Froth section

WA Working area IDA Inlet downcomer area LDA Liquid distribution area DA Disengaging area (outgassing area) ODA Outlet downcomer area DS Dead section BS Bubbling or froth section ES Entrainment section LB Liquid backup in downcomer to form gas(vapor) seal... 

Ap, is the hydrostatic pressure drop. This is due to the gas flowing through the two phase regime, or froth section, of height on the tray... 

Place 20 g. of Orange II (Section IV,79) in a 600 ml. beaker and dissolve it in 250 ml. of water at 40-50°. Add, with stirring, 24-25 g. of sodium hyposulphite (Na SjO ) this discharges the colour and yields a pink or cream-coloured, finely-divided precipitate of a-amino-p-naphthol (compare Section IV,76). Heat the mixture nearly to boiling until it commences to froth considerably, then cool to 25° in ice, filter on a... 

Phenolsulphonephthalein (phenol red). Mix 10 g. of o-sulpho-benzoic anhydride (Section VIII,9), 14 g. of pure phenol and 10 g. of freshly fused zinc chloride in a small conical flask. Place a glass rod in the flask and heat gently over a flame to melt the phenol. Then heat the flask containing the well-stirred mixture in an oil bath at 135-140° for 4 hours. Stir from time to time, but more frequently during the first hour if the mixture froths unduly, remove the flask from the bath, cool and then resume the heating. When the reaction is complete, add 50 ml. of water, allow the water to boil and stir to disintegrate the product. Filter the crude dye with suction and wash it well with hot water. Dissolve the residue in the minimum volume of warm (60°) 20 per cent, sodium hydroxide solution, filter, and just acidify the filtrate with warm dilute hydrochloric acid (1 1). Filter the warm solution, wash with water, and dry upon filter paper. The yield of phenol red (a brilliant red powder) is 11 g. 

NFPA 30 also fails to recommend flow rate restrictions except a slow start until the downspout is submerged. Section 5-4 of this book provides for restricted flow rates throughout filling this should be applied wherever charge accumulation is possible due to low liquid conductivity and where flammable mixtures involving gas, mist or froth may be formed. 

The Nye Tray increases the area available for disengagement of this light froth. In addition to the normal perforated section, vapor can now flow into the Inlet area below the downcomer. Vapor enters the contact zone of the Nye Tray through the perforated face of the inlet panel, under the liquid coming out of the downcomer. 

Figure 19.8. The interaction of air and pulp in a froth flotation ceil and a series arrangement of such cells (a) Sectional schematic of flotation cell. Upper portion of rotor draws air down the standpipe for thorough mixing with pulp. Lower portion of rotor draws pulp upward through rotor. Disperser breaks air into minute bubbles. Larger flotation units include false bottom to aid pulp flow. (WEMCO Division, Envirotech Corp.). (b) A bank of three flotation cells. The floating concentrate is withdrawn continuously from each stage but the remaining pulp flows in series through the cells.

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