Various impurities present in contact process are sulphur or pyrite dust, arsenious oxide arid sulphuric acid fog. They poison the catalyst. Dust impurities are removed in dusting tower by

Options

A. By blowing steam to remove dust particle
B. By cottrell precipitators
C. By cooling the gases
D. All

Answer

To solve the question regarding the removal of dust impurities in the contact process, we will analyze the options provided and determine the correct method used in a dusting tower.

### Step-by-Step Solution:

1. **Understanding the Contact Process**:
- The contact process is used to produce sulfuric acid from sulfur dioxide (SO₂). During this process, various impurities such as sulfur dust, arsenic oxide, and sulfuric acid fog can contaminate the catalyst used in the reaction.

2. **Identifying the Role of the Dusting Tower**:
- The dusting tower is specifically designed to remove solid impurities (like dust) from the gases before they proceed to further processing.

3. **Analyzing the Options**:
- **Option 1: Blowing steam to remove dust particles**:
- This method is effective as steam can help agglomerate the dust particles, making them heavier, which facilitates their removal.
- **Option 2: By pottery precipitator**:
- A pottery precipitator (likely referring to an electrostatic precipitator) uses electric charges to attract and collect dust particles from the gas stream. This method is also effective for removing dust.
- **Option 3: By cooling the gases**:
- Cooling the gases can cause some dust particles to condense or settle out of the gas stream, thus aiding in their removal.
- **Option 4: Oil**:
- This option is not typically associated with the removal of dust in a dusting tower. Oil is not a standard method for dust removal in this context.

4. **Conclusion**:
- Options 1, 2, and 3 are valid methods for removing dust impurities in the dusting tower. However, option 4 does not apply. Therefore, the best answer that encompasses the effective methods is **Option 4: All** (assuming it means all methods except oil).

### Final Answer:
The correct answer is **Option 4: All** (excluding oil).