Design and performance test of shipboard scallops fresh-keeping system based on bottom cold seawater

Abstract: Most of Dalian Zhangzidao sea area is influenced by the Yellow Sea cold water mass, which has the characteristics of low temperature and high salt. By analyzing and investigating the refrigeration and fresh-keeping mode of fishing vessels and the cold water mass of the working sea area, a new type of high efficiency fresh-keeping and energy-saving mode was designed. In this mode, the bottom cold seawater is pumped into vessels to be used for freshness of Patinopecten yessoensis when transporting them or fishing for them. A test was be made to prove that the mode is reasonable.The research showed that scallops (Patinopecten yessoensis) with an average shell length: (11±2) cm and an average mass: (10±10) g were collected from the Dalian Zhangzidao sea area. Seawater was pumped from -1m and -25m depths of the Dalian Zhangzidao sea area to be used as experimental seawater. The design mode which was used to pump the bottom cold seawater was installed in the Liao Chang Yu Yun18009 transport ship. The experiment was conducted in ten areas and lasted four months. An insulation board which was 200 mm thickness was used to separate living seawater cabin in three test cabins. Each cabin capacity was 8m3, 80 boxes (510 mm×360 mm×265 mm) per cabin and 15 kg scallops per box. The seawater of -1m depth was pumped to cover the fresh scallops in the first cabin. The second cabin, which had-1m surface seawater 6h put inside in advance, was connected to a refrigeration device. Then the seawater was refrigerated for 6~8 hours until the temperature had gone down to 10-15℃. The -25 m depth seawater was pumped over fresh scallops in the third cabin with no need to refrigerate. Ten boxes were randomly selected from three cabins and checked for the rates of outer mantle shrink and mortality of the scallops after seven hours.The results showed that -1m surface seawater fresh-keeping scallops is less effective and that the resulting outer mantle shrink and mortality of scallops are serious and represent a trend from June to September. The effect of pumping -25m seawater on fresh scallops is better than refrigeration in June, and not significantly different from refrigeration from July to September. Total energy consumption from pumping-25m bottom seawater is 80kW.h on fresh scallops, but refrigerating surface seawater needs 1923.2 kW·h. The consumption of energy from refrigeration is about 24 times greater than that of pumping bottom seawater. Installation of a refrigeration unit costs about ninety thousand yuan, but installation of the mode of pumping bottom seawater requires fifteen thousand yuan. The cost of installing a refrigeration unit is six times greater than the cost of a device for pumping bottom seawater.Pumping bottom seawater to fresh can improve the vividness of scallops. It also has advantages in only requiring a small investment, providing an easy transformation and energy saving. Basically, transformation takes up less space for a scallops capture ship which is cabin restricted and unable to set up an efficient refrigeration unit. A scallop refrigerated carrier can take full advantage of the cold water mass to keep scallops fresh. It is able to significantly reduce energy consumption, and ensure the scallops vividness. This method meets the development needs of green industry.