Can this happen with a steam ejector?
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The vacuum creation in the atmospheric and vacuum distillation tower relies on steam ejectors; the non-condensable gases in the tower mix with steam at the inlet of the ejector and flow at high speed, thereby creating a negative pressure at that inlet. May I ask, if too much steam is generated, could this cause some of the steam to not have time to pass through the ejector nozzles, thereby accumulating at the inlet and creating positive pressure? This would prevent non-condensable gases from being expelled, and as a result, no negative pressure would be formed Those who know, please share. Thanks
A steam ejector utilizes high-speed water vapor flow to create a low-pressure area, thereby drawing in and extracting non-condensable gases or steam to achieve vacuuming. The working principle of a steam ejector is based on Bernoulli’s equation, which states that as the flow velocity increases, the static pressure of the fluid decreases, thereby enabling it to draw in the surrounding medium. Regarding the situation you described, if an excessive amount of steam is supplied to the steam injector, two possibilities arise: 1. The injector is designed with an appropriate capacity to handle excess steam: Typically, injectors are designed to accommodate variations in steam flow rates, so that even if there is a sudden surplus of steam, the built-in buffering and adjustment mechanisms can handle it. In this case, the excess steam can be properly diffused and accelerated at the nozzle, ensuring the proper operation of the ejector. 2. Excessive steam volume beyond the ejector’s handling capacity: If the actual steam flow far exceeds the designed handling range of the ejector, it may lead to an increase in pressure near the nozzle, thereby reducing the ejector’s ability to create negative pressure. In this case, the ejector will be unable to effectively remove the non-condensable gases, and it may even lead to the creation of a positive pressure, affecting the proper operation of the vacuum distillation column. In summary, there is indeed the concern you have – an excessive steam supply may interfere with the proper operation of the injector, preventing it from maintaining the required negative pressure. In practical operation, it is usually necessary to carefully control the steam supply volume and adjust it based on real-time system feedback to ensure that the steam injector can operate effectively and stably. .
The diameter of the injector is set according to the relevant process conditions, and its function also remains within the appropriate range. For example, the corresponding pressure, flow rate, and cross-sectional area of flow,,,,. Operations within the specified range will not encounter such problems. For reference.
If the steam flow is set too high, and the condensing effect of the rear condenser is poor, the higher the steam flow, the worse the vacuum pumping performance will be.
Yes, it will. The pressure of the power gas is optimal only within a certain range; too much or too little is not good
Positive pressure? Theoretically, it is possible, but the probability of it actually happening is low (the diameter of the steam pipes and valves is not very large during design, and the steam flow rate may not reach its maximum even after they are opened). But when the steam flow is increased, the cooling effect of the rear condenser is poor; as a result, the negative pressure does not increase and may even decrease. Therefore, in processes such as vacuum crystallization and flash evaporation that use ejectors to create negative pressure, the water temperature in the cooling tower must be reduced as much as possible to save steam.
The cross-sectional area of the steam ejector’s nozzle has limited the amount of steam that can be used; in other words, once the steam valve is opened to a certain degree, the flow rate no longer increases, unless the steam pressure is raised. With the cooling effect and pressure remaining unchanged, increasing the opening of the steam valve does not result in any positive pressure.
No, this issue has been taken into account in the design; the requirement of the design is the area of the throat. It works even at very low pressures. Unless there is a problem with the back pressure.
As long as it remains within the design parameters of the ejector, the greater the flow rate and the faster the flow velocity, the better the vacuum-pumping effect, right?
If the condenser at the back cannot handle the load, resistance will be generated; operating within the designed range is fine