Patent EA-002731-B1 (EA)
Title: Process and apparatus for gas purification and products obtained therefrom
Inventor: PARADOWSKI HENRI
IPC: B01D53/14
Filed: 2000-07-27
Abstract: 1. A process for purification of a source gas, in particular natural gas (GN), containing C1-C5  and heavier hydrocarbons in order to eliminate volatile mercaptan sulfur compounds without the use of gas adsorption or cryogenic expansion processes, for example in turbo-expander, wherein comprising cooling and partially drying a source gas (1), supplying the source gas to an absorption column (4) under pressure, the absorption column receiving a reflux fluid (5) and producing, as a head product (6), a purified gas with a mercaptan level of less than 30 parts per million, and a base product (13) supplied to a fractionating column (15) which separates the most volatile compounds (16) of the source gas, free from mercaptans, from a gasoline fraction (29) withdrawn from a base and containing mercaptans, the most volatile mercaptans being eliminated at the head (32,49) of at least one distillation column (31,48) producing a base end product (63) consisting of liquid gasoline with a mixture of C5 hydrocarbons and heavier hydrocarbons that, after a sweetening process so as to no longer contain volatile mercaptans (16,23), are mixed with the most volatile compounds (16,23) separated at a top of the fractionating column (15) and recompressed (24) from the source gas, to produce a mixture, cooling (72,2b) the mixture, and sending the mixture by reflux (5) to the absorption column (4) as the reflux fluid. 2. The process according to claim 1 wherein a principal stream of source gas (1) is subdivided into two parallel bypass streams (1a,1b), a first of which (2a) is cooled and supplied to a lower section of the absorption column (4), and a second of which (1b) is cooled and supplied to an intermediate zone of the absorption column (4). 3. The process according to claim 1or 2 wherein the base product of the absorption column, containing C2 hydrocarbons and heavier hydrocarbons and mercaptans, is expanded (14) before being supplied to the fractionating column (15) for separation of mercaptans from the most volatile compounds of the source gas. 4. The process according to claim 3 including expanding and supplying a base product (29) of the fractionating column (15), containing C3 hydrocarbons and heavier hydrocarbons and mercaptans, to a first gasoline distillation column (31), functioning as a depropanizer, and producing a base product (46) containing C4 hydrocarbons and heavier hydrocarbons and mercaptans. 5. The process according to any of claim 1 to 4 wherein a base product (46) of a first distillation column (31) contains C4 hydrocarbons and heavier hydrocarbons and mercaptans, including expanding and supplying the base product of the first distillation column to a second gasoline distillation column (48), functioning as a debutanizer, and producing a base product (63) containing the residual gasoline fraction consisting of C5 hydrocarbons and heavier hydrocarbons and mercaptans. 6. The process according to claim 4 including cooling a head product (16) of said fractionating column (15), free from mercaptans and containing C1, C2, and C3 hydrocarbons, by partial condensation and separating (20) the base product into a liquid phase (21) sent to said fractionating column (15) and a gaseous phase (23) which is recompressed (24) before being mixed (71) with at least a part of distallation end product of the gasoline fraction the other part is being recovered. 7. The process according to any of claim 1 to 6 including cooling a head product (32) of a first distillation column (15), containing C3 hydrocarbons and methylmercaptan, by complete condensation and separating the head product of the first distillation column into two partially liquid streams (35, 37), one of which (35) is sent to a head of the first distillation column (31) and the other of which (37) undergoes a sweetening process (39) to eliminate on one hand methylmercaptan in particular in a mixture with a sweetening agent to obtain a mixture of C3 (41) hydrocarbons free from mercaptans on the other hand. 8. The process according to any of claims 1 to 7 including cooling a head product (49) of a second distillation column (48), containing C4 hydrocarbons and residual volatile mercaptans, by complete condensation and separating the head product of the second distillation column into two partially liquid streams (52, 54), one of which (52) is sent to a head of the second distillation column (48) and the other of which (54) undergoes a sweetening process to eliminate on one hand residual volatile mercaptans (57) to obtain a mixture of C4 hydrocarbons (58) free from mercaptans. 9. The process according to any claims 1 to 8 including cooling (2b) the stream of source gas (1) and the reflux gas (5) with gas (6) emitted at a head of the absorption column (4) and, if necessary, with an auxiliary cooling fluid (7), such as propane, including reheating the gas emitted from the absorption column(4) by thermal exchange until close to room temperature. 10. An apparatus for the implementation of the process according to any of claims 1 to 9 comprising a compressor, a gasoline distillation column, a fractionating column, and an absorption column (4) to which are successively connected supply pipes for the source (1a,1b) and reflux gases (5), a main supply pipe (1) for the source gas (GN) branching into two bypass lines (1a,1b), one of which (1b), along with a reflux pipe (5), passes through a heat exchanger (2b), and wherein a head of the absorption column is connected to an output pipe for the process gas passing through the heat exchanger, the absorption column having a base (4) connected by a pipe to the fractionating column (15), a base of the fractionating column (15) being connected by a pipe (29) to at least one of the gasoline distillation columns (31,48) which has a base connected by an outlet pipe (63,66,70) to a delivery pipe (23) of the compressor (24) connected by pipe (16,23) to a head of the fractionating column (15), the outlet pipe (63,66,70) and the delivery pipe (23) joining (71) at the reflux pipe (5). 11. The apparatus according to claim 10 wherein the head of the fractionating column (15) is connected by a pipe (16) passing through a cooler-condenser (17) to an inlet of a phase separator (20) having a gas phase outlet (23) connected to the compressor (24) and having a liquid phase outlet (20) linked to an upper section of the fractionating column (15). 12. The apparatus according to claim 11 wherein the gasoline distillation comprises first and second gasoline distillation columns (31,48) connected in series having respective heads each connected through a cooler-condenser (33,50) to an inlet of a condensate reservoir (34,51) having on one hand an outlet opening into a return pipe (35,52) at an upper section of a corresponding gasoline distillation column (31,48) and on the other hand into a header pipe (37,54). 13. The apparatus according to claim 12 wherein the header pipe (37), linked to the first gasoline distillation column (31), opens at an inlet of a sweetening apparatus (31) having an outlet connected to a C3 hydrocarbon reservoir whilst the header pipe (54) linked to the second gasoline distillation column (48) opens into a C4 hydrocarbon sweetening system (56). 14. The apparatus according to any of claims 10 to 13 including a bypass line (68) for C5 hydrocarbons and heavier hydrocarbons connected to an outlet pipe (63) at a base of the second gasoline distillation column (48).