Additive for liquid ring pump operating liquid

Abstract

An operating liquid additive for a liquid ring pump 106 comprises a hygroscopic material and a carrier liquid in which the hygroscopic material is dispersed. The carrier liquid is non-hydrating. The h

Description

FIELD OF THE INVENTION The present invention relates to an additive fora liquid ring pump operating liquid, such as water. BACKGROUND Liquid ring pumps are a known type of pump which are typically commercially used as vacuum pumps and as gas compressors. Liquid ring pumps typically include a housing with a chamber therein, a shaft extending into the chamber, an impeller mounted to the shaft, and a drive system such as a motor operably connected to the shaft to drive the shaft. The impeller and shaft are positioned eccentrically within the chamber of the liquid ring pump. In operation, the chamber is partially filled with an operating liquid (also known as a service liquid). When the drive system drives the shaft and the impeller, a liquid ring is formed on the inner wall of the chamber, thereby providing a seal that isolates individual volumes between adjacent impeller vanes. The impeller and shaft are positioned eccentrically to the liquid ring, which results in a cyclic variation of the volumes enclosed between adjacent vanes of the impeller and the liquid ring. In a portion of the chamber where the liquid ring is further away from the shaft, there is a larger volume between adjacent impeller vanes which results in a smaller pressure therein. This allows the portion where the liquid ring is further away from the shaft to act as a gas intake zone. In a portion of the chamber where the liquid ring is closer to the shaft, there is a smaller volume between adjacent impeller vanes which results in a larger pressure therein. This allows the portion where the liquid ring is closer to the shaft to act as a gas discharge zone. Examples of liquid ring pumps include single-stage liquid ring pumps and multi-stage liquid ring pumps. Single-stage liquid ring pumps involve the use of only a single chamber and impeller. Multi-stage liquid ring pumps (e.g., two-stage) involve the use of multiple chambers and impellers connected in series. SUMMARY OF THE INVENTION In an aspect, there is provided a liquid ring pump operating liquid additive comprising a hygroscopic material and a carrier liquid in which the hygroscopic material is dispersed, the carrier liquid being non-hydrating. The hygroscopic material may be a powder. The liquid ring pump operating liquid additive may be a slurry. The liquid ring pump operating liquid additive may comprise a percent solids by weight of between 3% and 20%. The liquid ring pump operating liquid additive may comprise a percent solids by volume of between 3% and 20%. The hygroscopic material may have a particle size of between 50 nm and 50 pm. The liquid ring pump operating liquid additive may have a dynamic viscosity of above 0.05 Pa-s at a temperature of 20 °C. The hygroscopic material may be selected from a group of hygroscopic materials consisting of xanthan gum, tragacanth, carrageenan, agar agar, carboxymethylcellulose, a polysaccharide, a galactomannan polysaccharide, guar gum, alginate, sodium alginate, calcium alginate, and calcium carbonate. The carrier liquid may be selected from a group of carrier liquids consisting of a diol, a glycol, and ethylene glycol. In a further aspect, there is provided a liquid ring pump operating liquid comprising water and the liquid ring pump operating liquid additive of any-preceding aspect. The liquid ring pump operating liquid may have a percent solids by weight of between 0.1% and 50% and / or the percent solids of the liquid ring pump operating liquid by volume of between 0.1% and 50%. A dynamic viscosity of the liquid ring pump operating liquid may be above 1 mPa-s at a temperature of 25 °C. In a further aspect, there is provided a liquid ring pump comprising: a pump housing defining a pumping chamber; an impeller mounted eccentrically in the pumping chamber; and a liquid ring pump operating liquid within the pumping chamber, the liquid ring pump operating liquid being in accordance with any-preceding aspect. In a further aspect, there is provided a method of operating a liquid ring pump, comprising: adding a liquid ring pump operating liquid additive to water, thereby to create a liquid ring pump operating liquid; supplying the liquid ring pump operating liquid to the liquid ring pump; and pumping, using the liquid ring pump supplied with the liquid ring pump operating liquid; wherein the liquid ring pump operating liquid additive is in accordance with any preceding aspect. In a further aspect, there is provided a use of a liquid ring pump operating liquid additive according to any preceding aspect. In a further aspect, there is provided a use of a liquid ring pump operating liquid according to any preceding aspect. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration (not to scale) showing a vacuum system; Figure 2 is a schematic illustration (not to scale) of a liquid ring pump; and Figure 3 is a process flow chart showing certain steps of a process performable by the vacuum system. DETAILED DESCRIPTION Figure 1 is a schematic illustration (not to scale) showing a vacuum system 100. The vacuum system 100 is coupled to a facility 104 such that, in operation, the vacuum system 100 establishes a vacuum or low-pressure environment at the facility 104 by drawing gas (for example, air) from the facility 104. In this embodiment, the vacuum system 100 comprises a liquid ring pump 106, a motor 108, a separator 110, a pump system 112, a heat exchanger 113, and an operating liquid source 114. The facility 104 is connected to a gas inlet of the liquid ring pump 106 via a suction or vacuum line or pipe 116. A non-return valve may be disposed on the suction line 116. The nonreturn valve may be configured to permit the flow of fluid (e.g., a gas such as air) from the facility 104 to the liquid ring pump 106, and to prevent or oppose the flow of fluid in the reverse direction, i.e. from the liquid ring pump 106 to the facility 104. In this embodiment, the liquid ring pump 106 is a single-stage liquid ring pump. The liquid ring pump 106 is driven by the motor 108. Thus, the motor 108 is a driver of the liquid ring pump 106. The liquid ring pump 106 will be described in more detail later below with reference to Figure 2. The gas inlet of the liquid ring pump 106 is connected to the suction line 116. A gas outlet of the liquid ring pump 106 is connected to an exhaust line or pipe 118. The exhaust line 118 is coupled between the gas outlet of the liquid ring pump 106 and an inlet of the separator 110. The separator 110 is connected to the liquid ring pump 106 via the exhaust line 118 such that exhaust fluid (i.e., compressed gas, which may include operating liquid and / or water droplets and / or vapour) is received by the separator 110. The separator 110 is configured to separate the exhaust fluid received from the liquid ring pump 106 into gas (e.g., air) and the operating liquid. Thus, the separator 110 provides for recycling of the operating liquid. The gas separated from the received exhaust fluid is expelled from the separator 110, and the vacuum system 100, via a system outlet pipe 120. !n this embodiment, the separator 110 comprises a further inlet 122 via which the separator 110 may receive a supply of additional, or “top-up”, operating liquid from the operating liquid source 114. A controllable valve may be disposed along the further inlet 122 for controlling the flow of the additional operating liquid into the separator 110 via the further inlet 122. The separator 110 comprises an operating liquid outlet. The operating liquid outlet of the separator 110 is coupled to the pump system 112 via a first operating iiquid pipe 124 such that operating liquid may flow from the separator 110 to the pump system 112. In this embodiment, in addition to being coupled to the separator 110 via the first operating liquid pipe 124, the pump system 112 is coupled to the heat exchanger 113 via a second operating liquid pipe 126. The pump system 112 comprises a pump (e.g., a centrifugal pump) and a motor configured to drive that pump. The pump system 112 is configured to pump operating liquid out of the separator 110 via the first operating liquid pipe 124, and to pump that operating liquid to the heat exchanger 113 via the second operating liquid pipe 126. The heat exchanger 113 is configured to receive relatively hot operating liquid from the pump system 112, to cool that relatively hot operating liquid to provide relatively cool operating liquid, and to output that relatively cool operating liquid. In this embodiment, the heat exchanger 113 is configured to cool the relatively hot operating iiquid flowing through the heat exchanger 113 by transferring heat from that relatively hot operating liquid to a fluid coolant also flowing through the heat exchanger 113. The operating liquid and the coolant are separated in the heat exchanger 113 by a solid wall via which heat is transferred, thereby to prevent mixing of the operating liquid with the coolant. The heat exchanger 113 receives the coolant from a coolant source (not shown in the Figures) via a coolant inlet 128. The heat exchanger 113 expels coolant (to which heat has been transferred) via a coolant outlet 130. The heat exchanger 113 comprises an operating liquid outlet from which the cooled operating liquid flows (i.e., is pumped by the pump system 112). The operating liquid outlet of the heat exchanger 113 is coupled to a third operating liquid pipe 132. The heat exchanger 113 is coupled to the liquid ring pump 106 via the third operating liquid pipe 132. The liquid ring pump 106 is configured to receive operating liquid from the heat exchanger 113 via the first operating liquid pipe 132. In operation, the cooled operating liquid is pumped by the pump system 112 from the heat exchanger 113 to the liquid ring pump 106. Figure 2 is a schematic illustration (not to scale) of a cross section of the liquid ring pump 106. The liquid ring pump 106 comprises a pump housing 202 with a chamber 204 therein, a shaft 206 extending into the chamber 204, and an impeller 208. The impeller 208 comprises a central hub 210 mounted to the shaft 206, and a plurality of vanes 212 which extend outwards from the central hub 210. The vanes 212 extend along the axial iength of the central hub 210, the axial length of the hub 210 being perpendicular to the page of Figure 2. As is the case in Figure 2, the vanes 212 may extend outwards from the hub 210 in a direction that is oblique to the surface of the hub 210 in a direction that has a vector component that is radial and a vector component that is tangential with respect to the surface of the hub. Alternatively, the vanes 212 may extend radially outwards from the hub 210 perpendicularly to the surface of the hub 210. The central hub 210 and the vanes 212 (and / or the shaft, 206) may be integrally formed. The vanes 212 may be curved in the radial direction. The impeller 208 and shaft 206 are positioned eccentrically within the chamber 204 of the liquid ring pump 106 such that the clearance between the tip of the vanes 212 and the wall of the chamber 204 varies around the circumference of the housing 202. The motor 108 is operably connected to the shaft 206 to drive the shaft 206. !n operation, the chamber 204 is partially filled with the operating liquid 214 (also known as service liquid). When the motor 108 drives the shaft 206 and the impeller 208, thereby causing the shaft 206 and impeller 208 to rotate (as indicated in Figure 2 by an arrow and the reference numeral 215), the operating liquid 214 forms a liquid ring on the inner wall of the chamber 204, thereby providing a seal that isolates individual gas volumes between adjacent impelier vanes 212. The impeller 208 and shaft 206 are positioned eccentrically to the liquid ring, which results in a cyclic variation of the gas volumes enclosed between adjacent vanes 212 of the impeller 208 and the liquid ring. A gas inlet duct 216 of the liquid ring pump 106 is coupled to the suction line 116. The gas inlet duct 216 leads to an inlet opening 218 located within the chamber 204. The inlet opening 218 is within a region of the chamber 204 in which the vanes 212 of the rotating impeller 208 emerge from the liquid ring. In this region, the volumes between adjacent impeller vanes 212 and the liquid ring enlarge as the impeller 208 rotates. As a result of the enlarging volumes (and thus decreasing gas pressure), gas is sucked into the chamber 204 through the inlet opening 218. Thus, the portion of the chamber 204 where the liquid ring is further away from the shaft 206 may act as a gas intake zone. Gas flow into the liquid ring pump 200 via the inlet duct 216 and the inlet opening 118 is indicated by an arrow and the reference numeral 220. A gas outlet duct 222 of the liquid ring pump 106 is coupled to the exhaust line 118. The gas outlet duct 222 leads from an outlet opening 224 located within the chamber 204, to the exhaust line 118. The outlet opening 224 is within a region of the chamber 204 in which the vanes 212 of the rotating impeller 208 penetrate the liquid ring. In this region, the gas volumes between adjacent impeller vanes 212 reduce in volume as the impeller 208 rotates. As a result of the decreasing volumes (and thus increasing gas pressure), gas is forced out of the chamber 204 through the outlet opening 224. Thus, the portion of the chamber 204 where the liquid ring is closer to the shaft 206 may act as a gas discharge zone. Gas flow out of the liquid ring pump 106 via the outlet opening 224 and the outlet duct 222 is indicated by an arrow and the reference numeral 226. The liquid ring pump operating liquid 214 comprises a mixture of water and a liquid ring pump operating liquid additive, hereinafter referred to as the “additive”. The additive may be considered to be a dosing agent for the operating liquid (water) of the liquid ring pump, i.e. an agent that is added to, dosed, or blended with the water. The proportions of the water and the additive may be application dependent. This may be based, for example, on the size of pump chamber 204, the number of chambers, and / or the level of the process fluid 214. The additive comprises a hygroscopic material (which in this embodiment is a solid) and a carrier liquid in which the hygroscopic material is dispersed. The carrier liquid is non-hydrating. Thus, the mixing or combining together of the hygroscopic material and the carrier liquid, i.e. the dispersion of the hygroscopic material in the carrier liquid, does not cause the hygroscopic material to become a hydrate or become hydrated. Preferably, the hygroscopic material is a powder, i.e. a solid in powder form. The particle size of the hygroscopic material may be application dependent, but is preferably between about 50 nm and about 50 pm. In this embodiment, the additive is a slurry, i.e. a liquid or semi-liquid mixture comprising fine particles suspended or dispersed in a liquid. The percent solids of the additive by weight may be application dependent, and may be, for example, between about 1% and about 50%, or between about 3% and about 30%, or between about 3% and about 20%. The percent solids of the additive may be calculated by dividing the mass of the solids (i.e., the hygroscopic material) in a sample of the additive by the total mass of the sample additive (i.e., the hygroscopic material plus the carrier liquid) and then multiplying the result by 100. The percent solids of the additive by volume may be application dependent, and may be, for example, between about 1% and about 50%, or between about 3% and about 30%, or between about 3% and about 20%. The percent solids of the additive may be calculated by dividing the volume of solids (Le., the hygroscopic material) in a sample of the additive by the total volume of the sample additive, and then multiplying the result by 100. A dynamic viscosity of the additive may be application dependent. The dynamic viscosity of the liquid ring pump operating liquid additive may, for example, be above about 0.05 Pa-s at a temperature of 20°C, for example between about 0.1 Pa-s and 0.5 Pa-s at 20°C. The hygroscopic materia! may be selected from a group of hygroscopic materials consisting of xanthan gum, tragacanth, carrageenan, agar agar, carboxymethylcellulose, a polysaccharide, a galactomannan polysaccharide (e.g., guar gum), sodium alginate, calcium alginate and calcium carbonate. Preferably, the hygroscopic material includes a mixture of hydrocolloids. The carrier liquid may be selected from a group of carrier liquids consisting of a diol, such as a glycol (e.g., ethylene glycol). Preferably, the carrier liquid is ethylene glycol. A dynamic viscosity of ethylene glycol may be 16.1 mPa-s at 25°C. Thus, a dynamic viscosity of the liquid ring pump operating liquid additive when ethylene glycol is used as the carrier liquid is greater than 16.1 mPa-s at 25°C. Preferably, the liquid ring pump operating liquid additive comprises powdered xanthan gum dispersed in a glycol, preferably ethylene glycol. The liquid ring pump operating liquid additive is mixed or combined with water to provide the liquid ring pump operating liquid 214. The percent solids of the liquid ring pump operating liquid 214 (i.e., the mixture of the water and the additive) by weight may be application dependent, and may be for example between about 0.1% and about 50%. The percent solids of the liquid ring pump operating liquid 214 (i.e., the mixture of the water and the additive) by volume may be application dependent, and may be for example between about 0.1 % and about 50%. A dynamic viscosity of the liquid ring pump operating liquid 214 may be above about 1 mPa-s at a temperature of 25 °C. degrees Celsius. More preferably, the dynamic viscosity of the liquid ring pump operating liquid 214 may be between about 10 mPa-s and about 100 mPa-s at 25 °C. The viscosity of the process fluid may be maintained at between 5 and 50 centipoise at 20 °C e.g. relative to the size of the chamber, number of chambers and the fill level of the process fluid. Any known technique for measuring the dynamic viscosity of the liquid ring pump operating liquid additive and / or the liquid ring pump operating liquid 214 may be applied. Examples of such techniques include, but are not limited to, those implementing a vibrational viscometer, those implementing a rotational viscometer, those implementing a capillary viscometer, those implementing a falling sphere viscometer, and those implementing a consistometer. Figure 3 is a process flow chart showing certain steps of an embodiment of a method 300 of operating the liquid ring pump 106 in the vacuum system 100. It should be noted that certain of the process steps depicted in the flowchart of Figure 3 and described below may be omitted or such process steps may be performed in differing order to that presented below and shown in Figure 3. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally., comprising: At step s302, a supply of the liquid ring pump operating liquid is provided in the operating liquid source 114. At step s304, the operating liquid source 114 supplies the liquid ring pump operating liquid to the separator 110. At step s306, the pumping system 112 pumps the liquid ring pump operating liquid from the separator 110 to the liquid ring pump 106. At step s308, the motor 108 drives the liquid ring pump 106. At step s310, the liquid ring pump 106, suppled with the liquid ring pump operating liquid, pumps a fluid from the facility 104. During the pumping of the fluid by the liquid ring pump 106, the liquid ring pump operating liquid forms a liquid ring on the inner wall of the chamber 214, thereby providing a seal that isolates individual volumes between adjacent impeller vanes 212. At step s312, the liquid ring pump 106 pumps the fluid out of the vacuum system 100 via the separator 110 and the exhaust line 120. Thus, an embodiment of a method 300 of operating the liquid ring pump 106 in the vacuum system 100 is provided. The above-described method may be performed automatically, under control of one or more controllers. One or more of the controllers may be a proportional-integral (PI) controller, a proportional (P) controller, an integral (I) controller, a derivative (D) controller, a proportional-derivative (PD) controller, a proportional-integral-derivative controller (PID) controller, a fuzzy logic controller, or any other type of controller. The above-described liquid ring pump operating liquid additive advantageously tends to increase the (dynamic and kinematic) viscosity of the operating liquid of a liquid ring pump. This tends to improve the stability of the liquid ring during pumping. As a result, the power consumption by the pump tends to be reduced and pump efficiency tends to be improved. In the above embodiments, the hygroscopic material is supplied as a powder in its native form. The use of the carrier liquid (e.g., a glycol) to deliver the powder hygroscopic material to the water tends to facilitate introduction of the hygroscopic material into the water. The mixing of a powder hygroscopic material directly with water tends to be problematic. Uneven distribution of the hygroscopic material (e.g., lumps) may cause blockages in pipes and / or nozzles, and may reduce pumping performance. Furthermore, the powder hygroscopic material may be prone to settling, especially during periods of pump inactivity, which may cause blockages. The use of the carrier liquid to deliver the powder hygroscopic material tends to alleviate such problems. Moreover, the hygroscopic material tends to hydrate once in contact with the water. Were a powder hygroscopic material to be mixed directly with water, saturation of the hygroscopic materiai may be achieved in, for example, 8-24 hours depending on materials used. Accordingly, pre-mixing of the liquid ring pump operating liquid prior to use would typically be needed. The abovedescribed additive and method uses a suitable carrier liquid to disperse the hygroscopic material without hydrating it. The hygroscopic material is then introduced as a concentrated suspension or slurry, mixing with the water and hydrating during the subsequent hours of pump operation. Pre-mixing of the liquid ring pump operating liquid tends to be reduced or eliminated. The storage and transport of the liquid ring pump operating liquid additive tends to be easier than that of pre-mixed liquid ring pump operating liquid. In the above embodiments, the vacuum system comprises the elements described above with reference to Figure 1. However, in other embodiments the vacuum system comprises other elements instead of or in addition to those described above. In some embodiments, one or more of the elements of the vacuum system described above may be omitted. Also, in other embodiments, some or all of the elements of the vacuum system may be connected together in a different appropriate way to that described above. For example, in some embodiments, multiple liquid ring pumps may be implemented. In the above embodiments, the heat exchanger cools the operating liquid flowing therethrough. However, in other embodiments other cooling means are implemented to cool the operating liquid prior to it being received by the liquid ring pump, instead of or in addition to the heat exchanger. In the above embodiments, the liquid ring pump is a single-stage liquid ring pump. However, in other embodiments the liquid ring pump is a different type of liquid ring pump, for example a multi-stage (e.g., dual stage) liquid ring pump. Reference numeral list: 100 - vacuum system; 104 - facility; 106 - liquid ring pump: 108 - motor; 110- separator; 112- pump system; 113 - heat exchanger; 114- operating liquid source 116- suction line; 118- exhaust line; 120 - system outlet pipe; 122 - further inlet; 124 - first operating liquid pipe; 126 - second operating liquid pipe; 128 - coolant inlet; 130 - coolant outlet; 132 - third operating liquid pipe; 202 - housing; 204 - chamber; 206 - shaft; 208 - impeller; 212 - vanes 214 - operating liquid 215 - direction of rotation 216 - gas inlet duct 218 - inlet opening 220 - inward gas flow 222 - gas outlet duct 5 224 - outlet opening 226 - outward gas flow 300 - method s2~s12 - method steps

Claims

1. A liquid ring pump operating liquid additive comprising:a hygroscopic material; anda carrier liquid in which the hygroscopic material is dispersed, the carrier liquid being non-hydrating.

2. The liquid ring pump operating liquid additive of claim 1, wherein the hygroscopic material is a powder.

3. The liquid ring pump operating liquid additive of any preceding claim, wherein the liquid ring pump operating liquid additive is a slurry.

4. The liquid ring pump operating liquid additive of any preceding claim, wherein the liquid ring pump operating liquid additive comprises a percent solids by weight of between 3% and 20%.

5. The liquid ring pump operating liquid additive of any preceding claim, wherein the liquid ring pump operating liquid additive comprises a percent solids by volume of between 3% and 20%.

6. The liquid ring pump operating liquid additive of any preceding claim, wherein the hygroscopic material has a particle size of between 50 nm and 50 pm.

7. The liquid ring pump operating liquid additive of any preceding claim, wherein the liquid ring pump operating liquid additive has a dynamic viscosity of above 0.05 Pa-s at a temperature of 20 °C8. The liquid ring pump operating liquid additive of any preceding claim, wherein the hygroscopic material is selected from a group of hygroscopic materials consisting of xanthan gum, tragacanth, carrageenan, agar agar, carboxymethyicellulose, a polysaccharide, a galactomannan polysaccharide, guar gum, alginate, sodium alginate, calcium alginate, and calcium carbonate.

9. The liquid ring pump operating liquid additive of any preceding claim, wherein the carrier liquid is selected from a group of carrier liquids consisting of a diol, a glycol, and ethylene glycol10. A liquid ring pump operating liquid comprisingwater; andthe liquid ring pump operating liquid additive of any preceding claim.

11. The liquid ring pump operating liquid of claim 10, wherein the liquid ring pump operating liquid has a percent solids by weight of between 0.1% and 50% and / or the percent solids of the liquid ring pump operating liquid by volume of between 0.1% and 50%.

12. The liquid ring pump operating liquid of claim 10 or 11, wherein a dynamic viscosity of the liquid ring pump operating liquid is above 1 mPa s at a temperature of 25 °C.

13. A liquid ring pump comprising:a pump housing defining a pumping chamber:an impeller mounted eccentrically in the pumping chamber; anda liquid ring pump operating liquid within the pumping chamber, the liquid ring pump operating liquid being in accordance with any of claims 10 to 12.14, A method of operating a liquid ring pump, comprising:adding a liquid ring pump operating liquid additive to water, thereby to create a liquid ring pump operating liquid;5 supplying the liquid ring pump operating liquid to the liquid ring pump; andpumping, using the liquid ring pump supplied with the liquid ring pump operating liquid; whereinthe liquid ring pump operating liquid additive is in accordance with any of claims 1 to 9.1015. Use of a liquid ring pump operating liquid additive according to any one of claims 1 to 9.

16. Use of a liquid ring pump operating liquid according to any one of claims15 10-12.18

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