AU6648481A - Spouted and fluidised bed combustors - Google Patents

Description

TITLE

"SPOUTED AND FLUIDISED BED COMBUSTORS" TECHNICAL FIELD

This invention relates to spouted bed combustors and fluidised bed combustors. More particularly it concerns the construction of burners and fluid feed nozzles for spouted bed combustors. A variation of the invention encompasses the modification of fluid feed nozzles of a fluidised bed combustor to effect incipient fluidisation of bed material. In particular applications, the present invention extends to burner arrays for the establishment of an extensive area of spouts within a spouted bed combustor, and associated arrangements for the removal of dense debris from the combustor. Other applications of the present invention include the conversion of spouted bed combustors into fluidised bed operation, and the establishment of fluidised bed and/or spouted bed combustors in conventionally constructed oil-fired or gasfired furnaces. The present invention may also be included in combustors which have novel heat extracting jacketing arrangements. BACKGROUND ART

Fluidised bed combustors and spouted bed combustors are well-known to process control engineers. They are featured in most engineering handbooks, and form the basis for the Noyes Data Corporation's review "Fluidised bed combustion of coal and waste materials", which was published in 1977. A more recent review of fluidised bed and spouted bed combustors is the paper by Robert La Nauze, an officer of the Commonwealth Scientific and Industrial Research Organization, entitled "Fluidised bed combustion, A state-of-the-art review".

The application of fluidised bed combustors and spouted bed combustors to the burning of coal washery rejects has recently been the subject of a work programme of the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia. The results of that work have been published in, for example, "Industrial Research News" (Issue No. 118, October 1976), and in "Minerals Research in CSIRO" (Issue No. 7, September 1974). The same work was the basis for the combined spouted/fluidised bed combustor which is described and claimed in the specification of Australian patent No. 495,101. That combustor, in principle, is capable of self-sustaining combustion of a particulate or liquid feedstock containing carbonaceous material. DISCLOSURE OF THE INVENTION

The present invention is the result of further work in connection with fluidised bed combustors and spouted bed combustors, especially the latter, which has been undertaken to develop combustors which are particularly adapted for the combustion of liquid and particulate wastes containing carbonaceous materials. Examples of such wastes are industrial oil wastes, paint manufacturing process wastes, sawdust at sawmills, rice hulls and coffee grounds, as well as coal washery wastes. They are presented for combustion as liquids, slurries, sludges, powders or moist or dry particulate masses.

The prime objectives of the present invention are the more effective and efficient combustion of such wastes, and better running of combustors for extended periods of time. In particular applications of the present invention, other objectives include more efficient waste heat extraction, the establishment of a low cost and effective alternative to oil-fired and gas-fired burners for those who have already incurred the substantial capital cost of installing an oil-fired or gas-fired boiler, and more effective mixing of the bed and solid fuels.

The objectives noted above are achieved by the provision of new nozzles for injecting fluids into a spouted bed, by new combustor designs, by new heat exchanger arrangements, and by. establishing a fluidised bed or spouted bed combustion arrangement in place of the burners in conventional boilers.

According to the present invention, a new form of nozzle for injecting gases and fluid fuel into a bed of particulate material comprises an outer tube of generally circular cross-section and an inner tube mounted to be within and substantially coaxial with the outer tube, characterised in that

(a) the inner tube is adapted to carry a gaseous or liquid fuel and terminates near to the end of the outer tube but wholly within it;

(b) the outer tube is adapted for transport therethrough of air or other gas; and

(c) the end edge. of the outer tube lies substantially in a plane which, when the nozzle is in use in a spouted particulate bed, forms an acute angle relative to the horizontal.

Usually, the acute angle is less than or equal to the angle of repose of the worn-in particulate bed material.

If the fuel is particulate solid combustible material entrained in a stoichiometric excess of air, the inner tube may be omitted.

Typically, the burner will extend horizontally from the side wall of a combustor, but it need not be horizontal, nor need it project into the combustor from the side wall.

Also according to the present invention, a fluid feed nozzle for a fluidised bed or spouted bed combustor is characterised in that it comprises, in combination:

(a) an outer tube of generally circular cross-section; and (b) an inner tube located within and substantially coaxial with the outer tube; further characterised in that:

(1) the outer tube is adapted to carry air or other gas;

(2) the inner tube is adapted to carry a fluid feedstock for the combustor;

(3) the end edge of the outer tube is, when in use in a fluidised or spouted bed combustor, in a substantially vertical plane; and

(4) an inwardly extending annular flange is formed in or attached to the outer tube near its end, but farther from its end than the termination of the inner tube.

The term "fluid feedstock", when used in this specification, includes slurries and particulate material carried or entrained in a liquid or gas.

The fluid feed nozzle may contain apertures in its (in use) lower portion, through which gas from the outer tube can enter the. particulate material of the bed and provide incipient fluidisation of the bed material.

If the feedstock is particulate solid combustible material, entrained in air, the inner tube may be omitted from the fluid feed nozzle.

Further according to the present invention, a fuel and feed injection system for a spouted or spouted/ fluidised bed combustor is characterised in that it comprises a centrally terminating burner nozzle and an array of inwardly or outwardly directed feed nozzles, said array being located in the lower region of a combustion chamber, whereby, in use, an extensive spouted bed of particulate material is created within the combustion chamber with a first annular region of static bed material being formed on the floor of the combustion chamber around the discharge of the burner nozzle, and a second region of static bed material being formed in the vicinity of the wall or walls of the combustion chamber. Preferably, the burner and feed nozzles project horizontally.

Particulate fuels and bed materials mix very actively in such combustors.

If the combustion chamber has a generally circular cross-section, .and the array of nozzles is an annular array, the second region of static bed material will be of annular shape and will have an inclined inner surface. If the array of nozzles is inwardly-directed, the ends of the nozzles will project through the inclined inner edge of the second region of static bed material.

The nozzles are preferably equi-spaced in the array, which may be formed as a plurality of annular or rectangular arrays, located one above another in the lower region of the combustion chamber. Preferably the nozzles are of the type defined above.

When an array of nozzles is used, the floor of the- combustion chamber may contain drain ports in the region of floor between or within the two regions of static bed material, through which dense debris in the combustor, which will collect below or at the spouts of the bed and between the two regions of static bed material, may be removed from the bed without interrupting its operation, by draining and/or conveying material from these parts. A spouted bed combustor of this type can be converted into a fluidised bed combustor by feeding a course aggregate into the bed until it has built up over the ends of the nozzles and filled the lower sections of each spout. If heat is to be extracted from the combustion chamber of a spouted bed or fluidised bed combustor, the present invention is preferably installed in a combustion chamber having at least one substantially vertical metallic wall which forms at least part of a wall of a water chamber located outside the combustion chamber. Alternatively, or additionally, the present invention is installed, in a combustion chamber through which extends at least one substantially vertical metal tube or internal separator, the tube or separator interconnecting top and bottom header chambers.

The feed and burner nozzles of the present invention may also be used to convert an oil-fired, gas-fired or coal-fired boiler into a spouted bed or fluidised bed combustor by replacing the oil, gas or coal burners of the boiler with a particulate bed and first and second elongate ducts, the first elongate duct being adapted to carry air or other gas, the second elongate duct being adapted to carry a combustible fluid, a plurality of tubular extensions from each duct forming, within the particulate bed, an equal plurality of burner nozzles and/or feed nozzles of the present invention.

In such conversions, the nozzles will typically be formed on two sides of the ducts, which are themselves located within the particulate bed. Conveniently, the two ducts can comprise a pair of tubes, one of the tubes forming the combustible fluid duct and being located within the tube forming the first duct. The nozzles are then formed as branches extending from the tubes .

A variant of this use of the present invention is the conversion of an oil-fired, gas-fired or coalfired boiler into a spouted or fluidised bed combustor by replacing the oil or gas burners, or the coal-firing grate (as the case may be) with a particulate bed, within which is located an elongate duct having a plurality of tubular extensions branching therefrom, said duct being adapted to carry air within which liquid or particulate solid combustible material may be entrained, said extensions forming, within the particulate bed, burner or feed nozzles constructed in accordance with the present invention. Alternatively, liquid or solid combustible material may be introduced into the particulate bed, in which case there will be no entrained combustible material carried in the duct and the extensions will simply supply air to the particulate bed to enable the combustible materials in the bed to burn.

Embodiments of the present invention, and of combustors which incorporate the present invention, will now be described, by way of example, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of (a) a conventional fluidised bed combustor and (b) a conventional spouted bed combustor.

Figure 2 illustrates three constructions of a burner nozzle for a spouted bed combustor.

Figures 3 and 4 illustrate the construction of feed nozzles for a spouted bed combustor, which include incipient fluidising apparatus.

Figure 5 shows a spouted bed combustor in which spouts are created with an array of burner nozzles and feed nozzles.

Figure 6 is a plan view, from above, of the lower part of the inside of the combustion chamber of the combustor of Figure 5, with the bed material removed.

Figure 7 illustrates the conversion of a spouted bed combustor of the type illustrated in Figure 5 into a fluidised bed combustor.

Figure 8 is a schematic diagram, of a fluidised bed or spouted bed combustor in which a water jacket surrounds part of the combustion chamber and heat transfer tubes extend through the combustion chamber.

Figure 9 is a schematic diagrar. of two types of oil-fired or gas-fired boilers which have been converted into spouted or fluidised bed boilers.

Figure 10 illustrates, schematically, alternative ducting arrangements for the establishment of spouted or fluidised beds in place of oil or gas burners in boilers. DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Before discussing embodiments of the present invention, it is helpful to review the basic construction and operation of fluidised bed and spouted bed combustors

The fluidised bed combustor illustrated schematically in Figure 1(a) has a bed of particles 10 located within a combustion chamber 11 above a perforated grid 12. Hot air from a furnace enters the region 14 under grid 12, via air supply line 13. The region 14 is known as a plenum chamber. The grid 12 acts to distribute the air flow substantially evenly through the bed of particle 10, which initially are supported on grid 12. When the air velocity through the particles reaches a critical value, the particles are supported by the air flow and assume a turbulent movement akin to the boiling action of a liquid. The bed of particles is then said to be a fluidised bed. A material to be burnt is placed within bed 10 by any suitable means. The illustrated nozzle 15 may be used for injecting combustible liquids and gases into the bed-. If the material to be burnt is, say, insulation on an electrical wiring, the complete wiring is suspended in the fluidised bed. The air and combustio: produced gases leave the space 16 above the bed through exhaust gas duct 17, which usually leads to a cyclone 18 (where fines are extracted from the gas stream) and heat exchanger 19 (to recover high grade heat from the hot exhaust gases). The spouted bed combustor, which is illustrated schematically in Figure 1(b), operates in a similar manner except that the plenum chamber 14 and diffusion plate 12 are usually absent (they may be present for incipient fluidisation purposes). They are replaced by a single upwardly directed nozzle 20. High velocin gas through nozzle 20 creates a highly turbulent spout of bed particles 10A above the nozzle. As in the fluidised bed combustor, the exhaust gases leave the combustion chamber 11A through duct 17, and pass through cyclone 18A and heat exchanger 19A-

If the bed 10A of particulate material is a relatively deep bed, a mode of operation is established in which a spouted bed is formed immediately above the nozzle 20, but the upper region of the bed is a less- vigorously moving fluidised bed. Such a combustor has been termed a "spouted/fluidised bed combustor", to indicate its dual bed formation (see, for example, the specification of Australian patent No. 495,101).

There are, of course, numerous variants of these basic combustors, but all fluidised bed combustors and spoiited bed combustors operate essentially in the same way. In particular, the nozzles in spouted bed combustors generally enter the combustion chamber through the base of the chamber and discharge gases (and in some cases liquids and entrained particulate material) vertically upwards. Some nozzles have caps on them to prevent bed particles from falling into the nozzle orifice and blocking it when the gas flow is switched off.

It has not previously been appreciated that a burner nozzle, which also provides the air for the spout of the bed, need not be upwardly directed, but the air flow creating the spout can leave the nozzle in a substantially horizontal direction. This realisation opens up considerable opportunity to simplify spouted bed construction and at the same time produce spouted bed combustors which are more compact and easy to handle.

A burner nozzle embodying this realisation is illustrated in Figure 2(a). This nozzle comprises an outer tube 21 which enters a combustion chamber through its side wall 24 substantially horizontally, and which remains substantially horizontal when inside the combustion chamber. The end 23 of tube 21 lies substantially in a plane which is at an angle θ relative to the horizontal. Usually, the angle θ is equal to or less than the angle of repose of worn-in bed particles of the combustor. (The worn-in bed particles are generally more rounded than the particles of the bed before it has been fired, and consequently have a smaller angle of repose.) However, the nozzle of Figure 2(a) will continue to function well, even if the angle θ is greater than the angle of repose of worn-in bed particles.

Within tube 21, a second or inner tube 22, of much narrower bore than the tube 21, is supported by vanes 26. The second tube 22 is substantially coaxial with tube 21. The end 25 of tube 22 is near end 23 of tube 21 but is located within tube 21 a distance a from lowest part of end 23.

Tube 21 is connected to the air supply for the spout creation within the bed. Tube 22 carries combustible gas into the spouted bed, or a liquid fuel which is vaporised during its travel in tube 23 as it nears end 25 due to heat radiated from the bed particles of the combustor and/or heat conducted from the hot gases being conveyed through tube 21. Ignition of such combustible fuels may be by contact with the bed material; by electric spark, or by a pilot-flame, in accordance with known arrangements.

In a typical burner nozzle for a spouted bed combustor, tube 21 is made of 6 to 8mm thick vanadiumsteel or 310 or 253 MA stainless steel. Tube 21 has a typical outer diameter in the range from 60mm to 125mm, and carries pre-combusted gases, heated to a temperature in the range from about 800 C to about 1,100º C, at a rate of from about 50 standard litres per second to about 1,000 standard litres per second. Tube 22 is typically made from 10 to 16 gauge (BSG) stainless steel, has an outer diameter of from 6mm to 20mm, and carries . liquid or gas which leaves end 25 at temperatures greater than 30º C and at rates of from about 2 gaseous litres per second to about 40 gaseous litres per second.

Figures 2(b) and 2(c) illustrate alternative arrangements of burners of this type in a combustion chamber, which may be preferred in some combustor systems. It should be noted that the tube 21 of the embodiment depicted in Figure 2(c) is itself not horizontal, but that the plane of end 23C of this tube makes an angle θ relative to the horizontal which is usually equal to, or less than,but may in some circumstances be greater than, the angle of repose of the worn-in bed particles.

As already noted, the inner tube 22 may be omitted if the fuel is particulate solid combustible material entrained in a stoichiometric excess of air.

In the combustion of fluid wastes which contain or consist of carbonaceous materials, the burner nozzle of Figure 2 need only be used for starting up the fluidised bed if feed nozzles of the type illustrated in Figures 3 and 4 are also used in the spouted bed combustor. Figure 3 is a schematic sectional side view of a nozzle and Figure 4 is the section 4-4 of Figure 3. Like the burner nozzles illustrated in Figure 2, the feed nozzle of Figure 3 has an outer tube 31 for conveying air to the combustor chamber and an inner tube 32 which carries fluid feedstock. The outer tube enters the combustion chamber substantially horizontally through side wall 34. The inner tube 32 is supported by vanes 36 to be substantially coaxial with tube 31. The end 35 of tube 32 is near to, but a distance b inside, the substantially vertical end 33 of tube 31.

In addition to the substantially vertical end 33 of tube 31, the feed nozzle differs from the burner nozzle described above by having an annular flange 37 attached to or formed integrally with tube 31, located a distance c from the end 33, which is greater than distance b. Flange 37 extends radially into tube 31 a distance d. In a typical feed nozzle, tube 31 is constructed of vanadium steel or type 310 or 253 MA stainless steel which is from about 1mm to about 3mm thick, has an outer diameter in the range from about 50mm to about 100mm, and contains a flange which has dimension d of from about 5mm to about 20mm located a distance c of from about 50mm to about 125mm from its end 33. Tube 32 is typically made of 10 to 16 gauge (BSG) stainless steel, has an outer diameter of from about 6mm to about 20mm, and is located within tube 31 so that distance b is from about 40mm to about 120mm. Of course, these dimensions may be varied considerably, if the size and use of the combustor makes such variation necessary.

An optional, but preferred feature of feed nozzles of this type is the inclusion in the lower part of tube 31 of a plurality of incipiently fluidising apertures 38. Such apertures 38, in the typical feed nozzle detailed in the last preceding paragraph, will be circular, of diameter from about 6mm to about 20mm. Such apertures will be spaced apart a distance e of from about 50mm to about 200mm, and the aperture nearest to end 33 will be a distance f of from about 60mm to about 150mm from end 33. The apertures 38 are located in the lower portion of tube 31 such that the tangent to the tube at the position of the centre of any aperture 38 forms an angle ∅. relative to the horizontal, the angle ∅ being substantially equal to the angle of repose of the worn-in bed material of the combustor. The centres of apertures 38 on each side tube 31 are usually colinear. The effect of apertures 38 is to allow a portion of the air being conveyed in tube 31 to enter the bed of the combustor and create a state of incipient or partialincipient fluidisation within the bed particles alongside and above tube 31. This has two beneficial effects. It enables a spout to be established in the bed which "cuts back" relative to end 33 more than would be the case if the apertures 38 were not present; and, in addition, it enables lower air velocities and pressures to be used to establish the spouted bed. Both effects result in a more efficient bed operation.

It will be appreciated that only the end portion of the fluid feed arrangement will comprise the feed nozzle, so that tube 31 need not enter the combustion chamber of a spouted bed combustor through side wall 34, nor need it be horizontal at the point of entry into the combustion chamber, provided it terminates with a substantially horizontal length of tube 31. As already noted, the term "fluid feed" includes slurries and gas or liquid-entrained particulate materials, as well as gases and liquids, and the inner tube 32 may be omitted if the feedstock is particulate solid combustible material.

Using burner nozzles and feed nozzles of the types described above, the spouted bed combustor illustrated in Figures 5 and 6 may be constructed. This combustor has a combustion chamber which is generally circular or rectangular in cross-section, within which an extensive spout system is created by a generally circular array of nozzles located in the lower region of the combustion chamber. (Note that a rectangular array of nozzles could be substituted for the circular array, and that the nozzles in the array could be centrally located and directed outwardly towards the wall of the combustion chamber). As shown in the embodiment illustrated in Figures 5 and 6, burner nozzle 50 and feed nozzles 51 extend substantially horizontally through side wall 54 of the combustion chamber. In the drawings, two circular arrays, located one above the other, are shown, but a single array, or more than two arrays, may be used. A feature of this arrangement is that the spouted bed 58 formed in the combustion chamber has a shape such that regions of static bed material 55,56 are created at the base of the chamber. The first of these regions is a central, annular mound of particles 55, of generally triangular cross-section, formed around the end of nozzle 50. The second is an inclined annular region of particles 56, formed alongside and underneath nozzles 51,

The amount of static bed material 56 can be reduced by appropriate shaping of the combustion chamber at its lower corner 52. If more than one array of nozzles 51 is used to create the spouted bed, the arrays may be stepped, as shown in Figure 5, to ensure that the ends of the nozzles of one array project into the bed to an extent which ensures that the inclined inner surface of region 56 of static particles is the same for each array.

An advantage of this form of spouted bed is that a region of non-static bed particles exists between regions 55,56. Any dense debris produced as a result of the operation of the bed will collect in this region. If the collected dense debris builds up, it can foul the ends of nozzles 50,51 and interrupt or modify the spouting action of the bed. It is thus advantageous, if long periods of operation of the spouted bed are contemplated, for at least one drain port 57 to be constructed in the floor of the combustion chamber between the regions of static bed material 55,56. In principle, one drain port will suffice to extract collected dense debris during operation of the combustor, for the movements of the gas and particles in the spout will tend to distribute the dense debris uniformly around the floor of the combustion chamber between regions 55 and 56. However, if large particles of dense debris are generated in the bed, such particles may resist movement around region 55 when a single drain port 57 is opened and may prevent such movement of other particulate debris. It is thus preferable to have a plurality of drain ports 57 positioned in the floor of the combustion chamber around the region 55, for fully effective clearance of dense debris from the combustor during its operation, which may be effected by gravity drainage or by conveying (such as by use of screw conveyors).

The way in which dense debris collects in a spouted bed constructed as indicated in Figures 5 and 6 can be used to convert the spouted bed into a fluidised bed. This is done (and illustrated in Figure 7) by adding coarse aggregate 70 to the spouted bed. The coarse aggregate 70 will collect between the regions 55, 56 of static bed material. By adding sufficient coarse material to the combustor, the aggregate 70 will collect near the ends of the nozzles 50, 51 and provide a means whereby the gases from the nozzles 50, 51 are diffused through the region of coarse aggregate 70. The coarse aggregate thus becomes a diffusion device for the gases from the nozzles, the spouting operation of the bed is no longer maintained, the diffused gases form the bed material above the aggregate 70 into a conventional (if ruggedly) fluidised bed.

Conversion of this fluidised bed back to the spouted bed mode can be effected, without interruption to the operation of the combustor, by opening drain port(s) 57 until the aggregate 70 has been cleared from the combustion chamber.

One of the benefits of burning waste which contains carbonaceous material is that useful heat is produced. This has long been recognised.. Conventionally, as shown in Figures 1 and 2, the heat generated (and in some cases the heat put into the combustor) is extracted from the exhaust gases by heat exchangers (19,19A in .Figure 1). Another commonly used heat extraction technique is to pass tubes through the combustion chamber above the fluidised bed or spouted bed particles, for steam generation using water (or steam) passing through the tubes. A further, and novel, heat extraction mechanism is proposed for another form of combustor which uses the present invention. This is the provision of a water chamber which has a wall which forms at least part of the wall of the combustion chamber of a fluidised bed combustor or a spouted bed combustor.

Such an arrangement is illustrated in Figure 8, where a water chamber 80 is made with a metallic wall 81 which also forms part of the wall of the combustion chamber 82 of a spouted bed or fluidised bed combustor. Heat exchanger 83 will normally be included in the exhaust gas processing equipment to extract heat from exhaust gases, notwithstanding the removal of heat from the combustion chamber by water chamber 80. Wall 81 is typically of stainless steel.

A plurality of water chambers 80 may be used in conjunction with a fluidised bed or spouted bed combustor, or the entire combustion chamber 82 may be jacketed by a single water chamber 80.

A particularly beneficial feature of this waterjacketing, or partial water-jacketing, of the combustion chamber is the reduction in the amount of insulation required for the combustion chamber, and easier access to the combustion chamber for servicing of the combustor.

An additional, or alternative heat exchanger arrangement, also shown in Figure 8, is the inclusion of at least one vertical water tube 85 in the combustion chamber. The water tube or tubes 85, usually made of metal, connect an upper header tank 86 and a lower header tank 87, which in the illustrated embodiment form the upper and lower walls of the combustion chamber. It may be noted that only in spouted or fluidised bed combustors which have no plenum chamber is this particular, illustrated construction possible.

The vertical tube or tubes 85 need not be of constant internal or external dimensions. The tube or tubes may also carry fins 88 for at least part of their length to assist in heat transfer from the bed or from the gas region above the bed to water passing through the finned tube (either by convection or as a result of pumping). The heat transfer to the water contained in tube 85 or the array of tubes 85 may also be enhanced by inclining the tubes relative to the vertical.

A variation on this form of heat transfer arrangement, is the use of substantially vertical internal separators (not shown) within the combustion chamber, dividing the combustion chamber into regions, with direct connection between adjacent separators and upper and lower header tanks. In effect, this is the establishment, within a combustion chamber, of internal walls, with water flowing through the inside of the "walls".

With increased oil prices and reduced availability of oil or gas for burners, oil-fired and gas-fired boilers are becoming more expensive to run, and liable to interruptions in operation. Replacement of an oilfired or gas-fired burner, however, is a capital cost that, in many instances, cannot be justified. A feature of the feed nozzles and burners of the present invention is that they can be used in a conversion of existing oilfired and gas-fired boilers into boilers which have a fluidised bed or scouted bed combustor as their heat generating mechanism.

Figure 9 shows how a conversion may be effected with an oil-fired or gas-fired boiler of the fire-tube (package water-tube) type (Figure 9 (a)) and with an open-D type boiler (Figure 9 (b) ) . The construction of such boilers will be well known to process engineers and need not be described here. The oil or gas burners in the illustrated boilers have been replaced by a particulate bed 90 into which a substnatially horizontal air duct 91 and fluid fuel duct 92 extend. The ducts supply air and fuel to a plurality of burner nozzles 93 located within bed 90 along the length of ducts 91. Preferably the burner nozzles are of the type described above with reference to Figure 2(a) of the accompanying drawings. In operation, each nozzle 93 forms a spouted bed in which fuel is burnt,. and the exhaust gases of the bed take the place of the exhaust gases of the previous oil or gas burner in the boilers.

If some of the burner nozzles 93 are replaced with feed nozzles of the type illustrated in Figures 3 and 4, supplied by fluid waste material or non-gaseous fuel by a separate duct (not shown), the converted boilers comprise yet another method of extracting useful heat energy while removing a waste material from the environment.

If the burner nozzles 93 (and feed nozzles, if present) are spaced sufficiently closely, the individual spouted beds created by the nozzles combine to form a single elongated spouted bed in which combustion takes place and heat is produced.

Alternative ducting arrangements for boiler conversions are illustrated in Figure 10. Figure 10(a) is a schematic plan view of the ducting used in the exemplary embodiments of Figures 9(a) and 9(b). Figure 10(b) is an end-view, also schematic, depicting the construction of an elongate double linear array of burner nozzles 101 and feed nozzles 102 using simple rectangular ducts 103, 104 and 105 which are adapted to supply, respectively, air, fuel and combustible feed to the tubes forming the burner nozzles and the feed nozzles 102.

As already noted, a single duct with branching nozzles can be used for the conversion if the fuel for the spouted or fluidised bed combustor formed in the boiler is particulate solid combustible material which is entrained in a stoichiometric excess of air, or supplied otherwise to the particulate bed (in the latteralternative, the nozzles then supply air to the bed to enable the particulate material that is present to be burnt). Some burner nozzles, supplied with liquid or gaseous fuel, will be required to start the combustion process.

Similar conversions of coal-fired boilers can be effected by replacing the coal-firing grate with a particulate bed and the sort of combustion arrangement described above with reference to Figures 9 and 10.

Variations of the equipment and components described in this specification are, of course, possible without departing from the inventive concept. For example, neither the burner nor the feed nozzles described above need be made of circular tubes, and variations in the dimensions given for the locations of components, and their size, in respect of feed nozzle construction will occur, depending on the nature of the combustible material, the particle size of the bed of the combustor, and the overall dimensions of the combustor. INDUSTRIAL APPLICABILITY

Spouted bed combustors and fluidised bed combustors which include the present invention have many industrial uses. A number of these uses have been mentioned already in this specification, and they require no elaboration. However, it may be noted that a fluidised bed combustor of the type illustrated in Figures 5 and 6 of the accompanying drawings has been constructed to burn industrial oil wastes and paint factory wastes. This combustor has functioned well, as have similar combustors which have recently been built to dispose of, and recover heat from, coffee grains and rice hulls. Other combustors, incorporating the present invention, have been designed to burn sawdust at a saw mill and coal washery rejects.

Claims (13)

1. A nozzle for injecting gases and gaseous fuel into a bed of particulate material comprising an outer tube (21) and an inner tube (22), the inner tube (22) being mounted within and substantially coaxial with the outer tube (21), characterised in that:

   (a) the inner tube (22) is adapted to carry a gaseous or liquid fuel and has its termination (25) near to the end (23) of the outer tube (21), but within the outer tube (21);

   (b) the outer tube (21) is adapted for transport therethrough of air or other gas; and

   (c) the end edge (23) of the outer tube (21) lies substantially in a plane which, when the nozzle is in use in a spouted particulate bed, forms an acute angle (θ) relative to the horizontal.
2. A nozzle as defined in claim 1, further characterised in that the acute angle (θ) is less than or equal to the angle of repose of the worn-in particulate bed material.
3. A nozzle as defined in claim 1 or claim 2, in which the inner tube (22) is adapted to carry a fuel comprising a particulate solid combustible material that is entrained within a gaseous or liquid medium.
4. A fluid feed nozzle for use in a fluidised bed combustor or a spouted bed combustor, characterised in that it comprises, in combination: (a) an outer tube (31) of generally circular cross-section;

   (b) an inner tube (32) located within and substantially coaxial with the outer tube (31); and further characterised in that

   (i) the outer tube (31) is adapted to carry air or other gas;

   (ii) the inner tube (32) is adapted to carry a fluid feedstock for the combustor;

   (iii) the end edge (33) of the outer tube (31) is, when in use in the combustor, in a substantially vertical plane; and

   (iv) an inwardly extending annular flange (37) is formed in or attached to the outer tube (31) near its end (33), but farther from its end (33) than the termination (35) of the inner tube (32).
5. A fluid feed nozzle as defined in claim 4, further characterised in that a plurality of apertures (38) are formed in the lower portion of the outer tube (31).
6. A fluid feed nozzle as defined in claim 5, in which the tangent to the outer tube (31) at the position of each aperture (38) forms an acute angle (θ) relative to the horizontal which is substantially equal to the angle of repose of the worn-in bed material of the combustor.
7. A nozzle as defined in any preceding claim, in which the inner tube (22,32) is supported within the outer tube (21,31) by a plurality of vanes (36).
8. A fuel and feed injection system for a spouted or spouted/fluidised bed combustor, in which a bed of particulate material is located in the lower region of a combustion chamber, characterised in that the system comprises:

   (a) an array of inwardly or outwardly directed feed nozzles (51) located in the lower region of the combustion chamber, said array of feed nozzles (51) being effective, in use, to create an extensive spouted region (58) of the particulate material; and

   (b) a burner nozzle (50) , terminating centrally within the array of feed nozzles 51; further characterised in that the burner nozzle (50) is a nozzle as defined in claim 1 and each feed nozzle (51) is a nozzle as defined in claim 4.
9. A fuel and feed injection system as defined in claim 8, in which the array of feed nozzles (51) comprises at least one circular array of feed nozzles (51) extending into said combustion chamber through a side wall (54) thereof,
10. A fuel and feed injection system as defined in claim 8, in which the array of feed nozzles (51) comprises at least one rectangular array of feed nozzles (51) extending into the combustion chamber through a side wall (54) thereof.
11. 11. A spouted or spouted/fluidised bed combustor comprising a combustion chamber in which is located a particulate bed of material, characterised in that:

    (a) the supply of fuel and feed to the combustor is an injection system as defined in claim 8, which, in use, creates a spouted region (58) of particulate material, a first annular region (55) of static bed material generally underneath and encircling the discharge end of the burner nozzle (50), and a second annular region (56) of static bed material underneath the discharge ends of the feed nozzles (51) and in the vicinity of the wall or walls (54) of the combustion chamber; and

    (b) at least one closeable drain port (57) in the base of the combustion chamber, the or each drain port being located underneath the region between the first and second annular regions (55,56) of static bed material.
12. 12. A combustor as defined in claim 11, including an additional drain port (57) located in the base of the combustion chamber underneath the discharge end of the burner nozzle (50).
13. 13. A combustor as defined in claim 11 or claim 12, including the facility to introduce pre-sized solid particulate feed, bed or fuel particles into at least one active portion of the bed, in either an upcoming or down coming location, depending on the nature of the particulate feed, bed or fuel particles. A fluidised bed combustor comprising an operating spouted or spouted/fluidised bed combustor as defined in claim 11 or claim 12, into which a quantity of coarse aggregate (70) has been inserted, after establishing the spouted or spouted/fluidised bed combustor operation, in sufficient quantity to fill the regions surrounding the discharge ends of

    each nozzle (50,51), to thereby diffuse the fluid discharge from each nozzle (50,51).

    A combustor as defined in claim 11 or claim 12, further characterised in that at least part of the wall of the combustion chamber is a wall (81) of a water chamber (80).

    A combustor as defined in claim 11 or claim 12, further characterised in that at least one metal tube (85) extends from the top to the base of the combustion chamber, between an upper header (86) and. a lower header (37).

    A combustor as defined in claim 16, in. which the lower wall of the upper header (86) forms at least part of the roof of the combustion chamber and at least part of the upper wall of the lower header (87) forms at least part of the base of the combustion chamber.

    A combustor as defined in claim 17, in which the or at least one metal tube (85) carries fins (88) thereon.

    A combustor as defined in any one of claims 16 to 18, in which the metal tube (85) does not extend vertically between the lower header (87) and the upper header (86).

    A combustor as defined in claim 11 or claim 12, further characterised in that a plurality of substantially vertical internal separators are located within the combustion chamber, dividing the combustion chamber into regions, with direct connection between adjacent separators and upper and lower header tanks adapted to contain water. A spouted bed combustor or fluidised bed combustor for heating a boiler, comprising, in combination:

    (a) an elongate bed of particulate material (90) in the location of the conventional gas, oil or coal burner for the boiler;

    (b) a first elongate duct (91,103) located within said elongate bed (90), and adapted to carry air or other gas therethrough;

    (c) a second elongate duct (92,104) located within said elongate bed (90) and adapted to carry a fluid fuel therethrough;

    (d) a plurality of burner nozzles (93,101) extending into said elongate bed (90), each burner nozzle (93,101) being a nozzle as defined in claim 1, with its outer tube (21) connected to said first elongate duct (91,103) and its inner tube (22) connected to said second elongate duct (92,104).

    A combustor as defined in claim 21, further characterised in that said first and second ducts (91,92) are tubular ducts of circular cross-section, said second duct (92) being substantially coaxially located within said first duct (91), and said nozzles (93) are formed as spaced linear arrays of nozzles (93) on two sides of said ducts (91,92).

    A spouted bed combustor as defined in claim 21, further characterised in that said first and second ducts (103,104) are substantially rectangular in cross-section, a third elongate duct (105) of substantially rectangular cross-section is located within said elongate bed (90) and is adapted to carry a combustible fluid feedstock therethrough, and at least one feed nozzle (102) as defined in claim 4 is located within the elongate bed (90) with its outer tube (31) connected to said first duct (103) and its inner tube (32) connected to said third duct (105).

    A nozzle as defined in any one of claims 1 to 6, in which the inner tube is absent.

    A system as defined in any one of claims 8, 9 and 10, in which the inner tube of each nozzle thereof is absent.

    A combustor as defined in any one of claims 11 to 23, in which the inner tube of each nozzle thereof is absent.