GB2089673A

GB2089673A - Fluidised beds

Info

Publication number: GB2089673A
Application number: GB8035053A
Authority: GB
Original assignee: TECHNICAL DESIGN INTERNATIONAL
Current assignee: TECHNICAL DESIGN INTERNATIONAL
Priority date: 1980-10-31
Filing date: 1980-10-31
Publication date: 1982-06-30

Abstract

A fluidised bed incinerator, or regenerator, comprises an air-permeable bed support 14 which may slope downwards from a materials inlet 20 to an outlet 16. The apparatus is arranged to maintain a hot fluidised bed of a particulate refractory material above the support 14. A baffle plate 28, inclined to the vertical, may overlie a first bed zone 30. The fluidising airflow to the first zone 30 is preferably at or near to the transport velocity of the bed particles. The presence of the baffle 28 promotes turbulence in the first zone. The bed is maintained in a more agitated state in the first zone than in a second zone 32. Material being treated progresses from the inlet 20, through the first zone 30 of the bed, and through the second zone 32 to the outlet 16. As an incinerator, combustible waste is burned. As a regenerator, phenolic-based resin coatings are removed from foundry sand, the sand itself forming the fluidised bed. <IMAGE>

Description

SPECIFICATION Fluidised beds There is described in U.K. Patent Specification No. 1 299 125 a fluidised bed-incinerator comprising a horizontally-extending bed of a particulate refractory material (for example, sand) within a vessel, fluidising means for forcing air through the bed to maintain the bed fluidised, an inlet into the vessel arranged above one end of the bed and through which refuse ta be incinerated can be introduced, and an outlet from the vessel arranged below the surface of the bed at the opposite end of the bed from the inlet In use of the incinerator, the bed is pre-heated before refuse is introduced, to such a temperature that combustion of refuse introduced will be self-sustaining.

The fluidising means of that known apparatus is arranged to introduce such air flows into the bed as to cause the bed to circulate within the vessel. Upon the introduction of refuse through the inlet, the refuse is drawn down into the bed owing to the circulation of the bed and becomes intimately mixed with the hot refractory material of the bed. Combustion of the combustible content of the refuse results.

Sterile ashes and any non-combustible content of the refuse sink to the bottom of the bed and migrate towards the outlet, largely owing to the circulation of the bed. Operation of the incinerator can be continuous, with refuse being introduced through the inlet, and ashes and non-combustible material from the refuse being withdrawn through the outlet.

In that apparatus, the fluidising means is arranged not only to cause circulation of the bed but also to tluidisethe bed in a non-uniform manner to cause a greater degree of agitation of the bed at a region adjacent the outlet than at a region beneath the inlet, so that material being processed enters the less agitated region first and then progresses in the bed to the more agitated region.

It is one of the objects of the present invention to provide an improved fluidised bed incinerator.

The invention provides in one of its aspects an apparatus suitable for use in maintaining a hot fluidised bed of a particulate refractory material comprising means providing a heating chamber, fluidising means whereby in use of the apparaus a hotfluidised bed of a particulate refractory materal can be maintained in the chamber, an inlet whereby material to be processed can be introduced into the heating chamber, and an outlet whereby processed material can be discharged from the chamber, said fluidising means being arranged to maintain a fluidised bed which in a first zone of the heating chamber is in a more agitated state than in a second zone ofthe chamber, and the apparatus being so constructed arranged and adapted to operate that material introduced into the heating chamber through said inlet, in use of the apparatus, will progress through said first zone into said second zone.

An apparatus as set out in the last preceding paragraph may be used as an incineratorforthe disposal of solid or liquid combustible wastes. A hot fluidised bed of a particulate refractory material is established in the heating chamber and material to be processed is then introduced into the heating chamber through the inlet; the material is transported through the fluidised bed, the combustible waste content being consumed and ashes and any non-combustible material being discharged at the outlet.

It is another of the objects of the invention to provide an improved method of disposing of combustible wastes.

The invention provides in another of its aspects a method of disposing of combustible wastes comprising establishing a fluidised bed of a hot particulate refractory material, introducing material comprising combustible waste into the bed, and causing the material to progress through the bed as the combustible waste is burned, the fluidised bed comprising a first zone which is in a more agitated state than a second zone, and the material progressing through the first zone into the second zone.

We have found that by introducing the material firstly into the more agitated zone of the bed and secondly into the less agitated zone, complete combustion of the waste can be ensured with a minimum of air usage. Good thermal efficiency can be achieved, and the quantity of gas products requiring subsequent treatments can also be kept to a minimum.

However, an apparatus as set out in the last preceding paragraph but four may be used to process material which itself forms the fluidised bed.

It is yet another of the objects of the invention to provide an improved method of removing nonrefractory coatings from refractory particles.

The invention provides in another of its aspects a method of removing non-refractory coatings from refractory particles comprising maintaining the particles as a fluidised bed whilst heat removes the coatings.

We have found that a method as set out in the last preceding paragraph enables the coatings to be removed particularly efficiently.

Preferably the fluidised bed is maintained in a greater state of agitation in a first stage of treatment of the particles than in a second stage of treatment, for high thermal efficiency and a minimum of air usage. With advantage the treatment can be carried out in an apparatus as set out in the last preceding paragrah but eight; further particles to be treated can be added to the first zone and treated particles removed from the second zone in a substantially continuous process. The method may find particular application in the removal of phenolic-based resin coatings from foundry sand, to reclaim the sand for further use.

There now follow detailed descriptions, to be read with reference to the accompanying drawings, of two apparatuses and their use which are described to illustrate the invention by way of example.

In the accompanying drawings: Figure 1 is a diagrammatic view in longitudinal section through a fluidised bed incinerator; and Figure 2 is a diagrammaic view in longitudinal section through a fluidised bed regenerator.

Combustion chambers of the two apparatuses are similar, and make use of conventional fluidised-bed technology. Each apparatus comprises a vessel 10 adapted to contain a fluidised bed 12 in a heating chamber; the bed 12 will be maintained, in use of the apparatus, above an air-permeable support plate 14 which is inclined to the horizontal, to slope downwards towards an outlet 16 of the vessel, and beneath the support plate 14 are a plurality of chambers to which controlled amounts of air can be supplied through manifolds 18.

Each vessel comprises also a solids inlet 20 whereby solid material to be processed can be introduced into the heating chamber, the inlet being located above an opposite end of the bed 12 from the outlet 16. A liquids inlet 22, whereby liquid materials to be processed can be introduced into the heating chamber, is located beneath the solids inlet 20 at a level such that it will be below the surface of the fluidised bed. Above the solids inlet 20, auxiliary burners 24 are mounted in the wall of the vessel 10 and directed downwardly towards the support plate 14, for pre-heating of the bed and to assist with combustion or decomposition of materials with a low calorific value. A vent 26 allows hot gases to escape from the vessel 10.

Each apparatus comprises a baffle plate 28 located within the vessel 10 at a level such that it will be in a gas space above the surface of the fluidised bed. The plate, which can be of a ceramic material, a temperature-resistant alloy or any other suitable material, is inclined to the vertical to overlie a first bed zone 30 of the chamber, but not a second bed zone 32 of the chamber.

In use of the incinerator, Figure 1, a fluidised bed 12 of a particulate refractory material is maintained; a preferred bed material is dolerite, but other suitable materials such as ceramics, granite or sand could be used. The bed is pre-heated by means of the auxiliary burners 24 and air is delivered under pressure to the manifolds 18 so that air streams up through the support plate 14 to maintain the bed 12 fluidised; the air may also be pre-heated in order to assist with pre-heating of the bed. When the fluidised bed is in a steady state and at a suitable temperature, material comprising solid or liquid combustible waste can be introduced into the heating chamber through the inlet 20 (or the inlet 22, if appropriate) for processing.Owing to the slope of the support plate 14, the material being processed will progress through the bed 12 towards the outlet 16.

The air flows through the manifolds 18, and the position and inclination of the baffle plate 2' are arrangedsothatthefluidised bed in the two bed zones 30 and 32 is in quite different stages. In the firstzone 30, through which material being processed passes initially, the bed is in a state of great agitation. By association with the hot solid particles of the bed 12, in the presence of air, the combustible waste is heated to a temperature at which it ignites (or is thermally decomposed), the agitation of the bed particles enhancing the combustion. The air flows through the support plate 14 beneath the bed 12 in the first zone 30 are at or near to the transport velocity of the bed particles, and the turbulence of the particles is further promoted by the presence of the baffle plate 28 in the gas space above the bed.

The material being processed progresses from the first zone 30 to the second zone 32 on its passage towards the outlet 16. In the second zone 32 the bed 12 is in a less agitated, more quiescent, state and renders the combustion more complete. Having passed through the second zone 32, the combustion residues, decomposition products, and any noncombustible content of the material processed, are discharged through the outlet 16. Any bed material discharged can be returned to the heating chamber to rejoin the bed.

The regenerator, shown in Figure 2 is suitable for use in removing combustible, orthermallydecom- posable, non-refractory coatings from refractory particles, in particular phenolic-based resin coatings from foundry sand. The apparatus comprises a deceleration chamber 36 which is connected to the heating chamber by way of a flue passage 38 at the top of the vessel. Vents 40 allow collected sand to be drained from the chamber at intervals. A baffle plate 42 is located in the chamber opposite the entry from the flue passage 38.

Use of the regenerator is very similar to use of the incinerator except that the material to be processed itselfformsthefluidised bed 12. Sand to be processed is introduced into the heating chamber and fluidised, and the auxiliary burners 24 are operated to raise the temperature of the sand; in addition, liquid fuels are introduced through the liquids inlets 22 directly into the bed and burned. As with the incinerator, the fluidised bed 12 (of sand, in the regenerator) comprises an agitated region in a first zone 30 and a quiescent region in a second zone 32.

Further sand to be processed can be introduced through the solids inlet 20, and processed sand can be discharged through the outlet 16, in a substantially continuous process. Any sand particles carried from the heating chamber in the hot gases are caught in the deceleration chamber 36.

In the first zone 30, the coated sand particles are raised to a temperature at which the coating material ignites or is thermally decomposed. This heating is achieved by the heat of the bed and by contact with hot particles of regenerated or partly regenerated material. The particles in the first zone are agitated by air flows which are at or near the transport velocity of the particles, and the desired flow patterns are further enhanced by the presence of the baffle plate 28 in the gas space above the first zone 30.

In the second zone 32, where the bed 12 is relatively quiescent, the sand particles are maintained at a suitable temperature for a sufficient time to enable any remaining coating material to be volatilised, vapourised, burned or decomposed.

CLAIMS (Filed 2 not. 1981) 1. Apparatus suitable for use in maintaining a hotfluidised bed of a particulate refractory material comprising means providing a heating chamber, fluidising means whereby in use of the apparatus a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Combustion chambers of the two apparatuses are similar, and make use of conventional fluidised-bed technology. Each apparatus comprises a vessel 10 adapted to contain a fluidised bed 12 in a heating chamber; the bed 12 will be maintained, in use of the apparatus, above an air-permeable support plate 14 which is inclined to the horizontal, to slope downwards towards an outlet 16 of the vessel, and beneath the support plate 14 are a plurality of chambers to which controlled amounts of air can be supplied through manifolds 18. Each vessel comprises also a solids inlet 20 whereby solid material to be processed can be introduced into the heating chamber, the inlet being located above an opposite end of the bed 12 from the outlet 16. A liquids inlet 22, whereby liquid materials to be processed can be introduced into the heating chamber, is located beneath the solids inlet 20 at a level such that it will be below the surface of the fluidised bed. Above the solids inlet 20, auxiliary burners 24 are mounted in the wall of the vessel 10 and directed downwardly towards the support plate 14, for pre-heating of the bed and to assist with combustion or decomposition of materials with a low calorific value. A vent 26 allows hot gases to escape from the vessel 10. Each apparatus comprises a baffle plate 28 located within the vessel 10 at a level such that it will be in a gas space above the surface of the fluidised bed. The plate, which can be of a ceramic material, a temperature-resistant alloy or any other suitable material, is inclined to the vertical to overlie a first bed zone 30 of the chamber, but not a second bed zone 32 of the chamber. In use of the incinerator, Figure 1, a fluidised bed 12 of a particulate refractory material is maintained; a preferred bed material is dolerite, but other suitable materials such as ceramics, granite or sand could be used. The bed is pre-heated by means of the auxiliary burners 24 and air is delivered under pressure to the manifolds 18 so that air streams up through the support plate 14 to maintain the bed 12 fluidised; the air may also be pre-heated in order to assist with pre-heating of the bed. When the fluidised bed is in a steady state and at a suitable temperature, material comprising solid or liquid combustible waste can be introduced into the heating chamber through the inlet 20 (or the inlet 22, if appropriate) for processing.Owing to the slope of the support plate 14, the material being processed will progress through the bed 12 towards the outlet 16. The air flows through the manifolds 18, and the position and inclination of the baffle plate 2' are arrangedsothatthefluidised bed in the two bed zones 30 and 32 is in quite different stages. In the firstzone 30, through which material being processed passes initially, the bed is in a state of great agitation. By association with the hot solid particles of the bed 12, in the presence of air, the combustible waste is heated to a temperature at which it ignites (or is thermally decomposed), the agitation of the bed particles enhancing the combustion. The air flows through the support plate 14 beneath the bed 12 in the first zone 30 are at or near to the transport velocity of the bed particles, and the turbulence of the particles is further promoted by the presence of the baffle plate 28 in the gas space above the bed. The material being processed progresses from the first zone 30 to the second zone 32 on its passage towards the outlet 16. In the second zone 32 the bed 12 is in a less agitated, more quiescent, state and renders the combustion more complete. Having passed through the second zone 32, the combustion residues, decomposition products, and any noncombustible content of the material processed, are discharged through the outlet 16. Any bed material discharged can be returned to the heating chamber to rejoin the bed. The regenerator, shown in Figure 2 is suitable for use in removing combustible, orthermallydecom- posable, non-refractory coatings from refractory particles, in particular phenolic-based resin coatings from foundry sand. The apparatus comprises a deceleration chamber 36 which is connected to the heating chamber by way of a flue passage 38 at the top of the vessel. Vents 40 allow collected sand to be drained from the chamber at intervals. A baffle plate 42 is located in the chamber opposite the entry from the flue passage 38. Use of the regenerator is very similar to use of the incinerator except that the material to be processed itselfformsthefluidised bed 12. Sand to be processed is introduced into the heating chamber and fluidised, and the auxiliary burners 24 are operated to raise the temperature of the sand; in addition, liquid fuels are introduced through the liquids inlets 22 directly into the bed and burned. As with the incinerator, the fluidised bed 12 (of sand, in the regenerator) comprises an agitated region in a first zone 30 and a quiescent region in a second zone 32. Further sand to be processed can be introduced through the solids inlet 20, and processed sand can be discharged through the outlet 16, in a substantially continuous process. Any sand particles carried from the heating chamber in the hot gases are caught in the deceleration chamber 36. In the first zone 30, the coated sand particles are raised to a temperature at which the coating material ignites or is thermally decomposed. This heating is achieved by the heat of the bed and by contact with hot particles of regenerated or partly regenerated material. The particles in the first zone are agitated by air flows which are at or near the transport velocity of the particles, and the desired flow patterns are further enhanced by the presence of the baffle plate 28 in the gas space above the first zone 30. In the second zone 32, where the bed 12 is relatively quiescent, the sand particles are maintained at a suitable temperature for a sufficient time to enable any remaining coating material to be volatilised, vapourised, burned or decomposed. CLAIMS (Filed 2 not. 1981)

1. Apparatus suitable for use in maintaining a hotfluidised bed of a particulate refractory material comprising means providing a heating chamber, fluidising means whereby in use of the apparatus a

hot fluidised bed of a particulate refractory material can be maintained in the chamber, an inlet whereby material to be processed can be introduced into the heating chamber, and an outlet whereby processed material can be discharged from the chamber, said fluidising means being arranged to maintain a fluidised bed which in a first zone of the heating chamber is in a more agitated state than in a second zone of the chamber, and the apparatus being so constructed, arranged and adapted to operate that material introduced into the heating chamber through said inlet, in use of the apparatus, will progress through said first zone into said second zone.

2. Apparatus according to claim 1 comprising a baffle arranged in the heating chamber to overlie the bed to promote turbulence of the bed in said first zone.

3. Apparatus according to claim 2 in which the baffle comprises a baffle plate inclined to the vertical.

4. Apparatus according to any one of claims 1 to 3 in which the fluidising means is arranged to cause air to enter said first zone at or near to the transport velocity of the bed particles.

5. Apparatus according to any one of claims 1 to 4 comprising a bed support which is inclined to the horizontal and slopes downwards towards the outlet.

6. A method of disposing of combustible wastes comprising establishing a fluidised bed of a hot particulate refractory material, introducing material comprising combustible waste into the bed, and causing the material to progress through the bed as the combustible waste is burned, the fluidised bed comprising a first zion which is in a more agitated state than a second zone, and the material progressing through the first zone into the second zone.

7. A method according to claim 6 in which there is introduced into said first zone a fluidising air flow at or near to the transport velocity of the bed particles.

8. A method according to either of claims 6 and 7 in which a baffle overlies the bed to promote turbulence of the bed in the first zone.

9. A method according to any one of claims 6 to 8 in which a bed support is inclined to the horizontal and slopes downwards towards an outlet to cause the material to progress through the bed.

10. A method of removing non-refractory coatings from refractory particles comprising maintaining the particles as a fluidised bed whilst heat removes the coatings.

11. A method according to claim 10 in which the bed is maintained in a greater state of agitation in a first stage of treatment than in a second stage of treatment.

12. A method according to claim 11 in which the bed comprises a first zone which is in a more agitated state than a second zone, and the particles progress through the first zone into the second zone, further particles to be treated being added to the first zone and treated particles being removed from the second zone in a substantially continuous process.

13. A method according to any one of Claims 10 to 12 in which phenolic-based resin coatings are removed from sand particles.

14. Incinerator apparatus substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

15. Regenerator apparatus substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

16. A method of disposing ofcombustible wastes substantially as herein before described with reference to Figure 1 of the accompanying drawings

17. A method of removing non-refractory coatings from refractory particles substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.