Automatic Boiler Controlfor

Water tube Boiler

ABC(Automatic Boiler Control)

ABC

ACC : Automatic Combustion Control

FWC : Feed Water Control

STC : Superheated Steam Temperature Control

RTC : Reheated Steam Temperature Control

FDC : Furnace Draft Control

Others : Fan Speed Control, Tank level control

Fuel oil Temperature Control

GAH Cold end Metal Temperature Control

etc.

Purpose of ABC : To keep Boiler Mass and Energy balance

BOILER

Hydrogen H2Carbon CSulfur SNitrogen N2Oxygen O2Water H2OAsh Others

Nitrogen N2Oxygen O2Water H2OOthers

FUEL

AIR

WATER

STEAM

ASH

Combustion Gas

Carbon dioxide CO2Carbon monoxide COOxygen O2Nitrogen N2Nitrogen Oxide NOxSulfur Oxide SOxHydrogen H2Water (Moisture) H2O

Soot

BOILER MASS BALANCE

ABC(Automatic Boiler Control) BOILER MASS AND ENERGY BALANCE(1)

Purpose of ABC : To keep Boiler Mass and Energy balance

ABC(Automatic Boiler Control) BOILER MASS AND ENERGY BALANCE(2)

BOILER

BOILER ENERGY BALANCE

FUEL

Combustion Air

Heat Input by Combustion

Heat loss by Flue gas

Heat loss by Unfired carbon

Heat Input by

Feed Water

Heat loss by blow down

Heat output by Generated steam

Heat loss by Radiation

ACC(Automatic Combustion Control)

ACC Master Control (Main Steam Pressure Control)

Combustion Control•　 Fuel Flow Control•　 Combustion Air Control•　 Flue Gas Oxygen Control

Purpose of Master Control

: To maintain Main Steam Pressure

Master Control

1) One element Control (only by Main Steam Pressure)

2) Two element Control ( by Main Steam Pressure +

Feed forward signal by Main Steam Flow)

ACC(Automatic Combustion Control)

ACC FTPT

Main Steam

Fuel

FDF (Forced Draft Fan)

Burner

BOILER maintain Boiler

Energy balance

ACC(Automatic Combustion Control)Master Control(1)

Main Steam Pressure

Master Controller

(Main steam pressure controller)

To Combustion Controller

Set Point

To other boiler controller

One element Control

Load Distributor

A/M Station

ACC(Automatic Combustion Control)Master Control(2)

Main Steam Flow

Main Steam Pressure

Required Combustion SignalOne element

Two element

Time

Flow

, Pressure

Time Lug

ACC(Automatic Combustion Control)Master Control(2)

Two element Control

Main Steam Pressure Flow

To Combustion Controller

Main Steam Pressure Flow

To Combustion Controller

Type-1 Type-2

ACC(Automatic Combustion Control)Combustion Control

Master Controller

Fuel Flow Controller Combustion Air Flow Controller

Required Combustion Signal

COMBUSTION COMTROL

Air-Rich Combustion System

: to avoid air-less condition at load change

ACC(Automatic Combustion Control)Combustion Control

Master

Fuel flow ControllerAir flow Controller

Fuel Flow Control Valve FDF Inlet Vane Control Drive

Fuel Flow Air Flow

Low selector

Bias

High selector

Air-Rich Combustion System

Main Steam Press

ACC(Automatic Combustion Control)Combustion Control

Load

Constant

Load

Up

Load

Constant

Load

Down

Time

Air-Rich Combustion System

ACC(Automatic Combustion Control)Combustion Control

Air-Rich Combustion System (Double Cross-limit)

Main Steam Flow Main Steam Pressure

Fuel Flow Air Flow Flue Gas O2 Content

Master

Fuel FlowController

Air FlowController

O2 Controller

ACC(Automatic Combustion Control)Combustion Control

Load

Constant

Load

Constant

Load

Up

Load

Down

Time

Air-Rich Combustion System (Double Cross-limit)

ACC(Automatic Combustion Control)Combustion Control

O2 Controller

Min.

Max.Load

Required air Flow

O2 Content

Air Flow O2 Content(%)

O2 Controller

Air flow controller

from　 Steam flow

FWC (Feed Water Control)

Purpose of FWC (Feed water Control)

: to maintain steam drum water level at desired level (NWL)

High Water level : Increase Carry-over

Scaling to Superheater tube Tube overheating 　 Tube rupture

Scaling to turbine blade excessive vibration, reducing efficiency

Low Water level : poor water circulation Water tube overheating

Tube rupture

Method of FWC (Feed water control) 1) one element control (drum water level) 2) two element control (drum water level, steam flow) 3) three element control (drum water level, steam flow, water flow)

FWC (Feed Water Control)

BOILER

LT

FT

FT

FWC

Main Steam

Feed Water

Maintain BoilerMass Balance

Feed water Control Valve

FWC (Feed Water Control)One element Control

Drum Level

Set point

Feed water Control Valve

One Element Control

Drum Level

Steam Flow

Time

Reverse Response of Water Level

FWC (Feed Water Control)Two element Control

Drum Level Steam Flow

LevelController

Drum Level Steam Flow

LevelController

I0 = I1 + (I2-50)

FWC (Feed Water Control)Three element Control

Drum LevelSteam Flow Feed water Flow

LevelController

Feed waterController

Steam FlowFeed water 　　　 Flow

Drum Level

LevelController

STC (Superheated Steam Temperature Control)

Purpose of STC (Superheated Steam Temperature Control)

: to maintain main steam temperature at desired temperature

TE

STC

Min. Max.

Boiler Load

Spray Control Valve

From S/D

from Feed water

STC (Superheated Steam Temperature Control)

TETEFT

STC

Primary S/H Secondary S/H

From S/D

Spray Control Valve

from Feed water

STC (Superheated Steam Temperature Control)

Main SteamTemperature Steam Flow

Main SteamTemperature Steam Flow

Spray out SteamTemperature

Spray water control Valve

Spray water control Valve