Research paper Crude oil direct fired furnace model Ali Chaibakhsh a, * , Nasim Ensansefat a , Ali Jamali a , Ramin Kouhikamali a , Hamidreza Najafi b a Department of Mechanical Engineering, University of Guilan, Rasht, Guilan, 41938-33697, Iran b Farayand Sabz Pakan Engineering Company, No.117, Somaye Street, Tehran, Iran highlights  A semi-empirical dynamic mathematical model was developed for a crude oil preheat furnace.  Heat transfer in single and two phase flow regimes, combustion process were considered.  The model could be used for real-time simulation in MATALB ® Simulink environment.  The developed model is an appropriate tool for monitoring, fault diagnosis, and control. article info Article history: Received 24 October 2014 Accepted 25 February 2015 Available online 14 March 2015 Keywords: Fired heater Crude oil Mathematical model Thermodynamic behaviour Heat transfer abstract In this study, an accurate mathematical model was developed in order to describe the thermal behav- iours of a crude oil preheat furnace and to predict the outlet temperature of the crude process at different operating conditions. Based on basic heat and mass transfer rules, and thermodynamic relations, all sub- sections of furnaces including the combustion system, the convection and radiation sections were modelled. The crude process flow was considered as the mixture of 21 different components. The empirical correlations for crude process were adopted for estimating the physical properties of com- ponents and the heat transfer coefficients of process fluid for single-phase and two-phase flow regimes at the convection and radiation sections, respectively. The effects of flame height and combustion process conditions were also considered on the furnace dynamics. Available information from operational, geometrical variables and design values were used to define the parameters of the models. In order to show the feasibility and accuracy of the proposed modelling approach, the performances of the devel- oped model were evaluated by comparing its responses with the designed values (on design simulation). Finally, sensitivity analyses were performed by perturbing the model's inputs from nominal conditions to guarantee the capability of the developed model for long-term simulations. Obtained results indicate that the developed model for a direct fired furnace can be used for transient performance analysis at different operating conditions and real-time simulation experiments in MATALB ® Simulink environment. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Fired heaters have been known as the main preliminary units employed for hydrocarbon processing in petrochemical industries. The largest energy consumption part in refineries is associated with fired heater units. In this regard, achieving higher thermal effi- ciencies is the main concern in designing and also during operation. Due to significant energy consumption in such systems, a minor improvement in thermal efficiency would lead to considerable savings [1]. Increasing the area of heating surfaces could be ach- ieved by means of multiple-stream for process flow, which is a common way to obtain higher efficiencies [2]. In many petroleum refinery units, process fluids are fed to distillation columns to be separated into many smaller components that may include different elements with different boiling points. In this case, any variations in process temperature would affect the quality of products [3]. Fired heaters are inherent complicated and nonlinear systems and different incidences could strongly affect their operating conditions and thermal performances. Unplanned variations in process inlet flow rate are one of these factors [4]. The * Corresponding author. Tel.: þ98 13 33690270; fax: þ98 13 33690272. E-mail address: chaibakhsh@guilan.ac.ir (A. Chaibakhsh). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng http://dx.doi.org/10.1016/j.applthermaleng.2015.02.074 1359-4311/© 2015 Elsevier Ltd. All rights reserved. Applied Thermal Engineering 83 (2015) 57e70