E5: Select Gas Burners Flashcards
Gas burners can be either?
Mechanical or Non-Mechanical
What determines the type of gas burner is used?
How the combustion air is supplied
What’s another name for Non-mechanical gas burner?
atmospheric burner
What do non-mechanical rely on for combustion air?
Atmospheric pressure
What is High Fire?
max firing rate of a burner
Is the max fuel input / heat output a burner can safely be operated at.
Low fire
min input of fuel required to keep a burner from flaming out
Modulation
Vary gas input / vary heat output to a process in order to match heat load requirement / sustain the desired temp
What is Turndown ratio? (TURNED DOWN FOR WHAT!)
ratio of the max fuel input : min fuel input rate for modulating burner.
What is the Turndown ratio used for?
To help determine how low a boiler can modulate before it turns off
Port loading
the amount of gas-air mixture passing through a burner that will create a stable flame
What is port loading burner express as?
BTUs / square inch of port area
How can the port loading be changed?
By altering the orifice size or gas pressure (manifold pressure)
Port loading (NG) bn 25,000 - 30,000 BTUs / square inch indicates what?
Stable flame
An atmospheric burner has a venturi that sucks primary air into where?
The burner / mixes air and gas before ignition
How do Mechanical burners get their supply requirements for air combustion?
They use a fan or blower
How are Mechanical burners categorized?
by:
1) location of the fan / blower in relation to the combustion chamber
2) Air pressure being delivered via burner / where the gas + air are mixed in the burner
What are the different kinds of Mechanical burners?
1) Forced Draft Burner
2) Induced Draft Burner
3) Balanced draft burner
4) Fan - assisted burner
What is a forced draft burner?
Combustion air is supplied by a fan or blower at sufficient pressure that overcomes resistance of the burner / appliance
How does a forced air burner work?
Supplies air to burner / forces products of combustion through the appliance
Where is the fan or blower located?
Upstream of the combustion zone
How does a induced draft burner operate?
Uses mechanical draft produced by a fan located downstream / chimney side of combustion zone
How is an Induced draft fan designed?
to pull in required air supply for combustion / vent products of combustion w/ positive vent pressure
How is the Balanced Draft burner different?
It’s a combination of forced / induced draft
Where are Balanced Draft burners mostly seen?
Larger boilers w/ multiple passes where the flue gases have to travel long distances
What is a Fan assisted burner?
Is a burner in which the combustion air is supplied by a mechanical device (fan / blower) at sufficient pressure to overcome the resistance of the burner only.
Where is the fan located?
upstream: fan assisted conversion burner
downstream: Fan assisted combustion system
Fan assisted systems give more precise control over what?
the air entering the combustion chamber
Mechanical combustion products are vented how?
Naturally w/ a nonpositive vent stack pressure
What is a pre-mix burner?
Mix the required amounts of air / gas before ignition
What are 3 types of pre-mix burners?
(MAG)
1) Inspirator or Gas Jet mixer
2) Aspirating Mixer
3) Mechanical Mixer
Inspirator burner uses what type of gas?
High pressure gas of 10 psi or more
Inspirators can entrain / pre mix up to what % of required combustion air?
100%
How does an Aspirating mixer work?
Uses pressurized air, issued at high velocity via venturi to entrain / mix gas
Aspirating mixer are common where?
on residential / commercial condensing boilers dt their excellent turndown
What does an Aspirating mixer use to mix gas?
Pressurized air at high velocity via a venturi
How is a Mechanical mixer straight forward?
uses a fan or blower to mix / supply air and gas to burner
How do burners create a stable flame?
by balancing the different combustion properties of gas - air mixture
What happens when combustion limits are exceeded?
The combustion process won’t generate enough heat and flame will go out
What are the 4 combustion properties that effect the burner flame?
(LIMM)
1) Limits of flammability
2) Max flame speed
3) Ignition temp
4) Max flame temp
What are limits of flammability?
the upper and lower ranges of gas that support combustion
What is max flame speed?
The velocity the flame front moves towards the air-gas mixture
What is NG burn ratio?
4-15% fuel
A stable flame will has a what?
A balanced air-gas flow velocity / flame speed (that keeps the flame front close to burner spot)
What is ignition temp?
Is the temp at which an air-gas mixture will initiate / support combustion
What is flame temperature?
Max flame temp can only be reached at perfect combustion
True or False: Each fuel gas has its own max flame temp.
True
What is NG ignition temp?
700C - 1300F
What is the ignition temp of Propane?
490C - 920F
What is the ignition temp of Butane?
1980C - 3600F
What is a flame retention device?
When gas-air mixtures flow into sheltered areas / burns –> generating enough heat to ignite gas/air mixture leaving the burner head
What is a flame stabilizing device?
Provides shelter for the air-gas mixture to essentially ignite
What is the basics of an atmospheric burner?
a device that requires no fans or electrical supply
burns gas simply / efficiently
What are the 2 types of atmospheric burners?
1) Luminous
2) Bunsen burner
What does the luminous flame depend on for combustion?
the air around the flame (secondary air)
(it does not premix gas-mix mixture)
Why does the luminous flame have a small blue flame / large yellow flame?
Blue flame: hydrogen burns fast
Yellow flame: Carbon burns hot
Why does the Bunsen flame more efficient?
It premixes air w/ gas prior to ignition
True or False: a stable atmospheric Bunsen burner flame has several colour zones
True
each zone marks a stage in burning of the gas
What is the inner cone of a Bunsen flame?
Here gas is burned to form products (aldehydes, alcohols, CO + H)
Is the blue flame
Unburned gas mixture forms the shape of flame
What is the Outer cone
Here the secondary air around the flame diffuses into the flame takes part in burning
Inner cone products are completely burned here
Where does the highest flame temp occur?
Just above the outer cone tip
What is the Outer mantle?
- it’s colourless, surrounds outer cone
- contains no unburned gases
- Glows dt combustion products high temps
What are the 3 types of Bunsen flames?
(RON)
1) Reducing flame
2) Oxidizing flame
3) Neutral flame
What colour of flame will a Bunsen flame have if it’s stable?
Blue
What is a reducing flame?
Is a flame w/ low oxygen
What colour of flame will a reducing flame have?
Yellow dt the presence of unburned carbon (or hydrocarbons)
What’s the second name for a reducing flame?
Carburizing flame
Why is it called a Carburizing flame?
When being brazed or welded carbon is introduced into molten metal…
What is an oxidizing flame?
flame produced w/ an excessive amount of oxygen
What happens when you increase oxygen in an oxidizing flame?
flame shortens
colour darkens
hisses / roar
Is the oxidizing flame good or bad for welding / soldering?
No, it oxidizes the metal’s surface
What is the neutral flame?
The amount of oxygen is enough for burning
Oxidation / reduction does not occur
What colour of flame is the neutral flame?
clear blue due to a good balance of oxygen
What happens when a cold surface touches the inner cone of a bunsen burner?
temp decreases / causes incomplete combustion
What is an indicator of flame impingement?
Soot forming on the colder surface
Can impingement cause incomplete combustion in the occur in the outer cone?
No, this flame is too hot / maintains the temp for combustion
Is flow velocity the same at all points across a burner port?
No
What is a venturi?
Is a short tube w/ a constricted, throat - like passage
What does the narrowing passage of a venturi do?
Increases the velocity / creates a negative pressure in relation to the air surrounding the burner
What does a negative pressure do?
Sucks atmospheric air in
What is Bernoulli’s Theorem?
When velocity increases, the pressure decreases
When velocity decreases, the pressure increases
What is an air shutter?
its used to adjust the size of air openings to control primary air flow
What are the primary air control devices? (WBRS)
- Wing
- Butterfly
- Rotating or sliding disc
- Spoiler screw
Is the orifice part of the burner?
No
Gas pressure and orifice size controls what?
The volume / velocity of the gas being injected in the burner.
What happens if you adjust the manifold (gas supply) pressure?
Change velocity of gas stream / venturi affect = changes primary air amount being drawn in
What is a mixing tube?
Portion of the tube that mixes gas and air together
What is a burner head?
Where gas/ air mixture enters the burner
Area is greatest - velocity is lowest and pressure is at its highest point
Is a burner port an orifice?
Yes
What does a burner port do?
1) discharges gas/ air mixture
2) distributes flames
3) spreads flanes
(More ports = more flames = more secondary air)
What characteristics should a properly functioning burner have?
- uniform heat
- complete combustion
- stable flames
- ready ignition
- quiet operation
What does a small hard blue flame off of burner port indicate?
Too much primary air
Air shutter should be closed
What does a soft, blurred or yellow tipped flame off the burner port indicate?
Lack of primary air
Air shutter should be opened
What are 2 main categories of atmospheric burners?
(Main pilot in the atmosphere)
Main burner
Pilot burner
What are 2 common types of atmospheric main burners?
(Main single multiport)
Single port
Multiport
What in a Single port burner?
Has an inshot burner that fires HORIZONTALLY into heat exchanger
What is an upshot burner?
Burns vertically
Common in domestic storage type water heaters
What is the most common atmospheric burner used in appliances?
Multiport burners
What is a burner bed?
When a number of multiport burners are used together
What is a pilot burner?
A small flame used to ignite the main burner
What are 2 types of pilot burners?
(A-NON)
Aerated pilots
Non-aerated pilots
What do aerated pilots do?
They premix air and gas
Have a sharp blue flame
primary air is drawn through a tube or air duct
Do aerated pilots have a stable flame?
yes and they produce higher flame temperatures
What is the common problem with Aerated pilots?
clogging of the primary air openings due to dust and lint
What are non-aerated pilots?
Have a short flame w/ little yellow colouring
Does not have dust / lint problems
What are non-aerated pilots affected by?
drafts / main burner variations
What are the most common problems w/ atmospheric burners?
- flashback
- Extinction pop
- Flame lift off
- Floating flames
- Waving flames
- Flame roll out
- Yellow tipping
- Fluctuating flames
- Gas odour
What happens in flashback?
Gas/ air mixture ignites inside the burner to burn near the orifice
What kind of noise does flashback make?
roaring noise like a torch
Flashback creates incomplete combustion which produces what?
Carbon monoxide / aldehydes
Does flashback produce soot?
Yes due to incomplete combustion
What causes flashback?
very lean gas/air mixture
What eliminates Flashback?
reduce the primary air to the burner
(without produces yellow-tipped flames)
If the burner is underfired (in flashback) what should happen?
Check input rate / adjust in to correct input value (orifice size / manifold pressure)
What is extinction pop?
When flashback occurs when the burner is shut off
What noise does an extinction pop make?
Bang
When does extinction pop occur?
When the gas supply is turned off
Is extinction pop dangerous?
No and will not damage appliance
Can blow out pilot light tho
What are some remedies for extinction pop?
Reduce primary air supply to the burner
Where is extinction pop a common problem?
on long atmospheric burners
What is Flame liftoff?
It’s when part of the flame lifts or dances on the burner port
What causes flame liftoff?
when flow velocity of the gas/air mixture from a burner port is greater than the flame burning speed
aka high gas pressure
What kind of noise does a lifting flame create?
Roaring
What is a concern of flame liftoff?
incomplete combustion may escape flames
What are some remedies for lifting flames?
Reduce primary air
Also check, input is correct, orifice size / manifold pressure may need to be reduced first
(do not cause yellow tipping)
What is yellow flame due to?
Lack of primary air
What are Floating flames?
Are flames that do not have well-defined cones / appear to be reaching for air / roll around in the combustion chamber
flames are lazy looking
What kind of odour is present w/ floating flames?
a strong aldehyde odor
What do floating flames indicate?
incomplete combustion
Are floating flames dangerous?
Yes
What are some remedies for Floating flames?
appliance is overfired
2) Flue outlet too small
1) LACK OF SECONDARY AIR
What is the cause of Floating flame?
Poor venting
check for blockages at the flue collar
What is Waving flame?
is a result of drafts across burners = waving / unstable flame
What can cause waving flame?
a cracked heat exchanger
What are some remedies for waving flame?
eliminate external drafts across the floor
protect pilot with a suitable shield
What occurs in Flame rollout?
When flames rollout of the front of the combustion chamber when the burners are ignited
What can happen with Flame rollout?
fire hazard created, scorch appliance, burn wires or damage controls (can lead to flashblack)
What are some remedies for flame rollout?
Increase secondary air?
Check for blockages
What causes Flame rollout?
lack of combustion air dt over-firing of burners, poor draft or blockages in flue passage.
What is Yellow tipping?
when there is not enough primary air
What does yellow tipped flames indicate?
Incomplete combustion
Does yellow flames produce soot?
Yes
If there is a 1/32 build of of soot, this decreases efficiency losses by what?
16%
What do red or orange streak indicate?
dirt or dust in the primary air supply
What are remedies for yellow tipping?
Slowly open primary air shutter
Check the orifice - clean, realign or replace it if necessary.
What are Fluctuating Flames?
flames fluctuate over a period of time w/o adjust the burner.
Are fluctuating flames problematic?
No
What are some remedies for fluctuating flames?
(The farting hunter)
Faulty oversized hunting regulator or undersized gas piping.
What causes Fluctuating flames?
Unsteady gas pressures
True or false: normal burner operation has a negative pressure (vacuum) inside the primary air opening that draws air in.
True
How do you change input to a burner?
Adjust the manifold pressure or change area of the orifice
What is the most common type of a main burner orifice?
Fixed (plug)
Which gas range cap orifice has a higher heat value, cap is threaded clockwise = fixed flow through the needle hole?
Propane operation
Which gas range cap orifice has a lower heat value, greater flow rate required – orifice cap is unthreaded counter clock wise, away from needle?
Natural Gas
How is vol of gas (flow rate) expressed?
ft3 / hr - input = BTU / h
m3 / hr - input = kW
How is the K factor determined?
angle of approach to the orifice
K = 0.9
True or False: Heavier gas will flow less easily through an orifice.
True
What are the specific gravities of propane, NG and butane?
NG = 0.6
Propane = 1.5
Butane = 2.0
What does DMS mean?
Drill manufactured size
True or False: Always choose the smaller orifice so that the appliance is not overfired.
True
What is combustion air made of?
Primary air - 1/3 - mixed w/ gas
Secondary - 2/3 - Air around flame
Where is excess air?
on the outlet side =
5ft3 / 1000BTU
Draft control
is Dilution air
15ft3 / 1000BTU
What is combustion air rated as?
10ft3/ 1000 BTUs
Requires 80% N2 / 20% O2
