The innovation to the power cycle which OCEES International, Inc. employs is provided by OCEES strategic corporate partner Exergy, Inc. in the form of their patented Kalina Cycle^®. The Kalina Cycle^® is a variation of the more conventional closed-cycle OTEC system incorporating aqueous ammonia (ammonia/water mixture) as the working fluid instead of the conventional ammonia or propylene working fluid employed in earlier designs of closed-cycle OTEC power systems. The Kalina Cycle^® is a break-through technology for OTEC power systems providing a nearly 80% increase in efficiency over previous closed-cycle designs. Because the ammonia/water concentrations can be varied throughout the system to optimize according to system temperatures (sort of a "designer" working fluid) and by adding an extra component – the recuperator, heat losses generally experienced in other closed-cycle designs can be minimized and recovered, thereby improving the overall efficiency of the power cycle.

Click on the image to view an animation

The Kalina Cycle^® is a modified Rankine cycle with increased efficiency resulting from the altered properties of its ammonia/water working fluid, rather than the pure water or ammonia working fluid in a standard Rankine cycle. The Kalina Cycle^® specifically exploits the variable boiling and condensing temperatures of a variable concentration working fluid since an ammonia/water mixture can more closely follow the straight-line temperature change of the heat source or condensing medium in a counterflow heat exchanger.

     Compared to a conventional Rankine cycle, the temperature rise of the cooling water for the ammonia/water can be higher than that for condensing the more traditional anhydrous ammonia, thereby minimizing the cold deep seawater requirements saving capital costs and increasing the net power output of the plant over previous OTEC system designs. By utilizing the more efficient Kalina Cycle^® in the integrated OTEC system design, OCEES International, Inc. is able to reduce costs of power generation and provide emission free energy to the tropical island communities it services.

    The OTEC Kalina Cycle^® uses the four typical Rankine cycle phases: evaporation, expansion, condensation and feed. The evaporator and condenser components in an integrated OTEC Kalina Cycle^® system consist of numerous large plate heat exchangers with titanium plates for maximum corrosion resistance against seawater and maximum life-time efficiency. An additional piece of equipment, the recuperator, recovers heat from the warm but unvaporized liquid leaving the separator vessel. A brief simplistic process description follows.

     Generally, for OTEC applications and system temperatures, a mixture of approximately 60% ammonia – 40% water (by weight) enters the counterflow evaporator where it is heated by the warm surface seawater. The warmed vapor/liquid mixture travels to the separator where high quality ammonia vapor goes to the turbine. Warm "lean" liquid from the separator drains through the recuperator and heats an incoming quantity of 60/40 mixture working fluid.

     The high quality ammonia vapor from the separator enters a radial flow ammonia turbine and expands creating mechanical energy which is then converted into electrical energy via the attached generator system. Design of such ammonia turbine/generator systems is well established with system efficiencies approaching 85% or greater for OTEC applications.

     The turbine exhaust vapor is recombined with the cooled post-recuperator lean mixture. Both condensation and ammonia absorption then occur inside the counterflow condenser cooled by the cold, deep seawater supplied by the Cold Water Pipeline. The 60/40 liquid mixture then flows to the condenser hotwell where feed pumps take suction from the hotwell and pump the ammonia/water mixture back into the evaporator, completing the cycle.

Reliable Energy

     OCEES International, Inc. utilizes integrated OTEC systems power cycle designs which are scalable and modular for implementation into nearly every tropical island application with suitable access to cold, deep seawater. Sufficient redundancy of components is incorporated into every design to ensure periodic maintenance and repair procedures can be performed without compromising the supply of base-line power to the local community or power grid.

     Likewise, the modular nature of the system ensures proper "down stream" protection of discharge water streams (either to aquaculture applications or system discharge streams to the ambient ocean) from ammonia contamination, should an unlikely leak in the system occur, without compromising the plant’s performance and availability. Instrumentation and sensors to protect against any leakage is standard in OCEES International, Inc. OTEC system designs.