GB2261031A

GB2261031A - Rotary vane compressor

Info

Publication number: GB2261031A
Application number: GB9121668A
Authority: GB
Inventors: Allan Sinclair Miller
Original assignee: ROTOCOLD TECHNOLOGY Ltd; Rotocold Holdings Ltd
Current assignee: ROTOCOLD TECHNOLOGY Ltd; Rotocold Holdings Ltd
Priority date: 1991-10-11
Filing date: 1991-10-11
Publication date: 1993-05-05
Anticipated expiration: 2011-10-11
Also published as: CN1073237A; GB2261031B; GB9121668D0

Abstract

A rotary vane compressor comprising a stator 11 and a rotor 20 includes an auxiliary pipe 14 between the outlet 13 and the inlet 12 to introduce pressurised gas into each cell C on its travel to the inlet 12 to expand therein and thereby to impart mechanical work to the rotor 20. <IMAGE>

Description

ROTARY VANE COMPRESSOR WITH CAPACITY CONTROL The invention relates to compressors and in particular to compressors of the rotary vane type. Such a compressor typically comprises a stator rotor, the stator having an inlet and an outlet radially spaced from the inlet, the rotor being driven by a motor and caused to rotate in a forward direction past the inlet and then past the outlet thereby to transport gas from the inlet to the outlet, vanes being spaced apart about the rotor to define cells in cooperation with the wall of the stator, the wall of the stator being shaped to compress the gas in the cells in its travel from the inlet to the outlet.

It has been realised that it would be useful to have a means of reducing the swept volume of the compressor when required as this will reduce the power drawn from the motor to drive the rotor.

One known means of achieving a capacity reduction is to recirculate a proportion of the compressed gas emerging from the outlet back to the inlet but this increases the discharge temperature and does not reduce the power requirement. Another known means is to locate the gas inlet at a location where the cell is below the maximum volume but this affects the internal compression ratio and does not reduce the power requirement to any real extent.

It is one object of this invention to provide apparatus and a method for reducing the swept volume of a rotary vane compressor in such a way that the power requirement to drive the rotor is reduced. It is a further object to do this with minimal change to the compressor in terms of size, weight and cost.

In one aspect the invention provides a rotary vane compressor comprising a stator and a motor driven rotor, the stator having an inlet and an outlet the rotor being driven by a motor and cause to rotate in a forward direction past the inlet and then past the outlet thereby to transport gas from the inlet to the outlet, vanes being spaced apart about the rotor to define cells in cooperation with the wall of the stator, the wall portion of the stator being shaped to compress the gas in the cells in its travel from the inlet to the outlet characterised in that an auxiliary pipe extends from the pipe at the outlet to an auxiliary inlet in the wall of the stator at a position which the rotor passes on its return travel from the outlet to the inlet, the wall of the stator in the region of the auxiliary inlet being shaped to increase the volume of the cells as they travel towards the main inlet and to allow pressurised gas introduced into the cells from the auxiliary inlet to expand in the increasing cell volume, thereby imparting mechanical work to the rotor and reducing the power required by the motor driving the rotor when working at reduced capacity.

In another aspect, the invention provides a method of operating a rotary vane compressor comprising a stator having an inlet and an outlet, a rotor being present in the stator and arranged to rotate past the inlet and then past the outlet thereby to transport gas from the inlet to the outlet, vanes being spaced about the rotor to define cells in cooperation with the wall of the stator, the wall of the stator being shaped to compress the gas in the cells in its travel from the inlet to the outlet characterised by the step of introducing sufficient pressurised gas into each cell after it has travelled past the outlet to expand to occupy a proportion of the volume of the cell before it reaches the inlet thereby to reduce the volume of gas taken in from the inlet.

In order that the invention may be well understood it will now be described by way of illustration only with reference to the accompanying diagrammatic drawings, in which Figure 1 is a partial transverse section through a compressor of the invention; and Figure 2 is a schematic diagram showing the treatment of gas in a cycle.

The multivane gas compressor comprises a housing having a stator bore 11 containing a gas chamber, a main inlet 12 being present at one side of the chamber and an outlet 13 being radially spaced from the inlet 12. The chamber is not circular in crosssection but is shaped to provide a gas expansion zone and a gas compression zone. The chamber contains a rotor 20 driven from motor (not shown) connected to a shaft 21 for the rotor 20.

Slots 22 are radially spaced about the rotor and these contain vanes 23 which can slide in and out of the slots. Adjacent vanes 23 and the end walls of the stator define cells C to transport gas from the inlet 12 to the outlet 13. The wall of the stator leading from the inlet 12 to the outlet 13 is a compressive wall, i.e. is shaped such that the cells progressively decrease in volume from the main inlet 12 to the outlet 13 thereby to compress the gas. An auxiliary pipe 14 leads from the outlet 13 to an auxiliary inlet 15 between the outlet 13 and the main inlet 12 opposite the shaped wall. A solenoid or like valve 16 is present in the auxiliary pipe 14.

According to this invention, the wall portion 11B of the stator leading from the outlet 13 and the inlet 12 facing the compressive wall 11A is shaped to increase the volume of the cells C, as they travel towards the inlet 12 and, in particular, to allow the cells to increase in volume.

As shown in Figure 1, gas enters the compressor at the main inlet 12 filling each enclosed cell C. Each cell reduces in volume during its passage towards the discharge outlet 13 and the gas is compressed before exiting at the discharge port 13. As shown, the wall of the cylinder bore in stator 11A does not form a circle but is a shaped profile designed to provide the required cell volume ratios between point of entry 12 and exit 13 and entry 15 and entry 12.

With valve 16 closed the compressor will operate at full capacity, each empty cell filling to capacity during its passage passed the entry port 11 and emptying at the outlet 13. With valve 16 open each cell, as it passes the auxiliary inlet 15 will fill with high pressure gas fed from the auxiliary pipe 14. The volume of each cell C at the auxiliary inlet 15, is predetermined by the shape of the profile 11B according to the design requirement but typically would be such that the volume of gas when expanded by rotation of the rotor to the main inlet position 12 would be typically 50% of the maximum inlet cell volume. Thus the volume of gas admitted to the compressor is reduced by 50- s as each cell on reaching the main inlet 12 is already half filled. The proportion of 50% is not critical to the invention and will be varied according to the circumstances.

In the process of expanding the gas from inlet 15 to the main inlet 12 mechanical work is imparted to the shaft which reduces the external shaft power required to drive the rotor for compression of the gas.

Considering a typical case and referring to Figure 2, we will assume an inlet volume Vs of 12 units of volume and a discharge volume VD of 3 units and we will assume a pressure of 2 bar at the inlet and for the sake of simplicity we will approximate the discharge pressure as function of the volume ratio at 8 bar.

Thus gas at 8 bar enters the inlet cell at VE which has been designed for a volume of 1.5 units. 1.5 units of volume at 8 bar, when expanded to 12 units of volume at 2 bar, would resolve as 6 units of volume and the external volume of gas admitted to the compressor would be halved. The mechanical work imparted in expanding the volume VE at 8 bar to Vs at 2 bar would be approx.

30 w of the power for compression. In other words for a 50 -Ó reduction in capacity there would be a 30% reduction in power requirement.

The profile of the bore of the stator can be shaped to suit any set of volume ratios and capacity reductions required.

Claims

1. A rotary vane compressor comprising a stator (11) and a motor driven rotor (20), the stator having an inlet (12) and an outlet (13) the rotor (20) being driven by a motor and cause to rotate in a forward direction past the inlet (12) and then past the outlet (13) thereby to transport gas from the inlet (12) to the outlet (13), vanes (23) being spaced apart about the rotor to define cells (C) in cooperation with the wall (11) of the stator, the wall portion (11A) of the stator being shaped to compress the gas in the cells (C) in its travel from the inlet (12) to the outlet (13) characterised in that an auxiliary pipe (14) extends from the pipe at the outlet (13) to an auxiliary inlet (15) in the wall (11B) of the stator at a position which the rotor (20) passes on its return travel from the outlet (13) to the inlet (12), the wall (11B) of the stator in the region of the auxiliary inlet (15) being shaped to increase the volume of the cells as they travel towards the main inlet (12) and to allow pressurised gas introduced into the cells (C) from the auxiliary inlet (15) to expand in the increasing cell volume, thereby imparting mechanical work to the rotor (20) and reducing the power required by the motor driving the rotor (20) when working at reduced capacity.

2. A compressor according to Claim 1 characterised in that a valve (16) is present in the auxiliary pipe (14).

3. A compressor according to Claim 1 or 2 characterised in that the profile of the stator (11B) in the region from the auxiliary inlet (15) to the main inlet is dimensioned and/or shaped to allow the pressurised gas to occupy about half of the volume of the cell (C) when expanded to the pressure existing at the cell when it reaches the main inlet (12).

4. A compressor according to any preceding Claim characterised in that the vanes (23) travel in slots (22) present in the wall of the rotor (20).

5. A method of operating a rotary vane compressor comprising a stator (11) having an inlet (12) and an outlet (13) a rotor (20) being present in the stator and arranged to rotate past the inlet (12) and then past the outlet (13) thereby to transport gas from the inlet (12) to the outlet (13), vanes (23) being spaced about the rotor (20) to define cells (C) in cooperation with the wall of the stator, the wall (11A) of the stator being shaped to compress the gas in the cells (C) in its travel from the inlet (12) to the outlet (13) characterised bv the step of introducing sufficient pressurised gas into each cell (C) after it has travelled past the outlet (13) to expand to occupy a proportion of the volume of the cell (C) before it reaches the inlet (12) thereby to reduce the power required to rotate the rotor (20) and the volume of gas admitted to the cell (C) at the main inlet (12).

6. A method according to Claim 5 characterised bv introducing the pressurised gas via an auxiliary inlet (15) located between the outlet (13) and the main inlet (12).