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Waste to Energy Conversion of Chicken Litter through Solar-Driven Pyrolysis Process Haftom Weldekidan, Vladimir Strezov, Tao Kan, and Graham Town Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02977 • Publication Date (Web): 29 Nov 2017 Downloaded from http://pubs.acs.org on December 1, 2017
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Energy & Fuels
Waste to Energy Conversion of Chicken Litter through Solar-Driven Pyrolysis Process Haftom Weldekidan1, Vladimir Strezov1, Tao Kan1*, and Graham Town2 1
Department of Environmental Sciences, Macquarie University, Sydney, NSW 2109, Australia
2
Department of Engineering, Macquarie University, Sydney, NSW2109, Australia
* Email:
[email protected] Abstract: Application of solar energy for biomass pyrolysis is a promising technology for converting biomass to energy, fuels and other chemical substances with neutral CO2 emissions. Compared to the conventional pyrolysis process, the biomass conversion efficiency can be greatly improved if the pyrolysis heat is supplied from a concentrated solar system which can be achieved at reasonably moderate solar radiations. This paper discusses fast pyrolysis of chicken litter at different temperatures (560, 760, 860 and 900°C) supplied from a solar dish of maximum flux-density 69,087 W/m2 under 1000 W/m2 of net (all wave) solar radiation. Yields of the different product fractions (gas, liquid bio-oil and solid bio-char) were assessed using different techniques. The gas yield increased with temperature from 45.3 wt% at 560°C to its maximum value of 58.6 wt% at 860°C. Gas chromatograph results showed CO2, CO and CH4 as the dominant gases with contents of 30.2, 22.4 and 2.4 wt% respectively. When the temperature increased to 900°C lower gas yields of 48 wt% were produced. The gas chromatography–mass spectrometry analysis showed that the generated bio-oils (14–36 wt%) mainly contained fatty acids, phenols, sterols and nitrogen containing compounds. Scanning electron microscopic 1 ACS Paragon Plus Environment
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images of evolved bio-chars showed increasing porous structure with temperature, while the Fourier transform infrared spectroscopy of the bio-chars showed presence of –OH, aliphatic C-H and other functional groups in the bio-char which gradually disappeared with temperature. The obtained results revealed the potential use of solar energy in the waste to energy valorization of organic chicken litter waste. Key words: Solar pyrolysis, chicken litter, bio-oil, gas yield, solar radiation, waste 1. INTRODUCTION The growing demand for alternative energy sources is driving not only investigation of new and renewable alternative feedstocks but also clean production mechanisms. Biomass resources, such as municipal wastes, forest residues, agricultural waste, aquatic plants, energy crops and animal manures are recognized as the major sources of renewable energy.1 Chicken litter is a potential biomass fuel of animal origin produced in poultry farming. It consists manure, feathers, spilled food, chip woods and straw. Chicken farming is one of the largest industries and continuously growing due to the population increase.2 From 2013 to 2014, the world production of broiler and poultry meat increased to 95.8 million tonnes,3 resulting in more production of chicken manure and litter. In the US about 35 million tonnes of dry chicken litter is generated per annum;4 and Brazil, the second largest producer of broiler chickens in the world, generates around 8-10 million tonnes of litter per year.5 Total chicken litter production in Australia is estimated to be over 1 million tonnes (1.6 million m3) per annum.6 Traditionally, chicken litter has been applied as a fertiliser and soil conditioner which still remains the most important and largest end use of poultry litter. However, land application only is not a sufficient solution to the growing volume of chicken litter waste, as its excessive land use adversely impacts surface and ground water,7 degrades water quality8 and contributes to toxic 2 ACS Paragon Plus Environment
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Energy & Fuels
concentrations of ammonia nitrates.9 Chicken litter as ruminant feed supplement is also under pressure because of cattle health threats.10 Alternative mechanisms are increasingly required to address the disposal challenges of chicken litter. One potential means is to use more efficient energy conversion methods to generate energy-dense alternative fuels. Pyrolysis is one of the most attractive alternative options to obtain fuels and value added products from organic wastes, such as chicken litter. Pyrolysis is a thermochemical process which applies heat in the partial or total absence of an oxidising agent to convert biomass and other organic materials to more stable, high-energydensity solid material called bio-char, high-energy-density liquid product termed bio-oil, and relatively low energy density biogas.11 Gas products can be used for power generation, heating applications and production of chemicals.12 The bio-oils can be used in boilers and engines for energy and heat generation whereas the bio-char may be used as solid fuels or as soil conditioners, such as soil stabilization and for retention of nutrients and water.13-15 Yields of 60.1% bio-char with 38% organic carbon, 41.7g/kg nitrogen and 36.3 cmolc/kg maximum cation exchange capacity was found at 300°C Song and Guo16. Chicken litter pyrolysis at 450 to 550°C produced 40% of bio-char with high ash content (24-54 wt%) and rich in potassium and phosphorus components. The process was also observed to generate bio-oils (36-25 wt%) with relatively high nitrogen content (4 to 8 wt%), very low sulfur (
