Implications of sensor location in steam reformer temperature control

Hydrogen can be produced via steam reformation of many feedstocks. External heat sources provide the thermal energy required by the endothermic steam reformation reactions. Temperature control of the steam reformation reactor is critical to reactor performance and catalyst life. Closed-loop control systems are typically used to modulate the heat input rate based on a comparison between a set point temperature and a temperature measurement. The location of the temperature sensor relative to the heat input location is a choice made during reactor design that can have significant impact on reactor temperature control. In this paper we present an analysis of temperature data for an operating tubular methanol steam reformation reactor with 4 zones of discrete heating. We compare the temperature fluctuations measured using a feedback temperature sensor at the centerline farthest from the heat input, at the interior surface closer to the heat input, and at the exterior surface of the reactor tube in contact with the heat source. Temperature sensor locations at the centerline result in large temperature overshoot at the periphery of the catalyst bed near the heat input location, as well as large temperature fluctuations throughout the catalyst bed. Temperature sensor locations near the heat source result in reduced temperature fluctuations throughout the catalyst bed with virtually no temperature overshoot at any location. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.