Low pressure deethanization process and system

Abstract

A system and process for separating ethane and propane from a feed stream comprising dehydrated liquefied petroleum gas is disclosed. A distillation column operates at a lower pressure and temperature than conventional distillation columns. High purity liquid propane exits the bottom of the distillation column and is flashed through a cooling control valve becoming a two-phase stream with the vapor entering a heat pump compressor. The high or increased temperature compressed propane stream exiting the heat pump compressor is directed into the distillation column to drive the separation of the ethane and propane, allowing the elimination of a reboiler from the system and process.

What is claimed is: 
     
         1 . A system having a low operating pressure for separating ethane and propane from a feed stream, the system comprising:
 a distillation column having an upper end and a lower end and configured to receive the feed stream and release ethane from the upper end and propane from the lower end;   a heat pump exchanger configured to condense the ethane and vaporize the propane released from the distillation column;   a reflux control device configured to distribute ethane back to the distillation column from the heat pump exchanger;   a cooling control device configured to control an amount of propane entering the heat pump exchanger; and   a compressor assembly configured to compress propane vapor exiting the heat pump exchanger;   wherein the flowpath from the compressor assembly to the distillation column is configured to flow the compressed propane vapor exiting the compressor assembly into the distillation column to supply heat.   
     
     
         2 . The system of  claim 1  further comprising:
 a feed stream control device configured to control the feed stream entering the distillation column; 
 an overhead product control device configured to control the ethane exiting the system; 
 a bottoms product control device configured to control the propane exiting the system; and 
 a control system configured to actuate the control devices; 
 
     
     
         3 . The system of  claim 1  further comprising a heat rejection device configured to remove heat from the compressed propane vapor. 
     
     
         4 . The system of  claim 1 , wherein a dehydrating agent removes moisture from the feed stream prior to entering the distillation column. 
     
     
         5 . The system of  claim 4 , wherein the dehydrating agent is a molecular sieve. 
     
     
         6 . The system of  claim 4 , wherein the dehydrating agent is a dry glycol. 
     
     
         7 . The system of  claim 1 , wherein the cooling control device is further configured to introduce vapor to the propane. 
     
     
         8 . The system of  claim 1 , wherein the control system comprises sensors configured to measure system parameters. 
     
     
         9 . The system of  claim 8 , wherein the system parameters include at least one of pressure, temperature, composition, or flow rate. 
     
     
         10 . The system of  claim 1 , wherein the distillation column comprises less than 40 trays. 
     
     
         11 . The system of  claim 1 , wherein the distillation column comprises less than 35 trays. 
     
     
         12 . The system of  claim 1  further comprising a product interchanger configured to exchange the ethane product and propane product. 
     
     
         13 . The system of  claim 1  further comprising a reflux pump and accumulator configured to collect and deliver a reflux stream to the distillation column. 
     
     
         14 . The system of  claim 1  further comprising one or more economizers configured to remove liquid from the propane vapor. 
     
     
         15 . The system of  claim 1  further comprising a feed interchanger configured to regulate a temperature of the feed stream entering the distillation column. 
     
     
         16 . The system of  claim 1  further comprising a compression suction scrubber configured to remove liquid from the propane vapor. 
     
     
         17 . A process for separating ethane and propane from a feed stream at low pressure, the process comprising:
 introducing a feed stream to a distillation column to obtain ethane vapor and liquid propane;   condensing the ethane vapor to obtain liquid ethane;   removing a portion of the liquid ethane through an overhead product control device;   refluxing a portion of the liquid ethane back to the distillation column;   removing a portion of the liquid propane through a bottoms product control device;   flashing a portion of the liquid propane through a cooling control device to introduce vapor to the liquid propane;   vaporizing the liquid propane to obtain a propane vapor having a temperature and pressure;   compressing the propane vapor to obtain a propane vapor having a higher temperature and pressure; and   flowing the higher temperature and pressure propane vapor to the distillation column to supply heat to the distillation column.   
     
     
         18 . The process of  claim 17  further comprising removing heat from the higher temperature and pressure propane vapor through a heat rejection system or bypassing the heat rejection system before entering the distillation column. 
     
     
         19 . The process of  claim 17 , wherein a dehydrating agent removes moisture from the feed stream prior to entering the distillation column. 
     
     
         20 . The process of  claim 17  further comprising a product interchanger configured to exchange the ethane product and propane product. 
     
     
         21 . The process of  claim 17  further comprising a reflux pump and accumulator configured to collect and deliver a reflux stream to the distillation column. 
     
     
         22 . The process of  claim 17  further comprising one or more economizers configured to remove liquid from the propane vapor. 
     
     
         23 . The process of  claim 17  further comprising a feed interchanger configured to regulate a temperature of the feed stream entering the distillation column. 
     
     
         24 . The process of  claim 17  further comprising a compression suction scrubber configured to remove liquid from the propane vapor.