transportation of natural gas using liquid carriers at ambient temperature ben thompson
TRANSCRIPT
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Transportation of Natural Gas Using Liquid Carriers at Ambient Temperature
Ben Thompson
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Purpose of this Work
• In this work we evaluate the use of an existing storage method in transportation of natural gas using ships across the ocean.
• We consider the method to store natural gas in liquid hydrocarbon mixtures at moderate pressures and ambient temperature (OU/CBME patent).
• For this we will consider well-known storage architectures (Tube bundles & Coselle units)
• We will compare with the Liquefied method (LNG) and the High Pressure compressed gas method (CNG)
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Overview• Existing technology
• Previous work
• Present analysis
• Conclusions and recommendations
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Existing Technology
• Existing Patent: “High-Energy Density Storage of Natural Gas at Moderate Temperatures” (Supergas™)
• Natural gas dissolved in pure liquid propane.▫ Initial evaluation was at low temperatures and
moderate to high pressures.
▫ Maximum loading : 70 mol % methane at lower temperatures.
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Existing Technology
•Coselle units
•Composite piping
http://www.ngvrus.ru/images/15_41.jpg
http://i234.photobucket.com/albums/ee274/biopact3/biopact_coselle_CNG.jpg
http://www.lnf.infn.it/esperimenti/dear/hbp-700.jpg
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Compressed Natural Gas (CNG)• Natural gas is highly
compressed to pressures around 3000 psia.
• Ambient temperature.
• Cost effective when shipping distance is between 200 and 2500 miles.
http://www.marinelog.com/IMAGESMMIV/cng2.jpg
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http://dsp-psd.pwgsc.gc.ca/Collection/C89-4-70-1998E.pdf
Compressed Natural Gas Carrier
Coselle units Tube bundles
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Liquefied Natural Gas• Ambient pressure.
• Temperature: -161 ºC
• Cost effective with shipping distances greater than 2500 miles.
http://www.ferc.gov/images/photogallery/lng_sksummit.jpghttp://ahmadberlian.blogsome.com/images/LNG_tanker.jpg
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Density comparison • Densities:- CNG – 128 kg/m3
- LNG – 410 kg/m3
- Supergas ™ – 329 kg/m3
- This mixture has less methane (about 1/3 of the total mass) than CNG or LNG contributing to the density.
• Moles of Methane per cubic meter- Supergas ™ : 4800 at 80 degrees Fahrenheit and 1500 psi
- LNG: 25000 - CNG: 6400 at 60 degrees Fahrenheit and 3000 psi
• LNG has the highest energy content and Supergas ™ at this temperature has the lowest.
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Capacities• 145,000 ton capacity
tanker traveling at 18 knots.
• Every ship has same capacity so costs increase almost linearly to reach new distances.
• 14, 275 tons of natural gas could be stored on this tanker.
• Propane and equipment account for rest of weight.
0 2000 4000 6000 8000 10000 120000
5
10
15
20
25
30
35
Ships Required vs Shipping Distance
1 Million tpa
2 Million tpa
3.5 Million tpa
Shipping Distance (miles)
Sh
ips
Req
uir
ed (
# o
f sh
ips)
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Initial Conclusions• Use of carbon fiber reinforced piping to ship
natural gas in hydrocarbon carrier.
• 70 mol % methane mixture.
• 30 °F and 1500 psia.
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Issues we investigated• Variations in Density predictions and the
possible error in profitability.
• ASME codes.
• Use of other solvents.
• Loading and unloading costs.
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Density Prediction Methods
• Soave-Redlich-Kwong (SRK)
• Peng-Robinson (PR)
• BWRS
• 50/50 molar mixture of propane and methane.
• The above methods were modified using their respective liquid density calculation methods. API method was the default, but it was not used.
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Comparison of prediction methodsPressure vs Liquid Density
17.6
19.6
21.6
23.6
25.6
1200 1700 2200 2700
Pressure (psi)
Liqu
id D
ensi
ty (l
b/ft
3 )
SRK1
SRK3
SRK4
PR1
BWRS
2.0 % variation between SRK and PR equations of state.
SRK
PR
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Loading Station Specifics
• Equipment shown to the right.
• Mixer consists of 10 foot long, 24 inch ID stainless steel pipe.
• Upwards of 80,000 hp compressor power requirement.
Compression Compression
Heat Exchanger (Cooling)
Heat Exchanger (Cooling)
Mixer
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Methane Dissolution issues
• Additives to the mixture could increase the amount of methane dissolved within the propane.
• Both propane and methane are nonpolar, so any substance increasing nonpolar attractions will help this.
• Introduction of a fraction of some polar substance might cause this, but an agitator would be required for a continuous phase.
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Unloading Station Specifics
• Equipment: - Heat exchanger
- Flash drum - Expander - Distillation column (no condenser due to
large energy requirements to condense methane)
• Specifics:- 15 theoretical trays.
- Pre-cooling to 45 ◦F - Pressure drop in flash drum to 1000 psi - Column operating pressure of 500 psi - Column operating temperature of 20 ◦F - Only 98.9% of propane is recovered and it
should be higher.
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Projected Income for Various Shipment Methods and various Thermodynamic prediction methods
01
23
45
67
8
Pro
jec
ted
In
co
me
, $
MM
Coselle units
Stainless steelpipes
Compositereinforced steelpipes
SRKPR
BWRS
Economic Comparison
Thermodynamic Method effect:1.8% variation for Coselle units, 2.0% variation for composite pipes., 0.6% variation in stainless steel pipes.
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Net Profit
0
500
1000
1500
2000
2500
Equations of State
Net
Pro
fit
(MM
$)
Coselle Units
Stainless Steel Pipes
Composite Piping
SRKPR BW
RS
Economic Comparison
Coselle units and composite piping are on the scale of billions of net profit per year.
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Economic Comparison
Supergas ($/ton) LNG ($/ton)0
10
20
30
40
50
60
70
80
90
Comparison of Operating Costs
1 million tpa
2 million tpa
3.5 million tpa
Op
erat
ing
Co
st (
$/to
n)
• Operating costs of LNG decrease with increased production.
• This assumes constant operation.
• Supergas method assumes only operation on days of loading/unloading.
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Economic Comparison
0 1000 2000 3000 4000 5000 6000 7000 8000
-250
-200
-150
-100
-50
0
Net Profit vs Shipping Distance
$10/ton
$20/ton
$30/ton
$40/ton
$50/ton
$60/ton
$70/ton
$80/ton
$90/ton
$100/tonShipping Distance
Net
Pro
fit
($M
M)
• Shipping costs are the deterrent in the profitability of this method.
• Higher capacity tankers or lower cost tankers could limit this cost and make method profitable.
• Only high prices could make this method profitable.
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Economic Analysis
•LNG requires fewer ships to complete the specified capacity.
•Shipping costs rely on charter rate of $65,000.
0 2000 4000 6000 8000 10000 120000
50
100
150
200
250
Shipping Cost Comparison: LNG vs Supergas
Supergas 100mmtpa
Supergas 200mmtpa
Supergas 350 mmtpa
LNG 100 mmtpa
LNG 200 mmtpa
LNG 350 mmtpa
Shipping Distance, miles
Sh
ipp
ing
Co
st,
$MM
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ASME Codes
•Carbon fiber composite piping
•Required for low weight to be competitive
•No codes exist •Legal and safety
issues were not analyzed
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Other Solvents
• Other solvents explored:
▫ Heavier hydrocarbons in pure form and in mixtures.
▫ Acetone: 3000 psia for equivalent molar mixture
▫ Cyclohexane and other hydrocarbons.
• These solvents do not have any higher capacity for carrying methane at moderate pressures.
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Conclusions • Transportation using Supergas™ and carbon
reinforced pipes is not more profitable than LNG at any distance.
• Required shipping costs to meet the capacity supplied by LNG keep this method from being economical.
• Possible errors in the thermodynamic prediction methods for density only affect the profitability by 2.0% maximum
• Research on additives to enhance methane diffusion into solvent might be advisable.
• At high gas costs, around $100/ton, it may be profitable for short distances. But, LNG would gain the same benefits.