Airlift pump
Encyclopedia
An airlift pump is a simple pump
which is powered by compressed air.
This air is usually compressed by a compressor
or a blower
.
The air is injected in the lower part of a pipe that transports a liquid. It usually bubbles into another larger diameter pipe. By buoyancy
the air, which has a lower density
than the liquid, rises quickly.
By fluid pressure, the liquid is taken in the ascendant air flow and moves in the same direction as the air. The calculation of the volume flow of the liquid is possible thanks to the physics of two-phase flow.
Airlift pump technology is superb due to its simple structure. However, it has the following weaknesses:
s where sand
would quickly abrade mechanical parts. (The compressor is on the surface and no mechanical parts are needed in the well). However airlift wells must be much deeper than the water
table to allow for submergence.
Air is generally pumped at least as deep under the water as the water is to be lifted. (If the water table is 50 ft below, the air should be pumped 100 feet deep).
It is also sometimes used in part of the process on a wastewater treatment plant
if a small head is required (typically around 1 foot head).
They can also be used in ponds and aquaculture to aerate and mix the water.
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
which is powered by compressed air.
Principle
The only energy required is air.This air is usually compressed by a compressor
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
or a blower
Blower
Blower may refer to:* USS Blower , a submarine of the United States Navy* a ducted centrifugal fan, especially when used in a heating, ventilating, and air-conditioning system* a supercharger on an internal-combustion engine...
.
The air is injected in the lower part of a pipe that transports a liquid. It usually bubbles into another larger diameter pipe. By buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
the air, which has a lower density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
than the liquid, rises quickly.
By fluid pressure, the liquid is taken in the ascendant air flow and moves in the same direction as the air. The calculation of the volume flow of the liquid is possible thanks to the physics of two-phase flow.
Airlift pump technology is superb due to its simple structure. However, it has the following weaknesses:
- Weak suction
- Unstable flow rate
- Frequent clogging
- Difficult flow control
- Low lift
Utilization
Airlift pumps are often used in deep dirty wellWater well
A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...
s where sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
would quickly abrade mechanical parts. (The compressor is on the surface and no mechanical parts are needed in the well). However airlift wells must be much deeper than the water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
table to allow for submergence.
Air is generally pumped at least as deep under the water as the water is to be lifted. (If the water table is 50 ft below, the air should be pumped 100 feet deep).
It is also sometimes used in part of the process on a wastewater treatment plant
Sewage treatment
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
if a small head is required (typically around 1 foot head).
They can also be used in ponds and aquaculture to aerate and mix the water.
Inventor
The first airlift pump is considered to be invented by the German engineer , who lived in the second part of the eighteenth century. He discovered the airlift pump in 1797.Advantages and disadvantages
The following paragraph exposes the advantages and disadvantages of the airlift pump compared to other pumping techniques.advantages
- The pump is very reliable. The very simple principle is a clear advantage. Only air with a higher pressure than the liquid is required.
- The liquid is not in contact with any mechanical elements. Therefore, neither the pump can be abradedAbrasion (mechanical)Abrasion is the process of scuffing, scratching, wearing down, marring, or rubbing away. It can be intentionally imposed in a controlled process using an abrasive...
(which is important for sandwater wellWater wellA water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...
s), neither the contents in the pipe can be abraded (which is important for archeological research in the sea)
disadvantages
- cost: while in some specific case the operational cost can be interesting, most of the time, the quantity of air to compress is high compared to the liquid flow required..
- Conventional airlift pumps have a flow rate that is very limited. The pump is either on or off. It is very difficult to get a wide range of proportional flow control by varying the volume of compressed air. This is a dramatic disadvantage in some parts of a small wastewater treatment plant, such as the aerator.
- The suction is limited.
- This pumping system is suitable only if the headHydraulic headHydraulic head or piezometric head is a specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer...
is relatively low. If you want to obtain a high head, you have to choose a conventional pumping system. - Because of the principle, a lot of air remains in the liquid. In certain case, this can be problematic, as, for example, in a waste water treatment plant, before an anaerobic basin.