Alkali scrubbing desulfurization issues in flue gas from sulfur recovery units
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To address the flue gas emission issues in sulfur recovery units, alkali scrubbing for sulfur removal has been added. Although the process of removing sulfur from sulfur-containing flue gas is similar to that of catalytic flue gas desulfurization, the operating modes differ significantly. The SO2 concentration in sulfur-containing flue gas is low, resulting in less saline wastewater generated from desulfurization, or this wastewater can be discharged intermittently. Therefore, the circulating slurry in the flue gas absorption (scrubbing) system remains largely in a closed-loop state. What are the precautions to take? Control indicators? What problems occurred during operation?
The volume and concentration of flue gas emissions from sulfur recovery cannot be compared to those from flue gas desulfurization in catalytic cracking. We have implemented a pre-alkaline washing process here, but it has hardly been used; however, to ensure that emissions meet the required standards, the circulation of alkaline water in this washing process is kept at a low level, with regular checks on the condition of the alkaline water. Referring to the operational status of similar units, as long as the key parameter for evaluation is the pH value of the alkaline water, which remains within a certain range.
The high-salinity brine in the alkali washing tower of the Jinling Petrochemical III sulfur recovery unit exhibited a \"redening\" phenomenon; analysis revealed that the iron ion content in this brine was relatively high. The flue gas contains a small amount of SO2; when SO2 comes into contact with water, it forms sulfurous acid. Sulfurous acid reacts with ferrous ions to produce FeSO3, which then reacts with NaOH in the alkaline washing solution to form Fe(OH)2. Since the flue gas contains a certain amount of oxygen, Fe(OH)2 is further oxidized to form Fe(OH)3. Due to the repeated circulation of the slurry at the bottom of the tower, the amount of Fe(OH)3 in the slurry keeps increasing, resulting in the formation of reddish-brown flocculent precipitates. Question: Where do ferrous ions come from? Is the corrosion caused by improper control of the pH value of the circulating slurry?
Pay attention to the quality of the rinse water; if the water quality is not guaranteed, the structure of the packing in the caustic scrubber tower can lead to an increase in pressure drop.