Gas separation: processes – With control responsive to sensed condition – Liquid level sensed
Reexamination Certificate
2002-02-08
2003-04-22
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
With control responsive to sensed condition
Liquid level sensed
C095S161000, C095S163000, C095S166000, C095S231000, C095S251000, C096S160000, C096S163000, C096S165000, C096S173000, C096S193000, C096S247000, C096S266000
Reexamination Certificate
active
06551379
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to apparatus for use with 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, liquid hydrocarbon vapors, water and water vapors and is particularly directed to apparatus for use with 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 Heath 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.
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 at least some of the problems discussed above but improvements can be made to such a gas dehydrator.
BRIEF DESCRIPTION OF THE INVENTION
This invention provides apparatus for use with a field natural gas dehydrator in which the wet glycol from the absorber is fed into a three phase emissions separator apparatus which is provided with suitable apparatus, such as an overflow tank, that contains an amount of wet glycol, part of which is used as a circulating medium as described more fully below, and routes another part of the wet glycol, such as an amount equal to the amount of wet glycol received from the absorber, to a reboiler. In the description of the invention, the apparatus is described in its operating condition. The circulating wet glycol is used to cool the emissions from the still column of a reboiler and to provide the energy to create a vacuum using an eductor as described more fully below. By using the part of the 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 wet glycol can be pumped in greater volumes and used as a heat exchange medium for condensing the effluent from the still column of the reboiler. As explained more fully below, the volume of the wet glycol being pumped by the circulating pump is 20 to 30 times greater than the volume of the wet glycol exiting the absorber.
In one embodiment, this invention also provides a liquid water separator and removal apparatus that collects the liquid water condensed from the effluent from the still column so that substantially no water in the form of vaporized water or liquid water is returned into the emissions separator. Ideally, substantially all of the water in the vaporized water in the effluent is changed into liquid water in an effluent condenser apparatus and is fed into and removed in the liquid water separator and removal apparatus. This is accomplished in the instant invention by cooling the effluent to a temperature in the effluent condenser that condenses substantially all of the vaporized water and even some of the vaporized hydrocarbons to produce liquid hydrocarbons.
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 one embodiment of 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 first separator comprising a three phase emissions separator apparatus. When the invention is under operating conditions, the three phase emissions separator apparatus has liquid level control apparatus that provides for holding a predetermined amount of wet glycol some of which is to be circulated as described below and some of which wet glycol that is transferred to the still column of a reboiler apparatus that receives the wet glycol and changes such amount of wet glycol into dry glycol and vaporized effluent. Under operating conditions, the amount of wet glycol being transferred to the reboiler is substantially equal to the amount of wet glycol being fed into the three phase emissions separator apparatus from the absorber. An effluent condenser apparatus is provided for receiving the vaporized effluent. The effluent condenser apparatus comprises a hollow shell having a tube extending therethrough wherein the tube has an external spiral fin. The hollow shell has an inlet and an outlet so that the wet glycol can be circulated therethrough. The effluent from the still column is fed into the tube and is cooled by the circulating wet glycol. Circulating apparatus is provided for circulating wet glycol from the three phase emissions separator apparatus through the effluent condenser apparatus to change the vaporized effluent to at least liquid water, liquid hydrocarbons and uncondensed vapors, which are substantially hydrocarbon vapors, and returning the circulating wet glycol with other ingredients entrained therein to the three phase emissions separator apparatus. Second separator apparatus comprising liquid water separator and removal 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 wa
Klaas, Law, O'Meara & Malkin, P.C.
Spitzer Robert H.
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