OCR Text |
Show the basket was open so that the gases could freely flow through it. The basket was moved in and out of the reactor by means of a 0.32-cm- OD (1/8 in.) stainless steel tube connected to the horizontal support bar. The reactor was exhausted to a venturi educator where the exhaust gases were mixed with air and then vented outside the building. This allowed the reactor to be operated at a slight negative pressure (e.g., 1 to 4 in. of H«0), and the samples could be inserted and removed from the reactor without requiring mechanical seals of any kind. Tests with an oxygen probe demonstrated that there was no back-flow of atmospheric air or in-leakage into the combustion zone. When samples were removed from the reactor, they were rapidly quenched with an argon purge. Reactor temperatures were measured with a chromel-alumel (type K) thermocouple located at the preheater exit and by chromel-alumel (type K) and platinum-platinum-rhodium (type S) thermocouples which were inserted into the sample position before and after each run. Thermocouples were also installed on the preheater and reactor tube walls. The type K thermocouple used for measuring reactor temperatures was shielded in stainless steel. The type S thermocouple was unshielded. Because of the different emissivities (about 0.85 for the type K, about 0.30 for the type S), the type K thermocouple gave consistently higher readings (as it was absorbing radiation from the walls) and more closely approximated the steady-state, unreacting particle temperature. The type S thermocouple more closely approximated the gas temperature. Particle temperatures were measured directly with thermocouples and also with a Leeds and Northrup Model 8622 optical pyrometer. The thermocouples were made from 10 mil wire and inserted into a groove which had been filed into the particle surface." During devolati-lization the particles became plastic and swelled, usually engulfing the thermocouple junction well within the char. The thermocouple We attempted to drill holes in the particles without success. They invariably cracked before a sufficiently large hole could be made. 13 |