US2376701A - Combustion control - Google Patents

Description

May 22, 1945. J. J. KLINKER 2,376,701

COMBUSTION CONTROL Original Filed Sept. 13, 1941 JOHN J ftZ/NKER Patented May 22, 1945 UNITED STATES PATENT OFFICE 2,376,701 ooMeUs'rIoN oou'rnor.

John J. Klinker, Decatur, Ill., assignor to A. W. Cash Company, Decatur, 111., a corporation of Delaware Original application September 13, 1941, Serial No. 410,788. Divided and this application July 14, 1943, Serial No. 494,610

4 Claims. (01. 236-14) with the demand for heat. This application is a division of my prior application Serial No. 410,788 filed Sept. 13, 1941, now Patent No. 2,332,580, dated Oct. 26, 1943.

In furnaces of this type it is usual to start and stop the fuel supply at the same time as the'air 0 supply. The rate of fuel delivery during each opcrating period is ordinarily predetermined, but the rate of air flow usually varies with the resistance of the fuel bed. If the fuel bed is slightly thin the air flow will be increased, thereby increasing the rate of combustion and causing the fuel bed to become even thinner. Consequently it is not possible to burn the fuel efliciently. This dificulty becomes particularly serious when the demand for heat is low and the shut-down periods 0 are prolonged. During such periods combustion continues at an appreciable rate because of air which passes through the forced draftfan by natural draft, and the fuel bed therefore becomes badly depleted. 25

It is accordingly one object of the invention to provide a comparatively simple and efiicient apparatus for controlling combustion in a forced draft furnace of the start and stop type.

It is a further object of the invention to pro- 3 vide a simple and dependable apparatus for maintaining a predetermined rate of air flow in a forced draft furnace during the operating periods and for preventing substantially all air flow during the shut-down periods. 35

tion, of a forced draft furnace and associated 45 combustion control apparatus.

The embodiment illustrated comprises walls Ill forming a furnace combustion chamber ll fired by means of an underfeedstoker l2 having a retort l4 and tuyere blocks 15. Air is suppliedto 60 the space It beneath the retort by means of a forced draft fan l8 driven by a motorv 19. The motor illustrated is an electric motor directly connected to the fan, and it also servesto actuate the stoker [2 through a chain-and-sprocket drive 55 The heat from the furnace H is utilized to enerate steam in a boiler 22 mounted thereabove. The furnace gases flow in contact with the boiler heating surfaces and then escape through a gas outlet or uptake 23 to a suitable stack (not shown). The gas outlet 23 is provided with an adjustable damper 24 having an operating arm 25.

The damper 24 is controlled automatically bya suitable regulator responsive to variations in the pressure in the furnace It. For this purpose I preferably utilize an automatic regulator 21 of the type disclosed in the patent to Temple No. 1,992,048 granted February 19, 1935. This regulator comprises a pilot valve mechanism 28 supplied with a suitable fluid under pressure through a pipe 29 and connected by tubes 31 to a hydraulic motor 32. This motor 32 is connected to the damper operating arm by means of a rod 33. The regulator El is connected to the furnace I I by means of a pipe 34, so that thefurnace pressure is effective to actuate the regulator. The regulator is adjusted to maintain a furnace pressure slightly below atmospheric pressure, say a negative pressure of one-tenth inch water column.

The electric motor is is connected to a suitable electrical supply 35 by means of conductors 37' which lead, through an electro-magnetically actuated switchZ-ifi. This switch is provided with a holding coil 39, and the parts are so arranged that upon energization of this coil the switch will be closed and the motor is will start.

In order to control the rate of steam generation automatically, means is provided for starting and stopping the motor is at intervals in accordance with the demand for steam. For this purpose I have shown a pressure-actuated master switch M of the well-known mercury tube type connected by a pipe 42 to the steam delivery pipe 43 of the boiler22, and arranged to close at a predetermined minimum steam pressure and open at a predetermined maximum steam pressure. This switch 4! is connected in series with the coil 39 across two of the leads from the power supply 36, so that the master switch will control the operation of the switch 38. Obviously, a power source independent of the supply 36 could be utilized for control purposes if desired.

In order to control the rate of air flow to the furnace, a forced draft damper 45 is shown mounted in the duct 6 betweenthe fan 18 and the space I6 beneath the retort. This damper is provided with an operating arm ll which is connected by a rod 49 to a hydraulic motor 50. This motor is controlled by a regulator 52 of the same type as the regulator 21 and comprising a-pilot valve mechanism 53 supplied with a suitable fluid under pressure through a pipe 54 and connected by a pair of conduits 55 to the motor 50. The regulator 52 is subjected to a pressure differential which is a function of the rate of air flow to the furnace, and for this purpose I may utilize the pressure differential across the boiler gas passages. As shown, one side of the regulator is subjected to the pressure in the furnace H through a ipe 58 connected to the pipe 34. The other side of the regulator is connected by a pipe H to a three-way valve '12 having two aligned ports 13 and 14 with a reciprocable valve disk 15 between them. The port 13 affordscommunication between the pipe H and a pipe 11 leading to the gas outlet duct 23 anterior to the damper 24. The port 14 affords communication be tween the pipe H and a pipe 18 leading to the gas outlet duct 23 posterior to the damper 24. The valve disk 75 is controlled by a solenoid 80 which is connected across two of the conductors 31 between the stoker motor l9 and the switch 38. The arrangement is such that when the stoker is shut down the solenoid will be deenergized, and the disk 15 will close the port 13 and open the port 14. When the stoker is operating, the solenoid will be energized, and the disk 15 will close the port 14 and open the port '13.

The operation of the invention will now be apparent from the above disclosure. Assuming that the steam pressure is sufficiently high, the various parts will be positioned as illustrated. The master switch 41 will be open, the coil 39 will be deenergized, the switch 38 will be open, and the stoker motor l9 will be shut down. The regulator 21 will hold the damper 24 nearly closed, main taining a slight predetermined draft in the furnace H. The solenoid ,8!) will be deenergized and the valve 12 will connect the regulator 52 to the pipe '18, which will subject the regulator to a higher pressure differential than that for which it is adjusted and cause it to actuate the motor 50 in such a direction as to close the forced draft damper 45. Thus the damper 45 will be closed during the shut down period so that substantially no air can enter the furnace i I. If new the steam pressure drops sufficiently to close the master switch 4|, the coil 39 will be energized, the switch 38 will close and the motor 19 will start the fan I8 and stoker [2. The solenoid 80 will be .energized, lifting the valve 75 and connecting the regulator 52 to the pipe 11, so that this regulator will control the forced draft damper in accordance with the pressure differential across the boiler gas passages. since the regulators 21 and 52 are of the same type, the forced draft damper 45 will not open any faster than the uptake damper 24 will be opened to accommodate the increasing gas flow, so that no objectionable flarebacks will occur during the starting of the fan. The forced draft damper '45 will be automatically controlled by the regulator 52 to provide' a predetermined rate of air flow during each operating period, making it possible to maintain a desired fuel-air ratio despite changes in fuel bed resistance. As combustion continues and the steam pressure rises sufficiently to open the master switch 4!, the coil 39 will be deenergized, the switch 38 will open, the motor l9 will stop, and

fore it is intended to include all such changes and variations within the scope of the following claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A control system for a furnace having fuel supply means, a forced draft fan and a forced draft damper comprising means to start and stop the fuel supply means and the fan in accordance with the demand for heat, a motor to actuate the damper, a regulator to control the motor, means to subject the regulator while the fan is operating to a differential pressure which is a function of the rate of air flow to the furnace and thereby maintain the said rate of air flow substantially constant, and means operative while the fan is stopped to unbalance the regulator in such a direction as to effect closure of the damper.

2. A control system for a furnace having fuel supply means, a fan to supply forced draft air and a forced draft damper comprising means to start and stop the fuel supply means and the fan in accordance with the demand for heat, a motor to actuate the damper, a regulator to control the motor, means to subject the regulator while the fan is operating to a differential pressure which is a function of the rate of air fiow to the furnace and thereby maintain the said rate of air flow substantially constant, and means operative while the fan is stopped to subject the regulator to a pressure differential materially exceeding that for which it is adjusted and thereby effect closure of the damper.

3. A control system for a furnace having apassage for the flow of heating gases, a gas outlet duct, an uptake damper within the duct, fuel supply means, a forced draft fan and a. forced draft damper comprising means to start and stop the 40 fuel supply means and the fan in accordance with the parts will be restored to the positions shown the demand for heat, a motor to actuate the forced draft damper, a regulator to control the motor, means to subject the regulator to the pressure drop in the passage while the fan is operating and thereby maintain a predetermined rate of air flow to the furnace, and means operative while the fan is stopped to subject the regulator to the pressure drop between the furnace and the gas outlet duct beyond the uptake damper and thereby effect closure of the forced draft damper.

' 4. A control system for a furnace having a passage for the flow of heating gases, a gas outlet duct, an uptake damper within the duct, fuel supply means, a forced draft fan and a forced draft damper comprising means to start and stop the fuel supply means and the fan in accordance with the demand for heat, a motor to actuate the forced draft damper, a regulator to control the motor, a conduit connecting one side of the regulator to the furnace, a three-Way valve, a conduit connecting the other side of the regulator to the valve, two conduits connecting the three-way valve with the gas outlet duct anterior to and posterior to the uptake damper respectively, and control means for the three-way valve operative when the faniis running to close the conduit leading to the duct posterior to the uptake damper and operative when the fan is stopped to close the conduit leading to the duct anterior to the uptake damper, whereby a predetermined rate of air flow will be maintained while the fan is running, and the forced draft damper will be closed whenthe fan is stopped, v

JOHN J. mim cs.

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