Effect of heating rate and temperature on pyrolysis of asphaltenes … · 2018-04-17 · Effect of...
Transcript of Effect of heating rate and temperature on pyrolysis of asphaltenes … · 2018-04-17 · Effect of...
Effect of heating rate and temperature on pyrolysis of asphaltenes:
A study of char characteristics
Nirlipt Mahapatra1, Vinoj Kurian1, Ben Wang1,Frans Martens2 , Rajender Gupta1
1Department of Chemical & Materials Engineering, University of Alberta 2Nexen Energy ULC, Calgary, Canada
6th International Freiberg Conference on IGCC & XtL Technologies,
Coal Conversion and Syngas,
19-22 May 2014, Dresden/Radebeul, Germany
Outline
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Introduction
Experimental
Results & Discussions
Conclusions
Bigger Picture on Oil sands & Bitumen
What are Asphaltenes ?
Asphaltenes Gasification
Char Preparation Characterization
Char morphology & composition
Reactivity
Objective
Importance of char
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Oil Sands in Canada
Canada
3rd Largest Oil Reserves1 5th Largest Crude Oil producer1
1.8 MMbd
5.21 MMbd
Crude Oil production from Oil sands2
2012 2030
Oil sands are primarily obtained in Alberta (Western Canada)
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Bitumen
Bitumen (from Oil sands)6
HEAVY4,5
Higher Density, Viscosity, S, N, O,
Minerals & Carbon Residue (MCR/CCR)
15 wt.% Asphaltenes 7
Oil Sands Bitumen Crude Oil Extraction Upgrading
Asphaltenes
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Asphaltenes
Powdered asphaltenes
Archipelago structure MW: 4133 g/mol13
Heaviest fraction of Bitumen/ petroleum
liquids 8,9,10
50% of Carbon Residue in Bitumen11,12
Highest Sulfur & Mineral Content
Complex Structure
Cause problems during
• Production
• Refining
• Transportation
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Asphaltenes Gasification
Asphaltenes Gasification
Steam to SAGD
H2 to Hydrocracking
from de-asphalter
Asphaltenes have no use and pose disposal problems but are high
in calorific value
Gasification can provide a cleaner alternative 14,15,16
Asphaltenes as liquid streams are easier and cost effective to
handle than solid coke. 16
Schematic for Asphaltene Gasification integrated into Upgrading 16
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Gasification
Pyrolysis
Heterogeneous Char gas reactions
Gas phase reactions
Amount and characteristics of char and volatiles17-22
Temperature Residence Time Heating Rate Feed Size
Char is important
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Objective
Char • Structure & Composition • Morphology • Global Reactivity
Operating Temperature
Residence time at temperature
Heating rate
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Char Preparation
150-212 um solid asphaltene
feed
Mullite /Alumina tube
65 mm ID X 153 cm height
Electrical heating
Atmospheric pressure
Air and water cooled feeder
probe
N2 (entraining gas)
Entrained Flow Drop Tube Furnace
Proximate & Elemental Analysis
Scanning Electron Microscope (SEM) & Energy Dispersive X-Ray (EDX)
X-Ray Diffraction (XRD)
Fourier Transform Infrared Spectroscopy (FTIR)
Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
Thermogravimetry (TGA)
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Characterization
Sample Name Nominal Temperature
of DTF ( °C) Nominal Residence
Time (s)
800 °C Char 800
8.4 1000 °C Char 1000
1200 °C Char 1200
1400 °C Char 1400
11.8 s Char
1200
11.8
8.4 s Char 8.4
6.5 s Char 6.5
4.9s Char 4.9
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Operational Parameters
Pressure: 1 atm Feed Size: 150-212 µm
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Volatiles & Fixed Carbon
Temperature Residence Time
Temperature more pronounced effect
Temperature Residence Time => Volatiles FC
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H/C, Sulfur & Carbon
Temperature Residence Time => H/C S C
N, O content also decreases
Rate of decrease of H/C and S Decreases at higher temperatures
Temperature Residence Time LHR
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Re-condensed volatiles (minor)
Incomplete pyrolysis
Maximum weight loss region occurs between 350-500 ˚C with a maxima at 450˚C
Thermal Analysis
Asphaltenes Char
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CH -, aromatic CH CH2- and CH- (wag)
C=O carbonyl
CH2-S (wag)
-OH carboxylic acid
Infrared Spectra
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X-Ray Diffraction Crystalline reflection (00l) (turbostratic carbon)
2D Lattice Reflections (hk)
Turbostratic Carbon / Graphitization24
Temperature Residence time change not much effect
V, Ni most abundant in petroleum25,26
(porphyrinic and non-porphyrinic )
V, Ni accumulates in char
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Analysis of trace metals
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Discussions so far
Ash, V, Ni accumulates in char (0.60 wt.% asphaltenes and 2.18 wt.% ash 1400 ˚C Char)
Initally H/C ratio decreases fast due to de-alkylation and removal of H2S. At Higher Temperatures decrease is slow due to condensation & peri-condensation27
(and graphitization)
High Heating Rates Lower Char Yield
Thiophenic Sulfur remains while aliphatic Sulfur is lost as H2S. (IR Spectra and Elemental Analysis support ). Lost early as C-S < C-C 28
(Asphaltenes 40% aliphatic S; and 60% thiophenic S 23)
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800 ˚C Char Temperature
Nominal Particle Size
Bulk Density
Fraction of fragmented particles
Morphological Study (SEM) 1000 ˚C Char
1200 ˚C Char 1400 ˚C Char
Residence Time No noticeable change in morphology
*Similar magnifications 500X
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SEM of Char
1000X BSE SEM
1200 ˚C Char Cross-section Soot on Char Surface
25000X SE SEM
Structure of Char hollow “Cenosphere” with a vesicular porous wall White dots are minute soot deposits on char surface
26 EDX Mapping of 1200 ˚C Char (300X magnification)
V & Ni in minute quantities
aluminosilicates and iron oxides discrete particles
Sulfur evenly (more in bigger sized)
EDX Mapping of Char
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SEM of Low Heating Rate Char
600 ˚C LHR Char
900 ˚C LHR Char
Macro-porosity increases at higher temperatures
*Similar magnifications 500X
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Discussion on Char Morphology
Nominal particle size decreases and fragmentation increases at higher temperatures, thicker walls 29
Smooth surface of char could signify initial rapid melting of asphaltenes
Observable Porosity Higher Temperatures
Residence time (5-12s) less pronounced effect
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Char Steam(20%) Reactivity
Temperature Residence Time
Temperature Residence Time global char steam reaction rate Less pronounced for Residence Time
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Char CO2(100%) Reactivity Temperature Residence Time
Temperature Residence Time global char CO2
reaction rate (Boudouard Reaction)
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Discussion on Char global reactivity
Chars obtained at higher temperature have a decreased reactivity due to ordering of carbon structure (graphitization) 30-32or thermal annealing process33. May explain increase loss due to increase in residence time as well.
800 Deg. Char significantly higher reactivity. Great difference in morphology. Decrease in micro-porosity of char at higher temperatures and an increase in observed macro-porosity. 34
Pyrolysis temperature , residence time at temperature & heating rate affect the morphology, structure and reactivity of chars. • Increase in operating temperature
– Global gasification reactivity – Nominal particle size – H/C Ratio, Number of functional groups, N, S, O, Volatile matter – Aromaticity – Graphitization – Macro-porosity
• Increase in residence time at temperature (less pronounced effect) – Global gasification reactivity – H/C Ratio, Number of functional groups, N, S, O, Volatile matter
– Change in morphology, aromaticity & graphitization not noticeable
• Very high heating rates overcome mass transfer limitations and better pyrolysis occurs
Future Work: Estimation of surface area and intrinsic char reactivity
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