icm header logo v1

ICM Worldwide
icm header top-globe v1 

HRSG 3-Element Drum Level Control

HRSG (heat recovery steam generator) 3-Element Drum Level Control has an advantage over single-element drum level control. HRSG 3-Element Drum Level Control uses measured drum level, total steamflow rate from the HRSG and feedwater flow rate into the HRSG to control the flow of water into theHRSG.

Improving Steam Generation Efficiency

The HRSG is a D-style boiler. Water circulates through the D-shaped boiler tubes, where it begins to boil. The vapor bubbles separate from the boiling water in the steam drum. When drum pressure changes with steam load changes - which is known as "shrink/swell" - it changes the actual water inventory in the drum because the size and amount of steam bubbles in the liquid is changing.

Many plants tend operate with a higher level setpoint in the HRSG than is necessary to avoid low-water level nuisance trips. Currently the HRSG uses single-element drum level control. With single-element drum level control, changes in steam load can cause a significant "bounce" -also known as the shrink/swell effect-which can result in a "low-water level trip". The bounce in the level can be seen in the HRSG's sight glass.

    • HRSG 3-Element Drum Level Control significantly reduces the shrink/swell effect because it is programmed to match feedwater flow to steam flow during times of steam load changes.
    • HRSG 3-Element Drum Level Control only requires DCS programming changes - no additional hardware purchase required.
    • When HRSG 3-Element Drum Level Control is turned on, it is programmed to automatically switch from single- to 3-element control when predetermined operating conditions are met.