Flow rate, absorbent

An estimate of the minimum absorbent flow rate for a specified amount of absorption from the entering gas of some key component K for a cascade with an infinite number of equilibrium stages is obtained from Eq. (13-40) as... 

A hydrocarbon gas stream contains some heavy components which must be removed by absorption. The absorber has six theoretical stages and operates at 2750 kPa. The overhead product should contain 0.01 kmol/h nCg. Using the modular column section method, calculate the required absorbent flow rate and the product streams flow rates and compositions. The feed streams are deflned below, along with the component relative volatilities which are referred to pentane and assumed constant. The A -valuc of pentane at the column pressure of 2750 kPa is given by... 

It is required to determine the range of absorbent flow rates that would achieve the specified separation. Using the Kremser equation calculate the propane and butane flows in the products at different absorbent rates and recommend appropriate rates. Absorbent rates to be checked are 500, 600, and 700 kmol/h. 

Figure 5. Sulfur dioxide removal vs. absorbent flow rate...

Solve Example 12.8 by the Kremser method, but for an absorbent flow rate of 330 Ibmole/hr and three theoretical stages. Compare your results to the Kremser results of Example 12.8 and discuss the effect of trading stages for absorbent flow. 

Estimate the minimum absorbent flow rate required for the separation calculated in Example 12.8 assuming that the key component is propane, whose flow rate in the exit vapor is to be 105.4 Ibmole/hr. 

From the formula (20.8), it follows that the length at which absorption occurs becomes smaller with the increase of absorbent flow rate q and velocity U, and also with the reduction of pipe diameter d. An increase of the flow rate results in an increased volume concentration Wo of the absorbent, and hence in a larger phase contact surface area. Similarly, a velocity increase and reduction of the pipe diameter wUl reduce the size of drops in the gas stream, thus increasing the contact surface area. 

Set the initial compositions of absorbent xm and gas y , and also the absorbent flow rate q at operating conditions, or the volume concentration of the absorbent Wo = q/Pi-... 

The results of calculation of the equilibrium values (ui< +) are reported below. The calculation was carried out for nine values of pressure and five values of temperature that varied, respectively, in the intervals from 4 to 12 MPa and from 253 to 293 °K, and for five values of absorbent flow rate that varied from 0.1 to 2 kg/ m. The results are presented in Figs. 20.1 and 20.2. 

Fig. 20.4 Dependence of the coefficient of extraction (aka extraction factor) of heavy hydrocarbons from gas on pressure (o), temperature (b), and absorbent flow rate (c) 1 - one stage 2 - eight stages /-Cs+ II-C3+.

Usually the absorbent flow rate q is specifled in liters per 1000 under normal conditions. Then W is determined by the correlation (20.20). From (20.31) and (20.32), there follows... 

Since the absorbent flows continuously from plate to plate and is also repeatedly diluted by the absorbent coming out of the elements, the state of the absorbent layered on the plates can be characterized by residence times inside the element tg = Lgfug, and at the plate f = V/Qa, where V is the absorbent volume at the plate, Lg is the height of the element, Q is the absorbent flow rate, and Ug is the average vertical drift velocity of the gas inside the element (i.e. velocity along the symmetry axis of the element). A comparison of these two times for the characteristic parameter values shows that tg t). This means as it dwells at the plate, the absorbent has enough time to make numerous contacts with the gas inside the elements installed on this plate. 

The key parameter describing the absorbent state is the recirculation number, defined as the ratio of the absorbent flow rate through the contact elements to the general absorbent flow rate in the absorber. 

Cas flow rate, mill, m /day Absorbent flow rate, kg/mlll. Pressure, MPa Temperature, °C DEC concentration in the absorbent Dew point, temperature, °C... 

For an absorber, the design basis is the tower pressure the flow rate, composition, temperature, and pressure of the entering vapor feed the composition, temperature, and pressure of the absorbent and the fraction to be absorbed of one key component. The minimum molar absorbent flow rate is estimated from ... 

Rahbari-Sisakht et al. [54] investigated the effect of novel surface modifying macromolecules (nSMMs) on the morphology and performance of PSf hollow-fiber membrane for CO2 absorption. The performance of surface-modifled membrane in contactor application for CO2 absorption through distilled water as absorbent was studied. The results show that surface-modified membrane had higher performance compared to plain polysulfone membranes. With the membrane prepared from SMM in the spinning dope, a maximum CO2 flux of 5.8 X 10 mol/m s was achieved at 300 ml/min of absorbent flow rate, which was almost 76% more than the other membrane. In a long-term stability study, the initial flux reduction was found to be about 18% after 50 h of operation of the surface-modified membrane. 

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