Precautions for commissioning a hydrogen production plant

Different design institutes use different processes for design; some allow the two systems to be heated in a sequential manner, while others only enable a single cyclic operation of the entire system, without allowing separate cycling of the two systems. For the initial start-up of hydrogen production, if the pre-sulfurization of the hydrogenation catalyst and the reduction of the converter catalyst are carried out separately, it is possible to consider circulating heat in two separate systems; this not only speeds up the process but also allows plants that lack a hydrogen source and need to start up through ammonia cracking to use the ammonia produced by ammonia cracking in the converter as a hydrogen source for the pre-sulfurization of the hydrogenation catalyst. However, there is a problem: when a cycle is formed during the conversion process, the inlet temperature for conversion may become too low, as reducing the conversion catalyst requires an inlet temperature of over 480 degrees. The heating cycles for each of the two systems are somewhat more complex; it is necessary to prevent interference between them. Additionally, when introducing raw materials to produce hydrogen, it is required to disconnect the two systems, which makes the process more complicated and prone to errors. If normal operation is carried out without the need for catalyst reduction or pre-sulfurization, the temperature can be increased in a cyclic manner within one system; this simplifies the process, as only one compressor is required (which saves energy and provides a spare compressor as well). It is easy to raise the temperature at the inlet of the conversion unit, and making adjustments to the process when using raw materials to produce hydrogen is simple and straightforward. However, there is a potential risk: if there are still some hydrocarbons remaining in the desulfurization system, it may cause carbon deposition on the conversion catalyst before steam is supplied. This post was last edited by laiquanchang on 2009-4-5 19:58]

The issue of raising the temperature during startup is somewhat complex: whether it is the first time starting up or restarting after a shutdown, whether the conversion catalyst is in a pre-reduced state or a state awaiting reduction, and what medium should be used for reduction, among other factors. In practice, however, two-stage circulation is generally used to raise the temperature; if there is a problem with not being able to increase the temperature at the inlet of the conversion process, it is possible to reduce the circulation rate to the lowest allowable level for the hydrogen-to-catalyst ratio.

The feedstock hydrogenation crew should monitor the isothermal and adiabatic hydrogenation reactors as well as the desulfurization reactor. The degree of hydrogenation should be adjusted based on the properties of the feedstock and the analysis results regarding the olefin content and sulfur content after hydrogenation, in order to ensure that all parameters of the feed gas entering the conversion furnace are within acceptable limits and to protect the catalysts. Understanding the impact of changes in raw material properties on hydrogenation systems enables quick and accurate identification of such changes as well as the appropriate treatment methods. Be familiar with the methods for handling hydrogenation reaction systems in emergency situations to protect the conversion catalyst.