Hydro pneumatic micro power station using sea waves.

Samoilescu, Gheorghe ; Sergiu, Nicolae ; Dorian, Marin 等

1. INTRODUCTION

This paper will focus onto wave and wind regimes, from all range of intense meteorological phenomenon (Iulian 1990), (Demirbilek & Panchang 1998), (Trusca 2005).

Using statistics offered by Hydrological and Meteorological Institute of Bucharest, the annual average height of the waves in Black Sea is 0.46m (Holthuijsen & Booij 2004). This happens between constant pressure curves of 5-9m.

In order to design the hydro electric micro power station using waves the energetic balance is taken into consideration. It contains wave energy, waste energy produced by pressure over oscillating column and turbine and generator outputs.

Station's generator module has a tri phased generator excited by rare soil permanent magnets, in order to achieve a higher output. (Olaru & Lazar 1990)

Elements of micro station working regime: turbine start at [+ or -] 40[degrees] pale angle in order to ensure a quick start using low speed air; waves propagation direction is also the entrance one, in this way avoiding changes in energy flux direction; two systems possible to adopt for generator module over spinning protection--one is breaking the turbine over 50Hz and the other one changes the pale angle using a centrifugal device.

The pale angle changes automatically depending on air flux speed and loading torque. (Desire 1982)

Turbine has three possible working regimes:

--starting phase--the intake air flux creates a pressure over turbine pales until they reach maximum angle; the turbine starts spinning;

--low wave regime--the air flux increase the turbine spinning; pale angle changes depending on air speed and loading torque;

--height wave regime--turbine spinning overcome nominal value; at 30% overcome the system allows intake air to bypass the turbine; this design protects turbine structure and generator module.

2. POWER STATION CALCULUS

The calculus pattern was designed for this particular power station placed on Constanta level of the Black Sea. Starting parameters are:

--[P.sub.n] theoretical nominal power 5000 kW;

--n turbine spinning speed n = 3000 rot/min;

--[U.sub.n] nominal voltage 220 V;

--[[eta].sub.t] turbine output 0.5;

--[[eta].sub.g] generator output 0.92;

--[phi] diameter ratio--ratio between pale outer and inner diameter 0.7;

--[lambda] speed modulus--ratio between laminar turbine speed and air speed through turbine 1.25;

--L length of caisson's precincts 5 m;

--B length of caisson's precincts 3 m;

--[rho] density 1230 kg/m3;

--[gamma] specific weight 9926.

We calculated:

--[P.sub.t] turbine nominal power

[P.sub.t] = [P.sub.N]/[[eta].sub.g][W] [P.sub.t] = 5000/0.92 = 5435[W] (1)

--[P.sub.ta] turbine consumed power

[P.sub.ta] = [P.sub.N]/[[eta].sub.g] x [[eta].sub.t] [W] [P.sub.ta] = 5000/0.92 x 0.5 = 10869.5[W] (2)

--air speed inside turbine

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)

--turbine inner section

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (4)

--precincts inner section

[S.sub.i] = L x B = 5 x 3 = 15[m.sup.2][[m.sup.2]] (5)

--air speed in turbine channel

c = 2 x [P.sub.t]/[rho] x [S.sub.t] x [v.sub.t] x [[eta].sub.t] = 2.5435/1.23 x 0.0868 x 58.7 x 0.5 = 3469 m/s (6)

[v.sub.2] = 4 x [v.sup.2.sub.t] - c/4 x [v.sub.t] = 4 x [58.7.sup.2] - 3469/4 x 58.7 = 43.9 m/s (7)

v = 2 x [v.sub.t] - [v.sub.2] = 2 x 58.7 - 43.9 = 73.5 m/s (8)

--aerodynamic pressure

[DELTA]P = [rho] [v.sup.2] - v.sup.2.sub.2/2 = 1.23 [73.5.sup.2] - [43.9.sup.2]/2 = 2137 N/[m.sup.2] (9)

--volume decrease due to aerodynamic pressure

[v.sub.p] = [S.sub.i] x [h.sub.p] = 15 x 0.214 = 3.21 [m.sup.3] (10)

--air column height

[h.sub.p] = [DELTA]P/[gamma] = 2137/9986 = 0.214m (11)

--volume decrease debit due to aerodynamic pressure (equivalent debit of pressure gradient)

[Q.sub.p] = [v.sub.p]/T = 3.21/T [[m.sup.3]/s] (12)

--requested turbine air debit

Q = [S.sub.t] x v = 0.0868 x 73.5 = 6.379 [m.sup.3]/s (13)

Wave period dependence of wave height T = f(h) and wave length dependence of the same wave height [lambda] = f(h) are known for Constanta Black Sea area. Wave parameters for nominal power of system are determined.

The following values are considered:

--wave height--h = 1.1m;

--wave length--[[lambda].sub.v] = 17m;

--wave period--T = 4.2s;

--wave power

[P.sub.v] = [P.sub.ta] + [P.sub.p] = 624 x [h.sup.2] x [[lambda].sub.v]/T x L = 624 x [1.1.sup.2] x 17/4.2 x 5 (14)

--wave volume

[V.sub.v] = 1/[pi] x L x h x [[lambda].sub.v] = 1.59 x h x [lambda][[m.sup.3]] (15)

--wave debit

[Q.sub.v] = Q + [Q.sub.p] = 31.1/4.2 = 7.4 [m.sup.3]/s (16)

--equivalent debit of pressure gradient

[Q.sub.p] = [v.sup.p]/T = 3.21/4.2 = 0.764 [m.sup.3]/s (17)

--global output

[eta] = [P.sub.N]/[P.sub.v] = 5000/15.280 = 0.327 (18)

For turbine calculus [v.sub.t], n, [P.sub.t], [S.sub.t], [lambda] and [phi] are used. Other requested characteristics are calculated using the following relations:

--pale outer diameter

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (19)

--pale inner diameter

[D.sub.p2] = [phi] x [D.sub.p1] = 0.7 x 0.467 = 0.327[m] (20)

--turbine diameters

[D.sub.1] = [D.sub.p1] + 2[DELTA] = 467 + 3 = 470mm (21)

[D.sub.2] = [D.sub.p2] - 2[DELTA] = 327 - 3 = 324mm (22)

where [DELTA] is distance between pale and turbine carcass;

--pale length

[l.sub.p] = [D.sub.p1] - [D.sub.p2]/2 = 467 - 327/2 = 70mm (23)

--pale number

[N.sub.p] = 12 (24)

--pale cover coefficient

[beta] = 0.85 (25)

--pale angular opening

[alpha] = [beta] 360/[N.sub.p] = 0.85 x 360/12 = 25.5[degrees] (26)

--two consecutive pale angle (Desire 1982)

[phi] = 360/[N.sub.p] = 360/12 = 30[degrees] (27)

--pale angles

I = 25[degrees] i = 7[degrees] [alpha] = 18[degrees] (28)

--section ratio

[R.sub.S] = [S.sub.i]/[S.sub.t] = 15/0.0868 = 173 (29)

3. CONCLUSIONS

Hydro pneumatic system advantages are:

--very simple kinematic scheme;

--no gear box for turbine is needed; the turbine is directly coupled with turbine;

--energy transmission does not use liquid and the consequence is no water-tight system required;

--the system does not have kinematical structures in contact with the sea water; the corrosion is reduced.

The micro power station working is based on following principles:

--the system has a variable geometry turbine which allows starting at low air speed;

--the waves are coming into system on their propagation direction which is distinct from other solutions; this approach avoids energy flux direction changing;

--the system is able to capture and convert waves with different height;

--generator module protection against over spinning is realized through turbine breaking and pale angle changing by an centrifugal device.

Efficiency of implementing non polluting energy will be proved. In order to protect the environment, important knowledge and technology will be transferred into renewable resource conversion field.

The turbine will have a completely new design, having a variable geometry and over spinning protection.

4. REFERENCES

Demirbilek, Z. & Panchang, V. (1998). A Coastal Surface Water Wave Model of the Mild Slope Equation, Technical Report CHL--98--26, U.S. Army Engineer Research and Development Center, Vicksburg

Desire, L. G. (1982). Wind Energy, Eyrolles, Paris

Holthuijsen, L. H., Booij, N. et al (2004). User Manual for SWAN version 40.31, Delft University of Technology, Delft

Iulian, C. (1990). Waves Energy Exploit, Technical Publishing House, Bucharest

Olaru, G. & Lazar, P. D. (1990). Contributions Regarding Implementing of Energetic Dams in Black Sea", Marth-April, Energetic Magazine, Bucharest

Trusca, C. V. (2005). Research and Contributions Regarding Dynamics of Wave's Associate Phenomenons Near Sea Coast, PhD Thesis, Galati

***. Wavegen a world leader in marine renewable energy

***. WEC survey of energy resources