In the spray drying process, an alkaline slurry [usually Ca(OH)2] is injected into a spray dryer chamber through either a rotary atomizer or two-fluid nozzle injectors.
The atomized slurry droplets contact the hot flue gas in the spray dryer chamber (See Figure 1). The water in the alkaline (lime) slurry evaporates to cool the flue gas, and the lime reacts with the acid gases in the flue gas to form calcium- or sodium-based salts. The reaction or absorption chamber is designed to provide sufficient contact and residence time to produce a dry product leaving the chamber. The particulate exiting the chamber contains fly ash, calcium salts and unreacted lime that must be sent to a particulate control device, usually a fabric filter or electrostatic precipitator (ESP).
Fig.1 Spray dryer absorber
Collected solid reaction products from the system are sometimes recycled to the feed of the spray dryer to reduce alkaline sorbent use. Figure 2 provides a diagram of a typical spray drying system. The major components of a typical spray drying system are:
• Alkaline (lime) storage and slaking system
• Alkaline mixing and feed tanks
• Atomizer (rotary or nozzle)
• Spray dryer chamber
• Particulate control device (e.g. baghouse)
• Recycle system (optional)
Fig.2. Components of a spray dryer absorber system
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