Monday, November 5, 2007 - 8:52 AM
38b

Hysteresis In High Pressure Trickle Bed Reactor

Zeljko V. Kuzeljevic1, Werner Van der Merwe2, Milorad P. Dudukovic1, and Muthanna H. Al-Dahhan1. (1) Energy, Environmental and Chemical Engineering, Washington University in Saint Louis, One Brookings Drive, Saint Louis, MO 63130, (2) Chemical Engineering, University of Pretoria, Lynnwood Road 1, Pretoria, South Africa

Trickle Beds are three phase reactors in which gas and liquid phase are introduced at the top of the column and flow cocurrently through a packed bed. Most typically they are used in petroleum and petrochemical industry and in wastewater treatments.

Prediction of basic design parameters, like pressure drop and liquid holdup, is essential for understanding of these reactors. As evidenced by many researchers (Kan and Greenfield 1978, Levec et al. 1988, Christensen et al. 1986), these parameters vary not only with operating parameters (such as liquid and gas flowrates), but also with the flow history, i.e. they exhibit hysteresis. These and similar investigations have established dependence of extent of hysteresis on various system properties, like catalyst size, liquid surface tension, type of packing (porous/non-porous) etc.(Maiti et al. 2006). However, to authors' best knowledge, there is no systematic study of degree of hysteresis in high pressure Trickle beds, even though most of industrial applications are at elevated pressure (Al-Dahhan et al. 1997).

This study gives experimental evidence of hysteresis in High Pressure Trickle Bed Reactor. The investigation is performed in 6" column, water-air system, in the range of pressures of up to 6 barg. Operating procedure involved four pre-wetting modes: Levec, Super, Kan-gas and Kan-liquid (Loudon et al. 2006). This enabled systematic investigation of extent of hysteresis in pressure drop and liquid holdup. Results indicate very large difference (of up to 500%) in values of pressure drop and liquid holdup for the examined pre-wetting modes. Effect of elevated pressure on extent of hysteresis is found to be dependent on operating flowrates, i.e. closeness of experimental conditions to pulse-to-trickle transition line. For the low liquid/gas velocities, data indicate that hysteresis persists for any of the pressures in the range of our experimental conditions.

References:

Loudon, D., W. van der Merwe, et al. (2006). "Multiple hydrodynamic states in trickle flow: Quantifying the extent of pressure drop, liquid holdup and gas-liquid mass transfer variation." Chemical Engineering Science 61(22): 7551-7562.

Al-Dahhan, M. H., F. Larachi, et al. (1997). "High-Pressure Trickle-Bed Reactors: A Review." Industrial & Engineering Chemistry Research 36(8): 3292-3314.

Christensen, G., S. J. McGovern, et al. (1986). "Cocurrent downflow of air and water in a two-dimensional packed column." AIChE Journal 32(10): 1677-89.

Kan, K.-M. and P. F. Greenfield (1978). "Multiple hydrodynamic states in cocurrent two-phase downflow through packed beds." Industrial & Engineering Chemistry Process Design and Development 17(4): 482-5.

Levec, J., K. Grosser, et al. (1988). "The hysteretic behavior of pressure drop and liquid holdup in trickle beds." AIChE Journal 34(6): 1027-30.

Maiti, R., R. Khanna, et al. (2006). "Hysteresis in Trickle-Bed Reactors: A Review." Industrial & Engineering Chemistry Research 45(15): 5185-5198.


See more of #38 - Multiphase Reaction Engineering (20035)
See more of Catalysis and Reaction Engineering Division

See more of The 2007 Annual Meeting