GB2255175A

GB2255175A - Boilers

Info

Publication number: GB2255175A
Application number: GB9208773A
Authority: GB
Inventors: Mark Edward Crowther
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1991-04-25
Filing date: 1992-04-23
Publication date: 1992-10-28
Anticipated expiration: 2012-04-23
Also published as: CN1067106A; GB9208773D0; ZA922916B; GB2255175B; PL169915B1; GB9108880D0; PL294343A1

Abstract

In a solid fuel fired boiler having a reciprocating grate 6, there is provided in the combustion space 10 within the combustion chamber 4 a baffle 40 which causes the combustion gases to become turbulent, thus to reduce smoke generation and to enhance heat transfer. The plate 40 is apertured and/or has a serrated or castellated margin, or is defined by crossing water tubes, and may be movable longitudinally of the space 10. The plate 40 may be water cooled. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO BOILERS This invention concerns improvements in or relating to boilers, and has particular reference to solid fuel fired boilers in which fuel, for example coal, is burned on a static or moving grate.

One of the principal problems attaching to the burning of solid fuel is the production of what is commonly called smoke, which contains volatiles and particulates together with gases driven off as a result of the combustion mechanism. For some time past, considerable effort has been devoted to reducing atmospheric emissions in an endeavour to promote environmental acceptability with the concomitant objective of enhancing efficiency by improving heat transfer.

An object of the present invention is therefore to provide a solid fuel fired boiler having means enabling the reduction in noxious emissions and the improvement of heat transfer.

Accordingly a solid fuel fired boiler includes a combustion chamber, a grate for supporting a fuel bed disposed within the chamber, an inlet for fuel to be introduced onto the grate, a combustion space above the grate, an exhaust outlet from the combustion space for gaseous products of combustion, a heat exchanger associated with the combustion chamber to receive heat therefrom, and a gas permeable baffle arranged in and across the combustion space such that in use the gaseous products of combustion are caused to become turbulent prior to their egress from the combustion chamber.

The grate may be a static or moving grate, in which latter case the grate may be of the reciprocating type.

The gas permeable baffle may conveniently be in the form of a plate suspended from the roof of the combustion chamber and the plate may fill the combustion space. The permeability of the plate may be afforded by suitable openings in the plate.

Alternatively, the plate may be provided with a profiled margin or profiled margins, for example the margins may be castellated or serrated, in order to provide the permeability.

The baffle is advantageously disposed within the combustion space in order to promote the maximum degree of turbulence in the combustion gases prior to their egress therefrom. Such turbulence extends the residence time within the high temperature combustion zone thus affording a greater opportunity to burn out the volatiles and precipitate the particulates onto the firebed supported on the grate.

Additionally, the turbulence so generated by the baffle occasions an improvement in the heat transfer to the heat exchanger.

The position of the baffle may be fixed or in the alternative the baffle may be moveable within the combustion space such that its optimum disposition can be selected. The baffle may be water cooled. Conveniently, the cooling water may be taken from the main body of the boiler. A pump may be used to assist the flow of water through the baffle. Alternatively an independent water supply and return system may be provided.

The baffle may comprise tubing through which cooling water is adapted to flow. The tubing may advantageously be connected into the working fluid circuit of the boiler. The tubing may consist of at least two tubes spaced apart longitudinally of the boiler and depending into the combustion space. The tubes may conveniently cross over such that together they bridge the combustion space laterally thereof. The tubes may be inclined so as to promote circulation and also to prevent the build-up of any particulates on their outer surfaces.

The heat exchanger may be provided with a flue gas path and a further baffle may be situated in said path in order to promote turbulence therein to enhance heat transfer from the exhausting gases to the working fluid of the exchanger, ie water.

By way of example only, two embodiments of boiler according to the invention are described below with reference to the accompanying drawings in which: Figure 1 is a cut-away schematic of a boiler to which the present invention can be applied; Figure 2 is a diagrammatic sectional view of part of a first embodiment of the boiler in accordance with the present invention; Figure 3 is an enlarged diagrammatic end view of a detail of the boiler shown in Figure 2.

Figure 4 is a cross section taken through the combustion space of a second embodiment of the boiler; and Figure 5 is a longitudinal cross section of the boiler corresponding to Figure 4.

Referring first to Figure 1, there is shown generally at 1 a solid fuel fired boiler having a casing 2 defining therewithin a combustion chamber 4 which accommodates a reciprocating segmented grate 6 driven by actuators 8. A fuel inlet 5 is provided for the chamber 4 and is connected to feed screw elevators 7 for delivering fuel thereto. An air inlet 9 is provided at the front of the boiler 1 and communicates with the combustion chamber 4.

A combustion space 10 is formed above the level of the grate 6 and communicates at the back of the boiler 1 with a reversing chamber 12 for the passage of exhaust gases to a flow path in the form of a pass 14 which registers with the smoke tubes 16 of a heat exchanger 18. The heat exchanger also includes a water space 20 in direct heat transfer relation with the combustion chamber 4 and a water space 22 through which the tubes 16 pass.

Exhaust gases of combustion exiting from the tubes 16 flow into a cyclone grit arrestor 24 which discharges separated grits into an ash removal conduit 26 extending from beneath the grate 6 to a waste material receptacle 28. A screw conveyor 30 powered by a motor 31 is installed in the conduit for transporting the ash residue falling off the grate 6 into the ash receiving area 32 beneath the grate 6.

Referring now to Figures 2 and 3, the side sectional view of the combustion chamber 4 shows the disposition in and across the chamber of a gas permeable baffle plate 40 which is suspended from the roof 42 of the chamber at 44 in such manner that its position can be varied longitudinally of the chamber 4. Also shown is a further gas permeable baffle plate 46 located in the pass 14 of the heat exchanger 18 and the baffle plate 46 is similarly suspended at 47 in a movable fashion lengthwise of the pass.

The baffle plates 40 and 46 have profiled margins remote from their respective suspension points 44 and 47 and in this particular example the profiles are akin to castellations 50.

The baffle plates also have perforations 51.

In operation, solid fuel, for example coal, is introduced to the combustion chamber 4 through the inlet 5 and onto the grate 6 for combustion in air provided through inlet 9, ignition being started electrically through ignition ports 52. A firebed 60 is created on the grate 6 and the gaseous products of combustion rise therefrom into the combustion space 10 and flow towards the back of the boiler. The grate 6 is provided with a reciprocating action by actuators 8 and thus the firebed is agitated to improve combustion and to move ash along the grate. Upon encountering the baffle plate 40 (not shown in Figure 1), the gases are forced to alter direction and in so doing become turbulent before passing through the castellations 50 and perforations 51.This turbulence lengthens the residence time of the gases in the combustion space 10 thereby allowing the opportunity for secondary combustion to occur to destroy the volatiles, thereby reducing smoke emission. At the same time, the heat transfer to the water in space 20 is improved and accordingly the overall efficiency of the boiler is enhanced.

The exhaust gases having passed the baffle plate 40 then travel through the reversing chamber 12 into the pass 14 wherein they encounter the baffle 46 and again turbulence occurs to bring about the same effect on the gases prior to their egress through the tubes 16. The gases emerge from the heat exchanger 18 and flow into the cyclone grit collector wherein they are cleaned prior to atmospheric discharge. Grits collected descend into the conduit for discharge via the screw conveyor 30 into the receptacle 28. Ash falling off the grate 6 descends into the region 32 for removal by the screw 30 in the same way as the grits.

Referring now to Figures 4 and 5, like numerals of reference have been employed for parts common with those of the preceding figures. In the second embodiment of boiler the baffle 70 comprises at least two tubes 72, 74 which depend into the combustion space 10 and which are connected into the water circuit of the boiler. In this respect, the tubes 72, 74 are connected into the water space 20 in the roof of the combustion space 10 and into the water jacket 76 comprising the lateral walls of the combustion space 10. Each tube 72 crosses the other tube 74 so that together they bridge the combustion space.

The tubes 72, 74 in use constitute the baffle and cause gas-borne particulates impinging thereon to precipitate out of the gas stream through retardation. At the same time, the baffle is cooled by the very nature of the tubes being connected into the water circuit of the boiler, and simultaneously heat transfer is enhanced.

The present invention thus provides the means for effecting secondary combustion in the combustion space of the combustion chamber, thus reducing smoke generation from the boiler by promoting turbulent conditions within the combustion space.

The added advantage of the invention resides in the enhanced heat transfer resulting from the turbulence accorded by the baffle provided in the combustion chamber and/or the first pass.

It is to be understood that the number of baffles can be greater than one in the combustion chamber and in the gas pass.

Claims

1. A solid fuel fired boiler including a combustion chamber, a grate for supporting a fuel bed disposed within the chamber, an inlet for fuel to be introduced on to the grate, a combustion space above the grate, an exhaust outlet from the combustion space for gaseous products of combustion, a heat exchanger associated with the combustion chamber to receive heat therefrom, and a gas permeable baffle arranged in and across the combustion space such that in use the gaseous products of combustion are caused to become turbulent prior to their egress from the combustion chamber.

2. A boiler according to Claim 1 in which the grate is a reciprocating grate.

3. A boiler according to Claim 1 or 2 in which the gas permeable baffle is in the form of a plate suspended from the roof of the combustion chamber.

4. A boiler according to any one of the preceding claims in which the baffle is movable within the combustion chamber to assume different positions.

5. A boiler according to any one of the preceding claims in which the baffle is profiled adjacent at least one margin.

6. A boiler according to Claim 5 in which the profile is constituted by serrations.

7. A boiler according to Claim 5 in which the profile is constituted by castellations.

8. A boiler according to any one of the preceding claims in which a further baffle is located within a gas pass of the heat exchanger.

9. A boiler according to any of the preceding claims in which the baffle is water cooled.

10. A boiler according to any one of the preceding claims in which the baffle comprises tubing.

11. A boiler according to Claim 10 in which the baffle comprises at least two tubes depending into the combustion space.

12. A boiler according to Claim 11 in which the two tubes together extend laterally across the combustion space.

13. A boiler according to Claim 12 in which the tubes cross over one another within the combustion space.

14. A boiler according to Claim 10 or 11 in which the tubing is connected into the working fluid circuit of the boiler.

15. A solid fuel fired boiler substantially as hereinbefore described with reference to the accompanying drawings.