FI85416C - FOERFARANDE OCH ANORDNING FOER REGLERING AV FUNKTIONEN HOS EN VIRVELBAEDDSREAKTOR MED CIRKULERANDE BAEDD. - Google Patents

Description

1 85416

Method and apparatus for controlling the operation of a fluidized bed reactor with a circulating bed - Förfarande och anordning för regiering av functionen hos en virvelbäddsreaktor med circulerande bädd

The present invention relates to a fluidized bed reactor in which the upper part of the reactor chamber is connected to a horizontal cyclone separator for separating the solids contained in the fluidized bed reactor and in which return channels are arranged between to return the separated solid to the bottom of the reactor chamber.

Combustion chamber temperature control is necessary for optimal combustion, especially when many different fuels with different calorific values are burned in the same combustion chamber. To achieve optimal sulfur absorption, the temperature should remain in the range of 800-950 C. Control of the combustion temperature is problematic in known methods if the calorific value of the fuel or the load on the boiler varies greatly.

It is an object of the present invention to enable the combustion temperature of a fluidized bed reactor to be adjusted so that it remains at the desired level regardless of changes in the reactor load or the calorific value of the fuel.

In known methods, the temperature is controlled by: - changing the excess air - circulating the flue gases back to the reactor - changing the suspension density in the combustion chamber - dividing the bed into separate functional parts - cooling part of the bed material with a separate heat exchanger a

Reducing the combustion temperature by increasing the excess air reduces the efficiency of the reactor, as this increases the flue gas losses and increases the power demand of the air blowers.

If the combustion temperature of a fluidized bed reactor is controlled by recirculating the flue gases to the reactor, as shown, for example, in British Patent Application No. 2030689, the total power requirement of the boiler increases due to the larger amount of gas flowing through, thus increasing investment and operating costs.

The change in the suspension density affects the heat transfer to the cooling surfaces in the boiler and thus to the temperature of the combustion chamber. The suspension density can be changed, as disclosed in U.S. Patent 4,165,717, by varying the ratio and amounts of secondary to primary air. However, the control range is limited because changes in the secondary / primary air ratio also affect process parameters other than temperature.

Controlling the combustion temperature by cooling the bed material in an external heat exchanger, as disclosed in U.S. Patent 4,111,158, is a complex and difficult to control process. This method of temperature control incurs additional investment and operating costs, as a separate fluidized bed with cooling surfaces is required in parallel with the circulating bed reactor.

U.S. Patent 4,240,377 discloses a method of controlling the temperature of a fluidized bed reactor in which a portion of the bed material on top of the grate is made to flow upward through a heat exchanger from which it is returned cooled to the bed. This method also incurs additional investment and operating costs.

Controlling the combustion temperature by inactivating part of the bed has proved difficult in practice, because, as disclosed in U.S. Patent 3,970,011, it causes e.g. erosion of bed heat transfer surfaces and sintering of bed material.

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The fluidized bed reactor of the present invention is characterized in that it comprises a single substantially reactor chamber-wide cyclone separator connected to a plurality of return ducts separated by a partition into parallel units and at least a portion of the return ducts provided with means for passing different return ducts.

When part of the return ducts are closed, the heat transfer surface contacted by the solid decreases, as a result of which the solid is returned to the combustion chamber hotter, whereby the temperature of the combustion chamber rises if the other process parameters remain unchanged.

As more return channels are opened, the heat transfer surface increases, causing the solids to return to a colder temperature and the combustion chamber temperature to drop.

The advantages of the invention are e.g. the following: - the utilization of the invention does not cause additional space requirements, nor additional investment and operating costs - the structure is simple and safe to operate - the adjustment of the operation is simple - the adjustment range increases.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 schematically shows an embodiment of the invention in vertical section, Figure 2 shows a section of Figure 1 along line A-A, Figure 3 shows another embodiment, and Figure 4 shows a section of Figure 3 along line B-B.

The steam boiler shown in Figures 1 and 2 comprises a combustion chamber 5 delimited by four walls 1-4 formed of pipes welded to each other in a manner known per se.

4 d 541 6

The tubes form the heat transfer surfaces of the boiler and are connected to the circulation system of the boiler in a manner not shown in more detail.

The lower part of the combustion chamber has a fuel inlet duct 6. It also has a primary gas inlet duct 7 and a secondary gas inlet duct 8.

A horizontal cyclone separator 9 is formed on top of the combustion chamber. The cyclone separator is formed by the front and rear walls 1 and 3 of the combustion chamber and a tubular wall 10 running parallel to the rear wall 3 of the combustion chamber. so as to form the roof 12 of the combustion chamber and then run parallel to the cylindrical part of the front wall so as to form the inner and outer walls 14 and 15 of the separator gas inlet duct 13.

The rear wall 3 of the combustion chamber and the wall 10 running parallel to it form two opposite walls of the return ducts 16 connecting the separator to the lower part of the combustion chamber, which act as heat transfer surfaces.

The return channels are separated by parallel partition 17 into units operating in parallel. The end walls 18 of the separator have a degassing opening 19.

The solid flue gases leaving the combustion chamber are directed to the vortex chamber 20 of the separator tangentially connected to the gas inlet duct 13.

The solid enriched on the outer circumferences of the vortex chambers is discharged from the vortex chamber through the gap 21 formed between the walls 3 and 10 by the gas flow and is returned to the combustion chamber via the return ducts 16. The purified gases exit through openings 19 in the end walls of the vortex chambers.

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At its lower end, the return duct forms a U-shaped fluidizing chamber 22 into which air can be fed through a pipe 23. If no air is supplied to the fluidization chamber, it acts as a lock, whereby the return channel in question is filled and the solid returned to the reactor passes through the other return channels. The solids flow through the return duct can also be controlled by changing the amount of air supplied to the chamber 22 by means of the valve 24. In this way, different amounts of solids flow through the return channels. When some of the return channels are kept closed, some of the solids circulating in the reactor are stored in them. The solid stored in the return duct can be returned in a controlled manner by adjusting the air flow to it. In this way, the suspension density of the solid in the combustion chamber and thus the heat transfer to the heat transfer surfaces of the combustion chamber can be influenced.

Because the solid, under its own weight and carried by the gas stream, flows downward in the return duct, only small amounts of air are needed in the fluidization chamber to keep the return duct open.

In an alternative embodiment shown in Figures 3 and 4, an adjustment flap 122 is provided at the upper end of each return passage 116 to adjust the amount of solids passing through the return passage and to close it completely. From the lower end of the return channel, the solid flows freely into the reactor. In other respects, the structure of the reactor is as shown in Figures 1 and 2.

Example 1

In the steam boiler of Figures 1-3, coal was burned with an effective calorific value of 28 MJ / kg at a nominal steam output of 65 MW and an combustion temperature of 880 ° C. 40 MW of heat was recovered with a heating surface of 185 m2 of the combustion chamber and 120 m2 of heating surfaces of six parallel return ducts.

6 85416 With a steam output of 20 MW, i.e. a load of about 30%, the same combustion temperature was achieved as with the rated output by closing the three return channels.

Example 2

Peat with an effective calorific value of 8 MJ / kg at a nominal steam output of 65 MW was burned in the same boiler. To adjust the combustion temperature to about 870 ° C, the cooling effect of the return channels was reduced by closing the four channels, whereby the solid was directed to the reactor through the second and fifth return channels. In this case, 30 MW of heat was recovered in the reactor and return channels.

The invention is not limited to the exemplary embodiments, but can be modified and applied within the scope of the inventive idea defined by the claims. It is clear that the return channels can, for example, be of different sizes or that the devices for adjusting the amount of solids are arranged in only a part of the return channels.

Claims (5)

7 85416 A Lei bed reactor, the upper part (2) of the reactor channel (1) being connected to a horizontal cyclone separator (9) for separating the solids contained in the gases leaving the Lei bed reactor and having return channels (16, 116) formed between the opposite walls and the bottom of the reactor chamber. from the tube wall (3) of the combustion chamber (5) and the wall (10) running parallel to it, for returning the separated solid in the separator to the lower part of the reactor chamber, characterized in that it comprises one cyclone separator (9) of wide reactor chamber width (16). , 116), which are separated by parallel partitions (17) into parallel units, and that at least some of the return channels are provided with devices (22, 122) for adjusting the amount of solid flow passing through the different return channels. Fluidized bed reactor according to claim 1, characterized in that said means for controlling the amount of solids comprise a fluidizing chamber (22) arranged in the lower part of the return pipe with air supply devices (23, 24). A fluidized bed reactor according to claim 2, characterized in that said means for controlling the amount of solids comprise a control valve (122). Fluidized bed reactor according to Claim 1, 2 or 3, characterized in that the means (22, 122) for adjusting the amount of solids are arranged at the upper end of the return channels (16, 116). Fluidized bed reactor according to Claim 1 or 2, characterized in that the means (22, 122) for adjusting the amount of solids are arranged at the lower end of the return channels (16, 116). β 35416