US2892616A - Rotary regenerative air preheater - Google Patents

Description

June 30, 1959 w. FIRGAU ROTARY REGENERATIVE AIR PREHEATEZR Filed Jui 12, 1956 United States Patent ROTARY REGENERATIV E AIR PREHEATER Werner Firgau, Heidelberg-Pfafiengrund, Germany, as-

signor to Svenska Rotor Maskiner Aktiebolag, Nacka, Sweden, a corporation of Sweden Application July 12, 1956, Serial No. 597,440

2 Claims. (CL257-6) This invention relates to a rotary regenerative air preheater with a rotor subdivided into chambers and a pipe line containing a fan for returning the leakage air and the entrapped air to the main air duct. In known types of air preheater of this kind the intake end of the pipe, with returns to the main air stream the leakage air and the air trapped in the chamber that is about to enter the flue gas duct, is located on the cold side of the preheater and it discharges into the flue gas duct on that edge of the cover plate where the sector chambers filled with flue gas move out of the flue gas duct into a neutral zone before re-entry into the air duct. The point of re-entry of this return pipe is on the hot side of the air preheater so that the by-pass'ed air re-enters in concurrent flow with the flue gas. The principal distinguishing feature of the present invention from known types of regenerative preheaters consists in that the reentry opening of the return pipe is located on the cold side of the air preheater. In other words both withdrawal and re-entry of the by-passed air is completed on the cold side.

This solution would at first sight appear to be ineffective because re-entry is eifected against the direction of flow of the flue gas stream and this would require a correspondingly increased power output of the fan incorporated in the return pipe. However, the present invention is based upon a proper appreciation of the fact that this slight increase in power expenditure becomes acceptable when it is borne in mind, that unlike what happens in the known form of construction, a reduction in the temperature of the storage mass by contact with the relatively cool returned air before the storage plates have been able to transfer their heat to the air that is to be heated, is thereby avoided. The improvement in thermal efliciency secured by the present invention more than offsets the slight increase in power required for the fan.

To illustrate the principle upon which the invention is based an exemplary form of construction is shown in the drawing with reference to which the basic structural details of the invention as well as the thermal economy of the novel arrangement will be more particularly discussed and explained.

The drawing represents this illustrative form of construction in the form of a development of the peripheral surface of the rotor and of the paths of the currents, in the plane of the paper.

The rotor 1 which is subdivided into sector chambers by partition walls 2 may be assumed to move from right to left, as indicated by the arrow. The neutral zones are covered by plates 3 and 3', 4 and 4', in the conventional manner. The channel in the centre is the flue G whereas the air duct L is shown at either extremity in the development of the rotor surface. The flue gases stream from below upwardly so that the air corrmpondingly moves from the top downwardly, as shown by the corresponding arrows. In the drawing the cold side K of 2,892,616 Patented June 30, 195.3

2 the airpreheater is shown at the top, whereas the hot side H is shown at the bottom.

The leakage airas well as the air trappedin the chamberthat is about to enter the. flue is returned through the return pipe 5 which includes a fan 6. The direc: tion of flow inthis pipe is also indicated by an arrow.

In the position of the rotor 1 shown in the drawing the sector 7 is just about to enter the flue G. The leakage air and the air trapped in sector 7 are therefore exhausted through the duct 5 which opens alongside the edge. of the cover plate 3, and thus such air is prevented from entering the flue G.

The exist opening of the duct 5 is opposite the rotor sector 8; This latter sector is about to leave the flue G and to pass through the neutral zone covered by the plates 4. and 4' into the air duct L. The flue gas con: tained in sector 8 is ejected and replaced by the by-passed air emergi-ngfrom pipe 5. Consequently sector 8 will be substantially filled with air instead of being'filled with flue gas. when it enters the air-duct.

With reference to the storage plates-inserted intothe sector chambers it was hitherto customary to arrange them more or less parallel with the periphery. However, it is also known that they can be disposed radially. Both possibilities are applicable to the present invention. It should be said, however, that a radial arrangement of the storage plates is to be preferred in forms of construction embodying the present invention. Radial plates provide a further subdivision of the space in addition to the division created by the partition walls 2 so that the development of currents parallel with the periphery inside the individual sector chambers is: thereby prevented. Moreover, the individual subsections of low height (in practice about 10 mm.) formed by the storage plates impose a direction upon the currents, which prevents any undesirable mixing of entrapped air and flue gas within the chambers that are to be exhausted and/or refilled. Consequently, the extraction of the air from chamber 7 and the removal and replacement of gas in chamber 8 tend to be cleaner than when the storage plates are mounted parallel with the rotor periphery. In forms of construction embodying the invention the use of radially or nearly radially disposed storage plates is therefore the best available disposition among the various known possible solutions.

Such a subdivision of the rotor sectors into partial spaces to be dealt with in succession for the purpose of air return may also be effected by providing a grating with radial or substantially radially disposed bars in front of the end face of the rotor 1, such an arrangement forming the subject matter of an earlier patent. It is, in any case, practical to provide such a cover grating irrespective as to how the storage plates are disposed because the unavoidable gap between the return pipe 5 and the storage mass is. reduced and the direction of flow is more satisfactorily controlled.

The advantages, gained from the point of view of thermal efliciency, which arise as a result of both the exhaust end and the pressure end of the return pipe 5 being on the cold side of the air preheater follow from the following considerations.

If, as has been customary, the return air which has a temperature in the region of 100 C. is injected on the hot side of the preheater where the temperature of the storage plates is about 400 C. the latter will be materially cooled by the injected air owing to the wide difference in the respective temperatures. The lower temperature of the storage plates on the hot side therefore materially lowers the temperature to which the hot air current can be heated. On the other hand, if the chambers are filled with air on the cold side where the temperature of the storage plates is only about 0., there is no cooling efiect, but on the contrary the plates are slightly heated. The temperature of the storage plates on the hot side is in practice hardly affected so that the theoretically maximum available exit temperature of the heated air current is still at the stated elevated temperature of 400 C.

The above considerations will show that the application of the principle underlying the invention permits a substantially better utilisation of the heat contained in the flue gases than is the case when the return pipe 5 dis charges on the hot side of the preheater.

What I claim is:

1. Rotary regenerative heat exchanger for gaseous media comprising a rotor having a plurality of sector-like compartments carrying regenerative heat exchange material, a stationary structure comprising a casing for said rotor and end plates having inlet and outlet openings separated by angularly related separating portions and providing for a primary and a secondary passage through said heat exchanger for flow in countercurrent direction of a primary gaseous medium to be heated and a secondary gaseous medium to be cooled of lower pressure than said primary medium, respectively, said rotor being located so that said compartments traverse said passages successively and move between said end plates to pass directly from one to the other of said passages, a channel interconnecting the radial edges of the separating portions defining said secondary passage on the side of the rotor where said primary medium enters and said secondary medium is discharged, said channel including a fan for returning to said primary passage leakage primary medium and primary medium trapped in the compartment that is about to enter the secondary passage, said channel being arranged to discharge into the compartment that is leaving the secondary passage and to discharge the returned primary medium on the side of the heat exchanger where said primary medium enters and said secondary medium is discharged.

2. Rotary regenerative heat exchanger as claimed in claim 1, in which said regenerative mass comprises plates mainly radially disposed in the rotor.

, References Cited in the file of this patent UNITED STATES PATENTS

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