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Basic Controls For BoilersMENTOR : PROFESSOR VIDITA TILVA
BY:
AASHEESH TANDON (12BIC044)
PAXAJ SHUKLA (12BIC056)
1. Introduction
How does a boiler works?
A boiler is a water containing vessel which transfers heat from afuel source (oil, gas or coal) into steam which is piped to a pointwhere it can be used to run production equipment, to sterilize, to provideheat, to steam-clean, etc.
1. Introduction
The energy given up by the steam is sufficient to convert it back into the form of water. When 100% of the steam produced is returned to be reused, the system is called a closed system.
1. Introduction
Since some processes can contaminate the steam, so it is not always desirable to feed the condensate back into the boiler. Asystem that does not return the condensate is called an open
system.
2. Basic type of boilers
The two main types of boilers are:
• Firetube
Fire or hot gases are directed through the inside of tubes within the boiler shell which are surrounded by water.
• Watertube
Fire or hot gases are directed to and around the outside of tubes containing water, arranged in a vertical position.
3. Why need boiler controls?
1. Increase uptime and availability
2. Reduce flue gas emissions
3. Maintain boiler safety
4. Control operating costs
4. Combustion control for boilers
A combustion control system is broken down into :
(a) fuel control
(b) combustion air control
4. Combustion control for boilers
There are three general types of combustion control schemes used today:
(a) series,
(b) parallel, &
(c) series-parallel controls.
4(A). Hardware Used In Combustion Control
(a) ON/OFF controls
(b) Positioning systems
(c) Metering control system
4.(B) Combustion Control Methods
Burner combustion control generally includes one or a combination of the following methods:-
Excess air regulation
Oxygen trim
Burner modulation
Air/Fuel cross-limiting
Total heat control
5. Feedwater Control For Boilers
Feedwater control is the regulation of water to the boiler drum.
Risks :
If the level is too high, may interfere with the internal operation of internal devices in the boiler drum, such as - flooding of steam purification equipment can occur.
If the level is too low, reduction in efficiency of the treatment and recirculation function, undesired pressure build up, over heating of boiler coils/tubes.
5.(A) Components Affecting Drum Water Level
steam bubbles
Drum pressure
‘swell‘ : surge in water level as a result of the drum pressure decreasing
'shrink‘ : decrease in water level as result of drum pressure increasing
5.(B) Single And Two Element Control Systems
Single Element :
controls feed water flow based on drum level
Response is very slow
Two Element :
uses steam flow changes as a feed forward signal
flow and level transmitters are summed by a computing relay
response is faster
5.(C) Three Element Control
Used when :
unstable feedwater system exists
if large unpredictable steam demands are frequent
5. Application Chart For Drum Level Control System
5.(C) Five And Seven Element Control
Five element control is better than Three Element control in terms of :
steam flow measurement is temperature compensated, &
drum level measurement is pressure compensated.
Seven Element control is better than Five Element control in terms of :
Transmitters for blow down flow
Transmitters for soot blower flow
5. Feedwater Control for Boilers
Advantages :
1. Multiple element feedwater control can help:
i. Faster response of systems.
ii. More accurate control.
iii. Maximum system stability.
2. Metering control system maintains combustion efficiency over wide load changes and over long period of time
3. Parallel combustion control can be used in any size of boilers
5. Feedwater Control for Boilers
Disadvantages :
1. Boilers require quick responding controls.
2. Level of the water in the boiler must be kept above 50% of height.
6. Other Control Functions
A. Furnace air and draft control
B. Steam temperature control
C. Steam pressure and load control
THE END