Method of removing solid carbon dioxide

Abstract

The invention provides a method of removing solid carbon dioxide from cryogenic equipment, including the steps of: (a) introducing a stream including ethane to the cryogenic equipment to convert solid carbon dioxide to liquid form whereby a mixture of liquid ethane and liquid carbon dioxide is formed; and (b) removing the mixture of liquid ethane and liquid carbon dioxide from the cryogenic equipment. In particular, the method can be used in a liquefied natural gas (LNG) plant wherein cryogenic equipment contains LNG, and the method includes the steps of: (a′) removing the LNG from the cryogenic equipment; (a) introducing a stream including ethane to convert solid carbon dioxide to liquid form whereby a mixture of liquid ethane and liquid carbon dioxide is formed; and (b) removing the mixture of liquid ethane and liquid carbon dioxide from the cryogenic equipment. The result is an effective cleaning method for fouled LNG equipment.

1 . A method of removing solid carbon dioxide from cryogenic equipment, comprising the steps of:
 (a) introducing a stream including ethane to said cryogenic equipment to convert solid carbon dioxide to liquid form whereby a mixture of liquid ethane and liquid carbon dioxide is formed; and   (b) removing the mixture of liquid ethane and liquid carbon dioxide from the cryogenic equipment.   
   
   
       2 . The method of  claim 1 , wherein the stream including ethane contains at least 35% mol ethane. 
   
   
       3 . The method of  claim 1 , wherein the stream including ethane is liquid. 
   
   
       4 . The method of  claim 1 , wherein the cryogenic equipment is taken off-line before introducing the stream including ethane. 
   
   
       5 . The method of  claim 1 , in which the cryogenic equipment is used to produce liquefied natural gas. 
   
   
       6 . The method of  claim 1 , in which the stream including ethane contains carbon dioxide up to 65% mol. 
   
   
       7 . The method of  claim 1 , in which the method further comprises the step of separating the mixture of liquid ethane and liquid carbon dioxide to form a first product enriched in ethane and a second product enriched in carbon dioxide. 
   
   
       8 . The method of  claim 7 , in which the first and second product are separated by distillation, extraction, absorption, crystallisation, decanting, multi-stage extraction or other chemical treatments or any combination thereof. 
   
   
       9 . The method of  claim 1 , in which the mixture of liquid ethane and liquid carbon dioxide is azeotropic, and is separated to form a first product enriched in ethane and a second product enriched in carbon dioxide by extractive distillation or membrane-based separation techniques or a combination thereof. 
   
   
       10 . The method of  claim 7 , in which one or more alkanes or their isotropes are introduced to the mixture prior to the separation step. 
   
   
       11 . The method of  claim 7 , in which the stream that includes ethane comprises the first product that is recycled to the step (a). 
   
   
       12 . A method of removing solid carbon dioxide from cryogenic equipment, wherein the cryogenic equipment contains liquefied natural gas, the method comprising the steps of:
 (a′) removing the liquefied natural gas from the cryogenic equipment;   (a) introducing a stream including ethane to convert solid carbon dioxide to liquid form whereby a mixture of liquid ethane and liquid carbon dioxide is formed; and   (b) removing the mixture of liquid ethane and liquid carbon dioxide from the cryogenic equipment.   
   
   
       13 . The method of  claim 12 , wherein the stream including ethane contains at least 35% mol ethane. 
   
   
       14 . The method of  claim 12 , wherein the stream including ethane is liquid. 
   
   
       15 . The method of  claim 12 , wherein the cryogenic equipment is taken off-line before introducing the stream including ethane. 
   
   
       16 . The method of  claim 12 , in which the cryogenic equipment is used to produce liquefied natural gas. 
   
   
       17 . A method of producing liquefied natural gas, wherein natural gas is introduced in cryogenic equipment and is cooled down to form liquefied natural gas, and further wherein solid carbon dioxide is removed from the cryogenic equipment by:
 (a) introducing a stream including ethane to the cryogenic equipment to convert solid carbon dioxide to liquid form whereby a mixture of liquid ethane and liquid carbon dioxide is formed; and   (b) removing the mixture of liquid ethane and liquid carbon dioxide from the cryogenic equipment.   
   
   
       18 . The method of  claim 17 , wherein the stream including ethane contains at least 35% mol ethane. 
   
   
       19 . The method of  claim 17 , wherein the stream including ethane is liquid. 
   
   
       20 . The method of  claim 17 , wherein the cryogenic equipment is taken off-line before introducing the stream including ethane. 
   
   
       21 . The method of  claim 17 , wherein the stream including ethane contains carbon dioxide up to 65% mol. 
   
   
       22 . The method of  claim 17 , wherein the liquefied natural gas is removed from the cryogenic equipment prior to the step (a). 
   
   
       23 . A method of producing liquefied natural gas, wherein natural gas is introduced in cryogenic equipment and is cooled down to form liquefied natural gas, and further wherein solid carbon dioxide is removed from the cryogenic equipment by:
 (a) introducing a stream including ethane to the cryogenic equipment to convert solid carbon dioxide to liquid form whereby a mixture of liquid ethane and liquid carbon dioxide is formed; and   (b) removing the mixture of liquid ethane and liquid carbon dioxide from the cryogenic equipment, wherein the solid carbon dioxide is already present on a surface of said cryogenic equipment prior to said introducing said stream.   
   
   
       24 . The method of  claim 23 , wherein the stream including ethane contains at least 35% mol ethane. 
   
   
       25 . The method of  claim 23 , wherein the stream including ethane is liquid. 
   
   
       26 . The method of  claim 23 , wherein the cryogenic equipment is taken off-line before introducing the stream including ethane. 
   
   
       27 . The method of  claim 23 , further comprising the step of adjusting the relative percentages of ethane and carbon dioxide for a given pressure and temperature such that the mixture of liquid ethane and liquid carbon dioxide is near azeotropic. 
   
   
       28 . The method of  claim 23 , in which the stream including ethane contains carbon dioxide up to 65% mol. 
   
   
       29 . The method of  claim 23 , in which the method further comprises the step of separating the mixture of liquid ethane and liquid carbon dioxide to form a first product enriched in ethane and a second product enriched in carbon dioxide. 
   
   
       30 . The method of  claim 29 , in which the first and second product are separated by distillation, extraction, absorption, crystallisation, decanting, multi-stage extraction or other chemical treatments or any combination thereof. 
   
   
       31 . The method of  claim 23 , in which the mixture of liquid ethane and liquid carbon dioxide is azeotropic, and is separated to form a first product enriched in ethane and a second product enriched in carbon dioxide by extractive distillation or membrane-based separation techniques or a combination thereof. 
   
   
       32 . The method of  claim 29 , in which one or more alkanes or their isotropes are introduced to the mixture prior to the separation step. 
   
   
       33 . The method of  claim 29 , in which the stream that includes ethane comprises the first product that is recycled to the step (a).