Multiple beds

Figure 5. Example of multiple bed cross-flow scrubber.

Fluid Iron Ore Reduction (FIOR) is a process for reducing ore to iron with a reducing gas in a fluid bed. For thermodynamic efficiency, iron ore reduction requires counter current flow of ore and reducing gas. This is achieved in FIOR in a multiple bed reactor. Precautions are necessary to prevent significant back mixing of solids between beds, since this would destroy counter current staging. 

Demineralized water is water from which all the minerals have been removed by ion-eNchange. It is used where pure water is needed for a process and as boiler feed water. Mixed and multiple-bed ion-exehange units are used for this purpose, one resin converting the cations to hydrogen and the other removing the acid radicals. Water can be produced that has less than I ppm of dissolved solids. 

Basically, tliere are two classes of anunonia converters, tubular and multiple bed. The tubular bed reactor is limited in capacity to a maximum of about 500 tons/day. In most reactor designs, the cold inlet synthesis gas flows tlirough an annular space between the converter shell and tlie catalyst cartridge. This maintains the shell at a low temperature, minimizing the possibility of hydrogen embrittlement, which can occur at normal synthesis pressures. The inlet gas is then preheated to syntliesis temperature by the exit gas in an internal heat e.xchaiiger, after which it enters tlie interior of the anunonia converter, which contains tlie promoted iron catalyst. 

ExxonMobil extended the Hydrofining technology to produce a 200 ppm diesel, with the Diesel Oil Deep Desulfurization technology, DODD. The reactor is packed with multiple beds of different catalysts. A preceding history of commercial experience provided data to build a model for deep HDS and pave the way to a new technology, MAK Fining. 

Although PSA is a batchwise process, by using multiple beds in a sequential manner the overall process is operated in a continuous fashion. Each bed may contain layers of different adsorbent materials selective for specific contaminants in the hydrogen gas stream to be purified. Each bed undergoes a sequence of four basic steps in a PSA cycle adsorption, depressurization, purge at low pressure, and repressurization. This sequence of cyclic operations for each bed is shown schematically for a four-bed PSA process in Figure 8.4 (Yang, 1987 Cassidy, 1980 Miller and Stocker, 1999). 

A practical means of approaching the performance of multiple bed cycles that only requires two beds is the thermal wave approach patented by Shelton [8] and illustrated in Fig. 14. 

Elf-SRTI An industrial chromatographic process developed by Elf Aquitane Development and the Societe de Recherches Techniques et Industrielles. Multiple beds are used. Used for separating perfume ingredients and proposed for separating aliphatic hydrocarbons. 

MRU [Methanol recovery unit] A process for removing methanol from the unreacted components from the synthesis of methyl /-butyl ether. It uses selective adsorption on multiple beds of a zeolite such as 4A. Developed by Union Carbide Corporation and now licensed by UOP as of 1992, eight units had been licensed. See also ORU. 

This approach is proven for design and prediction of the performance of multiple-bed down-flow reactors. The complication, and a critical difference between this and a bubble column, is that the gas bubbles are formed in situ. The gas flux, and thus gas hold-up, will vary over the bed height. For the down-flow beds, a simplified linear gas hold-up profile was inherent in the design models, but with no apparent penalty in design accuracy. 

Add multiple bed density taps to the regenerator to determine quality of fluidization and identify a damaged or partially plugged air distributor... 

Capital costs for open single-bed filters installed in Germany are estimated at 25 to 95/ft of filter area depending on the size of the system. Costs for filters with multiple beds are about twice as high. For opeu siugle-bed filters iustalled in the United States, cost per square of filter... 

In industrial practice, a multiple-bed reactor (Fig. 3.24) is normally used for the synthesis of ammonia, rather than the single-stage reactor illustrated in Fig. 3.22. Because the reaction takes place at high pressures, the whole series of reactions is contained within a single pressure vessel, the diameter of which is minimised for reasons of mechanical design. 

The multiple-bed process uses essentially the same range of bed lengths and adsorbent particle sizes The time cycles of the three beds can be sequenced In such a way that compressed feed is always flowing to the process This reduces the size of the feed surge tank or completely eliminates the need for it. In general the fraction of the overall cycle devoted to the feed pulse in the multiple-bed process Is much greater - about... 

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