Through this study, we design closed cycles for the demonstration and commercialization of OTEC using seawater temperature difference, and design the scale of OTEC using PID and sequence for autonomous and unmanned distribution of plants. The performance characteristics were analyzed.
Selection of working fluid for designing the basic cycle, analysis of heat source, and evaluation of temperature difference potential were carried out, and the control range for automation of the working fluid pump RPM control was selected through the operating characteristic fertilizer of the 20kW pilot plant.
R32, an environmentally friendly and low-risk refrigerant, was designed through the selection of the optimum working fluid, and the seawater heat source of the final selected site(Kiribati) was applied at an average of 30 ℃ per year, and the heat sink was also applied at
Through static simulation of MW-grade seawater temperature differential power generation, the heat source temperature was reduced and the decrease amount according to the temperature change of evaporator pressure and turbine output was 45 kPa/℃ and 101.7 kW/℃, respectively. And 84.3 kW/℃ change were predicted.
In addition, PID control and sequence control algorithms and control elements were selected to build a closed seawater temperature differential control system for practical use of seawater temperature differential generation. By applying the selected control values, we implemented dynamic simulation of seawater temperature differential power generation, reviewed the accuracy of control and system stability, and confirmed the start and stop operation characteristics according to the sequence change.
At this time, the power reduction of the maximum 997.6kW occurred in the turbine according to the temperature change of the surface seawater, and it was confirmed that the power reduction rate increased at the point of dryness below 1(at 28.0 ℃).
In order to construct a control system by optimally applying the proportional value, integral value, and derivative value, the RPM control accuracy of the refrigerant pump and the reaction rate value were compared. Integral value 0.09min and derivative, which are control values with a low RPM accuracy of 2.45, were compared. The value 0.06min is 39S which is below average in terms of control responsiveness. Applying the integrated value 0.06min showing the responsiveness below average and the derivative value 0.08min applying the control system of OTEC with 33℃ reaction speed and accuracy of 2.73RPM The system safety was derived through.
The start of the OTEC shows a rapid increase in flow rate up to 110 kg/s, the maximum RPM flow rate of the pump at 600RPM as the initial refrigerant pump is started, and then decreases to the full flow rate after the valve at the turbine inlet is 100% open.
The shutdown process is stopped by a 30% reduction in flow rate and 50% output at the 10% point where the bypass valve is first opened, with the turbine inlet closure and the full opening of the bypass valve at 25% of the rated output.
Finally, the performance characteristics and economic feasibility of each region were compared for the commercialization of seawater temperature differential power generation.
Regional electricity sales generated approximately 8,487 thousand dollar in Kiribati, which had a high power cost of 0.327 $/kWh, and approximately 1,278 thousand dollar in lakes, generating 0.29 $/kWh.
With the supply of 50MW commercial plants, Australia and Kiribati have high net present values of $ 108,000 and $ 580,000, respectively, and their internal returns are more than 8.5% and 19.6%, respectively.
In this paper, we designed static and dynamic cycles for the construction of unmanned facilities and control system facilities of OTEC plants. In the future, a guideline for establishing a control system for a seawater thermal power plant was presented. In addition, it is expected to be used as basic data for the dissemination through economic analysis.