PART - 1 of 2 ROTOCONE VACUUM DRYER/ ROTARY CONE VACUUM DRYER/ DOUBLE CONE VACUUM DRYER (RCVD/ RVD/ DVD)

WHAT IS MEANT BY RCVD/ RVD/ DVD OR WHAT DOES RCVD/ RVD/ DVD STAND FOR: 

Rotocone Vacuum Dryer Or Doublecone Vacuum Dryer is one of the most popular Vacuum Drying Equipment used in Pharma API (Active Pharma Ingredients) manufacturing primarily. The other usage of RCVD or RVD or DVD also include Drying Operations in Chemical or Food industry. It is so popular because it gently dries the wet material containing moisture Or solvent. Also, since its a vacuum dryer, it also allows you to recover the solvent (such as Methanol, IPA etc) which can be reused for some other purpose.

MATERIAL OF CONSTRUCTION:

In pharma API, all Contact Parts are usually SS316 Or Higher Grade, and Non Contact Parts are SS304 (Or Mild Steel in case of Non-GMP set up). Incase of Highly Corrosive chemicals, the Contact Parts are recommended to be Hastelloy (C22 Or C276), Or Halar Coated SS304 Or PU Coated SS304.

SURFACE FINISH: 

Usually in Pharma Industry, the product contact surface needs to be extremely smooth as per GMP (Good Manufacturing Practice) guidelines. This also helps in preventing the surface corrosion due to electrolytic cell formation. Hence the Product Contact surface is usually is minimum 240 grit Mirror Finish and Non Contact surface is 180 grit matt finish. Incase of a Non-GMP set up, if Mild Steel is used (for Product Non Contact in some cases), the surface is either epoxy painted Or coated with protective layer.

(Pic Ref:   www dot promasengineers dot com)

MAJOR COMPONENTS OF AN RCVD: 

The components can be listed as under:

1. RCVD Bowl: A central cylindrical shaped vessel with top and bottom cones usually angled at 45 degree.

2. RCVD Jacket: A metal jacket for Heating and Cooling the external surface of the bowl. Jacket includes central circular cylindrical portion, top and bottom cone.

3. Charging Hole Or Manhole with Openable or Hinged Door: A manhole and a closing lid is provided for both charging the wet material and maintenance purpose. Usually manhole is big enough for either accessing the interiors by hand Or for manual entry of a person inside the bowl.

4. Bottom Discharge Valve (usually butterfly valve): A suitable diameter of discharge valve is provided for unloading the dry mass at the end of the operations.

5. Vacuum Pipe with Vacuum Bulb: The horizontal hollow pipe (either of heavy schedule or bored out of a solid rod) is provided for extraction of vapors generated through the filter on the vacuum bulb (either a normal cloth filter Or sintered mesh filter).

6. Mechanical Seal between Vacuum Pipe and RCVD Bowl interface: Because the RCVD bowl rotates, while, the vacuum pipe is stationary, and, at the same time, vacuum pipe protrudes through the bowl horizontally, a mechanical seal is needed which allows smooth rotation of the bowl without vacuum or material leakage. In some arrangements, the seal sits exactly between the gap Or machined steps created between the vacuum pipe and the bowl. However, in some designs, before the mechanical seal, a PTFE (also known as Teflon) bush is fixed at the interface and further (after the PTFE bush) the mechanical seal is fixed.

7. Hot Fluid Or Steam Connection to RCVD Jacket: A horizontal pipe is provided (which is usually provided on the drive end) for supplying the hot fluid (usually Hot Water Or Steam Or extremely rarely  Other Hot Fluid). Usually the piping is done such that the hot fluid travels through the core pipe and gets distributed in the RCVD jacket through the channeling effect. The same fluid when exchanges heat with the surface looses its temperature and returns back to the same pipe, however, now through the annular space created by other bigger pipe that parallelly covers the core pipe. It means Pipe In Pipe arrangement, where, the inner pipe carries supply fluid and outer pipe carries the returning fluid going back to the heating source.

8. Support Structure with base frame Or base plate: A support structure of hollow metal shapes viz. SS304 Or Mild Steel RHS Or SHS (Rectangular Hollow Sections Or Square Hollow Sections) are used to support the RCVD from both the sides i.e. Drive Side, as well as, Vacuum Side. Either a base frame of structural steel is provided Or simply base plates are provided at the bottom of the legs to grout it on the floor Or anchor it on the pedestal.

9. AC Motor: AC motor of 415 Volts, 1440 rpm, 50 to 60 Hz and of adequate power (considering a suitable starting torque at full load condition) is chosen. Voltage and Frequency can vary depending on the country of usage. Some countries use either 110 Or 220 Volts only, whereas, other countries use Voltage ranging from 415 to 450 Volts. Frequency varies too from country to country.

10. Drive and/or Gearbox: A suitable drive is chosen that is suitable to the motor, as well as, keeping in mind the reduction ratio. In some case, the gearbox is provided with Spur Wheel and Pinion Wheel arrangement (usually for higher capacity RCVDs) for the limitations of the gearbox size and reduction ratios. Whereas, in some cases, directly the gearbox is provided with motor for directly reducing the RPM from 1440 to 10-12. The selection of gearbox depends on RPM (rotations per minute) and client's need. Both Helical Bevel, as well as, Worm Reduction gearboxes are popular.

11. Couplings, Bearings and Plummer blocks: Suitable couplings are used between drive and motor. In many of the designs, the drive end shaft enters into the hollow gearbox, which is directly coupled with a motor. Bearings and Plummer blocks are provided on both the sides (i.e. drive and non-drive) to support the RCVD bowl, as well as, to allow it to rotate freely. 

12. Electromechanical Brake Or Pneumatic Brake: It becomes essential to break the speed of the RCVD at times, hence, electromechanical brake (works on the principle of EMI) Or pneumatic brake is provided that ensures the RCVD rotational motion is broken and it comes to a halt immediately. These kinds of brakes are especially needed for a Helical Bevel Gearboxes, which does not lock the shaft from reverse rotation.

13. Variable Frequency Drive (VFD): AC Frequency Drive is provided to control Or vary the speed of rotation between 6 to 12 rpm usually.

14. Safety Railing: An openable safety railing is provided with a limits switch Or proxy sensor, which ensures that RCVD rotates only when the railing is closed. If someone accidently Or purposefully opens the railing to go near the RCVD, the motor stops immediately, hence, mitigates the possibility of any accident.

15. Instruments viz:

a. Product Temperature Sensor: A horizontal RTD sensor passing through central vacuum pipe, with probe open to the vapors and/or the powder mass inside the RCVD bowl.

b. Vacuum Guage Or Compound Guage on the RCVD Manhole: A dial type guage is provided to note the vacuum as well as pressure inside the RCVD bowl.

c. Pressure Guage on the RCVD jacket: Ideally the jacket pressure should not exceed 3bar (as a practice). More pressure may cause damage to the RCVD bowl surface.

d. Temperate Sensor on Condenser

e. Pressure and Vacuum Guage for Receiver and Its Jacket respectively.

OTHER PARTS OF THE RCVD SYSTEM:

1. Condenser: Usually a Shell and Tube Type Heat Exchanger is used to condense the vapors coming out of the RCVD. Usually the process side fluid (vapors) are passed through tubes, whereas, on the Shell side the utility fluid (mostly chilled water Or cooling water) is circulated. However, it can be the other way around too (depending on the heat load calculations). Condenser can be insulated and cladded for avoiding heat loss to the ambience.

2. Receiver: A solvent recovery receiver is provided at the bottom of the STHE condenser. Receiver can be a vertical cylindrical with legs support Or Horizontal cylindrical with saddle support. A vacuum breaking arrangement is provided with a control/ On-Off valve on the receiver.

3. Vacuum Pump: A suitable capacity Vacuum Pump is connected to the system (mostly to the receiver), which creates vacuum inside the RCVD bowl, and, also facilitates the extraction of the vapors hence complements the condensation process. 

4. Water Heating system Or Low Pressure Steam (for heating RCVD surface): Incase of a Hot Water System, a dedicated skid mounted vertical cylindrical vessel is provided with external heating i.e either with steam (LPS) Or with Electrical Heaters. A circulation pump pushes the hot water into RCVD jacket and the return water goes back into the Hot Water Generation tank. The level guage/switch on this tank ensure water doesn't spill over, and, make up water valves gets ON when level goes down. The Temperature sensor on the Hot Waters Tank, as well as, RCVD jacket inlet sensor together controls the flow of Steam (through PID control valve) Or the Electrical Heater, thus ensures the inlet water temperature stays in control. Incase of direct steam heating, the PID valve ensures steam is throttled and uniform temperature is maintained in the jacket.

5. Nitrogen Purging system: A very small nitrogen container can be provided with control valves, that can facilitate the intermediate and periodic gushing or N2 gas, which pushes the vapors out towards the condenser and also cleans the vacuum bulb filter. The N2 is purged through the same vacuum pipe, hence, vacuum needs to be stopped temporarily while purging.

Let us discuss the design and other need based considerations that goes into planning and designing an RCVD in PART -II of this post. Meanwhile, please feel free to contact incase of any queries, questions Or suggestions on this Or any other topic at shg.techo@gmail.com