Analysis, modeling, and control of a commercial-scale downdraft gasifier.
详细信息
- 作者：Chee ; Chia Shian.
- 学历：Doctor
- 年：1990
- 毕业院校：Kansas State University
- 专业：Engineering, Agricultural.;Engineering, Chemical.;Artificial Intelligence.;Computer Science.
- CBH：9108398
- Country：USA
- 语种：English
- FileSize：9290593
- Pages：335
文摘
Even though downdraft gasification has been practiced for more than a century, the complex process is not well understood due to the lack of comprehensive engineering analysis. It has not been until recently that analyses of the primary operating parameters influencing the gasifier performance have been reported. This dissertation investigates three aspects of wood chip-air gasification in a 0.6-m commercial-scale downdraft gasifier; the analysis of some secondary operating parameters, fluid mechanical modeling, and control development.;Systematic experiments have ben conducted to investigate the influence of three secondary operating parameters on the gasifier performance; these include the tuyere air flow, grate flow area, and tree species. Results have shown that normal aspiration of tuyeres yielded the optimal performance while the grate flow area could be reduced significantly without decreasing the throughput. Tree species variation confirmed that chips with a higher wood internal porosity produce a lower char yield.;Two analyses related to the fluid mechanical modeling have been performed; they concern the evaluation of the irregularity of the char particles and the examination of the axial pressure and temperature profiles. The former employ the concept of fractals for determining a perimeter fractal dimension, d$\sb{\rm PF}$, capable of assessing the ruggedness of the char perimeter; the latter locate the various gasifier zones as well as identify the segments of appreciable flow resistance. The low d$\sb{\rm PF}$ indicated a relatively smooth char perimeter; thus, no consideration of the shape irregularity in the development of fluid mechanical model is needed. Furthermore, analyses of the pressure profiles have identified three consecutive segments of appreciable flow resistance: the tuyere, char, and grate segments. This analysis has permitted the establishment of a fluid mechanical model for the gasifier through the segmental application of the Ergun equation; the validity of this model has been verified experimentally for a wide range of operating conditions.;Finally, a methodology for self-generating fuzzy IF-THEN rules for controlling the energy output rate of the gasifier has been developed. The resultant rules have been shown to be in accordance with those derived statistically. Moreover, a simple expert system has been constructed for advising an operator on appropriate conditions necessary to achieve a specified gasifier performance.