Pollution Control Unit

What is the difference between pollution control units?

Pollution Control units, also referred to as Scrubbers are systems that remove a high percentage of grease, vapor and odors from the cooking process through a means of filtration. The devices fall into 2 major categories, media filter type and electrostatic precipitators (ESP).

Both systems have a form of odor abatement technology associated with them. The most common are an odor neutralizing spray or activated carbon bed.

In addition, an exhaust fan that pulls the grease laden vapors through the filtration and odor abatement components is included.

In order to understand how a Pollution Control Unit (PCU) works it’s important to understand what is in the exhaust stream of a commercial cooking operation. There is grease particulate of varying sizes, ranging from vapor to large micron particulate ,as well as water vapor and volatile organic compounds (VOC’s).   The particulate distribution is also process dependent. For example, if you were to cook 1000 lbs. of burgers on a charbroiler, you would expect to see 55 lbs. of total emissions (on average). Of that, about 62% is particulate and the balance vapor and VOC’s.  If you cooked those same burgers on a griddle,  you might see about 17 lbs. of total emissions (on average).  Of that, about 65% would be particulate and the balance vapor and VOC’s.  The ability of a PCU to remove those emissions is a function of the efficiency of the filtration.

Media Filter Units

These systems come with multiple filters in combination, typically 2 or 3 stages, from a prefilter, to a bag filter, a combined pre and bag filter and a final stage filter. The filters increase in efficiency by stage. First stage is the lowest efficiency filter and is applied to take out the larger grease particles, the second stage will be incrementally more efficient and remove slightly smaller grease particles and final stage removes the smallest particles down to a fractional micron level.

Most systems have some form of filter life monitoring. As the filters load and pressure drop across the filter increases, this can be measured to determine when the filter is dirty and needs to be changed. Advanced filtering systems have variable frequency drives that adjust the fan speed as pressure loss increases so the system can maintain design exhaust airflow. Further still, there are controls that vary the air volume being exhausted through the Pollution Control Unit based on the cooking activity.

It is important that replacement filters used in scrubbers are compatible with the application. Using the wrong filter type will result in a poorly operating unit. First cost on  filter type units is less than that of an ESP type, but ongoing replacement filter cost (operating/maintenance) should be factored into any selection to get a complete picture of life cycle costs. There are calculators available from manufacturers to assess first and maintenance cost to determine the best choice in an air cleaner.

ESP, Electrostatic Precipitators

These systems utilize something called an “ionizing-collector cell”; it resembles box with a series of parallel plates in a frame about the size of a small trunk. There are typically multiples of these “cells” based on the total exhaust volume required.  The front part of this box has  “ionizing” electrode that creates a positive charge.  Behind that, there are plates with another positive charge and grounded plates between them. When grease particulate passes through this front part , the particles are positively charged. The positively charged grease is repelled to the ground plates by the positively charge plates and collects on them, taking the grease out of the air stream.  The efficiency of an ESP is related to the surface area of the cells (more cell area, greater opportunity to collect grease), voltage gradient and the method of ionization.

Electrostatic Precipitators

More advanced systems have a wash spray mechanism that would be programmed to clean the collecting cells nightly. This requires a drain  to a grease trap and a hot water connection to the unit. In the absence of a wash system, manual cleaning of the cells would be required as the plates coat with grease and lose their effectiveness. A high volume operation would almost certainly opt for a wash system. In either event, the cell would be taken out of the unit for periodic deep cleaning and inspection. Some systems have a wire as the ionizing medium and they are subject to breakage.

Depending on the system, an ESP can come with coarse filters before and after the collecting cell that are used to prevent larger particulate from fouling the cell or suppress water mist from being pulled down stream after a wash.

Odor Abatement

Either a filter unit or an ESP unit would have one of 2 main odor abatement technologies. The first is an odor neutralizing spray. This spray is injected into the clean air stream after the filters on a timing schedule. The frequency of spray is based on the volume of cooking.  This is a consumable item and must be replaced as it is depleted.

The other method of odor abatement is using activated carbon beds. The air coming off the collecting cells pass through the carbon bed. The gases are adsorbed by the carbon, reducing odor. The most effective carbon tested has been determined to be coconut shell. Once the carbon is depleted or adsorbed what it can, it must be replaced with fresh carbon.

While there is no objective standard for odor reduction or levels to meet, there are monitoring systems on the market that can measure the VOC concentrations entering and leaving the carbon to determine the effectiveness and life expectancy of the carbon.

No method is 100% effective, but the use of these systems significantly reduces smoke and odors.

Tags: , , , ,
Previous Post
Demand Control Ventilation
Code Issues

Is Demand Control Ventilation required on all projects?

Next Post
air ceiling registers
Design

How do replacement air ceiling registers affect the hood?

Leave a Reply

Your email address will not be published. Required fields are marked *