A rigorous mathematical model for online prediction of tube skin temperature in an industrial top-fired steam methane reformer

During the steam reformer operation, monitoring of tube skin temperature is extremely important to any program concerned with maximizing furnace tube life and maintaining safe furnace operation. It can also be an important tool in troubleshooting, debottlenecking and optimizing the plant's operations. As a result of having reliable tube skin temperature data, the heat flux profile can be adjusted to correct the unit performance for prevention of overheating, hot spots formation and thermal aging of tubes and pigtails before failure. The present study details a rigorous and reliable online model to predict the skin temperature of tubes in an industrial top-fired primary reformer. The model is designed to run online and has a solution time of less than 1.5 min starting from a poor initial guess that can be determined automatically from plant data. The model predicts the most important variables such as heat flux, composition and conversion profiles along the tube length, process gas temperature, maximum tube-wall temperature and tube pressure drop based on considering mass transfer limitation in catalyst pellets using a one-dimensional heterogeneous model. The predictions of model were compared with two previously reported works and operating data from the top-fired steam reformer of an industrial ammonia plant under normal conditions which showed a well compatibility. The model results demonstrated a maximum skin temperature of 905 degrees C at location 2.6 m from top of tube length at plant rates greater than 90% of full capacity. Applying the model in the plant to adjust the tube skin temperature resulted in 605.4 Nm(3)/h of natural gas fuel saving. The outcome from this work is not only valuable in terms of operation, but can also prevents the overheating and failure of tubes and pigtails which extends the life of these constitutes in the reformer. Before implementing modifications in reformer design or its configuration, it is important to evaluate the maximum temperature of reformer tube. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.