5 replies to this topic

[karan]

Dear All,

 

I want to know about our present design in detail, if any one can then it would be very greatful to him.

 

Our design is:

 

We have Naphtha stripper rebolier which is using 60kg/cm2g HP steam through one Flow control valve which is given to control third tray temperature and due to control valve the pressure get reduced as per saturation temperature of naphtha. I just want to know why this flow control is required, if we use without it the steam flow will be controlled by saturation temperature required and condensate produced and flow will occur.

 

Other question is in condensate pot why equalisation line is required, and how condensate flow and why condensate drum is below 3m of reboiler bottom, if it is equal then what is the problem,can anyone explain me.

 

Thanks!

[himant]

A ) Before answering above, it is very important to have PFD or hand-made sketch.

 

From your query, I can only figure out that

1. Feed to reboiler is coming from sump tray.

2. Exchanger is kettle type

3.Column bottom pump is controlling the reboiler level not the column sump tray level

 

I don't know if above is correct or not. 

 

B ) Equalization line is given to equalize your condensation drum pressure and reboiler steam side pressure. By doing so, flow from reboiler to condensate shall be based on differential head (by gravity only) which will be smooth otherwise your condensation level in reboiler or condensate drum will fluctuate like anything

[karan]

Thanks HImant for ur reply.

 

1. Echanger is kettle type
2. Feed is coming from bottom chimney tray.
3. Temperature we are controlling of third bed which is having cascading controlling with inlet flow control valve.

 

Now i understand equalisation purpose but i also want to know that what is the purpose of flow control valve at inlet steam line which is high pressure (60Kg/cm2g), it is used to stripped out H2S from naphtha which is having high FBP of around 220'C. If we dont have flow control valve at inlet of steam line then as steam condensed the steam would flow and condensate drum level we are controlling, so can anyone explain it.

[Bobby Strain]

If you post a sketch we can be helpful.

 

Bobby

[karan]

Please find attachment drawing and my querries are highlighted in that drawings.

 

Thank you!

Attached Files

•  New_Microsoft_Excel_Worksheet.xlsx   13.42KB   43 downloads

[himant]

1. Steam @ upstream of control valve is not saturated, it is superheated. When you reduce the pressure of steam across control valve, degree of superheat increases. And that degree of superheat is nullified by installing a de-superheater which is used to control the temperature of steam.

Clearly, you have missed the de-superheater which must be located downstream of control valve

2. If you don't want control valve, how do you intend to maintain temperature of third tray or in other words, i.e. provide required amount of reboiler duty

3. Reason for height: When condensate will flow from reboiler to condensate drum, there will be friction losses. This friction loss (in terms of pressure is balanced out by gravitational head (using equalization line)

Case 1: If elevation is more than 300, then there won't be minimum condensate level in reboiler and  flow of steam will be difficult to control as it will simply pass through without complete condensation

Case 2: If elevation is less than 300, then the level in reboiler will increase, which will create the back-pressure for steam and again reboiling duty will suffer.

 

Now, let us see what experts have to say!

 

Regards

Himant