This paper details the findings of a study conducted to evaluate the performance of a newly developed spray applied Insulation System (Ins-X) as well as an existing Composite Blanket Cladded Insulation System (Ins-Y) for cold service (cryogenic) applications such as that encountered in Pentane/LPG (liquified petroleum gas) storage. One of the options to assess the insulative property of candidate insulation system materials is to measure the thermal gradient or the temperature difference (ΔT) between the inner and outer surface of the insulated storage container. The lower the value of ΔT the better the quality of the insulation system.
Currently there is no standard laboratory method to make such ΔT measurements under simulated field cryogenic conditions. For this study, a novel laboratory test technique and apparatus was developed to simulate low temperature cycling (–6.7, –12.2, –17.8 and –23°C) encountered in Pentane/LPG storage steel spheres. The ΔT between the cooled inner surface and the insulated outer surface of steel panels was measured at different thicknesses of the insulation systems and steel panel thicknesses of 1.91 and 2.54 cm. The new apparatus was found to provide an elegant and reproducible method of making ΔT measurements in the laboratory under simulated field conditions for assessing the quality and performance of insulation systems for cryogenic service.
Cryogenic vessels are specifically designed to store cryogenic liquids at very low temperatures, such as –196 °C for liquid N2, –252 °C for liquid H2, –160° C for LNG (liquified natural gas), etc. In case of Pentane/LPG (liquified petroleum gas), though the temperature is higher in the range of –7 to –23° C, cryogenic steel spherical vessels are used for storage as shown in Figure 1.
The large temperature difference between the internal cryogenic liquid and the external environment causes an extremely strong heat transfer between the two, which must be prevented by the thermal insulation material to ensure secure storage of the cryogenic liquid1. Without a good insulation structure, a large amount of the stored liquid (e.g., liquid H2, or liquid N2) will inevitably escape from the cryogenic tank2. Reducing the heat leakage from cryogenic vessels has been studied by focusing on the insulation materials and structure of the vessels and the thermal insulation performance of different materials have been studied by various researchers3-5.
