Thermal post-combustion unit

A thermal post-combustion unit with a combustion chamber having a combustion space to which exhaust air can be supplied, having a burner for heating the combustion space, whereby clean air is produced, having an inlet for exhaust air and having an outlet for clean air. A flow path connects the inlet to the combustion space. Exhaust air can be heated by a heat-exchanger system. The flow path comprises a first, second and third flow section, wherein the first flow section is connected to the inlet and the exhaust air flows from the third flow section to the combustion space, wherein the flow sections connect to one another at diversion ends so that the exhaust air flows through two successive flow sections with different flow directions. Heat-exchanger pipes extend at least inside the first and the second flow section or at least the first and the second flow section extend inside heat-exchanger pipes.

RELATED APPLICATIONS

This application claims the filing benefit of German Patent Application No. 10 2014 018 178.2, filed Dec. 9, 2014, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a thermal post-combustion unit havinga) a combustion chamber which in turn comprises:aa) a combustion space to which exhaust air can be supplied;ab) a burner by means of which the combustion space can be heated, whereby clean air is produced;ac) an inlet for exhaust air;ad) an outlet for clean air;b) a flow path which connects the inlet to the combustion space;c) a heat exchanger system, to which at least some of the generated and hot clean air can be supplied and by means of which exhaust air which flows through the flow path can be heated.

BACKGROUND OF THE INVENTION

Thermal post-combustion units of this type are commercially known and are used in particular in processes which produce exhaust air, which contains volatile organic components (abbreviated as VOC). This exhaust air is cleaned by thermal post-combustion, in which the exhaust air is heated in the combustion space and the impurities are oxidised.

With regard to the energy balance of the unit and the effectiveness of the combustion, it has been established here that the exhaust air should be pre-heated on its flow path to the combustion chamber.

SUMMARY OF THE INVENTION

An object of the invention is now to improve a unit of the type mentioned at the outset.

This object may be achieved in a unit of the type mentioned at the outset in thatd) the flow path comprises a first, second and third flow section, wherein the first flow section is connected to the inlet and the exhaust air flows from the third flow section further to the combustion space, wherein the flow sections are connected to one another at diversion ends in such a way that the exhaust air flows through two successive flow sections with different flow directions;whereine) heat-exchanger pipes extend at least inside the first and the second flow section orf) at least the first and the second flow section extend inside heat-exchanger pipes.

It is thus possible for the flow path to extend in a virtually serpentine fashion, thereby increasing the useful path lengths along which heat transfer to the exhaust air can take place without needing to increase the longitudinal extent of the unit for this. As a result of the flow sections and the heat-exchanger pipes always nesting inside one another, the heat transfer in the first and the second flow section takes place more efficiently.

It is favourable if one, two or all of the flow sections are formed by annular spaces which surround the combustion space radially.

There are then preferably at least two annular spaces, which are arranged radially adjacent and between which there is an intermediate wall. As a result, the annular spaces are as closely adjacent as possible in the radial direction, which complies with the desire for a low spatial requirement of the unit in the radial direction.

In an advantageous alternative design, at least the first and the second flow section are formed by flow channels which are arranged alternately next to one another, are separated by chamber walls in the longitudinal direction of the housing and surround the combustion space radially. Instead of being arranged next to one another in the radial direction, the flow sections here are therefore arranged adjacently in the circumferential direction.

The number and/or the diameter and/or the design of the heat-exchanger pipes in the first flow section and the heat-exchanger pipes in the second flow section are generally the same. To enable a certain degree of influence on the flow conditions and the heat transfer, it can be favourable if the number and/or the diameter and/or the design of the heat-exchanger pipes in the first flow section and the heat-exchanger pipes in the second flow section are different. It is possible to set different flow rates in the individual flow sections through the number and the cross-sections of the heat-exchanger pipes. This likewise influences the heat transfer between the media.

To heat the exhaust air even more effectively, in particular at the start of its flow path, the heat-exchanger system can advantageously comprise an annular heat-exchanger space, which has an inlet connection and an outlet connection, which radially surrounds the first flow section externally and which can be supplied with a heat-exchanger medium which is different from the clean air.

It is to be understood that the aspects and objects of the present invention described above may be combinable and that other advantages and aspects of the present invention will become apparent upon reading the following description of the drawings and detailed description of the invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated.

Reference is firstly made toFIGS. 1 and 2; these show a schematic view of a thermal post-combustion unit10with an external housing12which defines a longitudinal axis14and in which a combustion chamber16with a combustion space18is accommodated.

The combustion space18or the atmosphere located therein can be heated to a specific temperature with the aid of a burner20. To this end, the burner20is supplied with a fuel gas or a fluid fuel by way of a fuel line22.

The combustion space18is supplied with exhaust air, which is laden with contaminants and is to undergo cleaning, by way of a channel system24which is connected to an inlet26on the external housing12. The channel system24comprises a flow path28which connects the inlet26to the combustion space18. In the present exemplary embodiment, this flow path28comprises three flow sections30,32and34, through which the exhaust air flows with a different flow direction. The first flow section30extends from the inlet26to a first diversion end36, which connects the first flow section30to the second flow section32. The second flow section32extends from the first diversion end36to a second diversion end38which in turn connects the second flow section32to the third flow section34. The exhaust air then flows from the third flow section34further to the combustion space18. The third flow section34here can lead directly into the combustion space18or further sections of the flow path28can follow.

The flow sections30,32,34are connected to one another by way of the diversion ends36,38in such a way that the exhaust air flows through two successive flow sections30and32or32and34with different flow directions. The flow directions in two adjacent flow sections30,32or32,34are opposed in the present exemplary embodiments and are illustrated in each case by arrows.

The supplied exhaust air is heated in the combustion chamber18, whereby contaminants contained therein are burned and clean air is produced. The clean air can then flow out of the combustion chamber16through an outlet40whereof the flow cross-section can be adjusted by a flap which is not provided specifically with a reference numeral.

A heat-exchanger system42is present, to which at least some of the generated and hot clean air can be supplied as a heat-exchanger medium and through which at least exhaust air, which flows through the first and the second flow section30and32, can be heated.

To this end, heat-exchanger pipes44extend in the first flow section30for the exhaust air and heat-exchanger pipes46extend in the second flow section32for the exhaust air, which heat-exchanger pipes have clean air flowing through them and exhaust air, which flows through the respective flow sections30,32, flowing over them so that heat from the clean air is transferred to the exhaust air. InFIGS. 2 to 4, only one of the respective heat-exchanger pipes44,46is provided with a reference numeral in each case.

In this case, the walls of the heat-exchanger pipes44,46therefore form a heat-exchanger surface for exhaust air and the hot clean air flows over their radial interior surface in the axial direction. In a modification which is not shown specifically, the conditions can also be reversed and the first flow section30can extend inside a first heat-exchanger pipe and the second flow section32can extend inside a second heat-exchanger pipe. In this variant, the respective wall of the flow sections30,32forms a heat-exchanger surface for exhaust air and clean air flows over its radial exterior surface.

With reference to the flow directions of the exhaust air in the flow sections30,32and the clean air in the heat-exchanger pipes44,46, the heat-exchanger system42operates in accordance with the counter-flow principle so that clean air flows through the heat-exchanger pipes44,46in the opposite direction to the flow direction of the exhaust air in the respective flow section30,32. To this end, the heat-exchanger pipes44,46are connected to one another by a diversion channel48. The heat-exchanger pipes44,46can alternatively be connected to one another by curved pipe pieces.

The clean air is supplied to the heat-exchanger pipes44,46through a respective heat-exchanger inlet50located at the second diversion end38. The heat-exchanger pipes46lead into a respective heat-exchanger outlet52which is located at the height of the inlet26as seen in the longitudinal direction.

In the exemplary embodiment shown inFIGS. 1 and 2, the flow sections30,32,34are formed by annular spaces54,56and58which are adjacent in the radial direction and surround the combustion space18radially. The annular spaces54,56,58are closed at the end faces. The first annular space54is radially delimited on the outside by the housing1.

An intermediate wall60is present between the first annular space54and the second annular space56. A further intermediate wall62is present between the second annular space56and the third annular space58. The third annular space58is radially delimited on the inside by a section of a combustion-space wall64and leads into a supply space66which leads to the combustion space18.

Near the first diversion end36in the circumferential direction, the intermediate wall60has a number of through openings68which connect the first annular space54to the second annular space56. In corresponding manner, near the second diversion end38in the circumferential direction, the further intermediate wall62has a number of through openings70which connect the second annular space56to the third annular space58.

As shown inFIG. 2, the heat-exchanger pipes44extend through the first annular space54and are arranged in a regular distribution in the circumferential direction. The heat-exchanger pipes46extend through the second annular space56in corresponding manner.

When the exhaust air now flows through the three flow sections30,32and34on its path to the combustion chamber18, it is heated in stages since the freshly generated clean air with the highest temperature flows into the heat-exchanger pipes46in the second annular space56and cools on the path to the heat-exchanger pipe44in the first annular space54and through this heat-exchanger pipe, so that the clean air exits the heat-exchanger system42at the heat-exchanger outlets52with the lowest temperature.

The exhaust air flowing into the flow path32is therefore firstly heated by the coolest clean air in the heat-exchanger system42and absorbs the heat from continuously hotter clean air on the further flow path32so that the exhaust air arrives at the combustion chamber18with the highest temperature.

In the exemplary embodiment according toFIGS. 1 and 2, the heat-exchanger pipes44in the first annular space54and the heat-exchanger pipes46in the second annular space56are identical in terms of their diameter, their dimensions and their arrangement.

In a second exemplary embodiment shown inFIG. 2, there are fewer heat-exchanger pipes46in the second annular space56than there are heat-exchanger pipes44in the first annular space54. With this, the diameters of the heat-exchanger pipes46in the second annular space56are greater than the diameters of the heat-exchanger pipes44in the first annular space54.

However, this can be adapted in such a way that the flow and heat-transfer parameters in the two annular spaces54,56correspond to one another.

In general terms, the number and/or the diameter and/or the design of the heat-exchanger pipes44in the first flow section30and the heat-exchanger pipes46in the second flow section32can be different. Different designs relate to all structural properties of the heat-exchanger pipes, such as different wall thicknesses of the pipes, the materials used for pipes and the geometrical structure of the pipe walls and the like.

FIG. 4shows a third exemplary embodiment, in which the first and the second flow section30,32are constructed not as annular spaces but as flow channels72,74, which are arranged alternately next to one another in the circumferential direction, are separated by chamber walls76in the longitudinal direction of the housing12and surround the combustion space18radially. In this arrangement, the flow channels72define the first flow section30and the flow channels74define the second flow section32. A heat-exchanger pipe44extends in each flow channel72and a heat-exchanger pipe46extends in each flow channel74.

In the present exemplary embodiment, the flow channels72have a larger cross-section than the flow channels74. So that, in such a case, the flow and heat-transfer parameters remain unaltered from those with the same channel cross-sections, the heat-exchanger pipes44in the flow channels72have a greater cross-section than the heat-exchanger pipes46in the flow channels74.

FIG. 5shows a fourth exemplary embodiment of a thermal post-combustion unit10, which corresponds substantially to the post-combustion unit10according to the first exemplary embodiment according toFIGS. 1 and 2. Additionally, the heat-exchanger system42therein has a heat-exchanger annular space78, which has an inlet connection80and an outlet connection82, which radially surrounds the first flow section30, here in the form of the annular space54, externally and which can be supplied with a heat-exchanger medium which is different from the clean air.

It is thus possible for the outer jacket of the housing12to be cooled more effectively to reach lower surface temperatures in the insulated outer surface of the unit10. If the outlet connection82is structurally and fluidically connected to the exhaust-air inlet26, the heat-exchanger annular space78can function as a cooling jacket through which exhaust air flows. In this, as the exhaust air serves as a heat-exchanger medium which is different from the clean air.

It is to be understood that additional embodiments of the present invention described herein may be contemplated by one of ordinary skill in the art and that the scope of the present invention is not limited to the embodiments disclosed. While specific embodiments of the present invention have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims.