Refrigeration – Cryogenic treatment of gas or gas mixture – Liquefaction
Reexamination Certificate
1998-09-18
2001-08-07
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Liquefaction
C062S611000
Reexamination Certificate
active
06269656
ABSTRACT:
TECHNICAL FIELD
Method and apparatus for a system of producing liquified natural gas, and more particularly to such a system which is associated directly with a well head or other high pressure natural gas source and requires no external power source.
BACKGROUND ART
The present invention is based upon the discovery that a simple, efficient, open, partial conversion system for the production of liquid natural gas (LNG) can be provided if natural gas, taken directly from the well head or other source under high pressure and cleaned (if required), is immediately thereafter split into two high pressure flow portions. The first high pressure flow portion is the source of the liquid natural gas fraction, the vent remainder of the first flow portion constituting a cold saturated vapor used thereafter as a coolant for the system. The second high pressure flow portion is cooled and is used solely as a coolant for the system. The second flow portion and the remainder of the first flow portion are ultimately conducted to an appropriate receiver having a pressure lower than that of the well head or other source. Neither of the first and second flow portions is reduced in pressure to a level less than the pressure within the receiver.
Prior art workers have devised many types of partial conversion and total conversion systems for the production of liquid natural gas. This is exemplified in U.S. Pat. No. 3,735,600 wherein an open cycle is taught utilizing well head gas. In this system, however, once the well head gas has been purified, it is not immediately split into two flow portions. The arrangement of equipment components differs from that of the present invention, as do the steps performed in the reference system.
Other exemplary prior art natural gas liquification systems are taught, for example, in U.S. Pat. Nos. 3,818,714 and 4,970,867, both of which demonstrate the more complex prior art approaches.
DISCLOSURE OF THE INVENTION
According to the invention there is provided both an apparatus and a method for a system of producing liquid natural gas. A first embodiment of the system is associated directly with a well head or other source which provides a supply of high pressure natural gas. The gas flow obtained from the source is cleaned, unless the source provides natural gas clean enough to enable the formation of a liquid natural gas fraction, and thereafter is split into first and second high pressure flow portions. The first portion of the flow goes directly to a first or primary heat exchanger where it is cooled. Thereafter, the first flow portion passes through a second heat exchanger or super cooler where it is further cooled. The super cooled high pressure first flow portion is throttled into a liquid natural gas collector wherein a part of the first flow portion flashes to liquid natural gas, and the vent remainder of the first flow portion constitutes a cold saturated natural gas vapor.
The second portion of the flow is cooled in an expander by work extraction and then passes through the primary heat exchanger, serving as the cooling medium therefor. The remaining very cold, saturated gas of the first flow portion in the liquid natural gas collector is vented through the super cooler heat exchanger as the cooling medium therefor and then combines as an additional cooling medium with the second flow portion as it enters the primary heat exchanger. The warmed combined flows, having served as the cooling medium for the primary heat exchanger, are conducted therefrom to a lower pressure receiver such as a gas distribution pipeline. In the expander, the second flow portion is reduced in pressure to a level equal to or somewhat higher than that of the receiver. The remaining part of the first flow portion in the liquid natural gas tank is also reduced to a pressure equal to or somewhat greater than that of the receiver. Thus both flow portions can be introduced into the receiver.
A second embodiment of the system of the present invention is also associated directly with a well head or other source of high pressure natural gas. Following cleaning, if required, the natural gas from the source is split into first and second high pressure flow portions. The first flow portion goes directly to a primary heat exchanger where it is cooled. Thereafter, the first flow portion is throttled into a liquid natural gas collector wherein a part of the first flow portion flashes to liquid natural gas. The second portion of the flow is cooled in an expander by work extraction. The vent remainder of the first flow portion from the liquid natural gas tank is joined by the cooled second portion of the gas flow from the expander. These combined flows pass through and act as coolant for the single heat exchanger and are then introduced into an appropriate receiver.
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Doerrler William
Frost Brown Todd LLC
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