Patent ID: 6612820
Filing Date: 2003-09-02
Classification: F04C,Y10S

Abstract:
A method for lubricating and sealing bearings and gears associated with a plurality of rotors of a screw compressor and isolating a process fluid to be compressed from a lubricant for the bearings and gears, the screw compressor having the process fluid and the rotors in a working chamber, the rotors having shafts supported by the bearings, the bearings contained in a plurality of bearing chambers, the shafts passing from the working chamber to the bearings in the bearing chambers, the working chamber having a low pressure inlet end and a high pressure outlet end for the compressible fluid, comprising:providing a low bearing chamber pressure to a first bearing chamber adjacent the low pressure inlet end of the working chamber, the low bearing chamber pressure at least equal to about 90% of the pressure at the low pressure inlet end of the working chamber; providing a high bearing chamber pressure to a second bearing chamber adjacent the high pressure outlet end of the working chamber, the high bearing chamber pressure at least equal to about 90% of the average pressure at the high pressure outlet end of the working chamber; pumping oil to the bearings in the plurality of bearing chambers under separate pressure; sealing the first and second bearing chambers from the working chamber by seals having a bore around each rotor shaft, the seals comprising a body having a first end adjacent the working chamber and a second end adjacent a bearing chamber and an inner groove in the bore intermediate to the ends, the inner groove of each seal connected to a source of buffer gas; providing a buffer gas to the seals adjacent the first bearing chamber, the buffer gas having a low pressure adjacent the groove greater than the low bearing chamber pressure, a portion of the low pressure buffer gas entering the first bearing chamber; providing a buffer gas to the seals adjacent the second bearing chamber, the buffer gas having a high pressure adjacent the groove greater than the high bearing chamber pressure, a portion of the high pressure buffer gas entering the second bearing chamber; releasing the oil in the first bearing chamber and the portion of the low pressure buffer gas from the first bearing chamber to maintain the low bearing chamber pressure wherein the oil in the first bearing chamber and the portion of the low pressure buffer gas are returned to a first reservoir for separation of the buffer gas from the oil; and releasing the oil in the second bearing chamber and the portion of the high pressure buffer gas from the second bearing chamber to maintain the high bearing chamber separate pressure, wherein the oil in the second bearing chamber and the portion of the high pressure buffer gas are returned to a second reservoir for separation of the buffer gas from the oil at the high bearing chamber pressure, and further returning oil to the first reservoir at the low bearing chamber pressure.