Application of LOHC technology in stationary large-scale hydrogen storageIssuing time:2024-06-20 17:04 Fixed large-scale hydrogen storage has gradually emerged along with the development of the green hydrogen industry, aiming to address the mismatch in time between green hydrogen production and consumption. Green hydrogen is typically produced from renewable energy sources such as wind and solar power, which can result in significant fluctuations in hydrogen production every day, hour, or even minute. However, the use of hydrogen, such as in ammonia synthesis, methanol synthesis, hydrogenation processes (aviation fuel hydrogenation, hydrogen metallurgy), etc., generally cannot match this level of flexibility in consumption. Therefore, large-scale hydrogen storage is needed as a hub to connect green hydrogen production and users such as chemical plants. The challenges of large-scale hydrogen storage Currently, the scale of hydrogen storage, a key hub in integrated green hydrogen chemical projects, is growing increasingly larger. It is understood that the Kuqa green hydrogen project has a hydrogen storage capacity of 2.1 million standard cubic meters, the Yili green electricity to hydrogen project stores 4 million standard cubic meters, the Alashan aviation fuel project stores 7.8 million standard cubic meters, and the Xing'an League green methanol project has reached a hydrogen storage volume of 118 tons, close to 13 million standard cubic meters. From a regulatory perspective, hydrogen storage exceeding 5 tons is classified as a significant hazardous source due to its flammability and explosibility. In November 2022, the Ministry of Housing and Urban-Rural Development of China released a draft of the GB 50177-2005 "Hydrogen Station Design Standard (Draft for Comments)," which only specifies requirements for fire protection distances for storage capacities below 5 million standard cubic meters, without providing any regulatory guidance for capacities exceeding this threshold.  In traditional hydrogen storage routes, gas sphere tanks are characterized by relatively mature construction and management of individual tanks, simple structure, fast hydrogen charging and discharging speeds, and flexible control. However, due to the extremely low density of hydrogen, a large number of hydrogen storage sphere tanks and a significant amount of land are required to provide a large storage capacity. For example, to store 500,000 cubic meters of hydrogen, using 1.5MPa 2000m3 sphere tanks and considering effective storage capacity, 25 sets would be needed, occupying nearly 50 acres of land. The storage of hydrogen in gaseous sphere tanks is not inherently safe. There are extremely high requirements for quality and management systems during the design, manufacturing, and operation processes, and accidents or human errors can also lead to safety risks. Regarding accidents involving hydrogen storage tanks, there was a case of a 1,000 cubic meter hydrogen tank leakage and fire at the Yantai Chemical General Plant, which was caused by tank corrosion and puncture, as well as improper operations by staff. When the scale of hydrogen storage expands to dozens of large spherical tank clusters, the risk may significantly increase. It is precisely because of this that some projects encounter regulatory conflicts and resistance from government authorities during the design and approval process when using large-scale hydrogen sphere tank clusters. LOHC technology can better address the related challenges The characteristic of LOHC technology is that it converts hydrogen into an intrinsically safe hydrogen storage liquid. Nitrogen-containing heterocyclic hydrogen storage liquids can be stably stored at normal temperature and pressure, with stable chemical properties, non-flammable, non-explosive, non-toxic, and excellent safety performance. After testing by authoritative third-party certification institutions, the fire safety rating of the hydrogen storage liquid is class B3, with better safety performance than fuel oil (diesel). Since this technology essentially converts hydrogen into nitrogen-containing heterocyclic substances for storage, it is not subject to the GB 50177 hydrogen storage limit of 30,000 cubic meters/500,000 cubic meters; the hydrogen storage liquid is also not classified as a hazardous chemical, and large-scale hydrogen storage will not be identified as a major hazard source.  The mass density of LOHC is greater than 5%, and the volumetric density is significantly better than that of gaseous hydrogen storage. In large-scale hydrogen storage scenarios, compared to medium and low-pressure gaseous storage spheres, the land use for LOHC is only 10-20% of that required. As shown in the figure below, in terms of safety assessments for specific projects, the advantages of using LOHC are evident. Regarding government approvals, especially for projects located near industrial parks and densely populated areas, the difficulty of obtaining government approval will be significantly reduced. 
LOHC systems are more economical in large-capacity hydrogen storage scenarios The one-time investment in an LOHC system has the following characteristics: it becomes more economical with larger hydrogen storage capacity. The core reason lies in the fact that, within the LOHC system, although the hydrogen storage and release equipment account for part of the initial investment, the costs related to storage capacity mainly come from the storage liquid and the storage tank, and the investment costs of these two components are much lower than those of other hydrogen storage routes. Therefore, as the amount of stored hydrogen increases, the cost increase of the LOHC system is relatively mild, providing significant advantages in total investment costs for large-scale hydrogen storage.  Comparison of costs between LOHC systems and gaseous sphere tank hydrogen storage: has advantages at large scale Based on this characteristic, and also due to not being subject to hydrogen storage regulations, the project can design the hydrogen storage scale to the most ideal range when using the LOHC system. Increasing the hydrogen storage capacity can extend the operating hours of downstream chemical systems, reduce the frequency of load adjustments, and significantly decrease the use of expensive grid electricity, thereby reducing the unit cost of the final product and eliminating the adverse impact of additional carbon emissions from grid electricity.  Off-grid electricity usage costs corresponding to different hydrogen storage capacities in a project In addition, the LOHC system can bring additional economic benefits to the project. During certain months, the total production of green hydrogen significantly exceeds the demand from downstream chemical industries (including maintenance months), and at this time, LOHC can be used to store this excess hydrogen for long-term periods. This stored hydrogen can be used for supply in other months, and it can also be transported over long distances using ordinary tank trucks to sell to customers within hundreds of kilometers, thereby generating additional economic benefits. Currently, Hywin's first LOHC facility has successfully operated in a location in Northeast China since October 2023, and it has passed on-site evaluation and outcome assessment by authoritative third-party institutions. It is believed that with further development of the industry, LOHC technology will bring value to more projects. |
