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Flue gas measuring technology for the trades Combustion diagram: Ideal operating range of heating installations
The aim of flue gas measuring technology is to ensure the environmentally friendly and economic operation of furnaces. The given formulae and tables can be used to understand flue gas measuring technology. They are also stored in the Testo flue gas analysers. All of the calculations are carried out automatically.
Lack of air
Fuel/ air mixture
Flue gas components
s los as g e Flu
Excess air
Carbon dioxide (CO
2)
Ideal operating range of furnaces
Ideal operating range of furnaces
Ca rbo nm on oxi de (C O)
) en (O 2 Oxyg
λ =1
Efficiency ( η )
Gross and net efficiency
Combustion efficiency is calculated by subtracting the combusting losses from 100% or maximum efficiency. Taking into account the condensation heat, values of more than 100% are possible in furnaces which operate in the so-called gross calorific value mode. This impossible value shown in the display indicates that the furnace is in the correct operating mode.
Efficiency values are calculated to give two values, gross and net. Gross values are calculated including losses due to the water content of fuels. Net values exclude these losses, this results in the net value being higher than the gross efficiency. The most important factor in calculating the efficiency level is the difference between the flue temperature and the ambient temperature. Testo analysers can simultaneously measure both ambient and flue gas temperatures.
Efficiency of a small furnace η = 100 % - qA qA = Flue gas loss (%)
Excess air
FT = Flue gas temperature AT = Ambient temperature K1, K2 = Specific fuel factors for net and gross K = Specific fuel factors for net and gross CO = Measures CO values in % CO2 = Measures CO2 values in % Q = Specific fuel factors for net and gross X = (MH20 = 9 x H) Moisture and hydrogen content fuel specific
Table of fuel specific factors Fuel
V K K K K gr net CO2 1 2
Natural Gas
0.350 0.390 11.9 40 44.3
Fuel Oil, Class D
0.480 0.510 15.4 53 56.4
Fuel Oil Classes
0.510 0.540 15.8 54 57.2
E,F & G (heavy oil) Coal
0.620 0.650 18.4 63 66.0
Anthracite
0.670 0.690 19.1 65 66.5
Coke
0.750 0.760 20.6 70 71.1
LPG propane
0.420 0.450 13.8 48 51.8
LGP butane
0.430 0.460 14.1 48 51.6
Calculating CO2 CO2 =
CO2max x (21 - O2) 21
Calculation of flue gas efficiency EFF =
-
K x FT-AT CO2
X x 210* - 42 x AT + 2.1 x FT Q K*2 x CO CO2 + CO
*Net Values
Excess air calculation λ In order to achieve full combustion it is necessary to supply the combustion with more air than is theoretically necessary. The ratio of this air to the theoretical air requirement is known as excess air.
Excess air value λ λ=
21 % O2 21 % O2 - % O2
- 1 x 100
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Flue gas measuring technology for the trades Efficiency
Why you should choose Testo flue gas analysers
Maximum efficiency is achieved if there is slight air excess and the flue gas efficiency is as high as possible. For further technical details contact your Testo sales office.
Optimum setting of heating installations
For maximum efficiency
CO2 should be as high as possible CO should be within safe limits (very low)
Chemical absorption kit 16 years ago chemical kits, the bimetallic thermometer and the smoke tester were the only aids available to adjust the optimum operative range in furnaces. The chemical kits always had one major disadvantage: a continuous measurement during adjustment work is not possible.
The effect of a correction to a burner setting was not immediately indicated. It is only with the following measurement that a result was shown.
This time-consuming and therefore very expensive method of flue gas measurement helped the electronic flue gas analysers to become an immediate success.
Then reset … shake again … adjust… shake etc.
NOX measurement
Electronic flue gas analysers from Testo
NOX consists of NO and NO2. NO2 levels in smaller heating installations which are less than 3 % of the total NOX level can be ignored. The measurement of NOX is becoming more important for the correct adjustment of modern NOX reduced burners. This is required by the manufacturer to adjust and approve the system since “low NOx” is becoming more and more important as a sales argument.
The flue gas analysers from Testo have been proving themselves for 16 years now. They are ready to operate after one minute and can continuously measure values.
In this way the rapid measurement and adjustment of furnaces is guaranteed. The life of the inserted measuring cells is between 2 and 3 years.
Gas measuring cells The chemical measuring cells in Testo flue gas analysers are used throughout the world and are of the highest technical standard. Many hours of work are required in Research and Development to create a suitable environment for the gas cells which includes the optimisation of the gas paths,
correct calculation of crosssensitivities and the uncomplicated method of changing the gas measuring cells by the user.
institutes measuring different measuring cell types have given Testo a headstart in this field.
16 years’ experience in the development of flue gas analysers as well as many years of cooperation with independent
This headstart is passed on to the customer in the form of compact, robust, high precision instruments and easy to change measuring cells.
- TÜV approval (D)
- ETV certification (CDN, USA)
- SCAQMD test (USA, CA)
- EAM approval (CH)
- GOS standard (CIS countries)
- Fulfills CTM-030 (EPA) (USA)
International approvals and tests Testo flue gas analysers are used worldwide and therefore have different approvals. Take testo 350 for example: