Comprehensive natural gas processing

Abstract

The present invention related to a process and an apparatus for efficient and cost-effective comprehensive processing of natural gas, including the removal of moisture and the recovery of the higher hydrocarbons components (C 2 + ). The said apparatus comprises the following major components: an integrated natural gas processor with a dehydration section and a higher hydrocarbons absorption section; a heat transport medium cooler; an absorbent cooler; a fractional distiller for separating the light oil from the heavy oil absorbent; an inhibitor regenerator; and a refrigeration unit. The present invention provides a low-cost natural gas comprehensive processor processing that is universally applicable to both terrestrial and off-shore natural gas exploitation. The said apparatus also provides an efficient and cost-effective natural gas dehydrator when the dehydration section is used independently without incorporating the absorption section.

1. A comprehensive gas processor for removing the moisture and recovering the higher hydrocarbons (i.e., C 2   + ) therein either on-situ in a gas field or in a plant comprising:
 (a) an integrated gas processor comprising two sections working on a hybrid process, i.e., an integration of two different processes within a single casing; 
 i) a refrigeration-dehydration section working on refrigeration process wherein the inlet gas contacts with a counter-flowing stream of dispersed cold heat-transport medium containing a non- or low-volatile hydrate inhibitor with boiling point higher than 180° C. and the moisture of said gas is condensed and removed with the cold heat-transport medium; and  
 ii) an absorption section working on low-temperature absorption process wherein the dehydrated gas contacts with a counter-flowing stream of dispersed liquid absorbent with a higher hydrocarbon gas solubility higher  greater than 20 scf/gal wherein the higher hydrocarbons (i.e., C 2   + ) are absorbed.  under said absorption conditions;  
 
 (b) a heat-transport medium cooler comprising a pre-cooling stage and a deep-cooling stage wherein in said pre-cooling stage said heat-transport medium is pre-cooled with the cold outlet gas left said integrated gas processor and in said deep-cooling stage the medium is deep-cooled with the refrigerant provided with a refrigerator;  
 (c) an absorbent cooler comprising a pre-cooling stage and a deep-cooling stage wherein in said pre-cooling stage said recycling absorbent is pre-cooled with the cold outlet absorbent left said integrated gas processor and in said deep-cooling stage the absorbent is deep-cooled with the refrigerant provided with a refrigerator;  
 (d) a fractional distiller for separating the absorbed higher hydrocarbons as a product from the outlet absorbent left said integrated gas processor and then the separated absorbent is recycled back to said integrated gas processor;  
 (e) an inhibitor regenerator for concentrating the low-volatile hydrate inhibitor to be recycled and discharging the wastewater;  
 (f) a refrigerator for providing the refrigerant to said deep-cooling stages of said heat-transport medium cooler and said absorbent cooler;  
 (g) a pipeline for delivering the recovered higher hydrocarbons; and  
 (h) a gas inlet pipeline and a pipeline for delivering the processing gas.  
 
     
     
       2. A comprehensive gas processor of  claim 1  wherein the dehydration section of said integrated processor and its accessories (comprising said heat-transport medium cooler, said inhibitor regenerator, said refrigerator, and said gas inlet-pipeline and a pipeline for delivering the processed gas) are operated independently as a gas dehydrator without incorporating the absorption section. 
     
     
       3. A comprehensive gas processor of  claim 1  wherein said heat-transport medium is an aqueous solution of calcium chloride or other ionizing salts and the regeneration rate of said solution is less than 5 liter per kg of wastewater to be discharged . 
     
     
       4. A comprehensive gas processor of  claim 1  wherein said heat-transport medium is an aqueous solution of ethylene glycol or other organic compounds with boiling points  higher than 180° C. and the regeneration rate of said solution is less than 5 liter per kg of wastewater discharged. 
     
     
       5. A comprehensive gas processor of  claim 1  wherein said absorbent is heavy oil (i.e., hydrocarbon mixture with molecular weight higher than 100) or other organic compounds with hydrocarbon gas solubility higher than 20 scf/gal liquid. 
     
     
       6. A comprehensive gas processor of  claim 1  when working on inlet gas pressure greater than 5.0 MPa wherein said refrigerant to said deep-cooling stages of said heat-transport medium cooler and said absorbent cooler is provided with a gas expansion device with the inlet gas pressure is greater than 5.0 MPa. 
     
     
       7. A gas expansion device of  claim 6  wherein said expansion device is a triple-sectional free-piston gas expander-compressor-booster comprising:
 (a) a gas expansion cylinder and a gas compression cylinder;  
 (b) a co-shaft gas expansion piston and gas compression piston; and  
 (c) a co-shaft gas-fueled booster piston-engine providing supplemental power for compressing said expanded gas to the required delivery pipeline pressure.  
 
     
     
       8. A continuous process for separating moisture and hydrocarbons higher than methane from a natural gas stream at pipeline or wellhead pressure, comprising removing said moisture and said hydrocarbons heavier than methane as a C 2   +    mixture, including the following steps:    ( a )  Cooling said natural gas stream by directly contacting the natural gas stream with a low temperature counter - flowing heat - transport medium containing an aqueous solution of a gas - hydrate inhibitor at pipeline or well - head pressure and at a rate sufficient to cool said gas to the low temperature required by the absorption Step  ( c ) , and the majority of water moisture is condensed and dissolved into the heat - transport medium and, at the same time, a portion of higher hydrocarbons is also condensed as a liquid that is insoluble to the heat transport medium      ( b )  Separating the insoluble condensed higher hydrocarbons liquid from the condensed water  ( already dissolved into the heat - transport medium )  as a portion of the product stream;      ( c )  Extracting said dehydrated, depleted cold natural gas stream leaving Step  ( a )  by flowing counter - flow to the cold natural gas stream a cold absorbent with a higher hydrocarbon  ( i.e., C   2   + )  solubility greater than  20  scf/gal under said absorption conditions and at a rate sufficient to produce a rich absorbent stream containing C   2   +    mixture and a small portion of methane, and a cold residue natural gas stream of gas transport pipeline quality;      ( d )  Regenerating said rich absorbent by fractionating the rich absorbent leaving Step  ( c )  at reduced pressure and separating from said absorbent the absorbed C   2   +    mixture as a product stream;      ( e )  Cooling the heat - transport medium leaving Step  ( a )  to said sufficiently low temperature in two steps: first with the cold stream of the residue gas leaving Step  ( c ) , then with the refrigerant provided by an external refrigerator;      ( f )  Separating the condensed water moisture from said heat transport medium by evaporating a small portion of the heat - transport medium leaving Step  ( a )  under reduced pressure, and recycling the concentrated inhibitor solution to the heat - transport medium stream;      ( g )  Recycling the regenerated absorbent leaving Step  ( d )  by compressing it to pipeline or well - head pressure, and cooling it to the required low temperature in two steps: first with the rich absorbent leaving Step  ( c ) , then with the refrigerant provided by an external refrigerator; and      ( h )  Delivering the residue gas leaving Step  ( e )  into the gas transport pipeline.     
     
     
       9. The process of  claim 8 , wherein the cold stream of the residue gas leaving Step ( c )  is expanded to a lower pressure and much lower temperature to provide sufficient internal refrigeration.   
     
     
       10. The process of  claim 9 , wherein in Step ( e )  the heat - transport medium leaving Step  ( a )  is cooled to said sufficiently low temperature with the cold stream of the said expanded residue gas.   
     
     
       11. The process of  claim 8 , wherein in step ( a )  the said heat transport medium is an aqueous solution of calcium chloride or other ionizing salts with a potential regeneration rate less than  5  liter per kg of wastewater to be discharged.   
     
     
       12. The process of  claim 8 , wherein in step ( a )  the said heat transport medium is an aqueous solution of ethylene glycol or other organic compounds with a potential regeneration rate less than  5  liter per kg of wastewater to be discharged.