Production of fuels and chemicals from a solar driven pyrolysis of animal and agricultural wastes
thesisposted on 28.03.2022, 17:14 authored by Haftom Weldekidan
Energy is very important in meeting our basic needs. It is also one of the fundamental requirements in the industrial, transportation and agricultural sectors which determine the overall economic development of nations. In this work pyrolysis of different types of wastes, mainly chicken litter and rice husk, was performed at different heating rates and ranges of temperature obtained from a concentrated solar radiation. Review of solar based technologies and their applications to solar-assisted biomass utilization and conversion technologies were performed to identify the gaps and study the type of bio-fuels that can be produced from solar driven biomass pyrolysis. Prospective solar concentrators were assessed for their efficiency, maximum temperature and applications. Based on the information obtained from the literature and the gaps identified in the review, parabolic dish was selected as a prospective solar concentrator that can achieve higher temperatures at relatively better concentration ratio. Thus a parabolic dish of 1.8 m aperture diameter and a focal length at 0.655 m was designed and manufactured at Macquarie University. The dish was laminated with an 88% reflective aluminium polyethylene terephthalate (PET) and mounted on a rotating structure for adjusting the height and azimuth angles of the sun. Experiments were conducted to measure the maximum achievable temperature and select reactors from different types of materials which should be placed at the focal region. Quartz glass and stainless steel tubes were the best performing reactors, achieving maximum temperature of 1100°C at 900 to 1000 W/m². The feedstock (chicken litter and rice husk) were collected from Carlingford, Sydney then dried and crushed to a sieve size of 280 μm and then packed separately in the quartz glass reactor for the solar pyrolysis experiments which were conducted at different solar temperatures (500 to 900°C). Gases were the main products obtained from the pyrolysis of the chicken-litter waste, generated in the range of 45-59 wt% followed by bio-char (16-40 wt%) and bio-oils (14-36 wt%). The pyrolysis gas was composed of CO2, CO, CH4, H2 and other light weight hydrocarbons, while the bio-oils which contained phenols, acids and N-containing compounds can be applied to produce solvents, cleaning agents, paint removers, detergents as well as in the synthesis of dyes, aspirin and plastics. Bio-oil and bio-char were the dominant yields in solar pyrolysis, reaching up to 44 wt.% and 43 wt.%, respectively. The bio-char had large glass-like cylindrical holes with many porous and loose structures which are the required properties for the bio-char to be a candidate material for contaminant adsorbent in waste water treatment. The quality of the solar pyrolysis products was further upgraded using CaO and char catalysts. The catalysts were separately applied in different proportions in an in-situ and ex-situ modes with the chicken litter, and subjected to the solar pyrolysis at 500 to 800°C. In all cases there was substantial decrease in CO2 accompanied by an increase in the formation of CO from 10 to 63 wt% and H2 from 1 to 15 wt%. Similarly, addition of CaO exhibited considerable deoxygenation performance of the fatty acids up to 3%. Solar pyrolysis experiments performed on the chicken litter and rice husk biomass at higher temperatures (800 to 1600°C) and heating rates (10 to 500°C/min) produced highly combustible gases with higher heating values of 7255 ± 566 kJ/kg. Overall, the obtained results revealed that solar-assisted pyrolysis of biomass could be a promising technology for fuel and chemical production.