In the past, process engineers had some things to consider when choosing vacuum sources for processes requiring less than the atmospheric pressure. Experience, reliability, cost, and vacuum level in similar methods were all that matters. These considerations haven’t disappeared, but like ever things in life, more complications have appeared. These concerns might include:
Sewage considerations like clean water and clean air act
Potential for recovery and recycling of materials and solvents removed with the use of vacuum streams
Methods of reduction and energy requirements
The flexibility and expandability of subtracting or adding capacity
Accuracy of the vacuum control
Engineers selecting vacuum sources to meet the needs mentioned above has a large variety of units to choose from:
Air or steam ejectors
Root-type rotary boosters
Rotary vane
Screw-type
Claw-type
Liquid-ring
Rotary piston
There are other types of vacuum pumps available in the market. Still, the remaining models like ion, turbo-molecular, cryogenic, and diffusion pumps are usually not considered economical or practical for rough uses like those found in pharmaceutical and chemical applications. These devices are typically applied in industries like manufacturing plants for semi-conductors.
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Selecting the perfect vacuum technology for pharmaceutical and chemical processing applications is usually not that simple. First, a system needs to deliver the right pumping speed at a certain pressure and make sure that the required downtime is met.
Second, it can’t be too sensitive to process the gas and needs to match every requirement when it comes to Clean-In-Place or CIP gas and cleaning recovery. Economic efficiency and reliability also play an important role when deciding which technology to use.
Dry Screw Vacuum Pumps
This technology is widely used in pharmaceutical and chemical industries. The first of its kind used in pharmaceutical and chemical markets was launched in the early 90s. These devices have an advantage since they don’t require fluids to compress the processed gas.
In this device, two screw-shaped rotary blades, rotate in different directions. The medium is trapped between the screw chambers and the cylinder, transported, and compressed to the gas outlet. During the process of compression, the rotors don’t contact the cylinder or each other.
Minimal clearance and precise manufacturing between the moving parts, make sure that this operating principle, as well as guarantees, have low ultimate pressures of less than 0.1 Torr. Modern versions of these pumps have variable pitch screws, which results in the compression of the processed gas across the screw’s length.
It has the advantage of making sure that it will have the same temp throughout the chamber, which can be controlled and monitored. This device uses cooling jackets, making sure that even temperature distribution, as well as higher thermal stability and efficiency, are all over its body.
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Generally speaking, it operates at temperatures enough to prevent unit condensation of process gases. It enables the gas to avoid contamination, or reacting with operating fluids, as well as preventing corrosions, because of process liquids attacking the parts of the unit.
The standard materials used for wet-processed parts that contact pumped mediums are ductile iron. This metal has a special coating that makes it almost entirely resistant to all known chemicals that can cause corrosion. In most applications, it is recommended that users warm the device before turning on and purge the pimp with an inert, non-condensable gas (usually Nitrogen) to help remove the vapor before the shutdown.
In some applications, experts recommend flushing the pump with suitable cleaning fluids to help remove the process material in the unit before the shutdown to avoid forming deposits as the unit cools down. Another characteristic of this type of pump is its flushing capability. It is valuable because this type of pump does not use operating fluids. With different systems and coatings, this kind of device can be set to be compatible with any available chemical.
Liquid Ring Vacuum Pumps
This type of vacuum pump is rolling a positive displacement pump with impellers that are eccentrically placed in cylindrical casings. Liquid sealant flows through vacuum pumps and its impeller rotation create liquid rings inside the housing that help seal the spaces between individual blades.
Gases are conveyed in spaces between shafts, the blades, and liquid rings. Because of the placement of the impeller, the number of these spaces usually increases, drawing more vapor in the device inlet. As the blades continue to rotate, the areas’ size is reduced, the fumes are compressed and discharged through the unit’s exhaust ports.
The pump can be operated as a continuous flow system or a total or partial recirculation sealant system. The unit has proven to be reliable and strong when it comes to chemical processes. The fluid in the chamber continuously dissipates the compressed heat, so that the pump operates isothermally.
It means that processed gas doesn’t heat up to a notable degree, and the device operates at low temperatures, dramatically reducing the risk of unnecessary and unwanted reactions. Low-operating temperatures also assist in the condensation of the vapor, which increases the pumping speed of the device, but adds processed liquid to seal fluids.
The condensed fluid can affect the vacuum capability, and the capacity of the device, as well as generate sealant that needs to be treated before disposal. The liquid is usually used to help create the ring. Organic solvents, mineral oils, or Ethylene Glycol is also used in practice.
The pressure of the device depends on the pressure of the vapor in the seal liquid, as well as the viscosity and density of the sealant used will affect its power consumption. Liquid ring vacuum pumps are readily available in different models, configurations, and seal arrangements, and in most materials of constructions, from exotic to a simpler one.
Conclusion
It is imperative to consult with experts in this line of business and consider the condition of the process, integration of process controls, and processed gases, as well as reliability, safety, and economic efficiency. Usually, these factors can lead to customized systems that are tailored to the right requirements.
