Dead spots

Presence of Solids When a pump is required to pump a hquid containing suspended solids, there are unique requirements which must be considered. Adequate clear-liquid hydraiilic performance and the use of carefully selected materials of construction may not be all that is required for satisfacdoiy pump selection. Dimensions of all internal passages are critical. Pockets and dead spots, areas where solids can accumulate, must be avoided. Close internal clearances are undesirable because of abrasion. Flushing connections for continuous or intermittent use should be provided. 

In the Agitair Rotation machine (Fig, 19-76), the impeller is a Rat rubber-covered disk with steel Fingers extending downward From the peripheiw, A rubber-covered stabilizer eliminates dead spots in the agitation zone and improves biibble-ore contact. The degree oF aeration is controlled bv regulating air volume on each cell with an individual air v alv e. Air is supplied at 10 x lO Pa (1,5 IbF/iir),... 

Belt or apron feeders can also be used to give uniform feed from a bin, but care must be taken that dead spots are not produced in the... 

The copolymers have been used in the manufacture of extruded pipe, moulded fittings and for other items of chemical plant. They are, however, rarely used in Europe for this purpose because of cost and the low maximum service temperature. Processing conditions are adjusted to give a high amount of crystallinity, for example by the use of moulds at about 90°C. Heated parts of injection cylinders and extruder barrels which come into contact with the molten polymer should be made of special materials which do not cause decomposition of the polymer. Iron, steel and copper must be avoided. The danger of thermal decomposition may be reduced by streamlining the interior of the cylinder or barrel to avoid dead-spots and by careful temperature control. Steam heating is frequently employed. 

Injection moulding cylinders should be free from dead spots and a temperature gradient along the cylinder is desirable. 

I.tine shaped tt p to prwince t cmi-Ununus /Tfiu of air ttver the irofs-sectivnat ana of the talnnet wit hall f chantjclling ot dead spots. 

The entire system is operated at high temperatures to increase the solubility of potassium carbonate. Therefore, the designer must be careful to avoid dead spots in the system where the solution could cool and precipitate solids. If solids do precipitate, the system may suffer from plugging, erosion, or foaming. 

Avoid dead spots. Coke grows wherever there is a cold spot in the system. Use dry dome steam to purge hydrocarbons from the stagnant area above the cyclones. Dead spots cause thermal cracking. 

Furnace areas require baffles to deflect the gases back and forth between the tubes. Correct baffle arrangements are necessary to maintain combustion gas velocity, ensure correct temperature differentials, prevent short circuiting of the gas path, and minimize dead spots, which encourage the deposition of flyash. 

Higjier degree of dispersion because of lack of dead spots... 

The location of the reinjection wells with respect to the recovery well is also an important consideration. Locating the wells too closely can create counterproductive effects. Locating the reinjection wells too far away from the recovery well may significantly reduce the desired effect or eliminate the benefits altogether. If the latter is the case, dead spots may result and may cause short-circuiting of the LNAPL pool hydrocarbon plume. Once this happens, off-site migration of the plume is possible. In fact, reinjection wells placed and spaced improperly can, in some instances, accelerate off-site migration. 

Polymer flow issues are concerns on the part of plant operations personnel that can arise when one proposes to put an in-line NIR probe (or pair of probes) into a polymer reactor or transfer line. These concerns tend to be plant or process-specific. Plant personnel are likely to be concerned if the probe will change the pressure drop in the line, create a cold spot in the reactor or line, protrude into the flow stream, or create dead spots (e.g. recessed probes or the downstream side of protruding probes). There may also be plant- or process-specific resfricfions on where probes (or analyzers) can be located, on pipe sizes, on the use of welds, and on materials of construction. It is critical to involve plant operations personnel (including process operators) as early as possible in discussions about probe design and location. 

Because of the limited thermal stability of, e.g., Ecoflex /starch compounds, dead spots in the feed block adapter or the film die have to be avoided. As a consequence, reduction of the film width by closing the die with metal bars (deckling) is not recommended for Ecoflex /starch compounds. 

Identify appropriate blending time and speed ranges, dead spots in blenders, and locations of segregation in intermediate bulk containers (IBCs). 

Dead spots and crevices - where equipment parts are not continuously wetted by oxygen-containing liquids - are prone to severe corrosion. Therefore, fabrication of this equipment should be done to avoid such vulnerable spots. An effort should also be made to reduce the potential for process contamination by corrosive agents such as sulfur (through oil in liquid NH3), H2S (along with C02) and chlorides (from cooling water)88. 

Some mixing chambers have curved bottoms that enhance movement of materials. Others have internal baffles or some similar design to increase turbulence and eliminate dead spots in the chamber. Shafts can enter the chamber from the top (allowing easier cleanup) or from the bottom (allowing easier vacuum degassing). 

Mixing equipment should be evaluated for the presence of dead spots, which may affect blend uniformity (i.e., valves and discharge ports). All production equipment should be assessed for suitability of use in the manufacturing process this should include ease of cleaning and ability to maintain control parameters (including sterilization, if applicable). Test results consistently at or near the upper or lower limits indicate problems with the process or incompatibility with the equipment. All equipment should be adequately identified in each batch record. A detailed description of all equipment should be given in the submission as well. The suitability of the equipment for the process can be... 

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