Control / alarm set point for desuperheater

[delf]

Dear Sir

I am sorry to bother you this simple control / alarm set point question.

Case 2 is a simple direct temperature control through a temperature sensor located downstream and send a siganl to the valve controller to increase
or decrease the water supply.
Case 1 is a complex temperatrue control.

My question is to improve system response to quick change, the input singals to the pressure and water valve are ratio. Could any one kindly explain to me what kind control is better in opertabilty view or process view?

Ex. I notice the temperature control valve alaways installed close to the desuperheater for operatabilty
And, how can we obtain alarm setpoint of pressure control for case 2? Can we look up the header pressure or just pick up 13 barg between the presssure high alarm (14barg) and low alarm (12barg) ?

Thank you so much for your kindly reply.

 

[delf]

control variable with significant capacitance dealy time should be avoided. For example, tempeaure control with a large column using reflux fow. So why the case 1 is better than case 2 in this desuperheater case (attache file)?

thank you so much.

 

[glowing]

Think of it like your furnace. You may set a stat at 22C, but it is going to stray up and down a couple degrees (say 19-25C). Not a big deal in the house. If you use a VFD on the furnace you will maintain that 22C. View the VFD as said control valve. It maintains Set-Point, as opposed to basically floating around it.