OTEC SYSTEM

PREPARED BY:- MAYANK PATEL
MECHANICAL DEPARTMENT
IIST,RAJPUR
OCEAN THERMAL ENERGY CONVERSION (OTEC) SYSTEM

 Open cycle ocean thermal energy conversion (OTEC) system
 OTEC is also known as claude cycle.
 The system incorporates a de-aerator to remove some of the non-condensable gases
entrained with the warm surface seawater. The degassed warm water then flow to
the flash evaporator. The flash evaporator chamber is maintained under saturation
pressure (vacuum) corresponding to that water temperature. Low pressure steam
obtained is separated and passed through a turbine to extra energy.
 The exhaust of the turbine is condensed in a direct contact condenser. Cold water
drawn from a depth of about 1 km is used as cooling water in a contact condenser.

Indrashil institute of science & technology

 The resulting mixture of used cooling water and condensate is
disposed in a sea.
 If a surface contact condenser is employed, the condensate could be
used as desalinated water. Thus an open cycle OTEC plant can provide
a substantial quantity of desalinated water. In this cycle the operating
pressures of working fluid in the boiler, turbine and condenser are
much lower and its specific volume is much higher. Such high specific
volumes result in larger turbine size and hence more costly.
INDRASHIL INSTITUTE OF SCIENCE &
TECHNOLOGY

 Close cycle OTEC system
 Close cycle OTEC also known as Anderson cycle.
 In this cycle warm surface water is used to evaporate a low boiling point working
fluid such as ammonia, Freon propane etc.
 Warm water from ocean surface is circulated through a pump to a heat exchanger
which acts as boiler to generate Freon vapour at high pressure, this vapour expands
in the vapour turbine to develop mechanical power.
 It is used to drive an electric generator which produce electric energy. Freon
vapour from turbine at low pressure is condensed in the condenser with help of
cold water drawn from the depth of ocean through a pump.

 The Freon condensate is pumped again in the boiler. Because of the low quality of
the heat, large surface areas of heat exchanger are required to transfer significant
amount of the heat and large amount of water needs to be circulated.
 The operating pressures of the working fluid at the boiler and condenser are much
higher and its specific volume is much lower as compared to that of the water in
open cycle system.
 Such pressures and specific volumes result in the turbine that is much smaller in
the size and hence less costly as compared to that open cycle system.
 The overall efficiency of such plant is very low in the range 2 to 3 % only.

Hybrid cycle OTEC
 The raw ocean water which is pumped into evaporator and condenser, contains
microorganisms which stick in water side of both the heat exchangers.
 This biological impurity of sea water that deposits and grows on the evaporator and
condenser metal surfaces, crating thermal resistance for the heat transfer is known as
bio-fouling.
 The hybrid cycle is an attempt to combine the best feature and avoid worst feature of the
open and close cycles.

 Warm water from ocean surface is flash evaporated under vacuum. Low pressure
steam obtained is separated and passed through a Freon evaporator.
 The heat of steam is then transferred to Freon. The evaporator is isolated from the
sea water thus bio fouling of evaporator can be avoided. Remaining cycle is same as
closed cycle OTEC.

Tidal power plants
1. Dam or barrage
2. Sluice ways
3. Power house
Single basin system
Double basin system

 Single basin system
1. Single ebb cycle system
 When the flood tide (high tide) comes in the sluice gates are opened to permit sea water
to enter the basin or reservoir, while the turbine sets are shut. The reservoir thus starts
filling while its level rises till maximum tide level is reached.
 At the beginning of the ebb tide the sluice gates are closed. Then the generation of the
power takes place when the sea is ebbing (flowing back of tide) and the water from the
basin flows over the turbines into the lower level sea water.
 The turbines are keep working until the rising level of the next flood tide and the falling
reservoir level together reduce the effective head on the turbines to the extent where it
can no longer work safely and effectively. The turbine are then closed and sluice gates
opened again to repeat the cycle of operation.

2. Single tide cycle system
 In single tide cycle system the generation is affected when the sea is at flood tide. The
water of the sea is admitted into the basin over the turbines.as the flood tide period is
over and the sea level starts falling again the generation is stopped. The basin is drained
in to the sea through the sluiceways.
 The ebb tide has a long duration than the flood tide the ebb operation provides an
increased period of the actual work.it has been estimated that the energy produced by an
ebb cycle system can be as much as 1.5 times that by a tide cycle system. The tide cycle
requires a deeper reservoir, thus it requires greater construction costs.
 The main disadvantages in both the ebb cycle as well as the tide cycle is the intermittent
nature of their operation.

 Double basin system
 In the arrangement to basin at different level is provided.
 In the one basin called upper basin (high pool) the water level is maintained above that
of the lower basin (low pool). The high level basin gates are called inlet gates and low
level gates as outlet gates.
 In this system the turbines are located in between the two adjacent basins.at the
beginning of the flood tide the turbine are shutdown. The gates of upper basin A are
opened and those of lower basin B are closed. The basin A is thus filed up while the
basin B remains empty.

 When the water level in basin A provides a sufficient difference of the head between the two
basins. The turbines are stared. The water flows from A to B through the turbines and power
generated. The power generation thus continuous simultaneously along with filling up of the
water in basin A.
 When the tide reaches its peak value. The water level in basin A is maximum, the inlet sluice
are then closed .therefore the water level in the upper basin falls and that in the lower basin
rises.
 When the rising level in basin B becomes equal to level of the falling tide the outlet sluice are
opened. When the tide reaches its lower most level the outlet gates are closed.
 After some time the tide rises when its level becomes equal to the low level of the upper basin
the inlet gates are opened. Consequently the level of water in basin A starts rising tus cycle is
repeated.

Wave energy conversion devices:-
1. Float type wave energy converter:-
 The buoy is floating part of the system which rises and falls with rise
and fall of waves. The resulting vertical motion is used to operate the
piston of an air pump through linkage. The pump may be anchored to
the sea bed. Several float operated air pumps are used to store energy in
compressed air storage.
 The compressed air is used to generate electricity through an air turbine
coupled to a generator.

2. Dolphin type wave converter
 This devices uses the float which has two motions. The first is a rolling
motion about its own fulcrum with the connecting rod. Revolving
movements are caused between the float and connecting rod. The other
is a neared vertical or having motion about the connecting rod
fulcrum.it causes relative movements are between the connecting rod
and stationary dolphin.
 In both the cases the movement are amplified and converted by gear in
to continuous rotary motions that drive two electrical generators.

3. Oscillating water column type
 It consists basically of a chamber in the sea exposed to the wave action
through a opening on the side. The air inside the chamber is alternative
compressed or expanded because of the wave action.
 Consequently pulsating bi directional air movement occurs through an
opening at the top of the chamber.
 This bi directional flow can be converted through a system of four valves
to uni directional flow.
 This is achieved by having two valves open and two valves closed at any
given instant of time.
 This uni directional flow drives an air turbine which in turn is coupled to
an generator. Indrashil institute of science & technology

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OTEC SYSTEM

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