Wet Type FGD and Semi dry FGD

[Roger00]

Hi All,

Anyone can give the comparison between semi dry and wet type FGD in terms of initial investment, operational and maintenance, cost in the long term, environmental concerns, and byproduct of each system are sellable?

thanks

 

[davefitz]

environmentally the semi dry is superior in that it has zero liquid discharge ZLD. The wet FGD has a secret environmental issue that one isn't supposed to discuss- all of the trace minerals , including heavy metals, in the coal ash are removed in the FGD operation ( good) and concentrated in the blowdown purge flow (bad). The purge /blowdwon is meant to limit the chloride concentration in the FD and thus limit rate of metal corrosion.

Most US wet FGD simply discharge the blowdown/purge to surface waters , perhaps after treatment to reduce Hg and perhaps Se, sometimes with no treatment whatsoever. However, the levels of other heavy metals remains high , yet unmonitored and not yet regulated by the 1970's Clean Water Act. I know of one case where the blowdown is completely untreated and discharges directly to a seepage pit that drips into the Floridan aquifer, which is the source of drinking water for all of Florida and most of Georgia. And completely legal.

"Whom the gods would destroy, they first make mad "