GB2086020A - Improvements relating to grates for shell boilers - Google Patents

Abstract

The invention relates to a grate 12 for a shell boiler which comprises grate bars 18, arranged above an open topped grate box 22. The one piece assembly serves to prevent unwanted leakages of air from the grate box. The grate box may be subdivided into sections (24, 26). Furthermore, secondary air pipes 40 can be arranged to pass through the grate box. <IMAGE>

Description

SPECIFICATION Improvements relating to grates for shell boilers The present invention relates to shell boilers, in particular to boilers in which solid fuel is burnt in a grate to provide combustion gases whereby water in the boiler shell is heated. More particularly, the invention relates to the boiler furnace zone where the solid fuel is burnt.

In a broad aspect, the present invention relates to a one piece grate assembly for a shell boiler comprising grate bars arranged above a box open at the top.

As distinct from prior arrangements in which the grate bars simply rest on appendages projecting from the interior of a grate box which is already in the boiler furnace zone, the one piece grate assembly of the invention offers the advantage of preventing unwanted leakages of air from the grate box. The air will thus pass, as required, only through the bars of the grate into the furnace zone.

Advantageously, pipes carrying secondary air, to be introduced into the furnace zone in the region above the grate, pass through the grate box.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a vertical section through a coal burner having a grate assembly according to the invention; and Figure 2 is a front elevation of a coal burner unit incorporated in a boiler.

In Figure 1 , the coal burner unit generally designated 10 comprises a grate assembly 1 2 above which there is formed a furnace zone 14.

Coal, or other suitable solid fuel is fed into the furnace zone 14 via a delivery tube 1 6 and the coal is distributed over the grate 1 8 of the grate assembly 12 by means of a coal distributor 20.

The grate 1 8 is fed from beneath with primary air and the coal is burnt on the grate to provide heated combustion gases. These gases pass out of the furnace zone 1 4 and are subsequently used to heat water in the shell boiler. The grate assembly 12 is made in a single piece and comprises the grate 18 fitted into an open-topped grate box 22.

The grate box 22 is divided longitudinally into front and rear sections 24 and 26. Alternatively the grate box may be undivided or comprised of more than two sections.

Since the grate assembly 12 is made in a single piece, it is much more convenient to fit the grate assembly into the furnace zone, and the possibility of primary air escaping from the grate box 22 other than via the grate 18 is substantially eliminated. This ensures that the coal on the grate 18 is burnt efficiently as possible.

Figure 2 helps to illustrate the manner in which air is fed to the grate assembly 12 and to the furnace zone 14. In Figure 2, a motor unit 30 also houses a fan (not shown) which provides a supply of air. The air passes through control valves 32, 34, 36 and 38. Control valves 32 and 34 regulate the supply of air to the front and rear sections 24 and 26 of the grate box 22 respectively. Control valves 36 and 38 control the supply of air to the secondary air pipes. Control valve 36 controls the supply of air to the rear secondary air pipes, as shown at reference numeral 40 in Figure 1, whilst the control valve 38 controls the supply of air to the front secondary air pipes, indicated by reference numeral 42. The secondary air is fed to the furnace zone 40 in the region above the grate 18.The purpose of the secondary air is to mix high velocity air with volatile gases which are given up when the cold coal introduced to the grate meets the hot fire within the furnace zone 14. The high velocity air from the secondary air pipes mixes with the volatile gases and ensures efficient combustion of the coal within the furnace zone.

It is to be noted from Figure 1 that the rear secondary air pipes 40 pass through the grate assembly 12, and the grate assembly is constructed accordingly.

The secondary air pipes 42 then pass vertically through the rear refractory wall 44 of the furnace zone 14 and open into the rear of the furnace zone. The pipes 40 pass through the refractory wall 44 via apertures 46 in the refractory wall 44.

It is also envisaged that the grate assembly may be bolted to the air box of the coal burner, the whole making a packaged coal burner unit.

1 A one piece grate assembly for a shell boiler comprising grate bars arranged above a box open at the top.

2. A grate assembly as claimed in Claim 1, wherein the box is divided into two or more sections.

3. A shell boiler comprising a grate box as claimed in Claim 1 or Claim 2 and having secondary air pipes for introducing high velocity air into the furnace zone without the secondary air contacting the fuel, wherein the secondary air pipes are arranged to pass through the grate assembly.

4. A grate assembly for a shell boiler constructed substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements relating to grates for shell boilers The present invention relates to shell boilers, in particular to boilers in which solid fuel is burnt in a grate to provide combustion gases whereby water in the boiler shell is heated. More particularly, the invention relates to the boiler furnace zone where the solid fuel is burnt. In a broad aspect, the present invention relates to a one piece grate assembly for a shell boiler comprising grate bars arranged above a box open at the top. As distinct from prior arrangements in which the grate bars simply rest on appendages projecting from the interior of a grate box which is already in the boiler furnace zone, the one piece grate assembly of the invention offers the advantage of preventing unwanted leakages of air from the grate box. The air will thus pass, as required, only through the bars of the grate into the furnace zone. Advantageously, pipes carrying secondary air, to be introduced into the furnace zone in the region above the grate, pass through the grate box. The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a vertical section through a coal burner having a grate assembly according to the invention; and Figure 2 is a front elevation of a coal burner unit incorporated in a boiler. In Figure 1 , the coal burner unit generally designated 10 comprises a grate assembly 1 2 above which there is formed a furnace zone 14. Coal, or other suitable solid fuel is fed into the furnace zone 14 via a delivery tube 1 6 and the coal is distributed over the grate 1 8 of the grate assembly 12 by means of a coal distributor 20. The grate 1 8 is fed from beneath with primary air and the coal is burnt on the grate to provide heated combustion gases. These gases pass out of the furnace zone 1 4 and are subsequently used to heat water in the shell boiler. The grate assembly 12 is made in a single piece and comprises the grate 18 fitted into an open-topped grate box 22. The grate box 22 is divided longitudinally into front and rear sections 24 and 26. Alternatively the grate box may be undivided or comprised of more than two sections. Since the grate assembly 12 is made in a single piece, it is much more convenient to fit the grate assembly into the furnace zone, and the possibility of primary air escaping from the grate box 22 other than via the grate 18 is substantially eliminated. This ensures that the coal on the grate 18 is burnt efficiently as possible. Figure 2 helps to illustrate the manner in which air is fed to the grate assembly 12 and to the furnace zone 14. In Figure 2, a motor unit 30 also houses a fan (not shown) which provides a supply of air. The air passes through control valves 32, 34, 36 and 38. Control valves 32 and 34 regulate the supply of air to the front and rear sections 24 and 26 of the grate box 22 respectively. Control valves 36 and 38 control the supply of air to the secondary air pipes. Control valve 36 controls the supply of air to the rear secondary air pipes, as shown at reference numeral 40 in Figure 1, whilst the control valve 38 controls the supply of air to the front secondary air pipes, indicated by reference numeral 42. The secondary air is fed to the furnace zone 40 in the region above the grate 18.The purpose of the secondary air is to mix high velocity air with volatile gases which are given up when the cold coal introduced to the grate meets the hot fire within the furnace zone 14. The high velocity air from the secondary air pipes mixes with the volatile gases and ensures efficient combustion of the coal within the furnace zone. It is to be noted from Figure 1 that the rear secondary air pipes 40 pass through the grate assembly 12, and the grate assembly is constructed accordingly. The secondary air pipes 42 then pass vertically through the rear refractory wall 44 of the furnace zone 14 and open into the rear of the furnace zone. The pipes 40 pass through the refractory wall 44 via apertures 46 in the refractory wall 44. It is also envisaged that the grate assembly may be bolted to the air box of the coal burner, the whole making a packaged coal burner unit. CLAIMS

1 A one piece grate assembly for a shell boiler comprising grate bars arranged above a box open at the top.

2. A grate assembly as claimed in Claim 1, wherein the box is divided into two or more sections.

3. A shell boiler comprising a grate box as claimed in Claim 1 or Claim 2 and having secondary air pipes for introducing high velocity air into the furnace zone without the secondary air contacting the fuel, wherein the secondary air pipes are arranged to pass through the grate assembly.

4. A grate assembly for a shell boiler constructed substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.