Tuesday, June 24, 2008

Advantages of compressed air as an energy vector

Advantages of compressed air as an energy vector
A vehicle powered by compressed air offers a lot of advantages in comparison with a normal combustion engine or an electrical motor. The idea of using compressed air as an energy vector can, for example, also by applied to a hybrid vehicle, with cylinders functioning on compressed air and an additional battery working on electricity, creating a vehicle powered solely on electrical-pneumatic propulsion.Advantages of vehicles powered by compressed air:
The costs involved to compress the air to be used in a vehicle are inferior to the costs involved with a normal combustion engine.
Air is abundant, economical, transportable, storable and, most importantly, nonpolluting.
The technology involved with compressed air reduces the production costs of vehicles with 20% because it is not necessary to assemble a refrigeration system, a fuel tank, spark plugs or silencers.
Air itself is not flammable
The mechanical design of the motor is simple and robust
It does not suffer from corrosion damage resulting from the battery.
Less manufacturing and maintenance costs.
The tanks used in an air compressed motor can be discarded or recycled with less contamination than batteries.
The tanks used in a compressed air motor have a longer lifespan in comparison with batteries, which, after a while suffer from a reduction in performance.

Energy Storage
The use of compressed air for storing energy is a method that is not only efficient and clean, but also economical. In 1973 CAES (Compressed Air Energy Storage) installed their first compressed air energy storage plant in Germany, making use of natural underground caves for compressed air storage and taking advantage of the surplus energy produced by the generating plants. Later on similar plants were installed in the United States (Alabama and Ohio).These plants are designed to operate 24 hours a day; they charge during the night and they discharge during the day. The advantage of these kinds of plants is that they make use of the surplus of electricity (at low cost) by turning it into compressed air stored underground. Later on this energy is used in a turbine generator to help the electricity network during periods of high demand.

A specific example, which is yielding good results, is the power supply system installed in Alabama, USA. In this case the reservoir is of a constant volume, in comparison with others where there is subterranean connection with water deposits. The air is compressed gradually with cooling intermissions. This is done to reach good efficiency on the storage stage of the energy in the periods when there is a surplus of energy.

At the peak hours the compressed air is used to help gas turbines. This is also done using a recuperative cycle of good thermodynamic efficiency, with combustion and post combustion , and heat recovery of exit gases.No matter how efficient the recuperative cycle is completed, they will never reach the total efficiency of normal gas turbines. In comparison with normal gas turbines the efficiency level will be around 75%. Actually, during the generation stage the accumulative energy is transformed; all the energy that is generated by the gas turbines is used to drive the electricity generator, so the energy that is necessary to drive the electricity generator is not derived from compressors. This explains the limited efficiency on this type of gas turbines.The drawing above corresponds with the first installation of this kind in Alabama, U.S.A., as mentioned earlier. Underneath you will find the functional data of this installation.• Power: 110MW• Location: Mac Intosh – Alabama (USA.)• Maximum capacity: 26 hours• Ratio: 1.7 hours of compression for every hour of generating• Efficiency: 75-76,1 %• Costs: 500 U$S/KW (1988)Compressed air as a form of energy can also be used to describe the technology on a smaller scale, like the cars operated by compressed air or wind turbines that store the energy in carbon fiber tanks. The storage of compressed air as a form of energy is a very viable solution to adapt to the irregular energy supply of wind turbines and the fluctuation in demand.

Power collecting system by vehicle traffic
The objective of this system is to produce electricity at low cost and in a non polluting way. It was invented by Nelson Gonzą¹les Acosta, native to the Dominican Republic. The process to produce electricity is based on installing a ramp with an angle of around 45 degrees that descends every time a vehicle drives over it.

As the ramp comes down a system of plates is activated that compresses the leftover air and impels it towards a tank where it is collected.

The compressed air is then lead towards the deposit through a system of pipes. Once the air is stored, it is injected towards a pneumatic turbine which puts a belt in motion that is connected with a generator. This is where the electricity is produced and distributed to the network.