Efficient oxidative coupling of methane processes and systems

Abstract

The present disclosure provides oxidative coupling of methane (OCM) systems for small scale and world scale production of olefins. An OCM system may comprise an OCM subsystem that generates a product stream comprising C2+ compounds and non-C2+ impurities from methane and an oxidizing agent. At least one separations subsystem downstream of, and fluidically coupled to, the OCM subsystem can be used to separate the non-C2+ impurities from the C2+ compounds. A methanation subsystem downstream and fluidically coupled to the OCM subsystem can be used to react H2 with CO and/or CO2 in the non-C2+ impurities to generate methane, which can be recycled to the OCM subsystem. The OCM system can be integrated in a non-OCM system, such as a natural gas liquids system or an existing ethylene cracker.

What is claimed is: 
     
         1 . A method for producing hydrocarbon compounds including two or more carbon atoms (C 2+  compounds), the method comprising:
 (a) performing an oxidative coupling of methane (OCM) reaction in an OCM reactor to produce an OCM effluent stream comprising carbon monoxide (CO), carbon dioxide (CO 2 ), hydrogen (H 2 ), one or more C 2+  compounds including ethane (C 2 H 6 ) and ethylene (C 2 H 4 ), and methane (CH 4 ); 
 (b) directing the OCM effluent stream to a heat recovery steam generator (HRSG) system; 
 (c) with the HRSG system, transferring heat from the OCM effluent stream to a water stream to produce steam; 
 (d) separating the OCM effluent stream into a first stream comprising at least some of the one or more C 2+  compounds and a second stream comprising CO, CO 2 , H 2 , and CH 4 , 
 wherein the method has a carbon efficiency of at least about 50%. 
 
     
     
         2 . The method of  claim 1 , further comprising directing the OCM effluent stream to a cracking unit prior to step (b). 
     
     
         3 . The method of  claim 2 , further comprising directing a stream comprising C 2 H 6  to the cracking unit, wherein the stream comprising C 2 H 6  is external to the OCM reactor. 
     
     
         4 . The method of  claim 2 , wherein the cracking unit is a portion of the OCM reactor. 
     
     
         5 . The method of  claim 1 , further comprising directing at least a portion of the second stream to a methanation unit to react H 2  with said CO or CO 2  to form a CH 4  stream. 
     
     
         6 . The method of  claim 5 , further comprising directing at least a portion of the CH 4  stream to the OCM reactor. 
     
     
         7 . The method of  claim 5  further comprising directing at least a portion of the CH 4  stream into a natural gas pipeline. 
     
     
         8 . The method of  claim 5 , wherein the methanation unit has a methanation catalyst that converts CO or CO 2  into CH 4  at a selectivity for the formation of CH 4  that is at least about 10-fold greater than a selectivity of the methanation catalyst for formation of coke from CO or CO 2 . 
     
     
         9 . The method of  claim 1 , wherein an inlet temperature of the OCM reactor is at most about 600° C. 
     
     
         10 . The method of  claim 1 , further comprising: (i) directing a first portion of the second stream and an air stream to a gas compressor, and burning the first portion of the second stream to compress the air stream to produce a compressed air stream; (ii) separating the compressed air stream in an air separation unit (ASU) into a third stream comprising 02 and a fourth stream comprising N 2 ; and (iii) directing the third stream to the OCM reactor. 
     
     
         11 . An oxidative coupling of methane (OCM) system for producing olefins comprising:
 (a) an OCM subsystem comprising an OCM reactor that (i) takes as input a feed stream comprising methane (CH 4 ) and a feed stream comprising an oxidizing agent, and (ii) generates a product stream comprising C 2+  compounds and non-C 2+  impurities;   (b) a heat recovery steam generator (HRSG) system fluidly and/or thermally coupled to the OCM subsystem, wherein the HRSG system is configured to transfer heat from the product stream to a water stream to produce steam; and   (c) a separation subsystem fluidly coupled to the OCM subsystem and the HRSG system that is configured to separate the product stream into (i) a first stream comprising C 2+  compounds and (ii) a second stream comprising carbon monoxide (CO) hydrogen (H 2 ), carbon dioxide (CO 2 ), and CH 4 ,   wherein the system operates at a carbon efficiency of at least about 50%.   
     
     
         12 . The system according to  claim 11 , further comprising a methanation subsystem fluidly coupled to the separation subsystem and to the OCM subsystem, wherein the methanation subsystem is configured to convert H 2  and CO 2  and/or CO into CH 4  from at least a portion of the second stream. 
     
     
         13 . The system according to  claim 11 , wherein the OCM subsystem comprises at least one post-bed cracking unit within the OCM reactor or downstream of the OCM reactor, wherein the post-bed cracking unit is configured to convert at least a portion of alkanes in the product stream to alkenes. 
     
     
         14 . The system according to  claim 11 , further comprising an air separation unit (ASU) housing a gas turbine combined cycle (GTCC) unit fluidly coupled to the separation subsystem and to the OCM subsystem, wherein the GTCC unit is configured to accept at least a portion of the second stream to burn as fuel for driving a compressor that provides compressed air to the ASU, and wherein the ASU is configured to separate the compressed air into an oxygen (O 2 ) stream and a nitrogen (N 2 ) stream and to direct the O 2  stream to the OCM subsystem. 
     
     
         15 . The system according to  claim 12 , further comprising a heat exchanger in fluid communication with the OCM subsystem and the methanation subsystem, wherein the heat exchanger is configured to transfer heat from the product stream to an effluent stream comprising CH 4  from the methanation subsystem. 
     
     
         16 . The system according to  claim 11 , wherein the system consumes less than about 150 MMBtu of energy per ton of ethylene (C 2 H 4 ) or C 3+  compounds enriched. 
     
     
         17 . The system according to  claim 11 , wherein the separation subsystem comprises an acetylene conversion unit configured to convert acetylene in the first stream to ethane (C 2 H 6 ) and/or ethylene (C 2 H 4 ). 
     
     
         18 . The system according to  claim 11 , further comprising a sulfur removal system in fluid communication with the OCM subsystem, wherein the sulfur removal system is configured to remove sulfur-containing compounds from the feed stream comprising CH 4 .