US2488267A - Air heater system - Google Patents

Description

NW. 15 194% .5. CASSIE 2,488,267

AIR HEATER sysma 2 Shee'ts-Sheet 1 Filed Aug. 30, 1947 IN WIN TOR JEhn Cass ie WJM Nov. 15, 1949 J. CASSYIE 2,488,267

AIR HEATER SYSTEM Filed Aug. 30, 1947 2 Shams-Sheet 2 INVEN TOR \7'o hr; Cassie Patented Nov. 15, 1949 AIR HEATER SYSTEIVI John Cassie, Hyde Park, Masa, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 30, 1947, Serial No. 771,467 Claims. (01. 257-244) This invention relates to systems for the extraction of heat from the flue gases of steam plants, and the heating of air for combustion with the extracted heat.

In steam power plants it is usual to connect air heaters to the outlets of forced draft fans,

flue gases being passed over the exteriors of the v air heater tubes, and the fans blowing the air for combustion, through the. tubes. At low boiler loads, the upstream header sheet of such an air heater, is often below the dew point temperature of corrosive vapors in the flue gases, with the result that acid condenses on the sheet and corrode same. For preventing this, it has been the practice to recirculate heated air from the downstream end of the air heaters into the inlets of their associated fans, thereby recirculating previously heated air through the air heaters and decreasing the volume of cold air passed therethrough. Without inlet boxes on the fans, the outlet ends of the recirculation ducts have to be close to the inlets of the fans for preventing cold air instead of the recirculated, heated air, from entering the fans between the outlets of the recirculation ducts and the fan inlets. Such ducts interfer with the natural flow into the fan inlets when no recirculation is required, thus reducing the capacities and efficiencies of the fans. If an inlet box is used for each fan inlet, the capacity and efliciency of the fan may not be afiected but the cost of the fan is greatly increased since a longer fan shaft and larger bearings are required.

Another method of recirculating the heated air Without affecting the performance of a forced draft fan, is to provide a separate fan for recirculating the heated air. This, of course, adds to the cost of the system.

This invention overcomes the disadvantages described in the foregoing by providing the outlet end of a recirculation duct with an extension shaped to discharge the recirculated air efliciente ly into the fan inlet for which it is provided, the

I duct extension being retractable so that when recirculation of the heated air is not required, it can be withdrawn from the fan inlet so as not to interfere with the natural flow of air thereinto.

Objects of the invention are to reduce the cost of, and to improve the performance of, air heater systems for steam power plants.

The invention will now be described with reference to the drawings, of which:

Fig. l. is a side elevation, partially in section, of an air heating system embodying this invention, the outlet end of the recirculation ducts be- 2. ing extended for supplying the fan inlets;

Fig. 2 is a sectional view along the lines 22 of. Fig. 1;

Fig. 3 is a view similar to Fig. 1 except that the outlet ends of the recirculation ducts are retracted from the fan inlets, and

Fig. 4 is a sectional view along the lines 4-4 of Fig. 3.

The forced draft fan III has an air inlet II on each side of its wheel [2, and has its outlet l3 connected through the transformation duct I4 to the inlet of the air heater IS, the outlet of which supplies heated air through the duct IT to the combustion chamber of a boiler. For simplifying the drawing, the motor for driving the fan, and the journals for the fan shaft are not shown.

The air heater l5 contains the plurality of tubes l8 through the interiors of which the air from the fan is blown. The duct I9 supplies flue gas from the boiler over the exteriors of the tubes I8 for heating the air passing therethrough, this construction being conventional.

The recirculation ducts 20 have their inlets 2! connected into the interior of the heated air duct l1, and have their outlet ends 22 formed around the retractable ducts 23. The ducts 23 have the air outlets 24 having their upper and. lower sides formed in circular arcs thecenters of which are recirculated air into aligned with the centers of the air inlets H of the fan, and the radii of which are such that the outlets 24 extend partially around the fan inlets concentrically in alignment therewith when the ducts 23 are fully extended as illustrated by Figs. 1 and 2.

The ducts 20 contain the dampers 25 which are adapted to be adjusted by an attendant for regulating the volume of air recirculated through the fan, and contain the dampers 26 which contact the inturned upper ends of the ducts 23, and which are adapted to be closed by the ducts 23 when they are retracted as illustrated by Figs. 3 and 4.

The retractable ducts 23 are adapted to be retracted to the positions shown by Figs. 3 and 4 when no recirculation of air through the air heater is required, and are adapted to be extended to the positions shown by Figs. 1 and 2 when recirculation is required. This retraction and extension of the ducts 23 would in the embodiment illustrated, be accomplished manually by an attendant.

When the steam load of the associated boiler or boilers, is so low that condensation of acid from the flue gas might condense on the tubes would be extended to the positions shown by Figs. 1 and 2. At such times the inturned upper ends of the ducts 23 would move downwardly sufficient distances to permit the inner ends of the pivoted dampers 26 to fall -by gravity thus opening these dampers. The attendant would then set the dampers 25 to provide the volume of recirculated air which experience or instruments would indicate as being necessary for the reduced boiler load. With the ducts 23 extended, their outlets are in such close alignment with the fan inlets that the heated air therethrough is drawn directly into the fan inlets without escaping into the apparatus room, and that no room air is drawn into the fan inlets in the spaces between the outlets 24 and the fan inlets. The increased volume of heated air through the heater tubes will raise the temperature of their outer surfaces above the dew point temperature of the corrosive vapors in the flue gases.

When the plant load has risen to the point that no recirculation of heated air is required, the attendant will retract the ducts 23 to the positions shown by Figs. 3 and 4. When this is done the inturned upper ends of the ducts 23 will move the dampers 26 to closed positions thus shutting off the flow of air through the ducts 20 and 23, regardless of the positions of the dampers 25. With the ducts 23 fully retracted, their outlets 24 are sufficiently removed from the inlets II of the fan that they do not interfere with the air flow thereinto of air from the apparatus room.

While one embodiment of the invention has been described for the purpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangement of apparatus illustrated, as modifications thereof may be suggested by those skilled in the art, without departure from the essence of the invention.

What is claimed is:

1. In an air heating system including an air heater and a fan for moving air through the heater, a recirculation duct connecting the outlet of the heater with the inlet of the fan for recirculating air from the heater therethrough, dampering means in said duct, said duct having an outlet adjustable in one position to overlap the inlet of the fan, and adjustable in the opposite position so as to be substantially out of the path of the air entering the fan, and means for opening said dampering means when said outlet is moved to said one position, and for closing said dampering means when the outlet is moved to the opposite position. A

2. In an air heating system including an air heater and a fan for moving air through the heater, the fan having a circular, axial inlet, a recirculation ductconnecting the outlet of the heater with the inlet of the fan for recirculating air through the heater, said duct having an outlet adjustable in one position to overlapsaid inlet, and adjustable in the opposite position so as tobe substantially .out of the path of the air entering said inlet, said duct outlet having inner and outer portions curved in concentric circular arcs which when said outlet of said duct is adjusted to said one position, are concentric with said fan inlet.

3. The invention claimed in claim 2 in which dampering means in the duct is opened by movement of the duct outlet to the one position, and is closed by movement of the duct outlet to the opposite position.

4. In an air heating system including an air heater, a fan formoving air through the heater, and a recirculation duct for recirculating air through the heater, said fan having a circular, axial inlet, the combination of an outlet duct slidable in the recirculation duct to one position where the outlet thereof overlaps said 'fan inlet, and slidable to the opposite position where its outlet is substantially removed from the path of l the airentering the fan inlet, said outlet duct having inner and outer portions forming said outlet which are curved in circular arcs concentric with said fan inlet.

5. The invention as claimed in claim 4 in which dampering means in the recirculation duct is opened by movement of the outlet duct to the one position, and is closed by movement of the outlet duct to the opposite position.

' JOHN CASSIE.

REFERENCES CITED FOREIGN PATENTS Country Date Great Britain Oct. 16, 1933 Number

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