The Use of Ozone and Activated Carbon in Commercial Kitchen Ventilation for Odour Control

Ozone Odour Control Kitchen

The use of ozone generators and activated carbon in commercial kitchen ventilation systems for controlling odours is well-known and endorsed by BESA in their DW 172 Specification for Kitchen Ventilation Systems, as well as by EMAQ+ in their guidance on controlling odour and noise from kitchen exhaust systems.

Understanding Residence Time

Residence time, also known as contact time or dwell time, is crucial when using ozone or activated carbon for odour control. This term refers to the time that the air carrying the odour is in the presence of ozone or activated carbon.

For ozone to be effective, it generally requires a minimum of 2 seconds of dwell time. This means that if the air velocity is 6-8 meters per second, you will need 12-16 meters of ductwork after the ozone injection point for effective odour treatment. However, this is not always possible in a commercial kitchen setup.

Activated carbon requires a minimum of 0.2 seconds of contact time to control odour. This is the time taken for air to pass through the activated carbon filter, allowing the odour molecules to be adsorbed. The challenge is that activated carbon systems are large and bulky, especially if an odour control scheme requires 0.8 seconds of contact time. To treat an average flow rate of 2 cubic meters per second, a 0.2-second activated carbon system would be 1.2 meters high, 1.2 meters wide, and 0.75 meters long. If 0.8 seconds of contact time is needed, the system length increases to 3 meters, which many commercial kitchens cannot accommodate.

Combining Ozone and Activated Carbon

The issue of needing extensive ductwork for ozone or bulky systems for activated carbon can be overcome by using them together. Activated carbon can also be used to remove excess ozone by converting ozone (O3) into oxygen (O2). This is particularly important for low-level extraction systems or when the extraction point is close to a receptor, such as a window, door, or air intake louvre. The activated carbon prevents ozone from re-entering the building and eliminates any residual ozone smell around the discharge point.

For optimal results, activated carbon should be placed at the end of the extraction system just before the fan. This creates a reaction chamber where ozone can act on food odours. The bigger the distance between the ozone injection point and the carbon filter, the longer the ozone and odours have to react.

When combined, ozone injection and activated carbon can reduce the required duct length. Ozone injection alone needs a minimum of 2 seconds of dwell time, which is often impractical. However, combining ozone injection with 0.1 seconds of activated carbon, for example, can halve the required residence time. Thus, a 2-second ozone residence time can be reduced to 1 second, and a 0.2-second activated carbon residence time can be reduced to 0.1 seconds.

Extending the Life of Activated Carbon with Ozone

According to EMAQ+, activated carbon should be replaced every 4-6 months, and ozone lamps should be swapped every 12 months. By combining ozone and activated carbon, the life of activated carbon can be extended. For instance, in a KFC restaurant that initially had to replace their activated carbon every 6 weeks, the interval extended to 12 months after installing an ozone injection system, resulting in a return on investment in less than 6 months.

In addition to extending the life of activated carbon, combining it with ozone can reduce the amount of activated carbon needed by half, making it a more cost-effective solution for ongoing maintenance.

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