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Combustion of natural gas in a turbulent fluidized-bed reactor

Posted on:1999-09-03Degree:Ph.DType:Dissertation
University:Ecole Polytechnique, Montreal (Canada)Candidate:Sotudeh Gharebaagh, RahmatFull Text:PDF
GTID:1462390014469189Subject:Engineering
Abstract/Summary:
Combustion of natural gas in fluidized bed reactors emerges as a promising technology for heat generation, waste-to-energy applications by low calorific fuel upgrading and also can be considered as an excellent example of highly exothermic reactions. Effective handling of highly exothermic chemical reactions in these reactors has made the fluidized bed technology gain a high rate of application in petroleum and petrochemical industry. Combustion of natural gas in a turbulent bed reactor can be carried out at temperatures well below 1000°C and hence capable of meeting all environmental requirements such as CO and NOx emission levels.; The main objective of present study is to assess the feasibility of high temperature combustion of natural gas in turbulent fluidized bed reactors of inert particles. Specific objectives are as follows: to evaluate the combustion behaviour of inert particles and to determine the reaction scheme; to determine the appropriate hydrodynamic regime of fluidization and combustion mode for natural gas combustion; to characterize gas sparger hydrodynamics and mixing; to predict the reactor performance by coupling the kinetics and the hydrodynamics.; The kinetic evaluation of inert particles was achieved by studying the combustion of a lean mixture of methane in a fixed bed reactor of inert particles. The experimental data obtained in this way shows the accelerating catalytic effect of inert particles is quite small. In addition, the inhibition effect is considerably higher at moderately high temperatures (<850°C) and it may be neglected at high temperatures well above 1000°C.; The appropriate hydrodynamic regime of fluidization was determined by promoting natural gas combustion in bubbling and turbulent fluidization regimes at relatively high temperatures (800--1000°C). The experimental results show that the fluidized bed reactors offer excellent thermal, uniformity and temperature control. Furthermore, the power generated by the turbulent fluidization regime is much higher than that for bubbling fluidized bed reactors while respecting all environmental requirements.; In order to understand the non-premixed combustion, the sparger hydrodynamics were extensively studied using FCC and sand particles. The aim was to characterize different discharge modes, bubbling and jetting conditions around the sparger using a pressure measurement technique, mixing and reaction studies. For industrial scale reactors, the dominant discharge mode is the bubbling conditions around the sparger. Under these considerations, experimental studies show that the bubbles tend to retain their identity. Under jetting conditions, a highly turbulent area may be formed around the sparger leading to high degree of attrition. Due to the large industrial impact of bubbling conditions, the radial and axial dispersion of gas in a hot fluidized bed reactor of 20-cm diameter of FCC and sand particles was investigated using a gas chromatography with CH4 or CO2 as tracers. The effect of sparger configuration and particle size was also investigated.; The ultimate step consisted of building a mathematical model in order to simulate the performance of the reactor by combining a reduced natural gas combustion mechanism and bed-sparger hydrodynamics model. The model predicts reasonably the experimental data, explaining the reactions as well as hydrodynamic effects. (Abstract shortened by UMI.)...
Keywords/Search Tags:Natural gas, Combustion, Bed, Fluidized, Turbulent, Inert particles, Experimental
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