WASHINGTON UNIVERSITY
THE HENRY EDWIN SEVER INSTITUTE OF TECHNOLOGY
DEPARTMENT OF CHEMICAL ENGINEERING
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STEADY STATE AND DYNAMIC REACTOR MODELS FOR COUPLING
EXOTHERMIC AND ENDOTHERMIC REACTIONS
by
Ramaswamy C. Ramaswamy
Prepared under the direction of Prof. P.A. Ramachandran and Prof. M.P. Duduković
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A dissertation presented to the Henry Edwin Sever Graduate School of
Washington University in partial fulfillment of the
requirements of the degree of
DOCTOR OF SCIENCE
May 2006
Saint Louis, Missouri
WASHINGTON UNIVERSITY
THE HENRY EDWIN SEVER INSTITUTE OF TECHNOLOGY
DEPARTMENT OF CHEMICAL ENGINEERING
ABSTRACT
STEADY STATE AND DYNAMIC REACTOR MODELS FOR COUPLING
EXOTHERMIC AND ENDOTHERMIC REACTIONS
by
Ramaswamy C. Ramaswamy
Advisors: Professor P.A. Ramachandran and Professor M.P. Duduković
May 2006
Saint Louis, Missouri, USA
Several endothermic reaction systems, such as synthesis gas generation from hydrocarbons, can benefit from coupling with a suitable exothermic reaction. The coupling of exothermic and endothermic reactions can be achieved in the following configurations: (i) Recuperative coupling (counter-current reactor, co-current reactor), (ii) Regenerative coupling (reverse-flow reactor) and (iii) Direct coupling (directly coupled adiabatic reactor). However, the comparative performance studies of various modes of coupling are not available in the literature. Hence, the overall objectives of this research are to develop steady state and dynamic reactor models to study and compare the different modes of coupling (counter-current, co-current, and adiabatic reactors), and to investigate such coupling in the catalytic partial oxidation of methane to synthesis gas.
The steady state and transient pseudo-homogeneous plug flow models have been used to analyze and compare the different modes of coupling. Model predictions are used to assess the effects of design and operational parameters on conversion of endothermic reaction and on the hot spot. Measures to reduce the hotspots by inert packing and by shifting the operating regime are investigated. These model predictions are used as the guidelines for the selection of a suitable mode of coupling for the desired application. The performance of different reactors is also compared based on the exergy losses in each system.
A new robust numerical tool, that combines the boundary element method (BEM) and the arc-length continuation technique, is developed to investigate the coupling of exothermic and endothermic reactions within the catalyst particle. This algorithm has been used to identify and analyze the multiple steady states exhibited by the catalyst particles.
As a case study, the catalytic partial oxidation of methane to syngas in a short contact time packed bed reactor has been investigated using steady state and transient heterogeneous plug flow and axial dispersion models. Some of the hotly debated issues, such as the effects of gas hourly space velocity and the presence of steam in the feed on the conversion of methane and the observed temperature peak, are addressed. The evidences to support the occurrence of wrong-way behavior in the short contact time reactor are presented.
dedicated to
My Father
Shri. R. Chidambareswara Bhattar