Designing a gas scrubber involves several considerations, including the type of gas contaminants you need to remove, the desired removal efficiency, the flow rate of the gas, and the type of scrubbing solution you plan to use. 

The basic steps for designing a gas scrubber and provide some key calculations:

1. Identify Contaminants: Determine the types and concentrations of contaminants in the gas stream you want to remove. Common contaminants include sulfur dioxide (SO2), hydrogen sulfide (H2S), ammonia (NH3), particulate matter, and volatile organic compounds (VOCs).

2. Determine Scrubbing Solution: Select an appropriate scrubbing solution based on the type of contaminants. Common scrubbing solutions include water, alkali solutions (e.g., sodium hydroxide or caustic soda), or other chemicals depending on the specific contaminants.

3. Calculate Gas Flow Rate (Qg): Determine the flow rate of the gas stream you want to treat. This is typically measured in cubic meters per hour (m³/hr) or cubic feet per minute (CFM).

4. Calculate Contaminant Mass Flow Rate (m_contaminant): Calculate the mass flow rate of the contaminants in the gas stream. This can be calculated as:

   m_contaminant = Qg × C_contaminant

   where:

• Qg is the gas flow rate (in m³/hr or CFM).

• C_contaminant is the concentration of the contaminant in the gas stream (in g/m³ or lb/ft³).

5. Determine Removal Efficiency (η): Decide on the desired removal efficiency for the gas scrubber. This is typically expressed as a percentage. For example, if you want to remove 90% of a specific contaminant, η would be 90%.

6. Calculate Required Scrubbing Solution Flow Rate (Qs): To achieve the desired removal efficiency, you'll need to calculate the flow rate of the scrubbing solution required. This can be calculated as:

   Qs = (m_contaminant / η) / C_s

   where:

• m_contaminant is the contaminant mass flow rate (in g/hr or lb/hr).

• η is the removal efficiency (expressed as a decimal, e.g., 0.90 for 90% removal).

• C_s is the concentration of the scrubbing solution (in g/L or lb/gal).

7. Design the Scrubber: Based on the required scrubbing solution flow rate, design the scrubber vessel, packing material (if applicable), and any additional equipment needed, such as pumps and spray nozzles.

8. Safety and Environmental Considerations: Ensure that the design complies with safety and environmental regulations. This may include the proper disposal of contaminated scrubbing solution and compliance with emission limits.

9. Testing and Validation: After building the scrubber, conduct tests to validate its performance and make adjustments as needed to achieve the desired removal efficiency.

Please note that gas scrubber design can vary significantly depending on the specific application and requirements. It's essential to consult with experts in the field and consider the specific properties of the contaminants and scrubbing solution in your design calculations.