Tapping processes

The carbide impurities tend to distill and are reoxidized in the upper, cooler region of the charge. This process forms cmsts near the top of the charge or around the cooler part of the reaction cmcible and causes trouble in furnace operation. Large amounts of dissolved calcium siUcate and alurninate may form a viscous melt and impede the tapping process. FerrosiUcon is commonly removed from the cmshed carbide by electromagnets. 

One such process is the TAP process, the basic patent being held by Dow. It was developed in Japan by Asahi in conjuction with Toshiba. Foam expansion after mould filling is made possible by use of retractable mould cores. Because of the difficulty of allowing expansion in more than one direction this process has been largely limited to the production of flat products. Efficient gas sealing systems are also vital and the process needs close control. For this reason it has not been widely used in either Europe or North America. 

This technique permits estimation of the volumetric flow rate at any level above a source, provided that the result is matched to the gravitational fume acceleration terms applicable near the source. The result of such an analysis is shown in Fig. 13.30. The emission flow rate from an electric arc tapping process has been estimated at any level above the steel ladle using the stopwatch technique in conjunction with the plume theory. 

Rosin. Rosin resin, also known as colophony, is collected from one of over 100 different types of trees that grow throughout Europe, Asia, North America, and New Zealand. The term colophony seems to derive from the ancient city of Colophon, in Lydia, which produced a high-quality resin. Rosin is drawn directly from living trees in a tapping process that entails inducing outflow of the resin from the trees. Rosin has been used as an adhesive and size and in the preparation of paints. 

Open system The behaviour of the REE in a periodically replenished, periodically tapped, processes continuously fractionated (RTF) magma chamber (Section 4.2.2) is described by O Hara and Matthews (1981). Using chondrite-normalized values of Ce/Yb to represent the slope of the REE diagram, and Sm values as a measure of REE... 

Fig.9 shows ac tensammetric curves of double distilled, tap, process and Rhine river (Basle) waters as measured in the authors laboratory as compared to distilled water (curve 1, Fig.9). A significant depression of the current is observed for both the process and Rhine water.

Fig. 136.1 Schematic section of a pine trunk showing the main layers that can be removed in resin tapping processes (Adapted from [185])...

There are limits to the level of zinc in final slag, because as the oxygen potential is lowered to reduce more zinc, the tendency to reduce FeO and form iron is increased. At slag temperatures of 1350°C the presence of metallic iron can cause considerable difficulties in the tapping process. Generally zinc levels are not reduced much below six per cent in final slag for this reason. 

During this process some water will have condensed in the steam-trap D and also in the distillation bulb F. If at the end of the steaming-out process, the Bunsen burner is removed from the generator A, the pressure in A will be reduced owing to steam condensation, and the liquid in F will be sucked back into D provided that the benL-over tube is carefully adjusted, the bulb F may be almost completely emptied of liquid as desired. Finally the condensed water in the steam-trap D may be run out by op ing the tap Tj. 

A fundamental requirement in powder processing is characterization of the as-received powders (10—12). Many powder suppHers provide information on tap and pour densities, particle size distributions, specific surface areas, and chemical analyses. Characterization data provided by suppHers should be checked and further augmented where possible with in-house characterization. Uniaxial characterization compaction behavior, in particular, is easily measured and provides data on the nature of the agglomerates in a powder (13,14). 

There are three types of TAP emissions continuous, intermittent, and accidental. Both routine emissions associated with a batch process or a continuous process that is operated only occasionally can be intermittent sources. A dramatic example of an accidental emission was the release of methyl isocyanate [624-83-9] in Bhopal, India. As a result of this accident, the U.S. Congress created Tide III, a free-standing statute included in the Superfund Amendments and Reauthorization Act (SARA) of 1986. Title III provides a mechanism by which the pubHc can be informed of the existence, quantities, and releases of toxic substances, and requires the states to develop plans to respond to accidental releases of these substances. Eurther, it requires anyone releasing specific toxic chemicals above a certain threshold amount to aimuaHy submit a toxic chemical release form to EPA. At present, there are 308 specific chemicals subject to Title III regulation (37). 

Advantages of the pitot method of measurement are low pressure loss and easy installation. In some cases, installations in existing lines are made without process shutdown by hot tapping the line (7). 

Gum Karaya. Gum karaya [19000-36-61] or sterculia gum is the dried exudate of the Sterculia urens tree, which is now cultivated in India, the primary producing area. The best quahty gum is collected by tapping the trees during the period April to June with a second collection of lower quahty product later in the year. The gum is allowed to dry on the trees, and the cmde gum is collected and sorted according to color and purity. It is further sorted and processed to powdered gum karaya in the country of use. The quahty of supphes varies greatly (43). 

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