Gas use

Generally, a substance that is in a gaseous state at normal temperature and pressure is called a gas. A wide variety of gases, classified by nature, can be divided into inorganic gases and organic gases; according to ancient classification, can be divided into constant gas and trace gases, classified by use, can be divided into general industrial gases and special industrial gases. We can discuss it for the following purposes.

(1) General industrial gases

    It refers to various gases of ordinary purity which are produced by various industrial scales and purification methods, and are generally classified into the following types.

1. Chemical raw material gas

    (1) The air separation gas is subjected to cryogenic rectification: pressure swing adsorption or membrane separation to remove impurities such as nitrogen, oxygen, argon, ammonia, fluorine and helium. This type of gas has a large output and is a large variety of industrial gases.

    (2) The decomposition products of natural gas coal or petroleum constituents are present in the coal-bearing or petroleum-bearing strata, the main component is methane, and the content is above 95%.

    (3) A product obtained by thermal decomposition of a hydrocarbon cracking gas naphtha or the like, containing various low-grade hydrocarbon gases.

    (4) Gaseous products of coke oven gas coal at 800 ° C or higher, the main components are hydrogen and methane.

    (5) The product of water gas steam and red heat medium, the main components are carbon monoxide and hydrogen. If water vapor and air simultaneously react with the red hot coal, a half water gas is generated.

    (6) The pyrite furnace gas contains 6%-9% sulfur dioxide for the production of sulfuric acid.

    (7) Lime roasting kiln gas 32% - 40% carbon dioxide, used in the alkali industry.

2. Gaseous fuel

    The above-mentioned natural gas, cracking gas, coke oven gas, water gas, etc., can be used as a gaseous fuel in addition to chemical and petrochemical production raw material gases.

3. Exhaust gas

    The flue gas of the combustion furnace is composed of N2, 02, CO2, CO, water vapor and a small amount of other gases; a small amount of SO2 or N02 in the exhaust gas of the sulfuric acid plant or the nitric acid plant; the various exhaust gases of the organic chemical plant, etc. The situation is different and the composition is more complicated.

4. Factory air

    Because the production equipment leaks, the air in the production plant often contains production gas. Some of them endanger human health, while others cause spontaneous combustion or explosion accidents.

(2) Special industrial gases

    It refers to various gases produced by special processes (such as cryogenic, pressure swing adsorption, etc.). In terms of purity, variety, performance, and use, it is strictly produced and used according to certain specifications. Such gases can be further classified into high purity gas or ultra high purity gas, standard gas, and a mixed gas having a specific composition. The output of special industrial gases is not large, but it has strict requirements on its purity or composition, the highest allowable content of harmful impurities, packaging, storage and transportation of products, and belongs to high-tech and high value-added products. There are also many types of specialty gases, which are mainly divided into four categories, namely, high-purity gas, zero-point gas, standard gas, and general mixed gas.

1. High purity gas

    High purity gas is a gas with a guaranteed purity. The content of the main component must be greater than a certain value, and the content of the impurity component must be less than a certain value. The purity is generally more than 99%, and the highest can reach 99.9999%.

2. Zero gas

    The so-called zero gas is the gas used to calibrate the zero point of the test instrument. The zero point does not have to be a concentration value of zero. In order to calibrate the zero point, almost all gases below the concentration value (for example, one thousandth or less of the full scale concentration value) are used, but there is also a full scale concentration value of one tenth or less. If this value is determined, the gas can be used as a zero gas.

    However, high-purity gases can generally be used directly as zero-point gas, because the zero point of the detector is almost zero concentration and the content of impurities in the high-purity gas is extremely small. In the case of zero gas use, if the specific component is below a certain value and does not interfere with the component, even if the concentration is not so high, the gas is often used as a zero gas. The most common zero gas is mostly nitrogen or refined air, so some books are also called zero-grade air.

3. Standard gas

    Standard gases are primarily used to calibrate various gas analyzers. This type of gas must be calibrated to the concentration value. These gases are used in a wide range of applications. For example, when measuring automobile exhaust gas, the CO and CO2 content are almost determined by a non-discrete infrared analyzer, and the hydrogen content is determined by a hydrogen flame ionization detector. The amount of ammonia oxidation is high. In order to make these instruments have better precision, standard gas must be used. In order to correct a full detection line of these instruments, at least three points are required. In most cases, nine points are required together with the zero point. Prepare 8 standard mixtures with different concentrations to calibrate the detector.

4. General mixed gas

    A gas prepared by mixing two or more kinds of gases, and only needs to be marked with a rough concentration to satisfy the use requirement, and this gas is called a general mixed gas. Sides such as deep-sea divers breathe 20%-60% of oxygen, and the rest are nitrogen or nitrogen mixed gas; for example, carbon dioxide laser gas can be used with carbon dioxide 4%-16%, chlorine 10%-250%, the rest is A mixture of cockroaches.

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