DK144220B - Boiler for fluid-bed combustion - Google Patents

Description

in 144220

BACKGROUND OF THE INVENTION The invention relates to a fluid-bed combustion boiler in an inert material vortex layer which is maintained in the boiler's combustion chamber during operation of the combustion and fluidization air through the bottom of the chamber from an underlying air chamber, in which a conduit for supplying combustion and fluidization air, which boiler has at least one duct for removing fluidized material from the combustion chamber.

10 As is well known, fluid-bed combustion involves combustion in a fluidized bed or fluidized bed of an inert material, such as sand, ash, limestone or dolomite, which is maintained in the lower part of the combustion chamber by means of the blown air. Among the significant advantages of this technique are the lower combustion temperature in relation to combustion directly in an ambient air mass, thereby reducing the flue gas content of certain harmful substances, such as nitrogen oxides.

20 When selecting an inert material that reacts chemically with sulfur, highly sulfur-containing solid or liquid fuel can be combusted with minimal emissions of sulfur compounds, thus saving costly plants for desulphurizing the flue gases.

25 The amount of ash remaining after combustion of the fuel will, to a large extent, accumulate in the fluidized bed, thereby increasing its volume. By intermittently tapping material from the fluidized bed through the said withdrawal channel (s), the height of the layer can be kept substantially constant or at least within given upper and lower limits, which is a prerequisite for proper operation of the boiler. In this case, the bottled material is removed by means of a screw conveyor which, for the high temperature of the material, typically 700-900 ° C, must be water-cooled. As the material due to its grainy structure is poorly heat conducting, the conveyor must have a considerable length,. to allow the material to be thoroughly stirred during transport so that virtually all of its individual particles come into direct contact with chilled surfaces before being released for further handling. The known plants for transporting the fluidised bed material are therefore both space consuming and expensive.

A boiler according to the present invention is not condemned in that the outlet duct opens into the air chamber, that the bottom of the air chamber is perforated, that means for introducing a secondary air flow into the air chamber through its bottom, and that a discharge line containing a shut-off means, opens into the air chamber between the bottom of it and the mouth of the air supply line for periodic removal of fluidized bed material. With the invention, significant savings have been achieved in both the installation and operating costs of the boiler and a reduction of the boiler system's total space requirements. This is because the hot material discharged from the vortex layer is cooled in the air chamber located below the combustion chamber, where the material, under the influence of the secondary air flow, forms a secondary vortex layer. Due to the intense turbulence of the secondary vortex, the material is cooled quickly and efficiently to such a low temperature that it can then be removed from the air chamber through a simple uncooled discharge line. The entire amount of heat bound in the bottled material is recovered in the secondary air, which, together with the primary air introduced into the chamber over the secondary vortex layer, flows into the combustion chamber through its perforated bottom.

35 Unburned residue of the fuel, which accompanies the bottled vortex material down into the air chamber, will be incinerated here, further improving the heat economy. After opening the shut-off member in the outlet line, the cooled material can be transported out of the air chamber by the secondary air flow alone, i.e. without mechanical transport means. Since the ash and the actual inert vortex material often have different particle sizes, the pneumatic removal of the material mixture from the air chamber can be utilized to produce some separation of the constituents of the mixture by wind sieving, whereby a substantial portion of the inert material at low cost can be recovered. eg. for re-introduction into the combustion chamber or for other use if the material has been unsuitable for re-use in the fluidised bed by chemical reaction with 15 components in the fuel.

In order to maintain a suitable height of the secondary vortex layer in the air chamber, it is desirable that the area of the perforated bottom 20 of the air chamber be smaller than the area of the combustion chamber bottom.

Advantageously, the outlet of the outlet duct in the air chamber may be shielded from the air supply conduit opening in the chamber. Hereby, an undesirable entrainment of the tapped material is limited by the upward flow of air through the bottom of the combustion chamber.

When the removal duct passes through the combustion chamber bottom, a perforated slider may be built into the duct just below the chamber bottom. Hereby, a substantially uniform air flow through the entire area of the combustion chamber can also be maintained during the operating periods between intermittent swirl layer withdrawals.

The means for introducing the secondary air flow may comprise a branch line starting from the main air supply line leading to the chamber, and a shut-off member in the branch line, and the main line may contain an adjustable throttle between the branch line and the air chamber. By throttling the primary air flow when the shut-off member of the branch line is open, a simple overpressure in the secondary air stream can be provided to fluidize the secondary vortex, while maintaining a substantially unchanged total flow of air through the bottom of the combustion chamber. .

Alternatively, the means for introducing the secondary air stream into the air chamber may be a separate fan. In this embodiment, it is possible to control the quantity flow of the secondary air and its overpressure relative to the pressure in the air chamber completely independent of the primary air flow.

• The shut-off means in the outlet line may be controlled by an air temperature sensor in the air chamber between its bottom and the main air supply line outlet in the chamber. In this way, the intermittent removal of the material from the air chamber can be initiated when the temperature sensor, which is closed by the closed shut-off member 20 in the secondary vortex layer, indicates that the material is suitably cooled.

The bottom of the air chamber may be stepped by at least two sections located at different heights separated by openable and closed intermediate walls, and the discharge duct from the combustion chamber then opens over the highest section, while the discharge line exits from the chamber above the lowest bottom section. By opening and closing the partition walls as the material is drained from the primary fluidized bed and the removal of cooled material from the air chamber, the processes running in this chamber, respectively, after combustion of combustible parts in the fluidised bed material and cooling of the material, can take place. roughly in each zone of the 35 chamber of the corresponding sections of the chamber floor.

The invention will now be explained in more detail with reference to the schematic drawing, in which FIG. 1 is a vertical longitudinal section through the lower part of a first embodiment of a boiler according to the invention; FIG. 2 is a sectional view taken along line II-II of FIG. 1 and 5 in FIG. 3 is a view of FIG. 2 corresponding section through a changed embodiment of the boiler.

The FIG. 1 and 2, a highly simplified illustrated boiler has a combustion chamber 1, which is defined by four vertical side walls 2, a perforated bottom wall 10 3 and a top wall not shown, in which a discharge opening for the flue gases can be formed. An air chamber 4 with two opposing downwardly converging side walls 5 and 6 is located below the combustion chamber bottom wall 3. The air chamber bottom wall 7 is perforated analogously to the bottom wall 3, and below the wall 7 there is a secondary air chamber 8.

A main conduit 9 for supply of combustion and fluidizing air opens into the air chamber 4 through its sidewall 5. From the conduit 9, a branch line 10 is discharged, which opens into the secondary air chamber 8. Individually activatable shut-off and throttle means 11 and 12 shown in the drawing shown as rotary dampers, are respectively located in the conduit 9 between the connection of the branch conduit 10 and the opening in the air chamber 4 and in the branch conduit.

A vertical tube 13 extends through the bottom wall 3 of the combustion chamber into the air chamber 4, where it opens above the bottom wall 7 of this chamber at a lower level than the mouth of the air conduit 9. The tube 13 inside-3 holds close to the bottom wall 3 a shut-off member 15, shown as a slider pierced by openings corresponding to the openings in the perforated wall 3. From the lower part of the air chamber 4 close to its bottom wall 7, a discharge pipe 16, which also contains a locking member 17, is shown as a slider.

As explained above, the combustion takes place in a fluidized bed of a suitable particulate material, which is kept fluidized by blowing from below with air supplied through the conduit 9 and via the air chamber 4 flowing through the openings in the bottom wall 3 and the openings in the damper 15 when closed. In FIG. 1 and 2, the fluidized fluidized bed is merely marked by its irregular - and still changing - surface 18.

The supply of fuel to the combustion chamber 1 can be effected in any suitable manner, either directly into the fluidized layer or from above into the layer. In order to control the combustion temperature, one or more pipe hoses may be incorporated in the part of the combustion chamber occupied by the fluidized layer which is flowed by an adjustable flow of water 15. Moreover, the heat energy developed in the boiler can be utilized in any suitable way, e.g. for the production of steam or hot water in pipes, of which the boiler side walls 2 are constructed, or for the production of hot flue gas, e.g. for a drying plant.

The vertical tube 13 mentioned above serves to periodically remove material from the fluidized bed in the combustion chamber 1 as the height of this layer as explained above increases during boiler operation.

To this end, the shut-off member 15 is opened for a period of 25 suitable length, whereby material flows through the pipe into the air chamber 4. At the same time, the shut-off damper 12 in the branch line 10 is opened during normal operation and the damper 11 in the main line 9 is adjusted to suitably throttle the main air flow. From the branch line 10, air now flows into the secondary air chamber 8 and up through the perforated bottom wall 7 of the primary air chamber 4, thereby causing the material flowing into the chamber 4 to form a secondary vortex layer, as in FIG. 1 and 2 are indicated 35 at its surface 19. The damper 17 is provisionally closed.

As initially explained, the secondary air flow flowing through the bottom wall 7 causes a cooling of the secondary fluidized bed and at the same time a post-combustion of any residual combustible material followed by the material discharged from the combustion chamber through the pipe 13. The amount of heat thus delivered is transferred to the secondary air flow which, together with the primary air flow from the conduit 9, continues into the combustion chamber 1 as preheated combustion and fluidization air, 10 and is thus recovered in the combustion process.

When any post-combustion has been completed and the cooling of the material in the secondary vortex layer in the air chamber 4 is sufficiently advanced, which can be detected by the temperature sensor 20 located in the vortex layer 15, the damper 17 is opened, and the material from the secondary vortex layer is blown out through the outlet pipe 16 as a result of the overpressure prevailing in the air chamber 4. When the air chamber 4 is emptied, the damper 12 is closed and the damper 11 is fully opened, after which the operation continues until the damper 15 is next opened to drain material from the primary fluidized bed in the combustion chamber. .

The components of the embodiment shown in FIG. 3 illustrates 25 embodiments which may be identical to those of FIG.

1 and 2 are denoted by the same reference numerals.

The major departure from the first described embodiment lies in the design of the perforated bottom wall 22 of the primary air chamber 21, which is constructed of staircase with three sections 23, 24 and 25 extending across the chamber at successively decreasing height from the bottom wall of the secondary air chamber. 26 under the wall. At the transition between the individual sections, transverse intermediate walls 27 are arranged, which from the position shown in the drawing can be pivoted in a clockwise direction, thereby permitting passage 8 of material from a higher section of the bottom wall 22 to a lower lying section.

The discharge tube 13 from the combustion chamber 1 opens over the highest positioned section 23 5 with a sloping orifice 14 at a short distance from one oblique side wall of the chamber 21. The outlet pipe 16 for the cooled material opens over the lowest positioned section 25. The supply air 28 for the secondary chamber 26 shown in the bottom of the chamber, as shown in FIG. 1 may be branched from the main air line 9, but it could also be connected to the pressure side of a separate fan not shown. This connection option is of course also available in the embodiment of FIG. 1 and 2.

15 The embodiment of FIG. 3 can be operated in such a way that the post-combustion of combustible parts in the material taken out of the combustion chamber 1 takes place wholly or substantially on the section 23, while in the following sections 24 and 25 there is substantially only a cooling of the material. down to a suitable outlet temperature. During the post-combustion and cooling, the intermediate walls 27 are held in the closed positions shown, and when the damper not shown in the pipe 13 is opened to drain material from the combustion chamber 25, the walls 27 are simultaneously opened so that the material lying on the bottom wall 22 is successively displaced on the lower bottom sections until the material is finally removed through the outlet pipe 16.

It will be appreciated that the number of take-out pipes 30 13 from the combustion chamber and the position of the pipes in plan view may vary with the size of the area of the bottom wall 3 and with the general design of the primary air chamber and its connection for the combustion air. The perforated bottom walls of the combustion chamber and primary air chamber may be specifically designed as described in the parallel Danish patent application No. 3611/79, but may also be more conventional. The discharge tube or tubes from the combustion chamber could also be located without 5 on the boiler with inlet and outlet nozzles in the walls of the combustion chamber and the primary air chamber, respectively.

The dampers mentioned above and any other actuating means which come into operation in connection with a periodic material removal from the fluid bed in the combustion chamber can be controlled automatically, whereby, for example, the operation sequence. may be triggered by a signal from a sensor measuring the pressure drop through the primary fluidized bed, which depends on the height of the bed. Similarly, the shut-off means in the discharge line from the primary air chamber can be opened by a signal from the temperature sensor in the secondary vortex layer.

Claims (5)

144220 ίο A fluid-bed combustion boiler in an inert fluid vortex layer which is maintained during boiler operation in the boiler's combustion chamber (1) by injecting combustion and fluidization air through the bottom (3) of the chamber from an underlying air chamber (4) , 21), wherein a conduit (9) for supplying combustion and fluidizing air, which boiler has at least one duct (13) for removing fluidized material from the combustion chamber, known as the discharge duct (13) the air chamber (4, 21), the bottom chamber of the air chamber (7, 22) being perforated, the means (10, 28) for introducing a secondary air flow into the air chamber through its bottom, and an outlet line (16) containing 15 a shut-off member (17) opens into the air chamber between its bottom and the mouth of the air supply line (9) for the periodic removal of fluidized bed material. Boiler according to claim 1, characterized in that the area of the perforated bottom of the air chamber (7, 22.) is smaller than the area of the bottom (3) of the combustion chamber. Boiler according to claim 1 or 2, characterized in that the opening 25 (14) in the inlet chamber (13) of the outlet duct (13) is shielded from the air supply line (9) opening in the chamber. Boiler according to any one of claims 1-3, wherein the removal duct (13) passes through the bottom (3) of the combustion chamber, characterized in that a perforated slider (15) is built into the duct (13) near the chamber bottom (3). . Boiler according to any one of claims 1 to 4, characterized in that the means for introducing the secondary air flow comprise a branch line (10), which starts from the main air leading to the chamber (4).