Impact of Fuel Quality on Design of Steam Generator

P M V SubbaraoProfessor

Mechanical Engineering Department

The Influence of Natural Resources on Development….

Basic The Theme Steam Generator Design

• Constrains:

• Imposed by Cycle Design (pmax, Tmax, etc.)

• Fuel Combustion Related.

• Heat Transfer Related

• Safety and Reliability Related.

! steamQMaximize

Details of Basic Processes

• Flow of Air and Prepared Fuel – Fluid Dynamics.

• Generation of Thermal Energy – Using Natural Resources.

– Combustion Sciences.

• Transfer of Thermal Energy to working fluid.

– Science of Heat Transfer.

Duties of A Furnace

• Dixon’s Theory:

• Generate an environment of excited fuel and oxygen molecules.

• All the fuel molecules should be surrounded by oxygen molecules.

• Facilitate frequent collisions among excited fuel molecules and excited fuel molecules.

• A successful collision can lead to combustion.

• Realization of Dixon’s Theory using Coal is highly challenging.

• Many possible technologies are available to realize above conditions with varying levels of success and expenditure.

• These are called Three Ts and one S technologies.

Five Requisites for Good Combustion

• Fuel

• MATt Theory:– M : Proper mixing of the reactants.

– A: Sufficient air.

– T: Conducive temperature

– t: Sufficient time Satisfactory density of reactant.

Fourth DF systems contains various auxiliaries to satisfy MATt theory as completely as possible.

Realization of MATt Theory

• Mixing: Fuel preparation systems.

• Air: Draught systems.

• T : Preheating of fuel.

• t : Dimensions of combustion chamber. : Turbulence generation systems.

The Three Ts & One S Practice

Technology Time Temperature Turbulence Size

Stoker large Medium Low Big

Pulverized Short High Medium Tiny

Cyclone Short+ V High High Medium

Fluid Bed Medium Low High Medium

Size the Coal and Add the Air !!!

Major Components of Coal Fired Steam Generator

Major Components of Solid Waste SG

The Timing - 1

The Timing - 2

Typical 455 M

We pulverized coal-fired drum

boiler —

B&

W C

arolina-type Radiant boiler

Basic Geometry of A Furnace

Boiler Furnace

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

• The furnace is designed to perform two functions simultaneously, namely:

• 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.

• 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.