Comparison of Wall-Temperatures of Two Types of Large Capacity Cylinders for Tube Trailers During CNG Loading Processes

Tube trailers with large capacity gas cylinders have been widely used to deliver compressed natural gas (CNG) in China in recent years. Most of the large capacity cylinders are full steel cylinders (Type CNG-1), and the tube trailers with large capacity glass fiber hoop-wrapped composite cylinders with steel liners (Type CNG-2) have entered into Chinese market since 2011. The tube trailers with CNG-2 cylinders can carry more gases than those with CNG-1 cylinders, but need more loading and cooling time to control their wall-temperatures according to the experiences of on-site operators in gas stations. In this paper, the wall-temperatures of those two types of large capacity cylinders on two tube trailers have been tested using a thermal infrared imaging camera during CNG loading processes in two natural gas stations in China. And numerical simulation on the CNG loading processes has been carried out to investigate the temperature changes of the gases and the shells of the cylinders. The results show that CNG-2 cylinders can have less maximum temperatures of the gases and the shells and less wall-temperature increments at the cost of lower loading rate and longer loading time.