Process and plant for the production of synthesis gas and generation of process condensate

Abstract

Process and plant for producing a synthesis gas by catalytic steam reforming of a hydrocarbon feedstock in a steam reforming unit, wherein water is removed from the synthesis gas as a process condensate, wherein boiler feed water is introduced in the process, and wherein said process or plant produces at least two separate steam streams: a pure steam which is generated from at least a portion of said boiler feed water by the cooling of synthesis gas, and a process steam which is generated by evaporating at least a portion of the process condensate by using synthesis gas, optionally together with pure steam and/or flue gas from the steam reforming unit.

Claims

1. A process for producing a synthesis gas by catalytic steam reforming of a hydrocarbon feedstock in a steam reforming unit, said steam reforming unit optionally generating a flue gas, wherein water is removed from the synthesis gas as a process condensate, wherein boiler feed water is introduced in the process, said process comprises producing at least two separate steam streams: i) a pure steam stream which is generated from at least a portion of said boiler feed water (BFW) by the cooling of synthesis gas; and ii) a process steam stream which is generated by evaporating at least a portion of the process condensate by the cooling of synthesis gas, and wherein step ii) is conducted in a process condensate boiler (PC-boiler).

2. The process according to claim 1, wherein generating the process steam stream ii) also comprises the cooling of at least a portion of said pure steam stream.

3. The process according to claim 1, wherein the steam reforming unit is an autothermal reforming (ATR) unit, or a combination of a conventional steam methane reformer (SMR) and an ATR unit, from which a raw synthesis gas is produced, and wherein said synthesis gas is a process gas produced by passing said raw synthesis gas through a catalytic water-gas shift (WGS) conversion stage comprising the use of one or more water-gas shift conversion units.

4. Process according to claim 3, wherein said one or more water-gas shift conversion units comprises using a first shift conversion unit and subsequently a second shift conversion unit and, optionally, a third shift conversion unit, and wherein said cooling of the synthesis gas in generating the process steam stream ii) is the cooling of a synthesis gas stream exiting said first or second shift conversion unit.

5. The process according to claim 3, wherein the process condensate is preheated with: pure steam used in said step ii), or a condensate thereof; and/or a portion of synthesis gas withdrawn after said WGS conversion stage.

6. The process according to claim 1, wherein a portion of the pure steam stream is used as export steam.

7. The process according to claim 1, wherein the process steam stream is mixed with the hydrocarbon feedstock prior to entering the steam reforming unit.

8. The process according to claim 1, wherein the synthesis gas is converted into a hydrogen product stream, the process condensate being generated in a process condensate separator, in which the process condensate separator also generates a water-depleted synthesis gas stream of which at least a portion is passed through a hydrogen purification stage to form the hydrogen product stream and an off-gas stream.

9. The process according to claim 2, wherein the pure steam stream after being used for generating the process steam stream, is condensed and admixed to the boiler feed water (BFW) introduced in the process.

10. A plant for producing a synthesis gas comprising: a steam reforming unit for converting a hydrocarbon feedstock into said synthesis gas and optionally generating a flue gas; a process condensate separator for removing water from said synthesis gas thereby forming a water-depleted synthesis gas stream and a process condensate stream; a boiler feed water (BFW) system comprising one or more BFW heat exchangers for generating a pure steam stream, by indirect cooling in one or more heat exchangers of said synthesis gas; a process condensate (PC) system comprising a process condensate boiler (PC boiler) for generating a process steam stream, said PC boiler comprising: a heat exchange unit for evaporating at least a portion of said process condensate stream by the cooling of synthesis gas; and optionally: a heat exchange unit for evaporating at least a portion of said process condensate stream by the cooling of at least a portion of said pure steam stream as heat exchange medium, and/or a heat exchange unit for evaporating at least a portion of said process condensate stream by the cooling of flue gas.

11. The plant according to claim 10, further comprising: one or more water-gas shift conversion units for enriching said synthesis gas in hydrogen; and a hydrogen purification unit for producing: a hydrogen product from at least a portion of said water-depleted synthesis gas stream; and an off-gas stream.

12. The plant according to claim 10, wherein the steam reforming unit is an autothermal reforming (ATR) unit, or a combination of a conventional steam methane reformer (SMR) and an ATR unit.

13. The plant according to claim 10, further comprising: process condensate pressure means for leading said process condensate stream to said process condensate boiler; a condensate pot and/or condensate drum for collecting a condensate product from said pure steam stream used during the generation of said process steam stream, and, optionally, pressurizing means for transporting and mixing said condensate product with BFW introduced in the plant.

14. The plant according to claim 10, further comprising a heat exchanger for indirect heating of the process condensate upstream said process condensate boiler.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1 shows a process plant layout where only pure steam is used for the generation of process steam in a PC boiler. The generated process steam without being mixed with pure steam, is added to the hydrocarbon feedstock for the steam reforming.

[0058] FIG. 2 shows another process layout according to an embodiment of the invention, where pure steam and synthesis gas are used for the generation of process steam in a PC boiler.

DETAILED DESCRIPTION

[0059] With reference to FIG. 1, a process plant 100 is shown, where a hydrocarbon feedstock (not shown) is catalytically reformed in a steam reforming unit such as a conventional SMR unit (not shown) for producing a raw synthesis gas 12 which passes through a first boiler feed water (BFW) preheater (heat exchanging unit) 110, thereby generating a preheated synthesis gas stream 14 that is passed through a catalytic shift conversion stage comprising in this layout one medium shift conversion unit 120. From this shift conversion unit, a synthesis gas stream 16 enriched in hydrogen is produced which is then cooled in a second BFW preheater 110′, thus creating cooled synthesis gas stream 18, which is further cooled in third BFW preheater 110″, thus generating a cooled synthesis gas stream 20. Water from the synthesis gas 20 is removed in process condensate (PC) separator 130. The process condensate is separated as stream 28, while the water depleted synthesis gas stream is withdrawn as stream 22 and subsequently passed through a hydrogen purification unit, such as a PSA-unit 140, under the formation of a hydrogen product 24 and PSA-off gas 26.

[0060] Boiler feed water (BFW) is introduced in the process/plant as BFW import stream 34 and is then used as heat exchanging medium in the third BFW preheater 110″, thus forming a first preheated BFW stream 36. This stream may be combined with condensate stream 56 (see description farther below) to form preheated BFW stream 38. Part of this preheated BFW stream 38 is then used as stream 40 in second BFW preheater 110′ and as stream 44 in first BFW preheater 110, thus generating preheated BFW streams 42, 46 which are then combined in BFW stream 48.

[0061] BFW stream 48 (saturated steam) is then used as pure steam stream 48′ and as heat exchanging medium in a PC boiler 180. In the PC boiler 180, process steam 32 is generated by evaporation of the process condensate stream 28, which is pressurized by pump 150 and first preheated in preheater (heat exchanging unit) 160 to form a preheated process condensate stream 30. The preheater 160 uses a condensate 52 of the pure steam 48′,50 which was used in the PC boiler 180, as heat exchanging medium. The condensate stream 52 is withdrawn from condensate pot 170. From condensate collector (drum) 190 the above-mentioned condensate 56 (generated from the pure steam) is pressurized and mixed with BFW stream 36.

[0062] The process/plant thus shows two separate systems: a BFW system comprising BFW heat exchangers (110, 110′, 110″) for generating a pure steam stream 48, 48′ from BFW 34 introduced in the process/plant, and a PC system comprising PC boiler 180 for generating a separate process steam stream 32, by evaporating process condensate 28 obtained from the synthesis gas. The PC boiler 180 uses the pure steam stream 48′ as heat exchange medium therein. The process steam 32, without being mixed with pure steam, is then suitably added to the hydrocarbon feedstock, e.g. natural gas, used in the steam reforming unit, e.g. conventional SMR unit, not shown.

[0063] Now with reference to FIG. 2, a process plant 200 is shown, in which PC boiler 280 includes: a heat exchange unit 280′ for evaporating process condensate stream by using pure steam as heat exchange medium, as well as a separate heat exchange unit 280″for evaporating process condensate by the cooling of synthesis gas.

[0064] As in FIG. 1, hydrocarbon feedstock (not shown) is catalytically reformed in a steam reforming unit such as an ATR unit (not shown) for producing a raw synthesis gas 212 which passes through a first boiler feed water (BFW) preheater (heat exchanging unit) 210, thereby generating a preheated synthesis gas stream 214 which is passed through a catalytic shift conversion stage comprising a first unit in the form of a MT-shift unit 220, and second unit in the form of LT-shift unit 220′.

[0065] From the first unit 220, a synthesis gas 216 is withdrawn which is then used as heat exchanging medium and thereby cooled in heat exchange unit 280″ arranged within PC boiler 280. The cooled synthesis gas is further cooled in preheater 210′ before entering the LT-shift unit 220′ thereby producing a synthesis gas enriched in hydrogen 216′. Part of this stream 216′ is divided and used to preheat, via preheater or heat exchanging unit 260, the process condensate stream 228, which is pressurized by pump 250 to the PC boiler 280.

[0066] Another part of the synthesis gas stream 216′ is further cooled in BFW preheater 210″ using BFW import stream 234 being introduced into the process. The thus further cooled synthesis gas is then combined with the cooled synthesis gas from preheater 260 and passed to PC separator 230. From the PC separator 230 a water depleted synthesis gas stream 220 is withdrawn which is finally passed to hydrogen purification unit 240, such as PSA-unit, under the formation of a hydrogen product stream 224 and PSA off-gas stream 226. The removed water in the PC separator 230 is withdrawn as said PC condensate stream 228, which results after passing through the PC boiler 280 in process steam 232. This process steam 232, without being mixed with pure steam, is then added to the hydrocarbon feedstock used in the steam reforming unit.