- Email: [email protected]
Comparison of the fuel properties and the combustion behavior of PET bottle caps with lignite
Available online at www.sciencedirect.com
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy Procedia Procedia 00 136(2017) (2017)000–000 22–26 Energy www.elsevier.com/locate/procedia
4th International Conference on Energy and Environment Research, ICEER 2017, 17-20 July 2017, Porto, Portugal Theof 15th International Symposiumand on District Heating and Cooling Comparison the fuel properties the combustion behavior of PET bottle caps with lignite Assessing the feasibility of using the heat demand-outdoor a b a, Nurdan Irem Unal , Siddikafor Mertdinc , Hanzadedistrict Haykiri-Acma , Serdar Yaman * temperature function a long-term heat ademand forecast Chemical Engineering Department, Istanbul Technical University, Istanbul, 34469, Turkey
a
a,b,c a a b c Metallurgical*, andA. Materials Department, Istanbul Technical University, Istanbul, ,34469, Turkey I. Andrić PinaEngineering , P. Ferrão , J. Fournier ., B. Lacarrière O. Le Correc b
a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract
This study focuses on evaluation of used PET bottle caps as energy resource. Fuel properties of PET bottle caps were determined considering proximate analysis and HHV. In addition, combustion properties were investigated based on DSC profile and the Abstract functionalities were determined by FTIR technique. The fuel properties of PET were compared with those of a Turkish lignite, concluding that the HHV of PET is 3.5 times higher than that of lignite, what shows that using PET in energetic purpose may be District heating networks aresome commonly addressed in the as characteristics one of the most decreasing the promising approach. There are important differences on literature the burning andeffective functionalsolutions groups offorlignite and PET greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat samples. sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, the investment return ©prolonging 2017 The Authors. Published byperiod. Elsevier Ltd. The main scope of this paper is to assess the feasibility of using demand –Conference outdoor temperature for heat demand Peer-review under responsibility of the scientific committee of thethe 4thheat International on Energyfunction and Environment forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Research. buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenariosfuel; werelignite; developed Keywords: Combustion; PET (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation 1.(the Introduction scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the PET (Polyethylene Terephthalate) is a long-chain polymer that is a member of polyester family and it is one of the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and most widely-used polymeric materials many items including toys,increased electricalfor appliances, devices, packages, renovation scenarios considered). On theinother hand, function intercept 7.8-12.7% medical per decade (depending on the bottles, household substances, cables, polyester-based fibers, etc [1]. Accordingly, more than 56 million tons of PET coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and was annually consumed in 2010 and 33.3 million tons of which was comprised of fibers while PET bottles formed improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +90-212-2853351; fax: +90-212-2852925. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change
1876-6102 © 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the 4th International Conference on Energy and Environment Research. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 4th International Conference on Energy and Environment Research. 10.1016/j.egypro.2017.10.256
Nurdan Irem Unal et al. / Energy Procedia 136 (2017) 22–26 Nurdan Irem Unal et al. / Energy Procedia 00 (2017) 000–000
23
18.9 million tons [2]. Thus, huge amount of plastic wastes is formed that causes serious environmental pollutions and negative effects on ecology. That is, these materials are highly difficult to be digested in nature by natural effects since the digestion process is too slow and requires very long times. Namely, PET is by far the most significant pollutant in oceans [3]. Plastic wastes in seas threat the life of species including the fish, mammals, sea birds, turtles, etc. According to the report of U.S. Marine Mammal Commission in 1996, 136 species of fish, 6 species of turtles, 51 species of fish-eating birds, and 32 species of mammals have been adversely affected by waste plastics. Since, PET materials in water seem jelly fish or caviar, marine species that eat PET materials cannot digest them and finally this causes death of these species [4]. Recycle of PET materials is of great importance since it is produced from non-renewable fossil fuels. The recycle methods for PET materials are usually classified as primary, secondary, tertiary, and quaternary methods. Of which, the primary recycle method is the recycle of clean/new PET inside a factory by re-extrusion [5]. On the other hand, the secondary recycle method in other words mechanical recycle bases on separation and cleaning of waste PET from the pollutants and then granulation of the cleaned PET for reusing. However, heavily polluted PET cannot be recycled by secondary recycle method [2, 5]. Besides, ternary recycle methods mainly cover various chemical methods such as hydrolysis, aminolysis, methanolysis, glycolysis or pyrolysis [5, 6]. Alternatively, the purpose of the quaternary method is rather to take advantage of the energy potential and the calorific value of the waste organic substances instead of obtaining recycled new material. For this, incinerators are employed where the waste PET is burned under controlled conditions through which the only final combustion products will be water and CO 2. The heat obtained from the waste material is used for steam generation and space heating [7]. From this point of view, the quaternary method highly differs from the other options of PET recycle. Besides, lignites account for the most important national energy sources in Turkey. Therefore, a number of lignitefired power stations have been operated throughout the country. However, Turkish lignites are very low quality coals with low calorific values and fixed carbon contents and their ash yields and moisture contents are also very high [8]. In addition, the efficiency of the lignite-firing combustion systems is not high enough that leads unburnt carbon remained in ash and economic losses due to incomplete burning [9]. Therefore, blending these lignites with some waste materials that have enough calorific value may improve the burning efficiency and will help to diminish the unburnt carbon. However, the fuel properties and the combustion behavior of these waste materials should be known very well for such an application. For this reason, waste PET materials will be used in this study as an alternative fuel. In this context, PET bottle caps were used since they have good energy potential in unit volume associated with high density that leads less volume occupancy compared to the main body of PET bottle. Also, comparison of the fuel properties and the combustion behavior of PET bottle caps with those of a Turkish lignite sample from Afsin-Elbistan region, which is one of the largest lignite deposits in Turkey, was carried out. 2. Materials and methods The caps were collected from several different commercial brands of PET water bottles sold in Turkey. In sample preparation stage, these caps were granulated by a domestic metallic grate to decrease the particle size to several millimeters. The caps and the granulated samples are shown in Fig. 1. On the other hand, Afsin-Elbistan lignite sample was first kept in open containers for several days to reduce its excessive moisture content and to get the air-dried sample. The representative sample was taken from the bulk according to standard procedures. Particle size of lignite was decreased by breaking the sample with a hammer mill and then a coal grinder was used to reduce the particle size to pass through a sieve that has openings of 250 μm. Proximate analysis of both samples was performed according to ASTM standards, while the higher heating value (HHV) was determined using IKA C2000 model calorimeter.
Nurdan Irem Unal et al. / Energy Procedia 136 (2017) 22–26 Nurdan Irem Unal et al. / Energy Procedia 00 (2017) 000–000
24
Fig. 1. PET bottle caps and granulated sample.
Combustion characteristics of PET and lignite were tested using TA Instruments SDTQ600 model thermal analyzer that has 0.1 μg balance sensitivity, a temperature range of up to 1500 °C, platinum/platinum-rhodium thermocouples, temperature sensitivity of 0.001 °C, and alumina as reference material. In this way, Differential Scanning Calorimetry (DSC) curves were obtained that enables to determine the heat flows during the combustion process. For this analysis, 10 mg of ground samples were placed into alumina crucible and burning was implemented up to 900 °C with a heating rate of 40 °C/min under dry air flow at 100 mL/min. FTIR (Fourier Transform Infrared Spectroscopy) spectra of both samples were obtained using Perkin Elmer, Spectrum 100 model device. All the analyses and the tests were performed at least duplicate and the mean results were taken provided that the deviations are within 5%. 3. Results and discussion Proximate analysis results as well as the results of HHV of the samples are given in Table 1. It is likely to mention that the fuel properties of PET and lignite are highly different from each other. The higher heating value of PET is 3.5 times higher than that of lignite. This shows the fact that the calorific value of PET is considerably better than lignite and this material can be used as a supplementary fuel to prepare some fuel blends that have improved calorific value compared to the lignite sample used in this study or any of the low quality coal samples. The high ash yield and the low fixed carbon content of lignite can be regarded as the main factors that lower the HHV. Moisture content of lignite also deteriorates the calorific value. Besides, it should be taken into account that the high ash yield of lignites leads undesirable deposit problems in combustion systems. In contrast to this, being almost ash-free makes PET a very interesting alternative fuel. On the other hand, the most striking fuel property of PET is that it does not leave any fixed carbon content and almost all of its structure is converted to volatile products. Table 1. Proximate analysis results. Sample Lignite PET
Moisture (%) 6.97 0.03
Volatiles (%) 48.94 99.53
Ash (%) 34.96 0.44
Fixed Carbon (%) 9.13 -
HHV (cal.g-1) 3052 10931
Fig. 2 represents the FTIR spectra that explain the functional groups found in the samples of lignite and PET comparatively and Table 2 summarizes the corresponding organic bands on these spectra depending on the wavenumbers. Namely, C-H wagging, C-H bending, C=C stretching, C-H stretching, and asymmetrical C-H bonds are the most extensive FTIR bands for PET, while C-H vibration, C-O-C stretching, C-H aromatic bonds, C-H stretching, and C=C bonds are the main functionalities in the lignite sample. These characteristics also reveal the fact that these samples have highly different properties [10, 11]. Low rank coals such as lignites are very rich in oxygen content and it is in agreement with the oxygen containing functional groups of Afsin-Elbistan lignite. On the other hand, the bonds between carbon and hydrogen formed the most striking absorption bands on FTIR spectrum of PET.
Nurdan Irem Unal et al. / Energy Procedia 136 (2017) 22–26 Nurdan Irem Unal et al. / Energy Procedia 00 (2017) 000–000
25
Fig. 2. FTIR spectra. Table 2. Peaks on FTIR spectra. Afşin – Elbistan Lignite
PET Wavenumbers (cm )
Band
Wavenumbers (cm-1)
Band
717
Aromatic C-H out of plane
713
C-H vibration Aromatic C-H out of plane
1472
C-H bending C=C stretching
874
C-O-C stretching C-H aromatic
2848
C-H stretching
1035
C-O-C vibration
2914
C-H asymmetric
1420
C-H2 stretching C=C
-1
DSC burning profiles of both samples are illustrated in Fig. 3 and these burning curves make it possible to observe the heat flows from sample to surroundings and vice versa depending on temperature. Namely, negative heat flows indicate that the sample takes heat from the surroundings, while the positive heat flows predict exothermal phenomena arising from the combustion of the sample.
Fig. 3. DSC burning profiles.
Moisture removal from the sample and the phase transformations and decompositions of ash forming inorganics are the main sources of the negative heat flows (endothermic phenomena). However, combustion curves on these burning profiles are the dominant heat flows and the mentioned endothermic peaks are almost ignorable in comparison
26
Nurdan Irem Unal et al. / Energy Procedia 136 (2017) 22–26 Nurdan Irem Unal et al. / Energy Procedia 00 (2017) 000–000
to the huge exothermic peaks of combustion. Some significant information can be obtained from the shape and the extent of these exothermic burning curves. That is, the ignition points can be determined from the transition to the exothermic region from the first endothermic region where moisture is lost. For instance, it can be seen that the ignition point of PET is higher than that of lignite. Actually, the ignition points were determined as 224 °C for lignite and 282 °C for PET. Some of the ingredients in the mineral matter of lignite may show catalytic effects to lower the ignition point. It was also found out that lignite not only ignites at lower temperature but also it gives most of the heat of combustion at lower temperatures compared to that PET. Besides, the maximum heat flow of PET is higher than lignite and it is in accordance with the fact that the higher heating value of PET is considerable higher than that of lignite. The maximum heat flows were determined as 31.3 mW/mg and 42.4 mW/mg for lignite and PET, respectively. Also, temperatures at which these maximum heat flows are observed were 392 °C for Afsin-Elbistan lignite and 545 °C for PET. The burning profile of lignite is consisted of two different parts. One of which that shows the maximum heat flows belongs to the homogeneous burning of the combustible volatile matter, which the other that has relatively smaller heat flows are resulted from the heterogeneous burning of the fixed carbon through surface oxidation. Since, PET does not have any fixed carbon content, only one burning peak is available that is forming from the combustion of the volatile matter. 4. Conclusion This study confirmed that waste PET materials can be evaluated in combustion process as alternative fuel source. Comparison of the fuel properties of PET with Afsin-Elbistan lignite based on their proximate analysis tests and the higher heating value results revealed that the fuel properties of PET bottle caps are by far superior to lignite. The calorific value of PET is disproportionally high and it almost leads no ash over burning. Considering these fuel properties, it can be suggested that PET materials may be used for preparation of fuel blends in which low quality/low rank coals are used. In this way, significant improvements can be performed in the fuel properties of these low quality coals such as Turkish lignites. On the other hand, it was determined that the chemical properties and the functional groups found in PET and lignite differ seriously and this may create some discrepancy in the combustion behaviors of individual ingredients in such fuel blends. Accordingly, DSC burning profiles of samples indicated some serious differences in the combustion characteristics of these samples. That is, the onset of burning for lignite takes place relatively at lower temperatures and consequently the main part of the combustion process occurs at lower temperatures in comparison to the burning of PET. In addition, burning of lignite takes place in two different regions that is a different nature of lignite combustion against burning of PET materials. References [1] [2]
Brydson JA. Plastics materials. 7th edition. Oxford: Butterworth Heinemann. 1999. p.724. Bartolome L, Imran M, Cho BG, Al-Masry WA, Kim DH. Recent developments in the chemical recycling of PET. In: Achilias D, editor. Material Recycling – Trends and Perspectives. Intech Open Access Publisher: 2012. p. 67. [3] Derraik JGB. The pollution of the marine environment by plastic debris: A Review. Mar Pollut Bull 2002;44:842-52. [4] Sheavly SB, Register KM. Marine debris & plastics: Environmental concerns, sources, impacts and solutions. J Polym Environ 2007;15:3015. [5] Sinha V, Patel RM, Patel VJ. Pet waste management by chemical recycling: A review. J Polym Environ 2010;18:8-25. [6] Tayyar EA, Ustun S. Use of recycled PET (in Turkish). J Pamukkale Univ 2010;16:53- 62. [7] Klass DL. Biomass for renewable energy, and Chemicals. San Diego, CA: Academic Press;1998. [8] Kucukbayrak S, Durus B, Mericboyu AE, Kadioglu E. Estimation of calorific values of Turkish lignites. Fuel 1991;70:979-81. [9] Kurama H, Kaya M. Usage of coal combustion bottom ash in concrete mixture. Constr Build Mater 2008;22:1922-8. [10] Vijayakumar S, Rajakunar PR. Infrared spectra analysis of waste pet samples, Int Letters of Chem, Phys Astronomy 2012;4:58-65. [11] Sharma RK, Wooten JB, Baliga VL, Hajaligol MR, Characterization of chars from biomass-derived materials, pectin chars. Fuel 2001;80: 1825-36.
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy Procedia Procedia 00 136(2017) (2017)000–000 22–26 Energy www.elsevier.com/locate/procedia
4th International Conference on Energy and Environment Research, ICEER 2017, 17-20 July 2017, Porto, Portugal Theof 15th International Symposiumand on District Heating and Cooling Comparison the fuel properties the combustion behavior of PET bottle caps with lignite Assessing the feasibility of using the heat demand-outdoor a b a, Nurdan Irem Unal , Siddikafor Mertdinc , Hanzadedistrict Haykiri-Acma , Serdar Yaman * temperature function a long-term heat ademand forecast Chemical Engineering Department, Istanbul Technical University, Istanbul, 34469, Turkey
a
a,b,c a a b c Metallurgical*, andA. Materials Department, Istanbul Technical University, Istanbul, ,34469, Turkey I. Andrić PinaEngineering , P. Ferrão , J. Fournier ., B. Lacarrière O. Le Correc b
a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract
This study focuses on evaluation of used PET bottle caps as energy resource. Fuel properties of PET bottle caps were determined considering proximate analysis and HHV. In addition, combustion properties were investigated based on DSC profile and the Abstract functionalities were determined by FTIR technique. The fuel properties of PET were compared with those of a Turkish lignite, concluding that the HHV of PET is 3.5 times higher than that of lignite, what shows that using PET in energetic purpose may be District heating networks aresome commonly addressed in the as characteristics one of the most decreasing the promising approach. There are important differences on literature the burning andeffective functionalsolutions groups offorlignite and PET greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat samples. sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, the investment return ©prolonging 2017 The Authors. Published byperiod. Elsevier Ltd. The main scope of this paper is to assess the feasibility of using demand –Conference outdoor temperature for heat demand Peer-review under responsibility of the scientific committee of thethe 4thheat International on Energyfunction and Environment forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Research. buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenariosfuel; werelignite; developed Keywords: Combustion; PET (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation 1.(the Introduction scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the PET (Polyethylene Terephthalate) is a long-chain polymer that is a member of polyester family and it is one of the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and most widely-used polymeric materials many items including toys,increased electricalfor appliances, devices, packages, renovation scenarios considered). On theinother hand, function intercept 7.8-12.7% medical per decade (depending on the bottles, household substances, cables, polyester-based fibers, etc [1]. Accordingly, more than 56 million tons of PET coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and was annually consumed in 2010 and 33.3 million tons of which was comprised of fibers while PET bottles formed improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +90-212-2853351; fax: +90-212-2852925. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change
1876-6102 © 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the 4th International Conference on Energy and Environment Research. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 4th International Conference on Energy and Environment Research. 10.1016/j.egypro.2017.10.256
Nurdan Irem Unal et al. / Energy Procedia 136 (2017) 22–26 Nurdan Irem Unal et al. / Energy Procedia 00 (2017) 000–000
23
18.9 million tons [2]. Thus, huge amount of plastic wastes is formed that causes serious environmental pollutions and negative effects on ecology. That is, these materials are highly difficult to be digested in nature by natural effects since the digestion process is too slow and requires very long times. Namely, PET is by far the most significant pollutant in oceans [3]. Plastic wastes in seas threat the life of species including the fish, mammals, sea birds, turtles, etc. According to the report of U.S. Marine Mammal Commission in 1996, 136 species of fish, 6 species of turtles, 51 species of fish-eating birds, and 32 species of mammals have been adversely affected by waste plastics. Since, PET materials in water seem jelly fish or caviar, marine species that eat PET materials cannot digest them and finally this causes death of these species [4]. Recycle of PET materials is of great importance since it is produced from non-renewable fossil fuels. The recycle methods for PET materials are usually classified as primary, secondary, tertiary, and quaternary methods. Of which, the primary recycle method is the recycle of clean/new PET inside a factory by re-extrusion [5]. On the other hand, the secondary recycle method in other words mechanical recycle bases on separation and cleaning of waste PET from the pollutants and then granulation of the cleaned PET for reusing. However, heavily polluted PET cannot be recycled by secondary recycle method [2, 5]. Besides, ternary recycle methods mainly cover various chemical methods such as hydrolysis, aminolysis, methanolysis, glycolysis or pyrolysis [5, 6]. Alternatively, the purpose of the quaternary method is rather to take advantage of the energy potential and the calorific value of the waste organic substances instead of obtaining recycled new material. For this, incinerators are employed where the waste PET is burned under controlled conditions through which the only final combustion products will be water and CO 2. The heat obtained from the waste material is used for steam generation and space heating [7]. From this point of view, the quaternary method highly differs from the other options of PET recycle. Besides, lignites account for the most important national energy sources in Turkey. Therefore, a number of lignitefired power stations have been operated throughout the country. However, Turkish lignites are very low quality coals with low calorific values and fixed carbon contents and their ash yields and moisture contents are also very high [8]. In addition, the efficiency of the lignite-firing combustion systems is not high enough that leads unburnt carbon remained in ash and economic losses due to incomplete burning [9]. Therefore, blending these lignites with some waste materials that have enough calorific value may improve the burning efficiency and will help to diminish the unburnt carbon. However, the fuel properties and the combustion behavior of these waste materials should be known very well for such an application. For this reason, waste PET materials will be used in this study as an alternative fuel. In this context, PET bottle caps were used since they have good energy potential in unit volume associated with high density that leads less volume occupancy compared to the main body of PET bottle. Also, comparison of the fuel properties and the combustion behavior of PET bottle caps with those of a Turkish lignite sample from Afsin-Elbistan region, which is one of the largest lignite deposits in Turkey, was carried out. 2. Materials and methods The caps were collected from several different commercial brands of PET water bottles sold in Turkey. In sample preparation stage, these caps were granulated by a domestic metallic grate to decrease the particle size to several millimeters. The caps and the granulated samples are shown in Fig. 1. On the other hand, Afsin-Elbistan lignite sample was first kept in open containers for several days to reduce its excessive moisture content and to get the air-dried sample. The representative sample was taken from the bulk according to standard procedures. Particle size of lignite was decreased by breaking the sample with a hammer mill and then a coal grinder was used to reduce the particle size to pass through a sieve that has openings of 250 μm. Proximate analysis of both samples was performed according to ASTM standards, while the higher heating value (HHV) was determined using IKA C2000 model calorimeter.
Nurdan Irem Unal et al. / Energy Procedia 136 (2017) 22–26 Nurdan Irem Unal et al. / Energy Procedia 00 (2017) 000–000
24
Fig. 1. PET bottle caps and granulated sample.
Combustion characteristics of PET and lignite were tested using TA Instruments SDTQ600 model thermal analyzer that has 0.1 μg balance sensitivity, a temperature range of up to 1500 °C, platinum/platinum-rhodium thermocouples, temperature sensitivity of 0.001 °C, and alumina as reference material. In this way, Differential Scanning Calorimetry (DSC) curves were obtained that enables to determine the heat flows during the combustion process. For this analysis, 10 mg of ground samples were placed into alumina crucible and burning was implemented up to 900 °C with a heating rate of 40 °C/min under dry air flow at 100 mL/min. FTIR (Fourier Transform Infrared Spectroscopy) spectra of both samples were obtained using Perkin Elmer, Spectrum 100 model device. All the analyses and the tests were performed at least duplicate and the mean results were taken provided that the deviations are within 5%. 3. Results and discussion Proximate analysis results as well as the results of HHV of the samples are given in Table 1. It is likely to mention that the fuel properties of PET and lignite are highly different from each other. The higher heating value of PET is 3.5 times higher than that of lignite. This shows the fact that the calorific value of PET is considerably better than lignite and this material can be used as a supplementary fuel to prepare some fuel blends that have improved calorific value compared to the lignite sample used in this study or any of the low quality coal samples. The high ash yield and the low fixed carbon content of lignite can be regarded as the main factors that lower the HHV. Moisture content of lignite also deteriorates the calorific value. Besides, it should be taken into account that the high ash yield of lignites leads undesirable deposit problems in combustion systems. In contrast to this, being almost ash-free makes PET a very interesting alternative fuel. On the other hand, the most striking fuel property of PET is that it does not leave any fixed carbon content and almost all of its structure is converted to volatile products. Table 1. Proximate analysis results. Sample Lignite PET
Moisture (%) 6.97 0.03
Volatiles (%) 48.94 99.53
Ash (%) 34.96 0.44
Fixed Carbon (%) 9.13 -
HHV (cal.g-1) 3052 10931
Fig. 2 represents the FTIR spectra that explain the functional groups found in the samples of lignite and PET comparatively and Table 2 summarizes the corresponding organic bands on these spectra depending on the wavenumbers. Namely, C-H wagging, C-H bending, C=C stretching, C-H stretching, and asymmetrical C-H bonds are the most extensive FTIR bands for PET, while C-H vibration, C-O-C stretching, C-H aromatic bonds, C-H stretching, and C=C bonds are the main functionalities in the lignite sample. These characteristics also reveal the fact that these samples have highly different properties [10, 11]. Low rank coals such as lignites are very rich in oxygen content and it is in agreement with the oxygen containing functional groups of Afsin-Elbistan lignite. On the other hand, the bonds between carbon and hydrogen formed the most striking absorption bands on FTIR spectrum of PET.
Nurdan Irem Unal et al. / Energy Procedia 136 (2017) 22–26 Nurdan Irem Unal et al. / Energy Procedia 00 (2017) 000–000
25
Fig. 2. FTIR spectra. Table 2. Peaks on FTIR spectra. Afşin – Elbistan Lignite
PET Wavenumbers (cm )
Band
Wavenumbers (cm-1)
Band
717
Aromatic C-H out of plane
713
C-H vibration Aromatic C-H out of plane
1472
C-H bending C=C stretching
874
C-O-C stretching C-H aromatic
2848
C-H stretching
1035
C-O-C vibration
2914
C-H asymmetric
1420
C-H2 stretching C=C
-1
DSC burning profiles of both samples are illustrated in Fig. 3 and these burning curves make it possible to observe the heat flows from sample to surroundings and vice versa depending on temperature. Namely, negative heat flows indicate that the sample takes heat from the surroundings, while the positive heat flows predict exothermal phenomena arising from the combustion of the sample.
Fig. 3. DSC burning profiles.
Moisture removal from the sample and the phase transformations and decompositions of ash forming inorganics are the main sources of the negative heat flows (endothermic phenomena). However, combustion curves on these burning profiles are the dominant heat flows and the mentioned endothermic peaks are almost ignorable in comparison
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to the huge exothermic peaks of combustion. Some significant information can be obtained from the shape and the extent of these exothermic burning curves. That is, the ignition points can be determined from the transition to the exothermic region from the first endothermic region where moisture is lost. For instance, it can be seen that the ignition point of PET is higher than that of lignite. Actually, the ignition points were determined as 224 °C for lignite and 282 °C for PET. Some of the ingredients in the mineral matter of lignite may show catalytic effects to lower the ignition point. It was also found out that lignite not only ignites at lower temperature but also it gives most of the heat of combustion at lower temperatures compared to that PET. Besides, the maximum heat flow of PET is higher than lignite and it is in accordance with the fact that the higher heating value of PET is considerable higher than that of lignite. The maximum heat flows were determined as 31.3 mW/mg and 42.4 mW/mg for lignite and PET, respectively. Also, temperatures at which these maximum heat flows are observed were 392 °C for Afsin-Elbistan lignite and 545 °C for PET. The burning profile of lignite is consisted of two different parts. One of which that shows the maximum heat flows belongs to the homogeneous burning of the combustible volatile matter, which the other that has relatively smaller heat flows are resulted from the heterogeneous burning of the fixed carbon through surface oxidation. Since, PET does not have any fixed carbon content, only one burning peak is available that is forming from the combustion of the volatile matter. 4. Conclusion This study confirmed that waste PET materials can be evaluated in combustion process as alternative fuel source. Comparison of the fuel properties of PET with Afsin-Elbistan lignite based on their proximate analysis tests and the higher heating value results revealed that the fuel properties of PET bottle caps are by far superior to lignite. The calorific value of PET is disproportionally high and it almost leads no ash over burning. Considering these fuel properties, it can be suggested that PET materials may be used for preparation of fuel blends in which low quality/low rank coals are used. In this way, significant improvements can be performed in the fuel properties of these low quality coals such as Turkish lignites. On the other hand, it was determined that the chemical properties and the functional groups found in PET and lignite differ seriously and this may create some discrepancy in the combustion behaviors of individual ingredients in such fuel blends. Accordingly, DSC burning profiles of samples indicated some serious differences in the combustion characteristics of these samples. That is, the onset of burning for lignite takes place relatively at lower temperatures and consequently the main part of the combustion process occurs at lower temperatures in comparison to the burning of PET. In addition, burning of lignite takes place in two different regions that is a different nature of lignite combustion against burning of PET materials. References [1] [2]
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