GB2101283A - Solid fuel combustion equipment - Google Patents

Abstract

Combustion heating apparatus for burning sort bituminous solid fuel, includes a main combustion chamber (10), a pre-combustion chamber (11), an interposed ash separator (12) and an underfeed conveyor type fuel stoker (13). The pre-combustion chamber has a water jacket (21) which also extends up to the ash separator. The stoker includes a screw conveyor (26) which pushes the soft coal up on to the hearth (28) where combustion air is supplied from below through tuyeres (30). Alternative forms of stoking arrangements are described. <IMAGE>

Description

SPECIFICATION Solid fuel combustion equipment This invention relates to combustion heating equipment for burning solid fuels and is intended to assist in burning especially the softer bituminous fuels as opposed to fuels such as anthracite and coke. The invention may also be applied to conversions of existing gas or coal fired boilers to the burning of soft bituminous fuels.

To burn soft fuels effectively it is necessary to control the combustion conditions and, of course, also to provide means for introducing the fuel to the high temperature combustion zone. It is usually important that combustion air should be supplied into or below the combustion zone and it may also be necessary to supply secondary air above or at a downstream point. Problems arise in providing a suitable conveyor or other system for feeding the fuel to the combustion zone and further problems arise from the fact that the combustion gases from the bituminous soft fuel usually have a high fly ash or grit content causing cleaning and maintenance problems in any associated boiler. It is particularly difficult to solve these problems if converting an existing gas, oil or hard coal fired boiler.

Accordingly it is an object of the invention to provide an improved combustion system which will meet at least some of the existing problems.

Broadly stated from one aspect the invention consists in combustion heating apparatus including a main combustion chamber having an inlet, and an outlet for combustion gases, and a precombustion chamber having an outlet for combustion gases connected to the inlet of the main combustion chamber, and including a conveyor, stoker or hopper for introducing a solid fuel into the precombustion chamber. Preferably the conveyor is power operated and it is particularly desirable that the conveyor should be an underfeed stoker for certain types of fuel.

As stated the conveyor and precombustion chamber are preferably designed to burn soft bituminous fuels and the apparatus preferably includes means for supplying combustion air into or below the burning fuel.

According to a particular preferred feature of the invention the apparatus includes a grit or fly ash separator located in the duct between the precombustion chamber and the main combustion chamber. The separator may be a vortex or cyclone separator and in any case it preferably has no high speed moving parts.

The apparatus is especially useful for converting an existing boiler and according to another preferred feature of the invention the precombustion chamber is designed as an addition to an existing main combustion chamber, and has an access opening for the conveyor which is larger than the access or inlet opening for the main combustion chamber.

The main combustion chamber may form part of a boiler or steam generator and the precombustion chamber may be formed with a water jacket which may be used to preheat the boiler feed water, or for other purposes.

From another aspect the invention consists in combustion heating apparatus comprising a main combustion chamber having an inlet for fuel and/or air, and an outlet for combustion gases, a precombustion chamber having means for supplying and burning solid fuel therein and a grit or fly ash separator located between the precombustion chamber and the main combustion chamber.

The precombustion chamber in such an arrangement may include a gravity feed system for the solid fuel.

The invention may be performed in various ways and a number of embodiments will now be described by way of example with reference to the accompanying drawings in which Figure 1 is a diagrammatic side elevation illustrating a combustion heater assembly according to the invention, Figure 2 is a diagrammatic plan view illustrating another embodiment with twin stokers, Figure 3 is another diagrammatic plan view illustrating alternative positions for hoppers, stokers and clinker cleaning doors, Figure 4 is a side elevation illustrating another example of precombustion chamber constructed in sections all incorporating water heating jackets, Figure 5 is an end view of the unit of Figure 4, Figure 6 is a side view of another form of precombustion chamber according to the invention, Figure 7 is an end view of the example of Figure 6, Figure 8 is a diagrammatic side elevation illustrating one form of ash/grit arrester, Figure 9 is an illustration of an alternative cyclone ash separator, Figure 10 is a diagrammatic side view illustrating a chain grate stoker feeding a precombustion chamber, and Figure 11 is a diagrammatic side elevation illustrating one form of gravity feed hopper for a precombustion chamber.

Referring first to the example of Figure 1, the equipment consists essentially of a main combustion chamber or boiler 10, a precombustion chamber or burner 11, an interposed ash/grit separator 12, and a fuel feeder 13. The boiler 10 is in this example an existing oil, gas, or hard coal fired unit with standard combustion equipment which does not need to be described here in detail. In the case of a boiler or steam generator it may include water tubes or fire tubes, and it may be of the dry back or wet back type. It may or may not include a surrounding water jacket. The boiler has a main inlet 1 5, a combustion gas outlet 1 6 and it will normally include a secondary air supply system 18, which may or may not be retained.

It is in practice difficult or impossible to convert such a boiler to burn soft bituminous coal whether in particulate or powered form.

The precombustion unit 11 in this example comprises a cylindrical shell 20 provided with a surrounding waterjacket 21, which also extends into the duct 22 and may, if needed, also extend around the ash arrester 1 2. The precombustion chamber is provided with an underfeed stoker comprising a hopper 25 and a screw conveyor 26 driven by a motor 27. The soft coal is pushed upwards by the screw conveyor into the fire zone or hearth 28 where combustion air is supplied via tuyeres 30 located around the hearth itself such that at least part of the air is forced upwardly through the burning coal. This is the only feasible method of burning soft coal effectively. In addition, secondary air is supplied through a lateral nozzle 31 directing air above the burning coal to assist in completing the combustion.The hot combustion gases at a temperature of 1600 C or more pass through the ash arrester 12 into the main boiler 10 and it will be appreciated that the quantity of ash and grit entering the main boiler and the furnace tubes wil be considerably reduced.

In some cases it may be feasible and useful to burn extra fuel in the main boiler 10, though this is not normal nor necessary. If adopted it is likely that the fuel could be coal, gas or oil.

Figure 10 illustrates an alternative form of stoker of the travelling chain grate type comprising an endless chain link conveyor belt 30 extending into the combustion zone 31 of the precombustion chamber 11. This stoker is fed from a hopper 32 and is driven by a motor 33. This type of stoker is adaptable also to burning hard coals.

In the embodiment illustrated in Figure 2, the main boiler 10 is formed with two combustion zones or furnaces 1 0a, Ob these are each associated with a corresponding section 11 a or 11 b of a precombustion chamber 11, which is provided with two separator underfeed stokers 26a, 26b. A separate clinker removal door 29a, 29b is provided at each end of the chamber 11.

Between each of the precombustion zones 11 a, 11 b and the boiler furnaces 1 0a, 1 Ob a fly ash/grit arrester 12a, 12b is included in the transfer duct.

Figure 3 illustrates another example where a precombustion chamber 11 is connected to the boiler 10 via an ash separator 1 2 and three alternative positions are provided for the coal feed hopper and stoker at 13a. 13b and 13c. This may be convenient where the available space at the front of the boiler is limited. The clinker removal door may be located at any blank hopper position.

In the example of Figures 4 and 5, the precombustion chamber is built up from four or more individual precast sections 40, 41, 42 etc.

Each of these includes an internal combustion zone 45, a stoker tuyere 46 and a surrounding water jacket 47. The water jackets may be coupled to an outlet header 48, which may be arranged to supply pre-heated water to the main boiler 10.

In the further example of Figures 6 and 7 the precombustion chamber is of arched shape, as seen in the end view of Figure 7 and has an open bottom to rest on brickwork. The combustion hearth 50 is supplied with soft ccal via an underfeed stoker 51.

Figure 8 illustrates one form of fly ash separator. The ash containing combustion gases from the precombustion chamber enter at 55 and pass through a slightly constricted throat 56 where their velocity is increased. They impinge on a stationary bladed cone 57 provided with tapered helically twisted blades or vanes 58 which impart rotary motion to the gases. A vortex or cyclone is generated in a separator bucket or dish 60 from which the heavy particles are flung off and removed through a duct 61 provided with a controlled dump valve or gate. The relatively clean combustion gases then issue at 62 and pass on to the main boiler.

In the alternative illustrated in Figure 9 the ash separator is in the form of a cyclone. The hot gases enter at 65 tangentially and form a rapidly rotating vortex. Ash particles striking the sides of the vortex fall to the bottom and are discharged periodicaily through a dump gate 66 and relatively clean gases are collected in the central duct 67 and pass on to the boiler at 68.

In the further example illustrated in Figure 11, the prevombustion burner 70 is designed with an overhead gravity feed hopper 71, which may be designed to feed broken coal, hard or soft, or may be designed as a fluidised bed burner. The combustion products pass to the ash/grit arrester 72 and then to the main boiler 73.

It will be appreciated that the main combustion chamber 10 may be in the form of a heater for any purpose, i.e. a furnace, kiln, air heater, oven, or heat treatment plant. The combustion gases from the main unit 10 may be used to preheat combustion air or to preheat water for the boiler.

Claims (14)

1. Combustion heating apparatus including a main combustion chamber having an inlet, and an outlet for combustion gases, and a precombustion chamber having an outlet for combustion gases connected to the inlet of the main combustion chamber, and including a conveyor, stoker or hopper, for introducing a solid fuel into the pre-combustion chamber.

2. Apparatus according to claim 1, in which the conveyor is power operated.

3. Apparatus according to claim 2, in which the conveyor is an underfeed stoker.

4. Apparatus as claimed in any of the preceding claims, in which the conveyor and pre-combustion chamber are designed to burn soft bituminous fuels, and including means for supplying combustion air into or below the burning fuel.

5. Apparatus as claimed in any of the preceding claims, including a grit or fly ash separator located in the duct between the pre-combustion chamber and the main combustion chamber.

6. Apparatus as in claim 5, in which the separator is a vortex or cyclone separator.

7. Apparatus as in claim 6, in which the separator has no high speed moving parts.

8. Apparatus as claimed in any of the preceding claims, in which the pre-combustion chamber is designed as an addition to an existing main combustion chamber, and has an access opening for the conveyor which is larger than the access or inlet opening for the main combustion chamber.

9. Apparatus according to any of the preceding claims, in which the main combustion chamber forms part of a boiler or steam generator.

10. Apparatus as in any of the preceding claims, in which the pre-combustion chamber is formed with a water jacket.

11. Combustion heating apparatus comprising a main combustion chamber having an inlet for fuel and/or air, and an outlet for combustion gases, a pre-combustion chamber having means for supplying and burning solid fuel therein, and a grit or fly ash separator located between the precombustion chamber and the main combustion chamber.

12. Apparatus according to claim 11, in which the separator is of the cyclone or vortex type without high speed moving parts.

13. Apparatus according to claim 11, or claim 12, in which the pre-combustion chamber includes a gravity feed system for the solid fuel.

14. Combustion heating apparatus substantially in any of the forms described herein with reference to the accompanying drawings.