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Liquid ring compressor

Liquid ring compressor description/claims

The present invention relates to a compressor, in particular a liquid ring compressor.

Most compressors work with approximate adiabatic process, i.e. without exchanging heat during the compression phase. In practice, e.g. a reciprocating compressor, emit quite a lot of heat, but it is only a small part of this heat which is emitted during compression, most of it is after, or in the end phase. A turbo compressor often has very close adiabatic process.

Some, a bit more special compressors can work very close to isothermal, i.e. the heat which is generated is continuously led away and the temperature is kept unchanged. Examples of these are water driven ejectors and liquid ring compressors, where both are frequently used with vacuum. A screw compressor with oil injection works polytropic, i.e. somewhere between adiabatic and isothermal.

The isothermal process requires less energy supplied than the adiabatic. The difference increase rapidly with increasing pressure difference, as shown in the diagram in FIG. 1. This shows theoretical values, calculated for air based upon formula for ideal gas. Air and gases which in a state which is not in the proximity of the critical point, behave very close to ideal.

For most objectives it is not desirable with hot gas after compression, and from this and the energy consumption, the isothermal process is preferred in theory.

When this, despite the above, is not employed today, the reason can be found in that existing isothermal or close isothermal compressors have too large hydraulic and dynamic losses. It is an exception for vacuum pumps which n reality is liquid compressors with high pressure difference, p2/p1, but with little pressure height, p2−p1. These can operate with low peripheral speeds on the liquid ring. Another problem is in the technical challenge to be able to remove heat continuously during compression.

Within vacuum both ejector and water ring compressors are frequently used. An ejector exploit the mass speed in a water jet in which the cross section expands and thereby can pull another medium with it. The ejector transform dynamic pressure to static pressure. However, an ejector system has relatively high losses in pump, in nozzle, by impact and friction. Ejectors are rarely used to anything else than the vacuum field. Within prior art the water ring compressor is closest to the compressor according to the present invention.

A liquid ring compressor consists mainly of an impeller which rotates eccentric in an outer enclosure together with a ring of water which the centrifugal force keeps in place against the periphery. The inlet is normally positioned as an opening in one or both of the end walls of the enclosure where the gas is drawn, into the gaps of the impeller. Accordingly, it is arranged openings in the end walls on the pressure side, where the compressed gas is pushed out. All the types can have stationary commutators arranged centrally within the rotor where inlet and discharge happens radially.

Liquid ring compressor does not transform the energy in the water in the same way as the ejector. The static pressure in the ring of water remains constant. The ring of water acts as a piston in every cell of the rotor. The principle for an ordinary liquid ring compressor is shown in FIG. 2, where a ring of liquid 23 rotates eccentric in a stationary enclosure 22, drive by a rotor 21 where the gap between the impeller will draw in gas on one side of a revolution and compress the gas on the other.

The static pressure in the ring of water has to be the same as the compression pressure, otherwise the water will be pressed out of the cell, i.e. the water ring will be deformed. Thereby it is given that a certain pressure height, p2−p1, require a minimum centrifugal force. A liquid ring compressor usually has considerably higher pressure height and therefore requires higher speed of rotation than a vacuum pump.

The highest loss of friction in a conventional water ring compressor arise when the rotor is touching the wall of the enclosure. The clearing must here be very small, something which involves the water against the enclosure's periphery to have the same speed as the impeller tips of the rotor. Furthermore it must be very little clearance between the sides of the rotor and the enclosure. Also in these gaps there will be high frictions.

Generally the friction losses increase with a square of the speed increase, and in practice the water ring compressor looses level of energy in relation to energy in relation to an adiabatic compressor even at relatively low pressure ratios.

Without these friction losses, the liquid ring compressor has many advantages. It is very simple and can be one stage up to relatively high pressure ratios.

It is apparent that if that the enclosure around the ring of water rotated together with this, the hydraulic friction losses would be minimal. Thus, such a compressor would for normal pressure ratios could exploit the isothermal energy advantages almost in full.

An earlier suggestion disclosed with an outer, rotating cylinder tried to solve the problem of friction, without this leading to a feasible solution. U.S. Pat. No. 5,100,300 and U.S. Pat. No. 5,370,502 describes liquid ring compressor with a cylinder which floats on a film of liquid or gas between the cylinder and the outer stationary enclosure. By floating on a liquid film, it is doubtful whether it would be achieved any reduction in the friction, and with gas it would probably not be possible to achieve sufficient bearing capacity and stability, such that the cylinder do not touch the enclosure.

In a later patent, U.S. Pat. No. 5,395,215, from the same firm, it is suggested a bearing of this cylinder in an outer enclosure, where a number of rollers are inserted in the wall of the enclosure where the cylinder is supported by the rollers. This do not seem realistic with the actual rotational speeds the rollers will achieve. A subsequent patent, U.S. Pat. No. 5,653,582, returns back to fluids as the peripheral bearing for the rotating cylinder and suggestion to the basic solution.

U.S. Pat. No. 5,251,593 discloses as the previous application that it is an intricate problem to get to, in relation to each other, eccentric bearings in combination with a stationary canals for the inlet and discharge of the gas. This publication indicates a bearing of the outer rotating cylinder on one side and the rotor on the opposite side, where a stationary plate close to the open end of the rotor has canals for inlet and discharge. It is mainly two decisive weaknesses with this design. The first is the one-sided bearing this solution gives, where the bearing load becomes uneven and too high. At the same time large axial to thrust forces arise. The other weakness is the problems with achieving a reasonable gas tight sealing between the outer rotating cylinder, and the plate where the inlet and discharge canals are positioned in a circular plate, inlaid in the open end of the rotor. It would here be gas leaks backwards from cell to cell and in addition out through the circular gap between the stationary plate and the rotor. The principle is unrealistic for practical purposes.

Despite may studies and suggestions over many years, it evidently has not been possible to reach a design which fulfil the requirements to function satisfactory. Thus at present there exists no liquid ring compressor with such co-rotating rotor. The above mentioned publications indicates that one has been tied up to the starting point for a rotor and communicator system like those in conventional vacuum pumps and compressors for relatively low pressure, with the above mentioned limitations in speed. This is reflected in relatively wide rotors with communicator on each side, which lead to long bearing distance and high bearing loads. In a compressor with liquid ring in the outer co-rotor, the geometry will be wrong, which will lead to bearing relationship which is unsuitable for existing bearing types. With communicator on each side, it becomes four sections with gaps where there exists leakage from the zones on the pressure side.

The compressor according to the present invention has the objective to solve this problem which up to know has prevented a water ring compressor to exploit the above mentioned advantages with a co-rotor for the liquid ring. Another objective is to achieve almost isothermal compression with a new, very efficient direct injection of liquid into the gas during the whole compression stage.

Water as injection liquid has very good thermal properties, and is desirable to use with those gases which allow this. But, as for pumps and the like, the design for a liquid compressor with a co-rotor require a distinct division between water and the bearing of the co-rotor. From the development of screw compressors with water injection it is known and it has been problems with sealing on the pressure side of the screws. Firstly, water has small to little lubricating effect on the sealing which must have relatively high pressure towards the axle and therefore high wear. Furthermore, water penetrates easily through even the finest caps, and especially high pressure. Below it will be evident that the compressor according to the present invention solves the sealing problem by eliminating the reasons for them. The aforementioned objectives will be satisfied with the liquid ring compressor according to present invention as it is defined in the attached claims.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which FIG. 1 shows a diagram with theoretical energy needs independence of pressure relation ship, FIG. 2 shows schematic the principle for a liquid ring compressor, FIG. 3 a liquid ring compressor according to the present invention in a divided longitudinal view, FIG. 4 is a cross section of FIG. 4, FIG. 5 shows the compressor as mounted, sectioned design, FIG. 6 shows details of the rotor, FIGS. 7a to and 7b shows details of the communicator, and FIG. 8 shows details of the bearing to the co-rotor, seals and the system for airing of the zones at the bearings.

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• Utility Patent

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