5.2 Development of Liquid Hydrogen Transportation Tanker

The New Sunshine Program envisages hydrogen as a possible energy source in the 21st Century and liquid hydrogen (LH2) is considered to be a source of hydrogen energy. In this context, WE-NET research is in progress with the technical examination by experts of all aspects regarding the use of LH2 as an energy source for the purpose of establishing a basis to judge the feasibility of LH2 application.

The LH2 Transport Tanker Development Group in WE-NET Subtask 5, has been working on the development of a LH2 tanker for the efficient and safe mass transportation of LH2 from the production site to areas of consumption. The research activities in the last five years are listed below.

(1) FY 1993

  • Survey on data regarding the physical values (properties) of LH2 and various materials
  • Survey on current technologies used for LNG vessels and hydrogen tanks on the ground
  • Examination of the technical issues involved in the development of a LH2 transport tanker

(2) FY 1994

  • Examination of the required specifications for the concept design
  • Examination of element technologies regarding the hull, tank, tank support, heat insulation of the tank and dome, etc. of a ship
  • Conceptual design of a 200,000 m3 LH2 tanker

(3) FY 1995

  • Examination of the required performance of the heat insulation structure and candidate heat insulation structures
  • Examination of each candidate heat insulation structure

(4) FY 1996

  • Concrete examination of the technological problems regarding each heat insulation structure
  • Proposal of the required tests to solve the technological problems

(5) FY 1997

  • Specimen design for the heat insulation element test for each heat insulation system
  • Examination of pending problems of the heat insulation structure (system) and solutions based on the specimen design
  • Examination of the items to be tested in the Phase II period

5.2.1 R&D Goals

Goals of studies in the Phase I are that to make a conceptual design of large-scale liquid hydrogen tanker ships, and to select technical items to be developed necessary for constructing it.

The research objectives in FY 1998 were to conduct the following work based on the achievements of the previous research:

  1. Evaluate the coefficient of thermal conductivity of PUF under the LH2 temperature by means of the heat insulation element test.
  2. Review the data and know-how obtained by the PUF panel test in order to contribute to the specimen design for the coming insulation tests.
  3. Make the specimen design of super-insulation (SI) test piece and vacuum panel test piece for the insulation test in the coming year.

5.2.2 Results in FY 1998

5.2.2.1 PUF Panel Test as Heat Insulation Element

(1) Specimen for The Heat Insulation Test
The research in FY 1997 concluded that the aspect ratio (2D/d) between the diameter (2D) and thickness (d) would have to be at least 6 in order to eliminate the error caused by heat invasion from the side face within an allowable value. Based on this consideration, a PUF panel with a diameter of 1,180 mm and a thickness of 200 mm was finally fabricated. In addition, a 5 mm thick copper plate was fixed to the high temperature face of the panel using an adhesive and a 1.5:150 taper was given to the peripheral of the low temperature face in order to prevent a gap due to thermal deformation between the low temperature face of the PUF panel and the LH2 measuring tank.

(2) Measuring of Data
A total of 20 thermocouples were installed to measure the temperature, consisting of 9 points on the low temperature face, 9 points on the high temperature face and 2 points on the side face respectively. Data on the degree of vacuum within the testing apparatus, quantity of evaporated gas from the LH2 measuring tank and degree of contact between the specimen and testing apparatus were also gathered.

(3) Results
Under a thermally equilibrium state, the following data were obtained:

Temperature at low temperature face of PUF:60 K
Temperature at ordinary temperature face of PUF:271 K
Degree of vacuum in testing apparatus:6 x 10-6 Torr
Flow rate of evaporated gas from LH2 measuring tank:10 NL/min
Coefficient of thermal conductivity:0.012 W/mK

(4) Conclusions

  1. While a coefficient of thermal conductivity of 0.023 W/mK was used for the thermal performance computation up to FY 1997, the latest test results halve the value to 0.012 W/mK, which will contribute to the revised conceptual design of the LH2 tanker with reduced insulation thickness.

  2. The heat insulation test apparatus could provide low enough degree of vacuum of 10-4 Torr by applying vacuum pumps ( rotary pump + turbo pump ) , and a cryo-pump effect of the LH2 tank was also confirmed.

  3. The test has been originally planed to measure a thermal coefficient at 20K~270K, but the data were obtained at 60K~271K. However, an insulator around the tanks in the actual tanker will contact to the tank not perfectly, therefore, the test might simulate the insulation close to that in the actual tanker.

5.2.2.2 Examination of Specimen Design

(1) Vacuum Panel
Two types of vacuum panel, i.e. with seams and seamless, were proposed. In FY 1998, a preliminary test using a small vacuum panel was conducted to obtain the necessary data to determine the specifications of the specimen for the planned heat insulation element test scheduled in FY 1999 and thereafter. The specifications of the small vacuum panel used in the latest test are as follows:

Diameter : 280 mm
Thickness : 50 mm
Facing : Stainless steel (SUS304) with 0.3 mm in thickness
Core materials : Ceramics, silica beads or polyurethane foam

  1. Aging Test on Coefficient of Thermal Conductivity
    Many of the thermal conductivity were measured during 203 days of leaving the panels in the ambient condition. The coefficient of thermal conductivity slightly increased in the case of the ceramic cored panel but showed mostly no change in the case of the other panels. In terms of thermal coefficient, polyurethane foams cored panel recorded the lowest among the panels with different cores.

  2. Thermal Shock Test
    Liquid nitrogen was used to rapidly cool the vacuum panel to chech whether or not harmful deformation or damage occurred to the vacuum panel. The test results confirmed that no harmful deformation or damage occurred to any of the panels.

  3. Thermal Deformation Test
    Liquid nitrogen was used as the cooling agent to quantitatively measure the deformation (warping) of the vacuum panel. The test results showed that silica beads panel recorded the smallest deformation.

  4. Evacuation Time for Panel Preparation
    Evacuation time was measured to obtain an enough degree of vacuum in the panel, and the necessary time to prepare the actual panels was estimated.

  5. Specification of the Specimen for the Thermal Insulation Test
    Specification of the specimen, which will be prepared in Phase II, was determined as follows:

    Diameter : 1,200mm
    Thickness : 200mm
    Coating : SUS304 with thickness of 0.5mm for the top and
    the bottom and 0.3mm for the side
    Core material : Polyurethane foam

(2) Super Insulation (SI)

  1. Specimen Design
    Performance of super insulation is well known that it is affected keenly by its conditions, that is, degree of vacuum, density of radiation shield layers, connection between shield layers, etc. The thermal insulation test should be conducted in order to obtain data considering those conditions. Specimen design was carried out including the consideration above.

  2. Evaluation on Effect of Degree of Vacuum
    In order to confirm the effect of degree of vacuum in the insulation test, three procedures were proposed and checked preliminarily:
    • Measure the thermal conductivity on the way before reaching the high vacuum while evacuating the apparatus
    • Inject He gas into the apparatus and adjust the degree of vacuum
    • Cover the specimen with other panel and adjust the degree of vacuum inside the cover
    As a result of the preliminary study, it was found that each of those proposed procedures might include problems in accuracy of the data, etc. Further studies are necessary previous to the insulation test including the another procedures.

5.2.2.3 Materials for LH2 Tank

The background of the IGC code used for the design of LNG tankers was investigated, and based on the findings in this investigation, the views of the Tanker Group on the specific properties of materials required for the LH2 tank and required data on materials in the coming years were finalized.

(1) Regulations for LNG Tankers
IGC code internationally regulates performances of liquefied gas carriers based on their cargo and its storage method. Concept of IGC code on independent tank systems as listed below, and membrane tank system was reviewed as listed below.

  1. Independent tank type A
  2. Independent tank type B
  3. Independent tank type C
Design concept of "Leak detection before failure" for the Independent tank system B, which was the base concept for developing the LH2 tanker, was also summarized.

(2) Properties Required for LNG Tank Materials
Material properties required for LNG tankers were summarized. In order to design the Independent tank type A, it is necessary to analyze fatigue fracture, fracture propagation and brittle fracture in the fracture mechanism analysis. The following data are necessary concerning the base materials and their welded part.

  1. Evaluation of the life of fatigue fracture
    - SN curve for base materials and their welded part
  2. Evaluation of the life of fracture propagation
    - Characteristics of fracture propagation properties of base materials and their welded part
For designing LH2 tankers, in addition to the data at LH2 temperature mentioned above, following data are required:
  1. Sensitivity for hydrogen embrittlement
  2. Characteristics on low-temperature embrittlement
  3. Other properties of the material

(3) Examination of Aluminum and Stainless Steel as Tank Mmaterials
Aluminum and stainless steel are the candidate for tank material for LH2 tankers. Further studies on these materials are expected in association with close communication with the Cryogenic Materials Technology Subtask (Subtask 6).

(4) Conclusions

  1. Design and material requirements for LH2 tanker will be conducted under the concept of "Leak detection before failure" based on that for LNG tanker design.

  2. In order to achieve the concept above, it is necessary to obtain various data on materials relating to LH2 technologies.

  3. Required characteristics for the tank materials would temporarily be as same level as those for LNG tankers. If strength, brittleness or other properties of the materials at 20K(LH2 temperature) are found to be different from those at 110K(LNG temperature), both of material improvement and revision of design conditions should be conducted.

  4. Materials for the tank will be aluminum alloy or stainless steel. Selection of the materials will be made after enough data are obtained and evaluated.

5.2.3 Research Plan for FY 1999

One or two test piece(s) of thermal insulation structures out of those designed in this fiscal year will be prepared and measured its thermal conductivity, and checked its insulation performance at 20K.

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