Time Reduction for Batch transfer by using a pump

[pradeepbarola]

Refer to the attached image

Overview
The feed to V12 comes from distillation unit, where batch production rate is 16 Ton/day and at 220 degC. At first it is cooled to 160 degC in V12. Now this bulk is transferred from V12 to V18 using N2 gas pressure. All the transfer lines are jacketed (steam is used) to maintain the temperature. Once the receiving is completed (transfer takes 3-3.5 hrs) V18 outlet is opened and the pastillation unit is started (throughput=500kg/hr)

Process Description
1. Pastillation unit is stopped and V18 is de-pressurized to atmosphere, and vent is closed after that.
2. V12 is pressurized upto 1.5 atm using N2 gas, V12 uptake valve is opened and melt is transferred from V12 to V18
3. At the end N2 is taken through the transfer line and V18 develops about .5/.7 bar pressure.
4. V18 receiving valve is closed
5. V12 vent is opened.
6. Pastillation unit is started.
Problems faced
1. It takes around 3-3.5 hours for V12 to V18 transfer.
2. Pastillation unit can be started only after the transfer(as it is pressurized only after the transfer is complete)
Questions
1. Eliminate this 3-3.5 hr delay, and start the pastillation unit as soon as there is sufficient bulk in V18.
2. What should be the operation mode, batch or continuous. What should be the capacity of the gear pump for the purpose ?

Proposed Solution
Using a gear pump to transfer the bulk from V12 & V18

Challenges
1. Softening point for this bulk is around 90 degC. If a pump is used a big challenge is to avoid chocking in pump internals.
2. Once there is no material on the suction side, remaining material in the transfer lines can`t be pumped.
3. Making a control logic for pump operation(When will it transfer to V18 or V12 depending on the level in V18)
a. Refer to the attached pic for control logic
i. If the vessel V18 outlet is open it has to be pressurized using N2 gas, which will in turn put back pressure in the transfer line.

Addressing the challenges: Suggestions needed
1. Either provide continuous heating to the pump, to maintain the temperature well above softening point.(Cost of Heating (24X7) !)
2. Using a recirculation line from the pump discharge to the V12 vessel.(24X7 pump energy consumption !)
3. To avoid loses in transfer line, using N2 gas to transfer the material at the end of transfer. This N2 will increase the pressure in V18 as well.(advantageous)
These are the solutions thought at the beginning of this project, please provide your comments on this and also suggest if something better comes to your mind.
Kindly let me know for any queries regarding the process.
Thanks in advance 

 

[rollingstein]

Why cannot you feed from V12 directly to pastillation unit? What's the role of V18?

2. Once there is no material on the suction side, remaining material in the transfer lines can`t be pumped.

Can't pump be sited very close to V18? Then very short line length remains after pump.

 

[rollingstein]

V12 is pressurized upto 1.5 atm using N2 gas, V12 uptake valve is opened and melt is transferred from V12 to V18

Can't you pressurize V12 to a higher pressure?

What is the line size and line length? Even with, say, a 4 inch line I'm getting velocities barely 4 ft/sec even if you wanted to pump out the whole 15 m3 tank in half an hour.

That seems an eminently feasible flow velocity for a liquid. Without knowing your viscosity and density the rest is hard to know.

Your description sounds like you are working with something that will have viscoelastic properties. True?

 

[pradeepbarola]

Thanks for the reply.
Yes it is viscoelastic, basically vulkanox, a rubber melt.

If the pump is kept closed to V18, losses would be too much(friction + drop across the filter) ans moreover preference is to keep the piping network same where the pump discharge would be joined to N2 uptake line, close to V12.( If you could suggest something better, I am open to that).

Details for pipe size and length I can provide you in a day.

V18 is used as a buffer vessel, reasons for keeping the same, I can confirm you in a day as well. Keeping low pressure for N2 is because of the compressor capacity.

Now there are three options
1) Sending the melt from V12 directly to the pastillation unit.
2) Using higher pressure N2(need to check for the feasibility & cost impact)
3) Using a pump(then there would be added problems as I mentioned in the write-up)

Please provide you comments on this.

Have a nice day :)