3 replies to this topic

[Bodhisatya]

Dear All

 

I am in a middle of Commissioning of a old Nitrogen Plant of medium capacity.

 

The Turbine of this plant is out of order and required cold for Cryogenic Distillation would be provided by injecting external Liquid Nitrogen.

 

The Liquid supply will happen via the same route through which Distillate (Liquid Nitrogen) produced in Storage Tank.The path has two Globe valves (one angled ,other one straight).

 

About 75 Nm3/hr of LIN would be required to generate refrigeration.

 

So on a nutshell the  direction of flow through those mentioned valves would be contrary to the original mode.

 

On asking the original Licenser ,they said reverse flow is possible,while valve vendor says it is not .

 

We are in a fix now.To change the valve direction,a major modification is required inside cold box,to top of that there is a space constraint.

 

Asking esteemed forum members to throw some light on the above matter.Is Reverse Flow via globe valve possible?

 

Regards

Bodhisatya 

[MTumack]

It is certainly possible, although it will change your flow coefficients and performance across the valve quite a bit depending upon the valve.

 

Acquire some information from valve manufacturer with respect to the altered flow coefficients of said valve in both flowing directions, and do some math to figure out how much flow you can effectively get through with the valve one way compared to the other. Determine whether the valve flowing "backwards" meets your requirements for it, and if so I wouldnt worry about it any further.

 

Depending on your valve manufacturer and the valve's exact geometry, flowing up through the valve or down through the valve can change the Cv, Kv, and Xt of the valve by numbers as high as 20%, in my experience. That being said, some valves will see very minor differences if any at all.

 

I suppose the other question is; you are commissioning an old plant? How long has it been running well like this, and has the performance thus far been acceptable? I mean, if you have like 10 years of working performance of these valves functioning exactly how they have been required, it is kind of hard to say "Hey this is an unnacceptable configuration" no?

[Bodhisatya]

I

 

I suppose the other question is; you are commissioning an old plant? How long has it been running well like this, and has the performance thus far been acceptable? I mean, if you have like 10 years of working performance of these valves functioning exactly how they have been required, it is kind of hard to say "Hey this is an unnacceptable configuration" no?

As said earlier until now the plant was running with a turbine and flow through these valves were in the direction as specified,now that the requirement for reverse flow has rose,the applicability of them has come under scrutiny. 

 

An Additional info to get better guidance,one valve is equal % in nature .while the other is linear in relationship.

 

In additional to getting required flow,pressure drop through these valves is also a point to ponder,as per Vendor datasheet drop across these valves for forward flow is 0.1 bar.Can we get a roughly quantify the drop in reverse direction?

 

As we are getting very luke warm response from valve vendor ,I am trying to find answers via this esteemed forum.

[MTumack]

I don't think anyone here could estimate your valves performance in the reverse flow condition.

 

Given your manufacturers lack of data (or lack of resounding endorsement anyhow), I'd say your options are as follows:

 

1) Make the modifications necessary to have flow through the valves recommended direction.

 

2) Send out the valve to have its performance evaluated rigorously in its reverse flow orientation and see if that is acceptable for your service, then make a decision based upon your new knowledge.

 

I would lean towards the first option, personally. The second one you are kind of spending money to flip a coin on whether or not you need to spend money. That being said, i have no idea how much it would cost to find performance values such as Cv, Kv, and Xt.

 

EDIT: I should add, it is also a possibility that some of your valves internal components are designed to have flow go through unidirectionally and would need to be replaced. Most notably the seals I think.

Edited by MTumack, 02 February 2015 - 10:51 AM.