9 replies to this topic

[Rajesh Patel]

Hi 

I am working for vent size calculation for 38% HCL storage tank. I want to know how to calcuate out breathing for HCL storage tank in case of tank filling at 20m3/hr. As I understand it will not be as outbreathimg is equal to filling rate beacuse there will be HCL vapour generation during filling. I do not know how to calculate vapour generation rate. 

Thanks

Raj

[fallah]

Raj,

 

Lack of adequate info...

 

-Temperature of the feed to the tank

-Operating temperature/pressure of the tank

-Is tank N2 blanketed?

[Rajesh Patel]

Thanks Fallah for taking your intrest. 

 

Max feed temperature: 60C

According to tank mechanical drawing, design temp / press: Amb / Atm

N2 blanket: NO. Storage tanks are venting to vent scrubber. 

 

Let me tell reason behind this question. We have installed new scrubber for storage tank vent. This project was already finished before my joining but by some reason not taken in operation. And no one present involved in this project. So we had review old HAZOP and there was no record of prssure drop calculation from storage tank to scrubber and so many other pressure drop calculations. I got action to do pressure drop calculation in all pipe lines. 

 

Thanks

Rajesh 

[fallah]

Raj,

 

Thanks for your explanation...But please submit the maintain pressure of the vent scrubber. Also a simple sketch can be helpful...

 

Indeed, as far as i know the boiling point of HCl 38% in atm pressure is 48 C. Then as per max feed temperature of 60 C it might most often be in boiling condition if the tank would be atmospheric...

Edited by fallah, 18 November 2013 - 05:09 AM.

[Rajesh Patel]

Thanks Fallah 

 

I have spoken to senior operator in plant and as per trend, HCL temp coming out from absorber is never greater than 25C.

 

I have made a system sketch but i do not know how to attach here.

 

As per mechanical drawing of scrubber see below design data which is not great information.

Design temperature: 30C

Design pressure: ATM + BACK PRESSURE.

 

Thanks

Rajesh  

[fallah]

Raj,

 

Please specify "back pressure". To attach the sketch use the "More Reply Options" located beside "Post" option.

[Rajesh Patel]

Thanks Fallah

 

This back pressure I need to calculate which will be presssure drop in vent line from storage tank to the inlet of scrubber. And to calculate pressure drop i need to know vapour load. I am confused here will there be HCL flash? How will effect on vapour load?

 

Thanks for quick update. 

Best regards

Rajesh

Attached Files

•  System sketch .pdf   162.79KB   154 downloads

[fallah]

Raj,

 

Let's take the feed temperature of HCL equal to 30 C. then the vapor pressure of HCL 38% at 30 C would be around 0.3 bara. It means with a 4" vent line size through which (HCl+H2O) vapor would continuously be released there might be a pressure build up (you haven't specified any source pressure for incoming HCL feed) or a pressure equal/less than 0.3 barg inside the tank. Considering you have already fixed the line sizes, tha vapor load might be estimated by trial and error. Indeed, appears the system would be operated in batch condition due to liquid accumulation inside the tank.

[Rajesh Patel]

Dear Fallah

Here I want to know mainly, Do I need to consider flashing of HCL vapour during filling to calculate vapour load. 

If yes than which method do i need to use for HCL flashing calculation.

Thanks

Rajesh 

[fallah]

Raj,

 

Yes, you should consider HCl flashing for vapor load determination, but in this way you need to have estimated pressure profile from incoming HCl source to end of outgoing vent line of the scrubber...

Edited by fallah, 18 November 2013 - 11:40 AM.