Ball valves – Ideal control valve solution for delayed coking

Demands of delayed coking

Delayed coking units are a semi-continuous process used to create additional liquid and gas product from petroleum residue. The residue entering the delayed coking process has a high percentage of solids that can accumluate and restrict flow through strainers and valves. The process involves heating petroleum residue to the thermal cracking temperature in a furnace. Control valves are used to regulate the flow into the furnace. 

As the following customer example has proven, switching to Neles™ ball valves can allow a refinery to run at full capacity, gaining an additional daily output exceeding $15,000 in value. Could you believe that the return on investment for converting to ball valves can be less than two weeks of production.

Finding the right valve design 

At one particular refinery eccentric plug valves were installed to control the oil/coke fines 
going into the furnace. Plug valves have shafts that extend into the flow stream causing
solids in the media to build-up and restrict flow. The restricted flow through these valves 
gradually reduced output until the build-up was so severe it caused an unexpected trip in a furnace cell, nearly shutting down the entire coker unit. 

In an attempt to resolve the problem the refinery replaced the eccentric plug valves with
globe valves with flow paths and trims with a similar tendancy to accumulate solids, 
restricting flow. The refinery then installed reduced bore ball valves, resolving the plugging problem. However, there were control accuracy issues from backlash in the ball and stem 
connection.

The refinery ultimately turned to Valmet representatives to discuss possible options. The 
challenge was to find a control valve that would prevent the accumulation of coke fines, have consistant control, and provide maximum througpout. 

Unobstructed flows with Valmet solutions

To overcome the challenges, Valmet’s solution was to install Neles™ D-series trunnion ball 
valves. These valves already had more than 40 years of proven success in challenging 
control applications. The D series ball valves have no obstructions in the flow path that can
accumulate media and obstruct flow.

The selected valves have a one-piece stem ball design that has zero backlash. This allows 
for tighter, more accurate control in smaller steps. Designed to handle coke fines with self-cleaning trim, they have proven to be the best choice for this particular case and example. The Neles D-series valve’s solids proof seat prevents the accumulation of solids behind the seat. 

They are now proven to deliver reliable, long-term control performance in the demanding 
delayed coker applications at the refinery in question. Valmet warmly recommends these ball valves to all refineries wrestling with similar challenges with reliability issues resulting from solids build up.

Text by Michael Bouckaert