Since the coal tar is distilled under reduced pressure, the outlet temperature of the heating furnace is significantly lower than that of atmospheric distillation, reducing the operating temperature of the system, preventing the hydrogenation, decomposition and polymerization of the tar components, stabilizing the tar components, and simultaneously saving gas; In the mixed components, the yield of naphthalene is obviously improved; the quality of the asphalt is stable, and the change range of the softening point is small; the direct steam is not needed at the bottom of the tower, the amount of steam is significantly reduced, and the generation of part of the wastewater is reduced. So now vacuum pumps are widely used in the field of coal tar processing. The 300,000t coal tar processing project of Tangshan Kabosi Kailuan Carbon Chemical Co., Ltd. introduced the atmospheric and vacuum technology from Cobbs of the United States to produce light oil, industrial naphthalene, wash oil, phenol oil, and eucalyptus oil from coking coal tar. , Heavy oil, hard asphalt, carbon black oil, soft asphalt, fuel oil and other products, the negative pressure required by the process provided by the vacuum system.
The key part of the vacuum system is the vacuum pump.
1 vacuum pump classification and selection 1.1 vacuum pump classification (two-stage), molecular pump, Roots pump; two. Steam injection pump: mercury diffusion pump, oil diffusion pump, oil jet pump; Dry type pump: sputter ion pump, titanium sublimation pump, adsorption pump, condensate adsorption pump.
The mechanical pump is vacuumed by the principle of mechanical pumping. It consists of a stator, a rotor and a rotary vane. Mechanical pumps generally have a low degree of vacuum.
The steam jet pump utilizes heating and vaporization to cause the momentum of high-velocity steam to be carried out to carry out gas molecules and thus to draw a vacuum, but steam pollution generally occurs. Each principle of the dry pump has a big difference, the advantage is no pollution, high vacuum, the disadvantage is high technical requirements, equipment investment.
1.2 Selection of Vacuum Pump According to the performance of the vacuum pump and the design requirements of the vacuum system of Tangshan Kabo Sikai Carbon Chemicals Co., Ltd., the company adopted a liquid ring vacuum pump. According to the similar principle of dissolving, the product washing oil of our company was used as a seal. The oil satisfies the minimum 5 kPa (absolute) operating condition requirements of the company's tar processing towers. Compared with other types of vacuum pumps, the liquid ring vacuum pump has the following features: compact structure, high number of revolutions of the pump, and generally can be directly connected with the motor without a deceleration device.
The small size of the structure and the small footprint allow for large displacements.
Compressed gas is basically isothermal, so it can extract flammable and explosive gases. Since there are no exhaust valves and friction surfaces, dusty gases, condensable gases and soda water mixtures can be removed. Inhale evenly, stable and reliable, simple operation and easy maintenance.
2 Vacuum system and its control parameters As shown, the tar vacuum system consists of seal oil circulation tank, seal oil circulation pump, seal oil water cooler, vacuum pump, tower top pressure Zhang Chao: application of vacuum pump in coal tar distillation The oil in the sealed sump is conveyed to the vacuum pump. The seal oil circulation is controlled at 3m3/h. The vacuum pump continuously extracts the gas phase material at the top of the tower. The pressure at the top of the tower sets the required pressure of each tower process through the DCS system, and the pressure is automatically adjusted through the valve control to achieve automatic control. Most of the gas phase material is dissolved in the wash oil and is sent to the seal oil circulation tank by the vacuum pump. The tank liquid level will gradually rise and the temperature will increase. The temperature of the seal oil circulation is controlled by the seal oil cooler and is controlled at about 25°C. After the liquid level is raised, the seal oil can be poured into the raw material tar tank through the oil level control valve of the seal oil tank for re-distillation. The liquid level is maintained at about 50°%.
3 Factors affecting vacuum degree and treatment methods The vacuum system in the company's vacuum system has experienced a drop in vacuum during operation, and the maximum vacuum cannot be extracted. There are several reasons: The temperature is too low or too high will affect the gas phase material in the seal oil. The solubility in the medium, thus affecting the degree of vacuum, so in the summer due to high temperatures to turn off the heating system of the vacuum; winter to be normally open, while closing the inlet of the small seal oil cooler, if necessary, want to pass a small amount of steam into the water cooler.
The amount of seal oil circulation, the amount of sealing oil into the vacuum pump should be kept at about 3m3/h. If it is too high, the degree of vacuum will be reduced. If it is too low, the equipment of the vacuum pump will be damaged.
The viscosity of the sealing oil. During the operation, naphthalene oil, naphtha, diterpene, and heavy oils dissolve in the seal oil along with the gas phase, so that the viscosity of the seal oil increases, and the amount of seal oil circulation decreases. The degree of vacuum, so it is necessary to change the washing oil regularly every week to ensure the viscosity and quality of washing oil.
The choice of sealing oil, before the company used cost-effective water to seal the oil, in order to save costs, but water and tar components are insoluble, and the saturated vapor pressure of water is small, affecting the degree of vacuum, so be sure to follow similar The principle of compatibility is to select a sealing oil with a large saturated vapor pressure. 481 Due to the strong corrosiveness of the washing oil, after a period of use, the vacuum pump housing, the impeller, the rotor, the automatic pressure regulating valve on the top of the tower, and the bypass valve cause some corrosion, resulting in a drop in the performance of the vacuum pump. Lax, affect the vacuum, so the equipment should be regularly overhauled.
The vacuum pump is not smooth in front of the pump. It may be that the vacuum pump is not open in front of the pump, or it may be caused by the plugging of the vacuum cooler in front of the pump. We can turn off the water in the water cooler, turn on the steam, and then close the vacuum pump inlet valve and import it from the vacuum pump. The method of steam purging can be used to clear the pipeline, and the purge line can also be purged from the reflux pump of each tower.
The sealed oil tank is connected to the flue gas main, used for cold weather in winter, and the main flue gas pipeline may be blocked, resulting in poor circulation of the gas pumped by the vacuum pump to the sealed oil tank. The pressure fluctuations of the towers are relatively large, and the heat pipe may be used to add heat or The steam purges the flue gas manifold to clear the pipeline.
4 Technical Improvements Suggested sealing oil circulation is controlled by hand valves, flow fluctuations, operators often need to manually adjust, it is recommended to use the automatic adjustment valve in the future, so more stable, so that the vacuum pump to run efficiently.
The automatic adjustment valve at the top of the tower has a relatively narrow range of adjustment, and sometimes requires manual adjustment by the operator. It is recommended that the valve be changed during the equipment modification to increase the adjustment range and reduce the operator's operation.
It is recommended not to replace the seal oil with water, although the cost of running costs is reduced a lot, but the use of water as a working fluid, the saturation vapor pressure is small, the vacuum pump suction pressure is smaller, the ultimate pressure can only reach 2000 ~ 4000Pa; use oil to do work Liquid, its saturated vapor pressure, the vacuum pump's maximum suction pressure, up to 130Pa. With coal tar blending technology is mature, coal tar pitch market demand, liquid ring vacuum pump efficiency is low, generally 30% ~ 50 %, is not conducive to the company's future expansion and reconstruction, it is recommended that the company upgrade the vacuum pump.
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