One of the common methods for desulfurization is the Merox Desulfurization Process. In this process, petroleum derivatives are washed using caustic soda and water in three stages. The Merox tower consists of three sections.
In the first stage, which includes 15 tower trays, the gas is initially washed with a 10% caustic soda solution. The gas moves upward from the bottom, while the caustic soda flows downward from the top of each tray, washing the gas. The gas then enters the second section of the tower, which also contains 15 trays. Here, a 20% caustic soda solution mixed with the Merox catalyst is pumped from the bottom of the adjacent caustic soda tank and poured onto the 30th tray. As the gas moves upward and the caustic soda-Merox mixture flows downward, the gas is stripped of all sulfur compounds and mercaptans, which remain in the solution.
The third section of the tower consists of 3 trays, designed to remove any residual impurities from the gas. In this stage, the gas is washed with water, which is pumped to the top of the tower. Any remaining caustic soda that might escape with the gas is captured, and ultimately, the gas exiting the tower is completely sweetened. The only remaining moisture in the gas must then be removed.