420803 Multi-Domain Modeling and Operation of a Steam Methane Reforming Furnace

Monday, November 9, 2015: 1:50 PM
Salon G (Salt Lake Marriott Downtown at City Creek)
Liangfeng Lao, Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, Andres Aguiire, Chemical Engineering, UCLA, Los Angeles, CA and Panagiotis D. Christofides, Department of Chemical and Biomolecular Engineering and Department of Electrical Engineering, University of California, Los Angeles, Los Angeles, CA

In current hydrogen manufacturing plants, steam methane reforming (SMR) processes play a key role in converting methane into hydrogen, carbon monoxide and carbon dioxide by a sequence of net endothermic reactions. For industrial-level SMR processes, the furnace condition monitoring is difficult due to the large spatial scale of the furnace and of the  high operating temperature. One main task of furnace operation is to avoid hot spots on reforming tube walls. Therefore, SMR furnaces are usually operated slightly below designed values to keep tube wall temperature at a safe margin away from carbon formation temperature and avoid potential tube rupture [1].

The goal of this work is to develop an industrial-level SMR computational fluid dynamics (CFD) model that can provide the temperature distributions in both furnace chamber and reforming tubes for a given set of process inputs. The model is designed to provide acceptable simulation result by certain simplification, so that the model can be used to monitor tube wall temperatures in a real-time mode. The tube wall temperature profiles will help plant operators mitigate the risk of tube rupture due to hot spots. To develop the entire SMR furnace CFD model, a full-size computer-aided design (CAD) model based on an industrial SMR plant was first designed. The CAD model includes all the components of the SMR plant, i.e., reforming tubes, burners and flue gas tunnels. Computationally efficient structured mesh with robust convergence performance was generated for the CFD model design by using ANSYS ICEM CFD [2].  We realize the CFD model of full furnace in the commercial CFD software, ANSYS Fluent [3], based on the generated mesh. Specifically, suitable approximation methodology was adopted to model the reforming tubes and the methane reforming reactions inside the tubes using the reacting channel model. The adoption of reacting channel model greatly reduces the computational burden of the real-time CFD simulation and guarantees the model accuracy at the same time.

Specifically, to realize the methane reforming reaction, we used a complete surface reaction mechanism [4] in the CFD model by reaction mechanism package, CHEMKIN [5] and also an intrinsic reaction mechanism [6] by a user defined function design. Detailed turbulent model and radiation models were used to describe the momentum and heat transport phenomena in the furnace chamber. The above CFD model design strategy has been successfully tested on a small scale model and model accuracy has been validated. The second stage of the  work focusing on simulating the full-scale model and calculating maximum tube wall temperatures that ensure safety limit satisfaction is currently being conducted and the results show its promise for implementation in an industrial setting and the calculation of reforming tube-safe operation strategies.

[1] F. Beyer, J. Brightling, P. Famell, and C. Foster. Steam reforming 50 years of development and the challenges for the next 50 years.  AIChE 50th Annual Safety in Ammonia Plants and Related Facilities Symposium, Toronto, Canada, Sep. 26-29, 2015.

[2] ANSYS ICEM CFD Tutorial Manual, Version 15.0, 2013.

[3] ANSYS FLUENT Theory Guide, Version 15.0, 2013.

[4] L. Maier, B. Schadel, and K. Delgado. Steam reforming of methane over nickel: development of a multi-step surface reaction mechanism. Topics in Catalysis. 2011; 54: 845-858

[5] Chemkin Theory Manual, CK-THE-10131-1307-UG-1, 2013.

[6] J. Xu and G. Froment. Methane steam reforming, methanation and water-gas shift: I. Intrinsic kinetics. AIChE Journal. 1989; 35: 88-96.

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