US3413998A - Air flow proportioning apparatus - Google Patents

Description

United States Patent O 3,413,998 AIR FLOW PROPORTIONING APPARATUS Arthur S. Vaughan, Mllburn, NJ., assignor to Foster Wheeler Corporation, Livingston, NJ., a corporation of New York Filed May 5, 1965, Ser. No. 453,461 5 Claims. (Cl. 137-118) ABSTRACT OF THE DISCLOSURE An air flow proportioning apparatus utilizing two venturis with throats of substantially equal cross-sectional area and means actuated by the pressure drops across said venturis for opening and closing dampers in accordance with a predetermined rate of ow.

As the trend toward larger and larger steam generators continues, it is essential to resort to opposed ring of the steam generators with opposed burner banks. With opposed fring, it is often essential to proportion the flow of air to the two separate banks.

Therefore, it is an object of this invention to provide an apparatus for proportioning any given total air ow into two separate ows.

In accordance 'with this invention, two virtually identical venturis are each located in a separate duct. A separate damper is located downstream from each venturi. A system is provided to control the operation of the dampers which is actuated by the pressure drop across the venturis.

The invention may be better understood from the following detailed description considered in conjunction with the accompanying drawing which is a schematic diagram of the apparatus.

Referring now to the drawing, a furnace 11 has a front side 13 and a rear side 15. Located at the front side 13 is a group of front burners 17, and located at the rear side 15 is a group of rear burners 19. Air is supplied to the front burners 17 by a front duct 21. Similarly, air is supplied to the rear burners 19, by a rear duct 23. The air is supplied to the front duct 21 and the rear duct 23 from a fan 25 or other source of air which is most usually connected to the front duct 21 and rear duct 23 through a main duct 27.

Located Within the front duct 21 is a front venturi 29. Similarly, a rear venturi 31 is located within the rear duct 23. It should be also noted that it is advisable that both the front venturi 29 and the rear venturi 31, which are virtually identical in shape and size, be approximately the same distance from the source of air 25.

Within the front duct 21 a short distance downstream of the front venturi 29 away from the fan 2S is a front damper 33. Downstream of the rear venturi 31 is a rear damper 35.

A front throat tube 37 senses the pressure at the throat of the front venturi 29 while a front upstream tube 39 senses the pressure entering the front venturi 29. These two pressure signals from the front venturi 29 are relayed to a front, low-differential pressure transmitter 32 which determines the diiferential in pressure between the throat and the entrance of the front venturi 29. The front, low differential pressure transmitter 32 transmits this differential as a front, low-differential signal through a tube 41. Similarly, a rear throat tube 43 senses the pressure at the throat of the rear venturi 31 While a rear upstream tube 45 senses the pressure entering the rear venturi 31. These two pressure signals from the rear venturi 31 are relayed to a rear, low-differential pressure transmitter 47 which determines the differential in pressure between the throat and the entrance to the rear venturi 31. The rear low-differential pressure transmitter 47 determines the dif- 3,413,998 Patented Dec. 3, 1968 ice ferential between the throat and entrance and transmits this differential as a rear, low-differential pressure signal through a tube 49.

The front, low-dierential signal is transmitted through the tube 41 to a diaphragm 51 of a computing relay 53. The rear, low-differential signal is transmitted through the tube 49 to the opposite side of the diaphragm 51. A permanent pressure, preferably 9 p.s.i., is applied to the diaphragm 51 by a spring 55. Thus, when the front, lowdifferential signal and the rear, low-differential signal are equal, the computing relay 53 will transmit a 9 p.s.i. pneumatic signal through the tube 57 to a proportional and reset controller 59. The predetermined extent of proportioning of ilow between the front duct 21 and the rear duct 23 is manually applied through a manual loader 61. The manual loader 61 transmits a load signal to the proportional and reset controller 59 through a tube 63. The proportional and reset controller 59 combines the signals into a control signal which is fed to a front pneumatic actuator 65, and a rear pneumatic actuator 67, through a tube 69. Located along the tube 69 is an auto-manual control station 71 which permits manual operation of the front and rear pneumatic actuators 65, 67 without operation of the previously described pneumatic system. The front pneumatic actuator is mechanically connected to the front damper 33 while the rear pneumatic actuator 67 is connected to the rear damper 35.

One of the two pneumatic actuators 65, 67 is adapted to close its respective damper at 3 p.s.i. and open it at 9 p.s.i. The other pneumatic actuator is adapted to close its respective damper at 15 p.s.i. and open it at 9 p.s.i. Thus, only one damper can be partially or totally closed and the other damper must be open to limit the amount of pressure drop that can be caused by the dampers.

The symbol S is used on the drawing to indicate that supply air is being fed to the respective piece of equipment.

Since partial closing of one damperI increases the flow resistance to the total flow, the fan output must be increased under these circumstances. Therefore, the abovedescribed pneumatic system must be interconnected with the air-flow control system. Accordingly, a tube 73 is connected to the tube 41 and a tube 75 is connected to the tube 49. In this way, the front, low-differential signal and the rear, low-differential signal are transmitted to an airow totalizer 77 which in turn sends a total air-flow signal through Va tube 79 to the combustion control system 81. Generally, the combustion control system operates a pneumatic fan actuator 83 through a tube 85 which opens and closes a shutter 87 of the fan 25.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. An apparatus for proportioning the air ow to a furnace between the front burner bank and the rear burner bank, comprising:

a source of pressurized air;

a front duct connected to said source of pressurized air;

a rear duct connected to said source of pressurized air, said front duct and said rear duct being of equal cross-sectional area;

a front venturi located in said front duct;

a rear venturi located in said rear duct, said front and rear venturis having throats with equal cross-sectional areas;

a front damper located downstream of said front venturi in said front duct and adapted to be opened and closed to control the flow of air through said front duct;

a rear damper located downstream of said rear venturi in said rear duct and adapted to be opened and closed to control the ow of air through said rear duct; and

means actuated by the pressure drops across said venturis for opening and closing said dampers in accordance with a predetermined proportional rate of 5. An apparatus for proportioning air ow to a furnace between the front burner bank and the rear burner bank comprising:

a source of pressurized air;

llow between the front and rear ducts, said means for opening and closing said `dampers opening and closing said front and `rear dampers such that one of said dampers is wide open at all times. 2. An appa-ratus according to claim 1 wherein said a front duct connected to said source of pressurized means for opening and closing said dampers is pneumatic. air;

3. An apparatus according to claim 1 `wherein said a rear duct connected to said source of pressurized means for opening and closing said dampers includes: air, said front duct and said rear duct being of submeans for determining the difference in pressure drop stantially equal cross-sectional area;

across the front venturi and the rear venturi and afront venturi located in said front duct; converting the difference into a first signal; a rear venturi located in said rear duct, said front and means for comparing the rst signal with a predeterrear venturis having throats with equal cross-sectional mined signal and forming a second signal; and areas; actuating means mechanically connected to said front 2 a front damper located downstream of said front and rear dampers and adapted to be operated by venturi in said front duct and adapted to be opened said second signal. and closed to control the ow of air through said 4. An apparatus according to claim 1 wherein said front duct; means for opening and closing said dampers includes; a rear damper located downstream of said rear venturi a front, pneumatically-operated, low-differential presin said rear duct and adapted to be opened and closed sure transmitter connected to said front venturi and t0 COIltrOl the OW Of air llhrOugh Said rear duct; adapted to transmit as a pneumatic signal the pressure a front means connected to said front venturi to transditerential across said front venturi; mit the pressure differential across said front venturi; a rear, pneumatically-operated, low-differential presa rear means connected to said rear venturi to transsure transmitter connected to said rear venturi and mit the pressure different acoss said rear venturi; adapted to transmit as a pneumatic signal the pres` a computing relay means connected to both said front sure differential across said rear venturi; means and said rear means to compare the signal a pneumatically-operated differential computing relay from the front means and the signal from the rear connected to both said front, pneumatically-operated, means and to transmit a signal representing that low-differential pressure transmitter and said rear, COIIlPariSOIl; pneumatically-operated, low-differential pressure a proportional and reset controller means to receive transmitter and adapted to compare the pneumatic signal from the front, pneumatically-operated, lowdifferential pressure transmitter and the pneumatic signal from the rear, pneumatically-operated, lowdiierential pressure transmitter and to transmit a pneumatic signal representing that comparison;

the signal from said computing relay means;

a loader means to transmit a signal in accordance with a predetermined proportioning of the air ow to said proportional and reset controller means, said proportional and reset controller means being adapted to transmit a signal representing the signals from said computing relays and said loader means; and

means to actuate in accordance with the signal from the proportional and reset controller means the front damper and the rear damper such that at least one damper is maintained wide open at all times.

References Cited UNITED STATES PATENTS controller being connected with said manual loader 1 206 806 12/1916 Borden 137 g7 and adapted to receive the pneumatic signal from 1620240 3/1927 Smoot 1379g X said manual loader and transmit a signal represent- 2395384 2/1946 Ziebolz 137 98 X ing the signals from said pneumatically-Operated dif- 3103228 9 /1963 Davenport 137 93 ferential computing relay and said manual loader; and FOREIGN PATENTS a pair of pneumatically-operated actuators, one of 843,621 3/ 1939 France,

which is mechanically connected to said front damper and the other of which is mechanically connected to said rear damper and both of which are pneu- WILLIAM F. ODEA, Primary Examiner.

D. I. ZOBKIW, Assistant Examiner.

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