Level Measurement in Steam Boiler
Level Measurement, Control and Safety
A steam boiler delivery exactly what is being consumed in the system The steam boiler is always set for a specific steam
pressure, and the operation of the steam boiler is solely controlled by means of this steam pressure set point.
A steam boiler is an autonomic device. It is purely self-controlled unit and must thus never be manually
controlled by others from safety reasons.
Boilers must be designed to operate efficiently and safely while responding rapidly to demand changes.
Maintaining a stable interface level is critical to the safe and efficient operation of the boiler.
Safety
Most of the boiler failures can be attributed to low water conditions. For safe boiler operations this must be kept
under check. Low-water level conditions in the boiler occur when the water in the boiler drum falls below the
low water level mark.
With low water level conditions, severel boiler damage can be happen. If the boiler keeps runnig with low water
level conditions, boiler ‘s furnace and the steel tubes can melt.This is called boiler collapse. If the boiler is feed
with water in this conditions, boiler explotion can happen.
High water levels raise steam exit velocities and result in priming or boiler water carryover in to the distribution
system. Priming results in wet dirty steam while carry-over can result in dangerous water hammer and pipe or
equipment damage.
On/Off Control
In on/off control the feed pump is switched on/off via a level
sensor or a differential pressure sensor. When the water
level falls to the “Pump on” level, the pump starts pumping
a large quantity of relatively cold water into the boiler.
This will reduce the quantity of steam and cause the
steam pressure to fall.
Modulating Control
In this type of system the water level in the boiler is controlled by
a feed valve, which is controlled by a level controller and a level
probe positioned on the boiler. The feed valve controls the water
intake, which is adjusted according to steam consumption.
This, however, requires that the feed pump is set to continuous
operation. This system operates smoothly and is ideal for
all types of steam boilers, both small and large, and will
minimise the risk of over-boiling. Also thewater level in
the boiler is controlled directly by the variable speed
pumps without using a feed valve.
- Single Element System
Measures boiler level and regulates feedwater flow to maintain that level. Adequate for single boiler utility plants with
relatively static loads. - Two Element System
Measures boiler level and steam flow and regulates feedwater flow to maintain boiler level. Recommended for utility
plants with multiple boilers and relatively static loads. - Three Element System
Measures boiler level, steam flow and feedwater flow, and regulates feedwater flow to maintain boiler level. Strongly
recommended for utility plants with dynamic loads.
