Abstract:
A liquid ring pump system includes structure configured to automatically and actively vary the amount of seal liquid injected into the sweep of the pump (in order to boost gas discharge pressure) based on one or more variable operating parameters of the pump.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to liquid ring pumps, and more particularly to controlling the flow of seal liquid injection into the “sweep” portion of such pumps. 
     Liquid ring pumps are well known, as is shown, for example, by Adams U.S. Pat. No. 3,289,918 (which is hereby incorporated by reference herein in its entirety). The Adams patent shows that it is known that the compression ratio of a liquid ring pump can be increased by injecting additional seal liquid into the liquid ring in the pump at an appropriate location between the gas intake and gas discharge of the pump (i.e., in the so-called “sweep” of the pump). However, the known means for introducing such pressurized seal liquid tend to have fixed flow characteristics. This can be a disadvantage when certain operating conditions of the pump change and/or when certain changes are made in the operating configuration of the pump. 
     In view of the foregoing, it is an object of this invention to provide improved liquid ring pumps. 
     It is a more particular object of the invention to provide liquid ring pumps with improved seal liquid injection arrangements. 
     SUMMARY OF THE INVENTION 
     These and other objects of the invention are accomplished in accordance with the principles of the invention by providing liquid ring pumps with seal liquid injection that is actively controlled based on at least one operating parameter of the pump. For example, the seal liquid may be supplied from a pressurized source via a variable flow control valve. At least one operating condition of the pump (e.g., seal liquid injection pressure) is monitored to provide information for controlling the amount by which the variable flow control valve is opened. Valve control structure is provided for using that information to open the valve by an amount appropriate to the current pump operating condition information. For example, if seal liquid injection pressure is the pump operating condition being monitored, the seal liquid flow control valve may be controlled to maintain a desired seal liquid injection pressure. Other examples of pump operating conditions or parameters that may be monitored in order to provide alternative or additional information for control of the seal liquid flow control valve include pump speed, gas inlet pressure and/or temperature, and gas discharge pressure and/or temperature. Control may be based on monitoring multiple operating parameters. For example, both gas inlet pressure and gas discharge pressure may be monitored to allow control to be based on the gas pressure differential at which the pump is operating. In that example, the seal liquid flow control valve may be controlled to be closed or open relatively little when the gas pressure differential is low, and to be open to a greater degree when the gas pressure differential is higher. 
     Among the advantages of using the present invention are that it helps to prevent liquid ring pumps from stalling, and that it otherwise improves the operating stability of such pumps. It also facilitates the use of external seal liquid sources. Such sources tend to have a constant pressure, which can be too high for the liquid ring pumps under some operating conditions, such as during start-up. However, because the present invention provides for active control of the pressure of seal liquid injected into the pump, a seal liquid source having a constant pressure can now be used without difficulty. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified, partly schematic view of an illustrative liquid ring pump installation in accordance with the invention. 
     FIG. 2 is similar to FIG. 1, but shows another illustrative liquid ring pump installation in accordance with the invention. 
     FIG. 3 is a simplified block diagram showing another illustrative embodiment of a system generally like the FIG. 2 system in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The illustrative liquid ring pump installation shown in FIG. 1 includes liquid ring pump  10  and separator  50 . Liquid ring pump  10  includes a stationary, hollow, annular housing or casing  12 , within which rotor  20  is mounted for rotation about axis  22  in the direction indicated by arrow  24 . Rotor  20  includes a plurality of blades  26  equally spaced from one another around axis  22 . Each blade  26  extends radially out and axially along relative to axis  22 . A quantity of pumping or seal liquid  30  is maintained in housing  12  and is formed into a recirculating ring inside the housing by rotation of rotor  20 . The approximate inner surface of this seal liquid ring is indicated by the chain-dotted line in FIG.  1 . Rotor  20  is eccentric to housing  12  and therefore also eccentric to the liquid ring recirculating in the housing. 
     Gas to be pumped is supplied to pump  10  via gas inlet conduit  40 . This gas enters the working space of the pump via inlet port  42 . Inlet port  42  is located where the chambers bounded by adjacent rotor blades  26  and the inner surface of liquid ring  30  are increasing in size in the direction  24  of rotor rotation. Accordingly, these expanding chambers pull gas to be pumped into the pump. 
     After passing beyond inlet port  42 , the chambers enter the so-called “sweep” portion of the pump and then begin to get smaller again. Where the chambers are decreasing in size, the gas in those chambers is compressed. When the gas has been sufficiently compressed, the chambers begin to communicate with discharge port  44 , via which the compressed gas exits the working space of the pump. From discharge port  44  the compressed gas exits the pump via discharge conduit  46 . Some seal liquid also typically exits the pump with the compressed gas. 
     Conduit  46  conveys the compressed gas and seal liquid to separator  50 . Separator  50  separates the gas from the liquid and allows the gas to exit the depicted components via conduit  52 . At least some of the seal liquid from separator  50  is fed back into pump  10  via variable flow control valve  60  and conduit  62 . In particular, conduit  62  feeds this seal liquid back into liquid ring  30  in the sweep area of the pump, where it has the effect of increasing the volume of the liquid ring and thereby boosting the pressure of the gas discharged via discharge elements  44 ,  46 , and  52 . Any net loss of seal liquid from the components shown in FIG. 1 is made up from seal liquid supply conduit  14 . 
     Considering the feedback of seal liquid via elements  60  and  62  in more detail, the pressure for forcing this seal liquid to flow back into the sweep of pump  10  comes from the pressure of the compressed gas in separator  50 . Variable flow control valve  60  controls the amount or rate of this flow. The amount by which valve  60  is opened at any given time is controlled by valve control structure  70 . Structure  70  may be any suitable structure that is appropriate to the (1) type of mechanism used for valve  60 , (2) the type of information supplied for control, and (3) any other desired considerations such as the speed and precision with which it is desired to control the valve. In the example shown in FIG. 1, the pressure of the seal liquid in conduit  62  is monitored as indicated by sensor line  72  to provide information for use by valve control structure  70  to control valve  60 . Seal liquid pressure in conduit  62  is an indication of pressure (liquid and gas) in the sweep area of the pump to which conduit  62  is connected. 
     In an illustrative mode of operating the system shown in FIG. 1, elements  60 ,  70 , and  72  are configured to control valve  60  to maintain a predetermined, desired, substantially constant seal liquid pressure in conduit  62  (at least after pump  10  has been in operation long enough to have passed through a start-up period). If the seal liquid pressure in conduit  62  falls below the desired constant pressure, that is sensed by sensor  72 , and control  70  responds by increasing the amount by which valve  60  is open. This increases the flow of seal liquid into the sweep of the pump via conduit  62 , thereby restoring pressure in the sweep to the desired constant value. Conversely, if the seal liquid pressure in conduit  62  rises above the desired pressure, that is sensed by sensor  72 , and control  70  responds by decreasing the amount by which valve  60  is open. This decreases the flow of seal liquid into the sweep of the pump, thereby lowering pressure in the sweep to the desired value. In this way, the seal liquid pressure in conduit  62  is held substantially constant, despite possible changes, for example, in gas inlet pressure in conduit  40 . Maintaining the seal liquid pressure in conduit  62  constant helps to give pump  10  a constant gas discharge pressure (in conduit  46 / 50 / 52 ), which may be desirable in many applications. 
     Basing control of valve  60  on the pressure of the seal liquid in conduit  62  is only one example of how valve  60  may be controlled. FIG. 2 shows another illustrative embodiment in which more operating parameters of the pump are monitored and are therefore available for use in determining how much valve  60  should be opened. In the embodiment shown in FIG. 2 valve control structure  70  also includes information processor  80 . Information processor  80  may include any number of sensor inputs, such as sensor input  102  (indicating the speed of the motor  100  provided for rotating the rotor in pump  10 ), sensor input  41  (indicating the pressure and/or temperature of the gas in pump inlet conduit  40 ), sensor input  47  (indicating the pressure and/or temperature of the gas in discharge conduit  46 , and sensor input  72  (described earlier in connection with FIG.  1 ). Processor  80  processes the information from any or all of such sensor inputs to produce an output  82  for causing control  70  to open valve  60  by the amount determined (by processor  80 ) to be appropriate for the current operating condition(s) of pump  10 . For example, processor  80  may include a suitably programmed microprocessor. Processor  80  may follow a predetermined algorithm, using information from the above-mentioned sensors as inputs, in order to best control valve  60  in view of the current operating conditions of the system. 
     As just some illustrations of how processor  80  in FIG. 2 may respond to certain conditions, low motor  100  speed (corresponding to low pump  10  speed), low gas pressure differential between conduits  40  and  46 , and/or very low or very high seal liquid pressure in conduit  62  may be taken to indicate that pump  10  is just beginning to operate and that the amount by which valve  60  should be open is relatively small or even zero. On the other hand, higher motor  100  speed (corresponding to higher pump  10  speed), high gas pressure differential between conduits  40  and  46 , and/or seal liquid pressure in conduit  62  that is neither excessively high nor excessively low may be taken to indicate that pump  10  is ready for valve  60  to be opened by a greater amount. 
     It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. For example, those skilled in the art will appreciate that the invention is equally applicable to liquid ring pumps having many different, otherwise known constructions, such as pumps with flat, conical, or cylindrical port structures. The invention is also applicable to pumps having multiple lobes. It is applicable to single- and double-ended pumps. It is applicable to any stage of multi-stage pumps. If desired, the seal liquid fed or fed back to the liquid ring pump may be cooled (e.g., by passing it through a heat exchanger). The source of pressurized seal liquid for injection into the sweep of the pump does not have to be a separator as shown in the drawings. Seal liquid from any other suitable source can be used instead if desired. As was mentioned in the above Summary section, the seal liquid source can be an external source having a constant pressure, even though that pressure would (without the present invention) be too high for the pump under some or even all operating conditions. FIG. 3 shows a system that can be basically similar to the system shown in FIG. 2, except that in FIG. 3 the seal liquid for injection into liquid ring pump  10  comes from an external seal liquid source  110 , which, as has been mentioned, can have a constant pressure.