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Flue gas analysisFlue gas analysis

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Flue GasFlue Gas When fuels are burnt and produce the mixture ofWhen fuels are burnt and produce the mixture of gasesgases

like CO2, CO and O2 are evolvedlike CO2, CO and O2 are evolved..

If these gases still contain combustion heat, as soon asIf these gases still contain combustion heat, as soon asthey have conveyed their energy to the absorbingthey have conveyed their energy to the absorbing

surfaces of a heat exchanger, they are called heatingsurfaces of a heat exchanger, they are called heating

gases orgases orflue or stack gasflue or stack gas

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Significances of flue gas analysis (Significances of flue gas analysis (From theFrom the

constituents of COconstituents of CO22, CO and O, CO and O22 of flue gas)of flue gas) Free Co shows that the combustion is incompleteFree Co shows that the combustion is incomplete amt ofamt of

air used to be increasedair used to be increased

Free OFree O22 shows air supply is very much in excess, to ensureshows air supply is very much in excess, to ensure

complete combustion, it is essential to provide a certaincomplete combustion, it is essential to provide a certainamount of excess air.amount of excess air.

Presence of appreciable amt of both, CO and OPresence of appreciable amt of both, CO and O22 indicatesindicatesthe combustion is irregular and nonthe combustion is irregular and non--uniformuniform

Some parts of the furnace the air is excess and some otherSome parts of the furnace the air is excess and some otherparts air supply is insufficientparts air supply is insufficient-- combustion is irregular andcombustion is irregular andneeds immediate attentionneeds immediate attention

Determine the amount of air needed for completeDetermine the amount of air needed for completecombustion of fuelcombustion of fuel

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Flue Gas analysisFlue Gas analysis--OrsatOrsat ApparatusApparatus

Flue Gas analysisFlue Gas analysis-- is carried out by Orsat Apparatusis carried out by Orsat Apparatus

Used to measure volumes of carbon dioxide, oxygenUsed to measure volumes of carbon dioxide, oxygen

and carbon monoxide within a fixed volume of a flueand carbon monoxide within a fixed volume of a fluegas (100cc).gas (100cc).

To find the volume of a particular gas, the sampledTo find the volume of a particular gas, the sampled

gas is passed through a specific solution whichgas is passed through a specific solution whichabsorbs only the required gas.absorbs only the required gas.

The flue gas is passed through a sequence ofThe flue gas is passed through a sequence of

solutions each can remove one of the gases.solutions each can remove one of the gases.

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A solution ofA solution of

caustic potash (250 g KOH incaustic potash (250 g KOH in

dist. water)dist. water) is used to absorb theis used to absorb the carboncarbon

dioxidedioxide,,

A mixture ofA mixture of pyrogallic acid (25 g)pyrogallic acid (25 g), caustic, causticpotash(200 g) and (500 ml)potash(200 g) and (500 ml) dist.waterdist.water is usedis used

to absorb theto absorb the oxygen,oxygen,

To absorb theTo absorb the carbon monoxidecarbon monoxide.. AmmoniacalAmmoniacal

cuprous chloridecuprous chloride (100 g Cu(100 g Cu22ClCl22 + 125 ml+ 125 ml

liquid NHliquid NH

33 + 375 ml water) is used.+ 375 ml water) is used.

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Orsat Flue gas AnalyzerOrsat Flue gas Analyzer

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OrsatsOrsats apparatus consists of a horizontal tubeapparatus consists of a horizontal tube

having 3 way stopcock at one end and ahaving 3 way stopcock at one end and ameasuring burette at the other end.measuring burette at the other end.

The horizontal tube is connected to three differentThe horizontal tube is connected to three differentabsorption bulbs for the absorption of COabsorption bulbs for the absorption of CO22, O, O22and CO respectively.and CO respectively.

The lower end of the burette is connected to theThe lower end of the burette is connected to thewater reservoir.water reservoir.

The water level in the burette can be raised orThe water level in the burette can be raised or

lowered by raising or lowering the waterlowered by raising or lowering the waterreservoir.reservoir.

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Flue Gas AnalysisFlue Gas Analysis --PrecautionPrecaution All air from the burette is expelled by lifting the reservoirAll air from the burette is expelled by lifting the reservoir

bottlebottle

It is quite necessary to keep the absorbent bulbs in a certainIt is quite necessary to keep the absorbent bulbs in a certain

order to absorb different gasesorder to absorb different gases

This is because the absorbent used for OThis is because the absorbent used for O22 can absorb somecan absorb some

COCO22 and the detected would be less than the actual amountand the detected would be less than the actual amount

First bulbFirst bulb -- to absorb COto absorb CO22

Second bulbSecond bulb-- to absorb Oto absorb O22

Third bulbThird bulb to absorb COto absorb CO

The % of CO in flue gas is very small and that would beThe % of CO in flue gas is very small and that would be

measured quite carefullymeasured quite carefully

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Step 2Step 2::

The stopper of the absorption bulb 1The stopper of the absorption bulb 1containing KOH solution is opened and all gascontaining KOH solution is opened and all gasis forced into this bulb by raising the wateris forced into this bulb by raising the water

reservoir. The gas is again sent to burette byreservoir. The gas is again sent to burette bylowering the reservoir.lowering the reservoir.

The process is repeated several times to ensureThe process is repeated several times to ensurethe complete absorption of COthe complete absorption of CO22

The unabsorbed gas is sent back to buretteThe unabsorbed gas is sent back to burette The decrease in volume of flue gas in theThe decrease in volume of flue gas in the

burette indicates the volume of COburette indicates the volume of CO22 in 100mlin 100ml

of flue gasof flue gas

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Step 3:Step 3:

The volume of OThe volume of O22 and CO are similarlyand CO are similarlydetermined by passing the remaining gasdetermined by passing the remaining gasthrough alkaline Pyrogallic acid bulb andthrough alkaline Pyrogallic acid bulb andammoniacal cuprous chloride bulb respectivelyammoniacal cuprous chloride bulb respectively

The gas remaining in the burette after theThe gas remaining in the burette after theabsorption of COabsorption of CO22,O,O22 and CO is taken as Nand CO is taken as N22