Article: Fans, blowers, compressors and vacuum pumps
This article discusses:
- The main parameters when choosing the type of air displacement
- How fans move air
- How do blowers move air
- How compressors move air
- How vacuum pumps move air
The experts at Dinnissen Process Technology are available to answer all your questions:
Get in touch with Juul Jenneskens 077 467 3555
The most important parameters when choosing the type of air displacement
The way the air displaces the product is generated is the core of the pneumatic conveying system and is seen as the heart of the system. The two most important parameters when choosing the way the air is moved are the required volume flow rate and the pressure to be delivered. To calculate the volume flow, the flow is recalculated to the flow at atmospheric pressure (101.3 KPa) at a standard temperature of 200 C. The required values of these parameters depend on several factors. Is Air Transport or Dense Phase Transport being used? What kind of product must be transported? What properties do the transported products have? What is the transport distance? What is the pipe diameter? At what speed should the product be transported? These are all questions that need to be answered.
There may be air available within the facility but it is energetically unwise to apply it. Each choice will have its own pros and cons. Some ways of generating air have limitations. Some are more suitable for blow transport than for suction transport. The power requirements for the supply of air can be high. Especially if the product has to be moved over a long distance at a high flow rate. When compressing air, it is heated, the term for this is Boyle Gay-Lussac. Due to their properties, some products require that the air be cooled back before it is used. When the air is cooled, there is a possibility that condensation will form. As a result, in a number of cases the air must also be dried.
These are the different ways to move air are for pneumatic conveying applications:
- Fans
- Blowers
- Compressors
- Vacuum pumps
Pet food installation with vacuum pumps
How fans move air
In pneumatic conveying applications where fans are used, these often have a flat blade type. They are mainly used for short-distance air transport. Where the chance of blocking of the line is small and the supply of product does not vary much. Fans are used for both blowing and suction conveyors. In addition, they are used in combined suction-blowing systems; also called closed loop systems. It is even possible to transport light non-abrasive materials through the fan. With this method of pneumatic transport, it must be thoroughly investigated whether the product does not grow on the fan blades. This has a negative impact on the capacity of the system, the lifespan of the fan and the energy consumption of the system. Fans are not suitable for use under higher pressure and for heavy duty applications. This is because their business characteristics are generally not satisfactory for this task or application. The rotation speed of the fan should be as low as possible. A higher speed will affect the wear of the system. It is best to choose a fan with a critical speed that is at least 1.5 times the speed at which the pneumatic conveyor system is running.
The biggest problem with fans is that the air flow is very dependent on the pressure loss in the transport pipe. The constant speed characteristic tends to level out at high operating pressures. Suppose the air speed in an Air transport is 20 m / s, then it only takes 2.5 seconds for the air to pass through the full length of the pipeline in a 50 meter long pipeline. A short increase in the supply of product can therefore very quickly affect the required pressure. If this causes the transport air speed to fall below the minimum value, the product will precipitate in the pipe, causing it to become blocked in a very short time.
Closed-loop system
Some ways of generating air have limitations
How do blowers move air?
Just like fans, blowers are used for short-distance air transport. Blowers are used for both blowing and suction transports. Unlike fans, they are not used in closed loop systems. Blowers are not suitable for feeding the material through. This is because they consist of 2 rotors that rotate and mesh with each other with little play. In practice, blowers have a range of -500 mBar in a suction transport and up to 1.1 bar pressure in a blow transport. This pressure range makes them less suitable for a Dense Phase Transport. The increase in pressure leads to an increase in the temperature of the air. The rule of thumb is that every 100mBar pressure increase leads to a 100C temperature increase in the air. As with fans, an increase in pressure will lead to a reduction in the air flow. This must be taken into account in the design of the blow conveyor system because it can cause blockages. Blowers are better suited to deal with this than fans.
How compressors move air
A compressor is a device that compresses a gas, often air, and makes it available at higher pressure. With this gas, the density and temperature will strongly increase due to pressure increase. Fans and blowers mainly let air flow. In contrast to a compressor, only a very small increase in pressure occurs here.
A compressor sucks in air and will then compress it. A complete system often consists, in addition to a compressor, of a buffer vessel in order to be able to absorb large consumption in a short time at a relatively constant pressure. In addition, if necessary, the quality of the gas can be improved with air dryers, air coolers and compressed air filters.
The constant pressure supplied with a compressor in combination with a buffer vessel makes it suitable for use in a Dense Phase Transport.
How vacuum pumps move air
A vacuum is generated with a vacuum pump. The vacuum pump creates the vacuum by drawing the gas from the pneumatic pipework. Its operation is based on the rotary vane principle. This includes partitions on an eccentric shaft. These vanes move from the outside to the inside through the rotating shaft and thus create an underpressure in the system. Vacuum pumps have a range of up to - 950 mBar. In practice, pneumatic transport does not go deeper than -800 mBar. A point of attention in a vacuum transport is the receiving hopper. If not properly constructed, it can implode.
An overview of the four ways of moving air for pneumatic transport is given in the table below:
| Air generated by: | Type of pneumatic conveying | Application | Pressure | Pros | Cons |
| Fan |
|
| 100 mBar |
|
|
| (vacuum) Blower |
|
| -450 mBar - 1,1 Bar |
|
|
| Compressor |
|
| 1 - 5 Bar |
|
|
| Vacuum pump |
|
| -700 mBar |
|
|
Name: Han Joosten
Expert in the field of hygienic process lines
Feel free to contact us if you have any questions about this topic. My colleagues and I are ready to assist you!
Get in touch with Han Joosten 077 467 3555 [email protected]
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