Envision Technologies 1AIChE Spring Conference April 13, 2005Atlanta. Georgia
Tailoring Coker Residence Time Distributions for Improved Liquid Yields:
The Envision Technologies Cross-Flow Coker (ETX)
Robert Pinchuk†
W. Brown†, W. McCaffrey‡, O. Asprino‡, G. Monaghan†
†Envision Technologies Corp.‡ Department of Chemical Engineering and Materials Engineering , University of Alberta
Envision Technologies 2AIChE Spring Conference April 13, 2005Atlanta. Georgia
Basic Mechanism of Liquid Product Formation in Coking
•Complete reaction of feed requires 30 -120 seconds, depending upon temperature
•Ideally products are removed within a couple of seconds
•Optimal residence times of the different phases differ by an order of magnitude
Feed(liquid)
Over-Cracked Gases
Gas Phase
Liquid Phase Liquid
Products(gas)
Coke(Solid)
Liquid Products
(gas)
(Product Vaporization)
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How to optimize yield of liquid products
• Can improve liquid yields by matching optimal residence times– decouple the two phase so that each residence time can be set
independently
• Lower reaction temperatures will increase liquid yields
What configuration offers the greatest flexibility?
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ETX CokerCross-Flow Fluidization
Fluidization gas
Cool solids
Liquid feed
Hot solids
Fluidization gasand reaction products
• Fluidized bed of hot solids provides the energy for the reaction– Solids flow through the reactor horizontally
• The feed is sprayed onto the solids near the solids feed point• Product is recovered along the length of the reactor with the fluidizing gas
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Cross-Flow Fluidization
• Commercial fluidization technique most commonly used for drying
• Want to apply this commercial technology to heavy oil processing
• Often referred to as “plug-flow” fluidization because of the solids mixing pattern– this is a major advantage of this
reactor configuration
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Perceived Benefits of the Design
1. Independent control over gas and liquid fluxes allows for optimized residence times
2. Plug-flow of the solids eliminates losses of feed due to short-circuiting and reduces the required reactor size
3. Shallow Bed reduces gas phase residence time and overcracking
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Residence time distributions
• Cold flow experimental program used to study and confirm benefits of the design
• Process scaled down based on the dimensional analysis
• 0.75 m x 0.75 m square bed– larger than typical experimental bed– close to expected commercial size
5.01 )( pmf
H gdu
=Πmf
exH u
u=Π 2
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Solids Mixing
• Horizontal mixing experiments done in a square reactor with no bulk solids flow
• Mixing curves fit with a two dimensional dispersion model to extract dispersion coefficient
• Dispersion coefficients measured between 200 and 20 cm2/s
– Affected by bed depth and fluidization velocity
– Compare well with published data
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Solids Residence Time Distribution
• Can predict solids residence time distribution in the ETX reactor by overlaying dispersion on a bulk flow
• Solids residence time distribution approaches that of a plug flow reactor
• Solids carry the reacting feed so the feed residence time distribution is the same as the solids
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2time / mean residence time
Frac
tion
of T
race
r Rel
ease
d fro
m R
eact
or
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Gas Phase Mixing
• Experiments performed to establish effect of reactor configuration on over-cracking
• Negative step change experiments done in cold-flow unit
• Model based completely on correlations for bed properties available in the literature with no adjustable parameters.
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Effect of Temperature
• Evidence that lower reaction temperatures improves liquid yields
• Sequential processes of liquid production, evolution then degradation
• Decoupling these processes is a common approach taken by many researchers
• Gas side effects are well represented in the literature
• Liquid side dependence on temperature has not been shown
Over-Cracked Gases
Liquid ProductsFeed
Liquid Side• Reaction• Vaporization
Gas Side• Reaction
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Liquid Side Effect
• Effect of temperature on liquid side studied in a small quartz reactor
• Athabasca vacuum residue cracked at different temperatures
• Film thickness of 250 microns
• Liquid products condensed weighed and analyzed
• Coke weighed and analyzed
• Non-condensable gasses were not collected
Condenser
Molten Salt Bath
Sweep Gas
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Coke Yield
• Reaction temperatures between 450°C and 550°C
• No effect of temperature on coke yield
• Other studies have shown a slight increases in coke yield as temperature is increased ~ 1% over a temperature increase of close to 100°C
– experimental technique was not sensitive enough to see this
14
16
18
20
22
24
26
440 460 480 500 520 540 560Temperature, oC
Cok
e Yi
eld,
%
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Gas and Liquid Yields
• Increase in temperature leads to a trade-off between gas and liquids
• 5% increase in liquid yield with a temperature decreases from 530°C to 470°C
• Result seems analogous to gas phase over-cracking but on a much faster time scale
• Actual gas phase over-cracking was not occurring because gas phase temperature was too low and gas phase residence time was too short
0
2
4
6
8
10
12
440 460 480 500 520 540 560Temperature, oC
Gas
Yie
ld, %
67
68
69
70
71
72
73
74
75
76
440 460 480 500 520 540 560Temperature, oC
Liqu
id Y
ield
, %
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Product Quality
• Aromatic carbon content and H/C of products was measured
• Product quality was shown to decrease with reaction temperature
• Liquid product quality and yields are not independent
– an increase in the gas yield means that less hydrogen ends up in the liquids 20
22242628303234363840
460 480 500 520 540Temperature (deg-C)
Aro
mat
ic C
arbo
n C
onte
nt (%
)
1.5
1.55
1.6
1.65
1.7
1.75
H/C
(mol
ar ra
tio)
Aromatic Carbon
H/C
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Final Hydrogen Distribution
8%16%73%530°C
7%13%78%500°C
8%9%82%470°C
CokeGasLiquid Products
Reaction Temperature
• Final distribution of hydrogen among coking products is significantly affected by reaction temperature
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Impact of ETX attributes Solids Residence Time
•Solids mixing in ETX reactor approaches plug-flow
•Feed that exits before [time/reaction time] < 1 is partially wasted
•Current fluid bed coking technology is well mixed
-required to compensate for short-circuiting with larger reactor
•ETX reactor can be made 20 times smaller than a well-mixed reactor
Well -Mixed
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2time / required reaction time
fract
ion
of tr
acer
rele
ased
ETX
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Impact of ETX attributesGas phase over-cracking
• Combine the gas phase mixing model with an over-cracking kinetic model
• Models shows effects of reactor configuration on over-cracking
• Model also allows for some extrapolation outside of experimental spacecommercial units
– current fluidized bed cokers lose between 5% and 8% of their products to over-cracking
– allows for some comparison to commercial units
• ETX coker gives 2% increase in liquid yield over Fluid Coking because of the shallow bed
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Leveraging the ETX design advantagesHigh Capacity Reactor
• Similar operating conditions as the similar process of fluid coking– Operational confidence– Same amount of coke production
• Solid mixing pattern allows a smaller reactor with increased capacity– 65% increased capacity over a fluid coker– 10,000 bbl/day unit 3 m high, 2 m wide, 6 m long
• Shallow bed provides a yield benefit by reducing over-cracking– Expected 2% increase in product yield from reduced gas phase residence time
• Solids mixing pattern eliminates short-circuiting and losses of partially reacted feed
• Burner temperature 50°C cooler than typical fluid coker– Energy and emission reduction
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Further Leveraging the ETX Advantage
• Effect of temperature on liquid yield – Over-cracking model showed the potential for a 5% decrease in over-cracking
losses by reducing the reaction temperature from 530°C to 470 °C – Hot coking experiments showed the potential for a 5% increase in liquid yield,
due to liquid side effects, by reducing the reaction temperature from 530°C to 470 °C
• Combining maximum liquid and gas side effects gives a potential increase in product yield of 9% over current technology (liquid and gas side effects quoted on different basis)
– This yield increase is accompanied by an increase in product quality
• Cost of lower temperatures is reduced reaction rate leading to increased reactor size and decreased capacity
– Reducing reaction temperatures by 10°C can double reactor size requirements
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ETX Design can Capture Yield Benefit
• ETX design is already ahead in capacity
• The ETX design can capture 4% of the potential yield increase with no capacity loss compared to fluid coking
0
1
2
3
4
5
6
7
8
470 480 490 500 510 520 530 540Mean Reaction Temperature (deg C)
Yie
ld In
crea
se O
ver F
luid
Cok
ing
(%)
0
50
100
150
200
250
300
Cap
acity
(bbl
/m3/
day)
Fluid CokerCapacity
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Benefits of the ETX design
• Cross –flow design allows for independent control over liquid and gas residence times
• Shallow bed reduces gas phase degradation by reducing gas-phase hold-up
• Solids mixing pattern allows for maximum capacity and eliminates losses from short-circuiting– Allows the ETX design to capture 4% liquid yield increase with no loss
of capacity– Increase in liquid yield is accompanied by an increase in product quality
• Application of commercial fluidization technology to upgrading
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Acknowledgements
• Industrial Research Assistance Program (IRAP)
• University of Alberta
• National Center for Upgrading Technology (NCUT)
• Coanda Research and Development Corp.
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