PRESENTED BY :SATABDY JENAMTECH( POWER AND ENERGY SYSTEMS)ROLL NO.: T14EE003NIT MEGHALAYA

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CONTENTS

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INTRODUCTION

Exhaust gas generated through combustion processes is called flue

gas or stack gas. Its composition depends on the type of fuel and

the combustion conditions, e.g. the air ratio value. The common

fuels consist pimarily of carbon and hydrogen with their compounds

and the flue gases resulting from combustion contain oxides of these

elements and those of the impurities together with any excess air

and under some conditions, evolved from the heated material. Many

flue gas components are air pollutants and must therefore, due to

governmental regulations be eliminated or minimized by special

cleaning procedures before the gas is released to the atmosphere.

The exhaust gas in its original status is called raw gas, after cleaning

it is called clean gas. 3

An analysis of the flue gases gives evidence of efficiency of combustion and is a prime factor in controlling the operation for maximum results and in arriving at improvements in design.

Flue gas analysis indicates the air to fuel ratio. It is often desirable to predict the quantity and

analysis of the products of combustion to determine flue sizes and furnace pressure and to predict the magnitude of stack or flue gas losses.

There are equations to permit the calculation of the quantities of gases in the combustion products of gaseous fuels either by volume or by weight. The percentages to be submitted in all these equations are percentages by volume.

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COMPONENTS OF FLUE GAS

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SAMPLING Samples of flue gases are taken by means of

a tube and an aspirator bulb being drawn either directly into the analyzer or stored in glass sampling tubes for analysis at a later date. Sample tubes must be made of a gas tight material and it depends on temperature as follows:

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ORSAT TYPE

FYRITE TESTER

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1. GAS LIQUID CHROMATOGRAPHY: Gas liquid chromatography is a comparatively new

technique with a wide field of applications. It consists of the separation of the constituents of a flue gas by absorption on a packed column from a moving stream of carrier gas. The length of time each constituent gas is retained on a specific column is constant under given conditions. It is known as the retention time and it depends upon the temperature, flow rate of the carrier gas, size of column and the molecular

structure of the gas. For separating O2, N2, and CH4

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Column material Linde Molecular Sieve type 5A

Column length 2 meters

Operating temperature 40 centigrades

Sample size 1 ml

For seperating Air, methane, ethane, CO2 and propane

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Column material Silica gel

Column length 2 meters

Operating temperature 40 centigrades

Helium flow 50 ml/min

Sample size 1 ml

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Mass spectroscopy is primarily a lab technique requiring more expensive equipment than gas chromatography. In this procedure the molecular species making up a gaseous mixture are ionized and dissociated by electron bombardment, the resulting positive ions of different masses are then accelerated in an electric field and separated magnetically. A spectrogram is obtaibed showing the mass of each constituent and this is compared to a similar spectrograph for a known mixture. Instrumentation for mass spectroscopy is considerably expensive.

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For detection of CO :

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METHODS USED PURPOSE

Hoolamite iodine pentoxide indicator

To detect 0.1% or more of CO

Iodine pentoxide apparatus To trace amounts with precision and accuracy

Pyrotannic acid method To detect CO in blood

Infra red absorption Used when a standard reference sample is available

Colorimetric tubes To detect 0.001 to 0.1 % CO

Length of stain indicator Used for good accuracy

Water vapor is determined by sampling and the flue gas must reach the instrument at a temperature above the dew point. Dew point is defined as the temperature at which the vapor phase is in equilibrium with a minute quantity of liquid phase in any system. More simply it is the temperature at which condensation begins to occur.

The gas concentration is measured in ppm. Ppm means part per millions. 100 ppm is equivalent to 0.01%,1000 ppm is equivalent to 0.1%,10000

ppm is equivalent to 1%. Pollutants can be measured in mg/Nm3 ( milligrams per cubic meter ). This is mass refer to a volume in normal condition ( 0°C 1013 mBar ). Ppm is converted in this unit with a coefficient differen t for each gas.

Example : CO mg/Nm3 = CO ppm x 1.25 The conversion to an energy related unit can again be

done by multiplying a constant which is different for individual gases(mg/kWh :milligrams per kilowatt-hour of energy ).

Example : CO mg/kWh = CO ppm x 1.074

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CONCLUSION

Since flue gases consist of the end products of a combustion process, their composition is of interest and important from the view point of: 1.safety 2.efficiency and 3.computation of specific values which might affect the continuity of a process. In combustion process the common personnel hazard is carbon monoxide which can result from incomplete combustion. An operational hazard can be the formation of an explosive mixture. This hazard can be present wherever combustible gases or vapors are in contact with a substance which will support combustion and the properties are in the explosive range. Flue gas analysis can be used to detect and to confirm and locate suspected condition of this nature.

The use of flue gas analysis to promote efficiency are varied and many. Efficiency and economy do not necessarily imply the complete oxidation in the least amount of oxygen or air. It is the reason by which the goals for good utilization can be reached :

for gas appliances to operate safely without liberating injurious quantities of toxic gases.

for gas appliances to operate near optimum efficiency. 20

References :  [1] Flue gas analysis, Wikipedia [2] Products of combustion of gaseous fuels,

by Edwin L. Hall ARA Lab. [3] North American combustion handbook, by

the North American Manufacturing Company, Ohio

[4] Gas Liquid chromatography, by Stephen Dal

[5] Modern Gas Analysis, by P.W.Mullen [6] Manual for Hydrocarbon Analysis, by

AATM Special Technology Publisher No. 332

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