Hot processes

In contrast to the cold isostatic pressing process, the hot process can readily employ powders having spherical or noninterlocking particles. The powder is simply poured in and vibration packed into a container of desired shape. The powder mass is then simultaneously compacted and bonded during the treatment. 

Sodium alumiaate is used ia the treatment of iadustrial and municipal water suppHes and the use of sodium alumiaate is approved ia the clarification of drinking water. The FDA approves the use of sodium alumiaate ia steam generation systems where the steam contacts food. One early use of sodium alumiaate was ia lime softening processes, where it iacreases the precipitation of ions contributing to hardness and improves suspended soHds removal from the treated water (17). Sodium alumiaate reacts with siHca to leave very low residual concentrations of siHca ia hot process water softeners. Sodium alumiaate is often used with other chemicals such as alum, ferric salts, clays, and polyelectrolytes, as a coagulant aid (18,19). 

Hot Process Softening. Hot process softening is usually carried out under pressure at temperatures of 108—116°C. At the operating temperature, hot process softening reactions go essentially to completion. This treatment method involves the same reactions described above, except that raw water COg is vented and does not participate in the lime reaction. The use of lime and soda ash permits hardness reduction down to 0.5 g/gal, or... 

Removal of SiOg by the hot process, to the levels shown, may require the feed of supplemental magnesium oxide. Sludge recirculation is necessary. All raw water constituents will be diluted by the steam used for heating by approximately 15% if the process is hot. 

Rehoiler Connected to the bottom of a fractionating tower, it provides the rehod heat necessary for distillation. The heating medium maybe either steam or a hot-process fluid. 

Where the phosphate coating is required to be more than 5 g/m an extra hot process is used, as noted later, when the use of toner (accelerator) becomes redundant, as it is ineffective above 70°C. 

Hot process 80-90°C for 5-7 minutes will provide a phosphate coating of more than 5 g/m. ... 

To the same solution add a few drops of phenol phthalein, and titrate it against N/10 NaOH until a pink colour appears, which will indicate the total acidity of the bath. This is approximately 35 to 37 for a concentration of 5% for a hot process and 60 to 64 for a concentration of 10% for a cold process. Obtain the standard total acidity of the hot or cold process chemicals from the manufacturer. 

The hot process is generally not recommended as it may dissolve the phosphate coating... 

Siiica S1O2 Scale in boilers and cooling water systems Insoluble turbine blade deposits due to silica vaporization Hot process removal with magnesium salts adsorption by highly basic anion exchange resins, in conjunction with demineralization distillation... 

Boiler ducts or flues Electric lamps Hot process equipment Welding metal Induction brazing Hot plates Soldering irons ... 

Ammonia Plant 1. Where possible, use natural gas as the feedstock for the ammonia plant, to minimize air emissions. 2. Use hot process gas from the secondary reformer to heat the primary reformer tubes (the exchanger-reformer concept), thus reducing the need for natural gas. 

Having determined the individual heating loads and cooling ctq)acities of all process streams for all temperature intervals, one can also obtain the collective loads (capacities) of the hot (cold) process streams. The collective load hot process streams within the zth interval is calculated by summing up the individual loads of the hot process streams that pass through that interval, i.e.. 

As has been mentioned earlier, within each temperature interval, it is ther modynamically as well as technically feasible to transfer beat from a hot process stream to a cold process stream. Moreover, it is feasible to pass heat from a hot process stream in an interval to any cold process stream in a lower interval. Hence, for the zth temperature interval, one can write the following heat-balance equation ... 

Fleat load from hot process equipment with a relatively simple configuration (e.g., tanks with hot water, solution, or oil) can be calculated using the following equation ... 

FIGURE 10.31 Canopy hoods over a cold process (left) and a hot process (right). 

FIGURE 10.3 2 Canopy hood with an airflow rate less than the thermal updraft airflow from a hot process. 

Capture efficiency measurements may be used to evaluate the function of a canopy hood (see Section 10.5). Capture velocity is not a feasible evaluation tool, since a canopy hood does not generate an air velocity close to the source. It is also possible to use exposure measurements for workers outside the plume area. Since most hot processes generate visible contaminants, visual inspection of the flow, especially around hood edges, might provide a qualitative evaluation. Many contaminants could however be invisible when diluted and smoke generators (Section 10.5) may be necessary to find leakages (temporary or permanent) around the hood edges. 

Air Extraction from the Enclosure A textbook approach to enclosure design for a hot process would follow a procedure of determining the in-draft veloc-... 

Waste heat (WH) boilers are essentially indirect (nonfired) steam generators that recover the heat energy present in hot gases of combustion (e.g., from a gas turbine) or from hot process stream gases. 

Both hot and cold processes are employed, although the hot process, which takes place at or above 212 °F (100 °C), is usually preferred for boiler FW applications, because it produces water of lower hardness levels and usually a lower silica content as well. Also, less lime is needed because the carbon dioxide with which it would normally react is driven off at the higher temperatures. Sometimes caustic soda (sodium hydroxide) is used in place of soda, depending on the alkalinity of the water and the chemical costs however, irrespective of the process or chemicals used, the major precipitants are always calcium carbonate and magnesium hydroxide. 

Chelants should not be used downstream of hot process or hot lime soda softening MU water treatment. 

The reactions seem to be primarily radical combinations, with some abstractions being evident. There is some question about failure of bond rupture. On the other hand it is clear that bond reformation does occur at each of the several possible stages by hot processes, by fast, but scavenger-sensitive processes, and during thermal treatment. 

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