Published on Apr 02, 2024
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Boiler Instrumentation and Controls
Introduction
==> Instrumentation and controls in a boiler plant encompass an enormous range of equipment from simple in the small industrial plant to the complex in the large utility station.
==> Boiler Instrumentation Control is the control over the industrial boilers.
==> It consists of several control loops to control various systems related to a boiler.
==> The main control of boilers include combination control and feed water control.
==> To do the various operations in control different hardware methods are used
Control Loops
==> Combustion controls
==> Amounts of fuel and air must be carefully regulated to keep excess air within close tolerances-especially over the loads.
==> This is critical to efficient boiler operation no matter what the unit size, type of fuel fired or control system used
==> Feed water control
==> Industrial boilers are subject to wide load variations and require quick responding control to maintain constant drum level.
==> Multiple element feed water control can help faster and more accurate control response
Figure
==>
Combustion Control
==> A combustion control system is broken down into (a) fuel control and (b) combustion air control subsystems.
==> The interrelationship between these two subsystems necessitate the use of fuel air ration controls
==> The primary boiler fuels are coal, oil and gas.
==> The control of gas and oil fuels requires simplest controls- ie, a control valve in the fuel line
==> Therefore by controlling the steam supply one can establish balance between the demand for steam (process load ) and supply of water
Feedwater Control
==> Feedwater control is the regulation of water to the boiler drum. It provide a mass accounting system for steam leading and feedwater entering the boiler.
==>The water is admitted to the steam drum and after absorbing the heat from furnace generates the steam produced by the boiler
==>Proper boiler operation requires that the level of water in the steam drum should be maintained within certain band.
==>An increase in the level of water may interfere with the internal operation of internal devices in the boiler drum.
Partial vaporization in evaporating tubes
==> Figure
Single and Two Element Control Systems
==> For small boilers having relatively high storage volumes and slow changing loads ,single element control system is used.
==> It controls feed water flow based on drum level. Response is very slow because a change in feedwater flow takes a long time to show up the level change.
==> As a result the steam drum causes water to increase and decrease in volume, resulting in false measurements
==> This control is used in intermediate boilers as well as large boilers
Three element control
==> Boilers that experiences wide and rapid load changes require three element control.
==> Three element control is similar to two element system except that the water flow loop is closed rather than open
==> Control action, the third element based on feedwater flow.
==> The feedwater flow measurement provides corrective action for variation in feedwater pressure
Conclusion
==> The various goals of boiler control includes:
==> To minimize excess air
==> To minimize blowdown
==> To minimize steam pressure
==> To measure efficiency
==> To find when to perform maintenance
References
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