Method and system for degassing

Abstract

The invention relates inter alia to a method of degassing gas, preferably air, from a liquid, preferably water. The method utilizes a degassing system comprising a tank having a volume being in fluid communication with a gas venting device configured for outletting gas from the volume, and a pump configured to provide a reduced pressure in the tank relatively to a system pressure in an associated liquid based heat transfer system containing the liquid to be degassed. Preferred embodiments comprises calculation of a duration of a treatment step.

Description

[0001] METHOD AND SYSTEM FOR DEGASSING

[0002] FIELD OF THE INVENTION

[0003] The invention relates inter alia to a method of degassing gas, preferably air, from a liquid, preferably water. The method utilizes a degassing system comprising a tank having a volume being in fluid communication with a gas venting device configured for outletting gas from the volume, and a pump configured to provide a reduced pressure in the tank relatively to a system pressure in an associated liquid based heat transfer system containing the liquid to be degassed. Preferred embodiments comprises calculation of a duration of a treatment step.

[0004] BACKGROUND OF THE INVENTION

[0005] Many water based systems, such as cooling or heating systems experience some influx of air, whereby the water may become saturated and even air pocket may arise in the system. Air in water is typically considered undesired as it may lead to undesired performance of the water based system. Thus, such systems are typically equipped with a degassing system in which the water of the water based system is degassed.

[0006] A typically degassing system comprising a tank having a reduced pressure (relatively to the pressure in the system) and into which the water to be degassed flows through a nozzle. Due to the reduced pressure, provided by a pump, air is released from the water and accumulates in the tank. The water flowing into the tank is subsequently fed back into the water based system.

[0007] Such degassing systems are typically operated in cycles where each cycle comprising a treatment step during which water flows into the tank and air accumulates in the tank, and an idle step during which the air accumulated in the tank is purged out from the tank and into the atmosphere surrounding the tank.

[0008] While such degassing system are proven to be able to degas water, the energy consumed by the pump is substantial. Today, the a degassing system is typically operated in a manner where the energy consumption of the pump is not in focus and the pump is operated according to a predefined operating schedule which schedule may be different whether a commission situation or a maintenance situation is encountered.

[0009] While a predefined operating schedule aims at degassing and has less focus on the energy consumption of the pump, the inventors have surprisingly realized that the energy consumption is often higher than what is actually needed to perform an effective degassing of the water based system. Accordingly, the utilization of the degassing system is less than optimal.

[0010] BACKGROUND OF THE INVENTION

[0011] It is an object of the present invention to provide a more efficient utilization of a degassing system. It is a further object of the invention to provide a more energy efficient utilization of a degassing system.

[0012] SUMMARY OF THE INVENTION

[0013] The invention relates in a first aspect to a method of degassing gas, preferably air, from a liquid, preferably water, the method utilizes a degassing system comprising a tank having a volume being in fluid communication with a gas venting device configured for outletting gas from the volume, and a pump configured to provide a reduced pressure in the tank relatively to a system pressure in an associated liquid based heat transfer system containing the liquid to be degassed, the degassing system is operated, during use, in cycles each comprising

[0014] • a treatment step with a duration treatment time during which the liquid to be degassed is inlet through a nozzle at a volume flow into the volume in which the reduced pressure is provided by the pump whereby gas is released from the liquid and accumulated in the tank, and

[0015] • an idle step during which the accumulated gas is outlet from the tank through the gas venting device by displacing the accumulated gas with liquid to be degassed being accumulated in the tank, the method comprising:

[0016] • obtaining a temperature of the liquid being or to be degassed and the quantity of the volume flow,

[0017] • calculating the treatment time based on the gas concentration in the liquid to be degassed, the gas concentration in the liquid downstream of the tank such as at an outlet of the pump, the obtained temperature, the quantity of the volume flow and the reduced pressure so that the amount of degassed gas, during a treatment step is equal to or smaller than the volume and

[0018] • carry out at least one cycle with a duration of treatment step being equal to or less than the determined treatment time.

[0019] It has been found in connection with the present invention that calculating the treatment time so that the amount of degassed gas is equal to or smaller than the volume of the tank, and carry out the treatment step with the calculated treatment time provides inter alia the advantage that the system is used in an advantageous manner, inter alia since the treatment step is ended prior to or when the tank being filled with degassed gas. Accordingly, the pump may be stopped when the treatment time runs out, thereby reducing the energy consumption of the pump compared to a scenario where the pump runs continuously. Further, the method preferably adapts the degassing to situations where gas concentration in and / or the temperature of the liquid to be degassed varies from cycle to cycle.

[0020] An amount of degassed air during a treatment step being "smaller than the volume" preferably refers to securing that gas is not sucked into the pump, which may occur when the tank is essentially occupied by released gas. Typical values for "smaller than the volume" are smaller than 95%, such as smaller than 90% such as smaller than 85% of the volume and preferably larger than 80% of the volume.

[0021] Terms used herein are used in manner being ordinary to a skilled person. Some the terms used are elucidated here below:

[0022] "Liquid based heat transfer system" or "liquid based system" is used to reference a system in which liquid is used to carry heat from one or more heat sources to one or more heat loads. The liquid based system may be configured and / or used for heating or cooling purposes. The preferred embodiments disclosed in the section "Detailed description of the preferred embodiments" are disclosed with the liquid being water so that the liquid based heat transfer system is referred to as water based heat transfer system. In these embodiments, the gas to be degassed is typically air, such as atmospheric air. However, the invention is not limited to the liquid being water as other liquid may be used as long as they can contain gas.

[0023] "Gas venting device" is preferably used to denote a device comprising or being fluidic connected to a check valve for conducting gas in one direction only (out from the volume of the tank) from an inlet to and outlet, when the pressure drop over the gas venting device exceed a predefined amount. In addition, the gas venting device is configured to shut-off when the inlet is subjected to liquid. In preferred embodiments, the air venting device is a conventional float based air venting device in which the float controls opening and closing of a venting valve through which air is vented out to the surroundings.

[0024] Preferred embodiments of a degassing system comprising a processor. Such a processor may be configured to control the pump of the degassing systems, such as configured to control the pump to provide the reduced pressure in the tank and / or to control the pump to run during the treatment step and / or control the pump to be stopped during the idle step.

[0025] Such a processor preferably comprises a CPU and software instructions to calculate the treatment time.

[0026] Preferred embodiments of a degassing system comprising one or more sensors, such temperature sensor(s), pressure sensor(s) and / or combined pressure and temperature sensor(s). Preferably, such sensor(s) is(are) in connection, such as in electrical connection with the processor to receive measurement from the sensor(s) of the temperature and / or pressure.

[0027] The pump may preferably be a variable speed pump, such as a variable speed impeller pump. In such a variable speed pump, the speed of the pump typically sets the reduced pressure. BRIEF DESCRIPTION OF THE FIGURES

[0028] The present invention and in particular preferred embodiments thereof will now be described in more detail with regard to the accompanying figures. The figures show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0029] Fig. 1 is a schematic illustration of a degassing system according to an embodiment of the invention, the degassing system is illustrated as being fluidic connected to a water based heat transfer system containing liquid to be degassed;

[0030] Fig. 2 is a schematic illustration of a degassing system comprising a processor configured to carry out a method according to the invention;

[0031] Fig. 3 is a flow chart illustrating a preferred embodiment of a method of calculating a treatment time according to the invention;

[0032] Fig. 4 is a cross sectional view of a degassing system according to a preferred embodiment of the invention;

[0033] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] Reference is made to Fig. 1 schematically illustrating a degassing system according to a preferred embodiment. The degassing system is fluidic connected to a water based heat transfer system containing a fluid to be degassed. In many preferred embodiments, the liquid to be degassed is water and the gas being air. However, the invention is not limited to water and air.

[0035] In the disclosed embodiment, the degassing system 1 comprises a tank 2 having a volume Vtank which is in fluid communication with a gas venting device 5. The gas venting device 5 is configured for outletting gas from the volume. A pump 3 is provided which pump 3 is configured to provide a reduced pressure Ptank in the tank 2 relatively to a system pressure Psys in the water based heat transfer system containing the liquid to be degassed. As also illustrated in Fig. 1, the pump 3 draws fluid into the volume of the tank 2 and feed the fluid from the volume of the tank 2 back into the water based heat transfer system. As the pressure in the volume of the tank 2 is reduced relatively to the pressure in the water based heat transfer system, air will be released from the water and accumulated in the volume as will disclosed in greater details here below.

[0036] In preferred embodiment of a method according the invention, the degassing system is operated, during use, in cycles each comprises:

[0037] • a treatment step, and

[0038] • an idle step.

[0039] The treatment step is carried out with a duration treatment time ttreat during which the liquid to be degassed is inlet through a nozzle 4. The nozzle 4 is preferably a device being configured to provide droplets thereby increasing the surface area of the water to be degassed to increase the speed at which air is released from the water. The nozzle 4 also provides in some embodiments a throttling to allow the pressure to be reduced in the tank 2. In other embodiments a separate throttling valve may be arrange upstream of the tank 2. A combination of throttling by the nozzle 4 and a separate throttling valve is considered with the scope of the invention.

[0040] To avoid clogging of the nozzle 4, a filter (as illustrated in Fig. 1) may be arranged upstream of the nozzle 4 to filter out particles that could otherwise clog the nozzle 4.

[0041] The inflow during the treatment step is provided at a volume flow Qnoz of water into the volume Vtank in which the reduced pressure Ptank is provided by the pump 3 whereby gas is released from the liquid and accumulated in the tank 2.

[0042] During an idle step, the accumulated gas is outlet from the tank 2 through the gas venting device. This outlet is provided by displacing the accumulated gas with liquid to be degassed being accumulated in the tank 2. During the idle step the net inflow into the volume of the tank is larger than zero. Preferred embodiments resides inter alia in calculation of the duration of the treatment time where the treatment time is calculated to optimize the use of the degassing system. One way of optimize the use of the degassing system is use a treatment time providing an amount of degassed air being equal to a less than the tank volume.

[0043] One way of calculating the treatment time resides in the use of the continuity equation as presented in the following. By use of the continuity equation, the amount of gas released in a treatment step can be calculated by:

[0044] Am — tfreatQnoz(.^s ~ ^s,min) wherein

[0045] Am is the mass of gas released ttreat isthe treatment time Qnozis the volume flow into the tank volume per time unit Csis the gas concentraion, that is the concentration of air in the water flowing into the tank volume .min isthe gasconcentration, that is the concentration of air in the water flow out of the tank volume

[0046] The gas concentration has the unity [mass / volume] although it may be expressed by different unities. The concentration is different from degree of saturation. In the regards to preferred embodiments the liquid to be degassed as well as the liquid flowing out of the tank into the tank as well the liquid after the pump but prior to being fed into the liquid based heat transfer system is assumed to be saturated to 100%. While this is an assumption, the impact on the calculated treatment time has been found to be so small so that the assumption provide good degassing results. One result of the assumption could be that the tank is filled with less gas compared to a situation where the liquid was saturated to 100%.

[0047] It is noted that the volume flow Qnoz is considered constant during a treatment step.

[0048] This equation can be re-arranged as: Assuming air being an ideal gas (temperature given in Kelvin): m PV = —RT

[0049] M

[0050] Where M is the molar weight of the air (gas) and R is the gas constant.

[0051] The amount of air that can be contained in the tank can be estimated by:

[0052] The volume of the tank Vtank is considered known and constant since the dimensions of the tank 2 used is considered to be selected during a design phase of the degassing system.

[0053] Since the water to be degassed in many embodiments does not chance temperature during its passage into the tank, it can be assumed that: tank =Sys

[0054] However, the invention is not limited to this assumption. Rearranging the equations provides the following equation for calculating the treatment time:

[0055] The gas concentrations Cs; Cs mincan be provided in different manners and may be provided based on the following relations where Hsis Henry's constant. Here the assumption of 100% saturation has been used. Cs minmay be determined based on the pressure in the tank, although Cs minmay also be determined at an outlet of the pump. Alternatively, the concentrations may be found by table look-up or diagram look-up.

[0056] Henry's constant may be calculated based on the following equation:

[0057] Where H is enthalpy. The value of Hoand — can be found in a table of physical properties. Typical values applicable in relation to degassing water in accordance with the present invention are

[0058] To= 298.15 K

[0059] Accordingly, by obtaining the temperature of the water to be degassed or being degassed, Henry's constant may be calculated based on the above, whereby the concentrations cs; Cs mincan be calculated based on the pressures Ptank and Psys by the above equations.

[0060] A degassing may accordingly comprise the following steps:

[0061] • obtaining a temperature Ttank, Tsysof the liquid being or to be degassed and the quantity of the volume flow Qnoz,

[0062] • calculating the treatment time (ttreat) based on the gas concentration in the liquid to be degassed Cs, the gas concentration in the liquid after a treatment step Cs,min, the obtained temperature, the quantity of the volume flow Qnoz and the reduced pressure Ptank so that the amount of degassed air during a treatment step is equal to or smaller than the volume Vtank, and

[0063] • carry out at least one cycle with a duration of treatment step being equal to or less than the determined treatment time ttreat.

[0064] The volume flow Qnoz can be provided in different ways. For instance, the a flow sensor may be used to determine the volume flow or the volume flow may be calculated as detailed below.

[0065] In some instances, the water based heat transfer system is well defined from e.g. a specification of the water based heat transfer system and the operation of the pump is also well defined. Thereby, Ptank Psys Ttank and / or Tsysare known - or at least assumed to fulfil specification whereby the treatment time can be calculated.

[0066] In other embodiments, Ptank Psys Ttank and / or Tsysare determined by measurements.

[0067] The reduced pressure Ptank is typically a pre-selected value. The value is typically set in accordance with the capacity of the pump 3 used and the pressure in the water based heat transfer system. Typical values for the reduced pressure is between 0.2 bar and 0.8 bar. However, since degassing will occur when the pressure is lower than the pressure in the water based heat transfer system, degassing may be carried out as long as the pressure in the tank is reduced, that is lower than the pressure in the water based heat transfer system.

[0068] A number of treatment cycles are often needed in order to obtain an effective degassing, which in many cases refers to that the concentration of air in the water is reduced to an acceptable level being larger than zero %, such as reduced to e.g. 80 %.

[0069] The calculation of the treatment time may comprise a single calculation of a treatment time or the treatment time may recurrently calculated.

[0070] The tank volume can typically be selected as desired as long as the tank volume is smaller than the volume of water contained in the water based heat transfer. In preferred embodiments, the tank volume is in the order of such as of 0.005%, such as 0.01% of the water contained in the water based heat transfer system. However, it has been found in connection with preferred embodiments of the invention that a larger tank volumes may increase the efficiency of the degassing.

[0071] In a preferred embodiment, calculation of the treatment time ttreat is illustrated in Fig. 3. In this embodiment, a step is introduced taking into account that a desired tank pressure Ptank may or may not be obtainable by the pump. This step is

[0072] • Calculate Ptank = max (Psys—Ppump,max Ptank, ref)

[0073] Here "max" refers to the maximum value of the two parameters shown in the paranthes. PpUmp,max is the maximum available pump pressure the pump can provide and can be found e.g. from specification on the pump. Ptank, ref is the desired tank pressure. In a non-limiting example, the system pressure is Psys=4.5 ba r, Ppump,max — 3.7 bar and Ptank,ref= 0.2 bar. The above max function then calculates Ptank as:

[0074] Ptank = max (4.5 bar - 3.7 bar; 0.2 bar) = 0.8 bar Kindly observe that Ppump,max is the value the pump can reduce a pressure.

[0075] In some embodiments, the treatment time ttreat is calculated during one idle step of the at least one cycle. This is typically done recurrently and when done during an idle step, an upcoming treatment step may be carried out with the treatment time newly calculated which may improve the accuracy in the calculated treatment time as it can be based on most recent temperatures and pressures (if determined).

[0076] The duration of the idle step is preferably selected as the time it takes to essentially displace all gas accumulated in the tank 2. To assure that all gas accumulated is displaced, a safety margin may be added to the duration of the idle step, typically in the order of 5-10 % of a selected time. Displacement of the gas (air) is carried out by inflow of water and during the inflow the pressure in the tank will gradually increase and reach the system pressure Psys. Accordingly, the duration of the idle step may be determined as the point in time where the pressure in the tank 2 has become substantially constant, such as at value substantially equal to the system pressure Psys.

[0077] In preferred embodiments, the pump 3 is a pump having a variable RPM. In such embodiments, the pump 3 is typically operated at an RPM during the treatment step to provide the reduced pressure in the tank 2. If the pump 3 cannot obtain the reduced pressure in the tank 2, the pump 3 is typically or operated at maximum RPM during a treatment step and operated at a lower RPM, such as zero RPM, during the idle step.

[0078] In preferred embodiments, the pump 3 is operated in a close-loop control wherein the prevailing reduced pressure Ptank is measured and the pump is controlled so that the prevailing reduced pressure is substantially equal to a preselected reduced pressure, if possible. By "prevailing" is referred to the actual pressure in the tank.

[0079] As outlined above, the gas concentration of the liquid to be degassed Cs and / or the concentration of the liquid after degassing Cs,min may determined based on a calculation involving Henry's constant. Alternatively, the concentration may be determined based on a table look-up holding corresponding values of

[0080] C = f(M- P- Hs~)

[0081] In preferred embodiments the quantity of the volume flow Qnoz is calculated based on a flow coefficient Kvof the nozzle 4 and a difference between the system pressure Psys and the reduced pressure Ptank. Alternatively, a flow sensor may be used to determine the volume flow Qnoz.

[0082] The determination of the treatment time ttreat may advantageously be based on the reduced pressure Ptank prevailing during degassing as this may provide a more accurate calculation of the treatment time, especially if larger deviations between an assume reduced pressure and a prevailing pressure occur.

[0083] In some embodiments, such as the one illustrated in Fig. 4, a pressure sensor is present providing a measurement of the pressure inside the tank or a pressure measurement being representative of the pressure in the tank, which is the case for the embodiment of Fig. 4 where the pressure sensor is located at the inlet of the pump 3 slightly downstream of the tank 2. This pressure sensor can be used to determine both reduced pressure Ptank and the system pressure Psys. The reduced pressure Ptank is determined during a treatment step and the system pressure Psys is determined at the end of an idle step where the pressure in the tank 2 settles at the system pressure in the associated water based system.

[0084] Accordingly, the prevailing reduced pressure is typically determined during one of the at least one treatment steps and the system pressure (Psys) is determined during one of the least one idle step(s).

[0085] Preferably, the temperature Ttank or Tsysof the liquid being or to be degassed is obtained by a sensor configured to determine the temperature of the liquid inside the tank or configured to determine a temperature representative of the liquid inside the tank. The latter is the case with the embodiment shown in Fig. 4 where the temperature sensor and pressure sensor are built into a common housing and placed at the inlet of the pump 3. The temperature measurement are preferably obtained when a stationary pressure is obtained. Accordingly, the system pressure and the temperature of the liquid being or to be degassed may be determined during one of the at least one idle step by a sensor sensing the temperature and the pressure (or representative thereof) in tank 2 when being substantially filled with water from the water based heat transfer system.

[0086] As indicated, a plurality of consecutive cycles are preferably carried out to obtain an effective degassing. Typically, a treatment step follows directly after the end of an idle step, although a waiting period could be introduced between the end of an idle step and begin of a treatment step. Such a plurality of consecutive cycles may be referred to as a treatment period, and a plurality of treatment periods may be carried out typically with a waiting period in-between each treatment period. A waiting period refers to a situation where one or more treatment steps are not carried out.

[0087] In preferred embodiments involving a number of cycles, calculation of the treatment time may be carried out for a number of, such as for all, treatment steps of the plurality of consecutive cycles.

[0088] When commissioning a water based system, there is often greater demand for degassing than for instance during maintenance of the water based system. To meet such a greater demand during a commissioning of the associated water based heat transfer system a plurality of consecutive cycles may be out, preferably in a continuous manner, for a duration being longer than 24 hours, such as longer than 48 hours, preferably longer than 72 hours and preferably shorter than 240, such as shorter 480 hours. A degassing during commissioning often serves two purposes, namely first removal of free air and then reducing the concentration to an acceptable level, such as below 90% or below 80%. Removal of free air is considered to takes place by the degassing reduces the concentration of air in the water during its passage through the tank 2 whereby the water when flowing in the water based system will be able to absorb free air in the water based system. Subsequently to a degassing during commissioning of the associated water based heat transfer system, a number treatment periods each comprising a plurality of consecutive cycles are repeatedly carried out during a fixed amount of treatment time, wherein in-between each treatment period no cycles are carried out.

[0089] Reference is made to Fig. 4 illustrating in a cross sectional view a preferred embodiment of degassing system for degassing gas, preferably air, from liquid preferably being water. As illustrated, the system comprising a tank 2 having a volume Vtank being the interior volume of the tank 2. The tank 2 is in fluid communication with a gas venting device 5 configured for outletting gas from the volume. Since gas accumulates above a liquid surface inside the tank 2, the gas venting device 5 is suitably arranged at upper end of the tank 2.

[0090] A pump 3 is arranged below the tank 2, although the pump 3 may be arranged differently. The pump 3 is configured to provide a reduced pressure Ptank in the tank 2 relatively to a system pressure Psys. In Fig. 4 the pump 3 is a centrifugal pump with four pump stages arranged on a shaft 10 driven by an electrical motor 11. A flow channel 12 is provided between the first stage of the pump 3 and the tank 2 to allow for flow of liquid from the tank 2 an into the pump 3. Inflow to the degassing system occurs through the inlet and outflow from the degassing system occurs through the outlet 14 (kindly note that in use, the caps arranged on the inlet and outlet 13, 14 are removed). The capped outlet shown below the outlet 14 is an outlet which can be used to drain the degassing system 1 and during use of the degassing system, this outlet is capped.

[0091] In the illustrated preferred embodiment, the flow of liquid through the inlet 13 leads liquid to a nozzle 4 configured to provide droplets from the inflowing liquid. The outlet of the nozzle directs the droplets in a upward direction which has been found to increase the degassing.

[0092] A pressure sensors 9 configured to determine a pressure in the tank 2 is arranged in the flow channel 12. It can be reasonably assumed that pressure changes occurring during the flow of liquid into and the through the channel are negligible so that measuring the pressure in the flow channel provides the pressure in tank 2, whereby the measure pressure is assigned to be the pressure in the tank 2 or a pressure representative thereof.

[0093] A temperature sensors 9 configured to determine a temperature of liquid present in the tank 2 is also arranged in the flow channel 12. In the illustrated embodiment, the pressure sensor and the temperature sensor are combined into single sensor. It can be reasonable to assumed that the temperature changes occurring during the flow of liquid into and the through the channel are negligible so that measuring the temperature in the flow channel provides the temperature in tank 2 or a temperature representative thereof.

[0094] A processor 8 is arranged inside a casing of the degassing system 1. Electrical connections are provided (not illustrated) between the combined pressure and temperature sensor 9 so that the processor 8 can receive measurements of the pressure and temperature. The processor 8 is configured by comprising software instructions to carry out a degassing cycle as disclosed herein. The processor may also be configured by software instructions to carry out degassing e.g. as disclosed herein.

[0095] ITEMIZED LIST OF PREFERRED EMBODIMENTS

[0096] Item 1. A method of degassing gas, preferably air, from a liquid, preferably water, the method utilizes a degassing system (1) comprising a tank (2) having a volume (Vtank) being in fluid communication with a gas venting device (5) configured for outletting gas from the volume, and a pump (3) configured to provide a reduced pressure (Ptank) in the tank (2) relatively to a system pressure (Psys) in an associated liquid based heat transfer system containing the liquid to be degassed, the degassing system is operated, during use, in cycles each comprising

[0097] • a treatment step with a duration treatment time (ttreat) during which the liquid to be degassed is inlet through a nozzle (4) at a volume flow (Qnoz) into the volume (Vtank) in which the reduced pressure (Ptank) is provided by the pump (3) whereby gas is released from the liquid and accumulated in the tank (2), and

[0098] • an idle step during which the accumulated gas is outlet from the tank (2) through the gas venting device by displacing the accumulated gas with liquid to be degassed being accumulated in the tank (2), the method comprising:

[0099] • obtaining a temperature (Ttank, Tsys) of the liquid being or to be degassed and the quantity of the volume flow Qnoz),

[0100] • calculating the treatment time (ttreat) based on the gas concentration in the liquid to be degassed (Cs), the gas concentration in the liquid downstream of the tank, such as at an outlet of the pump (3) (Cs, min), the obtained temperature, the quantity of the volume flow (Qnoz) and the reduced pressure (Ptank) so that the amount of degassed air during a treatment step is equal to or smaller than the volume (Vtank), and

[0101] • carry out at least one cycle with a duration of treatment step being equal to or less than the determined treatment time (ttreat) .

[0102] Item 2. A method according to item 1, wherein the treatment time (ttreat) is calculated during one idle step of the at least one cycle.

[0103] Item 3. A method according to any one of the preceding items, wherein the duration of the idle step is selected as the time it takes to essentially displace all gas accumulated in the tank (2), preferably including a safety margin. Item 4. A method according to any one of the preceding items, wherein the pump is a pump having a variable RPM, and wherein the pump (3) is operated at an RPM during the treatment step to provide the reduced pressure in the tank (2) or operated at maximum RPM if the reduced pressure (Ptank) cannot be obtained, and operated at a lower RPM, such as zero RPM, during the idle step.

[0104] Item 5. A method according to any one of the preceding items, wherein the gas concentration of the liquid to be degassed (Cs) and / or the concentration of the liquid after degassing (Cs,min) is / are determined based on a calculation involving Henry's constant or by a table look-up.

[0105] Item6. A method according to any one of the preceding items, wherein the quantity of the volume flow (Qnoz) is calculated based on a flow coefficient (Kv) of the nozzle (4) and a difference between the system pressure (Psys) and the reduced pressure (Ptank) .

[0106] Item 7. A method according to any one of the preceding items 1-5, wherein the quantity of the volume flow (Qnoz) is determined by a flow sensor.

[0107] Item8. A method according to any one of the preceding items, wherein the determination of the treatment time (ttreat) is based on the reduced pressure (Ptank) prevailing during degassing.

[0108] Item 9. A method according to any one of the preceding items, wherein the reduced pressure (Ptank) and / or the system pressure (Psys) in the associated water based system is obtained by a pressure sensor configured to determine the pressure inside the tank.

[0109] Item 10. A method according to item 9, wherein the prevailing reduced pressure is determined during one of the at least one treatment steps and the system pressure (Psys) is determined during one of the least one idle step(s).

[0110] Item 11. A method according to any one of the preceding items, wherein the temperature (Ttank, Tsys) of the liquid being or to be degassed is obtained by a sensor configured to determine the temperature of the liquid inside the tank. Item 12. A method according to any one of the preceding items, wherein the system pressure and the temperature of the liquid being or to be degassed are determined during one of the at least one idle step by a sensor sensing the temperature and the pressure in tank (2) when being substantially filled with water from the water based heat transfer system.

[0111] Item 13. A method according to any one of the preceding items, wherein a plurality of consecutive cycles are carried out.

[0112] Item 14. A method according to item 13, calculation of the treatment time is carried out for a number of, such as for all, treatment steps of the plurality of consecutive cycles.

[0113] Item 15. A method according to any one of the preceding items, wherein during a commissioning of the associated water based heat transfer system a plurality of consecutive cycles are out, preferably in a continuous manner, for a duration being longer than 24 hours, such as longer than 48 hours, preferably longer than 72 hours and preferably shorter than 240, such as shorter 480 hours.

[0114] Item 16. A method according to any one of the preceding items, wherein, preferably subsequently to a commissioning of the associated water based heat transfer system, a number treatment periods each comprising a plurality of consecutive cycles are repeatedly carried out during a fixed amount of treatment time, wherein in-between each treatment period no cycles are carried out.

[0115] Item 17. A method according to any one of the preceding claims, wherein the liquid is water and the gas is air.

[0116] Item 18. A method according to any one of the preceding claims, wherein the liquid based heat transfer system is a water based heat transfer system.

[0117] Item 19. A degassing system for degassing gas, preferably air, from liquid preferably being water, the system comprising

[0118] • a tank (2) having a volume (Vtank) being in fluid communication with • a gas venting device (5) configured for outletting gas from the volume,

[0119] • a pump (3) configured to provide a reduced pressure (Ptank) in the tank (2) relatively to a system pressure (Psys)

[0120] • one or more pressure sensors (9) configured to determine a pressure in the tank (2) or a pressure representative thereof

[0121] • one more temperature sensors (9) configured to determine a temperature of liquid present in the tank (2) or a temperature representative thereof, and

[0122] • a processor (8) configured receive measurements carried out by the one or more pressure sensors (9) and the one or more temperature sensors (9) and to carry out the method according to any one of the preceding items based on the received measurements.

[0123] Item 20. A degassing system according to item 19, wherein the liquid is water and the gas is air.

[0124] Item 21. A method according to any one of the preceding claims, wherein the liquid based heat transfer system is a water based heat transfer system.

[0125] List of reference symbols used :

[0126] 1 Degassing system

[0127] 2 Tank

[0128] 3 Pump in degassing system

[0129] 4 Nozzle

[0130] 5 Gas venting device

[0131] 6 Check valve

[0132] 7 Filter

[0133] 8 Processor

[0134] 9 Combined pressure and temperature sensor

[0135] 10 Shaft

[0136] 11 Motor

[0137] 12 Flow channel

[0138] 13 Inlet

[0139] 14 Outlet

[0140] Vtank Volume (of tank)

[0141] Vsys Volume of water in water based system

[0142] Qnoz Volume flow into the tank (volume per time unit)

[0143] Ptank Pressure in tank

[0144] Psys Pressure in water based system

[0145] Ttank Temperature of liquid in tank

[0146] Tsys Temperature of liquid in water based system

[0147] KvFlow coefficient of nozzle

[0148] Cs Air concentration in the water of the water based system

[0149] Cs,min Air concentration in the treated water leaving the tank

Claims

CLAIMS1. A method of degassing gas, preferably air, from a liquid, preferably water, the method utilizes a degassing system (1) comprising a tank (2) having a volume (Vtank) being in fluid communication with a gas venting device (5) configured for outletting gas from the volume, and a pump (3) configured to provide a reduced pressure (Ptank) in the tank (2) relatively to a system pressure (Psys) in an associated liquid based heat transfer system containing the liquid to be degassed, the degassing system is operated, during use, in cycles each comprising• a treatment step with a duration treatment time (ttreat) during which the liquid to be degassed is inlet through a nozzle (4) at a volume flow (Qnoz) into the volume (Vtank) in which the reduced pressure (Ptank) is provided by the pump (3) whereby gas is released from the liquid and accumulated in the tank (2), and• an idle step during which the accumulated gas is outlet from the tank (2) through the gas venting device by displacing the accumulated gas with liquid to be degassed being accumulated in the tank (2), the method comprising:• obtaining a temperature (Ttank, Tsys) of the liquid being or to be degassed and the quantity of the volume flow Qnoz),• calculating the treatment time (ttreat) based on the gas concentration in the liquid to be degassed (Cs), the gas concentration in the liquid downstream of the tank, such as at an outlet of the pump (3) (Cs, min), the obtained temperature, the quantity of the volume flow (Qnoz) and the reduced pressure (Ptank) so that the amount of degassed gas during a treatment step is equal to or smaller than the volume (Vtank), and• carry out at least one cycle with a duration of treatment step being equal to or less than the determined treatment time (ttreat) .

2. A method according to claim 1, wherein the treatment time (ttreat) is calculated during one idle step of the at least one cycle.

3. A method according to any one of the preceding claims, wherein the duration of the idle step is selected as the time it takes to essentially displace all gas accumulated in the tank (2), preferably including a safety margin.

4. A method according to any one of the preceding claims, wherein the pump is a pump having a variable RPM, and wherein the pump (3) is operated at an RPM during the treatment step to provide the reduced pressure in the tank (2) or operated at maximum RPM if the reduced pressure (Ptank) cannot be obtained, and operated at a lower RPM, such as zero RPM, during the idle step.

5. A method according to any one of the preceding claims, wherein the gas concentration of the liquid to be degassed (Cs) and / or the concentration of the liquid after degassing (Cs,min) is / are determined based on a calculation involving Henry's constant or by a table look-up.

6. A method according to any one of the preceding claims, wherein the quantity of the volume flow (Qnoz) is calculated based on a flow coefficient (Kv) of the nozzle (4) and a difference between the system pressure (Psys) and the reduced pressure (Ptank) .

7. A method according to any one of the preceding claims 1-5, wherein the quantity of the volume flow (Qnoz) is determined by a flow sensor.

8. A method according to any one of the preceding claims, wherein the determination of the treatment time (ttreat) is based on the reduced pressure (Ptank) prevailing during degassing.

9. A method according to any one of the preceding claims, wherein the reduced pressure (Ptank) and / or the system pressure (Psys) in the associated liquid based system is obtained by a pressure sensor configured to determine the pressure inside the tank.

10. A method according to claim 9, wherein the prevailing reduced pressure is determined during one of the at least one treatment steps and the system pressure (Psys) is determined during one of the least one idle step(s).

11. A method according to any one of the preceding claims, wherein the temperature (Ttank, Tsys) of the liquid being or to be degassed is obtained by a sensor configured to determine the temperature of the liquid inside the tank.

12. A method according to any one of the preceding claims, wherein the system pressure and the temperature of the liquid being or to be degassed are determined during one of the at least one idle step by a sensor sensing the temperature and the pressure in tank (2) when being substantially filled with liquid from the liquid based heat transfer system.

13. A method according to any one of the preceding claims, wherein a plurality of consecutive cycles are carried out.

14. A method according to claim 13, calculation of the treatment time is carried out for a number of, such as for all, treatment steps of the plurality of consecutive cycles.

15. A method according to any one of the preceding claims, wherein during a commissioning of the associated liquid based heat transfer system a plurality of consecutive cycles are out, preferably in a continuous manner, for a duration being longer than 24 hours, such as longer than 48 hours, preferably longer than 72 hours and preferably shorter than 240, such as shorter 480 hours.

16. A method according to any one of the preceding claims, wherein, preferably subsequently to a commissioning of the associated liquid based heat transfer system, a number treatment periods each comprising a plurality of consecutive cycles are repeatedly carried out during a fixed amount of treatment time, wherein in-between each treatment period no cycles are carried out.

17. A method according to any one of the preceding claims, wherein the liquid is water and the gas is air.

18. A degassing system for degassing gas, preferably air, from liquid preferably being water, the system comprising• a tank (2) having a volume (Vtank) being in fluid communication with• a gas venting device (5) configured for outletting gas from the volume,• a pump (3) configured to provide a reduced pressure (Ptank) in the tank (2) relatively to a system pressure (Psys)• one or more pressure sensors (9) configured to determine a pressure in the tank (2) or a pressure representative thereof• one more temperature sensors (9) configured to determine a temperature of liquid present in the tank (2) or a temperature representative thereof, and • a processor (8) configured receive measurements carried out by the one or more pressure sensors (9) and / or the one or more temperature sensors (9) and to carry out the method according to any one of the preceding claims based on the received measurements.

19. A degassing system according to claim 18, wherein the liquid is water and the gas is air.

Images