Patent Grant
11493239
The present invention addresses liquid natural gas (LNG) production in the proximity of or collocated with a gas pressure letdown facility (i.e., City Gate, wellhead, etc.) and claims the method of using the Non-Freezing Vortex Tube (U.S. Pat. No. 5,749,231, Tunkel, L.) to substantially reduce the energy consumption of the process by reducing the temperature of natural gas being fed to a liquid natural gas plant.
Natural gas conversion into LNG takes place at gas temperature of −260° F. (−162° C.) and pressure of approximately 4 prig (0.28 Bar). The conventional process (shown in
The large energy consumption associated with LNG production can be substantially reduced by placing an LNG plant in close proximity to a pressure letdown facility and utilizing the available cooling load (Joule-Thomson temperature drop of the pressure regulated main pipeline gas flow/wellhead gas) to precool high pressure LNG feed gas upstream of the conventional liquefaction process. Conventionally, the practical application of this cooling load is complicated by the possibility of depressurized gas freeze up. This is addressed by applying the Non-Freezing Vortex Tube (U.S. Pat. No. 5,749,231, Tunkel, L.) as a primary pressure regulator of a portion of the high-pressure main transmission gas flow on the pipeline (without interrupting any of the LNG plant's raw material feed gas flow rate/volume and pressure). The Non-Freezing Vortex Tube set up in parallel with a pressure reducing line of a letdown facility operates under the available pressure differential of the non-regulated and regulated gas pressures. This is the driving force of the Non-Freezing Vortex Tube. The Non-Freezing Vortex Tube configured as dual stream (hot and cold outlet unit) chills LNG feed in an indirect contact heat exchanger (shell and tube style) by the vortex tube cold outlet flow with the temperature reduced by the combined Joule-Thomson and Vortex phenomenon. After the heat exchanger, the Vortex Tube low pressure hot and cold outlet streams are recombined and injected back into the gas pipeline network downstream of the pressure letdown facility, circumventing the traditional preheat/reduction process.
The present invention improves the efficiency of the LNG manufacturing process, applying a chilling (precooling) effect to the LNG feed gas with a completely free cooling load in the form of cooling energy generated in the Non-Freeze Vortex Tube's cold outlet flow during the course of routine pressure regulation of pipeline or wellhead gas using the available pressure letdown facility's high pressure input and low pressure output. This cold energy provided by the cold outlet of the Non-Freezing Vortex Tube is used to reduce the inlet temperature of the natural gas prior to the deep chilling/liquefaction of the feed gas in a turbo-expander and cold box. Specifically, the Non-Freeze Vortex Tube is fed by high pressure natural gas at pipeline/wellhead gas temperature. In the Non-Freezing Vortex Tube, the gas is separated into hot and cold segments at the vortex tube outlets without the use of any external energy source. See. U.S. Pat. No. 5,749,231. The cold outlet flow of the Non-Freezing Vortex Tube is sent to an indirect contact heat exchanger where it operates to cool the separate and distinct flow of high-pressure natural gas from the transmission line or wellhead that feeds into a turbo expander and subsequently the cold box. The result is a lower gas inlet temperature at the inlet of the LNG plant, achieved without the use of any external energy source, which results in less energy use in the liquefaction/refrigeration process to reduce the natural gas temperature to −162° C. where the gas becomes liquid natural gas (LNG).
The present invention discloses several preferred embodiments of a method to minimize the external energy requirement for converting natural gas into LNG at an LNG plant located in proximity of or collocation with a natural gas pressure letdown facility (e.g., pipeline pressure regulation station or natural gas wellhead). Specifically, in a preferred embodiment, a method is disclosed whereby Non-Freezing Vortex Tubes (U.S. Pat. No. 5,749,231) with cold and hot side outlet operating under the available pressure differential at the letdown facility and fed by a portion of said facility's gas flow are arranged to feed indirect contact shell and tube style (or other indirect contact) heat exchangers. These heat exchangers work to reduce the temperature of the separate high-pressure natural gas, thus reducing the amount of energy needed to convert the gas into liquid form as compared with the prior art process shown in
The present invention will now be described in terms of the presently preferred embodiment thereof as illustrated in the drawings. Those of ordinary skill in the art will recognize that many obvious modifications may be made thereto without departing from the spirit or scope of the present invention.
The invention is associated with the operation of a natural gas pressure letdown facility (e.g., city gate station, district regulation station, or wellhead where formation gas is depressurized in a choke) where natural gas at high pressure is “letdown” to lower pressures. Upstream of a pressure letdown facility, a liquid natural gas (“LNG”) plant can be installed to utilize natural gas at a higher pressure to increase flow rate and increase the pressure differential between inlet and liquefaction pressure to achieve free cooling duty.
In a preferred embodiment of the present invention (see
A portion of high-pressure gas flow from upstream of the letdown station (112) is dried in a dryer (110) and is then directed to a HEX (111) to heat exchange with the VT cold outlet (107). The stream 114 out of the HEX (111) is high-pressure precooled liquid natural gas (“LNG”) feed gas ready for liquefaction from a lower temperature than the prior art process.
This LNG feed gas (114) then proceeds to a turbo expander where the pressure is reduced, and the temperature dropped, followed by a refrigeration cold box system to further reduce temperature such that the LNG feed gas (114) becomes LNG. This process requires a great amount of energy and the less the temperature differential between the LNG plant inlet feed gas temperature (114) and −165° C. (the temperature that natural gas turns to a liquid), the less energy that is used. The present invention dramatically reduces that inlet gas temperature to provide significant benefit to the LNG plant without any external energy source at this LNG Feed Gas Precooling stage (via chiller, refrigerator, etc.). Instead, the cooling load applied to LNG feed gas via VT 106's cold outlet 107 and heat exchanger 111 is generated by the combined Joule-Thomson and Vortex physical phenomena which take place in the VT and put into practical application by the Non-freezing Vortex Tube disclosed in U.S. Pat. No. 5,749,231. See,
The additional benefit of this preferred embodiment is the reduced energy consumption at the pipeline/wellhead pressure letdown facility in gas preheating, and reduced energy consumption in the refrigeration compressors used to bring the gas to cryogenic liquid phase. The VT (106) provided for non-freezing pressure regulation of a portion of the upstream gas (101) which otherwise would be treated in a preheater. Accordingly, there will be reduced carbon emissions in the operation of the refrigeration compressors because they will use less energy per ton of LNG produced, requiring less horsepower given the same output.
In another preferred embodiment (shown in
Another preferred embodiment (shown in
This preferred embodiment can be applied at a Letdown facility were the first VT (306) volumetric capacity is substantially smaller than the Letdown Facility main flow (301) capacity, but is large enough to apply the VT (306) cold outlet (307) (preferably, 40% to 70% of the VT 306 inlet flow) to efficiently precool its own upstream gas flow through HEX (315) as well as to feed the second VT (319). The second VT (319) volumetric capacity is also substantially smaller than the Let Down Facility main flow (301) capacity, but is large enough to apply the second VT (319) cold outlet (320) (preferably, 40% to 70% of the VT 319 inlet flow) to efficiently precool the direct LNG feed line as well as to efficiently precool the second VT (319) inlet gas in the intermediate HEX through valve (318). See,
Specifically, a first stage/upstream VT (306) connected to a source of high-pressure gas (301) and operates at a gas pressure ratio no less than two to one from inlet to outlet pressure. The cold outlet (307) of this VT (306) is split in two parts. One part goes through valve (316) and is directed to the 1st stage/upstream HEX (315) where it cools the VT (306) inlet gas line and then transmits through line (317) from HEX 315 and is dumped into the downstream low-pressure pipeline gas line. The second part of the cold stream (307) is directed to the 2nd stage/midstream HEX (322) and into the second VT (319) that operates under a gas pressure ratio no less than two to one from inlet to outlet pressure. The cold gas 320 exiting the second VT (319) is divided into two parts. One part through the valve (318) is directed to the 2nd stage/midstream HEX (322) to cool down the inlet of the second VT (319). This gas flow (323)—after passing through the 2nd stage/midstream HEX and fulfilling its thermal duties—is joined with line 317 and further, combined with the gas in line 313 and discharged into the low-pressure pipeline gas line 302. The second part of second VT (319) cold gas flow (320) is directed to the Feed Gas/Downstream HEX (311) where it cools the LNG feed gas line. The hot gas discharge from VT (306) through line 308 and second VT (319) through line 321 are delivered to the low-pressure collector line (313) and dumped into the low-pressure gas line. The LNG feed gas line taken upstream of the gas preheater (304) in line 312 is dried in a dryer (310) and then directed to the Feed Gas HEX (311) to come out as the high pressure precooled LNG feed gas that is directed to a turbo expander and liquefaction cold box refrigeration system, producing the final product of liquid natural gas (LNG). See,
Those of ordinary skill in the art will recognize that the embodiments just described merely illustrate the principles of the present invention. Many obvious modifications may be made thereto without departing from the spirit or scope of the invention as set forth in the appended claims.
This application claims priority to Provisional Application 62/738,553 filed on Sep. 28, 2018.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3892070 | Bose | Jul 1975 | A |
| 4612646 | Zerr | Sep 1986 | A |
| 5193341 | Sibbertsen et al. | Mar 1993 | A |
| 5344478 | Zurecki et al. | Sep 1994 | A |
| 5582012 | Tunkel | Dec 1996 | A |
| 5749231 | Tunkel | May 1998 | A |
| 5911740 | Tunkel | Jun 1999 | A |
| 5937654 | Tunkel | Aug 1999 | A |
| 6289679 | Tunkel | Sep 2001 | B1 |
| 6379411 | Turner et al. | Apr 2002 | B1 |
| 6442947 | Mitchell | Sep 2002 | B1 |
| 6962199 | Tjeenk | Nov 2005 | B1 |
| 7565808 | Sullivan | Jul 2009 | B2 |
| 7654095 | Sullivan | Feb 2010 | B2 |
| 9707620 | Zhu et al. | Jul 2017 | B2 |
| 9797659 | Wan et al. | Oct 2017 | B2 |
| 20020194988 | Betting et al. | Dec 2002 | A1 |
| 20060163054 | Spitzl | Jul 2006 | A1 |
| 20060230765 | Fedorov et al. | Oct 2006 | A1 |
| 20080133110 | Vetrovec | Jun 2008 | A1 |
| 20100132818 | Dell et al. | Jun 2010 | A1 |
| 20100139292 | Grand et al. | Jun 2010 | A1 |
| 20130067905 | Eckert | Mar 2013 | A1 |
| 20130186132 | Banszky | Jul 2013 | A1 |
| 20170131027 | Mak | May 2017 | A1 |
| 20170151511 | Lu | Jun 2017 | A1 |
| 20170185113 | Wang | Jun 2017 | A1 |
| 20170303433 | Delano et al. | Oct 2017 | A1 |
| 20180259227 | Tunkel | Sep 2018 | A1 |
| Number | Date | Country |
|---|---|---|
| 939115500.7 | Nov 1995 | RU |
| Entry |
|---|
| Hilsch, R., THe Use of the Expansion Gases in a Centrifugal Field as Cooling Process, Oct. 10, 1946, The Review of Scientific Instruments, vol. 18, No. 2. (Year: 1946). |
| Office Action dated May 30, 2019 in U.S. Appl. No. 15/975,951. |
| Office Action dated Nov. 1, 2018 in U.S. Appl. No. 15/975,951. |
| Office Action dated Dec. 14, 2017 in U.S. Appl. No. 14/559,334. |
| Office Action dated Jun. 30, 2017 in U.S. Appl. No. 14/559,334. |
| Number | Date | Country | |
|---|---|---|---|
| 20200103146 A1 | Apr 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62738553 | Sep 2018 | US |
