Waste Management 29 (2009) 1399–1408
Contents lists available at ScienceDirect
Waste Management
journal homepage: www.elsevier.com/locate/wasman
High-temperature thermal destruction of poultry derived wastes for energy
recovery in Australia
N.H. Florin, A.R. Maddocks, S. Wood, A.T. Harris *
Laboratory for Sustainable Technology, School of Chemical and Biomolecular Engineering, University of Sydney, NSW 2006, Australia
a r t i c l e
i n f o
Article history:
Accepted 8 October 2008
Available online 28 November 2008
a b s t r a c t
The high-temperature thermal destruction of poultry derived wastes (e.g., manure and bedding) for
energy recovery is viable in Australia when considering resource availability and equivalent commercial-scale experience in the UK. In this work, we identified and examined the opportunities and risks
associated with common thermal destruction techniques, including: volume of waste, costs, technological risks and environmental impacts. Typical poultry waste streams were characterised based on compositional analysis, thermodynamic equilibrium modelling and non-isothermal thermogravimetric
analysis coupled with mass spectrometry (TG–MS). Poultry waste is highly variable but otherwise comparable with other biomass fuels. The major technical and operating challenges are associated with this
variability in terms of: moisture content, presence of inorganic species and type of litter. This variability
is subject to a range of parameters including: type and age of bird, and geographical and seasonal inconsistencies. There are environmental and health considerations associated with combustion and gasification due to the formation of: NOX, SOX, H2S and HCl gas. Mitigation of these emissions is achievable
through correct plant design and operation, however, with significant economic penalty. Based on our
analysis and literature data, we present cost estimates for generic poultry-waste-fired power plants with
throughputs of 2 and 8 tonnes/h.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
Currently, in the absence of stringent environmental legislation,
the direct land application of untreated poultry derived waste (e.g.,
manure, mixtures of manure and biomass bedding material and
egg shells) is the most common disposal technique (Kelleher
et al., 2002). It has been purported that the land application of
poultry derived wastes is the most desirable solution for poultry
wastes in Australia due to the infertile nature of Australian soils
(Runge et al., 2007). However, there are environmental and health
hazards associated with this disposal method, including the possibility of eutrophication of waterways through nutrient runoff
(Heathman et al., 1995) and the presence of arsenic, heavy metals
and pathogens in the untreated waste (Haapapuro et al., 1997; Li
and Shuman, 1997; Jackson et al., 2006). Were more stringent legislation introduced – as has occurred in most European countries –
land application of untreated waste would likely become uneconomic. Composting is an alternative to direct land application,
which results in reduced volumes for disposal, improved consistency of waste, and the elimination of pathogens, although additional equipment and handling costs are incurred and the
problems of nutrient runoff and heavy metal contamination remain (Ihnat and Fernandes, 1996; Vervoort et al., 1998). The gen* Corresponding author. Tel.: +61 2 9351 2926; fax: +61 2 9351 2854.
E-mail address: a.harris@usyd.edu.au (A.T. Harris).
0956-053X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.wasman.2008.10.002
eration of electricity and heat from poultry derived wastes based
on high-temperature thermal destruction techniques, i.e., combustion, gasification and pyrolysis, is a highly promising waste management solution. Nevertheless, there remain technical and
operational challenges associated with the processing of poultry
wastes due to the inherent variability of the waste stream and high
costs in comparison to direct land utilisation. With the increasing
drive for energy generation from renewable sources and the anticipated introduction of more stringent environmental legislation,
we contend that these processes will become economically viable
options in the future. Opportunities for improving the economic
viability also exist with the co-combustion and gasification of
poultry derived waste with other agricultural and forestry wastes.
In this paper we investigate pyrolysis, gasification and combustion techniques for the thermal destruction of common poultry derived wastes (i.e., manure, bedding and a mixture of these) in
Australia. Specifically we: (i) review combustion and gasification
technologies operating at commercial-scale in Europe, in particular
focussing on the environmental impacts and process operability
constraints of these processes; (ii) determine the potential for electricity generation in Australia from poultry wastes; (iii) characterise typical waste and product streams based on thermodynamic
equilibrium modelling and thermogravimetric analysis coupled
with mass spectroscopy; and (iv) develop indicative cost estimates
for two generic poultry-waste-fired power plants, located in
Australia.
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N.H. Florin et al. / Waste Management 29 (2009) 1399–1408
1.1. Thermochemical processes
High-temperature technologies for the destruction of poultry
wastes are differentiated by the reaction atmosphere: combustion
involves the reaction of the waste with oxygen or air; gasification
involves the conversion of the waste in the presence of gasifying
agents such as H2O, CO2, or air at below stoichiometric levels;
and pyrolysis involves the conversion of waste in an inert atmosphere (Higman and van der Burgt, 2003). The selection of the most
suitable technology depends on the fuel characteristics and the desired end-use applications. For example, combustion of poultry
waste is most suitable for producing heat for the generation of process steam or electricity (Whitely et al., 2006a); pyrolysis can produce activated carbon (Whitely et al., 2006b); and the gasification
of poultry waste can produce a H2-rich fuel gas, suitable for direct
use in a gas engine, gas turbine or fuel-cell (McKendry, 2002;
McLellan et al., 2005). The different technologies, including up to
date commercial status, are discussed below.
1.1.1. Combustion
Five major poultry litter combustion plants are in operation
Worldwide, four in the UK and one in the USA. These plants are
now owned by energy power resources (EPR), but were built by
Fibropower and Fibrowatt. Several additional power plants have
been proposed in the USA, The Netherlands, Ireland and Western
Australia, with further sites being investigated in Belgium, France,
Germany, Italy, Japan, Portugal and Spain (Energy Justice Network,
2004).
The first commercial power plant for the combustion of poultry
manure was commissioned in 1992 at Eye in the UK (Energy Power
Resources, 2007). The plant, a conventional moving grate boiler
and steam cycle, burns 140,000 tonnes of chicken litter per year
sourced from farms in the surrounding areas, resulting in an output
of 12.7 MW. Two more plants were constructed in Glanford (13.5
MW) and Thetford (38.5 MW) by Fibrowatt. A typical flow diagram
of a poultry-waste-fired power plant is given in Fig. 1.
Fluidised bed technology has been employed in the construction of poultry-waste-fired power plants. For example, a plant at
Westfield, Scotland (owned by EPR) uses bubbling fluidised bed
technology to combust 110,000 tonnes of waste per year, producing 9.8 MW. The advantage of a fluidised bed is the good mixing of
the bed material, which promotes good heat transfer rates between
the gas and solids, and facilitates uniform temperature control.
Furthermore, the removal, or addition, of solids (e.g., bed material,
catalysts and ash) from the reactor is relatively straightforward
due to the fluidity of the bed (Higman and van der Burgt, 2003).
1.1.2. Gasification
Gasification has been demonstrated for numerous biomass fuels
including a variety of woody fuels (van der Drift et al., 2001), sewage sludge (Manya et al., 2006), animal manure (Buckley and Schwarz, 2003), rice husks (Natarajan et al., 1998), almond shells
(Rapagna and Latif, 1997) and olive oil waste (Garcia-Ibanez
et al., 2004). Unlike combustion, the gasification of poultry derived
waste has been limited to small-scale and laboratory applications.
A small farm based gasification plant in The Netherlands uses
poultry manure as the feedstock (Buffinga et al., 2005). A fluidised
bed gasifier produces heat for use on the farm and electricity for
the grid, while the ash is utilised by a road construction company.
This plant, commissioned in 2001, was the first of its kind in The
Netherlands, and consequently a long payback period of seven
years was estimated. It is anticipated that the payback period of future installations would be less than five years (BTG Biomass Technology Group). A schematic of the process is shown in Fig. 2.
Co-gasification of biomass materials, including poultry wastes,
in fossil fuel power stations provides an opportunity to reduce carbon emissions in existing power plants. This is advantageous for
both poultry farmers and energy providers. Considerations must
be given when combining a low ash fuel such as coal with poultry
waste, which has high ash content. Studies performed in a 10 kW
fixed bed gasifier showed that ash content influences the rate of
fuel conversion (Priyadarsan et al., 2005). Although differences in
the fuel properties between coal and poultry waste suggested that
operating parameters of coal gasifiers would need adjustment to
accommodate for the fuel mixtures, Priyadarsan et al. (2005) still
concluded that co-gasification was feasible. We discuss the influence of fuel-bound minerals in §3.0. While there is considerable
scope for co-gasification in the Australian energy sector, further research is required to determine the gasification behaviour of coal
and waste mixtures case-by-case.
1.2. Potential for electrical generation from poultry litter combustion
in Australia
We used the fuel processing capacity of the four commercial
power plants in the UK (Table 1) to provide a basis for estimating
Fig. 1. Flow diagram for a poultry litter power plant.
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N.H. Florin et al. / Waste Management 29 (2009) 1399–1408
Fig. 2. Process for the small-scale farm based gasification of poultry manure (BTG Biomass Technology Group, 2001).
Table 1
Operating poultry litter combustion plants in the UK.
Location
Fuel
Capacity
(MW)
Capacity-to-feedquantity (MW/kt)
Eye
160,000 (poultry derived waste,
horse bedding 12% and feathers 7%)
420,000 (poultry derived waste)
110,000 (poultry derived waste)
12.7
0.0794
38.5
9.8
0.0917
0.0891
Thetford
Westfield
the potential for electricity production from poultry derived
wastes in Australia. Runge et al. (2007) estimate the volume of
available poultry waste in Australia at about 1.60 million m3yr1
with density varying due to the quantity of manure, type of bed
material and moisture content. Using poultry waste densities from
the literature reported in Table 2, the total electrical capacity of
poultry waste in Australia was determined to range from 57–
88 MW. This estimate indicates the potential for energy generation
from poultry waste in Australian, considering that the largest commercial plant in Europe has a capacity of 38.5 MW (Table 1).
1.3. Emissions from thermochemical processes
NOx and SOx emissions are produced by the oxidation of fuelbound nitrogen and sulfur during combustion. During biomass gasification and pyrolysis, there is considerably less oxygen available
Table 2
Estimated electricity production capacity from poultry waste in Australia.
Density
(kg/m3)
Low
720,000
Medium
840,000
High
960,000
Mass = volume density
(tonne)
Capacity = mass capacityto-feed ratio (MW)
density
450
density
525
density
600
57–66
67–77
76–88
for NOx and SOx production. In this case, the fuel-bound nitrogen
is typically converted to N2 instead of NOx during gasification
(Buckley and Schwarz, 2003). In comparison to coal, the sulfur content in biomass feedstocks, including poultry derived waste, is low,
and thus, SOx emissions may be less of a problem (Higman and van
der Burgt, 2003). Calcium and magnesium inherent in poultry derived waste also reduce SOx emissions by forming sulfates – the
gas-solid interactions between the inorganic species in poultry derived waste and the evolved gas species during high-temperature
thermal destruction are discussed in §3.0.
1.4. Ash utilisation
The high-temperature thermal destruction of poultry derived
waste concentrates the nutrients in the ash. Although nitrogen
and organic matter are lost during combustion and gasification,
the remaining nutrients, >25 wt.% of the poultry waste, remain
after fuel conversion as a rich mixture of silica, potassium, magnesium and calcium and lower concentrations of aluminium, iron,
titanium, sodium and sulfur (Tables 3 and 4). Due to an increase
in density of the ash compared with the poultry derived waste,
by about 1.5–2.5 times, and the concentration of the nutrients during combustion and gasification, the resulting nutrient densities
Table 3
Proximate and ultimate analysis for poultry derived waste including two manure
samples and one typical litter sample (sawdust) sourced from Australian poultry
farms.
Sample
description
Proximate analysis (% dry)
Moisture Ash
(%)
yield
Volatile
matter
Fixed
carbon
C
Manure (1)
Manure (2)
Sawdust
12.9
24.4
18.1
47.5
63.1
75.3
7.1
11.7
23.2
24.12.84.30.23.6
35.04.26.80.411.0
52.16.00.20.220.9
45.4
25.2
1.6
Ultimate analysis (% dry)
H N S HHVa (MJ/
kg)
a
HHV calculated from proximate and ultimate analysis: HHV (MJ/kg) = (34.91 C) + (117.83 H) – (10.34 O) – (1.51 N) – (10.05 S) – (2.11 Ash), where C, H,
N, O, S and Ash are mass fractions (e.g., Higman and van der Burgt, 2003).
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N.H. Florin et al. / Waste Management 29 (2009) 1399–1408
Table 4
Summary of elemental data based on an ash compositional analysis.
Ash composition (wt%)
Sample
description
SiO2
Al2O3
Fe2O3
TiO2
K2O
MgO
Na2O
CaO
SO3
Manure (1)
Manure (2)
25.8
3.8
5.8
0.6
5.2
<0.01
1.15
0.02
4.3
7.1
4.1
4.1
1.5
3.1
37.7
54.6
2.9
5.2
(i.e., mass nutrients/volume ash) are about 10–17 times higher in
the ash compared to the as-received waste (Bock, n.d.). The concentration of nutrients reduces transportation and storage costs,
and the lower volume improves handling and consistency – these
characteristics are highly desirable for use as a fertiliser.
2. Experimental
2.1. Characterisation of the poultry derived waste streams
Three representative poultry wastes were characterised using
‘‘proximate and ultimate” analysis (Table 3). Due to the high mineral content, we also analysed the ash composition using inductively coupled plasma (ICP) analysis; these results are presented
in Table 4. The proximate analysis gives the sample moisture content, volatile content (i.e., the amount of gas given off when the
sample is heated to 950 °C), the free carbon, and the ash yield
(inorganic matter). The ultimate analysis gives the elemental composition as a percentage by weight (wt.%). Table 3 also gives the
higher heating value (HHV).
2.2. Computational thermodynamics
Computational thermodynamics (or thermodynamic modelling) has been used successfully to develop, investigate and optimise chemical reaction processes for many years (Smith and
Missen, 1982). The basic concept of thermodynamic modelling is
thermodynamic equilibrium, whereby the final state of each point
in a system exists in thermal, mechanical and chemical equilibrium
and there are no flows across the system boundaries. In practice,
this requirement means that the processes leading to thermodynamic equilibrium must occur faster than the changes on the system’s boundaries. For example, when the thermodynamic
equilibrium of combustion processes is investigated, it is usual to
assume adiabatic combustion; and when the processes in a chemical reactor are modelled, it is assumed that the rates of chemical
reaction are much greater than the velocity of flow, and thus, there
is sufficient time for chemical equilibrium to be achieved.
In this work we used thermodynamic modelling to predict the
gas composition exiting a reactor, across a range of important process conditions for the high-temperature destruction of poultry derived wastes, including: (i) temperature, (ii) reaction atmosphere,
and (iii) the influence of key solid species. For example, CaO was
targeted as a key additive with the capacity for CO2 capture, desulphurisation, and with catalytic activity for tar elimination and char
gasification (Sutton et al., 2001; Corella et al., 2006; Florin and Harris, 2008a).
The commercial equilibrium modelling package, FactSage 5.4.1
(EQULB Module),1 was used in this work. This modelling package requires specification of the molar composition of the feedstock and a
list of product species likely to be involved in the thermodynamic
equilibrium. We used an average feedstock composition (Table 5),
1 I
Factsage 5.4.1 was released in January 2006. The software and database package
was jointly developed by Thermfact/CRCT <www.crct.polymtl.ca> and GTT Technologies: <www.gtt-technologies.de>.
which was determined from ultimate and proximate analysis and
from the literature (e.g., Whitely et al., 2006a,b; Davalos et al.,
2002; Bock, n.d.; Murphy, 2002; Higman and van der Burgt, 2003).
Table 5 gives the molar composition for a feedstock assumed to be
20%-wt. moisture, 55%-wt. volatile matter and 25%-wt. ash, taking
a basis of 1 kg; 46 gas species and 29 solid species were considered
to participate in equilibrium (Table 6). This species list was determined from the literature (e.g., Li et al., 2004. Hu et al., 2006; Corella
et al., 2006).
2.3. Thermogravimetric–mass spectrometric analysis
Pyrolysis, gasification and combustion are all being actively
studied as techniques to recover the energy content of waste materials. These processes, for any fuel, at commercial-scale, require
knowledge of the volatiles evolution behaviour as a function of
temperature (Harris and Zhong, 2008). In this work we conducted
a series of non-isothermal experiments using temperature ramp
thermogravimetric analysis coupled with mass spectroscopy
(TG–MS) to investigate the combustion and pyrolysis of poultry derived wastes. This technique makes possible the rapid measurement of the temperature decomposition profile of poultry waste
subject to pyrolysis or combustion reaction conditions, and the
mass spectra of the evolved species are simultaneously recorded.
In a TG–MS experiment, a sample of poultry derived waste is subjected to a temperature program while its mass is continually
monitored. Rapid data acquisition, whereby the evolved product
species are sampled in real time, enables the elucidation of impor-
Table 5
Average composition and species distribution determined from proximate and
ultimate analysis.
Composition
Species distribution
Molar amount–1 kg basis (mol)
20 wt.% Moisture content
55 wt.% Volatile matter
H2O
C
N
H
S
O
Cl
SiO2
Al2O3
Fe2O3
TiO2
K2O
MgO
Na2O
CaO
SO3
11.10
16.97
1.70
23.64
0.05
20.63
0.00
0.77
0.09
0.05
0.02
0.12
0.30
0.08
2.09
0.14
25 wt.% Ash yield
Table 6
List of components considered for modelling the high-temperature thermal destruction of poultry derived waste.
Component list
Hydrocarbons
Oxygenated gaseous
compounds
Nitrogenous gaseous
compounds
Sulfonated gaseous
compounds
Chloride species
Solid species
Oxides
Carbonates
Sulfonated species
Chloride salts
Hydroxides
C, H, H2, CH, CH2, CH3, CH4, C2H2, C2H3, C2H6
O, O2, OH, H2O, HO2, H2O2, CO, CO2, HCO, CH3OH,
C2H4O, CH3COOH,
N, N2, NH, NH2, NH3, CN, HCN, NO, NO2, N2O, NCO,
HNCO
S, S2, HS, H2S, CS, CS2, SO, SO2, SO3, COS
Cl2, HCl
C(graphite), S
Na2O, MgO, Al2O3, SiO2, SO3, K2O, CaO, TiO2, Fe2O3
Na2CO3, MgCO3, K2CO3, CaCO3, FeCO3
Na2SO3, Na2SO4, MgSO4, K2SO4, CaSO3, CaSO4, CaS
NaCl, KCl, CaCl2, FeCl2, FeCl3
Ca(OH)2
N.H. Florin et al. / Waste Management 29 (2009) 1399–1408
tant reaction pathways during decomposition. Small sample
masses (typically from 1–5 mg) are used to ensure that the sample
temperature does not lag the measured temperature. If a temperature lag does exist or the particle size is too large (e.g., >2 mm,
Dümpelmann et al., 1991), it is impossible to separate the effects
of heat and mass transfer from the reaction kinetics. While small
samples are advisable for achieving reproducible kinetic data, the
sensitivity of the MS sets a lower limit on the sample size (Florin
and Harris, 2008b). All experiments were performed using a Thermal Analysis SDTQ6000 (TA Instruments, Delaware, USA) and a
Pfeiffer Vacuum ThermoStar SD301 (Pfeiffer Vacuum Inc., USA).
The coupled apparatus, shown in Fig. 3, comprises an alumina
pan supported on a horizontal balance arm, held within a furnace.
A sweep of Ar and air of 500 ml/min was used for the pyrolysis and
combustion experiments, respectively. Evolved gases are flushed
from the vicinity of the decomposing solid and subsequently delivered to the mass spectrometer via a heated capillary (200 °C) to
minimise condensation of heavy species on the capillary walls.
3. Results and discussion
3.1. Characterisation of the sources and composition of poultry litter
Results from the ultimate and proximate analyses are presented
in Table 3. Three samples were analysed, including two manure
samples and one litter sample that was predominantly sawdust.
There is significant variation in the physical composition of the
two manure samples, e.g., manure (1) has an ash content of
45.4 wt.% compared to manure (2) with an ash content of only
24.4 wt.%; and manure (2) has almost twice the moisture content
of manure (1). These fundamental differences in the physical properties add to the operational and technical challenges of a hightemperature destruction technology. Major factors likely to influence the composition of the poultry manure include: (i) the type
of birds, (ii) age of the birds, (iii) the birds’ diet, and (iv) feed use
efficiencies (McGahan et al., 2006). The age of the birds will vary
1403
and the diet of the birds will be strongly dependent on geography
and seasonal variability.
Table 3 also shows data for a typical litter material, in this case
sawdust. Litter is used to adsorb the manure produced by the hens.
Thus, poultry derived waste will be composed of a mixture of manure and litter. The nature and composition of this overall waste
stream depends on the amount of litter used. Furthermore, a range
of different litter materials are used depending on local availability,
including: sawdust, straw, mill wood wastes and shredded paper
(McGahan et al., 2006). We consider both waste streams separately
to facilitate a general analysis. The proximate data for the sawdust
sample shows a low ash yield (1.6 wt.%) and a high amount of volatile matter (75.3 wt.%), consistent with standard wood wastes
(Higman and van der Burgt, 2003).
Due to the high ash content of both manure samples investigated, we present an elemental composition analysis in Table 4.
Again, there is significant variation between the two manure samples, particularly with respect to the mass fractions of SiO2 and CaO
and minor species: Fe2O3, TiO2 and K2O. Notably, the CaO content
is high for both manures (1) and (2). The high amount of mineral
matter is expected to have a significant influence on the high-temperature destruction of poultry derived waste, including catalytic
effects, and gas-solid interactions between the evolved gas species
and active mineral species including CaO. The influence of mineral
matter on the decomposition of poultry derived waste is discussed
in §3.2 and 3.3.
We make seven general observations regarding the thermal
destruction of poultry derived waste based on compositional data
presented in Tables 3 and 4:
(i) The volatile fraction and molar ratio of C, H, O of poultry litter is similar to typical biomass fuels, such as soft wood
(Higman and van der Burgt, 2003). This similarity highlights
the potential merit in using poultry derived wastes as an
alternative feedstock for high-temperature technologies
where conventional biomass feedstocks are currently used.
Fig. 3. Modified thermogravimetric analyser coupled with mass spectrometer (TG–MS) for the decomposition of poultry wastes and the simultaneous analysis of evolved
product gas species (Florin and Harris, 2008b).
N.H. Florin et al. / Waste Management 29 (2009) 1399–1408
(ii) The relatively high N and S contents, compared to typical
biomass fuels, increases the risk of SOX and NOX emissions
during combustion, or fuel conversion in an O2 rich
atmosphere.
(iii) The presence of fuel-bound Cl presents an additional risk of
acid gas formation.
(iv) Poultry derived waste has very high moisture content which
may limit the overall thermal efficiency of a conversion process due to the additional energy input necessary for drying.
(v) Poultry derived waste has a very high ash content. High levels of K and Na oxides can be problematic due to fouling and
slagging (Bock, n.d.; Murphy, 2002). Removal of solid buildups on the walls of the reactor would be necessary to maintain reactor performance, and the potential disruption to
operations will impact overall process efficiency.
(vi) The presence of high amounts of CaO may minimise the
need for downstream pollution control for the removal of
CO2 and SO2 via carbonation and sulfation reactions, respectively (e.g., Gullet and Bruce, 1987; Abanades and Alvarez,
2003; Hughes et al., 2004).
(vii) The catalytic influence of inorganic species on the decomposition of biomass feedstocks is widely reported – the presence of trace amounts of alkali and alkali earth metals
have been observed to influence tar elimination, char formation and char gasification reactions (e.g., Varhegyi et al.,
1988; Richards and Zheng, 1991). The amount and variability of the mineral matter inherent in poultry derived waste is
expected to catalyse the decomposition process adding technical and operational complexity to a high-temperature
destruction process.
3.2. Computational thermodynamic modelling
3.2.1. Combustion
We used a thermodynamic model to predict the distribution of
product species for the combustion of poultry derived waste in air,
in this case with an equivalence ratio (ER) of one. ER is defined as
the ratio of O2 in the feed stream to the theoretical amount of O2
for complete combustion according to Eq. (1).
Cn Hm Op þ ðn þ m=4 p=2ÞO2 þ 3:8ðn þ m=4 p=2ÞN2
! nCO2 þ ðm=2ÞH2 O þ 3:8ðn þ m=4 p=2ÞN2
ð1Þ
The concentrations of major gas products, CO2, H2O and N2 (approx. 18 vol.%, 26 vol.% and 56 vol.%, respectively), were not influenced by the temperature of combustion from 300–1000 °C. Fig. 4
shows five minor species that were present with concentrations
greater than 1 ppm, including: H2, CO, SO2, H2S and HCl. CO emissions are problematic because they are harmful to human health
(US EPA, 2007). An increase in the CO concentration was predicted
with increasing temperature from 300–1000 °C; thus a maximum
acceptable level of CO may limit the process operating temperature. H2S concentration – which must be controlled to low levels,
i.e., < 10 ppm (US EPA, 2007) – was predicted to decrease corresponding to an increase in the temperature. Acid gas species, SO2
and HCl were also predicted across the temperature range investigated – adding to the challenge of operating a combustion system
for the thermal destruction of poultry derived waste.
The concentrations of the gas species shown in Fig. 4 were influenced by gas-solid reactions with mineral species in the ash. Specifically, the reactivity of the alkali and alkali earth metal oxides
with CO2, SO2 and Cl presents the possibility of utilising these
in situ inorganic species for the management of fuel-bound pollutant emissions. However, the strong influence of temperature on
these gas-solid reactions will likely determine the suitable operat-
1x100
H2
1x10-1
CO
1x10-2
Mole fraction (—)
1404
1x10-3
H2S
1x10-4
SO2
1x10-5
HCl
1x10
-6
1x10-7
1x10-8
1x10-9
1x10-10
300 400 500 600 700 800 900 1000
Temperature (°C)
Fig. 4. Contaminant species present in hot combustion gas as a function of the
combustion temperature.
ing temperature for optimal pollution control. The following predictions were made:
(i) Na2O was predicted to react with CO2 to form Na2CO3 at all
reaction temperatures investigated.
(ii) Na2O was predicted to react with SOx to form Na2SO4 across
the temperature range from 300–1000 °C.
(iii) NaCl was predicted to be present at temperatures <780 °C.
(iv) MgO was predicted to reacts with CO2 to form MgCO3 at
temperatures <360 °C.
(v) K2O was predicted to react completely with SOx to form
K2SO4 across the temperature range from 300–1000 °C.
(vi) CaO was predicted to react with CO2 to form CaCO3 at temperatures <780°C.
(vii) SiO2, Al2O3 Fe2O3, TiO2 were not predicted to participate in
the reaction system under the conditions investigated.
3.2.2. Pyrolysis and gasification
Fig. 5 shows the predicted yield of product species for the thermal destruction of poultry derived waste via: (a) pyrolysis, (b)
steam gasification, and (c) steam gasification in the presence of
additional CaO. Major permanent gas species are displayed, including: H2, CH4, H2O, CO and CO2; and minor products, including: NH3,
H2S, COS, and HCl as a function of temperature from 300–1000 °C.
CH4, CO2, and H2O were the main product species from the
pyrolysis of poultry derived waste at temperatures <500 °C
(Fig. 5a). At higher temperatures an increase in the H2 and CO concentrations was predicted. A maximum H2 concentration of 31.0 gH2/kg-fuel was observed at 720 °C, while an increasing trend was
observed for CO across the range of temperatures investigated.
Fig. 5b shows the influence of additional water vapour on the gas
product distribution. A general increase in the permanent gas
yields was predicted in the presence of additional H2O, for example, the maximum H2 yield was 37.4 g-H2/kg-fuel. The increase in
the H2 yield may be inferred from the general reforming reaction
according to Eq. (2), which is enhanced by an increase in H2O.
Cn Hm Op þ ð2n pÞH2 O ! nCO2 þ ðm=2 þ 2n pÞH2
ð2Þ
Fig. 5c displays the influence of additional CaO on the final
product distribution. A significant decline in the CO2 yield is observed in the low to moderate temperature range because CO2 is
removed from the reaction system by CaO, according to Eq. (3).
The increase in the H2 yield up to 47.6 g-H2/kg-fuel, and the de-
1405
N.H. Florin et al. / Waste Management 29 (2009) 1399–1408
Gas yield (g/kg-fuel)
a
400
H2
350
CH4
300
NH3
250
H2O
200
CO
150
CO2
100
H2S
COS
50
0
300 400 500 600 700 800 900 1000
HCl
Temperature (°C)
b
Gas yield (g/kg-fuel)
400
350
300
250
200
CO þ H2 O ! CO2 þ H2 ðexothermicÞ
ð4Þ
Our modelling predictions show the potential for producing a
synthesis gas rich in H2 and CO from poultry derived waste via a
steam gasification process. However, the presence of pollutants,
including: NH3, H2S, COS, and HCl will add to the technical complexity of the process. For example, when additional CaO was present, the H2S yield was maintained at <0.01 g/kg-fuel up to about
620 °C; however, at higher temperatures, from 650–1000 °C, H2S
was predicted at 1–2 g/kg-fuel. Fuel-bound Cl was predicted in
the form KCl at low temperatures (<400 °C). Gas cleaning would
be necessary to manage Cl emissions (i.e., in the form of HCl gas)
at gasifier operating temperatures >450 °C.
3.3. TG–MS study of the high-temperature destruction of poultry
derived waste
150
100
50
0
300 400 500 600 700 800 900 1000
Temperature (°C)
450
400
Gas yield (g/kg-fuel)
ð3Þ
3.3.1. Combustion experiments
Fig. 6 shows the decomposition profiles corresponding to the
combustion of the two manure samples and sawdust. These experiments were conducted in air at a heating rate of 40 °C/min. The
different decomposition profiles and the final sample weights at
1000 °C reflect the variable compositions (Table 3). The decomposition profiles proceed in parallel up about 400 °C before deviations
in the rate of decomposition were observed, which are likely due to
the interactions between the different inorganic species in the ash
and the evolved CO2 and H2O.
500
450
c
CaO þ CO2 ! CaCO3 ðexothermicÞ
350
300
250
3.3.2. Pyrolytic weight loss experiments
Pyrolytic weight loss experiments were conducted for both
manure samples and the litter sample – the decomposition profiles
are presented in Fig. 7. For these experiments we used a heating
rate of 40 °C/min in an Ar atmosphere. The decomposition profiles
shown in Fig. 7 dramatically diverge, indicating different reaction
pathways that are attributable to the physical compositions and
elemental distributions of the samples (Table 3 and 4). Manure
(2) displayed the highest conversion to gas, consistent with the
high volatile content reported in Table 3. The pyrolysis of manure
(2) is characterised by a stepped decomposition profile, which is
likely due to the catalytic activity of the inorganic matter in the
ash, and the gas-solid interactions between the inorganic species
and the evolved product gases discussed in §3.2. The varied
decomposition behaviours observed for the three waste samples
200
150
100
100
Manure (1)
90
50
Manure (2)
80
0
300 400 500 600 700 800 900 1000
Fig. 5. Predicted gas species for the pyrolysis and gasification of poultry derived
waste: (a) pyrolysis (b) steam gasification with fuel-to-steam ratio of one; and (c)
steam gasification with fuel-to-steam ratio of one and additional CaO so that the
ratio of C-to-CaO equals one.
Weight (%)
Temperature (°C)
Sawdust
70
60
50
40
30
20
crease CO may be inferred from the water-gas shift reaction given
by Eq. (4). At temperatures exceeding about 700 °C, the equilibrium product distribution in Fig. 5c readjusts and conforms to
the distribution shown in Fig. 5b, where the higher temperature favours the endothermic decomposition of CaCO3 back to CaO and
CO2.
10
0
100
300
500
700
900
Temperature (°C)
Fig. 6. Weight loss corresponding the combustion of poultry derived waste in air.
N.H. Florin et al. / Waste Management 29 (2009) 1399–1408
To better elucidate the nature of the decomposition mechanism,
the pyrolytic weight loss profiles were compared with the mass
spectra for the evolved species. Figs. 8a and b show the mass spectra of the evolved gas species from the decomposition of manure
(1) with the derivative weight curve overlayed. The mass spectra
for the permanent gas species, including: H2 (m/e = 2), CH4 (m/e
=15), H2O (m/e = 18), CO (m/e = 28) and CO2 (m/e = 44) are displayed in Fig. 8a. Minor species, including: higher hydrocarbons
C2H2+ (m/e = 26) and C2H3+ (m/e = 27), and aldehydes (m/e = 29,
30, 31 and 43), are presented in Fig. 8b. The decomposition involves three main steps, delineated by temperature. The first
decomposition step is dominated by a dehydration mechanism,
evidenced by the close correspondence of the first decomposition
peak and the H2O peak (m/e = 18). A secondary decomposition
peak is observed at about 450 °C and corresponds with the evolution of CO2, the higher hydrocarbons and aldehydes (Fig. 8b). The
third decomposition peak, which was observed at about 700 °C,
is likely associated with the decomposition of CaCO3.
The influence of additional CaO on the pyrolytic decomposition
of manure (1) is displayed in Figs. 8c and d. Consistent with the
computational thermodynamics, the presence of CaO was observed
to strongly influence the distribution of evolved gas species. The
ion current intensities corresponding CO and CO2 are significantly
diminished, consistent with the inferred CO2 capture and water–
100
Manure (1)
90
Manure (2)
80
Sawdust
Weight (%)
70
60
50
40
30
20
10
0
100
300
500
700
900
Temperature (°C)
Fig. 7. Pyrolytic decomposition profiles for poultry derived waste streams in an Ar
atmosphere.
highlights the potential challenges for a high-temperature thermal
destruction process.
0.16
0.7
0.14
0.6
0.12
0.5
0.1
0.4
0.08
0.3
0.06
0.2
0.04
0.1
0.02
0
200
300
400
500
600
700
c
1.6
0.12
m/e=2
1.4
0.1
1.2
Ion current (—)
0.8
Derivative weight (%.wt/°C)
Ion current (—)
a
0.08
1
0.8
0.06
0.6
0.04
0.4
0.02
0.2
0
800
0
200
300
Temperature (°C)
500
600
700
m/e=15
m/e=18
m/e=28
m/e=44
0
800
Temperature (°C)
d
0.2
0.05
m/e=26
0.18
0.045
m/e=27
0.16
0.04
m/e=29
0.035
m/e=30
Ion current (—)
Ion current (—)
b
400
Derivative weight (%.wt/°C)
1406
0.14
0.12
0.1
0.08
0.03
0.015
0.04
0.01
0.02
0.005
300
400
500
600
Temperature (°C)
700
800
m/e=43
0.02
0.06
0
200
m/e=31
0.025
0
200
300
400
500
600
700
800
Temperature (°C)
Fig. 8. The mass spectra of the evolved gas species during the pyrolysis of manure (1), with and without additional CaO: (a) mass spectra of permanent gas species evolved
during the pyrolytic decomposition without additional CaO – the bold line represents the rate of weight loss and is displayed on the right vertical axis, and ion current
intensity is displayed on the left vertical axis without units because the signals were adjusted to a zero baseline; (b) mass spectra of minor species evolved during
decomposition, without additional CaO; (c) mass spectra of permanent gas species evolved during the pyrolytic decomposition with additional CaO such that the Ca-to-C ratio
equalled one; and (d) mass spectra of minor species for decomposition with additional CaO.
N.H. Florin et al. / Waste Management 29 (2009) 1399–1408
Table 7
Indicative costing for a generic poultry-derived-waste-fired power plant.
Capacity (tonne/hr)
Electrical output (MWe)
Equipment costs (AUD)
System (1)
System (2)
2
1.5
8,425,000
8
6
27,875,000
gas shift mechanisms, according to Eqs. (3) and (4). These experimental results highlight the potential operating challenges associated with a high-temperature thermal destruction process,
whereby operational complexity is primarily derived from the high
and variable mineral content. In situ mineral matter, including CaO,
dramatically influences the decomposition behaviour and the final
distribution of the product gases. Thus, the feasibility and technical
operability of high-temperature thermal destruction technologies
will likely depend on the variability of the feedstock.
4. Costing for a poultry-waste-fired power plant
We have prepared indicative costings for a generic poultrywaste-fired power plant using the data reported in §2.0 and §3.0
and the literature. The capital costs were estimated at two scales:
(i) 2 tonnes per hour (i.e., 16,000 tonnes per yr, dry basis); and (ii) 8
tonnes per hour system (i.e., 64,000 tonnes per yr, dry basis). The
estimates have been developed to within ± 25% accuracy using a
generic mix of manure and litter, based on the data reported in Tables 3 and 4 and the literature. The proposed system involves hightemperature thermal destruction of poultry derived waste using a
proprietary slow pyrolysis technology, with the subsequent gasification of the char to maximise energy production. The combustible
product gas from the pyrolysis and gasification units is used for the
production of electricity in an internal combustion engine. Based
on a typical analysis of poultry derived waste, the plants produce
approximately 1.5 and 6 MW of electricity, respectively (Table 7).
The equipment costs, presented in Table 7, include: wet feed system, a rotary dryer system, dry storage and handling, pyrolysis unit
with gas clean-up, char gasifier, char storage, generator and control
instrumentation. Due to the significant variability in poultry derived waste, the cost estimates should be used as a guideline.
The cost may be decreased significantly using an on-farm generating system – that is, outside built up areas – by reducing costs
associated with materials handling and odour removal.
5. Conclusions
The most appropriate disposal technique for poultry derived
waste is dependent upon: cost; environmental impact; quantity
of the waste generated; and local, state and federal regulations.
Land application of untreated waste is currently the most economical solution under current environmental legislation in Australia –
however, direct land application is far from the most suitable use
of this renewable biomass resource. In this paper we have considered the viability of high-temperature thermal destruction technologies in Australia for energy recovery from poultry derived
wastes. There is potential for producing electricity and heat from
poultry waste in Australia based on the estimated resource availability, and considering the demonstrated operation of commercial-scale cogeneration facilities in the UK. The major technical
and operating challenges are associated with the variability of
the waste in terms of: moisture content, presence of inorganic species and type of litter. This variability is subject to a range of
parameters including: type and age of bird, and geographical and
seasonal inconsistencies. There are environmental and health considerations associated with combustion and gasification due to the
1407
formation of: NOX, SOX, H2S and HCl gas. Mitigation of these emissions is achievable through correct plant design and operation,
however, with significant economic penalty. There is potential to
utilise inherent inorganic species, including CaO and MgO, for the
management of carbon and sulfur emissions; however, the practicability of this approach should be examined case-by-case. The ash
from combustion, pyrolysis and gasification may also be utilised as
a slow release fertiliser. Furthermore, combining poultry derived
waste with other agricultural or forestry wastes may also enhance
the economic viability of the high-temperature thermal destruction and energy technologies.
Acknowledgements
The authors are grateful for the financial support of the Australian Egg Corporation Ltd (AECL) and the assistance of BEST Energies
Australia Pty Ltd in preparation of the plant costings.
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