Separation of hydrogen chloride and sulfur dioxide from exhaust gases by controlled water absorption method

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In 2016, we developed a separation scheme for the pressurized distillation of sulfur dioxide and hydrogen chloride. The compression distillation approach enables a relatively thorough separation of sulfur dioxide and hydrogen chloride, yielding anhydrous, almost pure liquid hydrogen chloride and sulfur dioxide. Multiple units are in industrial operation, achieving good economic benefits and social value. To this day, it remains the most thorough solution preferred for such mixed exhaust gases. However, compressed distillation also has its obvious limitations: it operates at high pressures and requires significant investment ； Due to the complexity and high corrosiveness of exhaust gas components, high requirements are placed on compressors. At present, no small compressors suitable for such harsh conditions can be found; therefore, the minimum required volume flow rate for the exhaust gas is 100 m3/hr or more ； There are very strict requirements regarding the composition of process exhaust gases; gases containing large amounts of non-condensable gases, chlorine, small amounts of water, alcohols, and substances with similar boiling points are not suitable for direct separation in compression distillation units. Often, complex pre-treatment processes are required before separation can be carried out, or the separation may even be impossible. To address the exhaust gas treatment issues of users with low amounts of sulfur dioxide and hydrogen chloride acidic exhaust gases, as well as those with complex exhaust gases, we have developed a control-based water absorption and separation solution. This process operates at atmospheric pressure and requires relatively low investment ； There is no mandatory requirement for air volume ； Wide adaptability to exhaust gas components ； The device has a high degree of automation and can operate automatically without human intervention, as long as the exhaust gas flow remains relatively stable. The limitation of this approach is that it only produces by-product hydrochloric acid and wet sulfur dioxide, and its separation efficiency is inferior to that of the compression distillation method (the sulfur dioxide content in the hydrochloric acid is below 0.5%, which is far better than the approximately 4% sulfur dioxide impurity level in traditional methods) ； Wet sulfur dioxide is suitable for being processed into aqueous solutions such as sodium sulfite and sodium thiosulfate for export, or it can be dried, compressed, and condensed into cylinders for export as well. The process for controlling water absorption includes: pretreatment – control of water absorption – post-treatment of the recovered materials. The key to this process lies in optimizing and precisely automating the process parameters related to water absorption at each stage; this enables the production of hydrochloric acid and wet sulfur dioxide with higher purity compared to conventional water-based or alkali-based absorption methods. It allows for the recycling of waste gases, resulting in low overall operating costs. It represents another viable option for the resourceful treatment of hydrogen chloride and sulfur dioxide-containing exhaust gases.