Method of cooling using extended binary refrigeration system

Abstract

A method of cooling using an extended binary refrigerant system containing methane and a C3 hydrocarbon such as propylene and/or propane is disclosed. The extended binary refrigerant from a compressor final discharge is separated into a methane-rich vapor fraction and at least one C3 rich liquid fraction so as to provide various temperatures and levels of refrigeration in various heat exchange stages. The method and corresponding refrigeration system can be utilized in plants utilizing low pressure or high pressure demethanizers.

1 . A method comprising cooling a feed gas using an extended binary refrigerant containing a mixture of methane and a C3 hydrocarbon selected from the group consisting of propylene and propane, said extended binary refrigerant being compressed in a multistage compressor having a first stage and a last stage with a last stage discharge containing at least 60 mol % C3 hydrocarbon, and being divided into a liquid coolant stream and a gaseous coolant stream after compression. 
     
     
         2 . A method according to  claim 1 , wherein said C3 hydrocarbon is propylene. 
     
     
         3 . A method according to  claim 2 , wherein at least 90 wt % of said C3 hydrocarbon is propylene. 
     
     
         4 . A method according to  claim 1 , wherein said last stage discharge contains 10-40 mol % methane and 60-90 mol % C3 hydrocarbon. 
     
     
         5 . A method according to  claim 2 , wherein said last stage discharge contains 15-25 mol % methane and 75-85 mol % propylene. 
     
     
         6 . A method according to  claim 2 , wherein said extended binary refrigerant contains 18-22 mol % methane and 78-82 mol % propylene. 
     
     
         7 . A method according to  claim 1 , wherein the extended binary refrigerant can provide refrigeration within the temperature range of about −136 Deg. C. to about 25 Deg. C. 
     
     
         8 . A method according to  claim 1 , wherein said feed gas contains an olefin and the method comprises removing said olefin from said cooled feed gas by fractionation. 
     
     
         9 . A method according to  claim 8 , wherein said olefin is ethylene. 
     
     
         10 . A method according to  claim 8 , wherein said feed gas further includes hydrogen and methane. 
     
     
         11 . A method according to  claim 8 , wherein said last stage discharge contains 10-40 mol % methane and 60-90 mol % C3 hydrocarbon. 
     
     
         12 . A method for cooling with an extended binary refrigerant comprising:
 (a) compressing a mixture comprising 10-40 mol % methane and 60-90 mol % of at least one C3 hydrocarbon selected from the group consisting of propylene and propane in a multistage compressor to produce an extended binary refrigerant vapor,   (b) cooling said extended binary refrigerant vapor to condense a portion thereof and provide a vaporous methane-rich binary refrigerant stream and a liquid C3 hydrocarbon-rich binary refrigerant stream,   (c) employing said methane-rich binary refrigerant stream and said C3 hydrocarbon-rich binary refrigerant stream to effect cooling, and   (d) returning said methane-rich binary refrigerant stream and said C3 hydrocarbon-rich binary refrigerant stream to said multistage compressor.   
     
     
         13 . A method according to  claim 12 , wherein said methane-rich binary refrigerant stream and said C3 hydrocarbon-rich binary refrigerant stream cool a charge gas comprising hydrogen, methane and ethylene. 
     
     
         14 . A method according to  claim 13 , wherein said charge gas is used to produce ethylene. 
     
     
         15 . A method according to  claim 12 , wherein the extended binary refrigerant can provide refrigeration within the temperature range of about −136 Deg. C. to about 25 Deg. C. 
     
     
         16 . In a method for the production of olefins from a charge gas containing hydrogen, methane and ethylene wherein said charge gas is cooled by a refrigeration system having a series of heat exchangers, a method for cooling said charge gas comprising:
 (a) compressing an extended binary refrigerant vapor containing methane and a C3 hydrocarbon selected from the group consisting of propylene and propane, in a multistage compressor having a first stage and a last stage with a last stage discharge;   (b) cooling to condense a portion of said extended binary refrigerant vapor from said last stage discharge to form a remaining extended binary refrigerant vapor and a heavy refrigerant stream having a greater percentage of propylene than said selected mixture;   (c) separating said heavy refrigerant stream from said remaining extended binary refrigerant vapor in a separator;   (d) cooling to condense at least a portion of said remaining extended binary refrigerant vapor from said separator to form a light refrigerant stream;   (e) bringing said heavy refrigerant stream and said light refrigerant stream into heat exchange contact with themselves and each other and with said charge gas in said series of heat exchangers whereby said charge gas is cooled, said heavy refrigerant stream is cooled and then heated and vaporized, and said light refrigerant stream is first cooled and at least partially condensed and then vaporized; and   (f) returning said light refrigerant stream and said heavy refrigerant stream to said compressor.   
     
     
         17 . A method according to  claim 16 , wherein said cooling to condense at least a portion of said binary refrigerant vapor comprises cooling with cooling water. 
     
     
         18 . A method according to  claim 16 , wherein a portion of said heavy refrigerant stream obtained in (c) is used for cooling in (b). 
     
     
         19 . A method according to  claim 16 , wherein said light refrigerant stream is partially condensed by said heavy refrigerant stream and is further condensed through self-refrigeration. 
     
     
         20 . A method according to  claim 16 , wherein the compressor further includes an intermediate stage. 
     
     
         21 . A method according to  claim 20 , further including using a portion of said heavy refrigerant stream for cooling at least one of an ethylene fractionator reboiler, a deethanizer condenser and a depropanizer condenser. 
     
     
         22 . A method according to  claim 16 , wherein the content of propylene in said last stage discharge is greater than 50 mol %. 
     
     
         23 . A method according to  claim 16 , wherein the content of propylene in said liquid refrigerant stream is greater than 80 mol %. 
     
     
         24 . A method according to  claim 16 , wherein the extended binary refrigerant can provide refrigeration within the temperature range of about −136 Deg. C. to about 25 Deg. C. 
     
     
         25 . A method according to  claim 16 , wherein said method for cooling is utilized to increase the total refrigeration capacity of an existing olefins plant employing a cascade refrigeration system having separate propylene and ethylene refrigeration systems. 
     
     
         26 . A method according to  claim 16 , further including using the liquid stream formed in (f) to provide additional refrigeration duty. 
     
     
         27 . A method according to  claim 16 , wherein the light refrigerant vapor, at low pressure, is injected into the liquid refrigerant stream entering an ethylene fractionator condenser downstream of a valve regulating flow of said liquid refrigerant stream into said ethylene fractionator condenser. 
     
     
         28 . A method according to  claim 16 , wherein the direct refrigeration duty of said extended binary refrigerant is decreased by heat exchange between an ethane recycle to a cracking heater produced at the bottom of said fractionating tower, after pressure letdown, and a gross overhead vapor flowing from the top of said fractionating tower. 
     
     
         29 . A method according to  claim 16 , where the direct refrigeration duty of said extended binary refrigerant is decreased by heat exchange between an ethane recycle to a cracking heater that is produced at the bottom of said fractionating tower, after pressure letdown, and said refrigerant flowing to the ethylene fractionator condenser. 
     
     
         30 . A method according to  claim 16 , wherein the first light hydrocarbon separation tower is a depropanizer comprising two towers at different pressures, and the higher pressure tower overhead vapor is at least partially condensed in an interreboiler to provide reflux for the higher pressure tower. 
     
     
         31 . A method according to  claim 16 , further comprising the step of deethanizing said charge gas wherein no deethanizer condenser is provided and reflux for said deethanizer is withdrawn proximate a feed tray where a deethanizer gross overhead enters said fractionating tower. 
     
     
         32 . A method according to  claim 16 , wherein said extended binary refrigerant vapor leaving said compressor comprises no more than 1 mol % hydrogen. 
     
     
         33 . A method according to  claim 16 , wherein said extended binary refrigerant vapor leaving said compressor has no more than 10 mol % propane. 
     
     
         34 . A method according to  claim 20 , where said extended binary refrigerant is configured to increase the total refrigeration capacity of an existing olefins plant by replacing a cascading refrigeration system having separate propylene and ethylene refrigeration systems. 
     
     
         35 . An extended binary refrigerant comprising a mixture of methane and a C3 hydrocarbon selected from the group consisting of propylene and propane, the extended binary refrigerant containing 10-40 mol % methane, 60-90 mol % of at least one C3 hydrocarbon selected from the group consisting of propylene and propane, and not more than about 2 mol % hydrogen, the total mol % of methane, C3 hydrocarbon and hydrogen being 100%. 
     
     
         36 . The extended binary refrigerant of  claim 35 , wherein the C3 hydrocarbon is propylene. 
     
     
         37 . The extended binary refrigerant of  claim 35 , wherein the refrigerant can provide refrigeration within the temperature range of about −136 Deg. C. to about 25 Deg. C. 
     
     
         38 . The extended binary refrigerant of  claim 35 , wherein said refrigerant contains 15-25 mol % methane and 75-85 mol % propylene.