초록

Process and apparatus for separation of LNG allow both maximum enriching of the methane product in methane at any initial LNG composition, and to production the methane product in fully liquid state for the customer.

대표청구항 ▼

I claim: 1. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to flow in a first path in a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that

I claim: 1. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to flow in a first path in a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that has a concentration section and a stripping section, c) operating the distillation column to separate the partially vaporized initial LNG stream into a methane enriched overhead gas stream and into an ethane enriched liquid product stream, d) warming the methane enriched gas stream while flowing in a second path in the heat exchanger, e) compressing the warmed methane enriched gas stream, and cooling the compressed methane enriched gas stream to a temperature at or near ambient, f) further cooling the compressed and cooled methane enriched gas stream to liquid state while flowing in a third path in the heat exchanger, g) and distributing the compressed and liquefied methane enriched gas stream into two streams, one of which is expanded and then introduced to the top of the distillation column as a reflux, and the other of which is expanded and provided as a methane product. 2. The process of claim 1 wherein step a) includes pumping the initial LNG from a storage region to said heat exchanger. 3. The process of claim 1 wherein said ethane enriched liquid stream is removed from an intermediate tray in the distillation column, and wherein a propane-butane enriched bottom liquid is produced in the distillation column, as a propane-butane product. 4. The process of claim 1 wherein the fluid pressure in the distillation column is between 72-174 psia; an upper compressor is employed to compress the methane enriched gas stream in step e), the compressor having a discharge pressure between 174 and 363 psia. 5. The process of claim 1 wherein said other stream is derived from said one stream, within the distillation column. 6. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that has a concentration section and a stripping section, c) operating the distillation column to separate the partially vaporized initial LNG stream into a methane enriched overhead gas stream and into an ethane enriched liquid product stream, d) warming the methane enriched gas stream, e) compressing the warmed methane enriched gas stream, and cooling the compressed methane enriched gas stream to a temperature at or near ambient, f) further cooling the compressed and cooled methane enriched gas stream to liquid state, g) and distributing the compressed and liquefied methane enriched gas stream into two streams, one of which is expanded and then introduced to the top of the distillation column as a reflux, and the other of which is expanded and provided as a methane product, h) and wherein the fluid pressure in the distillation column is between 15 and 72 psia; and wherein a compressor is employed to compress the methane enriched gas stream in step e), the compressor having a discharge pressure between 58 and 174 psia. 7. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that has a concentration section and a stripping section, c) operating the distillation column to separate the partially vaporized initial LNG stream into a methane enriched overhead gas stream and into an ethane enriched liquid product stream, d) warming the methane enriched gas stream, e) compressing the warmed methane enriched gas stream, and cooling the compressed methane enriched gas stream to a temperature at or near ambient, f) further cooling the compressed and cooled methane enriched gas stream to liquid state, g) and distributing the compressed and liquefied methane enriched gas stream into two streams, one of which is expanded and then introduced to the top of the distillation column as a reflux, and the other of which is expanded and provided as a methane product, h) and wherein the step g) expansions are throttling processes, which are controlled to thereby control the relative flow distributions of said two streams. 8. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that has a concentration section and a stripping section, c) operating the distillation column to separate the partially vaporized initial LNG stream into a methane enriched overhead gas stream and into an ethane enriched liquid product stream, d) warming the methane enriched gas stream, e) compressing the warmed methane enriched gas stream, and cooling the compressed methane enriched gas stream to a temperature at or near ambient, f) further cooling the compressed and cooled methane enriched gas stream to liquid state, g) and distributing the compressed and liquefied methane enriched gas stream into two streams, one of which is expanded and then introduced to the top of the distillation column as a reflux, and the other of which is expanded and provided as a methane product, h) and wherein the composition of the initial LNG is about 0. 3% of nitrogen, about 85.8% of methane, about 9.6% of ethane, about 3% of propane, about 1% of i-butane, about 0.3% of total i-pentane and n-hexane; the composition of the methane product is about 0.34% of nitrogen, about 98% of methane, about 1.7% of ethane; and the composition of the ethane product is about 65.5% of ethane, about 24.1% of propane, about 8% of i-butane, about 2.4% of total i-pentane and n-hexane, wherein said stated percentages are mol percentages. 9. The method of claim 8 wherein the fluid pressure in the distillation column is 6 bara (87 psia); a compressor is employed to compress the methane enriched gas stream in step e), the compressor having a discharge pressure of 15 bara (217 psia); the vapor mole fraction of the partially vaporized initial LNG at introduction to the distillation column is 0.84%; the number of theoretical trays in the distillation column is 12, including 4 trays in the tower upper section, and 8 trays in the tower lower section. 10. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that has a concentration section and a stripping section, c) operating the distillation column to separate the partially vaporized initial LNG stream into a methane enriched overhead gas stream and into an ethane enriched liquid product stream, d) warming the methane enriched gas stream, e) compressing the warmed methane enriched gas stream, and cooling the compressed methane enriched gas stream to a temperature at or near ambient, f) further cooling the compressed and cooled methane enriched gas stream to liquid state, g) and distributing the compressed and liquefied methane enriched gas stream into two streams, one of which is expanded and then introduced to the top of the distillation column as a reflux, and the other of which is expanded and provided as a methane product, h) said ethane enriched stream being removed from an intermediate tray in the distillation column, and wherein a propane-butane enriched bottom liquid is produced in the distillation column, as a propane-butane product, and i) and wherein the composition of the ethane product is about 1.3% of methane, about 75.8% of ethane, about 21.9% of propane, about 1% of i-butane; the composition of the propane-butane product is about 0.2% of ethane, about 34.5% or propane, about 49% of i-butane, about 16.3% of total i-pentane and n-hexane; the number of theoretical trays in the distillation column is 12, including 4 trays in the tower upper section, 3 trays in the tower middle section, and 5 trays in the tower lower section, wherein said stated percentages are mol percentages. 11. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that has a concentration section and a stripping section, c) operating the distillation column to separate the partially vaporized initial LNG stream into a methane enriched overhead gas stream and into an ethane enriched liquid product stream, d) warming the methane enriched gas stream, e) compressing the warmed methane enriched gas stream, and cooling the compressed methane enriched gas stream to a temperature at or near ambient, f) further cooling the compressed and cooled methane enriched gas stream to liquid state, g) and distributing the compressed and liquefied methane enriched gas stream into two streams, one of which is expanded and then introduced to the top of the distillation column as a reflux, and the other of which is expanded and provided as a methane product, h) and wherein fluid pressure in the distillation column is about 1.2 bara (17 psia), the compression discharge pressure is about 6 bara (87 psia); the vapor mole fraction of the partially vaporized initial LNG at introduction to the distillation column is about 0.88; and the number of theoretical trays in the distillation column is 12, including 4 trays in a tower upper section, and 8 trays in tower lower section. 12. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that has a concentration section and a stripping section, c) operating the distillation column to separate the partially vaporized initial LNG stream into a methane enriched overhead gas stream and into an ethane enriched liquid product stream, d) warming the methane enriched gas stream, e) compressing the warmed methane enriched gas stream in a methane compressor having a discharge pressure, and cooling the compressed methane enriched gas stream to a temperature at or near ambient, f) further cooling the compressed and cooled methane enriched gas stream to liquid state, g) and distributing the compressed and liquefied methane enriched gas stream into two streams, one of which is expanded and then introduced to the top of the distillation column as a reflux, and the other of which is expanded and provided as a methane product, h) and wherein the methane compressor discharge pressure decreases. 13. A process for enriching LNG in methane, comprising the steps: a) feeding an initial LNG stream to flow in a first path in a heat exchanger wherein the LNG stream partially vaporizes, b) feeding the partially vaporized initial LNG stream into a middle region of a distillation column that has a concentration section and a stripping section, c) operating the distillation column to separate the partially vaporized initial LNG stream into a methane enriched overhead gas stream and into an ethane enriched liquid product stream, d) warming the methane enriched gas stream while flowing in a second path in the heat exchanger, e) compressing the warmed methane enriched gas stream, and cooling the compressed methane enriched gas stream to a temperature at or near ambient, f) further cooling the compressed and cooled methane enriched gas stream to liquid state while flowing in a third path in the heat exchanger, g) and distributing the compressed and liquefied methane enriched gas stream into two streams, one of which is expanded and then introduced to the top of the distillation column as a reflux, and the other of which is expanded and provided as a methane product, h) and wherein said other stream is derived from said one enriched liquefied gas stream by separation in the column, and prior to said expansion of said other stream.