Q & A > Question Details
In our Naphtha Stabilization unit, feed after preheating leaves the HE through a 10" dia pipe and then immediately split in to two vertical risers of 4" dia and again joins back to a 10" dia pipe before entering the stabilizer. What is the purpose of this risers with reduced dia? In P& ID it is mentioned as two phase flow.
13/12/2016 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Called “slug flow,” it is often ignored during design. Many years ago, a paper was published showing an atmospheric crude unit with a grade mounted overhead condenser to save capex and provide ease of maintenance. Condenser outlet was multiple risers with valves up to the overhead accumulator. I don’t think it was built, and I have never seen a column with such risers.
12/12/2016 A: Leonardo Leite Garcia de Souza, Petrobras SA / Duque de Caxias Refinery, llgs394041@yahoo.com.br
Two-phase flows may show instabilities inside long vertical pipes if the velocity is not high enough. Splitting the flow through two 4" pipes intends to increase the velocity in each pipe, avoiding the above mentioned instabilities.