ID C IDC Technologies - Technical Training That Works BOILER PLANT OPERATION Presented By Mr....

IDC

IDC Technologies - Technical Training That Works

BOILER PLANT OPERATIONBOILER PLANT OPERATION

Presented By Mr. Sivanand RayPresented By Mr. Sivanand RayFleet Management Training Fleet Management Training

InstituteInstitute

IDC


INSTRUMENTATION USED ON A SHELL BOILER

Fire-tube type boiler reviewed for simplicity

Instrumentation:» Items that provide operator with indication of

condition within the boiler» Ensure indications are within SAFETY limits

and design OPERATIONAL PARAMETERSOperating pressures, temperatures, flows, water

level

M4-2

IDC


INSTRUMENTATION

PRESSURE GAUGE» Normally Bourdon type of gauge» Large with large numbers» Graduated approximately double the

pressure of safety valve setting, not < than 1,5

» Located on top of shell/drum on an independent nozzle

» Supplied with a siphon (“pigtail”) to develop a water seal

» Must be calibrated at least once a yearM4-3

IDC


INSTRUMENTATION

PRESSURE TRANSMITTER» Where a remote pressure indicator required, an

electrical signal used» Separate transducer» Mounted on same branch as pressure indicator

M4-4

IDC


INSTRUMENTATION LEVEL COLUMNS

» Provides VISIBLE water level indication» Minimum 25NB pipe line connecting column to

boiler» TWO water gauge glasses for boiler pressure

>28 bar» Normally simple gauge glass type

Installed such that with lowest reading on gauge glass, 75 mm water over highest point of tubes

Visible range of water level approx. 125mm from NWL

» Daily routine blow down to remove debris, scale, sludge

M4-5

IDC


Typical Water Level Gauge for Low Pressure Boiler

M4-6

IDC


Electronic and digital water level indicators

M4-7

IDC


INSTRUMENTATION LEVEL SWITCHES

» Float type (Mobrey)» Single-element control (on-off or

modulating)» Normally located in an external chamber» TWO chambers mandatory

Low level alarmLow-low-level shut down

» Weekly routine test to check correct operation of switches

M4-8

IDC


INSTRUMENTATION

TEMPERATURE MEASUREMENT» Flue gas exit temperature» An increase indicates fouling problems» Thermocouples, insulated from gas

sampling tube

M4-9

IDC


TYPICAL PROCESS AND INSTRUMENTATION DIAGRAM (P&ID)

COAL FIRED LP BOILER» Instrumentation» Control loops

OIL OR GAS FIRED LP BOILER» Instrumentation» Control loops

M4-10

IDC


CONTROL AND SYSTEM OPERATING PHILOSOPHY

CONTROLS :» Regulate the various quantities

indicated by the instruments» Shut down (with interlocks) the plant if

parameters exceeded» Manual operation to sophisticated

automatic computer operation (DCS)

M4-11

IDC


CONTROL AND SYSTEM OPERATING PHILOSOPHY

To control a boiler, following quantities require to be regulated :» Fuel/air ratio to maintain optimum

combustion conditions» Water flow to match steam flow from boiler» Steam flow and pressure to regulate heat

input » Combustion chamber pressure (balanced

draught boilers)» Combustion safety

M4-12

IDC


COMBUSTION CONTROL

Manual control cannot continuously control combustion in a reliable and efficient manner

Automatic control systems used :» maintains fuel-air ratio to furnace at an

optimum» maintains a relatively constant steam pressure

Combustion control mechanisms vary slightly depending on fuel fired

No matter what fuel, four aspects that are regulated:

Air supply; Fuel supply; Ratio of fuel to air; Flame safety

M4-13

IDC


COMBUSTION CONTROL

Two basic types of combustion control systems:» Positioning» Metering

Pneumatic or Electrical control drives

M4-14

IDC


COMBUSTION CONTROL Positioning Type Control:

» Designed to control based on a change in steam pressure

» Components : Master steam pressure controllerFuel control valve with cam for oil / gas or feed

control drive for coal Combustion air fan inlet vanes / outlet damper

operator

» Simplisticcannot maintain fuel – air ratio at optimum over

full load range

M4-15

IDC


COMBUSTION CONTROL

Metering Type controller :» Components as per Positioning type

with :Fuel flow measuring device Air flow signal

» Fuel-air ratio is controlled by a relay» Capable of adjusting fuel-air ratio and

where fuel pressure may vary

M4-16

IDC


General Selection Chart for Combustion Control Systems

Type of Fuel Type of Control Steam GenerationSystem Capacity Ranges

(kg/hr)Coal Modulating positioning to 27 500

Full metering (Steam/air flow) 18 000 – 36 000Full metering withOxygen compensation above 36 000

Fuel Oil & Gas Modulating positioning to 11 500Full metering (Steam/ air flow) 11 500 – 45 000 Full metering with Oxygen compensation above 45 000

M4-17

IDC


STEAM PRESSURE CONTROL

Main purpose of a steam boiler is to produce steam within a definite pressure range

Steam pressure dictated by :» process plant steam demand» heat input to the boiler furnace

Pressure fluctuates between minimum and maximum settings

M4-18

IDC


STEAM PRESSURE CONTROL

Modulating control linked to upper and lower pressure limits» On-off pressure switch – low or high fire

burner» Definite limitation exists on burner

minimum firing rateturndown ration varies : 4:1 gas; 2:1 oil

M4-19

IDC


FEED WATER SUPPLY CONTROL

Purpose is to provide sufficient feed water flow to ensure all heat transfer surfaces are cooled with water

Visible water level provided by :» Two simple gauge glasses» More sophisticated devices (electrodes,

capacitance or conductivity type) Water sensor controls :

» Normally two independent» Float operated » Thermostatic

M4-20

IDC


FEED WATER SUPPLY CONTROL

Typical arrangements of feed water plant :» Two or more pumps (standby) from hot

well tank (10-15 min. storage)Either on-off operation or a feed valve station

» Feed valve station : Check valveStop valveFeed control valve c/w isolation and bypass

valves

M4-21

IDC


FEED WATER CONTROL SYSTEMS

ON AND OFF FEED WATER PUMP» Small boilers with relatively large water

storage, slow load changes» Typical float operated water level

controller, mounted at water line» Also serves either as low-water level

alarm or low water cut off

M4-22

IDC


FEED WATER CONTROL SYSTEMS

MODULATING LEVEL CONTROLLERS» Boilers with relatively small water

volume relative to steam demand» Thermostatic type regulator feeds water

continuously to the boiler, stabilising the water level

» THREE types of modulating controllers :Single Element Level Controller Two Element Level Controller Three Element Level Controller

M4-23

IDC


Schematic of Three Element Level Controller

M4-24

IDC


SOME CONSIDERATIONS REGARDING WATER LEVEL CONTROL

Rapid changes in steam flow rate can cause SURGING of the water level and carry-over

VERY IMPORTANT that the :» steam qualities» characteristics of boiler (size, firing system) MUST be properly matched to the OPERATING characteristics of water level controlling system

Highest water level, NWL, lowest level for safe operation should be MARKED on boiler outer shell

M4-25

IDC


FURNACE PRESSURE CONTROL Only really required on coal fired boilers

with FD and ID fan Required to :

» prevent excessive negative pressure and uncontrolled air entering furnace

» products of combustion to percolate back to coal supply

Controller transmitter range not too narrow» typically +250 to –1250 Pa» ideal control point –100 Pa

M4-26

IDC


AUTOMATIC CONTROLS

Instrumentation employed same as that for manual operation

Rapid and continuous development of electronic control systems means systems for boilers are now DIVERSE

Selection shall depend on owner / purchaser present complexity of control systems

M4-27

IDC


AUTOMATIC CONTROLS

ASPECTS that do not vary whether auto/manual :» Principles of operation» Areas of control (control loops)» Direct reading of instruments» Safety devices and interlocks» Selector for “manual” or “automatic”

M4-28

ID C IDC Technologies - Technical Training That Works BOILER PLANT OPERATION Presented By Mr....

Documents

Transcript of ID C IDC Technologies - Technical Training That Works BOILER PLANT OPERATION Presented By Mr....