Analysis of the different types of compressors and explanation of their general operation, to facilitate knowledge of their characteristics and applications.
The technology of compressed air and gases, however static enough, is constantly evolving. Manufacturers have spent many years researching new designs that adapt to different market demands.
The compressorsor Vacuams pumps have applications in hundreds of industries and processes, so alternatives and adaptability of manufacturers' designs are manifold.
What is commonly known as a gas compressor, comprises a series of machines with different structures and designs.
By their main application, they could be divided into five groups:
Compressors:
Machines designed to compress gases at any pressure, above atmospheric pressure. In general, we speak of a compressor when working with pressures above 3 bar.
Fans:
Machines designed to compress gases at very low pressures, close to atmospheric pressure. In fact, the fans barely increase the pressure a few grams above atmospheric.
Blowers:
Compressors that work at low pressure. They should be included in the same group as the compressors, but they are differentiated to avoid confusion. The pressures of this equipment are higher than those of the fans, but they are considered to be below 3 bar.
Bomb of void:
They are also compressors, but their work is not intended to compress air, but to draw it from a container or system, lowering the pressure to values below 1 atmosphere. Vacuum pumps can also be used as a compressor, but in very specific applications and with very low-pressure values.
Booster compressors:
They are a type of compressors that work with a pressure in the suction, higher than atmospheric. They are usually installed in combination with a traditional compressor, to raise its final pressure.
However, the main classification of the different types of compressors is made by their basic operating principle. In this case, the compressors are divided into two large groups:
Positive displacement compressors:
The operating principle of these compressors is based on the decrease in the volume of air in the compression chamber where it is confined, producing an increase in internal pressure until reaching the expected design value, at which time the air is released to the system.
Dynamic compressors:
The operating principle of these compressors is based on molecular acceleration. The air is drawn into the impeller through its inlet hood and accelerated at high speed. It is then discharged directly to diffusers located next to the impeller, where all the kinetic energy of the air is transformed into static pressure. From this point, it is released into the system.
Both systems can work with one or more stages, depending on the final pressure required for the compressed air. In the case of multi-stage compressors, the air, when released from the first stage, passes directly to the second, where the process described above is repeated. Between each stage, an intercooler is installed that reduces the compression temperature to the value required by the next stage.
Each group of compressors uses different designs for the compression process. Next, we will explain the main ones of each of them.
POSITIVE DISPLACEMENT COMPRESSOR
PISTON COMPRESSOR
SCREW COMPRESSOR
PADDLE COMPRESSOR
ROTARY LOBE OR PLUNGER COMPRESSOR
SCROLL COMPRESSORS
BOMB OF VOID
DYNAMICS COMPRESSOR
RADIAL CENTRIFUGAL COMPRESSORS
CENTRIFUGAL AXIAL COMPRESSORS
POSITIVE DISPLACEMENT COMPRESSORS
ESSORPISTON COMPRESSOR
In this type of compressor, the air is sucked into a cylinder, by the action of a piston driven by a connecting photo on the right, we see the diagram of an ATLAS COPCO piston compressor on and a crankshaft. That same piston, when performing the opposite movement, compresses the air inside the mentioned cylinder, releasing it to the network or to the next stage, once the required pressure is reached.
In the photo on the right, we see the diagram of an ATLAS COPCO piston compressor with two cylinders, where you can see how the cylinder on the right, in a downward movement, is sucking in the air from outside, while the cylinder from the left, with an upward movement, is compressing it.
Screw custom compressors can be lubricated or oil-free. In the case of exempt compressors, the suction and compression chamber is isolated from any contact with the compressor Lubricant, working dry and preventing the compressed air from being contaminated with the equipment lubricants.
SCREW COMPRESSOR
pressor technology is based on the movement of air, through the chambers that are created with simultaneous rotation and in the opposite direction, of two screws, one male and the other female. As can be seen in the diagram, the air fills the spaces created between both screws, increasing the pressure as the volume in the aforementioned chambers decreases.
The direction of air movement is linear, from the suction side to the pressure side, where the outlet nozzle is located.
In the diagram below, you can see the section of a rotor assembly, where you can see the screws inside the casing.
This type of technology is manufactured in two different executions, lubricated screw compressors, and free screw compressors. The difference between the two lies in the lubrication system.
In the lubricated screw compressor, oil is injected into the rotors to lubricate, seal and cool the rotor assembly. This type of compressor is the most common in the industry, because, in most applications, the residual oil that remains in the compressed airline is not an obstacle to the process. In the photo below you can see a lubricated screw compressor from KAESER.
The execution of oil-free compressors requires a more complex design than in the previous case, due to the fact that oil cannot be injected inside the rotors. In this type of compressor, the aim is to supply air that is not contaminated by lubrication oil.
This does not mean that they do not require lubrication, but that no lubricant is injected between the rotors, making these elements work dry.
For the compression process at pressures higher than 3 bar, it is required to install two compressor units that work in series, driven by a common gearbox. As can be seen in the photo below, corresponding to a BOGE-free screw compressor, both rotary assemblies are connected to a single motor by a said gearbox.
In the photo you can see the different components; the "compressor block" comprises the gearbox and the two compressor units.
PADDLE COMPRESSOR
Another design within positive displacement compressors is that of equipment that uses a vane rotor. The system consists of the installation of a floating vane rotor inside a casing, placing it eccentrically to it.
As can be seen in this MATTEI diagram, during the rotation of the rotor, the floating blades leave and enter from the inside, forming chambers between the rotor and the casing, which are filled with air.
As the rotor is located in an eccentric position to the central axis of the casing, the chambers grow in the suction zone, producing a depression that causes the entry of air. As they move with the rotation of the rotor, the chambers are reduced towards the impulsion zone, compressing the air inside.
In the photo on the right, you can see a rotor with its vanes on an HYDROVANE compressor.
ROTARY LOBE OR PLUNGER COMPRESSOR
Another positive displacement compressor is one that uses lobe rotors or rotating pistons. To more accurately illustrate its operation, we will use a schematic of the MPR equipment.
The operating principle is based on the rotation of two-lobe rotors inside the casing. As can be seen in the illustration above, the rotors rotate synchronously and in the opposite direction, forming chambers between them in which air enters. In this case, the lobes are limited to displacing the air, managing to increase the pressure as a function of the backpressure with which they are at the outlet of the equipment. This backpressure is given by friction losses and the pressure needs of the system with which it works. These compressors are widely used as blowers, that is, low-pressure compressors.
In this type of compressor, the rotors can be bilobar or centrilobular. There is also a similar execution that uses claw rotors, as can be seen in the image below, belonging to an ATLAS COPCO compressor.
The operation is the same as that explained above, but in this case, due to the special shape of the rotors, the impulsion chamber reduces its space to increase the air pressure. These compressors manage to raise the pressure to values higher than 7 barg.
SCROLL COMPRESSORS
Another technology within the positive displacement group is that of scroll-type compressors. They are not well-known equipment, but they have a typical application in oil-free applications.
These compressors have a displacement that is called orbital. Compression is done by volume reduction. The compressor set is made up of two spiral-shaped rotors. One of them is fixed in the housing and the other is mobile, driven by the motor. They are mounted with an offset of 180º, which allows smaller and smaller air chambers to be created in their movement. In the photo below we see a section of an ATLAS COPCO scroll compressor.
BOMB OF VOID
Vacuum pumps are also positive displacement equipment. Many of its designs are used interchangeably as compressors or as vacuum pumps. There are piston, screw, vane, or lobe vacuum pumps.
The operation of all of them is similar to that of their counterpart compressor, but with the characteristic that they are designed to suck from the inside of a container or network and not to compress the air or gas they suck in.
As a more exceptional case, we highlight the design of liquid ring vacuum pumps. As can be seen in the lower-left diagram, corresponding to a NASH pump, in this equipment, there is a fixed vane rotor, eccentrically installed in the pump casing. Inside the casing, there is a fluid which is generally water. When the rotor rotates at its nominal speed, the centrifugal force it exerts on the fluid makes it stick to the internal walls of the casing, forming suction and compression chambers with the rotor blades, whose operation is similar to that of the vane compressor. Shown in the lower right photo is a FLOWSERVE SIHI liquid ring vacuum pump.
DYNAMIC COMPRESSORS
RADIAL CENTRIFUGAL COMPRESSORS
Traditional centrifugal compressors belong to this group. In this equipment, the air enters directly into the central area of the rotor, guided by the suction hood. The rotor, turning at high speed, blows the air over a diffuser located behind it and is guided to the impulsion body.
In the photo below, you can see a section of a BOGE pneumatic levitation centrifugal compressor. In this section, the two compression stages where the rotors are housed can be clearly seen.
In these compressors, the air enters directly through the suction hood (1) towards the rotor (2) and diffuser (3), exiting to the next stage or to the network through the volute (4).
Another example can be seen in the section of a SULZER centrifugal blower, where the centrifugal rotor installed at the end of the shaft can be seen in detail.
A traditional turbocharger can be a team with two or more compression stages. Between each stage, coolers are designed to lower the compression temperature before the air reaches the next rotor is installed. In the photo below, we can see an INGERSOLL RAND turbocharger, mounted on a bench common to the engine, coolers, and control panel.
Turbochargers are usually equipment designed for large flows, although in recent years, manufacturers have made an effort to design equipment of reduced sizes and smaller flows. With these premises, a new generation of magnetic levitation or pneumatic levitation centrifugal compressors has appeared.
CENTRIFUGAL AXIAL COMPRESSORS
These teams are less common in the industry. They differ from the previous ones in that the air circulates parallel to the axis. Axial compressors are made up of several discs called rotors. Between each rotor, another disk called a stator is installed, where the air accelerated by the rotor increases its pressure before entering the next disk. In the suction of some compressors, guide vanes are installed, which allow orienting the air stream so that it enters at the appropriate angle.
In the photo below, you can see an axial compressor from MAN, which works in combination with a radial stage, where the pressure is increased to higher values.
In general, all the compressors described in the different groups can be adapted to multiple applications or regulations, such as API or ATEX. Manufacturers add additional elements so that each team can work in different applications or be equipped with the accessories that the end-user may require.
The use of one technology or another depends on each application, service, or pressure required. We are also Provide that type of machine-like High pressure compressor in Pakistan