A study of continuous lignite combustion in a spouted bed | |
| Author | Prasong Wongvicha |
| Call Number | AIT Diss. no. ET-92-3 |
| Subject(s) | Combustion Spouted bed processes |
| Note | A dissertation submitted in partial fulfillment of the requirement for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | A considerable amount of investigation on spouted bed combustion has been carried out in recent years. Most of the experimental tests have, however, focused on the feasibility evaluation of the technique. The few modelling works performed to date have been restricted to single particle or batchwise combustion. In this study a comprehensive model for char burning in a continuous spouted bed has been formulated. Essential informations related to modelling such as kinetic parameters for the char employed and char attrition rate are obtained from correlations developed from experiments. Finally, analysis of combustion efficiency under various conditions is performed. Kinetic parameters, the pre-exponential factor and the activation energy, of two types of lignite char, two types of lignite coke and electrode carbon have been experimentally determined based on the Semenov' s thermal ignition theory adopted to single coal ignition. Two approaches were employed for searching ignition point: ihe Thermogravimetric analysis (TGA) and the digital controller furnace. The TOA in this study, however, failed to provide required information, presumably due to oxidation before ignition could really occur. Attrition of fuel particles during combustion has been studied experimentally under variation of spouting gas velocity, bed temperature, and feed size. Experimental data obtained were used to generate a representative correlation for attrition rate and particle shrinkage rate. The Attrition _rate constant was found to be slightly dependent on the operating bed temperature. Its value was found to be 4 - 6 times higher than that reported for fluidized beds. A simulation model of continuous lignite char combustion in a spouted bed has been developed; the model can predict bed oxygen concentrations, bed char particle size distribution function, bed carbon loading, mean diameter of bed char, and the fractional contributions of combustion in spout, annulus, and fountain. The approach involves taking into account the spouted bed hydrodynamics, a burning law for individual particles, and the combined mass balances for bed char and oxygen in the three typical regions of the bed. The mean particle shrinkage rate due to combustion is taken as the weighted average of the individual shrinkage rates owing to combustion in spout, annulus, or fountain and the respective fractional residence time in these regions. The distribution of bed fuel particles was obtained from the mean particle shrinkage rate and provides necessary information for gas phase oxygen balance done over small strips divided ii along the bed height, beginning from the bottom in spout and annulus and fountain. The reliability of the model is tested by comparing with experimental measurements on size distribution function, mean diameter of bed char, and bed carbon loading. The results of Thai lignite char combustion have been expressed as combustion efficiency and losses under different operating conditions. The combustion efficiency was 89 - 98.5 % for feed particle size ranging from 2 - 4 mm with excess air ranging from 107 - 185 %. The operating bed temperature had a strong influence on the combustion efficiency. |
| Year | 1992 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Energy Technology (ET) |
| Chairperson(s) | Bhattacharya, Sribas C. |
| Examination Committee(s) | Mora, Jean-Claude ;Chongrak Polprasert ;Luengo, Carlos A. |
| Scholarship Donor(s) | The Government of Japan ; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1992 |