Can you please explain me what is superficial gas velocity and what does it depicts about the fixed bed?
What is loading time? I looked at the rules of thumb engineering, the loading time for vapor phased carbon bed adsorption should be 100 - 300 bed volume per hour. But I do not understand what it means.
What is working charge as well? As you can see from the attached diagram, it says working carge is 5 to 20% wt... I do not understand.
Dear Md Badriadib Aldrin Suhaini,
The following is a description of the terms of concern. In addition, attached are two publications which illustrate in detail the design, cost & mechanism of vapor phased carbon bed adsorption.
Superficial velocity
Superficial velocity (or superficial flow velocity), in engineering of multiphase flows and flows in porous media, is a hypothetical (artificial) flow velocity calculated as if the given phase or fluid were the only one flowing or present in a given cross sectional area. Other phases, particles, the skeleton of the porous medium, etc. present in the channel are disregarded.
Superficial velocity is used in many engineering equations because it is the value which is usually readily known and unambiguous, whereas real velocity is often variable from place to place, its mean not readily available in complex flow systems, and subject to assumptions.
Superficial velocity can be expressed as:
us = Q/A
where:
us - superficial velocity of a given phase, m/s
Q - volume flow rate of the phase, m3/s
A - cross sectional area, m2
WORKING CAPACITY
The “conditioning cycles” are the number of cycles (often about five) that are required to achieve a stable amount of adsorption and regeneration. Carbon, after undergoing the conditioning cycles, is capable of adsorbing about 50% of the amount that was adsorbed by the virgin material. Zeolite is capable of adsorbing about 90% of the amount adsorbed by the virgin material. Polymers can vary over the range of 50% to 90%. This “conditioned isotherm” also defines the “working capacity” of the adsorbent. The fact that carbon and some polymers will typically
desorb only 50% as much as the virgin material is thought to be caused by the continued recapture of molecules (i.e., depressed vapor pressure) in the micro-pores.
Hoping this will be helpful,
Rafik
Dear Rafik, superficial velocity is the velocity of a gas flowing through a packed bed reactor considered as if the solids were not present in the reactor. this velocity is readily available and can be used in calculations. for example, for a for a first order reaction in packed bed, the material balance equation for calculating the concentration of A in a bed of height H and solid fraction f is: lnCA0/CA = kfH/u0: where k = rate constant; f = fraction of solids in the reactor; H = height of bed and u0 is superficial velocity of the gas through the bed. Hope this will help you in you problem.
Superficial gas velocity is a measure to find how quickly one phase passes through a system (e.g. a pipe) when we have multi-phase flow within the system so that the presence of other phases (liquids and/or solids) are ignored. That is, we want to calculate the velocity of the intended phase through the system provided that the system has only this phase; to this end, we can divide the volumetric flow rate of the phase by the cross-sectional area of the system it is passing through.
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