3 replies to this topic

[dsahmed]

Typical arrangement for blow down of hydrocarbons is to use ball valve (on-off valve) installted with RO. A suggestion is being made to use globe valve insted of ball valve for the following reason:

• Ball valve opens too quickly which may cause bending of RO leading to size changes and higher flow on next use.
• Ball valve does not throttle flow and opening will erode the ball & sealing. Globe valve, with soft seats, will have minimal damage and can also be used for pressure control.
• Fisher D type valve may be appropriate for separator flow discharge.

Peers opinion will be higly appreciated.

[fallah]

Typical arrangement for blow down of hydrocarbons is to use ball valve (on-off valve) installted with RO. A suggestion is being made to use globe valve insted of ball valve for the following reason:

• Ball valve opens too quickly which may cause bending of RO leading to size changes and higher flow on next use.
• Ball valve does not throttle flow and opening will erode the ball & sealing. Globe valve, with soft seats, will have minimal damage and can also be used for pressure control.
• Fisher D type valve may be appropriate for separator flow discharge.

Peers opinion will be higly appreciated.

*RO thickness is calculated based on flowrate and the fluid velocity
*Ball material in BDV is selected based on probable erosion.
Throttling is performed by RO and ball valve just is an full bore on/off valve.
Control globe vave is subjected to two major unwanted scenarios.Failed OPEN type leads to high blowdown flowrate and failed CLOSE one would be opposed to blowdown intention.Certainly,your proposal about globe valve is not manual type and you mean control type!
*I actually don't know what you mean

[JoeWong]

One of the point you that you may to have evaluate is the reliability and availability of control globe valve with control function.

Stuck globe valve could limit flow during blowdown.

There are many similar application (BDV+RO) worldwide. It shall be designed to take the high flow scenario.

[Art Montemayor]

dsahmed:

Whoever is advising you - or worse, instructing you - to employ a globe valve as a Blow Down Device is seriously in need of some engineering experience and hands-on knowledge. The reasons given are typical of persons who don't understand applied Fluid Mechanics and also don't know the reasons behind a ball valve + resistance orifice being applied. I strongly advise you to REJECT what you have been told or advised. The bases for the globe valve are totally irrelevant and make little or no common sense.

Fact #1: ALL blow downs (where the source is greater than 30 psig) will be done under SONIC ("CHOKED") FLOW. This means that the flow rate - whatever it is designed to be - will be essentially CONSTANT. There is no throttling required - or desired. This is a major point not even discussed by the person(s) advocating the use of a globe valve.

Fact #2: All manual globe valves have a threaded stem - whether internal or external. This is a potential SAFETY hazard in the event the threads freeze or corrode and require exceptional high torque to operate the valve. I personally do not accept this risk in an operating environment where human lives may be at stake.

Fact #3: If your globe valve is an air-actuated one, then it is no more than a ball valve - but without a simple, maintenance-free means of controlling the choked flow rate. The fixed orifice does this without any moving parts - how can anyone possible improve on this safety feature?

Fact #4: Of course the ball valve DOES NOT throttle the flow! The velocity through the ball is approximately the same as it is in the connected pipe - assuming you are employing full bore ball design. The flow is throttled at the RO, where choked flow is generated. This is pure Fluid Mechanics at its simplest application.

Fact #5: The RO will NOT BEND if designed correctly by a capable and experienced engineer. I sincerely hope you are dealing with professional, intelligent engineers who understand this simple fact.

Fact #6: A Fisher D type valve plays no logical sense in what is being recommended. It is an excellent and time-proven PROCESS CONTROL VALVE. Fisher never designed it for blow down service. There is no actuator that you can apply that will fix the inevitable choked flow produced to be accurately what you have to design the blow down operation for.

Let us all apply some common sense here: ALL blow down operations have to be designed to follow the common design basis of reducing the source vessel pressure at a given, maximum rate. In order to carry out this design basis, you must establish a means of controlling a desired flow rate through the blow down valve. The ONLY way you can carry out this operation with a Fisher D type valve is to install a flow detection device downstream with a controller operating the valve action. And this does not guarantee that the valve can fail open or closed!

Instead of doing the above with complicated instrumentation and other devices, practical and experienced engineers know that it is far simpler and SAFER to use a ball valve + an RO directly downstream. A simple, air-actuated cylinder turns the valve 90 degrees and the RO does the rest of the job. What could be simpler - and safer?

I distinctly remember going through this same logic exercise on a similar topic in these Forums in the past. If you use the SEARCH function, you can find similar threads.