A LDPE (Low Density Polyethylene) factory consist of a 2-3 km tubular reactor, operating at high pressure (> 2500 bar) and rather high temperature (200-300°C). Raw material used in the process is ethylene and different co-monomers. The tube is divided into zones in which oxygen compounds are injected to form free radicals and thereby initiate the polymerization. Today, only pressure and temperature are measured, but other interesting parameters to measure would be parameters like; ratio between polyethylene (produced product) and ethylene gas (solid/gas ratio), gas composition, distribution of the injected oxygen compound and more.
Along the reactor there are special mechanical couplings, allowing connections of temperature- and pressure sensors used for the online measurements. Other sensors, requiring direct contact with the medium, could be installed in a similar manner. If measurements are done from outside of the reactor, it must be able to penetrate the 30 mm thick tube wall.