Systems and methods for capturing natural gas liquids from oil tank vapors

Abstract

A hydrocarbon vapor capture and processing system is disclosed to reduce both carbon emissions and conventional pollution, while producing financial returns by turning waste vapors into high quality NGLs. In one embodiment, the hydrocarbon vapor is sent to a compressor for compression. Compressed vapor is then cooled via an air cooler, before being condensed by a refrigerator to form a liquid. The resulting two-phase flow is then separated into a dry gas stream and a liquid stream using a cyclonic separator. The dry gas stream may be transmitted as a light gas to sales line. The resulting liquid stream is passed to a stripping column to produce NGLs. The system offers great benefits to the environment and public health, by providing a technology that drastically cuts carbon emissions and noxious pollution, while incentivizing drillers to implement such measures through its ability to produce revenue.

What is claimed is: 
     
         1 . An apparatus to capture natural gas liquids (NGLs) from oil tanks, comprising:
 a compressor to withdraw hydrocarbon vapors from the oil tanks; and   a cooling system to condense liquids from said hydrocarbon vapors resulting in a natural gas liquids (NGLs) stream and a light gas stream.   
     
     
         2 . The apparatus of  claim 1 , wherein the compressor is connected to a refrigerated evaporator to condense liquid components of the hydrocarbon vapors. 
     
     
         3 . The apparatus of  claim 2 , wherein the refrigerated evaporator is connected to a cyclonic separator. 
     
     
         4 . The apparatus of  claim 3 , wherein liquid product from the cyclonic separator connects into a stripping column warmed from below by a reboiler. 
     
     
         5 . The apparatus of  claim 4 , wherein the stripping column and the reboiler remove dissolved air, methane, and excess ethane from the hydrocarbon vapors. 
     
     
         6 . The apparatus of  claim 5 , wherein the cyclonic separator, the stripping column and the reboiler are integrated into a single unit. 
     
     
         7 . The apparatus of  claim 6 , wherein the compressor is powered by the light gas stream taken from the cyclonic separator. 
     
     
         8 . The apparatus of  claim 7 , wherein the light gas stream produced by the cyclonic separator has a Caterpillar methane number above 40, making it suitable for powering compressors and onsite generators. 
     
     
         9 . The apparatus of  claim 1 , further comprising one or more electrical motors powered by electricity produced by an electric grid or by onsite power generators. 
     
     
         10 . The apparatus of  claim 1 , wherein the cooling system is a two-stage refrigerator. 
     
     
         11 . The apparatus of  claim 1 , wherein the cooling system is a one-stage refrigerator. 
     
     
         12 . The apparatus of  claim 1 , wherein the light gas stream produced is sufficient to meet a power requirement of the apparatus, without any reliance of power on an electric grid. 
     
     
         13 . The apparatus of  claim 1 , wherein the apparatus operates autonomously with capacity to be remotely monitored and controlled. 
     
     
         14 . The apparatus of  claim 13 , further comprising hardware and software capable of operating completely autonomously within defined operating ranges. 
     
     
         15 . A method for capturing natural gas liquids (NGLs) from hydrocarbon vapors in reservoirs, comprising:
 drawing the hydrocarbon vapors from a reservoir;   compressing the hydrocarbon vapors to a pressure between 15 to 500 psia;   cooling the hydrocarbon vapors to a temperature between −30 and +20° C.;   condensing liquids from the hydrocarbon vapors from the cooling step;   separating two-phase flow from the condensing step using a cyclonic separator, to produce a liquid stream and a dry gas stream;   passing the liquid stream into a stripping column to produce natural gas liquids (NGLs); and   pumping the natural gas liquids (NGLs) to a collection tank.   
     
     
         16 . The method of  claim 15 , wherein the pressure is between 100 and 200 psia. 
     
     
         17 . The method of  claim 15 , wherein the temperature is between −10 and +10° C. above ambient temperature. 
     
     
         18 . The method of  claim 15 , wherein the temperature is approximately 5° C. 
     
     
         19 . The method of  claim 15 , wherein the temperature is approximately −4° C. to achieve 70% propane capture. 
     
     
         20 . The method of  claim 15 , wherein at least a portion of the dry gas stream is injected into a sales line for disposal. 
     
     
         21 . The method of  claim 15 , wherein the dry gas stream extracted from the cyclonic separator is used to produce power and/or to drive pneumatic devices. 
     
     
         22 . The method of  claim 15 , wherein a reboiler is used with some ethane and propane rejected downstream. 
     
     
         23 . The method of  claim 22 , wherein an exhaust gas stream from the reboiler is used to provide process cooling. 
     
     
         24 . The method of  claim 22 , wherein the reboiler's temperature is brought to between 30 and 50° C. 
     
     
         25 . The method of  claim 15 , wherein the temperature is below about −50° C., and the method is operated at 1 bara. 
     
     
         26 . The method of  claim 15 , wherein the pressure is 3 bar to operate the method at temperatures in the −20° C. range. 
     
     
         27 . The method of  claim 15 , wherein the pressure is 10 bar or higher to operate the method at temperatures of 5° C. or more. 
     
     
         28 . The method of  claim 15 , wherein high pressures are employed to operate the method with minimal cooling to eliminate ice formation.