GB2591119A

GB2591119A - Control method and system

Info

Publication number: GB2591119A
Application number: GB2000667.2A
Authority: GB
Inventors: Peter Currie Ian
Original assignee: Quantum Engineering Developments Ltd
Current assignee: Quantum Engineering Developments Ltd
Priority date: 2020-01-16
Filing date: 2020-01-16
Publication date: 2021-07-21
Also published as: GB202000667D0

Abstract

A control system (200, fig 2) for a pumped liquid system 10 having a surge vessel 16 is used to maintain liquid level in the surge vessel 16 within predetermined amounts by determining a gas temperature of a gas contained in the surge vessel 16, comparing the determined gas temperature with a threshold temperature and using this to determine if gas should be added to, or removed from, the surge vessel 16 to enable a level of liquid L in the surge vessel to be maintained within predetermined amounts. The surge vessel 16 is used to dampen spikes or surges in pressure in the system.

Description

Title: Control Method and System

Description of Invention

The present invention relates to a method of operating a control system for a pumped liquid system and an associated control system.

In a pumped liquid system, flow-rate changes in the liquid (being a non-compressible fluid) can lead to pressure "spikes" or surges, which can lead to pressures in pipes of the system exceeding maximum operating pressures, or introducing negative pressures or even vacuum conditions in the system. Surges may have a negative impact on the pumped liquid system, for example damage to components of the pumped liquid system, for example fatigue, stress or shock to pipes and/or pipe joints, a risk of burst pipes, contamination of the liquid, supply disruption, non-compliance with regulations, financial loss. Flow rate variation in the system may be caused by normal liquid pump stop-start sequences, pump damage and/or failure, power supply damage and/or failure and general control and valve damage and/or failure in the liquid system, or even as a result of a major liquid flow valve being opened or closed, or rapidly changing demand.

It is known to provide pumped liquid systems with a surge vessel in which there is provided a trapped volume of gas, typically air, such that in the event of a surge, the tapped air volume in the vessel damps the surge.

It is known in the art to maintain the liquid level in such a surge vessel substantially constant against a varying head (i.e. pressure generated by pumps). This requires frequent operation of a compressor, which is not energy efficient, and can be noisy.

Surge vessels of the kind described may be partially or entirely located outdoors and therefore exposed to weather conditions, for example diurnal and seasonal temperature fluctuations. This can have an impact on the accuracy and efficacy of known systems..

An aim of the present invention is to provide an improved system and method for damping surges in a pumped liquid system.

There is provided a method of operating a control system for a pumped liquid system, the pumped liquid system including a surge vessel, the method including determining a gas temperature of a gas contained in the surge vessel, comparing the determined gas temperature with a threshold temperature, enabling a level of liquid in the surge vessel to vary, whilst maintaining a volume of the gas contained in the surge vessel between predetermined limits.

The method may include maintaining the gas pressure of the gas contained in the surge vessel between predetermined limits.

The method may include determining a volume of the gas contained in the surge vessel.

The method may include comparing a determined parameter with a corresponding predetermined value.

The determined parameter may be the level of liquid in the surge vessel.

The determined parameter may be a change of the level of liquid in the surge vessel.

The determined parameter may be a rate of change of the level of liquid in the surge vessel.

In the event that one or more of the determined parameters exceeds the corresponding predetermined value, the method may include performing a correction step The correction step may include adjusting the liquid level in the vessel.

The method may include providing a plurality of corresponding predetermined values for the or each parameter.

Determining the gas temperature may include determining an ambient air temperature of the surge vessel.

Determining the gas temperature may include determining a temperature of gas in the surge vessel.

Determining the gas temperature of the gas in the surge vessel may include determining an average gas temperature There is also provided a control system for a pumped liquid system, the control system being operable in accordance with the claimed method.

There is also provided a pumped liquid system including a surge vessel and a control system as set out in the claims.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is an illustrative view of a pumped liquid system; and Figure 2 is a schematic representation of a control system for a pumped liquid system.

Referring to Figure 1, there is shown a pumped liquid system 10, including a supply of liquid 12, a fluid conduit 14, a surge vessel 16 and a pump 18. It will be understood that Figure 1 is a simplified system, and the fluid conduit 14 may include a plurality of pipes through which fluid may flow. The pump 18 may include a single pump or a plurality of pumps. The or each pump 18 may operate at variable speeds and may operate to pump liquid in the system 10 from one location to another. The operation of the or each pump may control the source and/or destination of a flow or quantity of liquid. The pumped liquid system 10 may also include a valve 20. The valve 20 may be operable to control the flow of gas, e.g. air, into and/or out of the pumped liquid system 10.

The valve 20 may be operable to control the flow of gas, e.g. air, into and/or out of the vessel 16.

The surge vessel 16 includes an opening 160 which may be fluidly communicable with the fluid conduit 14. The opening 160 may be located at an in-use lower end of the surge vessel 16. Liquid may flow towards and/or through the opening 160 under stable conditions. For example the liquid may settle towards an in-use lower end of the surge vessel, where the opening 160 is located. The opening 160 may be located in an alternative part of the surge vessel 16, and suitable arrangements may be made for directing the liquid towards the opening 20.

The surge vessel 16 may be provided with a pressure gauge 162. The pressure gauge 162 may be operable to determine the pressure of a volume of gas, e.g. air 24 in the surge vessel 16. The pumped fluid system 10 may also include a compressor 164 for adjusting the volume of gas 24 in the surge vessel 16.

The pumped liquid system 10 is provided with a control system 200. The control system 200 includes a liquid level sensing apparatus 210. The control system 200 may also include a temperature sensing apparatus 220. The temperature sensing apparatus 220 may include a liquid temperature sensing device 230. The temperature sensing apparatus 220 may include a gas temperature sensing device 240. The gas temperature sensing device 240 may be operable to sense the temperature of ambient air outside the surge vessel 16. The gas temperature sensing device 240 may be operable to sense the temperature of the gas inside the surge vessel 16. The gas temperature sensing device 240 may include a plurality of temperature sensors. The control system 200 may also include a pressure sensing apparatus 250. The pressure sensing device 250 may be operable to sense the pressure of the gas in the surge vessel 16. The control system 200 may include a control unit 260 which is operable to receive inputs from the liquid level sensing apparatus 210, the temperature sensing apparatus 220 and the pressure sensing apparatus 250. The control system 200 may be operable to control the operation of the compressor 164. The control system 200 may include a user interface 270. The user interface 270 may be part of a remote device. The user interface may be part of a portable and/or wireless device, for example a mobile phone or tablet or the like.

The liquid level sensing apparatus 210 may include one or more physically actuated switches, or any other suitable method. The liquid sensing apparatus 210 may be operable to determine an increase and/or a decrease in liquid level L. The liquid level sensing device 210 may include a differential pressure device 25 and or capacitance probes, and or may utilise radar, or any other method for sensing the level of the liquid in the surge vessel 16.

The control system 200 may include a data logger 280. The data logger 280 may be a storage device, for example, configured to store information about 30 the pumped liquid system 10. The data logger 280 may be configured to communicate with other parts of the control system 200, for example the control unit 200 -continuously, intermittently, or upon request (for example, by the user and/or in the event of a particular condition or parameter being determined by the control system 200). The data logger may be configured to compile data relating to the pumped liquid system 10 over time. The data logger 280 may be configured to store information about the compressor 164 for example, time of start and/or stop, duration of operation, frequency of starts and/or stops, and the like. The data logger 280 may be configured to store information about operation of the control system 200 -for example, time of start and/or stop of the pump 18, duration of operation of the pump 18, frequency of starts and/or stops, and the like.

The data logger 280 may be configured to compile information from more than one part of the control system 200 at a particular time The data logger 280 may display data to a user via the user interface 270.

The control system 200 or part thereof may therefore be controllable using a remote device. As knock-on effects of changes in the liquid level L in the surge vessel 16 may be felt throughout the pumped liquid system 10, remote monitoring may be beneficial in allowing engineers and the like to be able to monitor the control system 200 while working on another part of the pumped liquid system 10, for example.

In use, the surge vessel 16 includes a volume of liquid 22 and a volume of gas, e.g. air, 24. The volume of liquid 22 contained in the surge vessel 16 defines a liquid level L. An initial air volume (IAV), i.e. the volume of gas in the surge vessel 16, may be dependent upon system-specific parameters. The pumped liquid system should be balanced, i.e. operating parameters, for example the optimum liquid level L and initial air volume, should be determined and set.

The control system may be operable to monitor one or more of: the liquid level L in the surge vessel 16, the ambient air temperature outside the surge vessel 16, the temperature of the volume of liquid 22 in the surge vessel 16, the pressure of the gas 24 in the surge vessel 16 and the temperature of the gas in the surge vessel 16.

Under normal (i.e. non-surging) operating conditions, it is desirable for the liquid level L to remain within a range, which may be determined by the configuration of the pumped liquid system 10 and/or the configuration, orientation or arrangement of the surge vessel 16. This range is determined to ensure that adequate surge protection may be provided by the surge vessel 16. Under normal (non-surging) operating conditions of the pumped liquid system 10 the pressure, i.e. head, in the fluid conduit 14 may remain within a range determined by the purpose and/or configuration of the pumped liquid system. Under normal operating conditions, the flow rate of liquid through the opening 160 is negligible. The pressure of the gas 24 in the surge vessel 16 is maintained substantially constant under steady state "normal conditions".

In the event of a surge, the dynamic pressure of the fluid in the fluid conduit 14 varies. A decrease in the dynamic pressure, for example as a result of a pump stop or failure, causes liquid to flow out of the surge vessel 16, through the opening 160, into the fluid conduit 14. An initial variation in dynamic pressure may initiate a cyclically varying flow rate of fluid through the opening 160, i.e. into and out of the surge vessel 16. The flow of liquid into and out of the surge vessel 16 acts to damp the surge, i.e. to return liquid pressure in the fluid conduit to within its normal operating range (e.g. a stable or steady state condition).

A decrease in the flow rate of liquid in the conduit 14 causes an increase in the flowrate of liquid out of the surge vessel 16, causing a drop in the liquid level L, and an increase in the flowrate of liquid in the fluid conduit 14. This changes the dynamic pressure in the fluid conduit 14 which, in turn, causes liquid to flow back into the surge vessel 16, through the opening 160, thus causing a rise in the liquid level L. This cycle continues, with the magnitude of the fluctuation in flow rate and the magnitude of the fluctuation of the flow rate decreasing over time. The magnitude of the fluctuation of the flowrate and period of the cycle may depend on a physical shape or profile -i.e. length, cross-section, configuration (e.g. bends), etc -of the fluid conduit 14.

In order to ensure that the surge vessel 16 is capable of providing adequate surge protection, it is desirable to maintain the liquid level L within a predetermined range, which is determined by the parameters and/or purpose of the pumped liquid system 10. For example, it may be desirable to maintain the liquid level L within a percentage of a predetermined liquid level L during normal operating conditions of the pumped liquid system 10. The liquid level L is dependent upon the volume of the gas 24 in the surge vessel 16. The total volume of the surge vessel 16 is equal to the sum of the volume of liquid 22 and the volume of the gas 24.

In accordance with Charles' gas law, when the pressure of a quantity of dry ideal gas is held constant, the temperature of the gas On Kelvin) and the volume of the gas will be in direct proportion, i.e.: V = kT (1) Where V is the volume of the gas, T is the temperature of the gas, and k is a non-zero constant.

As mentioned above, all or part of the surge vessel 16 of the pumped liquid 30 system 10, may be subject to varying ambient air temperatures. This may be a diurnal variation in temperature -the geographical location of the surge vessel 16 may mean the diurnal temperature ranges are very large -or a seasonal variation in temperature, for example. It will be appreciated that other factors may also affect the ambient air temperature, causing fluctuations in the ambient air temperature.

The control system 200 may monitor the ambient air temperature and the temperature of the gas inside the vessel 16, via the gas temperature sensing device 240, which provides an indication of the ambient air temperature and the temperature of the gas inside the surge vessel 16 to the control unit 260.

The temperature of the liquid 22 in the surge vessel 16 may also be monitored.

The temperature of the liquid 22 may be used as a reference value. A temperature differential between the ambient air temperature and the temperature of the liquid 22 may be determined. The temperature sensing device 240 may take temperature measurements at different locations relative to the surge vessel 16. The temperature sensing device 240 may include a plurality of transducers, each of which is operable to sample temperatures, which may include ambient air temperature(s). The temperatures may be sampled multiple times per second. An average ambient air temperature may be obtained. It is possible for temperature gradients to occur within the surge vessel 16, and determining an average ambient air temperature, corrects for such gradients. The liquid temperature may be sensed at multiple locations, using a plurality of transducers within the surge vessel 16 and an average liquid temperature determined.

It is thus possible to determine the temperature of the gas 24 in the surge vessel 16, and hence determine the volume of the gas 24. In the event of an increase in temperature, the volume of the gas 24 will increase, thus decreasing the liquid level L. The pressure is maintained substantially constant, such that the liquid level L is able to vary. As mentioned above, it is desirable to maintain the liquid level L between predetermined limits, such that adequate surge protection may be provided by the vessel. If there is insufficient liquid in the surge vessel 16 when low pressure occurs in the fluid conduit 14, then the fluid flow in the pumped liquid system 10 may be affected which can result in reduced protection of the system. If there is too much liquid in the surge vessel 16, the surge vessel 16 may be unable to accommodate the ingress of sufficient liquid into the vessel 16 during a surge.

In the event that the liquid level sensing apparatus 210 indicates that the liquid level L has reached one of an upper or lower liquid level threshold, the control system 200 may provide an indication that the liquid level is approaching or has moved outside one of the predetermined limits. The indication may be in the form of an alarm. The control system 200 may provide an indication that the liquid level L has changed by a predetermined amount. The control system 200 may be operable to perform a correction step, in the event that the liquid level is moving towards and/or has reached a predetermined limit, for example the upper or lower liquid level threshold.

The control system 200 may be operable to perform a correction step in the event that the liquid level L has changed by a predetermined amount. A correction step may adjust the liquid level L such that it returns to within the predetermined limits. This correction step may include controlling operation of the compressor, to adjust the gas volume in the surge vessel. The performance of a correction step may be automatic, for example in the event of the control system 200 determining that a correction is necessary. Alternatively, a correction step may be effected manually, for example by a user or an engineer.

The control system may be programmed with a normal operating temperature or a range of normal operating temperatures. The or each normal operating temperature may be dependent upon geographical location of the surge vessel, which may affect diurnal ambient air temperature ranges. The control system may be programmed with a plurality of normal operating temperatures or a number of ranges. For example, the normal ambient air temperature at night is typically lower than during the day, and so the control system may be programmed to take this into account. Seasonal variations in temperature may also be taken into account. Ambient air temperatures which are outside the normal or expected range may indicate that it is necessary to perform a correction step, to ensure that the surge vessel continues to provide adequate surge protection despite the conditions not being as expected for the time of day or time of year. Ambient air temperatures outside the normal or expected range may be an indication of an error or fault. Therefore it is advantageous to take multiple ambient air temperature readings, and also to monitor the liquid temperature. This way, faults and errors can be disregarded or smoothed.

A pumped fluid system 10 may include a plurality of surge vessels 16 and a plurality of conduits 14 and must be balanced. Parameters, for example expected ambient temperatures and "normal" operating conditions may be different for each surge vessel 16 may be determined individually. Each surge vessel 16 may have a corresponding control system 200. Each control system 200 may be programmed with the appropriate settings, e.g. normal ambient temperatures (or temperature ranges) for its respective surge vessel 16. The settings may be different for each surge vessel 16. Each surge vessel 16 in a pumped liquid system 10 may advantageously be located at the same height above sea level and/or have the same substantially horizontal cross section. These measures simplify balancing the pumped liquid system 10.

An advantage of the present invention is that it is possible to maintain conditions which enable adequate surge protection regardless of variation in ambient temperature, without having to operate the compressor frequently or continuously. The operating times of the compressor are significantly reduced compared with known systems. This is reduces the energy consumed by the compressor 164, and therefore provides an environmental benefit.

Furthermore, the compressor requires less maintenance and will be required to be replaced much less frequently than the compressors of known systems This provides a further environmental benefit.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

Claims

CLAIMS1. A method of operating a control system for a pumped liquid system, the pumped liquid system including a surge vessel, the method including determining a gas temperature of a gas contained in the surge vessel, comparing the determined gas temperature with a threshold temperature, enabling a level of liquid in the surge vessel to vary, whilst maintaining a volume of the gas contained in the surge vessel between predetermined limits.
2. A method according to claim 1 including maintaining the gas pressure of the gas contained in the surge vessel between predetermined limits.
3 A method according to claim 1 or claim 2 including determining a volume of the gas contained in the surge vessel.
4. A method according to any of the preceding claims including comparing a determined parameter with a corresponding predetermined value.
5. A method according to claim 4 wherein the determined parameter is the level of liquid in the surge vessel.
6. A method according to claim 4 or claim 5 wherein the determined parameter is a change of the level of liquid in the surge vessel.
7. A method according to any of claims 4 to 6 wherein the determined parameter is a rate of change of the level of liquid in the surge vessel.
8. A method according to any of claims 4 to 7 wherein in the event that one or more of the determined parameters exceeds the corresponding predetermined value, the method includes performing a correction step.
9 A method according to claim 8 wherein the correction step includes adjusting the liquid level in the vessel.
10. A method according to any of the preceding claims including providing a plurality of corresponding predetermined values for the or each parameter.
11. A method according to any of the preceding claims wherein determining the gas temperature includes determining an ambient air temperature of the surge vessel.
12. A method according to any of the preceding claims wherein determining the gas temperature includes determining a temperature of gas in the surge vessel.
13. A method according to any of the preceding claims wherein determining the gas temperature of the gas in the surge vessel includes determining an average gas temperature.
14. A control system for a pumped liquid system, the control system being operable in accordance with the method of claims 1 to 13.
15. A pumped liquid system including a surge vessel and a control system according to claim 14.