Re: DMC on Alky Spent Acid

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: Jim,

: I've done APC on several Alky units and have never seen anyone try closed-loop acid strength control.  I did some work with a client in 1998 who was in the process of installing acid strength analyzers on their H2SO4 unit, and planning to control acid strength with a DMC controller.  As far as I know, though, other equipment problems have prevented that DMC project from starting yet.

: Having worked on your Alky a little, I know some of the operational issues and would think that there are probably good benefits to doing the acid strength control.  Why not go ahead and make a few step tests and see what the models look like?  As far as designing the controls, I see little reason to combine the acid strength control with the rest of the unit operation.  I would expect it to be a very slow, say 3 to 5 min, executing controller manipulating the acid flows and using feed flows, compositions and whatever you can get as DVs.  The various acid strength measurements would probably be the only CVs.  If I remember right, the spent acid flows are successfully cascaded from the settler levels on this unit, so the APC is probably quite feasible.

: Sounds like an interesting project - good luck.

: Regards,
: Doug

: 
: : We have installed coriollis meters on our acid from our Alky contactors.  The coriollis meters provide a continuous density measurement which we are successfully using to infer acid strength.  

: : Assuming one can continuously monitor acid strenghth from the contactors, what are the issues regarding trying to create a DMC controller to regulate Acid makeup.   Has anyone developed an initial design criteria for this problem? 

: : Thanks


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