100 and 400 ppm chlorine (as HCl)
MODIFICATIONS TO THE CONDITIONING SYSTEM TO STUDY IMPINGER CHEMISTRY
For mercury analysis, two sample streams were taken from the bottom of the reaction chamber and introduced into a wet-chemical conditioning system, shown in Figure 5.2. In the baseline conditioning system, one stream was bubbled through an acidic 2% SnCl2 solution to reduce all mercury to elemental form. This stream represented the total mercury concentration present in the system. The other stream was passed through a solution containing 10 wt% KCl and 0.5 wt% Na2S2O3 to capture oxidized mercury. Sodium thiosulfate was added to prevent oxidation of elemental mercury by halogens in solution (8). This stream represented the elemental mercury concentration present in the system. A 5 wt% NaOH solution was used to remove acid gases from each of the sample streams. The impingers had a flow-through arrangement on the liquid side, so that they were continually being refreshed. The two sample streams then passed through a chiller to remove any water. The baseline configuration of the conditioning system is shown in Figure A.1.
Total Side of the Conditioning System
To determine if the bromine compounds produced in the reactor are affecting the chemistry in the impingers on the total side of the flue gas conditioning system, different
Mercury Reactor SnCl2- HCl KCl NaOH To 4-Port Sampler and Tekran Analyzer NaOH
Elemental Side of the Conditioning System Total Side of the
Conditioning System
impinger solutions are evaluated. The usual configuration for the total side is an impinger containing 2 wt% SnCl2 and 3 wt% HCl in water, followed by an impinger containing NaOH. The solution in the first impinger is modified or, in some cases, additional impingers are added to improve the reduction from total to elemental mercury. Some of these modifications include the increase or decrease in the concentration of the SnCl2- HCl solution, the addition of one or two NaOH impingers before the SnCl2-HCl impinger (Figure A.2) and the substitution of the SnCl2-HCl solution by a mixture of hydroxylamine hydrochloride and sodium hydroxide (NH2OH*HCl-NaOH) (Figure A.3).
Elemental Side of the Conditioning System
To determine if the measurements on the elemental side of the conditioning system are affected by the bromine species in the reactor, different impinger solutions were evaluated as well. The default configuration for the elemental side was an impinger containing 10 wt % KCl and 0.5 wt % sodium thiosulfate in water, followed by an impinger containing NaOH. The solution in the first impinger is modified or, in one case, the first impinger is eliminated and only the NaOH impinger is used on the elemental mercury side. To determine the overall effect of the SO2 on mercury oxidation by bromine, some measurements of the SO2 concentration along the reactor in both gas and liquid phases is made; these results are an indication of the points of the system where the highest SO2 consumption is taking place and in which phase the highest interaction between oxidized mercury and SO2 species could be taking place.
The solutions in the first impinger that were tested included (1) the standard configuration of 10 wt% KCl and 0.5 wt% sodium thiosulfate in water, followed by an
Mercury Reactor SnCl2- HCl KCl NaOH To 4-Port Sampler and Tekran Analyzer NaOH
Elemental Side of the Conditioning System
Total Side of the Conditioning System
NaOH
To 4-Port Sampler and Tekran Analyzer NH2OH-HCL NaOH KCl NaOH NaOH NaOH Mercury Reactor
Total Side of the Conditioning System
Elemental Side of the Conditioning System
impinger 5 wt % NaOH; (2) the standard configuration without the sodium thiosulfate; (3) replacement of the KCl and sodium thiosulfate with 12 wt % of tris (hydroxymethyl) aminomethane (THAM) and 0.3 wt % ethylenediamine tetra acetic acid (EDTA); and (4) a single impinger containing 5 wt % sodium hydroxide.
The elemental side of the conditioning system was also modified by the addition of one impinger or, in some cases, a packed bed to further study mercury-bromine-SO2 interactions that could be occurring in the conditioning system. The default configuration for the elemental side was an impinger containing 10 wt% KCl and 0.5 wt% sodium thiosulfate in water, followed by an impinger containing NaOH, as shown in Figure A.1. The modifications implemented were (1) an additional impinger of a 5 wt % NaOH solution before the KCl impinger in the standard configuration (Figure A.4), (2) a bed with 2 grams of hydrated lime at 1200C (Figure A.5) (3). The objective of these modifications was to remove the SO2 before it reaches the KCl impinger; this was helpful in determining if any extent of the inhibitory effect of SO2 on mercury oxidation by bromine was occurring in the liquid phase.
The temperature of this bed which was increased up to 500oC was expected to increase SO2 adsorption. However it did not show that effect.
To avoid liquid phase interactions among bromine, mercury and SO2, a packed bed with 40 grams of NaOH pellets heated at 120oC was installed just before the KCl impinger. The results were inconclusive and not reproducible due to the interaction of the NaOH with the quartz frit installed in the packed bed to support the pellets.
To 4-Port Sampler and Tekran Analyzer NH2OH-HCL NaOH KCl NaOH NaOH NaOH Mercury Reactor
Total Side of the Conditioning System
Elemental Side of the Conditioning System
Figure A.4. Additional impinger of a 5 wt % NaOH solution before the KCl impinger in the standard configuration.
Lime Bed
Figure A.5. Packed bed with 1 g of hydrated lime heated at 1500C. The same experimental setup was used for the NaOH pellets bed.
APPENDIX B