FI87107C - SAETT ATT FOERHINDRA FUKTUTFAELLNING I PNEUMATISKA TRANSPORTLEDNINGAR I EN PFBC-KRAFTANLAEGGNING OCH EN PFBC-KRAFTANLAEGGNING - Google Patents

Description

87107

Method for preventing moisture condensation on the pneumatic conveyors of the PFBC power plant and the PFBC power plant

The invention refers to a method for preventing condensation in the pneumatic conveyors, tanks or other parts of a PFBC power plant during start-up. In addition, it means the transportation system. The invention is intended to be applied in a system for conveying crushed or ground solid material, for example for the supply of crushed coal or crushed sulfur absorber, for combustion in a pressurized furnace on a fluidized grate or for the removal of ash or other dust separated from a scrubber.

Under certain operating conditions, the temperature of the transport gas or the temperature of the walls of the transport lines or tanks may have to be below the dew point of, for example, water vapor or sulfuric acid in the transport gas. This water vapor then condenses as droplets into the transport gas or condenses as moisture on the cold surfaces of pipelines and tanks. Moisture condensation is usually local. As moisture condenses, solid particles, primarily fine fractions, adhere to water droplets and wet surfaces, forming deposits. The thickness of these deposits increases until ... the surface temperature exceeds the dew point. Deposits can cause the wires to fill up and this is a big problem.

In a PFBC power plant, critical conditions for filling may occur when starting a cold plant. By heating all important components to a temperature above the dew point of the water vapor in the transport gas, the risk of condensation can be eliminated. It is difficult to heat in all places where there is a risk of moisture condensation, such as corners, bends in the pipe or areas of very thick materials.

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According to the characterizing part of claim 1, energy is introduced into the conveying system in the form of electromagnetic waves, preferably from the microwave area, for heating and evaporating the water droplets in the conveying gas and the condensed moisture of the pipe and tank walls.

Evaporation takes place by dielectric heating of water droplets and moisture. The absorption of microwave energy depends on the dielectric constant of a substance and increases as this value increases. Because the dielectric constant ε of liquids, such as water, is high, primarily water droplets and condensed moisture absorb microwave energy. The metal surfaces of pipelines and tanks conduct electricity and reflect microwaves. Only the amount of energy wasted is absorbed. Microwaves look for every corner of a space. This means that water droplets and condensed moisture heat up and evaporate wherever there are droplets or moisture. Heating energy is directed to the right places and used efficiently.

Absorbed energy: P ~ f · / κ where f = frequency · '· κ = relative dielectric constant = e / e0 ε0 = dielectric constant in vacuum

Therefore, in order to achieve the best power, a high frequency must be selected. In the established heating technique, frequencies are used in the range of 1-30 GHz (about 1-30 cm). The frequency of the current heating may conveniently be located in this frequency range.

Fig. 1 schematically shows the invention, Fig. 2 the invention applied to a power plant burning fuel on a pressurized fluidized grate, the so-called To the PFBC plant, and Figure 3 shows the connection of the microwave generator to the transport line of the plant of Figure 2.

Fig. 1 shows a conveying line 1 for conveying a powdery substance 2, to which a microwave generator 3 is connected by a tube 4. Here, a microwave-permeable plate 5, for example a glass plate, is placed. The plate is necessary to prevent dirt from penetrating the microwave generator. Elevated pressure in lines or a tank, such as in a PFBC plant, also forms a pressure barrier.

In Figures 11, denotes a pressure vessel, 12 a furnace and 13 closed cyclone-type purifiers for this pressure vessel. Only one purifier 13 is shown, but in reality there is a purification plant with several parallel cyclone groups 13 connected in series. through. The turbine drives a compressor 19. The turbine compressor unit 18 can be connected to the starter motor 20 by a switch 29. Alternatively, a generator integrally connected to the turbine compressor unit can be used as the starter motor. In the compressor 19, the compressed combustion air condensed; is introduced into the space 22 in the pressure vessel 11 by a line 21. Combustion air flows from the space 22 through the nozzles 23 at the bottom of the fireplace 24 to the fireplace 12 and fluidizes the material on the grate 14. The grate 14 has a bundle of pipes 25 in which steam is generated using a steam turbine (not shown). This bundle of pipes also cools the grate 14. Separated in the cyclone 13, the dust is led by a line 26 to a cooled dust outlet 27, in the shaft 2 of which the combustion air flowing to the nozzles 23 is cooled. , this. The dust is transported by wire to 30 non-shown collection tanks.

The fuel is fed to the furnace 12 by a pneumatic conveying system 31. It includes a supercharger 32 for the conveying gas. Its inlet side is connected to the space 22 in the pressure vessel 11 and its outlet side to the transport line 87107 4 for supplying fuel to the grate 14. It also includes a lock hopper system with a first atmospheric tank 34 and two series-closed shut-off tanks 35 and 36. 37 and 38 are control valves 40 or 41. The outlet line 42 from the tank 36 has an outlet line driven by the motor 44. At the junction 45 of the line 42 and the line 33, there is a choke in the form of a nozzle 46 upstream. Nozzle 46 is preferably a Laval nozzle. When using a Laval nozzle, a constant velocity of the transport gas in all essential lines 33 is achieved, regardless of the pressure after the nozzle 46, when it falls below the pressure before the nozzle by at least about 5%. Other types of choke require a higher pressure difference for a constant velocity of the transport gas in line 33 as the pressure varies after the nozzle and more compressor operation.

Microwave generators can be connected to different parts of the plant. The microwave generator 50 may be connected to the carbon or absorbent transport line by line 51. The microwave generator 52 may be connected to the furnace by a line 53 and terminate at the top. From the top 15, the microwaves can be passed further through line 16 to cyclone 13 and further through line 16 and ash remover 27. It is possible to connect the microwave generator 54 on the line 55 to one or more dust separators 13. The microwaves can then enter the turbine via the cyclone 13 and the line 17, whereby condensation of moisture and dust deposits can also be prevented. In addition, it may be convenient to connect the microwave generator 56 to the dust transport line 26 at some turning point. Such a connection is shown on a larger scale in Figure 3. Line 57 has a microwave permeable window 58.

Claims (3)

5 87107 A method for preventing condensation in the pneumatic conveyors (26, 33), tanks (12, 13) or other parts (18) of a PFBC power plant during start-up of the plant, characterized in that the lines (26, 33), the tanks (12, 13 ) or other parts (18) are energized as microwaves which evaporate the water formed at the dew point and condensed on the surfaces. 2. A PFBC power plant comprising tanks (12, 13), pneumatic conveyors (26, 33) and other parts (18), characterized in that in order to prevent moisture condensation in the tanks (12, 13), pneumatic conveyors (26, 33) or other parts (18), a microwave generator (50, 52, 54, 56) is connected to one or more of said parts. Power plant according to Claim 2, characterized in that a microwave-permeable plate (58) is arranged between the microwave generator (50, 52, 54, 56) and one line (26, 33), tanks (12, 13) or other part. . 6 87107