US-12617676-B2 - Process and plant for the production of synthesis gas and generation of process condensate

US12617676B2US 12617676 B2US12617676 B2US 12617676B2US-12617676-B2

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.

Inventors

Steffen Spangsberg CHRISTENSEN
Nitesh BANSAL

Assignees

TOPSOE A/S

Dates

Publication Date: 20260505
Application Date: 20210317
Priority Date: 20200522

Claims (13)

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 comprising 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 the 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 the synthesis gas, wherein the process steam stream is generated in a process condensate boiler (PC-boiler), wherein generating the process steam stream also comprises the cooling of at least a portion of said pure steam stream.
2 . 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.
3 . The process according to claim 2 , 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 is the cooling of a synthesis gas stream exiting said first or said second shift conversion unit.
4 . The process according to claim 2 , wherein the process condensate is preheated with: pure steam used for generating the process steam stream, or a condensate thereof; and/or a portion of synthesis gas withdrawn after said WGS conversion stage.
5 . The process according to claim 1 , wherein a portion of the pure steam stream is used as export steam.
6 . The process according to claim 1 , wherein the process steam stream is mixed with the hydrocarbon feedstock prior to entering the steam reforming unit.
7 . 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.
8 . The process according to claim 1 , 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.
9 . The process according to claim 1 , wherein the steam reforming unit is a steam methane reformer (SMR).
10 . The process according to claim 9 , wherein the steam methane reformer (SMR) is a tubular reformer.
11 . The process according to claim 9 , wherein a raw synthesis gas is produced from the steam methane reformer (SMR), 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.
12 . The process according to claim 11 , 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 is the cooling of a synthesis gas stream exiting said first or said second shift conversion unit.
13 . The process according to claim 11 , wherein the process condensate is preheated with: pure steam used for generating the process steam stream, or a condensate thereof; and/or a portion of synthesis gas withdrawn after said WGS conversion stage.

Description

FIELD OF THE INVENTION The present invention relates to a process and plant for producing a synthesis gas and/or a hydrogen product under the production of process steam originating from process condensate formed during the process, and which may be consumed internally in the process or plant, and pure steam as export steam which is generated from boiler feed water by the cooling of synthesis gas. BACKGROUND OF THE INVENTION In processes and plants for producing of synthesis gas (syngas), i.e. a gas rich in hydrogen and carbon monoxide, the synthesis gas can be further used in the production of valuable intermediate or end products, for instance hydrogen. The synthesis gas is normally produced by so-called catalytic steam methane reforming and/or autothermal reforming. As a result of steam methane reforming, the synthesis gas (syngas) contains water which typically needs to be removed. The removal of water is normally conducted in a separator under the generation of a process condensate (PC) stream and a water-depleted synthesis gas stream. Also, as part of the process, boiler feed water (BFW) is used to indirectly cool the produced synthesis gas by means of so-called BFW-preheating units. The BFW is thereby transformed into a saturated steam, also denoted as pure steam. This pure steam is normally free of impurities, i.e. contaminants, generated during the process such as carbon dioxide, methanol, ammonia and acetic acid, and thus this pure steam is suitable for use as export steam, since customers usually demand a high steam quality. On the other hand, such contaminants albeit in small amounts are present in the process condensate, so steam generated from this stream is not suitable for use as export steam. Normally, process condensate is stripped with steam in a PC-stripper. The stripped process condensate is mixed with BFW and used for steam production and export steam. The stripped process condensate still contains small amounts of impurities which may contaminate the generation of pure steam. US 2005/0288381 A1 discloses a method of recycling process stream condensate from a steam reforming system. Process steam is generated in a PC-boiler by heat exchange with a portion of pure steam generated in a separate steam production system. The process steam and the other portion of the pure steam are then combined and used to form a hydrocarbon/steam stream as feed for the steam reforming. EP 3235785 A1 discloses a process in which process condensate is evaporated to form process steam by using a portion of the generated pure steam. For the generation of the pure steam, synthesis gas and flue gas from the steam reforming process is used. EP 3235784 A1 is similar to EP 3235785 A1 and discloses a process in which process steam is generated by evaporating process condensate using pure steam as the heat exchanging medium. GB 2006814 A discloses a process in which process steam is generated by a process condensate passing to circulation heating unit using pure steam as heat exchanging medium. U.S. Pat. No. 9556026 discloses a process in which process steam is generated by heat exchange with synthesis gas of a water condensate in serially arranged heat exchanger units, and subsequently passing the thus preheated water condensate to a steam drum to make the process steam using flue gas from a steam methane reformer as heat exchanging medium. The prior art does not disclose combining in a single step the use of synthesis gas formed by steam reforming optionally together with pure steam and/or flue gas from steam reforming, for evaporating the process condensate. SUMMARY OF THE INVENTION It is an object of the present invention to avoid contamination of a pure steam generated from boiler feed water with impurities from a process condensate stream formed during the process. It is another object of the present invention to provide a simpler and more flexible process and plant for generation of pure steam and process steam. These and other objects are solved by the present invention. Accordingly, in a first aspect the invention is a process for producing a synthesis gas by catalytic steam reforming of a hydrocarbon feedstock in a steam reforming unit, said 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, and wherein said process produces 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). In an embodiment according to the first aspect of the invention, step ii) also comprises the cooling of at least a portion of said pure steam stream, and/or the cooling of said