Interact with the simulation of an electrostatic precipitator (ESP) above. The ESP is a big air cleaner for factories and power plants. It uses electricity to pull tiny dust and mist out of smoky gas before the gas goes up the stack. Inside the box are thin wires kept at a very high voltage next to large metal plates that are grounded. The high voltage makes a faint “corona” around the wires, which is a cloud of charged ions. As the dirty gas flows past, those ions bump into the dust particles and give them an electric charge, kind of like when a balloon rubs on your sweater and becomes “static.”
Once the particles are charged, the electric field pushes them sideways toward the plates. Positive particles are pulled one way, negative the other, but either way they end up sticking to a plate instead of staying in the air stream. The cleaned gas keeps moving forward and exits the ESP. Every so often, the plates are cleaned: in a dry ESP, mechanical “rappers” gently shake the plates so the dust falls into hoppers; in a wet ESP, water rinses the plates so sticky mist and very fine droplets wash off.
ESP performance depends on keeping the electric field strong and the gas flow smooth, and on the dust being “just right” electrically—if it holds charge too well or not well enough, efficiency drops. When everything is tuned properly, an ESP can remove well over 99% of particles with very little resistance to airflow. That’s why they’re widely used to protect the air around power plants, cement kilns, and other heavy industries.
