The adsorption capacity of the adsorbents is expressed by static adsorption capacity and dynamic adsorption capacity. The static adsorption capacity is the largest amount of adsorbed substance when the adsorbents per unit mass (or unit volume) reach the adsorption equilibrium under certain temperature and certain concentration of absorbed components, that is the ratio of the maximum adsorptive capacity (equilibrium value) that can be reached by the adsorbents to the adsorbents.
The dynamic adsorption capacity is the adsorptive capacity when the absorbents reach the "conversion point" (expressed by the average adsorptive capacity per unit of absorbents in the adsorber ). Generally, it is calculated by "conversion time", that is, the time from the fluid contacting the absorbents layer to the "conversion point. "Turning effect point" is the point where the concentration of absorbed component increases obviously when fluid flows out of the absorption layer. Since gas (or liquid) continuously flows through the surface of the adsorbents, The adsorbents flow away before reaching the saturation (the adsorbable capacity does not reach the maximum), so the dynamic adsorption capacity is smaller than the static adsorption capacity, generally taking 40% of the static adsorption capacity ~ 60%. Dynamic adsorption capacity is used in design.
There are many factors affecting the adsorption capacity, mainly including:
1) the temperature of the adsorption process and the partial pressure of the absorbed components. Under the same partial pressure (or concentration) of the absorbed component, the adsorption capacity decreases with the increase of temperature; while at the same temperature, the adsorption capacity decreases with the partial pressure (or concentration) of the absorbed component) increase and increase. But it has a limit that after the partial pressure increases to a certain extent, the adsorption capacity is basically irrelevant to the partial pressure. Thus it can be seen that the temperature of the adsorption process should be reduced as much as possible to improve the adsorption effect.
2) flow rate of gas (or liquid. The higher the flow rate is, the worse the adsorption effect will be. The decrease of dynamic adsorption capacity is due to the short contact time between gas (or liquid) and absorbents. Lower flow rate, better adsorption effect. But if the flow rate is designed too low, the volume of the adsorber needed should be very large. Therefore, it is necessary to select a relatively appropriate flow rate value (it is advisable to have empirical data when designing ).
3) the degree of regeneration and perfection of the absorbents. The more complete the regeneration and desorption is, the larger the adsorption capacity will be; otherwise, the smaller the adsorption capacity will be. The degree of regeneration perfection is related to regeneration temperature (or pressure) and the concentration of absorbed components in the regeneration gas.
4) thickness of absorbents. Because the adsorption process is conducted in layers, it is related to the thickness of the absorption layer (length of the adsorption zone. The absorption layer should not be too thin. When it is too thin, it is too late to adsorb because of the short contact time. Even if the cross-sectional area of the absorption layer is larger, it is useless. The absorption layer is thick, and the absorption effect is good. For example, the pressure of silica gel is 0.6MPa, the content of carbon dioxide is 300×10-6, and the temperature is-110 ~ When it is-120℃ and the flow rate is 1L/(min • cm2), each gram of silica gel has a relatively large adsorption capacity on carbon dioxide, which is about 25 ~ 50 mL/g. When designing, take 28 mL/g, and the content of carbon dioxide in the outlet airflow is less than 2×10-6. The dynamic adsorption capacity of silica gel on acetylene, 4.5L/kg or 2.63 mg/kg (silica gel) is often used domestically ).
