Technical Development for Large Storage of Liquid Hydrogen in WE-NET

A.Iwata, S.Kamiya and E.Kawagoe
KAWASAKI HEAVY INDASTRIES.LTD.
118,Futatsuzuka,Noda,Chiba,278 Japan

Abstract

In Japan, International Clean Energy Network Using Hydrogen Conversion System (World Energy NETwork : WE-NET) is a large scale project which will provide a comprehensive solution to the global dilemma of producing and utilizing energy, while simultaneously preserving the environment.
WE-NET project which extends over until 2020, is divided into three phases. In Phase‡T of this project (1993-1996), surveys and elemental research are in progress under nine subtasks. The technical development for large-scale liquid hydrogen storage is included in subtask 5. In this subtask, liquid hydrogen benefiting transport and storage, will be dealed with the alternative energy of Liquid Natural Gas (LNG), and further, it is estimated that the scale of the liquid hydrogen facilities will be fairly larger than existing ones.
In this paper, the survey, basic research and development of elemental technology are described as the interim report of working-group of large-scale liquid hydrogen storage in subtask 5.
Development of the liquid hydrogen storage facilities can be broadly classified into two R&D items ; <1> Design of the total system for the large-scale liquid hydrogen storage and <2> Research of the equipments for the large liquid hydrogen storage. In the item <1>, we investigated the current technologies of similar large cryogenic liquid storage system, existing liquid hydrogen storage system, peripheral technologies for in-ground storage tank and underground bedrock storage tank. As the results of preliminary studies of the large-scale storage system,we made the basic process flow of liquid hydrogen storage plants. In the item <2>, we investigated the material and structure of the thermal insulation for the large liquid hydrogen storage tank. And we conducted the conceptual report of four large liquid hydrogen storage tanks which have different structures of the thermal insulation, and their capacity is the final target capacity, 50,000m³ per unit tank.

‚PDIntroduction

‚QDResults

(2) Research of existing liquid hydrogen storage equipment The existing liquid hydrogen storage equipment utilize the gas pressure feed system for feeding the tank liquid hydrogen from the storage; sop that, the design tank pressure of 0.5 or 0.7 MPaG is adopted in may cases. Plate thickness of this type tank increase, as its capacity is larger. Considering material, processing, and X-rays inspection at the site, the maximum practical plate thickness is 50 mm. Accordingly, the maximum capacity is 16,000 m³, assumed that internal pressure is 0.5 MPaG.

(3) Research of peripheral technologies for in-ground storage tank
The in-ground storage tank features highly earthquake proof design, as well as safety in protecting liquid leakage. The in-ground storage tank is more advantageous for the storage with a large capacity, because of good cryogenic properties as well as security and safety.
The result of the study has revealed that a minimum temperature of -160Ž is assumed for the studied cryogenic properties of reinforced and prestressed concrete and their components, concrete, reinforced bar and prestressed steel are assumed for LNG storage. To have satisfactory performances against possible liquid leakage in the event of earthquake, it is necessary to test cryogenic properties on the -250Ž level for reinforced and prestressed concrete component members.

(4) Study of basic process flow for a large amount of liquid hydrogen storage
To configure the system flow of the liquid hydrogen storage equipment, we estimated the storage plant size and basic process flow. In this study, two types of plants, which are adjacent to the storage plants adjacent to the hydrogen liquefaction plant and the power plant, were studied .
We show the basic process flow and plot-plan of the liquid hydrogen storage plant adjacent to the hydrogen liquefaction plant at Figure-1 and Figure-2.
As the next step, we plan to continue to follow the interface conditions with the progress in other sub-tasks, to develop the basic flow of the storage plant into each unit flow, and to study its detailed specifications.

2.2 Research of the storage equipment
(1) Thermal insulation material and structure
We investigated the similar large cryogenic storage tanks such as LNG storage tanks and so on. The investigation has revealed that the application of the thermal insulation structure for LNG directly to the liquid hydrogen is difficult, and it is important to make efforts on the study and research of the large thermal insulation structure for the liquid hydrogen temperature.
And we have studied the existing liquid hydrogen storage tanks. The result of the study has revealed that the largest capacity of the existing liquid hydrogen storage tank in Japan is 540m³ at the Tanegashima Space Center, outside Japan, 3218m³ at J.F.Kennedy Space Center of NASA, largest tank with perlite vacuum insulation in the world.
As a result, the perlite vacuum insulated storage tank is used for the large capacity because of relatively stable performance and excellent workability,in case of allowing site space. On the other hand, the multilayer vacuum insulated storage tank is used in the smaller storage tank because of its capability of making an effective use of storage tank space and minimizing the thermal insulation and heat capacity. However, the large liquid hydrogen storage system planned in the WE-NET requires development of technologies such as thermal insulation support structure of the internal tank (liquid storage), and so on.

(2) Conceptual report of large storage tank for liquid hydrogen
Based on the provisional interface conditions of liquefaction plant, tanker and power plant, the storage tank specification was set to the followings; storage capacity of the tank 50,000m³, storage pressure 0.02MPaG, and targetted thermal insulation performance 0.1% per day as same as, the same as that of the domestic LNG storage tank. Under above conditions, storage types were classified with major emphasis placed on thermal insulation structure. Thus the conceptual design was worked out, and technological tasks were picked up. The classified insulation types are vacuum insulation using the powder material, using the solid material, and non-vacuum insulation using the powder material, and as tank types are aboveground flat-bottomed tank, spherical tank, and membrane tank.
In the study of these various insulation types, firstly, we studied the parameter of the storage shape which would minimize the heat load, thereby calculating the optimum dimensions. As a example, the aboveground flat-bottomed tank with vacuum insulation using the powder material is shown at Table-2. In order to improve the thermal insulation performance, we devised various methods of using the thermal insulation shield, and made their thermal analysis. We have confirmed that substantial improvement of the performance is possible.
At the non-vacuum insulation type, we could get designed the realizable storage tank from the viewpoint of its strength. However, the insulation thickness had to be made much larger than those of other vacuum insulation methods. And because of non-vacuum insulation, only helium gas can be used as filling gas into the thermal insulation space, in order to ensure that gas contacting with the internal tank can not liquefy at the liquid hydrogen temperature.
The future task is to evaluate the above mentioned thermal insulation methods and to find out the optimum method, considering the storage tank structure.

‚RDConclusion

‚SDLiterature Reference

1) M.Murase, "R&D Plans for WE-NET (World Energy Network)", International Hydrogen and Clean Energy Symposium 1995.
2) K.Fukuda, "Current R&d Activities in WE-NET Project", International Hydrogen and Clean Energy Symposium 1995.