With respect to benchmarking technologies, the reference
scheme of single stage treatment without pre-dusting (1S) consists
in the injection of sodium bicarbonate through a Venturi-shaped
reactor, followed by a fabric filter (Fig. 2b). Reactions (R4)–(R6)
take place in the system and the process scheme itself is actually
the same as the 2nd stage of the reference 2S system. Although
listed among the BAT for acid gas abatement (European
Commission, 2006), the 1S scheme has the drawback of not segregating
SBW from fly ash. This prevents the possibility of recycling
the SBW to produce sodium carbonate as described for the 2nd
stage of the 2S system. Therefore, the 1S system is often integrated
with a de-dusting stage prior to the injection of bicarbonate (predusting,
Fig. 2c). The pre-dusting device can be either an electrostatic
precipitator (ESP-1S) or a fabric filter (FF-1S). 1S, ESP-1S
and FF-1S configurations share the same approach to acid gas
removal (Reactions (R4)–(R6)) and differ only in the investment
and operating costs related to the pre-dusting equipment and in
the consequent fate of the SBW.