Gas separation: processes – Liquid contacting – And degasification of a liquid
Reexamination Certificate
1999-06-15
2001-05-29
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Liquid contacting
And degasification of a liquid
C095S163000, C095S166000, C095S231000, C095S165000, C095S193000, C095S247000, C095S266000
Reexamination Certificate
active
06238461
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to natural gas dehydrators of the type used to remove water and water vapor from a natural gas stream composed of a mixture of natural gas, liquid hydrocarbons, water and water vapors and is particularly directed to field natural gas dehydrators.
BACKGROUND OF THE INVENTION
An example of such a field natural gas dehydrator is disclosed in U.S. Pat. No. 5,766,313 to Rodney Thomas Health and the disclosure therein is specifically incorporated herein by reference thereto. In general, such systems comprise a separator means for receiving the oil and water liquids from “wet” (water vapor laden) gas; and a water absorber means, which employs a liquid dehydrating agent such as glycol, for removing the water vapor from the wet gas and producing “dry” gas suitable for commercial usage. The glycol is continuously supplied by a pump to the absorber means in a “dry” low-water vapor-pressure condition and is removed from the absorber means in a “wet” high-water vapor-pressure condition. The wet glycol is continuously removed from the absorber means and circulated through a reboiler means, which includes a still column, for removing the absorbed water from the glycol and heating the glycol to provide a new supply of hot dry glycol. Heating of the glycol in the reboiler means is generally accomplished through use of a gas burner mounted in a fire tube. The hot dry glycol from the reboiler means passes through a heat exchanger, where the hot dry glycol transfers some of its heat to incoming wet glycol going to the still column. The dry glycol subsequently passes to a dry glycol storage tank. A glycol passage means is provided to enable passage of wet glycol from the absorber means to the reboiler means and to pump dry glycol from the storage tank to the absorber means.
Besides water, the wet glycol going to the still column of the reboiler of the natural gas dehydrator will contain natural gas and absorbed hydrocarbons. A large part of the natural gas flowing with the wet glycol to the still column is the natural gas required to power the glycol pump. The balance of the natural gas and other hydrocarbons are absorbed or entrained into the glycol during the water-absorption step in the absorber means.
On many dehydrators, a volume of natural gas is intentionally induced into the reboiler in order to dry the wet glycol to a higher concentration than can be accomplished by simply adding heat. The process of intentionally inducing a volume of natural gas into the reboiler is referred to as gas stripping.
In the still column of the reboiler of the natural gas dehydrator, the water, natural gas, and other hydrocarbons are separated from the glycol by the pressure reduction from the absorber pressure to approximately atmospheric pressure in the still column and by the application of heat from the burner in the fire tube of the reboiler.
The water, natural gas, and other hydrocarbons contained in the wet glycol stream which are separated in the still column from the wet glycol will be exhausted into the atmosphere through the atmospheric vent on the still column. The hydrocarbon vapors released through the still column of a natural gas dehydrator are air pollutants. Specifically, certain hydrocarbons such as benzene, toluene, ethylbenzene, and xylene, commonly referred to as BTEX have been proven to be carcinogenic.
The gas dehydrator disclosed in U.S. Pat. No. 5,766,313 offers solutions to the problems discussed above but improvements can be made to such a gas dehydrator.
BRIEF DESCRIPTION OF THE INVENTION
This invention provides a field natural gas dehydrator in which the wet glycol from the absorber is fed into a three phase emissions separator which is provided with suitable apparatus, such as an overflow tank, that collects an amount of the wet glycol, for a purpose described more fully below, and then routes any additional amount of wet glycol to a reboiler. The collected wet glycol is used as a circulating medium to cool the emissions from the still column of a reboiler and to provide the energy for an educator as described more fully below. By using the collected wet glycol as the pump circulating medium, the lubricity, vapor pressure, viscosity, and etc. of the circulating medium remain relatively constant from dehydrator to dehydrator; therefore overcoming potential pump problems which could occur if a circulating medium with changing physical constants, from dehydrator to dehydrator, was used.
Also, the collected wet glycol can be pumped in greater volumes to be used as a heat exchange medium for condensing the effluents from the still column of the reboiler. As explained more fully below, the volume of the collected wet glycol being pumped by the circulating pump is 20 to 30 times greater than the volume of the wet glycol exiting the absorber.
This invention also provides a liquid water removal separator that collects the liquid water condensed from the effluents from the still column so that substantially no liquid water is entered into the emissions separator.
The invention also provides a system for collecting the gases from the level controllers used in the natural gas dehydrator so that the collected gases may be used as fuel for the burner of the reboiler.
In accordance with this invention, a natural gas dehydrator is provided wherein a supply of natural gas is fed into an absorber wherein it is subjected to dry glycol to remove undesirable materials therefrom so that the dry glycol is changed into wet glycol that is removed from the absorber and fed at reduced pressure into a three phase emissions separator apparatus. One part of the three phase emissions separator apparatus has structure for holding a predetermined amount of the wet glycol. The three phase emissions separator apparatus has additional structure for receiving excess wet glycol from the structure. A reboiler apparatus receives the excess wet glycol and changes the excess wet glycol into dry glycol and effluents. A condenser apparatus is provided for receiving the effluents. Circulating apparatus is provided for circulating wet glycol from the structure through the condenser apparatus to change the effluents to at least liquid water, liquid hydrocarbons and uncondensed vapors and returning the circulating wet glycol to the three phase emissions separator apparatus. Liquid water removal separator apparatus is provided for receiving the at least liquid water, liquid hydrocarbons and uncondensed vapors for separating and removing the liquid water. Additional apparatus is provided for removing the liquid hydrocarbons and the uncondensed vapors from the liquid water removal separator apparatus and feeding the liquid hydrocarbons and the uncondensed vapors to the three phase emissions separator apparatus.
The additional apparatus comprises an eductor having an inlet port, an exit port and a vacuum port. A first conduit through which the circulating wet glycol flows is connected to the inlet port. A second conduit extends between the outlet port and the three phase emissions separator apparatus. A third conduit extends between the liquid water removal separator apparatus and the vacuum port to form a vacuum in the liquid water removal separator apparatus.
The liquid water removal separator apparatus comprises a hollow shell having a partition therein for forming at least a first and a second chamber in the hollow shell. A first outlet port is formed in the first chamber and is connected to the third conduit so that a vacuum is formed in the first chamber. A first inlet port is formed in the first chamber so that the at least liquid water, liquid hydrocarbons and uncondensed vapors from the condenser apparatus can flow into the first chamber and be separated into at least an upper layer comprising the uncondensed vapors, a middle layer comprising the liquid hydrocarbons and a lower layer comprising the liquid water. The first outlet port is located so that the uncondensed vapors and the liquid hydrocarbons can flow through the first outlet port into the third conduit. T
Kelly Joseph J.
Klaas, Law, O'Meara & Malkin, P.C.
O'Meara William P.
Spitzer Robert H.
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