EP3458718B1

EP3458718B1 - Improved liquid ring pump

Info

Publication number: EP3458718B1
Application number: EP17723493.7A
Authority: EP
Inventors: Mark Gordon GLAISTER; Andries DE BOCK
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2016-05-17
Filing date: 2017-05-08
Publication date: 2024-05-01
Anticipated expiration: 2037-05-08
Also published as: WO2017199001A1; EP3458718A1; CN209687716U; GB2550365A; GB201608622D0; AU2017266497A1; AU2017101844A4; BR112018073624A2; RU192390U1; US20190277287A1; GB2550365B

Description

The present invention relates to an improved pump component, and a pump comprising said improved component. In particular, the present invention relates to a liquid ring pump component, to reduce the power consumed during operation of a liquid ring pump comprising said component.
Liquid ring vacuum pumps and compressors are well known in the art for pumping a variety of process fluid compositions. The pumping mechanism of a typical liquid ring pump is shown in Figure 1. A liquid ring 100 is formed around an outer periphery of a generally cylindrical pumping chamber 102 on rotation of a rotor 104 mounted for rotation about an axis X which is eccentric to the central axis C of the pumping chamber 102. The rotor has a plurality of blades 106 that extend radially outwardly from a hub 108 and are equally spaced around the rotor. On rotation of the rotor 108, 106, the blades 106 engage the liquid conveyed to the chamber, from a source of liquid 110, forming an annular ring 100 inside the pumping chamber 102. The liquid ring provides both the axial seal at the rotor ends and the radial seal between adjacent blades 106.
The eccentricity of the rotor axis X with respect to the central axis C of the chamber 102 displaces the liquid ring 100 away from the rotor hub 108 in the inlet region 112 of the pump, forming an expanding compression region 114 between adjacent rotor blades 106 into which gas flows through the inlet port 112 of the pump. Conversely, continued rotation into the exhaust region of the pump displaces the liquid ring 100 towards the rotor hub 108, compressing the gas in the decreasing volume compression region 114 between adjacent blades 106 until it is expelled through the outlet port 116 of the pump. This results in a piston-type pumping action on the gas passing through the pump. That is, the compression regions 114 increase and decrease in volume through rotation of the rotor. The compression regions 114 are defined by adjacent rotor blades 106, the liquid ring 100, and an outer surface 118 of the hub. Accordingly, gas is pumped through a single stage for each rotation of the rotor.
A large contribution to power loss in liquid ring pumps has been attributed to frictional drag of the liquid ring 100 against the stationary walls defining pumping chamber 102. As shown in Figure 1, the walls of the chamber 102 are stationary with respect to the liquid ring 100 and so, as the liquid ring continually circulates against their surfaces at high velocity, the fluid drag can represent a significant power loss.
One solution to overcome power loss due to friction, described in EP0492792 , is to provide a rotating canister within the pumping chamber that contains, and rotates with, the liquid ring 100. By providing a rotating canister that rotates with the liquid ring, the drag and thus power losses are significantly reduced. However, this design introduces significant complexity into the liquid ring pump which, in addition to the additional cost of the unit, creates scalability issues.
Another solution, described in US20110194950 , is the use of a textured surface to control boundary layer separation reducing, to some extent, the drag between the liquid ring and pumping chamber surfaces. However, this design requires a very specific pre-determined pattern to be applied to the chamber surfaces which add unnecessary complexity when manufacturing the liquid ring pump.
The present invention aims at least to mitigate one or more of the problems associated with the prior art.
In a first aspect the present invention provides a liquid ring pump component at least partially coated with a coating comprising at least one alkoxysilane, wherein the coating on the pump component is, in use, in contact with a work fluid.
Other preferred and/or optional aspects of the invention are defined in the accompanying claims.
In order that the present invention may be well understood, several embodiments thereof, which are given by way of example only, will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a radial cross section through a prior art liquid ring pump.
Figure 2 shows a radial cross section through a liquid ring pump according to the present invention.
Figure 3 shows an exploded view of a section of a two stage liquid ring pump according to the present invention.

With Reference to Figure 2, a radial cross section through a liquid ring pump according to the present invention is illustrated. The same reference numerals used to denote features in Figure 1 have been used to denote the identical features in Figure 2 and, for brevity, will not be explained further.
The surface of the casing, or stator component, 102, has a coating 123 comprising an alkoxysilane, such as methyltrimethoxysilane and/or phenyltrimethoxysilane, applied thereto. It will be appreciate that these are just two examples and other alkoxysilanes with the following properties are suitable alternatives.
The coating 123 may be applied at room temperature and requires little or no component surface preparation. Once applied, for example by spraying the coating onto the desired area of the component 102, 108, 106, or dipping the component in a coating solution, the coating 123 self-seals to form a highly hydrophobic glass like ceramic surface coating 123.
The alkoxysilanes can be applied to leave coatings with thicknesses of just 6 µm, which is considerably less than the minimum radial clearance between the rotor blades 106 and internal surface of the stator 102. Thus, because the radial clearance is sealed by the liquid ring 100, no additional machining operations are required pre or post application. This also means that the coating 123 can be applied to existing liquid ring pumps already in operation to provide the benefits thereof retrospectively.
Once applied, the coating 123, develops a surface with a low coefficient of friction which in turn greatly reduces the power losses, in use, due to reduced friction between the liquid ring 100 and the coating 123 on surface of the chamber 102. The coatings also advantageously improve heat transfer from the work fluid thus increasing convective heat loss through the stator and to the external atmosphere.
Axial chamber walls (not shown) which define the rest of the chamber 102 shown in Figure 2 are also preferably coated with the coating comprising at least one alkoxysilane to further reduce the power losses and improve heat transfer (where required).
This is better illustrated in figure 3, which shows an exploded view section of a two-stage liquid ring pump according to the present invention. The pump comprises two inlets 212 and two outlets 216 through which gas is conveyed to and from the pumping chamber 202. The pumping chamber 202 is defined by two axial end plates 202b which are connected to either end of a generally cylindrical chamber 202a. The work fluid, usually water, for the liquid ring is conveyed to the chamber 202 from a liquid source via the inlets 210 located in the axial end plates 202b and coaxial with the shaft 201. The axis of the shaft 201 is again eccentric to the central axis of the chamber 202. On rotation of the shaft 201 the work fluid conveyed to the chamber 202 engages with the rotor blades 206 extending radially outward from a hub 208 to form an annular liquid ring (not shown) in the pumping chamber. The pumping action of the liquid ring pump is substantially identical to that described and illustrated for figures 1 and 2 except that gas can enter the pump via two inlets 212 and is exhausted via two outlets 216.
In order to reduce power losses due to friction, the surfaces of at least the chamber walls 202a and 202b defining the chamber 202 are provided with a coating comprising an alkoxysilane.
In both the examples shown in figures 2 and 3 it is also advantageous to coat at least part of the surface of the rotor 106, 206, rotor hub 108, 208, and shafts 201 (not shown for figure 2) that, in use, will come into contact with the moving work fluid to further reduce power losses due to friction. As the rotor blades 106, 206 are intimate contact with the moving work fluid to form the ring 100, it is advantageous to coat at least their leading surface with the coating 123.
The coatings according to the present invention last considerably longer that known organic coatings applied to surfaces to reduce fluid friction due to the alkoxysilane's ability to completely coat the pump component surfaces, filling micro-voids and micro-cavities. This, together with the lack of micro-porosity associated with known organic coatings, protects metal components from oxidation mechanisms such as pitting and provides a superior surface finish. In addition, the coating forms a hard, abrasion resistant layer that protects the chamber 102, 202 and rotor 106, 108, 206, 208 surfaces from abrasion by suspended solids contained within the work fluid captured from pumped process gases.
The hydrophobic coatings formed provide resistance to water ingress along the coating-metal substrate interface of a coated component which, together with the improved bonding process, provides high resistance to de-bonding in cases where the protective coating is penetrated down to the metal substrate.
Thus the improved components and pumps according to the present invention provide significant reductions in power loss and increased longevity compared to the known textured surface or organic coatings, whilst reducing the complexity associated with the rotating canister designs.

Claims

A liquid ring pump component at least partially coated with a coating, characterised by the coating comprising at least one alkoxysilane, wherein the coating on the pump component is, in use, in contact with a work fluid.
A liquid ring pump component according to claim 1, wherein the pump component is at least one of a rotor component, a stator component and a rotor shaft component.
A liquid ring vacuum pump comprising a component according to claim 1 or 2.