How To: Wet Scrubbers
A fantastically visual way to explain the science behind wet scrubbers, this demonstration can be used to stimulate discussions around their many applications in industry and research.
Theory
Wet scrubbers are used to remove harmful, water soluble gases from an air flow by dissolving them in water or in aqueous solution. In some cases, where the primary gases are acidic, the water will be dosed with sodium hydroxide. This prevents the release of these gases into the atmosphere and, by capturing them in solution, facilitates the process of neutralising and treating harmful compounds, so they can be safely disposed of.
Kit List
Set up
Exhibition Cost
Around £40-£50. All components, except cabbage water and ammonia will be reusable and a 500 mL bottle of ammonia is usually enough for a 4-day event with demonstrations every 15-20 minutes.
Exhibition Weight
5-10 kg, depending on size of tube and amount of cabbage water prepared.
Exhibition Size
Would fit into a carry-on sized case.
Resources Required
Electrical power for the aquarium pump.
Fresh water to rinse the kit at the end of each day.
Drainage for disposing of the water at the end of the day.
Things to look out for
Do NOT let anyone sniff the ammonia, it can cause serious injury if the fumes dissolve in the lungs. Ensure you disconnect the pump between demonstrations to avoid ammonia fumes from escaping. If the ammonia fumes are taking longer to fill the tube, you may need to drain the Dreschel bottle (gas wash bottle) into your waste solution, neutralise with vinegar, and add fresh ammonia. It is worth having plenty of paper towel for mopping up spills.
Theory
Wet scrubbers are used to remove harmful, water soluble gases from an air flow by dissolving them in water or in aqueous solution. In some cases, where the primary gases are acidic, the water will be dosed with sodium hydroxide. This prevents the release of these gases into the atmosphere and, by capturing them in solution, facilitates the process of neutralising and treating harmful compounds, so they can be safely disposed of.
Kit List
- Clear tube (preferably acrylic), no more than 7 cm in diameter, approximately 30 cm long
- Funnel – to fit, snugly, over the end of the tube
- Adhesive – epoxy resin advised
- Sieve plate to fit in funnel, at bottom of tube
- Clear beads to fill the tube
- Small spouts
- Aquarium pump
- Flexible tubing to fit aquarium pump and spouts
- Large liquid container for draining
- Dreschel bottle
- Clamp stand with clamps
- Household ammonia
- Red cabbage water (and vinegar in hard water areas)
- Beaker for pouring
- Tray to hold the apparatus in case of spillage
Set up
- Drill a hole in the side of the funnel, below the seat point of the tube (test fit). Using the epoxy adhesive, fit the spout at an angle to prevent water draining in.
- Fit the sieve into the funnel and fix it to the end of the tube, using plenty of the epoxy adhesive. When the adhesive has cured, fill with water and block the spouts to ensure that the assembly is water tight.
- Fill the tube with the beads, leaving 5 cm at the top of the tube empty. Holding the tube upright with the clamp stand, fit a flexible tube to the funnel tip, the end of which is in the liquid container to be kept on the floor below the demonstration for drainage.
- Fill the Dreschel bottle with household ammonia and fit another flexible tube to the angled spout, the other end of which should be fitted to the Dreschel bottle outlet. A third flexible tube should connect the Dreschel bottle inlet to the aquarium pump outlet. You will need the pump set to its highest speed.
- Hold the tube and the Dreschel bottle into the tray to catch any spills. Fill the beaker with cabbage water.
- Turn on the pump and explain the application you have in mind for the wet scrubber (i.e. dissolving acidic fumes from a fume hood in an analytical prep lab). It will take around 30 seconds (depending on the volume of the tube) for the ammonia to fill the tube to a visible level.
- Pour a solution of slightly acidic red cabbage water into the open top of the tube. Ensure that the water is well pigmented or the colour change will be difficult to see. As the ammonia dissolves, the water will change from red to blue.
Exhibition Cost
Around £40-£50. All components, except cabbage water and ammonia will be reusable and a 500 mL bottle of ammonia is usually enough for a 4-day event with demonstrations every 15-20 minutes.
Exhibition Weight
5-10 kg, depending on size of tube and amount of cabbage water prepared.
Exhibition Size
Would fit into a carry-on sized case.
Resources Required
Electrical power for the aquarium pump.
Fresh water to rinse the kit at the end of each day.
Drainage for disposing of the water at the end of the day.
Things to look out for
Do NOT let anyone sniff the ammonia, it can cause serious injury if the fumes dissolve in the lungs. Ensure you disconnect the pump between demonstrations to avoid ammonia fumes from escaping. If the ammonia fumes are taking longer to fill the tube, you may need to drain the Dreschel bottle (gas wash bottle) into your waste solution, neutralise with vinegar, and add fresh ammonia. It is worth having plenty of paper towel for mopping up spills.
