Airpreheater for Conservation of Flue Gas Energy P

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….

Steam Temperatures Gas Temperatures • • • • Platen Super Heater: Inlet Temperature: 1236. 4 0 C Outlet Temperature: 1077 0 C Final Super Heater: Inlet Temperature: 1077 0 C Outlet Temperature: 962. 4 0 C Reheater: Inlet Temperature: 962. 4 0 C Outlet Temperature: 724. 3 0 C Low Temperature Super Heater: Inlet Temperature: 724. 30 C Outlet Temperature: 481. 3 0 C Economizer: Inlet Temperature: 481. 3 0 C Outlet Temperature: 328. 5 0 C • • • • Platen Super Heater: Inlet Temperature: 404 0 C Outlet Temperature: 475 0 C Final Super Heater: Inlet Temperature: 475 0 C Outlet Temperature: 540 0 C Reheater: Inlet Temperature: 345 0 C Outlet Temperature: 5400 C Low Temperature Super Heater: Inlet Temperature: 3590 C Outlet Temperature: 404 0 C Economizer: Inlet Temperature: 254 0 C Outlet Temperature: 302 0 C

Combustion Losses Pendent SH Platen SH Furnace absorption C & R losses CSH Reheater Hot Exhaust Gas losses ~3280 C Economizer

Design 1: 500 MW

Design 1: 500 MW

LMTD for various Devices: Model 1

Design 1: 500 MW

Thermal Structure of A Modern Fuel Fired SG DPNL SH Platen SHTR drum R H T R screen tubes LTSH Economiser stack BCW pump Furnace APH Bottom ash ESP ID Fan

Thermal Balance in Air Pre-Heater. • The energy rate gained by air • The energy rate lost by flue gas • Overall Convective rate of Heat Exchange • Overall Coefficient of Heat Transfer, U

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 OR • At stead operation: OR

Stockholm 1920 The 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 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 Development of New World Wide Industry • The use of the Ljungström Air Preheater started in the 1920 s 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