20240826 - Tail SO2 gas on SMBS Production.pptx

SMBS problem of tail gas

1. SMBS PRODUCTION

2. 1. Background: SMBS Production Sulfur is burned into sulfur dioxide. The resulting gas then reacted with a concentrated Na 2 CO 3 or NaOH solution to produce sodium bisulfite (NaHSO 3 ). S (s) + O 2 (g)  SO 2 (g) Na 2 CO 3 (s) + SO 2 (g) + H 2 O (l)  Na 2 SO 3 (aq) + CO 2 (g) + H 2 O (l) Na 2 SO 3 (aq) + SO 2 (g) + 2 H 2 O (l ) ⇌ 2 NaHSO 3 (aq) + H 2 O (l) Sodium bisulfite can be crystallized/dehydrated into sodium metabisulfite ( Na 2 S 2 O 5 ) . 2 NaHSO 3 (aq ) ⇌ Na 2 S 2 O 5 (s) + H 2 O (l) 1/11

3. 2. Problem: Tail SO 2 gas Tail SO 2 is a gas that not reacted with alkali. Some of the tail SO 2 gas from production will be converted into SO 3 (unwanted) if there is excess O 2 in the air. If SO 2 is wanted to fully convert into SO 3 Need high temperature, 300 – 400°C Need catalyst, V 2 O 5 Existing process Tail SO x gas is transferred into wet scrubber and reacted with alkali and lime producing slurry gypsum . Scrubber 2/11

4. 3. Objectives To eliminate gypsum produced from scrubber. Why? The “gypsum” produced in this process has poor quality and disposal cost of this product is expensive . How? Stop using Ca(OH) 2 as neutralizing agent (Only use NaOH or Na 2 CO 3 in the scrubber). Solution from this reaction is recycled into alkali liquor tank (ALT). To minimize tail SO 2 wasted. Why? Tail SO 2 gas can be converted into SO 3 gas. The gas will react with water producing high quantity of diluted sulfuric acid. Disposal cost of diluted sulfuric acid is also expensive. How? Utilization of crystallization tank in the process to cooldown the product thus prevent SO 2 gas released from reactor. 3/11

5. 4. Experiment Both Na 2 CO 3 and NaOH were reacted with SO 2 gas from burner and tail SO 2 gas from Alkali Liquor Tank (ALT). The reaction was done in same condition. In this experiment, the concentration of 600 mL alkali used were Na 2 CO 3 25% and NaOH 20% to obtain final concentrations of NaHSO 3 40% solution. Three reactors were used to investigate the reactivity of the alkaline and tail SO 2 gas that released from reactions. 6/11

6. 5. Conclusions 11/11 Na 2 CO 3 or NaOH can be used solely in scrubber without using lime. Condition: If the tail SO 2 gas from main reaction did not change into SO 3 gas. The mixed solution can be transferred into alkali liquor tank. Using crystallization tank definitely reduce tail SO 2 gas into air. Problem: Super-saturated solution from crystallization tank must be pumped up into centrifugal separator. When transferring this solution, it is suspected that crystallization may occur in the pipe causing clogging.