Combustion And Performance – Flashcards

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Properties of Gas
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Gases are Hydrocarbons
React readily with Oxygen
Known as Combustion
3 diff groups (family of gases)
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1st Family of Gas
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Manufactured Gas
Any gas produced through industrial process
coke gas, coal gas and towns gas
phase out og general use
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2nd Family of Gas
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Natural Gas.
formed from decomposition of organic material.
Main component Methane in UK 82-97% of total volume of gas
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3rd Family of Gas
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Liquid Petroleum Gas (LPG)
LPG is a by product from extraction of natural gas.
LPG can be either Propane or Butane
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Odour and Colour of Gases
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Nat gas,propane and Butane all colourless and odourless
Odorants are called Thiols
Nat gas-methyl
LPG-t butyl mercaptan,ethyl mercaptan
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Toxicity of Gases
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Nat gas and LPG do not contain Co
still a risk of asphyxiation due to gas displacing Oxygen.
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Specific Gravity (Relative Density)
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Air S.G = 1
Nat Gas = 0.6-0.7 (lighter than air)
Propane =1.5
Butane= 2 (Heavier than air)
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Calorific Value
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Is the amount of energy released when a specific quantity of gas is burnt under standard ref conditions
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Wobbe Number
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Is an indication of the heat which can be produced from a burner using a particular gas
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Flammability Limits
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is the range of concentration of gas mixed with air.
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Ignition Temperature of natural gas
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ignition temps
Methane -632*C-704*C
Propane- 493*C-547*C
Butane-413*C-527*C
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Combustion
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Combustion is a chemical reaction between the fuel gas and oxygen
which produces 2 main gases
Carbon Dioxide CO2
Water Vapour H2O
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CH4+2O2=CO2+2H2o
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The Chemical equation for complete combustion of Methane
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CH4
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Chemical Symbol for
Methane.
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Stoichiometric Combustion
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A theoretical concept which can only be achieved under strict laboratory conditions
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Equation for IN-COMPLETE combustion of natural gas
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CH4 + 1.5O2= CO + 2H2O
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The Flame speed of natural gas
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0.36m/s
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Explosive limits of natural gas
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5% to 15% Gas in Air
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Chemical produced by burning natural gas
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1.Alcohol
2.Aldehyde
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What % of O2 is required to sustain life
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Between 19%-21%
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. What is the approximate volume of air required to completely burn 5 m3 of natural gas?
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50m3
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Causes of Incomplete Combustion
Inadequate Ventilation
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Supply of combustion air to the appliance burner has become restricted or contaminated
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Causes of Incomplete Combustion
Vitiation of Atmosphere
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Where the air used to supply the appliance becomes
DEFICIENT IN OXYGEN
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Causes of Incomplete Combustion
Contamination Of Burner
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Debris deposits build up creating a restriction to the air floe to the burner
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Causes of Incomplete Combustion
Poor Flueing
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POCs not being removed will re enter the area and re-circulate into the appliance combustion chamber.
As the air has already been burnt its O2 has been reduced and no longer support complete combustion
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Causes of Incomplete Combustion
Blocked Flueways
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Flueways are the path that POCs pass through,when this is restricted the POCs re enter the chamber affecting combustion
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Causes of Incomplete Combustion
Flame Chilling
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Hitting a surface cooler than temp of ignition.
No longer supports complete combustion
This can happen when flame touches a heat exchanger.
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Causes of Incomplete Combustion
Flame Impingement
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When one flame touches another or cold surface
Incomplete combustion is created by one flame robbing the other of secondary air or by chilling
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Causes of Incomplete Combustion
Gas Rich Mixture
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Supplying too much gas (over gassing)
Too much gas will create a "reducing flame"
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Causes of Incomplete Combustion
Lean Gas Mixture
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Created either by supplying not enough gas(under gassing).
or correct amount of gas but too much air
too much air creates an "Oxidising" flame
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