.
System of drainage of the processed raw material
In large biogas installations slimes, or the waste raw material drain off by means of auger pompes.
For the small and average biogas installations made on the basis of reactors of our construction, it is the most favourable to drain off slimes by gravity in the container located below reactors. Thus the system of drainage represents a usual sewer with the conforming cock. Main technological feature is the terminal of a tube which should provide impossibility of suction in a reactor of air at drainage.
Automatics of control of biogas installation
The block of automatics which controls all parameters is necessary for uninterrupted functioning biogas installation and maintains the given temperature and intensity of response. Operation of the block of automatics bases on the information removed by several data units: a temperature detector of raw material in a reactor, level sensors of raw material in a reactor. Being based on these indications, and also on signals of the timer, the block of automatics switches on and off system of preheating, mixing system, and also signals about the beginning and the end of a gulf and drainage of raw material.
The block of automatics of our development bases on standard inexpensive controllers. For management of a powerful loading, such as electroheating elements or engines of mixing system, are applied magnetic actuators.
Algorithms of operation of biogas installation
Depending on quantity of reactors biogas installation can have some algorithms of operation basing a continuous or intermittent cycle.
At the first fill of a reactor to biogas installation necessarily there should be a quantity of anaerobic bacteria. Naturally these bacteria live in “rumen” of large beeves.
Therefore dung of cows – the best raw material for start of operation of biogas installation. Also as “sour” the slimes – the waste raw material of biogas installation can serve. After a fill and a warming up of raw material up to the demanded temperature there can pass one week while gassing will achieve nominal quantities. The cycle of fermentation lasts from two weeks about one month, but slimes drain off when gassing apparently falls. Slimes drain off on two third, leaving in a reactor one third as “sour”. Then the cycle repeats. It is clear, that at such intermittent algorithm of operation of biogas installation, gassing will be irregular and consequently biogas is difficult for using for any useful purposes.
There is a regime of a continuous cycle when, for example, every day from a reactor 1/20 volumes of slimes drain off, and the same amount of raw material is filled in. Gas thus is precipitates out evenly, but biofertilizings are obtained poor-quality as in drained off slimes there are 1/20 not refermented raw materials. It is harmful as well from the ecological point of view.
To operational development of biofertilizings up to demanded condition in that case apply the cabinet of end fermentation.
The schema parallel and the series connection of reactors for escalating power of biogas installation
The cabinet of end fermentation actually represents one more reactor. This idea has prompted us on one of the key moments of our production technology of biogas installations.
It is possible to make biogas installations with several reactors. At magnification of quantity of reactors there is a same system of a fill and system of drainage of raw material (is more exact, they increase slightly) a gas heating system it is possible to design with such reserve that the same boiler could pull some reactors, the system of automatics increases only for necessary number of modules of management in temperature. That is, at magnification of power of biogas installation by addition of additional reactors, cost of installation grows not proportionally to magnification of bulk volume of reactors, and it is less.
Reactors can be connected collaterally and serially. If N reactors are joined collaterally the unloading and a fill in each of reactors is by turns made through everyone 20/N days (in view of duration of a cycle in 20 days). Thus each reactor once in 20 days is emptied on two third, and then filled with fresh raw material. Quality of biofertilizings thus will be maximal, but production of biogas insufficiently even, especially, if reactors a little.
If to connect reactors serially it is necessary to drain off and fill in every day 1/20 total working capacities of reactors (it compounds 80 % of the common capacity of reactors). Production of biogas thus will be maximally even. Quality of fertilizings will depend on quantity of reactors.
Mesophilic and thermophilic duties of biogas installation
There are some views of anaerobic bacteria, each of which maximally efficiently works at the certain temperature. In this case distinguish various temperature schedules of fermentation. In practice two regimes are used: mesophilic (30-40°C) and thermophilic (51-55°C).
In a thermophilic regime response goes twice more promptly, and accordingly biogas twice precipitates more promptly out. Also the thermophilic regime has advantages from the point of view of ecology as in this regime causative microorganisms are destroyed almost completely all. But the thermophilic regime demands greater power inputs on maintenance of necessary temperature of reaction, and also greater precision of maintenance of temperature. Besides quality of biofertilizings in this regime is obtained worse, than in mesophilic.
The mesophilic regime makes less rigorous demands to precision of maintenance of temperature, but not always can suit from the point of view of ecology.
If biofertilizings are main for us the mesophilic regime is a uncontested choice. If it is necessary to save essentially on cost of biogas installation the thermophilic regime suits. In fact the installation working in a thermophilic regime has twice greater transmissive capacity, and, accordingly, can be reduced twice in comparison with the installation working in a mesophilic regime, at processing the same amount of raw material.