CONICAL BLENDER - DRYER WITH DOUBLE HELICAL RIBBON:
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As the name suggests, this equipment consists of a vertical conical vessel with a top entry agitator, which has the conical shaped double helical ribbon welded to. The vessel, as well as, the ribbon is limpeted. With circulation of hot utility (viz. Hot Water Or Low Pressure Steam) through the limpet and the ribbon, the wet mass can be heated to evaporate the solvent Or moisture and with vacuum application, the vapors of solvent Or water can be recovered by condensation.
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| Drawing ref: RAHI ENGenius Solutions LLP, Ankleshwar |
WORKING PRINCIPLE:
Conical Dryer-Blender works on the principle of Vacuumized Drying. The water Or solvent in the wet mass evaporates due to the heated body, shaft and the limpet. The vapors generated are extracted and condensed by the external heat exchanger and vacuum application. Low rpm rotation of the helical ribbons (which is limpted too) continuously shuffle the mass from bottom to top. The overall efficiency is much higher than any static vacuumized dryer, as the rate of heat transfer is high. On the other hand, Conical Blender can be used merely for blending operations also.
ADVANTAGES:
- Multipurpose (i.e. Dryer cum Blender): The Helical Ribbons are designed in such a way that the wet powder mass travels to and fro between vertically i.e. between two ends of the shaft. Incase of Drying, this helps in excellent heat transfer. In case of only Blending, this helps in thorough mixing in minimum time.
- Gravity Advantage due to Vertical and Conical shape: Both charging and discharging of the powder mass is easy, as, material has to follow the gravitational flow. For bottom discharge, suitable control valve (either knife gate valve Or zero hold up ball valve) is provided.
- Recommended for Large Batches and Minimum Human Exposure: This equipment is more recommended for Chemical applications (i.e. Non Pharma applications), as, it can handle bigger production batches (say several tons). Material charging can done with the help of vacuum or pneumatic conveying too.
- Simplicity of Operation: Operating this equipment is no different than operating a reactor. Mostly this can be mounted on lug supports such that if top dish and distillation assembly is on one floor, the material discharge will be on the floor below.
- Provision of Solvent Recovery: Solvent recovery rate is very high, as compared with other Or traditional vacuum dryers.
- Easy to Automate: Level of automation is mostly Non-Complex Or Straightforward
- Choice of MOC (Material of Construction): This equipment is generally not used in Pharmaceutical preparations. However, if required, the material of construction can be SS316 Or Hastelloy Or Halar/ PU/ PFA coated SS304. This can take care of the corrosive material and its vapors.
- Cleaning and Maintenance: The inside body is occupied with the limpted double helical ribbon set. That makes it difficult in washing, cleaning and doing mechanical maintenance (if any).
- Bottom Holdup i.e. some quantity of mass may remain unstirred Or undried: The bottom most part of the ribbons is designed to lift the material upwards during operation. However, due to the conical shape of the vessel, as well as, nature of the bottom valve used, there may be chances of material hold-up Or material accumulation at the bottom, which can lead to non-uniform mixing and drying in that particular area only.
- Design related challenges: Circulation of the Hot Utilities such as Hot Water Or LPS (low pressure steam) through the ribbons, shaft and the vessel limpet can be challenging.
- Not Recommended for Pharma Applications: The QC guidelines used in Pharma industries doesn't permit inaccessibility of the contact parts, as cleaning and sterilization (if any) can be a big concern. Also, the batches in Pharma -API are not very big usually. Therefore, this kind of an equipment is not used in pharmaceutical drying.
MAJOR COMPONENTS OF THE CONICAL DRYER-BLENDER:
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1. Vertical Conical Shell with Limpet and Insulation and Top dish: This vertical conical limpeted vessel is designed to handle both large quantity of mass under high temperature and vacuum. The limpet usually covers almost 80% of the height of the vessel. It is further insulated with hot insulation material such as Mineral Wool Or Rock Wool and further cladded. The top dish is designed to take weight of the drive assembly, as well as, has a number of nozzles including the manhole.
2. Vertical Stirrer: A specially designed vertical pipe (either of heavy schedule Or bored out of a solid rod) has double helical ribbon welded to it such that hot utility (both incoming and outgoing) is properly paved Or channeled through it. It is well balanced dynamically, as well as, passes through a suitable Mechanical Seal (fulfilling the vacuum and temperature requirements). As per the required torque calculations, the AC frequency Motor and Gearbox is designed. Usually the final RPM is not more than 8 to 10 rpm. Suitable couplings may be provided inside the vessel, as well as, outside before gearbox in order to protect the drive assembly from damage due to rare case of jamming of ribbons. A soft starter along with VFD (variable frequency drive) is recommended to manage the torque.
3. Double Helical Ribbon Blades: Conically shaped double helical ribbon is manufactured out of stainless steel flats with limpet welded at the bottom with smooth finishing (so that no material deposition should take place). Angle of the helix should be such that bottom to top movement of material should be facilitated.
4. Vacuum Filter Assembly: A vertical cylindrical filter housing mounted on the vacuum nozzle located on the top dish. The filtration assembly includes a course PP filter (say 10 micron) whose objective is to arrest the dried powder particles from going into the condenser Or vacuum pump along with the vapors.
5. Chopper assembly Or Lump Breaker Assembly: A high speed chopping set of blades (rotating at around 200 to 300 rpm) mounted inside of the conical vessel (on the lateral surface) can be optionally provided with a gearbox and an AC frequency motor.
6. Condenser: Typically a Shell and Tube Type Heat Exchanger is used to condense the vapors coming out of the Conical Dryer. 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.
7. Receiver: A solvent recovery receiver is provided at the bottom of the STHE condenser. Receiver can be either Vertical Cylindrical with legs supports Or Horizontal Cylindrical with saddle supports. A vacuum breaking arrangement is provided with a Control/ On-Off valve on the receiver.
8. Vacuum Pump: A suitable capacity Vacuum Pump is connected to the system (mostly to the receiver), which creates vacuum inside the Conical Dryer, and, also facilitates the extraction of the vapors, hence complements the condensation process.
9. Water Heating system Or Low Pressure Steam (for heating the Dryer, Shaft, Ribbon): 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 the Limpet, 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, sensor on the Inlet of the Limpet coil 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 limpet.
10. Nitrogen Purging system/ Air Pressure system: A nozzle can be provided with control valve, that can facilitate the intermediate and periodic gushing or N2 gas, which pushes the vapors out towards the condenser. Same nozzle can be used for providing the Air Pressure to facilitate the filtration operation. Vacuum needs to be stopped temporarily while purging.
11. CIP Or Spray Ball arrangement: Optionally, spray balls can be provided on the top dish of the conical shell, which can facilitate cleaning and washing of the main vessel post the batch operation is over.
FACTORS TO BE TAKEN INTO CONSIDERATION WHILE DESIGNING A CONICAL DRYER- BLENDER:
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1. Available Floor Space, Availability of the Utilities and Floor Layout/ Elevation:
Conical Dryer can be either mounted with Legs Or on Lugs supports. In case of a bigger capacity Dryer, the lugs mounting arrangement is recommended, such that, it hangs from a floor with lugs supports. The utility equipments such as Hot Water Tank, Vacuum Pump, Chilled Or Cooling Water, Steam, Nitrogen and Electrical Panel etc must be planned properly for the ease of the operations. As a usual practice all these things are planned simultaneously and in sync with each other. Also, a GAD (General Arrangement Drawing) is superimposed on Autocad Layout Drawing to see the feasibility of installation during the design stage.
2. Material of Construction: MOC selection must be made in accordance with the process parameters.
3. Level of Automation: Depending on the needs of the Production Department and the budget allocation, the level of automation can be decided.
4. Statutory and Safety compliance: Sometimes, due to company policy and FDA mandate, special features are incorporated such as Touch Screen HMI (Human Machine Interface) with PLC (Programmable Logic Control). In some cases, there can be further sophistication by adopting special Data Security measures such as 21 CFR Chapter 11 compliance, which allows password protected individualistic logins and maintains record of each activity by each user. Overall, Safety, GMP guidelines along with respective FDA mandates has to be followed while designing a Dryer.
5. Batch Size Calculations: A basic Process Calculations must be done including Heat Load Calculations. This helps in deciding the optimum batch size, as well as, the time cycle, hence monthly Or timely production throughput.
6. Product Specific Operational Challenges (based on the previous experience Or Studies): Since it is a capital purchase, the careful attention must be given to the specific needs of the Production Team, concerns and apprehensions of the Engineering and Maintenance, as well as, the Safety and Statutory department, which helps ensure the production goes smooth.
7. Mechanical and Process Design, as well as, Sizing of the Equipments: Stress analysis/ calculations must be done under varying parameters such as temperature, vacuum and pressure. Similarly, the thickness calculations must be done keeping in mind the static and dynamic loads.
Please feel free to contact me regarding any questions, queries Or additional assistance needed on Design, Sales, Qualification or other aspects at shg.techo@gmail.com
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