air-preheater for conservation of flue gas energy p m v subbarao professor mechanical engineering...
TRANSCRIPT
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Air-preheater for Conservation of Flue Gas Energy
P M V Subbarao
Professor
Mechanical Engineering Department
Minimize Final Exhaust Gas Temperature….Properly Utilize Enthalpy of Flue Gas….
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Gas Temperatures
• Platen Super Heater:• Inlet Temperature: 1236.4 0C• Outlet Temperature: 1077 0C• Final Super Heater:• Inlet Temperature: 1077 0C• Outlet Temperature: 962.4 0C• Reheater:• Inlet Temperature: 962.4 0C• Outlet Temperature: 724.3 0C• Low Temperature Super Heater:• Inlet Temperature: 724.30C• Outlet Temperature: 481.3 0C• Economizer:• Inlet Temperature: 481.3 0C• Outlet Temperature: 328.5 0C
Steam Temperatures
• Platen Super Heater:• Inlet Temperature: 404 0C• Outlet Temperature: 475 0C• Final Super Heater:• Inlet Temperature: 475 0C• Outlet Temperature: 540 0C• Reheater:• Inlet Temperature: 345 0C• Outlet Temperature: 5400C• Low Temperature Super Heater:• Inlet Temperature: 3590C• Outlet Temperature: 404 0C• Economizer:• Inlet Temperature: 254 0C• Outlet Temperature: 302 0C
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Furnace absorption
Platen SH
Pendent SHCSH
Reheater
Economizer
Combustion Losses C & R losses Hot Exhaust Gaslosses
~3280C
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Design 1: 500 MW
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Design 1: 500 MW
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LMTD for various Devices: Model 1
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Design 1: 500 MW
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DPNL SH
Platen SHT
R
RHTR
LTSH
Economiser
APH ESP ID Fan
drum
Furnace
BCWpump
Bottom ash
stack
screentubes
Thermal Structure of A Modern Fuel Fired SG
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Thermal Balance in Air Pre-Heater.
• The energy rate gained by air )( ,, inairoutairairair hhmQ
LMTDaphgasair TUAQQ
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• The energy rate lost by flue gas
• Overall Coefficient of Heat Transfer, U
)( ,, outgasingasgasgas hhmQ
• Overall Convective rate of Heat Exchange
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The Creative Design……
• Heat exchanger is complete only if there are Donor, Receiver and Mediator in Equilibrium.
• Presence of all the three necessary?• Time sharing & Space Sharing• Time Sharing : Donor And Mediator for sometime and
Mediator and Receiver for sometime : Repeat!• Space sharing: All present always.• Central Limit Theorem : It is impossible to have time and
space sharing in one system.• Time Sharing : Regenerators• Space Sharing : Recuperators
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The concept of Time Sharing
• At any time:
• The overall heat transfer coefficient, U
me
me
as
as
g
gas
h
U
1
1
adust
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me
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OR
• At stead operation:
condg
gas
Rh
U
1
1
acond
air
hR
U1
1
OR
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Stockholm 1920The Ljungström Air Preheater
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Historical Significance of Landmark
• Throughout the history of boilers there have been many advancements in order to obtain a better performance and lower fuel consumption.
• Ljungström Air Preheater invented by Fredrik Ljungström, then Technical Director at Aktiebolaget Ljungström Ångturbin (ALÅ) is the most successful invention.
• The first installation in a commercial boiler saved as much as 25% of the fuel consumption.
• In a modern Steam generator the Ljungström Air Preheater provides up to 20% of the total heat transfer in the boiler process, but the Ljungström Air Preheater only represents 2% of the investment.
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Economic Impact of the Landmark
• The use of a Ljungström Air Preheater in a modern power plant saves a considerable quantity of fuel.
• The cost of the preheater is generally recovered after only a few months.
• The total world-wide fuel savings resulting from all Ljungström Air Preheaters which have been in service is equivalent to 4,500,000,000 tons of oil (1994).
• An estimate shows that the Ljungström Air Preheaters in operation annually saves about $30 Billion US.
• The distribution of thermal power capacity in which Ljungström Air Preheaters are installed over the world is shown in the table below.
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Landmark Contribution to Developmentof New World Wide Industry
• The use of the Ljungström Air Preheater started in the 1920s throughout the whole world.
• In the beginning the marketing of the Ljungström Air Preheater was made in close connection with ALÅ.
• but most of the deliveries have actually been made through a network of licensees throughout the world.
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Rotary or Regenerative Air Pre-Heater
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Stationary-Plate Type Air Pre-Heater
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Regenerative Pre-Heaters
• Rotates with a low speed
• Rotor is divided into 12 or 24 sections and 12 or 24 radial divisions.
• Each sector is divided into several trapezoidal sections with transverse division plates.
• Heat storage pales are placed in these sections.
• Weight : 500 tons.
• This consists of : rotor, sealing apparatus, shell etc.
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Schematic diagram of the rotary air preheater in thermal power plant.
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Thermodynamic process and flow diagram
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Leakage in APH
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Multiple Channel RAPH
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Fluid flows in rotary regenerator
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