The Build And Application Of The Reaction Network Model For Jetting Fluidized Bed Coal Gasifier

Coal gasification is the most promising technology in the field of coal clean and effective conversion, and is also the essential part of the coal-derived poly-generation system. As one of the most important coal gasification technology, jetting fluidized bed coal gasifier exhibits broad application prospects in China. Due to the difficulty in scaling up and operating steadily for a relatively long time, it is necessary to investigate the jetting fluidized bed coal gasification theory involving the mass transfer and reactor volume effects etc. Then, it will be possible for us to obtain how the syngas composition varies along with the operating parameters and scaling reactor volume. This work will contribute to design, optimize and scale up fetting fluidized bed gasifier in both theory and practice. A large number of experimental studies have proved that there are obvious flaws in the process of coal gasification study conducted by the traditional experimentation. Compared with the traditional experimental approaches, the mathematical model of jetting fluidized bed gasifier is a more convenient and effective method to explore its coal gasification reaction theory.Based on the hydrodynamics property of jetting fluidized bed and knowledge of reactor's burning zone and gasifying zone as well as divisions of reactor area, firstly CHEMKIN software is employed to establish a reactor network model of jetting fluidized bed coal gasifier. Model involves two-phase flow between materials, heat and mass transfer as well as coal gasification process in the environment of mixed gases of H2O, O2, N2, etc. Secondly, the gas compositions under different operating conditions are obtained based on the reactor network model, and the corresponding changeablerules are presented. Finally we attempt to explain how the reactor volume affects on jetting fluidized bed syngas composition, which will provide some instructive information for the fundamental research and the technical development of the jetting fluidized bed coal gasification technology, especially for ash-agglomerating fluidized bed gasifier.Based on the established reactor network model and the corresponding simulation and and analysis, the following conclusions can be acquired:1. We established a reactor network model of jetting fluidized bed coal gasifier, divided the gasifier reaction zone by introduced the jetting diameter and jetting depth as the theoretical basis, thus the more accurate regional reaction volume is obtained. The reactor network model can reflect the regional gasification reaction process in the gasifier, which is better than taking the gasifier as a whole (that is so-called"black box"theory).2. We consider more factors such as the heat loss carried by ash slag, furnace wall heat loss, the coal property, the quality of gasification agent in different inlet, the structure of the gasifier, and volume effects in the calculation process. The results indicate that the model is more equivalent with the actual jetting fluidized bed gasifier. This model is used to calculate the pilot plant of ash-agglomerating pressurized fluidized bed coal gasifier, and the calculated results are basically consistent with the experimental data. It is reasonable to say the model has some reliability to certain degree. It can be applied to predict the effects of operation parameters on gasifying characteristics of jetting fluidized bed gasifier and reflect the variation of the internal gas production.3. Results show that the jet region is one of the most critical factors affecting gas compositions and long-time steady operating for jetting coal gasifier. The oxygen feed rate into center nozzle and coal feed rate result in obvious changes of jet region. Within the calculation range, with the increase of oxygen feed rate into center nozzle, jet region increased nearly twice, temperature increased by 306K and high-temperature region moved up, material efficiency of carbon conversion rose from 68% to 97% (jet region temperature had exceeded ash melting temperature), and in generated gas, CO and H2O content changed obviously. CO content increases along with the increase of oxygen feed rate into nozzle, and mole fraction is 9.34%, 17.62% and 20.64% respectively; while H2O content decreases, mole fraction is 50.40%, 40.70% and 38.49% respectively. The change of the outlet gas composition from dense-phase region is the reason syngas changing. With the increase of coal processing capacity, jet region temperature decreased by 252K, the gasifier overall temperature decreased, and material efficiency of carbon conversion reduced from 98% to 74%. Dilute phase region has a great effect on effective gas composition in final products, especially H2 and H2O content. Under the three conditions, H2O content reduces, and mole fraction is 44.11%, 40.70% and 39.07% respectively; H2 mole fraction is 16.72%, 19.18% and 20.88% respectively.4. Based on the hydrodynamic likeness of jetting fluidized bed, two kinds of reactor enlarging, constant slenderness ratio and similar reactor hydrodynamic, are analyzed to compare the features of feeder material, residence time of coal particle and syngas composition. The results show that constant slenderness ratio enlarged reactor has longer residence time and better dynamical similarity, meanwhile give the outlet syngas composition in good agreement with original reactor.