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Flue gas measuring technology for the trades

Excess air calculation

In order to achieve full combustionit is necessary to supply thecombustion with more air than istheoretically necessary. The ratio ofthis air to the theoretical airrequirement is known as excessair.

Efficiency ( )η

Combustion efficiency is calculatedby subtracting the combustinglosses from 100% or maximumefficiency. Taking into account thecondensation heat, values of morethan 100% are possible in furnaceswhich operate in the so-calledgross calorific value mode. Thisimpossible value shown in thedisplay indicates that the furnace isin the correct operating mode.

Ideal operating range of furnaces

Excess air value21 % O2= - 1 x 100

21 % O2 - % O2

Efficiency of a small furnace

= 100 % - qAqA = Flue gas loss (%)

Table of fuel specific factors

Fuel Kgr

Knet

VCO2

K1

K2

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

CO2max x (21 - O2)CO2 =21

FT = Flue gas temperatureAT = Ambient temperatureK1, K2 = Specific fuel factors for net and grossK = Specific fuel factors for net and grossCO = Measures CO values in %CO2 = Measures CO2 values in %Q = Specific fuel factors for net and grossX = (MH20 = 9 x H) Moisture and hydrogen

content fuel specific

Calculation of flue gasefficiency

K x FT-ATEFF = CO2

X x 210* - 42 x AT + 2.1 x FT-

Q

K*2 x CO-

CO2 + CO *Net Values

Gross and net efficiency

Efficiency values are calculated togive two values, gross and net.Gross values are calculatedincluding losses due to the watercontent of fuels. Net values excludethese losses, this results in the netvalue being higher than the grossefficiency. The most importantfactor in calculating the efficiencylevel is the difference between theflue temperature and the ambienttemperature. Testo analysers cansimultaneously measure bothambient and flue gas temperatures.

Flue

gas

com

pone

nts

Flue gas loss

Carbon dioxide (CO2)

Carbon monoxide (CO)

Oxygen (O2)

Fuel/air mixture

Lack of air Excess air

=1λλ

λλ

Excess air

Combustion diagram: Ideal operating range of heating installations

Idea

l ope

ratin

g ra

nge

of fu

rnac

es

The aim of flue gas measuringtechnology is to ensure theenvironmentally friendly andeconomic operation of furnaces.The given formulae and tables canbe used to understand flue gasmeasuring technology. They arealso stored in the Testo flue gasanalysers. All of the calculationsare carried out automatically.

ηλ

λ

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175

Efficiency

Maximum efficiency is achieved ifthere is slight air excess and theflue gas efficiency is as high aspossible. For further technicaldetails contact your Testo salesoffice.

NOX measurement

NOX consists of NO and NO2. NO2

levels in smaller heatinginstallations which are less than 3% of the total NOX level can beignored. The measurement of NOX

is becoming more important for thecorrect adjustment of modern NOX

reduced burners. This is requiredby the manufacturer to adjust andapprove the system since “lowNOx” is becoming more and moreimportant as a sales argument.

Testo flue gas analysers are usedworldwide and therefore havedifferent approvals. Take testo350 for example:

- TÜV approval (D)

- EAM approval (CH)

- ETV certification (CDN, USA)

- GOS standard (CIS countries)

- SCAQMD test (USA, CA)

- Fulfills CTM-030 (EPA) (USA)

International approvals and tests

Why you should choose Testo flue gas analysers

For maximum CO2 should beefficiency as high as

possible

CO should bewithin safe limits(very low)

Optimum setting of heating installations

Chemical absorption kit

16 years ago chemical kits, the bi-metallic thermometer and thesmoke tester were the only aidsavailable to adjust the optimumoperative range in furnaces. Thechemical kits always had one majordisadvantage: a continuousmeasurement during adjustmentwork is not possible.

Electronic flue gas analysers from Testo

The flue gas analysers from Testohave been proving themselves for16 years now. They are ready tooperate after one minute and cancontinuously measure values.

Gas measuring cells

correct calculation of cross-sensitivities and the uncomplicatedmethod of changing the gas meas-uring cells by the user.

16 years’ experience in thedevelopment of flue gas analysersas well as many years ofcooperation with independent

Flue gas measuring technology for the trades

The chemical measuring cells inTesto flue gas analysers are usedthroughout the world and are of thehighest technical standard.Many hours of work are required inResearch and Development tocreate a suitable environment forthe gas cells which includes theoptimisation of the gas paths,

The effect of a correction to aburner setting was not immediatelyindicated. It is only with thefollowing measurement that a resultwas shown.

Then reset … shake again …adjust… shake etc.

institutes measuring differentmeasuring cell types have givenTesto a headstart in this field.

This headstart is passed on to thecustomer in the form of compact,robust, high precision instrumentsand easy to change measuringcells.

This time-consuming and thereforevery expensive method of flue gasmeasurement helped the electronicflue gas analysers to become animmediate success.

In this way the rapid measurementand adjustment of furnaces is guar-anteed. The life of the insertedmeasuring cells is between 2 and 3 years.

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