200ton급 선망운반선의 해수냉각시스템 성능분석

Abstract

The purse seine is a way of catching the catches with net at night. However, in Korea most of these offshore fishing boats are aging. The transport vessels of these purse seine serve to transport catches. Crushed ice is mostly used for cooling the fish hold tank of Korean carriers. Conventional crushed ice causes problems such as sharp crystals, poor catch quality due to salinity and temperature changes, and high purchase cost and weight. The seawater cooling system proposed in this paper supplies the cooled seawater to the fish hold tank through the direct cooling of the seawater. Therefore, by introducing a seawater cooling system that directly cools seawater, it is possible to improve the problem of the ice-cold cooling method using crushed ice and to expect catches of high value-added. In this paper, performance of seawater cooling system was analyzed by installing an experimental device on the land before installing the seawater cooling system on the ship. Based on the above performance analysis on land, the seawater cooling system was designed and manufactured, and the performance was analyzed after installation on the 200ton class fishing carrier. In addition, the results were compared with the results of the performance analysis on land and the field operation performance analysis. Through the results, the economic feasibility of the system was analyzed and the applicability, technical feasibility, and economic feasibility of the seawater cooling system were examined. In order to select material of the heat transfer tube of the flooded-type evaporator, the experimental apparatus was manufactured prior to the manufacture of the experimental apparatus on land. Experimental results confirmed the heat transfer performance according to the material of the heat transfer tube. The experiment was carried out with the evaporation temperature and the incoming seawater temperature as variables. As a result, Al-brass was higher heat transfer efficient than titanium, Co-nickel, and 26 fpi fin was higher heat transfer efficient than 19 fpi fin. The performance of the seawater cooling system manufactured based on above result was measured at 1 ℃ intervals from 27 ~ 32 ℃ at the seawater inlet temperature in condenser. As the seawater inlet temperature increases, the performance decrease was confirmed, and COP 3.58 ~ 3.34 was confirmed. After the installation of the seawater cooling system with the same specifications as the seawater cooling system used in the experiment, the system performance was confirmed to be reduced by about 23% compared to the land experiment. The reason for the decrease in performance is due to the low specific heat from seawater, the pressure loss due to the longer piping, the difference in operating methods in the field operation, the increase in the flow rate and the size of the fish hold tank. As a result of economic analysis based on these results, payback period was 6.7 years, social discount rate 4.5%, net present value of about 300 million KRW, internal rate of return 14.6%, and benefit cost ratio 1.46 in installing in the original fishing carrier. When installing in the new fishing carrier, the payback period is 4 years and the social discount rate is 4.5%, with net present value of KRW 430 million, internal rate of return of 25.6%, and benefit cost ratio of 1.46. In both cases, therefore, the internal rate of return was higher than the social discount rate of 4.5% and the benefit cost ratio was higher than 1, indicating that the system was economic.