Optimizing Distillate Yields and Product...
Transcript of Optimizing Distillate Yields and Product...
Optimizing Distillate Yields and Product Qualities Srini Srivatsan, Director - Coking Technology
Email: [email protected]
Overview
Delayed coker yield determinants
Case study
Product quality optimization
Conclusions
Optimizing Distillate Yields and Product Properties
2 © Amec Foster Wheeler 2015. All Rights Reserved.
► Feedstock Properties
► TBP cutpoint / distillation
► API gravity
► Viscosity
► Concarbon residue (CCR)
► Asphaltenes (C7 Insolubles)
► Sulfur
► Nitrogen
► Metals/ash
► Crude type/source
► Operating conditions
► Coking cycle time
Delayed Coker Yield Determinants
3
0
20
40
60
80
100
Test Run SYDECPrediction
Yie
ld, w
t%
Actual versus Predicted Yields
C4-
C5+ Liquids
Coke
Feed properties have the
most impact on yields
© Amec Foster Wheeler 2015. All Rights Reserved.
Delayed Coker Feedstocks
4
Straight Run
– Paraffinic
– Non-paraffinic
• Asphaltic
• Aromatic/naphthenic
– Distillates (VGO)
Cracked feeds
– Hydrocracked resids (H-oil, fixed bed HDS, etc.)
– Thermally cracked resids (visbreaker tar)
– Distillate tars (slurry, coal tar, pyrotar, etc.)
– Unconverted oil (UCO)
SDA pitch
Shale oil residues (kerogen derived)
Feedstock type influence
yield selectivity
© Amec Foster Wheeler 2015. All Rights Reserved.
Paraffinic Feeds
► Cracks easily
► Makes more gas, more
lighter distillates and less
coke
► High sodium in feed could
result in accelerated heater
fouling
► Stability when blended with
asphaltenic residue could be
an issue
Aromatic Feeds (Decant Oil)
► Low CCR content high
Coke/CCR ratio
► High aromatic content high
HCGO yield
► Potential to change coke
morphology (shot sponge)
DCU Non-Typical Feed Impacts
5
Yield model calibrated for wide range of feedstock types
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Yield Corrections for Unusual Feeds
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Coke yield for unusual feeds like AR and FCC decant oil are to be corrected. Coke yield to CCR ratio is higher for such feeds although actual coke make is much less as CCR is low.
0 10 20 30 40 50 60 70
Co
ke /
CC
R
CCR
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Temperature: Higher is better
Pressure: Lower is better
Recycle: Lower is better
However…
Lower recycle increases HCGO
- End point
- CCR
- Heptane insoluble (nC7 asphaltenes)
- Metals (Ni + V)
Effect of Operating Conditions
7
Process Variables for Maximizing Liquid Yields
© Amec Foster Wheeler 2015. All Rights Reserved.
► FEED IS VR FROM MIDDLE EAST
► CCR = 24 / API = 6
► OBJECTIVE IS TO MAXIMIZE REVENUE
► LCGO & LPG PRICED @ 1.49 X HCGO
► LIQUID PRODUCTS:
► LPG
► Naphtha IBP - 150 C
► LCGO 150 C - 370 C
► HCGO 370 +
Case Study - Selection Of Operating Conditions
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Case Study Selection of Operating Conditions - Impact on Yields
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Maximizing C5+ liquid yields usually maximizes revenue unless
Coker is hydraulically constrained in revamp scenario
Coke is highly valued, i.e. specialty grade coke
HCGO does not go to a high conversion unit
Maximum C5+ Intermediate
Yields
Higher LCGO
CD Pressure Base
TPR Base
Yields as Wt % Fresh Feed (FF)
Fuel Gas (w/ H2S) 5.0 5.1 5.2
LPG 3.7 3.9 4.1
Naphtha 10.3 10.9 12.2
LCGO 26.5 28.0 30.6
HCGO 24.8 21.5 15.6
Coke 29.7 30.6 32.3
Total C5+ Liquids 61.6 60.4 58.4
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0
10
20
30
40
50
60
70
80
90
100
Max C5+ Intermediate Yld Max LCGO
Wt%
, F
F
Coke
HCGO
LCGO
Naphtha
LPG
Fuel Gas
BASED ON PRICING, MAX. LCGO CASE INCREASES REVENUE BY $10 MM /YEAR EVEN THOUGH C5+ LIQUID YIELDS ARE LOWER BY 2.8 WT% (FF BASIS)
Case Study Selection Of Operating Conditions – Impact on Yields
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Effect of Pressure on Liquid Distribution
30
35
40
45
50
55
10 15 20 25 30 35
L
CG
O o
r H
CG
O /
To
tal L
iqu
id (w
t%)
Coke Drum Pressure, psig
LCGO
HCGO
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LCGO and HCGO Distribution in TLP (Case specific)
© Amec Foster Wheeler 2015. All Rights Reserved.
HCGO – Processing Options
► Most desired option is to send HCGO to Hydrocracker. However,
quality limitations have to be recognized
► Feed to FCC. However if FCC bottoms is sent to the coking unit,
this recycle could cause a build-up of refractory type material.
FCC pre-treatment would be required. Limits to how much FCC
decant oil can be processed in a coker
► VGO hydrotreater – More tolerant to HCGO contaminants. Take a
hit on conversion
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13
ASTM D1160, °C Max C5+ Intermediate Yields Max. LCGO
IBP 382 382 381
10% 393 391 388
30% 424 418 409
50% 459 447 433
70% 501 484 464
90% 546 526 500
EP 572 550 521
Note: Distillations are based on theoretical yields (perfect fractionation). Actual distillation will show a tail based on fractionation efficiency
HCGO Distillation
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0
1
2
3
4
5
6
Max C5+ Int. Yld Max LCGO
Co
nta
min
an
ts (
rela
tive
sc
ale
)
CCR C7 Insolubles, wppm Ni+V There is a balance between maximizing
liquid yields and keeping HCGO “clean”
Product Properties - HCGO
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450
500
550
600
650
1.0 1.1 1.2 1.3 1.4 1.5
HC
GO
EP, C
TPR
@ constant P, T
HCGO Processing in a Hydrocracker
► Hydrocracker licensors restrict the EP of HCGO stream to lower
contaminant levels and increase catalyst life
► HCGO with EP as high as 578 C (1072 F) has been processed in
Hydrocracker making quality product.
► US Gulf coast installation, operating since 2000
► 35,000 BPSD Capacity. 55% HCGO, 25% Light cycle oil, 20% SR HVGO
► 2 stage HCK, Common recycle gas loop, 50% conversion of 343 C + (650 F +)
material with 13,000 BPSD fed to FCC (bottoms from first reactor)
► HCGO Quality
CCR 0.48 wt%
Asphaltenes <100 ppmw
Ni + V 1.82 ppmw
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17
► Use spray pattern and backup
spray system for ultra-low
recycle operations
► 5% recycle or lower
► Open Wash Zone
► Use of Sheds
► Distribute vapor flow
► Impingement of liquid mist
► Subject to coking: Open design
HCGO Product Quality Control
Coke
Drum
OVHD
Vapor
Wash Oil
Spray
Chamber
Wash
Oil
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LCGO Quality
Typical Specifications for LCGO
► Flash point
► Distillation - D86 90% and/or EP, Gap (LCGO - HCGO)
Flash point met by addition of LCGO stripper
Distillation – Specification achieved by varying draw rates, internal
reflux, addition of trays between LCGO draw and HCGO P/A return
in the fractionator
Consider total draw-off tray with pump back for more stable
operation
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LCGO Quality – Partial Draw vs. Total Draw
T - 10COKER
FRACTIONATOR
T - 22
S-5
T - 4
T - 12
LC
P - 1
HCGO
STRIPPER
LCS-1
T - 1
P - 2
T - 1
T - 19
LCGO PRODUCT
PUMPS
T - 4
T - 13
LC
T - 11
LI
LCGO PRODUCT (LCGO)
TO HYDROTREATING
FC
HCGO PRODUCT (HCGO)
TO VGO UNIFING UNIT
FC
HCGO PRODUCT
PUMPS
LCGO
STRIPPER
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Total draw offers better control of flow. Easier to control
quality if changing cut points later (revamp)
Naphtha Quality
Typical Specifications for Naphtha
► Vapor Pressure
► Distillation - D86 90% and/or EP, Gap (Naphtha - LCGO)
► Si content (to be watched)
Issues with low Naphtha EP
► Low Fractionator overhead temperatures – can lead to salt deposition in top section
of column
► Recommend a back end Naphtha Splitter
Other Considerations
► Provide water wash section in the fractionator
► Consider Si guard bed followed by di-olefin reactor upstream of naphtha Hydrotreater
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► Delayed Coker yields are
dependent on feedstock quality,
operating conditions and cycle
time
► Limitations of downstream processing units impact selection of DCU operating conditions
► Maximizing C5+ Yields may not be the best option for every refiner
► Naphtha and distillate yields can be optimized by careful selection of operating parameters and design considerations
Conclusions
© Amec Foster Wheeler 2015. All Rights Reserved.