WO1993015360A1

WO1993015360A1 - Incineration apparatus

Info

Publication number: WO1993015360A1
Application number: PCT/GB1993/000115
Authority: WO
Inventors: Peter Hodson
Original assignee: Richards Engineering Limited
Priority date: 1992-01-31
Filing date: 1993-01-19
Publication date: 1993-08-05
Also published as: GB2264352A; GB9202049D0; AU3817093A

Abstract

Incineration apparatus (1) for incinerating a particulate material comprises a furnace housing (2), means (7) for introducing material to be incinerated into the housing (2), and means for forming a fluidised bed in the material in the lower part of the housing (2). A plurality of independently-operable fuel gas supply means (6a-c) supply fuel gas to different regions of the fluidised bed, and there are provided means (15, 16, 17) for measuring the temperature of at least some of the regions.

Description

Title : Incineration Apparatus

This invention relates to apparatus for the incineration of granular or particulate material, in particular to apparatus for the thermal reclamation of a material such as foundry sand.

Used foundry sand may be subjected to reclamation so that it can be re-used in foundry processes. Such reclamation can take the form of mechanical attrition, whereby the sand is broken down into grain-size particles. However, used foundry sand contains a high proportion of chemical bonding agents, eg phenolic resins, and after a while these agents reach such a level that the properties of the sand deteriorate, even with mechanical reclamation. Consequently, there is a need for a thermal reclamation technique whereby the chemical agents are incinerated, leaving relatively clean sand. Such thermal reclamation is typically conducted in a furnace having a fluidised bed.

In a fluidised bed furnace, material to be treated is fed in and incinerated, the waste gases escaping through a flue stack at the top of the furnace. The reclaimed material is removed either periodically or continuously.

A problem which is encountered in furnaces of this type is that addition of material to be treated causes a localised drop in temperature which must be compensated by an increased supply of fuel gas. This may have the consequence, however, that other parts of the fluidised bed may be overheated.

Attempts have been made to alleviate this problem by the use of several distinct fluidised beds within the furnace, the beds being separated by weir arrangements and the supply of gas to each bed being controlled independently. Furnaces of this kind are, however, of relatively complex construction and hence are expensive. There has now been devised an incineration furnace including a fluidised bed which overcomes or substantially mitigates the above-mentioned problems.

According to the invention, there is provided incineration apparatus for incinerating a particulate material, the apparatus comprising a furnace housing, means for introducing material to be incinerated into the housing, means for forming a fluidised bed in the material in the lower part of the housing, a plurality of independently-operable fuel gas supply means for supplying fuel gas to different regions of the fluidised bed, and means for measuring the temperature of at least some of the regions.

The apparatus according to the invention is advantageous primarily in that it enables close control of the processing temperature in an incineration furnace. The different regions of the fluidised bed may be maintained at the same temperature or temperature gradients or other profiles may be established. The supply of fuel to one region may be altered without changing the temperatures of the other regions, which may lead to economies in fuel consumption. Also, compared with multiple-bed furnaces the apparatus is of relatively simple, and hence inexpensive, construction.

The apparatus according to the invention may be used for the incineration of a wide range of particulate materials, but is of particular utility in the thermal reclamation of a base material from a mixture of that material with a combustible substance. One example of such a base material is foundry sand. Another material which may be incinerated using the apparatus according to the invention is dewatered sewage.

The fuel gas supply means preferably comprises suitable arrangements of pipes fitted with, for example, nozzles or bubble caps. The means for measuring the temperatures of the various regions of the fluidised bed may, for example, be thermocouples. Control means may be provided to automatically adjust the supply of fuel gas to each region in response to the measured temperatures.

The apparatus may be of the type described in our co-pending UK Patent Application No 9200341.7 or may be of more conventional design.

The material to be incinerated may be fed directly into the lower part of the fluidised bed as described in our co-pending UK patent application no 2244939A, in which case the .material may be fed into the fluidised bed from below the latter. Alternatively, the material may be fed onto the bed from above by conventional means.

The means for introducing the material into the housing may, for example, be a mechanical or pneumatic conveyor.

In cases where the material is fed to the fluidised bed in batches, a plurality of feeds is preferably provided which operate in sequence. For example, where two such feeds are provided, these can operate alternately.

The invention will now be described in more detail, by way of illustration only, with reference to the accompanying drawing, in which

Figure 1 shows a sectional side view of a thermal reclamation apparatus according to the invention, and

Figure 2 is a detailed view of part of the apparatus of Figure 1.

Referring to Figure 1, a thermal reclamation apparatus (generally designated 1) according to the invention is of the type described in our co-pending UK Patent Application No 9200341.7 and comprises a generally bell-shaped furnace housing 2 of mild steel. The furnace housing 2 is lined with a layer 3 of closely packed ceramic fibre which is secured to the housing 2 by hooks and skewers (not shown) in a conventional manner. At the top of the housing 2 there are provided an access door 4 for maintenance and a stack 5 through which flue gases can escape.

Within the lower region of the housing 2, and inwardly spaced therefrom, there are provided three air/gas manifold arrangements 6a-c. Material to be reclaimed is introduced from below through a pneumatic conveyer pipe 7 and forms a bed 8 at the base of the apparatus. A layer of vacuum-formed ceramic fibre board 9 is provided around the lower portion of the ceramic fibre lining 3 to prevent penetration of the material into the lining 3.

Air/gas introduced through the manifold arrangements 6a-c fluidises the bed 8, except in the regions shown by cross- hatching. These latter regions act as an insulating layer between the fluidised bed 8 and the housing 2. The fluidised bed 8 comprises three zones A,B,C corresponding to the three manifold arrangements 6a-c. The temperature of each zone A,B,C may be independently monitored by means of thermocouples 15,16,17.

An exit chute 10 is located towards the right as shown in Figure 1 with its opening a short distance below the level of the bed 8.

As can be seen from Figure 2, the manifold arrangement 6c actually comprises two manifolds - a pre-heated air manifold 21 and a gas/air manifold 22. The arms of both manifolds 21,22 terminate in bubble caps 2la,22a. The other manifold arrangements 6a and 6b are of similar form. In the gas/air ainifold 22, mixing of the gas and air takes place in the bubble caps 22a. This has the important advantage that it prevents excessive heating of the gas before mixing with the air in the bubble caps 22a, and hence prevents cracking of the fuel gas.

In use, material to be reclaimed (such as a comminuted mixture of foundry sand and phenolic resin bonding agent) is fed from, for example, a silo or hopper (not shown), and introduced into zone A of the bed 8 via the conveyor tube 7. The material thus enters the fluidised bed 8 from below, through the interstices between the bubble caps of the manifold arrangement 6a. There is a net transport of material from -left to right as shown in Figure 1, material being introduced at the left and passing out of the furnace through the exit chute 10 at the right, ie the material passes through zones A, B and C in succession.

As the material enters the bed 8 and passes from left to right, the temperature of each zone A,B,C is monitored by means of the thermocouples 15,16,17. In order to maintain the desired temperature in each zone A,B,C, the supply of gas/air mixture to the manifold arrangements 6a-c is controlled independently. For example, as fresh material is introduced to zone A the temperature in that zone may start to fall and the supply of gas/air mixture will be increased to compensate.

The temperatures in the three zones A,B,C may be maintained at substantially the same level, or at differing levels. For instance, a temperature gradient, either increasing or decreasing, may be established. Similarly, the temperature in each individual zone may be maintained at a substantially constant level or may be varied.

Claims

1. Incineration apparatus (1) for incinerating a particulate material, the apparatus (1) comprising a furnace housing (2), means (7) for introducing material to be incinerated into the housing (2), means (6a-c) for forming a fluidised bed (8) in the material in the lower part of the housing (2), a plurality of independently-operable fuel gas supply means (22) for supplying fuel gas to different regions (A,B,C) of the fluidised bed (8), and means (15,16,17) for measuring the temperature of at least some of the regions (A,B,C) .

2. Apparatus as claimed in Claim 1, wherein the fuel gas supply means (22) comprises arrangements of pipes fitted with nozzles or bubble caps (22a) .

3. Apparatus as claimed in Claim 1 or Claim 2, wherein the fuel gas supply means (22) comprises a plurality of air/gas manifold arrangements.

4. Apparatus as claimed in Claim 3, wherein at least one of the air/gas manifold arrangements comprises a pre-heated air manifold (21) and a gas/air manifold (22).

5. Apparatus as claimed in Claim 4, wherein the arms of the gas/air manifold (22) are provided with bubble caps (22a) and mixing of the gas and air takes place in the bubble caps.

6. Apparatus as claimed in any preceding claim, wherein the means for measuring the temperatures of the various regions of the fluidised bed are thermocouples (15,16,17).

7. Apparatus as claimed in any preceding claim, wherein control means are provided to automatically adjust the supply of fuel gas to each region in response to the measured temperatures.

8. Apparatus as claimed in any preceding claim, wherein material to be incinerated is fed directly into the lower part of the fluidised bed (8).