Screw compressor equipment for accommodating low compression ratio and pressure variation and the operation method thereof

In a screw compressor equipment comprising a screw compressor driven by a driving machine of variable rotation speed, a method of operating the equipment comprising;

• calculating a polytropic exponent according to a kind of the gas to be compressed and the structure and operating conditions of the compressor;
• controlling the positioning of an internal volume ratio control valve of the screw compressor based on a calculated internal volume ratio so that the polytropic efficiency of the screw compressor is always maximum;
• controlling the flow rate of fluid through the screw compressor by controlling the rotation speed of the driving machine,
• wherein said equipment is applied in a use for low compression ratio in the case of compressing gas of relatively high suction pressure to a constant discharge pressure, or in a use for low compression ratio or fluctuating compression ratio in the case of compressing gas of fluctuating suction pressure to a constant discharge pressure,
• the internal volume ratio control valve straddling both a male and a female rotor, having a control shaft by way of which the valve can be moved in a direction parallel to both the rotors and being provided with a cut in the discharge side end part thereof, and
• the internal volume ratio is controlled to be 1.9 to 1.0 through controlling the timing of the communication of a tooth groove space with a discharge port by moving the control valve by way of a controller.

A method of operating a screw compressor equipment, a compressor which compresses sucked fluid enclosed in a tooth groove space formed by meshing of a male rotor and a female rotor accommodated in a casing by a change of the volume of the space as the rotors rotate being driven by a variable rotation speed driving machine,

• wherein the equipment is applied in a use for low compression ratio in the case of compressing gas of relatively high suction pressure to a constant discharge pressure, or in a use for low compression ratio or fluctuating compression ratio in the case of compressing gas of fluctuating suction pressure to a constant discharge pressure, an internal volume ratio control valve straddling both the rotors and having a control shaft by way of which the valve can be moved in a direction parallel to both the rotors and being provided with a cut in a discharge side end part thereof, a computing device for calculating a polytropic exponent according to the kind of gas to be compressed and operating conditions of the compressor, and a controller for moving and fixing the internal volume ratio control valve to and at a position determined based on the internal volume ratio calculated by said computing device are provided, and
• the internal volume ratio is controlled to be 1.9 to 1.0 by controlling the timing of the communication of the tooth groove space with the discharge port by moving the control valve by way of said controller.