Preferential feeding

It should be realized also that either option shown in Fig. 9 or 10 will produce a non-symmetrical flow pattern inside the blow tank (i.e., due to preferential feeding at the blow tank outlet) and hence, promote the possibility of arching, rat holing and/or formation of dead regions. For these reasons, the combined fluidizing-discharge-cone and cone-dosing valve system shown in Fig. 8 is preferred. 

Intermediate surge can be provided at a lower temperature. This is often practiced when the intermediate material is thermally unstable. To minimize heat losses, it is usually desirable to devise a control strategy that preferentially feeds the hot material into the next column (e.g., Fig. 19.14). However, such a strategy will be self-defeating if implemented at the expense of excessive flow fluctuations to the downstream column. In Fig. 19.14, column I s bottom flow controller must be set low enough so that the column level controller always stays on control. 

The tick life cycle is comprised of three developmental st larvae, nymph and adult. Tick larvae can acquire bacteria from infected hosts and subsequently transmit them to mammals once they molt to nymphs. During the nymph stage, I. scaptdaris preferentially feeds on small wild rodents, where transmission of vector-borne pathogens to the mammalian host is most efficient. The adult tick attaches and feeds on medium to large mammals including humans and can also contribute to pathogen transmission. ... 

Solvent power characterizes the miscibility of solute and solvent. This concept covers two types of uses dissolving a solid or reducing the viscosity of a liquid. The solvent power should be as high as possible. However, a solvent used as an extractant should also be selective, i.e., extract certain substances preferentially from the feed being treated. 

Naphtha at one time was a more popular feed, and alkah-promoted catalysts were developed specifically for use with it. As of 1994 the price of naphtha in most Western countries is too high for a reformer feed, and natural gas represents the best economical feedstock. However, where natural gas is not available, propane, butane, or naphtha is preferentially selected over fuel oil or coal. 

In pelletizing, the water—carbon slurry is contacted with a low viscosity oil which preferentially wets the soot particles and forms pellets that are screened from the water and homogenized into the oil feed to the gasification reactor (see Size enlargement). 

The selectivity of pervaporation membranes varies considerably and has a critical effect on the overall separation obtained. The range of results that can be obtained for the same solutions and different membranes is illustrated in Figure 41 for the separation of acetone from water using two types of membrane (89). The figure shows the concentration of acetone in the permeate as a function of the concentration in the feed. The two membranes shown have dramatically different properties. The siUcone mbber membrane removes acetone selectively, whereas the cross-linked poly(vinyl alcohol) (PVA) membrane removes water selectively. This difference occurs because siUcone mbber is hydrophobic and mbbery, thus permeates the acetone preferentially. PVA, on the other hand, is hydrophilic and glassy, thus permeates the small hydrophilic water molecules preferentially. 

Many appHcations use screws with constant pitch to feed material from a slotted opening. The configuration shown in Figure 9a shows a constant pitch and constant diameter causing a preferential flow channel to form at the back (over the first flight) of the screw. This type of flow destroys the mass flow pattern and potentially allows some or all of the problems discussed about fiinnel flow. 

Liquid-liquid fractionation, or fractional extraction (Fig. 15-6), is a sophisticated scheme for nearly complete separation of one solute from a second solute by liquid-liquid extraclion. Two immiscible liquids travel countercurrently through a contaclor, with the solutes being fed near the center of the contactor. The ratio of immiscible-liquid flow rates is operated so that one of the phases preferentially moves the first solute to one end of the contactor and the other phase moves the second solute to the opposite end of the contactor. Another way to describe the operation is that a primaiy solvent S preferentially extracts, or strips, the first solute from the feed F and a wash solvent... 

Lube oil extraction plants often use phenol as solvent. Phenol is used because of its solvent power with a wide range of feed stocks and its ease of recovery. Phenol preferentially dissolves aromatic-type hydrocarbons from the feed stock and improves its oxidation stability and to some extent its color. Phenol extraction can be used over the entire viscosity range of lube distillates and deasphalted oils. The phenol solvent extraction separation is primarily by molecular type or composition. In order to accomplish a separation by solvent extraction, it is necessary that two liquid phases be present. In phenol solvent extraction of lubricating oils these two phases are an oil-rich phase and a phenol-rich phase. Tne oil-rich phase or raffinate solution consists of the "treated" oil from which undesirable naphthenic and aromatic components have been removed plus some dissolved phenol. The phenol-rich phase or extract solution consists mainly of the bulk of the phenol plus the undesirable components removed from the oil feed. The oil materials remaining... 

In the industrial process, the chlorocarbon and liquid hydrogen fluoride feeds are pumped simultaneously into a complex liquid mixture of Sb(lII) and Sb(V) chlorofluondcs at temperatures in the 60-150 °C range The products are generally more volatile than the reactants and therefore distill preferentially from the reactor vessel, thus the reactor can be operated continuously. 

Liquid solvents are used to extract either desirable or undesirable compounds from a liquid mixture. Solvent extraction processes use a liquid solvent that has a high solvolytic power for certain compounds in the feed mixture. For example, ethylene glycol has a greater affinity for aromatic hydrocarbons and extracts them preferentially from a reformate mixture (a liquid paraffinic and aromatic product from catalytic reforming). The raffinate, which is mainly paraffins, is freed from traces of ethylene glycol by distillation. Other solvents that could be used for this purpose are liquid sulfur dioxide and sulfolane (tetramethylene sulfone). 

The effects of the feed ratio in the lipase CA-catalyzed polymerization of adipic acid and 1,6-hexanediol were examined by using NMR and MALDI-TOF mass spectroscopies. NMR analysis showed that the hydroxyl terminated product was preferentially formed at the early stage of the polymerization in the stoichiometric substrates. As the reaction proceeded, the carboxyl-terminated product was mainly formed. Even in the use of an excess of the dicarboxylic acid monomer, the hydroxy-terminated polymer was predominantly formed at the early reaction stage, which is a specific polymerization behavior due to the unique enzyme catalysis. 

So far, the separation of azeotropic systems has been restricted to the use of pressure shift and the use of entrainers. The third method is to use a membrane to alter the vapor-liquid equilibrium behavior. Pervaporation differs from other membrane processes in that the phase-state on one side of the membrane is different from the other side. The feed to the membrane is a liquid mixture at a high-enough pressure to maintain it in the liquid phase. The other side of the membrane is maintained at a pressure at or below the dew point of the permeate, maintaining it in the vapor phase. Dense membranes are used for pervaporation, and selectivity results from chemical affinity (see Chapter 10). Most pervaporation membranes in commercial use are hydrophyllic19. This means that they preferentially allow... 

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