Physical treatments for reducing biomass ash and effect of ash content on pyrolysis products
Type of DegreeMaster's Thesis
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There is increasing concern of greenhouse gas effect and the depletion of fossil fuels. Different renewable energy sources such as hydro, wind, solar have been considered as a potential replacement for fossil fuel. Bio-energy, energy produced from biological component such as animal and plant products, is one of the renewable energy that is extensively being researched around the globe. Biofuels produced from woody biomass is largely affected by its properties such as moisture content, ash content, heating value and particle size. Woody biomass is pretreated and preprocessed such that the resulting properties best suit the conversion process. Soil particles, also known as detrital ash lowers, energy value of biomass and its thermochemical conversion process into products. This study aims to reduce the amount of soil contaminants in woody biomass and study the effect of ash content on pyrolysis products. Vibratory sieve shaker, hammer mill, and mixer were selected as the physical treatment processes used to remove soil particles from surface of woodchips and thereby reducing the ash content. Vibratory sieve shaker produces vibratory force, mixer generates rotary motion as a result woodchips collide with each other which can separate the soil particles form the woodchips. Hammer mill breaks the woodchips by beating action of the hammer, and the impact force generated can separate the dirt particles from the woodchips. The treatments were tested on (i) sweetgum, (ii) residual pinewood, (iii) whole pinewood, and (iv) dirty pinewood that were at different levels of ash and moisture contents. The ash and moisture contents of dirty pinewood was maintained at required levels by adding calculated amount of soil and water. All of the three treatment processes significantly reduced (p<0.05) the ash content of the whole pinewood, residual pinewood and sweetgum that had initial ash contents of about 2%. Mixer reduced the ash content of sweetgum, whole pinewood and residual pinewood from 2.14%, 2.31% and 1.69% to 1.71%, 1.73% and 1.20%, respectively. Similarly vibratory sieve shaker reduced the ash content to 1.66%, 1.90% and 1.24%. However, the hammer mill treatment was more efficient in reducing the ash content for pinewood with higher ash content (>5%) significantly compared to other two process. The ash content of pinewood with initial ash content of 6.64%, 8.34% and 10.40% was reduced to 1.88%, 3.36% and 3.15%, respectively by hammer mill treatment. The reduction in ash content resulted into increases in volatile matter and heating value of the treated biomass. Ash reduction rate was highest at 10% moisture content for samples treated with vibratory sieve shaker and with mixer. Hammer mill significantly reduced ash content at different moisture content level but no significance reduction between different moisture contents was observed. Pyrolysis was carried on the woodchips at ash contents 0.56%, 1.16%, 2.77%, 4.40%, 6.87%, 8.35% and 15.52% to understand the effect of ash reduction from physical treatments. Increasing ash content of biomass decreased the volatile matter, carbon and hydrogen contents of biomass thereby reducing bio-oil yield reduced from 47.09 % to 26.28 %. The water content and ash content of bio-oil increased with increase in ash content of biomass. The carbon and hydrogen content of the bio-char decreased with the increase in the ash content of the biomass. Furthermore, the ash content of the bio-char increased which resulted in the decrease of heating value of the bio-char.