What Is Hydrogen Energy?

Hydrogen appears mainly in the form of a compound state on the earth. It is the most widely distributed substance in the universe. It constitutes 75% of the mass of the universe and is a secondary energy source. In the 21st century, hydrogen energy may become a pivotal energy source on the world energy stage. Hydrogen production, storage, transportation, and application technology will also become the focus of much attention in the 21st century. Hydrogen has the characteristics of high calorific value, which is 3 times that of gasoline, 3.9 times that of alcohol, and 4.5 times that of coke. The product of hydrogen combustion is water, the cleanest energy source in the world. Rich resources and sustainable development.

Secondary energy is connected

Hydrogen is at the top of the periodic table. Its atomic number is 1, and it is

Hydrogen energy is regarded as the clean energy with the greatest development potential in the 21st century. Human beings have been interested in the application of hydrogen energy 200 years ago. Since the 1970s, many countries and regions in the world have conducted extensive research on hydrogen energy.

As early as 1970,

(1) Rely on hydrogen energy

Famous Russian Scholar in 1869

The storage of hydrogen is a vital technology, which has become the bottleneck for the large-scale utilization of hydrogen energy. The problem of hydrogen storage involves all aspects of hydrogen production, transportation, and final application. The problem of hydrogen storage is not resolved, and the application of hydrogen energy is difficult to promote. Hydrogen is a gas, and its transportation and storage is more difficult than solid coal and liquid petroleum. Generally speaking, hydrogen can be stored in the form of gas, liquid, compound, etc. The main hydrogen storage methods include high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, and hydrogen storage material hydrogen storage.

High-pressure gaseous hydrogen storage is the most commonly used hydrogen storage method, and it is also the most mature hydrogen storage technology. After being compressed, the hydrogen is stored as a gas in a cylinder. The more widely used is a hydrogen storage steel cylinder with a filling pressure of 15.2 MPa. It is a widely used, simple and convenient way to store hydrogen. It has low cost, fast filling and deflation, and can be carried out at normal temperature. However, its biggest weakness is that the hydrogen storage density per unit mass is only about 1% (mass fraction), which cannot meet the requirements of higher applications. Therefore, it is necessary to improve the hydrogen storage pressure of the container through the improvement of materials and structure under the premise of meeting safety to increase the hydrogen storage density, and at the same time reduce the cost of hydrogen storage to meet commercial applications.

Low-temperature liquid hydrogen storage means that at 101kPa, hydrogen is frozen to -253 ° C or lower to become liquid hydrogen. Liquefied hydrogen has the characteristics of high storage efficiency, large energy density (12 ~ 34MJ / kg), and high cost. The liquefaction of hydrogen requires a lot of energy. Theoretically, the liquefaction of hydrogen consumes 28.9kJ / mol of energy. The energy consumed in the actual process is about 2.5 times the theoretical value. The energy consumption per kilogram of liquid hydrogen is above 11.8MJ. Because the temperature difference between the liquefaction temperature and room temperature is 200 In addition, the latent heat of evaporation of liquid hydrogen is small, so the vaporization of liquid hydrogen caused by the intruding heat infiltrating from the container cannot be ignored. The surface area of the tank is proportional to the second power of the radius, and the volume of liquid hydrogen is proportional to the third power of the radius. Therefore, the ratio of liquid hydrogenation in large tanks caused by permeated heat is smaller than in small tanks. Therefore, the applicable conditions of liquid hydrogen storage are long storage time, large amount of gas, and low electricity price. ^[3]

The transportation of hydrogen energy mainly includes the transportation of compressed hydrogen, the transportation of liquid hydrogen, the transportation using hydrogen storage medium, the transportation using pipelines and the transportation of manufacturing materials. Compressed hydrogen transportation is the transportation of compressed hydrogen gas into high-pressure gas, which is suitable for the occasion of transporting to the off-site hydrogen production type hydrogenation station. The characteristics of this method are that no phase change occurs during transportation, storage and consumption, and the energy loss is small, but the amount of one transmission is relatively small, so it is suitable for occasions with short distances and small transportation amounts. For small-scale applications such as laboratory use, hydrogen cylinders can be used to transport compressed hydrogen, and large-scale transport methods are required for hydrogenation stations. To this end, tractors have been developed that reproduce large pressure vessels. For tractor transport, what is important is the amount that can be transported at one time, but the size of tractors traveling on ordinary roads is subject to road traffic laws, especially the quality and size control. The steel container is too heavy to increase the loading capacity, and efforts are being made to reduce weight and pressure to increase the hydrogen loading capacity.

The principle of transporting liquid hydrogen is similar to that of compressed hydrogen. The main difference is that liquid hydrogen is stored in the tank, which requires higher thermal insulation performance. Because the liquefaction efficiency during the production of liquid hydrogen is low, the energy efficiency of the overall transportation is reduced. In addition, when transferring liquid hydrogen from a liquid hydrogen tank to a hydrogen storage tank of a hydrogenation station, the evaporation loss when the piping is cooled to the temperature of the liquid hydrogen cannot be ignored. In addition, it is also important to prevent the incorporation of substances that may accumulate in the liquid hydrogen tank, such as water vapor, nitrogen, and oxygen. It can be seen that when the scale of transportation is large, it is beneficial to improve energy efficiency and reduce transportation costs.

Transport by using a hydrogen storage medium is a method of using hydrogen storage technology to absorb hydrogen to a carrier for transportation. However, the lower hydrogen storage mass percentages of the above-mentioned several hydrogen storage carriers mean that the total mass of this method is greater when the same mass of hydrogen is transported. It can be known that in order to reduce transportation costs during transportation, quality is more important than volume, so this is the main disadvantage of this method. Taking organic hydride as an example, this method is introduced. Under certain conditions, hydrogen is reacted with cyclohexane to generate liquid benzene, and then the benzene is stored in an oil tank, and then the benzene is transported to the destination by a tank truck, and the benzene is dehydrogenated and separated by a certain chemical reaction Get hydrogen.

Pipeline transportation will be a very advantageous method both in terms of cost and energy consumption. Pipeline transportation of hydrogen has been put into practical use in large industrial complexes. New combinations that take advantage of pipeline characteristics are being studied. For example, the use of existing city gas pipelines to transport a mixture of natural gas and hydrogen, and the idea of extracting and purifying hydrogen at a hydrogen station as needed are being explored. If the pressure of the pipeline itself is increased, no compressor is needed in the hydrogenation station. Because the storage and transportation of hydrogen has more or less technical problems or economic problems, the hydrogen production raw materials can be directly transported to the hydrogenation station, and then the hydrogen is produced and used or stored directly. Common raw materials include various hydrocarbons, methanol, etc. The transportation technology of these raw materials is mature and the cost is low. However, if the scale of the hydrogen refueling station is required to be large, it will have better benefits. ^[2]