US2886294A - Air heater and dust collector - Google Patents

Description

May 12, 1959 e. F. DAVEY 4 AIR HEATER AND DUST COLLECTOR Filed Oct. 26, 1955' I '2 Sheets-Sheet 1 l5 :1 I 4/10 1 20% I o I i v I H l4- I9 I r I l6 3 5m uvmvrox.

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AIR HEATER AND DUST COLLECTOR Filed Oct. 26, 1955 2 Sheets-Sheet 2 INVENTOR. GERALD F. DHVEY United States Patent AIR HEATER AND DUST COLLECTOR Gerald F. Davey, Holden, Mass., assignor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Application October 26, 1955, Serial No. 542,851 4 Claims. (Cl. 257-1) This invention relates to an air heater and dust collector and, more particularly, to apparatus arranged to heat combustion air entering a steam generating unit by bringing the air into heat exchange relationship with flue gases leaving the unit and to remove flyash and dust from the flue gases.

It is common practicein the art of generating steam for power purposes to increase the efficiency of the steam generating unit by heating incoming combustion air by passing it in heat exchange relationship to the outgoing flue gases, whereby the flue gas temperature is lowered and heat loss up the stack is reduced at the same time that the combustion air is preheated to a desirable amount. Although there are many types of heat exchange apparatus in which this process may take place, the most desirable from the standpoint of initial cost and of maintenance is the so-called tubular air heater in which the flue gases pass internally of tubes, while the incoming combustion air passes over the outer surfaces of the tubes. However, one drawback of the tubular air heater is that it is subject to corrosion. This corrosion generally takes place at the portion thereof in which the coldest combustion air comes in heat exchange relationship to the coldest flue gases. It is in this part of the air heater that the conditions of temperature exist which promote the condensation of certain corrosive agents in the flue gas, the most prominent of these being sulphuric acid. It has been noted, also, that in the portions of the air heater which are subject to corrosion, there are substantial deposits of flyash. There is considerable reason to believe that the deposits of flyash act as agents, to absorb the condensed sulphuric acid in the manner of a blotter, and thus hold the corrosive agent in contact with the tube walls; otherwise, the corrosive acids would be re-evaporated by the scrubbing action of the gases passing through the tubes and no corrosion, or little corrosion, would take place. Attempts in the past to reduce this flyash accumulation, however, have had little effect, and there is a great need in the field for a means of discouraging the deposits of flyash on the tube walls. Apparatus for removing dust from the flue gas and depositing it in a hopper or the like have been complicated and expensive. The present invention satisfied this need in a novel manner.

It is, therefore, an outstanding object of this invention to provide an air heater wherein deposits of flyash and the like on the heat exchange surfaces are maintained at a minimum, while the flyash is taken out of the flue gas in a more desirable location.

It is another object of the invention to provide a tubular air heater having means for scrubbing the internal walls of the tubes to assure optimum heat exchange between flue gases flowing within the tubes and combustion air flowing over the exterior surfaces of the tubes.

A still further object of the present invention is the provision of a means for reducing flyash accumulation within the tubes of a tubular air heater, and increasing it in a more desirable location which means is inexpensive to manufacture, requires a minimum of maintenance, and

2,886,294 Patented May 12, 1959 which may be applied to existing air heaters with a mini mum of difficulty.

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 specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to certain of its structural forms as illustrated by the accompanying drawings in which:

Figure 1 is a general view of a steam generating unit embodying the principles of the present invention,

Figure 2 is an enlarged view of a portion of the apparatus shown in Figure 1,

Figure 3 is a sectional view of an air heater and dust collector constructed accordingto a modified version of the invention, and

Figure 4 is a sectional view of an air heater showing a still further modification of the invention.

Referring first to Figure 1, wherein is shown the general features of the invention, a steam generating unit, indicated generally by the reference numeral 10, is shown as comprising a furnace 11 and a boiler 13 of the usual type, the furnace having burners 12 mounted in the front wall. An air heater and dust collector 14 is mounted to receive flue gases originating in the furnace 11 and passing through the boiler 13. The air heater is mounted rearwardly of the steam generating unit, has a gas entrance chamber 15 mounted in communication with the back pass of the boiler 13 and has an exit chamber 16 which is connected to the stock not shown, by means of a breeching 17. A forced draft fan 18 is connected to the air heater to introduce air into the system. The air heater 14 is of the tubular type and consists generally of a lower tube sheet 19 and an upper tube sheet 20 joined by tubes 21. As is best shown in Figure 2, a wire 22 passes centrally through each of the tubes 21. The upper end of the wire passes through an upper wall 23 of the air heater and is held in a fixed position thereby. As is evident in the drawing, the upper end of the wire is threaded and a nut 24 is passed thereover, there being a washer 25 inserted between the nut 24 and the wall 23. Because of the fact that the tubes 21 are vertical and the wall 23 is slightly inclined to horizontal, the washer 25 is wedge-shaped. The threaded end of the wire 22 is exaggerated in the drawings to show the manner in which the nut is mounted thereon. The lower end of the wire 22 passes through a lower duct wall 26 and has its extreme end threaded to fit a nut 27. In this case the wall 26 is very greatly inclined to horizontal so that a washer 28 having an extreme wedge shape is used between the nut 27 and the wall 26. The wa1126 may be formed as a hopper to receive an accumulation of flyash. The Wire 22 is of very high quality, being formed of stainless steel or other non-corrosive type of metal and being drawn with a very smooth finish. A type of wire which will operate very well in this situation is music wire. The nuts 27 and 24 are drawn up so that the wire is stretched tightly between the walls 23 and 26.

The operation of the invention will now be clearly understood in view of the above description. Gases originating in the flame produced by the burners 12 leave the furnace 11 and pass through the boiler 13. These gases leave the boiler at a considerably reduced temperature, but there is still considerable heat left in them. The gases enter the chamber 15 and pass downwardly through the tubes 21 internally thereof, passing outwardly through the chamber 16 and the breeching 17. Combustion air i the incoming combustion air. After being preheated,

aseaaaa the. combustion air passes to the burners 12 where it' is used in the combustion process. The gases passing downwardly through the tubes contain a number of materials. They contain for one thing corrosive gases which condense at a fairly high temperature. When these gases reach the point in the tubes 21 where they are about to be discharged into the chamber 16, they are at their lowest temperature because of the fact that the incoming combustion air is passing over that section of the tubes. This is true because of the general practice of flowing the com bustion air in counterflow to the flue gases so that the coldest combustion air is heated by the coldest flue gases. At this point the situation is ideal for the deposit of corrosive. liquids or condensates on the walls of the tubes. At the same time the flue gases contain fine particles of unburned ash, and if the walls of the tubes are made wet by the condensation of acids and the like on the surface thereof, the flyash has a tendency to stick and, in many cases, they form a deposit which eventually plugs the entire tube so that nothing can pass through. In ad.- dition to plugging the tubes and increasing the resistance of the air heater as a whole, these ashes act as holders for the corrosive liquids and serve to promote corrosion. However, when the nuts 24 and 27 have been tightened up properly, each of the wires 22 is permitted. to vibrate at a frequency determined by the tension and the size of the wire. With a proper adjustment, the wire will be resonant to a frequency which is to be found in the flue gases and will vibrate with a very great displacement. With a proper selection of wire size and tension, the amount of displacement of these vibrations will be exact- 1y suificient to maintain the walls of the tubes clean and polished without any substantial wearing of the wire itself. As a matter of fact, it has been noted that the vibration of the wire in an air current causes a flow of current along the wire so that flyash will be deposited at the lower end of each wire. This has been noted in particular in the case of guy wires in old style biplanes where a substantial deposit of dust is always to be found on the lower wing surrounding the entrance of the wire therein at the lower end of the wire. Since all flue gases contain acoustical vibrations, it will not be difficult in any given case to select a wire and a proper tension to maintain the tubes in a condition which is free of flyash, and therefore, to a great extent free of corrosion.

In Figure 3 is shown another manner in which the principles of the present invention may be carried out. In this case an air heater 34 contains tubes 35 mounted between an upper tube sheet 36 and a lower tube sheet 37. A wall 38 resides in spaced relationship to the upper tube sheet 36 and defines therewith a gas entrance chamber 39. In a similar manner a wall 40 resides in spaced relationship to the lower tube sheet 37 and defines therewith a gas exit chamber 41. A wire 42 formed of noncorrosive material and drawn with a smooth surface finish resides generally centrally of each tube 35. The tube 42 hangs suspended from the wall 38, its upper end being threaded and having a nut 43 threaded thereon. A wedge-shaped washer 44 resides between the nut 43 and the wall 38 to compensate for a slight inclination of the wall 38 and to assure that the wire is mounted vertically. At the lower end of the wire 42 is mounted an aerodynamic member 45, which in this embodiment of the invention is shown as a hollow cone formed with a notch 46' in its lower edge to promote spinning and off-center movement. The wire is connected to the apex of the cone. The operation of this embodiment of-the invention isvery similar to that of the construction shown in Figure 2. The flue gases entering the chamber 39 and passing downwardly through the tube 35 to the exit chamber 41 invariably contain certain. acoustical vibrations. These flue gases striking the aerodynamic chamber cause it to move sideways because of its non symmetrical construction. This combined with the pulsations in the flue gas sets up vibrations in the wire 42 and with a proper selection of wire of length, and of weight of aerodynamic member, the vibration will be sufiicient for a displacement such that the walls of the tubes will be kept clean and polished. As indicated in dotted lines, the wire at any given time will have nodes and anti-nodes along its length, but as is well known, these nodes and antinodes pass up and down on the wire so that every portion of the surface of the tube will be polished by the wire at frequent intervals.

In Figure 4 an air heater 54 is shown as comprising a series of tubes 55 extending between an upper tube sheet 56 and a lower tube sheet 57. A wall 58 resides in spaced relationship to the upper tube sheet 56 and defines therewith a gas entrance chamber 59. A similar wall 60 lies in spaced relationship to the lower tube sheet 57 and defines therewith a gas exit chamber 61. Between the walls 58 and 60 extends a wire 62 formed of non-corrosive material and drawn with a very smooth surface. The lower end of the wire 62 passes through the wall 60 and is threaded to receive a nut 63. Between the nut 63-and the wall 60 resides a washer 64 which is formed with inclined upper and lower surfaces to compensate for the fact that the wall 60 is inclined to horizontal and to insure that the wire 62 is held in absolutely vertical relationship axially of the tube 55. At its upper end the wire 62 passes through the Wall 58 centrally of an aperture 65. Fastened over the aperture 65 is a dome-shaped'diaphragm 66 formed of rubber or similar resilient material which has centrally thereof a metallic plate bonded to the rubber and through which plate the upper end of the wire 62 passes. The wire is welded to the plate 67 and is integral therewith. The outer edges of the diaphragm 66 are held to the wall 58 at the edges of the aperture 65 by means of an annular clamping plate 68 held to the wall 58 by fastening means not shown. At its upper end the wire is provided with a weight 69. It will be understood then that with a proper selection of wire size and material with a proper tension on the nut 63 and with the proper weight 69, the wire 62 will vibrate at resonant frequency to a dominant acoustical vibration inthe flue gases passing through the tube 55. At resonant frequency the wire will vibrate to polish and keep clean the inner surface of the tube and thereby reduce flyash accumulations while causing them to exist at the foot of each wire. Furthermore, forced vibrations may be set up in each wire by striking the weight 69; for instance, a stream of water from a hose may be sprayed over the top of the air heater occasionally to set the wires in motion.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. An air heater and dust collector for use with a furnace comprising a first tube sheet, a second tube sheet spaced from the first, a first wall spaced from the first tube sheet and defining therewith an entrance chamber adapted to receive flue gas from the furnace, a plurality of tubes extending between the tube sheet and adapted to receive the flue gases from the entrance chamber, a second wall spaced from the second tube sheet and defining therewith an exit chamber adapted to receive the flue gases from the tubes, a wire of corrosion-resistant material extending through each tube generally axially thereof, and means mounting the wire for substantial vibration within the tube, the size of the wire being selected so that the nodes of vibration extend adjacent the surface ofthe tube to prevent the accumulation of material thereon.

2. An air heater and dust collector for use with a 'furnace comprising a first tube sheet, a second tube sheet wall and at the other end to the second wall, the ends of the wire extending through the walls and being threaded to receive nuts for determining the tension in the wire extending between the walls, the size of the wire being selected so that the nodes of vibration extend adjacent the surface of the tube to prevent the accumulation of material thereon.

3. An air heater and dust collector for use with a furnace comprising a first tube sheet, a second tube sheet spaced from the first, a first wall spaced from the first tube sheet and defining therewith an entrance chamber adapted to receive flue gas from the furnace, a plurality of tubes extending between the tube sheets and adapted to receive the flue gases from the entrance chamber, a. second wall spaced from the second tube sheet and defining therewith an exit chamber adapted to receive the flue gases from the tubes, a wire of corrosion-resistant material extending through each tube generally axially thereof, one end of the wire extending through the first wall and being threaded to receive a nut, and an aerodydynamic member attached to the other end of the wire,

of tubes extending between the tube sheets and adapted to receive the flue gases from the entrance chamber, a second wall spaced from the second tube sheet and defining therewith an exit chamber adapted to receive the flue gases from the tubes, a wire of corrosion-resistant material extending through each tube generally axially thereof, one end of the wire extending through the second wall and being threaded to receive a nut thereon, the other end of the wire extending through the first wall and being supported at the wall against substantial lateral movement, and a weight attached to the said other end of the wire, the size of the wire being selected so that the nodes of vibration extend adjacent the surface of the tube to prevent the accumulation of material thereon.

References Cited in the file of this patent UNITED STATES PATENTS 535,664 Bott Mar. 12, 1895 2,233,066 Watson Feb. 25, 1941 FOREIGN PATENTS 488,876 Germany Ian. 9, 1930 553,753 Great Britain June 3, 1943

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