combustion introduction by raj

7/27/2019 Combustion Introduction by raj

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Bomb calorimeter


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If the fuel is solid, it is usually crushed, passed

through a sieve, and then pressed into the form ofa pellet in a special press.

The size of pellet is estimated from the expected

heat release, and is such that the temperature riseto be measured does not exceed 2-3 K.

If a liquid fuel is being tested, it is contained in a

gelatine capsule and the firing may be assisted byincluding in the crucible a little paraffin of knowncalorific value.


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The water equivalent of the calorimeter is

determined by burning a fuel of known calorificvalue (e.g. benzoic acid) in the bomb.

The calculation for the calorific value of the fueltestes is as follows:

Mass of fuel x Calorific Value= (mass of water+water equivalent of bomb)x corrected temperaturerise x specific heat capacity of water.


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Boys gas calorimeter


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For a gaseous fuel a continuous supply of the

gas is metered and passed at constant pressureinto the calorimeter, where it is burned in anample supply of air.

The products of combustion are cooled asnearly as possible to the initial temperature of

the reactants by a continuously circulatingsupply of cooling water.


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The gas pressure and temperature are measured

and the amount of gas burned is referred to 1.013bar and 15C.

The temperature rise of the circulating water ismeasured, and the condensate from the productsof combustion is collected.

A test is carried out over a fixed time period. Thewater flow rate is measured and the condensate isweighed.


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(Volume of fuel at 1.013 bar and 15C)

x(calorific value) = (mass of water circulated)x(specific heat capacity) x (temperature rise of

water)

The calorific value of the fuel is obtained in

megajoules per cubic metre of gas.


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Products of combustion

Depends on

Available time for reaction reaction rate Mixing of fuel oxidizer

Temperature and pressure

Can be determined by measurements

Orsat analyzer

Gas chrmomatograph

Infra-red analyzer

Flame ionization detector


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Orsat Gas Analyzer

Potassium Hydroxide (CausticPotash) for CO2

Alkaline Pyrogllol for O2

Ammoniacal Cuprous chloride

for CO


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Construction

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 ofalkaline

pyrogallic acid (25g pyrogallic acid+200g

KOH in 500 mL of distilled water) and it canabsorb CO2 and O2.


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Construction (contd.) 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, when only O2 will be

absorbed ( because CO2 has already been removed) and

finally through ammonical cuprous chloride bulb, where only

CO will be absorbed.


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Non-dispersive infrared (NDIR)

Gas Analyzer

CO

CO2

Sulphur

Nox

Hydrocarbons


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Gas Chromatograph A Gas Chromatograph is used to detect the components

based on the selective affinity of components towardsthe adsorbent materials.

The sample is introduced in the liquid/gas form withthe help of GC syringe into the injection port,

Sample is vaporized at injection port then passesthrough column with the help of continuously flowingcarrier stream (mobile phase), mainly H2 (for TCD),

Gets separated/detected at the detection port withsuitable temperature programming


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Gas Chromatograph


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Detectors - FID


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Flame Ionization Detector

Detection of ions formed during combustion of

organic compounds in a hydrogen flame.

The generation of these ions is proportional to the

concentration of organic species in sample gas.

Hydrocarbons generally have molar response

factors that are equal to number of carbon atoms

in their molecule

Carbon monoxide and carbon dioxide are not

detectable by FID.


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FID Advantages Cost: Flame ionization detectors are relatively inexpensive to acquire and

operate.

Low maintenance requirements: Apart from cleaning or replacing the FID

jet, these detectors require no maintenance.

Rugged construction: FIDs are relatively resistant to misuse.

Linearity and detection ranges: FIDs can measure organic substance

concentration at very low and very high levels, having a linear response of

10^6. Disadvantages

Flame ionization detectors cannot differentiate between different organic

substances.

They also cannot detect inorganic substances. In some systems, CO and CO2can be detected in the FID using a methanizer, which is a bed of Ni catalyst that

reduces CO and CO2 to methane, which can be in turn detected by the FID.

FID flame oxidizes all compounds that pass through it; all hydrocarbons and

oxygenates are oxidized to carbon dioxide and water and other heteroatoms are

oxidized according to thermodynamics. For this reason, FIDs tend to be the lastin a detector train and also cannot be used for preparatory work.


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Detectors - TCD


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Thermal Conductivity Detector (TCD)

The thermal conductivity detector (TCD), also

known as a Katharometer, is a bulk property detectorand a chemical specific detector

This detector senses changes in the thermalconductivity of the column effluent and compares it to a

reference flow of carrier gas. Since most compounds have a thermal conductivity

much less than that of the common carrier gases of

helium or hydrogen, when an analyte elutes from thecolumn the effluent thermal conductivity is reduced,and a detectable signal is produced.


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Thermal Conductivity Detector (TCD)

all compounds, organic

and inorganic, have athermal conductivitydifferent from helium,all compounds can be

detected by thisdetector.

The TCD is often calleda universal detectorbecause it responds toall compounds.

combustion introduction by raj

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