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Journal of Environmental Management 154 (2015) 177e182

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Journal of Environmental Management

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Recovery of energy and iron from oily sludge pyrolysis in a fluidizedbed reactor

Linbo Qin a, Jun Han a, *, Xiang He a, Yiqiu Zhan a, Fei Yu b

a College of Resources and Environment Engineering, Wuhan University of Science and Technology, Wuhan, 430081 Hubei, Chinab Department of Agricultural and Biological Engineering, Mississippi State University, MS 39762, USA

a r t i c l e i n f o

Article history:Received 21 March 2013Received in revised form12 February 2015Accepted 16 February 2015Available online 27 February 2015

Keywords:Oily sludgePyrolysisFluidized bedEnergyIronRecovery

* Corresponding author.E-mail address: hanjun@wust.edu.cn (J. Han).

http://dx.doi.org/10.1016/j.jenvman.2015.02.0300301-4797/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

In the steel industry, about 0.86 ton of oily sludge is produced for every 1000 tons of rolling steel. Due tothe adverse impact on human health and the environment, oily sludge is designated as a hazardouswaste in the Resource Conservation and Recovery Act (RCRT). In this paper, the pyrolysis treatment of oilysludge is studied in a fluidized bed reactor at a temperature range of 400e600 �C. During oily sludgepyrolysis, a maximum oil yield of 59.2% and a minimum energy loss of 19.0% are achieved at 500 �C. Theenergy consumption of treating 1 kg oily sludge is only 2.4e2.9 MJ. At the same time, the energy ofproduced oil, gas and solid residue are 20.8, 6.32, and 0.83 MJ, respectively. In particular, it is found thatthe solid residue contains more than 42% iron oxide, which can be used as the raw material for ironproduction. Thus, the simultaneous recovery of energy and iron from oil sludge by pyrolysis is feasible.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Oily sludge, generated from the rolling steel process, is a wasteproduct comprising dense slurry of iron fines in lubricating oil andwater with other contaminants such as heavy metals (Biswal et al.,2009). It was estimated that about 0.86 ton of oily sludge wasproduced for every 1000 tons of rolling steel in China (Liu, 1997).Due to the adverse impact on human health and the environment,oily sludge is designated as a hazardous waste in the ResourceConservation and Recovery Act (RCRT) (Liu et al., 2011;Ramaswamy et al., 2007; Zhou et al., 2009). Hence, the disposalof oily sludge without treatment is strictly prohibited. At present,the conventional disposal methods include landfilling (Bossertet al., 1984; Hejazi et al., 2003), chemical extraction (Zubaidy andAbouelnasr, 2010), incineration (Li et al., 1995; Sankaran et al.,1998), biodegradation (Biswal et al., 2009; Liu et al., 2009) andpyrolysis (Liu et al., 2008; Schmidt and Kaminsky, 2001). Landfillingis becoming unfeasible because of the rapid depletion of availablesites and the high cost. Chemical extraction is either too costly oronly partially effective (Zubaidy and Abouelnasr, 2010). Incinera-tion has the shortcomings of high energy consumption with

producing secondary pollutants such as SOX, NOX, heavy metals,and particulate matter, which inhibits the wide application of thistechnique (Karamalidis and Voudrias, 2007; Yao and Naruse, 2009).

Compare with combustion or incineration, oily sludge pyrolysishas received more attentions because of its mild operation condi-tions, energy recovery (pyrolysis oil and gas), and less pollutants.Liu et al. (2008) studied the effects of the operating temperature(350e550 �C) on the products during oily sludge pyrolysis in anexternally heated fixed bed reactor. The results indicated that themass fractions of solid residues, liquids, and gases products were56.00e67.00%, 25.60e32.35%, and 7.40e11.65%, respectively. Theheating values of solid residues, liquids, and gases products were13.8e34.4 MJ/kg, 44.41e46.6 MJ/kg, and 23.94e48.23 MJ/Nm3,respectively. Moreover, themain compositions of the liquid fractionwere alkanes and alkenes (C5eC29), and the gaseous fractions werepredominantly HCs and H2. Schmidt and Kaminsky (2001) claimedthat about 70e84% of the oils could be separated from oily sludgeduring pyrolysis in a fluidized bed reactor at a temperature range of460e650 �C. They also found that the yield of CxHy was highest at600e700 �C. However, the yield of oil decreased significantly withincreasing the heating rate, which was also demonstrated by Shieet al. (2000). Although numerous studies of pyrolyzing the oilysludge from oil refining or petrochemical industries have been re-ported (Karayildirim et al., 2006; Liu et al., 2008; Schmidt and

Table 2

L. Qin et al. / Journal of Environmental Management 154 (2015) 177e182178

Kaminsky, 2001; Shie et al., 2000), only a few reports focus on theoily sludge from the steel industry (Houbart, 2012; Liu et al., 2013).In fact, the components of oily sludge from steel industry aredifferent with those from the oil refining industry. The iron con-centration in the oily sludge from iron and steel industry is rela-tively high. Hence, the investigation of simultaneous recycling ofenergy and iron during oily sludge treatment is very interesting(Houbart, 2012).

The aim of this study was to investigate the simultaneous re-covery of energy and iron resources from oily sludge using pyrolysisin a fluidized bed reactor at a relatively low temperature(400e600 �C). Meanwhile, the effect of temperature on the distri-bution and composition of the pyrolysis products (non-condens-able gases, oil and solid residue) was also studied.

2. Experimental

2.1. Materials

The oily sludge used in this experiment was obtained from therolling steel process of an iron and steel company in Wuhan city,China. The proximate analysis and ultimate analysis were sum-marized in Table 1.

The oil content of oily sludge is measured by solvent extraction,also as Table 1. The oil extraction method was described by Zubaidyand Abouelnasr (2010). 40 g of oily sludge were added to specifiedamounts of chloroform. The mass ratio of solvent-to-sludge was5:1. After mixing oily sludge and solvent, the sample was filtered,dried to remove solvent, and then weighed. The filtrate wasdistilled using a batch simple distillation apparatus. In addition, theinorganic materials of the solid residues in the oily sludge areanalyzed by X-ray fluorescence spectrometry (XRF).

2.2. Experimental apparatus and procedures

The oily sludge pyrolysis was carried out in a fluidized bedreactor with an internal diameter of 0.4 m and a vertical length of1.2 m. The system consisted of a stainless steel reactor, a coolingsystem for separating water and the condensable oil, and a gascleaning/drying system followed by gas measurement devices. Thereactor was electrically heated, and the temperature was measuredwith thermocouples and controlled. The experimental tempera-tures were 400, 450, 500, 550, and 600 �C. In order to maintain aninert atmosphere, nitrogenwas fed into the reactor at a flow rate of1.0 L min�1 for 30 min. The residence time of the gaseous productsin the reactor was about 13 s.

When the temperature of the reactor reached the pre-deter-mined temperature, the oily sludge was continuously fed by aninjector with a feeding rate of approximately 2.0 g/min, and thefeed time was 50 min in each runs. The gases released from oily

Table 1Chemical characteristics of the oily sludge.

Ultimate analysis (W%) Low heatingvalue/MJ Kg�1

Ca Ha Oa,b Na Sa

72.72 5.20 14.96 4.05 2.07 28.28

Proximate analysis (W%) Components (W%)

Fixed carbona Asha Volatilea Moisturec Oil contentc Solid residuec

9.35 16.67 73.98 32.64 48.06 19.30

a Dry base.b Calculated by difference.c As received basis.

sludge passed through two consecutive condensers to collect thecondensed oil and water. After a filter, the pyrolysis gas wasanalyzed by a gas analyzer (Gasboard-3100, Cubic optoelectronicCo., China) to record the calorific value and concentrations of CO,CO2, H2, CH4, CmHn, and O2. The total volume of the non-con-densable gas was also measured by a cumulative flow-meter. Afterthe pyrolysis process, the solid residue, liquid fraction including oiland water were collected and weighed. In this experiment, eachrun was repeated 3 times and the average data were used.

The water content in the liquid fraction was analyzed accordingto Chinese standard: Coking products-Determination of moisturecontent (GB/2288-2008). 100 g of pyrolysis oil were added to theflask contained 50 ml toluene. After mixing pyrolysis oil and sol-vent in the flask, the flask was heated, and the water in the oilysludge was evaporated and condensed in the receiving tube. Afterall water was condensed in the receiving tube, the volume of waterin the receiving tube was recorded.

Finally, the oil samples were filtered and dried to remove dustand moisture. And then the sample was characterized usingGCeMS (Agilent 19091S-433, Agilent Corp. USA). The GC was fittedwith a 30 m � 0.25 mm capillary column coated with a 0.25 mmthick film of 5% phenyl methyl silox (HP-5 MS). The carrier gas flow(He) was 1 ml/min, and the split ratio was 10:1. The initial oventemperature of 40 �C was kept isothermal for 4 min and thenheated to 300 �C at a heating rate of 10 �C/min, and held at thistemperature for 10 min. The injector was pulsed split at 250 �C andthe temperatures of the MS source and MS quad were 230 �C and150 �C, respectively. The full-scan mode with mass-to-charge (m/z)ratios from 30 to 500 was used, and the solvent delay was 2 min.The chromatographic peaks were identified with the help of theNational Institute of Standards and Technology (NIST) mass spectradata library.

X-ray fluorescence spectrometry (XRF, Rigaku Corp, Japan) andscanning electron microscopy (SEM, JCM-5000, JEOL Corp, Japan)were also used to further understand the composition and mor-phologies of the solid residues.

3. Results and discussions

3.1. Characteristics of oil sludge

The amount of solvent recovered through distillation wasrecorded and compared to the amount originally added prior to themixing step. The volume of the distillate bottoms, comprising therecovered oil, was recorded. The results indicate that the originaloily sludge contains more than 48 wt.% of oils. The composition ofthe oil from the original oily sludge is shown in Table 2. It is

Chemical composition of the oil extracted from the original oily sludge.

Chemical composition of the oil

No. Compounds Conc./% No. Compounds Conc./%

1 Undecene 2.34 14 Tetradecanoic acid 3.182 Undecane 4.16 15 Heptadecane 2.123 Dodecene 3.44 16 Heptadecanone 5.464 Dodecane 2.22 17 Dibutyl phthalate 1.215 Tridecylene 2.22 18 Hexadecanoic acid 7.806 Tridecane 2.84 19 Octadecenic acid 7.107 Tetradecene 6.14 20 Eicosane 2.588 Pentadecane 5.16 21 Docosane 1.269 Naphthalene 2.36 22 Myristic acid 4.0810 Hexadecene 5.18 23 Hexacosane 1.6611 Hexadecane 4.82 24 Octacosane 4.3012 Heptadecene 3.86 25 Nonacosane 1.3213 Pentadecanone 3.88 26 Others 9.31

L. Qin et al. / Journal of Environmental Management 154 (2015) 177e182 179

indicated that the oils contain about 32.44% alkanes, 23.18% al-kenes, 22.16% aliphatic acid, 9.34% ketones, 2.36% aromatic hydro-carbons, and 10.52% substituted aromatics. The X-ray fluorescencespectrometry (XRF) results show that iron oxide in the solid resi-dues of the oily sludge is as high as 42.10% (in Table 3).

Fig. 1. Products distribution of oily sludge pyrolysis.

3.2. Effect of temperature on the product yields

Fig. 1 shows the distribution of gas, condensed oil, solid residueand water yields during oily sludge pyrolysis under different re-action temperatures. It can be seen that there is no significantvariation in the gas yield when the temperature increases from 400to 500 �C. As the temperature is further increased, the gas yieldincreases dramatically and reaches its maximum value (57.48 wt.%)at 600 �C. Meanwhile, the water content seems to be independentof the reaction temperature. As for solid residue, the yield slightlydecreases with increasing the reaction temperature. It is also foundthat the oil yield increases from 45.54 to 59.20 wt.% with increasingtemperature from 400 to 500 �C, and then significantly decreasesfrom 59.20 to 11.21 wt.% as the temperature increases from 500 to600 �C, which is consistent with other studies (Liu et al., 2008). Thevaporization of oil has not been completed when the temperatureis below 500 �C. The oil contents in the solid residue pyrolyzedunder 400 and 500 �C are 8.15% and 0, respectively. Hence, theincrease of gaseous products at 400e500 �C was predominantlydue to the further vaporization of oil, which was proven by thevariation of the solid residue yield and oil content in the solidresidues. While the increase of the gaseous products at 500e600 �Cwas predominantly due to the secondary cracking or thermaldecomposition of the oils because there was a greater decrease inoil yield (Permsubscul et al., 2007).

Fig. 2. Gases composition at different temperatures.

3.3. Effect of temperature on the gas composition

The effect of temperature on the gas composition is shown inFig. 2. The results indicates that H2, CO, CO2, CH4 and some C2 andC3 hydrocarbons (C2H2, C2H4, C2H6 and C3H8) are the main com-ponents (N2 free-vol.%) during oily sludge pyrolysis. The H2 contentincreases from 13.28 to 28.29 % as the temperature increased from400 to 600 �C. It is also found that the CO and CH4 contentsdecrease, follow by increase when the temperature increase from400 to 600 �C. The percentage of CO and CH4 reached their mini-mum value (3.98 and 18.85%, respectively) at 500 �C. In contrast,the content of CmHn increased from 28.22 to 32.44% at 400e550 �C,followed by a decrease to 30.9% at 600 �C. While the percentage ofCO2 sharply decreased from 34.02 to 10.46% with increasing tem-perature. The formation of CO and CO2 at low temperatures(<450 �C) was mainly caused by the breaking of carbonyl andcarboxyl functional groups in the oily sludge. Meanwhile, thepresence of steam promoted the steam reforming reaction of thevolatile matter and partial gasification of the solid carbonaceousmaterial, as shown by Eqs. (1) and (2) (Midilli et al., 2002; Wanget al., 2007), which cause the increase of CO concentration when

Table 3Chemical components of the solid residue.

Chemical composition of the solid residue

No. Compounds Wt.% No. Compounds Wt.% No. Compounds Wt.%

1 Na2O 4.57 6 SO3 12.02 11 Fe2O3 42.102 MgO 2.80 7 K2O 0.67 12 Ni2O3 0.583 Al2O3 1.61 8 CaO 27.64 13 CuO 0.214 SiO2 2.93 9 TiO2 0.21 14 ZnO 0.405 P2O5 3.98 10 MnO 0.28

temperature is above 550 �C. Non-condensable products may alsoundergo heterogeneous reactions with each other. For example,CH4 and CO concentration may be affected by methane reformingand CO shift reactions, as shown in Eqs. (3) and (4) (Leung et al.,2002).

Steam reforming reaction:

OrganicsðgÞ þ H2OðgÞ4COþ H2 (1)

Steam gasification reaction:

CðSÞ þ H2OðgÞ4COþ H2; DH298K ¼ 131 KJmol�1 (2)

CH4 reforming reaction:

CH4 þ H2O4CO2 þ 3H2; DH298K ¼ 206:1 KJmol�1 (3)

CO shift reaction:

COþ H2O4CO2 þ H2; DH298K ¼ �41:5 KJmol�1 (4)

Meanwhile, high temperatures can promote the cracking re-actions of CmHn (C2H4, C2H6 and C3H8). The typical reactions are(Zhang et al., 2011):

C2H64C2H4 þ H2 (5)

C2H44CH4 þ C (6)

In addition, it was also found that the pyrolysis gas producedfrom treating 100 kg oily sludge under 400, 450, 500, 550 and600 �C were 7.34, 10.89, 11.23, 56.22 and 64.58 m3, respectively. Atthe same time, the low heating value of pyrolysis gas (including N2)

Table 5Detail analyses of the oil obtained from the original oily sludge and pyrolysisprocess.

No. Compounds Conc. %

Original 400 �C 450 �C 500 �C 550 �C 600 �C

1 Nonane e 0.23 0.38 0.17 e 0.322 Cyclopentane e 0.51 0.54 1.32 0.85 0.153 Decane e 0.29 0.52 0.61 0.85 e

4 Dodecene 4.16 2.01 2.90 2.92 5.17 4.995 Undecane 4.16 0.84 1.49 1.17 1.27 0.776 Undecene 2.34 1.26 1.65 2.37 2.96 2.687 Dodecane 2.22 0.63 0.90 0.99 0.66 0.658 Tridecane 2.84 1.58 1.82 1.91 2.55 2.979 Tridecene 2.22 1.58 1.70 2.51 3.46 3.5510 Cyclopropane e 3.21 3.42 4.78 5.84 6.1111 Pentadecane 5.16 6.29 4.93 4.42 5.48 7.1112 Tetradecene 6.16 e 2.01 2.99 2.02 2.6313 Tridecanoic acid e 1.13 0.85 1.85 1.00 0.3414 Heptadecane 4.82 1.09 1.17 2.11 1.24 0.8015 Heptacosane 2.12 1.33 1.29 1.14 0.78 1.3616 Eicosane 2.58 e e e e e

17 Docosane 1.26 e e e e e

18 Hexacosane 1.66 e e e e e

19 Hexadecene 5.18 2.59 2.91 3.15 3.79 5.0720 Octacosane 4.30 e e e e e

21 Nonacosane 1.32 e e e e e

22 Heptadecene 3.86 e e e e e

23 Dodecanoic acid e 8.63 9.00 6.28 5.96 4.8624 Tetradecanoic acid 3.18 3.58 4.28 5.25 3.54 2.0625 n-Hexadecanoic acid 7.80 3.73 6.10 8.68 3.42 2.1126 Octadecanoic acid 7.10 1.67 1.16 0.81 2.01 2.7327 Phthalic acid 1.21 0.55 0.73 0.82 4.43 6.7328 Myristic acid 4.08 e e e e e

29 Pentadecanone 3.88 3.81 3.44 3.04 1.94 3.7230 Hexadecanone e 0.34 0.43 e e 0.2831 Heptadecanone 5.46 5.30 4.80 4.15 2.91 5.7532 Tridecanone e 1.80 1.88 1.73 0.64 1.7433 Nonadecanone e 0.93 0.90 1.03 0.92 0.8234 3,4-Dihydro-3,3,9-

trimethyl-1(2H)-acridone

e 4.37 4.08 3.88 1.77 4.49

35 Benzene e 12.44 7.30 1.16 11.89 0.8536 Benzenamine e 2.90 2.14 1.98 1.43 0.7437 Dibutyl phthalate e 3.02 1.98 1.41 7.16 9.9838 Naphthalene 2.36 e e 2.13 3.06 3.3639 Pyrene e e e e e 0.66Others (Wt.%<0.3%) 9.31 22.36 23.3 22.61 11.00 9.62

L. Qin et al. / Journal of Environmental Management 154 (2015) 177e182180

under 400, 450, 500, 550 and 600 �C were 13.47, 14.23, 15.33, 23.14and 24.90 MJ/Nm3, respectively. Therefore, pyrolysis gas can beused as a fuel for boiler or furnace, and it also may be reused in thepyrolysis system as an auxiliary fuel to supply energy.

3.4. Effect of temperature on the oil composition

The main components of the pyrolysis oil are summarized inTables 4 and 5. The total ion count (TIC) of chromatograms for theoils can be found in the Supplementary material (Figs. 1e5).Generally, the main components of the oil can be divided into fivegroups: alkane, alkenes, aromatic hydrocarbons, heavy oxygenatedhydrocarbons and substituted aromatics hydrocarbons. The alkanesinclude tridecane (Peak 8), cyclopropane (Peak 10), pentadecane(Peak 11), and heptadecane (Peak 14), while the alkenes containdodecene (Peak 4), tridecene (Peak 9), tetradecene (Peak 12), andhexadecene (Peak 19). Aromatic hydrocarbons include benzene andtheir respective alkyl derivatives (Peak 35e38) and the heavyoxygenated hydrocarbons are carboxylic acids (Peak 23e28) andketones (Peak 29e33). The substituted aromatics containing N, S,Cl, and O, such as quinoline and aromatic hydrocarbons, are alsodetected in the oil. From Table 4, it can be seen that the concen-trations of alkanes increase from 16.00 to 20.24% with increasingtemperature from 400 to 600 �C. Similarly, the amounts of alkenesalso increase from 7.44 to 18.92% with the temperature increase.While the content of carboxylic acids in the pyrolysis oil firstlyincrease and then decrease at 400e600 �C, the maximum yieldoccurs at about 500 �C. In contrast, the amount of ketones in thepyrolysis oil decrease from 16.55 to 8.18% when the pyrolysistemperature increase from 400 to 550 �C, followed by increase to16.80% at 600 �C. Moreover, aromatic compounds are also detectedin the pyrolysis oil. Compared with the original oil obtained fromthe oily sludge, the yields of alkanes and alkenes in the pyrolysisoils are low, while the fractions of ketones and aromatic com-pounds are considerably higher than those of the original oil. Thepyrolysis oils are more complex and the main compositions of theoils are dependent on the reaction temperature. The above phe-nomena can be explained by the following reasons: the main for-mation mechanism of the oils includes vaporation, secondarycracking of oil, and the breaking of peptide bonds in the proteins.Moreover, the cyclization and amidation also have some contri-butions to the distribution and component of oil. The DielseAlderreaction mechanism is considered as the main contributor for theformation of aromatic compounds (Zhang et al., 2011). Table 6shows the final analysis and low heating value of the pyrolysisoils. The results indicates that the mass fractions of carbon andhydrogen in pyrolysis oil are 67.47e72.19% and 10.82e14.14%,respectively, and the low heating value varies from 34.46 to36.79 MJ/kg. According to Chinese standard “Automobile dieselfuels” GB/19147-2009, the recovery oil can be reused as fuel forboiler or the raw material of producing diesel.

3.5. Effect of temperature on the solid residue composition

The elemental composition and oil content in the residues are

Table 4The oil obtained from the original oily sludge and pyrolysis process.

Compounds Conc. %

Original 400 �C 450 �C 500 �C 550 �C 600 �C

Alkane 32.44 16.00 16.46 18.62 19.52 20.24Alkenes 23.18 7.44 11.17 14.57 17.40 18.92Arboxylic acids 22.16 19.29 22.12 23.69 20.36 18.83Ketones 9.34 16.55 15.53 13.83 8.18 16.80Aromatic hydrocarbons 2.36 18.36 11.42 6.68 23.54 15.59

also investigated, as shown in Table 7. The amount of oil in theresidue decreases from 8.15 to 0% with increasing reaction tem-perature from 400 to 500 �C, and there is no oil in the residue astemperature is above 500 �C. Moreover, the elemental compositionin the residues is independent of the reaction temperature when itis above 450 �C. The morphologies of the solid residues are pre-sented in Fig. 3. At 400 �C, the surface of the residue is smooth,which mean that there is some oil in the residue (consistent withthe ultimate analysis). When the reaction temperature increases to450 �C, the solid residue is easily aggregated, and part of the surfaceis still smooth. Above 450 �C, the residue is loose and porous. These

Table 6The elemental analysis and lower heating value of the pyrolysis oil.

Temp/�C Elemental analysis/% Low heating value (MJ/Kg)

C H O(diff.) N S Q

400 68.72 11.20 14.46 4.75 0.87 34.46450 71.44 10.82 12.01 4.65 1.08 35.84500 72.19 13.69 11.14 4.08 0.90 36.79550 70.69 13.07 10.64 4.53 1.07 36.40600 67.47 14.14 12.94 4.43 1.02 34.59

Table 7Analysis of the residues.

Temp./�C Ultimate analysis (Wt.%) Low heatingvalue (MJ/kg)

Oil content/%

C H O(diff.) N S

400 42.72 4.20 44.26 4.75 4.07 13.71 8.15450 38.44 3.82 47.91 4.65 4.18 7.69 0.78500 31.19 3.19 55.64 4.78 4.20 7.14 0550 31.69 3.07 55.49 4.58 4.17 7.02 0600 31.47 3.14 55.74 4.63 4.02 7.11 0

L. Qin et al. / Journal of Environmental Management 154 (2015) 177e182 181

phenomena could be explained by the oils in the residue beingcompletely decomposed. Fig. 4 demonstrates that the inorganiccomposition of the pyrolysis residue is independent of the reactiontemperature. Moreover, the mass fractions of iron oxide and

Fig. 3. SEM analyses of the residu

calcium oxide in the residues are approximately 42 and 26%,respectively, which are the dominant compounds in the solid res-idue. Interestingly, the iron content of iron ore in China is only30e60%. Hence the content of iron in the residue is satisfactory foriron-making. Meanwhile, calcium oxide in the residue can be usedas a desulphurization and fluxing agent during the iron-makingprocess. Thus, the reuse of the residues from oil sludge pyrolysis inthe iron industry is feasible.

3.6. Energy balances of the products

The effect of the pyrolysis temperature on the energy distribu-tion of the products obtained from oily sludge pyrolysis is pre-sented in Table 8. It can be seen that the energy fraction of thepyrolysis oils increases slightly when the temperature increases

es at different temperatures.

Fig. 4. XRF analyses of the residues at different temperatures.

Table 8Mass and energy distribution of the products.

Energy balance Reactiontemperature/�C

400 450 500 550 600

Energy distributionof the products

Energy fractionof oil/%

41.82 49.27 58.78 27.20 10.02

Energy fractionof gaseous/%

14.76 17.11 19.87 42.00 61.64

Energy fractionof residue/%

11.42 3.84 2.34 2.78 2.13

Fraction ofenergy loss/%

32.01 29.77 19.00 21.02 26.21

L. Qin et al. / Journal of Environmental Management 154 (2015) 177e182182

from 400 to 500 �C. As the temperature is further increased, theenergy fraction of the oils is increased dramatically and reaches themaximum value of 61.64% at 600 �C. These results are consistentwith the variations in the mass fractions of products for oily sludgepyrolysis over the temperature range 400e600 �C. In contrast, theenergy fraction of the residue slightly decreases with increasingreaction temperature. It is also found that the fraction of the energyloss firstly decreases, and then increase when the temperature in-creases from 400 to 600 �C, and the minimum energy loss occurs at500 �C. At 500 �C, the energy fractions of the oil, gaseous and solidresidues are 58.78, 19.87 and 2.34%, respectively. The total recoveryof the energy was 81% and energy loss was 19%. The energy con-sumption of treating 1 kg oily sludge is only 2.4e2.9MJ. At the sametime, the energy of produced oil, gas and solid residue are 20.8,6.32, and 0.83 MJ, respectively.

4. Conclusions

The pyrolysis of oily sludge from an iron companywas studied ina fluidized bed reactor at a temperature range of 400e600 �C. Theenergy and iron from the oily sludge were simultaneous recycledwhen the hazardous oily sludge was safely disposed by pyrolysis.The recovery oil (59.20%) was composed of alkane, alkenes, car-boxylic acids, ketones and a few types of aromatic hydrocarbons,which can be used as fuel for boiler or the raw material of pro-ducing diesel. In addition, the solid residues after pyrolysis con-tained more than 42% iron oxide, which could be recycled as a rawmaterial for iron-making.

Acknowledgments

This work was partly supported by National Natural ScienceFoundation of China (50806053) and Foundation of State KeyLaboratory of Coal Combustion (FSKLCC1113).

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.jenvman.2015.02.030.

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