Waste Management 32 (2012) 701–709

Contents lists available at SciVerse ScienceDirect

Waste Management

journal homepage: www.elsevier .com/locate /wasman

Characterization of cellulosic wastes and gasification products from chicken farms

Paul Joseph ⇑, Svetlana Tretsiakova-McNally, Siobhan McKennaSchool of the Built Environment and the Built Environment Research Institute, University of Ulster, Newtownabbey BT37 0QB, County Antrim, Northern Ireland, UK

a r t i c l e i n f o a b s t r a c t

Article history:Received 15 April 2011Accepted 13 September 2011Available online 19 October 2011

Keywords:Chicken litterGasification processWaste managementEnergy recovery

0956-053X/$ - see front matter Crown Copyright � 2doi:10.1016/j.wasman.2011.09.024

⇑ Corresponding author. Tel.: +44 28 902368755; faE-mail address: p.joseph@ulster.ac.uk (P. Joseph).

The current article focuses on gasification as a primary disposal solution for cellulosic wastes derivedfrom chicken farms, and the possibility to recover energy from this process. Wood shavings and chickenlitter were characterized with a view to establishing their thermal parameters, compositional natures andcalorific values. The main products obtained from the gasification of chicken litter, namely, producer gas,bio-oil and char, were also analysed in order to establish their potential as energy sources. The experi-mental protocol included bomb calorimetry, pyrolysis combustion flow calorimetry (PCFC), thermo-gravimetric analyses (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR)spectroscopy, Raman spectroscopy, elemental analyses, X-ray diffraction (XRD), mineral content analysesand gas chromatography. The mass and energy balances of the gasification unit were also estimated. Theresults obtained confirmed that gasification is a viable method of chicken litter disposal. In addition tothis, it is also possible to recover some energy from the process. However, energy content in the gas-phase was relatively low. This might be due to the low energy efficiency (19.6%) of the gasification unit,which could be improved by changing the operation parameters.

Crown Copyright � 2011 Published by Elsevier Ltd. All rights reserved.

1. Introduction equipment costs, the odour produced during the process and

Current practices for the disposal of the chicken litter includespreading on agricultural land and re-use as a compost materialin the mushroom industry. There are problems associated withboth methods of disposal, primarily, owing to the increasing lackof land available, regulation constraints and the environmentalconcerns regarding an over-application of this material (Kelleheret al., 2002; Szogi and Vanotti, 2009; Bitzer and Sims, 1988). Inaddition, over-use of chicken litter on land can cause both the pol-lution of water resources and the imbalance of nutrients in the soil.This could lead further to eutrophication of water bodies, thespread of pathogens, the production of phytotoxic substances, airpollution and emission of greenhouse gases. All of these factorshave profound negative effects on the environment, human healthand the health of livestock.

Composting and anaerobic digestion are the established alter-native biological processes for the treatment of chicken litter.Composting of chicken litter has been shown to be a successfulprocess with the ability of selling the end material as a fertiliser.However, this methodology has also some serious drawbacks(Tiquia and Tam, 2000). The process generally results in the pro-duction of a fertiliser with a lower market value and the possi-bility of ammonia pollution of the atmosphere or nitratepollution of the water sources (Kelleher et al., 2002). Further-more, composting is usually uneconomical due to the high

011 Published by Elsevier Ltd. All

x: +44 28 90368726.

the decreasing availability of land. Anaerobic digestion of chickenlitter, on the other hand, is a reasonably efficient conversiontechnology, which produces bio-gas containing methane. How-ever, detailed research in this area has highlighted the variousdisadvantages of anaerobic digestion including high capital costs,specialist operating conditions to ensure methane production,minimum waste reduction during the process, and a large per-centage of the generated energy is generally required to runthe process on site (FEC Services Ltd., 2003).

The third alternative disposal technique other than gasificationis direct combustion of the chicken litter. This process generallyproduces heat and bottom ash containing particles of uncombu-sted material. The char has a potential to be used as a fertiliseron land. However, direct combustion could cause air pollution ifit is not monitored correctly. A recent study has concluded thatgasification seemed to be the most economical solution for theeffective disposal of chicken litter with the benefit of energygeneration (Belgiorno et al., 2003). Generally, the gasification ofsolid wastes showed that the process offers considerable amountof energy recovered at low emission levels.

It is becoming increasingly clear that the long-term viability oftraditional methods of chicken litter disposal is not desirableowing to various environmental and legislative constraints. Theimplications of these constraints have encouraged the develop-ment into alternative methods of disposal, especially in recentyears. There are a number of thermo-chemical conversion technol-ogies (e.g. pyrolysis, combustion and gasification) available toproduce a valuable fuel from chicken litter (Sheth and Babu, 2009).

rights reserved.

702 P. Joseph et al. / Waste Management 32 (2012) 701–709

Generally, there are a number of benefits regarding small-scalegasifiers compared to large-scale gasification plants, for example,the elimination of chicken litter transportation costs to a farmerdue to the process being on-site. In addition, the electricity pro-duced by the gasification process can be used directly to run thefarm operations (Singh et al., 2007; Malkow, 2004). Thus, the pro-cess could potentially play an important role in achieving a sus-tainable energy economy.

The current study investigates the thermo-chemical aspects ofgasification and the use of cellulose-based materials for the pro-cess. The main aim of this research was to determine the thermalcharacteristics of cellulosic wastes derived from chicken farms. Inorder to achieve this, various experimental techniques wereconducted on these cellulosic wastes to determine their thermalbehaviours, compositions and calorific values. These cellulosicwastes primarily include wood shavings and chicken litter. Thewood shavings were used in the current work as a control sampleto compare with the chicken litter.

A further aim was to establish the possibility of recovering en-ergy from the gasification of the cellulosic waste. The gasificationof chicken litter yielded a certain quantity of char and oil-basedsuspension (i.e. by-products), as well as the primary product, agas fraction. An analysis of the by-products from the gasificationprocess was conducted to assess their characteristics. The overallexperimental protocol of the programme was designed with a viewto establishing whether the by-products from the gasificationprocess could be utilised as a fuel, or whether they are merelyproducts of waste that will require some sort of cost-effectivedisposal procedure.

2. Experimental

2.1. Materials

Wood shavings, obtained from Agnew and Company (Redhill,County Cavan, Ireland), were used as the bedding material priorto the stocking of birds in the broiler farm. The farm was of a med-ium size, and had a capacity of 140,000 broilers at any time with anannual turnover of 840,000 broilers. The wood shavings were pro-duced from Finnish spruce trees, and were estimated to have amoisture content of between 14 and 18 wt.%. The chicken litterwas carefully collected from different parts of the chicken housein order to ensure the uniformity of the sample.

Fig. 1. Scheme of the g

The producer gas was the main component obtained from thegasification process. Six samples of the gas were collected: threesamples produced from the gasification of dry chicken litter andthree samples from the gasification of wet chicken litter. Thesesamples were collected, at high and low operating flow rates ofthe unit, in gas-bags for the gas chromatographic analyses.

The char that was obtained as a by-product of the chicken littergasification was likely to be consisted of some un-burnt carbona-ceous matter, and might contain particles of chicken litter due toincomplete combustion. This char was collected from the sealedbarrel, at the gasification plant, and stored in airtight bags. Theoil samples, also by-products from the gasification process, weretaken from the top and from the bottom of the oil storage tankfor chemical separation using different solvents.

2.2. The gasification apparatus

The gasifier, preloaded with the chicken litter, was started fromthe ambient temperature. The flare ignited shortly after a start-upand the gasifier operated continuously for the entire duration ofthe process. The temperature was measured by using two temper-ature probes inserted into the reaction zone. The gasificationprocess of the chicken litter occurred in the reactive environmentof air yielding gaseous species, char and bio-oil. The gasifier wasa pilot scale, capable of accepting the chicken litter at a rate of49 kg per hour. The unit operated continuously for 24 h prior tothe experiment.

A schematic diagram of the gasification process is shown inFig. 1. The fuel (chicken litter) was admitted to the gasificationchamber above the zone of reaction and then onto a grate forminga mound of litter. There were several small holes in this grate, forentry of air from the bottom of the gasifier, and was subsequentlyblown up through the litter mound. The temperature of the unitwas maintained at ca. 320 �C; however, the temperature in its corewas estimated to be in the region of ca. 500 �C. The chicken litterpassed through various zones within the unit prior to the releaseof the gasification products from it (Fig. 2). The raw gas producedexited via the top of the unit, passed through two fans, which gen-erated the updraft, control flow rate and control air intake. The gasproduced by the updraft gasifier tended to be quite contaminatedwith noticeable levels of tars/oils and moisture. For this reasonthe gas was then passed through two scrubber units which werefilled with metal packing. The tars/oils were removed from thehot gas, after striking at the cold surface of metal packing, and

asification process.

Fig. 2. Scheme of the updraft gasification unit.

P. Joseph et al. / Waste Management 32 (2012) 701–709 703

passed down into an oil storage tank situated below. The metalpacking was kept cool by the circulation of cold water aroundthe exterior shell of the scrubber units. The gas was then passedthrough a further cooling system with a view to lowering the mois-ture content in the gas. The gas was then mixed in a tank to ensureits homogeneity. From the mixing tank, the gas could be either fedinto a generator for electricity production or ignited to provide theheat. The process yields a certain amount of char, which fell downthe side of the gasification unit and through the holes in the grate.It was collected at the base of the main gasifier unit and then trans-ferred via a circular auger into a sealed barrel. The updraft gasifica-tion unit outlined above (Fig. 2) had certain salient features such assimplicity, ease of use, robustness and mobility owing to its smallscale.

3. Results and discussion

3.1. Chemical separation

The samples of bio-oil, taken from the top and from the bottomof the oil storage tank, were subjected to chemical separations,involving partitions between aqueous and organic layers of severalsolvents with a view to establishing the amount of water present.Four different solvents were added to the oil-based samples:water, diethyl ether, dichloromethane and chloroform. It was

observed that diethyl ether and dichloromethane achieved thehighest degrees of separation, on both oil samples, in a separatingfunnel. The extracted ethereal layer was carefully evaporated fromaluminium pans (at ca. 120 �C in a vacuum oven for several hours)to establish the weights of the leftover residues.

It was calculated that the bio-oil collected directly from the topand bottom of the oil storage tank contained 94.4 and 96.5 wt.% ofwater, respectively. These relatively high values of water contentsin bio-oil samples would severely restrict their ability to be used asa fuel, even though this by-product was produced in large quanti-ties during the gasification (20.8 kg of bio-oil produced from 49 kgof litter). The acidity of the oil samples was also higher thanexpected: pH value was 4.2, which is lower than the pH of 5.93reported by Mante and Agblevor (2010).

3.2. Bomb calorimetric measurements

Calorific values of wood shavings, chicken litter and char weredetermined with the aid of IKA C 200 bomb calorimeter. The mea-surements were conducted on samples of wood shavings andchicken litter in the form of pellets, weighing ca. 1 g. The char sam-ples could not be pressed into pellets and, therefore, they werecompacted into gelatine capsules and then placed into the samplecrucible. The ‘bomb’ was filled with oxygen up to 3.0 MPa ofpressure, and subsequently ignited. The final calorific values were

Fig. 4. TGA curves of wood shavings (1), chicken litter (2) and char (3) recorded inair.

704 P. Joseph et al. / Waste Management 32 (2012) 701–709

displayed by the instrument, by employing proprietary software.For each samples triplicate runs were done for better accuracy ofthe results.

Assuming complete combustion, the wood shavings had acalorific value of 18.27 ± 0.06 MJ/kg. This was approximately 26%higher than the chicken litter (13.54 ± 0.01 MJ/kg) and approxi-mately 31% higher than char (12.63 ± 0.11 MJ/kg). The calorificvalue of the wood shavings obtained was found to be similar tothe value of 18.02 MJ/kg as reported previously (Mante andAgblevor, 2010). In other reports (Quiroga et al., 2010; Kim andAgblevor, 2007; Bock, 2004), similar experiments yielded calorificvalues of 19.12 MJ/kg for wood waste, 19.54 MJ/kg for wood chipsand 20.38 MJ/kg for sawdust. The differences in calorific valuesobtained can be attributed to the differences in the chemical com-positions and water contents of the base ligno-cellulosic materialsused for the different studies. The calorific value of the chickenlitter sample obtained was in close agreement with that found inthe literature precedents (Kelleher et al., 2002; Quiroga et al.,2010). The average calorific value for the char sample was foundto be 12.63 ± 0.11 MJ/kg, which is only 9% less than the calorific va-lue of the chicken litter. The higher than expected calorific value ofthe char indicates that the gasification process was incomplete,leading to a formation of gaseous products with lower energy con-tent. This might be due to the fact that the char exited the gasifica-tion unit before it underwent the complete combustion, and hencehad the relatively higher energy content. In addition, this is alsoassociated with relatively lower operating temperature of the unitas well as on the inefficiencies by which the air circulation wasmaintained in the unit during the experiments.

Fig. 5. TGA curves of wood shavings (1), chicken litter (2) and char (3) recorded inoxygen.

3.3. Thermo-gravimetric analyses (TGA)

The thermo-gravimetric analyses were conducted on samples ofwood shavings, chicken litter and char, using Mettler Toledo TGA/SDTA851e instrument. The TGA were carried out on ca. 10 mg ofsamples, at a heating rate of 10 �C/min in atmospheres of nitrogen,air and oxygen, at a flow rate of 50 cm3 per minute, from 30 to1000 �C. The TGA runs on samples were primarily performed inorder to establish the various physio-chemical changes that occurwhen they were heated in atmospheres of nitrogen, air and inoxygen (Figs. 3–5).

As can be seen from Fig. 3, there were initial weight losses forthe wood shavings, chicken litter and char, up to about 120 �C. Thisfirst stage of weight loss is due to the removal of moisture, presentin the form of bound water, in the pores and on the surface of the

Fig. 3. TGA curves of wood shavings (1), chicken litter (2) and char (3) recorded innitrogen.

samples (Gottipati and Mishra, 2010). The subsequent stages(between 120 and 500 �C) of weight losses for wood shavings couldbe attributed to the decomposition of the constituents (hemicellu-loses, cellulose and lignin), and to further decomposition of thecharcoal formed (Bock, 2004; Gaur and Reed, 1995). The percent-ages of residues at 500 �C for wood shavings, chicken litter andchar were 21, 44 and 86 wt.%, respectively. These values recordedat 1000 �C decreased to 16 wt.% for wood shavings, to 36 wt.% forchicken litter and to 74 wt.% for char. This indicates that at temper-atures above 500 �C there were relatively minor weight losses inwood shavings, chicken litter and char of 5, 8 and 12 wt.%, respec-tively. The decomposition temperatures and the degradation of thechicken litter were also similar to the results reported previously(Kim and Agblevor, 2007; Singh et al., 2008). The TGA curve of charhad four weight loss regimes in the region of main decomposition,which could be attributed to the heterogeneous nature.

Generally for the samples, the thermograms in air (i.e. in an oxi-dative atmosphere) showed multistep decomposition processes asin nitrogen, but the residual weights at 1000 �C were much lowerowing to enhanced oxidation (Gottipati and Mishra, 2010). Moreor less similar trends were observed during the TGA runs in pureoxygen, except in the case of chicken litter, which could beattributed to its complex compositional nature (e.g. the presenceof N-containing compounds) and the heterogeneity. However,maximum oxidation of the cellulose materials was affected in thepresence of oxygen, thus giving rise to the minimum amounts ofresidues.

P. Joseph et al. / Waste Management 32 (2012) 701–709 705

In addition, a correlation can be seen from the calorific valuesobtained from the bomb calorimetry and the TGA residues in oxy-gen (Table 1). The higher the calorific values of the samples, thelower the percentages of residues obtained from the TGA runs ofwood shavings, chicken litter and char.

Fig. 6. FT-IR spectra of wood shavings (1) and chicken litter (2).

3.4. Differential scanning calorimetry (DSC)

Differential scanning calorimetric (DSC) analyses were per-formed on samples of wood shavings, chicken litter and char inan inert atmosphere of nitrogen, at a flow rate of 50 cm3 per min-ute, by employing a DSC Q100 V9.8 Build 296 instrument. The tem-perature range for each sample was between 20 and 180 �C. Thesample size ranged from 3 to 6 mg, which were accurately weighedprior to each run.

The endotherms observed on the DSC curves which are centredaround 90 �C could be associated with the release of bound waterfrom the samples. Also, the DSC gave an indication of the amountof thermal energy required to remove the bound water from eachsample. The energy required to remove the bound water from thesamples were: 216.2 J/g for the wood shavings; 517.2 J/g for thechicken litter; 118.6 J/g for the char. There was a correlationbetween these values and the amount of water contained in thecase of wood shavings and chicken litter. The values might alsoreflect the difference in the binding energy contents of the waterin each sample as well. As is expected water molecules are stronglybound to the nitrogenous waste compounds present in the chickenletter.

3.5. Fourier transform infrared (FT-IR) spectroscopy

The FT-IR spectra were recorded for the samples of woodshavings, chicken litter and char. The instrument used for the anal-ysis was a Thermo-Nicolet FTIR, Nexus model 470. Spectra wereobtained over a frequency range of 4000–500 cm�1 in the attenu-ated total reflectance (ATR) mode. Each sample was groundedusing a pestle and mortar to ensure homogeneity before recordingthe spectra.

As is expected the FT-IR spectrum of the wood shavings (Fig. 6)showed the characteristic features of a typical ligno-cellulosicmaterial (Coates, 2000; Davalos et al., 2002). The spectrogram ofthe chicken litter was similar to that previously reported (Manteand Agblevor, 2010); however, the peaks were very broad and of-ten overlapped (Fig. 6). The peak at 2921 cm�1 can be assignedto methylene (CH2) asymmetric stretch of aliphatic hydrocarbons.The peak at 1630 cm�1 can be assigned to amide carbonyl (C@O)stretch, while the peak at 1005 cm�1 indicates a high presence ofphosphorus-containing functionality in the chicken litter. The peakat 1389 cm�1 can be assigned to organic sulphates and the peak at3214 cm�1 was assigned to hydroxyl groups (OH) hydrogenbonded stretch (Muller et al., 2009). This signal can be explainedby the presence of wood shavings in the chicken litter. The FT-IRof chicken litter indicates that it might contain some carbohy-drates, along with nitrogenous and inorganic compounds.

The char produced ill-resolved FT-IR spectra showing broadpeaks indicative of large amounts of water retention. The quality

Table 1Correlation of calorific values and TGA residue percentages recorded in oxygenatmosphere.

Samples DHcomb (MJ/kg) Residue in oxygenat 1000 �C (wt.%)

Wood shavings 18.27 ± 0.06 2.14Chicken litter 13.54 ± 0.01 28.42Char 12.63 ± 0.11 42.03

of this spectrum could be attributed to a poor transmittance duringspectral acquisition as it was recorded in the reflective mode. Fordefinite peak assignments, a better resolved spectrum, possiblythrough diffuse reflectance FT-IR, need to be obtained.

3.6. Elemental (C, H, N and S), ash and moisture content analyses

The elemental compositions (C, H, N and S) of the wood shavings,chicken litter and char were conducted by employing a Perkin–Elmer PE2400CHNS elemental analyser, in duplicate. The moistureand ash contents of the chicken litter were measured in accordancewith CEN TS 14774 and CEN TS 14775, respectively.

The results obtained for the elemental, moisture content andash content analyses are presented in Table 2. As can be seen fromthe table below, the ash content of the chicken litter was 11.3 wt.%,which is relatively lower than reported previously (Kim andAgblevor, 2007; Bock, 2004). This could be explained by the varia-tions within the chicken litter, for example, by the type of beddingand by the moisture content. The nitrogen content in the chickenlitter was 3.7 wt.%, compared to less than 0.5 wt.% for the woodshavings. This is attributed to the protein and urea content in thechicken litter. The higher nitrogen content generally increasesthe potential for NOx emission during gasification/combustion.However, on the other hand, the char obtained from the gasifica-tion of the chicken litter still contains almost 93% of nitrogen pres-ent in the litter. This indicates that there will be minimal amountsof NOx released during the process. Ideally, the halogen contents ofthese materials should be established in order to assess the toxicity(primarily the propensity to form dioxins/dibenzofurans) uponcombustion.

3.7. Mineral content analyses

The analyses of the mineral contents were performed on thesample of char. X-ray Fluorescence (XRF), using an ELTRA CS-800automatic carbon/sulphur analyser, a Philips PERL’X 3 automaticglass bead casting machine and a Philips MagiX pro-XRF, were

Table 2Results of elemental, ash and moisture content analyses.

Component Wood shavings Chicken litter Char

Moisture content (wt.%) 14–18 21.5 –Carbon (C) (wt.%) 45.8 30.5 36.4Hydrogen (H) (wt.%) 6.7 6.7 2.1Nitrogen (N) (wt.%) <0.5 3.7 3.4Sulphur (S) (wt.%) <0.5 0.5 <0.5Ash (wt.%) – 11.3 –

Fig. 7. Raman spectrum of the char sample.

706 P. Joseph et al. / Waste Management 32 (2012) 701–709

employed for the purpose of estimating the chemical composi-tions. The XRF analysis was conducted in accordance with DIN51729-10 (Analysis of coal and coke ash by X-ray fluorescence). Thechar was also analysed to determine its P and K values. The charwas digested, by refluxing under a vacuum using concentrated sul-phuric acid prior to the analyses.

The results obtained from the mineral content analyses on thechar are presented in Table 3. These values are slightly higher thanthat reported previously (Bock, 2004). The composition of the charproduced, especially in terms of the P and K weight percentages,from the gasification of chicken litter makes it a viable option foruse as a fertiliser on land.

3.8. Raman spectroscopy

Raman spectrum was recorded on the char sample using an ISALabRam 300 system, with 632.8 (1.96 eV) laser and with a spectralresolution of 2 cm�1. The spectra were collected over five sweepsof 10 s each and a 10% filter (giving a spot power of approximately1 mW, considering a maximum laser power of 10 mW). The Ramanspectrum of the char has two broad peaks, at 1334 and 1571 cm�1

(Fig. 7). These peaks, both originating from pre-graphitic struc-tures, could be assigned to the defect (D) band and to the graphitic(G) band, respectively. Such observations favourably compare withthose reported in the literature (Li et al., 2006).

3.9. X-ray diffraction (XRD)

Powder XRD patterns were obtained for wood shavings andchar by employing a Bruker AXS D8 Advance diffractometer havinga Cu Ka X-ray source (k = 1.54 Å; 40 mA; 40 kV). Typical scanparameters consisted of a range of 2h values, from 10 to 50, with0.05 increments and 10 s dwell.

The wood shavings gave well-resolved diffractogram asexpected for a ligno-cellulosic material (Fig. 8a). On the contrary,the pattern from the char (Fig. 8b) was rather diffuse andill-resolved; however it contained broad features of crystallinedomains, both aromatic and graphitic, centred around 20 and 30degrees, respectively (Zhu and Shi, 2003; Zhou et al., 2008). Theseobservations broadly complement the corresponding findings fromthe Raman spectrum in that they clearly show patterns owing tothe presence of pre-graphitic structures in the ash.

3.10. Pyrolysis combustion flow calorimetry (PCFC)

Pyrolysis combustion flow calorimetric (PCFC) measurementswere carried out using a Fire Testing Technology Ltd. (FTT) MicroCalorimeter, which basically works on the principle of oxygendepletion calorimetry (Lyon and Walters, 2004; Cogen et al.,2009). Accurately weighed (ca. 5 mg) of the solid samples werefirst heated to about 900 �C at constant heating rate of 1 K s�1, in

Table 3Mineral content of the char.

Main components Content (wt.%)

SO2�3

7.23

SiO2 6.34Al2O3 1.23Fe2O3 1.06CaO 21.50MgO 5.90K2O 16.51Na2O 6.52TiO2 0.10P2O5 25.12MnO�3 0.22

a stream of nitrogen flowing at a rate of 80 cm3 min�1. The thermaldegradation products, thus obtained, were then mixed with a20 cm3 min�1 stream of oxygen prior to entering a combustionchamber maintained at a temperature of 900 �C. Each samplewas run in triplicate and the data obtained were averaged overthe three measurements. The instrument also generates plots ofthe heat release rates (HRR) against the temperature and gives val-ues for the maximum amount of heat released per unit mass perdegree of temperature (i.e. heat release capacity measured inJ g�1 K�1), the latter being a reliable indicator regarding flammabil-ity of a material (Table 4).

As can be seen from the table, the peak heat release rate(pkHRR), the total heat released (THR) and the heat releasecapacity (HRC) normalized to the mass is maximum for the woodshavings, followed by the litter and least for the char. This hasstrong correlations with the heats of combustion, and hence withthe effectiveness of combustion, as measured by the bomb calo-rimeter (see Table 1). However, from a point of view of the fire haz-ard upon storage, as reflected by the corresponding values ofpkHRRR, THR and HRC, the wood shavings possess the maximumand the char the minimum with the litter some way in between.The enhanced microbial activity of chicken litter on storage mightposses additional risk of ‘self-heating’ and evolution of combusti-ble lower hydrocarbons, that could lead to self-heating and sponta-neous ignition/explosion.

3.11. Gas chromatography (GC)

Gas chromatographic (GC) analyses were conducted on the pro-ducer gas samples obtained from the gasification of wet or drychicken litter, and at low and high flow rates of the unit. The chick-en litter was a heterogeneous mixture with the original woodshavings that were used as the bedding material. The gasificationunit was running for 24 h prior to the collection of the test samplesto ensure the gasifier temperature and flow rates are stabilized.Prior to obtaining any gas sample, it was tested to establish itsmoisture content in accordance with BS EN 14790 (Stationarysource emissions – Determination of the water vapour in ducts). Thetemperature and flow rates were also measured at a point priorto the gas burner.

Overall, six samples of gas were taken: two samples were pro-duced from the gasification of wet litter at a low flow rate; two sam-ples – from dry litter at a low flow rate; one sample – from dry litterat a high flow rate; one sample from wet litter at a high flow rate.Each sample was filtered using a heated filter prior to collection.The gas was extracted from the sample stream via an unheated

Table 4Data obtained from pyrolysis combustion flow calorimetry (PCFC).

Product Temp to pkHR ± 5.9 (�C) pkHRR ± 6.42 (W g�1) THR ± 1.77 (kJ g�1) HRC ± 6.487 (J g�1 K�1)

Wood shavings 381.9 121.87 10.43 123.758Chicken litter 314.0 44.47 8.75 45.214Char 510.4 9.63 1.28 9.785

Fig. 8. X-ray diffractograms of wood shavings (a) and char (b).

Table 5Composition, moisture content and calorific values of producer gas samples.

Component Run 1 Run 2 Run 3 Run 5 Run 6

Moisture content (vol.%) 13.94 13.94 8.99 11.42 14.01Hydrogen sulphide (ppm) <10.0 <10.0 <10.0 36 12Carbon dioxide (vol.%) 8.9 8.9 5.5 14 10Carbon monoxide (vol.%) 6.9 6.9 8.5 9.4 3.1Ethane (vol.%) <0.16 <0.16 0.12 0.36 0.16Hydrogen (vol.%) 5.2 5.2 5.5 7.8 3.2Methane (vol.%) 0.88 0.88 0.76 1.7 0.67Nitrogen (vol.%) 68 68 69 60 70Oxygen (vol.%) 9.4 9.4 11 6.5 12Calorific value (MJ/m3) 1.9 1.9 2.0 2.9 1.1

Sample contained in Run 4 had deflated upon arrival to the laboratory, and there-fore, is classified as a void sample.

P. Joseph et al. / Waste Management 32 (2012) 701–709 707

sampling line into a Tedlar bag using a vacuum chamber,Vac-U-Chamber. The gas samples were then tested using the follow-ing analytical techniques: GC-TCD (Gas Chromatography onThermal Conductivity Detector) and GC–MS (gas chromatogra-phy–mass spectrometry). Table 5 shows the composition of thegas obtained from the gasification of six chicken litter samples. Eachsample is labelled according to the ‘run’ number (Run 1 – wet chick-en litter at a low air flow rate of 65.86 m3/h; Run 2 – wet chicken lit-ter at a low air flow rate of 65.73 m3/h; Run 3 – dry chicken litter at alow air flow rate of 65.33 m3/h; Run 4 – void run; Run 5 – dry chickenlitter at a high air flow rate of 96.85 m3/h; Run 6 – wet chicken litterat a high air flow rate of 96.77 m3/h). The table also shows themoisture content of the gas samples in accordance with BS EN

Fig. 9. Mass balance for the gasification unit.

14790. The temperature of the exit gas obtained was between 32and 38 �C. The temperature inside the reactor increased as the flowrate increased. As expected gaseous products from the wet chickenlitter had higher moisture content than those from the dry chickenlitter (13.94 vol.% and 8.99 vol.%, respectively). It also shows thatthe moisture content of the gas increases as the flow rate of the unitrises.

As previously noted by Russell (2008), the producer gas from airgasification has a relatively low calorific value of 4 MJ/m3. It wasalso indicated that this can be associated with the dilution effectof nitrogen present in air. Our results indicate that the calorific val-ues of the producer gas vary from 1.1 to 2.9 MJ/m3, depending onthe moisture content of the chicken litter and a flow rate of theunit. The data from the analysis of the gas produced from bothchicken litter samples, at both high and low flow rates, stronglysuggest that the relative intake of the air within the unit was high.This gives rise to excessive combustion and a poor quality of a pro-ducer gas. The gas sample obtained from the dry chicken litter at ahigh flow rate (Run 5) shows the lowest level of oxygen content at6.5 vol.% and the lowest level of nitrogen content at 60 vol.%. Theseconditions allowed generating the producer gas with the highestcalorific value of 2.9 MJ/m3. It is also characterized by the highestconcentrations of hydrogen, methane and carbon monoxide.

3.12. Mass and energy balance

An overall efficiency of the gasification plant could be obtainedthrough mass and energy balance for the whole process (Figs. 9

Fig. 10. Energy balance for the gasification unit.

708 P. Joseph et al. / Waste Management 32 (2012) 701–709

and 10). The energy flow was calculated as mass flow rate � calo-rific value. The mass and energy of the material input (chicken lit-ter) was compared to the mass and energy of the material output(char, oil and producer gas). The updraft gasifier takes in 49 kg/hof chicken litter (38.5 kg dry litter and 10.5 kg water) and theoutput consists of 14 kg/h of char and 20.8 kg/h of oil (1.2 kg oilyliquid and 19.6 kg water). The air intake is 67.1 m3/h, which isapproximately equivalent 67.1 kg/h. The gas output has a flow rateof 65.33 m3/h and density of 1.245 kg/m3 and therefore a mass of81.3 kg/h.

The updraft gasifier has an input energy value of 663.46 MJ/h(chicken litter) and an output of energy of 176.82 MJ/h (char)and 130.66 MJ/h (producer gas). This indicates that 356 MJ/r is lostduring the process. It was found that the overall gasification pro-cess was only 19.6% efficient.

4. Conclusions

The overall aim of the present work was to determine thecharacteristics of the cellulosic wastes derived from chickenfarms and their gasification products, and to establish the feasi-bility of recovering energy from the gasification of the wastematerials. The materials analysed included wood shavings, chick-en litter, producer gas, char and oil. The main conclusions of thework are:

� The calorific value of the wood shavings was found to beapproximately 26% higher than that of chicken litter. Thismeans that the more wood shavings present in the chicken lit-ter, the higher the calorific value achieved, and hence the moreenergy can be recovered.� The elemental analyses showed that the chicken litter con-

tained more nitrogen compared to wood shavings, owing tothe presence of nitrogenous compounds (urea and faeces). Thechicken litter had C/H ratio of 4.55 compared to 6.84 for woodshavings and 17.33 for char.� The gas chromatography indicated that the quality of primary

gas produced from the process was variable. The highest calo-rific value (2.9 MJ/m3) was achieved for the gas obtained fromdry chicken litter, at a higher flow rate in the unit. It is envis-aged that appropriate alterations to the operating parametersof the gasification unit would result in a producer gas havinghigher calorific value.� The char had N, P and K values of 3.4, 25 and 16 wt.%, respec-

tively, pointing towards its possible use as a fertiliser substitute.The relatively higher NPK values also indicated a prematureremoval of the char, from the gasification process, and thusresulting in incomplete conversion.� It was established from the present study that the bio-oil pro-

duced from the gasification process was of poor quality, havinghigh moisture content (up to 95 wt.%) and low pH level (4.2).� Careful mass and energy balances of the plant showed that the

quantity of energy recovered from the gas is inadequate. This isattributed to the technical operating parameters of the gasifica-tion unit, and will require rigorous adjustments in order toimprove the quality of gas produced.

It is recommended as future work to make appropriate changesto operating parameters of the gasification unit, in order to obtainproducer gas with the optimum calorific value. This might beachieved by reducing the air intake of the unit, thus reducing thelevels of oxygen and nitrogen in the gaseous phase, which wasdiluting it. A further suggestion is to operate the unit at the highflow rate and increasing the temperature profile. This might pro-vide more favourable conditions for complete combustion of the

char by-product. The higher temperature might reduce the calorificvalue of the char and in turn add to the calorific value of the gas. Inaddition, in order to obtain a more quantitative analysis of theenergetics of the whole process, the Equivalent Ratios (ERs) shouldbe known and set to optimum values (0.2–0.3). The char is valuableas a fertiliser and hence control of its mineral content is alsoimportant. Reducing the calorific value of the char will not neces-sarily lessen its value as a fertiliser. It is also recommended toestablish the composition of the organic fraction of bio-oil and todetermine its calorific value.

Acknowledgements

We greatly acknowledge the Nanotechnology and IntegratedBioengineering Centre (NIBEC), University of Ulster, UK, for allow-ing us to use some their analytical facilities. One of us, SMK, is alsograteful to the Fire Safety Engineering Science and Technology Cen-tre (FireSERT), University of Ulster, UK, for the provision of an MScstudentship.

References

Belgiorno, V., De Feo, G., Della Rocca, C., Napoli, R.M.A., 2003. Energy fromgasification of solid wastes. Waste Management 23, 1–15.

Bitzer, C.C., Sims, J.T., 1988. Estimating the availability of nitrogen in poultrymanure through laboratory and field studies. Journal of Environmental Quality17, 47–54.

Bock, B.R., 2004, Poultry litter to energy: technical and economic feasibility.Available from: <http://www.brbock.com/RefFiles/PoultryLitter_Energy.doc>.(accessed 23.03.11).

Coates, J., 2000. Interpretation of infrared spectra, a practical approach. In: Meyers,R.A. (Ed.), Encylopedia of Analytical Chemistry. John Wiley & Sons Ltd,Chichester, pp. 10815–10837.

Cogen, J.M., Lin, T.S., Lyon, R.E., 2009. Correlations between pyrolysis combustionflow calorimetry and conventional flammability tests with halogen-free flameretardant polyolefin compounds. Fire and Materials 33, 33–50.

Davalos, J.Z., Roux, M.V., Jimenez, P., 2002. Evaluation of poultry litter as a feasiblefuel. Thermochimica Acta 394, 262–266.

FEC Services Ltd, 2003. Anaerobic digestion, storage, oligolysis, lime, heat andaerobic treatment of livestock manures. Available from: <http://www.scotland.gov.uk/Resource/Doc/1057/0002224.pdf>. (accessed 23.03.11).

Gaur, S., Reed, T.B., 1995. An atlas of thermal data for biomass and other fuels, NREL/TP-433–7965. Golden, Colorado.

Gottipati, R., Mishra, S., 2010. Application of biowaste (waste generated in biodieselplant) as an adsorbent for the removal of hazardous dye-methylene blue-fromaqueous phase. Braz. J. Chem. Eng. Online 27, 357–367.

Kelleher, B.P., Leahy, J.J., Henihan, A.M., O’Dwyer, T.F., Sutton, D., Leahy, M.J., 2002.Advances in poultry litter disposal technology – a review. BioresourceTechnology 83, 27–36.

Kim, S.-S., Agblevor, F.A., 2007. Pyrolysis characteristics and kinetics of chickenlitter. Waste Management 27, 135–140.

Li, X., Hayashi, J., Li, C., 2006. FT-Raman spectroscopic study of the evolution of charstructure during the pyrolysis of a Victorian brown coal. Fuel 85, 1700–1707.

Lyon, R.E., Walters, R.N., 2004. Pyrolysis combustion flow calorimetry. Journal ofAnalytical and Applied Pyrolysis 71, 27–46.

Malkow, T., 2004. Novel and innovative pyrolysis and gasification technologies forenergy efficient and environmentally sound MSW disposal. Waste Management24, 53–79.

Mante, N.O.D., Agblevor, F.A., 2010. Influence of pine wood shavings on thepyrolysis of poultry litter. Waste Management 30, 2537–2547.

Muller, G., Schopper, C., Vos, H., Kharazipour, A., Polle, A., 2009. FTIR-ATRspectroscopy analyses of changes in wood properties during particle- andfibreboard production of hard- and softwood trees. Bioresources 4, 49–71.

Quiroga, G., Castrillon, L., Fernandez-Nava, Y., Maranon, E., 2010. Physico-chemicalanalysis and calorific values of poultry manure. Waste Management 30, 880–884.

Russell, A., 2008. Producer gas for power generation. Available from: <http://www.practicalaction.org/practicalanswers/product_info.php?products_id=381{1}1&attrib=1>. (accessed 25.03.11).

Sheth, P.N., Babu, B.V., 2009. Modeling and simulation of downdraft biomassgasifier. Proceedings of 2009 Annual Meeting of AIChE, Nashville, TN, USA,November 8-13, 2009. Available from: <http://www.discovery.bits-pilani.ac.in/’bvbabu/Fullpaper_PNS_BVB_AIChEMtg_2009.pdf>. (accessed 23.03.11).

Singh, K., Risse, M., Worley, J., Das, K.C., Thompson, S., 2007. Adding value to thepoultry litter using fractionation, pyrolysis, and pelleting. ASABE Paper No.74064. St. ASABE, Joesph, Mich.

Singh, K., Risse, M., Worley, J., Das, K.C., Thompson, S., 2008. Effect of fractionation offuel properties of poultry litter. Applied Engineering in Agriculture 24, 383–388.

P. Joseph et al. / Waste Management 32 (2012) 701–709 709

Szogi, A.A., Vanotti, M.B., 2009. Prospects for phosphorus recovery from poultrylitter. Bioresource Technology 100, 5461–5465.

Tiquia, S.M., Tam, N.F.Y., 2000. Fate of nitrogen during composting of chicken litter.Environmental Pollution 110, 535–541.

Zhou, S., Song, L., Wang, Z., Hu, Y., Xing, W., 2008. Flame retardation and charformation mechanism of intumescent flame retarded polypropylene

composites containing melamine phosphate and pentaerythritol phosphate.Polymer Degradation and Stability 93, 1799–1806.

Zhu, S., Shi, W., 2003. Thermal degradation of a new flame retardant phosphatemethacrylate polymer. Polymer Degradation and Stability 80, 217–222.