Hydrogen energy is pollution-free and has a high calorific value, which makes it clean energy with great development potential. The transportation of hydrogen energy is a key part of its utilization.
In principle, hydrogen will exist in liquid form at a certain low temperature. Therefore, cryogenic technology of liquid hydrogen storage can be used. Hydrogen is first compressed to produce a mixed liquid, and the liquid is separated to obtain high purity liquid hydrogen.
1. The background of liquid hydrogen storage
Liquid hydrogen storage is now ready for large-scale deployment. Similar to the hydrogen liquefaction industry, it also needs to be scaled up to meet the needs of global trade. The commercial-scale project is expected to use 50,000 cubic meters of tanks for hydrogen energy storage.
In addition, there is currently no ship transportation, which is limited to the project's outlook. This area is still about a decade away from large-scale deployment. Gasification of liquid hydrogen can be easily achieved by heating seawater or air. From a technical point of view, liquid hydrogen storage has a high volumetric energy density. Therefore, it is particularly suitable for transportation situations with limited storage space.
If only considered in terms of mass and volume, liquid hydrogen storage is an extremely ideal way to store hydrogen. However, from a practical application point of view, liquid hydrogen storage still has many limitations.
For example, the cost and efficiency of hydrogen liquefaction at scale remain unclear, and hydrogen-powered vessels are not yet operational. Hydrogen liquefaction requires ultra-low temperatures, which require higher costs and energy consumption.
2. Current status of hydrogen liquefaction technology
Hydrogen liquefaction was first realized in 1898, and has since been used in the semiconductor industry, as fuel for military vehicles, and in other fields. In general, liquid hydrogen is transported by train freight cars, which means that most hydrogen liquefaction plants currently in operation are small in scale.
Due to the limitations of current technology, hydrogen liquefaction equipment has its own defined maximum scale, which limits the scale of the hydrogen liquefaction industry. In view of the above problems, there are also corresponding solutions.
Further engineering and de-risking are required before it can be used in the hydrogen liquefaction industry. A reference industry for liquid hydrogen is liquefied natural gas. If hydrogen liquefaction is to take its place in the global hydrogen trade, it is possible to reduce costs by exploring and increasing the size of average facilities around the world.
3. Liquid hydrogen storage industry
Hydrogen liquefaction facilities Several companies have announced the construction of several small hydrogen liquefaction units, but there are currently no facilities for large-scale global trade.
Origin Energy is building a 300 MW project. The facility is expected to be operational by 2025 and is currently in the design and front-end engineering phases. The U.S. project has entered the design phase.
The project is being run by Australia and is scheduled to start operations in 2025. The initial design liquid hydrogen production capacity is 90 t/d, and sufficient space is available to expand the capacity to double the initial capacity.
4. Analysis of liquid hydrogen storage cost
① Hydrogen liquefaction cost
● Liquefaction process
The hydrogen liquefaction temperature is -253°C, which requires multiple condensation cycles and consumes a lot of energy. In practice, energy consumption is much higher than the ideal estimate.
● Energy consumption
The energy consumption in the liquefaction process mainly comes from heat exchanger, hydrogen conversion, purification, nitrogen liquefaction and adiabatic treatment processes. The specific energy loss is also related to the specific process configuration. The simplest process can be summarized as cooling and expansion.
Depending on the pressure applied during the cooling process, the coolant used, the turbine or throttle valve used for expansion, and the type of cycle, the liquefaction process is also varied. After considering various factors, the actual energy consumption of hydrogen liquefaction varies with the size of the facility.
The largest energy losses occur in internal hydrogen heat exchangers, compressors and refrigeration circulation heat exchangers. Based on this, the proposed cycle efficiency improvement scheme includes:
- Cyclic efficiency improvement scheme
- Energy is recovered from the shaft of a hydrogen turbine
- Use an improved refrigerant blending cycle
- Replace the throttle valve with an expander
- Reduces pressure drop in injectors that throttle pre-cooled hydrogen
● Cost of efficiency
In most cases, cost and efficiency must be considered. There are two main factors to consider: the economic impact of increasing the size of the facility, and the impact of the facility on cost.
As can be seen from the above, the increase in the size of liquefaction facilities is one of the necessary conditions for their use in global trade. Therefore, it is possible to reduce costs simply by increasing the scale. But this path is limited by the device: The device is too big.
The additional costs associated with transportation and assembly may outweigh the cost reductions caused by the scale-up, which may be due to the limitations of the size of road transport. For example, in the LNG industry, this obstacle can be overcome by using ship transportation or pre-packaged-on-site assembly to enable larger-scale equipment construction.
In addition to the scale of the facility described above, a variety of issues will increase the cost of a hydrogen liquefied fuel facility. These factors include inadequate infrastructure and materials in remote areas.
Organic liquid hydrogen storage technology can be transported using traditional facilities. Unique safety and ease of transport compared to other technologies. However, this technology still has many technical problems, and it will be very promising in the future. Liquid hydrogen storage is mainly used in the aerospace field, and there is also hope for the future layout of home energy storage.
② Cost of liquid hydrogen storage and transportation
● Ship transportation
If some hydrogen is considered for hull driving, the available prime mover includes internal combustion engines and fuel cells. Fuel cells have low levels of noise, vibration and pollution. For solid oxide fuel cells operating at high temperatures, they can also be combined with steam turbines to increase overall system efficiency by up to 80%.
However, it is mostly used in small boats and has high requirements for gas purity. Some fuel cells take a long time to start, and their tolerance to load changes is also poor. At present, the top 10 hydrogen fuel cell companies have begun to distribute the transportation through liquid hydrogen storage.
Internal combustion engines are more efficient in larger sizes, have a high average power density, are low-cost, have a long life, and can withstand large load changes. However, noise and vibration problems are more serious, and overall efficiency is relatively low.
5. Development trend of liquid hydrogen storage
The liquid hydrogen storage can learn from the LNG industry's experience and get the experience.
● Development path
LNG is the closest commercial process to hydrogen liquefaction. From the perspective of the industrial development path of liquefied natural gas, the first commercial-scale liquefied natural gas plant in the United States has been completed.
And by the end of 2020, the global LNG trade volume will account for 13% of global natural gas production. The size of the project is increasing at a similar rate, and as the scale changes, its cost gradually decreases. From the early 1970s to the early 2000s, the cost of LNG was almost halved. Ten years later, the cost has more than quadrupled.
The reasons for this include the increased cost of energy supply and limited infrastructure in remote areas following the construction of the facility. At the same time, drawing on the LNG industry, the factors that need to be considered in the future hydrogen liquefaction industry will also include supporting equipment, related buildings and labor costs.
● Shipping process
The initial scale of LNG transport is about 10 times the current market average. For reference, the average delivery time for LNG carriers is 2.5 to 4 years, which is a point to consider when planning global trading projects for liquid hydrogen. For the circulation of liquid hydrogen, the development of new facilities is necessary.
Equipment from existing LNG plants can be reused for hydrogen liquefaction to reduce costs. Other facilities, including refuelling facilities, transportation facilities, etc., must be built from the ground up. There are a number of factors to consider when determining the exact location of the filling facility.
● Regasification process
LNG has a higher temperature than liquid hydrogen, so equipment and strategies suitable for use in the LNG industry are also suitable for liquid hydrogen. An alternative application is to use the cooling capacity of liquid hydrogen for liquefaction of natural gas, or vice versa.
6. ConclusionLiquid hydrogen storage has many benefits, and from its industry background, the problem that needs to be solved is that the cost is too high. The production method can refer to natural gas technology, storage and transportation, etc., and a lot of testing and application is needed to find the best solution. However, most of the applications are in the demonstration project stage and have not been promoted on a large scale.