Absorption column diameter calculation

Methods for quick sizing trayed fractionation and absorption column diameter have been reduced here to equations to facilitate programming for calculators or computers. Three methods are discussed and it is not a bad idea to compare results with all three. 

The dynamic losses can only be estimated by first sizing the pipe diameter of the line between the absorption column and the bleaching column. This is performed using recommended liquid velocities (Ref. P1, p. 163) in conjunction with the known volumetric flowrate. The area calculated can be translated into a standard pipe diameter. The dynamic losses are then estimated by two methods. The first employs Genereaux s formula (Ref. P1, p. 160) ... 

The calculation of column diameter for distillation and absorption columns %h,6 is usually based on the flooding velocity, which, in turn, requires values of the flooding capacity factor, Cf- Fair s flooding-capacity plot for sieve trays [1] correlates the flooding capacity factor with a flow parameter Flv for each tray-spacing value, t, as shown in Figure 2. The flow parameter involves the liquid mass flow, LMi, and vapor mass flow, F v (both in lb/ s), as well as the densities of the two streams. 

Determining the number of theoretical and actual trays in a distillation column is only part of the design necessary to ensure system performance. The interpretation of distillation, absorption, or stripping requirements into a mechanical vessel with internal components (trays or packing, see Chapter 9) to carry out the function requires use of theoretical and empirical data. The costs of this equipment are markedly influenced by the column diameter and the intricacies of the trays, such as caps, risers, weirs, downcomers, perforations, etc. Calculated tray efficiencies for determination of actual trays can be lost by any unbalanced and improperly designed tray. 

Deleye and Froment (1986) have reported the data on absorption of CO2 in aqueous solution of monoethanol amine (MEA) in a packed bed absorber. Gas containing CO2 at a partial pressure of 2 atm is to be purified by absorption into an aqueous solution of MEA in a packed bed filled with 5 cm diameter steel pal rings. Assuming excess concentration of MEA in the solution, the reaction between CO2 and MEA is treated as pseudo-first order reaction with rate constant k = 7.194 x 1(P s L A quantity of 6500 rcF/h of gas is treated with 1000 m /h of MEA solution. Partial pressure of CO2 is to be reduced to 0.02 bar. Column diameter is 2 m and it is operating at a pressure of 14.3 bar and a temperature of 315 K. Calculate the height of the bed. The following data are reported. 

A column 0.6 m diameter and 4 m high is, packed with 25 mm ceramic Raschig rings and used in a gas absorption process carried out at 101.3 kN/m2 and 293 K. If the liquid and gas properties approximate to those of water and air respectively and their flowrates are 2.5 and 0.6 kg/m2s, what is the pressure drop across the column In making calculations, Carman s method should be used. By how much may the liquid flow rate be increased before the column floods ... 

Procedure (See Chromatography, Appendix IIA.) Use a high-performance liquid chromatograph equipped with an ultraviolet detector that measures absorption at 254 nm and a 25- to 30-cm x 4-mm (id) stainless-steel column, or equivalent, packed with octadecyl silane chemically bonded to porous silica or ceramic microparticles 5 to 10 pun in diameter, or equivalent. Maintain the mobile phase at a pressure and flow rate capable of giving the required resolution (see below). Inject a volume, up to 25 pL, of the System Suitability Solution in a similar manner. Calculate the resolution, R (>3.6), between calcium formyltetrahydrofolate and Folic Acid by the equation... 

As Eg is usually small the detrimental effect of gas phase dispersion on the performance of bubble columns can be neglected in columns less than 20 cm in diameter (61). For illustrating the influence of gas phase dispersion some computed conversions are presented in Fig. 10 (J ). The simulations refer to CO2 absorption in carbonate buffer in a column 5 m in length. Eq was calculated from eqn. (15). The liquid phase dispersion does not affect the conversion in the present case as the process takes place in the diffusional regime of mass transfer theory. As shown in Fig. 10, the decrease in conversion due to gas phase dispersion increases with increasing diameter and gas velocity. However, in the favorable bubbly flow regime and in small diameter columns the effect is less pronounced. 

Gas absorption can be carried out in a column equipped with sieve trays or other types of plates normally used for distillation. A column with trays is sometimes chosen instead of a packed column to avoid the problem of liquid distribution in a large diameter tower and to decrease the uncertainty in scaleup. The number of theoretical stages is determined by stepping off plates on a y-x diagram, and the number of actual stages is then calculated using an average plate efficiency. The plate and local efficiencies are defined in the same way as for distillation [Eqs. 

The absorption tower will be filled with 50-mm ceramic Pall rings. Design for a gas-pressure drop not to exceed 400 Pa/m of packed depth. Assume that cooling coils will allow isothermal operation at 300 K. The gas will enter the column at the rate of 1.0 m3/s at 300 K and 1 atm. The partial pressure of methanol in the inlet gas is 200 mmHg (ScG = 0.783). The partial pressure of methanol in the outlet gas should not exceed 15 mm Hg. Pure water enters the tower at the rate of 0.50 kg/s at 300 K. Neglecting evaporation of water, calculate the diameter and packed depth of the absorber. 

For an individual tray in a tray column, the problem resolves to 27 non-linear algebraic equations in 27 unknowns. Solution of each tray has to be incorporated into a separate algorithm for the iterative tray-to-tray calculations. The performance of a 0.11m valve tray column was successfully simulated, and the method has been adopted as a basis for the design of commercial scale absorbers up to 8.5m in diameter used for the selective absorption of in the presence of CO ... 

In the case of larger-diameter packing elements, e.g. in absorption with a mostly mass transfer resistance in one phase, the liquid flow is mostly turbulent, with Rcl > 12.3. Here, Eqs. (5-2) and (5-6) lead to the following equations for calculating the pressure drop of irrigated packed columns with any type of column internal ... 

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