Years ago, a colleague who had done his share of service calls remarked, "The three biggest problems in keeping combustion systems operating are, one: dirt, two: dirt and three: dirt." I'm inclined to agree.

Why Dirty Industrial Conditions Affect Oven and Burner Operation

You don't have to walk into too many plants to realize everyone has a different tolerance for dirt. Some places you can eat off the floor. In others, you don't even want to think of eating long after you've left the place. Some products or government standards demand cleanliness or you're out of business. But, there are plenty of places where dirt can enter the system without causing any catastrophic product problems, yet it still works its mischief. The combustion air system is a major one. Years ago, a colleague who had done his share of service calls remarked, "The three biggest problems in keeping combustion systems operating are, one: dirt, two: dirt and three: dirt." I'm inclined to agree.

Most modern combustion systems get their air from a fan -- a combustion blower pushing air through the burner, an exhaust fan pulling air in around the burner, or a combination of the two. Although they weren't intended to be, these fans also are efficient vacuum cleaners. Anything passing near their inlets is apt to get sucked in with the airstream and deposited in the burner system or oven. Airborne dust and dirt are the most common contaminants, but bigger stuff sometimes finds its way in too. I recall seeing a piece of plastic film about to disappear into a fan inlet -- someone had unwrapped his sandwich nearby and tossed the trash on the floor.

If your manufacturing operations generate airborne mists of sticky substances like oils, the problem is compounded. The mist gets drawn into the air system, where it deposits on the fan blades and inside the fan housing and piping. Along comes some dust, and it sticks to these components like it was glued on. Layers of goo and dust continue to alternate until you've got a serious buildup of junk.

This buildup will begin to starve your oven for air. Have you been bothered by any of these problems recently?

Apparent Loss of Heating Capacity

The oven can't get up to the temperatures it used to, or production has to be backed off to allow the oven to catch up.

The Burner Flame Seems to be Getting Longer

In fact, you're getting concerned that it's about to bore a hole in the recirculating fan or some downstream ductwork.
Airborne dust, pollen and other contaminants can choke your combustion system.

If so, it's time to check the system for dirt.

If your burner, like many, has a squirrel cage fan, start there. Those scoop-shaped fan blades are naturals for trapping dirt. Look for buildup in the fan housing while you're at it. Next, take a peek at the air ports in the burner head or diffuser plates. Many of them have lots of little openings, and it doesn't take a huge amount of gunk to start plugging them up. Don't forget to check out your air piping and ductwork, too. It's truly amazing where this crud can get a toe hold.

Don't have to go mucking around, you say? Your system is protected by inlet filters? Good, but when did you check them last? All a filter does is force the junk to collect outside the system, making it easier to remove. If you let the filter load up with grease, dust and dirt, your system will eventually be gasping for air, and that brings us to the next problem. Fans are big, noisy things, and most of them are located on the tops of ovens, off in dark corners or other out-of-the-way places. Out of sight, out of mind, and the buildup on the filters just gets thicker and thicker.

How do you deal with this all-too-natural tendency to forget the air filters? If you've established a preventative maintenance program, make filters one of the checklist items. Say, once a month, change every filter panel, no matter how clean it looks. If you favor high tech solutions, consider connecting a sensitive differential pressure switch across the filter. When the filter loads up, the differential switch makes and activates a flashing light or alarm.

However you choose to skin the cat, do it now. You'll reap the rewards in better productivity, more sensitive control and reduced maintenance.