Hydraulic compressor

Last updated December 23, 2024

A hydraulic compressor is a means of compressing air using hydraulic energy. There are two very different types of machines referred to as hydraulic compressors.

One type is a mechanical air compressor that is driven by a hydraulic motor. It is a method of converting hydraulic power to pneumatic power.^[1] This type of hydraulic compressor is used in various applications where hydraulic power is already available and a relatively small amount of compressed air is needed, as it is not very efficient compared to an electrically driven compressor.^[1]

The other type of hydraulic compressor uses the potential and kinetic energy of a stream of water to entrain air and carry it to a separating chamber at a higher pressure where the air accumulates above the water, and the water is allowed to drain. The system has few, if any, moving parts, and is also inefficient, so it is used where the kinetic or potential energy of water is cheaply available.

Design

The advantage of a hydraulic compressor of the second type is the ability to perform isothermal compression without any moving parts, making it relatively reliable and having low maintenance costs. A flow of water is used to entrain air and carry it downward through a pipe, called the downcomer pipe. Air is sucked into the water flow by the static pressure differential. As the mixture of air and water goes down the pipe, the pressure rises. The mixture enters the stilling chamber, which is designed to reduce flow velocity, allowing the air bubbles to separate from the water by buoyancy. The compressed air leaves the chamber through another vertical pipe, called the raiser pipe, and the water leaves through a submerged drain near the bottom of the stilling chamber.^[2]

The main issue with these compressors is the development of the scale and dimensions of the chamber (compressed air storage). The price of the chamber can be more costly than the installation itself, depending on the size.^{[ clarification needed ]} Despite the relatively high cost of energy, the hydraulic compressor uses significantly less electricity^{[ clarification needed ]} and increases the production of renewable energy resources.^[3]

Cost Breakdown

Fig 2: 0: Energy Cost, 1: Compressor Cost, 2: Maintenance Cost (Based on 24/7 operation, $0.08/kWh, full load operation).^[4]

Most of the expenses from integrating a compressor is the energy cost, as depicted in figure 2. The main factors are the type and size of the compressor. That is what determines the utility and power draw of the machine. To be most efficient, the air production capacity should match the air requirements to avoid bottlenecks and unnecessary energy being lost in the form of heat when the air is released.^[4] By optimizing utilization or preventing leakage, companies can increase their profit margins.

The design of the piping can also affect the cost of the system. A pipe structure without sharp corners or dead-heads can help maintain pressure and an efficient passage for compressed air. Designers have to think about the type of material that will be used in the hydraulic system. Aluminum, for example, has a lower weight and corrosion resistance than the more traditional material, steel.^[4] Because it is much lighter than steel, aluminum pipes allow welders and technicians to manufacture and install them easier. The diameter of the pipe is also crucial since smaller diameters tend to have more pressure differential. That would cause more pressure energy to be converted to heat or vibration, thereby decreasing the compressor's lifespan^[5]

Efficiency

To calculate the compressed airflow power, the equation $W=mRT*ln(\beta )$ can be used to measure the maximum efficiency of a hydraulic compressor. However, in a real-world scenario, airflow loss needs to be accounted for. This can be done by applying the energy conservation equation for an isothermal flow (assuming water and air have the same pressure and velocity): $loss=m[RT*ln(P0/P1)-V^{2}/2]$ . Many other factors can also cause the loss of air, such as collision against walls or the friction between water and air bubbles.^[6]

The flow of compressed air produced increases when the mass flow rate of liquid circulating the system also increases. This flow can be calculated only at specific parts of the hydraulic pump, as various configurations can be implemented. Examples of these configurations include a parallel or series pumping arrangement. The pump curve can be defined using a derivation of the quadratic equation: $Q=-b\pm *\surd (b^{2}-4a(c-H))/2a$ . The equation calculates the efficiency of the pump head or driver, which can be graphed with electrical power consumed to compare hydraulic systems.^[7]

Related Research Articles

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<span class="mw-page-title-main">Pneumatics</span> Use of pressurised gas in mechanical systems

Pneumatics is the use of gas or pressurized air in mechanical systems.

<span class="mw-page-title-main">Air compressor</span> Machine to pressurize air

An air compressor is a machine that takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a pneumatic device that converts mechanical power into potential energy stored in compressed air, which has many uses. A common application is to compress air into a storage tank, for immediate or later use. When the delivery pressure reaches its set upper limit, the compressor is shut off, or the excess air is released through an overpressure valve. The compressed air is stored in the tank until it is needed. The pressure energy provided by the compressed air can be used for a variety of applications such as pneumatic tools as it is released. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank. A compressor is different from a pump because it works on a gas, while pumps work on a liquid.

Centrifugal compressors, sometimes called impeller compressors or radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.

The Brayton cycle, also known as the Joule cycle, is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. It is characterized by isentropic compression and expansion, and isobaric heat addition and rejection, though practical engines have adiabatic rather than isentropic steps.

Compressed-air-energy storage (CAES) is a way to store energy for later use using compressed air. At a utility scale, energy generated during periods of low demand can be released during peak load periods.

Fluid power is the use of fluids under pressure to generate, control, and transmit power. Fluid power is conventionally subdivided into hydraulics and pneumatics. Although steam is also a fluid, steam power is usually classified separately from fluid power. Compressed-air and water-pressure systems were once used to transmit power from a central source to industrial users over extended geographic areas; fluid power systems today are usually within a single building or mobile machine.

A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.

A hydraulic accumulator is a pressure storage reservoir in which an incompressible hydraulic fluid is held under pressure that is applied by an external source of mechanical energy. The external source can be an engine, a spring, a raised weight, or a compressed gas. An accumulator enables a hydraulic system to cope with extremes of demand using a less powerful pump, to respond more quickly to a temporary demand, and to smooth out pulsations. It is a type of energy storage device.

For fluid power, a working fluid is a gas or liquid that primarily transfers force, motion, or mechanical energy. In hydraulics, water or hydraulic fluid transfers force between hydraulic components such as hydraulic pumps, hydraulic cylinders, and hydraulic motors that are assembled into hydraulic machinery, hydraulic drive systems, etc. In pneumatics, the working fluid is air or another gas which transfers force between pneumatic components such as compressors, vacuum pumps, pneumatic cylinders, and pneumatic motors. In pneumatic systems, the working gas also stores energy because it is compressible.

A compressed-air vehicle (CAV) is a transport mechanism fueled by tanks of pressurized atmospheric gas and propelled by the release and expansion of the gas within a pneumatic motor.

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Turbomachinery, in mechanical engineering, describes machines that transfer energy between a rotor and a fluid, including both turbines and compressors. While a turbine transfers energy from a fluid to a rotor, a compressor transfers energy from a rotor to a fluid. It is an important application of fluid mechanics.

An air pump is a pump for pushing air. Examples include a bicycle pump, pumps that are used to aerate an aquarium or a pond via an airstone; a gas compressor used to power a pneumatic tool, air horn or pipe organ; a bellows used to encourage a fire; a vacuum cleaner and a vacuum pump. All air pumps contain a part that moves which drives the flow of air. When the air gets moved, an area of low pressure gets created which fills up with more air.

<span class="mw-page-title-main">Rotary-screw compressor</span> Gas compressor using a rotary positive-displacement mechanism

A rotary-screw compressor is a type of gas compressor, such as an air compressor, that uses a rotary-type positive-displacement mechanism. These compressors are common in industrial applications and replace more traditional piston compressors where larger volumes of compressed gas are needed, e.g. for large refrigeration cycles such as chillers, or for compressed air systems to operate air-driven tools such as jackhammers and impact wrenches. For smaller rotor sizes the inherent leakage in the rotors becomes much more significant, leading to this type of mechanism being less suitable for smaller compressors than piston compressors.

A trompe is a water-powered air compressor, commonly used before the advent of the electric-powered compressor. A trompe is somewhat like an airlift pump working in reverse.

<span class="mw-page-title-main">Airlift pump</span> Pump using density difference due to injected air in the liquid

An airlift pump is a pump that has low suction and moderate discharge of liquid and entrained solids. The pump injects compressed air at the bottom of the discharge pipe which is immersed in the liquid. The compressed air mixes with the liquid causing the air-water mixture to be less dense than the rest of the liquid around it and therefore is displaced upwards through the discharge pipe by the surrounding liquid of higher density. Solids may be entrained in the flow and if small enough to fit through the pipe, will be discharged with the rest of the flow at a shallower depth or above the surface. Airlift pumps are widely used in aquaculture to pump, circulate and aerate water in closed, recirculating systems and ponds. Other applications include dredging, underwater archaeology, salvage operations and collection of scientific specimens.

References

1 2 "What Is A Hydraulic Air Compressor?". VMAC. 2021-01-21. Retrieved 2021-10-21.
↑ Bidini, G; Grimaldi, C N; Postrioti, L (1997-08-01). "Thermodynamic analysis of hydraulic air compressor-gas turbine power plants". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy. 211 (5): 429–437. Bibcode:1997PIMEA.211..429B. doi:10.1243/0957650971537321. ISSN 0957-6509. S2CID 110676872.
↑ Millar, Dean L. (2014-08-01). "A review of the case for modern-day adoption of hydraulic air compressors". Applied Thermal Engineering. 69 (1): 55–77. Bibcode:2014AppTE..69...55M. doi:10.1016/j.applthermaleng.2014.04.008. ISSN 1359-4311.
1 2 3 "Energy Efficiency in Air Compressors". Pumps and Systems Magazine. 2020-04-22. Retrieved 2021-10-21.
↑ "Piping System Tips for Energy Efficiency | Compressed Air Best Practices". www.airbestpractices.com. Retrieved 2021-10-29.
↑ Bidini, G; Grimaldi, C. N.; Postrioti, L (1999-05-01). "Performance analysis of a hydraulic air compressor". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy. 213 (3): 191–203. Bibcode:1999PIMEA.213..191B. doi:10.1243/0957650991537545. ISSN 0957-6509. S2CID 110551941.
↑ Millar, Dean; Pourmahdavi, Maryam (2021-02-04). "A Method for Pump Manifold Performance Calculations in Hydraulic Air Compressors". Journal of Fluids Engineering. 143 (4). doi:10.1115/1.4049672. ISSN 0098-2202. S2CID 233596169.

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[:0-1] 1 2 "What Is A Hydraulic Air Compressor?". VMAC. 2021-01-21. Retrieved 2021-10-21.

[:2-2] Bidini, G; Grimaldi, C N; Postrioti, L (1997-08-01). "Thermodynamic analysis of hydraulic air compressor-gas turbine power plants". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy. 211 (5): 429–437. Bibcode:1997PIMEA.211..429B. doi:10.1243/0957650971537321. ISSN 0957-6509. S2CID 110676872.

[3] Millar, Dean L. (2014-08-01). "A review of the case for modern-day adoption of hydraulic air compressors". Applied Thermal Engineering. 69 (1): 55–77. Bibcode:2014AppTE..69...55M. doi:10.1016/j.applthermaleng.2014.04.008. ISSN 1359-4311.

[:1-4] 1 2 3 "Energy Efficiency in Air Compressors". Pumps and Systems Magazine. 2020-04-22. Retrieved 2021-10-21.

[5] "Piping System Tips for Energy Efficiency | Compressed Air Best Practices". www.airbestpractices.com. Retrieved 2021-10-29.

[6] Bidini, G; Grimaldi, C. N.; Postrioti, L (1999-05-01). "Performance analysis of a hydraulic air compressor". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy. 213 (3): 191–203. Bibcode:1999PIMEA.213..191B. doi:10.1243/0957650991537545. ISSN 0957-6509. S2CID 110551941.

[7] Millar, Dean; Pourmahdavi, Maryam (2021-02-04). "A Method for Pump Manifold Performance Calculations in Hydraulic Air Compressors". Journal of Fluids Engineering. 143 (4). doi:10.1115/1.4049672. ISSN 0098-2202. S2CID 233596169.

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