Background of the invention

[0001] The invention relates to a regenerative heat exchanger comprising a frame, a rotor pivotally mounted to the frame, a heat transfer honeycomb system arranged in the rotor, means for conveying a warm gas flow through the heat transfer honeycomb system, and means for conveying a cold gas flow through the heat transfer honeycomb system, whereby heat brought by the warm gas flow to the heat transfer honeycomb system is transferred in the heat transfer honeycomb system to the cold gas flow, heating it, whereby the means for conveying both the warm and the cold gas flows are arranged to convey said flows radially through the heat transfer honeycomb system.

[0002] In a typical rotating heat exchanger, the rotor is a honeycomb-like disc wherein through-flow channels of a heat transfer honeycomb system formed thereby are parallel with the rotation shaft of the rotor. Gas or air flows travel in a direction opposite to that of the honeycomb system, i.e. in an axial direction of the rotor. One of said flows may pass above the rotor while the other may pass below the rotor, in which case the flows are separated from one another e.g. by horizontal walls provided at the level of the shaft of the rotor.

[0003] The problem with the prior art heat exchanger is its operation under high temperatures and high operating pressures. In such a case, thermal expansion takes place mainly in the rotating rotor whose diameter increases as a consequence of the thermal expansion. This, in turn, makes the rotor challenging or even impossible to seal to the frame surrounding it.

Summary of the invention

[0004] An object of the invention is thus to provide a novel rotating heat exchanger for enabling the above-mentioned problems to be solved. This object is achieved by the heat exchanger according to the invention, which is characterized in that the frame comprises a casing part defining an inner space and a rear plate and a front plate closing the casing part axially, a shaft of the rotor being pivotally mounted to the rear and the front plate, whereby the means for conveying a warm gas flow through the heat transfer honeycomb system comprise a warm gas flow inlet channel provided in the front plate and an outlet channel provided on one side of the casing part, and the means for conveying a cold gas flow through the heat transfer honeycomb system com- prise a cold gas flow inlet channel provided in the front plate and an outlet channel provided on another side of the casing part, opposite the first side.

[0005] Further, it is appropriate that the heat transfer honeycomb system is formed by a plurality of heat transfer honeycombs arranged radially on an outer circumferential section of the rotor and inserted in pipes provided inside the rotor, whereby an inner circumferential section of the rotor is divided radially into flow division compartments which in number equal the number of heat transfer honeycombs and which lead to respective heat transfer honeycombs.

[0006] In the present invention, owing to the frame structure of the heat exchanger, possible radial thermal expansion of the rotor does not cause sealing problems. Further, the rotor and the end plates are easy to seal e.g. by means of labyrinth seals dimensioned according to the largest and smallest possible thermal expansion. In conventional rotating heat exchangers, no sealing is conventionally used at all but the rotor is only dimensioned to travel close enough to the frame structure surrounding its circumference.

List of figures

[0007] The invention is now described in closer detail by means of one preferred embodiment and with reference to the accompanying drawings, in which

Figure 1 generally shows a gas turbine system;

Figure 2 is an explosive view of a heat exchanger according to the invention;

Figure 3 is a side view of the heat exchanger according to Figure 1 , assembled;

Figure 4 is a sectional view taken from Figure 3 of the heat exchanger according to Figure 1 , assembled;

Figure 5 is a front view of the heat exchanger according to Figure 1 , assembled; and

Figure 6 is a rear view of the heat exchanger according to Figure 1 , assembled.

Detailed description of the invention

[0008] Figure 1 schematically shows a gas turbine system for producing electric energy, the regenerative heat exchanger according to the invention being particularly suitable for the system. As its main components, this system comprises a turbine 1 , a compressor 2, a heat exchanger 3, a combustion chamber 4, a generator 5, and a frequency converter 6.

[0009] A runner wheel of the turbine 1 and the compressor 2 are connected to the same shaft 7, and the generator 5 is connected by an intermediate shaft 8 to an entity formed by the turbine 1 and the compressor 2. The compressor 2 compresses inlet air it has taken and blows the compressed air to the heat exchanger 3 to be pre-heated. The pre-heated air is conveyed to the combustion chamber 4, whereto fuel is also fed. A mixture of air and fuel burns in a flame tube located inside the combustion chamber 4 and advances therefrom as a flue gas flowing at a high speed, rotating the runner wheel of the turbine 1. The runner wheel of the turbine 1 , in turn, rotates the compressor 2 and the generator 5. After the turbine 1 , the pressure of the flue gas drops close to air pressure, but it still contains a lot of heat energy which is conveyed back to the heat exchanger 3 in order to carry out the aforementioned preheating.

[0010] Referring next to Figures 2 to 6, as its basic elements the regenerative heat exchanger 3 according to the invention comprises a frame 9, a rotor 10 pivotally mounted to the frame 9, a heat transfer honeycomb system 11 arranged in the rotor 10, means 16, 17 for conveying a warm gas flow through the heat transfer honeycomb system 11 , means 18, 19 for conveying a cold gas flow (air flow) through the heat transfer honeycomb system 11 , whereby heat brought by the warm gas flow to the heat transfer honeycomb system 11 is transferred in the heat transfer honeycomb system 11 to the cold air flow, heating it, as shown in Figure 1.

[0011] The essential point in this novel heat exchanger 3 is that both the warm and the cold gas flows are conveyed radially through the heat transfer honeycomb system 11 , and a structure for implementing this will be described next.

[0012] The concept gas or gas flow is to be understood to also contain air or air flow. In this example, the cold gas flow is an air flow while the hot gas flow is a gas flow containing flue gases.

[0013] In order to convey the gas flows, the frame 9 comprises a casing part 12 defining an inner space, and a rear plate 13 and a front plate 14 axially closing the casing part 12, a shaft 15 of the rotor 10 being pivotally mounted to the rear and the front plate 13, 14. In such a case, the means for conveying a warm gas flow through the heat transfer honeycomb system comprise a warm gas flow inlet channel 16 provided in the front plate 14 and an outlet channel 17 provided on one side of the casing part 12, and the means for conveying a cold gas flow (air flow) through the heat transfer honeycomb system 11 comprise a cold gas flow inlet channel 18 provided in the front plate 14 and an outlet channel 19 provided on another side of the casing part 12, opposite the first side.

[0014] The heat transfer honeycomb system 11 is formed by a plurality of heat transfer honeycombs 20 arranged radially on an outer circumferential section of the rotor 10 and inserted in pipes 21 provided inside the rotor 10. Similarly, an inner circumferential section of the rotor 10 is divided radially into flow division compartments 22 which in number equal the number of heat transfer honeycombs 20 and which lead to respective heat transfer honeycombs 20 and which at the same time are in connection with the inlet channels 16 and 18 provided on opposite sides of the shaft of the rotor 10.

[0015] The heat transfer honeycombs 20 are metal honeycombs which may be coated with a catalytic material and which thus at the same time serve as flue gas purifiers. They are also highly resistant to high temperatures and provide a large heat transfer surface area.

[0016] The hot and cold gas flow outlet channels 17, 19 are connected to collection chambers 23, 24 defined from above by the casing part 12 of the frame 9, the rear and front plates 13, 14 and, on the other hand, by an outer circumference 25 of the rotor 10, whereto the heat transfer honeycombs 20 open up. The collection chambers 23, 24 extend on opposite sides of the casing part 12 to seals 26, 27 which separate them from one another and which divide the chambers 23, 24 to extend to circumferential areas of equal magnitude and which at the same time become sealed against the outer circumference 25 of the rotor 10. The cross section of the collection chambers 23, 24 changes in a direction of their circumference. The purpose of this structure is to even out changes in mass flow when the rotor 10 rotates and gas flows through the heat transfer honeycombs 20.

[0017] The seals 26, 27, which are preferably made of graphite, extend in a direction of the circumference of the rotor 10 substantially over a distance having the length of the diameter of one heat transfer honeycomb 20, and the seals 26, 27 are by means of springs 28 or pressure forced against the circumference 25 of the rotor 10. The springs 28 are supported against an inner surface of a cover 3 , 32 closing a given seal space 29, 30. [0018] An electric motor and a gear system (not shown) are mounted to the rear plate 13 in order to rotate the rotor 10.

[0019] The operation principle of the above-described heat exchanger is as follows:

Warm gas is conveyed to the inlet channel 16 which is provided in the surface of the front plate 1 and which at the same time serves as a channel for guiding and turning the flow, and from this channel the gas passes via the flow division compartments 22 through the heat transfer honeycombs 20, simultaneously heating them. From the heat transfer honeycombs 20, the cooled gas is conveyed to the collection chamber 23 and is discharged therefrom to the outlet channel 17. The rotor 10 constantly rotates at a low speed and, similarly, cold gas (air) is conveyed to the inlet channel 18 provided in the surface of the front plate 14 and therefrom via the flow division compartments 22 through the heated heat transfer honeycombs 20, whereby heat energy contained in the heat transfer honeycombs 20 is absorbed into the cold gas (air). From the heat transfer honeycombs 20, the heated gas (air) is conveyed to the collection chamber 24 and is discharged therefrom to the outlet channel 19. The gas (air) thus pre-heated may be led to the combustion chamber 4 described in the beginning, whereas the cooled gas (flue gas) is removed from the system.

[0020] The above description of the invention is only intended to illustrate the basic idea according to the invention. A person skilled in the art may thus vary its details within the scope of the accompanying claims.