Pump as turbine

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Pump as turbine installed to recover energy within the premises of an Irish rural water network in 2019 Pump as Turbine (PAT).jpg
Pump as turbine installed to recover energy within the premises of an Irish rural water network in 2019

A pump as turbine (PAT), also known as a pump in reverse, is an unconventional type of reaction water turbine, which behaves in a similar manner to that of a Francis turbine. The function of a PAT is comparable to that of any turbine, to convert kinetic and pressure energy of the fluid into mechanical energy of the runner. They are commonly commercialized as composite pump and motor/generator units, coupled by a fixed shaft to an asynchronous induction type motor unit. [1] [2]

Contents

Unlike other conventional machines which require being manufactured according to the client’s specifications, pumps are a very common piece of equipment widely available in different sizes and functionality anywhere around the globe. When used as a turbine, the rotor moves in the opposite direction, or in reverse, as to when it is operating as a pump. In this manner, it allows the motor to generate electrical power.

History

First mentions of the possibility of using pumps as turbines (PAT) dates back to the early 1930s and are associated to lab experiments performed by Thoma and Kittredge, [3] who first identified the potential for a common pump to function quite efficiently as a turbine by reversing the flow.

Subsequently, in the second half of the 20th century, a new impulse for research on this topic came from the pump manufacturing industry. During this time, established collaborations with several research institutes helped develop an in-depth understanding of the phenomena associated with PAT utilization. Efforts were made to develop methods to predict characteristic and efficiency curves. [4] This helped determine the Best Efficiency Point (BEP) of these machines, in turbine mode, and related it to its specifications when used as a pump. [5]

The adoption of PATs has the potential to turn economically feasible even hydropower potentials in the "pico" scale (i.e. less than 5 kW of installed capacity), since they only cost a fraction of a conventional hydro turbine. [6] Recent examples of such schemes are two pilot plants built in 2019 in Ireland and Wales. [7]

Pumped-storage hydroelectricity

In micro Pumped-storage hydroelectricity (PSH), the same pump/PAT could be used for pumping and generating phases [8] by changing rotational direction and speed. The best efficiency point in pumping usually differs from its reverse mode: [3] a variable-frequency drive coupled to the motor/generator would be needed in order to change from pumping to generating mode and to react efficiently to the PSH load fluctuation. [8]

Types

Among the existing designs of hydraulic pumps/PATs, "centrifugal" or "radial" units are the most used worldwide in a wide variety of application fields. [9] The name is derived from the radial path followed by the fluid in the rotor: from the centre to the periphery when running as a pump and in the opposite direction when flow is reversed. [10] To achieve a higher head drop across the machine, more impellers can be assembled in series to create a multistage unit. Conversely, a double flow radially split pump/PAT design involves a single radial open rotor fed by two symmetric inlets and enable processing a higher flow rate with respect to a standard radial unit. [9] A second type of pump/PAT design is the axial one, in which the fluid interacts with a propeller following a trajectory parallel to the pump axis. Such units are particularly suitable to processing high flow rates with low head difference. Finally, mixed flow pumps/PATs stand in between the applicability range of radial and axial units and have an impeller shaped in a similar way as a Francis turbine. [10] Another special pump/PAT design is that of submersible units, which can possibly be fitted inside a pipe connected to draft tube exploiting small head differences in flowing rivers.

Related Research Articles

<span class="mw-page-title-main">Pump</span> Device that imparts energy to the fluids by mechanical action

A pump is a device that moves fluids, or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy.

<span class="mw-page-title-main">Turbine</span> Rotary mechanical device that extracts energy from a fluid flow

A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical power when combined with a generator. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels.

<span class="mw-page-title-main">Tesla turbine</span> Bladeless centripetal flow turbine

The Tesla turbine is a bladeless centripetal flow turbine invented by Nikola Tesla in 1913. It functions as nozzles apply a moving fluid to the edges of a set of discs. The engine uses smooth discs rotating in a chamber to generate rotational movement due to the momentum exchange between the fluid and the discs. The discs are arranged in an orientation similar to a stack of CDs on a pole.

<span class="mw-page-title-main">Turbopump</span> Pump driven by a gas turbine

A turbopump is a propellant pump with two main components: a rotodynamic pump and a driving gas turbine, usually both mounted on the same shaft, or sometimes geared together. They were initially developed in Germany in the early 1940s. The purpose of a turbopump is to produce a high-pressure fluid for feeding a combustion chamber or other use. While other use cases exist, they are most commonly found in liquid rocket engines.

<span class="mw-page-title-main">Submersible pump</span> Pump designed to work submerged in fluid

A submersible pump (or electric submersible pump is a device which has a hermetically sealed motor close-coupled to the pump body. The whole assembly is submerged in the fluid to be pumped. The main advantage of this type of pump is that it prevents pump cavitation, a problem associated with a high elevation difference between the pump and the fluid surface. Submersible pumps push fluid to the surface, rather than jet pumps, which create a vacuum and rely upon atmospheric pressure. Submersibles use pressurized fluid from the surface to drive a hydraulic motor downhole, rather than an electric motor, and are used in heavy oil applications with heated water as the motive fluid.

<span class="mw-page-title-main">Centrifugal compressor</span> Sub-class of dynamic axisymmetric work-absorbing turbomachinery

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

<span class="mw-page-title-main">Compressor</span> Machine to increase pressure of gas by reducing its volume

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.

<span class="mw-page-title-main">Torque converter</span> Fluid coupling that transfers rotating power from a prime mover to a rotating driven load

A torque converter is a device, usually implemented as a type of fluid coupling, that transfers rotating power from a prime mover, like an internal combustion engine, to a rotating driven load. In a vehicle with an automatic transmission, the torque converter connects the prime mover to the automatic gear train, which then drives the load. It is thus usually located between the engine's flexplate and the transmission. The equivalent device in a manual transmission is the mechanical clutch.

<span class="mw-page-title-main">Francis turbine</span> Type of water turbine

The Francis turbine is a type of water turbine. It is an inward-flow reaction turbine that combines radial and axial flow concepts. Francis turbines are the most common water turbine in use today, and can achieve over 95% efficiency.

<span class="mw-page-title-main">Impeller</span> Rotor used to increase (or decrease in case of turbines) the pressure and flow of a fluid or gas

An impeller, or impellor, is a driven rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid.

<span class="mw-page-title-main">Axial compressor</span> Machine for continuous flow gas compression

An axial compressor is a gas compressor that can continuously pressurize gases. It is a rotating, airfoil-based compressor in which the gas or working fluid principally flows parallel to the axis of rotation, or axially. This differs from other rotating compressors such as centrifugal compressor, axi-centrifugal compressors and mixed-flow compressors where the fluid flow will include a "radial component" through the compressor.

<span class="mw-page-title-main">Turbomachinery</span> Machine for exchanging energy with a fluid

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.

<span class="mw-page-title-main">Centrifugal pump</span> Pump used to transport fluids by conversion of rotational kinetic energy

Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from which it exits.

<span class="mw-page-title-main">Axial-flow pump</span> Type of pump consisting of a propeller in a pipe

An axial-flow pump, or AFP, is a common type of pump that essentially consists of a propeller in a pipe. The propeller can be driven directly by a sealed motor in the pipe or by electric motor or petrol/diesel engines mounted to the pipe from the outside or by a right-angle drive shaft that pierces the pipe.

<span class="mw-page-title-main">Gas turbine engine compressors</span> Engine component

As the name suggests, gas turbine engine compressors provide the compression part of the gas turbine engine thermodynamic cycle. There are three basic categories of gas turbine engine compressor: axial compressor, centrifugal compressor and mixed flow compressor. A fourth, unusual, type is the free-piston gas generator, which combines the functions of compressor and combustion chamber in one unit.

<span class="mw-page-title-main">Centrifugal fan</span> Mechanical fan that forces fluid to move radially outward

A centrifugal fan is a mechanical device for moving air or other gases in a direction at an angle to the incoming fluid. Centrifugal fans often contain a ducted housing to direct outgoing air in a specific direction or across a heat sink; such a fan is also called a blower, blower fan, or squirrel-cage fan. Tiny ones used in computers are sometimes called biscuit blowers. These fans move air from the rotating inlet of the fan to an outlet. They are typically used in ducted applications to either draw air through ductwork/heat exchanger, or push air through similar impellers. Compared to standard axial fans, they can provide similar air movement from a smaller fan package, and overcome higher resistance in air streams.

<span class="mw-page-title-main">Radial turbine</span> Type of turbine

A radial turbine is a turbine in which the flow of the working fluid is radial to the shaft. The difference between axial and radial turbines consists in the way the fluid flows through the components. Whereas for an axial turbine the rotor is 'impacted' by the fluid flow, for a radial turbine, the flow is smoothly orientated perpendicular to the rotation axis, and it drives the turbine in the same way water drives a watermill. The result is less mechanical stress which enables a radial turbine to be simpler, more robust, and more efficient when compared to axial turbines. When it comes to high power ranges the radial turbine is no longer competitive and the efficiency becomes similar to that of the axial turbines.

<span class="mw-page-title-main">Fan (machine)</span> Machine used to produce air flow

A fan is a powered machine used to create a flow of air. A fan consists of a rotating arrangement of vanes or blades, generally made of wood, plastic, or metal, which act on the air. The rotating assembly of blades and hub is known as an impeller, rotor, or runner. Usually, it is contained within some form of housing, or case. This may direct the airflow, or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic motors, handcranks, and internal combustion engines.

Industrial fans and blowers are machines whose primary function is to provide and accommodate a large flow of air or gas to various parts of a building or other structures. This is achieved by rotating a number of blades, connected to a hub and shaft, and driven by a motor or turbine. The flow rates of these mechanical fans range from approximately 200 cubic feet (5.7 m3) to 2,000,000 cubic feet (57,000 m3) per minute. A blower is another name for a fan that operates where the resistance to the flow is primarily on the downstream side of the fan.

A rotodynamic pump is a kinetic machine in which energy is continuously imparted to the pumped fluid by means of a rotating impeller, propeller, or rotor, in contrast to a positive-displacement pump in which a fluid is moved by trapping a fixed amount of fluid and forcing the trapped volume into the pump's discharge. Examples of rotodynamic pumps include adding kinetic energy to a fluid such as by using a centrifugal pump to increase fluid velocity or pressure.

References

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  2. Williams, A.A. (September 1996). "Pumps as turbines for low cost micro hydro power". Renewable Energy. 9 (1–4): 1227–1234. Bibcode:1996REne....9.1227W. doi:10.1016/0960-1481(96)88498-9.
  3. 1 2 Thoma, D; Kittredge, C (1931). "Centrifugal pumps operated under abnormal conditions". Power: 881–884.
  4. Novara, Daniele; McNabola, Aonghus (2018-10-15). "A model for the extrapolation of the characteristic curves of Pumps as Turbines from a datum Best Efficiency Point". Energy Conversion and Management. 174: 1–7. Bibcode:2018ECM...174....1N. doi:10.1016/j.enconman.2018.07.091. ISSN   0196-8904.
  5. Singh, Punit (2005). "Optimization of internal hydraulics and of system design for PUMPS AS TURBINES with field implementation and evaluation". Universität Karlsruhe (TH): Diss. Institut für Wasserwirtschaft und Kulturtechnik. CiteSeerX   10.1.1.459.9416 .
  6. Novara D.; Carravetta A.; McNabola A.; Ramos H. M. (2019-05-01). "Cost Model for Pumps as Turbines in Run-of-River and In-Pipe Microhydropower Applications". Journal of Water Resources Planning and Management. 145 (5): 04019012. doi:10.1061/(ASCE)WR.1943-5452.0001063.
  7. "Demonstration Sites". Dwr Uisce. Retrieved 2019-11-06.
  8. 1 2 Morabito, Alessandro; Hendrick, Patrick (2019-10-07). "Pump as turbine applied to micro energy storage and smart water grids: A case study". Applied Energy. 241: 567–579. Bibcode:2019ApEn..241..567M. doi: 10.1016/j.apenergy.2019.03.018 .
  9. 1 2 Grundfos Industry (2004). Pump Handbook (PDF). Archived from the original (PDF) on 2020-01-10.
  10. 1 2 Ramos, Helena (2000). Guidelines for Design of Small Hydropower Plants (PDF).