Patent Application
20180245594
The present invention relates to liquid ring pumps, and more specifically to a control system for liquid ring pumps.
Liquid ring pump systems utilize a sealing liquid to form a seal within the pump. The quantity of liquid in the pump can affect the operation of the pump. For example, too much liquid can result in extra work being required to produce the desired flow of compressed fluid. Conventional liquid ring pump systems are manually-controlled for specific, predetermined conditions. As such, existing pump systems typically cannot adjust to different operating characteristics or dynamic process conditions.
The invention is directed to a pump system that includes a liquid ring pump driven by an electric motor. A variable speed drive can power the motor, and sensors are positioned throughout the system to measure various parameters of the system. A controller receives signals from the sensors and, in response to the signals, controls the variable speed drive and/or the flow of sealing water to the liquid ring pump, among other aspects of the pump system.
For example, in one aspect, the invention is directed to a method of controlling a liquid ring pump in a pump system includes monitoring a vacuum pressure of the liquid ring pump using a pressure transmitter configured to transmit a vacuum pressure signal to a controller in operative communication with the liquid ring pump. The method also includes maintaining a predetermined vacuum pressure in the liquid ring pump under variable vacuum flow demand within the pump system in response to the vacuum pressure signal by controlling, via instructions from the controller, a parameter of the liquid ring pump based on a comparison of the vacuum pressure signal to the predetermined vacuum pressure by the controller.
In another aspect, the invention is directed to a method of controlling a liquid ring pump in a pump system, the liquid ring pump driven by a motor controlled by a controller, includes monitoring a parameter in the liquid ring pump using a transmitter configured to transmit a signal indicative of the monitored parameter to the controller in operative communication with the liquid ring pump. The method also includes comparing the signal with a predetermined threshold in the controller. The method further includes disabling a motor start function of the motor in response to the signal indicating that the monitored parameter exceeds the predetermined threshold.
In another aspect, the invention is directed to a pump system includes a liquid ring pump configured to compress a fluid. The pump system also includes a variable speed motor operatively coupled to the liquid ring pump to drive the liquid ring pump under variable vacuum flow demand within the pump system. The pump system further includes a transmitter coupled to the pump system and configured to monitor a parameter of the pump system and to transmit a signal indicative of the monitored parameter. The pump system also includes a controller in communication with the transmitter and the motor, the controller programmed to perform instructions to operatively control the liquid ring pump in response to the signal from the transmitter indicative of the monitored parameter.
To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.
The liquid ring pump 102 illustrated in
It should be noted that the term “pump” is used herein when describing the liquid ring pump 102, however it should be understood that the pump and the arrangements described herein are equally applicable to vacuum systems or compressor systems. As such, the system described herein should not be limited to pumps alone.
In some constructions, a liquid or gas bypass passage is also provided to aid in operation at pressure ratios below the maximum pressure ratio of the pump. In some constructions, a valve such as a solenoid operated valve is selectively opened and closed to vent either sealing liquid or gas to reduce the pressure differential in the pump, thereby reducing the work required to operate at a pressure ratio below the maximum rated pressure ratio.
The rotor 208 includes a plurality of vanes arranged to define compression chambers or spaces during operation. The port member 210 is a conical port member 210 that is partially received within a conical opening in the rotor 208. The port member 210 includes a plurality of apertures or openings that are arranged to direct fluid into the rotor 208 and out of the rotor 208 at the desired positions and orientations.
Those of ordinary skill will understand that there are many different arrangements of liquid ring pumps. The illustrated construction is a single stage pump with a conical port member 210. Other constructions could include two or more stages or could include planar port plates. It should be clear that the systems described herein should not be limited to use with a liquid ring pump 102 as described herein. Rather, the system is equally applicable to other systems and arrangements that include liquid ring pumps 102.
In operation, the liquid ring pump 102 draws fluid to be compressed into the pump via the inlet 106. The motor 104 drives the rotor 208 to rotate the rotor 208 about an axis. Rotation of the rotor 208 produces a ring of sealing liquid that cooperates with the vanes of the rotor 208 to form a series of closed spaces. The axis of the rotor 208 is offset from the center of the ring of sealing liquid such that the closed spaces reduce in volume from the inlet 106 to the outlet 108. As the fluid is compressed and discharged, some of the sealing liquid is typically carried with the stream of compressed fluid. Thus, additional sealing liquid must be periodically admitted into the pump via the sealing liquid inlet 216. The quantity of sealing liquid and the speed of the motor 104 are two variables that can be adjusted to achieve a desired operational characteristic.
A plurality of measuring instruments 326 are positioned throughout the pump system 300 and are arranged to provide measurements to a controller 316 that can be a programmable logic controller (“PLC”). Typical measurements may include the inlet fluid temperature and pressure, the outlet fluid temperature and pressure, the sealing liquid temperature, and other temperatures, pressures, fluid levels, valve positions, etc. in the pump system 300 that may be desired.
Control members 302 are positioned throughout the pump system 300 to control different components and operations. The control members 302 are each connected to the controller 316 to allow the controller 316 to control the respective control members 302. For example, a valve can be positioned to open a drain connected to the sealing liquid outlet 322. Other control members 302 may include a motor controller for controlling the operation of the sealing liquid pump 312, valve controllers for controlling the opening of a liquid or gas vent system, or other operational characteristics of the pump system 300. Another control member 302 includes the variable frequency drive (“VFD”) or other motor controller that controls the operation of the liquid ring pump 102 via the motor 104. The controller 316 is connected to each of the control members 302, including any VFDs or motor controllers, to allow the controller 316 to control the motor(s) and pump(s).
In operation, the pump-motor assembly 100 operates to draw in fluid to be compressed. A supply of sealing liquid, usually, water is also provided to the pump to form the liquid ring and the make-up for carry over that exits the pump with the compressed fluid. The flow of compressed fluid and any carry over flows to the moisture separator 310 where the carryover is separated and redirected back to the liquid ring pump 102 for reuse. The compressed fluid exits the moisture separator 310 and may pass through a filter or other conditioning devices (e.g., heat exchangers, etc.) before passing to a point of use.
Various temperatures, pressures, flow rates, and the like, are measured and monitored by the controller 316. Using this data, the controller 316 is able to control the speed of the motor 104 that drives the pump-motor assembly 100, and together or separately, the quantity of liquid in the liquid ring pump 102 can be closely controlled to assure that the desired output pressure is achieved for the intended application.
For example, the controller 316 can reduce the speed of the motor 104 and the pump 102 to reduce the volumetric flow rate. Alternatively, the controller 316 can increase or decrease the flow of sealing water to the pump 102. Additionally, the controller 316 could vent sealing liquid or gas to reduce the pressure ratio of the pump 102 as may be desired or necessary under the operating conditions present at any given time.
In another example, the controller 316 can be used to “lock-out” the motor start function based on a liquid level transmitter to ensure the pump 102 does not start with too much or too little liquid within the pump 102. In addition, a pressure transducer can transmit the pump backpressure to the controller 316 prior to a start to assure that the pump 102 is not started against an excessive or undesirable backpressure.
Also, the controller 316 can be programmed to monitor the actual wear on the bearings to determine if they need to be replaced or if other maintenance might be required. In another construction, the operating time is monitored to determine maintenance cycles and to assure common wearing parts are replaced in a timely fashion prior to failure. Recommended maintenance schedules dependent on the model and size of the pump as well as operating conditions or duty cycles could be programmed into the controller 316 to further enhance system reliability.
In addition to “locking-out” the motor 104, the controller 316 can also be programmed to coordinate an automated permissive start procedure. In this example, the controller 316 would check essential parameters prior to startup to ensure a start condition that is safe and that is optimal for system performance.
In one application, a liquid ring vacuum pump is required to maintain a specific vacuum level of 500 mbar. The liquid ring vacuum pump includes a programmable logic controller, a variable frequency drive that is coupled to a motor that is driving the pump, and pressure transmitters (“PT”) to monitor the vacuum level at the inlet and discharge of the pump. The pump initially operates at a speed of 1750 revolutions per minute (“RPM”) to maintain the vacuum level of 500 mbar at the pump inlet. As the vacuum demand from the process increases or decreases, the pump needs to change speed to maintain the vacuum of 500 mbar at the inlet. For this to take place, the inlet vacuum PT reads the vacuum level at the inlet; if the PT at the inlet reads a value less than or more than the desired vacuum, the PLC would then send a signal to the VFD to change the pump speed accordingly. The change in speed will create more or less vacuum at the inlet. The PLC will continue to modulate the speed of the pump to maintain the desired vacuum level. Limits can be written into the logic that will only allow the pump to speed up and slow down within the specified limits. The limits can be pump limits, motor limits, or other system limits.
Modulating the speed of the motor to maintain the desired vacuum level rather than varying other parameters, such as water quantity within the pump or varying the amount of liquid/vapor bypass, allows the pump to operate more efficiently. This provides a potential cost savings to the pump user if the motor is able to run at lower speeds and lower seal water flow rates.
In some constructions, the PLC can send a signal to one or more solenoid-operated drain valves to automatically purge the liquid ring pump to help remove possible contamination from the machine. This can be on a timed schedule or can take place when the pump is experiencing higher than normal vibration or possibly a decrease in capacity—each of which can be sensed by instrumentation and provided to the PLC. By automatically draining the liquid in the pump, the user can lengthen the time between machine rebuilds or other costly maintenance requirements. This feature could also help users maintain higher capacity for the pump, for longer periods of time. This increases the pump efficiency over the life of the pump.
In another application, the PLC monitors and varies the seal water flow rate to maintain the inlet vacuum level of the pump. Varying the seal water flow rate, while running the pump at its design speed, provides the most efficient operation of the pump at various vacuum levels.
The pump system 300 provides a programmable platform for the pump 102 to be able to be controlled based on different operating characteristics that are specific to many different applications and installations, and give the pump 102 versatility in being controlled by several factors and interactions between operating characteristics that can change depending on the application. With the programmability of a PLC, for example, the control, monitoring, and operation of the pump system 300 can be tailored to different applications based on specific process needs.
This application claims priority to U.S. Provisional Application No. 62/463170, filed on Feb. 24, 2017, the entire content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62463170 | Feb 2017 | US |
