Effect of Hydrothermal Temperature on the Steam Gasification

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Biofuels and Biomass

Effect of Hydrothermal Temperature on the Steam Gasification Performance of Sewage Sludge: Syngas Quality and Tar Formation Yuheng Feng, Tianchi Yu, Kunyu Ma, Genli Xu, Yuyan Hu, and Dezhen Chen Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00696 • Publication Date (Web): 01 May 2018 Downloaded from http://pubs.acs.org on May 4, 2018

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Effect of Hydrothermal Temperature on the Steam Gasification Performance of Sewage Sludge: Syngas Quality and Tar Formation Yuheng Feng*, Tianchi Yu, Kunyu Ma, Genli Xu, Yuyan Hu and Dezhen Chen Thermal and Environmental Engineering Institute, School of Mechanical Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China *Corresponding author Yuheng Feng, Thermal and Environmental Engineering Institute, Tongji University, 200092, Shanghai, China Tel.: +86 21 65985009; Fax: +86 21 65982786 E-mail address: [email protected] Abstract Hydrothermal pretreatment enhances both dewaterability and energy density of the municipal sewage sludge before steam gasification. Nevertheless, the effect of treatment condition on syngas quality and tar production was not clear. In this study, the hydrochars derived at different hydrothermal temperatures of sewage sludge were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and BET analysis. Then the gasification experiment of raw sludge and hydrochars was conducted in a fixed bed reactor to evaluate key parameters of syngas and tar including yield, chemical composition and HHV. The results showed that the treatment substantially improved the diffusion condition on the sludge surface, while raising the temperature led to a certain extent of pore collapse. The surface area and pore volume of the raw sludge was increased by 7.66 and 1.73 times after treated at 200oC, leading to 4.2% increase of H2 content in syngas from gasification of derived char despite the apparent loss of volatile species. The lowest tar formation was also from hydrochar produced at 200oC, due to the enhanced in-situ reforming. In addition, the treatment didn’t favor the reduction of PAH content in tar. This study provided basic data for the determination of hydrothermal temperature of sewage sludge targeting high-quality syngas and tar inhibition. Key words: sewage sludge, hydrothermal treatment, steam gasification, tar formation 1. Introduction With the accelerating urbanization in China, the yield of sewage sludge from waste water

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treatment has been increasing rapidly in recent years. Heavy pollution will be caused if the sludge was not properly disposed1. Compared with traditional disposal methods for sewage sludge such as landfilling, incineration and anaerobic digestion, gasification is a promising thermochemical method with less pollutant emission and short processing time

2-3

. During gasification of solid

fuels, steam is usually supplied into the reactor to enhance the hydrogen production. For sewage sludge, the hydrogen yield could be increased by two times when using steam as the gasification agent compared with air gasification 4. The energy consumption for moisture removal is a very high cost before the high-temperature thermochemical conversion of sewage sludge 5. Hydrothermal treatment not only reduces the cost for mechanical dehydration effectively 6, but also inhibited the emission of NH3 and HCN during the subsequent thermal chemical conversion7. In addition, it raises hydrogen yield from sludge gasification8-10. However, only single hydrothermal operation condition was tested in most of the studies which examines the treatment on hydrogen production during subsequent gasification process. The hydrothermal condition involves residence time and operating temperature. Compared with the holding time, the operating temperature is a much more effective factor affecting the property of the product biofuel 11. Tar formation during the gasification process of biomass12 causes operational problems in downstream utilization of syngas etc. power generation and chemical conversion 13. Therefore, its inhibition and removal are among the critical issues in the application of syngas from gasification of biomass including sewage sludge14. Zhang 15 used hydrothermal treatment to upgrade the low rank coal and examined the pyrolysis tar yield. However, few studies referred to the effect of hydrothermal treatment of sewage sludge on the tar formation during steam gasification. This study focused on the effect of hydrothermal temperature on syngas quality and tar formation during steam gasification of hydrochars from sewage sludge. The hydrochars were produced in a sub-critical hydrothermal reactor at 200-260oC. The surface properties of raw sludge and hydrochars were examined by SEM, BET and FTIR. Then the samples were gasified in steam atmosphere in a fixed bed batch reactor. The key parameters of syngas and tar were evaluated including yield, chemical composition and HHV. This work provided basic data for the optimization of hydrothermal treatment condition of sewage sludge before steam gasification. 2. Materials and methods


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2.1 raw sludge and hydrochars The raw activated sludge was obtained from a municipal water treatment plant in Jiading District, Shanghai, with water content 80.76%. Around 1kg of the raw sludge was treated in a 2L sub-critical hydrothermal reactor at 200oC, 220oC, 240oC and 260oC and the holding time was 0.5h. The sludge left in the reactor was centrifugalized and dried at 105oC for 10h. The hydrochars produced at different temperatures were named as HT-200, HT-220 and so on. The proximate and ultimate analysis of the dried raw sludge and hydrochars was presented in previous study by the same group7. 2.2 steam gasification experiment A vertical tube furnace was used as the fixed bed for steam gasification of the sludge and hydrochars as in Fig 1. Before the test, 10g of dried sample was placed in the up zone of the furnace held by a butterfly valve. Once the temperature of the heating zone has reached 900oC, the steam with the flow rate 0.5g/min was supplied into the furnace carried by argon at 80ml/min. After 15min, the atmosphere in the furnace was stable. Then the sample was fed to the heating zone by turning on the buttery valve. The condensable phase in the flow from the furnace was trapped by an ice bath with dichloromethane while the non-condensable syngas was gathered by a gas collecting bag, with a gas meter before the bag to measure the syngas volume. The steam/hydrochar mass ratio was set at 2.4:1.


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Fig 1. Schematic of the steam gasification fixed bed of dried sludge and hydrochars: (1) flow meter; (2) peristaltic pump; (3) steam generator; (4) electrical furnace; (5) thermocouple; (6) orifice plate; (7) butterfly valve; (8) ice bath; (9) gas meter; (10) gas collecting bag 2.3 syngas and tar analysis The gas composition (H2, CH4, C2H6, C2H4 CO, CO2) was analyzed by a gas chromatograph (GC 3420A) equipped with a thermal conductivity detector (TCD) and two columns (including 5A and GDX-104), using argon as the carrier gas. Tar was extracted from the trapped condensed phase by dichloromethane. After filtered by needle tube type filter, it was analyzed by GC-MS (SHIMADZU QP2010 Ultragas chromatograph) with a capillary column (30m RESTEK×0.25mmID; 0.25μm film thickness). The GC injection port was at 300oC. The heating program of GC was set as 35oC for 5 min, 35-300oC at 6oC /min and 300oC for 10min. The identification of the tar component was performed by comparing its mass spectrum with the spectrums in NIST library and the relative proportion was determined with normalizing the corresponding peak area of by the total peak value ion chromatogram (TIC). 2.3 Hydrochars characterization The surface morphology of the dried sludge and hydrochars was examined by a field emission gun environment scanning electron microscope (FEGE-SEM, FEI Quanta250). The physical characteristics of the samples, including the specific surface area, the total pore volume, and the pore diameter, were measured via N2 adsorption using an ASAP 2020 micropore analyzer (Micromeritics Co., USA) at -196.15oC in liquid N2. The specific surface area and pore volume was calculated according to the Brunauer-Emmett-Teller (BET method). In the FTIR analysis of the samples, the sample was thoroughly mixed with KBr (FTIR grade, from Merck) in the mass ratio 1:100 and then made into pellets. The analyses were performed using an EQUINOXSS/HYPER, Bruker Vertex 70 spectrometer (Bruker Co., Germany) in the region 4000-400cm-1 at the resolution 0.5cm-1. 2.4 Steam gasification characteristics

The indexes of steam gasification of dried raw sludge and hydrochars were obtained by the following methods, including yield and HHV of gas and tar yield. Gas yield (Gp) was estimated by: G = (V − V )/


(1)

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msample is the mass of the dry sample fed into gasification reactor. Vmeter is the total gas volume passed through the meter during the gasification process. Var is the total volume of Ar supplied as carrier gas during gasification. The HHV of syngas was calculated by: HHV (/ ) = ∑ HHV × V

(2)

where HHVi is the HHV of the component I and Vi is the volume fraction of the component i in syngas from GC analysis.

After separated with aqueous phase by separating funnel, the organic fraction of the condensed phase collected by ice bar was placed in an evaporating dish for the evaporation of dichloromethane. The liquid left was weighted to obtain the tar yield. 3. Results and discussion 3.1 Surface morphology and BET analysis The SEM images of dried sludge, HT-200 and HT-260 were displayed in Fig 2. Both fabric and plate-like structure were found for the raw sludge. Compared with raw sludge, the HT-200 maintained a fabric structure, which indicated that the cellulose in sludge hardly decomposed during the treatment at 200oC. Meanwhile, a lot more pores were found and the plate-like structure disappeared. This was due to the devolatilization of the organic components such as proteins during the treatment. For HT-260, the fabric structure disappeared and the surface became substantially smoother, with less pores identified. These variations showed the temperature raise caused the further release of the volatiles combined with fierce hydrolysis of cellulose, leading to the pore collapse and the more compacted structure. Similar result could be concluded from Table 1, which compared the specific area and pore characteristics of raw sludge, HT-200 and HT-260. Hydrothermal treatment at 200oC raised the surface area of the raw sludge for by 10 times and the pore volume by nearly 2 times. On the other side, raising the hydrothermal temperature to 260oC resulted in a slight decrease of the surface area and an apparent reduce of the pore volume of char.


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(a)

(b)

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(c)

Fig. 2. Scanning electron microscope images of dried sludge (a), HT-200 (b) and HT-260(c) Table 1. Surface area and pore properties of dried sludge and hydrochars Sample Dried sludge HT-200 HT-260

Specific surface area （m2/g） 3.78 37.22 36.86

Total pore volume （cm3/g） 0.019 0.052 0.038

Average pore diameter(nm) 22.652 6.007 4.304

2. Functional group by FTIR analysis FTIR spectrums of the raw sludge and the hydrochars produced at 200oC to 260oC were displayed in Fig 3. The assignments of the bands in the spectrum according to literature16 and the corresponding absorbance were in Table 2. It could be found that most of the bands of the organic groups were significantly reduced when the sludge was treated at 200oC, including methylene group, hydroxyl group, carboxyl group, esters and amide. This evidenced the occurrence of dehydration, decarboxylation, demethanation and deamination during hydrothermal treatment of the sludge. Conversely, the height of the band at 1030cm-1 was raised by 6.9%, indicating the aliphatic ethers were relatively stable in this treatment condition. When the hydrothermal temperature was raised to 220oC, a more intense decrease was found for all the groups identified, by at least 32.7%. The variation of the peak height was relatively small when the temperature ranged from 220oC to 260oC. Therefore, there was a break point between 200oC to 220oC, at which fierce decomposition and hydrolysis of the organic components occurred in the sludge matrix. This is the cause of the pore collapse over 200oC in the surface morphology and BET analysis.


1030

1540

1645

1710

2925

2850

Dried sludge

HT-200 Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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3320

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HT-220

HT-240 HT-260 4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumber(cm )

Fig 3. FTIR spectrums of dried sludge and hydrochars Table 2. Band assignments of FTIR spectrum for dried sludge and hydrochars. Wavenumber (cm-1)

Vibration

Functional group or component

Dried sludge

HT-200

HT-220

HT-240

HT-260

3320

–OH stretching

Hydroxyl or carboxyl group

0.368

0.233

0.118

0.101

0.077

0.437

0.394

0.192

0.205

0.183

0.338

0.269

0.133

0.146

0.130

0.396

0.287

0.131

0.116

0.094

asymmetric – C–H stretching symmetric – C–H stretching –C=O stretching –COO stretching

Aliphatic methylene group Aliphatic methylene group

1540

–N–H in-plane bending

Amide II and secondary amines

0.323

0.212

0.089

0.078

0.064

1455

–C=C stretching

Aromatic ring carbon

0.250

0.224

0.119

0.114

0.094

2920

2850

1645

Amide I Carboxylates


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1240

1030

–C–N stretching –C–O–C stretching –C–O–R stretching –C–O stretching

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Amide III 0.168

0.116

0.078

0.066

0.048

0.408

0.436

0.280

0.274

0.225

Esters Aliphatic ethers Alcohols

3.2. The effect of hydrothermal temperature on syngas quality 3.2.1. Syngas components The mole fraction of different components of syngas produced from the gasification of died sludge and hydrochars was displayed in Fig 4. As the primary component in the syngas from dried raw sludge, the content of H2 was 52.0%. The maximum yield of H2 from gasification of fixed carbon in sludge was calculated according to 2:1 water-gas reaction (3)

CO + H$ O ⇋ CO$ + H$

The result showed that it took only 36.3% of total H2 yield. This indicated that most of the H2 was from the cracking or reforming of volatile species released, due to the minor content of fixed carbon in sludge. For syngas from HT-200, the H2 content was raised to 56.2%. The surface area and the pore volume of the char was significantly raised by treating at 200oC, improving the diffusion of steam and tar on the surface of hydrochar, promoting both water gas-reaction and in-situ reforming of tar1. On the other side, the fixed carbon content in the sludge was increased by the treatment, which raised the reactant of water gas reaction. Moreover, alkali or alkali earth metal (K, Na, Ca, Mg) was also concentrated in the hydrochars9, which played the role as catalyst in the hydrogen production during steam gasification and tar reforming. The increase of the hydrothermal temperature showed little effect on the H2 content, with the variation less than 0.5%, although the content and the gasification activity of fixed carbon were both increased with the hydrothermal extent7. The volatile content was decreased from 50.14% for HT-200 to 41.95% for HT-2607, leading to the reduce of H2 production from this path. On the other hand, pore collapse occurred when the treating temperature was raised, affecting the diffusion condition on the sample surface. In addition, the hydrophilic groups in the char which favored the steam


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gasification including hydroxyl group and carboxyl group was sharply decreased 7.

60

50

Mole fraction(%)

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Hydrocharbons H2 CO2 CO

40

30

20

10

0

raw sludge

HT-200

HT-220

HT-240

HT-260

Fig 4. Mole fraction of different components in syngas from steam gasification of dried sludge and hydrochars There was a continuous decrease of CO2 content in syngas, from 28.7% for raw sludge to 21.9% for HT-260. This was mainly due to the removal of oxygen content groups in sludge matrix with hydrothermal extent. CO content in syngas from HT-200 was 11.3% while that from raw sludge and other hydrochars was between 12% to 13%, since the better surface diffusion achieved when treated at 200oC promoted catalytic condition of water-gas shift reaction. In addition, the total content of gaseous hydrocarbons including CH4, C2H4 and C2H6 fluctuated within 6% - 8%. It was the lowest compared with the other compounds identified, probably caused by fierce steam reforming in the reactor.

3.2.2. Gas yield and HHV The high heating value (HHV) and the yield of the syngas from dried sludge and hydrochars were displayed in Fig 5. Compared with dried sludge, the gas yield was slightly raised from 0.762Nm3/kg for raw sludge to 0.764 Nm3/kg for HT-200 in spite of the significant reduce of combustible content in the sample. This was probably caused by the reduction of tar yield by the treatment. As mentioned above, the fierce devolatilization and hydrolysis above 200oC led to the pore collapse in sludge matrix, so the surface structure was not improved for gasification,


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resulting in the decrease of the gas yield for the chars produced between 220oC to 260oC. As to HHV, there was an apparent raise for HT-200 compared with dried sludge from 11.3MJ/Nm3 to 12.6MJ/Nm3, mainly due to the increase of H2 and the decrease of CO2 in the syngas. When raising the treatment temperature from 200oC to 220oC, it was obviously lowered since the hydrocarbons with the highest heating value among in gas was reduced by around 18%. Above 220oC, there was a slightly continuous increase of HHV with the hydrothermal temperature due to the CO2 decrease.

Gas yeild HHV

0.8

14

3

3

LHV(MJ/Nm )

0.6

Gas yeild(Nm /kg)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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12

0.4

0.2 10

0.0 Dried sludge

HT-200

HT-220

HT-240

HT-260

Fig 5. HHV and yield of syngas from steam gasification of dried sludge and hydrochars

3.3. Tar formation The tar yield and the relative contents of different components in tar from GC-MS analysis were displayed in Fig 6. Pretreatment of the sludge at 200oC showed a significant inhibition of the tar, with the yield decreased from 45mg/g to 25mg/g (on the basis of dried sample fed into the reactor). Yu1 found that the sewage sludge char itself was an effective catalyst of tar cracking. Therefore, the substantial increase of the surface area and pore volume of the sludge enhanced the catalytic performance of the char. In addition, a certain amount of the volatiles containing tar


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components was removed by the treatment. Since the reduce of the surface area and pore volume of the sample, raising the hydrothermal temperature to 220oC caused an increase of the tar yield in spite of the volatile decrease of the sample. The tar yield was maintained at around 35mg/g between 220oC to 260oC. Aliphatic hydrocarbon Monoaromatic hydrocarbons PAHs Oxygenated hydrocarbons Heterocyclic-N compounds Aromatic nitriles Tar yeild

35

60

50 30 40

25 20

30

15 20

Tar yeild(mg/g)

Relative content(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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10 10 5 0

0 Dried sludge

HT-200

HT-220

HT-240

HT-260

Fig 6. Tar yield and tar components from steam gasification of dried sludge hydrochars It could be found that the evolution of heterocyclic-N compounds has the same tendency with the N content in the sample, which decreased continuously with the hydrothermal level below 240oC and raised at 260oC. They were from the devolatilization of pyrrole and pyridine structure and the polymerization of stable protein in the sample. On the contrary, no correlation was found between the oxygenated hydrocarbons content and the oxygen content in the sample. The relative content of PAHs was 18.4% in tar from raw sludge while it was above 20% for all the hydrochars. Xu17 found that hydrothermal condition promoted the formation of PAHs. The mechanism could refer to the process of pyrolysis, including cyclopentadienyl recombination18 or Diels-Alder reaction19. Monoaromatic hydrocarbons including benzene, toluene, styrene and their alkyl derivatives were the primary compounds in tar from all the samples, with the content above 30%. The tendency of monoaromatic compounds was in the opposite direction of PAHs. Nitrile compounds were among the major compounds during pyrolysis of sewage sludge1.


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However, benzonitrile was the only nitrile found in tar here, with the content lower than 4%, indicating the high conversion of nitrile compounds into HCN during steam gasification.

4. Conclusion This study investigated the hydrothermal treatment temperature of sewage sludge on the char characteristics, syngas quality and tar formation during the subsequent steam gasification. The surface property analysis showed that the treatment significantly increased the pore volume and surface area of the sludge. The surface area and pore volume of the raw sludge was increased by 7.66 and 1.73 times after treated at 200oC. On the other hand, raising the hydrothermal temperature above 200oC resulted in the pore collapse thus the sharp decrease of different functional groups. In the gasification experiment, the highest hydrogen fraction (56.2%), gas yield (0.764 Nm3/kg) and HHV (12.6MJ/Nm3) of the syngas and lowest tar yield (25mg/g) were all achieved at HT-200. Nevertheless, the PAH content in tar was raised by the treatment, above 20% for all the hydrochars. Therefore, both syngas and tar production from the hydrochars were affected by comprehensive factors such as surface property and fixed carbon/volatile matter content of the sample and 200oC is the optimal temperature to achieve higher syngas quality and lower tar formation.

Acknowledgements This work was supported by National Natural Science Foundation of China [grant number 51706156], Shanghai Rising-Star Program [grant number 17QC1401000], CAS Key Laboratory of Renewable Energy [grant number Y707k41001] and Visiting Scholar foundation of Key Lab of Clean Energy Utilization in Zhejiang University [grant number ZJUCEU2015017]. References 1. Yu, G.; Feng, Y.; Chen, D.; Yang, M.; Yu, T.; Dai, X., In Situ Reforming of the Volatile by Char during Sewage Sludge Pyrolysis. Energy & Fuels 2016, 30, (12), 10396-10403. 2. Cieślik, B. M.; Namieśnik, J.; Konieczka, P., Review of sewage sludge management: standards, regulations and analytical methods. Journal of Cleaner Production 2015, 90, (Supplement C), 1-15. 3. Choi, Y.; Cho, M.; Kim, J., Steam/oxygen gasification of dried sewage sludge in a two-stage gasifier: Effects of the steam to fuel ratio and ash of the activated carbon on the production of hydrogen and tar removal. Energy 2015, 91, (Supplement C), 160-167. 4. Nipattummakul, N.; Ahmed, I. I.; Kerdsuwan, S.; Gupta, A. K., Hydrogen and syngas production


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from sewage sludge via steam gasification. International Journal of Hydrogen Energy 2010, 35, (21), 11738-11745. 5. Manara, P.; Zabaniotou, A., Towards sewage sludge based biofuels via thermochemical conversion – A review. Renewable and Sustainable Energy Reviews 2012, 16, (5), 2566-2582. 6. Escala, M.; Zumbuehl, T.; Koller, C.; Junge, R.; Krebs, R., Hydrothermal Carbonization as an Energy-Efficient Alternative to Established Drying Technologies for Sewage Sludge: A Feasibility Study on a Laboratory Scale. ENERGY & FUELS 2013, 27, (1), 454-460. 7. Feng, Y.; Yu, T.; Chen, D.; Xu, G.; Wan, L.; Zhang, Q.; Hu, Y., Effect of Hydrothermal Treatment on the Steam Gasification Behavior of Sewage Sludge: Reactivity and Nitrogen Emission. Energy & Fuels 2017,. 8. Gai, C.; Chen, M.; Liu, T.; Peng, N.; Liu, Z., Gasification characteristics of hydrochar and pyrochar derived from sewage sludge. Energy 2016, 113, 957-965. 9. Gai, C.; Guo, Y.; Liu, T.; Peng, N.; Liu, Z., Hydrogen-rich gas production by steam gasification of hydrochar derived from sewage sludge. International Journal of Hydrogen Energy 2016, 41, (5), 3363-3372. 10. Moon, J.; Mun, T.; Yang, W.; Lee, U.; Hwang, J.; Jang, E.; Choi, C., Effects of hydrothermal treatment of sewage sludge on pyrolysis and steam gasification. Energy Conversion and Management 2015, 103, 401-407. 11. Zhao, P.; Shen, Y.; Ge, S.; Yoshikawa, K., Energy recycling from sewage sludge by producing solid biofuel with hydrothermal carbonization. Energy Conversion and Management 2014, 78, 815-821. 12. Barman, N. S.; Ghosh, S.; De, S., Gasification of biomass in a fixed bed downdraft gasifier – A realistic model including tar. Bioresource Technology 2012, 107, (Supplement C), 505-511. 13. Devi, L.; Ptasinski, K. J.; Janssen, F. J. J. G., A review of the primary measures for tar elimination in biomass gasification processes. Biomass and Bioenergy 2003, 24, (2), 125-140. 14. Li, C.; Suzuki, K., Tar property, analysis, reforming mechanism and model for biomass gasification—An overview. Renewable and Sustainable Energy Reviews 2009, 13, (3), 594-604. 15. Zhang, D.; Liu, P.; Lu, X.; Wang, L.; Pan, T., Upgrading of low rank coal by hydrothermal treatment: Coal tar yield during pyrolysis. Fuel Processing Technology 2016, 141, (Part 1), 117-122. 16. He, C.; Zhao, J.; Yang, Y.; Wang, J., Multiscale characteristics dynamics of hydrochar from hydrothermal conversion of sewage sludge under sub- and near-critical water. Bioresource Technology 2016, 211, 486-493. 17. Xu, Z. R.; Zhu, W.; Li, M.; Zhang, H. W.; Gong, M., Quantitative analysis of polycyclic aromatic hydrocarbons in solid residues from supercritical water gasification of wet sewage sludge. Applied Energy 2013, 102, 476-483. 18. Böhm, H.; Jander, H.; Tanke, D., PAH growth and soot formation in the pyrolysis of acetylene and benzene at high temperatures and pressures: Modeling and experiment. Symposium (International) on Combustion 1998, 27, (1), 1605-1612. 19. Cunliffe, A. M.; Williams, P. T., Composition of oils derived from the batch pyrolysis of tyres. Journal of Analytical and Applied Pyrolysis 1998, 44, (2), 131-152.


Effect of Hydrothermal Temperature on the Steam Gasification

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