Method and system for air separation using a supplemental refrigeration cycle

Abstract

A system and method for air separation using a supplemental refrigeration cycle is provided. A portion of the refrigeration required by the air separation plant to produce a liquid product stream is supplied via a supplemental refrigeration circuit configured to direct a cooled refrigerant produced by the turboexpander through the main heat exchanger of the air separation plant. The refrigeration capacity is controlled by removing or adding a portion of the refrigerant in the supplemental refrigeration circuit to adjust the inlet pressure while maintaining a substantially constant volumetric flow rate and substantially constant pressure ratio across the compressor. Removing the refrigerant from the supplemental refrigeration circuit decreases the refrigeration imparted by the supplemental refrigeration circuit and thus decreases the production of the liquid product stream. Adding refrigerant allows for an increase in the refrigeration imparted by the supplemental refrigeration circuit and thus allows for increased production of the liquid product stream.

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         10 . An air separation plant configured to produce at least one liquid product stream, the air separation plant comprising:
 an air intake circuit configured to compress and purify an incoming feed air stream;   a distillation column system configured to rectifying the compressed and purified feed air stream by a cryogenic rectification process to produce at least one liquid product stream;   a main heat exchanger operatively associated with the compressed and purified feed stream and distillation column system and configured to cool the compressed and purified feed stream to a temperature suitable for the rectification of the feed air stream;   a supplemental refrigeration circuit coupled to the main heat exchanger and comprising a compressible working fluid that includes a portion of the compressed and purified feed air stream; a compressor section configured to compress the working fluid; and a turboexpander section configured to expand the working fluid to generate cooled working fluid, wherein the cooled working fluid is warmed in the main heat exchanger so as to impart the portion of the refrigeration required by the air separation plant to produce the at least one liquid product stream and the warmed working fluid is recirculated to the compressor section of the supplemental refrigeration circuit after having passed through the main heat exchanger;   a vent system disposed upstream of the turboexpander section and configured for removing a portion of the working fluid in the supplemental refrigeration circuit thereby decreasing the refrigeration imparted by the supplemental refrigeration circuit and the production of the at least one liquid product stream;   a source of working fluid coupled via one or more control valves to the supplemental refrigeration circuit upstream of the compressor section and configured for adding working fluid to the supplemental refrigeration circuit thereby increasing the refrigeration imparted by the supplemental refrigeration circuit and the production of the at least one liquid product stream;   a controller operatively connected to the vent system and control valves and configured to control the removal and addition of working fluid through the supplemental refrigeration circuit to adjust the inlet pressure such that the working fluid circulates within the supplemental refrigeration circuit at a substantially constant volumetric flow rate through the compressor section and turboexpander section of the supplemental refrigeration circuit and the pressure ratio across the compressor section is maintained substantially constant.   
     
     
         11 . The air separation plant of  claim 10  wherein the vent system is configured to maintain the working fluid in the supplemental refrigeration circuit at or below a prescribed maximum pressure. 
     
     
         12 . The air separation plant of  claim 10  further comprising a second vent configured to vent a portion of the working fluid downstream of the turboexpander section of the supplemental refrigeration circuit to maintain the working fluid in the supplemental refrigeration circuit at or below a prescribed maximum pressure and to maintain the cooled working fluid directed to the main heat exchanger at or below a prescribed maximum temperature. 
     
     
         13 . The air separation plant of  claim 10  wherein the source of working fluid coupled via one or more control valves to the supplemental refrigeration circuit further comprises a source of make-up working fluid to be added to the supplemental refrigeration circuit upstream of the compressor section of the supplemental refrigeration circuit to maintain the inlet pressure to the compressor section at or above a prescribed minimum pressure. 
     
     
         14 . The air separation plant of  claim 10  wherein the one or more control valves further comprise an intake charge valve arrangement disposed between the compressed and purified feed air stream and the supplemental refrigeration circuit configured to modulate the supply of the working fluid and adjust the inlet pressure to the compressor section. 
     
     
         15 . The air separation plant of  claim 10  wherein the compressor section of the supplemental refrigeration circuit further comprises a compressor having adjustable guidevanes and the compressor is operatively associated with the controller to adjust the guidevanes to maintain substantially constant pressure ratio across the compressor section. 
     
     
         16 . The air separation plant of  claim 15  wherein the turboexpander section of the supplemental refrigeration circuit further comprises a turbine having adjustable or configurable nozzle arrangement, the turbine operatively associated with the control unit to control or adjust the nozzle arrangement to maintain substantially constant volumetric flow rate of the working fluid through the compressor and turbine of the supplemental refrigeration circuit. 
     
     
         17 . The air separation plant of  claim 16  wherein the controller is a microprocessor based controller that operatively controls the flow of the working fluid through the supplemental refrigeration circuit to maintain substantially constant volumetric flow rate and substantially constant pressure ratio across the compressor section through the removal of working fluid, the addition of working fluid, the adjusting of compressor guidevanes, and the adjusting of turbine nozzles in response to the refrigeration required to produce the liquid product stream.