GB2227304A - Thermal regenerators - Google Patents

Abstract

A thermal regenerator containing horizontally supported bed material, for use for example in reversing regenerative burner systems, comprises a covered container through which hot gases pass between inlet/outlet ports 13, 14 along a restricted flow path defined by gas-impermeable walls 4, 5 and a baffle 17. The gases enter the bed 3 via surface region 11, flow through aperture 18 below the baffle 17 and exit from the bed via surface region 12. The restricted flow path encourages more gas/bed material contact. The container construction avoids the necessity of a gas permeable wall at the 'hot' end of the regenerator. <IMAGE>

Description

THERMAL REGENERATORS The present invention relates to thermal regenerators and, more particularly, to thermal regenerators for use in reversing regenerative burner systems.

In a reversing regenerative burner system there may be two burners (I and II) to which fuel gas and combustion air are supplied alternately so that the burners fire alternately.

As burner I is firing, burner II acts as a flue through which pass the hot combustion product gases. Each burner has associated with it a respective thermal or heat regenerator containing, for example, a packed bed of heat storage material such as refractory (eg. ceramic) particles which is heated up by the hot combustion product gases when the burner is acting in the flue mode. When the modes of the burners are reversed, burner I ceases firing and becomes the flue, whilst combustion air now passes through the thermal regenerator associated with burner II where the air is heated before entering burner II and mixing with fuel gas. Burner I is now acting in the flue mode.

It is known that the packed beds in thermal regenerators may be supported vertically within a container. In such a case the container may comprise impermeable insulated side walls with the packed bed resting under gravity on top of a gas permeable flow distributor plate at the lower relatively cold end of the regenerator. The upper relatively hot end of the packed bed does not require any mechanical restraint. Since the distributor plate operates under relatively cool conditions, for example say under 5000C, it can be fabricated or machined in metal.

In situations where, for example, space is limited or flow configuration associated with a system dictates, it may be more convenient to support the bed of heat storage material generally horizontally.

One way in which this may be achieved is to provide a permeable distributor plate at each end of the bed in order to support the heat storage material "horizontally".

In such a case the plate at the intended 'hot' end of the bed may have to be constructed out of materials capable of withstanding high temperatures for example in the region of 10000C or more. Some ceramics can withstand such temperatures but are difficult and costly to fabricate, and some permeable ceramic structures may also fail mechanically due to the combined thermal shock caused by rapid temperature changes in the regenerators and mechanical stresses imposed by the supported bed material.

Metals which are to withstand these temperatures are also costly and prone to oxidation.

A further problem which has been encountered with 'horizontally' supported beds is that the bed material may 'slump'. This results in a low resistance gas flow path being formed across the top part of the bed and this can severely reduce the gas/solid contact and regenerator effectiveness.

An object of the invention is to overcome or alleviate one or more of the above-mentioned problems.

According to the invention a thermal regenerator comprises a covered container containing a bed of heat storage material supported by side walls, two spaced apart openings which form inlet/outlet ports, at least one of which inlet/outlet ports communicates with the interior of the bed substantially only via an upper surface region of the bed, and at least one first baffle means of substantially gas-impermeable material between the two spaced apart openings which at least in part defines a first aperture beneath the surface of the bed to permit gas flow past the first baffle means.

Conveniently, the two spaced apart openings communicate with the interior of the bed substantially only via two respective upper surface regions of the bed.

The first aperture maybe in the lower half of the bed, in which case the aperture may be defined at least in part by the first baffle means and the bottom of the container.

In such an embodiment, the flow of gas through the regenerator may thereby be caused to follow a generally Ushaped path.

In another embodiment, the regenerator may comprise two or more first baffle means and further comprise a second baffle means between the or each adjacent pair of first baffle means, wherein the or each second baffle means is of substantially gas-impermeable material which at least in part defines a second aperture at a different level to the first apertures in the adjacent pair of first baffle means to permit flow of gas past the second baffle means.

Thus, gas flowing through the regenerator follows a generally undulating or tortuous path.

Preferably, the or each aperture in the second baffle means is above the upper surface of the bed, in which case the or each such aperture may be defined at least in part by the associated second baffle means and the top of the container.

The side walls supporting the bed material may be. spaced from opposing walls of the container and openings may be provided in or above the side walls to allow communication between the inlet/outlet ports and the respective upper surface regions of the bed.

The bed may comprise regions or layers of different packing material. Preferably, the packing material in the layers or regions in the vicinity of one or more apertures in the first baffle means, and/or second baffle means when present, beneath the surface of the bed is of higher voidage (space/solid ratio) or lower specific surface area (solid surface area/volume) than in the remaining layers or regions with a view to reducing pressure drop across the bed.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which : Figure 1 is a schematic side view in section of one embodiment of thermal regenerator according to the invention, Figure 2 is a schematic side view in section of another embodiment of the invention, and Figure 3 is a schematic side view in section of an embodiment similar to that in Figure 1, wherein the bed comprises layers of different packing material.

With reference to the Figure 1, a thermal regenerator comprises a container 1 with a removable cover or lid 2 and containing a bed 3 of heat storage material which is supported laterally at opposite sides by substantially gas-impermeable side walls or plates 4,5 made of, for example, solid metallic or ceramic material.

The side walls 4,5, which are spaced from the respective end walls 6,7 of the container, extend upwardly from the base 8 of the container and terminate short of the top cover 2 to define therewith openings 9,10 above the surface regions 11,12 of the bed material. Gas inlet/outlet ports 13,14 are provided in the end walls 6,7 of the container and as can be seen from the drawing there is communication or a flow path between the inlet/outlet ports and the interior of the bed via the spaces 15,16 between the side walls 4,5 and respective end walls 6,7, the openings 9,10 above the side walls and the surface regions 11,12 of the bed.

The surface regions 11,12 are separated from each other by a first baffle means 17 which extends downwards from the cover 2 into the bed 3. The first baffle means is substantially gas-impermeable apart from the aperture 18 provided beneath the upper surface regions 11,12 in the lower half of the bed between the baffle means 17 and the bottom 8 of the container. The aperture 18 permits gas flow past the first baffle means 17 which may be in the form of a solid metal or ceramic plate.

In use, for example in a reversing regenerative burner system, hot combustion product gases emanating from a gasfired burner (not shown) can flow for example via port 13 into, through and out of the regenerator generally following the flow path indicated by the arrows in Figure 1. As can be seen the hot gases are constrained to follow generally a single undulation or U-shaped path through the bed. The aperture 18 adjacent to the bottom of the bed 3 provides a restricted flow path past the baffle means 17.

The gases are therefore forced to flow substantially to the bottom of the bed, thereby encouraging increased gas/solids (bed material) contact and avoiding or lessening bed 'slumping' problems as mentioned above.

Since the bed support at the 'hot' end of the bed is a solid plate fabrication of more costly support designs which are permeable to the hot gases is avoided.

When the regenerator operates to heat combustion air prior to its introduction into a burner (not shown) the air can enter via port 14, flow through and leave the regenerator in a direction opposite to that shown by the arrowed flow path in Figure 1.

Figures 2 and 3 show features which are present in Figure 1 and these features bear references corresponding to those in Figure 1 and will not be described further.

The embodiment in Figure 2 comprises a plurality of first baffle means 17 in the form of solid metal or ceramic baffle plates. Between each adjacent pair of first baffle means is a second baffle means 19 which is similar in construction to the side walls 4 or 5.

Thus, each second baffle means 19 is in the form of a solid metallic or ceramic plate which extends upwardly from the base 8 of the container and terminates short of the top cover to define therewith apertures or openings 20 above the surface of the bed material. In this embodiment, hot combustion product gases flow into the bed via port 13, through the bed material 3 following the arrowed flow path and between the adjacent first and second baffle means and past such baffle means via apertures 18 or 20. As can be seen from figure 2, the gases follow a generally undulating or serpentine path.

In the opposite mode, air enters the bed via port 14, flows through and leaves the regenerator in a direction opposite to that shown by the arrowed flow path in figure 2.

The plates 17,19 may but not necessarily be, equally spaced from each other, and the number and spacing of the plates can be so chosen as to maximise thermal performance or efficiency and to control pressure drop across the bed.

For example, with reference to the embodiment in figure 2, it is preferred that the left-hand end of the chamber, as viewed, receives in-coming hot combustion product gases since it is this end which has the larger distance between the side wall and nearest baffle means 17 and thus the larger flow path where the pressure drops would otherwise be greatest.

The kind of packing material between adjacent plates may be varied to alter the overall performance of the regenerator, as required.

The embodiment in Figure 3 is the same as that in Figure 1 except that the bed 3 is comprised of different layers 21,22,23,24,25 of heat storage material so that pressure drop across the bed may vary. For example, in the layer 23 where the gas flow changes directions in the vicinity of the apertures in the plates, bed packing of higher voidage (space/solid ratio) may be used to reduce velocities in this area.

In any of the three embodiments described above the lid or cover 2 of the container 1 may be removed without the or each plate 17 also being removed with it. Removal of the lid or cover alone enables inspection, cleaning and repair to be carried out without other sections of the bed being disturbed. For example, in the assembled regenerator, the or each plate 17 may be integral with the container, and the top portion of the or each plate may be located in a slot 2a extending across the container in the cover 2.

This arrangement has been shown in Figure 3 but is equally applicable to other embodiments such as those described with reference to figures 1 or 2. Ceramic fibre or seal which is resistant to high temperatures may be used to prevent unwanted gaseous flow between the top portion of the or each first baffle means 17 and the cover 2, or elsewhere, if required.

In a modification (not shown), the side wall 5 supporting the bed material i.e. the side wall at the intended "cold" end of the regenerator may be replaced by a gas permeable flow distributor plate, such as a perforated plate, which may extend over the whole of the internal cross-sectional area of the container in that region.

Whilst particular embodiments of the invention have been described above, it will be understood that various modifications may be made without departing from the scope of the invention. For example, the apertures and openings need not be in part defined or bounded by the plates 17 or 19, or side walls 4 or 5 and the top 2 or bottom 8 of the container but may be wholly defined or bounded by the plates or side walls. Furthermore, opposite ends of the plates 17 may, alternatively, be located in vertical slots or recesses in the opposing walls of the container, with the recesses extending downwardly from the upper edges of the walls and terminating short of the base 8 of the container so that an aperture is defined between the base and the bottom edge of the plate 17.

Claims (11)

1. A thermal regenerator comprising a covered container containing a bed of heat storage material supported by side walls, two spaced apart openings which form inlet/outlet ports, at least one of which inlet/outlet ports communicates with the interior of the bed substantially only via an upper surface region of the bed, and at least one first baffle means of substantially gasimpermeable material between the two spaced apart openings which at least in part defines a first aperture beneath the surface of the bed to permit gas flow past the first baffle means.

2. A regenerator as claimed in claim 1, wherein the two spaced apart openings communicate with the interior of the bed substantially only via two respective upper surface regions of the bed.

3. A regenerator as claimed in claim 1 or 2, wherein the at least one first aperture is in the lower half of the bed.

4. A regenerator as claimed in claim 3, wherein the first aperture is defined at least in part by the first baffle means and the bottom of the container.

5. A regenerator as claimed in any of the preceding claims, comprising two or more first baffle means and further comprising, between the or each adjacent pair of first baffle means, a second baffle means of substantially gas-impermeable material which at least in part defines a second aperture at a different level to the first apertures in the adjacent pair of first baffle means to permit flow of gas past the second baffle means.

6. A regenerator as claimed in claim 5, wherein the or each second aperture is above the upper surface of the bed.

7. A regenerator as claimed in claim 6, wherein the or each second aperture is defined at least in part by the associated second barrier means and the top of the container.

8. A regenerator as claimed in any of the preceding claims, wherein the side walls supporting the bed material are spaced from opposing walls of the container and openings are provided in or above the side walls to allow communication between the inlet/outlet ports and the respective upper surface regions of the bed.

9. A regenerator as claimed in any of the preceding claims, wherein the bed comprises regions or layers of different packing material.

10. A regenerator as claimed in claim 9, wherein packing material in the layers or regions in the vicinity of one or more apertures in the first and/or second baffle means beneath the surface of the bed material is of higher voidage than in the remaining regions or layers.

11. A thermal regenerator substantially as hereinbefore described with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawings.