Taking care of turbines29 November 2010
A new technology developed by Brazilian company CARE Electric utilises river flows and allows for installation in practically any location, regardless of river width, depth and current
Austrian inventor Johann Hoffman has combined forces with Brazilian company CARE Electric to design a turbine system to capture energy from the natural flow of rivers; eliminating the need for dams, reservoirs and flooding of land. In acknowledgement of their work, CARE was one of 26 companies to be named as 2010 Tech Pioneers by the World Economic Forum.
The modular designed concept involves suspending turbines across the river and it is possible to place units successively downstream. The only real restriction or guideline is that each unit must be placed at a sufficient distance from the proceeding unit, allowing the river which was highly oxygenated by the turbine blades, to return to its natural state. Models can be designed to be adapted according to the size and flow of a river. The generating capacity is directly dependent on the volume of water flow and river conditions. The volume of energy to be installed is currently a multiple of 167kWh which is the installed capacity of the slow speed rotation generator available. Larger capacity generators are being developed.
In order to initiate installation, reinforced concrete is placed in the riverbed to support the structure. Partial blockage of the riverbed is required which is then eliminated as the installation is assembled.
Integral parts of the system are the supports placed on the riverbanks or, in wider rivers, also placed in the river. Hydraulic cylinders are fixed to these supports and serve to raise, lower and adjust the turbine position in relation to the height of the water. This hydraulic lifting system permits raising the turbines out of the water, totally liberating river flow in the event that there is an excess of water, when the height should be adjusted or when it is necessary to inspect the units, or perform preventive or corrective procedures.
The height of the riverbanks should be at least 1m above water level. The reason is that if flooding occurs the turbines can be totally or partially lifted out of the current flow avoiding excess pressure on the unit. If the riverbank is higher than what is recommended, larger units can be installed to increase the volume of power generated. As the water level rises or falls the turbines are automatically adjusted to the condition, which avoids flooding and adjusts pressure on the system.
When the turbines are in the operating position they rest on the concrete structure that is placed transversal to the riverbed. The positioning (lowering of the turbine) causes a temporary reduction in the area of the river flow and consequently the water level is backed up until it reaches the height of the submerged turbines. When it overflows it continues on its natural course.
The height of the water is regulated by steel plates which permit the control or adjustment of the speed of the turbine rotor as well as the control of the potential power force. This column of water added to the hydraulic potential and the river flow creates a hydraulic force on the blades when the steel port (door) is opened. The basic function of the ports or doors is to regulate the opening, and consequently the volume of water flow, which can be increased or decreased according to generating requirements.
The volume of water that passes through the port (opening) is determined by the project design. It increases in velocity at a rate proportional to the height of the water column. This volume creates a perpendicular hydraulic force or pressure on the surface of the blades attached to the axel of the rotor of the turbine, thereby creating the spinning motion of the rotor.
One of the most noteworthy points about the system is that by using 50% of the hydraulic energy contained in the river flow, the CARE system generates at a minimum of 90% of installed capacity. Other advantages are:
• The module nature of the turbine system means it is relatively fast and easy to build, especially in remote places where there is no distribution network. In areas like Africa, India, many countries in the Far East, Central and South America it offers significant advantages for quickly improving social conditions, health and education. Other markets include irrigation and mining operations.
• The normal flow of material contained in any river bed or current does not constitute a problem since the blades attached to the rotor are flexible allowing the passage of any material.
• The system is totally automatic; no staff are required since sensors control water flow, speed of rotation, water height etc. Cameras provide long distance monitoring via the internet.
• Units can be installed close to the source of consumption therefore the costs of a distribution net is negligible or not a consideration.
• All units provide fish runs.
• Canals can be installed in locations where there may be river traffic.
• Detailed planning associated with hydroelectric dams is not necessary and various installations may be conducted simultaneously.
Generating units can be installed in any river which provides the minimum conditions necessary to rotate the generators. In cases where ice is a consideration it may be necessary to install heating solutions.
The technology is in its initial phase; however larger units of 5MW are being developed. Recognition by the World Economic Forum is seen as international confirmation of the validity of the technology due to the reputation of forum and the rigorous evaluation process it adopts.
The authors are Eng. Wilson Pierazoli and Frank de Luca. Email: [email protected] or visit www.careelectric.com.br for more details.