Rate-based methods

Based on an average tray efficiency of 90 percent for the hydrocarbons, the eqiiilibniim-based model calculations were made with 36 equilibrium stages. The results for the distillate and bottoms compositions, which were very close to those computed by the rate-based method, were a distillate with 0.018 mol % ethylbenzene and less than 0.0006 mol % styrene, and a bottoms product with only a trace of methanol and 0.006 mol % toluene. 

Mori H., Oda A., Kunimoto Y., Aragaki T. Packed Column Distillation Simulation with a Rate-Based Method. J. Chem. Eng. Japan, Vol. 29, 307-314, 1996. 

While the bulk vapor and liquid phases are not at equilibrium with each other, there is equilibrium at the interface between phases with a movement from the bulk phase through the interface (Fig. 4.3). The net loss or gain for a component at the interface is expressed in a rate form (hence the alternate name, rate-based methods) ... 

An understanding of column hydraulics in both trayed and packed columns is essential for a complete performance analysis and design of such devices. The reader will find instructional coverage of these topics, as well as rate-based methods and tray efficiency, in subsequent chapters. 

Calculates continuous, multicomponent, multistage distillation, absorption, and stripping columns by equilibrium-stage and rate-based methods... 

Example 8 Calculation of Rate-Based Distillation The separation of 655 lb mol/h of a bubble-point mixture of 16 mol % toluene, 9.5 mol % methanol, 53.3 mol % styrene, and 21.2 mol % ethylbenzene is to be earned out in a 9.84-ft diameter sieve-tray column having 40 sieve trays with 2-inch high weirs and on 24-inch tray spacing. The column is equipped with a total condenser and a partial reboiler. The feed wiU enter the column on the 21st tray from the top, where the column pressure will be 93 kPa, The bottom-tray pressure is 101 kPa and the top-tray pressure is 86 kPa. The distillate rate wiU be set at 167 lb mol/h in an attempt to obtain a sharp separation between toluene-methanol, which will tend to accumulate in the distillate, and styrene and ethylbenzene. A reflux ratio of 4.8 wiU be used. Plug flow of vapor and complete mixing of liquid wiU be assumed on each tray. K values will be computed from the UNIFAC activity-coefficient method and the Chan-Fair correlation will be used to estimate mass-transfer coefficients. Predict, with a rate-based model, the separation that will be achieved and back-calciilate from the computed tray compositions, the component vapor-phase Miirphree-tray efficiencies. 

The principle of the traversing method is to measure the local velocity at one or several points of the flow cross-section and then calculate the flow rate based on this information. Generally speaking, an integration of the local velocity over the flow cross-section is made. Mathematically, this is expressed as... 

Basically there are two approaches to predicting the occurrence of erosion corrosion. Practical or experience based methods typified by Keller s approach for carbon steels in wet steam. Keller developed an equation that related the erosion corrosion rate as a function of temperature, steam quality, velocity and geometric factor. In recent years this approach has... 

A particularly attractive potential of plasma based methods is the ability to vary, continuously or discretely, the nature of the material deposited by varying the plasma parameters (eg flow rates, gas composition, power input, substrate temperature etc). This, of course, applies to organic as well as inorganic materials ( 3). This aspect of interface control is not yet well developed but is an exciting prospect. 

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