Process liquid flow rates

The most common alternative to distillation for the separation of low-molecular-weight materials is absorption. In absorption, a gas mixture is contacted with a liquid solvent which preferentially dissolves one or more components of the gas. Absorption processes often require an extraneous material to be introduced into the process to act as liquid solvent. If it is possible to use the materials already in the process, this should be done in preference to introducing an extraneous material for reasons already discussed. Liquid flow rate, temperature, and pressure are important variables to be set. 

Three examples of simple multivariable control problems are shown in Fig. 8-40. The in-line blending system blends pure components A and B to produce a product stream with flow rate w and mass fraction of A, x. Adjusting either inlet flow rate or Wg affects both of the controlled variables andi. For the pH neutrahzation process in Figure 8-40(Z ), liquid level h and the pH of the exit stream are to be controlled by adjusting the acid and base flow rates and w>b. Each of the manipulated variables affects both of the controlled variables. Thus, both the blending system and the pH neutralization process are said to exhibit strong process interacHons. In contrast, the process interactions for the gas-liquid separator in Fig. 8-40(c) are not as strong because one manipulated variable, liquid flow rate L, has only a small and indirec t effect on one controlled variable, pressure P. 

In concentrated wstems the change in gas aud liquid flow rates within the tower and the heat effects accompanying the absorption of all the components must be considered. A trial-aud-error calculation from one theoretical stage to the next usually is required if accurate results are to be obtained, aud in such cases calculation procedures similar to those described in Sec. 13 normally are employed. A computer procedure for multicomponent adiabatic absorber design has been described by Feiutnch aud Treybal [Jnd. Eng. Chem. Process Des. Dev., 17, 505 (1978)]. Also see Holland, Fundamentals and Modeling of Separation Processes, Prentice Hall, Englewood Cliffs, N.J., 1975. 

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 ... 

Rotary Atomization Spinning Disk 10-200 Spray drying. Aerial distribution of pesticides. Chemical processing Good mono-dispersity of droplets. Independent control of atomization quality and liquid flow rate Satellite droplets, 360° spray pattern... 

In air-assist atomization, air is needed usually to augment the atomization process only at low liquid flow rates when the pressure differential is too low to produce satisfactory pressure atomization. In some designs, however, air assistance may be required over the entire range of operating conditions if the atomization quality achieved with a pressure atomizer alone is always poor. In an air-assist atomization process, the impingement of a low-velocity liquid stream by a high-velocity air stream may occur either within or outside the... 

For a liquid (for example, water), the size of a drop formed at a sharp-edged tube opening can be reduced from 3.6 mm to 784 pm if the opening diameter decreases from 1 mm to 10 pm. Apparently, the dripping mechanism is concerned with large drops and low liquid flow rates. Therefore, it is a functional mechanism in drop formation processes common in nature. 

Recently, the size and shape of a liquid droplet at the molten tip of an arc electrode have been studied,12151 and an iterative method for the shape of static drops has been proposed. 216 Shapes, stabilities and oscillations of pendant droplets in an electric field have also been addressed in some investigations. 217 218 The pendant drop process has found applications in determining surface tensions of molten substances. 152 However, the liquid dripping process is not an effective means for those practical applications that necessitate high liquid flow rates and fine droplets (typically 1-300 pm). For such fine droplets, gravitational forces become negligible in the droplet formation mechanism. 

This process has a classical on-line instrumentation gathering measurements of liquid flow rates (at the input of the reactor and in the recirculation loop), temperature and pH in the reactor and biogas flow rate and composition i.e., CO2, CH4 and H2 content in the biogas) [30]. In addition, the following sensors were installed over the years a TOC analyzer, a titrimetric sensor [3] and a FT-IR spectrometer [29]. Since 1998, this instrumentation provides us with the following on-line measurements in the liquid phase every... 

Many authors claim that the dilution by the sheath flow would not significantly affect the detection sensitivity, because it is completely evaporated in the spray process. Moreover, it has been discussed that in this layered-flow approach, preferably the inner layer of the spray enters the collector opening. If this were true, the composition of sheath liquid would be less important. Anyhow, it has to be stated that there is a dilution problem in the sheath-flow approach. In addition, it has been proven many times that ESI is a concentration-sensitive, not mass-sensitive, process. Knowing this, it makes sense to reduce the sheath liquid flow rate to the minimum required for stable spray conditions. 

While the tower diameter must be designed to process the maximum expected liquid flow rate, it must also be designed to handle the maximum expected gas flow rale The superficial gas mass flow rate is also critical to the tower diameter selected and is defined in Eq 2 in terms of the gas flow rate, gas density, and tower cross-scctional area. 

Tower diameter selection is usually made with the maximum expected gas and liquid flow rates and depends on the size and type of tower packing The portion of Fig. 3 with solid lines illustrates the pressure-drop relationship for 1.5-m. [3.81 -cm] Pull rings supplied by the manufacturer for typical superficial gas and liquid flow rates used in the chemical processing industry.1 This relationship is usually available in graphical form from any manufacturer of packed-tower packing elements. While these... 

The countercurrent-flow fixed-bed operation is often used for physical absorption or for gas-liquid reactions rather than gas-liquid-solid processes. Shah [1] gives a comparison between a gas-liquid-solid (catalytic) fixed bed reactor and a gas-liquid-solid (inert) fixed-bed reactor. The major difference between these two types of reactors are the nature and the size of the packing used and the conditions of gas and liquid flow-rates. 

In processing the quantitative effect of the liquid flow-rate, the superficial gas velocity, and the total reactor pressure on the dynamic liquid hold-up, good results have been obtained by using ... 

An initial series of measurements concerned the accurate determination of the dilution factor. As is represented in Fig.5.16, the absolute position of the tubes of the process solution and of the sodium hydroxide solution over the rollers of the pump is different. One tube is situated higher on the roller than the other, which can lead to a small difference in flow rate. By determining the hydrogen peroxide concentration by means of titration of a sample taken from the bath and a sample taken at the exit of the detection cell (diluted solution), the dilution factor can be determined. Table 5.1 presents the results of 23 measurements of the hydrogen peroxide concentration, performed at a liquid flow rate of 11/h. It is concluded that the dilution factor equals 1.9773+0.0014, which in fact is very close to 2. 

An example of industrial relevance is the removal of sulfur dioxide (S02) from vent gases by absorption into water or a lime slurry (48). In the water absorption process, both gas-film and liquid-film resistance to mass transfer occurs. As a result the overall mass transfer rate is proportional to gas-flow rate and acceleration but inversely proportional to liquid-flow rate. Due to the fast reaction of S02 with lime, this system is only gas-film diffusion limited. The overall mass transfer rate is largely unaffected by gas- or liquid-flow rate and is proportional to acceleration, but to a lesser extent than the water absorption process. In both cases the overall mass transfer rate is reportedly much higher than the corresponding conventional packed towers. 

Absorption of hypochlorous acid into water, a liquid-side mass transfer-limited process, showed HTU values as low as 4 cm, with a strong dependence on liquid-flow rate. Heat of absorption removal was identified as a potential issue with absorption in rotating beds (9). 

The dynamic behavior of the coke gas purification process has been investigated systematically (139,140,145). For instance, local perturbations of the gas load and its composition have been analyzed. A significant dynamic parameter is represented by the liquid holdup. Figure 20 demonstrates the changes of the solvent composition after a decrease of the gas-flow rate from 67 m3/h to 36.4 m3/h and a simultaneous small increase in the liquid-flow rate. 

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