I can't say I've had this problem. Treating FGD waste for much of anything can present some problems. What type of scrubber do you have? What are you scrubbing, and what is the Thallium level?
A BW style wet FGD, dischargig to a settling pond then the clarified effluent processed in a GW zenon bioreactor( for Hg and Se removal) . 70 ppb Tl entering and leaving bioreactor ( positive ORP both stages, 5.5- 6 pH.
One biochemist suggested a a bioreactor can be configured to remove Tl, but the first stage needs a postive ORP and a different bactrial selection.
One german company indicated that the same processes that remove Hg will also remove Tl; they use activated carbon PAC injected upstream of teh FGD to remove Hg, so I assume they imply that PAC will also remove Tl.
That is a coincidence. I have now run two BW wet limestone FGDs, one in MO and now one in FL. We are not currently restricted on Thallium. We have a treated combined discharge from 5 units and only one has a scrubber. I would agree in theory that the activated carbon would remove the Thallium along with the Mercury. I know that some success has been achieved on biochemical treatment, so that is an option. What are your TI limits? Are you in an area with major water quality issues?
The next FGD project to startup next year has a 0.35 ppb Tl limit, but that is after dilution with other water discharge flows. That project burns the same coal , same WW treat process.
When we commissioned a new bioreactor cell 2 wks ago with new activated carbon media it completely removed the Tl from that stream, so this suggests that activated carbon will remove Tl prior to being blinded with Ca. We will track the rate of blinding or scaling with Ca ; it seems that PAC injection upstream of the FGD may be the better route as that also prevents release of Hg to the stack gases ( prevents conversion to elemental Hg) and may also remove Tl,; german firm claim the metals Hg and Tl can be isolated in a small stream of PAC solids that can be selectively removed from other FGD solids and thus reduce magnitude of floc/ sludge that need to be landfilled as hazardous to less than 4% of all FGD solids .
Injection of PAC prior to the FGD needs more PAC, because only part of the PAC will be captured in the FGD.
Within the FGD the retention is higher and less PAC necessary to bind mercury and other heavy metals. This binding prevents re-emission.
Mercury has to be oxidized, with Thallium I do not know.
FFEES:
You are right- I just heard from Evonik that the PAC is ultra-fine and injected in the FGD slurry.It passes thru the FGD primary and secondary hydrocyclones and also past the primary clarifier, ultimately collected in a secondary filter.
