PULVERIZED COAL EXHAUSTER FAN BEARING ASSEMBLY AND COOLING SYSTEM

TECHNICAL FIELD

[0001] This invention relates to an exhauster employable in solid fuel pulverizing and firing systems for fossil fuel furnaces, and more specifically, to an exhauster fan bearing assembly and cooling system for such solid fuel pulverizing and firing systems.

BACKGROUND

[0002] Three basic types of solid fuel pulverizer firing systems find common use.

These are the direct- fired system, the semi-direct fired system and the bin storage system. The simplest and most commonly used of these three systems, and the one to which the present invention is directed, is the direct-fired system in which solid fuel, e.g., coal, is fed in a suitable manner along with hot gases to a pulverizer. The solid fuel is simultaneously ground and dried within the pulverizer. The drying of the solid fuel is effected by the hot gases as the latter sweep through the pulverizer. As the hot gases sweep through the pulverizer they are cooled and humidified by means of the evaporation of the moisture contained in the solid fuel. Often, an exhauster is employed for purposes of removing the hot gases and the entrained fine solid fuel particles, i.e., the solid fuel that has been ground within the pulverizer, from the pulverizer. Moreover, this exhauster, when so employed, is located on the discharge side of the pulverizer and is operative to effect the delivery of the mixture of hot gases and entrained fine solid fuel particles to a fossil fuel furnace.

[0003] One prior art form of such a direct-fired solid fuel pulverizer firing system is depicted in U.S. Patent No. 3,205,843 entitled "Pulverized Coal Firing System", and reproduced in FIG. 6, in which it is disclosed that solid fuel passes through the inlet chute 23 of the pulverizer 26 on to the rotating bowl 32 thereof. The solid fuel thus admitted to the pulverizer 26 is pulverized therewithin by means of the grinding rollers 36 of the pulverizer 26, which are mounted within the pulverizer housing to provide a grinding action between the grinding rollers 36 and the grinding ring provided on the rotating bowl 32 of the pulverizer 26. Air passes up through the pulverizer 26 between the housing thereof and the rim of the rotating bowl 32 and as the air passes the rotating bowl 32, pulverized solid fuel is entrained in this air with the air-pulverized solid fuel mixture passing up into the classifier 40 of the

pulverizer 26, which is located in the upper portion of the pulverizer 26. The classifier 40 is effective to separate the coarse solid fuel fractions and return these fractions to the rotating bowl 32 of the pulverizer for regrinding, while the fine solid particles retained in the air stream pass through the outlet 42 of the pulverizer 26, which is located at the upper end of the classifier 40. From this outlet 42 of the pulverizer 26, the air pulverized solid fuel mixture is conveyed to the inlet of the exhauster 46 via conduit 44. The air-pulverized solid fuel mixture in turn is conveyed from the exhauster 46 to the fossil fuel furnace 10 through the ducts 48.

[0004] A prior art form of a typical bearing housing assembly 317 of an exhauster for a solid fuel pulverizer firing system is depicted in FIG. 7 of the present application. FIG. 7 is a cross sectional partial view of the bearing housing assembly 317. The bearing housing assembly 317 includes a bearing housing 360 mounted on a pedestal housing 362. To support the weight of a coal pulverizer exhauster fan assembly and to ensure that it is aligned with its drive motor, a horizontal fan shaft 334 is rotatably supported by opposing bearing assemblies 364 in the cylindrically-shaped, cast iron bearing housing 360. Each of the bearing assemblies 364 includes a bearing 366 and a corresponding end cap 368. As the shaft 334 turns, frictional torque in the bearings 366 generates heat. This heat is supposed to be removed from the bearings 366 by a small amount of oil 370 contained in the bottom of the bearing housing 360. The end caps 368 include a pair of labyrinth-type, housing end caps 368 disposed at opposite ends of the bearing housing 360 to form a seal between the shaft 334 and housing 360 to maintain the oil 370 within the housing 360. An oil drain 372 is located on the bottom of the housing 360 to drain the oil 370 therefrom. Heat is quickly transferred from the bearings 366 to the oil 370, conducted through the bearing housing 360 and into the ambient air in the plant.

[0005] The speed (e.g., approximately 900 rpm) at which the fan shaft 334 rotates is moderate for the bearings 366 specified and should not adversely affect bearing life. The load on the bearings 366 including the radial weights of the overhung fan and other component weights, plus a small thrust load due to differential pressure on the fan, the drive shaft 334 and coupling are very small compared to the dynamic load capacity of the bearings 366.

[0006] However, the relatively small oil reservoir and small convective surface area of the housing 360 are not capable of dissipating the desired amount of heat generated by the

bearings 366 and the heat conducted through the shaft 334 from the hot air supply to the fan casing. This causes an increase in the operating temperature of the oil 370 in the sump and in the bearing operating temperatures. The increased oil and bearing operating temperatures can be high enough to result in inadequate lubricant film separation of the bearing races and rollers, e.g., inadequate elastohydrodynamic (EHL) lubrication, thus resulting in a shortened lifespan of the bearings and lubricant.

[0007] Although solid fuel pulverizer firing systems constructed in accordance with the prior art to which reference has been made heretofore have been demonstrated to be operative for the purpose for which they have been designed, there has nevertheless been evidenced in the prior art a need for such solid fuel pulverizer firing systems to be further improved, and more specifically, a need for the exhauster employed therein to be improved. A limiting factor insofar as the operating efficiency of exhausters is concerned has heretofore been the need to facilitate cooling of the lubricant and bearings of the fan assembly. To this end, a need has thus been evidenced in the prior art for a new and improved solid fuel pulverizer firing system, and more specifically for a new and improved exhauster fan bearing assembly for such solid fuel pulverizer firing systems that would ensure proper cooling of the bearings and lubricant, thus requiring relatively less maintenance than known exhausters.

SUMMARY

[0008] According to the aspects illustrated herein, there is provided an exhauster fan bearing assembly for a pulverized solid fuel firing system. The exhauster fan bearing assembly includes a pedestal housing having an opening at a top portion, the pedestal housing defining an interior space with access thereto through the opening; a bearing housing disposed at the top portion of the pedestal housing, the bearing housing having first and second openings disposed at opposite ends of the bearing housing; first and second bearing assemblies disposed at the first and second openings, respectively; a shaft extending through the bearing housing via the first and second openings, the shaft rotatable about a shaft rotational axis via the first and second bearing assemblies; and a sump housing operably coupled to a bottom of the bearing housing. The sump housing extends through the opening and into the interior space of the pedestal housing. The sump housing defines a reservoir for a lubricant in fluid communication with the first and second bearing assemblies.

[0009] According to the other aspects illustrated herein, there is provided an exhauster for a pulverized solid fuel firing system. The exhauster includes a housing; an exhauster fan for exhausting coal through an exhauster fan housing, the exhauster fan being mountable within the housing on a shaft rotatable about a shaft rotational axis and the housing having an inlet generally aligned with the shaft rotational axis such that coal entering the housing through the inlet contacts the rotating exhauster fan and is redirected thereby along a radial outlet path, the exhauster fan including a plurality of blades; and an exhauster fan bearing assembly. The exhauster fan bearing assembly includes a pedestal housing having an opening at a top portion, the pedestal housing defining an interior space with access thereto through the opening; a bearing housing disposed at the top portion of the pedestal housing, the bearing housing having first and second openings disposed at opposite ends of the bearing housing; first and second bearing assemblies disposed at the first and second openings, respectively, the shaft extending through the bearing housing via the first and second openings, the shaft rotatable about the shaft rotational axis via the first and second bearing assemblies; and a sump housing operably coupled to a bottom of the bearing housing. The sump housing extends through the opening and into the interior space of the pedestal housing. The sump housing defines a reservoir for a lubricant in fluid communication with the first and second bearing assemblies.

[0010] The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:

[0012] FIG. 1 is a schematic representation of a solid fuel pulverizer firing system embodying an exhauster constructed in accordance with the present invention;

[0013] FIG. 2 is an enlarged front elevational view, in vertical section, of the exhauster of the solid fuel pulverizer firing system shown in Figure 1, taken along lines II- II of Figure 1 thereof;

[0014] FIG. 3 is an enlarged side elevational sectional view of the exhauster, taken along lines III-III of Figure 2;

[0015] FIG. 4 is a cross-sectional partial view of an exemplary embodiment of a bearing housing assembly of the exhauster in accordance with the present invention;

[0016] FIG. 5 is a cross-sectional partial view of another alternative exemplary embodiment of a bearing housing assembly of the exhauster in accordance with the present invention;

[0017] FIG. 6 is a schematic diagram of a prior art form of a direct-fired solid fuel pulverizer firing system as depicted in U.S. Patent No. 3,205,843; and

[0018] FIG. 7 is a cross-sectional partial view of a prior art bearing housing assembly.

DETAILED DESCRIPTION

[0019] Referring now to the figures, and more particularly to Figure 1 thereof, there is depicted therein a portion of a solid fuel pulverizer firing system 10 which comprises a furnace 12, a pulverizer 14, an exhauster 16, for effecting delivery of a mixture of hot gases and entrained fine solid fuel particles from the pulverizer 14 to the furnace 12, and an exhauster fan bearing assembly 17. Inasmuch as the nature of the construction and the mode of operation of solid fuel pulverizer firing systems per se are well-known to those skilled in the art, it is not deemed necessary, therefore, to set forth herein a detailed description of the solid fuel pulverizer firing system 10. Rather, for purposes of obtaining an understanding of a solid fuel pulverizer firing system which is capable of having cooperatively associated therewith an exhauster of the present invention such as the exhauster 16, reference is made to the more detailed description of the nature of the construction and the mode of operation of the components of a solid fuel pulverizer firing system disclosed in U. S. Patent No. 3,205, 843, which issued September 14, 1965 to A. Bogot.

[0020] Considering first the furnace 12, it is within the furnace 12 that in a manner well known to those skilled in this art combustion of the pulverized solid fuel and air is initiated. To this end, the pulverized solid fuel and air is injected into the furnace 12 through a plurality of burners 18, which are schematically depicted in Figure 1. In addition to the aforementioned pulverized solid fuel and air, there is also supplied to the furnace 12 the secondary air which is required to effectuate the combustion within the furnace 12 of the pulverized solid fuel that is injected thereinto through the burners 18.

[0021] The hot gases that are produced from construction of the pulverized solid fuel and air rise upwardly in the furnace 12. During the upwardly movement thereof in the furnace 12, the hot gases in a manner well-known to those skilled in the art give up heat to the fluid passing through the tubes 20, which are schematically depicted in Figure 1, that line all four of the walls of the furnace 12 in conventional fashion. Then, the hot gases exit the furnace 12 through a horizontal pass which in turn leads to a rear gas pass, both gas passes commonly comprising other heat exchanger surfaces (not shown) for generating and super heating steam, in a manner well-known to those skilled in the art. Thereafter, the steam commonly is made to flow to a turbine 22, which is in turn connected to a variable load, such as an electric generator (not shown), which in known fashion is cooperatively associated with the turbine 22, such that electricity is thus produced from the generator (not shown).

[0022] A description of the mode of operation of the solid fuel pulverizer firing system 10 will be described with reference to Figure 1. To this end, solid fuel is supplied to and is pulverized within the pulverizer 14. In turn, the pulverizer 14 is connected by means of a duct 24 to the exhauster 16 whereby the solid fuel that is pulverized within the pulverizer 14 is entrained therewithin in an airstream and while so entrained therein is conveyed from the pulverizer 14 through the duct 24 to the exhauster 16. With reference now to Figure 2, which is a front elevational sectional view of the exhauster 16, it can be seen that the airstream with the pulverized solid fuel entrained therewith is made to pass through the exhauster 16 by virtue of the movement of an exhauster fan assembly 26. The pulverized solid fuel while still entrained in the airstream is discharged from the exhauster 16 through an outlet 28. From the exhauster 16 the pulverized solid fuel entrained in the airstream is conveyed to the furnace 12 through the duct 7 denoted by reference numeral 30 in Figure 1, whereupon the pulverized solid fuel is combusted within the furnace 12.

[0023] A more detailed description of the exhauster fan assembly 26 now follows with reference to Figure 3, which is an enlarged side elevational sectional view of the exhauster 16 showing the exhauster fan assembly 26 thereof. The exhauster fan assembly 26 includes a fan 32 mounted on a shaft 34 for rotation of the fan about a shaft rotational axis SRA. The fan 32 rotates within a housing 36 which has an inlet 38 communicated with the duct 24 and generally aligned with the shaft rotational axis SRA such that coal entering the housing 36 through the inlet 38 contacts the rotating exhauster fan 32 and is redirected thereby along a radial outlet path, denoted by the arrow 40 in Figure 2.

[0024] The exhauster fan 32 includes a plurality of blades 42 and a hub 44. The hub

44 has an outer surface 46, a free end 48, and a bore 50 for receiving therein the free end 52 of the shaft 34 in an orientation in which the free end 52 of the shaft 34 and the free end 48 of the hub 44 are oriented in the same axial direction relative to the shaft rotational axis SRA. The outer surface 46 of the hub 44 is radially outwardly spaced from the bore 50 of the hub 44 and the blades 32 are mounted to outer surface 46 of the hub 44 at uniform angular spacings therearound and project radially outwardly therefrom.

[0025] Figure 4 is a cross-sectional partial view of an exemplary embodiment of a bearing housing assembly 17 in accordance with the present invention. Referring to Figure 4, the exemplary bearing housing assembly 17 includes a bearing housing 60 disposed at a top portion of a pedestal housing 62. The pedestal housing 62 has an opening 63 at the top portion thereof. The pedestal housing 62 defines an interior space 65 with access thereinto through the opening 63.

[0026] The bearing housing 60 includes first and second openings 67 and 69 disposed at opposite ends of the bearing housing 60. First and second bearing assemblies 64 are disposed at the first and second openings 67, 69, respectively. The opposite end of the free end 52 of the shaft 34 extends through the bearing housing 60 and through the first and second openings 67 and 69. The shaft 34 is rotatable about a shaft rotational axis SRA via the first and second bearing assemblies 64. In an exemplary embodiment as illustrated, the first and second bearing assemblies each include a fan shaft bearing 66 and a bearing cap 68.

[0027] A sump housing 80 is operably coupled to a bottom of the bearing housing 60.

The sump housing 80 extends through the opening 63 and into the interior space 65 of the pedestal housing 62. The sump housing 80 defines a reservoir for a lubricant (e.g., oil 70) in fluid communication with the first and second bearing assemblies 64.

[0028] In exemplary embodiments, the sump housing 80 is defined by a first end of a wall 82 extending substantially perpendicular from a base 84 of the sump housing 80 and defining a reservoir for the oil 70. A mounting flange 86 extends substantially perpendicular from an opposite second end of the wall 82 and is substantially parallel to base 84. The mounting flange 86 includes a plurality of mounting apertures to receive corresponding mechanical fasteners 88 to fasten the sump housing 80 to the bearing housing 60. In exemplary embodiments, the mechanical fasteners 88 include threaded fasteners, for

example, but are not limited thereto. The sump housing 80 is retrofitable to an existing bearing housing 360 as illustrated in Figure 6 to increase lubricant capacity and increase a convective surface area for cooling the lubricant (e.g., oil 370).

[0029] Referring again to Figure 4, each fan shaft bearing 66 includes a plurality of rollers (not shown). Further, each bearing cap 68 of a corresponding bearing assembly 64 includes a labyrinth-type housing end cap configured to prevent leakage of the lubricant (e.g., oil 70) from the first and second openings 67 and 69 of the bearing housing 60.

[0030] An oil level indicated by reference numeral 90 is observed by sight gauges 92

(only one shown) on opposite sides of the housing 60. The oil level 90 is maintained at approximately the centerline of the lowest roller in each of the bearings 66. However, there are a pair of different bearings 66 used in the assembly, and the position of their respective lowest rollers may vary. Therefore, the oil level 90 is set at the higher of the two lowest roller centerline positions. This oil level 90 is intended to provide good lubrication conditions for the bearings 66, prevent excessive heat generation due to lubricant viscous shear effects and oil leakage out of the labyrinth-type, housing end caps 68.

[0031] Referring now to Figure 5, an alternative exemplary embodiment of a bearing housing assembly 117 in accordance with the present invention is illustrated. The bearing housing assembly 117 of Figure 5 is the same as the bearing housing assembly 17 of Figure 4 except for the inclusion of an external cooling system 200 in thermal communication with the oil 70 in the sump housing 80.

[0032] The external cooling system 200 includes a cooling medium (not shown) in thermal communication with the lubricant (e.g., oil 70) in the sump housing 80 to remove heat from the lubricant, thereby maintaining a lower temperature of the lubricant to lubricate the bearings 66. The external cooling system 200 includes one tube 202 within the sump housing 80. The single tube is coiled and includes a tube inlet 204 at a first end and a tube outlet 206 at an opposite second end. In alternative exemplary embodiments, an array of tubes 202 is contemplated within the sump housing. Pn an exemplary embodiment, the cooling medium includes an on-site water source. The on-site water source provides cool water to the tube inlet 204 and heated water is returned to the on-site water source via tube outlet 206.

[0033] The arrangements disclosed in Figures 4 and 5 are both intended to retrofit an existing bearing housing (e.g., bearing housing 360 of FIG. 6) with an enlarged sump assembly while maintaining as many of the original parts as possible of the bearing housing assembly 417. The actual enlarged sump arrangement for different sizes and types of existing bearing housing assemblies will vary, but the design concept will remain the same.

[0034] The present invention having the improved bearing housing, as in the above described exemplary embodiments, incorporates a larger oil sump attached to the existing bearing housing and occupies the open space in the housing pedestal housing directly beneath the bearing housing. The new oil sump provides increased oil capacity and convective surface area to dissipate the heat generated during exhauster fan operation. It also allows for the addition of an optional water cooling system, for example, if desired or needed. In an exemplary embodiment, the optional water cooling system may be an array of water tubes within the larger oil sump, used to remove heat from the oil using an on-site water source as the cooling liquid.

[0035] The larger volume of oil in the enlarged sump increases the time it takes before the oil and bearings reach an undesirably high operating temperature, thus allowing more heat to be absorbed and time for the heat to be dissipated. In addition to this sump wall- to-air convection method, the oil-to-water convection method from a system of at least one submerged cooling tube can carry away heat internal to the sump. The amount of heat removed by the water-cooled tubing depends on the tube surface area and the flow rate and temperature of the water that is circulated. These factors can be selected to optimize heat removal from the oil for the desired end purpose.

[0036] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.