Power plants – Pressure fluid source and motor – Utilizing natural energy or having a geographic feature
Reexamination Certificate
2001-10-09
2003-04-15
Look, Edward K. (Department: 3753)
Power plants
Pressure fluid source and motor
Utilizing natural energy or having a geographic feature
Reexamination Certificate
active
06546723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydropower conversion method and system, and in particular, to a system and method of using a hydraulic gradient to create a temporary negative pressure for use in operating a pneumatic device.
2. Background of the Invention
Generation of electrical energy is needed to support the world's growing population and economy. Personal, commercial and defense energy demands are currently taxing the existing electrical energy supply. To meet the electrical energy demand, there has been great interest in exploiting renewable energy resources, such as hydroelectric power. Hydroelectric power is seen as an energy source which will reduce dependence on foreign energy and avoid potentially costly and possible negative environmental effects linked to non-renewable energy production technology. Examples of some environmental concerns include carbon dioxide emissions, acidic mine drainage from coal extraction waste, heat disposal and radioactive fission products produced during nuclear energy generation.
Hydroelectric energy has been seen as an alternative electrical energy generation system that has few potentially negative environmental effects. However, dams used in conventional hydroelectric power systems have been linked to negative physical, chemical and biological effects on the bodies of water to which these dams are disposed. These negative environmental effects manifest themselves in habitat destruction, obstructions to natural fish movement, poor water quality, over harvest and competition from non-indigenous species. Further, hydroelectric dams may degrade riverine habitat and impede movement of migratory fishes to and from their natal streams.
In a conventional hydroelectric power system, potential energy is used to accelerate water in a discharge line (i.e., penstock) of variable length, geometry and slope. The accelerated water is then directed through a turbine assembly designed to convert the kinetic energy of the water into mechanical energy. The gross head, H, available for acceleration is the elevation differential between the forebay water surface and the tailwater surface as provided by the formula:
Gross Head (ft)=(Elevation
forebay
)−(Elevation
tailwater
) (1)
The energy potential represents the product of gross head and the volumetric flow rate of water through the system as provided by:
Energy Potential (kWh)=306.6.•Q•H (2)
where
Q=water flow rate (ft
3
/s)
H=gross head (ft).
For effective use, H has a minimum value of 10 feet. As H drops towards the minimum acceptable value of 10 feet, the water velocities achieved become unacceptably low so as to be impractical for use in hydroelectric generation. Implementation of a conventional hydroelectric system with these low water velocities would require the employment of a large diameter, slowly rotating turbine design. Such a design would involve an excessive capital investment to deploy.
Bernoulli's equation applied to the forebay and the tailwater conditions allows calculation of the maximum water velocity (V
max
) in the turbine inlet as
(
P
γ
+
Z
+
V
2
2
G
)
forebay
=
(
P
γ
+
Z
+
V
2
2
G
)
tailwater
(
3
)
where
P=pressure (psig)
&ggr;=specific weight of water (lb/ft
3
)
V=velocity (ft/s)
G=gravity (32 ft/s
2
)
Z=elevation head (ft)
Since P and V at both locations are negligible and neglecting minor line losses (friction), V
max
is
V
max
(ft/s)={square root over ((2
g
(
Z
1
−Z
2
))}. (4)
For example, with H defined as Z
1
−Z
2
, of 10 feet, V
max
is 25.4 ft/s whereas an H of 100 feet provides a V
max
of 80.2 ft/s. Hence, for a given volumetric flow rate (Q), the penstock cross-sectional area required at H=10 feet is 3.16 times that required at H=100 feet. The lower water velocity also results in reduced turbine tip speeds and thus increases turbine shaft requirements, e.g., costs, for a given power output.
Torque applied to the turbine shaft determines the diameter of the turbine shaft. Further, the turbine shaft diameter is directly related to power and shaft speed:
torque
(
pound
-
inches
)
=
63025
·
HP
RPM
(
5
)
where
HP=horsepower
RPM=shaft speed (revolutions per minute).
Unfortunately, large values of H result in problems associated with greater forebay volumes and the need for equipment that allows for the movement of fish both upstream and downstream. Excessive shear, turbulence, flow separation, and gas supersaturation are also of primary concern.
A disadvantage with the design of conventional hydroelectric power generation systems is that these systems are unable to produce power under low-head conditions (i.e., less than ten feet) economically or without potentially negative environmental effects. Examples of such hydroelectric power designs include Pelton, Francis, Turgo, Kaplan and cross-flow designs. Due to the inability of these conventional systems to function under low-head conditions, several alternative designs have been developed for low-head applications.
For example, in EPO Patent 0,117,739 to Smith, there is disclosed a water engine design having reciprocating floats in vertical chambers that rise and fall with water levels as directed by inlet and exhaust valves. Power is transmitted by oscillation of a pivotally mounted beam assembly.
In U.S. Pat. No. 4,782,663 to Bellamy, there is disclosed a pneumatic hydroelectric power conversion system. Power is generated by passing water in sequence over flexible bags or membranes to displace air under the flexible bags. Power is developed by directing the displaced air through an air turbine coupled with a generator.
In U.S. Pat. Nos. 5,074,710, 4,095,423, 4,103,490 and 4,464,080, all to Gorlov, there are disclosed various apparatus that include one or more vertical chambers with parts of ingress and egress through which tidal or river flows are directed so as to alternately force air out and into the chambers via an air motor or a turbine.
In EPO Patent 0,339,246 to Loughridge, there is disclosed a power generation system similar to that of Gorlov but designed so as to introduce water alternately into one of two columns thereby tangentially creating a swirling action that minimizes hydraulic losses.
In U.S. Pat. No. 4,288,985 to Dyck, there is disclosed an apparatus that uses two reservoirs influenced by tidal action to force water back and forth through an air tight duct system in which a turbine is mounted for producing power.
In U.S. Pat. No. 5,377,485, EPO Patent 0,526,470 B1, and PCT Patent WO 91/17359, all to Bellamy, there are disclosed various power conversion systems that direct water through a duct and as a result, the water induces air into the duct. The induced airflow exits the duct through an exhaust duct and is drawn through an air turbine. The air is introduced into the duct by siphon, air injectors or venturis.
In EPO Patent 0,100,799 to Cary, there is disclosed an apparatus that makes use of a descending column of water to entrain and compress air on a continuous basis. The air is separated from the water at a particular depth through the use of a tangentially fed air inclusion chamber. The compressed air is then used to supply air to a gas turbine or ramjet.
In EPO Patent 0,162,814 to Burgnoli, there is disclosed an apparatus that improves the efficiency of a hydraulic air compressor, such as that described in the Cary patent, by recirculating air that is under negative gauge pressure as the air exits an air motor designed to produce power.
In U.S. Pat. No. 4,098,081 to Woodman, there is disclosed a power generation system that uses a plurality of tidal chambers which are filled in succession during rising tide and which are allowed to sequentially empty during falling tide. Air flows across a turbine as a manifold and a valve means communicates air pressure and vacuum from the tidal chambers.
The systems developed thu
Palmisano Angelo W.
Watten Barnaby Jude
Homer Mark
Lazo Thomas E.
Look Edward K.
The United States of America as represented by the Secretary of
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