Process for LPG recovery
Process and plant for recovering LPG in a refinery process combining the use of sponge absorber, deethanizer and debutanizer. The process and plant enable high LPG recovery and removal of hydrogen sulphide in the LPG product to low levels.
1. A process for recovering LPG from a fractionation section of a refinery process comprising the steps of:
(a) passing a feed stream comprising a stripper overhead product through a sponge absorber, and separating an off-gas stream from a top section of the sponge absorber and a light oil stream from a bottom section of the sponge absorber; and
(b) fractionating the light oil stream into:
(i) an overhead vapour in the form of a C 3 stripped stream comprising less than 20% butane or propane, without condensing and without recycling of condensed overhead vapour in the fractionating step;
(ii) a LPG product stream; and
(iii) a stabilized naphtha stream.
2. The process according to claim 1 further comprising mixing at least a portion of the C 3 stripped stream of step (b) with the stripper overhead product to form the feed stream of step (a).
3. The process according to claim 1 further comprising mixing a portion of the stabilized naphtha stream of step (b) with the off-gas stream of step (a).
4. The process according to claim 1 in which step (b) comprises the sub-steps:
(b1) fractionating the light oil stream in a deethanizer column, and separating the overhead vapour in the form of the C 3 stripped stream from a top section of the deethanizer column;
(b2) fractionating a stream from a bottom section of the deethanizer column in a debutanizer column, separating the LPG product stream from a top section of the debutanizer column, and the stabilized naphtha stream from a bottom section of the debutanizer column.
5. The process according to claim 4 further comprising using a portion of vapour from the debutanizer column as stripping vapour for the deethanizer column.
6. The process according to claim 5 further comprising feeding the vapour from the debutanizer column to the bottom section of the deethanizer column.
7. The process according to claim 1 , in which step (b) is conducted in a single column in the form of a dividing wall column.
8. The process according to claim 7 in which the dividing wall is provided at the upper section of the column.
9. The process according to claim 1 in which the refinery process is:
hydroprocessing comprising hydrocracking, crude distillation, fluid catalytic cracking, or delayed coking.
10. The process of claim 1 , wherein the only off-gas from the process for recovering LPG is taken from the off-gas stream of the sponge absorber.
11. The process of claim 1 , comprising mixing the entire C 3 stripped stream of step (b) with stripper overhead product to form the feed stream of step (a).