GB2027859A

GB2027859A - Heat treatment of material

Info

Publication number: GB2027859A
Application number: GB7927499A
Authority: GB
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1978-08-08
Filing date: 1979-08-07
Publication date: 1980-02-27
Also published as: GB2027859B

Abstract

A method for heat treating a material such as gypsum mineral, consists in burning a fuel in a fluidised bed (4) which is in heat exchange contact through bounding walls (24, 26) with beds (28, 30) of the material to be heated. Combustion gases are passed from the bed (4) through ducting (16, 18) and serve to fluidise at least partly and add heat to the beds (28, 30) through the agency of distributors (34, 36). The beds (28, 30) may contain material which reacts to heat treatment so that the beds are further fluidised by a product of the reaction. <IMAGE>

Description

SPECIFICATION Heat treatment of material This invention relates to the heat treatment of material in discrete form.

In particular, although not exclusively, the invention has reference to calcining and dehydration of crushed mineral matter, for example gypsum. In a conventional plant employed for such heat treatment, fuel, which may be solid, liquid or gaseous, is burnt in a combustion chamber and the hot combustion gases are applied to special containers in which the material is held. In order to maximise heat transfer, the gases are sometimes ducted through the material and around the side walls of the containers, the material being stirred. One disadvantage of these arrangements is that the combustion equipment utilises a number of parts each requiring maintenance and replacement from time to time.

Moreover, stirring of the material renders the plant less efficient than it would otherwise be.

Fluidised bed combustion has in recent years reached a stage of successful commercial exploitation because of its versatility in affording a high combustion intensity and efficiency, a continuous operation capability, automatic control of the combustion process and an ability to burn a wide range of fuels. It has already been appreciated that a fluidised bed combustor can be used for heating fluids, e.g. water or gases and that the combustion gases can be employed in waste heat recovery units.

It is an object of the present invention to provide a method and apparatus for the heat treatment of material in discrete form, using the fluidised bed combustion principle.

Accordingly a first aspect of the present invention provides a method for the heat treatment of material in discrete form, the method including the steps of burning a fuel in a fluidised combustion bed, arranging a heat treament bed of the material in close adjacency with the combustion bed such as to be in heat exchange relation therewith, and introducing combustion gases from the combustion bed into the heat treatment bed which is fluidised at least partly by said gases.

The fuel is conveniently burnt in the fluidised combustion bed at temperatures of about 800on or above.

Advantageously the combustion gases from the fluidised combustion bed are passed in heat exchange relation with the heat treatment bed prior to the introduction of the gases into the heat treatment bed. The gases, when introduced into the heat treatment bed, give up heat to the material as well as assisting in or effecting the fluidisation of the bed.

Preferably in the use of the method according to the first aspect of the invention, the level of material in the heat treatment bed is maintained above the top level of the fluid combustion bed.

Conveniently the combustion gases before their introduction into the heat treatment bed may be passed in heat exchange relation with the material to be treated before the material is fed into the heat treatment bed to preheat the material.

Alternatively the combustion gases may be used to preheat the fluidising and combustion air prior to the introduction of the air into the combustion bed.

The heat treatment bed may be fluidised wholly by the combustion gases from the combustion bed.

The material to be heat treated may be a calcium sulphate material e.g. gypsum. In such a case upon heat treatment a reaction occurs driving off water in the form of steam which has a fluidising effect in the material bed. In this instance, therefore, the heat treatment bed is fluidised by the vaporous reaction product and the combustion gases from the combustion bed.

According to a second aspect of the invention apparatus for the heat treatment of a material in discrete form includes a combustor adapted to contain a fluidised combustion bed of particulate material, a fuel inlet for the combustor, an exhaust gas outlet for the combustor, a heat treatment vessel disposed in close adjacency with the combustor and adapted to contain a bed of material in discrete form, a material inlet and a material outlet in the vessel, and inlet means for introducing into the vessel combustion gases from the combustor.

Preferably the inlet means are fluidising means for receiving and distributing the combustion gases into the vessel. The fluidising may be in the form of sparge pipes arrayed across the base of the or each heat treatment vessel.

Alternatively the fluidising means may comprise a gas-permeable support plate surmounting a plenum chamber for receiving the combustion gases.

Conveniently in one embodiment more than one heat treatment vessel is provided, the vessels being of cuboidal form located either side of the combustor on the side walls thereof. The combustor may alternatively be of circular section and the heat treatment vessel may then be of annular form surrounding the combustor. As a further alternative, the combustor is of annular section and surrounds a heat transfer vessel of circular section.

Conveniently heat exchange means are provided and arranged in heat exchange relation with the or each vessel and are adapted to receive the combustion gases from the combustor.

The heat exchange means may pass through the or each vessel or circumjacent thereto.

The heat exchange means may advantageously comprise ducting extending from the exhaust gas outlet into the vessel and through and in heat exchange contact with a bed of the material to be heated.

Conveniently and in order to optimise heat transfer, the combustor and the or each vessel have common bounding walls which have an extended area afforded by the use of protuberances and/or reentrants: for example, this may be achieved by an 'egg-box' type of design or by corrugations which can be of traditional sinusoidal or V-shaped or other suitable profile.

A heat exchanger may be provided for effecting heat transfer beween the combustion gases and the material to be heat treated prior to its introduction into the or each vessel in order to preheat the material, the combustion gases thereafter passing into the or each vessel. Alternatively, or in addition, a heat exchange may be provided for preheating the fluidising air for the combustor by means of the combustion gases.

By way of example only, one form of a method and apparatus for the heat treatment of a material in discrete form according to the invention is described below with reference to the accompanying drawing in which: Figure 1 is a diagrammatic sectional elevation; and Figure 2 is a sectional plan view of the apparatus of Fig. 1.

Referring to the drawing, apparaus for the heat treatment of material in discrete form includes a combustor 2 adapted to contain a fluidised bed 4 supported on a distributor 6 for fluidising gas, e.g. air. The distributor 6 is provided with a plurality of standpipes 8 each having outlets 10 extending radially at the top thereof. Valved outlets 1 2 are provided for removing material e.g. ash from the bed 4, and fuel inlet (only one 50 of which is shown) are located at each end of the combustor 2. A gas outlet 14 is provided in the combustor 2 and this communicates with manifolds 15, 1 7 which connect with heat exchange ducting 16, 1 8 extending into heat treatment vessels 20, 22 respectively.The vessels 20, 22 have common walls 24, 26 of stainless steel with the combustor 2 and end walls 25, 27, the walls 24, 26 being corrugated (see Fig. 2) up to a level above the top of material beds 28, 30 contained in the vessels 20, 22 respectively which have inlet means 21 for the material, for example gypsum, and outlet means 23 for the heat treated material, for example plaster. Conveniently the inlet and outlet means 21, 23 are located at opposite ends of the vessels 20, 22.

The heat exchange ducting 16, 18 of each vessel 20, 22 communicates with a distribution manifold 31, 32 to which are attached a number of hollow sparge pipes 34, 36 (only one of which in each vessel is shown) perforated with a plurality of holes, the pipes 34, 36 being disposed at the base of the vessels 20, 22, the holes being directed downwardly towards the base of the vessels.

In operation, the combustor 2 is started by passing hot gas to the distributor 6 and thence through the bed 4 to fluidise the bed and to raise its temperature to about 150"C after which gypsum is fed into the vessels 20, 22 to a height corresponding approximately to that of the bed 4 to form beds 28, 30. The bed 4 is continuously heated by this gas until the temperature reaches a level at which coal combustion is self-sustaining, the coal being introduced via inlet 50. The flow of hot gas is thereafter discontinued and replaced with cold air.

The hot gases of combustion issuing from the bed pass through the outlet 14 and the manifolds 15, 1 7 into the ducting 16, 1 8 which extends through the beds 28, 30 in the vessels 20, 22 thereby releasing heat to the gypsum. After their passage through the beds 28, 30 the gases enter the manifolds 31, 32 whence they proceed to issue through the sparge pipes 34, 36 into the beds 28, 30 to fluidise the beds which, during continuous operation, are at a level above the height of bed 4. The heat treated material is removed from the vessels 20, 22 at a predetermined rate to ensure adequate residence time therein at the usual temperature of about 150"C, suitable control means (not shown) being provided for regulating the temperature and the material input/output rates.

Compared with other types of heat treatment methods and apparatus, it is envisaged that the efficiency attainable by using the present invention will be of the order of 90% with an enhanced input of material to be heated. It is further envisaged that the present invention will be compact compared with other heat treatment plants of similar output.

Whilst the present invention removes the need for stirring some types of discrete mate rial to be heat treated, it may still be desirable to stir other materials.

It will be observed that for the method of the present invention no gas cleaning has been described and in fact combustion gases are fed directly into the material being heat treated even though they may have some contaminants which do not have any deleterious affect upon the material.

It will be understood that while the operation of the invention has been described in relation to the heat treatment of gypsum, other materials may be heat treated by using the method and apparatus of this invention.

CLAIMS (7 Aug 1979) 1. A method for the heat treament of a material in discrete form, the method including the steps of burning a fuel in a fluidised combustion bed, arranging a heat treatment

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The heat exchange means may advantageously comprise ducting extending from the exhaust gas outlet into the vessel and through and in heat exchange contact with a bed of the material to be heated. Conveniently and in order to optimise heat transfer, the combustor and the or each vessel have common bounding walls which have an extended area afforded by the use of protuberances and/or reentrants: for example, this may be achieved by an 'egg-box' type of design or by corrugations which can be of traditional sinusoidal or V-shaped or other suitable profile. A heat exchanger may be provided for effecting heat transfer beween the combustion gases and the material to be heat treated prior to its introduction into the or each vessel in order to preheat the material, the combustion gases thereafter passing into the or each vessel. Alternatively, or in addition, a heat exchange may be provided for preheating the fluidising air for the combustor by means of the combustion gases. By way of example only, one form of a method and apparatus for the heat treatment of a material in discrete form according to the invention is described below with reference to the accompanying drawing in which: Figure 1 is a diagrammatic sectional elevation; and Figure 2 is a sectional plan view of the apparatus of Fig. 1. Referring to the drawing, apparaus for the heat treatment of material in discrete form includes a combustor 2 adapted to contain a fluidised bed 4 supported on a distributor 6 for fluidising gas, e.g. air. The distributor 6 is provided with a plurality of standpipes 8 each having outlets 10 extending radially at the top thereof. Valved outlets 1 2 are provided for removing material e.g. ash from the bed 4, and fuel inlet (only one 50 of which is shown) are located at each end of the combustor 2. A gas outlet 14 is provided in the combustor 2 and this communicates with manifolds 15, 1 7 which connect with heat exchange ducting 16, 1 8 extending into heat treatment vessels 20, 22 respectively.The vessels 20, 22 have common walls 24, 26 of stainless steel with the combustor 2 and end walls 25, 27, the walls 24, 26 being corrugated (see Fig. 2) up to a level above the top of material beds 28, 30 contained in the vessels 20, 22 respectively which have inlet means 21 for the material, for example gypsum, and outlet means 23 for the heat treated material, for example plaster. Conveniently the inlet and outlet means 21, 23 are located at opposite ends of the vessels 20, 22. The heat exchange ducting 16, 18 of each vessel 20, 22 communicates with a distribution manifold 31, 32 to which are attached a number of hollow sparge pipes 34, 36 (only one of which in each vessel is shown) perforated with a plurality of holes, the pipes 34, 36 being disposed at the base of the vessels 20, 22, the holes being directed downwardly towards the base of the vessels. In operation, the combustor 2 is started by passing hot gas to the distributor 6 and thence through the bed 4 to fluidise the bed and to raise its temperature to about 150"C after which gypsum is fed into the vessels 20, 22 to a height corresponding approximately to that of the bed 4 to form beds 28, 30. The bed 4 is continuously heated by this gas until the temperature reaches a level at which coal combustion is self-sustaining, the coal being introduced via inlet 50. The flow of hot gas is thereafter discontinued and replaced with cold air. The hot gases of combustion issuing from the bed pass through the outlet 14 and the manifolds 15, 1 7 into the ducting 16, 1 8 which extends through the beds 28, 30 in the vessels 20, 22 thereby releasing heat to the gypsum. After their passage through the beds 28, 30 the gases enter the manifolds 31, 32 whence they proceed to issue through the sparge pipes 34, 36 into the beds 28, 30 to fluidise the beds which, during continuous operation, are at a level above the height of bed 4. The heat treated material is removed from the vessels 20, 22 at a predetermined rate to ensure adequate residence time therein at the usual temperature of about 150"C, suitable control means (not shown) being provided for regulating the temperature and the material input/output rates. Compared with other types of heat treatment methods and apparatus, it is envisaged that the efficiency attainable by using the present invention will be of the order of 90% with an enhanced input of material to be heated. It is further envisaged that the present invention will be compact compared with other heat treatment plants of similar output. Whilst the present invention removes the need for stirring some types of discrete mate rial to be heat treated, it may still be desirable to stir other materials. It will be observed that for the method of the present invention no gas cleaning has been described and in fact combustion gases are fed directly into the material being heat treated even though they may have some contaminants which do not have any deleterious affect upon the material. It will be understood that while the operation of the invention has been described in relation to the heat treatment of gypsum, other materials may be heat treated by using the method and apparatus of this invention. CLAIMS (7 Aug 1979)

1. A method for the heat treament of a material in discrete form, the method including the steps of burning a fuel in a fluidised combustion bed, arranging a heat treatment

bed of the material in close adjacency with the combustion bed such as to be in heat exchange relation therewith, and introducing combustion gases from the combustion bed into the heat treatment bed which is fluidised at least partly by said gases.

2. A method as claimed in claim 1 in which the combustion gases from the combustion bed are passed in heat exchange relation with the heat treatment bed prior to the introduction of the gases into the heat treatment bed.

3. A method as claimed in claim 1 in which the combustion gases before the introduction thereof into the heat treatment bed are passed in heat exchange relation with the material to preheat the material before the material is introduced into the heat treatment bed.

4. A method as claimed in claim 1 in which the combustion gases before the introduction thereof into the heat treament bed are passed in heat exchange relation with fluidising air for the combustion bed to preheat the air.

5. A method as claimed in any one of the preceding claims in which the upper level of the material in the heat treatment bed is maintained above the top level of the fluidised combustion bed.

6. A method as claimed in any one of the preceding claims in which the material in discrete form is calcium sulphate material.

7. A method as claimed in claim 6 in which the calcium sulphate material is gypsum.

8. A method as claimed in any one of the preceding claims in which the heat treatment bed is fluidised wholly by the combustion gases from the combustion bed.

9. Apparatus according to any one of the Claims 3 to 8 in which a distributor for fluidising gas is provided for the combustor and is of circular form with a plurality of perforated stand pipes for the exit of the gas into the combustor.

9. A method as claimed in claim 6 or 7 in which upon heat treatment, the material undergoes a reaction and in so doing the bed of material is at least partly fluidised by a product of the reaction.

10. A method for the heat treatment of a material in discrete form substantially as hereinbefore described.

11. Apparatus for the heat treatment of a material in discrete form including a combustor adapted to contain a fluidised combustion bed of particulate material, a fuel inlet for the combustor, an exhaust gas outlet for the combustor, a heat treatment vessel disposed in close adjacency with the combustor and adapted to contain a bed of material in discrete form, a material inlet and a material outlet in the vessel, and inlet means for introducing into the vessel combustion gases from the combustor.

1 2. Apparatus according to claim 11 in which the inlet means are fluidising means for receiving and distributing the combustion gases into the vessel.

1 3. Apparatus according to claim 12 in which the fluidising means are in the form of sparge pipes arrayed across the base of the heat treatment vessel.

14. Apparatus according to claim 11, 12 or 1 3 in which a distributor for fluidising gas is provided for the combustor and is of circular section with a plurality of standpipes for the exit of the gas into the combustor.

1 5. Apparatus according to any one of claims 11 to 1 4 in which more than one heat treatment vessel is provided, the vessels being located on either side of the combustor.

1 6. Apparatus according to any one of claims 11 to 1 5 in which heat exchange means are arranged in heat exchange relation with the or each vessel and are adapted to receive the combustion gases from the combustor.

17. Apparatus according to claim 16 in which the heat exchange means pass through the vessel.

1 8. Apparatus according to claim 1 7 in which the heat exchange means comprises ducting extending from the exhaust gas outlet into the vessel and through and in heat exchange contact with a bed of the material to be heated.

1 9. Apparatus according to any one of claims 11 to 1 5 in which a heat exchanger is provided and is adapted to receive the combustion gases from a combustion bed in the combustor for preheating material prior to the introduction thereof into the vessel.

20. Apparatus according to any one of claims 11 to 1 9 in which the combustor has common walls with the or each heat treatment vessel.

21. Apparatus according to claim 20 in which the common walls have protuberances and/or re-entrants to provide an extended surface area.

22. Apparatus according to claim 21 in which the common walls are corrugated.

23. Apparatus for the heat treatment of a material in discrete form substantially as herein before described with reference to Figs. 1 and 2 of the accompanying drawings.

CLAIMS (12 Feb 1979)

1. A method for the heat treatment of a material in discrete form, the method including the steps of burning a fuel in a fluidised combustion bed, arranging a heat treatment bed of the material in close adjacency with the combustion bed such as to be in heat exchange relation therewith, and fluidising the material of the heat treatment bed by means of the combustion gases from the combustion bed.

2. A method as claimed in Claim 1 in which the combustion gases from the fluidised combustion bed are passed in heat exchange relation with the heat treatment bed prior to fluidising the heat treatment bed.

3. Apparatus for the heat treatment of a material in discrete form including a combustor adapted to contain a fluidised combustion bed of particulate material, a fuel inlet for the combustor, an exhaust gas outlet for the combustor, a heat treatment vessel disposed in close adjacency with the combustor and adapted to contain a bed of material in discrete form, a material inlet and a material outlet in the vessel, heat exchange means passing through the vessel and communicating with the exhaust gas outlet of the combustor, and fluidising means located in the vessel and connected to the heat exchange means.

4. Apparatus according to Claim 3 in which more than one heat treatment vessel is provided, the vessels being located on either side of the combustor.

5. Apparatus according to Claim 3 in which the combustor is of circular section and the heat treatment vessel is of annular form surrounding the combustor.

6. Apparatus according to any one of Claims 3 to 5 in which the heat exchange means comprises ducting extending from the exhaust gas outlet into the vessel and through and in heat exchange contact with a bed of the material to be heated.

7. Apparatus according to any one of the Claims 3 to 6 in which the fluidising means are in the form of sparge pipes arrayed across the base of the or each heat treatment vessel.

8. Apparatus according to any one of the Claims 3 to 7 in which the walls of the combustor are corrugated.