Four Technical Requirements of Modern Coal Chemical Industry on Valve Products

Ⅰ. Requirements for chemical valve materials

Due to the existence of coal-oil slurry in the direct coal liquefaction reaction, the abrasion of chemical valves, pipelines and other equipment materials must be considered. Therefore, it is required that the materials used in the manufacture of valves have comprehensive properties that meet the requirements of use. Specifically, it should have:

1. The performance of compactness, purity and homogeneity as a description of the inner quality of the material is superior, which is particularly important for thick (or large section) steel.

2. To meet the requirements of chemical composition, room temperature and high temperature mechanical properties required by design specifications.

3. It must have anti environmental embrittlement performance so that it can be used in harsh environments for a long time, such as valves used in sewage treatment plant.

Ⅱ. Requirements of chemical valve process

Direct coal liquefaction not only has the characteristics of high temperature, high pressure, and presence of hydrogen in the hydrogenation unit, but also the coexistence of corrosion and wear conditions in the coal chemical industry. Therefore, the source of raw materials is very critical. Generally speaking, corresponding clear index requirements are put forward for the composition of the valve material, especially the content of harmful elements. Although this requirement is often higher than the basic general requirements of the material, for the quality of the final product, these composition indicators are not enough.

Therefore, the foundry should strictly control the source of raw materials. The processed raw materials should not only be smelted, but also further refined, especially by strengthening the control in front of the furnace. Only in this way can it be possible to ensure the quality of the castings.

Ⅲ. Structural requirements for chemical valves

The design of the valve structure should avoid coal slurry coking and make the valve failure and easy to clean. Coal-oil slurry has a characteristic: if the flow is poor or static, that is, the flow of the medium is not good, it will be deposited and polymerization reaction may occur, which will cause coking and lock the valve.

At present, all the shut-off valves used in the direct liquefaction coal slurry pipeline are ball valves. In operation, when it is necessary to cut off the pipeline to close the ball valve, the oil-coal slurry inside the valve ball cannot be discharged and is deposited in the spherical cavity, which may coke and lock. Therefore, it is not the most suitable choice to choose a ball valve under this working condition.

Ⅳ. Wear resistance requirements of chemical valves

The ball valve used in the slurry condition should adopt the metal hard seal form, and the valve seat and the ball are made of the same material to ensure that the two have the same expansion coefficient, and the ball will not "seize" under high temperature conditions. Since many operating conditions of the valve are difficult to open and close under high temperature conditions, this is caused by asynchronous thermal expansion between the valve core and the valve body.

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