الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
 |  | from | 224 |  |  |
| | | from | 224 | | |
Abstract
This thesis presents an experimental and numerical assessment of sawdust gasification in a fluidized bed. In the experimental part, a series of experiments were performed on sawdust pellets using air as an agent in a reactor column of 105mm inner diameter and 3500mm height. The sawdust pellets were about 5mm in diameter and 40-50mm in length. A mathematical model has been developed to simulate the gasification process, by integrating a pyrolysis sub-model with the hydrodynamic kinetic model. This model was used to study the effects of various operating parameters such as temperature, agent type, hydrodynamic parameters, and fuel type on the gasification performance, tar yields, and syngas composition. The model was tested using air/steam and air/steam/CO2 mixtures as agents. A comparative study was performed on different biomass feedstocks using the current model with previously published experimental results. The feedstocks used in this study include Napier Grass, Portuguese Peach Stone, Chinese Coal/rice straw, solid waste wood, rice straw and olive kernels. The experimental results showed that the content of H2 in the produce syngas increases with reactor temperature, while the tar, CO, and CH4 contents decrease. The results also showed that the low heating value (LHV) reached a peak value of 4.51MJ/Nm3 at 900°C and an equivalence ratio (ER) of 0.35. The maximum value of cold gas efficiency was 70.03% at ER=0.35 and 900ºC. The simulation results showed that, in the case of using air/steam mixture as an agent, the optimum heating value of sawdust gasification reached 4.8MJ/Nm3 at 900°C, ER=0.35, and SFR=1. In the case of using air/steam/CO2 mixture as an agent, the higher heating value was 6.75MJ/Nm3 at 900°C, ER=0.4, SFR=1, and CO2_R=1. The results of a comparative study on different feedstocks showed that the moisture content in the biomass fuel affect the syngas concentrations. The lower ratio of H/C in the biomass ultimate analysis gives a greater heating value, as well as more concentrations of CO and CO2. It was also shown in the case of using waste wood and rice straw feedstocks, a significant increase occurs in the carbon monoxide concentrations from 9% to 19% and in the carbon dioxide concentrations from 25% to 33.1%. Due to the higher values of the C/O ratio in their ultimate analysis. The fixed carbon and volatile matters in the proximate analysis of feedstock affect strongly the produced gas concentrations; as a result, it’s LHV. The model results were generally in good agreement with experimental results. The maximum difference between the model results and experimental results in case of low heating value calculation within the range of ±10.2 %. An economic study was performed to explore the syngas production benefits using different agents and different biomass fuels. The results showed that, in the case of using sawdust pellets and air as an agent, the production cost of syngas was lower than the price of natural gas by 6.3%. While the price in the case of using air/steam mixture as well as the mixture of air/steam/CO2 was cheaper than natural gas by 12.9% and 38.1%, respectively. The production cost in the case of using solid wood, rice straw, and olive kernels was lower than natural gas by 30.9%, 47.15%, and 56.1%, respectively.