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Significance Statement
There is a need for substitute application of manure produced from livestock waste materials due to its excess use as a nutrient source for crops leading to social and environmental problems. Thermal recycling can serve as a useful substitute which involves combustion, pyrolysis, gasification and liquefaction and can be applied to livestock waste materials in order to recover energy directly either as heat or energy carriers.
From past studies, thermochemical conversion processes on poultry litter and livestock waste have shown the capacity to convert these animal by-products into combustible gases, bio oils and biochar. The advantages of this process include; production of syngas used in engines and boilers for energy production, purification of gas before burning, higher energy conversion to electricity compared to traditional combustion process and application of solid byproducts from gasifiers on agricultural lands in order to improve soil permeability and reduce nutrient run-off.
Gasification, a thermochemical conversion process converts carbonaceous material into a useful gaseous product at elevated temperature in presence of limited amount of air. It can be undertaken using fixed or moving bed technologies, fluidized bed or entrained flow reactors. However, from various research using different technologies, proper fuel characterization remains essential due to feedstock heterogeneity and risk of sintering and agglomeration arising from some ash constituents despite it being a feasible process. The risk of bed agglomeration remains a bane to this process but it has also been proven that addition of limestone to poultry litter as fuel intake or its addition to silica bed could prevent agglomeration
A recent article of Pandey et al. (2016), published in the journal Energy Fuels, presented results obtained from experiments of poultry litter gasification using a bubbling fluidized bed gasifier. The article showed effects of equivalence ratio ER, gasifier temperature, steam-to-biomass ratio, reactor temperature and limestone addition on the poultry litter gasification process.
Limestone addition resulted in 12% decrease of total tar content. Concentration of product major components decreased except for ethylene and benzene but total gas yield remained stable with significant decrease in lower heating value and cold gas efficiency of 4.72 to 2.91MJ/Nm3 and 72.5% to 55.2% respectively with no significant effect on carbon conversion efficiency. When limestone was added to feed, 58% of total chlorine and 44% of total sulfur changed to 3% and 53% respectively at a temperature of 7000C and ER0.30. Concentration of hydrogen sulfide and COS in the product gas decreased with limestone addition suggesting that it might have favored the sulfur and chlorine recoveries in the bed.
With increasing temperature (700-8000C) the production of carbon monoxide, hydrogen, methane, ethane and benzene increased, while the production of ethane and hydrogen sulfide decreased. Gasification temperature had no effect on acetylene and toluene. Higher temperature increases product gas yield from 1.12 to 1.24 Nm3/Kgdaf and lower heating value from 2.91 to 4.24 MJ/Nm3 while decreasing total tar content from 7.22 to 6.26g/Kgdaf). Cold gas efficiency was also seen to increase from 55.2% at 7000C to more than 69.3% at 800 0C under operating conditions of ER0.30 while hydrogen conversion efficiency increased by 5% from temperature of 700 to 750 0C.
Maximum product gas yield, lower heating value, carbon conversion efficiency and cold gas efficiency was achieved at equivalence ratio of 0.25 at operating temperature of 8000C. Equivalence ratio has less influence on methane but concentration of ethane, benzene and toluene fell slightly with equivalence ratio while acetylene and hydrogen sulfide do not show any consistent trend over the range of temperatures and equivalence ratio studied. Equivalence ratio does not impact total tar yield and a significant drop from 6.36 to 2.93g/Kgdaf was observed at 750 0C due to oxidation reaction of aromatics. The same process condition at equivalence ratio of 0.25 and operating temperature of 8000C yielded a product gas of 10.78% for hydrogen, 9.38% for carbon monoxide, 2.61% for methane, 13.13% for carbon dioxide and lower heating value of 4.52 MJ/Nm3 and highest cold gas efficiency of 89.2%.
Steam injection was seen to increase hydrogen production by 53% when compared with no steam injection. Steam injection also improves chemical energy content of product gas resulting in an increase in cold gas efficiency and carbon conversion efficiency of around 5%.
The authors showed that limestone addition reduces the sulfur and chlorine content in the gas phase when the gasifier was running at relatively high temperature >7500C. Ammonia formation also decreased with an increase in gasifier temperature.
This study demonstrated that poultry litter can be gasified by blending with limestone making it possible to overcome the fluidization problems caused by mineral deposition of poultry litter ash yielding gases with similar heating value compared to cases without limestone addition but with significantly lower tar content.
Journal Reference
Daya Shankar Pandey1, Marzena Kwapinska*2, Alberto Gómez-Barea3, Alen Horvat1, Lydia E. Fryda4, Luc P. L. M. Rabou4, James J. Leahy1, Witold Kwapinski1. Poultry Litter Gasification in a Fluidized Bed Reactor: Effects of Gasifying Agent and Limestone Addition. Energy Fuels, 2016, 30 (4), pp 3085–3096.
[expand title=”Show Affiliations”]- Carbolea Research Group, Department of Chemical and Environmental Sciences and
- Technology Centre for Biorefining & Biofuels, University of Limerick, Limerick, Ireland
- Chemical and Environmental Engineering Department, Escuela Técnica Superior de Ingeniería, University of Seville, Camino de los Descubrimientos s/n, 41092 Seville, Spain
- Energy Research Centre of The Netherlands (ECN), Biomass & Energy Efficiency, Petten, The Netherlands
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