3 replies to this topic

[Sebastian_K]

Hi all

 

I've got a quick question I'm hoping some one can help me with.

 

I'm currently working on a project with a VOC recovery system.

Basically the system consists of a compressor and various shell&plate heat exchangers and it will be used to "recover" VOC from a crude oil carrier during loading.

 

VOC is a hydrocarbon gas mixture consisting of 13 different components, ranging from methane to n-Heptane also including O2, N2, CO2 and H2O.

 

The part I'm working on is a unit including the compressor, 1st stage VOC condenser and a separator to separate the liquified components. The 1st stage will only liquify some of the heavy components.

 

Here is what I need some help for. I'm assesing the heat exchanger which has been calculated by a vendor.

To asses the calculation from the vendor I've made a simple hand calculation, where I've derived the individual components partial pressure. The partial pressure is based on the molfraction which we have been informed by our client.

Now I've simply found boiling temperature for each component at the specific partial pressure in order to identify which component will be liquified. Then I've summarized that to get the total liquid flow.

 

My question is now, can I use this approach do a simple check of the heatexchanger calculation.

 

Best regards

Sebastian

[PingPong]

Your description of how you calculated condensed liquid is not clear to me, but doing it correctly by hand is very difficult as it involves iteration.

 

Normally one would use a process simulator like Hysys or PRO/II or Aspen Plus to do such calculation.

 

If you do not have access to those you can use free simulators like

DWSim

Chemsep

COCO

Prode

[Art Montemayor]

Sebastian:

 

I totally agree with PingPong in everything he advises you.

 

However, I note you mention that you intend to compress your VOC mixture (which contains oxygen).  I would seriously advise you to not compress any hydrocarbon mixture containing oxygen.  The resulting pressure and heat could lead to auto-ignition.  You either have to isolate or remove the oxygen from the hydrocarbons before going further.

[Bobby Strain]

There are a number of vendors who design and supply this equipment. Just make sure you get one with experience. And they are probably much better equipped to design than you are to check. Just ask to see the vendor calculations.

 

Bobby