Seeking advice on flash tank design issues
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Today I read most of the calculation explanations related to flash tanks on the forum, and I found them not particularly clear; moreover, 20570.8 seems to be quite different from the values used in the design of flash tanks. I have a hypothetical design and would like to seek the experts’ guidance. Saturated condensate at three different pressures enters the flash tank (0.6, 1.0, and 1.5 Mpa respectively; 1.5 Mpa is chosen here to ensure a sufficient safety margin through a conservative design). The total flow rate is 47 t/h, and the temperature is 198.3 degrees Celsius. The pressure of the flash steam is 0.3 Mpa; based on table references, the flash ratio is approximately 13%. At the flash vapor pressure, the latent heat of vaporization of saturated steam is 2170 kJ/kg; the flow rate of saturated steam is approximately 6.2 t/h, while the flow rate of saturated water is 40.8 t/h. According to what the experts on the forum have said before, the flow rate inside the tank should not exceed 2.44 (to prevent vibrations). So how do I determine the diameter and height of the flash tank I need to design? Another idea is to determine the volume based on a certain dwell time using the obtained data, and then to explore whether it’s feasible to iteratively redesign the height and diameter using this data It seems that none of the posts on the forum provide a systematic explanation; could some experts give us newcomers some guidance! Thank you so much!
You can simply use process simulation software such as Petrosim or Aspen for simulation
Is there anyone experienced who can take a look?
Since you already know the flow rate, it’s simple then. Think of the flash tank as a large pipe; with the flow rate, density, and velocity of the flash vapor, you can calculate the cross-sectional area (and thus determine the diameter of the tank)
To design a flash tank first, it is necessary to know the flow rate of the secondary steam; once the flow rate is determined, the diameter of the tank can be determined. Then, based on the feed volume of the liquid phase, a residence time is selected; using this residence time, the volume is calculated, and from this volume, the height of the liquid phase can be determined. The separation of secondary steam generally requires a separation space of 1.5 meters or more. Based on these factors, we can determine the specifications for the flash tank
It’s just that I don’t know how to determine this residence time
Actually, I did the calculations based on the gas-liquid separation tank, and the conditions on site were indeed a mixture of gas and liquid. But I’m wondering: if, as stated in the problem, it’s about depressurized flashing of condensates at different pressures, can such a situation still be handled using gas-liquid separation calculations?
Calculating based on residence time is actually an empirical method; a more reliable approach is to determine the diameter and height based on the heat transfer area!
Learned*.............