EMISSION MEASURING EQUIPMENT FOR CO2,CO & HYDROCARBON

ByVinod SangodeRoll No.143616 (T.E)

IntroductionThe measurement of exhaust emissions is very important for the control of air pollution from Internal Combustion engine. The most serious pollutants recognized from the gasoline engine exhaust are Carbon monoxide (CO),Oxides of Nitrogen (NOx), & Hydrocarbons(HC)

Methods of emission Measurement

Non-separation Method Separation Method

1. NDIR (Non-dispersive infrared)

2. CLD (Chemiluminescence detector)

1.Orsat gas analyser

2. FID (Flame Ionization detector)

Type of Analyzers used for measurement of different exhaust gas constituents.

Gas Component

Measurement Principle

CO NDIR (Non-dispersive infrared)

HC FID (Flame Ionization detector)

NOx CLD (Chemiluminescence detector)

Flame Ionization Detector (FID)

Principle of FIDPure hydrogen-air flames are practically ion-free but on introduction of even little amount of hydrocarbons the flame causes considerable ionization and becomes electrically conducting. The ionization current is proportional to the number of carbon atoms present in the hydrocarbon molecules

Detector Construction FID is constructed of a small volume chamber into which the gas chromatograph's capillary column in directly plumbed.

Usually the small diameter capillary is fitted directly into the bottom of the detector's flame jet.

Electronic ignition source:- The flame is lit using a electronic ignite, actually an electrically heated filament that is turned on only to light the flame.

Collector plate :- Ion which is formed during combustion is collected in collector electrode.

Hydrogen-air burner

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Working of FIDEffluent from the column enters burner base through Millipore filters which remove contaminatesHydrogen mixed with gas stream at bottom of jet and air or oxygen is supplied axially around the jet. Hydrogen flame burns at the tip, which also functions as the cathode and is insulated form the body by a ceramic seal,Collector electrode is above the burner tip and is made of platinum

The effluent from the GC column passes through the flame, which breaks down organic molecules and produces ions.

Flame Ionization: during combustion, a uniform proportion (about 0.0002%) of the molecules in this reaction do this instead: (simplified for clarity)CH4 + O2 C++ H2O + e- CO2 + H2Oor:CH4 + 3O2 C++ O2 + 2H2O + e- CO2 + 2H2O

The ions are collected on a biased electrode and produce an electrical signal.

MechanismMost organic compounds produce ions and electrons that can conduct electricity through the flame. The number of ions hitting the collector is measured and a signal is generated.

Carbon counting device that produces a current proportional to number of ions or electrons formed in the flamed gases.

The amount of ions produced is roughly proportional to the number of reduced carbon atoms present in the flame and hence the number of molecules.

The flame ionization detector responds to the number of carbon atoms entering the detector per unit of time, it is a mass-sensitive,

The output of FID depends on the number of carbon atoms passing through the flame in a unit time.

Hexane(C6H14) would give double the output of propane(C3H8)

Limitations Molecules that contained only carbon and hydrogen respond best in this detector but the presence of "heteroatom" in a molecule, such as oxygen, decreases the detector's response.Example:- The FID's response for methane(CH4) is fabulous but formaldehyde's (CH2O) is quite poor. Therefore, highly oxygenated molecules or sulfides might best be detected using another detector instead of the FID. Sulfides determination by the flame photometric detector and aldehydes and ketones analyzed with the photo ionization detector are alternatives to the use of the FID for those molecules.

NDIR (Non-Dispersive Infrared ) Analyzer

Beer-Lambert's Law is used for operation of NDIR analyzers by measuring the degree of absorption of infrared (IR) radiations when they pass through a column of gas. The fraction of incident radiations absorbed is given by,

I/I0 =(1-e-kcd) where I = Radiation energy absorbed I0 = Incident radiation energy k = characteristic absorption constant for the gas, m2 /gmol c = concentration of the gas, gmol/m3

d = length of the gas column, m

Measurement of CO & CO2

Principle of “NDIR”NDIR analyzer used for measuring the concentrations of CO & CO2

This device is based on the principle that the infrared energy of a particular wavelength , peculiar to certain gas , will be absorbed by gas . The infrared energy of other wavelengths will be transmitted by gas.

Example:-Carbon dioxide absorbs infrared energy in the wavelength band of 4 to 4.5 microns & transmits the energy of surrounding wavelength.

NDIR construction1. A wideband infrared radiation source

2. Sample cell & Reference cell

3. Detector cell & flexible diaphragm

4. Rotating shutter

Working of NDIRTwo parallel beam of infrared radiation from the source enters to two cell (sample cell & Reference cell).

These cells are internally highly polished & gold plated to ensure high transmission of radiation.

After passing through these cell the IR radiation received in two separate detector cells(it contains the gas whose concentration is to be measured ).

Detector cell contain equal amount of gas and separated by a flexible diaphragm .

The sample cell is flow-through tube that receives a continuous stream of mixture of gases to be analyzed.

When the particular gas to be measured is present in the sample , it absorbs the IR of characteristic wavelength, & transmits other IR of other wavelength to gas.

The radiant energy , after passing through cells , heats the gas in the corresponding chamber of detector.

Since no radiant energy is absorbed in reference cell, the corresponding chamber in detector is heated more & its pressure becomes higher than that in other chamber.

This pressure differential causes the diaphragm to move & vary the capacitance.

The Variation in the capacitance is proportional to the species of interest in exhaust sample.

ORSAT APPARATUS

CONSTRUCTION Consists of a water-jacketed measuring

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

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

The graduated burette is surrounded by a water-jacket to keep the temperature of the gas constant during the experiment.

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

The absorption bulbs have solutions for the absorption of CO2, O2 and CO respectively.

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

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

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

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

WORKINGSTEP 1◦The whole apparatus is thoroughly cleaned, stoppers greased and then tested for air-tightness.

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

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

STEP 1 Contd..◦The three-way stop-cock is opened to the atmosphere and reservoir is raised, till the burette is completely filled with water and air is excluded from the burette.

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

STEP 1 Contd..◦the sample gas mixed with some air is present in the apparatus. So the three-way stop-cock is opened to the atmosphere, and the gas expelled out by raising the reservoir.

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

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

STEP 1 Contd..◦For adjusting final volume, the three-way stop-cock is opened to atmosphere and the reservoir is carefully raised, till the level of water in it is the same as in the burette, which stands at 100 mL mark.

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

STEP 2◦The stopper of the absorption bulb, containing caustic potash solution, is opened and all the gas is forced into this bulb by raising the water reservoir.

◦The gas is again sent to the burette. ◦This process is repeated several times to ensure complete absorption of CO2 [by KOH solution].

STEP 2 Contd..◦The unabsorbed gas is finally taken back to the burette, till the level of solution in the CO2 absorption bulb stands at the constant mark and then, its stop-cock is closed.

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

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

STEP 3◦ The volumes of O2 and CO are similarly determined by passing the remaining gas through alkaline pyrogallic acid bulb and ammonical cuprous chloride bulb respectively.

◦The gas remaining in burette after absorption of CO2, O2 and CO is taken as nitrogen.

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