Thermal Planning of A Power Plant Steam Generator

P M V SubbaraoAssociate Professor

Mechanical Engineering DepartmentI I T Delhi

Planning for Realization of Constant Pressure Heat Addition……

Basic Geometry of A Furnace

Thermal Planning of A SG

•Heat loss from furnace surface.

•Combustion Losses

•Loss due to moisture in air.

•Loss due to moisture in fuel.

•Loss due to combustion generated moisture.

•Dry Exhaust Gas Losses

•~ 4 --- 5%

Heat gained by superheater & reheater

40%

Heat gained by economizer & air preheater

12%

Fuel Energy100%

Heat gained by boiling water40%

Hot gas

Flue gas

Sequence of Energy Exchange from Flue Gas to Steam

PLATEN SH

FLUE GAS

ECONOMIZER

EVAPORATOR

COVECTIVE SH

RH PENDENT SH

Burner

Flame

Hot Exhaust gases

Furnace Exit

Heat Radiation & Convection

Mechanism of Heat Exchange in Furnace

Structure of Furnace Wall

Boiler Furnace

• Structurally boiler furnace consists of the combustion space surrounded by water walls.

• The furnace volume is designed to perform:

• Release of the chemical energy of fuel by combustion

• The first task of combustion technology is

• to burn the fuel efficiently and steadily,

• to consume controlled excess air (as little as possible),

• To generate a flame with controlled shape which will generate lowest amount of pollutants.

• The furnace walls are designed to perform:

• Transfer of heat from the furnace to the working fluid inside the water walls.

• The important task of furnace heat removal is to produce a controlled Furnace Exit Gas Temperature (FEGT).

• FEGT is an important aspect of boiler safety.

Thermal (Heat Transfer) Performance of A Furnace

• The flame transfers its heat energy to the water walls in the furnace by Radiation.

• Convective Heat Transfer < 5%.

• Only Radiation Heat Transfer is Considered!

• Complexities:

• Non uniform temperature of tubes.

• Variation of furnace gas temperature along its– Height

– Width

– Depth.

Non uniform Heat Flux !!!!!

Cross-sectional distribution of Temperature