Cold start helium compressor

Abstract

This invention provides a means to start an oil lubricated air cooled helium compressor at ambient air temperatures in the range from −30° C. to 0° C. by heating the oil in the sump and opening one or more by-pass valves that allows oil to flow to the oil injection port of the compressor without passing through all of the after-cooler.

What is claimed is: 
     
         1 . An oil lubricated air cooled compressor which supplies helium to a cryogenic expander when the ambient temperature is in the range of −30° C. to 45° C., said system comprising;
 a compressor having a port in which oil is injected and mixed with the helium during compression, 
 a volume in which the discharge mixture of helium and oil separate such that most of the oil collects in a sump, 
 a heater in the sump, 
 an air cooled after-cooler having separate channels for helium and oil, 
 piping that directs all of the oil to flow from the sump through the after-cooler to the injection port in the compressor when the ambient temperature is greater than 0° C., 
 at least one by-pass valve that connects a point in the oil piping between the sump and an intermediate point in the after-cooler to the oil injection port when the ambient temperature is less than 0° C., 
 an oil management system that maintains a discharge temperature of less than 100° C. when the ambient air temperature is between −30° C. to 45° C. 
 
     
     
         2 . An oil lubricated helium compressor system in accordance with  claim 1  in which a by-pass valve connects the oil piping between the sump and the after-cooler to the oil injection port. 
     
     
         3 . An oil lubricated helium compressor system in accordance with  claim 1  in which a by-pass valve connects the oil piping between the entrance to the after-cooler and an intermediate point in the after-cooler to the oil injection port. 
     
     
         4 . An oil lubricated helium compressor system in accordance with  claim 1  in which a by-pass valve is one of an active and a passive valve. 
     
     
         5 . A method to start an oil lubricated air cooled compressor which supplies helium to a cryogenic expander when the ambient temperature is in the range of −30° C. to 0° C., said system comprising;
 a compressor having a port in which oil is injected and mixed with the helium during compression, 
 a volume in which the discharge mixture of helium and oil separate such that most of the oil collects in a sump, 
 a heater in the sump, 
 an air cooled after-cooler having separate channels for helium and oil, 
 piping that directs all of the oil to flow from the sump through the after-cooler to the injection port in the compressor when the ambient temperature is greater than 0° C., 
 a by-pass valve that connects a point in the oil piping between the sump and an intermediate point in the after-cooler to the oil injection port 
 
       the method comprising;
 1. heating the oil in the sump to a temperature greater than 0° C., 
 2. starting the compressor, 
 3. opening the oil by-pass valve when the compressor is started. 
 
     
     
         6 . A method to start an oil lubricated air cooled compressor which supplies helium to a cryogenic expander when the lubricating oil has a pour point higher than −45° C. and the ambient temperature is more than 10° C. warmer than the pour point, said system comprising;
 a compressor having a port in which oil is injected and mixed with the helium during compression, 
 a volume in which the discharge mixture of helium and oil separate such that most of the oil collects in a sump, 
 a heater in the sump, 
 an air cooled after-cooler having separate channels for helium and oil, 
 piping that directs all of the oil to flow from the sump through the after-cooler to the injection port in the compressor when the ambient temperature is greater than 0° C., 
 a by-pass valve that connects a point in the oil piping between the sump and an intermediate point in the after-cooler to the oil injection port the method comprising; 
 4. heating the oil in the sump to a temperature greater than 0° C., 
 5. starting the compressor, 
 6. opening the oil by-pass valve when the compressor is started.