The hottest industrial heating carrier and coolant

2022-08-13
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Methods and processes of industrial heating carrier and coolant

heat exchange in chemical production is usually carried out between two fluids, but the purpose of heat exchange is different. There are mainly two kinds, either heating (vaporizing) the process fluid or cooling (condensing) the process fluid

heating agent and heating method

(I) water vapor

water vapor is the most commonly used heating agent. In addition to improving the core competitiveness of the industry, saturated steam is usually used, and superheated steam is allowed under the condition that the steam is not overheated (overheated 20-30 ° C)

the main advantages of using steam as heating agent are: large latent heat of vaporization and relatively small steam consumption; Under a given pressure, the condensation temperature is constant, so if necessary, the temperature of the heated steam can be adjusted by changing the pressure. The heat transfer coefficient of steam condensation is very large [a = 5000 ~ 15000w/(M2 ·.K)], which can operate under low temperature difference; Cheap, non-toxic, no fire hazard, etc

the main disadvantages of water vapor are: the saturation temperature corresponds to the pressure one by one, and the corresponding pressure is high. Even the medium saturation temperature (200 ℃) corresponds to a considerable pressure (1.56x106pa), which requires high mechanical strength of the equipment and large investment costs

there are two methods of steam heating: direct steam heating and indirect steam heating

when directly heated by steam, water vapor is directly introduced into the heated medium and mixed with the medium. This method is applicable to the occasions where the condensate of the heated medium and steam is allowed to mix. The direct steam is introduced by the bubbler, which is usually arranged at the bottom of the equipment. The bubbler is generally a coil with many holes. When the steam bubbles, it passes through and stirs the liquid layer to directly exchange heat with the medium

when the indirect steam is heated, the flow transmitted through the intermediate wall of the heat exchanger is also reversed to transfer heat. When the steam is not completely condensed in the heat exchanger, part of the steam will be discharged with the condensate, resulting in an increase in steam consumption. In order to make the condensate discharge smoothly without taking away the steam, it is necessary to set a condensate extractor. The most commonly used extractor is the floating ball condensate extractor. Figure 9-5 shows a closed floating ball condensate extractor, which is composed of shell, guide pipe, floating ball (including guide rod), needle valve, etc. The mixture of steam and condensate enters the shell. When the liquid level in the shell rises to a certain height, the floating ball floats, the needle valve opens, the condensate is discharged, the liquid level drops, the floating ball falls, and the needle valve closes until the condensate accumulates to a certain height next time, and the valve opens again. In the condensate drain, a certain liquid level is always maintained to prevent steam from leaking out of the condensate drain. 1m3) when water at 100 ℃ changes into steam at 100 ° C, its volume is 1700m3, and when it changes into steam above 300 ° C, it is more than 3000m3. The danger of water vapor explosion and explosion accidents caused by water vapor are very common. The explosion caused by phase change is called steam explosion. The most common steam explosion accident is the explosion accident caused by water vaporization

 

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