Tray Hydraulic Parameters

The symbols are P for profit, / for equality constraints, g for inequality constraints, x for optimization variables, y for dependent variables, and / (constant) for updated parameters. The objective function is a scalar measure of plant profit it is usually the instantaneous profit ( /hr), because the optimization variables do not involve the time value of money. Typical equality constraints include material and energy balances, heat and mass transfer relationships, and thermodynamic and kinetic models, and typical inequality constraints include equipment limitations limit compressor horsepower, and distillation tray hydraulics. The optimization variables are flow rates, pressures, temperatures, and other variables that can be manipulated directly. The dependent variables involve intermediate values required for the detailed models for example, all distillation tray compositions, flow rates, and temperatures. Because of the fundamental models often used in RTO, the number of dependent variables can be quite large, on the order of hundreds of thousands. 

The various hydraulic parameters shonld be checked at various locations in the column. As a minimum this should be done at four points fora simple, single-feed column top tray, tray above tha feed tray, uuy below the feed tray, and bottom liny. 

TRAYS allows the design of sieve-trays, sieve-valve, tunnel-valve, Baycr-valves, bubble trays, Vario-Flex-valve - including all hydraulics parameters and tray efficiency for absorption, desorption and rectification. 

FIGURE 12.11. Key parameters for tray hydraulics (this graph is used for model illustration). 

Equation (5.32) is a simple linear relationship between the liquid holdup on a tray, M , and the liquid flow rate leaving the tray, L . The parameter P is the hydraulic time constant, typically 3 to 6 seconds per tray. 

Tray layout. The preliminary tray and downcomer layout is prepared in the column-sizing phase and refined during the hydraulic design phase. In addition to the parameters previously set, such parameters as hole diameter or the type of valve unit are determined. 

These regimes appear to be an approximate function of the dimensionless flow parameter, introduced earlier in connection with tray and packed column hydraulics ... 

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