Method and control system for controlling multiple throttled inlet rotary screw compressors

A method of operating a compressor system having a plurality of throttled inlet rotary screw compressors, said method comprising the steps of:

• (a) establishing a set-point pressure;
• (b) measuring the actual pressure of the fluid in the compressor system;
• (c) determining which of the rotary screw compressors are operating;
• (d) calculating the actual volumetric flow rate of fluid in the compressor system by:
• (i) sensing the inlet pressure of each operating throttled inlet rotary screw compressor;
• (ii) converting the inlet pressures to corresponding outlet volumetric flow rates;
• and
• (iii) summing said outlet volumetric flow rates;
• (e) determining the online volumetric flow rate capacity, wherein the online volumetric flow rate capacity is equal to the sum of the corresponding rated volumetric flow rate capacities for each of the operating throttled inlet rotary screw compressors;
• (f) loading one of the plurality of throttled inlet rotary screw compressors upon sensing that the actual pressure of the fluid in the compressor system is less than the set-point pressure and that the actual volumetric flow rate is equal to or greater than the online volumetric flow rate capacity.

A control system for controlling a compressor system, comprising:

• (a) a plurality of throttled inlet rotary screw compressors each having an inlet and outlet and being capable of compressing a fluid at a rated volumetric flow rate and pressure, each of said throttled inlet rotary screw compressors emitting an operational signal indicative of whether said corresponding throttled inlet rotary screw compressor is operating;
• (b) a plurality of pressure sensors, wherein one of said pressure sensors is located upstream of each of said throttled inlet rotary screw compressors;
• (c) another pressure sensor for sensing the actual pressure of the fluid in the compressor system;
• (d) a controller having a programmed set-point pressure, said controller having programmed values representing each of said throttled inlet rotary screw compressors' rated volumetric flow rate capacities and rated pressures, said controller receiving said operational signals from said plurality of throttled inlet rotary screw compressors, said controller receiving pressure signals from said pressure sensors located upstream of said inlets and calculating the actual volumetric flow rate of fluid in the compressor system from said pressure signals, said controller determining an online volumetric flow rate capacity, wherein the online volumetric flow rate capacity is equal to the sum of said rated volumetric flow rate capacities for each of said operating throttled inlet rotary screw compressors, said controller determining an excess volumetric flow rate for the compressor system, wherein the excess volumetric flow rate is equal to the online volumetric flow rate capacity minus the actual volumetric flow rate, said controller producing an unloading signal for one of said plurality of compressors upon sensing that the actual pressure of the fluid in the compressor system is greater than the set-point pressure and the corresponding rated volumetric flow rate capacity for said one compressor is less than the excess volumetric flow rate.

A control system for controlling a compressor system, comprising:

• (a) a plurality of throttled inlet rotary screw compressors each having an inlet and an outlet and being capable of compressing a fluid at a rated volumetric flow rate and pressure, each of said compressors emitting an operational signal indicative of whether said corresponding throttled inlet rotary screw compressor is operating;
• (b) a plurality of pressure sensors, wherein one of said pressure sensors is located upstream of each of said throttled inlet rotary screw compressors;
• (c) another pressure sensor for measuring the actual pressure of the fluid in the compressor system;
• (d) a controller having a programmed set-point pressure, said controller having programmed values representing each of said throttled inlet rotary screw compressors' rated volumetric flow rate capacities and rated pressures, said controller receiving said operational signals from said plurality of throttled inlet rotary screw compressors, said controller receiving pressure signals from said pressure sensors located upstream of said throttled inlet rotary screw compressors and calculating the actual volumetric flow rate of fluid in the compressor system from said pressure signals, said controller determining an online volumetric flow rate capacity, wherein the online volumetric flow rate capacity is equal to the sum of said rated volumetric flow rate capacities for each of said operating throttled inlet rotary screw compressors, said controller producing a loading signal for one of said throttled inlet rotary screw compressors upon sensing that the actual pressure of the fluid in the compressor system is less than the set-point pressure and the compressor system's actual volumetric flow rate is equal to or greater than the online volumetric flow rate capacity.