Abrasive solids

In selec ting the machines of choice, the use of specific speed and diameter best describe the flow. Figure 10-67 shows the characteristics of the three types of compressors. Other considerations in chemical plant service such as problems with gases which may be corrosive or have abrasive solids in suspension must be dealt with. Gases at elevated temperatures may create a potential explosion hazard, while air at the same temperatures may be handled qmte normally minute amounts of lubricating oil or water may contaminate the process gas and so may not be permissible, and for continuous-process use, a high degree of equipment rehability is required, since frequent shutdowns for inspec tion or maintenance cannot be tolerated. 

When abrasive solids are present and it is not permissible to introduce appreciable quantities of a secondary flushing fluid into the process, double internal seals are sometimes used (Fig. 10-114). Both sealing faces are protected by the flushing fluid injected between them even though the inward flow is negligible. 

When abrasive solid particles must be suspended, maintenance costs for the submerged shaft seal of a side-entering propeller may become high enough to make this type of mixer an uneconomical choice. 

Diesel fuel may contain ash-forming materials in the form of abrasive solids or soluble metallic soaps. These solids cause wear of injection equipment, pistons, piston rings, and liners as well as increasing engine deposits. Ash content is expressed as a percentage of the weight of the original test sample of the fuel when burned to completion m an open container. 

The surface hardness, as measured in a standard test, is an indication of a material s ability to resist wear. This will be an important property if the equipment is being designed to handle abrasive solids, or liquids containing suspended solids which are likely to cause erosion. 

Vacuum filtration has many advantages, not the least being the fact that the feed slurry, often containing abrasive solids in a corrosive liquid, can be delivered by gravity flow or by low pressure pumps which need only to overcome the resistance in the feed pipework. In addition, vacuum filtration equipment does not have to withstand high pressures... 

Although CMP slurry is supposed to be primarily abrasive solids, only those abrasives chosen by the slurry manufacturer should be used for polishing. The two largest sources of particulate contamination during... 

Screw pumps, because of multiple dams that reduce slip, are well adapted for producing higher pressure rises, for example, 6.895 MPa (1000 Ibfofo), especially when handling viscous liquids such as heavy oils. The all-metal pumps are generally subject to the same limitations on handling abrasive solids as conventional gear pumps. In addition, the wide bearing spans usually demand that the liquid have considerable lubricity to prevent metal-to-metal contact. 

Screw conveyors are suited to transport of even sticky and abrasive solids up inclines of 20° or so. They are limited to distances of 150 ft or so because of shaft torque strength. A 12 in. dia conveyor can handle 1000-3000 cuft/hr, at speeds ranging from 40 to 60 rpm. 

Drum dryers are built as single drum, double drum or twin drum units. In the twin drum unit the tops of the drums rotate away from each other while they rotate toward each other in a double drum unit. Double drum units with top feed at the drum nip are not suited to applications where large hard lumps are possible in the feed or where abrasive solids may settle from the feed. Both conditions may create excessive pressure between the drums. 

DilFerences ma also be due to the condition of the valve after it has been in service for a time. For example, a Class valve can he quickly turned into a Class II valve tor worse) by erosion due to abrasive solids, cavitation, or the wire drawing effects of flow across valve seats vhen the valve is sluu ofl or nearly so. 

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