[Terrapreta] Ammonia Scrubbing Technology, Issues of Hg and By Products of Coal Combustion

[Shengar at aol.com]

Ammonia Scrubbing Technology, Issues of Hg and other By products  of Coal 
combustion
 
 
I have been in contact with several chemical engineers, both corporate and  
government, that basically tell me that the TP/Ammonia scrubbing technology  
faces no practical hurdles. But when it comes to dealing with  the  fraction of 
volatilized mercury up stream scrubbing will be necessary. The  non-volatile 
uranium, thorium, fall out, and that radon also present  in coal combustion  is 
of no consequence for this process. 
 
Their general feeling is that direct liquidfaction and IGCC approaches to  
clean coal are complicated, expensive and except for pumping CO2 down oil gas  
wells other deep geologic strata sequestration is untested ,  expensive  and 
also limited in scope.
 
After a year of researching and running TP-Tech by way more competent  folks 
than I, in the many fields of study to which TP lends itself, I have found  no 
technological road blocks.

Injection of powdered activated carbon (PAC) into the flue gas is currently  
the front runner technology that is nearest commercialization for mercury (Hg) 
 removal. The PAC needs to be further enhanced with halogens, like bromine,  
to be really effective with subbituminous coals such as Powder River Basin  
coals. The Hg-loaded dust is then removed with filter bags (bag houses) or  
electrostatic precipitators. A problem is that fly ash is typically removed in  
the same unit, thus resulting in fly ash containing extra carbon (and Hg). That  
carbon generally makes the fly ash useless as a concrete amendment, thus  
destroying by-product market value.
 
In high-sulfur bituminous coal combustion the Hg in generally in ionic  form, 
and can be removed by wet scrubbers . Use of wet scrubbers is being  expanded 
significantly to address mandated SO2 control, thus also achieving a  
simultaneous co-benefit of Hg removal. The potential downside is the eventual  
disposition of the Hg that shows up in the byproduct gypsum obtainable from the  
scrubber sludge. Workarounds are being looked at for these cases above. 
 
There are a bunch of other approaches in various stages of  development. , 
one patent pending, but still only at the laboratory  scale, where the Hg is 
captured within the material of the filter bags, thus  keeping the Hg separated 
from the fly ash. The Hg is disposed of with the old  bags at the end of their 
life, or recovered from the bag material at that  time.
 
Danny Day's process can be fitted at the end of any of the Hg removal  steps, 
though there would be little, if any additional removal credit for NOx or  
SO2.
 
 
   

Erich J.  Knight 
Shenandoah Gardens
E-mail: shengar at aol.com
(540)  289-9750





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