Microwave-Induced Pyrolysis of Biomass Waste
Date Issued
2010
Date
2010
Author(s)
Huang, Yu-Fong
Abstract
This study utilized the microwave irradiation of single (focused) mode to induce the pyrolysis of biomass waste. Thus products with high heating values or economic worth can be obtained. In this study, rice straw was chosen to be the primary researching target. Some other common biomass waste was also researched for the purpose of results comparison. The increase of microwave power helped to promote the heating rate and maximal temperature of pyrolysis, so higher mass reduction ratio of feedstock can be achieved. Thus by applying higher microwave power, it is expectable that the irradiation time of microwave can be shortened. Besides, particle size of feedstock affected the reaction performance as well. This might imply that the smaller feedstock had the higher bulk density and the more contact area between particles. Therefore, the heat transfer inside the feedstock was enhanced, and the entire pyrolysis reaction turned to be more rapid.
By the results of specific surface area analysis and zeta potential analysis, it is expectable that the solid product (char) can be applied in the cation adsorption in the water and wastewater treatment. The result of copper adsorption experiment shows that, even under the acidic condition (pH 5), the adsorption removal rate of copper can be over 90%. The primary components of gas product (fuel gas) were hydrogen, carbon dioxide, carbon monoxide, and methane. The hydrogen content (50.67 vol.%) of the gas product was higher than of traditional pyrolysis (25 vol.%). Thus the technology of microwave-induced pyrolysis shall have the high potential to produce hydrogen-rich fuel gas. According to the result of quantitative analysis of gas product, stoichiometric analysis was also executed to conclude to a nearly balanced chemical equation. There were mainly three categories of compounds in the liquid product (tar): (1) long-chained aliphatic compounds; (2) polar compounds (e.g., phenol and its derivatives); (3) low-ringed polycyclic aromatic hydrocarbons (PAHs). The liquid product shall be low poisonous due to the low content of PAHs and their low ring numbers. The gravimetric percentages of gas, solid, and liquid product were 54.31 wt.%, 28.07 wt.%, and 17.62 wt.%, respectively. Over half of rice straw sample can be converted into gas product. This result is also better than the traditional manner of pyrolysis.
This study also researched relevant characteristics of rice straw, rice husks, corn leaves, coffee hulls, bamboo leaves, sugarcane bagasse, sugarcane peel, hemicellulose, cellulose, and lignin by means of thermal analysis-mass spectrometry (TA-MS) experiments. The result showed that the primary production of gas product occurred during the highest mass-loss rate of biomass waste. However, there was also an obvious production of hydrogen at higher temperatures (667-749 °C). From the semi-quantitative analysis of hydrogen content, both rice husks and bamboo leaves had lower hydrogen production, and coffee hulls had the most. The pyrolysis of biomass waste was assumed to be pseudo first-order reaction, and the Arrhenius equation was applied to the analysis of chemical kinetics. The activation energy and frequency factor of biomass waste differed a lot from each other, and showed an inverse proportion. This might be due to the difference among the contents of biomass waste. Besides, the reaction rate constants of biomass waste did not differ much, which was about one order at the most. This might be the reason why there was an inverse relationship between the frequency factor and the effective collision probability.
The gas product of microwave-induced pyrolysis of rice straw can be effectively generated under microwave power of 300 W, and the maximal reaction temperature can be reached in 10 minutes. Under this condition, the total heating value of the gas product was about 29.34 % of input energy needed. This percentage can be increased to about 57 % when adding heating values of the solid and liquid product. Therefore, in the microwave-induced pyrolysis, there was about 43 % of input energy that might be used for microwaves generation or extra energy consumption due to reflectional microwave power.
The technology feasibility of microwave-induced pyrolysis was assessed by SWOT analysis. The result shows that inner factors of technology maturity, performance, quality and quantity of products, and outer factors such as government policy, economy and energy, are most important for the feasibility. The promotion of microwave-induced pyrolysis should start with enhancement of technology productivity and performance to raise its competitiveness, and try to expand suitable market to increase its visibility and market proportion. According to the international and domestic energy situation and policy direction so far, the demand of renewable energy shall keep increasing. However, there are so many technologies relevant to renewable energy. It is believed that to maximize advantages and to minimize disadvantages of microwave-induced pyrolysis are best policies to make it more favorable.
Subjects
microwave-induced pyrolysis
biomass waste
char
tar
fuel gas
hydrogen
SDGs
Type
thesis
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