METHOD FOR STABLE OPERATION OF A STEAM REFORMING SYSTEM

Abstract

A method can be employed to regulate and stably operate a steam reforming system that is operated by steam reforming, that has a capacity utilization level that can be regulated, and that comprises a steam reformer, a hydrogenating and desulfurizing unit that is positioned upstream of the steam reformer and is configured for feedstock desulfurization, and a firing unit of the steam reformer. According to the method, a mandated capacity utilization level for the steam reforming system is established with automated regulation of the following continuously monitored parameter ratios: a hydrogen-to-feedstock ratio in the hydrogenating and desulfurizing unit, a steam-to-carbon ratio in the steam reformer, and a fuel-to-air ratio in the firing unit of the steam reformer.

Claims

1.-11. (canceled)

12. A method for regulating and stably operating a steam reforming system whose capacity utilization level is regulatable, with the steam reforming system comprising a steam reformer, a hydrogenating and desulfurizing unit positioned upstream of the steam reformer and configured for feedstock desulfurization, and a firing unit of the steam reformer, the method comprising establishing a mandated capacity utilization level for a production system with automated regulation of the following continuously monitored parameter ratios: a hydrogen-to-feedstock ratio in the hydrogenating unit; a steam-to-carbon ratio in the steam reformer; a fuel-to-air ratio in the firing unit of the steam reformer.

13. The method of claim 12 comprising: for a hydrogen stream and a feedstock stream to be introduced into the hydrogenating and desulfurizing unit, calculating setpoint values that produce the desired hydrogen-to-feedstock ratio as a function of the mandated capacity utilization level; adjusting the hydrogen stream to the respective setpoint value in advance of the feedstock stream to raise the capacity utilization level of the steam reforming system; and adjusting the feedstock stream to the respective setpoint value in advance of the hydrogen stream to lower the capacity utilization level of the steam reforming system.

14. The method of claim 12 comprising adjusting the hydrogen-to-feedstock ratio based on molar flow rates to a value in a range from 0.01 to 0.60.

15. The method of claim 12 comprising: for a steam stream and a feedstock stream, calculating setpoint values that produce the desired steam-to-carbon ratio as a function of the mandated capacity utilization level; adjusting the steam stream to the respective setpoint value in advance of the feedstock stream to raise the capacity utilization level of the steam reforming system; and adjusting the feedstock stream to the respective setpoint value in advance of the steam stream to lower the capacity utilization level of the steam reforming system.

16. The method of claim 12 comprising adjusting the steam-to-carbon ratio based on molar flow rates to a value in a range from 2.0 to 4.0.

17. The method of claim 12 comprising determining an amount of carbon carried by a feedstock into the steam reformer based on its molar mass fraction in the feedstock.

18. The method of claim 12 comprising determining an amount of carbon carried by a feedstock into the steam reformer based on a gas chromatography measurement or based on sampling and evaluation.

19. The method of claim 12 comprising: for an air stream and a fuel stream, calculating setpoint values that produce the desired fuel-to-air ratio as a function of the mandated capacity utilization level; adjusting the air stream to the respective setpoint value in advance of the fuel stream to raise the capacity utilization level of the steam reforming system; and adjusting the fuel stream to the respective setpoint value in advance of the air stream to lower the capacity utilization level of the steam reforming system.

20. The method of claim 12 wherein the capacity utilization level of the steam reforming system is 30% to 100%.

21. The method of claim 12 comprising changing at least one of the continuously monitored parameter ratios with defined permissible rates of change.

22. The method of claim 12 comprising calculating a time profile for a setpoint value of a steam stream to be introduced into the steam reformer as a function of a time profile of a feedstock stream in the hydrogenating and desulfurizing unit and as a function of a system-specific transit time between the hydrogenating and the sulfurizing unit and the steam reformer.

Description

[0030] The invention is described below by means of working examples, with reference to the appended figures, in which:

[0031] FIG. 1 shows a schematized representation of the method of the invention in the case of a rising capacity utilization level, and

[0032] FIG. 2 shows a schematized representation of the method of the invention in the case of a falling capacity utilization level.

[0033] FIG. 1 represents a working example of the method of the invention, in which a steam reforming system is regulated in the case of a rising capacity utilization method and hence a rising production of hydrogen, where the sequence of the changes of the respective variables is also taken into account in order to improve further the stability of operation of the system.

[0034] In one step the feedstock is prepared by hydrogenation in the hydrogenating stage and thereafter in the desulfurizing unit 1, by implementation of the hydrogenation at a specific hydrogen-to-feedstock ratio 2. In order to establish this feedstock-dependent ratio, the setpoint values of the hydrogen stream and of the feedstock stream, 3, are calculated as a function of the mandated capacity utilization level, which is typically raised on the user side (for example, manually or on the basis of the product delivery pressure). First of all the hydrogen stream is adjusted 4. This is followed by adjustment of the feedstock stream 5, in order to preserve the desired hydrogen-to-feedstock ratio. The hydrogen stream 4 is therefore adjusted in advance of the adjustment of the feedstock stream 5. Adjustment of the feedstock stream 5 here preferably begins before the setpoint value of the hydrogen stream has been reached. In this way the desired hydrogen-to-feedstock ratio 2 is established.

[0035] In a further step, in the steam reformer 6, the setpoint values of the steam stream and of the carbon stream 8 for the target capacity utilization level are first calculated, before entry into the steam reforming procedure, in order to ensure the proper functioning thereof, by establishment of a specific steam-to-carbon ratio 7. The amount of the carbon carried in by the feedstock here may be ascertained on the basis of its molar mass fraction in the feedstock, through suitable measurements—for example, a gas chromatography measurement, or by sampling and evaluation in the laboratory. Subsequently, the calculated steam stream 9 first, and thereafter the corresponding feedstock stream 10 for establishing the desired ratio, are adjusted. The steam stream 9 is therefore adjusted in advance of the adjustment of the feedstock stream 10. The adjustment of the steam stream 9 here begins preferably before the setpoint value of the feedstock stream 10 has been reached.

[0036] In order to ensure that the prescribed sequence is observed, provision may be made to calculate a time profile for the setpoint values of the feedstock streams and steam streams to be introduced into the steam reformer, as a function of the time profile of the feedstock stream in the hydrogenating and desulfurizing unit and of a system-specific transit time between the hydrogenating and desulfurizing unit and the steam reformer.

[0037] In a third step, in the firing unit 11 of the steam reformer 6, a specific fuel-to-air ratio 12 is established as a function of the capacity utilization level, by first calculating the setpoint values of the air stream and fuel stream 13. Subsequently, the calculated air stream 14 first, and thereafter the corresponding fuel stream 15 for establishing the desired ratio, are adjusted.

[0038] FIG. 2 describes the case, opposite to that of FIG. 1, of a falling capacity utilization level or a falling hydrogen production. It is essential here that the sequence of the adjustments to the respective streams is switched in comparison to the case shown in FIG. 1, in order to achieve the target degree of system stability.

[0039] It would be appreciated that the method steps described in the context of the working examples, concerning the sequence of the changing of the streams, can be employed not only in the entirety described (that is, in all three method steps), but also only in one or two of the three method steps described, with the application of all the method steps being preferred in terms of the assurance of system stability.

LIST OF REFERENCE NUMERALS

[0040] 1 Hydrogenating and desulfurizing unit [0041] 2 Hydrogen-to-feedstock ratio [0042] 3 Setpoint values of the hydrogen stream and the feedstock stream [0043] 4 Adjustment of the hydrogen stream [0044] 5 Adjustment of the feedstock stream [0045] 6 Steam reformer [0046] 7 Steam-to-carbon ratio [0047] 8 Setpoint values of the steam stream and the carbon stream [0048] 9 Adjustment of the steam stream [0049] 10 Adjustment of the feedstock stream [0050] 11 Firing unit [0051] 12 Fuel-to-air ratio [0052] 13 Setpoint values of the air stream and fuel stream [0053] 14 Adjustment of the air stream [0054] 15 Adjustment of the fuel stream