Rigorous model reforming

In practice, a refiner does not directly control the feed composition of MCP to the unit Typically, we blend in additional feed that has an IBP greater than 95-100 °C. Feeds with IBPs greater than 95-100 C contain little amounts of MCP and this ratio can be used to control the benzene yield of the unit By contrast, a refiner who wants to increase the production of benzene (to supply a chemical process) may want to increase the feed of MCP instead of operating the reformer at increasing severity and converting reactor products to benzene. Using a rigorous model can help us find and understand these types of trade-offs. 

Model Applications to Refinery Production Planning 307 Table 5.21 Reformer yields at various N+2A and C5+ reformate RON from rigorous model. 

I 5 Predictive Modeling of the Continuous Catalyst Regeneration (CCR) Reforming Process Table 5.23 Comparison of yield predictions from rigorous model and LP yield model. 

A rigorous dusty gas model and two simplified models have been used to simulate industrial steam reformers and methanators. The basic principles for the solution of both the nonadiabatic steam reformer and the adiabatic methanator are given. The details of developing solution algorithms from the models are left to the reader as a serious and extensive project. 

F.M. Alhabdan, M.A. Abashar, S. Elnashaie, A flexible software package for industrial steam reformers and methanators based on rigorous heterogeneous models, Mathematical and Computer Modeling, 16, 77-86, 1992... 

Heterogeneous model for industrial steam reformers In addition to the above results a relatively rigorous heterogeneous model which has been successfully checked against a large number of industrial steam reformers (Soliman et al., 1988 Elnashaie et al., 1992b) is used... 

To evaluate the potential of carbon formation in a steam reformer, it is therefore essential to have a rigorous computer model, which contains kinetic models for the process side (reactor), as well as heat transfer models for the combustion side (furnace). The process and combustion models must be coupled together to accurately calculate the process composition, pressure, and temperature profiles, which result from the complex interaction between reaction kinetics and heat transfer. There may also be a temperature difference between bulk fluid, catalyst surface, and catalyst interior. Lee and Luss (7) have derived formulas for this temperature difference in terms of directly observable quantities The Weisz modulus and the effective Sherwood and Nusselt numbers based on external values (8). 

Elnashaie and Abashar [34] developed a mathematical model to investigate the phenomena of diffusion and chemical reactions in porous catalyst pellets for steam reforming. The rigorous dusty gas model was compared to the simpler Wilke-Bosanquet model under the assumptions of steady-state, negligible viscous flow and isothermal conditions. It was found that at low steam to methane ratios the simplified diffusion model is adequate for simulating the reforming process, while at high steam to methane ratios the implementation of the dusty gas model is essential for accurate prediction of the behavior for this gas-solid system. 

A secondary issue relates to the cahbrahon and predichons from the rigorous reformer model. It is crihcal to ensure that the hydrogen balance is satisfactorily closed before beginning model development We define the hydrogen balance as follows ... 

The most important predictions from the reactor model are the overall yields of all the key products from the unit In case of the reformer, they are the net gas production, LPG (DA301 Ovhd. Liquid) and reformate (DA301 Bttm. Liquid). The yields in the above table are from the rigorous tray-by-tray fractionation section. Therefore, the effect of downstream fractionation is also included in these predictions. We note good agreement with the plant values. The AAD (counting all products) is less than 1.0%. 

A refinery LP and linear unit model represents a set of linear correlations that predict yield given an average yield value and changes in the certain operating variables. In this section, we discuss how to apply the rigorous reforming model in the context of a hnear unit model. The key information for a linear model of a nonlinear process is the DELTA-BASE vector ... 

---