CFB Presentation and Power Plant Overview

BASIC of CFB boiler 1. Introduction 2. Principle of CFB boiler 3. Combustion in CFB 4. CFB main components&equipments 4.1 Feed water system 4.2 Superheater system 4.3 Chemical feeding system 4.4 Combustion Air system 4.5 Fuel system 4.6 Flue gas system 4.7 Ash system 4.8 Make up sand and limestone system

Basic component

Steam Steam Outlet

Turbine

G CW in

Condenser CW out

Boiler

FW tank

P

Make up water

Cogeneration (Cogen) Steam Outlet

Steam

Turbine Low pressure use in process

G CW in

Condenser CW out

Boiler

FW tank

P

Make up water

Solid fuel combustion boiler Pulverized fuel Combustion boiler Stokers boiler

Fluidized bed boiler

Bubbling Bed

Circulating Fluidized Bed

Stokers boiler

Pulverized fuel Combustion boiler

Basic components of CFB Steam Outlet

Steam Water Steam Drum Downcomer

Water Wall

Fuel Limestone

Super Heater Hot Cyclone

Dust Collector Economizer

Fluidized Bed Combustion Chamber

Air Heater

Fly Ash

Loop Seal Ash Cooler

Feed Water Inlet Exhaust Gas

Bottom Ash To Ash Silo

Induced Draft Fan Secondary Air Fan Primary Air Fan

2. CFB principle PULVERIZED FIRING

GRATE FIRING (FIXED BED)

(ENTRAINED BED)

Velocity Furnace Temp.

2.5-3 m/s 1090-1370° C

CFB GAS

AIR

AIR FUEL

AIR ASH

BFB

GAS

GAS

FUEL

FLUIDIZED-BED FIRING

FUEL & SORBENT

ASH

4.5-9 m/s 1200-1540° C

FUEL & SORBENT

AIR ASH

AIR ASH

1.2-3 m/s 815-930° C

4.5-6.7 m/s 815-930° C

GAS

3. Combustion in CFB Requirement for combustion; 1) the presence of a fuel (a combustible material) 2) enough oxygen to support combustion and 3) enough heat to bring the fuel to its ignition temperature and keep it there.

The three "T"s of combustion, all necessary for good combustion Time Time to complete the combustion process

Turbulence Turbulence provides more effective mixing of fuel and air, causes even heat distribution and fills the entire combustor volume;

Temperature Temperature of the combustor atmosphere must be kept above ignition temperature. Preheating incoming combustion air increases temperature of the furnace atmosphere. Ignition temperatures and combustion temperatures vary with fuel type and preparation.

4. CFB main component & equipments 4.1 Feed water system 4.2 Superheater system 4.3 Chemical feeding system 4.4 Combustion Air system 4.5 Fuel system 4.6 Flue gas system 4.7 Ash system 4.8 Make up sand & limestone system

4.1 Feed water system (1) - Provide water to boiler corresponding to boiler load - Water feed at appropriate quantity, pressure and temperature - Feed water quality take cared by water treatment plant - Chemical dosing system control boiler water quality

4.1 Feed water system (2) SUPERHEATER

EVAPORATOR

NATURAL CIRCULATION (DRUM)

ECONOMIZER

FEED WATER PUMP

HEAT

4.2 Superheater system - Sat. steam generated from furnace and separator flow trough steam drum to crossover duct, back pass casing then SH coils - SH coils arrangement depend on boiler design - SH temperature controlled by desuperheater

4.3 Chemical feeding system - Purpose is to maintain boiler water/steam quality - Na3PO4 dos just before economizer

- Ammonia and Hydrazine dos at feed water tank

4.4 Combustion air system - Main combustion air are Primary and Secondary air - Primary air work as bed fluidized air, main combustion air and cooling for wall screw - Secondary air fulfill combustion (control excess air)

Boiler body

4.5 Fuel system Anthracite

- For CFB, coal is main fuel

Bituminus Sub bituminus Lignite

- Amount of sludge limited by bed temperature

4.6 Fuel gas system -

Flue gas + ash are products of combustion

-

Transfer heat to water wall

-

Along flue gas path, refractory lining will protect water wall from erosion and overheat

-

Furnace pressure controlled by ID fan (Induced Draft fan)

-

To maximize efficiency, combustion air heated at airpreheater.

-

Finally, before stack, dust in flue gas was collected at ESP (Electrostatic precipitator)

4.7 Ash handling system (1) -

Heavy solid particle accumulated at bed area is “Bottom Ash”

-

Light particle fly away with flue gas is “Fly Ash”

-

Bottom ash drained out from boiler via water cooled bottom ash screw

-

Part of fly ash transfer out at back pass hopper, then the very small fly ash will be collected at dust collector (ESP)

-

In some design, fly ash will be reused by fly ash recalculating sys.

4.8 Make up sand and Limestone -

-

Purpose of make up sand feeding is to: 1. Maintain Bed pressure 2. Sand work as heat transfer material Purpose of limestone feeding is to: 1. Capture SO2 Heat + CaCO3 CaO + SO2 + ½ O2

CaO + CO2 CaSO4 + Heat

2. Maintain bed pressure ( same as sand but more gentle) Less erosion

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