GB2059031A - Improvements relating to cyclone- type furnaces - Google Patents

Abstract

A cyclone furnace is provided for the combustion of pulverulent solid material, in particular wood waste (e.g. sawdust, wood chippings and bark fragments). The furnace includes at least three contiguous and intercommunicating chambers, the first one of which includes inlets for pulverulent solid material which is to be burnt, and tangential inlets for air or other combustion- supporting gas (4,5). The second chamber also with tangential gas inlets (12) is used to ensure that all of the solid material passing from the upstream chamber is fully consumed before the combustion products leave the furnace from a final chamber (40). In one embodiment of the invention, a further chamber is provided which includes a perforated support close to the bottom of the chamber adapted to support larger particles of pulverulent solid material which are separated from the five material supplied to the first chamber; means for supplying air through this perforated support is also provided. <IMAGE>

Description

SPECIFICATION Improvements relating to cyclone-type furnaces This invention relates to furnaces and more particularly to furnaces of the cyclone type.

It is known that pulverised or crushed fuel may be burned in a cyclone furnace where fine particles of fuel and air are injected together tangentially into a combustion chamber. The centrifugal forces acting on the particles keep them circulating close to the wall of the combustion chamber where they burn.

The combustion products leave the furnace via an aperture on the axis of the furnace. For the cyclone furnace to perform satisfactorily, the fuel must be in the form of fine particles.

However, in many situations, the fuel may come as a mixture of particles of various sizes-some too large to be injected tangentially into the furnace or, if fed into the furnace, such as would burn slowly and cause clogging of the furnace.

An object of the present invention is to enable fuel mixtures of fine particles as well as larger pieces to be burnt in a furnace of the cyclone type without sacrificing the high combustion intensity that can be obtained by burning the fuel particles in suspension in air.

Another object of the invention is to enable relatively moist waste material, especially saw dust, to be burnt efficiently.

According to one aspect of the present invention, there is provided a cyclone furnace for the combustion of pulverulent solid material, which furnace comprises at least three contiguous and intercommunicating chambers each of which includes a tangential inlet for air or other combustion-supporting gas, wherein (a) the first chamber includes an inlet for pulverulent solid material which is to be burnt and a burner to initiate ignition of the pulverulent solid material; (b) the second chamber is adapted to receive material which has undergone combustion in the first chamber, and includes a second inlet for pulverulent solid material which is to be burnt and a perforated support close to the bottom of the chamber adapted to support the larger particles of pulverulent solid material within the chamber; (c) means for supplying air or other combustion-supporting gas is provided so as to supply the air or gas from below, and so as to pass through, said perforated support into the second chamber; (d) the third chamber is adapted to receive material which has undergone combustion in the second chamber; and (e) the final chamber includes an outlet for combustion products.

The third chamber is provided with a tangential inlet for air or other combustion-supporting gas, but no pulverulent solid material is supplied to the third chamber; this arrangement ensures that all the solid material supplied to the first and second chambers is fully consumed before the combustion products leave the furnace.

The furnace can be equipped with means for separating the pulverulent fuel into coarse and fine fractions.

Preferably, the furnace includes a fourth chamber adapted to receive material which has passed through the third chamber, the fourth chamber serving to cause an enlargerment of the flow field of the gases coming from the third chamber, whereby particulate matter in the gases, e.g. unburnt fragments or ash, is separated from the gaseous flow before the combustion gases leave the furnace.

According to a second aspect of the present invention, there is provided a cyclone furnace for the combustion of pulverulent solid material, which furnace comprises at least three contiguous and intercommunicating chambers, wherein (a) the first chamber includes a tangential inlet for air or other combustionsupporting gas; a second inlet for pulverulent solid material which is to be burnt; and a burner to initiate ignition of the pulverulent solid material; (b) the second chamber is adapted to receive material which has undergone combustion in the first chamber, and includes a tangential inlet for air or other combustion-supporting gas; (c) the third chamber is adapted to receive material which has passed through the second chamber, the third chamber serving to cause an enlargement of the flow field of gases coming from the second chamber, whereby particulate matter in the gases is separated therefrom; and (d) the final chamber includes an outlet for combustion products.

The furnace can be arranged with the chambers side by side to give a generally horizontal arrangement and flow direction, or with the chambers stacked one above the other to give a generally vertical arrangement.

In either case, the inlets for pulverulent solid material into the first chamber (and in the first aspect as defined above into the second chamber) may be disposed in any convenient manner; they may, for example, be tangentially positioned or they may be disposed radially.

The burner may be positioned on the cyclonic axis of the first chamber, or it may be positioned to give tangential firing.

The furnace of the first aspect of this invention is particularly suited to the combustion of wood waste (e.g. sawdust, wood chippings, bark fragments etc) of various sizes. It is preferred to separate solid materials of widely varying particle size into a relatively fine fraction and a relatively coarse fraction, the fine fraction being supplied to the first chamber and the relatively coarse fraction being supplied to the second chamber.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a side elevation of one embodiment of the invention; Figure 2 is a vertical cross-section taken on the line A-A of Fig. 1; Figure 3 is a cross-sectional side elevation of a second embodiment of the invention; Figure 4 is a plan view of the embodiment shown in Fig. 3; Figure 5 is a side elevation of a third embodiment of the invention; and Figure 6 is an arrangement for separating fine from coarse particles of pulverulent solid material (fuel).

Fig. 1 shows a furnace with three chambers. The first chamber 1 (on the left as seen in the drawing) is a cyclone furnace where a mixture of air and fine fuel particles are injected tangentially via inlets 4 and 5, respectively into a substantially cylindrical combustion chamber. If desired, the air and fine fuel particles can be supplied via a common tangential inlet. Initially, the fuel-air mixture is ignited by a burner 6 positioned on the cyclonic axis of the chamber. An alternative arrangement is to have the burner positioned as shown at 6', where it produces tangential firing. After ignition, combustion of the fuelair mixture can proceed on its own. The desired condition of combustion can be controlled by proper adjustments of fuel and air supplies.

The combustion mixture from the first chamber enters the second combustion chamber 2 where larger pieces of fuel are burned in a fuel bed 7 with a perforated support in the form of a metal grille 8. The grille 8 slopes downwardly in the direction towards the third chamber. Air is forced via a pump 9 from underneath the fuel bed to enable the fuel to burn with greater intensity. Air is also injected tangentially into the chamber via a tangential inlet 10 to complete the combustion, and further fuel may be fed from an inlet 11 at the top as shown in Figs. 1 and 2 or from the side or from below the fuel bed. The fuel can be wood splinters and chippings, bark and other waste material.

The combustion mixture from the second chamber 2 then enters the third combustion chamber 3 where excess air is injected tangentially via inlets 1 2 to burn off any fuel particles that happen to escape combustion in the first two combustion chambers.

The combustion gases from the third chamber enter the fourth chamber 40 where particulate matter in the gases are removed before leaving the furnace via an outlet 41. This removal of the particulate matter in the fourth chamber is achieved by the following process.

The gases leaving chamber 1 and 2 already possess a swirling component of velocity. This swirl velocity is increased by further tangential injection of air in chamber 3. As the gases enter the stagnant environment of the fourth chamber, any particulate matter is thrown radially outwards towards the walls of the fourth chamber where it is trapped until removed via an outlet (not shown).

A second embodiment of the invention, in which the combustion chambers are stacked in a vertical arrangement, is shown in Figs. 3 and 4; this embodiment also has four combustion chambers. The same reference numerals are used to represent the same features as in Figs. 1 and 2.

A particularly useful application of the horizontal arrangement is as shown in Fig. 5 where the second chamber has been removed to facilitate the burning of saw dust only.

Such a saw dust burner may be operated such that the level of particulate matter in the exhaust gases is below 460 mg/m3, the maximum permissible level of particulate matter in exhaust gases according to the United Kingdom Air Pollution Standards requirements.

The horizontal arrangement also enables easy adaptation of the burner to fire horizontal waste heat boilers or heat exchangers.

The reference numerals used in Fig. 5 correspond part for part with those used in Figs.

1 and 2.

The mixture of fine particles and coarse pieces of fuel are preferably separated prior to being supplied to the furnace in an assembly as shown in Fig. 6. The coarse pieces of fuel are shown to be fed directly into the feed hopper 11 supplying the second chamber 2.

However, if there is excess of coarse pieces of fuel, it may be desirable to feed them into a storage hopper and subsequently to have them fed by a conveyor to the feed hopper 11 at a desired rate. The separator shown in Fig.

6 comprises a vibratory separator 1 3 from which fine particles, e.g. sawdust, are extracted and are supplied via a duct 14 to a hopper 1 5. From the hopper 1 5 they are fed by a screw feed 1 6 into a channel 1 7 which communicates with an inlet 1 8 into the first chamber 1 of the furnace. The inlet 1 8 is effectively a combination of inlets 4 and 5 as shown in Figs. 1 and 2. Air is supplied to inlet 1 8 from a pump, so that the incoming fine fuel particles are in suspension. The coarser material coming from vibratory separator 1 3 is fed into inlet 11 for the second chamber 2 of the furnace.

Claims (14)

1. A cyclone furnace for the combustion of pulverulent solid material, which furnace comprises at least three contiguous and intercommunicating chambers each of which includes a tangential inlet for air or other combustion-supporting gas, wherein (a) the first chamber includes an inlet of pulverulent solid material which is to be burnt and a burner to initiate ignition of the pulverulent solid material; (b) the second chamber is adapted to receive material which has undergone combustion in the first chamber, and includes a second inlet for pulverulent solid material which is to be burnt and a perforated support close to the bottom of this chamber adapted to support the larger particles of pulverulent solid material within the chamber; (c) means for supplying air or other combustion-supporting gas is provided so as to supply the air or gas from below, and so as to pass through, said perforated support into the second chamber; (d) the third chamber is adapted to receive material which has undergone combustion in the second chamber; and (e) the final chamber includes an outlet for combustion products.

2. A furnace as claimed in claim 1, which has a fourth chamber adapted to receive material which has passed through the third chamber, said fourth chamber serving to cause an enlargment of the flow field of gases coming from the third chamber whereby particulate matter in the gases is separated therefrom.

3. A furnace as claimed in claim 1 or 2, wherein the preforated support in the second chamber slopes downwardly in the direction towards the third chamber.

4. A furnace as claimed in claim 1, 2 or 3, wherein the burner in the first chamber is positioned on the cyclonic axis of the chamber.

5. A furnace as claimed in claim 1, 2 or 3, wherein the burner in the first chamber is positioned so as to effect tangential firing.

6. A cyclone furnace for the combustion of pulverulent solid material, which furnace comprises at least three contiguous and intercommunicating chambers, wherein (a) the first chamber includes a tangential inlet for air or other combustion-supporting gas; an inlet for pulverulent solid material which is to be burnt; and a burner to initiate ignition of the pulverulent solid material; (b) the second chamber is adapted to receive material which has undergone combustion in the first chamber, and includes a tangential inlet for air or other combustion-supporting gas; (c) the third chamber is adapted to receive material which has passed through the second chamber, said third chamber serving to cause an enlargement of the flow field of gases coming from the second chamber, whereby particulate matter in the gases is separated therefrom; and (d) the final chamber includes an outlet for combustion products.

7. A furnace as claimed in any preceding claim, wherein the chambers are arranged side by side to give a generally horizontal flow direction.

8. A furnace as claimed in any one of claims 1 to 6, wherein the chambers are stacked one above the other to give a generally vertical arrangement.

9. A cyclone furnace for the combustion of pulverulent solid material, substantially as hereinbefore described with reference to, and as illustrated in, Figs. 1 and 2, or Figs. 3 and 4, of the accompanying drawings.

10. A cyclone furnace for the combustion of pulverulent solid material, substantially as hereinbefore described with reference to, and as illustrated in, Fig. 5 of the accompanying drawings.

11. A furnace as claimed in any preceding claim, which further comprises means for sep- arating the pulverulent fuel into coarse and fine fractions.

1 2. A furnace as claimed in claim 11, which is equipped with a vibratory separator to separate the pulverulent fuel into a coarse fraction and a fine fraction.

1 3. A furnace as claimed in claim 12, wherein the furnace includes a hopper for receiving fine fuel material produced by the vibratory separator.

14. A cyclone furnace for the combustion of pulverulent solid material, substantially as hereinbefore described with reference to, and as illustrated in, Figs. 1, 2 and 6, 3, 4 and 6, or 5 and 6, of the accompanying drawings.