Systems and Methods for Improving the Efficiency of Combined Cascade and Multicomponent Refrigeration Systems

Abstract

Systems and methods for improving the efficiency of combined cascade and multicomponent refrigeration systems by utilizing one or more ejectors to reduce and/or eliminate compression stages. The systems and methods change the temperature profile, which reduces the energy consumption of both the mixed refrigeration system and the pre-cooling system.

1 . A system for chilling a feed gas, which comprises:
 a first heat exchanger enclosing a first portion of a feed gas line and a portion of a first chilled refrigerant line;   a first flash drum in fluid communication with the first chilled refrigerant line for receiving a two-phase refrigerant from the first heat exchanger, the first flash drum having a first vapor outlet line and a first liquid outlet line;   a second heat exchanger enclosing a second portion of the feed gas line and a portion of a second chilled refrigerant line;   a second flash drum in fluid communication with the second chilled refrigerant line for receiving a two-phase refrigerant from the second heat exchanger, the second flash drum having a second vapor outlet line and a second liquid outlet line;   a third heat exchanger enclosing a third portion of the feed gas line and a portion of a third child refrigerant line;   a drum in fluid communication with the third chilled refrigerant line for receiving a vaporized refrigerant from the third heat exchanger, the drum having a drum vapor outlet line;   an ejector in fluid communication with the drum vapor outlet line, the first chilled refrigerant line, and a compressed refrigerant line; and   a compressor in fluid communication with the first vapor outlet line, the second vapor outlet line, and the compressed refrigerant line connected to a chiller for chilling a compressed refrigerant in the compressed refrigerant line.   
     
     
         2 . The system of  claim 1 , further comprising a first expansion valve positioned between the first heat exchanger and the ejector for producing a chilled refrigerant in the first chilled refrigerant line. 
     
     
         3 . The system of  claim 2 , further comprising a second expansion valve positioned between the second heat exchanger and the first flash drum for producing a chilled refrigerant in the second chilled refrigerant line. 
     
     
         4 . The system of  claim 3 , further comprising a third expansion valve positioned between the third heat exchanger and the second flash drum for producing a chilled refrigerant in the third chilled refrigerant line. 
     
     
         5 . The system of  claim 1 , further comprising a pump positioned between the chiller and the ejector for pumping the chilled compressed refrigerant in the first chilled compressed refrigerant line. 
     
     
         6 . The system of  claim 1 , further comprising a supplemental refrigeration system in fluid communication with the feed gas line and an outlet line for one of a chilled feed gas and a liquified feed gas. 
     
     
         7 . The system of  claim 6 , wherein the supplemental refrigeration system includes a mixed refrigerant. 
     
     
         8 . The system of  claim 1 , wherein the compressor is in fluid communication with the drum vapor outlet line. 
     
     
         9 . The system of  claim 6 , further comprising:
 another ejector in fluid communication with the outline line and a boil-off gas line connected to a tank for holding boil-off gas.   
     
     
         10 . The system of  claim 9 , further comprising a let-down valve positioned in fluid communication with the outlet line for controlling flow of the chilled feed gas or the liquified feed gas in the outlet line to the another ejector. 
     
     
         11 . A method for chilling a feed gas, which comprises:
 introducing a feed gas stream through a first heat exchanger, a second heat exchanger and a third heat exchanger;   chilling the feed gas stream in the first heat exchanger by circulating a first chilled refrigerant stream adjacent the feed gas stream in the first heat exchanger using a compressor and a chiller to convert a first vapor refrigerant stream from a first flash drum into a liquid refrigerant stream and an ejector to convert the liquid refrigerant stream into the first chilled refrigerant stream;   chilling the feed gas stream in the second heat exchanger by circulating a second chilled refrigerant stream adjacent the feed gas stream in the second heat exchanger using a first liquid refrigerant stream from the first flash drum;   chilling the feed gas stream in the third heat exchanger by circulating a third chilled refrigerant stream adjacent the feed gas stream in the third heat exchanger using a second liquid refrigerant stream from the second flash drum;   transferring a vapor refrigerant stream from the third heat exchanger to a drum; and   returning at least a portion of the vapor refrigerant stream in the drum to the ejector for lowering the temperature of the first chilled refrigerant stream.   
     
     
         12 . The method of  claim 11 , further comprising expanding the first chilled refrigerant stream before circulating the first chilled refrigerant stream in the first heat exchanger. 
     
     
         13 . The method of  claim 12 , further comprising expanding the second chilled refrigerant stream before circulating the second chilled refrigerant stream in the second heat exchanger. 
     
     
         14 . The method of  claim 13 , further comprising expanding the third chilled liquid refrigerant stream before circulating the third chilled refrigerant stream in the third heat exchanger. 
     
     
         15 . The method of  claim 11 , further comprising pumping the liquid refrigerant stream from the compressor to the ejector. 
     
     
         16 . The method of  claim 11 , further comprising chilling the feed gas stream in a supplemental refrigeration system to produce one of a chilled feed gas stream and a liquified feed gas stream. 
     
     
         17 . The method of  claim 16 , wherein the supplemental refrigeration system includes a mixed refrigerant. 
     
     
         18 . The method of  claim 11 , further comprising returning at least a portion of the vapor refrigerant stream in the drum to the compressor. 
     
     
         19 . The method of  claim 16 , further comprising:
 recompressing a boil-off gas stream from a boil-off gas tank by transferring the one of the chilled feed gas stream and the liquified feed gas stream to another ejector; and   directing at least a portion of the boil-off gas stream through the another ejector.   
     
     
         20 . The method of  claim 19 , further comprising controlling a flow of the chilled feed gas stream or the liquified feed gas stream to the ejector with a let down valve.