Points to note for sulfur recovery in wet oxidation desulfurization

Thread Content

Wet oxidation desulfurization involves neutralizing the absorbed (dissolved) H2S in the liquid phase to form a new compound, HS-, which is then catalytically oxidized into elemental sulfur through the action of a catalyst. This sulfur is subsequently separated from the solution and removed from the system. From a technical perspective, every stage of the entire process – catalytic oxidation for sulfur release, flotation separation, and sulfur recovery – is important. Only with effective sulfur release can more elemental sulfur be produced, and only through proper flotation can more sulfur be separated and recovered. The sulfur recovery rate mainly focuses on: ① being consumed as by-product salts ； ②Retention, adhesion, and deposition within the equipment packing are not isolated factors; they need to be considered together in order to maximize sulfur recovery rates. 1. Control the growth rate of by-products: Side reactions are inevitable during the desulfurization of coke oven gas. The products of these side reactions, namely thiosulfates, sulfates, and thiocyanates (collectively referred to as by-products), accumulate in the absorption solution, resulting in an increase in solution viscosity and a decrease in alkalinity, which affects the efficiency of absorption and regeneration. Side reactions occur during both the desulfurization and regeneration processes. To reduce these side reactions and control the rate of increase in by-products, it is necessary to make adjustments and optimize the following aspects: (1) It is essential to ensure that H2S in the desulfurization tower dissociates and is completely converted into elemental sulfur after the reaction, thereby minimizing the concentration of HS- in the solution; therefore, catalysts with high activity, good resistance to poisoning, and stable performance are required. (2) The temperature of the desulfurization solution must be strictly controlled and kept low, with ammonia-based desulfurization taking place at temperatures between 30–40°C. Lowering the temperature can also reduce the introduction of tar mist, naphthalene, etc. into the system, and prevent high temperatures from affecting the polymerization and flotation of sulfur foam. (3) The appropriate alkalinity should be controlled (limited to meeting the export H2S standards); it should not be too high. Adjust the solution components appropriately; do not add the alkaline source abruptly. A pH value of >9.0 in the regeneration solution also causes the formation rate of by-products to increase linearly. (4) Enhance regeneration. The regenerating air in the regeneration tower must be sufficient to meet production requirements (it is preferable to have a separate supply) and delivered in a steady and appropriate amount. Sulfur foam should remain at the surface level; the thickness of the foam layer should not be too great (10-20 centimeters is sufficient). 2. Reducing losses and preventing tower blockage: (1) During the desulfurization reaction in a packed tower, an oxidation-regeneration and sulfur precipitation process also takes place; therefore, three phases—gas, liquid, and solid—coexist within the tower. If too much sulfur is removed and not promptly carried away with the solution from the desulfurization tower, it will inevitably remain behind, adhering to and depositing on the internal components of the tower as well as the packing. This adhesion leads to local blockages, resulting in uneven flow patterns such as bypass flow, channeling, and wall flow. As the dry areas expand, this can ultimately cause the tower to become blocked. Therefore, special attention must be paid to ensuring the solution circulation rate and spray density, so that the precipitated sulfur can be separated in a timely manner, allowing the sulfur produced by the reaction to be proportional to the sulfur carried away, with material balance being maintained. (2) The suspended sulfur content in the absorbed lean solution must be kept within the specified limits. (