Pneumatic
Conveying

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Our specialty is undoubtedly the pneumatic handling of dry bulk products. Since 1990, CON-V-AIR has worked in a multitude of applications, the most common being the pneumatic handling of various chemicals and minerals. We also process the pneumatic transfer of almost all food products (sugar, milk powder, flour, sesame seeds, spices, etc.), many chemicals (silica, borax, calcium carbonate, urea, carbon black, zinc stearate, etc.), pharmaceuticals, and even explosive products. Our varied experience allows us to appreciate the different products used by our customers and adapt our systems to the specific needs coming from their respective areas of activity.

Our systems have all types of air moving equipment to minimize the costs associated with the purchase of blowers and reduce the energy needed to operate the pneumatic transfer system. Moreover, we favour large diameter pipes that allow systems to operate at a lower pressure and gives the capability to increase the capacity in the event that the requirements of the process should change. This gives our customers a heavy-duty system that will still perform when the plant condition changes. We are known for the manufacturing of heavy-duty systems.

TYPICAL DILUTE PHASE CONVEYING CAPCITY CHART

For an equivalent lenght of 200 feet (20 feet per elbow).

This table is for reference only.


PHASES AND TECHNOLOGIES

Dilute phase (pressure)Pneumatic conveying systems in dilute phase (pressure) consist of the following:
  1. Blower (which pushes the air in the piping)
  2. Pneumatic conveying pipe and elbows along with compression couplings
  3. Feed System into the pipe (typically an airlock, and eductor or a screw pump)
  4. The system of separation of the air powder (generally a reception filter)
  5. Destination hopper
  6. Devices for unloading the destination tank.
Diluted in stage systems are adapted to transfer less than 10 kilograms per kilogram of powder conveying air. Typically, our pneumatic conveying systems in dilute phases are designed to transfer approximately 6 kilograms of product per kilogram of dry bulk conveying air. The diameter of the pneumatic conveying line is adjusted to this concentration ratio of powder / air and the pressure drop that will be generated by the operation of the system. If the loss calculated load is too large, we increase the diameter of the transfer line. The typical pressure of a dilute phase conveying system fed by a rotary valve will be of the order of 6 to 10 psi. When feeding from an eductor, the typical pressure will be less than 5 psi. Consequently, pneumatic transfer systems in dilute phase (also known in English lean phase) are always designed to operate at operating pressures below 15 psi. This point is the limit beyond which the regulation applies with regards to pressure vessels. To make a pneumatic transfer beyond this pressure, additional measures are required (certified welders, complex engineering, manufacturing more expensive).In most applications of pneumatic handling in dilute phase, the product is fed continuously to the pipe. The most frequently used is the feeder rotary valve. Care must be taken for optimal operation of rotary valves. In particular,
  1. Airlock RPM. The higher the speed of rotation will be, the greater leakage through the rotary valve will be. For very fine products such as flours, the leak reduces the effective volume of the unit and sizing should be done accordingly. At 10 psi, an airlock of 14 inches turning at 14 RPM will leak about 30 cubic feet / minute.
  2. Abrasion. For abrasives, the ends and the body of the rotary valve must be hardened to increase its lifetime. Offset rotary valves are also used to avoid filling the alveoli and to better control the problems related to abrasion in the rotors and the bodies of rotary valves.
  3. The shear. The same technique is used to reduce breakage of larger particles in the rotary valves, i.e., avoid filling the pockets of the airlock. This reduces attrition and increases the life of the valve.

Eductor

Another device for supplying a pneumatic conveyor line by positive pressure in a dilute phase mode is the eductor. The eductor uses the venturi effect to feed the line. A high-speed air jet creates a vacuum that sucks the powder. Then, a venturi converts part of the static pressure to velocity pressure to push the material in the transfer line.  The most common application of eductors is the continuous chemical feed of sorbent in the gas treatment industry. Activated carbon, lime or sodium carbonate is drawn from the output of a volumetric feeder to the injection points in the gas pipes. By mixing these adsorbents with the gas to be treated before the baghouse, it is thus possible to remove the mercury, acidity and other products harmful to the environment.

Another advantage of eductors for pneumatic transfer lies in the fact that they have no moving parts. They are very popular for applications with abrasive products and food products because they are easy to clean. The possible maximum conveying rates are, however, lower than for other air-handling devices. They are recommended for small conveying rates.

Semi dense phase​

Pneumatic transfer with a semi-dense phase system is achieved at a concentration ratio of powder / air greater than 10. These systems carry the powders at a pressure less than 15 psi. However, as these are batch systems, we do not have to worry about leakage through rotary locks. Thus, by increasing the pressure, we do not increase the leakage and therefore, the systems are more efficient. The most common application of this type of system is the pressurized truck or railcar unloading into a silo. One can reach flow rates of the order of 20 to 30 tonnes / hour in a line of 4 “(100 mm). In the factory, a transportation tank is filled at atmospheric pressure and then emptied into the conveying pipe. As the pressure of operation is below 15 psi, it is not as regulate the pressure vessels.

Dense phase

The dense phase systems are very similar to the systems in semi dense stage except that they operate at pressures above 15 psi. Therefore, special attention should be given to the design and manufacture of tanks and transfer lines are governed by the regulations on pressure vessels. Typically, an operating pressure of 40-50 psi is normal. The concentration ratio of product / air is of the order of 40. The most common applications include manipulation of the cement, sand and other abrasive or brittle products (carbon black). By transferring the products at a higher pressure, we can reduce abrasion in transfer lines and elbows and reduce the breakage of the particles.

Suction (Vacuum)

The vacuum pneumatic conveying systems have many advantages. Using suction to enter the product in the line avoids back flow into the local atmosphere of fine powders. Also, there are no shears to enter the product in the line.

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