The calculation of the calender-and-tube heat exchanger is based on empirical models validated on the laboratory scale. However, when doing an extrapolation at industrial scale, errors become significant because of the non-linearities of the thermophysical properties and the transfer coefficients along the heat exchanger. For that, a follow-up on the fouling resistance in heat exchangers of tube-calender type in Algiers' refinery is presented in this study. These exchangers are used to preheat the crude oil before its passage to the atmospheric column. The results obtained from the two cells of exchangers, which were studied, showed that the resistance and the deposit fouling increases with time following an exponential curve with the existence of the fluctuations caused by the instability of the flow. Bad cleaning of the exchangers involved the absence of an induction time, and consequently, caused high values of the resistance and the deposit fouling during a relatively short time.

List of symbols AThe heat transfer external surface (m 2 ) a ⊥ , a c⊥ The fluid passage area at side tube and side calender, respectively (m 2 ) C P The heat-storage capacity (kJ/kg °C) C Pf , Cp c The heat-storage capacity (kJ/kg °C) d The fluid circulating density at side tube di Tubes interns diameter (m) d 0,e Diamètre externe des tubes (m) d 4 15 Density D c , D e Diamètre de la calandre et diamètre hydraulique, respectivement (m) f t The friction factor F The correction factor G t The mass speed fluid circulating at side tube (kg/h m 2 ) h i The heat transfer coefficient at internal film (kW/m 2 °C) h 0 The heat transfer coefficient at external film (kW/m 2 °C) h i0 The heat transfer coefficient at internal film brought back to the external surface (kW/ m 2 °C) J hf , J hc Coefficient de transfert pour le fluide froid et chaud, respectivement (kW/m 2 °C) l Tubes length (m) m The cold fluid mass flow (the crude oil) (m 3 /h) m f , m c Débit massique pour le fluide froid et chaud, respectivement (kg/s) m f⊥ , m c⊥ Mass flow for the cold and hot fluid, respectively, concerning the straight section (kg/s) MLDTThe difference logarithmic temperature (°C) n c , n tThe devices and the master keys numbers P e , P s Inlet and outlet pressure of the crude oil respectively (Pascal)Abstract Crude oil fouling in refinery preheat exchangers is a chronic operational problem that compromises energy recovery in these systems. Progress is hindered by the lack of quantitative knowledge of the dynamic effects of fouling on heat exchanger transfer and pressure drops. In subject of this work is an experimental determination of the thermal fouling resistance in the tubular heat exchanger of the crude oil preheats trains installed in an Algiers refinery. By measuring the inlet and outlet temperatures and mass flows of the two fluids, the overall heat transfer coefficient has been determined. Determining the overall heat transfer coefficient for the heat exchanger with clean and fouled surfaces, the fouling resistance was calculated. The results obtained from the two cells of exchangers studies, showed that the fouling resistance increased with time presented an exponential evolution in agreement with the model suggested by Kern and Seaton, with the existence of fluctuation caused by the instability of the flow rate and the impact between the particles. The bad cleaning of the heat exchangers involved the absence of the induction period and caused consequently, high values of the fouling resistance in a relatively short period of time.

Fouling in crude distillation unit preheat train in petroleum refineries is a complex phenomenon. Besides, fouling of equipment by crude oil undergoes different mechanisms at different stages of preheating. Hence, understanding the fouling mechanisms is essential in formulating appropriate fouling mitigation strategies. In this respect, the use of the concept of threshold fouling conditions is one of the approaches for mitigating fouling through operating conditions. Indeed, during this study, a monitoring of the temporal fouling resistance evolution of the E102 exchanger battery of the Algerian refinery was carried out. However, this resistance was calculated based on the classical method proposed by Kern. Given that the monitoring of pressure drops is a widely used method in refineries so as to detect of fouling in the tubes of heat exchangers, it decided to study its evolution over time. Nonetheless, this study has effectively revealed that the heat exchanger battery had a clogging problem since the pressure drops increased over time. In addition, a considerable discrepancy was noted between the values read on the manometers and those calculated from a theoretical expression. In virtue of which, these deviations could be the consequence of measurement uncertainties or the instability of the operating conditions, and also to the fact of considering a constant internal diameter of the tubes.

R d : fouling resistance (m². °C/kW) U S : total coefficients of surface heat transfer at the dirty state (kW/ m². °C). U P : total coefficients of surface heat transfer at the clean state (kW/ m². °C). m: the flow mass of the cold fluid (the crude oil) (m 3 /h). C P : the heat-storage capacity (kJ/kg. °C), t e , t s : output and input temperatures of the crude oil, respectively (°C). T e , T s : output and input temperatures of the ebb of head respectively (°C). P e ,P s : inlet and outlet pressure of the crude oil respectively (bar) A: the external surface of heat transfer (m²). (FΔTm): the difference in the logarithmic temperature (°C). d 4 15 : density. h 0 : heat transfer coefficient of external film (kW/m². °C). hi 0 : heat transfer coefficient of internal film brought back to external surface (kW/m². °C).

No abstract