Hi everybody,

these days we are planning to design and implement our feed water system to be in 3 element instead of being in one element. that Feed water system in our boiler was running in 3 element system in the old DCS system but now we are shifting to YOKOGAWA DCS. but i wanna know how to implement such thing in DCS and what is the required compensation should i consider for steam and level, given that we using 3 DP Honeywell XMTR for steam drum level.

another question regarding this challenge for the feed water flow measuring. i think we should implement (mass flow meter) in DCS side. please how it is and what it is and why normal flow reading not directly coming to 3 element controlling.

Ahmed.........

 

mass flow meters take into account the density of fluid flowing through them. if it is purely water which is assumed being feedwater to a boiler, your density shouldn't change very much hence a mass flow meter might be overkill.

however it helps to balance water to steam as a mass flow in a 3 element control scheme.

 

Basic sensors shall be Steam flow, Feed water flow and Drum level. For 3 element controller controller 1 (LIC) shall be feed forward based on two inputs i.e. Drum level (Drum pressure compensated) and steam flow (Compensated for pressure & temperature). O/P of Controller 1 (LIC) shall be fed to controller 2 (FIC)as set point. Hence LIC & FIC both controller shall be in cascade. Process variable to controller 2 (FIC) will be directly from drum level.

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