GB2082300A - Grateless Pre-burner Furnace - Google Patents

Abstract

A grateless furnace (10, 10') has a combustion chamber (11, 11'), means (19, 19') to form a fire bed in the bottom thereof the combustion chamber (11, 11') having upper (27a, 27a') and lower (27b, 27b') regions, at least a part of the upper region (27a, 27a') thereof being lined with refractory material (29, 29') and the lower region 27b, 27b') of the chamber (11, 11') being cooled by water contained with a water jacket (30, 30'). <IMAGE>

Description

SPECIFICATION Improvements In or Relating to Furnaces This invention relates to a grateless furnace of the type, hereinafter referred to as of the type described, having a combustion chamber, means to introduce solid fuel into the combustion chamber, to form a bed of fuel (herein referred to as a fire bed) in the bottom thereof in which, in use, combustion takes place, and means to direct air (herein referred to as primary air) through the fire bed to assist in combustion. It will be appreciated that as a result of combustion, flames, hot gases, and other combustion products are produced, which are referred to hereinafter as hot gases.

A grateless furnace of the type described is known in which the combustion chamber is substantially enveloped by a water jacket to cool the walls of the combustion chamber to prevent damage thereto by the heat produced in the furnace.

However, water jackets have the disadvantage that continual maintenance is needed to ensure for example that there is no leakage of water from the jacket.

A further disadvantage is that when a furnace of the type described is used as a pre-burner in conjunction with a boiler, it is usual to make pipe connections between the water jacket of the furnace and the water space containing the water being heated in the boiler to provide a single water circulatory system to improve the efficiency of the boiler. This makes removal of the preburner furnace from the boiler for maintenance purposes, difficult.

A still further disadvantage is that, a proportion of the heat which would otherwise have been transferred from the furnace to the boiler, will be lost from the water jacket.

Grateless furnaces of the type described are also used in process heating, in which case the water jacket is only required to cool the walls of the chamber to prevent damage, and is not otherwise of importance. However, it is still necessary to remove the heat produced in the furnace which is an expensive nuisance.

A furnace of the type described having the internal walls thereof lined with a refractory material to protect the walls, is also known but it has been found that burnt fuel and other noncombustibles such as impurities in the fuel (herein referred to as clinker) at least some of which are converted by melting or fusing to slag, adhere to the refractory material thereby making removal of the clinker and slag difficult. Further, the refractory is prone to damage by the abrasion of the solid fuel particles, e.g. coal, and it is difficult to direct air through the fire bed as the nozzles through which the air is passed become damaged by the heat of the furnace.

Thus it is an object of the invention to provide a new or improved furnace of the type described which overcomes or reduces these problems.

According to the invention we provide a grateless furnace of the type described, the combustion chamber having upper and lower regions (as herein defined), at least a part of the upper region thereof being lined with refractory material and the lower region of the chamber being cooled by water contained within a jacket surrounding at least a part of said lower region of the combustion chamber.

By "lower region" we means a region at least below the fire bed and possibly extended upwardly beyond the fire bed. By "upper region" we mean a region not extending below the fire bed.

Thus a furnace in accordance with the invention is a hybrid of a water cooled and a refractory-lined furnace. By surrounding the lower region of the combustion chamber with a water jacket, this provides the advantage that the amount of heat lost to the water jacket is reduced as the area of the combustion chamber cooled by the water jacket is reduced, whilst the walls of the lower region of the furnace are cooled thereby preventing clinker and slag from adhering thereto.

A further advantage is that the abrasion of solid fuel particles against the water-cooled walls of the lower region of the combustion chamber is a negligible consideration.

Providing at least part of the upper region with a refractory lining, gives at least the following advantages.

First, clean combustion is encouraged, as smoke and other combustible gases given off from the solid fuel, are not cooled in the upper part of the furnace, and thus complete combustion is facilitated. This is of particular importance in high volatile fuels where the hydro carbons in the combustible gases are cracked thereby facilitating combustion and reducing sooting.

Secondly, heat produced as a result of combustion is not given up to a water jacket but reflected from the refractory material thus assisting in maintaining a high fire bed temperature and thus a high primary air temperature, to again facilitate combustion.

Thus the hybrid furnace defined above provides all the advantages of a water-cooled and refractory-lined furnace, whilst overcoming many of the disadvantages of these types of furnace.

Preferably the means for directing primary air through the fire bed comprises a plurality of apertures in a wall or walls of the lower region of the combustion chamber. There may be nozzles secured in the apertures, which nozzles extend downwardly through the water jacket and are thus cooled thereby, whereby damage to the nozzles due to heat produced in the furnace is considerably reduced.

Preferably, the means for introducing the solid fuel into the furnace comprises at least one channel which extends longitudinally along the length of the combustion chamber to ensure an even distribution of the fuel along the entire length of the combustion chamber. The channel or channels may extend through the water jacket from the exterior of the furnace where coal is supplied thereto, from for example, a hopper, to the interior of the combustion chamber.

The combustion chamber may be substantially cylindrical in section, the channel or channels being provided above a horizontal plane which contains the axis of the chamber.

Two channels may be provided, one either side of a vertical plane which contains the axis of the chamber.

The upper region of the combustion chamber which is lined with refractory material, may comprise at least part of the region which extends between and above said two channels.

One type of refractory material which has been found to be particularly suitable is that sold under the name Durax 1 600 concrete, although any other suitable refractory may be employed.

The upper region of the combustion chamber may be lined with rock wool insulation and the refractory material applied to the insulation. The refractory material may be held in position by the use of heat resisting metal supports which extend through the rock wool insulation or any other type of support.

A furnace in accordance with the invention may be used as a pre-burner which is adapted to be connected to and used in conjunction with a boiler, the furnace having an exhaust opening at one end of the combustion chamber, herein referred to as the rear end, by which flames and hot gases and other products of combustion (herein referred to as hot gases) may be directed into a heating chamber of the boiler.

Previously, in furnaces of the type described, the centre of the exhaust opening has been located only a small distance e.g. 50 mm. above the centre line or axis of the combustion chamber.

However, in a furnace in accordance with the invention, it has been found preferable to raise the opening so that the centre of the exhaust opening lies substantially a greater distance e.g. 1 50 mm.

or more above centre line or axis of the combustion chamber thereby to ensure the minimum amount of contact between the hot gases as they pass from the furnace into the boiler, and the wall of the opening.

Instead of making pipe connections between the water jacket of the furnace and the water space of the boiler, as is usual with known entirely water-cooled furnaces, the heated water of the water jacket may be passed through a heat exchanger to heat air, and the thus cooled water returned to the water jacket, the heated air being fed to the combustion chamber and used as a primary and/or secondary air supply to assist with combustion.

Thus pipe connections between the furnace and boiler are not necessary and this facilitates removal of the furnace from the boiler for maintenance.

The heated air from the heat exchanger may be pressurised by a fan and fed to an air reservoir from where a proportion of the air is directed to the fire bed as a primary air supply, and a proportion of the remaining air ducted to the combustion chamber above the level of the fire bed to provide a secondary air supply. A further proportion of the air in the reservoir may be fed to the rear of the combustion chamber to provide a tertiary supply, the tertiary air being combined with the hot gases to create a cyclone in the exhaust opening to ensure proper mixing of the hot gases and complete combustion of the fuel particles contained therein.

In a preferred furnace, the exhaust opening comprises a nozzle which is water cooled in part, and the tertiary air is circulated over the part of the nozzle which is not water cooled, thereby becoming heated, the tertiary air being passed through holes in the nozzle to enter the opening and create the cyclone.

The combustion chamber of the furnace may have a slag door at a forward end, the door being provided to facilitate the removal of clinker and slag from the interior of the furnace.

Two embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side section of a first embodiment of a furnace in accordance with the invention; Figure 2 is a section along the lines I-I of the furnace of Figure 1, with a hopper located above the furnace; Figure 3 is a side section of a second embodiment of a furnace in accordance with the invention; Figure 4 is a section along the lines 1I--II of the furnace of Figure 2 with a hopper located above the furnace.

Referring to Figures 1 and 2 of the drawings there is shown a solid fuel fired furnace 10 intended for use as a pre-burner in conjunction with a boiler (not shown).

The furnace 10 is of the grateless type comprising an elongate, substantially cylindrical combustion chamber 11 having a central axis A.

At one end 12 thereof, herein referred to as the forward end, a hollow slag door 13 is provided to permit access to the interior of the furnace 10 to facilitate the removal of clinker and slag therefrom, and for maintenance purposes. At the other end 14 of the combustion chamber, herein referred to as the rear end, an exhaust opening 1 5 is provided whereby hot gases may pass from the furnace 10 into the boiler and be used, for example, to heat water. A nozzle 1 6 which is adapted to extend into a heating chamber of the boiler, is located in the opening 1 5 and is partially water cooled and partially cooled by tertiary air, as described below. The spent gases are passed from the boiler to a flue.

Two channels 17 are provided which extend from the exterior of the furnace into the combustion chamber 11. Solid fuel may pass from a hopper 1 9 located above the furnace (shown only in Figure 2) via an inverted V-shaped guide 18 through the channels 1 7 into the combustion chamber 11 , the flow being regulated by gate valves 1 boa which may be controlled manually via handles 20 or automatically by solenoids actuated by pressure sensors or temperature thermostats of the furnace or boiler and/or an electronic control circuit which may be programmed to control the furnace to provide a predetermined output for a predetermined time.

The solid fuel falls downwardly towards the bottom of the combustion chamber 11 and forms a bed of fuel which, when combusted, provides a fire bed.

The channels 1 7 are each located either side of, and equidistant from, a vertical plane V and just above a horizontal plane containing axis A.

The combustion chamber 11 has a plurality of apertures 21, in the bottom thereof in which tubes 22 comprising primary air nozzles, are welded and extend generally downwards to an air reservoir 23 which has an air inlet 24.

The inlet 24 communicates with a duct D to which air is fed from a fan G. The air fed to the fan G is air heated in a heat exchanger (not shown) which extracts heat from the water jacket, as hereinafter described.

The duct D has a dividing wall W therein whereby the air from the fan G is divided into primary and secondary supplies, the primary supply passing to inlet 24 and thus into reservoir 23, and the secondary supply is passed into a further duct 25.

Dampers C are provided in the duct D to regulate the primary and secondary supplies.

Air from the reservoir 23 passes upwardly through the nozzles 22 and through the fire bed on the bottom of the combustion chamber 11, said air comprising a primary air supply which assists in combustion and maintains the entire fire bed at a high temperature.

The further duct 25 extends from the duct D to a hollow 31 in the slag door 13 wherein the secondary air passes into the slag door 1 3. The slag door 1 3 has apertures 32 therein whereby the secondary air supply passes into the combustion chamber above the level of the fire bed to further enhance combustion. It will be appreciated that the secondary air supply will be heated in the hollow door 1 3 thereby increasing the efficiency of the furnace.

A still further duct 33 directs a proportion of the primary air from the reservoir 23 to the nozzle 1 6 at the rear 14 of the furnace 10 to provide a tertiary air supply which is circulated around a hollow 1 6a of the nozzle 1 6 whereby the tertiary air is heated and the nozzle 1 6 cooled. The tertiary air then passes through holes 26 in the nozzle 1 6 into the opening 1 5 to create a cyclone to ensure proper mixing of the hot gases and complete combustion of the fuel particles contained therein.

The combustion chamber 11 is divided into two regions, an upper region 27a and a lower region 27b.

The upper region 27a of the combustion chamber 11, i.e. the region between and above the channels 17 is lined first with a layer of insulating rock wool 28 and then with a layer of refractory material 29 of the type known as Durax 1 600 concrete which wool and refractory are held in place by heat resisting metal supports (not shown). Thus the walls of the upper region 27a of the combustion chamber are protected from heat damage.

The lower region 27b of the combustion chamber i.e. the region below the channels 17, is provided with a water jacket 30 having an inlet 31 and an outlet (not shown) to cool the walls of the lower region 27b of the chamber 11. The primary air supply nozzles 22 the channels 1 7 and a part 1 6b of the nozzle 1 6 in the exhaust opening 15, extend through the water jacket 30 and are thus cooled thereby.

Thus the furnace 10 is a hybrid between a water cooled furnace wherein the entire combustion chamber is enveloped in a water jacket to cool the entire wall surface thereof, and a refractory lined furnace wherein the entire internal surface of the combustion chamber is lined with refractory material.

To improve the efficiency of the furnace 1 0, it is preferable for the heated water from the water jacket 30 to be fed to a heat exchanger (not shown) whereby the heat removed from the water is used to heat air. The thus cooled water is returned to the jacket 30 for cooling the walls of the lower region 27b of the furnace and the heated air is passed to the fan G from where it is fed under pressure to the reservoir 23 as hereinbefore described.

Exhaust nozzles 1 6 in pre-burner grateless furnaces are usually centred 50 mm. or so above the axis A of the combustion chamber. However, it has been found preferable in the furnace described to increase this distance d', to substantially 1 50 mm. to ensure the minimum amount of contact between the hot gases produced in the furnace and the internal surface of the nozzle 1 6 to provide an efficient transfer of heat from the furnace to the boiler.

Referring to Figures 3 and 4 of the drawings there is shown a second embodiment of a solid fuel fired furnace 10' in accordance with the invention intended for use as a pre-burner in conjunction with a boiler (not shown).

The furnace 10' is similar to the furnace 10 of Figures 1 and 2 and hence similar parts will be labelled by the said reference numerals with a prime sign added.

The furnace 1 0' is of the grateless type comprising an elongate, substantially cylindrical combustion chamber 11' having a central axis A'.

At the forward end 12', a hollow slag door 1 3' is provided to permit access to the interior of the furnace 10' for maintenance purposes. At the rear end 14' of the combustion chamber 11', an exhaust opening 15' is provided whereby hot gases may pass from the furnace 10' into the boiler and be used, for example to heat water. A nozzle 16' which is adapted to extend into heating chamber of the boiler, is located in the opening 15' and is partially water cooled and partially cooled by tertiary air as described below.

The spent gases are passed from the boiler to a flue.

Two channels 17' are provided which extend from the exterior of the furnace into the combustion chamber 11'. Solid fuel may pass from a hopper 19' located above the furnace (only shown in Figure 2) via inverted channel-shaped guide 18' through the channels 17' into the combustion chamber 11', the flow being regulated by gate valves (not shown) rotatable about pivots 1 8b which may be controlled manually via handles (not shown) or automatically by solenoids actuated by pressure or temperature thermostats of the furnace or boiler and/or an electronic control circuit which may be programmed to control the furnace to provide a predetermined output for a predetermined time.

The solid fuel falls downwardly towards the bottom of the combustion chamber 11' and forms a bed of fuel which, when combusted, provides a fire bed.

The channels 17' are each located either side of and equidistant from a vertical plane V' and just above a horizontal plane containing axis A'.

The bottom of the combustion chamber 11' is of V configuration and the sides 40,41 of the V each have a plurality of apertures 21' in which tubes 22' comprising nozzles which extend generally downwards to air reservoirs 42, 43, are weided. The reservoir 42 has an inlet 44 which communicates with a duct D' to which air is fed from a fan G'. The duct D' has a dividing wall W' therein whereby the air from the fan G' is divided into primary and secondary supplies, the primary supply passing to inlet 44 and thus into reservoir 42, and the secondary supply is passed into a further duct 25'.

Air from the reservoir 42 passes to reservoir 43 by a duct E' at the rear 14' of the furnace 10', and thus air from both reservoirs 42, 43 passes upwardly through the nozzles 22' and through the fire bed on the bottom of the combustion chamber 11', said air comprising a primary air supply which assists in combustion and maintains the entire fire bed at a high temperature.

The further duct 25' extends from the duct D' to spaces 31' in the roof of the furnace 1 0' wherein the secondary air passes downwardly through apertures 32' into the combustion chamber 11' above the level of the fire bed to further enhance combustion. It will be appreciated that the secondary air supply will be heated in the spaces 31' thereby increasing the efficiency of the furnace.

A still further duct (not shown) directs a proportion of the primary air from the reservoirs 42, 43 to the nozzle 1 6' at the rear 14' of the furnace 10' to provide a tertiary air supply which is circulated around a hollow 16a' of the nozzle 16' whereby the tertiary air is heated and the nozzle 1 6' cooled. The tertiary air then passes through holes 26' in the nozzle 16' into the opening 15' to create a cyclone to ensure proper mixing of the hot gases and complete combustion of the fuel particles contained therein.

The combustion chamber 11' is divided into two regions, an upper region 27a' and a lower region 27b'.

Part of the upper region 27a' of the combustion chamber 11', i.e. the region above the channels 17', is lined with a layer of refractory material 29' of the type known as Durax 1600 concrete. Thus this part of the upper region 27a' of the combustion chamber is protected from heat damage.

The lower region 27b' of the combustion chamber, i.e. the region extending slightly above and entirely below the channel 17', is provided with a water jacket 30' having an inlet (not shown) and an outlet (not shown) to cool the walls of the lower region 27b' of the chamber 11'. The primary air supply nozzles 22', the channels 1 7' and a part 1 6b' of the nozzle 1 6' in the exhaust opening 15', extend through the water jacket 30' and are thus cooled thereby.

Thus, this furnace 10' is also a hybrid between a water-cooled furnace wherein the entire combustion chamber is enveloped in a water jacket to cool the entire wall surface thereof, and a refractory-lined furnace wherein the entire internal surface of the combustion chamber is lined with refractory material.

At the apex of the V at the bottom of the chamber 11' there is an opening 45 which extends along substantially the entire length of the combustion chamber 11', through which slag produced during combustion of the solid fuel, may pass and be removed from the furnace. Thus as new fuel is fed into the chamber 11' from the hopper 19', burnt fuel and other noncombustibles will move in the fire bed under gravity towards the apex of the V and be converted to slag which will eventually pass through the opening 45 and be removed from the furnace.

A water cooled clinker tray 46 may be placed beneath the opening 45 to facilitate disposal of the slag. However, if desired, a conveyor or container may be piaced beneath the opening 45.

Although the bottom of the combustion chamber 11' has been described as being in a V formation, if desired, any other configuration having a downwardly inclined part to direct the slag and other non-combustibles to an opening in a low part of the combustion chamber may be used. Further, although the opening 45 has been described as extending over substantially the entire length of the combustion chamber 11', if desired, the opening 45 may extend over part or parts of the length of the combustion chamber, 11' only.

Although in the furnaces 10, 10' described above, the extent to which the combustion chamber is refractory lined has been described as comprising the region or part of the region between the channels 17 or 17' respectively, a greater or lesser region may be refractory lined, as desired.

Further, in each case the furnace 1 0, 1 0' has been described as being cylindrical but if desired, furnaces of another suitable shape may embody the invention. Further, although a pre-burner furnace has been described, a boiler may embody the invention.

The means for supplying solid fuel to the combustion chamber 11 or 11' has been described as comprising a hopper 1 9, 1 9' but any other means may be employed, although the means described provide the advantage that an even flow of fuel is provided to both sides of the furnace 1 0, 10' along the entire length thereof.

Claims (20)

Claims

1. A grateless furnace of the type described, the combustion chamber having upper and lower regions (as herein defined), at least a part of the upper region thereof being lined with refractory material and the lower region of the chamber being cooled by water contained within a jacket surrounding at least a part of said lower region of the combustion chamber.

2. A furnace according to claim 1 wherein the means for directing primary air through the fire bed comprises a plurality of apertures in a wall or walls of the lower region of the combustion chamber.

3. A furnace according to claim 2 wherein nozzles are secured in the apertures, which nozzles extend downwardly through the water jacket and are thus cooled thereby.

4. A furnace according to any one of the preceding claims wherein the means for introducing the solid fuel into the furnace comprises at least one channel which extends longitudinally along the length of the combustion chamber to ensure an even distribution of the fuel along the entire length of the combustion chamber.

5. A furnace according to claim 4 wherein the channel or channels extend through the water jacket from the exterior of the furnace where coal is supplied thereto to the interior of the combustion chamber.

6. A furnace according to claim 4 or claim 5 wherein the combustion chamber is substantially cylindrical in section, the channel or channels being provided along a horizontal plane which contains the axis of the chamber.

7. A furnace according to any one of claims 4 to 6 wherein two channels are provided, one either side of a vertical plane which contains the axis of the chamber.

8. A furnace according to claim 7 wherein the upper region of the combustion chamber which is lined with refractory material comprises at least part of the- region which extends between and above said two channels.

9. A furnace according to any one of the preceding claims wherein the refractory material is Durax 1 600 concrete.

10. A furnace according to any one of the preceding claims wherein the upper region of the combustion chamber is lined with rock wool insulation and the refractory material is appiied to the insulation.

11. A furnace according to claim 10 wherein the refractory material is held in position by the use of heat resisting metal supports which extend through the rock wool insulation.

12. A furnace according to any one of the preceding claims which is a pre-burner adapted to be connected to and used in conjunction with a boiler, the furnace having an exhaust opening at the rear end of the combustion chamber, by which hot gases are directed into a heating chamber of the boiler.

13. A furnace according to claim 12 wherein the centre of the exhaust opening lies a substantial distance above a centre line or axis of the combustion chamber thereby to ensure the minimum amount of contact between the hot gases as they pass from the furnace into the boiler, and the wall of the opening.

14. A furnace according to any one of the preceding claims wherein the heated water of the water jacket is passed through a heat exchanger to heat air, and the thus cooled water returned to the water jacket, the heated air being fed to the combustion chamber and used as a primary and/or secondary air supply to assist with combustion.

1 5. A furnace according to claim 14 wherein the heated air from the heat exchanger is pressurised by a fan and fed to an air reservoir from where a proportion of the air is directed to the fire bed as a primary air supply, and a proportion of the remaining air is ducted to the combustion chamber above the level of the fire bed to provide a secondary air supply.

16. A furnace according to claim 1 5 where dependent on claim 12 wherein a furnace proportion of the air in the reservoir is fed to the rear of the combustion chamber to provide a tertiary supply, the tertiary air being combined with the hot gases to create a cyclone in the exhaust opening to ensure proper mixing of the hot gases and complete combustion of the fuel particles contained therein.

17. A furnace according to claim 16 wherein the exhaust opening comprises a nozzle which is water cooled in part, and the tertiary air is circulated over the part of the nozzle which is not water cooled, thereby becoming heated, the tertiary air being passed through holes in the nozzle to enter the opening and create the cyclone.

1 8. A furnace according to any one of the preceding claims wherein the combustion chamber of the furnace has a slag door at a forward end, the door being provided to facilitate the removal of clinker and slag from the interior of the furnace.

1 9. A furnace substantially as hereinbefore described, with reference to and as shown in Figures 1 and 2 or 3 and 4 of the accompanying drawings.

20. A novel feature or novel combination of features, hereinbefore described and/or shown in the accompanying drawings.