Measuring Combustion Efficiency Using Flue Gas?

[turboco1]

Burning Bunker Fuel Oil:
Using chromatographic testing of flue gases, can a measured reduction in contaminating emission products in kg/h be translated to a measured reduction in the fuel oil being burned, kg/h?
i.e.
Change in Unburned Hydrocarbons in kg/h = 'x'barrils fuel oil

 

[mbeychok]

turboco1:

I am not very familiar with what chromatography can do. If your testing of "before" and "after" the reduction of unburned hydrocarbons can tell you the average molecular weight of the additional hydrocarbons that were burned, then you could get a pretty good estimate of their heating value (i.e., kJ/kg) and hence how much more heat was released. That additional heat release could then be translated to "x" barrels of fuel oil reduction.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[25362]

The products of incomplete combustion when burning low H/C mass ratio fuels, generally are (invisible) aldehydes, hydrogen and carbon monoxide, apart from (visible) black smoke.

If you could detect and measure all of these (before and after) you probably could make an assessment of the heat recovered by better burning.

I think, however, it would be easier to improve burning (for example, by better atomization and more xs air) and to make a mass-and-enthalpy balance to verify fuel savings.

 

[Flareman]

turboco1

What is the purpose of this study? If you are embarking on an academic exercise then of course you can analyze the flue gases and calculate what didn't burn. But is it worth the effort in the long run if you really want to improve the efficiency? In that respect I'm with 25362 (to some extent).

Unless the fuel is burning with "oodles" of black smoke, the probability is that you are already above 98% conversion (and probably actually better than 99%).
If your inefficiency is producing soot or dropping oil in the furnace you definitely need to address the burner atomization. In any event using more and smaller nozzle holes with the greatest possible distance detween them is always beneficial but the nozzle controls the flame shape and you have to think about possible flame impingement inside the furnace if you make changes (that would be even worse for efficiency) Review whether you can adjust the atomizing steam conditions or mechanical atomizing pressure. Check the fuel preheat temperature and make sure that the viscosity of the oil is not too high.

In the main, "inefficient" products such as CO and those nasty -CHO radicals which 25362 mentions (the invisible stuff) are more esily controlled (or improved) by changing the furnace temperature or residence time. For that you need to know what your furnace looks like, where the flue gases go and how long it takes to travel from one place to another. In an incinerator, you might be looking to get about 1 second residence above 1450 degF to clean up that stuff. In your case, you have to see where you cool down the flue gas because, I guess, this is a boiler or other heat transfer device. The faster you cool the flue gas, the worst (relatively) is the efficiency. That's why getting a clean compact flame with good atomization gets the job over and done with before the residence volumes become an issue.
At this point however, I might depart from 25362 just a little. Excess air control will certainly help you to "clean up" the combustion but it's as much about shaping how the air gets into the flame as it is about excess air per se. Excess air in itself is just another inefficiency, carrying heat out of the furnace. If you have a big convection bank then there are trade offs with flue gas volume and heat recovered but if you have a pedominantly radiant transfer requirement it's all about flame shape and reducing the excess air a little can possibly offset even a 1% fuel inefficiency.

Good luck.

 

[davefitz]

As has been stated above, a properly combusting flame envelope will evolve a pollutant emission stream with concentrations of pollutants in the range of 10-100 ppm, and this has only a small effect on combustion efficiency. You can make the calculation , the main difficulty is that many of the polutants are not measurable with typical plant instrumentation.

In some extreme cases , such as startups or low load operations, the pollutant concentrations can be in excess of 1000 ppm. The most typical item which is easily measured and used as a proxy for indications of other pollutants is CO, and there may be a rough correlation between CO levels and aromatics, dioxins, N2O, formaldehyde, etc. for each combustion technology. The use of the gas chromatograph might be useful for characterizing the low load behavior of teh plant, but once you put that information into a documented format, it becomes available for dicovery by permitting agencies. It has often been fascinating to see how these sorts of inconvenient emmission details become forgotten or invisible ( eg, N20 from fluid bed boilers, dioxin from garbage burning units, etc.)