GB2066435A - Rotary Grates - Google Patents

Abstract

A grate 1 is rotated in a horizontal plane about a central axis 3. Fuel is fed into the grate between an ash removal plough 11 and a fuel strike- off arm 10. The grate comprises a perforated metal plate 15 which supports perforated fire bricks 4 having tapered passages to prevent clogging by ash. The perforations are blanked off between the plough 11 and arm 10 which are both watercooled. <IMAGE>

Description

SPECIFICATION Travelling Grate Stoker Field of the Invention This invention relates to a travelling grate stoker, for burning a fuel, normally coal, to provide heat for the operation of a boiler or other heatconsuming apparatus.

Background to the Invention Travelling grate stokers of various forms are known. In such stokers, fuel is fed into a grate where it is burnt and from which the ash is discharged. Known stokers suffer from disadvantages such as lack of longevity of the travelling grate and difficulties in removing the ash.

Summary of the Invention According to the present invention, there is provided a travelling grate stoker wherein the grate rotates in a horizontal plane about a central axis.

Such a grate only has to support the weight of the coal on its surface and is subject to no other mechanical demands. The grate can therefore have its upper surface lined with refractory material, for example firebricks which are suitably perforated to allow air to pass through them.

To discharge ash from a rotary grate, an arm can be arranged across the grate from its center to its periphery so that the ash is swept off against the arm as the grate rotates.

To feed the fuel onto the grate in a uniform layer, a cut-off arm can be arranged extending generally radially across the grate, and a space can be enclosed between the ash removal plough and the cut-off arm which can be filled with fuel.

As the grate rotates, fuel will be withdrawn from this space under the cut-off arm to produce a fuel bed of uniform depth. The air necessary for combustion may be introduced in the form of a forced draught blown in underneath the grate, and able to pass upwards through the passages in the grate to permit combustion of the fuel. The space below the grate may be divided into separate chambers so that the amount of air passing through the grate at any particular area can be regulated.

Brief Description of the Drawings The invention will now be further described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a simplified perspective view of a rotary table stoker according to the invention; Figure 2 is a vertical cross-sectional view on the line Il-Il from Figure 3 of a rotary table stoker according to the present invention; and Figure 3 is a horizontal cross-section through the stoker on the line Ill-Ill from Figure 2.

Description of a Preferred Embodiment The stoker shown has a grate or table 1 mounted within a housing 2. The table is mounted on a rotatable shaft 3, for rotation within the housing. The upper surface of the table 1 is formed by a layer of firebricks 4 which have tapering passages 5 through them for the passage of air. The taper is intended to prevent the passagesJrom becoming blocked by fine fuel particles.

The firebricks 4 rest on a perforated metal supporting plate 6 which is secured to the shaft 3.

The shaft 3 is set in rotation by a motor 7 driving the shaft via sprocket wheels 8 and a drive chain 9, to rotate the table 1. The table will normally be driven at a speed of between one-half and two revolutions per hour.

Suspended above the table 1 are a fuel cut-off arm 10 and an ash removal plough 11. The lower edge of the fuel cut-off arm 10 is arranged about 10 cm above the upper surface of the table while the lower edge of the ash removal plough 11 is arranged as close as possible to the table surface.

Both the arm 10 and plough 11 are water-cooled.

A fuel hopper 12 feeds fuel, normally coal, to the space 13 enclosed between the arm 10 and plough 11. In use, this space will normally be full of coal. As the table rotates in the direction indicated by arrow 14, coal is drawn from this space 13 under the arm 10, so that a coal bed of uniform 10 cm depth is formed on the table. A blanking-off plate 15 is mounted below the table in the area enclosed within the arc 150, so that air will not pass through the table in this region.

A forced air draught is blown into the space 1 6 below the table through an inlet duct 1 7 and passes up through the passages in the table. The space 1 6 is subdivided by radial walls 18, 19, 20, 21. The wall 18 has a permanently open aperture 22, and the walls 19 and 20 each include an opening closed by a damper 23 which can be opened or closed from outside the housing to admit or exclude the air draught from the spaces between these walls. The wall 21 has no opening.

To ignite the fuel on the table, a refractory arch 24 is mounted on the coal cut-off arm 10 and extends over the area of the table between the arm 10 and the wall 18. To start up, wood or other easily combustible material is placed on the table below the arch 24. As the temperature of the burning material increases, the lower face of the arch 24 heats up, and once rotation of the table starts, sufficient heat will be radiated from the arch to ignite the coal bed emerging from under the arm 10. As the table rotates, the coal will burn in the air blown up through the bed, and the rate of rotation of the table will be controlled so that all the coal is burnt by the time it reaches the plough 11. As the table rotates past the plough 1 the ash is swept off into a chute 25.

The housing 2 has a lining 26 of refractory brickwork, and in the region of the chute 25, the brickwork is stopped at an angle which is parallel or inwardly divergent with respect to the plough 11.

Pipes 27 extend between the spaces below and above the table to introduce extra air above the table to burn up any fine particles which may be suspended above the table.

The heat generated within the housing 2 by the combustion of the fuel rises to heat a boiler or other heat-consuming apparatus 28 above the housing.

Claims (14)

Claims

1. A travelling grate stoker wherein the grate is arranged to rotate in a horizontal plane about a central axis.

2. A stoker as claimed in Claim 1, wherein the upper surface of the grate is formed of a refractory material.

3. A stoker as claimed in Claim 2, wherein the refractory material is perforated firebricks.

4. A stoker as claimed in Claim 3, wherein the perforations in the firebricks are tapered passages with the narrow ends of the passages opening into the upper surface of the grate.

5. A stoker as claimed in Claim 3 or Claim 4, wherein the firebricks are supported on a perforated metal plate.

6. A stoker as claimed in any preceding claim, wherein an ash removal plough extends across and above the grate from the centre to the outer periphery thereof and is angled so that ash on the grate is swept off to the outer periphery as the grate rotates.

7. A stoker as claimed in Claim 6, wherein the grate rotates within a housing which has an aperture in its wall through which ash can be discharged, and the upstream (seen in the direction of rotation of the grate) edge of the opening is parallel or inwardly divergent relative to the ash removal plough in a plane parallel to the grate.

8. A stoker as claimed in Claim 6 or Claim 7, wherein the ash removal plough is water cooled.

9. A stoker as claimed in any one of Claims 6 to 8, including a fuel cut-off arm arranged adjacent the ash removal plough so that the plough and the arm define a space between them which can be filled with fuel to form a fuel reservoir.

10. A stoker as claimed in Claim 9, wherein the fuel cut-off arm is water-cooled.

1 A stoker as claimed in Claim 9 or Claim 10, wherein the fuel cut-off arm supports a refractory ignition arch over part of the grate.

12. A stoker as claimed in any preceding claim wherein the grate is mounted in a housing and means are provided for creating a force draught into an air space in the housing below the bed, and through the bed, the air space below the bed being divided into a number of sections which can be connected to or isolated from one another.

1 3. A stoker as claimed in Claim 12, wherein the air passages through the grate are blanked off in the regions where fuel is fed onto the grate, is ignited and where ash is discharged.

14. A travelling grate stoker substantially as herein described with reference to the accompanying drawings.