Oil and natural gas, two natural hydrocarbon energy sources, are non-renewable, and will eventually be exhausted with the increasing consumption of fossil fuels. Therefore, it is urgent to find a new energy source that is independent of fossil fuels and rich in reserves. hydrogen energy
It is this kind of energy, the research of hydrogen energy also caters to the increasingly strict environmental protection policies of industrialized countries, so the research of hydrogen energy in various countries is becoming more and more active. The atomic number of hydrogen is 1, which is gaseous at normal temperature and pressure, and can be changed into liquid at ultra-low temperature and high pressure. As an energy source,
Hydrogen has the following characteristics:
1) Hydrogen accounts for 75% of the mass of the universe and has a large storage capacity.
2) Hydrogen has a high calorific value, which is three times that of gasoline.
3) Hydrogen has good combustibility and quick ignition, and is combustible in the range of 3%-97%.
4) Hydrogen has good recyclability, and the water generated by combustion reaction can be used to prepare hydrogen for recycling.
5) Hydrogen has many uses, which can generate heat energy, can be used in fuel cells, and can also be converted into solid hydrogen as a structural material. Dr. Eknomidis, a famous American oil expert, predicted that the energy that will dominate the future world will be hydrogen energy.
2 Main application fields of hydrogen energy
2. 1 sec aerospace
As early as the M War, hydrogen was used as a liquid propellant for the A-2 rocket. 1970 the take-off rocket used by the Apollo spacecraft in the United States also uses liquid hydrogen as fuel. At present, scientists are studying a "solid hydrogen" spacecraft. Solid hydrogen is not only used as the structural material of spacecraft, but also as the power fuel of spacecraft. During the flight, all the non-important components on the spacecraft can be consumed as energy, and the spacecraft can fly for a longer time.
2.2 Traffic
The research on hydrogen as power fuel in supersonic aircraft and long-range intercontinental passenger aircraft has been carried out for many years, and it has now entered the prototype and flight test stage. According to the forecast of Airbus Europe, by 2004, the aircraft produced in Europe will use liquid hydrogen as fuel. German Daimler-Benz Aerospace Company and Russian Aerospace Company started the experiment from 1996, and their progress confirmed that the safety of using liquid hydrogen in jet aircraft equipped with twin engines is sufficient. The United States, Germany, France and other countries use hydrogenated metal to store hydrogen, and Japan uses liquid hydrogen as fuel to assemble fuel cell demonstration vehicles, which have been tested on millions of kilometers of roads, with good economy, adaptability and safety. The United States and Canada plan to use locomotives fueled by liquid hydrogen and liquid oxygen on large railways from western Canada to eastern Canada.
2.3: Civil use
In addition to the automobile industry, fuel cell power generation systems are also widely used in civil fields. Hydrogen power generation, hydrogen medium energy storage and transmission, hydrogen air conditioning, hydrogen refrigerator, etc. Some have been realized, some are being developed and some are still being explored. At present, the development of fuel cell power generation system is also in full swing: small power station system with PEMFC as energy conversion device and large power station with SOFC as the main part are under development. 2.4. Other fuel cell systems based on hydrogen energy are not only used for automobile and civil power generation, but also for military applications. Germany and the United States have developed nuclear submarines powered by PEMFC. This type of submarine has the advantages of strong endurance, good concealment and no noise, and is favored by all countries.
3 Main problems of hydrogen energy application
3. 1: Preparation of Hydrogen
Whether hydrogen can be widely used is based on the hydrogen production process. At present, the main hydrogen production processes mainly include:
1) At present, hydrogen production by electrolysis of water from fossil fuels, nuclear energy, solar energy, hydro energy, wind energy and tidal energy is the main research direction, and the research on hydrogen production by solar energy is the most promising.
2) The method of thermochemical cycle decomposition of water to produce hydrogen is to add intermediates into the water reaction system, and finally decompose water into hydrogen and oxygen after different reaction stages, and the intermediates are not consumed;
3) Photochemical hydrogen production is to promote hydrolysis to produce hydrogen under the action of photocatalyst;
4) Hydrogen production from fossil fuels is a method of extracting hydrogen from minerals by chemical methods, such as coking and gasification of coal.
5) Hydrogen production from biomass is a method of extracting hydrogen from organisms through cracking or gasification;
6) Recover the by-product hydrogen from various chemical processes, such as chlor-alkali industry and metallurgical industry. Hydrogen production methods such as electrolytic water hydrogen production and biomass hydrogen production have now formed a scale. Among them, the low-cost electrolysis of water to produce hydrogen will still be the main method for large-scale preparation of hydrogen energy in the future, and the power consumption still needs to be reduced in the current application.
3.2: Hydrogen Transportation
There are roughly five kinds of hydrogen storage methods in industrial practical applications, namely:
(1) atmospheric storage, such as wet gas holder and underground storage;
(2) High pressure vessels, such as steel pressure vessels and steel gas cylinders;
(3) Liquid hydrogen storage: If liquid hydrogen storage is used, liquid hydrogen must be prepared first. Generally, three liquefaction cycles can be used to produce liquid hydrogen, among which the cycle with expander has the highest efficiency and is widely used in large hydrogen liquefaction plants. Throttle circulation efficiency is not high, but the process is simple and reliable, and it is widely used in small hydrogen liquefaction plants. Helium refrigeration hydrogen liquefaction cycle eliminates the danger of high-pressure hydrogen and runs safely and reliably. However, helium refrigeration system is not widely used in hydrogen liquefaction because of its complicated equipment.
(4) Metal hydride: hydrogen is stored when it is cooled and pressurized in a container made of hydrogen storage alloy; Heating the storage system or reducing its internal pressure will release hydrogen.
At present, the metal hydride alloy system mainly includes: l) LaNi _ 5 alloy; 2)MnNi5 series alloys, etc. 3)TiMn series alloys; 4)TiMn series alloy (ABZ); 5) magnesium alloy; 6) Nano-carbon, etc. (5) In addition to pipeline transportation, high-pressure vessels and liquid hydrogen tankers are also commonly used modes of hydrogen transportation in industry at present.
3.3 Development of Metal Hydride Hydrogen Storage Device
After the problems of preparation, storage and transportation of hydrogen are solved, the next research is the development of hydride hydrogen storage devices, which mainly include the following two categories:
Fixed hydrogen storage device
Stationary hydrogen storage can be used in a variety of situations, and its capacity is mainly large and medium. Medium-sized fixed hydrogen storage device based on TiFe0.9Mn0. 1 alloy developed by the United States; Japan has developed a laminated fixing device with MmNi4.5Mn0.5 hydrogen storage alloy. The storage tank developed by Germany with TiMn2 multi-element alloy is composed of 32 independent storage tanks in parallel, which is the largest storage tank in the world at present. China Zhejiang University developed two kinds of fixing devices with (MmCaCu)(NiA 1)5 pressurized hydrogen storage alloy and MINi4. 5 Mn0。 5 alloy.
3.3.2 Mobile hydrogen storage device
The mobile hydrogen storage device can not only carry and transport hydrogen, but also store hydrogen fuel in the fuel cell. As a mobile device, it needs to be stored and transported, so it requires light weight and large hydrogen storage capacity. Among them, the metal hydride hydrogen storage device does not need additional equipment (such as cracking purification system), which has high safety and is suitable for vehicle and boat applications; With normal temperature alloy, the mass storage density is basically the same as that of 15 M Pa high pressure steel cylinder, but the volume can be much smaller. For example, the hybrid propulsion system of the German Navy is in a submarine, where oxygen is stored in the form of liquid oxygen and hydrogen is stored in TIFe alloy.
3.4 The current work direction is based on the existing technology of PEMFC. Besides continuing to strengthen the research on key technologies of high-power PEMFC, we should also pay attention to the development of key technologies of PEMFC system engineering and system technology integration, which is the key to the practical process of PEMFC power generation system. In the aviation field, it is necessary to solve the problems of storage and production cost of hydrogen energy. At present, a research trend is to design the traditional wing into a new structure that can accommodate more liquid hydrogen. The problems in the automobile field are mainly two obstacles: low hydrogen storage density and high cost; the continuous driving range of cars powered by hydrogen storage alloys is limited, while cars powered by liquid hydrogen are limited mainly because of the high cost of liquid hydrogen supply system. Hydrogen has been widely used in aerospace power, such as large-capacity nickel-hydrogen batteries, but the following key problems remain to be solved in the large-scale application of hydrogen energy: l) cheap hydrogen production technology; 2) Safe and reliable hydrogen storage and transportation methods.
4 Future characteristics of hydrogen economy and society
With the progress of science and technology and the comprehensive progress of hydrogen energy system technology, the application scope of hydrogen energy will continue to expand, and hydrogen energy will penetrate into all aspects of human activities, so we can outline the general picture of hydrogen energy economy and society in the future:
L) Fossil energy (oil, coal, natural gas) is stored as chemical raw materials;
2) Build small power stations at home, cancel long-distance high-voltage transmission, and send hydrogen to thousands of households through the pipe network.
3) Various types of air-hydrogen fuel cells have become widely used power generation tools.
4) The power of internal combustion engine is prohibited, and cars, trains and airplanes are replaced by fuel cells, thus eliminating all potential energy pollution hazards and noise sources of diesel locomotives.
5) Every city and family has a perfect circulation system for energy supply and recovery.
6) Cancel thermal power generation. After the normal power supply of nuclear power plants, hydropower plants, wind power plants and tidal power plants is completed, the remaining electricity will be used as reserve energy for hydrogen production by electrolysis of water.
Five Countermeasures for Developing Hydrogen Energy in China
The research and application of hydrogen energy is an irreversible trend in history. At present, governments all over the world have done a lot of research on this. China has also invested a lot of manpower, material resources and financial resources in this respect, and achieved certain results. However, we should also see the gap between us and industrialized countries, and formulate corresponding hydrogen energy development strategies according to China's national conditions. Personally, I think it should include the following points:
(1) Hydrogen production by electrolysis of water is an important way to obtain hydrogen source. At present, due to the large power consumption and high electricity price, the popularization and application are limited. It is also an important subject to develop new hydrogen production process by electrolysis of water and reduce energy consumption.
(2) Pay attention to various new hydrogen production methods, such as hydrogen production by HZS, hydrogen production by biomass, hydrogen production by thermochemical water decomposition and the recovery of by-product hydrogen in chemical products;
(3) There are many researches on hydrogen storage materials in China, but there are few practical reports at present, so it is particularly important to carry out the transformation of scientific and technological achievements and the research on new hydrogen storage and transmission devices;
(4) The main application field of hydrogen energy in the future is fuel cell, and the domestic research in this field has already had a certain foundation, but it mainly focuses on the research of fuel cell components, and there are few reports on system integration. At the same time, due to factors such as capital and technology, there is still a big gap between China and foreign countries, so we should increase investment and catch up.
(5) The most promising way to develop hydrogen energy is to combine it with solar energy, so the research on solar cell systems and materials should also attract enough attention. Conclusion In terms of environmental protection and market demand, cleanliness and cost are two key parameters. There is no market for cleanliness. Therefore, reducing the utilization cost of hydrogen energy has become a top priority at present, and all industrialized countries attach great importance to this research. Among them, the US government has decided to allocate US$ 654.38+0.7 billion to develop hydrogen energy in the next five years, and strive to reduce the daily oil consumption by 65.438+065.438+000 by 2040. Among the 40 important automobile manufacturers in the world, 25 have decided to adopt hydrogen energy to adapt to the increasingly strict environmental protection policy. Therefore, although there are many difficulties at present, it is foreseeable that in the near future, the utilization of hydrogen energy will definitely enter all aspects of our lives.