US2053750A - Furnace pressure regulation - Google Patents

Description

- Sept. 8, 1936.

c. M. TERRY FURNACE PRESSURE REGULATION Filed March 8,

gnumm CHARLES 11. ERR) Patented Sept. 8, 1936 FUBNACE PRESSURE REGULATION Charles M. Terry, Decatur, 111., assignor to A. W.

Cash Company, Decatur, 111., a corporation of Delaware Application March a, 1935, Serial No. 10,088

8Clalms.

This invention relates to furnace pressure regulation, and more particularly to the regulation of pressure in a furnace having a forced draft air supply which is started automatically in response to a demand for heat.

It is common practice to control the pressure in a combustion chamber or furnace by regulating-the discharge of the gaseous products of com-' bustion from the furnace. This is ordinarily accomplished through the medium of an automatic regulator responsive to variations in furnace pressure and arranged to actuate a damper at the furnace outlet. The forced draft air supply to such a furnace is sometimes started automatically, usually by a thermostatic device or by a device responsive to variations in steam pressure. The sudden inrush of air causes the furnace pressure to increase, and the automatic regulator immediately starts to open the damper, which has remained nearly closed while the forced draft was shut down. In many cases the automatic regulator cannot open the damper with sufllcient rapidity to avoid a considerable increase in furnace pressure, and asa result flame and smoke issue into the room from all cracks and openings in the furnace walls.

It is accordingly the main object of the present invention to overcome this difficulty and provide simple and reliable means to ensure a free discharge of gases from the furnace when the forced draft air supply is started.

It is a further object of the invention to provide simple and reliable means to move the fur-= nace outlet damper automatically'to open posi tion just prior to each automatic starting of the forced draft air supply.

vention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

Referring to the drawing illustrating one embodiment of the invention, and in which like reference numeralsindicate like parts,

The single figure is a diagrammatic elevation, partly in section, of a. forced draft furnace having automatic means for regulating the pressure therein.

The embodiment illustrated comprises walls It! forming a furnace combustion chamber ll fired by means of. an underfeed stoker l2 having a retort l4 and tuyere blocks l5. Air is supplied to the space l6 beneath the retort by means of a forced draft fan l8 driven by a motor IS. The motor illustrated is an electric motor directly connected to the fan, and it also serves to actuate the stoker l2 through a chain-and-sprocket drive 20. The heat from the furnace II is utilized to generate steam in a boiler 22 mounted thereabove. The furnace gases flow in contact with 5 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.

. 10 The damper 24 is controlled automatically by a suitable regulator responsive to variations in the. pressure in the furnace ll.

For'this purpose I preferably utilize an automatic regulator 21 of the type disclosed in the patent to Temple No. 15 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 28 and connected by tubes 3| to a hydraulic motor 32. This motor 32 is connected to the damper operating arm 25 by means of a rod 33. The regulator 21 is connected to the furnace II by means of a pipe 34, so that the furnace .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 I9 is connected to a suitable electrical supply 36 by means of conductors 31 which lead through an electro-magnetlcally actuated switch 38. 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 I 9 will start.

In order to control the rate of steam generation automaticallm'means is provided for starting and stopping the motor l9 at intervals in accordance with the demand for steam. For this purpose I have shown a pressure-actuated master switch 4| of the well-known mercury tube type connected by a pipe 42 to the steam delivery pipe 43 of the boiler 22, and arranged to close at a predetermined minimum steam pressure and open at a predetermined maximum steam pressure. This switch 4| serves to control the supply of electricity from a suitable source 45 to a pair of power leads 46 and 41. The source 45 is shown as independent of the source 36, but it will be understood that this is not necessarily the case.

It will now be apparent that if the holding coil 39 is connected'directly across the power leads 46 and 47, as has been customary in the past, certain difliculties will arise. With the fan l8 shut down, combustion will be very slow, and the regulator 21 will hold the damper .24 in a nearly closed position to maintain the desired pressure in the furnace i I. If now the steam pressure drops sufllciently to close the switch 4|, and the fan motor I9 is immediately started, the regulator will be unable to open the damper fast enough to prevent a considerable increase in the furnace pressure, with attendant emission of flame and smoke.

In order to overcome this dimculty I provide means to vent the regulator 27 to atmosphere immediately upon closure of the pressure-actuated switch ll, and I provide means to interpose a slight time delay between closure of the switch 4| and closure of the switch 38. Since the regulator is adjusted for a slightly negative pressure, it will start to open the damper 2 immediately after being vented to atmosphere, and the time delay will allow completion of the opening movement before the forced draft supply is started.

In the preferred construction illustrated, a valve 49 is mounted in the pipe 35 to provide an atmospheric vent 50 controlled by a valve member 5|. The valve member normally rests by gravity in a position to close the vent. The valve member 5| is directly connected to the plunger 53 of a solenoid 54, the parts being so arranged that upon energization of the solenoid, the plunger and valve member will be raised and the vent 50 opened. It is also desirable to close communication with the furnaw H upon opening of the vent 50, so as to avoid a rush of air through the vent and into the furnace. For this purpose I provide a partition wall 55 which extends acrossthe interior of the valve -38 between the vent and the furnace. This wall is provided with a port 56 located directly above the vent to and in a position to be closed by the valve member 5i when latter is raised by energization of the solehold 53. It will be seen that this construction provides means whereby the regulator s. ma L connected to the furnace it when it is desire to control the furnace pressure, and to the mosphere when it is desired to open 2! fully and obtain high draft in while the forced draft supply is st An automatic switch mechani m vlded to cooperate with the various ctc. arts ensure the desired time delay between energize.- tion of the solenoid G6 and closure of the switch 38. This mechanism comprises a switch connected in series with the solenoid across the power leads it and d'l, and a switch '3 connected in series with the holdingcoii 31 across the power loads 45 and ll. The parts are so arranged that when the switch is closed, the switch Bil will be open, and vice verse... In the preferred construction both the switches and 60 are formed in a single glass tube 622 containing a small amount of mercury 2'53. The tube 62 is supported in a clip 65 which is pivotally mounted on a pin 86, suitable stops ti? and 33 being provided to limit the pivotal movement the clip. When the clip rests against the stop 3? the mercury 63 will close the switch 59, when the clip rests against the stop 68 the mercury will close the switch 66.

In order to actuate the switches 59 30, I provides. link 10 pivoted at its upper end to clip 84 and having a roller ii at its lower end. A coiled tension spring 12 is connected to link and holds the roller H in contact with the V shaped end of a lever H which is plvotally supported on a pin 15. The movements of the lever '54 are controlled by means of a solenoid "if; connected across the power leads 56 and 671 and proaooavso Movement of the lever 1 3 following energization of the solenoid i5 is retarded by a suitable dash pct 83 having a piston 85; connected by a piston rod so to the lever. The piston 89 is formed with ports 92 controlled by an annular valve 93 resting on the upper surface of the piston. A passage 95 connects the space above the piston with the space therebeneath, and a manually adjustable valve 95 is provided to control the flow in this passage. The dash pot is filled with a suitable liquid, such as oil.

The operation of the invention will now be apparent from the above disclosure. During the off period the parts will be in the positions shown in the drawing, with switches ti, 38 and 238 open, and switch 59 closed. The fan i8 and Stoker l2 will be shut down, and the valve member 5i will close the vent Elli. Under these conrlitions the regulator 2? will control the position 0; the damper 2d and maintain a pressure in the furnace it slightly below atmospheric pressure. If now the steam pressure drops to a predetermined value, the switch ll will close, energizing the solenoids i l and iii. The solenoid 54 will lift the valve member 5i, closing port 56 and cpening the vent 5D, wherev son the regulator 27 will start to move the d. KIDS-l 23 toward open position. At the same olenoid 16 will 'lll thereupon slowly raise the collar and turn lever i against resistanceo: the dash time delay which cm be adjusted by r a of the dash pot val 2 3 to reach its 0 Q, i have moved its v feast the roller ll, whereup pull the roller down the other throw the clip 5 against the lion. This will close the holding coil 39. closing: starting the motor 30, fan is and the same time, the switch [58 will be opened, deenergialng the solenoid 6G and dropping the valve member 58 into position to close the vent Bil. The regulator 2? will then control the damper i6 and maintain the desired pressure in the furnace M.

tron, the lever d point slightly e spring it will Upon increase in the steam press 1 e to a value I switch ll, solenoid l6 dcient to open the nd i. s ldin coil 80 will be vie-energized. the switch 38 and shut down the inc- Ulub ne'er iii and a, and the freely. The regulator 2'17 will continue to main tain the desired furnace pressure.

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

1. A control for c a the rod 79 and compress .he spring 85, which to allow the forced, draft air supply comprising a regulator normally responsive to the furnace pressure and arranged to maintain said pressure at a value slightly below atmospheric pressure by controlling the discharge of the gaseous products of combustion from the furnace, a device to start the forced draft air supply automatically in response to a demand for heat, and means to vent the regulator to atmosphere for a short time just prior to the starting of the forced draft air supply.

2. A control system for a furnace having a forced draft air supply comprising a regulator normally responsive to the furnace pressure and arranged tomaintain said pressure at a value slightly below atmospheric pressure by controlling the discharge of the gaseous products of combustion from the furnace, means providing a vent through which atmospheric pressure may be effective on the regulator, a valve member normally closing the vent, a device to start the forced draft air supply automatically in response to a demand for heat, and means to move the valve member and open the vent for a short time just prior to the starting of the forced draft air supply.

3. A control system for a furnace having a forced draft air supply and a damper to control the discharge of the gaseous products of combustion from the furnace comprising a regulator normally responsive to the furnace pressure and arranged to maintain said pressure at a value slightly below atmospheric pressure by controlling the damper, a device to start the forced draft air supply automatically in response to a demand for heat, and means to vent the regulator to atmosphere for a short time just prior to the starting of the forced draft air supply 4. A control system for" a furnace having a forced draft air supply comprising a regulator normally responsive to the furnace pressure and arranged to maintain said pressure at a value slightly below atmospheric pressure by controlling the discharge of the gaseous products of combustion from the furnace, means providing a vent through which atmospheric pressure may be effective on the regulator, a valve member normally closingthe vent, means to move thevalve member and open the vent in response to a demand for heat, means to start the forced draft air supply a short time after the vent is opened, and

' means to move the valve member and close the vent when the forced draft air supply is started.

5. A control-system for a furnace having a forced draft air supply comprising a regulator normally responsive to the furnace pressure and arranged to maintain said pressure at a value slightly below atmospheric pressure by controlling the discharge of the gaseous products of combustion from the furnace, a conduit arranged to transmit the furnace pressureto the regulator,

said conduit having a port therein and an atmospheric vent between the port and the regulator,

a valve normally closing the vent, a device to start the forced draft air supply automatically in response to a demand for heat, and means to move the valve into a position to open the vent and close the port for a short time just prior to the starting of the forced draft air supply.

6. A control system for a furnace having a forced draft air supply comprising a regulator, normally responsive to the furnace pressure and arranged to maintain said pressure-at a value slightly below atmospheric pressure by controlling the discharge of the gaseous products of combustion from the furnace, means providing a vent through which atmospheric pressure may be effective on the regulator, a valve member normally closing the vent, a solenoid to move the valve through which atmospheric pressure may be effective on the regulator, a valve member normally closing the vent, a solenoidto move the valve member and open the vent, a starting mechanism for the forced draft air supply, a coil to actuate the starting mechanism, two electrical power leads, a device to energize the power leads in response to a demand for heat, a switch connected in series with the solenoid across the powerleads, a switch connected in series withthe coil across the power leads, a solenoid connected across the power leads and arranged when energized to open the first switch and close the second switch, and meansto' provide a short time delay between energization of the last mentioned solenoid and actuation of the switches.

8. A control systemfor a furnace having a forced draft air supply comprising a regulator normally responsive to the furnace pressure and Cly closing the vent, a solenoid to move the valve member and open the vent, a starting mechanism for the forced draft air supply, a coil to actuate the starting mechanism, two electrical power leads, a device to energize .the power leads in-response to a demand for heat, a pivotally supported glass tube containing mercury and arranged to provide two switches one of which is open when the other is closed and vice versa, means connecting one switch in series with the solenoid across the power-leads, means connecting the other switch in series with the coil across the power leads, a solenoid connected across the-power leads and arranged when energized to tip the tube and close the switch which is connected with the coil and open the other switch, and a dash pot to provide a short time delay between energization of the last mentioned solenoid and tipping of the tube. i

' CHARLES M. TERRY.

Images