Clean combustion of natural gas in a turbulent fluidized bed reactor

Fluidized bed technology has gained in recent years a high rate of use in petrochemical industry, in heat generation, in solid wastes minimization, etc ... However, its potential as a zero {dollar}NOsb{lcub}x{rcub}{dollar} and CO emission technology for a clean combustion of natural gas remains untapped. The catalytic combustion of natural gas can be carried out at low temperatures to generate a clean and hot air for foodstuff or for domestic (building heating) use if the size of the combustor is reasonable.; The aim of this work was to carry out the feasibility study of the catalytic combustion of natural gas in a fluidized bed as a zero {dollar}NOsb{lcub}x{rcub}{dollar} and CO emission technology. A four-step methodology was used: (1) determination of the appropriate hydrodynamic regime of fluidization, (2) kinetic evaluation of the appropriate catalyst, (3) characterization of the bed hydrodynamics, (4) combustion in the fluidized bed and prediction of the reactor performance by coupling the kinetics and the hydrodynamics.; The results of the simulations with this algorithm clearly indicated the necessity to operate in the turbulent regime in order to achieve 100% conversion while generating a substantial power of combustion (50-500 kW). A pilot scale catalytic combustor of 100mm I.D. and 1.6 m tall was then designed and built. It was equipped for the hydrodynamic studies with a differential pressure transducer used to monitor pressure fluctuations and N aI (Tl) scintillation detectors used to monitor the radioactive gas tracer during residence time distribution (RTD) measurements.; The kinetic parameters of two catalysts with platinum (PSA) and with palladium (PC263) all from Procatalyse was evaluated in a tubular flow reactor of 7 mm in diameter at atmospheric conditions and in the temperature range of 400-600{dollar}spcirc C{dollar}. Their ignition temperature was 310{dollar}spcirc C{dollar} for the PSA and 275{dollar}spcirc C{dollar} for the PC263. Methane concentration was kept below 4% and a first order kinetic model was used to fit the data obtained over a wide range of gas residence times.; The RTD measurements were performed with {dollar}sp{lcub}41{rcub}Ar{dollar} as the radioactive tracer obtained by irradiation of {dollar}sp{lcub}40{rcub}Ar{dollar} in a Slowpoke nuclear reactor. The axial gas dispersion coefficient was derived from the responses recorded by two scintillion detectors as the result of an imperfect input injection below the porous distributor at various gas velocities, and with three different particles (FCC, sand, {dollar}PC263{dollar} catalyst).; The ultimate step consisted of carrying out the combustion of methane in the turbulent regime over the {dollar}PC263{dollar} catalyst in the 100 mm I.D. reactor. The conversion of methane obtained in this regime was higher than the conversion observed in the bubbling regime at similar number of reaction units and a simple plug flow model with axial dispersion was used to model our experimental data obtained between 450 and 500{dollar}spcirc C{dollar}. A perfect mixing model satisfactorily predicted the bubbling bed data.