Uses of Hydrogen

Living in a climate conscious society, electric and hydrogen comes to mind especially in the transportation sector whereby other alternatives are scarce and hard to implement. In the same vein, the uses of hydrogen are relatively diverse with it not only being limited to power generation through fuel cells. First thing that comes to mind is production of ammonia through Haber Process which is something we learned in our high school chemistry. Other uses of hydrogen include desulphurisation, hydrogenation to produce value added products as well as being used as rocket fuel in Centaur, Apollo and space shuttle vehicles (Heiney, 2021). Alternatively, hydrogen could be used to produce climate-neutral fuels more commonly known as efuels. Some common examples of these types of fuels are green methanol, green ammonia and synthetic natural gas which are compatible with current generation combustion engines (MAN Energy Solutions, n.d.). It is therefore not a doubt that hydrogen has many applications. The high energy density of hydrogen and wide application in various field makes it very desirable. However, the challenge of hydrogen lies within producing and transporting hydrogen efficiently.

Hydrogen production

In the current state, majority of hydrogen is produced from steam methane reforming which itself is not a climate friendly process as it involves natural gas, steam and heat to produce carbon monoxide and hydrogen. The most critical factor of this process which makes it not ideal for production of hydrogen is not the carbon monoxide itself but that the hydrogen produced from this method would contain less energy than the natural gas used at the start to produce hydrogen. Hence, for hydrogen to be a viable option, the method of producing it needs to be sustainable. This leave us with a few alternatives, a common method of producing green hydrogen is through electrolysis of water. This is a non-spontaneous process meaning energy is required to split water into hydrogen and oxygen. While this would be a clean process if the electricity provided is generated from renewable sources, we would lose quite a lot of energy generated from renewables just to convert it into this form. Another novel alternative currently being explored is photocatalysis whereby light is used to excite semiconductors to generate hydrogen more commonly known as photoelectrochemical cell. This is commonly split into single or dual photoelectrode configurations also known as S2 or D4 approach. Dual photoelectrode would be more efficient in harvesting solar energy due to its broader solar absorption range. However, this technology is still in its infancy and various research and development is required for it to be applicable in the industrial scale. Another alternative approach to this is biomass gasification, this process involves utilizing waste, dehydrating it, and then subjecting it to high temperatures with an oxidizing agent to produce synthetic gas (Ali, 2022). While this process helps to tackle waste as it produces useful products, the energy input to the process is pretty significant due to the high temperatures of 600-1000°C involved in the process. There are of course many other alternative pathways which could produce hydrogen. Methods such as thermolysis, biolysis as well as enzymatic processes are all interesting options which could be explored. Each production method would have its own inherent flaws and issues which needs to be addressed and there is no such thing as a universal solution. The hydrogen production methods need to take into account the resources available on site. However, for hydrogen to be a main stay in the energy chain, the method of producing it has to be clean and we usually refer to this type of hydrogen as green hydrogen. This is essential in reducing carbon footprint or else we would just be replacing one greenhouse gas with another or reducing emissions from consumer end but increasing emissions from producer end which would not make a dent in terms of environment carbon footprint.

MAN turbo tech for hydrogen production (hydrolysis) – On shore

A commercialized hydrogen production system is available from H-TEC SYSTEMS. H-TEC SYSTEMS, being a subsidiary of MAN Energy Solutions offers an innovative way to produce green hydrogen in their portfolio. Their technology is primarily based on proton exchange membrane electrolysis. This process is very similar to electrolysis except that a solid polymer electrolyte is utilized. This in combination with renewable energy and pure water could produce highly pure green hydrogen which could be used directly. The primary advantage of their systems is that their systems are able to operate at varying loads and the nature of PEM electrolysis negates the need for aggressive chemicals or liquid electrolytes (H-TEC SYSTEMS GmbH). Their solutions are also trialled and tested, ready to be deployed. For example, their ME450 Electrolyzer are self-contained in a 40ft container making it easy to transport just like any other shipping containers. With a nominal load of 1MW, the aforementioned system is able to produce around 450kg of hydrogen per day. Besides, they are also modular, allowing for multiple containers to be combined into one big production facility with options for water and hydrogen purification units. The hydrogen produced are of 5.0 grade. The only concern of the system is the water requirement for electrolysis which are TrinkwV 2020 at 260 kg/h (H-TEC SYSTEMS GmbH). This would not be an issue for areas with steady supply of water but would be an area of concern for remote areas whereby supply of clean water is scarce.

Electro chlorination

It is well known that electro chlorination produces hydrogen. Hence, we would like to investigate the potential of harvesting hydrogen from these electro chlorination production sites. In simple terms, electro chlorination is electrolysis using salt water. However, as opposed to hydrogen and water, this process produces sodium hypochlorite, and hydrogen gas. The sodium hypochlorite is commonly used to disinfect water for drinking or for use in swimming pools and is the desired product for this process. This process is widely used in areas all around the world ranging from industrial plants to oil rigs to treat water. Usually, the amount of sodium hypochlorite solution contains the range of 0.7% to 1% chlorine. This value is widely considered to be the optimal value whereby it is not harmful to human beings but strong enough to kill unwanted microorganisms (PRODOSE).

Harvest hydrogen from 4

In industry, hydrogen produced from electro chlorination would be entrained in the seawater. Hydrogen and seawater need to be sent to a disengagement tank whereby the seawater is depressurized, and hydrogen would be released (Mehmet Tontu, 2021). This is the point where hydrogen could potentially be harvested.

Utilities for 4 and 5

In a typical electro chlorination plant, seawater is fed to the electrolyser cell. Power to the electrolyser is provided by the transformer or rectifier. The electrolysed fluid then goes to a disengagement tank where the hydrogen and sodium hypochlorite could separate. Fans are usually integrated to the top of the tank to avoid explosion. The sodium hypochlorite solution is pumped according to requirement or dosage needed using pumps while the hydrogen coupled with air introduced by air blowers is vented. Nitrogen tanks are also integrated to the system to purge all gases when the system malfunctions (Mehmet Tontu, 2021).

Challenges for 4 and 5

Hydrogen has a tendency to explode in the purity range of 4% to 75% (Mehmet Tontu, 2021). Keeping this in mind, the challenge of harvesting hydrogen lies in the process where the disengagement tank is depressurized to allow hydrogen to be released from the salt water. Hence, for the sake of safety, most electro chlorination plants would keep the hydrogen level below 4% (Mehmet Tontu, 2021). This is done by introducing air and utilizing nitrogen to purge the system when malfunction occurs. Ideally for hydrogen to be harvested, the hydrogen produced on site needs to be of high purity as hydrogen itself is hard to transport and store. If the hydrogen produced is less than 4%, the gas transported or stored would consist of mostly air and would not make financial sense. This could only be mitigated if there is a process which could selectively separate hydrogen from the mixture meaning the hydrogen separated is relatively pure (>75% purity). Otherwise, the common concept of purifying components such as distillation which gradually increases the concentration of the desired products would result in catastrophic explosion as it would fall in the combustible mixture range as the product is being concentrated. Hence, operators of these kind of plants would commonly discard the hydrogen due to the difficulty and cost inherent in purifying the hydrogen as well as storing or transporting the hydrogen. Therefore, the economics of scaling up hydrogen harvesting for electro chlorination plants needs to be investigated to determine whether the amount generated is worth the investment required to develop an efficient way of harvesting hydrogen.

References

Ali, O. (2022, May 16). Biomass Gasification and the Future of Hydrogen Fuel. Retrieved from AZoCleantech: https://www.azocleantech.com/article.aspx?ArticleID=1537

Heiney, A. (2021, May 28). Space Applications of Hydrogen and Fuel Cells. Retrieved from National Aeronautics and Space Administration: https://www.nasa.gov/content/space-applications-of-hydrogen-and-fuel-cells

H-TEC SYSTEMS GmbH. (n.d.). Green hydrogen is our element. Retrieved from h-tec.com: https://www.h-tec.com/en/hydrogen/#

H-TEC SYSTEMS GmbH. (n.d.). H-TEC PEM Electrolyzer ME450. Retrieved from H-TEC SYSTEMS: https://www.h-tec.com/en/products/detail/h-tec-pem-electrolyser-me450/me450/

MAN Energy Solutions. (n.d.). Hydrogen. Retrieved from https://www.man-es.com/discover/decarbonization-glossary—man-energy-solutions/hydrogen

McManus, B. (2018, July 27). The Truth about Hydrogen. Retrieved from https://www.youtube.com/watch?v=f7MzFfuNOtY

Mehmet Tontu, M. B. (2021). Thermo-economic analysis of chlor-alkali electrolysis for hydrogen production in the electrochlorination plant: Real case. International Journal of Hydrogen Energy 46, 8391-8400.

PRODOSE. (n.d.). The Electrochlorination Process. Retrieved from https://prodoseltd.com/what-is-the-electrochlorination-process/