Thorough examination of the gas line The production unit uses cooling from liquid nitrogen to freeze the starter culture – for yogurt, for example. But the pelletizer never seemed to be getting enough liquid nitrogen. It was impossible to achieve stable process control; several people had to constantly watch it and also intervene frequently. To troubleshoot the problem, the experts from Messer first inspected the 70-meter nitrogen line between the gas tank and the unit. “Together with the customer, we carefully examined the entire nitrogen supply line and documented all suboptimal points of the installation,” explains Frank Gockel. “At first glance, we could see that some sections of the piping were not insulated. To a layperson, two meters of exposed pipe might seem harmless – surely that can’t matter much? To us, however, it was immediately clear that this had to be causing some of the inefficiency. The liquid nitrogen flows through the line at a temperature of less than -180 degrees Celsius. So, at a normal ambient temperature in the hall, there’s a temperature gradient of about 200 degrees. Without insulation, the gas absorbs enough heat along a two-meter section to partially vaporize in the pipe. Even if this effect involves a small quantity of nitrogen, it results in a tremendous expansion of the volume. When the gaseous nitrogen then takes up half of the total volume in the pipeline, there’s not enough liquid nitrogen available at the other end.