Characteristics of hydrogen:
Hydrogen (hydrogen) is the world'sThe lightest known gas。It has a very small density, only 1 14 times that of air.
Hydrogen is oneReducing agentHydrogen has low reactivity at room temperature, so the reducing effect of hydrogen needs to be carried out under high temperature conditions, and there is a strong oxidant, a catalyst, and a relatively high concentration of hydrogen.
Hydrogen is oneColorless, noneStinksIt is non-toxic, flammable and explosiveEasy to compressGases, and fluorine, chlorine, oxygen, carbon monoxide and air are mixed with the danger of **, among them, the mixture of hydrogen and fluorine can occur spontaneously in low temperature and dark environment**, and when the mixing ratio with chlorine is 1:1, it can also be in light**. Hydrogen is non-toxicIt is physiologically inert to the human body, but if the hydrogen content in the air increases, it will cause hypoxic asphyxia. Hydrogen is a highly flammable gas with a flash point of only 574 and can be burned at a volume fraction of 4% to 75% in the air.
Hydrogen isHighest thermal conductivityThe gas has excellent thermal conductivity of the substance with high thermal conductivity.
Hydrogen embrittlementIn the process of metal solidification, if the hydrogen atoms that are not released in time can penetrate into the metal, they will accumulate near the defect and be converted into atomic hydrogen (H) at room temperature, which will further aggregate to form molecular hydrogen (H2). The accumulation of hydrogen atoms in the metal reduces the stress required for the formation and propagation of cracks in the metal, making the metal more fragile. This effect is usually seen under stress and is known as hydrogen-induced cracking (HIC).
Uses of Hydrogen:
1. Chemical raw materials: hydrogen is a good chemical raw material, the largest consumption of hydrogen is synthetic ammonia, about 60% of the world's hydrogen is used to synthesize ammonia, and China's proportion is even higher. The second is the production of methanol from syngas (H2 CO2). Hydrogen and chlorine can be synthesized to produce hydrochloric acid. [13] In addition to ammonia production and synthesis of hydrochloric acid, hydrogen can also reduce the nitro group of organic matter to an amino group, such as nitrophenyl hydrogenation reduction can produce aniline.
2. Metal smelting: Because hydrogen has good reducing properties and no pollution, hydrogen can replace carbon as a reducing agent for metal smelting and metal welding.
3. Industrial fuel: liquid hydrogen is an excellent rocket fuel, its density is small, flammable, pollution-free, can be used as a propellant for the space shuttle, and the gas company dopes hydrogen to natural gas.
4. Filling gas: hydrogen has a small density, the gas with the lowest density under the same conditions, hydrogen balloons and airships are filled with the low density of hydrogen, but due to the flammability and explosiveness of hydrogen, helium is now mostly used as the filling gas.
5. Petroleum and petrochemical hydrogenation: Hydrogenation also uses the reducibility of hydrogen, and the hydrogenation of oil products in refineries is mainly divided into hydrorefining and hydrocracking. Hydrorefining is mainly to desulfurize, denitrify, deoxygenate, demetallic and olefin aromatic saturation of distillate oil to improve the odor, color and stability of oil, improve the quality of oil, and meet the requirements of environmental protection for the use of oil. Hydrocracking is the hydrogenation conversion of hydrocarbons and non-hydrocarbon compounds under the action of catalysts, and cracking, isomerization and a small amount of cyclization of alkanes and olefins; Polycyclic compounds are finally converted into monocyclic compounds, and the process uses different raw materials, adopts different process flows and operating conditions, and flexibly produces reforming raw materials, jet fuel, diesel, ethylene plant raw materials and liquefied petroleum gas according to market requirements.
6. Food hydrogenation: Food hydrogenation can ensure the stability of the taste of food, and it is also the reduction of hydrogen used.
7. Energy storage applications: automotive industry (new energy), fuel cells, batteries, etc.
8. Semiconductor industry applications: in the fields of semiconductors, electric vacuum materials, silicon wafers, optical fiber production and so on. In the electronics industry, hydrogen and oxygen are widely used as heat treatment gases and process gases. The purity of these gases has a great impact on the quality of the product, requiring high-purity hydrogen and oxygen. In general, hydrogen is supplied by one-time purification of salt electrolysis or petrochemical refining by-product gas, and then high-pressure charging into cylinders, etc. Since impurities such as nitrogen, carbon dioxide, carbon monoxide, and hydrocarbons in the hydrogen produced by these production methods cannot be completely removed, terminal purification devices of several tens of cubic meters per hour are also set up in semiconductor factories and can only be used after two terminal purifications.
The purpose of measuring the concentration of hydrogen
After understanding the characteristics of hydrogen and the use of hydrogen, we met customers who asked for hydrogen testing, and first of all, we had to understand the purpose of the customer's hydrogen concentration measurement, which was actually very simple.
Start by asking the customer if they want to test hydrogen in the environment or in a pipeline or unit.
If it is to measure hydrogen in the ambient air, it must be for the flammability and explosiveness of hydrogen. Concentration 0-1000ppm or lower limit of 0-100% lel (0-40000ppm).
If it is to measure hydrogen in a pipeline or device, it should be analyzed according to the process background and the purpose of the device. If it is a hydrogen storage device as a raw material, it is generally necessary to measure its purity, with a range of 0-100%vol, and some customers will ask how many 9s can the instrument measure, which means 999%vol,99.99%vol, such as hydrogen energy and the semiconductor industry, requires extremely high hydrogen purity. There are also hydrogen concentration measurement pipelines for process control, such as blast furnace gas hydrogen measurement, although the concentration of hydrogen reaches 4%vol will cause the risk of hydrogen in the furnace, but the blast furnace gas hydrogen measurement is not only to prevent the furnace, but also to analyze the furnace transportation situation, whether there is water leakage in the furnace body, whether the water content of the raw material is too high, whether the electrode is soft and broken, etc. For example, natural gas can be blended with hydrogen, because hydrogen is more flammable, and the natural gas can also improve thermal efficiency within a certain limit (under the same quality). However, the concentration of hydrogen blending should also be strictly controlled, because hydrogen can easily lead to metal hydrogen embrittlement, so the tolerance of pipelines and transportation equipment should also be considered.
How to choose a hydrogen detection instrument
Knowing the use of hydrogen, we can roughly judge the measurement range of hydrogen, no matter what kind of equipment hydrogen is used for, as long as it is to measure the concentration of hydrogen in the environment, it is to measure hydrogen leakage and prevent its explosion.
If the customer is to measure hydrogen leakage, want to find out the leakage source at the early stage of the leakage, portable, then it is recommended to choose the electrochemical principle of the sensor, the range of 0-1000ppm, if the customer wants to be fixed 24 hours ** detection, then choose the catalytic combustion principle of the sensor, the range of 0-100%LEL (4%vol of hydrogen corresponds to 100%LEL), the resolution of 1%LELThat is to say, when the instrument has a value, the hydrogen concentration in the environment has been obtained 400ppm, and the measurement is in a certain space, so if the customer wants to find out the leakage source earlier and more accurately, it is recommended to use the hydrogen detector based on the principle of pump suction electrochemistry.
As long as there is hydrogen in the factory or the process produces hydrogen, the production workshop must arrange a certain number of hydrogen alarms according to the requirements, and the combustible gas detector with the principle of fixed catalytic combustion can be selected.
If the customer says that it is to measure the hydrogen in the pipeline.
First of all, it is necessary to understand the hydrogen concentration to be measured by the customer, and if it exceeds 70%vol, it can be understood that the customer needs to measure the purity of hydrogen.
Assuming that the purity of hydrogen to be measured by the customer is in the range of 70%-99%, depending on the composition of the customer's gas, in addition to hydrogen, what other gases are there in the background gas, if it is a binary gas, and the background gas is a gas with a large difference in thermal conductivity, then you can consider using a detector based on the principle of thermal conductivity for analysis.
Suppose the purity of the hydrogen to be measured by the customer reaches 999%vol, this purity of hydrogen, customers have certain requirements for purity, but it is not very high, and the background gas impurity components of hydrogen refining are mainly oxygen and nitrogen, and the purity of hydrogen can be judged by measuring the concentration of oxygen.
Suppose the purity of the hydrogen to be measured by the customer reaches 99999%vol, which shows that the customer has extremely high requirements for the purity of hydrogen, so to measure the purity of hydrogen here, it is necessary to measure the possible impurities in the hydrogen purification process one by one, calculate the total content of impurities, and then reverse the purity of hydrogen. A chromatograph is needed here, and the detector must be of ultra-high precision, and the detector with the appropriate principle is selected for the impurity composition.
Assuming that the hydrogen concentration to be measured by the customer is in the range of 0-70%vol, then it means that this is not a hydrogen production or purification project. The gas composition that the customer wants to measure will be more complicated, and at this time, it is necessary to figure out what the customer's background gas components are, what is the range of concentration of each component, and the customer's budget. If the customer's budget is not high, then the chromatograph must not be considered, and the chromatograph is not suitable for making the best analysis instrument. For higher concentrations of hydrogen, the cost-effective detection method is the thermal conductivity detector, but the thermal conductivity detector not only responds to hydrogen, but also responds to other gases, so at this time, if you want to more accurately measure the content of hydrogen in the mixture, you also need to measure the composition of other gases in the background gas, each gas has its own suitable detector, and the background gas composition is measured one by one with the right detector. The hydrogen measurements are then corrected according to the concentrations of other gases. This method is also not very accurate, and the difference with chromatography is that there is no separation of the gas mixture. Therefore, there is a certain amount of cross-interference between the measured gas components. Therefore, although this method cannot achieve the effect of chromatography, the analysis speed is fast, and it can be used as the best qualitative analysis to interpret trends.
One last thing to note.
To measure the hydrogen concentration in the pipeline device, in addition to considering its measurement needs and measurement concentration, it is necessary to choose a detection method with appropriate principles. At the same time, it is also necessary to consider the pressure, temperature and background gas characteristics of the pipeline, impurities, etc., and make a pretreatment system in combination with the working conditions, so that the analytical instrument can operate effectively and safely for a long time.