US2817498A

US2817498A - Air heater

Info

Publication number: US2817498A
Application number: US317744A
Authority: US
Inventors: Earle C Miller
Original assignee: Riley Power Inc
Current assignee: Riley Power Inc
Priority date: 1952-10-30
Filing date: 1952-10-30
Publication date: 1957-12-24
Anticipated expiration: 1974-12-24

Description

Dec. 24, 1957 E. c. MILLER 2,817,498

AIR HEATER Filed Oct. 30. 1952 INVENTOR EARL; C. MILLER ATTORNEY nited States Patent AIR HEATER Earle C. Miller, Worcester, Mass, assignor to Riley Stoker Clprporation, Worcester, Mass., a corporation of Massac usetts Application October 30, 1952, Serial No. 317,744

2 Claims. (Cl. 257224) This invention relates generally to air heaters and more particularly to a heater apparatus for supplying air at a plurality of temperatures.

t is common practice in the steam generating art to make use of combustion gases to heat the incoming air that is to be used for combustion and like purposes. Usually combustion gases are used which have already passed through the boiler and which are at a relatively low temperature. in most furnaces associated with steam generating equipment, it is necessary and desirable to have air available at a number of different temperatures. For example, in the operation of a spreader stoker with a traveling grate, air at one temperature is needed for introduction under the grate and for passage upwardly therethrough and air at another temperature is needed for overfire jets to promote complete combustion and to prevent smoking. Apparatus for providing for multitemperature air have in the past been complicated and expensive and, furthermore, have not permitted a wide range in differences in air temperature. The present invention obviates these disadvantages in a novel manner.

It is therefore an outstanding object of the present invention to provide an air heater apparatus which will provide air at different temperatures for use in a furnace.

It is another object of the invention to provide a novel heat-exchange means for providing for heating of air to a plurality of widely divergent temperatures.

Another object of this invention is the provision of an air heater of simple and inexpensive construction.

Still another object of the instant invention is the provision of an air heater particularly adapted to providing heated air for a furnace having a spreader stoker with a traveling grate, the air to be used under the grate and in overfire jets.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

The single sectional view shows a preferred embodiment of the invention.

Referring to the drawing, an air heater 10, constructed according to the principles of the invention, is shown in use with a steam generating unit 11, having a furnace 12 and a boiler 13. The furnace 12 has a forward wall 14, a rear wall 15, side Walls 16, and a top wall 17 defining a combustion chamber 1%. At the lower portion of the furnace 12 and forming a bottom for the combustion chamber is a traveling grate 19 of the usual type having a plenum chamber 24 on its under side and provided with partitions 21 to permit control of air flow to various certain sections of the grate. Mounted on the outer side of the forward wall 14 is a spreader stoker 22 of the type having a rotary distributor 23; an opening 24 in the 2,817,498 Patented Dec. 24, 1957 forward wall is provided to permit fuel to be thrown into the furnace and onto the grate 19 by the stoker. The rear wall 15 is formed to provide an arch 25 overlying one end of the grate and at the nose of the arch is provided a horizontal row of overfire air nozzles 26. Another such row of nozzles 27 is provided at a higher position in the rear wall.

The boiler 13 is situated at the upper rear of the furnace and consists of an upper steam-and-water drum 28 and a lower mud drum 29 joined by downcomer tubes 30 and steaming tube 31. A refractory wall 32 extends upwardly from the mud drum 29 and constitutes an extension of the rear Wall 15 of the furnace. The upper edge of the Wall 32, the rear portion of the top wall 17, and the side walls 18 define a gas pass 33 at the upper, rear portion of the furnace. A baffle 34 hangs from the steam-and-Water drum 28 between the downcomer tubes 30 and the steaming tubes 31 and extends to within a substantial distance of the mud drum 29. Directly behind the downcomer tubes 3% is a back wall 35 which culminates at its lower portion in a fly-ash hopper 36. The back wall 35 and the battle 34 define a back gas pass 37 which merges with a large horizontal gas duct 38. The duct 38 is connected with the breeching 39 leading to the stack, not shown, by a bundle 40 of vertical gas tubes which are part of the air heater 10. Parallel to the bundle 4t and spaced rearwardly therefrom is a wall 41, the top portion of which is connected to the lower wall 45 of the duct 38 and the lower portion of which is attached to the top wall of an air entrance duct 42 which is served by a fan 4-3. A forward wall 44 resides forwardly of the bundle 4d and is spaced therefrom. The outer envelope of the air heater 10 is generally defined, therefore, by the forward wall 44, the rear wall 41, the lower wall 45 of the duct 38, the lower wall 46 of the duct 42, and side walls 47, only one of which is seen in the drawing. The upper wall 48 of the duct 42 extends horizontally toward the forward wall 44 and ends at a position somewhat spaced therefrom. A first baffle 49 extends horizontally from the wall 44 toward the rear wall 41 and ends at a position substantially spaced from the said rear wall; this baffle resides above and spaced from the upper wall 48 of the duct 42. A second baffle 50 extends from the rear wall 41 toward the forward wall 44 and ends at a position substantially spaced therefrom; this baffle is above and spaced from the baffle 49. A third baffle 51 extends rearwardly from the top edge of the forward wall 44, which edge is spaced substantially from the lower wall 45 of the duct 38. The baffle 51 extends horizontally to within a substantial distance of the rear wall 41.

Midway between the bafiles 49 and 51 and aligned with the baffle 50 is an opening 52 in the forward wall and this opening is provided with a movable shutter or damper 53 which is adjustable from the outside of the apparatus. The damper pivots on a horizontal axis which is medial of the opening 52. A similar opening 54 and damper 55 is provided midway between the baflie 49 and the lower wall 46 of the duct 42, the opening being centered somewhat above the plane of the upper wall 48 of the duct 42. A wall 56 is situated parallel to and substantially spaced from the forward wall 44, the wall 56 serving, with the forward Wall 44 and the side walls 47, to define an outer mixing chamber 57. The upper portion of the wall 56 and the upper edge of the forward wall 44 define an opening 58 into the mixing chamber 57 and a damper 59 resides therein. The bottom of the mixing chamber 57, defined by the lower edges of the

walls

44 and 56, is connected to one end of a hot air duct 60, the other end of which is connected to the plenum chamber 20 of the traveling grate 19. The upper end of the air heater 1!) has an 24 in the forward Wall of the furnace by the rotating distributor 23. The coal passes through the air in a pattern determined by the characteristics of the Stoker and the fines are burned in suspension, while the heavier portions of the fuel fall onto the traveling grate 19 where they burn under the influence of air passing upwardly through the grate from the plenum chamber 20. The hot products of combustion pass upwardly through the combustion chamber 18, heating water in the water wall tubes and in certain portions of the steaming tubes by radiation. The gases pass upwardly and pass rearwardly through the pass 33. From there they pass downwardly between the wall 32. and the baffle 34 heating the steaming tubes 31 by convection. The gases are reversed at the lower end of the baiile 34 and proceed upwardly in the back pass 37, but not before depositing a certain amount of fly-ash and cinder in the hopper 36. After passing upwardly through the back pass 37 and heating the water in the downcomer tubes 30 by convection, the gases enter the duct 38 and pass horizontally therealong. From the duct 33 the gases enter the upper ends of the tubes comprising the bundle 40, pass downwardly therethrough, and leave at the lower ends into the breeching 39, from whence they eventually pass into the stack. While the gases reside in the tube bundle 48 they are in heat exchange relation to any air which may reside extcrnally of the tube bundle. Air enters the air heater through the inlet duct 42 under the influence of the fan 4-3. if the dampers '5, 53, and 59 are closed, the air will leave the duct 42, after having passed through the portion of the tube bundle which resides in the duct, and makes a. reverse turn around the forward edge of the upper wall lb of the duct. Air then passes horizonta ly between the upper wall 48 and the baffle 49 and then makes an upwardly reverse turn around the free rearward edge of the baffie 49. It then passes horizontally between the baffle 49 and the baffle 50 before making a reverse turn around the free forward edge of the baflle fill. The air then passes horizontally between the baffles 5 and 51 and then makes a reverse turn around the free rearward edge of the baffie 51 and enters the horizontal passage between the bathe 51 and the lower wall 45 of the duct It then leaves the air heater through the opening 6i and flows through the duct 62 to the chambers 63 and 64- for distribution to the nozzles 27 and 26. Air thus delivered to the nozzles 26 and 27 is projected outwardly into the furnace to promote turbulence and more complete combustion, in the wellknown manner. Now, if any of the

dampers

53, 55, and 59 are open, some of the air will be tapped off into the mixing chamber 57, from whence it will flow into the duct Hill and through that duct into the plenum charm ber 2t). Air delivered to the plenum chamber is distributed by the partitions 21 to various portions of the grate and flows upwardly through the grate in the wellknown manner to support combustion.

it can be seen, then, that adjustment of the

dampers

53, 55, and 59 will bring about any desirable air temperature for delivery to the overfire jets and the grate. Any air which flows through the air heater it) without being tapped off into the mixing chamber 57 must necessarily pass outwardly into the conduit 62; such air has passed over all the tube surface in the bundle at and has not only been in contact with the heated surface of the tubes for the greatest length of time possible, but has also been in heat exchange relation to the hottest gases as they pass through the tubes at the upper portion of the bundle. If it is desired to have very hot air enter the chamber 57 for use under the grate, it is only necessary to close all the dampers but damper 5'9, whereupon the air entering the chamber will be at the same temperature as the air entering the duct 62 for use in the overfire jets. With such operation, the two air streams will be at the same high temperature. If relatively cold air is desired under the grate, it is only necessary to close all the dampers except damper 55, in which case the air tapped off rate the chamber 57 will have passed only over the small part of the tube bundle which resides in the duct 42. During this manner of operation of the apparatus, the temperature difference between the jet air and tin grate air is very great. In this connection it is to be noted that when air is tapped off early in the cycle of heating, there is a smaller flow of air through the remainder of the air heater, so that the air velocities are less and the transfer of heat is greater; the air going to the jet will thus be considerably hotter than when all the air passes through all the heater. It is possible, by judicious use of the dampers, to regulate the manner in which the flow of air originating in the fan 43 is di vided between the jets and the grate; furthermore, it is possible to regulate the temperatures of the gases which pass to these portions of the furnace.

While in accordance with the provisions of the statutes 1 have illustrated and described herein the best form of my invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

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

1. Air heater apparatus for use with a steam generating unit, comprising a casing having a front wall, a rear wall, side walls, and end walls, a bundle of parallel tubes extending from one end wall to the other and arranged for the passage therethrough of hot products of combustion, an inlet duct for supplying unheated air to one e1:- treme end of the heater, a first outle duct opening into the said front wall adjacent the said one end wall for supplying heated air to one portion of the said unit, a damper controlling the flow of gas through the front wall into the first outlet duct, a second outlet duct opening into the said casing adjacent the other said end wall for supply ing heated air to another portion of the unit after the air has passed over the entire surface of the tubes in the bundle, spaced battles extending partially across the casing alternately from the front and rear walls transversely of the bundle for causing the air to flow back and forth across the bundle on its way from the inlet duct to the outlet ducts, a bypass duct leading from the first outlet duct to the second outlet duct, a damper controlling the flow of gas between the second outlet duct and the bypass duct, the said front wall constituting one wall of the byp ss duct, an opening in the said front wall into the bypass duct intermediate of the end walls, and a damper controlling the flow of air through the said opening.

2. Air heater apparatus for use with a steam generating unit having a traveling grate, a back wall, a rear wall, and overfire air nozzles extending through said rear wall, comprising a vertically-elongated casing having a front wall adapted to be located adjacent the rear wall of the unit, a rear wall, side walls and end walls, a bundle of parallel tubes extending vertically from the upper end wall to the lower end wall and arranged for the passage downwardly therethrough of hot products of combustion, an inlet duct for supplying unheated air through the lower end of the heater, a first outlet duct opening into the said front wall adjacent the said lower end wall for supplying heated air to the traveling grate for passage upwardly therethrough, a damper controlling the flow of gas through the front wall into the first outlet duct, a second outlet duct opening into said casing adjacent the other said end wall for supplying heated air to the overfire air nozzles after the air has passed over the entire surface of the tubes of the bundle, spaced baflies extending partially across the casing alternately from the front and the rear walls transversely of the bundle for causing the air to flow back and forth across the bundle on its way upwardly from the inlet duct to the outlet ducts, a by-pass d-uct leading upwardly from the first outlet duct to the second outlet duct between the front wall of the heater and said back wall of the unit, a damper controlling 6 the flow of gas between the second outlet duct and the by-pass duct, the said front wall constituting one wall of the by-pass duct, an opening in the said front wall into the by-pass duct intermediate of the end walls, and a damper controlling the flow of air through the said opening.

References Cited in the file of this patent UNITED STATES PATENTS 1,812,458 Turkus June 30, 1931 2,511,647 Marshall June 13, 1950 2,578,783 Cruise Dec. 18, 1951