3-Element Steam Drum Level Control

3-Element Steam Drum Level Control

Master The Elements

WARE is All Things Steam, and that includes the latest and greatest in boiler technology. In this instance, we’re talking about 3-Element Steam Drum Level Control. 

WARE’s Director of Projects and Services Gerald Blain explains it best:

Steam drum level control means maximizing stability and responsiveness. Traditional methods and best practices dictate feeding the steam flow forward to the level PID loop and cascading the output of that loop to the setpoint of a boiler feedwater (BFW) flow loop. 

This arrangement is known as “Three Element Drum Level Control” (3E) because the algorithm uses level, BFW flow, and steam flow. This method is widely known and has been around for years. In recent years, though, there has been another form of 3 element feed control. This process was invented by Autoflame. 

Their 3-element level control has been granted a worldwide patent; being the only system that can combine firing rate, steam pressure, and water level within one controller for the purpose of improving feed water control. Safety, accuracy, and integrity are guaranteed. The levels which are commissioned when using capacitance probes and/or external level sensing 4-20mA device include high, control point, 1st low, 2nd low, and end of the probe.

It is important that the level of the water in the boiler be maintained appropriately to the amount of steam being generated. Should the water level drop below this ideal level by an excessive amount, it is necessary to stop the burner from firing. If there is insufficient water in the boiler, damage may occur to its structure and in extreme cases, an explosion is possible. 

The water level control herein is designed to maintain a satisfactory level of water in the boiler, whilst controlling and reporting low water level conditions. A key reason for having this 3-element control is to avoid having your feedwater valve close when it needs to be open. When encountering the significant load demand changes found in many process steam environments, systems without 3-element control will mistake a rapid load increase for a high-water condition and thus signal the feedwater valve to close. 

This high-water indication is caused when the rapid load swing occurs, causing an immediate pressure drop in the drum. This drop in pressure causes the water in the steam drum to swell, indicating a high-water level which signals the feedwater valve to close. In reality, the valve needs to stay open because there is a demand for steam creating this condition. This causes the valve to hunt and often go out on a low water alarm. 

The Autoflame firing rate controller is directly tied to the water level system -- and thus knows that the demand exists -- and uses an algorithm to reset the level and keep the valve open while the boiler recovers back to set pressure. This eliminates hunting and low water alarms. This 3-element control makes for smooth operation and actually lowers fuel cost due to more accurate steam set point control.

If you’d like to know more about the latest in 3-Element Steam Drum Level Control, please give us a shout. We’d love to show you how the Autoflame system can improve your performance, safety, reliability, and efficiency. If there’s anything else you need including service, maintenance, a rental boiler, or a new boiler, we’re here to help. 

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