The present invention relates to a heating arrangement for heating a fluid. In particular, the invention relates to a heating arrangement which can be used with a Stirling engine in a domestic combined heat and power (DCHP) system.
The system currently contemplated by the applicant has a gas fired linear-free piston Stirling engine which generates electrical power and heat. Some of the heat rejected by the Stirling engine is recovered and is used to provide some of the domestic heat demand. However, the amount of heat produced by the Stirling engine is not sufficient to meet the peak domestic heat load so that a supplementary burner is also required.
In the DCHP system, space considerations are paramount. The present invention therefore aims to provide a design of heat exchanger which is able to recover heat from the exhaust gas of the Stirling engine, and also from a supplementary burner which is compact.
According to the present invention there is provided a heating arrangement for heating a fluid, the arrangement comprising an elongate housing having a main axis, an inner chamber for a first fluid surrounding the axis, a plurality of axially extending fins projecting into the inner chamber; an exhaust gas inlet at one end of the inner chamber; a supplementary burner at the opposite end of the chamber arranged to fire radially outwardly onto the fins; and an outer chamber for a second fluid surrounding the inner chamber.
Such an arrangement can be made compact, particularly in view of the arrangement of the first chamber with the exhaust gas inlet at one end and burner at the opposite end. The fins which project into the chamber assist in the absorption of heat from the exhaust gas and the burner and the outer chamber ensures that this absorbed heat is transferred efficiently to the second fluid with little wastage.
In the case of a DCHP system based on the Stirling engine, the exhaust gas inlet is arranged to receive exhaust gas from the Stirling engine, and the second fluid is water which supplies the domestic heating system.
The efficiency of the heat recovery can be increased significantly if the exhaust gas and combustion gas from the supplementary burner are cooled to a temperature below the dew point of the gas. Under these circumstances, the water vapour from the combustion processes will condense and give up a significant amount of latent heat. Therefore, the arrangement of the present invention is preferably provided with a condensate outlet for condensate from the exhaust gas and combustion gas from the burner.
According to another preferred example, the arrangement further comprises a second chamber provided alongside and substantially parallel to the inner chamber, the inner and second chambers being linked at the opposite end so that the flow direction through the second chamber is opposite to the flow direction through the inner chamber, the second chamber having a second plurality of axially extending fins projecting into the second chamber, and the outer chamber also surrounding the second chamber.
Such an arrangement allows the combustion gases to initially pass along the inner chamber where they give up relatively high grade heat to the second fluid, they then pass in the opposite direction through the second chamber where they give up lower grade heat to the second fluid. In this case, the condensate outlet provided, is in the second chamber as it is in this chamber that the temperature of the gases will approach the dew point.
The construction of the heating arrangement of the present invention lends itself particularly to at least the part of the heating arrangement forming the inner chamber and fins being made of aluminium. In practice, the outer chamber can also be aluminium. This has advantages in terms of the manufacturing cost, size and weight. Preferably, at least the part of the arrangement forming the inner chamber and fins is extruded, again helping to reduce the manufacturing cost.
The present invention also extends to the combination of the heating arrangement defined above and a Stirling engine from which exhaust gas is emitted from an exhaust gas outlet, the exhaust gas outlet being connected to the exhaust gas inlet of the heating arrangement. With such a combination, the Stirling engine may be arranged with its hot end uppermost and the heating arrangement being positioned directly above the Stirling engine as this will provide a compact structure. If the heating arrangement with the second chamber is provided, this will be adjacent to the inner chamber, such that the exhaust gas from the Stirling engine will flow upwardly through the inner chamber and downwardly through the outer chamber.
Alternatively, the Stirling engine may be arranged with its hot end lowermost, in which case the heating arrangement is positioned directly below the Stirling engine. In this case, it may be sufficient only to use the heating arrangement with the inner chamber, as the condensate outlet can be positioned at the bottom of the inner chamber.
Examples of the heating arrangement in combination with a Stirling engine will now be described with reference to the accompanying drawings, in which:
The arrangement shown in
The Stirling engine 1 is supported on bracket 8 via a bellows seal 9 which also serves to provide a seal for the combustion gases from the burner 4 (this is described in detail in GB 0210929.6). The space between the burner 4 and bellows seal 9 is filled with an insulated material 10, an annular mass 11 suspended from the Stirling engine 1 by a plurality of springs 12 to absorb most of the vibrations which will occur in the Stirling engine 1.
Exhaust gases from the burner 4 flows around baffle 13 along exhaust gas path 14 to exhaust gas outlet 15.
As described so far, the features of the Stirling engine are generally known in the art. A detailed description will not be provided here. It should also be understood that alternative engine arrangements may be used with the context of the present invention as the only requirements for the heating arrangement is that it receives a supply of exhaust gas from some source.
The heating arrangement of
As well as receiving exhaust gas from the exhaust gas outlet 15, the heating arrangement has a second source of heat in the form of a supplementary burner 20 which is generally coaxial with the Stirling engine
The heating arrangement comprises a cylindrical inner chamber 21 into which a plurality of fins 22 extend from the outer wall. Each fin 22 is positioned in a generally radial plane, but is tapered in the radially inward direction as best shown in
As will be appreciated from
The supplementary burner 20 fires radially outwardly on to the upper part of the fins 22. The combined combustion gas stream flows upwardly towards the top of the inner chamber and passes out of the inner chamber at the top right hand corner of the inner chamber as shown in
The combustion stream flows downwardly through the second chamber and further heat is absorbed into the fins 25. At the base of the second chamber, the now cool combustion products enter a manifold 26 and are led along a suitable duct (not shown) to the flue of the appliance. In this manifold 26, any water that is condensed in the second chamber 24 will be collected and passes through a syphon trap 27 into a drain (not shown).
The inner chamber 21 and second chamber 24 are surrounded at their side and top surfaces by an outer chamber 30 through which water is arranged to pass from inlet 31 to outlet 32. This water receives the heat which has been absorbed by the first 21 and second 24 chambers and, in particular, the fins 22, 25. This water then supplies the domestic heat load. It should be noted that this water can also be part of the same circuit as the water supply 7 which cools the cooler 3 of the Stirling engine.
A second example is shown in
Also shown in
A third example is shown in
The heating arrangement 1 has the same general construction as
Essentially, the inner chamber 40 is arranged with an exhaust gas inlet 41 uppermost to receive exhaust gas from the Stirling engine exhaust gas outlet 15. The supplementary burner 42 is inserted through the bottom of the inner chamber 40. The inner chamber 40 has a plurality of radially inwardly extending fins 43 which have generally the same construction as the fins 22, 25 shown in
These fins 43 absorb heat from the exhaust gas from the Stirling engine and also from the burner which fires outwardly directly on to the fins. The combined combustion gases flow downwardly to a base manifold 44 before being led in a suitable duct (not shown) to the flue of the appliance. As with
Number | Date | Country | Kind |
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0311002.0 | May 2003 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB04/02061 | 5/12/2004 | WO | 1/23/2006 |