How do scrubbers remove harmful emissions from industrial smokestacks?

Answer 1

There are several different types:

Wet: Typically scrubbers are big round vertical tanks. The polluted gas stream flows upward through a media (think packing peanuts, but heavy plastic) as a downward flow of water washes the gas stream. This is a very typical and fairly effective way to remove pollutants. Facilities can achieve 95% removal efficencies IF the are monitoring their scrubbing conditions, such as pH and adding any reagents necessary for optimization.

Dry: Bag houses are a bunch of giant vacumn cleaner looking bags to physically filter the air. A shaker system shakes the bags, or changes the airflow to clean them and excess filtered particulate can then be collected and removed, reducing service intervals. Removes most particulates but ultrafines are sometime missed and the condition and maintanance of the bags and the shakers has everything to do with it.

Electronic: An ionic breeze on steroids, these electrostatically remove particulates from exhaust gasses. Old technology and typically found at old coal fired powered plants.

All these above will remove filterable or condensible contaminants but will do little to quell NOx emissions. The new fancy way is this:

Catalytic: Just like your car, or more like a modern diesel engine, a smoke stack can be fitted with a catalyst bed to help scrub NOx (oxides of nitrogen ie NO, No2, n20) with the addition of an ammonia source such as anhydrous ammonia or urea. This catalytic action must take place closer to the combustion than other methods, and typically run about 800*F. The ammonia reacts with the NO2 and with the assistance of a catalyst, reduces it down to N2 and 02. Continuous monitoring of ammonia injection, NOx and montitoring of "ammonia slip" out the other side of the system (too much ammonia and it wont all get used up...just the right amount and theres none left)

Thermal. Do little to change the levels of C02, o2 and NO2 as the exhaust gasses will be typical of natural gas combustion. The gas to be cleaned is passed through an incinerator to burn off anything left from an industrial process. These things save lives!

Been testing these things using ASTM, EPA, and various approved methods for years.

Answer 2

A purification device where smoke is passed through water to remove pollutants.