18-05-2013, 01:05 PM
Basis – Ratio Control
Basis – Ratio.ppt (Size: 169 KB / Downloads: 14)
To fully automate a large process, it is often necessary to provide coordination of multiple flows.
The technique of ratioing control loops is an effective way to provide this coordination.
Ratio station is used to specify ratio and to calculate setpoint of the dependent flow.
Ratioing based on the independent loop setpoint provides a noise free remote setpoint but will be incorrect if the independent loop can not maintain its setpoint
Example – Reactor Feed Ratio Control
Catalyst flow must be maintained in correct proportion to the feed flow for correct reactor operation and final product.
Ratio control automatically provides the correct proportion of catalyst to feed.
Automatic Ratio Adjustment
A process output that indicates the impact of the ratio of process inputs may be maintained at target by using feedback to adjust the ratio target
To the feedback control, the ratio station and associated flow loops are considered to be part of the process
Example – Slaker Control
Effective Alkali. EA, is maintained at target though the adjustment of lime to green liquor flow ratio.
As green liquor feed is increased, then lime flow is automatically increase in a proportion to maintain the target EA.