The attached file shows fewer details about the test rig. I think you may be planning following steps for the bio-oil extraction: 

1. Put mint leaves in water in a container and boil with immersion electric heater and keep on stirring continuously for more than 12 hours.

2. Direct the distilled oil vapour through aluminum coil immersed in cold water in another container to condense the extracted oil.

3. extract the oil and purify to remove water condensate.

For this, you have to design the rig carefully to consider following:

1. Mount the two containers at different elevations:

2. Both the containers should have pressure relief valves for safety.

3. The Aluminum coil should have non-return valve

4. The boiler (container) should be a pressure vessel having proper insulation and thermally strong.

5. Cable connected to the heater should be heat/fire resistant.

6. Stirrer must have speed control mechanism

7. Aluminum coil should have good support against vibration.

8. Terminal point of the aluminum coil carrying the hot oil should be properly connected to oil collecting pot with proper fire protection and away from the boiler/heater.

9. Aluminum coil should withstand highest internal positive pressure as well as maximum vacuum pressure.

10. There should be another mechanism to continuously feed mint leaf in the boiler and extract the residue after oil extraction.

11. Boiler level and pressure monitoring and control to be provided.

12. Keep away from the setup while operation.

13. oil leak detector to be provided.

14. Fire extinguisher and first-aid box nearby available

15. Electric circuit breaker to be nearby apart from fuse

16.Material selections of all the components to be done carefully to withstand the prevailing environment.

Regards,

-Sohail Ahmad Khan