A rather basic question: regarding theoretical trays and actual trays
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I’ve been learning *Hysys recently; I’m just starting out, mainly focusing on process balance calculations and simulations, and haven’t delved into process design yet. But there has always been a question: how is the conversion made between these theoretical trays and actual trays? For example, under certain operating conditions, I have an Absorber, and the process equilibrium simulated using 10 trays can meet my simulation requirements. So, during the process design phase, what additional parameters are needed to be obtained from the tray manufacturers in order to complete the design of the tower? And how do these parameters affect the process simulation? Well, I’ve only operated towers before and been inside them as well, but I’m not entirely sure how this particular thing was designed. I want to know these right now. Haha, the question might be a bit naive; please forgive me~~~~
First, it is necessary to determine which type of tray to use. Then come the specific dimensions of such trays, such as the liquid dropping baffle, liquid receiving tray, overflow weir, effective opening area, and so on. If it is a filler, then factors such as specific surface area, diameter, height, and so on
This is actually an empirical value; as mentioned above, first determine the type of tray, and then calculate the efficiency based on various parameters. The actual number of trays is obtained by dividing the theoretical number of trays by the efficiency. In the case of a packed tower, the packing height is determined based on the equivalent plate height.
If it is a plate tower, the plate efficiency is used for conversion. Some manufacturers of tower internals have extensive experience; depending on the different material systems, they use different plate efficiencies as substitutes. For general systems, it is around 60%, with some reaching 90% or even 100%. There is also the role of separating towers to consider; the plate efficiency of a distillation tower is higher than that of an absorption tower. For a packed tower, simply substitute the equivalent plate height to calculate the packing height. This packing manufacturer will provide such parameters: how many theoretical plates are equivalent to one meter of packing, or how many meters of packing is equivalent to one theoretical plate.
First, it is necessary to understand the difference between the theoretical plate and the actual plate. A theoretical plate represents a mass transfer process in which the gas and liquid phases are in equilibrium, and it is an ideal condition; the calculations are based solely on the driving forces and resistances of mass transfer. In fact, due to the mutual influences of flow within the tower, backmixing, gas-liquid contact time, non-uniformity of the gas and liquid phases, the physical properties of the gas and liquid itself, operating parameters, and the type of tray, the trays fail to reach an ideal equilibrium state; as a result, the actual tray efficiency is generally lower than the theoretical efficiency. As for by how much it is lower, it is highly dependent on factors such as the fluid system, operating conditions, type of tray, design of the tower internals, operating parameters (such as temperature, pressure, liquid-to-gas ratio, and flooding percentage), tower installation, and the cleanliness of the fluid system. Therefore, the data generated by Hysys simulations can generally be used as a reference; however, in actual design, the influence of multiple factors must be taken into account.