INVESTIGADORES
BUCALA Veronica
artículos
Título:
Optimization of Steam Reformers: Heat Flux Distribution and Carbon Formation
Autor/es:
PIÑA, JULIANA; BUCALA, VERONICA; BORIO, DANIEL
Revista:
INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING
Editorial:
BERKELEY ELECTRONIC PRESS
Referencias:
Año: 2003 vol. 1
ISSN:
1542-6580
Resumen:
Optimal heat ux distributions along the axial position of steam reformer tubes are analyzed, aiming to maximize the outlet methane conversion without violating the upper bounds speci ed for the tube skin temperature, Tw(z) and the local heat ux, Q(z). The possible occurrence of the carbon deposition phenomenon is considered as an additional constraint in the optimization problem by means of a kinetic criterion which accounts for the rate of carbon formation (rC,net). The problem of nding the axial heat ux pro le that leads to maximum methane conversion (or minimum tube skin temperature for speci ed production) without violating the upper limits imposed for Tw(z), Q(z) and rC,net is in principle a complex optimization process. In this work, a relatively simple semi-analytical method, that requires only iterative reactor simulations, is proposed. At conditions of fresh catalyst and for operations with typical feed compositions and temperatures, the carbon formation constraint is not active. For low values of the maximum allowable local heat ux (Qall), the optimal heating policies are monotonically increasing Tw(z) trajectories. Conversely, for higher Qall values the optimal Tw(z) shows an initial increase in the rst tube section followed by an isothermal section. Decreasing axial wall temperature pro les or Tw(z) curves with maximum are clearly not optimal. When the catalyst is strongly deactivated, the optimal manipulation of Q(z), or Tw(z), is an appropriate procedure to achieve carbon free conditions. As this heating policy consists basically in reducing the ring in the top section of the reformer tube, it leads to unavoidable production losses. The shape of the catalyst activity axial pro le has a considerable inuence on the risk of carbon formation. Increasing activity distributions (similar to those found when sulfur poisoning takes place) may result in severe carbon formation in the reformer top. An optimal control of the heat input can contribute to minimize this practical operation problem.