Dry scrubber is an air pollution control device designed to remove harmful pollutants from industrial exhaust gases without using liquids. Unlike wet scrubbers, which use liquid solutions to capture and neutralize pollutants, dry scrubbers use dry reagents (usually alkaline substances like powdered lime or sodium bicarbonate) to chemically react with and neutralize acidic gases.

Key Components and Functionality:

1. Pollutant Entry: Exhaust gases containing pollutants such as sulfur dioxide (SO₂), hydrogen chloride (HCl), or other acidic gases enter the scrubber.

2. Reagent Injection: A dry reagent, typically in powdered form, is injected into the gas stream. This reagent reacts with the pollutants to form solid byproducts.

3. Chemical Reaction: The acidic gases react with the alkaline reagent. For example:

• Sulfur dioxide (SO₂) reacts with calcium hydroxide (Ca(OH)₂) to form calcium sulfite (CaSO₃) or calcium sulfate (CaSO₄).

• Hydrogen chloride (HCl) reacts with sodium bicarbonate (NaHCO₃) to form sodium chloride (NaCl) and carbon dioxide (CO₂).

4. Particulate Collection: The resulting solid particulates from these reactions are captured by a filtration system, such as a fabric filter (baghouse) or an electrostatic precipitator.

5. Clean Gas Release: The now-cleaned gas, with most of the harmful pollutants removed, is then released into the atmosphere.

Types of Dry Scrubbers:

• Spray Dryers: These systems use a spray of alkaline slurry that evaporates, leaving behind solid particles that react with pollutants.

• Dry Injection Systems: The dry reagent is directly injected into the gas stream, and the resulting solid byproducts are collected.

Applications:

Dry scrubbers are widely used in industries where controlling air pollution is critical, such as:

• Power plants (to remove sulfur dioxide and other emissions from burning fossil fuels)

• Waste incineration facilities

• Cement production

• Chemical manufacturing

Advantages:

• No water consumption, making them ideal for areas with water scarcity.

• They generate less wastewater compared to wet scrubbers.

• Effective in removing acidic gases from industrial exhaust.

Disadvantages:

• They may be less effective than wet scrubbers in some applications.

• Handling and disposal of the solid waste byproducts can be challenging.

Dry scrubbers play an essential role in reducing industrial air pollution and helping industries meet environmental regulations.

How a Dry Scrubber Works:

1. Pollutant Introduction: Polluted gas enters the scrubber and is exposed to a dry reagent, typically in the form of powdered lime (Ca(OH)₂) or other alkaline materials.

2. Chemical Reaction: The pollutants in the gas react with the dry reagent. For example, sulfur dioxide reacts with lime to form calcium sulfite (CaSO₃) or calcium sulfate (CaSO₄), which are solid compounds.

3. Particulate Collection: The reaction forms solid particulate matter, which can be collected using a fabric filter (baghouse) or an electrostatic precipitator.

4. Clean Gas Release: The cleaned gas, now free of most pollutants, is then released into the atmosphere.