Hopper venting

Low absolute pressure calculations, 129 Low pressure system, 129 American Petroleum Institute, 399 American Society of Mechanical Engineers, 399 API Codes, 399 API oil field separators, 239 API, heat absorbed from fire, 451-453 Babcock steam formula, 103, 107, 108 Back pressure, 404 Effect of, 407, 408 Baffles, lank mixing, 311 Diagrams, 330 Bag filters/separators, 270 Bag materials, 274 Cleaning, 272, 273 Heavy dust loads, 271 Specifications, 271 Temperature range, 271 Bins, silos, hoppers venting, 516 Blast pressure, 496 Blowdown, 404... 

Concentrated add gas Coal lock hopper vent gas, gasifier gas, concentrated acid gas, catalyst regeneration off-gas Concentrated add gas, coal lock hopper gas Ash or slag... 

Gas liquor, coal lock hopper vent gas Gas liquor, coal lock hopper vent gas Gas liquor... 

If degradation occurs by a thermo-oxidative mechanism, air should be excluded from the extruder. This can be done by putting a nitrogen bianket on the feed hopper, vent port, or at the die, depending on where the air is introduced. If degradation occurs by hydrolysis, moisture has to be excluded from the process. If degradation occurs by a chemical reaction with the metal surfaces of screw and barrel, a nonreacting material of construction has to be selected for the screw and barrel. 

It may be necessary to contain dust by enclosing a weigh hopper and using dust seals or flexible connections to seal openings. Figure 19 shows an arrangement where the top of the hopper is fixed to the stmcture, and the hopper must have an effective vent which minimizes even transient pressure... 

Figure 20 shows an arrangement which is unaffected by air pressure fluctuations, because any force appHed to the material is canceled by an equal and opposite force appHed to the iaside top surface of the hopper. It may be desirable or necessary to vent the hopper for efficient material handling. 

Ferric sulfate is usually stored in the dry state either in the shipping bags or in bulk in concrete or steel bins. Bulk storage bins should be as fight as possible to avoid moisture absorption, but dust collector vents are permissible and desirable. Hoppers on bulk storage bins should have a minimum slope of 36 however, a greater angle is preferred. 

In the production of formic acid, a slimy of calcium formate in 50% aqueous formic acid containing urea is acidified with strong nitric acid to convert the calcium salt to free acid, and interaction of formic acid (reducant) with nitric acid (oxidant) is inhibited by the urea. When only 10% of the required amount of urea had been added (unwittingly, because of a blocked hopper), addition of the nitric acid caused a thermal runaway (redox) reaction to occur which burst the (vented) vessel. A small-scale repeat indicated that a pressure of 150-200 bar may have been attained. A mathematical model was developed which closely matched experimental data. 

Baghouse systems efficiently control particulate emissions from grinding and blending processes. Vents from feed hoppers, crushers, pulverizers, blenders, mills, and cyclones are typically routed to baghouses for product recovery. This method is preferable to using wet scrubbers. However, even scrubber effluent can be largely eliminated by recirculation. 

Fig. 7 Extruder and extrusion. 1 Drive unit, 2 barrel inlet, 3 temperature control, 4 feed hopper and dosing unit, 5 vacuum vent, 6 barrel, 7 screw. (Reproduced with permission from Reifenhauser)...

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