The extensive use of fossil fuels such as coal and oil has caused serious pollution to the global environment and even threatened the survival of mankind.
Threats. At the same time, the reserves of fossil fuels are limited and will be exhausted with over-exploitation. Therefore, efforts are being made to reduce the current situation.
Although regulated energy sources (such as coal and oil) will cause environmental pollution, the development and application of clean energy is the general trend. Hydrogen energy is one of the ideal clean energy sources, which has attracted people's attention. Hydrogen is not only a clean energy, but also an excellent energy carrier with storable characteristics. Energy storage is a way to make rational use of energy. Peak-valley difference between solar energy and wind energy dispersed intermittent power generation device and power grid load or
A lot of cheap electric energy can be converted into hydrogen energy for storage and reuse when needed. This energy storage method is flexible and decentralized. Hydrogen also has potential.
Transmission characteristics, such as converting electric energy into hydrogen energy under certain conditions, have certain advantages over electric power transmission. Scientists believe that hydrogen can be used for two purposes.
In the eleventh century, the energy stage will become the decisive energy.
L, the way of hydrogen production
1. 1 hydrogen production by electrolysis of water.
Hydrogen production by electrolysis of water is one of the widely used and mature methods at present. The process of hydrogen production from water is the combustion of hydrogen and oxygen to produce water.
Inverse process, so as long as a certain form of energy is provided, water can be decomposed. The efficiency of providing electric energy to decompose water to produce hydrogen is generally in
75-85%, its process is simple and pollution-free, but it consumes a lot of electricity, so its application is limited. Hydrogen production from electrolyzed water with peak-valley difference in power grid also has characteristics as a means of energy storage. China is rich in hydropower resources, and hydrogen production by hydropower generation and electrolysis of water has its development prospects. Solar energy is inexhaustible, and the method of producing hydrogen by photoelectricity is called solar hydrogen energy system, and experimental research has been carried out abroad. With the improvement of energy conversion efficiency, the reduction of cost and the extension of service life of solar cells, the prospect of hydrogen production is immeasurable. At the same time, solar energy, wind energy and ocean energy can also generate hydrogen through electricity, and use hydrogen as an intermediate energy carrier to adjust and store the converted energy, which makes the energy supply to users more flexible and convenient. The surplus electric energy of the power supply system can also be used to electrolyze water to generate hydrogen, so as to achieve the purpose of energy storage. There are hundreds of water electrolysis hydrogen production devices of various scales in China, but all of them are small electrolysis hydrogen production equipment, and their purpose is to produce hydrogen as raw materials rather than energy. With the gradual expansion of the application of hydrogen energy, the method of hydrogen production by electrolysis of water will be developed.
1.2 Hydrogen production from fossil fuels
Hydrogen production from coal, oil and natural gas is the main method of hydrogen production at present. The technology of this method is mature in China, and industrial production equipment has been built.
(1) Hydrogen production from coal
In China's energy structure, coal will be the main energy source for a long time to come. How to improve the utilization efficiency of coal
Reducing environmental pollution is a subject that needs continuous research, and converting coal into hydrogen is one of its ways.
There are two main methods to produce hydrogen-containing gas from coal: one is coking (or high temperature dry distillation) of coal, and the other is gasification of coal. Coking means that coal is made into coke at 90- 1000℃ under the condition of air isolation, and the by-product is coke oven gas. The composition of coke oven gas contains 55-60% (by volume) hydrogen, 23-27% methane and 6-8% carbon monoxide. 300-350m3 gas can be obtained per ton of coal, which can be used as city gas.
It is also a raw material for producing hydrogen. Coal gasification means that coal reacts with gasifying agent at high temperature, normal pressure or pressure and is converted into gas products. gasify
The agent is steam or oxygen (air), and the gas product contains hydrogen and other components, and its content varies with different gasification methods. There are a large number of small and medium-sized hydrogen plants in China, all of which use coal as raw material, and the hydrogen-containing gas produced after gasification is used as raw material for synthetic ammonia. This is a hydrogen source acquisition method with China characteristics. Using OGI fixed bed gasifier, water gas can be produced by intermittent operation. The device has less investment and simple operation. Its gas products are mainly composed of hydrogen and carbon monoxide, of which hydrogen can reach more than 60%, and pure hydrogen can be produced after conversion. Using coal gasification to produce hydrogen, the equipment cost accounts for the main part of the investment. Underground coal gasification method has been paid attention to in recent decades. Underground gasification technology includes coal.
High resource utilization rate, reducing or avoiding damage to the surface environment. China University of Mining and Technology has developed and improved "long passage and big interruption".
A new process of producing water gas by two-stage underground coal gasification on the ground, with hydrogen content above 50%. It has been put into industrial trial operation in Tangshan Liu Zhuang, with a daily output of 50,000 m3 of water gas. If it is purified by conversion and pressure swing adsorption, it can produce cheap hydrogen, which has certain development prospects in China. China has a good foundation in mastering the technology of hydrogen production from coal, especially a large number of hydrogen production devices in small and medium-sized synthetic ammonia plants are spread all over the country, creating conditions for providing hydrogen sources in the future. China's self-developed process of underground gasification of coal to produce water gas to obtain cheap hydrogen has been realized.
The phased results have development prospects and deserve attention.
(2) Hydrogen production from natural gas or light oil.
In this method, in the presence of a catalyst, hydrogen is generated by reaction and conversion with steam. The following reactions mainly occur:
CH4+H2O→CO+H2
Carbon monoxide +H2O→ carbon dioxide+Hz
CnH2h+2+Nh2O→nCO+(Zh+l)HZ
The reaction is carried out at 800-820℃. As can be seen from the above reaction, part of hydrogen comes from water vapor. The gas group obtained by this method
In China, the hydrogen content can reach 74% (volume ratio), and its production cost mainly depends on the price of raw materials. In China, the price of light oil is high and the cost of gas production is high, so its application is limited. Most large-scale synthetic ammonia and methanol plants use natural gas as raw material to catalyze steam conversion to produce hydrogen. China has done a lot of fruitful research work in this field and built a large number of industrial production devices. In China, an intermittent steam reforming process of natural gas was developed to produce raw materials for small ammonia plants. The method does not need to adopt a high-temperature alloy converter, and the equipment investment cost is low. The process of hydrogen production from petroleum and natural gas is very mature, but it is mainly used to prepare chemical raw materials due to the limitation of raw materials.
Materials.
(3) Using heavy oil as raw material, hydrogen is prepared by partial oxidation.
Heavy oil raw materials include atmospheric and vacuum residue and fuel oil after deep processing of petroleum. Heavy oil reacts with water vapor and oxygen to produce hydrogen.
Gas products. Partial heavy oil combustion provides heat and a certain reaction temperature for the endothermic reaction of conversion. The cost of the hydrogen product produced by this method
The cost of raw materials accounts for about one third, while the price of heavy oil is low, so people pay attention to it. China has built a large-scale hydrogen production plant by partial oxidation of heavy oil to produce hydrogen raw materials.
1.3 Hydrogen production from biomass
Biomass is rich in resources and is an important renewable energy. Biomass can produce hydrogen through gasification and microorganism.
(1) Hydrogen production from biomass gasification
Biomass raw materials such as firewood, wheat straw and rice straw. Is pressed and shaped, and then gasified or cracked in a gasifier (or cracking furnace) to produce hydrogen-containing fuel. China has made some achievements in the research of biomass gasification technology. In foreign countries, due to the improvement of conversion technology, biomass gasification has been able to produce water gas on a large scale, and its hydrogen content has also been greatly improved.
(2) Hydrogen production by microorganisms
Microbial hydrogen production technology has also attracted people's attention. Hydrogen can be produced by enzymatic reaction of microorganisms at normal temperature and pressure. biomass
Hydrogen-producing microorganisms mainly include chemotactic microorganisms and photosynthetic microorganisms. Belonging to chemotrophic microorganisms are various fermentation types.
Some strict anaerobic bacteria and facultative anaerobic bacteria ferment microorganisms, and the substrates that initially release hydrogen are various carbohydrates, protein, etc. Currently available
Patent of hydrogen production by carbohydrate fermentation, and the generated hydrogen is used as energy for power generation. Photosynthetic microorganisms such as microalgae and
The process of hydrogen production by photosynthetic bacteria is related to photosynthesis and is called photosynthetic hydrogen production.
1.4 Hydrogen production from other hydrogen-producing substances
Hydrogen production from hydrogen sulfide has been studied abroad. China is rich in H25 resources. For example, the natural gas extracted from Zhaolanzhuang oil and gas field in Hebei Province contains more than 90% H, with a reserve of tens of millions of tons, which is a valuable resource. There are many ways to produce hydrogen from hydrogen sulfide. In the 1990s, China carried out various researches, and all kinds of research results will provide valuable resources and clean energy for the future.
Lay the foundation of chemical raw materials.
1.5 recovery of by-product hydrogen in various chemical processes
There are a large number of chemical processes, such as electrolysis of salt to make alkali, fermentation to make wine, synthetic ammonia and fertilizer industry, petroleum refining industry.
By-product hydrogen, if appropriate measures are taken to separate and recover hydrogen, hundreds of millions of cubic meters of hydrogen can be obtained every year. This is unacceptable.
Neglected resources should be recycled. At present, the recovery of by-product hydrogen in chemical plants can provide a cheaper hydrogen source, which should be
Pay attention.
2. Decomposition and transportation of hydrogen
Hydrogen exists in gaseous form under general conditions, which brings great difficulties to storage and transportation. There are three kinds of hydrogen storage.
Methods: High pressure gas storage; Low temperature liquid hydrogen storage: metal hydride storage.
2.l gas storage
Gaseous hydrogen can be stored in underground warehouses or steel cylinders. In order to reduce the storage volume, hydrogen must be compressed first, which requires more compression work. Generally, the hydrogen storage weight of a high-pressure steel cylinder with an inflation pressure of 20mp only accounts for1.6%; Hydrogen storage weight of titanium bottle for space
Only 5%. In order to improve the hydrogen storage capacity, a microporous hydrogen storage device, namely microsphere bed, is being studied. The microsphere system is thin.
The wall (1- 10um) is filled with micropores (l0- 10um), and hydrogen is stored in the micropores. Microspheres can be made of plastic, glass, ceramics or metal.
2.2, low temperature liquid hydrogen storage
Hydrogen is cooled to -253℃ to become a liquid, and then stored in a high vacuum heat insulation container. Liquid hydrogen storage process firstly
When used in aerospace, its storage cost is expensive and its safety technology is complex. At present, the high thermal insulation hydrogen storage container is the focus of research, and now a kind of thermal insulation container filled with hollow microspheres has been developed. The thermal conductivity of silica microspheres is very small and the particles are very fine.
Convective heat transfer between particles can be completely suppressed, and doping partially aluminized microspheres (generally about 3%-5%) into non-aluminized microspheres can effectively
Cut off radiation heat transfer. This new type of heat preservation container does not need to be evacuated, and its heat preservation effect is far better than that of ordinary high vacuum heat preservation containers.
As an ideal liquid hydrogen storage tank, NASA has widely adopted this new type of hydrogen storage container.
2.3, metal hydride storage
There will be a reversible reaction between hydrogen and hydrogenated metal. When metal hydride is externally heated, it decomposes into hydrogenated metal and.
Release hydrogen. On the contrary, when hydrogen and hydrogenated metal form hydride, hydrogen is stored in it in the form of solid combination to store the hydrogenated metal of hydrogen.
Most of them are alloys composed of many elements. At present, there are many kinds of hydrogen storage alloys that have been successfully studied in the world, which can be roughly divided into four categories: one is
Rare earth osmium nickel, etc. , each kilogram of osmium nickel alloy can store 153L hydrogen. Second, the iron-titanium system is the most widely used hydrogen storage material at present, and its hydrogen storage capacity
It is four times that of the former, and the price is low and the activity is high. It can also release hydrogen at normal temperature and pressure, which brings great convenience to use. The third is magnesium, which is the metal element with the largest hydrogen absorption, but it needs to release hydrogen at 287℃, and the hydrogen absorption is very slow, so its use is limited. Fourthly, vanadium, niobium, zirconium and other multi-element systems are rare and precious metals, so the chemical and physical properties of hydrogenated metals, including equilibrium pressure-temperature curve, reaction generation and conversion rate, chemical and mechanical stability, are further studied. , is still a problem worthy of attention in the development and utilization of hydrogen energy. There are two kinds of metal hydride hydrogen storage devices, fixed and mobile, which can be used as the supply source of hydrogen fuel and hydrogen materials, absorb waste heat and store solar energy, and can also be used as hydrogen pump or hydrogen compressor.
2.4, hydrogen transportation
Although hydrogen has good transportability, both gaseous hydrogen and liquid hydrogen exist in the process of use, which cannot be ignored.
Special problems, first of all, because hydrogen is particularly light, compared with other fuels, the volume of unit energy in transportation and use is particularly large, even liquid hydrogen. Secondly, hydrogen is particularly easy to leak. The driving test of cars fueled with hydrogen proves that even the vacuum sealed hydrogen fuel tank has a leakage rate of 2% every 24 hours, while gasoline generally leaks 1% a month. Therefore, special sealing measures should be taken for hydrogen storage containers, hydrogen pipelines, joints and valves. Thirdly, the temperature of liquid hydrogen is extremely low, and severe frostbite will occur as long as a little drops on the skin, so special attention should be paid to taking various safety measures during transportation and use.
3. Utilization of hydrogen energy
As early as the Second World War, hydrogen was used as a liquid propellant for the A-2 rocket engine. 1960, liquid hydrogen was first used as space power fuel. The take-off rocket used by the Apollo spacecraft launched by the United States in 1970 also used liquid hydrogen as fuel. Now hydrogen is a common fuel in rocket field. For the modern space shuttle, it is more important to reduce the self-weight of fuel and increase the payload. The energy density of hydrogen is very high, which is three times that of ordinary gasoline, which means that the self-weight of fuel can be reduced by two-thirds, which is undoubtedly extremely beneficial to the space shuttle. Nowadays, the space shuttle uses hydrogen as the propellant of the engine, and pure oxygen is divided into oxidant. Liquid hydrogen is packed in an external propellant barrel, which requires 1450m3 for each launch and weighs about 100t.
Now scientists are studying a spaceship with "solid hydrogen". Solid hydrogen is used as structural material and spacecraft.
Power fuel. During the flight, all non-important components on the spacecraft can be converted into energy and "consumed". So that the spacecraft in the universe
You can fly longer.
Hydrogen is an important energy carrier in 2 1 century. Fuel cells with hydrogen as fuel combine hydrogen and oxygen to generate water during combustion, which is a clean power generation technology and conforms to the global environmental protection trend.
At present, in order to develop environmentally-friendly vehicles, world-famous automobile manufacturers have stepped up the updating of traditional vehicle fuels and decided to adopt hydrogen energy, which has set off a craze for developing hydrogen energy vehicles. Experiments show that cars using hydrogen fuel cells only emit carbon from traditional internal combustion engines.
30%, the air pollution caused is only 5% of the internal combustion engine. The American Automobile Manufacturers Association predicts that by 2002, the United States will produce about 500,000 vehicles-
654.38+00,000 hydrogen cars.
In addition to cars, from 200 years, the United States, Europe and Japan will promote hydrogen fuel on airplanes. According to the European Airbus Aircraft Company
It is predicted that by 2002 at the latest, aircraft produced in Europe can use liquid hydrogen as fuel on a large scale. Because the working temperature of liquid hydrogen is -253℃, it is necessary to improve the current aircraft fuel system. Experiments conducted by Daimler-Benz Airlines of Germany and Aeroflot of Russia from 1996 have proved that the safety of using liquid hydrogen on a jet plane equipped with twin engines is sufficient. In addition, compared with gasoline, hydrogen provides three times as much energy as gasoline, but even liquid hydrogen needs four times as much volume as gasoline, so the task facing aircraft designers is to design the traditional wing into a new structure that can accommodate more liquid hydrogen.
The research on the development and application of hydrogen energy in China is still in its infancy, but with the progress of technology, the requirements of the environment for clean energy are constantly improving.
The high utilization rate of hydrogen energy is the inevitable trend of development, and the demand for hydrogen source supply is bound to increase day by day. In the process of development, we should combine our national conditions.
Actively carry out research on expanding hydrogen sources and reducing prices in order to achieve better economic and social benefits.
4. Concluding remarks
In the near future, the "hydrogen economy society" will save fossil fuel resources such as oil and coal, basically cancel the internal combustion engine power system, realize pollution-free emission, alleviate the greenhouse effect, make the environment cleaner and the air fresher. At the same time, the utilization of hydrogen energy will also drive a series of emerging manufacturing industries such as renewable energy equipment: electrolytic water equipment, fuel cells, hydrogen storage devices, and promote economic development in an all-round way. The development of nuclear fusion power station, solar power station, wind power station and tidal power station can be further combined with hydrogen energy technology to raise the energy utilization level of mankind to a new level.
In a word, the research and development prospect of hydrogen energy is broad. With the gradual maturity and expansion of the application field of hydrogen energy, it will inevitably promote hydrogen production.
Legal research and development. Cheap hydrogen supply suitable for China's national conditions will further promote the application of hydrogen energy and benefit mankind for improving the environment.
People make contributions.