Dynamic Evidence of Multiplicity in a Reactive Distillation Column for Ultra-Low Sulfur Diesel Production
Systematic methods and tools for managing the complexity
Process Operation, Monitoring & Analysis (T4-2)
Keywords: dynamic simulation, reactive distillation, multiple steady states
An analysis of the operating conditions to obtain ultra-low sulfur diesel in a conventional trickle bed hydrodesulfurization (HDS) reactor (van Hasselt et al., 1999) suggests that reactive distillation (RD) could be an interesting technological alternative for deep HDS of diesel. However, although RD has several advantages, incomplete understanding of the system specific non linear phenomena caused due to interactions of chemical kinetics, phase equilibria and mass transfer, limits its widespread use. Various operating parameters may very strongly influence on the process performance. This parametric sensitivity of the column leads to a complex dynamic behaviour of the system.
A preliminary bifurcation analysis (López-Arenas et al., 2006) reveals the existence of multiple steady states (MSS) in a reactive distillation process for ultra-low sulfur diesel production. It was found that, the main variables that affect the steady state behavior are the feed stage and flowrate of the fed hydrocarbon mixture (HC), reflux ratio and holdup. Furthermore, the holdup, sulfur composition in the HC feed stream and the H2/HC feed ratio determines the final steady state achieved.
The purpose of this work is to analyze and predict the MSS through dynamic simulation when the reactive distillation column (RDC) is subject to different input disturbances. The dynamic simulations are carried out to analyze the open loop dynamic responses for some key disturbances of the system using step changes in the manipulated variable (for example: reflux ratio, holdup, HC feed stage, HC feed flowrate, reboiler duty) and recording the dynamic behaviour of the product conversions (DBT and 4,6-DMDBT, called controlled variables). The magnitude of the change in the manipulated variables should be reduced to around 0.5% or less than its nominal value.
With the use of dynamic simulation it was possible to determine a startup procedure and visualize a control structure for the RDC. The RDC design considered in this work was taken from Viveros-García et al. (2005).
van Hasselt, B.W., Lebens, P.J.M., Calis, H.P.A., Kapteijn, F., Sie, S.T., Moulijn, J.A., and van den Bleek, C.M. (1999). A numerical comparison of alternative three-phase reactors with a conventional trickle-bed reactor. The advantages of countercurrent flow for hydrodesulfurization. Chem. Eng. Sci., 54, 4791.
López-Arenas, T., Cárdenas-Guerra, J.C., Lobo-Oehmichen, R., and, Pérez-Cisneros, E.S. (2006). Multiple Steady States in a HDS Reactive Distillation Column. In Proceedings of the topic Distillation and Absorption, CHISA 2006, Czech Republic, 27-31 August.
Viveros-García, T., Ochoa-Tapia, J.A., Lobo-Oehmichen, R., de los Reyes-Heredia, J.A., and Pérez-Cisneros, E.S. (2005). Conceptual design of a reactive distillation process for ultra-low sulfur diesel production. Chem. Eng. J., 106, 119.
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 09:25 to 09:45, in session Process Operation, Monitoring & Analysis (T4-2).
