US3023716A - Pressure fired furnace - Google Patents

Description

March 6, 1962 Filed Jan. 22, 1957 H. H. REISMAN PRESSURE FIRED FURNACE 2 Sheets-Sheet 1 #1 vane/ m IN VEN TOR. HOWARD H.REISMAN ATTORNEYS I Mairch 6, 1962 H. H. REISMAN PRESSURE FIRED FURNACE Filed Jan. 22. 1957 2 Sheets-Sheet 2 INVENTOR. HOWARD H.REl$MAN ATTORNEYS United States Patent Ollice 3,023,716 Patented Mar. 6, 1962 3,023,716 PRESSURE FIRED FURNACE Howard H. Reisman, Rock Island, Ill. Deere & Company, Moline, Ill.) Filed Jan. 22, 1957, Ser. No. 635,376 7 Claims. (Cl. 110-72) This invention relates to a solid fuel type of furnace, and more particularly relates to a type of furnace structure which will permit pressure firing of stoker fed furnaces.

In many of the present day solid fuel or coal burning types of furnaces used in conjunction with large power plants, the conventional method-of supplying the coal to the furnace is by means of a stoker which feeds the coil to a grate inside of the furnace walls. Air required to burn this coal is normally supplied by a forced draft fan which feeds the air under the grate from where it moves upwardly through the coals. In order to prevent the furnace gases from leaking out the various openings around the stoker, it has been conventional in the past to provide a large smoke stack or chimney which produces a vacuum within the furnace and which tends to pull the gases through the circuit and out through the chimney. With the demand of increased elficiency within the boiler assembly making it necessary to install super heaters, economizers, and complicated networks of vents, and also with the demand for decreased air pollution, making it necessary to install various types of dust collectors and filters in order to clean the gases prior to their being discharged into the atmosphere, it has been found that it is impractical to build a chimney of such great height to draw the exhaust gases through the entire circuit. Consequently, in order to reduce the height of the chimney, it has been found necessary to provide an induced draft fan at the discharge end or opening of the furnace which will draw the exhaust gases from the furnace and deposit them in the chimney. Obviously, this also has prevented smoke from leaking around the stoker connections inasmuch as the purpose of the induced fan is to create a vacuum within the furnace.

The great disadvantages of an induced fan system lies in the primary cost of installation, and in the overall amount of power required to drive the fan. The initial cost for the normal type of power plant will amount to several thousand dollars, and the overall power required to drive the induced fans will in many instances amount to as high as 4% of the overall capacity of the unit. Also considered must be the overall cost of maintenance and repair. Therefore, the high overall cost of providing induced draft type furnace has made it desirable to operate the entire furnace and boiler under pressure so that the exhaust gases will move out through the chimney. This is normally done by providing a sealed furnace and by increasing the capacity of the forced draft fan so as to create pressure within the walls of the furnace sufiicient to drive the hot gases up through the boiler tubes and the other cooperating portions of the boiler to eventually be discharged from the furnace at the mouth of the smoke stack or chimney where they will be discharged into the atmosphere. This type of pressure fired furnace is not unusual for small heating boilers that are gas or oil fired or large utility boilers that use pulverized fuel or gas and OH fired. However, this latter type of furnace has not been practical with the solid fuel or coal burning units since it has as yet been impossible to provide connections between the stokers and the furnace which do not permit leakage externally from the furnace into the room containing the units. Also, since there is necessarily a requirement of removing the ash remains from the furnace, the pressurized type of furnace operated by solid fuel would create a problem of maintaining the pressure within the furnace while the ashes are being removed.

It is therefore the primary object of this invention to provide a furnace type structure which may use solid type fuels and which may incorporate a forced draft fan providing a pressure build up within the furnace walls.

It is the object and purpose of this invention to make a pressure type solid fuel burning furnace practical by enclosing the stoker in a pressurized room externally of the furnace walls which will make gases or air flow from the pressurized room or chamber into the furnace, thereby preventing external leakage of the furnace gases.

it is another object of this invention to provide in the furnace structure a fuel container or bunker which feeds directly into the stoker through a passage having means which positively feeds the fuel into the stoker but which prevents leakage of gases through the passage into the container or bunker.

It is still another object of this invention to provide a pair of interconnected hopper compartments for receiving the ashes from the furnace grate and which may be separately enclosed to permit removal of ashes from one of the compartments while the other is being filled thus at all times retaining the pressure within the furnace walls.

Other objects and advantages of the invention will become apparent to those skilled in the art as the nature of the invention is better understood from the following detailed description as shown in the accompanying drawing.

FIG. 1 is a schematic view of a boiler power plant which incorporates the features of the present invention.

PEG. 2 is a sectional view, also relatively schematic, showing an enlarged partial side view of the fuel burning area of the boiler, its associated stoker and stoker compartments, and the ash hoppers.

it should here be noted that while the specific operation of the pressure red type of furnace herein to be described is shown to operate in conjunction with a boiler unit, it should be recognized that this type of furnace could be used in conjunction with an incinerator, glass or brick making unit, etc., or any type of unit where such a furnace would be practical. The purpose of providing a boiler in this specific instance is for illustration only.

in the type of power plant shown in FIG. 1 there is provided Wall structure 10 forming a combustion chamber 11. The wall structure it? is normally made of fire brick, although any other conventional insulation material would be satisfactory. At the base of the fire chamber is a coal grate 12 which is also of conventional nature eing formed of a continuous flexible feeding element having an upper coal-receiving run 13 and a lower run or surface 12. The grate is mounted over two spaced apart sprockets 15, 16, one at least of which is driven to move the upper run or surface 13 so that the ashes resulting from combustion may be dropped over the end of the grate. Draft means in the form of a forced draft fan 26 and duct 19 provides for air to be driven into a plenum chamber 21. The pressure in the plenum chamber 21 is sufiicient to cause air to move through the grate 12 as indicated by the arrows 22 and following combustion to biuld a pressure within the combustion chamber 11. From the grate 12 the air and gases and other prodnets of combustion will move upwardly as indicated by the arrow 23 through tubes 27 where they will be vented downwardly, as indicated by the arrow 24, by the overhead 25 of the combustion chamber. Upright vents 26 direct the air and gases and products of combustion first downwardly then upwardly through more boiler tubes 27a and then downwardly again, passing finally in an upward flow through an economizer area 28. From the economizer area 28 the exhaust fluid matter and gases move into an air cleaner 29 and then through a discharge opening at the base of the smoke stack or chimney. The paths of the gases are indicated by the arrows 31. 32, 33, and 34. Details of the boiler, economizer, air cleaner, etc., may be treated as conventional, and are consequently omitted. However, it should be noted that the pressure created by the draft fan 20 is sufficient to create a pressure in the plenum chamber 21 and combustion chamber 11 so as to drive the gases through all of the various elements of the circuit as above described.

Positioned to receive the ashes from the grate 12 are a pair of ash hoppers 40 and 41 respectively. The ash hopper 40 receives the ashes directly from the end of the upper run 13 as the ashes are driven over the end of the grate at the sprocket 16. The second hopper 41 is interconnected to the first hopper 48 by means of an opening in a wall common to both of the hoppers. A closure member in the form of a sliding door 43 is provided to open or close the opening in the wall 42. The sliding door 43 is guided by guides 44, 45 fixed to the wall 42 and to a lower wall 46 of the hopper 40, respectively. The hopper 41 is provided with a discharge opening 47. The opening 47 may be closed by a damper 48 which in turn may be operated by the hand lever 49.

As may be seen in FIG. 2, ashes 50 passing from the grate 12 will fall and be trapped in the first hopper or compartment 40. With the damper 48 closing the dis- 7 charge opening 47, the door 43 may then be opened to permit the ashes to pass from the first compartment 40 into the second compartment 41. As the ashes pass into the compartment 41 the damper 48 will seal off both chambers 40, 41 so that pressure built up within the furnace chamber cannot extend through the opening 47. Upon the compartment 41 being filled the door 43 will then be closed again sealing 011 the first compartment and the second compartment 41 may then be emptied. Thus, at no time will the ash hoppers permit a substantial amount of air and gas .to leak out of the ash hoppers. Also, the ashes may be removed without first shutting down the entire unit.

The coal is stored in a bunker 55 from where it is gravity fed through a scale 56, through a duct 57, and eventually into a coal stoker indicated in its entirety as reference numeral 58. In the duct 57 is a positive means for feeding fuel into a hopper 59 of the stocker 58, the positive feed means being in the form of a star wheel 60 which also serves as a seal to prevent gases and air from passing upwardly through the passage 57 and into the bunker 55. The star wheel 60 may be driven in any conventional manner and may be automatically operated to constantly maintain coal in the hopper 59.

Other than the hopper 59 the stocker 58 comprises a horizontal passage 61 having its outer end under the hopper portion 59 for receiving coal therefrom and its inner end opening to the combustion chamber 11. In the horizontal passage 61 is a rotating member 62 including therein radially extending arms 63. The member 62 rotates in the direction of the arrow 64 and operates to contact the coal gravitating from the hopper 59 and to throw the coal into the chamber 11 in th manner shown in FIG. 2 at 65 where it spreads or falls on the upper surface of the grate 62, To those familiar with the art, this type of stoker is generally referred to as a spreader type stoker. As the upper run of the grate moves toward the mouth of the stoker 58 there will be a higher build up of coal and ashes. From the end of the grate 12, the ashes will gravitate into the hopper 40 as previously explained. The stocker 58 is composed of durable wall members 66 sufficiently strong and heat resistant to contain the coal and to withstand the temperatures of the furnace.

As may be noted in FIG. 2, the rotating member 62 does not close the mouth of the passage 61 and consequently unless otherwise restricted gas and products of combustion from inside the furnace might pass through the stoker 58 and hopper 59 into the room containing the power plant. Also, the mean connecting the stoker to the wall structure 19a, asindicated at 67, 68, is pervious to permit flow of gases between inside and outside of the furnace chamber 11.

Surrounding the hopper 58 is a pressurizzed compartment or enclosure 69 composed of upright wall structure 70 enclosing the stoker 58 from three sides, the fourth side being closed by the wall structure 10aof the furnace, and an overhead wall 71. The walls 70 are supported on a floor 72, and consequently the enclosure is sealed from the bottom by the floor. An opening is provided in the overhead 71 through which the lower end of the duct 57 may pass. An angle iron 73 surrounds the duct 57 and connects the duct to the overhead 71. One of the side walls '70 has an entrance 74 through which a human may enter for maintenance and repair to the stoker and its surrounding mechanism. A door '75 is provided to close the opening 74 and is hinged, as at 76, to the side wall 70. As may be seen from FIGS. 1 and 2, the enclosure completely surrounds'the hopper 58 and while possibly not sealed against gas leakage must be tight enough to maintain a pressure therein.

An air duct extends from the plenum chamber 21 into the enclosure 69. A pressure differential control mechanism, indicated as at '81 and mounted on the outer surface of the wall 78 has pressure gauge inlets 82, 83 extending into the fuel burning chamber 11 and the pressurized compartment 69, respectively. The control mechanism 81 operates through a suitable connection 84 and a damper mounted in the air duct 80'. The control mechanism is set whereby a pressure differential is maintained between the chamber 11 and the enclosure 69, the individual pressure in the chamber and enclosure being measured by the pressure gauges 82 and 83 respectively and upon the pressure within the compartment 69 decreasing to a set limit above the pressure within the fuel burning chamber 11 the control mechanism will operate to open the damper 85 to increase pressure Within the compartment 69. The pressure gauge inlets 82, 83 and the pressure control mechanism 81, while shown in representative form may be of any type commercially sold on the market. Details have purposely been omitted to emphasize that such pressure control mechanism is old and well known within the arts, there being no intention to include them per se as the invention.

A second compartment is provided adjacent to the opening 74 and door 75 of the compartment 69. The compartment 90 is provided with upright wall structure 91 and an overhead 92 and again the floor 72 encloses the compartment from the bottom. The upright wall structure 91 is provided with an opening 93. The opening 93 is provided with a door 94 hinged, as at 95, to the wall structure 91.

The purpose of the second compartment 99 is to provide an entrance in which a repair or maintenance man may enter prior to entering the compartment 69. The door 75 interconnecting the compartments 69 and 91 may be provided with some leakage, or a duct leading oil? of the air duct '80 may be fed directly into the compartment 99. In either case means are provided for a pressure build up within the compartment 90 substantially equal to the pressure built up in the enclosure 69 whereby when the door 75 is opened there will be a negligible pressure drop within the chamber or compartment 69.

In operation the compartment 69 offers the following feature. As mentioned previously the forced draft fan 20 will provide a pressure build up within the chamber 11 which unless otherwise restricted will pass through the small opening-s around the stoker 58, and due to the type of stoker will pass through the coal in the hopper externally of the fuel burning chamber 11. By providing a pressure build up within the compartment 69 greater than the pressure built up within the chamber 11 air or gases will pass from the compartment 69 into the chamber 11 and will thereby prevent noxious gases and/ or smoke from leaving the chamber 11. In this manner proper maintenance, repair and inspection may be made on the hopper 58 and its surrounding mechanism within the compartment 69 without endangering the workmen and also without necessitating the shutting down of the entire unit. It should be noted that by use of the double hoppers 40 and 41 for collecting the ashes and removing them from the unit, there will at no time need to be a shut down in the normal operation of the unit.

Unquestionably modifications of the details of the struc ture herein disclosed will occur to those skilled in the art. While the invention has dealt primarily and specifically with a pressurized compartment around the coal stoker any type of auxiliary mechanism required for operation of the furnace will undoubtedly find its use in a pressurized compartment to prevent leaks from the furnace. Therefore, while specific details of the present form of the invention have been shown for the purpose of clearly and concisely illustrating the principles of the invention, there is no intention to so limit the invention to the exact details but rather to the broad general principles described and taught.

What is claimed is:

1. A solid fuel-burning stoker-fed furnace assembly comprising: wall structure forming an enclosed fuel burning chamber having an opening therein for discharging fluid exhaust matter resulting from combustion; a grate in the chamber; a forced draft fan producing internal pressures in the chamber greater than the external pressure on the wall structure and operative to drive the exhaust matter through the opening; a spreader type stoker opening into the chamber and adapted to throw particles of the fuel over the grate; means connecting the stoker to the wall structure, said means and said stoker being pervious to permit unless otherwise restricted passage of gases and/or products of combustion; means forming a solid fuel storage space and including a fuel feeding passage to the stoker; a positive feeding element in the passage adapted to pass fuel into the stoker while preventing passage of gases and/ or products of combustion through the passage into the fuel storage space; a sealed enclosure surrounding the stoker and the means connecting the stoker to the wall structure; pressure means discharging into the sealed enclosure for maintaining internal pressure in the sealed enclosure; and pressure differential control means for operating the pressure means, said control means being operative to maintain a higher pressure in the sealed enclosure than in said fuel burning chamber to prevent the passage of said gases and products of combustion into the sealed enclosure.

2. A solid fuel-burning stoker-fed furnace assembly comprising: wall structure forming an enclosed fuel burning chamber having an opening therein for discharging fluid exhaust matter resulting from combustion; a grate in the chamber; pressure inducing means producing internal pressures in the chamber greater than the external pressure on the wall structure and operative to drive the exhaust matter through the opening; stoker means opening into the chamber and adapted to feed particles of the fuel on the grate, said stoker means being pervious to permit unless otherwise restricted passage of gases and products of combustion; an enclosure surrounding the stoker means; pressure means discharging into the enc1o sure for maintaining internal pressure in the enclosure; and pressure differential control means for operating the pressure means, said control means being operative to maintain a higher pressure in the enclosure than in said fuel burning chamber to prevent the passage of said gases and products of combustion into the enclosure.

3. The invention defined in claim 2 in which said pressure inducing means and said pressure means producing internal pressures in the chamber and enclosure respectively are created by a single forced draft fan having passages leading to the chamber and enclosure.

4. The invention defined in claim 2 further characterized by a second enclosure adjacent to the enclosure surrounding the stoker means and having a common Wall therewith; said common wall having an opening therein permitting egress and regress between the enclosures; a first door structure for closing said opening; a second door structure for said second enclosure spaced from the first door structure and operative to permit egress and regress between outside and inside of the second enclosure.

5. The invention defined in claim 4 further characterized by means providing substantially equal internal pressure within the enclosures.

6. The invention defined in claim 2 further characterized by first and second ash collecting hoppers interconnected through an opening for permitting ashes to pass from the first to the second hopper, said first hopper being positioned to receive ashes directly from the grate, said second hopper having a discharge opening at its base for eliminating ashes from the furnace; and first and second closure members adjustable to open or close said interconnecting opening and said discharge opening respectively.

7. The invention defined in claim 2 further characterized by structure defining a second enclosure adjacent to and opening into the pressurized enclosure surrounding the stoker; door structure aflfording egress and regress between the enclosures and inside and outside said second enclosure; and means effecting substantially equal pressure between the enclosures.

References Cited in the file of this patent UNITED STATES PATENTS 1,405,029 Stehmann Ian. 31, 1922 2,251,014 Firshing July 29, 1941 2,592,701 Jackson Apr. 15, 1952 2,730,997 Birkner Jan. 17, 1956 2,864,344 Artsay Dec. 16, 1958 FOREIGN PATENTS 444,230 Gre t Bfi s a M r- 6

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