US2293830A

US2293830A - Combustion control

Info

Publication number: US2293830A
Authority: US
Publication date: 1942-08-25
Anticipated expiration: 1959-08-25

Description

AU8- 2,5 1942 J. J. KLINKr-:R 2,293,830

coMBUsT'IoN CONTROL F5941 i. i

2 sheets-sheet 2 Filed Aug. 24. 1959 JOHN J. KLINKER Patented Aug. 25, 1942 unirse COMBUSTION CONTROL John J. Klinker, Decatur, Ill., assignor to A. W. Cash Company, Decatur, Ill., a corporation of Delaware Application August 24, 1939, Serial No. 291,687

3 Claims.

This invention relates to combustion control, and more particularly to the control of combustion in furnaces having a fuel bed through which air is caused to flow solely by maintenance of a sub-atmospheric pressure at the furnace outlet. This sub-atmospheric pressure may be produced either by a stack (natural draft), or by a fan or its equivalent (induced draft),

In furnaces of this type the rate of combustion is determined by the rate of air flow through the fuel bed, but this air flow is dependent upon several variables, including the draft available and the thickness and character of the fuel bed. Thus it is dificult to maintain any desired constant rate of combustion. The problem is even more serious in installations having a plurality of furnaces among which the load is divided, for if the fuel bed on one furnace becomes thin this furnace will operate at a higher combustion rate than the others, and the fuel bed will tend to become even thinner, accentuating the unbalanced conditions. Variations in the distribution of the draft among the respective furnaces will cause similar difficulties.

It is accordingly one object of the invention to provide a simple and inexpensive apparatus for controlling combustion in furnaces of the aforesaid type and for maintaining the rate of combustion at a desired value.

It is a further object of the invention to prof vide a simple and inexpensive apparatus for controlling combustion and ensuring a desired distribution of the load among a plurality of furnaces of the aforesaid type,

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specication and covered by the claims appended hereto.

Referring to the drawings illustrating one embodiment of the invention, and in which like reference numerals indi-cate like parts:

Fig. 1 is a front elevation of a pair of steam boiler furnaces and associated combustion control apparatus, certain parts being broken away for clearness of illustration; and

Fig. 2 is a view similar to Fig. 1 showing a modified form of the invention.

The embodiment illustrated in Fig. 1 comprises a pair of furnaces I0 set in battery and each having a grate H to which fuel may be supplied manually through the usual fire-doors l2. Associated with each furnace is a steam boiler I4, both boilers delivering steam to a main header I5. Each furnace is provided with the usual gas outlet duct or uptake I6 having a damper i8 therein, both uptakes being connected to a breeching i9 leading to a stack or other draftinducing means (not shown). Beneath each grate is a chamber 20 from which the air for combustion passes upwardly through the grate and the fuel bed. Air is admitted directly from the atmosphere into each chamber 29 through a restricted inlet opening 22 in the front wall thereof. Each chamber 2l) is located immediately anterior to the fuel bed, in which the initial combustion of the fuel takes place.

Ea-ch of the dampers i8 is regulated iny such a manner as to maintain a predetermined pressure in the corresponding chamber 2l) beneath the fuel bed, and to vary this pressure in accordance with changes in the demand for heat. The pressure in each chamber 2l) is of course always somewhat below atmospheric, since the air flow is slightly restricted in passing through the openings 22. Each damper is provided with a shaft 23 having an arm 24 thereon which is connected by a link 26 to the fluid-actuated motor 21 of a regulator 28 of the general type disclosed in the patent to Temple No. 1,992,048. This regulator comprises a pilot valve mechanism 30 connected to the motor 2l by two pipes 3l and supplied with fluid under pressure from a suitable source through a pipe 32. The pilot valve mechanism is controlled by a lever 34 actuated by a flexible diaphragm 35 which is loaded by a coiled tension spring 355. The regulator 28 is connected to the coresponding space 2l) beneath the grate Il by means of a pipe 33. This pipe is preferably provided with a restriction in the form of a valve 39, and with a restricted air inlet opening in the form of a branch pipe having a valve 4 I, these parts being so arranged that the diaphragm 35 is subjected to the pressure between the valves 39 and di. This pressure is of course a function of the pressure in the space 20.

The loading of the diaphragm 35 in both the regulators 28 is varied in accordance with the demand for heat. For this purpose there is provided a suitable regulator 43 responsive to variations in the steam pressure in the header l5, this pressure being transmitted to the regulator through a pipe M. This regulator may be of any suitable type, one satisfactory construction being shown in the patent to Temple No. 2,049,549. The regulator 4S is connected by a link 45 to an arm M on a horizontal shaft i8 rotatably supported in suitable bearings 49. This shaft carries two arms 5I, each of which is connected by a link 52 to a lever 53 on one of the regulators 28. Each lever 53 is connected to a vertically slidable screw 55 carrying a nut 56 to which the upper end of the corresponding spring 36 is secured. With this construction, the regulator 48 will respond to any variation in the steam pressure in the header I5, and by rotating the shaft 48 it will cause the screws 55 to move up or down as the case may be, thus changing the loading forces applied by the springs 35 to the diaphragme 35.

The operation of this embodiment of the invention will now be apparent from the a-bove disclosure. With a bed of fuel burning on each of the grates II, the air for combustion will enter the chambers 20 through the openings 22 and pass upwardly through the fuel. The gaseous products of combustion will give up most of their heat to the boilers I4 and then escape through the uptakes I5 to the breeching I9. The steam generated in the boilers will pass into the header I5 and thence to a place of use, There will be a continuous flow of a small stream of air inwardly through each valve 4I, pipe 38, and valve 39 to the corresponding space 20, and so long as the pressure in the space 29 remains constant the pressure effective on the diaphragm 35 will remain constant, and the uptake damper I8 will remain stationary. If however the pressure in the space should vary in the slightest degree for any reason, such as changes in the thickness or character of the fuel bed, changes in the draft loss through the boiler caused by soot accumulations, or changes in the ydraft available at the uptake IG, the diaphragm 35 will move and by actuating the pilot valve mechanism 36 it will cause the motor 21 to adjust the uptake damper I8 until the desired pressure is restored in the space 20. If the demand for steam should increase slightly, the steam pressure in the header I5 will decrease, and the regulator '33 will act through its mechanical connection with the screws 55 to raise these screws, increasing the tension of the springs 36 and throwing the regulators 28 out of balance. Consequently the motors 21 will open the dampers I8 until the pressure in the spaces 2! has ybeen lowered sufficiently to restore the regulators 28 to a balanced condition. Similarly a decrease in the demand for steam will result in an increase in the steam pressure, and a closing movement of the uptake dampers I8. In this manner a predetermined relationship will be maintained between the demand for steam and the rate of fiow of the combustion air as determined by the pressure differential across each inlet opening 22. Furthermore, the load will be equally divided between the two boilers, irrespective of differences in the fuel beds or other variable factors. By adjusting one or both of the valves 39 and 5I, it is possible to change the operating range of the regulator 28 and thus adapt the control system to the particular conditions encountered at each installation.

In Fig. 2 there is shown a modified form of the invention in which a somewhat different arrangement of the regulating apparatus is disclosed. Since the construction of the furnaces and boilers is the same as in Fig. 1, the same reference numerals have been utilized so far as they are applicable. In Fig. 2 the regulators 28 of Fig. l have been replaced 'by regulators 28a in which the nuts 55 that support the springs 35 are mounted on manually adjustable screws 58, these screws being xed in the axial direction. Furthermore each regulator 28a is provided with an additional diaphragm 59 which is connected to the main diaphragm 35 and forms a means whereby the loading of the main dia- Dhragm may be automatically varied. The pressure in each chamber 2O is transmitted to the corresponding regulator 28a through a pipe 60. Means is provided to apply a fluid pressure to the diaphragms 59 of both the regulators 28a, and to vary this fluid pressure in accordance with variations in the demand for heat, as indicated for example by changes in the steam pressure in the header I5. For this purpose I have shown a pilot controller 6I connected to the header I5 by a pipe 62 and supplied with a suitable pressure fluid, such as compressed air, through a pipe 63. A pipe 54 leads from the controller to the diaphragm chamber 66 of a pressure reducing and regulating valve 61. The pilot controller BI may be of any suitable and well-known construction adapted to reduce the pressure of the air supplied by the pipe 63 and to transmit the reduced pressure through the pipe G5, the amount of pressure reduction being varied in accordance with variations in the steam pressure transmitted to the controller through the pipe 62. The valve 61 is also of well-known construction and comprises a diaphragm 69 arranged to actuate a reciprocable valve member II which controls the flow of a suitable fluid, such as compressed air, from a supply pipe 13 to a delivery pipe 14. The diaphragm 69 is urged upwardly against the pressure in the chamber 65 by means of a spring 'I5 and by the fluid pressure at the delivery side of the valve member II. The delivery pipe 'I4 is connected to the regulators 28u by means of branch pipes TI which supply pressure to the loading diaphragms 59. Each branch pipe is provided with a restriction 78 and with a manually adjustable leak-off valve 79 leading to the atmosphere.

The operation of this embodiment of the invention will now be apparent from the above disclosure. The air for combustion will enter the chambers 20 through the openings 22 and pass upwardly through the fuel on the grates I I. The combustion gases will give up most of their heat to the boilers IB, which will generate steam and deliver the same through the header I5 to a place of use. So long as the steam pressure remains constant at the desired value, the controller 6I will transmit a constant pressure through the pipe 64 to the diaphragm 69, and the valve member II will be held slightly open against the force of the spring 'I0 and the pressure in the delivery pipe 14; allowing a steady flow of air from the pipe 'I3 to the pipe 'I4 and thence through the restrictions 78, branch pipes Il, and valves 'I9 to atmosphere. The pressure effective on the diaphragms 59 will remain constant, and the regulators 23a will be in a balanced condition, holding the dampers I8 stationary. If the pressure in either of the chambers 2B should vary in the slightest degree for any reason, such as changes in the fuel bed, soot accumulations in the boiler, variations in available draft, etc., the diaphragm 35 of the corresponding regulator 23a. will move and cause the motor 2l to make the proper adjustment in the position of the uptake damper I8. If the steam pressure in the header I 5 should vary, the controller 6I will change the air pressure effective on the diaphragm G9, and the valve member 'II will take a new position, changing the pressure in the delivery pipe 14. This will alter the loading of the regulators 26a, throwing them temporarily out of balance, until the dampers I8 have moved sufliciently to vary the pressure in the chambers 2i) and thus restore the regulators to a balanced condition. An increased steam pressure will cause the dampers i3 to move towards closed position, decreasing the flow of air for combustion, and vice versa. The load will be equally divided between the two boilers, regardless of variations which may occur in the ful beds, draft loss, or draft distribution. By adjusting the valves 19, it is possible to vary the operating range of each of the regulators 23a, to t the conditions encountered at the particular installation.

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

l. In combination with a fuel-burning furnace having a fuel bed, means to maintain a sub-atmospheric pressure at the furnace outlet, a chamn ber located immediately anterior to the fuel bed and provided with a restricted inlet opening through which air for combustion is drawn directly from the atmosphere solely as a result of said sub-atmospheric pressure, a gas outlet damper at the furnace outlet, and a regulator arranged to control the gas outlet damper in accordance with the pressure in the chamber, the regulator being adjustable so that the pressure differential across the said inlet opening may be varied to control the rate of flow of the air for combustion in a desired manner regardless of Variations in fuel bed resistance.

2. In combination with a fuel-burning furnace having a fuel bed, means to maintain a sub-atmospheric pressure at the furnace outlet, a chamber located immediately anterior to the fuel bed and provided with a restricted inlet opening through which air for combustion is drawn directly from the atmosphere solely as a result of said sub-atmospheric pressure, a gas outlet damper at the furnace outlet, an adjustable regulator arranged to control the gas outlet damper in accordance with the pressure in the chamber, and automatic means to adjust the regulator in accordance with the demand for heat, whereby the pressure differential across the said inlet opening will be varied and the flow of the air for combustion will be controlled in a desired manner regardless of variations in fuel bed resistance.

3. In combination with a plurality of fuelburning furnaces, each furnace having a fuel bed, means to maintain a sub-atmospheric pressure at the outlet of each furnace, a chamber located immediately anterior to each fuel bed and provided with a restricted inlet opening through which air for combustion is drawn directly from the atmosphere solely as a result of said sub-atmospheric pressure, a gas outlet damper at the outlet of each furnace, an adjustable regulator for each gas Outlet damper arranged to control the same in accordance with the pressure in the corresponding chamber, and automatic means to adjust all the regulators in accordance with the demand for heat from all the furnaces, whereby the pressure differential across each inlet opening will be varied to control the flow of the air for combustion in a desired manner regardless of variations in fuel bed resistance.

JOHN J. KLINKER.