Sulfur recovery unit

The reaction of acidic gases in the sulfur production furnace occurs in two steps: in the first step, part of the hydrogen sulfide reacts with oxygen to form sulfur dioxide; in the second step, the remaining hydrogen sulfide reacts with sulfur dioxide to produce gaseous sulfur. The first step is an exothermic reaction. If the wind remains unchanged while the acidity of the gas decreases, it is as if the acidity of the gas stays the same but the wind increases; in such a case, the reaction may occur in a peroxide-rich environment, ultimately leading to an excessive production of sulfur dioxide and an increase in the temperature of the sulfur production furnace.

The second step is also exothermic; you can refer to the book on operators

Could that be the reason? The temperature after the acidic gas preheater is 170; less feed means less heat is supplied to the acidic gas as well. With less acidic gas available in a timely manner, hydrogen sulfide remains in excess; the air flow rate stays the same, so the total amount of sulfur dioxide produced does not change. The total heat released in the first step also remains unchanged, but since less heat is allocated to the acidic gas, the overall temperature rises

I didn’t understand what you meant. Why is there less acidic gas, yet is hydrogen sulfide still in excess? Generally, to achieve the highest conversion rate, the air volume fed into the furnace should be strictly controlled in proportion. Too much or too little airflow will reduce the conversion rate. At the same time, if there is an excessive amount of wind, it not only leads to excessive heat release and thus an increase in temperature, but it also has a negative impact on the subsequent system due to the formation of excessive sulfur dioxide.

When 1 g of hydrogen sulfide burns completely, it produces liquid water and sulfur dioxide, releasing heat Q1. When it burns incompletely, it produces liquid water and sulfur, releasing heat Q2. When it burns even more incompletely, it produces gaseous water and sulfur, releasing heat Q3. Determine the values of Q1, Q2, and Q3. It is obvious that Q1 > Q2 > Q3. When burning incompletely to produce liquid water and sulfur, heat Q2 is released; sulfur can continue to burn and generate additional heat. When burning completely to produce gaseous water and sulfur, heat Q3 is released. The conversion of gaseous water into liquid water also releases heat, and sulfur can continue to burn and produce more heat. By understanding the amounts of heat released in these processes, we can understand why the temperature rises. Thinking further, if there is too little acidic gas, complete combustion will result in more heat than when there is an adequate supply of air. However, there is a limit to this: if the amount of acidic gas decreases slightly while the air supply remains unchanged, the temperature will rise; but if it decreases significantly, the temperature at the furnace tip will drop. For example, when the load of acidic gas is below 15%, the temperature at the furnace tip will definitely decrease.

It is understood in this way: since the air flow remains constant, the amount of heat generated also remains unchanged (the amount of reactants doesn’t change, and the acidic gas is partially burned; the amount required for the reaction is sufficient). Thus, less heating is needed for the excess acidic gas (all remaining acidic gas, apart from that that has completed the reaction, needs to be heated to the furnace temperature), which is why the furnace temperature rises!

Also, with improper air distribution, the reaction between hydrogen sulfide and sulfur dioxide is reduced; it does not increase! ! The reaction between hydrogen sulfide and sulfur dioxide is greatest only when the air-fuel ratio is appropriate! !

Teacher, this is how I understand it; I’m not sure if it’s correct: the air supply volume can only convert 1/3 of the hydrogen sulfide into sulfur dioxide. So, sulfur dioxide is produced in an amount relative to the excess air. But if only the amount of acidic gases decreases while the air supply remains unchanged, then the total amount of hydrogen sulfide converted into sulfur dioxide should remain the same, right? Then why does the temperature rise?

So, with the air volume remaining unchanged and the fluctuation in the amount of acidic gas decreasing, will the temperature in the sulfur production furnace rise or fall?