Heat pump on c2 splitter bottom to unload propylene refrigeration

Abstract

A method of cooling an ethylene discharge gas includes the steps of drawing a liquid ethane from a C 2 splitter; reducing a pressure of the drawn liquid ethane in a let-down valve to produce a cooled liquid ethane; cooling the ethylene discharge gas with the cooled liquid ethane in a vaporizer, the cooled liquid ethane exiting the vaporizer as an ethane vapor; pressurizing the ethane vapor in a heat pump to produce a heated vapor ethane; and returning the heated vapor ethane to the C 2 splitter. The ethylene discharge gas may be from an ethylene refrigerant compressor.

What is claimed is: 
     
         1 . A method of cooling a process stream, comprising:
 drawing a liquid ethane from a C 2  splitter;   reducing a pressure of the drawn liquid ethane in a let-down valve to produce a colder liquid ethane;   cooling the process stream with the colder liquid ethane in a vaporizer, the ethane exiting the vaporizer as vapor;   pressurizing the ethane vapor in a heat pump to produce a vapor ethane at higher pressure; and   returning the vapor ethane to the C 2  splitter.   
     
     
         2 . The method of  claim 1 , wherein the process stream is an ethylene discharge gas from an ethylene refrigerant compressor. 
     
     
         3 . The method of  claim 1 , wherein the C 2  splitter separates ethylene from ethane by distillation. 
     
     
         4 . The method of  claim 1 , wherein vaporizer uses indirect heating. 
     
     
         5 . The method of  claim 1 , wherein the ethane from the C 2  splitter has a pressure of P 1  and a temperature of T 1 , the ethane from the vaporizer has a pressure of P 2  and a temperature of T 2 , and the ethane from the heat pump at a pressure of P 3  and a temperature of T 3 , and wherein P 3  is greater than P 1 , P 1  is greater than P 2 , and T 1  is greater than T 2 . 
     
     
         6 . The method of  claim 1 , wherein:
 the process stream is ethylene discharge gas from an ethylene refrigerant compressor;   the C 2  splitter separates ethylene from ethane by distillation;   the vaporizer uses indirect heating;   the ethane from the C 2  splitter has a pressure of P 1  and a temperature of T 1 , the ethane from the vaporizer has a pressure of P 2  and a temperature of T 2 , and the ethane from the heat pump at a pressure of P 3  and a temperature of T 3 , and wherein P 3  is greater than P 1 , P 1  is greater than P 2 , and T 1  is greater than T 2 .   
     
     
         7 . A system for cooling a process stream, comprising:
 a C 2  splitter;   a let-down valve receiving ethane from the C 2  splitter and producing a colder liquid ethane;   a vaporizer receiving the colder liquid ethane from the let-down valve and cooling or condensing the process stream, the ethane exiting the vaporizer as an ethane vapor:   a heat pump pressurizing the ethane vapor and producing a vapor ethane at higher pressure; and   a line returning the vapor ethane to the C 2  splitter.   
     
     
         8 . The system of  claim 7 , further comprising an ethylene refrigerant compressor supplying the process stream, the process stream being an ethylene discharge gas. 
     
     
         9 . The system of  claim 7 , wherein the C 2  splitter separates ethylene from ethane by distillation. 
     
     
         10 . The system of  claim 7 , wherein vaporizer uses indirect heating. 
     
     
         11 . The system of  claim 7 , further comprising a propylene refrigeration unit cooling the process stream. 
     
     
         12 . The system of  claim 7 , wherein the ethane from the C 2  splitter has a pressure of PI and a temperature of T 1 , the ethane from the vaporizer has a pressure of P 2  and a temperature of T 2 , and the ethane from the heat pump as a pressure of P 3  and a temperature of T 3 , and wherein P 3  is greater than P 1 , P 1  is greater than P 2 , and T 1  is greater than T 2 . 
     
     
         13 . The system of  claim 7 , further comprising:
 an ethylene refrigerant compressor supplying an ethylene discharge gas, the ethylene discharge gas being the process stream;   a polypropylene refrigeration unit cooling the process stream ; and   
       wherein:
 the C 2  splitter separates ethylene from ethane by distillation; 
 the vaporizer uses indirect heating; and 
 the ethane from the C 2  splitter has a pressure of P 1  and a temperature of T 1 , the ethane from the vaporizer has a pressure of P 2  and a temperature of T 2 , and the ethane from the heat pump as a pressure of P 3  and a temperature of T 3 , and wherein P 3  is greater than P 1 , P 1  is greater than P 2 , and T 1  is greater than T 2 .