Abstract
Temperature is a key variable to evaluate the energy consumption and thermodynamic performance of traditional marine auxiliary machinery, chillers and piping systems. In particular, for the cryogenic storage tanks and fuel gas supply systems of LNG ships, explosion-proof and low-temperature-resistance properties bring new challenges to the onboard temperature measurement and monitoring. In order to promote the development of high-performance and safer monitoring systems for LNG ships, this paper adopted fiber Bragg grating (FBG) technology to ensure the measurement safety and accuracy of temperature sensors, and performs a series of experiments in a large temperature range on the chiller, pipeline, and cryogenic storage tank of an LNG ship and their long-term reliabilities. Firstly, the principle and composition of the designed FBG temperature sensors are introduced in detail, and the measurement accuracy and range of different metal-coated optical fibers were tested in a large temperature range and compared against the traditional thermistors. Then, the effects of different operating conditions of the LNG marine chiller system and cryogenic storage tank on the temperature measurements were investigated. In addition, the drift degrees of the optical fibers and industrial thermistors were analyzed to figure out their reliabilities for long-term temperature measurements. The results showed that for the long-period (16 months) monitoring of LNG ships in a large temperature range (105–315 K) under different shipping conditions, the optical temperature measurement based on FBG technology has sufficient accuracy and dynamic sensitivity with a higher safety than the traditional thermoelectric measurement. Besides, the ship vibration, ambient humidity, and great temperature changes have little impact on its measurement reliability and drifts. This research can provide references and technical supports to the performance testing systems of LNG ships and other relevant vessels with stricter safety standards.
Highlights
According to the statistics, 80% of the world’s freight is performed by ships
It can be seen that liquefied natural gas (LNG) power is undoubtedly the most effective alternative technology for petroleum ships in the field of ocean shipping or short-distance rivers [5,6]
Energy saving in ship cabins and auxiliary equipment is the most promising, direct, and effective way to save carbon emissions during the life cycle of ships
Summary
80% of the world’s freight is performed by ships. Convenient transportation has promoted the rapid development of shipping logistics, and brought the continuous increase in energy consumption during transportation [1,2]. Zhang et al [31] studied the temperature, strain, and humidity sensitivities of FBG using near-infrared low-loss multimode perfluorinated polymer fibers, and measured the corresponding linear displacements of Bragg wavelength All these studies are the applications at high or normal temperatures. The new optical fiber sensor has some basic applications in high temperature and low temperature, it is limited to the research and experimental development based on mechanism and numerical model, lacking of a long-term temperature measurement and drift stability test for the actual system. This paper conducts the long-term reliability temperature monitoring experiments for the LNG storage tank and chiller-piping system of LNG-powered ships based on FBG technology.
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