transportation of the liquid hydrogen |
| A.Abe | Ishikawajima-Harima Heavy Industries Co.Ltd. 2-1-1 Toyosu Koto-Ku Tokyo Japan |
| M.Nakamura | Kawasaki Heavy Industries Ltd. 3-1-1 Higashi Kawasaki Chuo-Ku Kobe Japan |
| I.Sato | Mitsubishi Heavy Industries Ltd 3-3-1 Minato-Mirai Nishi-Ku Yokohama Japan. |
| H.Uetani | Mitsui Engineering & Shipbuilding Co.Ltd. 1 Yahata Kaigan Dori Ichihara-City Chiba Japan |
| T.Fujitani | Ishikawajima-Harima Heavy Industries Co.Ltd. 2-1-1 Toyosu Koto-Ku Tokyo Japan |
Hydrogen is anticipated to be one of the promising energy used in the 21st century.In Japan ,researchfor establishing a hydrogen energy technology is being conducted in the WE-NET(world energy net-work) research program of the New Sunshine Project promoted by the Ministry of Trade and Industry since 1993 aiming the completion in 2020 .
As the first three years study of hydrogen tanker development, conceptual design of 200,000m3 hydrogen tanker based on the LNG ship technology and some investigations on the insulation and support system for hydrogen tank were carried out by the joint shipyard team in WE-NET program. Outline of our research and some considerations are reported.
One of the practical way to distribute
hydrogen energy world-widely is the transportation of liquid hydrogen
by tanker. The study of a large scale hydrogen tanker has been
carried out by the joint shipyards team in WE-NET program, based
on the LNG carrier technology of self-supporting tank designs
such as the Prismatic and Spherical tank designs in such a way
to extend them to accommodate the liquid hydrogen.
The WE-NET program is divided into 3 phases extending over 28 years period from 1993 to 2020 as shown in Table-1. Phase I research plan consists of basic studies and reviews . In phase II, fundamental technologies will be established through pilot-scale model test. In phase III, practical technologies for building the liquid hydrogen tanker will be developed.
| ITEM | Investigation of Basic Technology
Conceptual Design Preliminary Test | Establishment of Fundamental Technology
Pilot Model Test | Completion of Building Technology
Model Ship Test |
In the course of Phase 1 research ,firstly we have conducted the basic study of hydrogen technology , its actual applications and the overseas researches on hydrogen tankers , which was followed by the second years conceptual design of large scale hydrogen tanker to satisfy the future energy demand. And in the third year we have carried out the preliminary study of the basic elements of liquid hydrogen tank such as tank insulation system and tank support system.
Through these three years preliminary study, we have confirmed that the large scale tanker having over 200,000m3 capacity is suitable for our energy demand in 21st century, at the same time we have realized many technical difficulties for establishing the building technology of such large hydrogen tanker.
In this paper, outline of our research
and considerations are briefly reported.
Since hydrogen technology covers very wide range, WE-NET program is divided into 9 subtasks . Among them, subtask 5 is assigned for the research of storage and transportation technology of liquid hydrogen .
Tanker research team of subtask 5 is composed by the following 4 Japanese ship yards, which is chaired by professor Ohtsubo of the University of Tokyo.
Ishikawajima-Harima Heavy Industries Co. Ltd.(IHI)
Kawasaki Heavy Industries Ltd.(KHI)
Mitsubishi Heavy Industries Ltd.(MHI)
Mitsui Engineering and Shipbuilding Co. Ltd. (MES)
These four shipyards are the major builders of large LNG carrier of self-supporting tank system in Japan. IHI is the licenser of SPB LNG CARRIER with prismatic tank system,
and other 3 yards are the licensee of Moss Rosenberg Spherical tank system.
LNG tanker is a ship to carry LNG at boiling point of -163degree , and its essential features exist in its cryogenic cargo containment system(cargo tank, insulation and tank support), secondary barrier concept, hull structural arrangement, boil off gas treatment, etc.
LNG sea transportation started in 1959 by the world first LNG carrier Methane Pioneer with self-supporting prismatic aluminum tank, which was followed by Methane Princess, Methane Progress with the same tank system.
After that , in order to allow the large scale and low cost LNG transportation, membrane system LNG carrier was developed and put into market.
In 1970s, Moss spherical system was developed to meet the IMO TYPE-B concept. Owing to the above developments of LNG carrier technology, LNG transportation was increasing year
by year.
In 1985, SPB system with self- supporting prismatic IMO TYPE-B tank was developed in Japan and 2 large SPB LNG carriers have launched their service in 1993.
Comparing leading two cargo containment systems(Independent type and membrane type), it was suggested that the Independent type with thicker plate should be firstly targeted because it is considered to have less leak possibility of hydrogen at both welding joints and plate ,and to be suitable to increase insulation capability.
| Boiling Point
Specific Gravity Latent Heat Explosion Limit Higher Calorific
Value
| -253.0degree
71.0kg/m3 447.0kj/kg 4-76% 142,060kj/kg 12,770kj/m3 10,086,260kj/m3 | -163.0degree
424kg/m3 510.0kj/kg 5-15% 56,000kj/kg 45,920kj/m3 23,744,000kj/m3 | boiling point boiling point
atmosphere Gas(0degree,1atm) liquid |
Temperature of liquid hydrogen is lower
than LNG by 90degree ,in which circumstance even oxygen and nitrogen
are frozen. And the liquid density is as small as 1/6 of LNG ,
which makes the hull design difficult from the view point of keeping
draft for propeller immersion and maneuverability.
These features seem not to be solved
by the exter polation of LNG technology but will require the technical
break-through as shown in the next section.
The second issue is that liquid density
is extremely light. This is the good feature of hydrogen for
tank strength but makes the hull basic design much more difficult
to provide the adequate draft with small displacement. Consequently
it causes the problem of maneuverability and stability.
Considering that the hydrogen is 10 times
easier to evaporate than LNG by the same heat intrusion, large
tank volume and faster ship speed is preferable for the efficient
and economical transportation. Then twin hull ship becomes one
of the choice for hydrogen tanker.
As to the tank materials, stainless steel
or aluminum alloy used in LNG tank are basically applicable because
of its good resistance to the brittle fracture even in -253degree.
But in the future stage, detailed investigation and experiments
will be indispensable with regard to the fatigue and fracture
strength at -253degree.
Taking the above as our common understandings, we had conducted the conceptual design of hydrogen tanker in the second year.
1)Capacity of cargo tank
When a 1,000,000KW class power plant
consumes 1,200ton of liquid hydrogen per day, the required tank
capacity is approx.14,000ton including transportation loss which
is equal to 200,000m3/tanker ,assuming that a round voyage is
20 days and 2 ships are utilized to load every 10 days.
2)Number of cargo tanks
Considering the arranging factor to keep
ship balance in voyage, equipping factor for piping, stability
in damaged condition, we applied 4 tanks for spherical system,
and 2 tanks for prismatic system.
3)Endurance and ship speed
6000 nautical miles was set to cover
the almost of potential routes. Consequently ship speed of 20-25kt
was set to allow 6000n.mile per 10 days.
4)Ship type
Considering the required ship speed,
normal mono-hull ship is also applicable. Therefore mono-hull
and twin-hull design are studied .
5)Boil Off rate
We assumed that the hydrogen burning
engine would be applicable in the future and the boil off gas
would be utilized as the fuel of the main engine same as for LNG
ship. Design boil-off rate was set based on the above assumption.
Correlation between boil off rate and
the thickness of polyurethane foam insulation for 200,000m3 tank
is shown inFig.1. Correlation between engine power and required
boil-off rate in case of 100% burning is also indicated, assuming
that global exchange efficiency of hydrogen burning energy into
thrust power is set as 0.32.
Based on the required engine power estimated(Max100,000HP),
design boil-off rate is set as 0.2-0.4%/day taking the normal
burning ratio of 20-40% .
Then required insulation thickness was
assumed to be approx.1.0m for the conceptual design.
Spherical Tank - Mono-Hull and Twin Hull
Prismatic Tank- Mono-Hull and Twin Hull
Twin hull ship design of the spherical tank and the prismatic tank are shown in
Fig.2.
Because the insulation system was not studied in detail at this stage, clearance between tank and hull was set as approx.1.5m to accommodate the 1m thick PUF panel.
Calculated engine power is approx. 80,000HP regardless the tank system. Based on these conceptual designs, followings were confirmed.
1)With regard to the basic design elements
of hydrogen tanker(hull form, powering, general arrangement,
hull structure design etc.), we have confirmed that the conventional
technology for LNG carrier can be used effectively.
2)If the high performance insulation and
support system could be developed, 200,000m3 liquid hydrogen tanker
can be built taking advantage of matured ultra-large ship building
technology. At the same time, we have realized the significance
to develop the effective insulation system for liquid hydrogen.
3)While the tank strength is not so critical
because the liquid density is far smaller than LNG , unified design
philosophy and criteria based on the risk analysis for hydrogen
leak , accidental failure, collision and grounding to be established
like a IMO TYPE-B Code for LNG carrier.
4)For the more realistic study of the
hydrogen tanker, investigation of loading and unloading operation
including dome and piping design is indispensable because the
evaporation loss in such operation can be significant.
Based on the conceptual design of hydrogen tanker in the second year, following fundamental study was focused
in the third year.
1)Conventional PUF panel system
In the independent tank design of LNG
carrier, polyurethane foam having around 0.2m -0.6m thickness
is applied regardless the tank shape considering its good and
stable insulating performance.
Thermal conductivity of polyurethane foam is shown in Fig. 4.
As described in the previous chapter, approx.1m thick PUF panel could theoretically provide the target boil off rate of 0.2-0.4%/day for hydrogen tank.
But once tank is cooled down to -253degree,
not only the gas in the cell of PUF but even air or nitrogen gas
in the hold space is frozen and could possibly destroy the PUF
panel. In addition, the convection of gas in the gap between
the adjacent panels could degrade the insulation performance.
Therefore in the hydrogen tank design,
hold space shall be vacuumed to some level if PUF panel is applied.
Idea plan of PUF panel and hold vacuum
system is shown in Fig.5.
Based on a heat calculation, required
panel thickness is 400-500mm including vacuum effect. Required
vacuum level is set as 10-4torr which is assumed
to eliminate the effect of convection .
In this system, it is to be solved how
to make and maintain such a large hold space in vacuum condition
. In addition ,deterioration of vacuum by the gas in the cell
of PUF is to be considered.
Tentative answer is that vacuum pump
provides 10-2torr, then it will be depressurized
gradually to the level of 10-4torr by the effect of
cryogenic pump.
This can be one of the advantage of this
system together with its low material cost that residual insulating
capability by PUF itself prevents the sudden temperature increase
and consequent bursting evaporation of hydrogen in tank in the
case of accidental hold vacuum failure.
2)Vacuum panel system
Various type of vacuum insulation panel
have been developed for cryogenic use. Idea plan of the application
of typical panel is shown in Fig. 6.
One is composed by the light core material
covered by the continuous membrane sheet and inside is kept vacuum.
The other type is the multi-layer of thin foil covered by surface
sheet and inside is also kept vacuum.
These panels reportedly provide the good
insulation performance by the unit structure. And they don't
require the vacuumed hold space theoretically.
But considering the application to large
scale actual tanker, many problems are left to be solved .
One is the convection problem in the
gap of each panel, which is similar to PUF panel. And the other
is the heat transfer problem through the metallic covering skin.
These effects are difficult to calculate quantitatively but shall
be adequately evaluated for the actual application. Further,
the fact that even one panel vacuum failure causes the serious
decrease of global insulation performance is to be carefully investigated
because this type of panel has less residual insulating capability
without vacuum inside.
3) Vacuum and super insulation
Idea plan in case of super insulation
is shown in Fig.7. Based on the preliminary heat calculation,
target boil-off rate can be obtained by approx. 30 layers of foil.
This system may also requires some back
up insulation considering the accidental failure of vacuum condition.
2)Prismatic Tank
Prismatic tank system allows the free
contraction of tank regardless the extent of shrinkage thanks
to its support arrangement , which is shown in Fig.9. Tank vertical
load is supported by the horizontally slidable supporting blocks
on the deck. Tank lateral movement is supported by chocks (key
and key way guide) arranged in the center line and midtank to
form the anchor point at tank center. This arrangement permit
free contraction of hydrogen tank without causing any thermal
stress. Heat ingress can be minimized in this system,because
no metalic connection is provided between hull and tank.
Outline of the preliminary study of large
scale hydrogen tanker conducted in WE-NET program was reported.
While we have to say few concrete progress is available at this
moment, some results or considerations are summarized as follows.
1) In order to meet the demand of hydrogen energy network oriented by WE-NET program , large scale sea transportation of liquid hydrogen by tanker is necessary.
Based on this requirement, conceptual
design of 200,000m3 liquid hydrogen tanker is carried out introducing
the LNG ship technology.
2)Independent tank system for LNG ship(spherical
and prismatic) are basically applicable to the liquid hydrogen
tank.
3) Twin hull ship is suitable to accommodate
such very light cargo while keeping draft, stability and high
speed performance.
4)Insulation system is the most essential
issue for hydrogen tanker because even the nitrogen gas or air
is frozen at hydrogen temperature. In addition, prevention of
the deterioration of insulation performance due to the heat convection
between each panel shall be the important problem to be carefully
investigated.
5)While preliminary study of the insulation system has just started, following combinations can be the design alternatives and require further detailed investigations.
a)PUF Panel in Vacuumed or Non-Vcuumed Hold Space
b)Vacuum Panel Insulation in Vacuumed or Non-Vacuumed Hold Space
c)Super Insulation in Vacuumed Hold Space
It is suggested that, in any selection,
insulation system shall be provided with the essential redundancy
to prevent the accidental temperature increase and consequent
bursting evaporation of hydrogen in tank.
The authors would like to express our gratitude to Professor Ohtsubo of the University of Tokyo for his supports and valuable comments on our research.
We also would like to express our hearty
appreciation to Engineering Advancement Association of Japan for
the promotion and coordination of this research program.
1) G. Giacomazzi: Maritime Hydrogen Transportation
, Symposium-Exhibition "HydrogenWithin
a Clean and Renewable Energy System"
2)Engineering Advancement Association
of Japan:"Developement of Liquid
Hydrogen Tanker", 1994 (NEDO-WE-NET-9352)
3)Engineering Advancement Association
of Japan:"Developement of Liquid
Hydrogen Tanker", 1995 (NEDO-WE-NET-9452)