Air-preheater for Conservation of Flue Gas Energy
Transcript of Air-preheater for Conservation of Flue Gas Energy
Air-preheater for Conservation of Flue Gas Energy
P M V SubbaraoProfessor
Mechanical Engineering Department
Minimize Final Exhaust Gas Temperature….Properly Utilize Enthalpy of Flue Gas….
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
Furnace absorption
Platen SH
Pendent SHCSH
Reheater
Economizer
Combustion Losses C & R losses Hot Exhaust Gaslosses
~3280C
Design 1: 500 MW
Design 1: 500 MW
LMTD for various Devices: Model 1
Design 1: 500 MW
DPNL SH
Platen SHTR
RHTR
LTSH
Economiser
APH ESP ID Fan
drum
Furnace
BCWpump
Bottom ash
stack
screentubes
Thermal Structure of A Modern Fuel Fired SG
Thermal Balance in Air Pre-Heater.
• The energy rate gained by air )( ,, inairoutairairair hhmQ
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• The energy rate lost by flue gas
• Overall Coefficient of Heat Transfer, U
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• Overall Convective rate of Heat Exchange
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
The concept of Time Sharing
• At any time:• The overall heat transfer coefficient, U
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• At stead operation:
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Stockholm 1920The Ljungström Air Preheater
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.
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.
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.
Rotary or Regenerative Air Pre-Heater
Stationary-Plate Type Air Pre-Heater
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.
Schematic diagram of the rotary air preheater in thermal power plant.
Thermodynamic process and flow diagram
Leakage in APH
Multiple Channel RAPH
Fluid flows in rotary regenerator