Hydrogen provides and excellent decarbonization opportunity for several industries like steel and cement production, power generation, heating, refining amongst others with more and more industries starting to use hydrogen for its environmentally friendly nature.
This has developed a need for safe storage and transportation of this important material.
The common practice in the past was producing hydrogen wherever it was needed. However, as the use of hydrogen changes and expands so does the need for transportation.
While determining the best method for storage and transportation of hydrogen, safety and economics must be considered. A major challenge that needs to be overcome is the extreme pressure and temperature needed for storage and transportation.
Storage mechanisms for hydrogen in both gas and liquid form
1) High pressure gas cylinders
This is the most common hydrogen gas storage technique. It is done at high pressures (250 to 700 bar). This can be used for on-site storage as well as transportation of hydrogen using trucks. The permeability of the material selected for these tanks should be considered before being used.
2) Super-insulated low pressure liquid cryogenic storage vessels.
This is for liquid forms of hydrogen at 1 atm and - 252°C to prevent boil-off and product loss inside insulated tanks. This however has a large energy cost but allows for efficient transportation of large quantities of hydrogen over large distances including via ships.
3) Naturally occurring or specially engineered underground bulk storage.
4) Alternative molecules.
Hydrogen can also be stored by converting it into ammonia, methanol or ethanol in order to use existing storage systems. These chemicals do not require high pressure or low temperature storage. Thus helps reduce the cost to obtain special storage and transportation vessels. Liquid organic hydrogen carriers (LOHCs) which are compounds that can absorb and release hydrogen through reactions can also be used for effective storage and transportation. LOHC technology enables easy fueling of the fuel cell electric vehicles.
5) It can also be stored by adsorption on the surface of solids and absorption within solids.
Challenges during the handling of Hydrogen
1) Detecting leaks and managing safety concerns.
Safety is always of paramount importance for any chemical process for the protection of employees and plant infrastructure. Even though hydrogen is non-toxic, it is extremely flammable. It has a combustible range between 4 - 74% in air as compared to natural gas which has a range between 5 - 20%.
A safer environment can be ensured by conducting hydrogen leak tests and flames detection.
2) Minimize product loss
It is vital to measure and verify the amount of hydrogen as it moves through the supply chain through pipelines, loading and offloading sites and storage units. This allows minimization of theft and detection leaks to prevent loss of product and ensure safety of all around the supply chain.
3) Ensure hydrogen purity
The end use of hydrogen determines the purity required. The quality of hydrogen for uses like heavy duty transit is different from the requirements for blending into natural gas.
Thus it is vital to understand the purity of the hydrogen being produced, moved and used in order to ensure safety and meeting the customers requirements.
This can be mitigated by use of gas analyzers to check the purity of hydrogen through every step of storage and transport.
Transportation of Hydrogen
Factors like distance, geography, cost, energy loss and end use are key factors that determine which transportation method is efficient in hydrogen movement to the point of use. These methods include:
1) Pipelines
They offer a way to deliver large volumes of hydrogen. Pipes used to distribute natural gas can also be used to transport hydrogen blended with natural gas.
2) Trucks
Hydrogen tankers can be used to transport compressed hydrogen in high pressure tube trailers or liquefied hydrogen in a cryogenic storage unit. This method allows for quick deployment and endless flexibility.
3) Ships
This allows for long distance transportation using the oceans or seas. Cargo vessels can be retrofitted to allow safe shipping. These ships look similar to Liquefied Natural Gas (LNG) tankers. The difference with LNG is the construction materials and instruments used for process optimization and safety monitoring.
4) Alternative molecules.
Similar to using alternative molecules for hydrogen storage, hydrogen can be converted into an alternative molecules like methanol, ethanol or ammonia or LOHC to allow easy and safe transportation by allowing ambient temperatures and pressures for handling. In this method, the hydrogen should be reconverted back into hydrogen at the consumption point.
Hydrogen leaks
In order to ensure safety, minimize product loss and ensure compliance with regulations, quick leak detection in pipelines and storage units is extremely important and can be very difficult since hydrogen flames are invisible to the naked eye and conventional flame detection is risky for workers.
Multi-spectrum Infrared Hydrogen Flame Detectors are effective in detecting any hydrogen leaks even from a long distance and provides fast response and with reduced false alarms.
