Method and system for degassing liquid

Abstract

The invention relates to a method and system for liquid degassing. The degassing system preferably comprises: a centrifugal pump; a tank; a throttling device arranged at the upper end of the tank for receiving the liquid to be degassed passing through the throttling device; and an outlet arranged at the lower end of the tank and fluidly connected to the suction side of the centrifugal pump; a liquid outlet connection fluidly connected to the discharge side of the centrifugal pump to discharge at least partially degassed liquid; and a gas outlet fluidly connected to the tank to discharge gas accumulated in the tank during degassing of the liquid. In a preferred embodiment, a method includes selecting a process pressure to be attained in a tank upstream of a centrifugal pump and setting a rotational speed of the centrifugal pump to provide the selected process pressure to be attained.

Description

Technical Field

[0001] The present invention relates to a method and a system for degassing a liquid. The degassing system preferably comprises: a centrifugal pump; a tank; a throttling device, which is arranged at the upper end of the tank, the tank being used to receive the liquid to be degassed through the throttling device; and an outlet, which is arranged at the lower end of the tank and is fluidly connected to the suction side of the centrifugal pump; a liquid outlet connection, which is fluidly connected to the discharge side of the centrifugal pump to discharge at least part of the degassed liquid; and a gas outlet, which is fluidly connected to the tank to discharge gas accumulated in the tank during degassing of the liquid. In a preferred embodiment, the method comprises selecting a process pressure to be obtained in the tank upstream of the centrifugal pump and setting the rotation speed of the centrifugal pump to provide the selected process pressure to be obtained. Background Art

[0002] During the use of a liquid-based system such as an HVAC system or a general system that includes liquid circulation, air or other gaseous materials may be present in the liquid. Such gaseous materials may originate from liquid being added to the system from a liquid source that has not been degassed, which is often the case when tap water is used. Gaseous materials may also originate from entrainment of gas into a liquid-based system.

[0003] In particular, in liquid-based heating or cooling systems, air in the liquid results in a reduction in heating or cooling capacity because the specific heat capacity of air is significantly lower than that of the liquid, and thus the presence of air in the liquid results in a reduction in the specific heat capacity of the liquid containing air compared to the liquid without air. This reduction in specific heat capacity results in less efficient heating or cooling, particularly because more liquid has to be transported to meet a given heating or cooling capacity.

[0004] Another problem associated with air in liquids is that because air contains oxygen, it can cause corrosion on surface metal parts from the inside, which can cause leaks and / or increased flow resistance.

[0005] Yet another problem associated with air in liquid is cavitation in pumps or other areas where pressure drops because the gas in the liquid reduces the pressure at which cavitation occurs.

[0006] Systems for degassing liquids are known and generally comprise a plurality of discrete components, such as valves, tanks, pumps, which are assembled by fittings to form a degassing system, which is fluidly connected to a liquid-based system containing the liquid to be degassed. In addition, the pump, which causes the pressure in the tank to drop for degassing purposes, is run at a constant speed.

[0007] Although the pressure in the liquid-based system to be degassed should ideally be constant, the pressure often changes, for example due to temperature changes in the liquid. In other cases, the same degassing system is used for different liquid-based systems with different pressure characteristics. This often results in cavitation and / or less than ideal operation of the pump.

[0008] In order to avoid cavitation, a controllable throttling device is usually arranged on the discharge side of the pump to add flow resistance to the degassing system to avoid cavitation and such throttling device represents additional power consumption of the degassing system.

[0009] US 8,562,719 B2 shows an example of a degassing system comprising a manually adjustable outlet valve arranged at the discharge side of a pump.

[0010] Therefore, an improved method and system for degassing would be advantageous, and in particular a more efficient method or system for degassing would be advantageous.

[0011] Purpose of the Invention

[0012] It is an object of the present invention to provide a method and system for degassing which is less prone to cavitation.

[0013] Another object of the present invention is to provide a more energy-efficient method for degassing liquids.

[0014] Another object of the present invention is to provide an alternative to the prior art.

[0015] In particular, it can be seen that one object of the present invention is to provide a method and system that solves the above-mentioned problems of the prior art. Summary of the invention

[0016] Therefore, in a first aspect of the present invention, the above objects and several other objects are intended to be achieved by providing a method for degassing a liquid using a liquid degassing system, the liquid degassing system comprising:

[0017] a centrifugal pump having a suction side and a discharge side, the pump being a variable speed pump;

[0018] a tank, preferably having a vertical extension, having a liquid inlet connection including a throttling device arranged at the upper end of the tank for receiving the liquid to be degassed through the throttling device, and an outlet arranged at the lower end of the tank, fluidly connected to the suction side of the centrifugal pump;

[0019] a liquid outlet connection fluidly connected to the discharge side of the centrifugal pump to discharge the at least partially degassed liquid; and

[0020] • A gas outlet fluidly connected to the tank to vent gas accumulated in the tank during degassing of the liquid.

[0021] By arranging the throttling device at the upper end of the tank, efficient degassing can be provided. In a preferred embodiment, the liquid to be degassed enters the interior of the tank through the throttling device and possibly leaves the throttling device as droplets (such as mist). Due to the higher total surface area of ​​the droplets (such as mist), the formation of such droplets has an improved degassing effect.

[0022] In a first aspect, the method comprises:

[0023] arranging the liquid degassing system to be fluidly connected to the system being degassed carrying the liquid to be degassed so that the liquid flows into the tank;

[0024] · selection of the process pressure to be obtained in the tank upstream of the centrifugal pump;

[0025] • Setting the rotation speed of the centrifugal pump to provide the selected process pressure (Pt) to be achieved.

[0026] Thereby, the process pressure and the rotational speed of the centrifugal pump can be set in an energy-optimized manner and / or in a manner that at least mitigates cavitation.The rotational speed reference of the centrifugal pump is usually preferably used to reference the rotation of a characteristic part of the pump, such as the impeller of the centrifugal pump.

[0027] In a second aspect, the present invention relates to a method for degassing a liquid using a liquid degassing system, the liquid degassing system comprising:

[0028] A centrifugal pump having a suction side and a discharge side, the pump being a variable speed pump, typically driven by an electric motor with an electrical / electronic control to control the speed of the centrifugal pump;

[0029] a tank, preferably having a vertical extension, having a liquid inlet connection including a throttling device arranged at the upper end of the tank for receiving the liquid to be degassed through the throttling device, and an outlet arranged at the lower end of the tank, fluidly connected to the suction side of the centrifugal pump;

[0030] a liquid outlet connection fluidly connected to the discharge side of the centrifugal pump to discharge the at least partially degassed liquid; and

[0031] and a gas outlet fluidly connected to the tank to discharge gas accumulated in the tank during degassing of the liquid.

[0032] In a second aspect, a method is performed in one or more treatment steps, each treatment step having a duration between the start and the end of the treatment step achieved by starting and stopping a centrifugal pump, wherein the treatment step starts with liquid present in a tank, and, in one or more flushing steps, wherein gas accumulated in the tank during the treatment step is flushed out, the liquid degassing system being configured to determine during the treatment step an actual value of a degassing parameter, the degassing parameter being selected from:

[0033] the electrical power consumed by the electric motor during the driving of the centrifugal pump,

[0034] The speed of the electric motor, or

[0035] Handle stress realistically;

[0036] The method includes:

[0037] providing a dry-running threshold value for one of the degassing parameters, the dry-running threshold value representing a state in which the centrifugal pump is in an at least partially dry-running condition,

[0038] Determine the actual values ​​of the degassing parameters,

[0039] Comparing the actual value of the degassing parameter and ending the processing step if the actual value of the degassing parameter is outside the dry-running threshold.

[0040] Thereby, in particular it is detectable when substantially no more liquid is present in the tank, which can be used in particular for stopping the degassing, or other measures to be taken as described in detail herein.

[0041] In a third aspect, the present invention relates to a system for degassing a liquid, the system comprising:

[0042] A centrifugal pump having a suction side and a discharge side, the pump being a variable speed pump, typically driven by an electric motor with an electrical / electronic control to control the speed of the centrifugal pump;

[0043] a tank, preferably having a vertical extension, having a liquid inlet connection including a throttling device arranged at the upper end of the tank for receiving the liquid to be degassed through the throttling device, and an outlet arranged at the lower end of the tank, fluidly connected to the suction side of the centrifugal pump;

[0044] a liquid outlet connection fluidly connected to the discharge side of the centrifugal pump to discharge the at least partially degassed liquid; and

[0045] and a gas outlet fluidly connected to the tank to discharge gas accumulated in the tank during degassing of the liquid; and

[0046] a controller, such as a computer or similar computing device, which is typically configured by including a set of instructions,

[0047] To carry out the method according to the first and / or second aspect.

[0048] It is emphasized that although the preferred embodiments of the present invention are disclosed with reference to the degassing of liquids, the present invention is particularly useful in the degassing of water.

[0049] Each aspect of the invention may be combined with any of the other aspects. These and other aspects of the invention will become apparent from the following description with reference to the described embodiments.

[0050] The system being degassed is preferably used herein to mean a system containing a liquid to be degassed and to which a degassing system is fluidly connected to receive the liquid to be degassed and to deliver the at least partially degassed liquid. In a preferred embodiment, the system being degassed is an HVAC system (heating, ventilation and / or air conditioning system).

[0051] The process pressure to be achieved is generally used herein to denote the pressure at which degassing is to be carried out.

[0052] Actual process pressure is generally used herein to denote the actual pressure at which the degassing is performed. The actual process pressure may deviate from the process pressure to be achieved.

[0053] Water as used herein refers to a liquid containing water or a liquid that is substantially water. In a non-limiting example, the liquid containing water can be water with an antifreeze agent such as ethylene glycol.

[0054] Gas as used herein in relation to water deaeration generally refers to air.

[0055] The present invention can be implemented by means of hardware, software, firmware or any combination thereof. The present invention or some of its features can also be implemented as software running on one or more data processors and / or digital signal processors. Therefore, the method according to the present invention can be a computer-implemented method. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The present invention will now be described in more detail, particularly in accordance with a preferred embodiment of the invention, with reference to the accompanying drawings. The drawings illustrate ways of implementing the invention and should not be construed as limiting other possible embodiments that fall within the scope of the appended claims.

[0057] Figure 1 is a schematic illustration of a degassing system according to a preferred embodiment; the figure shows the components of the degassing system in a conceptual manner;

[0058] Figure 2is a schematic illustration of pressure changes in a liquid degassing system according to a preferred embodiment of the present invention;

[0059] Figure 3 is a schematic illustration of a method for determining a rotational speed of a pump in a liquid degassing system according to a preferred embodiment of the present invention;

[0060] Figure 4 is a schematic illustration of a method for determining a rotational speed of a pump in a liquid degassing system according to another preferred embodiment of the present invention;

[0061] FIG5 is a schematic graphical representation of processing steps according to a preferred embodiment;

[0062] Figure 6 is a schematic graphical representation of the processing steps according to the preferred embodiment introducing a processing cycle, a maximum processing time, a processing time and a minimum processing time;

[0063] Figure 7 is a longitudinal cross-sectional representation of a liquid degassing system according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0064] Hereinafter, a detailed description of various embodiments of a method for degassing a liquid is disclosed. This method utilizes a liquid degassing system that includes a plurality of components, as will be disclosed below. The method is designed to degas a liquid contained in a system being degassed as referred to herein.

[0065] An example of a system being degassed is an HVAC system (heating, ventilation and / or air conditioning system) and in this system the liquid is at a static pressure (assessed under no-flow conditions), usually elevated relative to atmospheric pressure. To degas a liquid, the liquid is introduced into a tank where the static pressure is reduced by the use of a pump. The reduced pressure combined with the flow rate of liquid into the tank being less than the flow rate of liquid out of the tank creates a free liquid surface in the tank with a gas phase above it. The main principle for degassing is described by Henry's law, which states that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.

[0066] refer to Figure 1 , which schematically shows a degassing system according to a preferred embodiment, which is used in combination with the method for degassing a liquid according to the present invention. Figure 1The components of a degassing system are shown in a conceptual manner. As shown, the system comprises a centrifugal pump 3 having a suction side and a discharge side, and the pump 3 is of a type having a variable and controllable rotational speed. A tank 30 is included in the system. The tank 30 has a vertical extension and has a liquid inlet connection 31, which includes a throttling device 43 arranged inside the tank 30 and located at the upper end of the tank, and the tank is used to receive the liquid to be degassed through the throttling device 43. The outlet is arranged at the lower end of the tank 30 and is fluidically connected to the suction side of the centrifugal pump 3. Therefore, due to the presence of the throttling device 43 and the pump 3 capable of providing suction, the pressure in the tank 30 can drop to a value lower than the pressure in the fluid upstream of the throttling device 43. In addition, due to the presence of the throttling device, the pump will suck out more liquid from the tank 30 than the liquid entering the tank 30, thereby providing a gradually increasing gas volume above the liquid level inside the tank 30.

[0067] The liquid outlet connection 32 is fluidly connected to the discharge side of the centrifugal pump to discharge the at least partially degassed liquid; and the gas outlet 39 is fluidly connected to the tank 30 to discharge the gas accumulated in the tank 30 during the degassing of the liquid. In a preferred embodiment, the gas outlet 39 includes a vent, such as an automatic vent. In addition, a check valve 44 can be arranged to prevent gas from flowing into the tank through the gas outlet 39. An optional filter or strainer 31 can be provided to filter or strain the liquid before it is introduced into the tank 30.

[0068] In many preferred embodiments it is useful to determine the pressure in the degassing system and to achieve this a pressure sensor 45 may be arranged in the degassing system. Figure 1 In the illustrated embodiment of the embodiment of FIG. 4 , the position of the pressure sensor 45 is located on the suction side of the pump 3 , but other positions for determining the pressure are possible, such as in the interior of the tank 30 .

[0069] When the degassing system is used for degassing, the degassing system is arranged to be fluidly connected to the system being degassed carrying the liquid to be degassed, so that the liquid flows into the tank 30. Figure 2 Schematically shown in FIG, wherein a throttling device 43, a tank 30 and a centrifugal pump 3 are shown in conjunction with the piping of the system being degassed. Although the piping is shown as open for flow, whereby some liquid bypasses the degassing system, one or more valves (not shown) may be arranged to direct liquid into the degassing system and at least partially block the bypass flow of liquid. Figure 2 The Ps in the table is used to indicate the pressure in the system being degassed.

[0070] The method according to a preferred embodiment may comprise selecting a process pressure Pt to be obtained in the tank 30 upstream of the centrifugal pump 3. This process pressure may be referred to as negative pressure, since it is generally lower than atmospheric pressure.

[0071] Once the process pressure Pt to be obtained is selected, the rotational speed of the centrifugal pump 3 is set to provide the selected process pressure Pt.

[0072] In many preferred embodiments, the pressure is determined by using a pressure sensor, as disclosed below, which is arranged to determine the actual process pressure. The pressure can preferably be determined as the pressure difference between the atmospheric pressure outside the degassing system and the pressure in, for example, the tank 3 or the suction side of the centrifugal pump.

[0073] It should be noted that, for example, the speed of the centrifugal pump can be selected using the pump characteristics of the pump (corresponding values ​​of pressure difference and volume flow for a plurality of different speeds). However, this may require at least an indication of the fluid pressure upstream of the throttling. In such an embodiment, the method may include the steps of determining the pressure Ps in the system being degassed and obtaining the flow resistance characteristics of the throttling device 43.

[0074] The pressure Ps in the system being degassed can be determined by a pressure sensor or estimated based on operating parameters of the system being degassed, for example, based on the fact that the system being degassed is usually set to operate at a specific pressure. The flow resistance characteristics of the throttling device include the flow through the throttling device 43 and the corresponding values ​​of the pressure loss across the throttling device.

[0075] When the process pressure Pt to be obtained is known, the rotation speed of the pump can be determined based on the pump characteristics of the centrifugal pump 3. The rotation speed is determined so that the centrifugal pump 3 provides a pressure difference across the centrifugal pump 3 that matches the sum of the pressure Ps in the system being degassed and the process pressure Pt to be obtained (Ps+Pt) with one of the flow resistance characteristics.

[0076] This is Figure 3 Described in detail in . Figure 3 A and B show two different operating points of the centrifugal pump 3, which are plotted in a graph to illustrate the centrifugal pump n i Pump characteristics (pressure head H and volume flow Q) at various speeds. In the graph, the flow resistance through the throttling device 43 is also plotted (pressure loss as a function of volume flow).

[0077] exist Figure 2In A, the pressure in the system being degassed is (non-limiting example) Ps=2.0 bar, and the process pressure Pt to be obtained is selected as Pt=0.8 bar (non-limiting example). Therefore, the pressure difference provided by the centrifugal pump is Ps+Pt=2.8 bar. Please note that the pressure in the system being degassed is given relative to atmospheric pressure, whereby Ps+Pt is 2.8 bar, which is equal to an absolute pressure of 0.2 bar. Here, it is assumed that the flow resistance between the discharge side and the system being degassed can be ignored, and the liquid outlet connection 32 connects the degassing system to the system being degassed. This is usually achieved by not arranging a valve or similar throttling device on the discharge side of the centrifugal pump 3.

[0078] like Figure 2 As shown in A, once Pt+Ps is known, the rotational speed of the centrifugal pump 3 is selected as the point of the pump characteristic at which the flow resistance characteristic of the throttling device 43 is equal to Pt+Ps.

[0079] During operation of the degassing system, the pressure in the system being degassed may change, for example to a pressure of Ps=1.0 bar. The sum of the pressures Pt+Ps is thus 1.8 bar. If the rotational speed of the pump 3 is not changed, the centrifugal pump will try to generate a pressure difference of 2.8 bar, which is obviously not achievable. The result is usually that cavitation will occur in the impeller of the centrifugal pump and the pump will operate under suboptimal energy conditions, for example using more power than is required to perform the degassing. In order to avoid this, as Figure 3 As shown in B, a new rotation speed of the centrifugal pump 3 is selected.

[0080] In another embodiment of the present invention, the rotational speed of the centrifugal pump can be determined by a so-called iterative process. In such an embodiment, setting the rotational speed of the centrifugal pump 3 to provide a selected process pressure Pt to be obtained may include determining the actual process pressure, wherein the actual process pressure is the pressure in the tank 30 or the pressure upstream of the centrifugal pump, such as the pressure on the suction side of the pump 3 or the pressure in the tank 30. It should be noted that the pressure loss between the tank 30 and the suction side of the centrifugal pump 3 is generally negligible, whereby, for the purposes of the present invention, these two pressures are replaceable. However, it is generally more practical to determine the pressure on the suction side of the centrifugal pump 2.

[0081] The iterative method comprises the steps of comparing the actual upstream pressure with the selected process pressure to be obtained Pt and, if there is a difference, adjusting the speed of the pump to set the actual upstream pressure substantially equal to the selected process pressure to be obtained Pt.

[0082] If the actual process pressure is less than the selected process pressure to be obtained, the rotation speed of the centrifugal pump 3 is increased, and if the actual process pressure is greater than the selected process pressure to be obtained, the rotation speed of the centrifugal pump is decreased.

[0083] Adjustments to the rotational speed are typically made incrementally, for example the rotational speed may be changed by a predetermined amount (e.g. 10 RPM increments) and the actual process pressure is compared to the selected process pressure to be achieved Pt after each increment of the rotational speed. This is typically done until the actual process pressure is substantially equal to the selected process pressure to be achieved Pt. Where the pressure in the system being degassed varies, for example, from time to time, adjustments to the rotational speed may be made while degassing is ongoing, although adjustments may not be made during periods of no pressure change.

[0084] Such an embodiment is Figure 4 It is schematically shown in Figure 4 In A, the degassing system operates at a pressure differential of 2.8 bar, based on the pressure in the system being degassed, Ps = 2 bar, and the actual process pressure of -0.8 bar. Figure 4 In the figures, the process pressures are given relative to atmospheric pressure which is defined as 0 bar.

[0085] In Figure A', the pressure in the system being degassed has dropped to Ps = 1.9 bar, whereby the actual process pressure is 0.9 bar, which is greater than the process pressure of 0.8 bar to be achieved. Therefore, the pressure difference to be achieved drops to 2.7 bar, and the rotation speed of the centrifugal pump 3 is set according to 2.7 bar. This is Figure 4 A”. In the case where the pressure Ps in the system increases, the process of adjusting the rotation speed of the centrifugal pump 3 is the same.

[0086] It should be noted that the examples regarding pressure levels do not limit the scope of the present invention.

[0087] The centrifugal pump 3 can be driven by a variety of different drivers, such as a hydraulic engine or an internal combustion engine. In many preferred embodiments, the degassing system includes an electric motor 5 with an electrical / electronic control, wherein the electric motor 5 is connected to the centrifugal pump 3 to drive the centrifugal pump 3. The electrical / electronic control device controls the speed of the electric motor, and thereby controls the speed of the centrifugal pump 3. The electric motor 5 can advantageously be liquid-cooled, such as by the liquid flowing through the degassing system. However, this embodiment may be limited to degassing liquids with relatively low temperatures (such as less than 70 degrees Celsius).

[0088] In a preferred embodiment, the pump 3 is driven by an electric motor, and the speed of the electric motor and thus the speed of the pump 3 is set by using a frequency converter that powers the electric motor driving the pump 3. In embodiments including a frequency converter, a mapping between the control input of the frequency converter and the speed of the pump 3 is preferably provided, whereby the corresponding speed can be set according to such mapping.

[0089] For example, although Figure 2The pump characteristic illustrated in may provide a mapping between pump speeds to meet a selected process pressure Pt based on throttle resistance, but such a pump characteristic may not be available or may not be as accurate as desired.

[0090] In this case, or as a general control method, a preferred embodiment includes controlling the rotation speed by a PID controller (Positive Integral Derivative Controller) or a PLC (Programmable Logic Controller). In such an embodiment, the actual degassing pressure in the degassing system is provided, for example as disclosed above with respect to the pressure sensor 45.

[0091] For the PID controller, the desired set point is the selected process pressure, the process variable is the actual process pressure (measured by pressure sensor 45), and the control parameter is the speed of pump 3. Thus, the PID controller will seek to minimize the difference between the actual process pressure and the selected process pressure by varying the speed of the pump.

[0092] As for the PLC controller, the PLC controller can be programmed to provide a speed signal to the pump 3 or to the frequency converter (when a frequency converter is used) based on an input signal representing the selected process pressure Pt.

[0093] Since the speed of the pump is controlled to set the speed of the centrifugal pump 3 to provide the selected process pressure, a substantially accurate control of the pressure is provided, which in turn optimizes degassing and reduces energy consumption. These benefits become greater when the pressure in the system being degassed varies over time because the speed can be varied, so as to provide a substantially constant process pressure, for example 0.2 bar (absolute pressure), thereby greatly reducing the risk of the pump running at a less efficient RPM (such as too high an RPM).

[0094] Therefore, the components of the degassing system according to the invention generally comprise a centrifugal pump 3 having a suction side and a discharge side and an electric motor with an electrical / electronic control, wherein the electric motor is connected to the centrifugal pump 3 to drive the centrifugal pump 3 .

[0095] The liquid degassing system further comprises a tank 30 having a vertical extension. The tank 30 has a liquid inlet connection 31 having a throttling device 43 arranged at the upper end of the tank 30 (for receiving the liquid to be degassed through the throttling device 43). "Arranged at the upper end" means that the liquid enters the tank 30 at the upper end. The tank 30 further has an outlet arranged at the lower end of the tank 30, and the outlet is fluidly connected to the suction side of the centrifugal pump 3.

[0096] The throttling device 43 provides throttling, whereby the pressure in the tank 30 can be reduced relative to the pressure of the liquid in the system being degassed by using the centrifugal pump 3. The throttling device 43 can be designed as or include the nozzle 20 so that the liquid leaving the nozzle leaves the nozzle in the form of droplets (such as mist). Due to the high total surface area of ​​the droplets, the formation of such droplets has an improved degassing effect.

[0097] The liquid outlet connection 32 is arranged to be fluidly connected to the discharge side of the centrifugal pump to discharge the at least partially degassed liquid. The gas outlet 39 is arranged to be fluidly connected to the tank 30 to discharge the gas accumulated in the tank 30 during the degassing of the liquid. The liquid outlet connection 32 is typically connected to the system being degassed in a manner that does not restrict the flow, whereby the pressure on the discharge side matches (e.g., is substantially equal to) the pressure in the system being degassed.

[0098] exist Figure 1 In the illustrated embodiment, optional auxiliary elements are also shown. In the illustrated embodiment, a gas outlet 39 comprising an automatic exhaust device and a check valve (non-return valve) is arranged downstream of the automatic exhaust device. A fluid connection is formed from the outlet of the check valve to the discharge port. A filter 46 is arranged to filter the liquid before the liquid enters the throttling device 43. Such filters are of a known type and are used during the filling process to filter out smaller particles in the liquid. The sensor 45 can be a pressure sensor or a combined pressure and temperature sensor, or even a separate pressure and temperature sensor.

[0099] The liquid to be degassed flows into the tank 30 with a reduced pressure provided by the centrifugal pump 3 in combination with the throttling device 43, whereby the gas escapes from the free surface of the liquid inside the tank 30. During this degassing process, the amount of liquid in the tank 30 gradually decreases (because the volume flow into the tank 30 is less than the volume flow out of the outlet connection 32), whereby the gas gradually occupies more and more of the tank volume. When the gas is to be discharged from the tank 30, the centrifugal pump is stopped and the gas is discharged through the gas outlet 39, which is the connection between the inside and the outside of the tank 30. When the pump is stopped, liquid will continue to flow into the tank 30, whereby the incoming liquid forces the gas accumulated in the tank to be discharged. Depending on the mode of embodiment of the gas outlet 39, the gas outlet 39 may include a check valve or other suitable valve means.

[0100] As described above, the degassing method is performed in one or more processing steps. Such a processing step is defined as having a duration between the start and end of the processing step, where the start is when the pump is started and the end is when the pump is stopped. In addition, the processing step is considered to start with liquid present in the tank 30, typically the liquid occupies the entire volume of the tank, but the present invention is not limited to a full tank.

[0101] After the treatment steps are performed, a flushing step is performed during which the gas accumulated in the tank 30 during the treatment steps is flushed out. It should be noted that flushing out should be broadly interpreted as covering the process of removing or allowing the gas accumulated in the tank 30 to flow out of the tank 30. In a preferred embodiment, flushing refers to the process of replacing the gas out through the gas outlet 39 by the incoming liquid.

[0102] In order to allow automation of degassing, for example, the liquid degassing system according to a preferred embodiment is configured to determine the actual value of a degassing parameter representing the operating state of the system during the processing step. Such a degassing parameter is preferably one of the following parameters:

[0103] The electric power consumed by the electric motor 5 during the driving of the centrifugal pump 3. Since the electric power consumed by the electric motor is indicative of the operation of the pump, this parameter can be used to detect whether the pump is pumping liquid, gas or a mixture of both. As a rule of thumb, pumping liquids requires more electric power than pumping gases due to the difference in density, so if the electric power decreases during a processing step, this indicates that gas has reached the pump.

[0104] The speed of the electric motor. In addition to the power consumed, the speed also indicates the operation of the pump. As a rule of thumb,

[0105] If the rotation speed increases during the process step, this indicates that gas has reached the pump.

[0106] Actual process pressure. During a process step, the pump is usually run at a speed that provides the desired pressure, such as at a constant speed, and the pressure in the tank is substantially constant; however, if the pressure in the tank drops, this indicates that gas has reached the pump.

[0107] As mentioned above, what these parameters have in common is an indication that gas has reached the pump, and this operating state is referred to as "running dry". It should be noted that the centrifugal pump used in conjunction with the present invention is preferably protected so as to be able to operate in a running dry mode at least for a short period of time, which can be achieved by appropriately selected seals and bearings. However, when the gas reaches the pump 3, it is no longer necessary to continue degassing because the gas occupies the entire volume of the tank 30, there is essentially no liquid in the tank 30 to degas, and the pump 3 is therefore stopped.

[0108] The stopping function is implemented by providing a dry-running threshold value for at least one of the degassing parameters, the dry-running threshold value indicating a state in which the centrifugal pump is in an at least partially dry-running condition, that is to say the fluid reaching the pump contains gas and liquid or is essentially gas. The system is configured to determine an actual value of the degassing parameter during the processing step, and to compare the actual value of the degassing parameter with the associated dry-running threshold value, and to terminate the processing step if the actual value of the degassing parameter is outside the dry-running threshold value. Termination of the processing step comprises stopping the pump.

[0109] Thresholds and endings can be implemented as:

[0110] i) Speed ​​threshold: If the speed is greater than the speed threshold, the processing step ends.

[0111] ii) Power threshold: If the electrical power consumed by the pump is less than the power threshold, the processing step ends.

[0112] iii) Pressure threshold: If the actual process pressure in the tank 30 is less than the pressure threshold, the process step is terminated.

[0113] Thereby, the need to introduce a liquid level sensor in the tank to detect when there is no liquid in the tank is alleviated or even avoided.

[0114] It should be noted that the degassing parameter may fluctuate over time and that appropriate averaging may be used to smooth out fluctuations in the degassing parameter. In some embodiments, determining the actual value of the degassing parameter may include a moving average calculation. While averaging may be used to smooth out fluctuations, it is best designed so that surges caused by gas entering the pump are not smoothed out as when surge begins, the pump is preferably stopped. Surges typically occur at different frequencies and other fluctuations and frequency differences may be used to design adequate averaging.

[0115] As described above, the processing step is terminated once the degassing parameter is outside the dry running threshold, which indicates that gas has reached the pump 3, which corresponds to the presence of substantially no liquid in the tank 30. On the other hand, the degassing parameter is at the limit when the liquid occupies the entire volume of the tank 30. In some preferred embodiments, this is used to define the dry running threshold relative to the initial stage when the tank 30 is substantially full of liquid. For example, in the case of a tank full of liquid, the rotation speed of the pump 3 is 4500PM, and the dry running threshold can be implemented as, for example, 10% of 4500PM or even greater than n RPM. However, the threshold can also be defined in other ways, for example based on an expected value when gas has not yet reached the pump 3.

[0116] When the treatment step is finished, one of the flushing steps disclosed above is performed. In order to increase the speed of the treatment process, the flushing step is usually performed substantially after the treatment step is finished, however, the flushing step can be performed at a later point in time. If the flushing step is to be postponed, a suitable valve arranged to prevent liquid from entering the tank 30 is usually arranged in the degassing system. It should be noted that the flushing step (as described in detail below) can be performed by stopping the pump, whereby the incoming liquid flow displaces the gas accumulated in the tank 30.

[0117] During the flushing step, the centrifugal pump (3) is stopped and the flushing step consists in introducing liquid into the tank to fill the tank 30 with liquid, whereby the introduced liquid displaces the gas out of the tank through the gas outlet 39. Since the pressure in the tank 30 at the end of the treatment step is lower than the pressure in the incoming liquid and the flow resistance in the centrifugal pump represents a considerable resistance compared to the resistance into the tank through the liquid inlet connection 31, the liquid flows into the tank, although it is expected that a small backflow through the pump 3 and into the tank 3 may occur.

[0118] The above public content is Figure 5A (first segment of the graph) and Figure 5B An example is given in . Figure 5A yes Figure 5A The enlarged curve diagram of the first section of the curve diagram of Figure 5B As shown, the treatment of the liquid includes a flushing step having a duration of a "flushing time" during which the liquid content in the tank 30 is increased from 0% to 100%.

[0119] Although the above disclosed method of comparing the dry-run parameter with a threshold value indicates the end of the treatment step, sometimes the amount of gas present in the liquid is so small that, despite the accumulation of gas in the tank, the dry-run condition is never reached, or it may take a disproportionately long time. In such a scenario, it has been found to be advantageous to end the treatment step based on another criterion besides dry-run, for example for power consumption reasons. One such criterion is Figure 5A The middle part of FIG. 1 shows that the processing step is limited to lasting a maximum processing step time limit. When the processing step time exceeds the maximum processing step time limit, the processing step is terminated by stopping the pump 3. Figure 5A As shown, the rate of change in the % liquid in the tank as a function of time is less when the maximum process step time limit criterion (middle section of the graph) is used compared to the rate of change using the dry run criterion (first section of the graph).

[0120] Figure 5A Another criterion that can be implemented to end the treatment step is also shown. The criterion shown relates to the temperature of the liquid, which is usually measured at a location between the tank 30 and the pump 3. Sometimes the temperature of the liquid is higher than the temperature that the equipment (such as the pump) or the degassing system can usually handle, and if the temperature reaches a preset temperature limit, the treatment step ends. The boiling temperature of the liquid also depends on the pressure, and as the pressure of the liquid decreases, the combination of pressure and temperature may cause the liquid to begin to boil and / or cavitation may occur in the pump. This boiling and / or cavitation should be avoided, and therefore if the temperature and pressure combination reaches boiling and / or cavitation conditions, the treatment step ends.

[0121] It may also be advantageous to postpone the treatment step after the flushing step. To this end, an idle time is introduced during which the pump is not running and the pressure in the tank 30 is balanced with the system being degassed. The flow through the degassing system is usually zero or substantially zero. This idle time is advantageous for saving energy, as it has been found that more efficient degassing can be obtained by introducing the idle time, as the system being degassed usually requires some time for the gas to adjust to the previous degassed state.

[0122] It was also observed that if degassing does not continue for longer than the treatment time T T Longer time periods provide more cost-effective degassing in terms of energy consumption. Figure 5A The time period is generally related to the system being degassed, and the processing step is performed within a time period not exceeding the processing time T. T It should be noted that the treatment time is usually repeated after a certain duration, for example during a 24 hour period, degassing is performed during the first 4 hours (treatment time equal to 4 hours) and repeated when the 24 hour period ends. Thus, two treatment periods are separated in time by a downtime, during which the same conditions as the idle time prevail. In some preferred embodiments, the treatment time and the downtime are preset by the user.

[0123] Since the system being degassed is often dynamic and in some cases involves adding fresh liquid to the system, it may be desirable to dynamically adjust the processing time in order to optimize degassing, often with boundary conditions to minimize energy consumption. One way to implement such dynamic adjustment of the processing time may include performing at least two processing steps within the processing time (e.g., one resulting from a previous adjustment or one preset by a user), and recording whether multiple processing steps within the processing time have been terminated by reaching the maximum processing step time. Since repeated termination of processing steps by meeting the maximum processing step time indicates that the amount of gas in the liquid of the system being degassed is low, reducing the processing time may often be beneficial because, in the worst case, extended degassing may not degas any gas from the liquid, but will still consume energy.

[0124] A different situation may also occur, namely that a plurality of treatment steps are terminated based on a dry-running parameter, which indicates a higher amount of gas in the liquid and that the treatment time can be beneficially increased. In this case, the method comprises carrying out at least two treatment steps within the treatment time and recording whether a plurality of treatment steps within the treatment time have been terminated by the actual value of the degassing parameter exceeding the dry-running threshold value, and increasing the treatment time in the event of confirmation.

[0125] An increase or decrease in the processing time may be determined by adding or subtracting a predefined time increment Δt from the processing time. The change Δt in the processing time may be proportional to the number of times within the processing time, the processing has been terminated according to the corresponding criteria.

[0126] Figure 6 A graphical representation of the processing time is provided, and a maximum processing time, a minimum processing time, and a cycle are introduced. The boxes marked "On" in the figure represent processing steps. As shown in the figure, the processing time is limited so that it cannot be longer than the maximum processing time or shorter than the minimum processing time. When an increase or decrease in the processing time is implemented, the increase or decrease is usually limited, i.e., does not exceed the maximum and minimum values. Figure 6 The cycles introduced in also represent repeated cycles, that is, one cycle is continued by the next cycle.

[0127] As described herein, the pressure in tank 30 will be reduced relative to the pressure of the liquid from the system being degassed. Therefore, prior to commencing the process step and with liquid present in tank 30, a value for the process pressure is obtained.

[0128] The negative pressure is the amount by which the pressure of the liquid in the tank 30 is reduced. For example, if the pressure of the liquid in the flow upstream of the restriction is 2.5 bar, the negative pressure may be -0.8 bar, which means that the final pressure in the tank 30 during the processing step is 1.7 bar. The magnitude of the negative pressure is usually set by the user.

[0129] If the negative pressure is known, the speed of the centrifugal pump 3 required to generate the negative pressure can be determined. This determination can be based on corresponding values ​​of pump characteristics such as Q (volume flow), head (pumping pressure) and pump speed.

[0130] Thus, a process step can be started and performed, which comprises rotating the centrifugal pump 3 at a determined rotational speed. This rotational speed can be reached by increasing the rotational speed. Similarly, when the rotation of the pump is to be stopped, this is usually done by reducing the rotational speed.

[0131] Since it is not absolutely guaranteed that a determined rotation speed of the centrifugal pump provides the negative pressure or treatment pressure to be obtained, the negative pressure generated in the tank 30 during the treatment step can be determined, and if the negative pressure deviates significantly from the negative pressure (treatment pressure) to be generated in the tank 30, the rotation speed of the centrifugal pump 3 is adjusted to account for the deviation. Here, it can be referred to as a pressure deviation of more than 10%, such as more than 5%, such as more than 4%, preferably more than 3%, or even more than 2%. In a preferred embodiment, this is implemented by using a PI (proportional integral) controller, which adjusts the rotation speed of the pump 3 based on the pressure measured in the tank 30 to provide the required negative pressure.

[0132] refer to Figure 7, which shows a longitudinal sectional view of a liquid degassing system according to a preferred embodiment of the present invention.

[0133] As will be apparent from the following disclosure, Figure 7 The embodiment shown and other similar embodiments may be evaluated to form a single unit which, when electrically connected to power the pump and other electronics contained in the unit and when fluidly connected to the system to be degassed, is suitable for performing the degassing method according to the invention. A preferred embodiment of the single unit comprises in the unit:

[0134] a centrifugal pump 3 having a suction side and a discharge side, the pump 3 being a variable speed pump;

[0135] a tank 30 preferably having a vertical extension and having a liquid inlet connection 31 comprising a throttling device 43 arranged at the upper end of the tank 30 for receiving the liquid to be degassed through the throttling device 43, and an outlet arranged at the lower end of the tank 30, fluidly connected to the suction side of the centrifugal pump 3;

[0136] a liquid outlet connection 32 fluidly connected to the discharge side of the centrifugal pump to discharge the at least partially degassed liquid; and

[0137] • A gas outlet 39, which is fluidly connected to the tank 30, to discharge gas accumulated in the tank 30 during degassing of the liquid.

[0138] In embodiments including a pressure sensor, such a sensor may also be included in the unit, preferably located at a position upstream of the centrifugal pump, such as in the tank 30 or fluidly between the tank 30 and the centrifugal pump 3 .

[0139] The illustrated liquid degassing system comprises a centrifugal pump 3 having a suction side and a discharge side. The centrifugal pump 3 is typically a pump comprising a plurality of impeller stages arranged on a common shaft 4, a so-called multistage pump, and the pumping capacity can be selected according to a given degassing requirement.

[0140] The illustrated degassing system further comprises an electric motor 5 with an electric / electronic control. The electric / electronic control is used to set the rotation speed of the electric motor 5. The electric motor is mechanically connected to the centrifugal pump 3 to drive the centrifugal pump 3 by connecting the output shaft of the electric motor 5 with a common shaft of the centrifugal pump.

[0141] The electronics of the liquid degassing system are preferably housed in a separate electronics housing 37 arranged above the electric motor 5 and close to the tank 30 and forming part of the housing 1. The electronics are preferably adapted to control the pump as further disclosed herein.

[0142] A tank 30 is provided in the liquid degassing system, and the tank 30 is arranged above the centrifugal pump 3. Figure 7 In the illustrated embodiment of the present invention, the tank 30 is arranged as a void in the liquid degassing system. The tank 30 and the centrifugal pump 3 are connected to each other via a construction unit 6, which comprises a liquid inlet connection 31 for supplying liquid to the liquid degassing system and a liquid outlet connection 32 for outputting liquid from the liquid degassing system. The construction unit 6 preferably provides fluid connections, in particular, between the tank 30 and the outside, between the tank 30 and the suction side of the centrifugal pump 3, and between the discharge side of the centrifugal pump 3 and the outside of the liquid degassing system.

[0143] The gas outlet 39 is arranged to be fluidly connected to the upper position of the tank 30. The gas outlet is configured to allow gas to flow out of the tank 30 while preventing gas from being sucked into the tank 30 through the gas outlet 39. In a preferred embodiment, the gas outlet is embodied as a one-way check valve. The purpose of the gas outlet 39 is to allow the gas collected in the tank 30 during the degassing process to be flushed out. As described herein, degassing includes creating a vacuum in the tank 30 by using a centrifugal pump, thereby causing gas to be generated above the surface of the liquid in the tank 30, and flushing the gas out by introducing liquid into the tank when the centrifugal pump is not running or running at a reduced speed. The incoming liquid will displace the gas out through the gas outlet 39.

[0144] A first fluid conduit 40 is provided connecting the liquid inlet connection piece 31 with the tank 30, and a second fluid conduit 41 is provided connecting the tank 30 with the suction side of the centrifugal pump 3. In addition, a third fluid conduit 42 connects the liquid outlet connection piece 32 with the discharge side of the centrifugal pump 3. Figure 7 As shown, these fluid lines are arranged in the construction unit 6 .

[0145] The liquid inlet connection 31 defines an external liquid inlet connection of the liquid degassing system, and the liquid outlet connection 32 defines an external fluid outlet connection of the liquid degassing system. Figure 7 In the illustrated embodiment of the invention, these openings are shown with protective caps which prevent dirt or other substances from entering the openings, for example during transport, and these caps will be removed when the degassing system is commissioned. As also shown, the centrifugal pump 3 is located downstream of the liquid inlet connection 31 and upstream of the liquid outlet connection 32 with respect to the fluid flow introduced through the inlet connection and discharged through the outlet connection. The construction unit 6 can be configured as a single-piece or multi-piece plastic injection molded component. Figure 7 In the embodiment shown, it is manufactured as a two-piece component.

[0146] like Figure 7As shown, the wall segment 30b of the construction unit 6 defines a wall segment of the tank 30. Thus, in the case where one or more wall segments of the tank are defined within the liquid degassing system and the wall segments are defined by the construction unit 6, when the construction unit is applied to the liquid degassing system, the void of the tank is defined.

[0147] The liquid to be degassed is preferably introduced into the tank 30 in the form of droplets or even mist. To achieve this, the first fluid conduit 40 has a nozzle 22 having a nozzle outlet 22a, which is configured to provide droplets or mist and is arranged within the interior of the tank 30, located at an upper position of the tank 30. In the illustrated embodiment, the nozzle outlet 22a is arranged to spray the liquid upward into the tank 30. However, other spray directions, such as upward or downward slanting or horizontal, can also be used. It is generally preferred that the spray forms a hollow cone, although the present invention is not limited to such a hollow cone. Although the first fluid conduit 40 will provide throttling to a certain extent, it is generally preferred to use the nozzle 22 to provide most of the throttling required to provide a reduced pressure in the tank 30. Therefore, the combination of the first fluid conduit 40 and the nozzle preferably forms a throttling device 43.

[0148] In a preferred embodiment, the nozzle 22 is arranged at the outlet position of the first fluid conduit 40 by being screwed, press-fitted or glued onto or into the fluid conduit 40 at the outlet of the first fluid conduit 40 .

[0149] In an alternative embodiment, the nozzle 22 is integrally formed with the first fluid conduit 40. Figure 7 , in which the channel of the first fluid conduit 40 is funnel-shaped toward the outlet in the process of closing the channel.

[0150] Although it may be advantageous to provide the first fluid conduit 40 as an integral part of the construction unit 6 (see Figure 7 ), but it may also be advantageous to arrange the first fluid conduit 40 in a releasable manner in the construction unit 6.

Claims

1. A method for degassing water for a heating, ventilation and / or air conditioning system, the method utilizing a liquid degassing system, the liquid degassing system comprising: a centrifugal pump (3) having a suction side and a discharge side, said pump (3) being a variable speed pump; a tank (30) having a vertical extension and having a liquid inlet connection (31) comprising a throttling device (43) arranged at the upper end of the tank (30) for receiving the liquid to be degassed through the throttling device (43), and an outlet arranged at the lower end of the tank (30) fluidly connected to the suction side of the centrifugal pump (3); a liquid outlet connection (32) fluidly connected to the discharge side of the centrifugal pump for discharging the at least partially degassed liquid; and A gas outlet (39) fluidly connected to the tank (30) to discharge gas accumulated in the tank (30) during degassing of the liquid The method comprises: fluidly connecting the liquid degassing system to a heating, ventilation and / or air conditioning system that is being degassed and that carries the water to be degassed, so that the water flows into the tank (30); · selection of the process pressure (Pt) to be obtained in the tank (30) upstream of the centrifugal pump (3); The rotation speed of the centrifugal pump (3) is set to provide the selected process pressure (Pt) to be obtained.

2. The liquid degassing method according to claim 1, wherein: The method further comprises Determine the pressure (Ps) in the system being degassed; Obtaining the flow resistance characteristics of the throttling device (43); determining the rotational speed of the centrifugal pump (3) based on the pump characteristics of the centrifugal pump (3), wherein the rotational speed provides a pressure difference across the centrifugal pump (3) that matches the sum of the pressure (Ps) in the system being degassed and the process pressure (Pt) to be obtained to one of the flow resistance characteristics.

3. The method according to any one of claims 1 or 2, wherein: The setting speed is controlled by PLC.

4. A method for degassing a liquid according to any one of the preceding claims, wherein: The setting of the rotation speed of the centrifugal pump (3) to provide the selected treatment pressure (Pt) to be obtained comprises: Determining the actual process pressure, which is the pressure in the tank (30) or the pressure upstream of the centrifugal pump, such as the suction side of the pump (3) or the pressure in the tank (30); - comparing the actual upstream pressure with the selected process pressure to be achieved (Pt) and, if there is a difference, adjusting the rotation speed of the pump to set the actual upstream pressure substantially equal to the selected process pressure to be achieved (Pt).

5. The liquid degassing method according to claim 4, wherein: The actual process pressure is determined in the tank (30) or on the suction side of the pump (3).

6. The liquid degassing method according to any one of claims 4 or 5, wherein: The rotation speed of the pump is adjusted by PID control.

7. The liquid degassing method according to any one of the preceding claims 4 to 6, wherein: The adjustment includes increasing the rotation speed of the pump (3) if the actual process pressure is less than the selected process pressure to be obtained, and reducing the rotation speed if the actual process pressure is greater than the selected process pressure to be obtained.

8. The liquid degassing method according to any one of claims 4 to 7, wherein: The adjusting speed is performed incrementally and after each increment of the speed, the actual process pressure is compared with the selected process pressure to be obtained (Pt) until the actual process pressure is substantially equal to the selected process pressure to be obtained (Pt).

9. A method according to any one of the preceding claims, wherein: The degassing system comprises an electric motor (5) with electrical / electronic control, which is connected to the centrifugal pump (3) to drive the centrifugal pump (3).

10. A method of degassing a liquid according to any preceding claim, when dependent on claim 9, wherein: The method is carried out as follows: in one or more treatment steps, each treatment step having a duration between the start and the end of the treatment step achieved by the activation and deactivation of said centrifugal pump, wherein the treatment step starts with the liquid present in said tank (30), and in one or more flushing steps, wherein the gases accumulated in the tank (30) during the treatment steps are flushed out, The liquid degassing system is configured to determine during a processing step an actual value of a degassing parameter, the degassing parameter being: the electric power consumed by the electric motor (5) during the driving of the centrifugal pump (3), the speed of the electric motor, or Handle stress realistically; The method comprises: providing a dry-running threshold value for one of the degassing parameters, the dry-running threshold value representing a state in which the centrifugal pump is in an at least partially dry-running condition, Determine the actual value of the degassing parameter, Comparing the actual value of the degassing parameter and ending the processing step if the actual value of the degassing parameter is outside the dry-running threshold value.

11. The method according to claim 10, wherein: Determining the actual value of the degassing parameter includes a moving average calculation.

12. The method according to claim 10 or 11, wherein: The dry-running threshold is defined relative to an initial stage in which the tank (30) is substantially full of liquid.

13. The method according to any one of the preceding claims 10 to 12, wherein: One of the flushing steps is performed after one of the treatment steps, the centrifugal pump (3) is stopped during the flushing step, and the flushing step includes introducing liquid into the tank to fill the tank (30) with liquid, whereby the introduced liquid displaces gas to the outside of the tank through the gas outlet (39).

14. The method according to any one of the preceding claims 10 to 13, wherein: The duration of each of the processing steps is limited to a maximum processing step time limit, and the method further comprises ending a processing step if the maximum processing step time limit has been reached.

15. The method according to any one of the preceding claims 10 to 14, wherein: The treatment step does not exceed the treatment time (T T ) for a duration of .

16. The method according to claim 14 or 15, wherein: At least two processing steps are performed within the processing time, and the method further comprises recording whether a plurality of the processing steps within the processing time have been ended by reaching the maximum processing step time, and reducing the processing time if confirmed.

17. The method according to claim 14, 15 or 16, wherein: At least two process steps are performed within the process time, and wherein the method further comprises recording whether a plurality of the process steps within the process time have been terminated by the actual value of the degassing parameter exceeding the dry-running threshold value, and increasing the process time in the event of confirmation.

18. The method according to any one of the preceding claims 10 to 17, wherein: Prior to commencing the processing step, and in the presence of liquid in the tank (30), the method further comprises: Provide the value of the treatment pressure (Pt) to be obtained; determining the rotation speed of the centrifugal pump (3) required to generate the process pressure to be achieved, and The treatment step is started and carried out by rotating the centrifugal pump (3) at a determined rotational speed, wherein the rotational speed of the centrifugal pump (3) is preferably achieved by increasing the rotational speed.

19. The method according to claim 18, wherein: The actual process pressure during the process step is determined and, if the actual process pressure deviates significantly from the process pressure to be achieved, the rotational speed of the centrifugal pump (3) is adjusted to account for this deviation.

20. A system for degassing a liquid, preferably water, comprising: A centrifugal pump having a suction side and a discharge side, the pump being a variable speed pump, typically driven by an electric motor with an electrical / electronic control to control the speed of the centrifugal pump; a tank, preferably having a vertical extension, having a liquid inlet connection including a throttling device arranged at the upper end of the tank for receiving the liquid to be degassed through the throttling device, and an outlet arranged at the lower end of the tank, fluidly connected to the suction side of the centrifugal pump; a liquid outlet connection fluidly connected to a discharge side of the centrifugal pump for discharging the at least partially degassed liquid; and and a gas outlet fluidly connected to the tank to discharge gas accumulated in the tank during degassing of the liquid; as well as • A controller configured to carry out the method according to any of the preceding claims.

21. The system of claim 20, wherein: The system is comprised in a single unit.

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