furnace construction & operations
TRANSCRIPT
Furnace
Construction &
OperationsPrepared by
Osama Hasan
GTE
Amm 3
Engro Fertilizers1
What is Furnace?
Converts
Chemical/Electrical Energy to Thermal Energy
Examples
Household Furnace
Metallurgical Furnace
Industrial Process Furnace
Non Reactive e.g. start-up furnace
Reactive e.g. primary reformer in ammonia plant
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Types
Draft
Natural Draft
Forced Draft
Induced Draft
Balanced Draft
Construction
Vertical
Horizontal
Fuel
Coal Fired
Gas Fired
Oil Fired
Electric Current
Process Type
Continuous
Batch
Burner Arrangement
Top Fired
Bottom Fired
Side-wall Fired
Terrace-wall Fired
Heating Method
Direct
Indirect
Tubes Arrangement
Horizontal Inline
Horizontal Staggered
Vertical Inline
Vertical Staggered
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Types: Construction
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Ve
rtica
l Fu
rna
ce
Ho
rizon
tal F
urn
ac
e
Types: Draft
The slight pressure difference between firebox and the
atmospheric pressure that produces the flow of gases
due to temperature difference
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Draft
Mechanical
Forced
Induced
BalancedNatural
Types: Burners
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Natural Draft FurnaceAir Registers Controls the air flow partially
Damper Controls the furnace pressure by manipulating the
resistance in flow of the flue gas Excessive opening leads to a significant decrease in
furnace pressure
Excessive closing leads to pressure building in furnace
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Reduced furnace pressure: Burner Lifting
Increase in draft
Flame-out
Refractory Damage
Incomplete combustion of fuel
Radiation zone temperature decreases
Increased furnace pressure: Burner backfire
Flue gases leak from peep door
Explosion
Rise in radiation zone temp.
Drop of heat duty in convection coil
Zones
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Tube BanksZones
Furnace
Radiation
Radiant
Shock
Convection Convection
Zones: Radiation
Fire Box
Area around the burners where gas combustion
occurs to produce heat and radiation
Burners
Devices used to inject, mix and burn the fuel
Refractory
Wall lining / insulation that accumulates,
insulates and radiates heat back to the tubes
and increases the heat transfer
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Zones: RadiationRadiant Tubes
High Pressure and high flow rate processpipelines loaded with catalyst receiving heatvia radiation from burners and refractory
Shock Tubes
Tubes which receive heat via radiation andconvection both
Types of Tubes:
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Bare
Finned
Studded
Zones: Convection
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Also called Heat Recovery Section
Arch section
Space between the convection section andradiant section, where flue gases are mixed tooffer uniform heat transfer in convection zone
Convection Coils
Coils carrying some fluid which recovers heatfrom the flue gases
Breeching
Area between the convection section andstack
Zones: Convection
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Arch Section
Convection Coil
Breeching Section
Zones: Convection
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Vent Stack
The chimney that
exhausts the flue gases
from breeching toatmosphere
Exhaust Damper
Draft regulator which
works similar to a butterfly valve to control the
air and heat flow
BurnersRaw Gas Burners
Air and gas is mixed andburnt at spider or burnerring
Air inlet is controlled viaback and forthmovement of air doors
Stable operating rangeis determined by the fuelgas pressure at theburner inlet
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Burners
Pre Mix Burners
Uses a jet of gas to draw the air into aspirator
Turbulence is maintained throughout the length of
the burner tube due to shape of the aspirator andthe velocity difference
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Burners
Combination Burner
Primary Air: Drawn intro
aspirator by force of the
gas jet. Mixed with gas
before it reaches burner
spider
Secondary Air: Drawn
into thimble and meetsthe mixture at spider.
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BurnersOil Burner / Gun
Uses steam to atomize oil into a fine mist
Stable operating range is determined by fuel oilpressure at the burner inlet and the atomizingsteam pressure at the burner inlet
Combination Burner
Operated on oil or gasor both
Startup is done via gassupply
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Refractories Heat resistant materials which insulate and
protect equipment structure due to theirexcellent resistance to heat, chemical attackand mechanical damage in hightemperatures and/or corrosive environment
Low iron-low silica content refractories:
Insulating castable
Insulating brick
Ceramic fiber
Ceramic module
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MetallurgyIn-service degradation mechanisms:
Thermal degradation (creep) The primary damage mechanism for high-
temperature service
Metal dusting Metal dusting is a high-temperature corrosion
mechanism that occurs in gaseous environmentswhere the carbon activity exceeds one and themetal temperatures are in the range of 450 to 700 °C
Stress relaxation cracking Cracking of a metal because of stress relaxation that
occurs during post weld heat treatment (PWHT) orduring service at elevated temperature
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Furnace
Operations
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ImpingementBurner Flame touching a tube in the firebox
Causes: Increased gas header pressure
Low furnace pressure
High draft across furnace Mechanical defect / damage of tubes
Problems: Hotspot on tube
Uneven expansion of the tube Tube rupture
Remedy: Installation Peep doors for monitoring
Regular inspection
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Flame Color
Blue Flame:
Complete combustion
Desired heating value
Yellow Flame:
Oxygen deficient / starving
Carbon monoxide rich
Less thermal energy
Increased fuel consumption
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Post BurningCauses Excess / false air
Tube leakage
Fuel gas preheat coil leakage
Un-burnt fuel carry over
Reaction Combustion of un-burnt fuel
Oxidation of carbon monoxide
Consequences Loss of energy
Explosion
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Heat Recovery May be used in forced draft
furnaces
Recuperative
Limited heat recovery
Regenerative
Blowing + heating / cooling of
air supply / flue gases
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Instrumentation
Skin Couples/TMT
Check tube wall metal temperatures
Draft Gauges
Measures draft inside the furnace
Flue Gas Analyzers
Analyzes for excess oxygen supply
Damper
Regulates air flow outward
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Startup: Checkup
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Remove
Check
Open
Close
•Flammable materials
•Tools and other sources of danger
•Burner
•Pilot Burner Valves
•Stack Damper
•Stack Damper
•Secondary air registers on furnace
•Peep Holes
•Fuel Valves
Startup: Purging Creates a draft and remove all flammable vapors or
gas from furnace
Purging time should be long enough to ensure allflammable vapors have been removed
Purging ensures elements of combustion (fuel, airand heat) are under controlled before we light theburners
Natural draft furnace uses steam;
Steam not only purges the furnace but also preheats itand creates an initial draft
Mechanical draft furnace uses air
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Startup: Lighting the BurnersPurging is immediately followed by lighting the burnersvia pilot / torch
To-Do
Introduce torch via secondary air inlet
Crack the burner gas valve
Steady the burner flame pattern by air registersadjustment
If fuel doesn’t ignite, purge again.
Ensure
Satisfactory gas header pressure
Safety precautions
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Shutdown
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Reduce fuel / heat
Reduce charge flow
Shutdown all burners
Reduce steam
Shut off Gas pilot
Close Gas header valve
Open Bleeder valves
Open air doors and
stack damper
Install blinds in fuel lines
Prepared by Osama Hasan
Graduate Trainee Engineer
Ammonia III – Plant II
Thank you
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