7 Flue gas measurement
Concentrations and effects on human beings:
>2.500 ppm Death after a few minutes
1000 ppm Heart palpitations after 30 minutes, dizziness after 1.5 hours, headache, confusion, delirium,
nausea after 2 hours, death after 6 hours
400 ppm Headache and nausea after 1 to 2 hours
100 ppm Significant impairment to health only after continuous inhalation
Limit value: 30 ppm – Maximum workplace concentration (MAK value)
7.1.8 Nitrogen oxides (NOX)
• Nitrogen oxide (approximately 95 %) and NO2
• Units: ppm, mg/Nm³ at 13 % O2, mg/MJ
•NO
x occurs when wood is combusted; from the nitrogen of the wood. Currently it can barely be influenced by
the boiler setting.
• NO is measured. NO
x is calculated from the measurement.
•NO
2 is a red-brown gas
• Irritates the lungs and causes ozone formation and acid rain
With natural wood (nitrogen content < 0.15 % by weight) the limit value must be maintained. If there are impurities
(clay, grain, etc.) that contain nitrogen the nitrogen oxide values increase. Significantly increased measured values
always indicate such impurities.
7.1.9 Hydrocarbons (HC, CxHy, Corg)
• Hydrocarbons, many different substances (gases, tar, smoke, acids)
• Units: ppm, mg/Nm³ at 13 % O
2, mg/MJ
• CxHy occur with gasification of the wood, before it burns. They are only found in the flue gas if there is
incomplete combustion, due to combustion temperatures that are too low.
• Difficult to measure due to the many compounds. However the emissions behave like the CO emissions behave
in the combustion of pure wood.
• “Smokehouse odour”, stinging heavy smoke, causes smog
7.1.10 Dust
• All solid particles in the flue gas: Fly ash, soot and fuel particles
• Unit: mg/Nm³ at 13 % O
2, mg/MJ
• The dust values are increased with fine fuels and if there is significant lack of oxygen (soot formation). In the
first case dust values can be lowered slightly with less primary air. In the second case dust values can be
lowered by supplying more oxygen.
• Different measurement processes are used:
Ringelmann scale: Soot content is determined via the degree of blackening of a filter disk or
Gravimetric determination: Flue gas is suctioned through a glass fibre filter. This filter is weighed before and
after the measurement. (1st Ordinance on Waste Incineration and Co-Incineration (BimSchV), type test).
MA-Easyfire 10.2008_EN.indd 75MA-Easyfire 10.2008_EN.indd 75 30.03.2009 13:30:12 Uhr30.03.2009 13:30:12 Uhr
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