A flow microreactor was employed to perform CTO (Constant Temperature Oxidation) tests in order to evaluate the kinetic parameters. A scheme of the reactor and of the ancillary apparatuses is reported in Fig. 2. The microreactor comprises a 300 mm height, 20 mm I. D. quartz tubular flow reactor, heated by an electrical furnace. A programmer – controller (ASCON) controlled the reactor temperature. Cylinder air and nitrogen (99.999 % purity) were mixed downstream of mass flow controllers (HI-TECH) for obtaining different oxygen partial pressures in the gas entering the reactor. HARTMANN & BRAUN continuous analysers determined exhaust gas concentrations: URAS 10E (for carbon monoxide and carbon dioxide) and MAGNOS 6G (for oxygen). Signals from the analysers were sent to a personal computer for data processing.
Samples to be tested were diluted with 180-350 pm quartz particles at a reacting matter to quartz mass ratio of 0.01 to avoid local rises of temperature during the tests. The diluted mixture was loaded to the reactor filling about 3 cm in length of its central zone. The remaining part of the reactor was filled with 700-2000 pm quartz particles. The test started raising the temperature to the desired value in nitrogen flow. Then the gas feed to the reactor was turned to the air stream starting the oxidation. Carbon bum-off was followed by monitoring, through the continuous analysers URAS 10E, the carbon mono and dioxide produced during gasification. Carbon mass balance was verified within 5% tolerance range for all tests. Kinetic experiments were carried out under constant operating conditions.
Fig. 2. Scheme of the flow reactor apparatus.
In all the mns parameters were kept at values such to allow the reactor working under differential conditions. The feeding gas flow rate was 500 cm3/min (STP). Operating pressure was 101 kPa. The temperature was investigated in the ranges 673-823 K. The initial mass of the sample was in the range 5-15 mg.