Petroleum Coke Gasification Temperatures and Flame Spectra in the

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Petroleum coke gasification temperatures and flame spectra in the visible region at high pressure Thangam Parameswaran, Marc A. Duchesne, Scott Champagne, and Robin William Hughes Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01751 • Publication Date (Web): 30 Sep 2016 Downloaded from http://pubs.acs.org on October 7, 2016

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Petroleum coke gasification temperatures and flame spectra in the visible region at high pressure

Authors: Thangam Parameswaran*, Marc A. Duchesne, Scott Champagne and Robin W. Hughes Natural Resources Canada, CanmetENERGY, 1 Haanel Drive Nepean Ontario Canada *Corresponding author: Thangam Parameswaran ABSTRACT: In recent years the mandate for CO2 reduction and clean power generation has led to the advancement of research in high pressure combustion and gasification. Traditionally, thermocouples monitor the wall temperature of a gasifier and gas analyzers record the composition of the syngas produced. This paper describes flame emission spectroscopic measurements performed in a pilot scale entrained flow gasifier operating at a maximum pressure of 15 bar (g) with petroleum coke as fuel. Low cost and availability make petroleum coke attractive for use in energy production. In the current work, flame spectra observed in the visible region (500 nm-800 nm) during petroleum coke gasification, in the pilot-scale gasifier at CanmetENERGY, are presented. These spectra were acquired with a cooled and purged fiber optic probe coupled to a spectrometer. Gasification flame spectra and information on reaction chamber temperature and the emission peaks of alkali metals and other spectral features observed in these measurements are discussed. The results show that flame emission spectroscopy is useful for gasifier performance monitoring.

Key words Petroleum coke, gasification, flame, temperature, spectral lines

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1. INTRODUCTION Petroleum coke is produced in large quantities by the petroleum refining industry. Gasification offers a means to convert petroleum coke into synthetic gases which can be used as fuels or serve as raw material for the chemical industry. In this process a carbonaceous fuel is allowed to react with a sub-stoichiometric amount of oxidizer at high temperature. Petroleum coke gasification is known around the world and Murthy et al.1 have reviewed various aspects of this technology using fixed bed, fluidized bed and entrained flow gasifiers. The performance of a gasifier is usually monitored by thermocouples which record the wall temperatures and an online chromatograph which analyzes the gases produced. Flame emission spectroscopy (FES) offers another means to measure temperatures and species emission in the reaction chamber. This paper presents and discusses the results of FES measurements in the pilot scale gasification facility at CanmetENERGY, when fired at 15 bar(g) with petroleum coke and oxygen. FES measurement is based on acquiring flame spectra and extracting the correlations between spectral changes and parameters of interest such as temperature and species emission in the reaction chamber. Chemiluminescence in flames and its correlation with hydrocarbon flame stoichiometry is a familiar phenomenon 2-3. The FES measurement system consists of a fiber optic probe coupled with a small spectrometer (with appropriate dispersing and detecting elements) which collects the flame spectral profiles from the test region and transfers the data to a computer. The data is processed subsequently or online to extract flame parameters of interest. This approach is useful to examine natural gas flames in bench and pilot scale facilities. Typically chemiluminescence observed in the visible region 300-600 nm of nonluminous hydrocarbon flames originate from the OH, CH and C2 species and are used to estimate air/fuel ratios and temperatures at atmospheric pressure. Sandrowitz et al.4 have utilized a fiber coupled spectrometer to correlate CH/OH ratios to fuel/air equivalent ratios in bench scale natural gas flames. Muruganadam et al.5 provide several references to similar applications of chemiluminescence in simple


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flames and have extended this approach to monitor equivalent ratios in gas turbine combustors. Spectrometer based measurements of flame stoichiometry in multi-burner furnaces under oxy-fuel and air-fuel firing conditions, are reported by Romero et al.6 Examples of spectra and the theory flame emission spectroscopy of gas flames are reviewed by Ziziak.7 At CanmetENERGY natural gas flames generated by industrial burners in a pilot scale facility were examined with FES and the correlation between CH, OH intensities with air/fuel ratio and CO emission were reported8. FES was also tested9 in a HITAC (High temperature air combustion) burner installed in this gas fired furnace. Under flameless conditions the OH and CH bands were barely detectable when the FES probe viewed the root of the burner. As the probe was moved away from this location these familiar peaks could be discerned better. Thus there is no reason to prevent the use of FES in flames produced by pollution reducing technologies referred to as MILD combustion10. When FES was applied to coal or biomass flames in industrial burners, OH and CH bands were not observed but emission peaks from sodium and potassium were invariably present11. This is similar to the observation made by other researchers12. All objects emit radiation by virtue of their temperature. An object or a body that perfectly absorbs radiation and emits it when in equilibrium is referred to as a blackbody. In flames, the soot particles are assumed to be in thermal equilibrium with the combustion products and emit continuous radiation.13 Therefore luminous flame spectra acquired from combustion using FES may also be used to estimate the temperature in the test region by using the blackbody approximation model for flame radiation .Research on the infrared spectral region (1-7 microns) of hydrocarbon flames has been reported even in the distant past3 and the CO, CO2 and H2O vibrational bands analyzed to estimate flame temperatures. The range of the spectrometer used in the current work is limited to the UV-visible region where the spectral peaks originate primarily from electronic transitions occurring in excited atoms or molecular species. These peaks are of course superimposed on the continuous blackbody type emission from the flame. The studies discussed above were conducted in flames at atmospheric pressure. 3 ACS Paragon Plus Environment

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Optical methods are highly suitable for combustion diagnostics because of their non-intrusive nature. This vast subject includes numerous techniques which make use of the emission and absorption properties of light. Laser based methods such as Raman spectroscopy, Fluorescence spectroscopy, Coherent antiStokes Raman spectroscopy, and Laser Doppler velocimetry are well reviewed by Eckbreth14. These methods are useful for temperature, species concentration and particle velocity measurements. Laser induced breakdown spectroscopy15, 16 also requires a powerful laser and is used to determine elemental concentrations of materials in the solid, liquid and gas phase. Research on light absorption spectroscopy with diode lasers17 or suitable lamp sources and Fourier transform infrared spectroscopy18 is widely applied in optical gas sensing of combustion gases. Thus there are several optical methods which have been applied for combustion research. Among the various techniques considered above, it is noteworthy that, flame emission spectroscopy or FES is by far the simplest because it uses the flame radiation as the light source and when coupled with a miniature spectrometer becomes attractive for industrial use. The purpose of the current work is to examine the usefulness of FES to monitor high pressure petroleum coke gasification with a simple and inexpensive method. In a recently reported investigation at CanmetENERGY a fiber coupled spectrometer probe was designed to examine the reaction chamber in a 15 bar(g) high pressure gasification facility when fired with coal19. Data acquired in this test campaign identified an anomalous condition when the flame turned very bright with unexpected high intensities and temperatures in the gasifier. This observation was subsequently related to a tilting of the flame, probably due to a partial plugging of the fuel line, leading to excessive heating and damage of the refractory and thus demonstrated the value of the FES approach for gasifier monitoring. While petroleum coke is widely used by industry, gasification flame spectra of this fuel, at atmospheric or high pressures, are not reported and discussed in literature. The current work extends the application of FES to examine petroleum coke gasification flames at high pressure. These investigations affirm the robustness and usefulness of the FES probe to collect gasification flame spectral data when 4 ACS Paragon Plus Environment

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fired with fuels with different slagging conditions and to compare the information on temperature and species emission obtained during coal and petroleum coke gasification at high pressure.

2. MATERIALS AND METHODS 2.1 Gasification facility Petroleum coke gasification tests reported in this paper were conducted with CanmetENERGY’s gasifier operated at 0.3-0.6 MWth and 15 bar(g) using a pneumatic feed system to supply petroleum coke20 through the central burner annulus with nitrogen as conveying gas21. Oxygen was injected through the burner by eight jets that impinged on the fuel stream at high velocity. When injected, steam passed through the outer burner annulus at a low velocity. A schematic diagram of the cross section of the gasifier as operated is provided in Figure 1. Type B ceramic sheathed thermocouples measured the temperatures at four locations on the refractory wall. These are labelled TE411, TE412, TE413 and TE414 from top to bottom at the nozzles shown in Figure 1. In this figure the inlets for fuel, oxygen and steam and the outlets for syngas and slag are located as shown. INSERT FIGURE 1 2.2 Measurement setup with fibre optic probe and spectrometer A fibre optic probe fabricated for these tests was inserted through an access port in the gasifier (Figure 1) such that the probe tip was close to the inner surface of the refractory wall. The access port selected is exposed to minimal slag deposition and provides line of sight close to the root of the flame. The probe consists of a metal coated fiber which can withstand temperatures as high as 700˚C, enclosed in a steel jacket which provides water cooling and nitrogen purge. At the inserted location the FES probe sees and collects the radiation from a portion of the flame and the wall facing the probe as well as the gasifier interior lying within an angle of 8.8º enclosing the central axis of the probe. It is estimated that the probe


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‘sees’ the gasifier wall close to the region at the same elevation as the thermocouples TE411 and TE412. More details about the probe are given in Ref. 17. A drawing for the probe tip is shown in Figure 2. The free end of the high temperature fibre is connected to a 30 m flexible fused silica (uncoated armored) fibre which is coupled to the data acquiring spectrometer located in the control room as shown in Figure 1. FES spectra from the gasifier were acquired with a wide range (200-800nm) Ocean Optics spectrometer system and the Spectrasuite software.

INSERT FIGURE 2

2.3 Operating conditions Petroleum coke gasification tests in this report were conducted under a variety of high pressure, oxy-fired operating conditions. Gasifier pressure was varied from 7 to 15 bar(g) and the fuel flow rate ranged from 35 to 66 kg/hr. For given fuel and steam flow rates, the oxygen flow rate was adjusted to achieve the desired temperature as recorded by the wall mounted thermocouple TE414. During these tests, FES was used as an additional diagnostic tool to monitor the temperature in the gasifier chamber and to identify and interpret any interesting features observed in petroleum coke flame spectral signatures. However, the flow rates of fuel, oxygen and steam were varied to produce the desired wall temperature rather than to directly study the effect of any one of these variables on the flame spectral signatures.

The gasifier was first pre-heated with natural gas to reach the prerequisite temperature for gasification. After the required preheating the gas flame was shut off and the cooled and purged FES probe was inserted and secured in the access port. The reactor was then pressurized, petroleum coke was introduced via the feeder, gasification was initiated by oxygen injection and flame spectra were collected as required. In the current investigation, spectra were acquired for short or extended time periods while ensuring that the integration time for a single spectrum was adjusted such that the maximum intensity was less than the saturation limit of 65535 counts. The integration times for the measurements reported here were in the 6 ACS Paragon Plus Environment

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range of 10 milliseconds to 500 milliseconds. Spectra were acquired and logged continuously at a rate of approximately one per 1-2 seconds. Thermocouple temperatures and flow rates were logged every two seconds.

3. RESULTS AND DISCUSSION 3.1 Flame spectral features An example of a flame spectrum collected during petroleum coke gasification is displayed in Figure 3. It is a plot of the raw spectral counts as a function of the wavelength of the radiation. Only the visible spectral region 500-800 nm, where the signal is strong, is shown. Approximate locations of the prominent emission features located in this region are indicated in Figure 3.

INSERT FIGURE 3

Table I compiled from the NIST (National Institute of Standards and Technology) handbook22 lists a number of atomic emission lines with high relative intensities close to the peak locations in Figure 3. The concentrations of these elements obtained from the XRD analysis of the petroleum coke used in our tests, are also given in this table. Before proceeding to interpret the observed spectral peaks it is necessary to examine these features and ensure that they arise from the flame and are not artifacts of experimental conditions or instrument response.

INSERT TABLE 1

3.2 Spectral analysis Grating and detector efficiency of a spectrometer vary with wavelength and the response of a spectrometer to the input radiation is not uniform at all wavelengths. Hence it is standard practice to 7 ACS Paragon Plus Environment

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correct the signature recorded by the spectrometer for instrument response by means of a reference spectrum collected from a blackbody standard source. If λ and T represent the wavelength and the temperature respectively, the spectrometer sensitivity correction is estimated as the ratio of the reference spectrum IB (λ, T) to the theoretical spectrum IT (λ, T) of a standard blackbody. In the present work the reference spectra were acquired with the same spectrometer and accessories used for the gasification data. The blackbody furnace was a Mikron M330 radiation source with known temperature and spectral profile. This is a tubular blackbody designed to reach a maximum temperature of 1700˚ C. To obtain a reference spectrum the blackbody was set at 1550˚ C as measured by its wall mounted thermocouple and 250 spectra were averaged to yield a raw reference spectrum. Spectrometer sensitivity or correction was estimated as the ratio of the reference spectrum IB (λ, T) to the theoretical spectrum IT (λ, T) of this blackbody at 1550˚ C as described in Ref.17. This is the recommended procedure to correct the shape of a CCD spectrometer signal for varying instrumental response and produce a spectrum with corrected relative (not absolute) intensities 23, 24. Figure 4 shows the petroleum coke gasification spectrum from Figure 3 after it was processed as described above.

INSERT FIGURE 4

A flame spectral profile consists of continuous and discrete emissions. Clearly the observed line or band emissions are superimposed on the continuous blackbody type emission from the flame. Every spectral feature that stands out from the continuous spectrum may not originate from a molecular or atomic emission. In the analysis flame spectral profiles acquired by the spectrometer were first corrected for background noise and then corrected for intensity variation as described in the previous paragraph. XRD analysis of the petroleum coke used in these gasification experiments revealed the presence of the elements Al, Ba, Ca, Li, Na and K, V as indicated in Table I. After correction for instrumental response the gasification flame spectra revealed a few peaks (or dips) in the visible region of 500- 800 nm where atomic spectra originating from electronic transitions occur. Table I lists the properties of a number of 8 ACS Paragon Plus Environment

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relatively strong atomic spectral lines occurring in the spectral region 540 - 780 nm. Here Aki are the associated transition probabilities for the emission lines. Among these the Na-I, K-I, Ba-I and Li- I lines have the electronic ground state of the atom as the lower level. Such lines are strong emissions with low Aki which is a measure of the line width. Therefore these are expected to be narrow. In this group we see that K-I (766, 769 nm) and Na-I (589 nm) have smaller Aki compared to Li-I (671 nm) and Ba-I (554nm) showing that Li-I and Ba-I peaks can be broader than the Na and K peaks. Table I includes only the stronger of the lines that relate to the metals of interest in the current context. In the region 670-671 nm lines from Ca-I, Li-I occur and have similar or narrower line widths compared to Na-I and K-I lines. The concentration of Li in the fuel is unknown. Therefore one can only speculate that the spectral feature near 670 nm is probably associated with Li and the significant amount of Ca measured by XRD. Table I shows a strong and broader line of Al-II at 624.335 nm and also lists a number of lines from various metal species which are present in the petroleum coke and which occur in the region 610-625 nm, suggesting that they may appear as a broadened feature due to many overlapping lines. 3.2.1 Flame tests of petroleum coke at atmospheric pressure To further investigate the origin of the observed spectral peaks, samples of the petroleum coke used in our tests were placed in a platinum crucible and introduced into a non-luminous methane air flame. Spectra were acquired with the same spectrometer setup as the gasification tests. The plots in Fig.5 also display spectral peaks at 553.4 nm, 589.4 nm, 670.5 nm and 766.3nm, 769.9 nm and several closely spaced peaks in the region 610-625 nm.

INSERT FIGURE 5

3.2.2 LIBS (Laser induced breakdown spectra) of petroleum coke at atmospheric pressure In addition to the flame tests a series of spectra were obtained with samples of the petroleum coke using the LIBS approach. In brief LIBS focuses a powerful pulsed laser beam to create a very high-temperature


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plasma in the test material and creates excited atoms which decay to emit their spectral lines. More details about this analytical method is outside the scope of the current work but are described by Cremers and Radziemiki[16]. The plots in Fig.6 show the spectral peaks near 553 nm, 670 nm, 589 nm, 766nm, 769 nm and several peaks in the region 610-625 nm, originating from laser induced excitation of the atoms in the petroleum coke.

INSERT FIGURE 6

The spectral line widths obtained from the NIST database are at atmospheric pressure. The gasification spectra reported in the current work were collected mostly at 15 bar(g) and some at 7 bar(g) which means that any observed spectral line will be further linearly broadened due to the higher pressure leading to more overlap between closely spaced peaks. Na and K have a low detection limit of 0.01 ppm in flames25 and are therefore easily observed and identified. When a peak occurs at a wavelength where more than one element has spectral lines as near 624 nm, using a higher resolution spectrometer will be helpful for better peak identification. In the gasification spectra the Na-I emission at 589 nm is a dip rather than a peak because of self-absorption. The Na atoms in the cooler outer region of the flame tend to absorb the energy emitted by the excited atoms in the hot centre of the flame to form a dip or reduction in intensity referred to as self-absorption.

3.3 Temperatures and peak intensities from petroleum coke spectra On examining the spectrum in Figure 4 it is observed that the region from 675 to 710 nm does not show discrete emission lines. This spectral region was therefore selected for fitting with theoretical spectra. Temperature was derived by comparing a measured spectrum with a pre-calculated library of theoretical blackbody spectra generated at temperatures intervals of five degrees as described in19. The theoretical


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blackbody spectrum that has the least sum of squared differences with the test spectrum was chosen as the best fit and the corresponding temperature was assigned to the flame spectrum.

During these tests the effects of fuel, oxygen, steam and pressure on the petroleum coke gasification process were investigated. On the first day, pressure was maintained at 15 bar (g). After preheat and pressurization, fuel flow was varied from 35 to 66 kg/hr. Temperatures from the thermocouples TE411 TE414, as well as those deduced from the flame spectra during a 90 minute period are plotted in Figure 7. From 12:00 to 12:40 steam and oxygen are roughly constant but fuel flow falls and rises. During this period FES temperature shows large fluctuations as large as +/- 100 ºC although there does not appear to be a definite trend with fuel flow changes. This is probably due to the changes in flame stoichiometry caused by fluctuating fuel flow at nearly constant oxygen flow. TE411 temperatures at this time show only minor variations. FES temperatures are about 150 ºC higher than TE411 suggesting that the gasifier interior, probed by FES, is hotter than the walls. After 12:40, steam and oxygen are increased and petroleum coke flow is also varied and this affects the FES and TE411 temperatures. Once again FES temperatures are higher than the thermocouple temperatures until the steam flow is reduced. During the entire period TE-414 was maintained constant by controlling the oxygen flow rate.

INSERT FIGURE 7

Flow rates and temperatures during the period 15:15 – 16:30 for Day 1 tests are displayed in Figure 8. During this time steam flow was held at ~ 10kg/hr. From 15:15 to 16:10, fuel is roughly constant and oxygen is allowed to increase and stabilize near 40 kg/h and this variation is reflected in the temperature rise. After 16:10, oxygen and fuel flow rates are reduced, TE411 and TE414 are steady, but FES temperatures decrease and approach TE411 values.

INSERT FIGURE 8 11 ACS Paragon Plus Environment

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Among the spectral peaks observed in Figure 3, the peaks at 589, 767 and 770 nm exhibited selfabsorption and the peak at 671 nm was relatively weak. In the analysis below, the intensities of the peaks at 554 nm and 624 nm were calculated as areas from the processed spectra and plotted. Variation of the latter two peaks during 15:15 – 16:30 is shown in Figure 9. The plots in this figure show that the peak near 554 nm is weaker than the peak near 624 nm. If this peak is associated with Al and the peak near 554 nm is associated with Ba then we may infer that this is perhaps because the concentration of Al (5467 ppm) is far greater than Ba at 46 ppm. During the test period at constant steam, fuel and oxygen display roughly similar changes and this trend is observed with the peak intensities as well.

INSERT FIGURE 9

On another day of testing, petroleum coke gasification was conducted at a lower pressure. The temperature plots for these tests, as pressure was reduced from 15 to 7 bar(g), are in Figure 10. After the pressure change occurred, around 15:50, FES and the thermocouple temperatures increase. This change cannot be attributed to the pressure change alone because the oxygen and steam flow rates were adjusted at the lower pressure. After oxygen and steam flows were stabilized, fuel flow continues to change. While this does not appear to influence TE414, TE411 displays some variation and FES shows stronger dependence on the fuel flow rate.

INSERT FIGURE 10 Spectral lines are expected to narrow and increase in intensity at lower pressures, and this may explain the peak intensity variations in Figure 11. Once again the intensities at 624 nm are stronger than those at 554 nm. After steam and oxygen have mostly stabilized at the lower pressure setting, the intensities of the peaks at 554 nm and 624 nm are weaker. During this period the intensities are generally higher at lower fuel flow rate and vice versa. When fuel increases at constant oxygen flow, flame stoichiometry is likely 12 ACS Paragon Plus Environment

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to deviate from optimal conditions with lower amount of oxygen than required, resulting in lesser reaction and lower spectral intensities.

INSERT FIGURE 11

3.4 Variation of temperatures and peak intensities averaged over two-minute intervals In the previous section, changes observed in the temperatures and peak intensities, measured at 1 or 2 second intervals, during selected time periods, were compared directly with the variation in the fuel, oxygen and steam flow rates. To get a clearer picture of any trends that may exist, flow rates and measured parameters averaged over consecutive two-minute intervals are examined in this section. Four time- periods (12:00 -12:20, 12:45 – 12:59, 13:01 -13:13, 15:19 – 15:29) when the steam was approximately constant, were selected for this purpose.

Mean temperatures thus obtained from Day 1 data at approximately constant steam flow and varying fuel/oxygen flows are graphed in Figure 12. In this figure instead of plotting fuel and oxygen flows separately, the fuel/oxygen ratio is used as a variable. For the four time-periods selected, Figure 12 indicates that steam flow is not as constant as assumed but changes on a small scale. In these two-minute averaged plots it is observed that FES temperatures are higher than TE411 and TE414 for all four steam conditions. It is interesting to note that TE414, which was targeted to be constant, displays trends of modest changes under varying steam and fuel/oxygen ratios. TE411 reveals similar trends, but the changes are larger, while FES temperatures respond even more to changes in steam and the fuel/oxygen ratio. Increasing steam injection is expected to lower the temperature in the gasifier while a decrease, in the fuel/oxygen ratio, is expected to result in a rise in temperature. The observed temperature is the combined outcome of the amount of steam and fuel/oxygen ratio.


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The mean standard deviations of the two-minute averaged variables from measurements on Day 1 and Day 2 are given in Table II. The standard deviations for the FES variables are higher compared to the flow rates and thermocouple temperatures probably because of the higher sampling rate.

INSERT FIGURE 12

Figure 13 displays FES peak intensity variations for the same time-periods presented in Figure 12. In this case the largest change in the peak intensities is observed at the lowest steam flow, where the peak at 624 nm is stronger than the peak at 554 nm. At higher steam flows accompanied by changes in fuel/oxygen ratios, the peaks are weaker making the calculation of their intensities less reliable. At these settings, 624 nm intensities are nearly equal to or less than the 554 nm intensities.

INSERT FIGURE 13

The data displayed in figures 14 and 15 correspond to two-minute averaged temperature and FES peak intensity variations respectively for the tests on Day 2. Figure 14 shows that if no steam is present FES temperatures are lower than TE411 values. With steam, FES temperatures are higher than TE-411 as observed in Day 1 tests. This trend is observed for the data at both pressures tested. When steam is stable and close to 21.5 kg/hr from 14:00 -14:18 and with no steam from 14:46 - 15:02 the decrease in all three temperatures with increase in fuel/oxygen ratio is easier to recognize in Figure 14. When steam is not stable as in the other two time periods shown in Figure14 the temperatures reflect the combined effect of varying steam and fuel/oxygen ratios.

INSERT FIGURE 14 Regarding peak intensities in Figure 15, with no steam (14:46 – 15:02) they are too weak to interpret. With steam, peak 624 nm is stronger than the peak at 554 nm at both pressures tested. 14 ACS Paragon Plus Environment

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INSERT FIGURE 15

4. CONCLUSION The performance of a cooled, purged fibre-coupled spectrometer probe for monitoring temperatures and species emissions, during oxy-fired petroleum coke gasification with steam, was investigated. These tests were conducted at a high pressure 7 bar (g) and15 bar (g)) in the pilot scale facility at CanmetENERGY. During gasification, flame emission spectroscopy (FES) derived temperatures were generally higher than those recorded by the wall mounted thermocouples. Both temperature probing methods yielded similar trends in temperature variation with respect to collective changes in the flow rates of petroleum coke, oxygen and steam. At constant steam flow rates, FES and wall temperatures tend to increase with decreasing petroleum coke/oxygen ratios. In addition to the familiar Na and K emission lines, FES also revealed spectral peaks close to the locations where atomic spectral lines originating from electronic transitions of Ba, Ca, Al, and Li are known to occur. Although the latter peaks are broader they are observed in the spectrometer sensitivity corrected spectra. Further, peaks were also observed at these wavelengths in the spectra of solid petroleum coke introduced in a flame and also in the LIBS spectra produced at atmospheric pressure. If a higher resolution spectrometer is used it is likely that other emission lines which are closely spaced in the region 610-624 nm, may be observed better. These studies demonstrated that FES measurements during petroleum coke gasification are feasible and that the signals respond to changes in the conditions occurring in the reaction chamber. The temperatures obtained from FES and the thermocouples are indicative of the reaction temperature. The intensities of the observed spectral peaks tend to be higher at higher temperatures. To detect more definitive dependencies between the FES-deduced parameters, which are temperatures and emission peak intensities, with the flow rates, fuel composition and pressure it will be necessary to conduct petroleum gasification tests while varying one of the operating conditions systematically while the others are held constant. Testing fuel samples


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with different known compositions under the same operating conditions will also be required to further evaluate the potential and the limitations of FES for monitoring species emissions during gasification.

Acknowledgements This work was supported by the Government of Canada’s Program of Energy Research and Development, and ecoENERGY Innovation Initiative. Richard Lacelle, Jeffery Slater, Christopher Mallon and Alex McCready assisted in the maintenance and operation of the gasification facility and the flame emission spectroscopy probe.


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References (1) Murthy, B.N., Sawarkar, A.N., Deshmukh, N.A., Mathew, A., Joshi, J.B. Petroleum Coke Gasification: A Review: The Canadian Journal of Chemical Engineering, 2014, 22, 441 - 468. (2) Gordon, A., Spectroscopy of flames, Chapman and Hall, 1974. (3). Mavrodineanu, R., Boiteux, H., (1965); Flame Spectroscopy, Wiley, New York. (4) Sandrowitz, A.K., Cooke, J.M., Glumac N.G. Flame emission spectroscopy for equivalent ratio monitoring, Applied Spectroscopy, 1998, 52, 658-662. (5).Muruganandam, T.M., Kim, B-H., Morrel,M.R., Nori,V., Patel, M., Romig, B.W., Setzman, J.M.. Optical equivalence ratio sensors for gas turbine combustors. 2008, Proceedings of the combustion institute. (6) Romero, C., Li, X., Kevyan, S., Rossow, R. Spectrometer based Combustion monitoring for flame stoichiometry and temperature control, Applied Thermal Engineering, 2005, 25, 659-676. (7) Zizak, G. Flame emission spectroscopy-Fundamentals and applications, http://www.tempe.mi.cnr.it/zizak/tutorial/cairol06-flame-emission.pdf (8) Parameswaran, T., Hughes, P., Wong J., Moffatt, J.B., Combustion monitoring with flame spectroscopy, Combustion Canada 03, 2003, Sep 21-24,, Vancouver , B.C., Canada (9) Parameswaran, T, Hughes, P, Lacelle, Richard, Abdel, I., Wong, K. Flame emission spectroscopy in a conventional and a HTAC burner operating in a pilot scale furnace, 7th High temperature air combustion and gasification international symposium 2008, Phuket, Thailand. (10) Li, P., Wang, F.; Tu, Y., Mei, Z.; Zhang, J., Zheng, Y., Liu, H., Liu, Z.; Mi, J., Zheng, C.Moderate or intense low-oxygen dilution oxy-combustion characteristics of light oil and pulverized coal in a pilotscale furnace Energy and Fuels 2014, 28 ( 2) 1524 - 1535 (11) Parameswaran, T., Hughes, P., Lacelle, R., Flame emission spectroscopy in a coal - biomass fired boiler, 26th Annual International Pittsburgh Coal Conference, Sep. 2009 Pittsburgh, PA, USA.


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(12) Rossow, R.A., Blackbody temperature calculations from visible and near IR spectra for gas fired furnaces, Ph.D. Thesis, July 2005 University of Missouri Columbia, USA., https://mospace.umsystem.edu/xmlui/bitstream/handle/10355/4124/research.pdf (13) Docquier, N., Candel, S., Combustion control and sensors, Progress in Energy and Combustion Science, 28, 2002, pp.107-120. (14) Eckbreth, A.C., Laser diagnostics for combustion temperature and species, Oct. 1996 CRC Press. (15) Miziolek, A.W., Palleshi, V., Schechter, I., Laser induced breakdown spectroscopy (LIBS) Fundamentals and applications, 2006, Cambridge University Press, New York. (16) Cremers, D.A., Radziemski, L.J., Handbook of Laser induced breakdown spectroscopy, 2006, John Wiley and Sons, England. (17) Doyle, W.M., Principles and application of Fourier transform infrared (FTIR) process analysis – A Review., Process control and quality, 1992. 2, 11-42. (18) Rieker, G.B., Jeffries, J.B., Hanson, R.K., Calibration free wavelength modulation spectroscopy for measurements of gas temperature and concentration harsh environments, Applied Optics, 2009, 48, 55465560. (19) Parameswaran, T. Hughes, R., Gogolek, P., Hughes, P., Gasification temperature measurement with flame emission spectroscopy, Fuel, 2014, 34, 579-587. (20) Duchesne, M.A., Hughes, R.W. , Lu, D.Y., McCalden, D.J., Anthony, E.J. , Macchi, A. Fate of inorganic matter in entrained flow slagging gasifiers: Pilot plant testing, Fuel Processing Technology, 2014, 125, 208-217. (21) Kus, F.T., Duchesne, M.A., Champagne, S., Hughes, R.W., Lu, D.Y., Macchi, M, Mehrani, P. Pressurized pneumatic conveying of pulverized fuels for entrained flow gasification, Powder Technology 2016, 287 408-411.


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(22) http://physics.nist.gov/PhysRefData/ASD/lines_form.html -This is the database maintained by the National Institute for Standards and Technology and the Physical Measurements Laboratories at Gaithersburg Maryland and Boulder Colorado, USA. (23) Gaigalas, A.K., Wang, Lili, He, Hua-Jun, DeRose, Paul DeRose Procedures for Wavelength Calibration and Spectral Response Correction of CCD Array Spectrometers, [J. Res. Natl. Inst. Stand. Technology 2009, 114, 215-228, (24) http://www.prolite.co.uk/File/Spectrometer_irradiance_mode.php (25) Parsons, M. L., Major, S., Forster, A. R., Atomic emission spectroscopy Applied Spectroscopy, 1983, 37, 411-418.


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Figure captions Figure 1 Schematic diagram of FES in the CanmetENERGY gasifier Figure 2 Probe tip with cooling and purging connections Figure 3 Petroleum coke flame spectrum during gasification Figure 4 Petroleum coke gasification flame spectrum after calibration Figure 5 Spectra of petroleum coke introduced in a methane air flame Figure 6 LIBS spectra of petroleum coke Figure 7 - Day 1: Temperatures and flow rates during petroleum coke gasification- 12:00-13:40 Figure 8 - Day 1: Temperatures and flow rates during petroleum coke gasification- 15:15-16:30 Figure 9 - Day 1: Peak intensities and flow rates in petroleum coke gasifier 15:15 – 16:30 Figure 10 - Day 2: Effect of pressure in addition to flow rates on gasifier temperatures Figure 11 - Day 2: Effect of pressure in addition to flow rates on peak intensities Figure 12 - Day 1: Two-minute averaged temperatures, fuel/oxygen flow ratios and steam flow rates Figure 13- Day 1: Two-minute averaged peak intensities, fuel/oxygen flow ratios and steam flow rates Figure 14- Day 2: Two-minute averaged temperatures, fuel/oxygen flow rate ratios and steam flow rates Figure 15- Day 2: Two-minute averaged peak intensities, fuel/oxygen flow ratios and steam flow rates


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Energy & Fuels

Table I Some atomic emission lines near peaks observed in the petroleum coke gasification spectra [22] Excitation Wavelength (nm)

Line strength Aki (108s-1)

Relative intensity (a.u.)

Metal XRD (ppm)

Al II

624.336

1.1

400

5467.8

Ba I

553.5481

1.19

1000

45.8

Ba II

614.1713

0.412

300

45.8

Ca I

610.2722

0.096

500

964.9

Ca I

612.2219

0.287

600

964.9

Ca I

616.2172

0.354

600

964.9

Ca I

671.768

0.12

60

964.9

Fe II

624.756

50

2653.5

KI

766.4899

0.379

1000

627.2

KI

769.8964

0.374

1000

627.2

K II

612.62

1000

627.2

Li i

610.3654

0.686

400

unknown

Li I

670.7775

0.369

500

unknown

Li I

670.7926

0.369

1000

unknown

Li II

548,356

0.228

500

unknown

Li II

548.511

0.228

400

unknown

Na I

588.995

0.616

1000

361.9

Na I

588.5924

0.614

500

261.9

VI

609.0208

0.26

110

964.9

VI

624.311

unknown

60

964.9


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Table II Mean standard deviations of two minute averaged variables from Day 1 and Day 2 tests Mean stdev.

FES temp

Peak 554 nm

Peak 624 nm

TE411

TE414

Steam

PC/O2

Day 1 tests

39.882

0.364

1.048

2.702

1.057

0.618

0.102

Day 2 tests

19.902

0.111

0.408

2.72

1.027

0.372

2.72


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Energy & Fuels

Figures 1-15 as tiff files

Figure 1 Schematic diagram of FES in the CanmetENERGY gasifier

Figure 2 Probe tip with cooling and purging connections

Figure 3 Petroleum coke flame spectrum during gasification


Energy & Fuels

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Figure 4 Petroleum coke gasification flame spectrum after calibration

Figure 5 Spectra of petroleum coke introduced in a methane air flame


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Figure 6 LIBS spectra of petroleum coke


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Figure 7 - Day 1: Temperatures and flow rates during petroleum coke gasification- 12:00-13:40 Figure 8 - Day 1: Temperatures and flow rates during petroleum coke gasification- 15:15-16:30


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Figure 9 - Day 1: Peak intensities and flow rates in petroleum coke gasifier 15:15 – 16:30


Energy & Fuels

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

Figure 10 - Day 2: Effect of pressure in addition to flow rates on gasifier temperatures

Figure 11 - Day 2: Effect of pressure in addition to flow rates on peak intensities


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Figure 12 - Day 1: Two-minute averaged temperatures, fuel/oxygen flow ratios and steam flow rates

Figure 13- Day 1: Two-minute averaged intensities, fuel/oxygen flow ratios and steam flow rates


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Figure 14- Day 2: Two-minute averaged temperatures, fuel/oxygen flow ratios and steam flow rates

Figure 15- Day 2: Two-minute averaged intensities, fuel/oxygen flow ratios and steam flow rates


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Energy & Fuels


Petroleum Coke Gasification Temperatures and Flame Spectra in the

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