The Best Filter for Removing Oil Smoke: Electrostatic vs. Media Filters

Determining which type of air cleaner is best for your application can be a real challenge. One of the determining factors is what type of pollutant you are capturing. For this analysis, we will be comparing electrostatic air cleaners vs media filtration on oil smoke.

Oil smoke is a submicron particle that is thermally generated. Some processes where it is a common pollutant include cold forming, high-speed CNC machining (swiss-style especially), using high-pressure oil coolant, industrial frying, centerless grinding, high-speed stamping, and some rubber and plastic forming operations.

What is electrostatic filtration? – Electrostatic filtration is a type of filtration that uses the principles of static electricity to charge particles and attract them to ground. They are made up of two main components. The first stage is the ionizer which induces the smoke or mist particles with a positive charge. The second stage is the collection cell which has alternating plates that are positively charged or grounded. When the positively charged particles pass through the collection cell, the positively charged plates push the particles to ground. It is similar to rubbing a balloon on your head and sticking it to a wall, but with a lot higher force. This method charges and collects even the smallest sub-micron particles.

What is media filtration? – Media filtration is a method of filtering out pollutants by using some type of physical barrier. This includes metal mesh, paper, cloth, fiberglass, and many other materials. These filters contain tightly woven fibers that intercept particles in the airstream while letting the clean air through. 

There are a few advantages to each of these systems, which is why the best solution is dependent on your situation. The advantages of electrostatic filtration are:

• Consistent pressure drop: Because they use static electricity to pull particles out of the air stream instead of “straining” them out. When they get dirty, the airflow stays very close to the same because the air resistance through the filters has not changed much at all.
• Energy efficiency: Another advantage of not pulling air through some type of media filter is that the blowers require ½ to ⅓  as much horsepower.
• Low maintenance costs: Electrostatics use reusable aluminum filters. If they are cleaned regularly and maintained properly, these filters can last for 40 years or longer. If you maintain them in-house, it only costs your time and cleaning supplies. Maintaining them with an external service like Bee Clean costs about $250-$500* per 1000 cfm per year.
• No filters to the landfill: The other advantage to reusable filters is that you don’t have to dispose of hundreds of pounds of dirty used filters every time you service your air cleaner. This is bad for the environment but also bad for your wallet. Used filters are considered hazardous waste until they are tested.
• Collected oil is largely returned to be reused or recycled as aluminum filters do not absorb the oil into them. This can add up as spent filters can carry out 5+ gallons of oil.
• Capture Efficiency: A properly sized electrostatic filter will capture 95% of oil smoke particles regardless of size. If you use a double-pass electrostatic, that number is increased to 99%.
• Price: Compared to long-life high-efficiency Media filters the purchase price is usually 10%-40% less.

The advantages of media filtration are:

• Easy to service: Compared to electrostatic filters, media mist filters are very easy to service because there are fewer working parts. The main thing you need to do is swap the filters and make sure the motor is still working.
• Simple Design: With a simple gauge, you can predict when media filters will need to be replaced, and very rarely are you going to have a problem between filter changes that will require a service call. Electrostatics can have a power supply go bad or an ionizer wire break, which will drastically affect their ability to filter out smoke and require a service call to fix them.
• Capture efficiency: If you use a filtration system that has a HEPA for the final stage of filtration, you will have a 99.97% capture efficiency on submicron particles. This efficiency is what they use in clean rooms and hospitals.

As you can see both methods of air filtration have their pros and cons. Sometimes it just comes down to personal preferences, and what you are used to. If you need help deciding which type of filter is best for your application we will be happy to help!