Patent Description:
Liquid ring pumps are a known type of pump which are typically commercially used as vacuum pumps and as gas compressors. Liquid ring pumps typically include a housing with a chamber therein, a shaft extending into the chamber, an impeller mounted to the shaft, and a drive system such as a motor operably connected to the shaft to drive the shaft. The impeller and shaft are positioned eccentrically within the chamber of the liquid ring pump.

In operation, the chamber is partially filled with an operating liquid (also known as a service liquid). When the drive system drives the shaft and the impeller, a liquid ring is formed on the inner wall of the chamber, thereby providing a seal that isolates individual volumes between adjacent impeller vanes. The impeller and shaft are positioned eccentrically to the liquid ring, which results in a cyclic variation of the volumes enclosed between adjacent vanes of the impeller and the liquid ring.

In a portion of the chamber where the liquid ring is further away from the shaft, there is a larger volume between adjacent impeller vanes which results in a smaller pressure therein. This allows the portion where the liquid ring is further away from the shaft to act as a gas intake zone. In a portion of the chamber where the liquid ring is closer to the shaft, there is a smaller volume between adjacent impeller vanes which results in a larger pressure therein. This allows the portion where the liquid ring is closer to the shaft to act as a gas discharge zone.

Examples of liquid ring pumps include single-stage liquid ring pumps and multi-stage liquid ring pumps. Single-stage liquid ring pumps involve the use of only a single chamber and impeller. Multi-stage liquid ring pumps (e.g. two-stage) involve the use of multiple chambers and impellers connected in series.

The publications <CIT>, <CIT>, <CIT>, <CIT>, <CIT> are exemplifications of liquid ring pump systems and control for smooth and improved operation.

The present inventors have realised it is desirable to provide for controlling of a liquid ring pump in a way that prevents or opposes cavitation in that liquid ring vacuum pump. Cavitation tends to be a significant cause of wear and failure in certain liquid ring pumps, especially those operating at a low-pressure/high-vacuum condition. Such control advantageously tends to reduce or eliminate wear caused by cavitation.

In a first aspect, the present invention provides a control system comprising: a suction line; an exhaust line; an operating liquid line; a liquid ring pump comprising a suction input coupled to the suction line, an exhaust output coupled to the exhaust line, and a liquid input coupled to the operating liquid line; a motor configured to drive the liquid ring pump; a first sensor configured to measure a first parameter, the first parameter being a parameter of an exhaust fluid of the liquid ring pump; a second sensor configured to measure a second parameter, the second parameter being a parameter of a gas being received by the liquid ring pump via the suction line; and a controller operatively coupled to the first sensor, the second sensor, and the motor, and configured to calculate a vapour pressure of the operating liquid using the measurement of the first parameter; and control the motor based on the measurement of the second parameter and the calculated vapour pressure of the operating liquid.

The suction line, the exhaust line, and the operating liquid line may be separate independent lines to each other, separately connected to the liquid ring pump. The suction input, the exhaust output, and the liquid input may be separate or independent ports to each other on the liquid ring pump.

The controller may be coupled to the motor via one or more variable frequency drives (e.g. a single variable frequency drive). The controller may control the motor via the one or more variable frequency drives.

The first parameter may be a temperature. The second parameter may be a pressure. The controller may be configured to calculate, determine, or estimate a vapour pressure of the operating liquid using the first parameter. The controller may be configured to control the motor based on a function of the second parameter and the calculated, determined, or estimated vapour pressure of the operating liquid. The vapour pressure of the operating liquid may be calculated, determined, or estimated to be: <MAT> where A is a constant, m is a constant, Tn is a constant, and T<NUM> is the first parameter.

The function of the second parameter and the vapour pressure of the operating liquid may be: <MAT> where P<NUM> is the second parameter, and <MAT> where Pwv is the vapour pressure of the operating liquid and Poffset is an offset value.

The controller may be configured to determine an operating speed for the motor based on sensor measurements of the first sensor and the second sensor, and to control the motor in accordance with the determined operating speed. The controller may be a controller selected from the group of controllers consisting of a proportional controller, an integral controller, a derivative controller, a proportional-integral controller, a proportional-integral-derivative controller, a proportional-derivative controller, and a fuzzy logic controller.

The control system may further comprise an operating liquid recycling system configured to recycle operating liquid in the exhaust fluid of the liquid ring pump back into the liquid ring pump. The operating liquid recycling system may comprise a separator configured to separate operating liquid from the exhaust fluid of the liquid ring pump. The operating liquid recycling system may comprise a cooling means configured to cool the recycled operating liquid prior to the recycled operating liquid being received by the liquid ring pump.

The control system may further comprise a non-return valve disposed on the suction line and configured to permit fluid flow into the liquid ring pump and to oppose fluid flow out of the liquid ring pump. The control system may further comprise one or more spray nozzle disposed on the suction line and configured to receive operating liquid and to spray the received operating liquid into the suction line. For example, the one or more spray nozzles may be configured to receive operating liquid via the operating liquid line.

The control system may further comprising: one or more regulating devices configured to control flow of the operating liquid into the liquid ring pump. The control system may further comprise a third sensor configured to measure a third parameter, the third parameter being a parameter of an operating liquid received by the liquid ring pump via the operating liquid line. The controller may be further operatively coupled to the third sensor and the one or more regulating devices, and configured to control the one or more regulating devices based on sensor measurements of the first sensor and the third sensor.

In a further aspect, the present invention provides a control method for controlling a system. The system comprises: a suction line; an exhaust line; an operating liquid line; a liquid ring pump comprising a suction input coupled to the suction line, an exhaust output coupled to the exhaust line, and a liquid input coupled to the operating liquid line; and a motor configured to drive the liquid ring pump. The method comprises: measuring, by a first sensor, a first parameter, the first parameter being a parameter of an exhaust fluid of the liquid ring pump; measuring, by a second sensor, a second parameter, the second parameter being a parameter of a gas being received by the liquid ring pump via the suction line; calculating a vapour pressure of the operating liquid ising the measurement of the first parameter and controlling the motor based on the measurement of the second parameter and the calculated vapour pressure of the operating liquid.

<FIG> is a schematic illustration (not to scale) showing a vacuum system <NUM>. The vacuum system <NUM> is coupled to a facility <NUM> such that, in operation, the vacuum system <NUM> establishes a vacuum or low-pressure environment at the facility <NUM> by drawing gas (for example, air) from the facility <NUM>.

In this embodiment, the vacuum system <NUM> comprises a non-return valve <NUM>, one or more spray nozzles <NUM>, a liquid ring pump <NUM>, a motor <NUM>, a separator <NUM>, a pump system <NUM>, a heat exchanger <NUM>, a controller <NUM>, a first pressure sensor <NUM>, a first temperature sensor <NUM>, a second pressure sensor <NUM>, a first level sensor <NUM>, a second level sensor <NUM>, and a second temperature sensor <NUM>.

The facility <NUM> is connected to an inlet of the liquid ring pump <NUM> via a suction or vacuum line or pipe <NUM>.

The non-return valve <NUM> and the spray nozzle are disposed on the suction line <NUM>. The non-return valve <NUM> is disposed between the facility <NUM> and the spray nozzle <NUM>. The spray nozzle <NUM> is disposed between the non-return valve <NUM> and the liquid ring pump <NUM>.

The non-return valve <NUM> is configured to permit the flow of fluid (e.g. a gas such as air) from the facility <NUM> to the liquid ring pump <NUM>, and to prevent or oppose the flow of fluid in the reverse direction, i.e. from the liquid ring pump <NUM> to the facility <NUM>.

The spray nozzle <NUM> is coupled to the heat exchanger <NUM> via a first operating liquid pipe <NUM>. The spray nozzle <NUM> is configured to receive an operating liquid (which in this embodiment is water) from the heat exchanger <NUM> via the first operating liquid pipe <NUM>. The spray nozzle <NUM> is configured to spray the operating liquid into the suction line <NUM> such that the operating liquid is mixed with the fluid (e.g. a gas such as air) in the suction line <NUM>.

In this embodiment, the liquid ring pump <NUM> is a single-stage liquid ring pump.

A gas inlet of the liquid ring pump <NUM> is connected to the suction line <NUM>. A gas outlet of the liquid ring pump <NUM> is connected to an exhaust line or pipe <NUM>. The liquid ring pump <NUM> is coupled to the heat exchanger <NUM> via a second operating liquid pipe <NUM>. The liquid ring pump <NUM> is configured to receive the operating liquid from the heat exchanger <NUM> via the second operating liquid pipe <NUM>. The liquid ring pump <NUM> is driven by the motor <NUM>.

<FIG> is a schematic illustration (not to scale) of a cross section of an example liquid ring pump <NUM>. The remainder of the vacuum system <NUM> will be described in more detail later below after a description of the liquid ring pump <NUM> shown in <FIG>.

In this embodiment, the liquid ring pump <NUM> comprises a housing <NUM> that defines a substantially cylindrical chamber <NUM>, a shaft <NUM> extending into the chamber <NUM>, and an impeller <NUM> fixedly mounted to the shaft <NUM>. The gas inlet <NUM> of the liquid ring pump <NUM> (which is coupled to the suction line <NUM>) is fluidly connected to a gas intake of the chamber <NUM>. The gas outlet (not shown in <FIG>) of the liquid ring pump <NUM> is fluidly connected to a gas output of the chamber <NUM>.

During operation of the liquid ring pump <NUM>, the operating liquid is received in the chamber <NUM> via the suction line <NUM> (from the spray nozzle <NUM>) and via the second operating liquid pipe <NUM>. Also, the shaft <NUM> is rotated by the motor <NUM>, thereby rotating the impeller <NUM> within the chamber <NUM>. As the impeller <NUM> rotates, the operating liquid in the chamber <NUM> (not shown in the Figures) is forced against the walls of the chamber <NUM> thereby to form a liquid ring that seals and isolates individual volumes between adjacent impeller vanes. Also, gas (such as air) is drawn into the chamber <NUM> from the suction line <NUM> via the gas inlet <NUM> and the gas intake of the chamber <NUM>. This gas flows into the volumes formed between adjacent vanes of the impeller <NUM>. The rotation of the impeller <NUM> compresses the gas contained within the volume as it is moved from the gas intake of the chamber <NUM> to the gas output of the chamber <NUM>, where the compressed gas exits the chamber <NUM>. Compressed gas exiting the chamber <NUM> then exits the liquid ring pump via the gas outlet and the exhaust line <NUM>.

Returning now to the description of <FIG>, the exhaust line <NUM> is coupled between the gas outlet of the liquid ring pump <NUM> and an inlet of the separator <NUM>. The separator <NUM> is connected to the liquid ring pump <NUM> via the exhaust line <NUM> such that exhaust fluid (i.e. compressed gas, which may include water droplets and/or vapour) is received by the separator <NUM>.

The separator <NUM> is configured to separate the exhaust fluid received from the liquid ring pump <NUM> into gas (e.g. air) and the operating liquid. Thus, the separator <NUM> provides for recycling of the operating liquid.

The gas separated from the received exhaust fluid is expelled from the separator <NUM>, and the vacuum system <NUM>, via a system outlet pipe <NUM>.

In this embodiment, the separator <NUM> comprises a further inlet <NUM> via which the separator <NUM> may receive a supply of additional, or "top-up", operating liquid from an operating liquid source (not shown in the Figures). A first valve <NUM> is disposed along the further inlet <NUM>. The first valve <NUM> is configured to control the flow of the additional operating liquid into the separator <NUM> via the further inlet <NUM>. The first valve <NUM> may be a solenoid valve.

The separator <NUM> comprises three operating liquid outlets. A first operating liquid outlet of the separator <NUM> is coupled to the pump system <NUM> via a second operating liquid pipe <NUM> such that operating liquid may flow from the separator <NUM> to the pump system <NUM>. A second operating liquid outlet of the separator <NUM> is coupled to an overflow pipe <NUM>, which provides an outlet for excess operating liquid. A third operating liquid outlet of the separator <NUM> is coupled to a drain or evacuation pipe <NUM>, which provides a line via which the separator can be drained of operating liquid. A second valve <NUM> is disposed along the evacuation pipe <NUM>. The second valve <NUM> is configured to be in either an open or closed state thereby to allow or prevent the flow of the operating liquid out of the separator <NUM> via the evacuation pipe <NUM>, respectively. The second valve <NUM> may be a solenoid valve.

The separator <NUM> further comprises a level indicator <NUM> which is configured to provide an indication of the amount of operating liquid in the separator <NUM>, e.g. to a human user of the vacuum system <NUM>. The level indicator <NUM> may include, for example, a transparent window through which a user may view a liquid level within a liquid storage tank of the separator <NUM>.

In this embodiment, in addition to being coupled to the separator <NUM> via the second operating liquid pipe <NUM>, the pump system <NUM> is coupled to the heat exchanger <NUM> via a third operating liquid pipe <NUM>. The pump system <NUM> comprises a pump (e.g. a centrifugal pump) and a motor configured to drive that pump. The pump system <NUM> is configured to pump operating liquid out of the separator <NUM> via the second operating liquid pipe <NUM>, and to pump that operating liquid to the heat exchanger <NUM> via the third operating liquid pipe <NUM>.

The heat exchanger <NUM> is configured to receive relatively hot operating liquid from the pump system <NUM>, to cool that relatively hot operating liquid to provide relatively cool operating liquid, and to output that relatively cool operating liquid.

In this embodiment, the heat exchanger <NUM> is configured to cool the relatively hot operating liquid flowing through the heat exchanger <NUM> by transferring heat from that relatively hot operating liquid to a fluid coolant also flowing through the heat exchanger <NUM>. The operating liquid and the coolant are separated in the heat exchanger <NUM> by a solid wall via which heat is transferred, thereby to prevent mixing of the operating liquid with the coolant. The heat exchanger <NUM> receives the coolant from a coolant source (not shown in the Figures) via a coolant inlet <NUM>. The heat exchanger <NUM> expels coolant (to which heat has been transferred) via a coolant outlet <NUM>.

The heat exchanger <NUM> comprises an operating liquid outlet from which the cooled operating liquid flows (i.e. is pumped by the pump system <NUM>). The operating liquid outlet is coupled to a fourth operating liquid pipe <NUM>. In this embodiment, the fourth operating liquid pipe <NUM> is connected to the first and second operating liquid pipes <NUM>, <NUM>. Thus, the heat exchanger <NUM> is connected to the spray nozzle <NUM> via the fourth operating liquid pipe <NUM> and the first operating liquid pipe <NUM> such that, in operation, the cooled operating liquid is pumped by the pump system <NUM> from the heat exchanger <NUM> to the spray nozzle <NUM>. Also, the heat exchanger <NUM> is connected to the liquid ring pump <NUM> via the fourth operating liquid pipe <NUM> and the second operating liquid pipe <NUM> such that, in operation, the cooled operating liquid is pumped by the pump system <NUM> from the heat exchanger <NUM> to the liquid ring pump <NUM>.

The controller <NUM> may comprise one or more processors. In this embodiment, the controller <NUM> comprises two variable frequency drives (VFD). One of the VFDs is configured to control the speed of the motor <NUM>. The other of the VFDs is configured to control the speed of the motor of the pump system <NUM>. As described in more detail later below with reference to <FIG> and <FIG>, the controller <NUM> is configured to receive sensor measurements from the sensors <NUM>-<NUM>. The controller <NUM> is further configured to process some or all of these sensor measurements, and based on this sensor data processing control operation of the motor <NUM> and the pump system <NUM>, via the VFDs.

The controller <NUM> is connected to the motor <NUM> via a first of its VFDs and via a first connection <NUM> such that a control signal for controlling the motor <NUM> may be sent from the controller <NUM> to the motor <NUM>. The first connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection. The motor <NUM> is configured to operate in accordance with the control signal received by it from the controller <NUM>. Control of the motor <NUM> by the controller <NUM> is described in more detail later below with reference to <FIG>.

The controller <NUM> is connected to the pump system <NUM> via a second of its VFDs and via a second connection <NUM> such that a control signal for controlling the pump system <NUM> may be sent from the controller <NUM> to the motor of the pump system <NUM>. The second connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection. The pump system <NUM> is configured to operate in accordance with the control signal received by it from the controller <NUM>. Control of the pump system <NUM> by the controller <NUM> is described in more detail later below with reference to <FIG>.

The controller <NUM> is connected to the first valve <NUM> via a third connection <NUM> such that a control signal for controlling the first valve <NUM> may be sent from the controller <NUM> to the first valve <NUM>. The third connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection. The first valve <NUM> is configured to switch between its open and closed state (thereby to allow or prevent the flow of the additional operating liquid into the separator <NUM>, respectively) in accordance with the control signal received by it from the controller <NUM>.

The first pressure sensor <NUM> is coupled to the suction line <NUM> between the facility <NUM> and the non-return valve <NUM>. The first pressure sensor <NUM> is configured to measure a pressure of the gas flowing in the suction line <NUM>, i.e. the pressure of the gas being pumped from the facility <NUM> by the action of the liquid ring pump <NUM>. The first pressure sensor <NUM> may be any appropriate type of pressure sensor. The first pressure sensor <NUM> is connected to the controller <NUM> via a fourth connection <NUM> such that the measurements taken by the first pressure sensor <NUM> are sent from the first pressure sensor <NUM> to the controller <NUM>. The fourth connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection.

The first temperature sensor <NUM> is coupled to the exhaust line <NUM> between the liquid ring pump <NUM> and the separator <NUM>. The first temperature sensor <NUM> is configured to measure a temperature of the exhaust fluid of the liquid ring pump <NUM> flowing in the exhaust line <NUM>, i.e. the temperature of the air and water mixture being pumped by the liquid ring pump <NUM> to the separator <NUM>. The first temperature sensor <NUM> may be any appropriate type of temperature sensor. The first temperature sensor <NUM> is connected to the controller <NUM> via a fifth connection <NUM> such that the measurements taken by the first temperature sensor <NUM> are sent from the first temperature sensor <NUM> to the controller <NUM>. The fifth connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection.

The second pressure sensor <NUM> is coupled to the separator <NUM>. The second pressure sensor <NUM> is configured to measure a pressure of fluid within the separator <NUM>. The second pressure sensor <NUM> may be any appropriate type of pressure sensor, and may include a combined pressure sensor and switch. The second pressure sensor <NUM> is connected to the controller <NUM> via a sixth connection <NUM> such that the measurements taken by the second pressure sensor <NUM> are sent from the second pressure sensor <NUM> to the controller <NUM>. The sixth connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection.

In some embodiments, the controller <NUM> is configured to control operation of one or both of the motor <NUM> and the pump system <NUM> (e.g. via respective VFDs) based on measurements received from the second pressure sensor <NUM>. For example, if measurements received from the second pressure sensor <NUM> indicate that the pressure in the separator <NUM> is too high (e.g. above a predetermined threshold value, such as <NUM> bar(g)), the controller <NUM> may reduce the speed of or shut down one or both of the motor <NUM> and the pump system <NUM>. The controller <NUM> may display a warning to a user of the vacuum system prior to controlling or shutting down one or both of the motor <NUM> and the pump system <NUM>, thereby allowing the user to perform remedial action prior to the controller <NUM> acting.

The first level sensor <NUM> is coupled to the separator <NUM>. The first level sensor <NUM> is configured to detect or measure a level of the operating liquid within the separator <NUM>, e.g. within the storage tank of the separator <NUM>. In particular, in this embodiment, the first level sensor <NUM> is configured to detect when the operating liquid level within the separator <NUM> reaches a first level corresponding to maximum level for the separator <NUM>. The first level sensor <NUM> is connected to the controller <NUM> via a seventh connection <NUM> such that, in the event that the operating liquid level within the separator <NUM> reaches the first (maximum) level, a corresponding signal or indication is sent from the first level sensor <NUM> to the controller <NUM>. The seventh connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection.

The second level sensor <NUM> is coupled to the separator <NUM>. The second level sensor <NUM> is configured to detect or measure a level the operating liquid within the separator <NUM>, e.g. within the storage tank of the separator <NUM>. In particular, in this embodiment, the second level sensor <NUM> is configured to detect when the operating liquid level within the separator <NUM> reaches a second level corresponding to minimum level for the separator <NUM>. The second level sensor <NUM> is connected to the controller <NUM> via an eighth connection <NUM> such that, in the event that the operating liquid level within the separator <NUM> reaches the second (minimum) level, a corresponding signal or indication is sent from the second level sensor <NUM> to the controller <NUM>. The eighth connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection.

In some embodiments, the controller <NUM> is configured to control operation of the first valve <NUM> based on measurements received from the first and/or second level sensors <NUM>, <NUM>. For example, if measurements received from the second level sensor <NUM> indicate that the operating liquid level is at or below the minimum level, the controller <NUM> may open the first valve <NUM> thereby to allow additional operating liquid to flow into the separator <NUM>. If measurements received from the second level sensor <NUM> indicate that the operating liquid level is at or above the maximum level, the controller <NUM> may close the first valve <NUM> thereby preventing additional operating liquid to flow into the separator <NUM>. In some embodiments, the controller <NUM> also controls operation of the second valve <NUM> via a communication link not shown in the Figures. The controller <NUM> may control operation of the second valve <NUM> based on measurements received from the first and/or second level sensors <NUM>, <NUM>. For example, if measurements received from the first level sensor <NUM> indicate that the operating liquid level is at or above the maximum level, the controller <NUM> may open the second valve <NUM> thereby to allow operating liquid to drain out of the separator <NUM>. In some embodiments, the second valve <NUM> is a manual valve operated by a user.

The second temperature sensor <NUM> is coupled to the second operating liquid pipe <NUM> between the heat exchanger <NUM> and the liquid ring pump <NUM>. The second temperature sensor <NUM> is configured to measure a temperature of the operating liquid flowing (i.e. being pumped by the pump system <NUM>) into the liquid ring pump <NUM> via the second operating liquid pipe <NUM>. The second temperature sensor <NUM> may be any appropriate type of temperature sensor. The second temperature sensor <NUM> is connected to the controller <NUM> via a ninth connection <NUM> such that the measurements taken by the second temperature sensor <NUM> are sent from the second temperature sensor <NUM> to the controller <NUM>. The ninth connection <NUM> may be any appropriate type of connection including, but not limited to, an electrical wire or an optical fibre, or a wireless connection.

Thus, an embodiment of the vacuum system <NUM> is provided.

Apparatus, including the controller <NUM>, for implementing the above arrangement, and performing the method steps to be described later below, may be provided by configuring or adapting any suitable apparatus, for example one or more computers or other processing apparatus or processors, and/or providing additional modules. The apparatus may comprise a computer, a network of computers, or one or more processors, for implementing instructions and using data, including instructions and data in the form of a computer program or plurality of computer programs stored in or on a machine-readable storage medium such as computer memory, a computer disk, ROM, PROM etc., or any combination of these or other storage media.

Embodiments of control processes performable by the vacuum system <NUM> will now be described with reference to <FIG> and <FIG>. It should be noted that certain of the process steps depicted in the flowcharts of <FIG> and <FIG> and described below may be omitted or such process steps may be performed in differing order to that presented below and shown in <FIG> and <FIG>. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally.

<FIG> is a process flow chart showing certain steps of a first control process implemented by the vacuum system <NUM> in operation. Although the first control process per se does not form part of the claimed invention, it could be implemented in addition thereto.

At step s2, the first temperature sensor <NUM> measures a first temperature T<NUM>. The first temperature T<NUM> is a temperature of the exhaust fluid of the liquid ring pump <NUM> flowing in the exhaust line <NUM>, i.e. the temperature of the air and water mixture being pumped by the liquid ring pump <NUM> to the separator <NUM>. The first temperature T<NUM> measurement is sent by the first temperature sensor <NUM> to the controller <NUM> via the fifth connection <NUM>.

At step s4, the second temperature sensor <NUM> measures a second temperature T<NUM>. The second temperature T<NUM> is a temperature of the operating liquid being received by the liquid ring pump <NUM> via the second operating liquid pipe <NUM>. The second temperature T<NUM> measurement is sent by the second temperature sensor <NUM> to the controller <NUM> via the ninth connection <NUM>.

At step s6, the controller <NUM> determines a temperature difference as the difference between the measured first temperature T<NUM> and the measured second temperature T<NUM>. Thus, in this embodiment, the temperature difference ΔT is calculated as: <MAT>.

At step s8, the controller <NUM> acts to reduce or minimize the temperature difference ΔT by adjusting of a first control variable v<NUM>(t).

In some embodiments, the controller <NUM> attempts to equalise the temperature difference ΔT with a first threshold value, or to cause the temperature difference ΔT to be within a first threshold range (e.g. a first threshold value +/- a constant). The first threshold value may be any appropriate value, for example <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. The first threshold value may be determined by testing, for example to determine a threshold value associated with high or optimum liquid ring pump efficiency. The first threshold value may be dependent on a size or power of the liquid ring pump <NUM>.

In this embodiment, the first control variable v<NUM>(t) is an operating speed of the motor of the pump system <NUM>.

In this embodiment, the controller <NUM> is a proportional-integral (PI) controller. Thus, the controller <NUM> applies correction/adjustment to the first control variable v<NUM>(t) based on proportional and integral terms of the temperature difference ΔT. The adjusted value of the first control variable v<NUM>(t) may be determined as a weighted sum of the control terms (i.e. of the proportional and integral parameters determined by the controller <NUM>).

In this embodiment, if the temperature difference ΔT is too high, for example ΔT is above a threshold value such as the abovementioned first threshold value, the controller <NUM> increases the first control variable v<NUM>(t). (Increasing the first control variable v<NUM>(t) corresponds to speeding up the pump system <NUM>).

Similarly, if the temperature difference ΔT is too low, for example ΔT is below a threshold value such as the abovementioned first threshold value, the controller <NUM> decreases the first control variable v<NUM>(t). (Decreasing the first control variable v<NUM>(t) corresponds to slowing down the pump system <NUM>.

At step s10, the controller <NUM> controls (using a VFD) the pump system <NUM> using the adjusted first control variable v<NUM>(t).

In particular, the controller <NUM> generates a control signal for the motor pump system <NUM> based on the adjusted first control variable v<NUM>(t) determined at step s8. This control signal is then sent from the controller <NUM> to the pump system <NUM> via the second connection <NUM>. The pump system <NUM> operates in accordance with the received control signal.

Thus, in the event that the temperature difference ΔT is too high, the pump system <NUM> is sped up in accordance with the increased first control variable v<NUM>(t). Thus, the flow rate of relatively cool operating liquid into the liquid ring pump <NUM> is increased. This tends to cause a reduction in the first temperature T<NUM> measured by the first temperature sensor <NUM>, thereby reducing the temperature difference ΔT.

Similarly, in the event that the temperature difference ΔT is too low, the pump system <NUM> is slowed down in accordance with the decreased first control variable v<NUM>(t). Thus, the flow rate of relatively cool operating liquid into the liquid ring pump <NUM> is decreased. This tends to cause an increase in the first temperature T<NUM> measured by the first temperature sensor <NUM>, thereby increasing the temperature difference ΔT.

After step s10, the process of <FIG> repeats, for example until the vacuum system <NUM> is shutdown. The process of <FIG> may be performed continually, or more preferably continuously during operation of the vacuum system <NUM>.

Thus, a first control process implemented by the vacuum system <NUM> is provided. The first control process comprises a control loop feedback mechanism in which continuously modulated control of the pump system <NUM> is performed.

Advantageously, the above described system and first control process allows for the control of operating liquid temperature in a liquid ring pump.

The above described system and first control process advantageously tends to provide for improved performance and efficiency of the liquid ring pump.

The above described system and first control process advantageously tends to reduce the likelihood of overloading the liquid ring pump with operating liquid. Furthermore, the likelihood and/or severity of hydraulic shock (also called "water hammer") tends to be reduced. This tends to reduce damage to the liquid ring pump. Advantageously, the above described system and first control process tends to provide reduced or minimised operating liquid consumption. The operating liquid tends to be recycled in the above described system and first control process. This tends to reduce operating costs of the liquid ring pump.

The above described system and first control process advantageously tends to reduce the likelihood and/or severity of cavitation occurring in the liquid ring pump.

Advantageously, if the thermal load of the above described system is low, the pump system will tend to slow down. Thus, energy consumption tends to be reduced.

The speed that the liquid ring pump <NUM> is running, i.e. the speed that the motor <NUM> drives the liquid ring pump <NUM>, may be dependent on how close the actual inlet pressure (i.e. the pressure in the suction line <NUM>) is to a target inlet pressure which may be defined by the facility <NUM>. Furthermore, the speed that the liquid ring pump <NUM> is running can be limited by the so-called "anti-cavitation control" process which will now be described in more detail with reference to <FIG>.

<FIG> is a process flow chart showing certain steps of a second control process implemented by the vacuum system <NUM> in operation in accordance with the invention. The process of <FIG> may be regarded as an "anti-cavitation control" process.

At step s12, the first temperature sensor <NUM> measures a first temperature T<NUM>. The first temperature T<NUM> is a temperature of the exhaust fluid of the liquid ring pump <NUM> flowing in the exhaust line <NUM>, i.e. the temperature of the air and water mixture being pumped by the liquid ring pump <NUM> to the separator <NUM>. The first temperature T<NUM> measurement is sent by the first temperature sensor <NUM> to the controller <NUM> via the fifth connection <NUM>.

At step s14, the controller <NUM> determines or estimates the vapour pressure of the operating liquid in the liquid ring pump <NUM> using the measured first temperature T<NUM>. In this embodiment, the operating liquid is water and, thus, the controller determines the vapour pressure of water for the first temperature T<NUM>, which is hereafter referred to as "the water vapour pressure Pwv". In this embodiment, the water vapour pressure Pwv is determined using an approximation formula, in particular the Antoine equation. The water vapour pressure Pwv is determined as: <MAT>.

In some embodiments, one or more of the parameters A, m, and Tn may have different value to that given above.

At step s16, the controller <NUM> adds a so-called offset value to the determined water vapour pressure Pwv, thereby to determine an updated pressure value. Thus, in this embodiment the updated pressure value P is determined as: <MAT> where: Poffset is the offset value.

The offset value Poffset may be considered to be a safety margin. The offset value Poffset may be any appropriate value including but not limited to a value between 1mbar and 10mbar, e.g. 1mbar, 2mbar, 3mbar, 4mbar, 5mbar, 6mbar, 7mbar, 8mbar, 9mbar, or 10mbar. In some embodiments, use of the offset value Poffset is omitted.

At step s18, the first pressure sensor <NUM> measures a first pressure P<NUM>, the first pressure P<NUM> being the pressure of the gas flowing in the suction line <NUM>, i.e. the pressure P<NUM> of the gas being pumped from the facility <NUM> by the action of the liquid ring pump <NUM>. The first pressure P<NUM> measurement is sent by the first pressure sensor <NUM> to the controller <NUM> via the fourth connection <NUM>.

At step s20, the controller <NUM> compares the measured first pressure P<NUM> to the determined updated pressure value P.

For example, the controller <NUM> determines an error value as the difference between the measured first pressure P<NUM> and the determined updated pressure value P. Thus, the error value ΔP may be calculated as: <MAT>.

At step s22, the controller <NUM> adjusts a second control variable v<NUM>(t) based on the comparison performed at step s20. For example, the controller <NUM> may act to increase the error value ΔP by adjusting a second control variable v<NUM>(t).

In some embodiments, the controller <NUM> may adjust the second control variable v<NUM>(t) if the error value ΔP is equal to a second threshold value (e.g. if ΔP = <NUM>) or within a second threshold range (e.g. if ΔP ≤ <NUM>). The controller <NUM> may adjust the second control variable v<NUM>(t) to cause the error value ΔP to increase.

In this embodiment, the second control variable v<NUM>(t) is an operating speed of the motor <NUM>. The controller <NUM> may adjust the second control variable v<NUM>(t) to cause an increase in the error value ΔP by adjusting or varying the second control variable v<NUM>(t) in a way that would cause a decrease in the operating speed of the motor <NUM>. This reduction in operating speed of the motor <NUM> would tend to cause the liquid ring pump <NUM> to draw less gas from the facility <NUM> in a given time, which would tend to cause an increase in the pressure of the gas flowing in the suction line <NUM>, i.e. the first pressure P<NUM>.

In this embodiment, the controller <NUM> is a proportional-integral (PI) controller. Thus, the controller <NUM> applies correction/adjustment to the second control variable v<NUM>(t) based on proportional and integral terms, e.g., of the error value ΔP. The adjusted value of the second control variable v<NUM>(t) may be determined as a weighted sum of the control terms (i.e. of the proportional and integral parameters determined by the controller <NUM>).

In this embodiment, if the error value ΔP is too high, for example ΔP is above a threshold value or above a desired threshold range such as the abovementioned second threshold value or range, the controller <NUM> increases the second control variable v<NUM>(t). (Increasing the second control variable v<NUM>(t) corresponds to speeding up the motor <NUM> driving the liquid ring pump <NUM>, which causes gas to be removed from the facility <NUM> more quickly, thereby decreasing the first pressure P<NUM> of the gas flowing in the suction line <NUM>.

Similarly, if the error value ΔP is too low, for example ΔP is below a threshold value or below a desired threshold range such as the abovementioned second threshold value or range, the controller <NUM> decreases the second control variable v<NUM>(t). (Decreasing the second control variable v<NUM>(t) corresponds to slowing down the motor <NUM> driving the liquid ring pump <NUM>, which causes gas to be removed from the facility <NUM> less quickly, which may result in an increase in the first pressure P<NUM> of the gas flowing in the suction line <NUM>.

At step s24, the controller <NUM> controls the motor <NUM> using the adjusted second control variable v<NUM>(t).

In particular, the controller <NUM> generates a control signal for the motor <NUM> based on the adjusted second control variable v<NUM>(t) determined at step s22. This control signal is then sent from the controller <NUM> to the motor <NUM> via the first connection <NUM>. The motor <NUM> operates in accordance with the received control signal.

In the event that the error value ΔP is negative, the motor <NUM> is slowed down in accordance with the decreased second control variable v<NUM>(t). Thus, the operating speed of the liquid ring pump <NUM> is decreased resulting in a decrease of the flow rate of gas through the suction line <NUM> from the facility <NUM>. This tends to cause an increase in the first pressure P<NUM> measured by the first pressure sensor <NUM>, thereby increasing the error value ΔP.

Increasing the error value ΔP means that the difference between the first pressure P<NUM> and the water vapour pressure Pwv is increased. In other words, the pressure of the gas received by the liquid ring pump is moved away from the water vapour pressure Pwv. This advantageously tends to reduce the likelihood of the inlet gas causing cavitation in the liquid ring pump <NUM>.

After step s24, the process of <FIG> repeats, for example until the vacuum system <NUM> is shutdown. The process of <FIG> may be performed continually, or more preferably continuously during operation of the vacuum system <NUM>.

Thus, an embodiment of a second control process implemented by the vacuum system <NUM> is provided. The second control process comprises a control loop feedback mechanism in which continuously modulated control of the motor <NUM> is performed.

Advantageously, the above described system and second control process tends to allow for the control of fluid temperatures and pressures within a liquid ring pump.

The above described system and second control process advantageously tends to provide for improved reliability of the liquid ring pump.

The above described system and second control process advantageously tends to reduce the likelihood and/or severity of cavitation occurring in the liquid ring pump. For example, cavitation may be caused in the liquid ring pump by the inlet pressure (i.e. the pressure of gas from the suction line) being at or below the vapour pressure of the operating liquid in the liquid ring pump. The above described second control process advantageously tends to adjust the inlet pressure to move it away from vapour pressure of the operating liquid, thereby reducing the likelihood of cavitation. Thus, damage to the liquid ring pump caused by cavitation tends to be reduced or eliminated.

In the above described control processes, the liquid ring pump is operated with variable speed drive (VSD). In other words, the controller controls the liquid ring pump to vary the speed at which the liquid ring pump pumps gas from the facility. When VSD is used, there may be a risk of the liquid ring pump shutting down if it is run at too low a speed. If the liquid ring pump was to shut down, gas from the chamber of the liquid ring pump may attempt to flow back from the chamber and out of the liquid ring pump to the facility. The non-return valve advantageously tends to prevent or oppose this undesirable flow of gas, and is particularly beneficial for the liquid ring pump operated using VSD.

Advantageously, the spray nozzle may be operated to vary the temperature of the operating liquid entering the liquid ring pump.

In the above embodiments, the vacuum system comprises the elements described above with reference to <FIG>. In particular, the vacuum system comprises the non-return valve, the spray nozzle, the liquid ring pump, the motor, the separator, the pump, the heat exchanger, the controller, the first and second pressure sensors, the first and second temperature sensors, and the first and second level sensors, and the connections therebetween. However, in other embodiments the vacuum system comprises other elements instead of or in addition to those described above. Also, in other embodiments, some or all of the elements of the vacuum system may be connected together in a different appropriate way to that described above. For example, in some embodiments, one or more of the non-return valve, the spray nozzle, the pressure sensors, the temperature sensors, and the level sensors may be omitted. In some embodiments, multiple liquid ring pumps may be implemented.

In the above embodiments, the heat exchanger cools the operating liquid flowing therethrough. However, in other embodiments other cooling means are implemented to cool the operating liquid prior to it being received by the liquid ring pump, instead of or in addition to the heat exchanger.

In the above embodiments, a separator is implemented to recycle the operating liquid back into the liquid ring pump. However, in other embodiments a different type of recycling technique is implemented. The recycling of the operating liquid advantageously tends to reduce operating costs and water usage. Nevertheless, in some embodiments, recycling of the operating liquid is not performed. For example, the vacuum system may include an open loop operating liquid circulation system in which fresh operating liquid is supplied to the liquid ring pump, and expelled operating liquid may be discarded. Thus, the separator may be omitted.

In the above embodiments, the liquid ring pump is a single-stage liquid ring pump. However, in other embodiments the liquid ring pump is a different type of liquid ring pump, for example a multi-stage liquid ring pump.

In the above embodiments, the operating liquid is water. However, in other embodiments, the operating liquid is a different type of operating liquid.

In the above embodiments, the controller is a PI controller. However, in other embodiments, the controller is a different type of controller such as a proportional (P) controller, an integral (I) controller, a derivative (D) controller, a proportional-derivative controller (PD) controller, a proportional-integral-derivative controller (PID) controller, or a fuzzy logic controller.

In the above embodiments, a single controller controls operation of multiple system elements (e.g. the motors). However, in other embodiments multiple controllers may be used, each controlling a respective subset of the group of elements. For example, in some embodiments, each motor may have a respective dedicated controller.

In the above embodiments, the temperature difference is determined to be ΔT = T<NUM> - T<NUM>. However, in other embodiments the temperature difference is determined in a different way, for example using a different appropriate formula. For example, the temperature difference may be a different function of the first temperature T<NUM> and/or the second temperature T<NUM>. For example, weights may be applied to the measured temperatures T<NUM> and T<NUM>.

In the above embodiments, the Antoine equation is used to estimate the water vapour pressure Pwv as <MAT>. However, in other embodiments, the water vapour pressure in a different appropriate way, for example using a different approximation such as the August-Roche-Magnus (or Magnus-Tetens or Magnus) equation, the Tetens equation, the Buck equation, or the Goff-Gratch equation. In some embodiments, the water vapour pressure Pwv is determined as <MAT>.

In the above embodiments, the error value ΔP is determined to be ΔP = P<NUM> - P. However, in other embodiments the error value is determined in a different way, for example using a different appropriate formula. For example, the error value may be a different function of the first pressure P<NUM> and/or the first temperature T<NUM>. In some embodiments, weights may be applied to the measured pressure P<NUM> and/or the updated pressure value P.

In the above embodiments, the pump is controlled to regulate or modulate flow of the operating liquid into the liquid ring pump. However, in other embodiments, one or more different type of regulating device is implemented instead of or in addition to the pump, for example one or more valves for controlling a flow of operating liquid. The controller may be configured to control operation of the one or more regulating devices.

Claim 1:
A control system comprising:
a suction line (<NUM>);
an exhaust line (<NUM>);
an operating liquid line (<NUM>);
a liquid ring pump (<NUM>) comprising a suction input coupled to the suction line (<NUM>), an exhaust output coupled to the exhaust line (<NUM>), and a liquid input coupled to the operating liquid line (<NUM>);
a motor (<NUM>) configured to drive the liquid ring pump (<NUM>);
a first sensor (<NUM>) configured to measure a first parameter, the first parameter being a parameter of an exhaust fluid of the liquid ring pump (<NUM>);
a second sensor (<NUM>) configured to measure a second parameter, the second parameter being a parameter of a gas being received by the liquid ring pump via the suction line; and
a controller (<NUM>) operatively coupled to the first sensor (<NUM>), the second sensor (<NUM>), and the motor (<NUM>), and characterised in that the controller (<NUM>) is configured to:
calculate a vapour pressure of the operating liquid using the measurement of the first parameter; and
control the motor (<NUM>) based on the measurement of the second parameter and the calculated vapour pressure of the operating liquid.