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Development of energy today takes place on a background the change of fuel and energy balance toward a coal constituent. In this connection more deployment of clean coal technologies becomes actual. One of such technologies is a method of incineration of combustible materials in a boiling layer. As it applies to coal a method allows effectively and ecologically safely to burn coals of different quality, including low-grade and wastes of enriching of coal. Technology is attractive also possibility of creation of compact fire-box equipment and automation of fire-box
At the same time efficiency of incineration of coal in a boiling layer depends on implementation of certain requirements to the fuel and to the process. To such requirements behave, for example, sorting of coal, stability of properties and expense at a serve in heating, evenness of serve of coal on the ground of layer, parameters of conduct of fire-box process is a temperature of layer, pseudofluidizing speed, pressure in heating.
In world practice caldrons found a wideuse with heating of boiling layer of different power. Reason of slow introduction of these ме-тодов in our country, besides the requiring the laboratory and pilot working questions of parameters of process and quality of fuel, it is possible to count also the deficit of investments in coal technologies. Therefore passing from the laboratory scale of options of boiling layer to industrial presented a certain technical and economic risk. Presently because of changes in the fuel state of affairs and increase of requirements to the extrass with foods of combustion interest rises in this problem.
At consideration of prospects of the use of hard fuel, in particular for power units of new generation, one of basic questions is his effective incineration. Under the last implementation of two requirements is first of all understood: incineration must be full, i.e. economical, and it must not result in the large extrass of harmful substances (first of all oxides of sulphur and nitrogen).
ДLong time for incineration used and the so-called torch method at that mixture of мелкоразмолотого coal and hot air is continuously given in the zone of burning continues to be used, supporting a conflagrant torch being a radiant and thermal energy source for heating of working body. For implementation of the requirements indicated higher worked out and inculcated in practice a number of regime and structural measures, that, nevertheless, can not decide a problem to a full degree. Therefore the last are 15 conducted searches ecologically of clean technologies of incineration of wide gamut of hard fuels, especially power hard fuels of subzero quality. In the number of such technologies there is technology of incineration of hard fuels in a circulatory boiling layer at atmospheric pressure.
Theoretical basis of functioning of caldrons with ПКС is an idea about a boiling layer. If in some chamber to set a grate on that to place the layer of coal, and to the grate to give air in a small amount, then after the preliminary warming-up of layer burning of fuel will begin from a surface with the selection of gaseous foods of combustion. At filling in of burning fuel on a grate the conflagrant fixed layer will be supported. The so-called stratified incineration of hard fuel will come true. If to increase the serve of air under a grate, then on the particles of fuel being on a grate, speed pressure, that will counteract to gravity, operating on every particle of fuel, will operate. At some speed of air of particle of fuel will appear in the self-weighted state in a lifting blast, and thickness of conflagrant layer will grow
At further growth of speed the separate bubbles of air appear in a layer, and the thickness of layer increases yet more. It is the so-called bubble boiling layer. It behaves how a boiling liquid behaves, from here and the name of method is incineration in a boiling layer.
At the yet greater expense of air there is a carrying capacity operating on the particles of fuel, the so large appears, that they do not have time to burn and break forth from a boiling layer. At the further increase of expense of air a visible layer disappears and takes place burning of accumulations of particles of fuel in all volume of chamber with intensive interfusion. Greater amount of particles of fuel does not have time to burn out and darts out from a chamber. Here on their way set a cyclone - cylindrical vessel in that foods of combustion move away from unfire-damaged particles. Foods of combustion are directed in the second part of caldron - конвективную mine - for heating of working body (waters and pair), and unfire-damaged particles move in an involute stream, cast aside to the walls, fall downward and again directed in the chamber of burning. This is a circulatory boiling layer. his Main feature consists of that circulatory material in hundreds of one times exceeds the amount of the air given for burning.
There is a number of charts, realizing technology. We will consider one of them. Coal from a bunker heads for the grate of heating under that for burning hot air is given. On it a limestone that enters into a chemical reaction with sulphur acts from other bunker, links it in future together with a dry ash taken from a caldron. Thus, the hit of sulphur is eliminated in smoke gases and then in an air pool. Appearing boiling layer passes to part of the warmth the working body, locomotive in screens the walls of heating facing that. From overhead part of heating mixture of foods of combustion and particles of fuel, not fire-damaged in a boiling layer, is directed in a cyclone, where dissociating of particles of unfire-damaged fuel is from foods of combustion. Unfire-damaged hot particles interfuse with the particles of fresh fuel, and this mixture enters conflagrant boiling layer. The products of combustion are in convective shaft, in which are located the other surfaces of heating of the working body: convective primary and intermediate super, economizer, air-heater. At the exit of convective mine from combustion products fly ash is removed, and then they come in electrostatic precipitators to remove residues fly ash, after which they are sent into the chimney for the diffusion in the upper layers of the atmosphere.
One of the main ideas, realized in CFB boilers, consists in the fact, that the temperature fluidized bed is a low - level 820-900°WITH. At such temperatures the formation of oxides of nitrogen goes very slowly. Note that in the flare coal dust furnace combustion temperature reaches 2000 °WITH. In turn, low temperature combustion is the large size of the particles of coal (from 2 to 25 mm) and their dissociation in a boiling layer, as opposed to the dust-coal combustion, where the size of the dust particles is located on the level of 200 m.
Another important idea is repeated circulation of hot mixture of ash, limestone and a relatively small number of supply of fresh fuel. It not only provides good сероочистку products of combustion, but also significantly intensifies the process of incineration.
CFB boilers, besides the mentioned above advantages are a number of others.
However, compared with пылеугольными boilers and CFB boilers are more complex, work in more severe conditions (erosion of the heating surfaces by dusty flow), have increased electric power consumption to drive high-pressure fans for air supply in the combustion zone and creation of a boiling layer.
Technical and economic estimates show that the CFB boilers in a power гоблоках 150-200 Mw provide the cost of electricity, capital costs, fuel costs, maintenance and repair, not exceeding similar costs for coal dust boilers with сероочисткой. It is thus underlined, that the results of the comparison depends on a number of factors and are determined by particular conditions.
Application area CFB - combustion of low-grade solid fuels for steam capacity up to 250 t/h as for new thermal power plants, as well as passing modernization. In the world currently operates more than 200 energy CFB, including mastered the power unit of 250 Mw. In Russia developed CFB boilers with evaporative capacity of 160, 500 and 1000 t/h for burning of black and brown coals of different fields.
Figure 1 shows the design of the STAP, which work in the forced mode allows you to receive the economic and environmental characteristics of boilers of low and average productivity. At the bottom of the air-distributing grid 1 there is a boiling layer 2 with the primary blast on highway 3 from the fan 4. In the above volume 5 on sites 6 run up the flow nozzle installed 7 secondary blast. Nozzle 7 secondary blast targeted the tangential to the conditional body rotation 8 and are directed towards a dead zones 9, in the root of the rising of the fluidized bed of the stream. Motion of particles in an ascending stream and after their separation in heating coincide with a vortical flow, burning and fire-box processes evenly spread in all volume of heating above a layer. Profile of volume is formed by a walling-up 10 and by fire-box screens 11. The flues of heating have statelessness bunkers 12 with ejector 13 return of carrying away, that, as well as system of the pneumatic pelting of fuel 14, by highways 15 secondary blowing connected to the ventilator 4. Must be in a presence and other elements necessary for exploitation and maintenance of heating of boiling layer.
