cfb presentation and power plant overview

7/23/2019 CFB Presentation and Power Plant Overview

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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 system4.5 Fuel system

4.6 Flue gas system

4.7 Ash system

4.8 Make up sand and limestone system

BASIC of CFB boiler


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Basic component

Steam

Steam Outlet

Make up water

Condenser

Turbine

FW tank

P

G

CW out

CW in

Boiler


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Cogeneration (Cogen)

Steam

Steam Outlet

Make up water

Condenser

Turbine

FW tank

P

G

CW out

CW in

Boiler

Lowpressure

use inprocess


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Solid fuel

combustion boiler

Stokersboiler

Pulverized fuelCombustion boiler

Fluidized bedboiler

Bubbling BedCirculating

Fluidized Bed


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Stokers boiler


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Pulverized fuel Combustion boiler


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Basic components of CFB

Steam

WaterSteam Drum

Downcomer

Fuel Limestone

Steam Outlet

Super Heater

Economizer

Feed Water Inlet

Ash Cooler

Loop Seal

Bottom Ash

To Ash Silo

Fly Ash

Primary Air Fan

Secondary Air Fan

InducedDraftFan

Dust CollectorHot

Cyclone

Air Heater

Water Wall

Exhaust Gas

FluidizedBed

CombustionChamber


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FUEL &S O R B E N T

G AS

AIR AS H

FUEL &S O R B E N T

G AS

AIR AS H

AIR

PULVERIZED F IR ING

FUELA IR

G A S

ASH

BFB C FB

FLUIDIZED -BED F IR ING

FUEL

G AS

AIR A SH

GRATE F IR ING

(F IXE D B ED ) (E N TR AIN ED B ED )

Velocity 2.5-3 m/s 4.5-9 m/s 1.2-3 m/s 4.5-6.7 m/s

Furnace Temp. 1090-1370C 1200-1540C 815-930C 815-930C

2. CFB principle


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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.


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TimeTime to complete the combustion process

TurbulenceTurbulence provides more effective mixing of fuel and air, causes even heat

distribution and fills the entire combustor volume;

TemperatureTemperature of the combustor atmosphere must be kept above ignition

temperature. Preheating incoming combustion air increases temperature ofthe furnace atmosphere. Ignition temperatures and combustion temperatures

vary with fuel type and preparation.

The three "T"s of combustion, all necessary for goodcombustion


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4. CFB main component & equipments

4.1 Feed water system


4.3 Chemical feeding system4.4 Combustion Air system

4.5 Fuel system

4.6 Flue gas system

4.7 Ash system

4.8 Make up sand & limestone system


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4.1 Feed water system (1)

- Provide water to boiler corresponding toboiler load

- Water feed at appropriate quantity, pressureand temperature

- Feed water quality take cared by watertreatment plant

- Chemical dosing system control boiler waterquality


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NATURAL CIRCULATION (DRUM)

SUPERHEATER

EVAPORATOR

ECONOMIZER

FEED WATER PUMP

HEAT

4.1 Feed water system (2)


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- Sat. steam generated from furnace and separatorflow trough steam drum to crossover duct, backpass casing then SH coils

- SH coils arrangement depend on boiler design

- SH temperature controlled by desuperheater


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4.3 Chemical feeding system

- Purpose is to maintain boiler water/steamquality

- Na3PO4dos just before economizer

- Ammoniaand Hydrazinedos at feed watertank


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4.4 Combustion air system

- Main combustion air are Primaryand Secondaryair

- Primary airwork as bed fluidized air, maincombustion air and cooling for wall screw

- Secondary airfulfill combustion (control excess

air)

Boiler body


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4.5 Fuel system

- For CFB, coal is main fuel

- Amount of sludge limited by bed temperature

Anthracite

Bituminus

Sub bituminus

Lignite


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4.6 Fuel gas system

- Flue gas + ash are products of combustion

- Transfer heat to water wall

- Along flue gas path, refractory liningwill protect water wallfrom erosion and overheat

- Furnace pressure controlled by ID fan(Induced Draft fan)

- To maximize efficiency, combustion air heated at air-preheater.

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


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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 bottomash screw

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

- In some design, fly ash will be reused by fly ash recalculating

sys.


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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

Less erosion

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

Heat + CaCO3 CaO + CO2

CaO + SO2

+ O2

CaSO4

+ Heat


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