Screw compressor for extremely high working pressure

Abstract

On screw compressors for extremely high discharge pressures, e.g. for application in refrigeration systems operating with CO2 in a transcritical process, featuring two rotors, a male rotor and a female rotor having a ratio of male-to-female rotor lobes of 4:6, 5:6 or 5:7, with the male rotor having a drive-shaft end, and both rotors are enclosed in a housing, the wrap angle of the profile section of the male rotor is less than 1.5 the lobe-pitch angle, and the working cycle from the beginning of suction till the end of discharge is less than 600° of the angle of rotation of the male rotor, and the length-to-diameter ratio of the profile section of the male rotor lies between 0.3 and 0.5.

Description

FIG. 1 shows a cross section of the screw compressor regarding the invention

FIG. 2 shows the rotor pair

FIG. 3 shows the screw compressor housing

FIG. 4 shows the cavity volume, as a function of the male rotor position

FIG. 1 shows a screw compressor according to the invention for compression of a working fluid to a discharge pressure of 100 bar, e.g. for application in refrigeration systems operating with CO₂ in a transcritical process featuring two rotors, a male rotor 1 and a female rotor 2 with the male rotor 1 having a drive-shaft end 3, and both rotors are enclosed in a housing 8 featuring at least an inlet port 7 for passing of the working fluid into the lobes of the rotor pair and at least an outlet port 9 for discharge of the gas due to rotation of the rotors. The profile sections of the rotors have shaft shoulders 4 enclosed in radial bearings 5 with the resulting axial forces being supported by axial bearings 6.

The profile section of male rotor 1 has five lobes, while profile section of the female rotor 2 has six lobes. The wrap angle of the male-rotor profile section is 1.4 times the value of the lobe-pitch angle and amounts to 100°. The axial length of the profile section of the rotor pair has the value of 1.4 times the axial lobe pitch of the male rotor.

For this case of operation, the bearings of the compressor according to the invention have been dimensioned sufficiently large. The service life of the bearings meets the requirements.

The internal leakage demonstrated by a geometrical relationship between the length of the rotor meshing line and the volume of the cavity is less by the factor 2 to 3 compared to known high-pressure screw compressors having a ratio of male-to-female rotor lobes of 6:8 so that the efficiency of the compressor according to the invention is higher than that of known high-pressure screw compressors.

LIST OF REFERENCE NUMBERALS USED:

• 1 male rotor
• 2 female rotor
• 3 driving shaft
• 4 shaft
• 5 radial bearing
• 6 axial bearing
• 7 inlet port
• 8 housing
• 9 outlet port
• 10 cavities
• 11 profile section
• 12 lobe pitch angle
• 13 wrap angle
• 14 economizer connection
• 15 transfer phase
• 16 male rotor diameter
• 17 profile length
• 18 connection to inlet port closes

Claims

1. Screw compressor for extremely high discharge pressures, e.g. for application in refrigeration systems operating on CO2 in a transcritical process, featuring two rotors, a male rotor and a female rotor having a ratio of male-to-female rotor lobes of 4:6, 5:6 or 5:7, with the male rotor having a driving-shaft, and both rotors being enclosed in a housing featuring at least an inlet port for passing of the working fluid into the cavities of the rotor pair and at least an outlet port for discharge of the gas out of the cavities of the rotor pair due to rotation of the rotors, with the profile sections of the rotors having shaft shoulders enclosed in radial bearings, and the resulting axial forces being supported by axial bearings, wherein the wrap angle of the profile section of the male rotor is less than 1.5 times the lobe-pitch angle of the male rotor, and the working cycle from the beginning of suction till the end of discharge is less than 600° of the angle of rotation of the male rotor.

2. Screw compressor according to claim 1, wherein the transfer phase has approx. double the magnitude of the lobe-pitch angle of the male-rotor profile.

3. Screw compressor according to claim 1 with an economizer connection arranged between the inlet port and outlet port in the compressor housing, wherein the economizer connection is so arranged on the housing enclosing the rotors that there is one flow connection to each of the cavities of the male-rotor- and female-rotor profile sections also during the transfer phase.

4. Screw compressor according to claim 1wherein the economizer connection is arranged on the housing enclosing the rotors in a manner that the flow connection exists exclusively during the transfer phase.

5. Screw compressor according to claim 1wherein the length-to-diameter ratio of the profile section of the male rotor lies between 0.3 and 0.5.

6. Screw compressor according to claim 1wherein the inlet port is designed so that the connection to the lobes of the rotor pair closes during the transfer phase.