(46c) Integrating Crude Oil Fouling Modelling and Experiments On a New High Pressure Pilot-Scale Test Rig

Crude oil fouling is a long-standing problem in oil refineries which causes major energy efficiency and economic losses, extra environmental emissions and disruption of operations, with related health and safety hazards. Because of the complex and interacting phenomena involved, the underlying mechanisms leading to fouling depositions are not well understood. Acquiring experimental data in a controlled laboratory environment representative of realistic refinery conditions, through very precise measurements, is a required step for gaining a better understanding of the fouling mechanisms and for testing mitigation strategies. This is important for improving refineries operational efficiency. Moreover, data on crude fouling behavior provide sensitive and important commercial information for oil companies which often base buying, pricing and allocation strategies on the quality of the crudes, including the ease with which they can be processed in specific refineries.

A state-of-the-art high pressure oil rig (HIPOR) has been built at Imperial College London by a team under the lead of Prof. G. F. Hewitt [1]. This facility is designed to process crude oil in two test sections (a tube and an annulus) up to 30 bars and 300 °C and to measure with accuracy key variables such as inlet and outlet temperatures, flowrates, heat fluxes and pressure drops. Moreover, temperature profiles across the length of the annular test section can be measured through a radiation equilibrium thermometer whilst the actual thickness of the foulant layer can be measured simultaneously using a novel dynamic gauging technique [2].

The traditional experimental approach to crude oil fouling research focuses on the collection of fouling data which are typically interpreted through overall, lumped heat balances to yield overall fouling resistances. In this paper, an integrated approach is discussed which combines the detailed data from the above experimental apparatus with sophisticated thermo-hydraulic modelling to tackle the fundamental issues involved in crude oil fouling.

A distributed, dynamic model that takes into account local fouling resistance and the thickness of the deposit layer across the length of a tube was recently proposed [3]. The model also includes the structural changes of the deposit over time (ageing) as well as the impact of surface roughness dynamics produced by the initial deposition and the complex interactions between hydraulic and thermal effects of fouling. That model is modified here to match the specific operating conditions and geometries of the test rig.

The synergies achieved by combining experimental and modelling activities are discussed. They include a way to better interpret the data obtained, to identify key parameters (e.g. thermal conductivity of fouling layer, sheer stress, etc) and to validate the mathematical model. This integrated approach also allows the rapid testing of alternative models of fouling, ageing and roughness dynamics and help explain the complex phenomena leading to deposition. Moreover, the use of model-based experiment design techniques to plan the experiments is discussed. The goal here is to devise effective experiments that maximize the information content and minimise experimental costs and time. References

[1] Macchietto, S., Hewitt, G. F., Coletti, F., Crittenden, B. D., Dugwell, D. R., Galindo, A., Jackson, G., Kandiyoti, R., Kazarian, S. G., Luckham, P. F., Matar, O. K., Millan-Agorio, M., Müller, E. A., Paterson, W., Pugh, S. J., S.M., R., and Wilson, D. I., 2009, "Fouling in Crude Oil Preheat Trains: A Systematic Solution to an Old Problem," Proc. International Conference on Heat Exchanger Fouling and Cleaning VIII, H. Müller-Steinhagen, et al., eds., Schladming, Austria.

[2] Tuladhar, T. R., Paterson, W. R., and Wilson, D. I., 2002, "Investigation of Alkaline Cleaning-in-Place of Whey Protein Deposits Using Dynamic Gauging," Food and Bioproducts Processing, 80(3), pp. 199-214.

[3] Coletti, F., Ishiyama, E. M., Paterson, W. R., Wilson, D. I., and Macchietto, S., 2010, "Impact of Deposit Ageing and Surface Roughness on Thermal Fouling: Distributed Model," AIChE J. Accepted for publication.