Patent Publication Number: US-6712080-B1

Title: Flushing system for removing lubricant coking in gas turbine bearings

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor. 
     BACKGROUND OF THE INVENTION 
     Gas turbines, including those used for propelling military vehicles, include two or more opposed bearings which must be continuously lubricated during gas turbine usage. This is accomplished by means of a lubricating system which provides the bearings with a lubricating fluid, such as natural or synthetic oil, to not only lubricate the bearings but to also provide for cooling. 
     When the gas turbine is shut down after usage, the residual heat from the turbine (which may be hundreds of degrees Fahrenheit) soaks back to the bearings leading to a possible coking condition. This is even more pronounced if there is insufficient engine idle time before turbine shut down. Basically, coking is the result of the lubricant becoming an oxidized solid oil deposit on the bearing surface and in the lubricant delivery system that can lead to insufficient lubricant supply to the bearings. This can result in engine seizure and/or a requirement for a complete engine overhaul, which is undesirable, particularly in tactical combat situations. 
     Accordingly, it is a primary object of the present invention to provide apparatus which flushes away the coked lubricant in rotating machinery bearings, particularly, in gas turbines which shut down at high temperatures. 
     SUMMARY OF THE INVENTION 
     A flushing system for removing lubricant coking in a turbine bearing, within a bearing housing having a fluid inlet and fluid outlet, includes a plurality of fluid containing tanks, at least a first of which contains a coking solvent, a second of which contains a cleaner and a third of which contains a lubricant. First and second couplings are provided with a first coupling being connected to the fluid inlet and the second coupling being connected to the fluid outlet, of the bearing housing. A supply pump has an outlet connected to the first coupling, and a return pump has an inlet connected to the second coupling. A first valving arrangement is connected between the tanks, and an inlet of the supply pump, and is operable to provide fluid from a selected one of the tanks to the supply pump for delivery to the bearing housing. A second valving arrangement is connected between an outlet of the return pump and the tanks, to supply return fluid from the bearing housing to the particular tank selected by the first valving arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood, and further objects, features and advantages thereof will become more apparent from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a simplified block diagram of a gas turbine and lubricating system. 
     FIG. 2 is a block diagram of the flushing system of the present invention, attached to a bearing as in FIG.  1 . 
     FIG. 3 is a more detailed presentation of the flushing system of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
     In FIG. 1, a rotating gas turbine  10  is supported by opposed first and second bearings  12  and  14 , although, more such bearings may be utilized, depending upon turbine size and design. 
     A lubricating system  16  is provided in order to supply the bearings with necessary lubrication and cooling during use, and when the gas turbine  10  shuts down, the lubrication system  16  also shuts down, leading to a possible coking condition, as previously explained. The present invention obviates this problem by flushing away any coked deposits, and to this end, reference is made to FIG.  2 . 
     In FIG. 2, the lubricating system  16  is illustrated as being connected to a representative bearing housing  20  for delivering lubricating fluid to the bearing, via a one-way valve  22  and fluid inlet  24 , and for receiving used lubricant from the bearing, via fluid outlet  26  and one-way valve  28 . Flushing system  30  is connectable with the bearing housing inlet  24  by means of coupling  32  and is connectable with the bearing housing outlet  26  by means of coupling  34 . 
     The flushing system  30  may be a permanent installation in a maintenance facility, or, may be a portable system in which a system carrier is wheeled up to the gas turbine-driven vehicle. To facilitate rapid servicing, the couplings  32  and  34  are preferably of the threadless quick-disconnect type which have respective male connectors  32   m  and  34   m , which mate with respective female connectors  32   f  and  34   f . When uncoupled, the female connectors  32   f  and  34   f  prevent fluid from exiting the connector. The portable system also includes respective flexible hoses  36  and  38 , which may be wound up upon the carrier. 
     A more detailed view of the flushing system  30  is presented in FIG.  3 . After the gas turbine on the vehicle has shut down, the flushing system  30  is wheeled up to the vehicle and is connected to the bearing inlet  24  and outlet  26  by unwinding the flexible hoses  36  and  38  and by bringing together the respective connectors of couplings  32  and  34 . 
     The flushing system  30  includes a plurality of fluid holding tanks  40 - 42 , a first of which contains a solvent for dissolving any coked oil. By way of example the solvent may be a 50-50 solution of tetrahydrofuran and cyclohexane which turns the coked lubricant into a fine powder. A second tank,  41 , contains a cleaner, such as alcohol or kerosene, to remove any solvent and dissolved coke material. A third tank,  42 , contains lubricant to re-lubricate the bearings. 
     By a valving arrangement, the liquids in the tanks  40 - 42  are selectively provided to the bearing housing  20  via coupling  32 , by means of a supply pump  44 , having an inlet  45  and outlet  46 , and liquid is withdrawn from the bearing housing  20  by means of a scavenge, or return pump,  47 , having an inlet  48  and outlet  49 . More particularly, the valving arrangement includes a first three-way valve  50  which is automatically, or hand operated, to selectively connect supply pump  44  with either solvent tank  40 , cleaner tank  41  or lubricant tank  42 . A similar three-way valve  52  is operative to selectively direct return fluid from return pump  47 , to either solvent tank  40 , cleaner tank  41  or lubricant tank  42 . 
     Prior to entering the return pump  47 , return fluid from the bearing is preferably filtered. This is accomplished with the provision of a filter station  56  comprised of three filters  58 - 60 , one for each of the tanks  40 - 42 , and selectively put into the fluid circuit by means of three-way valves  62  and  64 . These valves  62  and  64  are operated to direct fluid: A) to filter  58  when solvent from solvent tank  40  is being supplied, B) to filter  59  when cleaner from cleaner tank  41  is being supplied, and C) to filter  60  when lubricant from lubricant tank  42  is being supplied. 
     In operation, after coupling with the bearing housing  20 , the pumps  44  and  47  of the flushing system  30  are turned on such that, initially, solvent from tank  40  is provided to the bearing with the proper positioning of three-way valves  50 ,  52 ,  62  and  64 . The solvent is continuously supplied to the bearing for a period of time in order to dissolve the coked material. In order to assist in determining this period of time, a flowmeter  66  is provided in the fluid line from supply pump  44  to the bearing housing  20 . Based upon an increased flow rate of the solvent, as determined by the flowmeter  66 , the valving arrangement may be changed so as to next provide cleaner from tank  41  to remove the solvent from the bearing housing  20 . After another predetermined period of time, the three-way valves are positioned to supply lubricant from tank  42  for a few minutes, to replenish the bearing housing  20  with fresh lubricant prior to a subsequent start-up of the gas turbine. 
     In order to further monitor the system during the flushing operation, the system also includes a pressure gage  68  and a thermocouple  70 , both of which are connected to the fluid circuit downstream of the supply pump  44 . Additionally, if the pressure in the fluid line exceeds a certain value, a relief valve  72  is operative to direct the fluid from pump  44  back to three-way valve  52  via fluid line  74 . After the complete flushing operation, couplings  32  and  34  are disconnected and the gas turbine-driven vehicle may return to its assigned task. 
     As mentioned, the flushing system  30  may be completely portable for delivering the system to a gas turbine-driven vehicle for servicing. Accordingly, the components of the flushing system  30  may be carried on a wheeled cart, generally represented by the numeral  76 , in FIG.  3 . 
     It will be readily seen by one of ordinary skill in the art that the present invention fulfills the primary object set forth herein. After reading the foregoing specification, one of ordinary skill in the art will be able to effect various changes, substitutions of equivalents and various other aspects of the present invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents. Having thus shown and described what is at present considered to be the preferred embodiment of the present invention, it should be noted that the same has been made by way of illustration and not limitation. Accordingly, all modifications, alterations and changes coming within the spirit and scope of the present invention are herein meant to be included.