This invention relates to tidal power plants (TPP) More specifically, the invention relates to two-way generation tidal power plants with a barrage equipped with one-way hydraulic turbines (TWTPP).
All operating TPP with a barrage generate the power only during ebb. Le Rance in France was built as TWPP plant with barrage and two-way hydraulic turbines, however it cannot work during flood. So at present time still is very important to develop TPP generating the power during ebb and flood. Taking into the account the experience of Le Rance it is easy to see that only TWTPP with a barrage equipped with one-way hydraulic turbines can generate the power during ebb and flood.
Any two-way generation tidal power plant with a barrage and a power house with one-way hydraulic turbines connected to electric generators must have head and tail reservoirs located at the basin and the outer bay, or vice versa, formed by auxiliary barrages and parts of the main barrage. These auxiliary barrages and the parts of the main barrage are equipped with sets of vertical sliding sluices delivering water via the power house, during ebb from the basin to the outer bay and during flood from the outer bay to the basin.
This type of tidal plant was patented in 2008 (“Two-way generation tidal power plant with one-way turbines”, UK Patent, GB 2436857 B, 20.02.2008, Inventor: Alexander Gokhman). It can be seen from the disclosure and claims of this patent that during ebb the sluice sets in auxiliary barrages are open and the sluices in the parts of the main barrage are completely closed (during flood—vice versa). It is also clear that the discharge capacity of each of these sluices sets does not have to be more than two to three times greater than the discharge capacity of all turbines in the power house in order to prevent significant head losses at the inlet to the head reservoir and exit from the tail reservoir.
It is obvious that a plant according to the Patent GB 2436857 is more expensive than an ebb generation tidal power plant having the same number of units. Therefore, this increase of capital investment must be offset by a relative increase in daily energy output:
where:
In order compute Etw, Eebb, and Cinc I developed program (ENERGY) for the solving a well-known nonlinear first order ordinary differential equation:
where:
H=±(Zb−Zt) (3)
where:
The program ENERGY along with the values of Etw, Eebb, and Cinc computes the water volumes used for generation during each cycle for ebb TPP, Webu, and for TWTPP, Wtwu. It is obvious that the closer Wtwu and Webu are to the value of available volume, Wava, the larger are Etw and Eebb. Also clear that Wuse is larger for larger current turbines discharge capacity at one meter head:
(Q1)ph=KtDt2Q11(H) (4)
where:
The computations of Etw, Eebb, Ce, Wtwu, and Webu were done for the Cardiff-Weston power house in UK equipped with turbines with Dt=7.5 m working at the specific speed, N11=130 rpm, and with turbine efficiency, ηt, and cavitation coefficient, σ, as functions of Q11 shown in the following table:
The following Table 2 presents the results of computations for five variations of Kt: 100, 200, 300, 400, and 500 for Cardiff-Weston with Wava=3.019 km3/sec.
Table 2 shows that Etw grows faster than Eebb as growth of Kt increases. Indeed, Ce=0.815 for Kt=100 and Ce=1.337 for Kt=500.
The explanation for this fact is as follows. For the ebb generation TPP (ETPP) the basin is filled up during flood via sluices located in main barrage, so for ETPP generation always begins at the highest value of basin elevation (Zb)max. On the contrary for TWTPP claimed in Patent GB 2436857 during the flood the basin is filled exclusively via turbines and they are capable of filling the basin during the flood to level (Zb)fl.e which is lower than (Zb)max. For TWTPP ebb generation begins at (Zb)eb.b=(Zb)fl.e. So for TWTPP ebb always produces less energy than ebb for ETTP with the same turbines. The smaller Kt, the smaller the discharge capacity of the power house turbines and, therefore, smaller value of (Zb)fl.e and the ebb generation energy output. As a result, the value of Eebb is higher than Etw. As Kt increases the discharge capacity of the plant grows leading to growth of Ce.
Finally Table 2 shows that the tidal plant according to the Patent GB 2436857 produces even less energy than the ebb generation plant with Kt=100. For Kt=200 (the value accepted for the Cardiff-Weston barrage) this two-way plant gives only 5.8% more energy than the ebb plant with an increase in capital investment for construction around 10% and, therefore, from an economical point of view is not acceptable. For Kt≧300 the increase in energy is not sufficient to overcome the increase of construction cost, because the power house represents the predominant expense which grows proportionally to Kt.
The present invention discloses a two-way generation tidal power plant which differs from the plant claimed in Patent GB 2436857 by crucial feature. Its main barrage is equipped with high discharge capacity bypasses, sluices participating in energy generation by means of discharging water in parallel with turbines during the final phases of ebb and flood generations.
These bypasses must have a discharge capacity up to 15 times greater than the discharge capacity of the power house turbines in order to substantially increase the daily energy output E and the water volume used for generation during each cycle Wu comparing to the same values for the plant claimed in the Patent GB 2436857 with the same turbines.
Indeed, computations for Cardiff-Weston power house in UK equipped with turbines having Dt=7.5 m using my program ENERGY show the following result for number of turbines Kt=200:
The tidal plant claimed in the Patent GB 2436857 has E=73932.27 MWH and Wu=1.482 km3
The tidal plant according to the present invention has E=96, 253.74 MWH and Wu=2.596 km3
The increase in Wu is very important from an environmental point of view. Indeed Wu=2.596 km3 is very close to the available volume Wava=3.019 km3 which is equal to the volume of water replaced during one cycle under natural conditions without a barrage.
Referring now to
sluices 14 located at the head barrage 10 and connecting the head reservoir 8 with the basin 5,
sluices 13 located at the part of the main barrage 16 and connecting the head reservoir 8 with the outer bay 4,
sluices 11 located at the tail barrage 9 and connecting the tail reservoir 7 with the outer bay 4,
sluices 12 located at the part of the main barrage 15 and connecting the tail reservoir 7 with the basin 5,
bypasses 17 located at the part of the main barrage between shore 1 and the tail barrage 9 and connecting the basin 5 with the outer bay 4.
A two-way generation tidal power plant shown in
As presented above in Table 2 the increase of coefficient Ce comparing the daily output of two-way generation power plant with the daily output of ebb generation plant can be achieved by an increase of the discharge capacity of the plant by accepting a larger number of turbines, Kt, in the power house which causes a drastic increase in capital investment construction. In the present invention a substantial increase in the plant discharge capacity and, therefore, in Ce is achieved by bypassing the water in parallel with the power house turbines via sluices during ebb and flood final phases when the value of head, Ht, is relatively small. During the final flood phase bypasses 17 are used for this purpose. During the final ebb phase are used the bypasses 17, sluices 12 and 11, and sluices 14 and 13 for this purpose. The additional cost of construction of such a two-way tidal plant caused by the cost of bypasses 17 is much lower than the increase in the cost of the power house 6 due to the increase in Kt.
Bypasses 17 and other sluices 11, 12, 13 and 14 are vertical sliding gate sluices. Bypasses 17 have the following discharge capacity at one meter head:
(Q1)bp=KbpCdBbpHbp(2g)0.5 (5)
where:
There are two evident constraints on the values of Hbp during ebb, (Hbp)eb, and the flood, (Hbp)fl, at any given time:
(Zb)eb≧(Zcbpg)be+(Hbp)eb (6)
(Zt)fl≧(Zcbpg)be+(Hbp)fl (7)
where:
The discharge capacity of bypasses 17, (Q1)bp, must be up to fifteen times higher than the discharge capacity of turbines in the power house 6, (Q1)ph.
The reason for using sluices 12 and 11, and sluices 14 and 13 in addition to bypasses 17 during the ebb can be easily explained by the constraint (6) limiting the value of (Hbp)eb. Indeed, during the final ebb phase the value of (Zb)eb is small and according to (6) (Hbp)eb must be smaller than the optimal value of the bypass aperture height, [(Hbp)eb]op, required by the program ENERGY. On the contrary during the final flood phase the value of (Zt)fl is big and [(Hbp)fl]op always satisfies the constraint (7).
The use of bypasses 17 during the final flood phase and bypasses 17 together with sluices 11, 12, 13 and 14 during the final ebb phase substantially increases the energy output of the two-way tidal power plant and the water volume used for power generation per cycle. The computations by program ENERGY show that the two-way power plant with same turbines as shown in Table 1 and Table 2 with 200 units and with 200 bypasses 17 having Bbp=10 m will generate 96,253.74 MGH per diem. This is 1.30 times higher than the energy output of 73932.27 MGH presented in Table 2.
The Bulb hydraulic turbine presented in
∇[Zhw]max—the maximal head water level,
∇[Zhw]min—the minimal head water level,
∇[Ztw]max—the maximal tail water level,
∇[Ztw]min—the minimal tail water level,
∇[Zax]—the turbine axis level.
Also
The use of a Bulb turbine with a mixed-flow propeller runner and an exit stay apparatus instead of the commercially available Bulb turbine with axial propeller and without an exit stay apparatus substantially increases the discharge capacity of the power house at one meter head without an increase of |Hs|, i.e. leads to substantial increase in the energy output without additional capital investment for construction.
Number | Date | Country | Kind |
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GB 1003836.2 | Mar 2010 | GB | national |