TECHNICAL FIELD

The present disclosure relates to a system for heating a head of a Stirling engine.

BACKGROUND

A Stirling engine is a heat engine that is configured to operate by cyclic compression and expansion of a working fluid at different temperatures, so as to convert heat energy to mechanical work as a result of heat supply from external sources. Stirling engines may be supplied with heat from various sources.

For example, there are known systems wherein the Stirling engine is supplied with heat generated by a biomass burner.

A European patent application EP2589870 describes a power system for generating electric energy from biomass. The system comprises a Stirling engine and a gasifier for heating a working fluid of the Stirling engine. However, that document does not describe any specific details related heating the head of the engine.

A European patent application EP3153774 describes a cogeneration system based on a Stirling engine. The system comprises a generator supplied with gas. It relates to a problem of purification of hot gases which are used for heating the Stirling engine, but it does not describe any specific details related to how the head of the Stirling engine is supplied with heat.

A European patent application EP3008319 describes a Stirling engine supplied with heat from biomass combustion. The engine comprises a head which is surrounded by a block made of copper or aluminum. The block has its main part coated with a stainless steel layer or with an Inconel alloy.

The solutions described above have a problem related to effective absorption of power from a hot source, typically having a temperature ranging from 500 to 800°C, in contrast to a cold source having a temperature closer to the ambient temperature. The power of the hot source should be absorbed at a level a few times higher than the mechanical power of the engine output, because of a small surface of the engine head through which the heat energy can be absorbed. For example, it would be desirable to absorb heat power at the level of 200 kW/m ² . Such efficient power absorption cannot be simply reached by exposing the engine head to a stream of exhaust gas output from the biomass burner. Due to that, conventional known systems are not able to obtain high power form Stilling engines that are supplied with heat from biomass burners.

There is a need to provide an alternative construction of a system for heating a head of a Stirling engine, that would enable to efficiently absorb energy from a stream of exhaust gas leaving a burner, such as a biomass burner.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a system for heating a head of a Stirling engine with a heat of a gas from a burner, preferably a biomass burner. The system comprises a housing comprising: a lateral inlet stub tube for introducing the gas into the housing; a lateral outlet stub tube for removing the gas from the housing. The housing is surrounded by heat insulators. The housing with the heat insulators define a chamber that surrounds the head, wherein the chamber defines a space for heat exchange between the head and the gas flowing from the lateral inlet stub tube to the lateral outlet stub tube.

The housing may have a form of a pipe of a circular cross-section, an oval cross- section or a polygonal cross-section.

The lateral inlet stub tube and/or the lateral outlet stub tube may have a form of a pipe with a circular cross-section, a polygonal cross-section or an oval cross-section.

The heat insulators may be partially coated with an infrared-shielding layer or completely coated with the infrared-shielding layer.

The housing may further comprise a partition for restricting the space for movement of the gas, wherein the partition is arranged between the lateral inlet stub tube and the lateral outlet stub tube, inside the housing and above the upper surface of the head of the Stirling engine.

These and other features, aspects and advantages of the invention will become better understood with reference to the following drawings, descriptions and claims.

BRIEF DESCRIPTION OF DRAWINGS

The present invention is shown by means of example embodiments in a drawing in which:

Fig. 1 shows, in a longitudinal section, an embodiment of a system for heating a head of a Stirling engine, the head having a conical end; Fig. 2 shows, in a longitudinal section, an embodiment of a system for heating a head of a Striling engine, the head having a flat end;

Fig. 3 shows, in a cross-section, an embodiment of a heating system with a circular housing;

Fig. 4 shows, in a cross-section, an embodiment of a heating system with a oval housing;

Fig. 5 shows, in a cross-section, an embodiment of a heating system with a polygonal housing;

Fig. 6 shows, in a longitudinal section, an embodiment of a system for heating a head of a Striling engine, the head having a hemispherical end;

Fig. 7 shows, in a longitudinal section, an embodiment of a system for heating a head of a Striling engine, the head having a flat end and a main part conically narrowing in diameter;

Fig. 8 shows, in a cross-sectional view, a lateral inlet/outlet stub tube of a circular shape;

Fig. 9 shows, in a cross-sectional view, a lateral inlet/outlet stub tube of a polygonal shape;

Fig. 10 shows, in a cross-sectional view, a lateral inlet/outlet stub tube of an oval shape.

A system for heating a head of Stirling engine is shown in various embodiments in Figs. 1 - 10, which differ by constructional details, as described below, whereas the common features of the embodiments of the system are as follows.

The system for heating the head 1 of Stirling engine comprises a chamber 2 with a housing 11 , preferably in a form of pipe mounted coaxially with respect to the head 1. The housing 11 comprises a lateral inlet stub tube 12, 12’, 12” and a lateral outlet stub tube 13, 13’, 13”. Hot gas from a burner, such as a biomass burner, enter a chamber 2 through the lateral inlet stub tube 12, 12’, 12”. The chamber 2 is formed between a surface of the head 1 and a surface of the housing 12, 12', 12". In the chamber 2, the gas flow over the head surface and therefore transfer heat energy to the head 1 , causing a rise in temperature of the head 1. Subsequently, the gas exits the chamber 2 through the lateral outlet stub tube 13, 13’, 13”.

The housing 11 is surrounded by heat insulators 21 , 22, 23. A pipe insulator 21 , having a form of a pipe, cover an outer surface of the housing 11. Plate insulators 22, 23 provide a tight covering of the chamber 2 from the top and from the bottom. The heat insulators 21 , 22, 23 reduce loss of heat from the gas that is released to the surroundings of the heating system.

The housing 11 may be made of steel, preferably heat resistant steel, stainless steel or ceramic materials which are resistant to high temperature and components of the gas introduced into the chamber 2, so as to provide a good resistance of the housing to the harmful agents contained in the outlet gas generated by the biomass burner.

The heat insulators 21 , 22, 23 may be made of insulating materials resistant to high temperatures, such as ceramic fibers, mineral fibers, glass fibers, aerogels, spherulite, and suitably selected binders and fillers as well as other materials exhibiting low heat conductivity so as to provide good thermal insulation of the housing 11. Furthermore, the heat insulators 21 , 22, 23 may also include vacuum, air or another suitable gas or liquid surrounding the lateral inlet stub tube 12, 12’, 12”, the lateral outlet stub tube 13, 13’, 13” and the chamber 2.

Furthermore, the heat insulators 21 , 22, 23 may be at least partially coated with an infrared-shielding layer 21 A, 22A, 23A, which may be disposed inside the chamber 2 so as to separate the insulators 21 , 22, 23 from the interior of the chamber 2, or the insulators 21 , 22, 23 may be covered in whole with the infrared-shielding layer 21 A, 22A, 23A. The infrared-shielding layer 21 A, 22A, 23A may be made of a metal sheet, aluminum foil or other materials exhibiting a high coefficient of reflection of infrared radiation. In that case, the head 1 is heated by means of both: heat transfer from the inlet gas to the head 1 , as well as cumulated heat radiation that is emitted from a surface of the infrared-shielding layer 21 A, 22A, 23A (resulting from a geometry of that surface as well as the arrangement of that surface with respect to the head 1 of the Stirling engine).

In one embodiment, as shown in Figs. 1 and 3, the head 1 of the Stirling engine has a conical end 1A and a cylindrical main part 1 B. In other embodiment, as shown in Fig. 6, the head 1 of the Stirling engine has a hemispherical end 1A' and a cylindrical main part 1 B with protrusions 1 C (a gas head). For the heads 1 of such type, it is desirable to heat the cylindrical main part 1 B of the head 1. Therefore, the system further comprises a partition 14 (which may be made of the same material as the material of the housing 11 , whereas the partition 14 is mounted inside the housing 11 ). The partition 14 restricts the transfer of the gas above the conical end 1A (Fig. 1 ) or the hemispherical end 1A' (Fig. 6) of the head 1. Moreover, the partition 14 directs the gas to flow around the end 1A, 1A' of the head 1 which additionally generates turbulences within the folwing gas, increasing the effect of heat transfer to the head 1 of the Stirling engine.

In another embodiment, as shown in Figs. 2 and 5, the head T of the Stirling engine has a cylindrical main part 1 B and a flat end 1 D. In such construction the plate insulator 22 may be located directly above the head 1’. In other embodiment, as shown in Fig. 7, the head T of the Stirling engine has a conical main part 1 E that narrows in a direction away from a flat end 1 D.

The housing may have a circular cross-section 11 - as shown in Fig 3, an oval cross-section 1 T - as shown in Fig. 4 or a polygonal cross-section 11”, as shown in Fig.5.

Moreover, the lateral inlet stub tube 12, 12’, 12” and the outlet stub tube 13, 13’, 13” can have various cross-sectional shapes. For example, they may have a circular perimeter (as shown in Fig. 8), a polygonal perimeter (as shown in Fig. 9), which may be for example a rectangular perimeter, or an oval perimeter (as shown in Fig. 10).

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. Therefore, the claimed invention as recited in the claims that follow is not limited to the embodiments described herein.