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Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner
Journal of the Energy Institute xxx (xxxx) xxx
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Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner Karim Emara b, Ahmed Mahfouz a, *, H.A. Moneib b, Ahmed El-Fatih a, Ahmed Emara b a b
Mechanical Power Engineering Department, National Research Centre, Egypt Mechanical Power Engineering Department, Faculty of Engineering Mattaria, Helwan University, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 July 2019 Received in revised form 16 August 2019 Accepted 30 August 2019 Available online xxx
Waste tires and cooking oil pose a serious danger to human health and environment. Self-reacting pyrolysis system for waste tires is designed and constructed for converting waste tires into oil that could be used as a sustainable fuel. This study aims to analyze the thermal microstructure of conventional fuels like light diesel oil (LDO) and heavy diesel oil (HDO) as well as blended with waste cooking oil (WCO) and tires pyrolysis oil (TPO) using a co-axial burner via flame spectroscopy analysis. The first Blend 1 (B1) consists of 20% WCO þ 80% LDO, the second one (B2) consist of 20% WCOþ80%HDO and the last one (B3) was 20%TPO and 80% LDO by mass. This percentage was chosen carefully and according to previous combustion characteristics results. The experimental results showed that B1 will shrink C2 radicals by nearly 61% and 64.5% at Ф ¼ 0.63 and 0.96 respectively. B2 will decrease C2 radicals by nearly 19% and 82% at Ф ¼ 0.63 and 0.96 respectively. Finally, B3 will reduce C2 radical's intensity by nearly 39% and 58% at Ф ¼ 0.63 and 0.96 respectively. TPO produced CH emission radicals lower than that of LDO by nearly 5.9%. LDO droplets absorbed more radiation energy needed for excitation than that of WCO due to droplet size and fuel physic-chemical properties. B2 fuel is recommended to replace LDO at Ф ¼ 0.63 and 0.96. © 2019 Energy Institute. Published by Elsevier Ltd. All rights reserved.
Keywords: Waste tires pyrolysis oil Waste cooking oil Emission radical intensity Thermal microstructure Flame emission spectroscopy
1. Introduction Waste tires (WT) of cars and trucks represent a significant part of the world waste stream that is growing gradually in quantity and its disposal is considered to result in serious environmental pollution. One of the best methods for solid waste recycling (WT) is the pyrolysis treatment technology aiming the recovery of material (activated carbon) and generating energy (Syngas and oil) [1,2]. The parameters which affected the oil yield, type and characteristics were tire type, heating temperature, rate of heating, pellet size of shredded tire, gas flow and pressure [3e17]. Many researchers and scientists employed various designs of the pyrolysis reactors. The operating temperature used for the pyrolysis process ranged from 45 to 575 was applied on two different reactors shape where [4] used a conical spouted bed reactor while [5] used a fixed bed reactor. It was deduced that 475 C was an appropriate operating temperature to produce high concentrations of valuable chemicals, such as limonene (waste tire pyrolysis oil) TPO with a 58.2% yield. While [6e9] employed a rotary kiln reactor with a feed rate 4.8 kg/h. it was concluded that the oil yield was inversely proportional with operating temperature. Finally [10e17], carried out a pyrolysis process using a cylindrical shape reactor with inner diameter (Di) ¼ 30 cm. An effective chamber length of 40 cm supplied with electric heating unit (5 kW) was employed to generate a temperature of 600 C producing a volume of approximately 20 L of TPO. The TPO could be used as alternative fuel in combustion engines. Furthermore, the optimum operating temperature to maximum yield of high concentrations of valuable chemicals, such as limonene TPO was in the range of 300e500 C. The produced (waste tire oil) TPO serves as an alternative fuel due to intensive and extensive consumption of fossil fuels leading to the depletion of petroleum products. Another alternative fuel source is vegetables oils. The use of vegetable oils and/or their blends with diesel fuel in industrial burners has attracted attentions because of the physical and chemical properties of these vegetable oils that are close to those of diesel [18e20]. Waste cooking oil methyl ester (WCOME) and diesel blends can also be used as renewable energy fuel for diesel engines and burners in power
* Corresponding author. E-mail address: [email protected] (A. Mahfouz). https://doi.org/10.1016/j.joei.2019.08.008 1743-9671/© 2019 Energy Institute. Published by Elsevier Ltd. All rights reserved.
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stations and boilers. The biodiesel and its blends had better emission characteristics than conventional fuels [21]. The conversion of vegetable oils is highly costing, consuming time with low yield. Finally, direct use of (waste cooking oil) WCO through combustion processes or its blends will decrease fossil fuel consumption, reduce its environmental impact, create new jobs and protect humanity from diseases such as malaria, cholera, typhoid, water pipe blockage and poisoned water. Recently, a hyper-spectral imaging technique (HSI) was developed which consisted of a combination between optical spectroscopy as an analytical tool and two-dimensional object visualization obtained by optical imaging. In HSI, any image contains pixels, each pixel contains spectral information, which is added as a third dimension of values to the two-dimensional spatial image, producing a three-dimensional data cube file, sometimes referred to as hypercube data or as an image cube. Hyper-spectral data cubes contain absorption, reflectance, or fluorescence spectrum data for each image pixel. The spectral range in hyper-spectral data can extend beyond the visible range (ultraviolet, infrared) [22e24]. Hyper-spectral imaging is a new promising technology for measuring intensities and emissivity. References [25e27] reported that the HSI technique is used in combustion research by measuring spectroscopic intensities. This technology was used to measure spectroscopic intensity inside each pixel in a large number of continuous spectral wavelength bands [28]. In flame emission spectroscopy (FES), the energy from the flame provides the energy necessary to transfer electrons from the ground state to the excited states of free atoms. The intensity of radiation emitted by these excited atoms returning to the ground state provides the basis for analytical determinations in FES. These free atoms are converted to excited states through one of either two methods; absorption of additional thermal energy from the flame and absorption of radiant energy from an external source of radiation [29]. The thermal microstructure of turbulent diffusion flames for industrial boilers, furnaces and power stations are difficult to investigate and characterize. This is due to high turbulence, high surrounding flame temperature, exhaust and flame emissions and many zones formation depending on the wavelength and emissions released [30e33]. Flame emission spectroscopy for WCO, TPO and their blends with conventional fuels (HDO and LDO) was not performed before. Therefore, the reported research is aimed to introduce new alternative fuels and characterize spectral emissions in order to quantify the active emission radicals, determine rate of reaction zones. Comparative study was conducted between results of alternative fuels blends compared to conventional diesel fuels to justify the highest thermal energy gained and lowest environmental impact. This study also targeted waste cooking oil and waste tires oil as alternative sustainable fuels to reduce the burden of waste disposal, reduce their environmental damage, generate energy from waste and introduce new sustainable energy fuels. Finally, this could be applied to help the government to solve many problems in most sectors of life like health, environment, economics, energy, power and engineering. 2. Waste tire oil preparation test setup A self-reacting pyrolysis system for waste tires was designed and constructed as shown in Fig. 1 comprised of: (a) A cylindrical, horizontal bed reactor with a capacity of 50 kg of shredded waste tires to produce a volume of approximately 22 L of TPO (45%); an adequate quantity for testing characteristics of the produced oil. While the solid residue and the gas yields represent about 55% and 5% respectively from the total quantity of waste tires. The reactor is made of a 3 mm thick stainless-steel sheet (to ensure high thermal strength) and having a diameter and length of 500 mm and 600 mm respectively. The inside surface area along the reactor length is fitted with baffles to ensure uniform heat distribution and structural rigidity, as shown in Fig. 2. The outer surface of the reactor is properly insulated to eliminate heat loss. Also, a mechanism for angular rotation of the whole bed is included (3 rpm) to facilitate continuous stirring of the shredded tires leading to accelerated pyrolysis. (b) A shell and tube heat exchanger (Condenser): The produced vapor released from the reactor is rapidly cooled by a water-cooled shell and tube heat exchanger, Fig. 2 panel (B). The condenser tubes are made of copper of 0.628 m in length, 12.5 mm in diameter and 0.3 mm thickness. The calculated heat transfer coefficient equals 410 W/m2 ⁰C for a water flow rate of 0.02 kg/sec. (c) A gas/oil separator (disengage) where oil is collected (by gravity) at its bottom base and syngas pass via a tube at its top end to supply the heating burner (self-heating) of the reactor and hence reduces the main fuel supply; making the process more economical.
Fig. 1. Schematic diagram of the designed self-reacting pyrolysis system.
Please cite this article as: K. Emara et al., Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner, Journal of the Energy Institute, https://doi.org/10.1016/j.joei.2019.08.008
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Fig. 2. Schematic diagram of the cylindrical reactor; panel (A) and condenser design; panel (B).
(d) An ON/OFF temperature control unit is used to control the inside reactor temperature to within ± 3 C as shown in Fig. 1. This unit is comprised of a type- K thermocouple connected to a digital control indicator. A sound alarm is activated when the temperature exceeds an upper limit and the heating system shuts down. The TPO properties of produced TPO at 425 C (at 5 C/min heating rate) are closest to diesel fuel properties which is suitable to be used in diesel engines as a blended fuel. Moreover, at this temperature the main product is liquid (about 45% of the total waste tires quantity) which is a mixture of hydrocarbon depending on the initial composition of the waste material.
3. Waste cooking oil Waste cooking oil was collected from houses, apartments. WCO was filtered via 5 stages of mesh filters of 40 mm to avoid fuel line and nozzles blockage. This WCO is a blend of olive oil, soybean oil and sunflower. Eliminating waste cooking oil from houses and apartments was difficult but easy to be burned without recycling. Gas chromatography-mass spectrometry (GC-MS) which is a common technique for separating and analyzing components of WCO was reported in ref [31]. The main structures of fatty acids for WCO are oleic, palmitic, linoleic, stearic, linolenic, palmitoleic acids. The percentages of fatty acids by weight are 34.94%, 28.78%, 21.19%, 6.41% and 5.2% respectively [31]. 4. Experimental set up and facilities The experimental measuring system as shown in Fig. 3 consists of an airline, a fuel line and a hyper-spectral camera. The designed control unit is used to control in an effective way both the air and the fuel flow, thereby regulating the relative air/fuel ratio (which is defined with respect to the stoichiometric one) in each test. The airline was divided into a primary, high-pressure atomizing airline and a secondary airline that originated from the burner blower fan. The fuel line consists of a fuel tank, a valve, a solenoid valve (Delavan Nozzle Adapter DLN 17147 and twin Siphon Delavan nozzles model number 30609-28). Each nozzle is capable of producing up to 1.5 GPH. The nozzle had a mixing chamber where the primary air impinged on the liquid jet and formed a high-quality liquid gas mixture. The volume of fluid coming out of the nozzle is directly proportional to the pressure at which it is supplied to the nozzle. A hyper-spectral camera (model SOC710V) was used to capture radiation images. This camera captures intensities from each available wavelength in the form of a cube file. The spectral range of the camera is from 400 to 1000 nm separated by 4.6875 nm. The hyper-spectral
Fig. 3. Schematic diagram of the experimental setup.
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camera was set perpendicular to the flame horizontally at nearly 7 m away from flame to be able to capture all flame edges and avoid saturation of the measured data. An Arduino Uno card was interfaced with LABVIEW software program to control successive steps of operation of the Burner (Model: Giersch Enertech Group e Germany) [30,31]. Heavy diesel oil (HDO) and light diesel oil (LDO) were used as conventional fuels and base fuel. WCO and TPO were used as alternative fuels for the burner test. Blend 1 (B1) was formed of 20% WCO þ 80% LDO by mass for 6 L (according to the burner tank). Blend 2 (B2) was 20% WCOþ80%HDO also by mass. Blend 3 (B3) was 20%TPO and 80% LDO by mass. This percentage was chosen according to previous studies in ref [30]. The high percentage of blending ratios of WCO has the opposite effect on thermal characteristics of the blend as well as TPO that has a higher density and viscosity. These physical properties lead to improper atomization and vaporization of blends compared to base fuel. Combustion procedures were carried out at definite equivalence ratios Ф ¼ (0.63 and 0.96) where lean and near stoichiometric mixture. 5. Results and discussions 5.1. Physical and chemical properties of fuels All laboratory measurements were carried out at Egyptian Petroleum Research Institute (EPRI) and National Research Centre (NRC) Labs according to ASTM standards as shown in Table 1. All combustion processes measurements were done in cooperation with the National Research Centre (Mechanical power Dept.), Mattaria Faculty of Engineering (Laser and Nanotechnology Lab, Continuous Combustion Lab) and the Laser Photonics Research Center MTC (Physics Department). From laboratory measurements it is obvious that HDO had the highest heating value of 44.3 MJ/kg and sulphur content with 3.4%, while WCO was characterized with the lowest heating value of 36.59 MJ/kg. This fuel had the largest flash point for burning due to a high water percentage content and fatty acids. TPO had the largest carbon content of 92.08%wt. Both HDO and WCO had nearly equal densities. The most interesting characterization appeared when the WCO and TPO had oxygen molecules in its chemical form to complete its combustion. 5.2. Spectral emission contour radicals According to applied methods of [23] and Wien's Law [39] intensity contour are drawn. Images are captured by the hyper-spectral camera at clearly dark times in order to avoid any reflectance and noise from light in the measurements. These images are saved as a cube and Envi file extension type. Preprocessing steps are carried out to perform the analysis of emission contours, the thermo-micro structure of fuel flames and the maximum peak of intensity. Image-Lab, Hyper-toolkit, GLIMPS, Tecplot 360 EX 2017 R1 and Scyllarus software [34] were used in the image analysis techniques, identifying zones of reactions, the highest intensity peaks corresponding to wavelength. The images taken at 442 and 554 nm correspond to CH and C2 radicals. Therefore, by applying experimental methods which were previously used [23,27,35,36] to obtain emission contour spectra of flames for different fuels at wavelength 442 and 554 nm see Figs. 5e8 and Figs. 10e13 respectively. 5.2.1. CH radical intensity A) at Ф ¼ 0.63 (lean mixture): Fig. 4 depicts the maximum CH radical intensity peak which occurred for HDO, LDO, WCO, TPO, B1, B2 and B3 at Ф ¼ 0.63 and 0.96. WCO and B1 produced the lowest CH emission radicals due to presence of high percentage of oxygen molecules. These molecules helped in the oxidation process by avoiding the elimination of carbon monoxide (CO). Waste tire pyrolysis oil and B2 blend which produced CH emission radical of values 65 and 60 a.u. had lower amount than that of LDO as shown in Fig. 4. Light diesel oil produced the highest CH emission radicals because it's lighter density, easily atomized, lowest flash point and easily burned. However some fuel droplets are vaporized to the gaseous state without burning CH radicals. B) at Ф ¼ 0.96 (near stoichiometric): HDO, LDO and TPO fuels produced higher CH radicals compared to that at Ф ¼ 0.63 due to high carbon content and fuel flow rate. It is expected that near stoichiometric emissions will be reduced in exhaust gases not inside the flame because of continuous reactions inside flame core. Besides CH and C2 radicals are an indication for heat energy released as will be discussed in next section. Table 1 Physical and chemical Properties of the tested fuels [3,30,31]. Properties
HDO
LDO
WCO
TPO
B1
B2
B3
Density (kg/m3) Viscosity at 40 C (cSt) Calorific value (MJ/kg) Flash point ( C) Water content (%) Sulphur content (%) Carbon% (wt.) Hydrogen % (wt.) Oxygen % (wt.)
885 4.8 44.3 123 0.16 3.4 88.3 10.5 0
831 2.72 42.1 70 0.05 0.55 86.23 12.85 0
887 5.3 36.59 178 0.42 0 76.95 12.14 10.93
931 3.5 42 76 0.8 0.916 86.11 10.33 2
870 3.8 41.2 92.2 0.33 0.394 84.19 12.97 2.25
881 5 41.93 135.1 0.2 2.36 85.11 9.66 2.2
851 2.88 42.07 71 0.2 0.64 86.3 12.6 0.412
Please cite this article as: K. Emara et al., Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner, Journal of the Energy Institute, https://doi.org/10.1016/j.joei.2019.08.008
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180
5
170 160
160 140
Intensity, a.u.
120
120
120 95
100 80 80 60
65
60
55 40
40
30
60
Ф 0.63 0.96
38
22
20 0 HDO
LDO
WCO
TPO
B1
B2
B3
Tested fuels Fig. 4. Maximum CH radical intensity peak values for different fuel types at Ф ¼ 0.63 and 0.96.
TPO produced CH emission radicals lower than that of LDO by nearly 5.9% because of its nearly equal heating value to that of LDO and oxygen molecules that would help in rising up inflame temperature. Also, TPO emitted CH radicals higher than that of HDO by nearly 33.3% because TPO had lower viscosity and oxygen content. So, vaporization and combustion of TPO was done fast and easily. On the other hand, WCO and B2 achieved the lowest CH emission radicals. Much number of oxygen atoms decreased the formation of CH radicals where formation of CO2 and H2O was occurred as in WCO fuel. The emissions tend to be diminished, as they become stoichiometric because high molecules of oxygen reduced emissions besides low heating value of WCO. So, combustion of WCO generated lower thermal energy flame compared to conventional fuels due to improper atomization and glycerin and wax materials.
Fig. 5. CH emission contour radicals of HDO (pane A), LDO (panel B), WCO (panel C) and TPO (panel D) at Ф ¼ 0.63.
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Fig. 6. CH emission contour radicals of B1 (pane E), B2 (panel F) and B3 (panel G) at Ф ¼ 0.63.
Fig. 7. CH emission contour radicals of HDO (pane A), LDO (panel B), WCO (panel C) and TPO (panel D) at Ф ¼ 0.96.
5.2.2. C2 radical intensity A) at Ф ¼ 0.63 (lean mixture): Fig. 9 depicts the maximum C2 radical intensity peak, which occurred for HDO, LDO, WCO, TPO, B1, B2 and B3 at Ф ¼ 0.63 and 0.96. As mentioned in Fig. 9, LDO emitted the highest C2 emission radical of intensity 1400 a.u. at Ф ¼ 0.63 and 2200 a.u. at Ф ¼ 0.96. Therefore, both Please cite this article as: K. Emara et al., Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner, Journal of the Energy Institute, https://doi.org/10.1016/j.joei.2019.08.008
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Fig. 8. CH emission contour radicals of B1 (pane E), B2 (panel F) and B3 (panel G) at Ф ¼ 0.96.
CH and C2 contour radicals are expected to be supplementary, while WCO produced the lowest emission intensity having value of 140 a.u at Ф ¼ 0.63 and 320 at Ф ¼ 0.96 because of its low heating value compared to other fuels. B) at Ф ¼ 0.96 (near stoichiometric): LDO and HDO achieved the highest C2 emission radicals of 2200 and 2000 a.u., respectively because of high carbon content. On the other hand, WCO emitted the lowest C2 radicals because of its low carbon content in its chemical form compared to other fuels.
2500 2200 2000
Intensity, a.u.
2000
1400
1500
Ф 1000
1000 850
850
800 600
500
550
0.96
650 350
320 140
0.63
170
0 HDO
LDO
WCO
TPO
B1
B2
B3
Tested fuels Fig. 9. The maximum C2 radical intensity peak values for different fuel types at Ф ¼ 0.63 and 0.96.
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Fig. 10. C2 emission contour radicals of HDO (pane A), LDO (panel B), WCO (panel C) and TPO (panel D) at Ф ¼ 0.63.
Fig. 11. C2 emission contour radicals of B1 (pane E), B2 (panel F) and B3 (panel G) at Ф ¼ 0.63.
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Fig. 12. C2 emission contour radicals of HDO (pane A), LDO (panel B), WCO (panel C) and TPO (panel D) at Ф ¼ 0.96.
Fig. 13. C2 emission contour radicals of B1 (pane E), B2 (panel F) and B3 (panel G) at Ф ¼ 0.96.
Blending waste cooking oil by 20% mass to LDO will reduce C2 radicals by nearly 61% at Ф ¼ 0.63 and 64.5% at Ф ¼ 0.96. This reduction is due to effect of oxygen molecules that prevent formation of carbon monoxide and the high viscosity of WCO will obstruct the flow of B1 in order to avoid fuel droplet vaporization without burning. Consequently, low free C2 radicals are formed, while blending WCO to HDO will decrease C2 radicals by nearly 19% and 82% at Ф ¼ 0.63 and 0.96 respectively. The viscosity of both HDO and WCO had a value of 4.8 and 5.3 cSt. Therefore, HDO and WCO are nearly homogenous liquid when blended. The burning of B2 at Ф ¼ 0.96 will lower C2 radicals than that of HDO and even LDO, because the oxidation process occurred in a homogenously viscous fluid in the presence of 2.2 %wt. oxygen molecules. Blending TPO by 20% mass to LDO will decrease the C2 radical's intensity by nearly 39% and 58% compared to LDO at Ф ¼ 0.63 and 0.96 respectively. The B3 blend is characterized by a relatively high calorific value compared to WCO and TPO. The quality of flame pictures/images of the WCO fuel for a lean mixture is hazy and cloudy due to the low heat energy output and highwater content. Therefore, the camera cannot identify the place of heat released. The burning of pure WCO will produce a white, transparent cloud fog around the flame. Consequently, WCO flame images aren't clear as seen in panel C all over contour figures due to its low thermal
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energy. Consequently, no more excited atoms and emissions are released and captured by hyper-spectral camera. However for other fuels, the flame contour edges are clearly seen. For a near stoichiometric mixture, the flame images are clear with sharp edges because camera identified the area of heat released and intensity of excited atoms at this wavelength are observed as intensity as reported in next section. 5.3. Thermal microstructure of different fuels flame Relating inflame temperature to the active emission radicals inside the flame is significant to investigate and locate reaction zone and its rate. So, Axial and radial inflame temperatures were measured using thermocouple type S with diameter 50 mm. These readings are then averaged to obtain the average temperature at points along the axial flame plane. Inflame temperatures were shown versus CH and C2 emission radicals along the axial flame length plane at only Ф ¼ 0.63 and 0.96. CH radicals were emitted prior to advancing to the C2 reaction chain. OH radicals were produced through oxidation of CH before the final steps in the CHx (hydrocarbons) oxidation chain [37]. CH and C2 radicals intensity of a flame were taken at 432 nm and 554 nm, respecively [25e29]. Fig. 14 showed a comparison between LDO and B1 blend fuel in a microstructure analysis and radiation energy absorbed where the X-axis is represented by L/L0, L is the axial distance (5.5,15, 25, 35, 45, 55, 65, 80.5, 95, 115, 134.5, 170 and 195 cm) and L0 is the largest flame length L0 ¼ 200 cm occurred showing that: For LDO fuel At Ф ¼ 0.63, the average plane inflame temperature near the burner rim (L/L0 ¼ 0.0275) for LDO was higher due to good mixing and generating a high reaction rate. The region of higher inflame temperature will have higher intensity of CH and C2 emission radicals due to the higher rate of reaction resulting from excited atoms [27e29,37]. The maximum peak of excited atoms was shifted axially from L/ L0 ¼ 0.0275 to L/L0 ¼ 0.175 due to their turbulent flow direction. Consequently, the highest average plane flame temperature was nearly 855 C. The emissions intensities of CH and C2 radicals of the LDO fuel flame were 25 and 16 a.u. respectively. This zone had a high temperature and low radical concentration due to the low number of excited atoms and low radiation energy absorbed. These atoms did not absorb enough radiation energy for excitation because the fuel droplets were not fully vaporized. Therefore, the fuel droplets will absorb low radiation energy. The fuel droplet size is inversely proportional to the radiation energy absorption. The intensity of the radicals was directly proportional to the number of excited atoms [37]. At L/L0 ¼ 0.125, the temperature curve declined due to the decrease of fuel concentration. On the other hand, a sudden rise in intensity of radicals occurred far from nozzle opening because the angle of atomization became wider so that the atomization rate of fuel droplets could be determined in wider area. Hence, the fuel droplets were fully vaporized to the gaseous state. This vaporization will allow fuel atoms to easily absorb radiation energy from the surrounding flame temperature. Thus a high excitation was accomplished by generating high emission radicals [40] as shown in Fig. 14. After the position of L/L0 ¼ 0.4, the emission intensity of the radical curve declined because the flame radiation energy decreased, and the number of excited atoms will decrease. At Ф ¼ 0.96, the fuel flow rate increased and the average plane flame temperature near the burner rim decreased by nearly 21% compared to that at Ф ¼ 0.96 due to the higher fuel flow rate, accumulation of fuel particles, low mixing rate and the not fully vaporized and the low radiation energy of atoms gained for the LDO fuel. Therefore, the rate of reaction will be lowered and accompanied by a low CH and C2 emission radicals’ intensity at L/L0 ¼ 0.0275 with a value of 14 and 15 a.u., respectively. At L/L0 ¼ 0.325, a nearly linear increase of the emission intensity of the radicals occurs until the end of the thermal flame length. A high fuel flow rate will supply more heat and radiation energy reaching the position L/L0 ¼ 0.975, where the maximum peak heat energy released by the fuel of excited atoms are generated producing 152 a.u. and 1344 a.u. corresponding to CH and C2 radicals, respectively. For B1 blend fuel: At Ф ¼ 0.63, the average plane temperature was nearly 650 C. The intensity of CH and C2 was 6 and 10 a.u., respectively for the B1 blend. Both flame temperature and emission radicals of B1 were lower than that of LDO at the same condition and position (L/L0 ¼ 0.0275) because WCO has a higher viscosity, incomplete atomization and a lower heating value. Therefore, WCO fuel particles were difficult to be burned. The WCO droplets are bigger in size than LDO [38]. Thus, the absorption of radiation energy for atom excitation will be lower and occurred later at L/L ¼ 0.4. By increasing the combustion rate reaching Ф ¼ 0.96, the average plane flame temperature was decreased to 620 C. A sudden increase in CH and C2 intensity radicals reaching 47 a.u. and 563 a.u. occurred that corresponds to a position of L/L0 ¼ 0.4 and 0.6, respectively. By a comparison between LDO and B1 at Ф ¼ 0.63, the LDO atoms absorbed more radiation energy needed for excitation than the WCO droplets relating to their size and fuel physical-chemical properties. The LDO droplets are easily vaporized due to their measured physical characteristics are shown in Table 1. On the other hand, WCO particles in B1 blend encounter difficulties to be vaporized because of their higher density and viscosity. At Ф ¼ 0.96, the LDO atoms absorbed radiation energy from the flame surrounding temperature. These atoms are excited to higher energy levels along the flame, while in the B1 blend the fuel droplets absorb less radiation energy as affected by the flame temperature. Fig. 15 depicts a comparison between HDO and B2 blend fuel in a microstructure analysis and the radiation energy absorbed is as follows: For HDO fuel: At Ф ¼ 0.63, the average plane flame temperature near the burner rim (L/L0 ¼ 0.075) was 1100 C due to higher mixing, a higher heating value of HDO and a higher reaction rate. The maximum peak of intensity of the excited atoms having a value of 539 a.u. was shifted axially from L/L0 ¼ 0.075 to 0.175 because of the fast absorption of atoms for radiation heat energy from the flame. This is followed by a fast decrease of the CH and C2 radicals because of a low atomization rate at this zone. This zone has a lower radical's intensity because of a lower radiation energy absorbed for the exciting atoms. These atoms did not absorb sufficient radiation energy because the fuel droplets were not fully vaporized. Therefore, the fuel droplets will absorb lower radiation energy. Therefore, by increasing the fuel mass flow rate to Ф ¼ 0.96, the average plane flame temperature was increased from 1100 C to 1207 C. Thus, more radiation energy was provided and more intensity of the radicals was released ranging from 1329 a.u to 1460 a.u. for C2 radicals that occurred from L/L0 ¼ 0.125 to 0.275 along the flame length. This increase in intensity was due to the fact that more atoms were excited to a higher energy level.
Please cite this article as: K. Emara et al., Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner, Journal of the Energy Institute, https://doi.org/10.1016/j.joei.2019.08.008
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Fig. 14. Thermal microstructure analysis of LDO and B1 fuel at Ф ¼ 0.63 and 0.96.
B2 blend fuel: At Ф ¼ 0.63, the flame temperature increased at the first four axial positions by 50 C for the B2 blend. This increase in heat released may be related to oxygen molecules in WCO that enhance combustion [30,31]. The decline of radicals’ intensity was due to the lower radiation energy absorbed by both WCO and HDO oils. Therefore, the addition of WCO depressed the absorption, excitation of fuel atoms due to its lower heating value. On the other hand, at Ф ¼ 0.96, both temperature and radicals intensity curves have the same trend as LDO fuel at the same operating condition with different flame temperatures. By making a comparative investigation between HDO and B2 it was found that: Blending WCO to HDO will elongate the atomic period for radiation energy absorption because of micro-explosion phenomena. WCO enhanced flame core temperature due to the presence of oxygen atoms. The B2 fuel atoms absorbed enough energy for excitation where inflame temperature was nearly 1156 C that is higher than that of LDO at Ф ¼ 0.63 as well as Ф ¼ 0.96. Therefore, B2 fuel is recommended to replace LDO at Ф ¼ 0.63 and 0.96.
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Fig. 15. Thermal microstructure analysis of HDO and B2 fuel at Ф ¼ 0.63 and 0.96.
TPO was blended with LDO as B3. Fig. 16 shows the difference between LDO and B3 blend fuels in a microstructure analysis represented by the flame temperature of CH and C2 radicals. At Ф ¼ 0.63, the maximum average plane inflame temperature was 1209 C at L/L0 ¼ 0.125, where the CH and C2 radicals intensity was 7 a.u and 25 a.u., respectively. The maximum peak intensity of C2 and CH radicals was 482 a.u. and 44 a.u., respectively at L/L0 ¼ 0.475. At Ф ¼ 0.96, the maximum inflame temperature recorded was 1220 C at L/L0 ¼ 0.075, where the CH intensity was 5 a.u. and 14 a.u for C2. The maximum peak intensity of C2 and CH radicals were 842 a.u. and 81 a.u., respectively at L/L0 ¼ 0.575. By comparing between B3 and LDO fuel: B3 fuel has a low concentration of oxygen molecules compared to B1 fuel. This will lead to an increase of the inflame temperature reaching 1220 C which is favorable in many applications. The values of the radicals’ intensities were near to each other with small differences. Using WTPO as a fuel for industrial burners is one of the possible ways to solve the waste tires disposal problem. Also, the present study includes a mechanism of waste tires pyrolysis to produce alternative fuel. In this respect, the conversion of both waste tires and WCO to thermal energy creates a cleaner version of fuel, rather than the crude oil and will contribute to solving the energy crisis.
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Fig. 16. Thermal microstructure analysis of LDO and B3 fuel at Ф ¼ 0.63 and 0.96.
6. Conclusions The thermal flame microstructure of conventional fuels and their blends with both waste cooking oil and TPO were characterized with spectral peaks intensity. The thermal analysis of different fuels at various fuel/air equivalence ratios was investigated. Axial plane flame temperatures related to CH and C2 radicals were investigated for LDO, HDO, B1, B2 and B3 blends at Ф ¼ 0.63 and 0.96. These conclusions are summarized as follows: WCO and B1 produced the lowest CH emission radicals due to presence of a high percentage of oxygen molecules. TPO produced CH emission radicals lower than that of LDO by nearly 5.9%. Blending waste cooking oil by 20% mass to LDO will reduce C2 radicals by nearly 61% at Ф ¼ 0.63 and 64.5% at Ф ¼ 0.96. This reduction is due to the effect of oxygen molecules. Therefore, no free C2 radicals are formed. Blending of WCO to HDO will decrease C2 radicals by nearly 19% and 82% at Ф ¼ 0.63 and 0.96 respectively. Blending of TPO by 20% mass to LDO will decrease the C2 radical's intensity by nearly 39% and 58% compared to LDO at Ф ¼ 0.63 and 0.96 respectively. B3 blend is characterized by a relatively higher calorific value than that compared to WCO and TPO. For LDO the fuel droplets did not absorb enough radiation energy for excitation because the fuel droplets were not fully vaporized for a lean mixture. The fuel droplet size is inversely proportional with radiation energy absorption. The emissions intensity of radicals was
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directly proportional to the number of excited atoms. A rise in radical intensity occurred at a far distance from nozzle opening because the angle of atomization became wider so that the atomization rate of the fuel droplets occurred in wider area. Both flame temperature and emission radicals of B1 were lower than that of LDO at the same condition and position (L/L0 ¼ 0.0275) because WCO has a higher viscosity and a lower heating value. The WCO droplets are bigger in size than LDO. The LDO droplets absorbed more radiation energy needed for excitation than that of WCO which is due to the droplet size and fuel physic-chemical properties. Blending WCO to HDO will elongate the atom period for radiation energy absorption because of micro-explosion phenomena. WCO has enhanced flame core temperature due to presence of oxygen atoms. B2 fuel atoms absorbed enough energy for excitation. B2 fuel is recommended to replace LDO at Ф ¼ 0.63 and 0.96. Furthermore, B3 fuel had oxygen molecules compared to LDO fuel. This will help to increase the inflame temperature to reach 1220 C. Acknowledgments I would like to acknowledge my Prof. Dr. H.A. Moneib for his advices and leading us in scientific directions. Authors would like to thank Laser Photonics Research Center for supplying new trend measuring technique and continuous combustion lab as well as the National Research Centre for funding. References an, C. Ozalp, O. Kara, M. Ozcanli, Experimental investigation on performance and emission characteristics of waste tire pyrolysis oilediesel blends in a diesel [1] E. Hürdog engine, Int. J. Hydrogen Energy 12 (2017) 126. [2] T. Seljak, S.R. Opresnik, T. Katrasnik, et al., Combustion characteristics of tire pyrolysis oil in turbocharged compression ignition engine, Fuel 150 (2015) 226e235. [3] J.D. Martínez, N. Puy, R. Murillo, T. García, M.V. Navarro, A.M. Mastral, Waste tire pyrolysisea review, Renew. Sustain. 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Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner Karim Emara b, Ahmed Mahfouz a, *, H.A. Moneib b, Ahmed El-Fatih a, Ahmed Emara b a b
Mechanical Power Engineering Department, National Research Centre, Egypt Mechanical Power Engineering Department, Faculty of Engineering Mattaria, Helwan University, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 July 2019 Received in revised form 16 August 2019 Accepted 30 August 2019 Available online xxx
Waste tires and cooking oil pose a serious danger to human health and environment. Self-reacting pyrolysis system for waste tires is designed and constructed for converting waste tires into oil that could be used as a sustainable fuel. This study aims to analyze the thermal microstructure of conventional fuels like light diesel oil (LDO) and heavy diesel oil (HDO) as well as blended with waste cooking oil (WCO) and tires pyrolysis oil (TPO) using a co-axial burner via flame spectroscopy analysis. The first Blend 1 (B1) consists of 20% WCO þ 80% LDO, the second one (B2) consist of 20% WCOþ80%HDO and the last one (B3) was 20%TPO and 80% LDO by mass. This percentage was chosen carefully and according to previous combustion characteristics results. The experimental results showed that B1 will shrink C2 radicals by nearly 61% and 64.5% at Ф ¼ 0.63 and 0.96 respectively. B2 will decrease C2 radicals by nearly 19% and 82% at Ф ¼ 0.63 and 0.96 respectively. Finally, B3 will reduce C2 radical's intensity by nearly 39% and 58% at Ф ¼ 0.63 and 0.96 respectively. TPO produced CH emission radicals lower than that of LDO by nearly 5.9%. LDO droplets absorbed more radiation energy needed for excitation than that of WCO due to droplet size and fuel physic-chemical properties. B2 fuel is recommended to replace LDO at Ф ¼ 0.63 and 0.96. © 2019 Energy Institute. Published by Elsevier Ltd. All rights reserved.
Keywords: Waste tires pyrolysis oil Waste cooking oil Emission radical intensity Thermal microstructure Flame emission spectroscopy
1. Introduction Waste tires (WT) of cars and trucks represent a significant part of the world waste stream that is growing gradually in quantity and its disposal is considered to result in serious environmental pollution. One of the best methods for solid waste recycling (WT) is the pyrolysis treatment technology aiming the recovery of material (activated carbon) and generating energy (Syngas and oil) [1,2]. The parameters which affected the oil yield, type and characteristics were tire type, heating temperature, rate of heating, pellet size of shredded tire, gas flow and pressure [3e17]. Many researchers and scientists employed various designs of the pyrolysis reactors. The operating temperature used for the pyrolysis process ranged from 45 to 575 was applied on two different reactors shape where [4] used a conical spouted bed reactor while [5] used a fixed bed reactor. It was deduced that 475 C was an appropriate operating temperature to produce high concentrations of valuable chemicals, such as limonene (waste tire pyrolysis oil) TPO with a 58.2% yield. While [6e9] employed a rotary kiln reactor with a feed rate 4.8 kg/h. it was concluded that the oil yield was inversely proportional with operating temperature. Finally [10e17], carried out a pyrolysis process using a cylindrical shape reactor with inner diameter (Di) ¼ 30 cm. An effective chamber length of 40 cm supplied with electric heating unit (5 kW) was employed to generate a temperature of 600 C producing a volume of approximately 20 L of TPO. The TPO could be used as alternative fuel in combustion engines. Furthermore, the optimum operating temperature to maximum yield of high concentrations of valuable chemicals, such as limonene TPO was in the range of 300e500 C. The produced (waste tire oil) TPO serves as an alternative fuel due to intensive and extensive consumption of fossil fuels leading to the depletion of petroleum products. Another alternative fuel source is vegetables oils. The use of vegetable oils and/or their blends with diesel fuel in industrial burners has attracted attentions because of the physical and chemical properties of these vegetable oils that are close to those of diesel [18e20]. Waste cooking oil methyl ester (WCOME) and diesel blends can also be used as renewable energy fuel for diesel engines and burners in power
* Corresponding author. E-mail address: [email protected] (A. Mahfouz). https://doi.org/10.1016/j.joei.2019.08.008 1743-9671/© 2019 Energy Institute. Published by Elsevier Ltd. All rights reserved.
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stations and boilers. The biodiesel and its blends had better emission characteristics than conventional fuels [21]. The conversion of vegetable oils is highly costing, consuming time with low yield. Finally, direct use of (waste cooking oil) WCO through combustion processes or its blends will decrease fossil fuel consumption, reduce its environmental impact, create new jobs and protect humanity from diseases such as malaria, cholera, typhoid, water pipe blockage and poisoned water. Recently, a hyper-spectral imaging technique (HSI) was developed which consisted of a combination between optical spectroscopy as an analytical tool and two-dimensional object visualization obtained by optical imaging. In HSI, any image contains pixels, each pixel contains spectral information, which is added as a third dimension of values to the two-dimensional spatial image, producing a three-dimensional data cube file, sometimes referred to as hypercube data or as an image cube. Hyper-spectral data cubes contain absorption, reflectance, or fluorescence spectrum data for each image pixel. The spectral range in hyper-spectral data can extend beyond the visible range (ultraviolet, infrared) [22e24]. Hyper-spectral imaging is a new promising technology for measuring intensities and emissivity. References [25e27] reported that the HSI technique is used in combustion research by measuring spectroscopic intensities. This technology was used to measure spectroscopic intensity inside each pixel in a large number of continuous spectral wavelength bands [28]. In flame emission spectroscopy (FES), the energy from the flame provides the energy necessary to transfer electrons from the ground state to the excited states of free atoms. The intensity of radiation emitted by these excited atoms returning to the ground state provides the basis for analytical determinations in FES. These free atoms are converted to excited states through one of either two methods; absorption of additional thermal energy from the flame and absorption of radiant energy from an external source of radiation [29]. The thermal microstructure of turbulent diffusion flames for industrial boilers, furnaces and power stations are difficult to investigate and characterize. This is due to high turbulence, high surrounding flame temperature, exhaust and flame emissions and many zones formation depending on the wavelength and emissions released [30e33]. Flame emission spectroscopy for WCO, TPO and their blends with conventional fuels (HDO and LDO) was not performed before. Therefore, the reported research is aimed to introduce new alternative fuels and characterize spectral emissions in order to quantify the active emission radicals, determine rate of reaction zones. Comparative study was conducted between results of alternative fuels blends compared to conventional diesel fuels to justify the highest thermal energy gained and lowest environmental impact. This study also targeted waste cooking oil and waste tires oil as alternative sustainable fuels to reduce the burden of waste disposal, reduce their environmental damage, generate energy from waste and introduce new sustainable energy fuels. Finally, this could be applied to help the government to solve many problems in most sectors of life like health, environment, economics, energy, power and engineering. 2. Waste tire oil preparation test setup A self-reacting pyrolysis system for waste tires was designed and constructed as shown in Fig. 1 comprised of: (a) A cylindrical, horizontal bed reactor with a capacity of 50 kg of shredded waste tires to produce a volume of approximately 22 L of TPO (45%); an adequate quantity for testing characteristics of the produced oil. While the solid residue and the gas yields represent about 55% and 5% respectively from the total quantity of waste tires. The reactor is made of a 3 mm thick stainless-steel sheet (to ensure high thermal strength) and having a diameter and length of 500 mm and 600 mm respectively. The inside surface area along the reactor length is fitted with baffles to ensure uniform heat distribution and structural rigidity, as shown in Fig. 2. The outer surface of the reactor is properly insulated to eliminate heat loss. Also, a mechanism for angular rotation of the whole bed is included (3 rpm) to facilitate continuous stirring of the shredded tires leading to accelerated pyrolysis. (b) A shell and tube heat exchanger (Condenser): The produced vapor released from the reactor is rapidly cooled by a water-cooled shell and tube heat exchanger, Fig. 2 panel (B). The condenser tubes are made of copper of 0.628 m in length, 12.5 mm in diameter and 0.3 mm thickness. The calculated heat transfer coefficient equals 410 W/m2 ⁰C for a water flow rate of 0.02 kg/sec. (c) A gas/oil separator (disengage) where oil is collected (by gravity) at its bottom base and syngas pass via a tube at its top end to supply the heating burner (self-heating) of the reactor and hence reduces the main fuel supply; making the process more economical.
Fig. 1. Schematic diagram of the designed self-reacting pyrolysis system.
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Fig. 2. Schematic diagram of the cylindrical reactor; panel (A) and condenser design; panel (B).
(d) An ON/OFF temperature control unit is used to control the inside reactor temperature to within ± 3 C as shown in Fig. 1. This unit is comprised of a type- K thermocouple connected to a digital control indicator. A sound alarm is activated when the temperature exceeds an upper limit and the heating system shuts down. The TPO properties of produced TPO at 425 C (at 5 C/min heating rate) are closest to diesel fuel properties which is suitable to be used in diesel engines as a blended fuel. Moreover, at this temperature the main product is liquid (about 45% of the total waste tires quantity) which is a mixture of hydrocarbon depending on the initial composition of the waste material.
3. Waste cooking oil Waste cooking oil was collected from houses, apartments. WCO was filtered via 5 stages of mesh filters of 40 mm to avoid fuel line and nozzles blockage. This WCO is a blend of olive oil, soybean oil and sunflower. Eliminating waste cooking oil from houses and apartments was difficult but easy to be burned without recycling. Gas chromatography-mass spectrometry (GC-MS) which is a common technique for separating and analyzing components of WCO was reported in ref [31]. The main structures of fatty acids for WCO are oleic, palmitic, linoleic, stearic, linolenic, palmitoleic acids. The percentages of fatty acids by weight are 34.94%, 28.78%, 21.19%, 6.41% and 5.2% respectively [31]. 4. Experimental set up and facilities The experimental measuring system as shown in Fig. 3 consists of an airline, a fuel line and a hyper-spectral camera. The designed control unit is used to control in an effective way both the air and the fuel flow, thereby regulating the relative air/fuel ratio (which is defined with respect to the stoichiometric one) in each test. The airline was divided into a primary, high-pressure atomizing airline and a secondary airline that originated from the burner blower fan. The fuel line consists of a fuel tank, a valve, a solenoid valve (Delavan Nozzle Adapter DLN 17147 and twin Siphon Delavan nozzles model number 30609-28). Each nozzle is capable of producing up to 1.5 GPH. The nozzle had a mixing chamber where the primary air impinged on the liquid jet and formed a high-quality liquid gas mixture. The volume of fluid coming out of the nozzle is directly proportional to the pressure at which it is supplied to the nozzle. A hyper-spectral camera (model SOC710V) was used to capture radiation images. This camera captures intensities from each available wavelength in the form of a cube file. The spectral range of the camera is from 400 to 1000 nm separated by 4.6875 nm. The hyper-spectral
Fig. 3. Schematic diagram of the experimental setup.
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camera was set perpendicular to the flame horizontally at nearly 7 m away from flame to be able to capture all flame edges and avoid saturation of the measured data. An Arduino Uno card was interfaced with LABVIEW software program to control successive steps of operation of the Burner (Model: Giersch Enertech Group e Germany) [30,31]. Heavy diesel oil (HDO) and light diesel oil (LDO) were used as conventional fuels and base fuel. WCO and TPO were used as alternative fuels for the burner test. Blend 1 (B1) was formed of 20% WCO þ 80% LDO by mass for 6 L (according to the burner tank). Blend 2 (B2) was 20% WCOþ80%HDO also by mass. Blend 3 (B3) was 20%TPO and 80% LDO by mass. This percentage was chosen according to previous studies in ref [30]. The high percentage of blending ratios of WCO has the opposite effect on thermal characteristics of the blend as well as TPO that has a higher density and viscosity. These physical properties lead to improper atomization and vaporization of blends compared to base fuel. Combustion procedures were carried out at definite equivalence ratios Ф ¼ (0.63 and 0.96) where lean and near stoichiometric mixture. 5. Results and discussions 5.1. Physical and chemical properties of fuels All laboratory measurements were carried out at Egyptian Petroleum Research Institute (EPRI) and National Research Centre (NRC) Labs according to ASTM standards as shown in Table 1. All combustion processes measurements were done in cooperation with the National Research Centre (Mechanical power Dept.), Mattaria Faculty of Engineering (Laser and Nanotechnology Lab, Continuous Combustion Lab) and the Laser Photonics Research Center MTC (Physics Department). From laboratory measurements it is obvious that HDO had the highest heating value of 44.3 MJ/kg and sulphur content with 3.4%, while WCO was characterized with the lowest heating value of 36.59 MJ/kg. This fuel had the largest flash point for burning due to a high water percentage content and fatty acids. TPO had the largest carbon content of 92.08%wt. Both HDO and WCO had nearly equal densities. The most interesting characterization appeared when the WCO and TPO had oxygen molecules in its chemical form to complete its combustion. 5.2. Spectral emission contour radicals According to applied methods of [23] and Wien's Law [39] intensity contour are drawn. Images are captured by the hyper-spectral camera at clearly dark times in order to avoid any reflectance and noise from light in the measurements. These images are saved as a cube and Envi file extension type. Preprocessing steps are carried out to perform the analysis of emission contours, the thermo-micro structure of fuel flames and the maximum peak of intensity. Image-Lab, Hyper-toolkit, GLIMPS, Tecplot 360 EX 2017 R1 and Scyllarus software [34] were used in the image analysis techniques, identifying zones of reactions, the highest intensity peaks corresponding to wavelength. The images taken at 442 and 554 nm correspond to CH and C2 radicals. Therefore, by applying experimental methods which were previously used [23,27,35,36] to obtain emission contour spectra of flames for different fuels at wavelength 442 and 554 nm see Figs. 5e8 and Figs. 10e13 respectively. 5.2.1. CH radical intensity A) at Ф ¼ 0.63 (lean mixture): Fig. 4 depicts the maximum CH radical intensity peak which occurred for HDO, LDO, WCO, TPO, B1, B2 and B3 at Ф ¼ 0.63 and 0.96. WCO and B1 produced the lowest CH emission radicals due to presence of high percentage of oxygen molecules. These molecules helped in the oxidation process by avoiding the elimination of carbon monoxide (CO). Waste tire pyrolysis oil and B2 blend which produced CH emission radical of values 65 and 60 a.u. had lower amount than that of LDO as shown in Fig. 4. Light diesel oil produced the highest CH emission radicals because it's lighter density, easily atomized, lowest flash point and easily burned. However some fuel droplets are vaporized to the gaseous state without burning CH radicals. B) at Ф ¼ 0.96 (near stoichiometric): HDO, LDO and TPO fuels produced higher CH radicals compared to that at Ф ¼ 0.63 due to high carbon content and fuel flow rate. It is expected that near stoichiometric emissions will be reduced in exhaust gases not inside the flame because of continuous reactions inside flame core. Besides CH and C2 radicals are an indication for heat energy released as will be discussed in next section. Table 1 Physical and chemical Properties of the tested fuels [3,30,31]. Properties
HDO
LDO
WCO
TPO
B1
B2
B3
Density (kg/m3) Viscosity at 40 C (cSt) Calorific value (MJ/kg) Flash point ( C) Water content (%) Sulphur content (%) Carbon% (wt.) Hydrogen % (wt.) Oxygen % (wt.)
885 4.8 44.3 123 0.16 3.4 88.3 10.5 0
831 2.72 42.1 70 0.05 0.55 86.23 12.85 0
887 5.3 36.59 178 0.42 0 76.95 12.14 10.93
931 3.5 42 76 0.8 0.916 86.11 10.33 2
870 3.8 41.2 92.2 0.33 0.394 84.19 12.97 2.25
881 5 41.93 135.1 0.2 2.36 85.11 9.66 2.2
851 2.88 42.07 71 0.2 0.64 86.3 12.6 0.412
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180
5
170 160
160 140
Intensity, a.u.
120
120
120 95
100 80 80 60
65
60
55 40
40
30
60
Ф 0.63 0.96
38
22
20 0 HDO
LDO
WCO
TPO
B1
B2
B3
Tested fuels Fig. 4. Maximum CH radical intensity peak values for different fuel types at Ф ¼ 0.63 and 0.96.
TPO produced CH emission radicals lower than that of LDO by nearly 5.9% because of its nearly equal heating value to that of LDO and oxygen molecules that would help in rising up inflame temperature. Also, TPO emitted CH radicals higher than that of HDO by nearly 33.3% because TPO had lower viscosity and oxygen content. So, vaporization and combustion of TPO was done fast and easily. On the other hand, WCO and B2 achieved the lowest CH emission radicals. Much number of oxygen atoms decreased the formation of CH radicals where formation of CO2 and H2O was occurred as in WCO fuel. The emissions tend to be diminished, as they become stoichiometric because high molecules of oxygen reduced emissions besides low heating value of WCO. So, combustion of WCO generated lower thermal energy flame compared to conventional fuels due to improper atomization and glycerin and wax materials.
Fig. 5. CH emission contour radicals of HDO (pane A), LDO (panel B), WCO (panel C) and TPO (panel D) at Ф ¼ 0.63.
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Fig. 6. CH emission contour radicals of B1 (pane E), B2 (panel F) and B3 (panel G) at Ф ¼ 0.63.
Fig. 7. CH emission contour radicals of HDO (pane A), LDO (panel B), WCO (panel C) and TPO (panel D) at Ф ¼ 0.96.
5.2.2. C2 radical intensity A) at Ф ¼ 0.63 (lean mixture): Fig. 9 depicts the maximum C2 radical intensity peak, which occurred for HDO, LDO, WCO, TPO, B1, B2 and B3 at Ф ¼ 0.63 and 0.96. As mentioned in Fig. 9, LDO emitted the highest C2 emission radical of intensity 1400 a.u. at Ф ¼ 0.63 and 2200 a.u. at Ф ¼ 0.96. Therefore, both Please cite this article as: K. Emara et al., Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner, Journal of the Energy Institute, https://doi.org/10.1016/j.joei.2019.08.008
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Fig. 8. CH emission contour radicals of B1 (pane E), B2 (panel F) and B3 (panel G) at Ф ¼ 0.96.
CH and C2 contour radicals are expected to be supplementary, while WCO produced the lowest emission intensity having value of 140 a.u at Ф ¼ 0.63 and 320 at Ф ¼ 0.96 because of its low heating value compared to other fuels. B) at Ф ¼ 0.96 (near stoichiometric): LDO and HDO achieved the highest C2 emission radicals of 2200 and 2000 a.u., respectively because of high carbon content. On the other hand, WCO emitted the lowest C2 radicals because of its low carbon content in its chemical form compared to other fuels.
2500 2200 2000
Intensity, a.u.
2000
1400
1500
Ф 1000
1000 850
850
800 600
500
550
0.96
650 350
320 140
0.63
170
0 HDO
LDO
WCO
TPO
B1
B2
B3
Tested fuels Fig. 9. The maximum C2 radical intensity peak values for different fuel types at Ф ¼ 0.63 and 0.96.
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Fig. 10. C2 emission contour radicals of HDO (pane A), LDO (panel B), WCO (panel C) and TPO (panel D) at Ф ¼ 0.63.
Fig. 11. C2 emission contour radicals of B1 (pane E), B2 (panel F) and B3 (panel G) at Ф ¼ 0.63.
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Fig. 12. C2 emission contour radicals of HDO (pane A), LDO (panel B), WCO (panel C) and TPO (panel D) at Ф ¼ 0.96.
Fig. 13. C2 emission contour radicals of B1 (pane E), B2 (panel F) and B3 (panel G) at Ф ¼ 0.96.
Blending waste cooking oil by 20% mass to LDO will reduce C2 radicals by nearly 61% at Ф ¼ 0.63 and 64.5% at Ф ¼ 0.96. This reduction is due to effect of oxygen molecules that prevent formation of carbon monoxide and the high viscosity of WCO will obstruct the flow of B1 in order to avoid fuel droplet vaporization without burning. Consequently, low free C2 radicals are formed, while blending WCO to HDO will decrease C2 radicals by nearly 19% and 82% at Ф ¼ 0.63 and 0.96 respectively. The viscosity of both HDO and WCO had a value of 4.8 and 5.3 cSt. Therefore, HDO and WCO are nearly homogenous liquid when blended. The burning of B2 at Ф ¼ 0.96 will lower C2 radicals than that of HDO and even LDO, because the oxidation process occurred in a homogenously viscous fluid in the presence of 2.2 %wt. oxygen molecules. Blending TPO by 20% mass to LDO will decrease the C2 radical's intensity by nearly 39% and 58% compared to LDO at Ф ¼ 0.63 and 0.96 respectively. The B3 blend is characterized by a relatively high calorific value compared to WCO and TPO. The quality of flame pictures/images of the WCO fuel for a lean mixture is hazy and cloudy due to the low heat energy output and highwater content. Therefore, the camera cannot identify the place of heat released. The burning of pure WCO will produce a white, transparent cloud fog around the flame. Consequently, WCO flame images aren't clear as seen in panel C all over contour figures due to its low thermal
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energy. Consequently, no more excited atoms and emissions are released and captured by hyper-spectral camera. However for other fuels, the flame contour edges are clearly seen. For a near stoichiometric mixture, the flame images are clear with sharp edges because camera identified the area of heat released and intensity of excited atoms at this wavelength are observed as intensity as reported in next section. 5.3. Thermal microstructure of different fuels flame Relating inflame temperature to the active emission radicals inside the flame is significant to investigate and locate reaction zone and its rate. So, Axial and radial inflame temperatures were measured using thermocouple type S with diameter 50 mm. These readings are then averaged to obtain the average temperature at points along the axial flame plane. Inflame temperatures were shown versus CH and C2 emission radicals along the axial flame length plane at only Ф ¼ 0.63 and 0.96. CH radicals were emitted prior to advancing to the C2 reaction chain. OH radicals were produced through oxidation of CH before the final steps in the CHx (hydrocarbons) oxidation chain [37]. CH and C2 radicals intensity of a flame were taken at 432 nm and 554 nm, respecively [25e29]. Fig. 14 showed a comparison between LDO and B1 blend fuel in a microstructure analysis and radiation energy absorbed where the X-axis is represented by L/L0, L is the axial distance (5.5,15, 25, 35, 45, 55, 65, 80.5, 95, 115, 134.5, 170 and 195 cm) and L0 is the largest flame length L0 ¼ 200 cm occurred showing that: For LDO fuel At Ф ¼ 0.63, the average plane inflame temperature near the burner rim (L/L0 ¼ 0.0275) for LDO was higher due to good mixing and generating a high reaction rate. The region of higher inflame temperature will have higher intensity of CH and C2 emission radicals due to the higher rate of reaction resulting from excited atoms [27e29,37]. The maximum peak of excited atoms was shifted axially from L/ L0 ¼ 0.0275 to L/L0 ¼ 0.175 due to their turbulent flow direction. Consequently, the highest average plane flame temperature was nearly 855 C. The emissions intensities of CH and C2 radicals of the LDO fuel flame were 25 and 16 a.u. respectively. This zone had a high temperature and low radical concentration due to the low number of excited atoms and low radiation energy absorbed. These atoms did not absorb enough radiation energy for excitation because the fuel droplets were not fully vaporized. Therefore, the fuel droplets will absorb low radiation energy. The fuel droplet size is inversely proportional to the radiation energy absorption. The intensity of the radicals was directly proportional to the number of excited atoms [37]. At L/L0 ¼ 0.125, the temperature curve declined due to the decrease of fuel concentration. On the other hand, a sudden rise in intensity of radicals occurred far from nozzle opening because the angle of atomization became wider so that the atomization rate of fuel droplets could be determined in wider area. Hence, the fuel droplets were fully vaporized to the gaseous state. This vaporization will allow fuel atoms to easily absorb radiation energy from the surrounding flame temperature. Thus a high excitation was accomplished by generating high emission radicals [40] as shown in Fig. 14. After the position of L/L0 ¼ 0.4, the emission intensity of the radical curve declined because the flame radiation energy decreased, and the number of excited atoms will decrease. At Ф ¼ 0.96, the fuel flow rate increased and the average plane flame temperature near the burner rim decreased by nearly 21% compared to that at Ф ¼ 0.96 due to the higher fuel flow rate, accumulation of fuel particles, low mixing rate and the not fully vaporized and the low radiation energy of atoms gained for the LDO fuel. Therefore, the rate of reaction will be lowered and accompanied by a low CH and C2 emission radicals’ intensity at L/L0 ¼ 0.0275 with a value of 14 and 15 a.u., respectively. At L/L0 ¼ 0.325, a nearly linear increase of the emission intensity of the radicals occurs until the end of the thermal flame length. A high fuel flow rate will supply more heat and radiation energy reaching the position L/L0 ¼ 0.975, where the maximum peak heat energy released by the fuel of excited atoms are generated producing 152 a.u. and 1344 a.u. corresponding to CH and C2 radicals, respectively. For B1 blend fuel: At Ф ¼ 0.63, the average plane temperature was nearly 650 C. The intensity of CH and C2 was 6 and 10 a.u., respectively for the B1 blend. Both flame temperature and emission radicals of B1 were lower than that of LDO at the same condition and position (L/L0 ¼ 0.0275) because WCO has a higher viscosity, incomplete atomization and a lower heating value. Therefore, WCO fuel particles were difficult to be burned. The WCO droplets are bigger in size than LDO [38]. Thus, the absorption of radiation energy for atom excitation will be lower and occurred later at L/L ¼ 0.4. By increasing the combustion rate reaching Ф ¼ 0.96, the average plane flame temperature was decreased to 620 C. A sudden increase in CH and C2 intensity radicals reaching 47 a.u. and 563 a.u. occurred that corresponds to a position of L/L0 ¼ 0.4 and 0.6, respectively. By a comparison between LDO and B1 at Ф ¼ 0.63, the LDO atoms absorbed more radiation energy needed for excitation than the WCO droplets relating to their size and fuel physical-chemical properties. The LDO droplets are easily vaporized due to their measured physical characteristics are shown in Table 1. On the other hand, WCO particles in B1 blend encounter difficulties to be vaporized because of their higher density and viscosity. At Ф ¼ 0.96, the LDO atoms absorbed radiation energy from the flame surrounding temperature. These atoms are excited to higher energy levels along the flame, while in the B1 blend the fuel droplets absorb less radiation energy as affected by the flame temperature. Fig. 15 depicts a comparison between HDO and B2 blend fuel in a microstructure analysis and the radiation energy absorbed is as follows: For HDO fuel: At Ф ¼ 0.63, the average plane flame temperature near the burner rim (L/L0 ¼ 0.075) was 1100 C due to higher mixing, a higher heating value of HDO and a higher reaction rate. The maximum peak of intensity of the excited atoms having a value of 539 a.u. was shifted axially from L/L0 ¼ 0.075 to 0.175 because of the fast absorption of atoms for radiation heat energy from the flame. This is followed by a fast decrease of the CH and C2 radicals because of a low atomization rate at this zone. This zone has a lower radical's intensity because of a lower radiation energy absorbed for the exciting atoms. These atoms did not absorb sufficient radiation energy because the fuel droplets were not fully vaporized. Therefore, the fuel droplets will absorb lower radiation energy. Therefore, by increasing the fuel mass flow rate to Ф ¼ 0.96, the average plane flame temperature was increased from 1100 C to 1207 C. Thus, more radiation energy was provided and more intensity of the radicals was released ranging from 1329 a.u to 1460 a.u. for C2 radicals that occurred from L/L0 ¼ 0.125 to 0.275 along the flame length. This increase in intensity was due to the fact that more atoms were excited to a higher energy level.
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Fig. 14. Thermal microstructure analysis of LDO and B1 fuel at Ф ¼ 0.63 and 0.96.
B2 blend fuel: At Ф ¼ 0.63, the flame temperature increased at the first four axial positions by 50 C for the B2 blend. This increase in heat released may be related to oxygen molecules in WCO that enhance combustion [30,31]. The decline of radicals’ intensity was due to the lower radiation energy absorbed by both WCO and HDO oils. Therefore, the addition of WCO depressed the absorption, excitation of fuel atoms due to its lower heating value. On the other hand, at Ф ¼ 0.96, both temperature and radicals intensity curves have the same trend as LDO fuel at the same operating condition with different flame temperatures. By making a comparative investigation between HDO and B2 it was found that: Blending WCO to HDO will elongate the atomic period for radiation energy absorption because of micro-explosion phenomena. WCO enhanced flame core temperature due to the presence of oxygen atoms. The B2 fuel atoms absorbed enough energy for excitation where inflame temperature was nearly 1156 C that is higher than that of LDO at Ф ¼ 0.63 as well as Ф ¼ 0.96. Therefore, B2 fuel is recommended to replace LDO at Ф ¼ 0.63 and 0.96.
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Fig. 15. Thermal microstructure analysis of HDO and B2 fuel at Ф ¼ 0.63 and 0.96.
TPO was blended with LDO as B3. Fig. 16 shows the difference between LDO and B3 blend fuels in a microstructure analysis represented by the flame temperature of CH and C2 radicals. At Ф ¼ 0.63, the maximum average plane inflame temperature was 1209 C at L/L0 ¼ 0.125, where the CH and C2 radicals intensity was 7 a.u and 25 a.u., respectively. The maximum peak intensity of C2 and CH radicals was 482 a.u. and 44 a.u., respectively at L/L0 ¼ 0.475. At Ф ¼ 0.96, the maximum inflame temperature recorded was 1220 C at L/L0 ¼ 0.075, where the CH intensity was 5 a.u. and 14 a.u for C2. The maximum peak intensity of C2 and CH radicals were 842 a.u. and 81 a.u., respectively at L/L0 ¼ 0.575. By comparing between B3 and LDO fuel: B3 fuel has a low concentration of oxygen molecules compared to B1 fuel. This will lead to an increase of the inflame temperature reaching 1220 C which is favorable in many applications. The values of the radicals’ intensities were near to each other with small differences. Using WTPO as a fuel for industrial burners is one of the possible ways to solve the waste tires disposal problem. Also, the present study includes a mechanism of waste tires pyrolysis to produce alternative fuel. In this respect, the conversion of both waste tires and WCO to thermal energy creates a cleaner version of fuel, rather than the crude oil and will contribute to solving the energy crisis.
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Fig. 16. Thermal microstructure analysis of LDO and B3 fuel at Ф ¼ 0.63 and 0.96.
6. Conclusions The thermal flame microstructure of conventional fuels and their blends with both waste cooking oil and TPO were characterized with spectral peaks intensity. The thermal analysis of different fuels at various fuel/air equivalence ratios was investigated. Axial plane flame temperatures related to CH and C2 radicals were investigated for LDO, HDO, B1, B2 and B3 blends at Ф ¼ 0.63 and 0.96. These conclusions are summarized as follows: WCO and B1 produced the lowest CH emission radicals due to presence of a high percentage of oxygen molecules. TPO produced CH emission radicals lower than that of LDO by nearly 5.9%. Blending waste cooking oil by 20% mass to LDO will reduce C2 radicals by nearly 61% at Ф ¼ 0.63 and 64.5% at Ф ¼ 0.96. This reduction is due to the effect of oxygen molecules. Therefore, no free C2 radicals are formed. Blending of WCO to HDO will decrease C2 radicals by nearly 19% and 82% at Ф ¼ 0.63 and 0.96 respectively. Blending of TPO by 20% mass to LDO will decrease the C2 radical's intensity by nearly 39% and 58% compared to LDO at Ф ¼ 0.63 and 0.96 respectively. B3 blend is characterized by a relatively higher calorific value than that compared to WCO and TPO. For LDO the fuel droplets did not absorb enough radiation energy for excitation because the fuel droplets were not fully vaporized for a lean mixture. The fuel droplet size is inversely proportional with radiation energy absorption. The emissions intensity of radicals was
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directly proportional to the number of excited atoms. A rise in radical intensity occurred at a far distance from nozzle opening because the angle of atomization became wider so that the atomization rate of the fuel droplets occurred in wider area. Both flame temperature and emission radicals of B1 were lower than that of LDO at the same condition and position (L/L0 ¼ 0.0275) because WCO has a higher viscosity and a lower heating value. The WCO droplets are bigger in size than LDO. The LDO droplets absorbed more radiation energy needed for excitation than that of WCO which is due to the droplet size and fuel physic-chemical properties. Blending WCO to HDO will elongate the atom period for radiation energy absorption because of micro-explosion phenomena. WCO has enhanced flame core temperature due to presence of oxygen atoms. B2 fuel atoms absorbed enough energy for excitation. B2 fuel is recommended to replace LDO at Ф ¼ 0.63 and 0.96. 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Please cite this article as: K. Emara et al., Flame spectroscopy of waste tire oils and waste cooking oils blends using coaxial burner, Journal of the Energy Institute, https://doi.org/10.1016/j.joei.2019.08.008