Stage per packed bed

In order to analyse the packed bed process, it is necessary to consider both heat transfer from the solid to the gas and reaction heat which may be transmitted to the gas. The composition of the gas, and hence its physical properties, are determined by the rate of reduction, which in turn depends on each layer of the packed bed, and on the degree of reduction which has already occurred. In the reduction of haematite, there are three stages in the reduction, corresponding to the formation of Fe304 and FeO before the metal is formed. The thermal data for the reduction processes can be approximated by the respective heats of reduction by H2 and CO gases. Taking 1000°C as a typical mean temperature, the mean value for the heats of reaction per 2 gram-atom of iron are... 

Deaerator. The deaerator was designed to reduce the amount of air dissolved in the feed to a value equivalent to 0.005 cc. of oxygen per liter of salt water feed. It is a two-stage unit. The feed at 65° F. is sprayed into a vacuum of 41.4 mm. of mercury and then flows over a packed bed of ceramic Raschig rings maintained at a pressure of 16 mm. Very little liquid is flashed, so the feed is cooled less than 1° in the deaerator. 

Comment. The recommended published criteria surveyed by Kister (40) suggest that it is best to redistribute liquid approximately every 20 ft, and to have no more than 10 theoretical stages per bed. Both of these criteria suggest that the bottom section of the tower should have two packed beds with a redistributor in between, while the top section should contain one packed bed. 

McMullan et al describe the modification of a large diameter tower from sieve trays to IMTP packing [10]. Due to the very low liquid flow rates, only three to four distribution points were used per sq ft in the liquid distributor in order to avoid plugging, which could occur with smaller orifices. Experience has demonstrated that uniform liquid and vapor distribution is required to obtain the large number of theoretical stages needed for this separation. This column now is providing a total of 63 theoretical stages in four packed beds. 

Plastic Nutter Rings are rigid and energy efficient, and permit applications to produce pressure drops per theoretical stage and bed heights, not attainable with other random particle packing. 

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