Studies on Wax Deposit Removal by Heating of the Pipe Wall

This study investigates the fundamental mechanisms governing the thermal removal of wax deposits from pipelines by using both numerical simulations and experimental data from a laboratory test section. A two-dimensional computational model was employed to simulate the formation, growth, aging, and removal of wax deposits by solving the conservation equations of mass, momentum, energy, and mass of species coupled with a robust thermodynamic model to predict wax precipitation and phase distribution. Experiments were performed using a controlled setup in which wax deposition and removal were induced by cooling or heating the pipe wall. The thermal removal process was thoroughly characterized, with particular attention given to the influence of two key parameters: the aging time of the wax deposits and the temperature applied during the removal process. To evaluate the effect of heating, temperature levels above and below the wax appearance temperature (WAT) were tested. It was shown that more aged deposits required longer times for removal. Further, for heating wall temperatures below the WAT, removal occurred gradually at the deposit/liquid interface, while temperatures above the WAT led to a rapid, plug-like detachment of the wax deposit. It was shown that a significant portion of the wax could be removed even at temperatures levels several degrees below the WAT. In such cases, the remaining deposits were found to be less aged, potentially making them more amenable to secondary removal strategies, such as pigging. Additionally, the study revealed that the local WAT within the deposits could be up to 4 °C higher than the initial WAT of the wax mixture. An analysis of the energy requirements demonstrated that the most favorable balance between energy consumption and wax removal time was not achieved at the highest tested wall temperature levels. Instead, moderate heating provided, potentially, a more effective and economical solution for wax removal. Indeed, for the cases evaluated, increasing the removal temperature to WAT+15.4 °C resulted in approximately a 70% increase in the total energy required to fully remove the wax deposit when compared to a removal temperature of WAT+3.4 °C. However, this substantial increase in energy consumption led to only about a 15% reduction in the total removal time relative to the WAT + 3.4 °C case. These results indicate a reduction in removal efficiency when higher heating levels are applied, highlighting that moderate temperature increments above the WAT may offer a more suitable operational strategy.