The issue of pre-sulfurizing wash
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I would like to ask the teachers: for the exhaust gas flow in our sulfur plant, it goes from the hydrogenation reactor, where heat is removed through heat exchange, to the quench tower, then to the absorption tower and the alkali scrubbing tower, before reaching the exhaust gas furnace and finally the chimney. What is used in such pre-alkaline washing alkali scrubbers? What is the appropriate concentration of the alkaline solution? What criteria are used to determine when to replace the alkaline solution? Additionally, during operation the hydrogen sulfide concentration at the outlet of the absorption tower was 30 mg/m3; however, after passing through the alkali scrubber, this concentration rose to 200 mg/m3. When the alkali scrubbing cycle was stopped, the hydrogen sulfide concentration at the outlet of the alkali scrubber was 40 mg/m3. What could be the reason for this? (The process has been checked; there are no interferences with other processes.)
The function of the alkali scrubber is to use an alkaline solution to remove a portion of the hydrogen sulfide into the liquid phase, while the remaining hydrogen sulfide is sent to a furnace where it is burned to produce sulfur dioxide, which is then released. The concentration is generally designed to be 20%.
Normally, post-alkaline washing should be considered. Otherwise, it’s difficult for chimney emissions to meet the standards
Why is the alkali wash done first? An alkali solution concentration of 20%-30% is generally suitable.
I don’t know; we all use post-alkaline washing, with an alkali concentration of 30%, and Meston technology is employed
Our pre-alkaline cleaning process is the same as yours; we maintain a pH level of around 9, and both the alkaline solution and water are continuously added while the process proceeds. As for high hydrogen sulfide levels after alkaline cleaning, we haven’t conducted any tests on that. Currently, the amount of alkali added is relatively large, which allows the sulfur dioxide levels to remain just within acceptable limits
First, the hydrogen sulfide content at the outlet of the absorption tower is too high; the quality of your amine solution is poor. Furthermore, the alkali solution in the alkaline scrubber absorbs sulfur dioxide but not much hydrogen sulfide. The alkaline scrubber should be placed after the flue gas furnace, so that the sulfur dioxide emitted is of acceptable quality
Currently, those design institutes that employ pre-alkali washing in their designs do not take into account the reaction between carbon dioxide and alkaline solutions; they only consider, in a one-sided and wishful manner, the reaction between hydrogen sulfide and alkaline solutions. You can check the reaction equations above. There are also some design institutes that are affiliated with manufacturers of desulfurization agents; the pre-alkaline washing process requires the use of products supplied by these manufacturers, which results in higher costs.
What is the volume of device processing at your facility? How much alkali is consumed per day? Is the replaced alkaline solution discharged directly into the drain ditch?
Our alkaline solution is sent to the acidic water stripping unit
Hydrogen sulfide reacts with sodium hydroxide: (1) With a small amount of sodium hydroxide: NaOH + H2S = NaHS + H2O; (2) With an excess of sodium hydroxide: 2NaOH + H2S = Na2S + 2H2O. One of the chemical properties of sodium sulfide is that it decomposes in acids to produce hydrogen sulfide. It deliquesces in air, undergoing gradual oxidation; in the presence of acids, it produces hydrogen sulfide. So PH controls alkalinity. We discharge based on density values, or we can also do it based on pH