Boiler level control system

instrumentation
level-measurement

#1

Steam power is very important in industries, steam power is used to doing mechanical work. Steam is made in industries simply by boiling water in a boiler. So boilers are considered to be one of the main equipment in industries.

Boiler level control is crucial because, the level of water in boiler should not exceed a level and should not go a level below. If there is not enough water in the drum, the water tubes may run dry and burn through from the heat of the fire. If there is too much water in the drum, liquid water may be carried along with the flow of steam, causing problems downstream.

From the above figure, it is clear that a pneumatic control system works to control the level of water in the boiler. The LT (level transmitter) measures the level of water in the boiler and transmits the signal pneumatically in 3-15psi, to the controller, which is also an indicator of level, A 3-15psi control signal is produced by the controller comparing the measured signal and the setpoint.

The control valve is the final control element in the system, which is implemented to influence the flow rate of water. The control signal is produced either to open or close valve otherwise increases or decrease the flow of the water to the boiler.

If the level is too low, the controller the valve open fully to ensure complete flow through the pipe. If the level is high, the valve starts closing to reduce the flow and eventually the level of the tank.

A human operator supervising this boiler has the option of placing the controller into “manual” mode. In this mode the control valve position is under direct control of the human operator, with the controller essentially ignoring the signal sent from the water level transmitter. Being an indicating controller, the controller faceplate will still show how much water is in the steam drum, but it is now the human operator’s sole responsibility to move the control valve to the appropriate position to hold water level at setpoint – in manual mode the controller takes no corrective action of its own. Manual mode is useful to human operators during start-up and shut-down conditions.

When the controller is placed in the “automatic” mode, it will move the control valve to whatever position necessary to maintain a constant steam drum water level. The phrase “whatever position necessary” suggests the relationship between the controller output signal, the process variable signal (PV), and the setpoint (SP) is complex. If the controller senses a water level above setpoint, it will close off the valve as far as necessary to decrease the water level down to setpoint. Conversely, if the controller senses a water level below the setpoint, it will open up the valve as far as necessary to raise the water level up to setpoint.

How to increase Boiler efficiency?

To know about Level Measurement Errors


#2

Nice artical.
Can you also describe more about the single element and 3-element control to control the steam drum level.


#3

#4

What is the best measurement level for a boiler?. What type of them.