boiler plant operation
TRANSCRIPT
-
8/12/2019 Boiler Plant Operation
1/28
ID
IDC Technologies - Technical Training That Works
BOILER PLANT OPERATION
IDC Technologies Tech Briefs
(Mechanical Engineering)
-
8/12/2019 Boiler Plant Operation
2/28
ID
IDC Technologies - Technical Training That Works
INSTRUMENTATION USED ON A SHELLBOILER
Fire-tube type boiler reviewed for simplicity
Instrumentation:
Items that provide operator with indication ofcondition within the boiler
Ensure indications are within SAFETY limits and
design OPERATIONAL PARAMETERSOperating pressures, temperatures, flows, water
level
M4-2
-
8/12/2019 Boiler Plant Operation
3/28
ID
IDC Technologies - Technical Training That Works
INSTRUMENTATION
PRESSURE GAUGE Normally Bourdon type of gauge
Large with large numbers
Graduated approximately double the pressureof safety valve setting, not < than 1,5
Located on top of shell/drum on anindependent nozzle
Supplied with a siphon (pigtail) to develop awater seal
Must be calibrated at least once a year
M4-3
-
8/12/2019 Boiler Plant Operation
4/28
ID
IDC Technologies - Technical Training That Works
INSTRUMENTATION
PRESSURE TRANSMITTER Where a remote pressure indicator required,
an electrical signal used
Separate transducer Mounted on same branch as pressureindicator
M4-4
-
8/12/2019 Boiler Plant Operation
5/28
ID
IDC Technologies - Technical Training That Works
INSTRUMENTATION
LEVEL COLUMNS Provides VISIBLE water level indication Minimum 25NB pipe line connecting column to boiler
TWO water gauge glasses for boiler pressure >28bar
Normally simple gauge glass type
Installed such that with lowest reading on gauge glass, 75mm 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
-
8/12/2019 Boiler Plant Operation
6/28
ID
IDC Technologies - Technical Training That Works
Typical Water LevelGauge for Low Pressure Boiler
M4-6
-
8/12/2019 Boiler Plant Operation
7/28
ID IDC Technologies - Technical Training That Works
Electronic and digital water level indicatorsM4-7
-
8/12/2019 Boiler Plant Operation
8/28
ID IDC Technologies - Technical Training That Works
INSTRUMENTATION
LEVEL SWITCHES Float type (Mobrey)
Single-element control (on-off or modulating)
Normally located in an external chamber TWO chambers mandatoryLow level alarm
Low-low-level shut down
Weekly routine test to check correctoperation of switches
M4-8
-
8/12/2019 Boiler Plant Operation
9/28
ID IDC Technologies - Technical Training That Works
INSTRUMENTATION
TEMPERATURE MEASUREMENT Flue gas exit temperature
An increase indicates fouling problems
Thermocouples, insulated from gas samplingtube
M4-9
-
8/12/2019 Boiler Plant Operation
10/28
ID IDC Technologies - Technical Training That Works
TYPICAL PROCESS ANDINSTRUMENTATION DIAGRAM (P&ID)
COAL FIRED LP BOILER
Instrumentation
Control loops
OIL OR GAS FIRED LP BOILER
Instrumentation
Control loops
M4-10
-
8/12/2019 Boiler Plant Operation
11/28
ID IDC Technologies - Technical Training That Works
CONTROL AND SYSTEMOPERATING PHILOSOPHY
CONTROLS : Regulate the various quantities indicated by
the instruments
Shut down (with interlocks) the plant ifparameters exceeded
Manual operation to sophisticated automaticcomputer operation (DCS)
M4-11
-
8/12/2019 Boiler Plant Operation
12/28
ID IDC Technologies - Technical Training That Works
CONTROL AND SYSTEMOPERATING PHILOSOPHY
To control a boiler, following quantitiesrequire 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
-
8/12/2019 Boiler Plant Operation
13/28
ID IDC Technologies - Technical Training That Works
COMBUSTION CONTROL
Manual control cannot continuously controlcombustion 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 slightlydepending on fuel fired
No matter what fuel, four aspects that areregulated:Air supply; Fuel supply; Ratio of fuel to air; Flame safety
M4-13
-
8/12/2019 Boiler Plant Operation
14/28
ID IDC Technologies - Technical Training That Works
COMBUSTION CONTROL
Two basic types of combustion controlsystems: Positioning
Metering Pneumatic or Electrical control drives
M4-14
-
8/12/2019 Boiler Plant Operation
15/28
ID IDC Technologies - Technical Training That Works
COMBUSTION CONTROL
Positioning Type Control: Designed to control based on a change in
steam pressure
Components :Master steam pressure controller
Fuel control valve with cam for oil / gas or feedcontrol drive for coal
Combustion air fan inlet vanes / outlet damper
operator Simplisticcannot maintain fuelair ratio at optimum over
full load rangeM4-15
-
8/12/2019 Boiler Plant Operation
16/28
ID IDC Technologies - Technical Training That Works
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 wherefuel pressure may vary
M4-16
-
8/12/2019 Boiler Plant Operation
17/28
ID IDC Technologies - Technical Training That Works
General Selection Chart forCombustion 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 00036 000
Full metering with
Oxygen compensation above 36 000
Fuel Oil & Gas Modulating positioning to 11 500Full metering (Steam
/ air flow) 11 50045 000
Full metering with
Oxygen compensation above 45 000 M4-17
-
8/12/2019 Boiler Plant Operation
18/28
ID IDC Technologies - Technical Training That Works
STEAM PRESSURE CONTROL
Main purpose of a steam boiler is toproduce steam within a definite pressurerange
Steam pressure dictated by : process plant steam demand heat input to the boiler furnace
Pressure fluctuates between minimum
and maximum settings
M4-18
-
8/12/2019 Boiler Plant Operation
19/28
ID IDC Technologies - Technical Training That Works
STEAM PRESSURE CONTROL
Modulating control linked to upper andlower pressure limits
On-off pressure switchlow or high fireburner
Definite limitation exists on burner minimumfiring rate
turndown ration varies : 4:1 gas; 2:1 oil
M4-19
-
8/12/2019 Boiler Plant Operation
20/28
ID IDC Technologies - Technical Training That Works
FEED WATER SUPPLY CONTROL
Purpose is to provide sufficient feed water flowto ensure all heat transfer surfaces are cooledwith 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
ThermostaticM4-20
-
8/12/2019 Boiler Plant Operation
21/28
ID IDC Technologies - Technical Training That Works
FEED WATER SUPPLY CONTROL
Typical arrangements of feed water plant:
Two or more pumps (standby) from hot welltank (10-15 min. storage)
Either on-off operation or a feed valve station
Feed valve station :
Check valve
Stop valveFeed control valve c/w isolation and bypass
valves
M4-21
-
8/12/2019 Boiler Plant Operation
22/28
ID IDC Technologies - Technical Training That Works
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 orlow water cut off
M4-22
-
8/12/2019 Boiler Plant Operation
23/28
ID IDC Technologies - Technical Training That Works
FEED WATER CONTROL SYSTEMS
MODULATING LEVEL CONTROLLERS Boilers with relatively small water volume
relative to steam demand
Thermostatic type regulator feeds watercontinuously to the boiler, stabilising thewater level
THREE types of modulating controllers :
Single Element Level ControllerTwo Element Level Controller
Three Element Level Controller
M4-23
-
8/12/2019 Boiler Plant Operation
24/28
-
8/12/2019 Boiler Plant Operation
25/28
ID IDC Technologies - Technical Training That Works
SOME CONSIDERATIONS REGARDINGWATER LEVEL CONTROL
Rapid changes in steam flow rate can causeSURGING 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 OPERATINGcharacteristics of water level controlling system
Highest water level, NWL, lowest level for safeoperation should be MARKED on boiler outershell
M4-25
-
8/12/2019 Boiler Plant Operation
26/28
ID IDC Technologies - Technical Training That Works
FURNACE PRESSURE CONTROL
Only really required on coal fired boilerswith 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 toonarrow typically +250 to1250 Pa
ideal control point100 PaM4-26
-
8/12/2019 Boiler Plant Operation
27/28
ID IDC Technologies - Technical Training That Works
AUTOMATIC CONTROLS
Instrumentation employed same as thatfor manual operation
Rapid and continuous development of
electronic control systems means systemsfor boilers are now DIVERSE
Selection shall depend on owner /
purchaser present complexity of controlsystems
M4-27
-
8/12/2019 Boiler Plant Operation
28/28
ID IDC Technologies Technical Training That Works
AUTOMATIC CONTROLS
ASPECTS that do not vary whetherauto/manual : Principles of operation
Areas of control (control loops) Direct reading of instruments
Safety devices and interlocks
Selector for manual or automatic
M4-28