Process for producing synthesis gas

Abstract

1. A method for producing synthesis gas, comprising the steps of: a) reforming a hydrocarbon feedstock in a reforming section, thereby obtaining a synthesis gas containing CH4, CO, CO2, H2 and H2O, and impurities including ammonia; b) shifting the synthesis gas into a shifted synthesis gas in a shift section comprising one or more shift steps in succession; c) separating from said shifted syngas a process condensate resulting from cooling and optionally scrubbing said shifted syngas; d) passing the process condensate through a condensate vapor stripper using steam to strip dissolved shift by-products formed during the shift of the synthesis gas, including ammonia, methanol, and amines, from the process condensate to provide a stripper vapor stream; e) adding a portion of said stripper vapor stream from a process condensate vapor stripper to said hydrocarbon feedstock and / or to said synthesis gas downstream of said reforming section and upstream of a final shift step; wherein the remainder of the stripper vapor is purged.

Description

[Technical Field]

[0001] The present invention relates to a method for producing synthesis gas. [Background technology]

[0002] Synthesis gas is typically produced by reforming a hydrocarbon feedstock by either steam reforming (SMR), secondary reforming such as autothermal reforming (ATR), and two-stage reforming using SMR and ATR in series.

[0003] The synthesis gas exiting the reforming process contains hydrogen, carbon monoxide and carbon dioxide, along with unconverted hydrocarbons, usually methane.

[0004] The synthesis gas also contains small amounts of nitrogen which originate from the hydrocarbon feedstock or from the air used in the secondary or autothermal reformer. Summary of the Invention [Problem to be solved by the invention]

[0005] Nitrogen causes the formation of ammonia in the reforming section, which corresponds to the conditions in the final reforming step. Ammonia formation is an equilibrium reaction.

[0006] In many process applications, the carbon monoxide and carbon dioxide contained in the synthesis gas from the reforming process must be removed before the synthesis gas is introduced into the process. This is particularly true in the production of ammonia and hydrogen. [Means for solving the problem]

[0007] To this end, carbon monoxide is converted to carbon dioxide, which can be removed by known chemical or physical carbon dioxide processes.

[0008] Carbon monoxide is converted to carbon dioxide by passing the synthesis gas through a shift section where the carbon monoxide is converted to carbon dioxide by a water gas shift process.

[0009] It is well known that the shift reaction cannot be carried out without the formation of by-products. Most shift catalysts contain Cu. For these catalysts, one significant by-product formed in the shift reaction is methanol. Methanol reacts with ammonia, which is formed in the reforming process from nitrogen present in the hydrocarbon feed and / or the air mentioned above, to form amines.

[0010] Following the shift section, the shifted syngas is cooled and passed through a condenser where process condensate is separated from the shifted syngas.

[0011] The ammonia and amines contained in the shifted synthesis gas are condensed with the process condensate after the shift section.

[0012] Typically, the process condensate is sent to a medium pressure (MP) steam stripper where dissolved gases including ammonia and amines are stripped with steam, allowing the stripped condensate to pass to boiler feed water (BFW) water treatment.

[0013] Medium pressure is defined as a pressure 0.5 bar, preferably 1 bar, higher than the inlet pressure of the reforming section.

[0014] The steam leaving the steam stripper contains dissolved gases and ammonia and amine by-products. According to the present invention, a portion of this so-called stripper steam is added to the hydrocarbon feedstock and / or to the synthesis gas downstream of the reforming section and upstream of the final shift reactor. The remainder of the stripper steam is purged.

[0015] The amines react in the reforming section to form N2, CO2, CO, H2, and H2O.

[0016] Ammonia and amines added downstream of the reforming section and upstream of the last shift reactor accumulate in that section, thus causing an increase in the level of ammonia and amines in the process condensate. Newly formed ammonia is continuously introduced from the reforming section to the shift section. The formed amines and residual ammonia are removed only by the stripper steam introduced into the reforming section. The stripper steam added downstream of the reforming section does not contribute to amine removal. Its addition at this point is solely to control the steam / dry gas at the inlet of the shift section.

[0017] A problem arises when the feed steam to the reforming section has a high content of amines, as this leads to carbon formation in either the preheater or the catalyst bed in the reforming section.

[0018] The present invention solves this problem by purging a necessary portion of the stripper vapor, thereby reducing the amine level at the reforming section inlet to an acceptable level.

[0019] Accordingly, the present invention provides a method for producing synthesis gas, comprising the steps of: a) reforming a hydrocarbon feedstock in a reforming section, thereby obtaining a synthesis gas containing CH4, CO, CO2, H2 and H2O, and impurities including ammonia; b) shifting the synthesis gas into a shifted synthesis gas in a shift section comprising one or more shift steps in succession; c) separating from said shifted syngas a process condensate resulting from cooling and optionally scrubbing said shifted syngas; d) passing the process condensate through a condensate vapor stripper using steam to strip dissolved shift by-products formed during the shift of the synthesis gas, including ammonia, methanol, and amines, from the process condensate to provide a stripper vapor stream; e) adding a portion of said stripper vapor stream from a process condensate vapor stripper to said hydrocarbon feedstock and / or to said synthesis gas downstream of said reforming section and upstream of a final shift step; wherein the remainder of the stripper vapor is purged.

[0020] In one embodiment of the present invention, the condensate steam stripper is a medium pressure stripper, where medium pressure is defined as 0.5 bar, preferably 1 bar, higher than the inlet pressure of the reforming section, which allows the stripper steam to be used as process steam.

[0021] In a further embodiment, all of the stripper vapor can be introduced downstream of the reforming section upstream of the last shift reactor, with ammonia and amine accumulation in the shift section then being controlled by the flow rate of the stripper vapor purge stream.

[0022] The stripper vapor purge can be operated in a variety of ways.

[0023] In one embodiment of the present invention, the purge stripper vapor is passed to a hydrocarbon combustion step.

[0024] In this embodiment, the hydrocarbon combustion step is preferably on the fuel side of a steam reformer, or the hydrocarbon combustion step is on the fuel side of a fired heater.

[0025] Additionally, the purge stripper vapor is preferably mixed with the combustion air or hydrocarbon fuel before entering the hydrocarbon combustion step.

[0026] The amount of stripper vapor purged can be adjusted to remove all or part of the amines from the stripper stream added to the hydrocarbon feed and / or to the synthesis gas in step (e). In the case of partial removal, the remaining amines can be removed by admitting an acceptable level of amines to the reforming section via stripper vapor from the condensate vapor stripper.

[0027] The stripped condensate exits the bottom of the condensate steam stripper and is sent to water treatment. The present application relates to the invention described in the claims, but may also include the following as other aspects. 1. A method for producing synthesis gas, comprising the steps of: a) reforming a hydrocarbon feedstock in a reforming section, thereby obtaining a synthesis gas comprising CH, CO, CO, H, and H0, and impurities comprising ammonia; b) shifting the synthesis gas into a shifted synthesis gas in a shift section comprising one or more successive shift steps; c) separating from said shifted syngas a process condensate resulting from cooling and optionally scrubbing said shifted syngas; d) passing the process condensate through a condensate vapor stripper using steam to strip dissolved shift by-products formed during the shift of the synthesis gas, including ammonia, methanol, and amines, from the process condensate to provide a stripper vapor stream; e) adding a portion of said stripper vapor stream from a process condensate vapor stripper to said hydrocarbon feedstock and / or to said synthesis gas downstream of said reforming section and upstream of a final shift step; wherein the remainder of the stripper vapor is purged. 2. The method of claim 1, wherein the condensate vapor stripper is a medium pressure stripper. 3. The method according to claim 1 or 2, wherein the purge stripper vapor is passed to a hydrocarbon combustion step. 4. The method of claim 3, wherein the hydrocarbon combustion step is on the fuel side of a steam reformer. 5. The method according to claim 3, wherein the hydrocarbon combustion step is on the fuel side of a combustion heater. 6. The method according to any one of claims 3 to 5, wherein the purge stripper vapor is mixed with combustion air or hydrocarbon fuel before entering the hydrocarbon combustion step. [Example]

[0028] example See Figure 1 The flow numbers in the table below refer to the reference numbers in FIG.

[0029] Table 1 shows the case where the formed ammonia and amines are removed by converting them in the reforming section by adding 8.4% of the stripped steam to this unit.

[0030] Table 2 shows the case where 8% of the process condensate is purged to remove the ammonia and amines formed.

[0031] In both cases, there is the same buildup of ammonia and amines in the shift section, which can be reduced or eliminated by directing all stripped steam to either the reforming section or the process condensate purge.

[0032] [Table 1]

[0033] [Table 2] [Brief explanation of the drawings]

[0034]

Claims

1. 1. A method for producing synthesis gas, comprising the steps of: a) reforming a hydrocarbon feedstock in a reforming section, thereby obtaining a synthesis gas comprising CH, CO, CO, H, and H0, and impurities comprising ammonia; b) shifting the synthesis gas to a shifted synthesis gas in a shift section comprising one or more successive shift steps; c) separating from said shifted syngas a process condensate resulting from cooling and optionally scrubbing said shifted syngas; d) passing the process condensate through a condensate vapor stripper using steam to strip dissolved shift by-products formed during the shift of the synthesis gas, including ammonia, methanol, and amines, from the process condensate to provide a stripper vapor stream; e) adding a portion of said stripper vapor stream from a process condensate vapor stripper to said hydrocarbon feedstock only; wherein the remainder of the stripper vapor is purged.

2. The method of claim 1, wherein the amount of stripper vapor purged is adjusted to remove all or part of the amine from the stripper stream added to the hydrocarbon feed material in step e).

3. 3. The process of claim 1 or 2, wherein the condensate vapor stripper is a medium pressure stripper.

4. The method according to any one of claims 1 to 3, wherein the purge stripper vapors are passed to a hydrocarbon combustion step.

5. The method of claim 4 wherein the hydrocarbon combustion step is on the fuel side of a steam reformer.

6. The method of claim 4 wherein the hydrocarbon combustion step is on the fuel side of a combustion heater.

7. The method according to any one of claims 4 to 6, wherein the purge stripper vapors are mixed with combustion air or hydrocarbon fuel before entering the hydrocarbon combustion step.

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