Blockage

Blockages, usually caused by overloading of the sohds outlet orifice, is one of the most common causes of failure in cyclone operation. The cyclone cone rapidly fills up with dust, the pressure drop increases and efficiency falls dramatically. Blockages arise due to mechanical defects in the cyclone body (bumps on the cyclone cone, protruding welds or gasket) or changes in chemical or physical properties of the solids (e.g. condensation of water vapour from the gas onto the surface of particles). 

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Under certain conditions of temperature and pressure, and in the presence of free water, hydrocarbon gases can form hydrates, which are a solid formed by the combination of water molecules and the methane, ethane, propane or butane. Hydrates look like compacted snow, and can form blockages in pipelines and other vessels. Process engineers use correlation techniques and process simulation to predict the possibility of hydrate formation, and prevent its formation by either drying the gas or adding a chemical (such as tri-ethylene glycol), or a combination of both. This is further discussed in SectionlO.1. 

To prepare gas for evacuation it is necessary to separate the gas and liquid phases and extract or inhibit any components in the gas which are likely to cause pipeline corrosion or blockage. Components which can cause difficulties are water vapour (corrosion, hydrates), heavy hydrocarbons (2-phase flow or wax deposition in pipelines), and contaminants such as carbon dioxide (corrosion) and hydrogen sulphide (corrosion, toxicity). In the case of associated gas, if there is no gas market, gas may have to be flared or re-injected. If significant volumes of associated gas are available it may be worthwhile to extract natural gas liquids (NGLs) before flaring or reinjection. Gas may also have to be treated for gas lifting or for use as a fuel. 

The Z-spray inlet/ionization source sends the ions on a different trajectory that resembles a flattened Z-shape (Figure 10.1b), hence the name Z-spray. The shape of the trajectory is controlled by the presence of a final skimmer set off to one side of the spray instead of being in-line. This configuration facilitates the transport of neutral species to the vacuum pumps, thus greatly reducing the buildup of deposits and blockages. 

Special small ultrasound transducers, often referred to as endoscopic transducers, have been designed which can be inserted into blood vessels to examine blockages in arteries (43). These transducers operate at approximately 20 MHz and have a viewing distance of less than a centimeter. Such devices are capable of producing ultrasound images of the inside of arteries and veins. The quaUty of the ultrasound image is sufficient to determine the type of blockage. 

As a part of the power demonstration program of the AFC in the 1950s, the Enrico Fermi fast breeder reactor (Fermi-1) was built near Detroit by a consortium of companies led by Detroit Edison. Fermi-1 used enriched uranium as fuel and sodium as coolant, and produced 61 MWe. It suffered a partial fuel melting accident in 1966 as the result of a blockage of core coolant flow by a metal plate. The reactor was repaired but shut down permanently in November 1972 because of lack of binding. Valuable experience was gained from its operation, however (58). 

Multielevation piperacks are usually needed to handle all the required services for piping, electrical, utilities, and instmmentation. The two-level rack is one of the most common but three-level ones are also used. The utility lines are usually mn in the upper level and the process lines in the lower levels. The larger-diameter lines are located to the outside of the rack to be closest to the column supports. Access platforms are required at the battery limit to provide operators access to the block valves and blinds. If long mns of hot pipe are required, a portion of the pipe rack needs to be dedicated to an expansion loop. A horizontal space in the piperack is provided for a set of lines to be flat-turned into a set of expansion loops with the large pipes located on the outside. AH of the pipe turns are in the same horizontal plane, which is an exception to normal piping practice. A flat turn takes up and blocks space for other pipes. Flat turns are generally only made from the outside of the rack to minimize this blockage. 

Local anesthetics produce anesthesia by blocking nerve impulse conduction in sensory, as well as motor nerve, fibers. Nerve impulses are initiated by membrane depolarization, effected by the opening of a sodium ion channel and an influx of sodium ions. Local anesthetics act by inhibiting the channel s opening they bind to a receptor located in the channel s interior. The degree of blockage on an isolated nerve depends not only on the amount of dmg, but also on the rate of nerve stimulation (153—156). 

Fig. 5. In coronary bypass, an autologous saphenous vein is used to provide critical blood to the heart muscle, bypassing a blockage in the coronary artery.

High purity 75% ferrosihcon containing low aluminum and calcium can be used in continuously cast heats where nozzle blockage is a problem. In iron melting, this ahoy is desirable to minimize buildup on refractory faces in the furnace or on stopper rods or nozzles. Low aluminum ferroshicons can also help reduce hydrogen pin holes in castings poured in green-sand molds. 

Under typical chlorination conditions, most elements are chlorinated. Therefore, for every metric ton of titanium tetrachloride produced, lower grade feedstocks requite more chlorine. Minor impurities such as alkaline-earths, where the chlorides are relatively involatile, may either inhibit bed-fluidization or cause blockages in the equipment and requite particular consideration regarding feedstock specification. 

The mechanism of antiperspinant action has not been fully estabHshed but probably is associated with blockage of ducts leading to the surface by protein denaturation by aluminum salts. The FDA has mandated that an antiperspinant product must reduce perspiration by at least 20% and has provided some guidelines for testing finished products. Some antiperspinant chemicals are Hsted in Table 14 (63). 

Sieve plates usually have negligible hydraulic gradient. Bubble-cap plates can have significant gradient because of the blockage by the caps. Valve plates presumably are intermediate, with hydraulic-gradient characteristics approaching those of sieve plates. 

Cloth Blinding Continuous filters, except for precoats, generally use some type of medium to effect the separation of the solid and filtrate phases. Since the medium is in contact with the process solids, there is always the danger, and almost invariably the ac tual occurrence, of medium blinding. The term blinding refers to blockage of the fabric itself, either by the wedging of process solids or by solids precipitated in and around the yarn. 

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