Apparatus and process for removal of heavy hydrocarbons from a feed gas
An apparatus and process for removal of heavy hydrocarbons (e.g., hydrocarbons that include five or more carbons such as pentane and hexane, etc.) from a feed (e.g., a feed comprised of methane and impurities) can include a scrub column and a stabilizer column arranged so that a portion of a first stream output from the stabilizer column is fed to the scrubber column to function as a reflux stream. Embodiments are provided in which the scrub column produces a stream comprising mostly methane (e.g. over 85 mole percent methane) and reduced heavy hydrocarbons so that reduced operational costs and improved operational flexibility can be realized in downstream natural gas liquefaction operations.
1 . An apparatus for removal of heavy hydrocarbon impurities from a feed comprising methane gas and hydrocarbons having at least five carbon atoms, the apparatus comprising:
a scrub column positioned and configured to receive the feed and output a first scrub column stream and a second scrub column stream, the second scrub column stream comprising the hydrocarbons having at least five carbon atoms,
a stabilizer column positioned downstream of the scrub column to receive the second scrub column stream and configured to output a first stabilizer column stream and a second stabilizer column stream, the second stabilizer column stream comprising the hydrocarbons having at least five carbon atoms,
a phase separator positioned to receive the first stabilizer column stream and output a vapor stream and a liquid stream, and
a heat exchanger positioned to receive the vapor stream from the phase separator and a first portion of the liquid stream from the phase separator;
wherein the scrub column is positioned such that a portion of the first stabilizer column stream is fed to the scrub column as a scrub column reflux stream;
wherein the portion of the first stabilizer column stream that is fed to the scrub column as the scrub column reflux stream comprises the vapor stream from the phase separator and the first portion of the liquid stream from the phase separator;
wherein the heat exchanger is configured and positioned to cool a first portion of the feed before the feed is fed to the scrub column;
wherein the scrub column is positioned so that a third portion of the feed is passed through a side reboiler of the scrub column to cool that portion of the feed; and
wherein the heat exchanger and the scrub column are positioned such that the third portion of the feed cooled in the side reboiler is combined with the first portion of the feed and fed to the scrub column.
2 . The apparatus of claim 1 , comprising:
a reflux accumulator vessel positioned to receive the scrub column reflux stream, store the scrub column reflux stream, feed the scrub column reflux stream to the scrub column.
3 . The apparatus of claim 2 , wherein:
the heat exchanger is positioned to receive the first scrub column stream from the scrub column, and cool the scrub column reflux stream before the scrub column reflux stream is fed to the reflux accumulator vessel.
4 . The apparatus of claim 1 , comprising:
the heat exchanger is positioned to receive the first scrub column stream from the scrub column, and cool the scrub column reflux stream before the scrub column reflux stream is fed to the scrub column.
5 . The apparatus of claim 1 , wherein the scrub column is positioned so that the third portion of the feed passed through the side reboiler of the scrub column heats liquid from the scrub column to form a stripping vapor, the side reboiler positioned to output the stripping vapor to the scrub column.
6 . The apparatus of claim 1 , further comprising:
a reflux accumulator vessel positioned to receive the portion of the first stabilizer column stream that is fed to the scrub column, store the scrub column reflux stream, and feed the scrub column reflux stream to the scrub column; and
a pump positioned to drive the flow of the scrub column reflux stream from the reflux accumulator vessel to the scrub column;
wherein the stabilizer column is configured to operate at a pre-selected stabilizer column operational pressure range, and the scrub column is configured to operate at a pre-selected scrub column operational pressure range that is greater than the pre-selected stabilizer column operational pressure range.
7 . The apparatus of claim 1 , wherein:
the heat exchanger is configured and positioned to cool the scrub column reflux stream before the scrub column reflux stream is fed to the scrub column.
8 . The apparatus of claim 7 , further comprising:
a reflux accumulator vessel positioned to receive the scrub column reflux stream from the heat exchanger, store the scrub column reflux stream, and feed the scrub column reflux stream to the scrub column; and
a pump positioned to drive the flow of the scrub column reflux stream from the reflux accumulator vessel to the scrub column;
wherein the stabilizer column is configured to operate at a pre-selected stabilizer column operational pressure range, and the scrub column is configured to operate at a pre-selected scrub column operational pressure range that is greater than the pre-selected stabilizer column operational pressure range.
9 . A process for treating a feed gas comprising methane and hydrocarbons having at least five carbon atoms, the process comprising:
providing the feed gas to a scrub column operating at a pre-selected scrub column operational pressure range to output a first scrub column stream and a second scrub column stream from the scrub column, the second scrub column stream comprising the hydrocarbons having at least five carbon atoms;
feeding the second scrub column stream to a stabilizer column operating at a pre-selected stabilizer column operational pressure range to output a first stabilizer column stream and a second stabilizer column stream, the second stabilizer column stream comprising the hydrocarbons having at least five carbon atoms;
providing a portion of the first stabilizer column stream to the scrub column to provide a scrub column reflux stream to the scrub column;
splitting the feed into a first portion, a second portion, and a third portion, feeding the first portion to a heat exchanger positioned upstream of the scrub column, mixing the first portion exiting the heat exchanger with the second portion before providing a stream comprising the first and second portions to the scrub column; and
feeding the third portion to a side reboiler to form a stripping vapor, and feeding the stripping vapor to the scrub column,
wherein the process comprises mixing the third portion with
the second portion and the first portion before the first portion, second portion, and third portion of the feed are fed to the scrub column,
the second portion before the first portion, second portion, and third portion of the feed are fed to the scrub column, or
the first portion before the first portion, second portion, and third portion of the feed are fed to the scrub column.
10 . The process of claim 9 , comprising:
feeding the first stabilizer column stream to a phase separator to form a vapor stream and a liquid stream;
feeding the vapor stream and a portion of the liquid stream to a heat exchanger to form the scrub column reflux stream;
feeding the scrub column reflux stream from the heat exchanger to a reflux accumulator vessel; and
feeding the scrub column reflux stream from the reflux accumulator vessel to an upper section of the scrub column.
11 . The process of claim 10 , comprising:
feeding the first scrub column stream to the heat exchanger as a cooling medium to cool the vapor stream and the portion of the liquid stream fed to the heat exchanger to form the scrub column reflux stream.
12 . The process of claim 9 , wherein the pre-selected scrub column operational pressure range is between 45 bara and 65 bara, and the pre-selected stabilizer column operational pressure range is between 15 bara and 30 bara.
13 . The process of claim 9 , comprising:
mixing the third portion with the second portion and the first portion before the first portion, second portion, and third portion of the feed are fed to the scrub column.
14 . The process of claim 9 , wherein the pre-selected stabilizer column operational pressure range is lower than the pre-selected scrub column operational pressure range.
15 . The process of claim 9 , comprising:
mixing the third portion with the second portion before the first portion, second portion, and third portion of the feed are fed to the scrub column.
16 . The process of claim 9 , comprising:
mixing the third portion with the first portion before the first portion, second portion, and third portion of the feed are fed to the scrub column.