Ultra-low emission natural gas dehydration unit with continuously fired reboiler

Abstract

A natural gas dehydration system and method includes a contactor, a flash tank, and a still interconnected by a desiccant circulation system. A continuously fired reboiler is coupled to the still and the flash tank to bum the flash gas from the flash tank and heat the desiccant.

1 . A natural gas dehydration system, comprising:
 a contactor, a flash tank, and a regeneration system interconnected by a desiccant circulation system with dry desiccant entering the contactor along with wet gas to absorb water vapor and leave the contactor as wet desiccant, the wet desiccant entering and leaving the flash tank with flash gas separating in the flash tank, and the wet desiccant entering the regeneration system with the water vapor vaporizing and leaving as dry desiccant returning to the contactor; and   a continuously fired reboiler coupled to a still and the flash tank to burn the flash gas from the flash tank and regenerate the desiccant.   
     
     
         2 . A natural gas dehydration system as defined in  claim 1 , further comprising a flash-gas driven pump coupled to the desiccant circulation system to pump the desiccant. 
     
     
         3 . A natural gas dehydration system as defined in  claim 1 , further comprising a control system coupled to the reboiler to maintain a temperature of the desiccant above a predetermined minimum temperature. 
     
     
         4 . A natural gas dehydration system as defined in  claim 1 , further comprising a flash gas contactor disposed on the flash tank. 
     
     
         5 . A natural gas dehydration system, comprising:
 a contactor coupled to a wet gas source and a lean tri-ethylene glycol (TEG) source, and coupled to a dry gas storage and a first rich TEG outlet;   a flash tank coupled to the rich TEG outlet of the contactor and coupled to a second rich TEG outlet and a flash gas outlet;   a still coupled to the second rich TEG outlet;   a continuously fired reboiler coupled to the still and a flash-gas contactor configured to burn the flash gas to heat the rich TEG from the second TEG outlet and vaporize the water vapor and leave lean TEG; and   a TEG circulation system disposed between the contactor, the flash tank, the still and the reboiler.   
     
     
         6 . A natural gas dehydration system as defined in  claim 5 , further comprising a flash-gas driven pump coupled to the TEG circulation system to pump the desiccant, including hot desiccant for heat trace and lean desiccant to the flash-gas contactor. 
     
     
         7 . A natural gas dehydration system as defined in  claim 5 , further comprising a control system coupled to the reboiler to maintain a temperature of the desiccant above a predetermined minimum temperature. 
     
     
         8 . A natural gas dehydration system as defined in  claim 5 , further comprising a flash gas contactor disposed on the flash tank. 
     
     
         9 . A method for dehydrating natural gas, comprising the steps of:
 circulating a desiccant between a contactor, a flash tank, and a still with a reboiler;   introducing wet gas into the contactor with dry or lean desiccant, the dry or lean desiccant absorbing water vapor from the wet gas resulting in a rich or wet desiccant and dry gas;   extracting flash gas from rich or wet desiccant in the flash tank;   removing the water vapor from the rich or wet desiccant in the still by heating the rich or wet desiccant to vaporize the water vapor resulting in the dry or lean desiccant;   recirculating the dry or lean desiccant from the still to the contactor; and   continuously firing the reboiler with the flash gas from the flash tank.   
     
     
         10 . A method as defined in  claim 9 , further comprising the step of circulating lean desiccant from the still to a flash gas contactor disposed on the flash tank during winter. 
     
     
         11 . A method as defined in  claim 9 , further comprising the step of maintaining a temperature of the desiccant in the reboiler within at least a 10° C. temperature range. 
     
     
         12 . A method as defined in  claim 9 , further comprising the step of pumping the desiccant as a heating fluid with a flash-gas driven pump, and without a jet-gas circulation system and without a dry-gas driven circulation pump. 
     
     
         13 . A method as defined in  claim 9 , further comprising the step of washing and drying the flash gas to remove moisture and heavy hydrocarbons in the winter. 
     
     
         14 . A method as defined in  claim 9 , further comprising the step of burning all of the flash gas in the reboiler without venting or flaring the flash gas.