Q & A > Question Details
Normally Overflash is 3-5 Vol% of CDU Feed. How Overflash may be calculated so that the formula may be incorporated in DCS for optimum Heater Operation resulting in energy saving. Please share some reference for information & study please.
03/01/2012 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
As Mr. Ragsdale said, trying to estimate this from operating data is difficult and not advised to use to adjust control points on a continuous basis.
One thing that can be done is to build process simulations of your different operating modes (crude slates, cut points, coil outlet temperatures, throughput) and match them to operating data. You can then use the simulation data on overflash (assuming you get good agreement between simulation and operating data) to estimate the overflash in the plant. I don't think curve fitting the data and putting that into the DCS would work though - probably too many other variables to make it viable for online control - but it might provide some guidance for the operators.
26/12/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
One can draw envelopes at strategic locations around the top and bottom of the column, write the heat and mass balance equations, and solve by difference for the overflash quantity. Such information on an operating unit is not very consistent or steady, and does not serve well for online resetting of control points, however. It is much better to provide the piping and meter needed to measure the overflash as a flowing stream.