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One challenge in handling, transporting and storing hydrogen is its particle size. Because it is the lightest element known, its energy density per unit volume is very low. For the process to be effective, hydrogen needs to be compressed to high values, reaching 200-350 bar for hydrogen for transport and 700 bar for refuelling hydrogen cars.
Because of its properties, particularly the fact that it volatilises very quickly, the first attempts to use it began in the 19th century. The use of hydrogen in industry and transport was investigated - particularly as a power source for the early internal combustion engines. It was also used to launch balloons and other aircraft. Later, it was mainly used in the production of fertilisers, which enabled a rapid change in food production, and from the mid-20th century onwards, hydrogen was used in petroleum refining for hydrogenation.
Hydrogen can be burned directly and used in hydrogen cells.
It is increasingly being used in energy system balancing - surplus energy from RES that is not being used can be used to extract hydrogen through electrolysis. The ease with which hydrogen is stored and transported (in compressed form) makes it a gas that can be used as an 'energy store'. In this form, it can be stored in salt caverns or tanks, similar to those used to transport CNG.
In industrial processes - in refineries, in the metallurgical and fertilizer industries, it is used as an energy carrier, as it is characterized by high flexibility and can be easily transformed into electricity and vice versa - electricity can be used to produce hydrogen (e.g. in the process of electrolysis), which makes it possible to create closed energy cycles. Companies are already appearing that are equipped with an electrolyser integrated with a hydrogen turbine that produces both electricity and heat. The electrolyser enables surplus renewable energy to be converted into hydrogen, which can then be used to produce electricity again and feed it back into the electricity grid.
The annual use of hydrogen worldwide is approximately 70 million tonnes, mainly in transport, power generation, heating and industry. The main processes in which hydrogen is used are oil refining and ammonia production in the fertiliser industry. In industry hydrogen is mainly used in mixtures with other gases. Annual world production of hydrogen is estimated at about 120 million tonnes, of which about 60-70% is produced in dedicated installations, and about 30% in mixtures with other gases.
The demand for and possibilities of using hydrogen are growing dynamically due to its versatility. Increasing emphasis is being placed on obtaining hydrogen from electrolysis, which uses energy from renewable sources.
At the recent European Council summit, the heads of government of the European Union member states adopted a new CO2 reduction target for the European Union for 2030. It was decided that this target will be at least 55% of the 1990 level.
This approach is appropriate not only for EU countries, but also for the USA, which is adjusting its approach to the Paris agreements. The incoming Biden administration has made it clear that it wants to "make the United States the world leader in clean energy". The president has an ambitious plan, the highlights of which include an economy-wide target of zero emissions by 2050, investment ($400bn) in clean energy and innovation over 10 years and the creation of a new research agency focused on climate technologies. Fossil fuels, which have been used until now, are increasingly losing their raison d'être in favour of RES. Global companies are starting to reject carbon-intensive investments and banks are not serving customers who do not declare clean investments. The European Investment Bank, in line with its new policy, will stop lending to fossil fuel projects within two years and will align all financing decisions with the Paris Climate Agreement.
Hence the growing popularity of hydrogen, which can be obtained from various sources, some of which are zero-emission. The European Commission paid close attention to this source in July of this year. In its strategy, the Commission announced a preference for the development of green hydrogen and allocated the most funds to this. To date, hydrogen has been used in the petrochemical, fertiliser, metallurgical, cement and, in small quantities, in the food industry. However, it is now becoming increasingly important in the energy sector. And it is best - according to the EU and environmental organisations - if it is green, obtained in the process of electrolysis, i.e. from zero-emission sources. This produces the most desirable, high-purity, so-called "pentavalent" hydrogen (99.999), incomparably more expensive than the "blue" hydrogen obtained from natural gas or even the grey hydrogen produced from our coke. However, the one from coke oven gas emits lethal amounts of carbon dioxide and has little to do with purity. It is therefore intended that grey hydrogen will be replaced by green hydrogen produced on a massive scale from renewable raw materials and energies. Purple hydrogen, i.e. obtained by electrolysis from nuclear energy, is not ruled out either.
Various technologies are available worldwide for obtaining hydrogen, including electrochemical, chemical and biological methods. The most popular method besides electrolysis (electrochemical method) is steam reforming. In other words, high-temperature heating of e.g. crude oil under increased pressure to obtain hydrocarbons. The reaction takes place in the presence of a metallic catalyst, the steam reacts with methane to form synthesis gas. The same applies to the gasification of coal or coke or biomass. Reforming is classified as a chemical technology.
Another chemical method is pyrolysis. This is the decomposition of molecules of a chemical compound at elevated temperatures without the presence of oxygen or another oxidising agent. Typically, the pyrolysis process breaks down complex chemical compounds into compounds of lower molecular weight. Both organic materials (e.g. coal, biomass, waste) and inorganic materials (ceramic raw materials) are subjected to pyrolysis. On an industrial scale, the pyrolysis process of organic materials aims to convert raw materials (coal, biomass) into useful forms of energy, to recycle raw materials (waste polymers) and to produce intermediate products which are raw materials for further use. Thermochemical processing of organic raw materials by pyrolysis is one of the oldest industrial thermal processes known to man.
Biological methods include, for example, bacterial anaerobic fermentations and photo-fermentations. Hydrogen can be produced by a wide variety of microorganisms as a by-product of photosynthesis.
photosynthesis process. One example of such a microorganism is the alga Chlamydomonas reinhardtii, which produces hydrogen through the action of an enzyme when sulphate is removed from the medium. Photo-fermentation, on the other hand, is a process that uses bacteria that require simple organic compounds in addition to light energy to produce hydrogen. Ensuring optimal conditions for the growth of microorganisms, using photobioreactors, is a key part of the production process.
Unfortunately, grey is currently the predominant colour in our climate. And we are not just talking about hydrogen, but smog, weather conditions and pandemic moods.