Regeneration of adsorbent bed

One of the inherent problems in regeneration of adsorbent beds is disposal of the desorbed material. In activated... 

Figure 15.10. Incomplete regeneration of adsorbent bed by a thermal-swing cycle.

Hydrogen, which is highly volatile and non-polar or polarizable, is, when mixed with various impurities, practically unadsorbable, and is hence easy to purify by this method. The regeneration of adsorbent beds which have fi.xed the other components is usually carried out by raising the temperature obtained by a stream of hot gas which also acts as the desorbent the restoration of adsorption conditions then requires the beds to be cooled. These heat transfers are slow, making the process inapplicable to rapid cycles, and restricts it to the separation of small amounts of impurities. 

While adsorption equiUbrium considerations do justify the possibility to regenerate an adsorbent bed completely and to uniform levels, this is rarely achieved in practice in either thermal swing adsorption and is almost never the case in pressure swing adsorption. Some residual sorbate is always left on the sorbent and in general, except for TSA with only one or two sorbates, the residual loadings are almost always found as a non-uniformly distributed profile across the length of the bed. 

Lifetime of Adsorber Bed Before Regeneration 3 days 3 days... 

The simulation reported here consists of the following sequential operating procedure applied to an initially evacuated adsorber (I) charge up to P = 10 bar, (II) constant-pressure feed, and (III) discharge down to F = 1.25 bar. This example encompasses the major steps of every cyclic batch adsorption process for gas separation, in which regeneration of the bed is accomplished by reducing the pressure at essentially constant temperature, as is the case in pressure swing adsorption. The input parameters and output variables for each phase are listed in Table 1. 

When the bed is saturated, regeneration of the adsorbent is necessary. Carbon beds are typically regenerated with steam, hot air, or a combination of vacuum and hot gas. 

Most commercial adsorbents for gas-phase appHcations are employed in the form of pellets, beads, or other granular shapes, typically about 1.5 to 3.2 mm in diameter. Most commonly, these adsorbents are packed into fixed beds through which the gaseous feed mixtures are passed. Normally, the process is conducted in a cycHc manner. When the capacity of the bed is exhausted, the feed flow is stopped to terminate the loading step of the process, the bed is treated to remove the adsorbed molecules in a separate regeneration step, and the cycle is then repeated. 

Although most appHcations of fixed bed have multiple adsorber beds to treat continuous streams, batch operation using a single adsorber bed is an alternative. For purification appHcations, where one vessel can contain enough adsorbent to provide treatment for days, weeks, or even months, the cost savings and simplicity often justify the inconvenience of stopping adsorption treatment periodically for a short regeneration. 

When the mass transfer 2one is a major portion of an adsorbent bed, the equiHbrium capacity is poorly utilized. A lead—trim configuration uses the adsorbent mote fuUy. The feed flows successively through a lead bed and then a trim bed. The lead bed is neatly exhausted before it is taken out of service to be regenerated. When a lead bed is removed from adsorption, the trim bed becomes the lead, and a fuUy regenerated bed becomes the new trim bed. 

Industrial-scale adsorption processes can be classified as batch or continuous (53,54). In a batch process, the adsorbent bed is saturated and regenerated in a cychc operation. In a continuous process, a countercurrent staged contact between the adsorbent and the feed and desorbent is estabhshed by either a tme or a simulated recirculation of the adsorbent. 

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