Mathematical model of the oil primary processing furnace

Source abstract

Improving the precision of automatic control systems for process heaters is a critical factor in optimizing crude oil primary distillation units. The article introduces a dynamic mathematical model designed to maintain tight control over the outlet temperature, a vital parameter for subsequent high-quality fractionation. The object of the research i s a gable barrel-type oil refinery furnace within a primary crude oil processing unit, featuring a temperature control loop for the petroleum product at the coil outlet based on fuel gas flow rate. The modeling is based on the synthesis of transfer functions of system elements: the temperature sensor is represented as a first-order lag element, the actuator — as an integrating element, the control valve — as an aperiodic link and the controlled process — as an aperiodic link. A distinctive feature of the proposed approach is the comprehensive consideration of physicochemical factors: the variable calorific value of the fuel gas calculated via the Wobbe index; the heat accumulation capacity of the fire tube walls; and the dependence of crude oil specific heat capacity on its moisture content. The simulation model is implemented in the SimInTech environment; the research is conducted using computational experiments involving the sequential application of step disturbances. Therefore, the authors conclude that with an increase in the feedstock inlet temperature by 50 °C, a 30 % rise in the mass flow rate of oil and a fivefold increase in moisture content, the controlled variable reaches extreme values of 410, 350 and 340 °C relative to the setpoint of 370 °C, with a regulation time not exceeding 15 000 seconds. The developed model enables minimization of technological regime deviations providing conditions for precise fractionation.