System for compressing air and extracting nitrogen from compressed air

A system for extracting nitrogen from air to produce nitrogen having a substantially constant purity in spite of fluctuations in flow demand, comprising:

• a compressor for compressing air, said compressor including a pair of rotatable rotors, an inlet through which air flows into the compressor, a motor for driving the rotors and reducing means for reducing an effective length of the rotatable rotors which acts to compress air in order to cause the compressor to operate at less than full capacity;
• an air separator connected to the compressor for separating nitrogen from compressed air received from the compressor;
• a back-pressure regulator located downstream of the air separator for limiting nitrogen product flow;
• an oxygen content analyzer located between the air separator and the back-pressure regulator for determining an oxygen content of nitrogen product flowing out of the air separator;
• pressure regulating means for regulating a compressor discharge pressure exiting the compressor;
• means for causing operation of the reducing means when the compressor discharge pressure regulated by the pressure regulating means is greater than a predetermined value and for causing operation of the reducing means when the oxygen content analyzer determines that the oxygen content of the nitrogen exiting from the separator differs from a predetermined oxygen content, so that the operating level of the compressor is changed in response to changes in nitrogen purity as determined by the oxygen content analyzer.

A system for compressing air comprising:

• a screw air compressor for compressing air, said screw air compressor including a casing, a pair of rotatably driven rotors positioned in the casing, an inlet for allowing air to be introduced into the casing and reducing means for reducing an effective length of the rotors which acts to compress air so as to reduce an operating level of the compressor;
• operation means connected to the reducing means for causing operation of the reducing means in response to a signal air pressure;
• external control means connected to the operation means for sending a first signal to the operation means indicative of an externally inputted operating level for the compressor in order to cause operation of the reducing means so that the operating level of the compressor is changed to the externally inputted operating level;
• automatic internal control means connected to the operation means for automatically sending a second signal to the operation means when a compressor discharge pressure from the compressor exceeds a predetermined pressure in order to cause operation of the reducing means and reduce a current operating level of the compressor to a reduced operating level, the operation means causing operation of the reducing means during a reduced operating level of the compressor upon receipt of the second signal from the automatic control means to thereby further reduce the operating level of the compressor.