Smoke Density Monitor

By Lars Josefsson

It is very easy to achieve a smokeless fire without any special equipment for supervision. On the other hand, to achieve a smokeless fire and economic combustion will be a bit harder. The air supply has to be slightly in excess of the theoretical requirements. That is, the combustion air flow is reduced almost to the smoke limit. A plant that never shows traces of smoke at the funnel is not burning the fuel efficiently.

There are four instruments that will help you to achieve the optimal combustion:

1. Smoke Density Monitor.  High smoke density indicates uneconomical combustion and it might also cause penalty from the environmental protecting authorities.
2. Oxygen (O2) - Analyzer.   High O2 content indicates heating of unnecessary high quantity of combustion air.
3. Carbon monoxide (CO) - Analyzer.  High CO content indicates unburned hydrocarbons. This is not only uneconomical, the CO is also harmful to mans health. Besides, mixed with air, CO might be an explosion risk.
4. Carbon dioxide (CO2) - Analyzer.  Low CO2 content indicates poor combustion, but it doesn’t tell if more or less air is required.

The most important instrument, the Smoke Density Monitor, happened to be the cheapest of them and you can’t do without it if you are trying to optimize the combustion of your burners. A Smoke Density Meter equipment is very simple. A light beam is sent across the flue duct, from a light emitter to a light receiver. An electronic unit monitors the opacity. It indicates 0% if there is no black smoke present and 100% if the light beam is totally absorbed by the smoke. An alarm activates if the smoke density exceeds a preset limit.

Remember; the most perfect equipment and the most complete knowledge will not result in the highest economy unless they are consistently used in daily operation.

Smoke Density Monitor is a very important instrument

• The Smoke Density Meter light emitter and light receiver are normally scavenged by sealing air to keep them free from soot. Therefore it would be vise to install these units higher up in the flue duct than the O2-analyzer to prevent the measured O2 value from being influenced by the smoke density meter sealing air flow.
• Check and clean the glasses of the smoke density meter light emitter and the light receiver regularly.
• The smoke density monitor alarm should be overridden during the burners start and stop sequences, since the opacity normally increases before the flame has stabilized.
• Never adjust the O2 content all the way down to zero unless you have facilities to check the CO content. The production of CO in a furnace should be avoided at all times since increased CO gives a sharp rise in heat-loss.
  Inhalation of CO by operators can produce a lethal effect upon the cells of the lungs.
• It might be worthwhile to spend a few minutes studying the diagram below.

Maintaining correct fuel to air ratio is essential to provide an efficient combustion.
At deficiency of air, the oxygen available will not be sufficient to burn all the fuel.
At excess of air, fuel will be used to heat the excess air from the boiler-room temperature to the funnel temperature.

The FUEL OIL Calculation Program  can easily calculate the theoretic requirement of air per kilogram of fuel.