Comprehensive numerical investigation of mixing behaviour of crude oil using coupled jet impeller in large-scale storage tank

The crude oil received at a process plant is usually supplied from different oil reservoirs with different properties. These are homogenised in a storage tank by mixing with the help of an impeller rotating at a predefined speed. However, the impeller mixing system has a very high power requirement and is not highly efficient. In the jet mixing system, piping and other arrangements are required. Moreover, mixer nozzles are susceptible to clogging. Therefore, in this work, the mixing behaviour of crude oils with different densities using a coupled jet nozzle and impeller is investigated numerically. A three-dimensional numerical model of the tank using the mixture model and the RNG two-equation k-epsilon model is developed and validated with in-house experiments to determine the velocity profile inside the tank under steady-state conditions and the homogenisation time. Further, the changes resulting from the angle of the impeller-jet setup, the impeller rotational speed and the jet outlet velocity are investigated to obtain an optimum mixing time. The homogenisation in the tank is achieved in 4.16 h for the impeller mixing system. However, the homogenisation time is reduced to 1.8 h with the coupled jet-impeller mixing system. It is found that the coupled jet-impeller mixer system works more efficiently than a simple impeller mixer system. The orientation between the jet nozzle and impeller is 15 degrees, the jet flow rate is 351 m3/h with a corresponding jet outlet velocity of 12 m/s, and the impeller rotational speed of 700 revolutions per minute provides the most optimum time required for mixing. Furthermore, the time required for mixing the oil can be further optimised by increasing the tank temperature from 300 to 320 K, keeping the jet flow rate and impeller rotational speed constant.