Utilizing liquefied natural gas for cryogenic cooling of cracked gas from a light hydrocarbon catalytic cracker

Abstract

Novel processes are provided for the cooling of light hydrocarbon cracker effluent streams using Liquefied Natural Gas (LNG). The effluent streams are passed through LNG cold boxes where they are cooled by LNG. The cooling takes place as a result of direct or indirect heat transfer. As the LNG heats up from this process it can be fed into a light hydrocarbon cracker. The use of the present processes offers significant economic and environmental benefits over the typical industry practice of compression and cooling using C2/C3 refrigerants.

What is claimed is: 
     
         1 . A process for cooling an effluent stream of a light hydrocarbon cracking unit using liquefied natural gas (LNG) comprising:
 a) producing natural gas and subsequently converting the natural gas into LNG at a production site;   b) transporting the LNG to a light hydrocarbon cracking unit in a cryogenic temperature range with the cracking unit producing a cracking unit effluent stream; and   c) using the LNG as coolant to cool the cracking unit effluent stream.   
     
     
         2 . The process of  claim 1 , wherein the light hydrocarbon cracking unit cracks light hydrocarbons, comprising methane, ethane, propane, natural gas, or a mixture of these, into hydrogen and liquid C 2 + products. 
     
     
         3 . The process of  claim 1 , wherein step c) further comprises separating C 2  and heavier fractions from unconverted methane. 
     
     
         4 . The process of  claim 1 , wherein step c) comprises using direct contact cooling. 
     
     
         5 . The process of  claim 1 , wherein step c) comprises indirect contact cooling. 
     
     
         6 . The process of  claim 1 , wherein following step c) the LNG is added as feed into the cracking unit to produce cracked effluent once the LNG has sufficiently warmed. 
     
     
         7 . A process for cooling the effluent stream of a light hydrocarbon cracker using liquefied natural gas (LNG) comprising:
 a) feeding cold LNG to a LNG cold box;   b) cooling a reactor effluent stream from the cracker to a temperature of about −100° F. or less by passing the stream through the LNG cold box;   c) separating the effluent stream into a methane/hydrogen gas stream and a C 2 + liquid stream; and   d) passing the C 2 + liquid stream of step c) to a demethanizer.   
     
     
         8 . The process of  claim 7 , wherein the methane/hydrogen gas stream of step c) is passed to a hydrogen separation unit to separate hydrogen from unconverted methane or other light hydrocarbons. 
     
     
         9 . The process of  claim 7 , wherein the LNG that was fed to the cold box is added into the catalytic cracker following step d). 
     
     
         10 . The process of  claim 7 , wherein the LNG is only fed into the cracker unit once it has warmed. 
     
     
         11 . The process of  claim 7 , wherein the reactor effluent stream is partially compressed and then sent through the LNG cold box. 
     
     
         12 . The process of  claim 7 , wherein the cooling in the LNG cold box is by direct or indirect heat exchange. 
     
     
         13 . A process for cooling the effluent stream of a light hydrocarbon cracker with LNG, comprising passing LNG and cracked gas from the light hydrocarbon cracker to a column or contractor where the LNG comes into direct contact with the cracked gas. 
     
     
         14 . The process of  claim 13 , wherein the cracked gas is partially compressed prior to being passed to the column or contactor. 
     
     
         15 . The process of  claim 14 , wherein C 2 + products are separated from the cooled cracked gas product from the column or contactor and sent to a downstream cryogenic separation comprising a demethanizer for further separation.