Oversizing

If no appraisal was performed, and the development was started based, say, on the medium case STOMP of 48 MMstb, then the actual STOMP would not be found until the facilities were built and the early development wells were drilled. If it turned out that the STOMP was only 20 MMstb, then the project would lose 40 million, because the facilities were oversized. If the STOMP is actually 48 MMstb, then the NPV is assumed to be the same as for the medium case after appraisal. If the STOMP was actually 100 MMstb, then the NPV of + 40 million is lower than for the case after appraisal (+ 66 million) since the facilities are too small to handle the extra production potential. 

The wisest fan choice is frequently not the cheapest fan. A small fan operates well on its curve but may not have adequate capacity for maximum flow control, future needs, or process upset conditions. It may be so lightly constmcted that it is operating near its peak speed with no provision for speed increases in the future, if needed. As fan size is increased, efficiency generally improves and wheel speed is lower. These factors decrease operating cost and provide reserve capacity for the future. However, it is also possible to oversize a fan and impair its performance. 

Autofrettage of small bore tubes can be effected by pushing highly poHshed and generously lubricated oversized drifts or balls through the bore. 

After acid removal, scrap batteries are fed to a hammer mill in which they are ground to <5 cm particles. The ground components are fed to a conveyor and passed by a magnet to remove undesirable contamination. The lead scrap is then classified on a wet screen through which fine particles of lead sulfate and lead oxide pass, and the large oversize soHd particles are passed on to a hydrodynamic separator. The fine particles are settled to a thick slurry and the clarified washwater recirculated to the wet screen. 

A high, moisture content necessitates finer grinding of coal for rapid water release. For such coals, the classifier in the pulverizer is set to return more of the oversize material for further grinding. 

Most limestone quarries use either 100% ammonium nitrate [6484-52-2] (fertilizer grade) and fuel oil (ANFO), or a combination of ANFO and ammonium or gelatin dynamite, for blasting (see Explosives and propellants, explosives). After blasting, oversized boulders usually are reduced to manageable sizes by drop ball cranes. 

If a plant cmshes to obtain stone of 0.6 and 7.6 cm for lime-kiln feed, coarse aggregate, or fluxstone, much undersized material is also produced. Oversized material can be reduced by recycling through the cmsher system, but the subsized stone, called spall, is wasted in a spall pile. Such spalls have potential value as by-products for use as, eg, asphalt (qv) filler. 

Industrial screening is used essentially for separations over 0.2 mm and in conjunction with cmshers because the efficiency decreases rapidly as particle size decreases. The main objective is to remove undersize material that should not be circulated back to the cmshers, or to remove (scalp) oversize material or trash that should not report to the subsequent processing step. Other appHcations of screening include production of a specification size material (as in quarrys), dewatering, and trash removal from processed material. 

The products are an oversize (underflow, heavies, sands) and an undersize (overflow, lights, slimes). An intermediate size can also be produced by varying the effective separating force. Separation size maybe defined either as a specific size in the overflow screen analysis, eg, 5% retained on 65 mesh screen or 45% passing 200 mesh screen, or as a d Q, defined as a cut-off or separation size at which 50% of the particles report to the oversize or undersize. The efficiency of a classifier is represented by a performance or partition curve (2,6), similar to that used for screens, which relates the particle size to the percentage of each size in the feed that reports to the underflow. 

Oversized chips are sometimes sHced to control thickness in a slicing rechipper. The uniform thickness results in more even penetration of pulping liquors and therefore less screen rejects in the resultant pulp. 

The process of pulverized cuUet reduction yields a product having near-batch equivalent sizing (—12 mesh (<1.7 mm mm)) and in a furnace-ready condition. Foil-backed paper, lead and other metals, and some tableware ceramics can be removed in an oversized scalping operation after the first pass through the system. Other contaminants are reduced to a fine particle size that can be assimilated into the glass composition during melting. 

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