orsat apparatus

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FLUE GAS FLUE GAS ANALYSIS ANALYSIS ORSAT ORSAT APPARATUS APPARATUS

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Page 1: Orsat Apparatus

FLUE GAS FLUE GAS ANALYSISANALYSIS

ORSAT ORSAT APPARATUSAPPARATUS

Page 2: Orsat Apparatus

ORSAT APPARATUS ORSAT APPARATUS This apparatus involves the This apparatus involves the

following following IntroductionIntroduction Construction Construction WorkingWorking

Includes three steps.Includes three steps. Precautions Precautions CalculationCalculation

Page 3: Orsat Apparatus

INTRODUCTIONINTRODUCTION To have proper control on combustionTo have proper control on combustion

processprocess, an idea about complete or , an idea about complete or complete combustion of fuel is made complete combustion of fuel is made by the by the analysis of flue gasanalysis of flue gas. Thus,. Thus,(i) if the gases contain considerable (i) if the gases contain considerable amount of amount of carbon monoxidecarbon monoxide,, it it indicates that indicates that incompleteincomplete combustioncombustion is occurring (i.e. considerable is occurring (i.e. considerable wastagewastage of fuelof fuel is taking flue). is taking flue).

Page 4: Orsat Apparatus

INTRODUCTION Contd..INTRODUCTION Contd.. Also indicates the Also indicates the short supply of short supply of

oxygenoxygen for combustion for combustion(ii) if the flue gases contain a (ii) if the flue gases contain a considerable amount of considerable amount of oxygenoxygen, it , it indicates indicates the oxygen supply isthe oxygen supply is in in excessexcess, though the combustion may be , though the combustion may be complete.complete.

The analysis of flue gases made with The analysis of flue gases made with the help of the help of ORSAT’S APPARATUS.ORSAT’S APPARATUS.

Page 5: Orsat Apparatus

ORSAT APPARATUS ORSAT APPARATUS Contd..Contd..

Page 6: Orsat Apparatus

CONSTRUCTIONCONSTRUCTION Consists of a Consists of a water-jacketed measuring water-jacketed measuring

burette, burette, connected in series to a set of connected in series to a set of three absorption bulbs, three absorption bulbs, each through a each through a stop-cock. stop-cock.

The other end is provided with a The other end is provided with a three-three-wayway stop-cock, stop-cock, the free end of which is the free end of which is further connected to a further connected to a U-tube packed U-tube packed with glass wool with glass wool (for avoiding the (for avoiding the incoming of any smoke particles, etc.) incoming of any smoke particles, etc.)

Page 7: Orsat Apparatus

CONSTRUCTION Contd..CONSTRUCTION Contd.. The graduated burette is surrounded by The graduated burette is surrounded by a a

water-jacket water-jacket to keep the temperature of to keep the temperature of the gas constant during the experiment.the gas constant during the experiment.

The lower end of the burette is connected The lower end of the burette is connected to a to a water reservoir water reservoir by means of a by means of a long long rubber tubingrubber tubing..

The absorption bulbs are usually filled The absorption bulbs are usually filled with glass tubes, so that the surface area with glass tubes, so that the surface area of contact between the gas and the of contact between the gas and the solution is increased.solution is increased.

Page 8: Orsat Apparatus

CONSTRUCTION Contd..CONSTRUCTION Contd.. The absorption bulbs have solutions for The absorption bulbs have solutions for

the absorption of CO2, O2 and CO the absorption of CO2, O2 and CO respectively.respectively.

First bulb First bulb has has ‘potassium hydroxide’ ‘potassium hydroxide’ solutionsolution (250g KOH in 500mL of boiled (250g KOH in 500mL of boiled distilled water), and distilled water), and it absorbs only CO2.it absorbs only CO2.

Second bulb Second bulb has a solution of has a solution of ‘alkaline ‘alkaline pyrogallic acid’ pyrogallic acid’ (25g pyrogallic acid+200g (25g pyrogallic acid+200g KOH in 500 mL of distilled water) and KOH in 500 mL of distilled water) and it it can absorb CO2 and O2. can absorb CO2 and O2.

Page 9: Orsat Apparatus

CONSTRUCTION Contd..CONSTRUCTION Contd.. Third bulb Third bulb contains contains ‘ammonical cuprous ‘ammonical cuprous

chloride’ chloride’ (100g cuprous chloride + 125 mL (100g cuprous chloride + 125 mL liquor ammonia+375 mL of water) and liquor ammonia+375 mL of water) and it it can absorb CO2, O2 and CO.can absorb CO2, O2 and CO.

Hence, Hence, it is necessary that the flue gas is it is necessary that the flue gas is passed first through potassium hydroxide passed first through potassium hydroxide bulb, where CO2 is absorbed, then through bulb, where CO2 is absorbed, then through alkaline pyrogallic acid bulb, when only O2 alkaline pyrogallic acid bulb, when only O2 will be absorbed ( because CO2 has will be absorbed ( because CO2 has already been removed) and finally through already been removed) and finally through ammonical cuprous chloride bulb, where ammonical cuprous chloride bulb, where only CO will be absorbed.only CO will be absorbed.

Page 10: Orsat Apparatus

WORKINGWORKING STEP 1STEP 1

The whole apparatus is thoroughly The whole apparatus is thoroughly cleaned, stoppers greased and then cleaned, stoppers greased and then tested for air-tightness. tested for air-tightness.

The absorption bulbs are filled with their The absorption bulbs are filled with their respective solutions to level just below respective solutions to level just below their rubber connections.their rubber connections.

Their stop-cocks are then closed. The Their stop-cocks are then closed. The jacket and levelling reservoir are filled jacket and levelling reservoir are filled with water. with water.

Page 11: Orsat Apparatus

WORKING Contd..WORKING Contd.. STEP 1 Contd..STEP 1 Contd..

The three-way stop-cock is opened to the The three-way stop-cock is opened to the atmosphere and reservoir is raised, till atmosphere and reservoir is raised, till the burette is completely filled with the burette is completely filled with water and air is excluded from the water and air is excluded from the burette. burette.

The three-way stop-cock is now The three-way stop-cock is now connected to the flue gas supply and the connected to the flue gas supply and the reservoir is lowered to draw in the gas, reservoir is lowered to draw in the gas, to be analysed, in the burette. to be analysed, in the burette.

Page 12: Orsat Apparatus

WORKING Contd..WORKING Contd.. STEP 1 Contd..STEP 1 Contd..

the sample gas mixed with some air is the sample gas mixed with some air is present in the apparatus. So the three-way present in the apparatus. So the three-way stop-cock is opened to the atmosphere, and stop-cock is opened to the atmosphere, and the gas expelled out by raising the the gas expelled out by raising the reservoir. reservoir.

This process of sucking and exhausting of This process of sucking and exhausting of gas is repeated 3-4 times, so as to expel the gas is repeated 3-4 times, so as to expel the air from the capillary connecting tubes, etc. air from the capillary connecting tubes, etc.

Finally, gas is sucked in the burette and the Finally, gas is sucked in the burette and the volume of the flue gas is adjusted to 100 mL volume of the flue gas is adjusted to 100 mL at atmospheric pressure. at atmospheric pressure.

Page 13: Orsat Apparatus

WORKING Contd..WORKING Contd.. STEP 1 Contd..STEP 1 Contd..

For adjusting final volume, the three-For adjusting final volume, the three-way stop-cock is opened to atmosphere way stop-cock is opened to atmosphere and the reservoir is carefully raised, till and the reservoir is carefully raised, till the level ofwater in it is the same as in the level ofwater in it is the same as in the burette, which stands at 100 mL the burette, which stands at 100 mL mark. mark.

The three-way stop-cock is then closed.The three-way stop-cock is then closed.

Page 14: Orsat Apparatus

WORKING Contd..WORKING Contd.. STEP 2STEP 2

The stopper of the absorption bulb, The stopper of the absorption bulb, containing caustic potash solution, is containing caustic potash solution, is opened and all the gas is forced into opened and all the gas is forced into this bulb by raising the water reservoir. this bulb by raising the water reservoir.

The gas is again sent to the burette. The gas is again sent to the burette. This process is repeated several times This process is repeated several times

to ensure complete absorption of CO2 to ensure complete absorption of CO2 [by KOH solution]. [by KOH solution].

Page 15: Orsat Apparatus

WORKING Contd..WORKING Contd.. STEP 2 Contd..STEP 2 Contd..

The unabsorbed gas is finally taken back to The unabsorbed gas is finally taken back to the burette, till the level of solution in the the burette, till the level of solution in the CO2 absorption bulb stands at the constant CO2 absorption bulb stands at the constant mark and then, its stop-cock is closed. mark and then, its stop-cock is closed.

The levels of water in the burette and The levels of water in the burette and reservoir are equalised and the volume of reservoir are equalised and the volume of residual gas is noted. residual gas is noted.

The decrease in volume-gives the volume of The decrease in volume-gives the volume of CO2 in 100 mL of the flue gas sample.CO2 in 100 mL of the flue gas sample.

Page 16: Orsat Apparatus

WORKING Contd..WORKING Contd.. STEP 3STEP 3

The volumes of OThe volumes of O2 2 and CO are similarly and CO are similarly determined by passing the remaining determined by passing the remaining gas gas through alkaline pyrogallic acid through alkaline pyrogallic acid bulb and ammonical cuprous chloride bulb and ammonical cuprous chloride bulb respectively.bulb respectively.

The gas remaining in burette after The gas remaining in burette after absorption of COabsorption of CO22, O, O22 and CO is taken and CO is taken as nitrogen.as nitrogen.

Page 17: Orsat Apparatus

PRECAUTIONSPRECAUTIONS The reagents in the absorption bulb 1, 2 The reagents in the absorption bulb 1, 2

and 3 are brought to the and 3 are brought to the etched mark etched mark levelslevels one-by-one by operating the one-by-one by operating the reservoir bottle and the valve of each reservoir bottle and the valve of each bulb. Then their respective valves are bulb. Then their respective valves are closed.closed.

All the air in the reservoir bottle is All the air in the reservoir bottle is expelled to atmosphere by lifting the expelled to atmosphere by lifting the reservoir bottle and opening the three-reservoir bottle and opening the three-way to atmosphere.way to atmosphere.

Page 18: Orsat Apparatus

PRECAUTIONSPRECAUTIONS The three-way is then connected to the The three-way is then connected to the

flue gas supply and the reservoir bottle flue gas supply and the reservoir bottle is brought down, until the level in the is brought down, until the level in the burette becomes zero (burette becomes zero (i.e., i.e., 100 mL of 100 mL of gas is taken in the burette). The gas in gas is taken in the burette). The gas in the burette is expelled to the the burette is expelled to the atmosphere to remove any air left in the atmosphere to remove any air left in the joints, tubes, etc. This procedure is joints, tubes, etc. This procedure is repeated 2-3 times to ensure a right repeated 2-3 times to ensure a right sample of the gas taken for analysis.sample of the gas taken for analysis.

Page 19: Orsat Apparatus

PRECAUTIONSPRECAUTIONS It is quite necessary to follow the It is quite necessary to follow the order of order of

absorbing gases: absorbing gases: COCO22 first, O first, O22 second and second and CO last. This is because the absorbent used CO last. This is because the absorbent used for Ofor O22 ( (i.e., alkaline pyrogallic acid)i.e., alkaline pyrogallic acid) can can absorb only some COabsorb only some CO22 and the percentage and the percentage COCO22 left would be less; while the percentage left would be less; while the percentage of Oof O22 thus-detected would be more. The thus-detected would be more. The absorbent used for COabsorbent used for CO22, however, does not , however, does not absorb Oabsorb O22 or CO or CO22..

The % CO in the flue gas is very small The % CO in the flue gas is very small and and this should be measured quite carefully.this should be measured quite carefully.

Page 20: Orsat Apparatus

CalculationCalculation A hydrocarbon is burnt with A hydrocarbon is burnt with

excess air. The Orsat analysis of excess air. The Orsat analysis of the flue gas shows 10.81% COthe flue gas shows 10.81% CO22, , 3.78% O3.78% O22 and 85.40 N and 85.40 N22. Calculate . Calculate the atomic ratio of C:H in the the atomic ratio of C:H in the hydrocarbon and the % excess hydrocarbon and the % excess air.air.

Page 21: Orsat Apparatus

Calculations:Calculations: 100 moles of dry flue gas (i.e., excepting H100 moles of dry flue gas (i.e., excepting H22O)O) The Orsat analysis shows the compositions of the flue gases by not taking into account of The Orsat analysis shows the compositions of the flue gases by not taking into account of

HH22O.O. From the composition of air(mole %), From the composition of air(mole %), Here, nitrogen is the tie component.Here, nitrogen is the tie component. 79 mole of N79 mole of N22 h 21 mole of O h 21 mole of O22 Therefore, OTherefore, O22 that is entering the burner = 85.4 x 21/79 = 22.7 that is entering the burner = 85.4 x 21/79 = 22.7 C + OC + O22 à CO à CO22

1 mole of CO1 mole of CO2 2 h 1 mole of Oh 1 mole of O22 h 1 atom of C ( i.e.,1 mole of O h 1 atom of C ( i.e.,1 mole of O22 reacts with 1 atom of C to reacts with 1 atom of C to produce 1 mole of COproduce 1 mole of CO22))

Therefore, OTherefore, O2 2 used up for reacting with carbon = 10.81 mole and, used up for reacting with carbon = 10.81 mole and, Carbon in the hydrocarbon = 10.81 atomsCarbon in the hydrocarbon = 10.81 atoms OO2 2 reacted with Hydrogen in the hydrocarbon = 22.7 - (10.81 + 3.78) = 8.11reacted with Hydrogen in the hydrocarbon = 22.7 - (10.81 + 3.78) = 8.11 4H + O4H + O22 à 2H à 2H22OO 1 mole of O1 mole of O22 reacts with 4 atoms of hydrogen. reacts with 4 atoms of hydrogen. Therefore, hydrogen in the hydrocarbon = 8.11 x 4 = 32.44 atoms.Therefore, hydrogen in the hydrocarbon = 8.11 x 4 = 32.44 atoms. C:H ratio in the hydrocarbonC:H ratio in the hydrocarbon = 1 : 32.44/10.81 = = 1 : 32.44/10.81 = 1 : 31 : 3 Theoretical air demand = air needed for complete conversion of carbon to carbon dioxide Theoretical air demand = air needed for complete conversion of carbon to carbon dioxide

and hydrogen to water vaporand hydrogen to water vapor % excess air% excess air = 100 x (actual air used - theoretical air demand) / theoretical air demand = 100 x (actual air used - theoretical air demand) / theoretical air demand = 100 x (22.7 - (10.81 + 8.11))/( 10.81 + 8.11) = = 100 x (22.7 - (10.81 + 8.11))/( 10.81 + 8.11) = 20%20%