How to ensure the effectiveness of ammonia-based desulfurization of coke oven gas

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There are many factors that affect the efficiency of ammonia-based desulfurization of coke oven gas; the most direct influences come from the ammonia concentration and temperature, while other factors include the volume of the circulating liquid and the effectiveness of regeneration. The following discusses the factors that influence the desulfurization efficiency. 1. The level of free ammonia in the desulfurization solution directly affects the desulfurization efficiency; a higher level ensures better desulfurization results. The sources of alkali include not only the ammonia contained in coke oven gas itself, but also the ammonia water evaporated from the ammonia evaporation tower and the ammonia gas from that tower, as well as ammonia water purchased from outside. Generally, an HPF catalyst is used for desulfurization to keep the free ammonia content in the desulfurization solution at around 10; this yields good desulfurization results. If this level is too low, it has a significant negative impact on the efficiency of desulfurization. With a complexed iron catalyst, a high ammonia concentration is not required; a level of 6 or above is sufficient, as higher concentrations can instead accelerate the formation of by-products. 2. The gas temperature and the desulfurization liquid temperature affect the mass transfer process of absorption. The temperature of the gas at the inlet of the pre-cooling tower is generally between 35 and 50°C; after passing through the pre-cooling tower, the gas temperature should drop to around 30°C. If this temperature exceeds 35°C continuously, it has a significant impact on the desulfurization process. Additionally, the general principle for controlling the temperature of the desulfurization solution is to keep it as low as possible. Lowering the temperature of the desulfurization solution improves the desulfurization efficiency and reduces side reactions. For HPF desulfurization, the temperature of the desulfurization solution should be kept below 35°C; for complexed iron, a slightly higher range is acceptable, with a temperature below 40°C being sufficient. However, temperatures above 40°C, especially above 45°C, will severely affect the desulfurization process. 3. Sufficient oxygen is a necessary condition for the regeneration of the desulfurization liquid. Only when the catalyst is fully regenerated can it absorb adequately; regardless of the type of catalyst used, regeneration is a crucial step. Under the conditions that regeneration and flotation are satisfied, appropriately reducing the air volume can minimize side reactions and save energy; an air blowing intensity of 80–110 is appropriate. 4. The desulfurization efficiency is closely related to the circulation rate. The spray density in the desulfurization tower is required to be between 40 and 50. If the spray density is low, the gas-liquid contact area is insufficient, which significantly reduces the effectiveness. Furthermore, a low spraying density poses a high risk of tower blockage; similarly, regardless of the catalyst used, the circulation rate and spraying density must be maintained in accordance with the design specifications.