US2580173A - Adjustable temperature responsive - Google Patents

Description

Dec. 25, 1951 w. J. HATTON ADJUSTABLE TEMPERATURE RESPONSIVE DEVICE FOR COMBUSTION FURNACES 2 SHEETS-SHEET 1 Filed Sept. 9, 1949 INVENTOR WILLARD J, HATTON Dec. 25, 1951 w. J. HATTON ADJUSTABLE TEMPERATURE RESPONSIVE DEVICE FOR COMBUSTION FURNACES Fil ed Sept. 9, 1949 2 SHEETS-SHEET 2 MA mJ D R A L H W h 2 axadq 4 -44: W-

Patented Dec. 25, 1951 ADJUSTABLE TEMPERATURE BESPONSIVE 1 DEVICE FOR COMBUSTION FURNACES Willard J. Batten, Jackson, Micln, acsignor, by

mesne assignments, search, Inc W of Delaware Bituminous Coal Ren, D. 0., a corporation Application September 9, 1949, Serial lie. 114,773 2 Claims. (Cl. 200-137) This invention relates to such a device in which the thermal expansion and contraction of a wire element controls the operation of the device. More particularly, it relates to such a device for the eliluent gas passage of a stoker-fed combustion furnace for solid organic fuels to prevent loss of equilibrium in a fuel bed. This device is rapid and reliable in operation and capable of vernier adjustment for precise control of the temperature limit to which it is to be responsive.

In conventional stoker-fed combustion furnace systems for homes and small buildings, such as those employing the underfeed principle, holdfire operation is generally indirectly controlled by a room temperature-sensitive device or directly by a timing device or stack switch. Notwithstanding, during periods of continued warm weather in the temperate zone the fuel bed may undergo excessive thinning or ignition may be partially lost so as to produce a blow out when fuel and air are again supplied at the commencement of an on period. Such a "blow out occasions the building of a new fire.

When a timing device is used, it operates periodically without regard, so far as it itself is concerned, for the needs of the fuel bed for fuel. It is designed to feed a suillciency of fuel during the timer-on periods during hold-flre particularly to maintain the fuel bed in a stable burning condition to the next on period. However, unless this adjustment of the timer is most precise, even with conventional-furnaces, the fuel bed may be overloaded with unburned fuel and a combustion smothering tendency produced. In addition, the existence of a response lag owing to the relative insensitivity of any controlling limit switch, whether temperature-controlled or temperature and time-controlled, a ments the difliculty. The difllculty may be further aggravated when agglomerating bituminous coals are burned.

These operational problems are magnified if the combustion furnace system is one in which the combustion chamber is smaller and in which the burning rates are higher when compared with conventional furnace systems. A furnace system having such a relatively small combustion space and high burning rate when compared to conventional systems is disclosed in United States patent application Serial No. 93,562, filed May 16, 1949 in the names of Willard J. Hatton and Ralph A. Sherman. This furnace system burns such bituminous coals without detrimental agglomeration or clinkering. The invention of this application is particularly suitable for use with 2 that furnace system. although it may also be used with a wide variety of kinds and types of combustion furnaces.

The device of this invention is reliable and rapidly responsive to the thermal limitation that is preset; it is not subject to deterioration; is relatively simple in construction and operation; and is adjustable by a new vernier control to change the predetermined limit to which the device is responsive. In short, the adjustable temperature responsive device disclosed herein for combustion furnaces overcomes the foregoing difficulties previously encountered in the use of prior art switches. Other objects and advantages of this invention will be apparent from the following description and from the drawings, which are illustrative only, in which Figure 1 is a vertical cross sectional view of a residential downflow stoker-fed furnace suitable for use with a device made in accordance with this invention;

Figure 2 is a plan view of the entire assembly shown in cross section in Figure 1;

Figure 3 is a rear elevation of a preferred embodiment of the temperature responsive device of this invention;

Figure 4 is a cross sectional view of the said preferred embodiment taken along line IV-IV of Figure 3;

Figure 4A is a cross sectional view taken along IVA-IVA of Figure 4; and

Figure 5 is a schematic view of a circuit suitable for use with the device of this invention.

Referring to Figures 1 and 2 of the drawings, a furnace I is illustrated which has a casing I0 forming the outer wall of a jacket or boiler Illa. Jacket 10a contains a heat absorbing fluid such as water and has an inner wall consisting principally of a lower tubular inner wall section ll, an offset intermediate inner wall section I! and an upper inner wall section it. .A plurality of vertical flue pipes H are concentrically positioned around inner wall sections 12 and I3, and extend from offset wall portion It to an annular flue collar l5 thus connecting the latter to the lower portion of a combustion chamber 29. Flue pipes 14 are sealed around their respective edges to keep boiler Illa fluid tight.

A cover plate I! rests on the top of casing Ill and closes flue collar l5 to which respective portions of the furnace it is bolted or otherwise aflixed. A central opening I! is provided in cover plate ll which opening is in registry with the opening at the top of tubular wall section It. A turret head It closes opening it and has a port defined by surface 25.

20 therein for the admission of combustion air. A further port 2| in head I! is connected to the delivery end of a conveyor conduit 22 within which a feed screw (not illustrated) operates to feed bituminous coal or other fuel in predetermined amounts dependent upon the heat demand and control conditions operative at the time being. A cover 23 tightly closes a corresponding opening in the top of head l9. This cover may be removed to insert and ignite kindling at the commencement of operations if automatic ignition apparatus should not be provided.

Wall section I2 is lined with a refractory material 24 so disposed that the innermost surface 25 thereof is substantially in the form of a frusto conical part substantially forming an upper restricted portion of combustion chamber 29. This refractory 24 thereby increases in lateral thickness in an upward direction and generally inversely to the reduction in internal horizontal cross sectional area of the frusto-conical part Uppermost inner wall section l3 may be lined with a substantially vertical layer of refractory 26 which, at its lowermost edge, meets the uppermost edge of refractory layer 24. The interior space within refractory lining 26 may be regarded as the very top of combustion chamber 29 although the plane of ignition is adapted to remain within surface 25 which confines the upper part of the live fuel bed. a

The upper portion of combustion chamber 29 opens unrestrictedly into its lower portiomsubstantially forming the top of an inverted-T. This lower portion broadens out around a conical grate 3|. Grate 3| is supported in fixed, eccentric position on a rotating base 30. passes between base 30 and the lower section of jacket Illa into an ash pit 35 where it is removed. The lower section of jacket Illa behind wall section I I absorbs heat directly from the lower portion of the fuel bed, thereby aiding in the maintenance of temperatures at least in the lower portion of the fuel bed which discourage any material formation of clinker by the melting or fusion of ash. Additional cooling in the lower portion of combustion chamber 25 may be obtained if desired by the provision of some supplemental combustion air through a line 40 and ash pit 35. Such supplemental combustion air will also mix up and burn combustible which might otherwise tend to be present in the ash and in the gaseous combustion products. Normally, such supplemental combustion air would not be in excess of one-quarter by weight of the downflow primary combustion air supplied to the furnace through port 20.

A metal liner 2'! surrounds the lower portion of combustion chamber 29 in contact with lower wall section II. The inside of liner 2'! is in vertical registry with wall H above it so that fly ash may have substantially no non-vertical surface or land" on which to deposit in the furnace. A series of vertical grooves 28 are disposed around the inside of liner 2'! and cooperate with a plurality of grooves 34 in grate 3| and with its lower vertical edge 32 to break up such small clinker particles as may form. Sufficient clearance is left between the edge of base plate 30 and the interior of liner 21 so that only readily removable ash falls into ash pit 35. A sweep 31 is adjustably afiixed to the underside of base 30 and pushes ash out of ash pit 36 Ash- 4 tom of ash pit. 35 and casing Ill. Suitable 138- glng may be provided for all exposed portions of the furnace.

Base 35 is rigidly mounted on a hollow rotatable shaft 44 having passages therein (not shown) through which cooling water may be circulated if, under the particular circumstances of a given furnace, the temperature in the lower portion of the fuel bed tends to be too high. A hub block 4| is supported by closure 35 and supports a live fuel bed extending from the upper surface of plate 30 to the plane of ignition within refractory surface 25. A bushing 42 is provided at the end of a flxed bracket 43 to assist in the journaling of shaft 114 which is keyed at its upper end to base plate 30 and at its lower end to a worm wheel 45.. A worm gear 46 is driven either continuously or stepwise by appropriate control and driving mechanism (not shown) during the operation of the furnace system. Heat-absorbing fluid is supplied to jacket Illa through a pipe 41 and after circulation therethrough passes out through an outlet pipe 48. Gaseous combustion products including entrained material after passing through the fuel bed filling the lower endof the upperportion of combustion chamber 29 make an abrupt turn and pass laterally and then upwardly through the bed and into the proximate vertical flue pipes i4. Thence. they pass into flue chamber l5 and out through a duct 49 to a stack duct 50. The vertical surfaces of flue pipe I4 and the absence of horizontal ledges around the walls of combustion chamber 29 minimize any possibility of deposition of fly ash or soot.

Referring to Figures 3, 4 and 4A,'the preferred embodiment of the adjustable temperature responsive device of this invention comprises an enclosure 5|. Enclosure 5| includes a circular insulating base 52, rectangular side walls 53 fastened to base 52 by screws 54 and a cover 55 which fits into a corresponding recess 55 in walls 53. A

base plate 51 is fastened to base 52 by screws 58. Base plate 51 extends beyond base 52 and is seated on resilient gaskets 59 so that the entire enclosure including base plate 51 and a tubular casing '60 may as a, unit assembly be fastened by screws or bolts 6| to the wall of stack duct 50 in sealed relation around and extending through an opening 62 therein.

Casing is made of metal or suitable refractory and has side openings 63 therein for communication with the efliuent gases in duct 50. A peripheral rib 64 on casing 60 sets against a depending flange 65 on base plate 51 so that the casing may be welded in that position to base plate 51 or otherwise affixed. In this way the unscrewing of screws 6| will enable the device as a whole to be withdrawn from duct 50 for any repair or replacement that might be required. A perforated transverse interior wall 66 near the forward end of casing 50 forms a support for one end of a thermally responsive wire 51. For such support, a bead 63 is formed on the forward end of wire element 61 preferably from the metal of the wire although it may be made of fused glass or other suitable material; or a loop may be made at the end of the wire which will be held by the edges of the smaller axial opening in interior wall 55. This wire is selected for its known thermal through an opening 38 leading into an ash reexpansion and contraction properties and is not subject to deterioration under normal circumstances of use. For example, such a wire of preselected diameter and length may be made of a nickel and chromium alloy such as "Chromel A which has high resistance to creep and corrosion.

Wire 81 extends through an opening 88 in base 82 where it is welded to the stem 18 of a head post support II. An, integral flange 12 around support engagesa conical spring 18, the base of which is retained in a recess 14 on the rear face of base 52. By the precise selection of the properties and positioning of the associated parts, at normal temperature and pressure, a predetermined tensioning is produced in wire 81, and its linear expansion and contraction properties will be known to a precise degree.

A preselected conventional electrical microswltch I is pivotally mounted on brackets 16 extending upwardly from and integral with the bottom one of side walls 53. A yieldable contact pin 1'! projects from the surface of switch toward support 1| for engagement thereby usually at the instant the responsive temperature limit is reached. Yieldable contact 11 by its respective movements in opposite directions makes and breaks switch I5 either directly or by its con nection with an armature within the switch. An

adjustment screw assembly 18 bearsagainst a thrust boss 18 on the rear surface of switch 15 to hold the switch in a preset position about its pivotal center at brackets 18 and thus move pin 11 in a general axial direction relative the axis of wire 81 even though the exact path of pin I1 is arcuate. A spring 18a respectively fastened to the bottom one of side walls 53 and switch I5 holds boss 18 against assembly 19. An exteriorly threaded adjustment screw 19a is mounted in a tapped opening 88 extending at least part-way through cover 55 a sufllcient distance for any desired adjustment. Screw 19a is internally tapped at 8| through the center thereof extending rearwardly from the inner or forward end thereof. A

vernier screw rod 82 is externally threaded to fit into the tapped portion 8| in screw 19a. The external threads on screw 19a and rod 82 are preferably of the same hand but not of the same gage in terms of threads per linear inch. Rod 82 has a keyway 83 therein extending in an axial direction. A corresponding splineway recess 84 is milled in cover 55 for a key 85 in keyway 83.

Cover 55 is undercut at 88 so that a flanged portion 81 produced thereby may be split at 88 for engagement with a locking screw 89. Locking screw 89 may be used to tighten the divided parts of flange 81 on each side of recess 88 to lock adjustment assembly 19 in position after adjustment screw 19a has been set to obtain the predetermined temperature limit at which the device is to be responsive. If desired a calibrated scale may be placed on the rear side of cover 55 around the stem of screw 19a for ease of adjustment after the device has been calibrated.

-A vernier adjustment results for each manipulation of screw 19a corresponding to the differ-- ence in the linear travel of the respective screws 19a and 82 owing to the difference in gages.

- Thus, assuming both screws have right-hand threads and that adjustment screw 19a has 36 8 11 and support 1|. From this it follows that the particular adjustment just described would raise the temperature limit at which the device would be responsive, assuming switch 18 is the normally closed switch in the circuit to be described.

Conversely, as adjustment screw 18a. is turned out of cover 55, the temperature limit at which the device becomes responsive, for right-hand threads on screws 8| and 82, is progressively lowered. For a normally closed switch 18, contact 11 and support 1| are not in operative contact until the predetermined temperature limit in question is just about reached.

One circuit in which the device of this invention can be used is shown in Figure 5. An alternating current supply is available across lines 88 and 9|. A continuously-running conventional timer 92 is connected to line 9| and periodically conductively bridges the circuit to a line 83 for a brief interval. A relay coil 84 is connected across lines 93 and 98. A motor 95 is connected across a line 98 which in turn is connected to line 88 and a line 91 which leads to One of a pair of contact points 99 capable of being bridged by a relay armature 98. Motor 95 operates the stoker for feeding coal through conveyor conduit 22 by means of a feed screw. Uusualliu motor 85 also turns the air blower or fan (not shown) for supplying combustion air to furnace I through port 28. If desired, a relay may be placed across lines 98 and 91 to operate a clutch between motor 95 and the solid fuel supply in the event that the device of this invention is to be used to control the solid fuel feed only.

turns per inch, while rod 82 has 32 turns per I predetermined extension of wire element 81 will then be required for engagement between contact Whenever timer 92 electrically and conductively connects lines 9| and 93, relay 94 is energized closing switch 98-98 and switch |88|8 the latter switch comprising a pair of contacts I88 and a second relay armature |8|. One contact I88 is connected by a line I82 to one terminal of switch 15. The other terminal of switch I5 is connected by a line I83 to a line |84 which in turn is connected to line 9|. This circuit just enumerated forms a holding circuit for feeding of coal when and until normally closed switch 15 is opened by the thermal expansion of wire 81 at the instant the predetermined temperature limit is reached. This holding circuit extends from line 88 through coil 84, switch |88|8|, line I82, switch 15 and lines |83|84 and 9|.

During this holding even though the timer 92 immediately moves of! contact, breaking the electical connection between lines 9| and 93, switch 9899 remains closed, allowing motor to continue feeding fuel only so long as switch 15 remains closed. Thus, instead of relying on a predetermined timer-on period for the feeding of coal to the combustion furnace to maintain combustion during hold-fire operation, by the device of this invention all that the timer 92 does is to initiate an on" period leaving it to the quick and precise acting switch 15 to terminate that fuel feed on period when the stack temperature climbs to the desired maximum limit. At the instant of reaching that limit, support opens switch 15 and the coal feed at least is stopped for all practical purposes since the momentary pulses occasioned by the rotation of timer 92 will not be suflicient to feed such coal. In this way, a sensitive correction of deteriorating fuel bed thinning is reliably obtained without any delay.

Although this invention has been described using right-hand threads for the Vernier adjust- 7 ment, it is apparent that left-hand threads of different gages may also be used.v Further, the circuit in Figure 5, illustrated by one" possible circuit since it is within the skill of those in the art to use a microswitch which is normally open and to combine it with a circuit to permit the microswitch to disconnect the motor despite the continuance of any actual timer-on" period. Moreover, while the maximum stack temperature is controlling in the embodiment described herein, the device can also be used to avoid falling below a minimum stack temperature. This could be done by initiating the further feeding of fuel and air, for example, if the stack temperature should reach a predetermined low limit. Still other variations and uses for devices embodying the advance of this invention may be made by those skilled in the art within the spirit of this invention and the scope of the appended claims.

I claim:

1. An adjustable temperature responsive device for combustion furnaces, comprising in combination, an enclosure for said device adapted to be attached to the duct for eiiiuent gases from such a combustion furnace, a wire resistant to deteriorationat temperatures encountered within said duct, a support for one end of said wire within said duct, a head post support for the other end of said wire outside said duct, said duct having an opening for the passage of said wire, a spring engaging said head post support to maintain such wire under tension, an electrical switch pivotally mounted in said enclosure and adjacent said head post support, a yieidable armature for said switch engaging said head post support, a threaded adjustment screw mounted in said enclosure, said screw being internally tapped along the axis thereof inwardly from the inner end thereof, a threaded thrust rod threadably engaging said internal, tapped portion of said screw, said threads on said screw and said rod being of the same hand but differing gauge, and a key to prevent said rod from rotating, whereby a vernier adjustment of the armature of said switch relative said head post support may be obtained in changing the predetermined temperature limit to which said device is responsive in effecting a corrective condition in said furnace.

v2. An adjustable temperature responsive device for combustion furnaces, comprising in combination, a wire thermally responsive to the temperature of gases passing through a duct connected to such a combustion furnace, a support for mounting the outer end of said wire in fixed position within said duet so as to expose said wire to said eiiiuent g s, an opening through said duct to the outsid J thereof in coaxial relation to said wire, a headpost assembly connected to the inner end of said wire, a spring to maintain said wire under tension, means for centering said spring relative to said opening, a microswitch pivotaliy connected adjacent said headpost, a yieidable contact in such switch adapted to be abutted by said headpost upon the occurrence of a predetermined increase in the length of said wire, a vernier adjustment screw assembly engaging said switch to adiustably limit the position of said yieidable contact relative to said headpost, and a spring to maintain said engagement between said switch and said adjustment screw assembly.

. WILLARD J. HA'I'I'ON.

nsrsamvcss crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS

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