GB2430484A

GB2430484A - Furnace gas cooler and cleaner utilising movable heat resistant bodies

Info

Publication number: GB2430484A
Application number: GB0600019A
Authority: GB
Inventors: Michael Harris
Original assignee: M G H RECYCLING Ltd
Current assignee: M G H RECYCLING Ltd
Priority date: 2005-09-27
Filing date: 2006-01-03
Publication date: 2007-03-28
Also published as: GB0519619D0; GB0600019D0

Abstract

A furnace gas cooling and cleaning apparatus, comprising a chamber 1 having a gas in let 2 at a lower part thereof and a gas outlet 3 at an upper pan thereof, the chamber containing a plurality of relatively movable heat resistant bodies (e.g. refractory spheres) and having an outlet at the lowermost pan of the chamber provided with a movable shutter 8 by which the bodies can leave the chamber, means for conveying the bodies from the chamber along a mesh tray 9 and for contacting the bodies with cooling and cleaning water provided by sprays 16, a lifting bucket conveyor 17 to lift the cooled wet bodies to the top of the chamber, and valve means in the form of a rotating vane feeder 19 at the top of the chamber for admitting the cooled wet bodies into the chamber whilst preventing the escape of gases from the chamber. Preferably, the exhaust gases pass upwardly through a body of spheres in the chamber while the spheres are circulated through the chamber. The apparatus is designed particularly for cooling and cleaning furnace exhaust gases prior to filtration of particulates, for example, in a bag filter.

Description

FURNACE GAS COOLER AND CLEANER

Field of the Invention

This invention relates to a cooler and cleaner for furnace gases, for example from an incinerator furnace.

Background to the Invention

Furnaces are used for a wide variety of purposes, some of which, for example the incineration of animal carcasses, produce particulate pollutants. To meet environmental laws, these need to be filtered from the exhaust gas stream before it is discharged to the atmosphere. A convenient and economical type of gas filter is the bag filter, which uses a porous bag of a woven or non-woven textile material. While the fibres used to form the material may be heat-resistant to some extent, bag filters cannot be operated at the high temperatures at which combustion gases leave the furnace - typically in excess of 1000 C. It is there- fore necessary to cool the gases first.

Conventional gas coolers comprise a water-cooled heat exchanger in which the gases are passed through tubes surrounded by a body of cooling water. While this can give effective cooling, there is a tendency for the tubes to be gradually blocked by the gas-borne particulates deposited inside them. This requires the furnace to be shut down periodically to permit cleaning of the heat exchanger, a costly process in itself, quite apart from the cost of shutting down the furnace.

It is therefore desirable to find some other way of cooling the gases.

Summary of the Invention

The invention provides a furnace gas cooling apparatus as defined in Claim 1.

The means for cooling the bodies may comprise a cooling tray where contact with the ambient air removes heat from the bodies, or it may comprise means for contacting the bodies with cleaning and cooling water, for example a water spray.

The bodies are solid objects of any shape permitting the objects to move relative to each other so as to pass downward through the chamber without jamming together. Conveniently, the bodies will be at least approximately spherical. Preferably, the bodies are at least of a size which will pass through a mesh no smaller than 10mm, and more preferably no smaller than 20mm. BaIls from 25 to 50mm diameter have been found to be especially effective, being sufficiently large to ensure a reasonable gas flow rate therethrough while pre- senting a large enough surface area for heat transfer and for the capture of par- ticulate impurities on the surface thereof.

The bodies may be of ceramic material or of metal, for example stainless steel.

The bodies are preferably conveyed from the lower end of the chamber by a vibrating mesh screen, passing beneath water spray heads serving to cool the bodies and wash off any particulates and other contaminants captured by the bodies during their passage through the chamber.

The screen suitably delivers the bodies into a water-filled sump, from where they are conveyed back up to the top of the tower. The temperature of the gases emerging from the chamber may be monitored and controlled by in- creasing or decreasing the speed at which the bodies are conveyed back to the top of the chamber, for example by a bucket conveyor, and increasing or de- creasing the opening of a throat at the base of the chamber controlling the egress of the bodies from the chamber.

It has been found that furnace gases at approximately 1000 C entering the apparatus can be cooled to substantially ambient temperature by passage through a chamber containing approximately 1 metre depth of 25mm ceramic balls. It has also been found that very little dust remains in the gases dis- charged from the apparatus, such that the life of the bag filters is substantially increased, or the final filter may even be unnecessary. The particulates are re- moved from the water in a settlement tank or lagoon, permitting the water to be reused, and the solids disposed of.

A fan may be used to draw the gases through the apparatus.

As an alternative to the final bag filter on the outlet of the apparatus, a second, similar apparatus may be connected to the outlet. The second appara- tus may include in the chamber a water spray or water sprays to ensure that the recirculating bodies are kept wet so as to entrain and remove any residual par- ticulates in the cooled gas flow from the first apparatus. This second apparatus could also be used independently as a gas cleaner.

Brief Description of the Drawing

In the drawings, which illustrates diagrammatically exemplary embodimerits of the invention: Figure 1 shows an apparatus according to one embodiment; and Figure 2 illustrates a control system applicable to the apparatus shown in Figure 1.

Detailed Description of the Illustrated Embodiment

Referring first to Figure 1, the apparatus comprises a chamber I in the form of a vertical cylinder having an exhaust gas inlet 2 in the side thereof adja- cent to the lower end of the chamber. The chamber I is suitably formed of steel lined with a refractory liner. In use, the gas inlet 2 will be connected to the gas outlet of a furnace. The gas inlet 2 will have a mesh across it to prevent the egress of the solid contents of the chamber 1, while allowing the passage of the exhaust gases. The mesh may be formed, for example, of intersecting steel rods or bars. The upper part of the chamber I has a gas outlet 3 to which is connected a conduit 4 leading to a centrifugal fan 5 driven by an electric motor 6 and serving to draw the gases through the chamber. The outlet 7 of the fan 5 may be coupled to a bag filter of conventional form (not shown) to remove any residual suspended solid particles from the gas flow before it is discharged to the atmosphere.

The chamber I contains a large number of ceramic spheres, for example of 25 to 50mm diameter, and has at the lowermost part thereof an outlet for the spheres provided with a movable shutter 8 to control the height of the opening, thereby controlling the rate at which the spheres leave the chamber. The spheres are discharged from the chamber I on to a mesh tray 9 mounted above a channel member 10 mounted on rubber blocks 11 carried by supports 12. An electric motor 13 mounted beneath the channel rotates an eccentric weight 14 to vibrate the channel member and mesh tray, thereby causing the spheres to flow along the tray and to drop from the end of the tray into a sump 15. Water sprays 16 mounted above the tray 9 spray water on to the spheres on the tray, cooling them and washing off any pollutants adhering to the spheres. The wa- ter collects in the channel 10 and is discharged into the sump 15. Run- off from the sump carrying suspended dust and like pollutants is directed to a settlement tank or lagoon (not shown), where the solids settle out for disposal. The water can then be recycled, after treatment if necessary to remove soluble pollutants.

A bucket conveyor 17 extends into the sump 15 to lift the wet spheres therefrom and carry them to the upper end of the chamber, where they are dis- charged into a chute 18 through an opening in the front face thereof. The chute 18 is provided with a rotating vane feeder 19 at the lower end thereof, permitting controlled flow of the spheres back into the chamber, while preventing escape of the gases flowing through it. The vane feeder 19 is driven by an electric mo- tor 20 (Figure 2).

Referring now to Figure 2, the apparatus may be controlled, according to one embodiment of the invention, by means of a controller 21, which monitors the gas outlet temperature by means of a sensor 22 in the gas stream, for ex- ample a thermocouple, and then increases or decreases the flow rate of the spheres through the chamber. This can be achieved by increasing or decreas- ing the height of the opening in the lower part of the chamber by raising or low- ering the shutter 8. This may be effected by a motor 23 operating a rack and pinion drive on the shutter. At the same time, the rate at which the spheres are transported to the top of the chamber may be increased or decreased by in- creasing or decreasing the speed of the motor 24 driving the bucket conveyor 17, and the rate of admission of the spheres may be increased or decreased by changing the speed of rotation of the vane feeder 19 by controlling the speed of the motor 20. The controller 21 may be a simple programmable process controller; such devices are well-known. If necessary, the rate of feed of the spheres along the mesh tray 11 may be influenced by controlling the speed of the vibration motor 13.

While the illustrated embodiment includes water cooling and washing of the spheres, it will be appreciated that the invention is not limited to the use of water, and includes the use of air cooling of the spheres, for example by simple heat transfer to the ambient air, or by the use of a forced flow of cooling air us- ing a fan. The spheres may, in such circumstances, be provided with a rough- ened surface to facilitate temporary adhesion of particulate matter, thereby pro- viding a cleaning function for the gas stream as well as cooling.

Claims

1. A furnace gas cooling apparatus, comprising a cooling chamber having an exhaust gas inlet at a lower part thereof and a gas outlet at an upper part thereof, the chamber containing a plurality of relatively movable heat- resistant bodies and having an outlet at the lowermost part of the chamber by which the bodies can leave the chamber, means for conveying the bodies from the chamber and for cooling the bodies, a lifting conveyor to lift the cooled bod- ies to the top of the chamber, and valve means at the top of the chamber for admitting the cooled bodies into the chamber while preventing escape of ex- haust gases therefrom.

2. Apparatus according to Claim 1, wherein the means for cooling the bodies comprises means for contacting the bodies with cleaning and cooling water.

3. Apparatus according to Claim 2, wherein the means for contacting the bodies with water comprises a water spray.

4. Apparatus according to Claim 2 or 3, wherein the means for con- tacting the bodies with water comprises a sump into which the bodies fall and through which water flows.

5. Apparatus according to any preceding claim, wherein the bodies are spherical.

6. Apparatus according to any preceding claim, wherein the bodies are sized so as to pass through a mesh no smaller than 10mm.

7. Apparatus according to Claim 6, wherein the bodies are sized so as to pass through a mesh no smaller than 20mm.

8. Apparatus according to Claim 7, wherein the bodies have a di- ameter of 25 to 50mm.

9. Apparatus according to any preceding claim, wherein the bodies are formed of a ceramic material.

10. Apparatus according to any of Claims I to 8, wherein the bodies are formed of metal.

II. Apparatus according to Claim 10, wherein the bodies are formed of stainless steel.

12. Apparatus according to any preceding claim, wherein the means for conveying the bodies from the chamber comprises a vibrating mesh surface.

13. Apparatus according to any preceding claim, wherein the lifting conveyor is a bucket conveyor.

14. Apparatus according to any of Claims 1 to 12, wherein the lifting conveyor comprises an auger.

15. Apparatus according to any preceding claim, wherein the valve means comprises a rotary vane feeder.

16. Apparatus according to any preceding claim, wherein the gas out- let is connected to a bag filter.

17. Apparatus according to any of Claims 1 to 15, wherein the gas outlet is connected to a gas cleaning apparatus, comprising a cleaning chamber having a gas inlet at a lower part thereof and a gas outlet at an upper part thereof, the chamber containing a plurality of relatively movable bodies and hay- ing an outlet at the lowermost part of the chamber by which the bodies can leave the chamber, means for conveying the bodies from the chamber and for contacting the bodies with cleaning water, a lifting conveyor to lift the wet bodies to the top of the chamber, and valve means at the top of the chamber for admit- ting the wet bodies into the chamber while preventing escape of gases there- from.

18. Apparatus according to any preceding claim, wherein the gas out- let is connected to an extractor fan.

19. A furnace gas cooling apparatus, substantially as described with reference to, and/or as shown in, the drawings.

20. A furnace having an exhaust gas outlet coupled to the exhaust gas inlet of an apparatus according to any preceding claim.

21. Gas cleaning apparatus, comprising a cleaning chamber having a gas inlet at a lower part thereof and a gas outlet at an upper part thereof, the chamber containing a plurality of relatively movable bodies and having an outlet at the lowermost part of the chamber by which the bodies can leave the cham- ber, means for conveying the bodies from the chamber and for contacting the bodies with cleaning water, a lifting conveyor to lift the wet bodies to the top of the chamber, and valve means at the top of the chamber for admitting the wet bodies into the chamber while preventing escape of gases therefrom.

22. Apparatus according to Claim 21, wherein the bodies are spheri- cal.

23. Apparatus according to Claim 21 or 22, wherein the chamber in- cludes at least one water spray for spraying water on to the bodies therein.