200.00 ppm

Note: Ash is marketed under the trade name Vitalin.

Note: Ash is marketed under the trade name Vitalin.

In the flash-drying process (see Figure 10.10.1), the wet, dewatered sludge is mixed with dry sludge from the dryer cyclone. This preconditioned mixture contacts a gas stream of 1000 to 1200°F, which moves it at a velocity of several thousand feet per minute. In this turbulent, high-temperature zone, the moisture content of the sludge is reduced to 10% or less in only a few seconds. As the mixture enters the dryer cyclone, the hot gases are separated from the fine, fluffy heat-dried sludge. Depending on the mode of operation, the flash-dried sludge is either sent to the sludge burner and incinerated at 1400°F, or it is sent to the fertilizer cyclone and recovered as a saleable fertilizer product. When the incoming wet sludge contains about 18% solids, about 6500 Btu (Ate lb of coal plus 1 cu ft of natural gas) are required to produce 1 lb of dry sludge (15,000 kJ/kg) (Shell 1979).

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