4 replies to this topic

[Takechi]

Dear all expert

 

I am junior engineer. My work is about process design.

When I study the process engineering design gudeline. It is identify only criteria or guideline that we need use it for design or calculation. But it is not tell us the reason why we need use that criteria, what is theory or concept to support that criteria. Such as why criteria of shell and tube heat exchanger temp approach = 10 C, Air cool 15 C, Pressure drop of inlet line PSV < 3% of set P, Flow and pressure control valve's %EQ charateristic use %EQ  and etc.

 

If anyone have document that both process eng. design guideline and theory/concept to support that guideline.

 

Could you please share to us.

 

Your help is my appreciate.

 

Best regard,

 

Sapao

[Bobby Strain]

You really should not post as a student. After you gain experience you will begin to understand guidelines. There are many sources. But the ones you should heed are those of your employer and/or your client.

 

Bobby

[Saml]

Sapao, it is a kind of a broad question that belongs more to a book than to a formum.

 

Also, never trust blindly the design guidelines. You, as an engineer is the one who design. Guidelines are just that.

It is different if they are part of a client requirements or internal company design criteria. Then, you should learn to identify when it may be wrong to follow them, that is, the exceptions.

 

I would suggest the following approach:

- pick one.

- try to find out what might be the rationale. There is plenty of information around.

- post it here.

- others will provide their oppinion.

- repeat.

 

This way, you learn by doing. You get things done. Others will make their contribution.

 

Now, I pick one:

 

Valves: most of the controllers logic assume that the response to the output is linear. If the gain change at different valve opening, you may find it difficult to tune the controller. So, you use a valve with a characteristic that provides the most linear response of your controlled variable to the valve output. In the case of flow, where frictional pressure drop in the piping is an important part of the total pressure drop, equal percent provides a more linear flow response than a linear valve for a given change in the output.

 

If the pressure drop is caused mostly by the valve, like in a pressure let down valve, then a linear valve may be more suitable (pay attention to the "may")

Edited by Saml, 17 June 2018 - 01:07 PM.

[ankur2061]

Hi,

I understand your dilemma and appreciate your questioning attitude. The chemical process industry has evolved over the last 80-90 years. Some of the guidelines and practices being utilized today have been tested for their efficacy since the early days of the chemical process industry and have been found to be effective and workable even today and hence have become established norms. Now there may be more effective guidelines and precision values of certain process variables such as momentum, approach etc using advanced simulation tools but the fact remains that many of these established norms and numbers are field tested over numerous installations over long years and thus have become the de facto guidelines. The whole idea of using these established norms is not to re-invent the wheel.

Having said that, I would certainly advise young engineers to question the boundaries of the established norms. In fact I have posted a blog post for a very similar topic which I would recommend you to read. Here is the link:

https://www.cheresou...-and-practices/

Regards,
Ankur

[Takechi]

Many thank all expert for sharing to us.

 

Sapao