STATISTICAL EVALUATION OF PROCESSING DATA FROM THE RH RU HG MATRIX STUDY
An evaluation of the statistical significance of Rh, Ru, and Hg on DWPF Sludge Receipt and Adjustment Tank (SRAT) cycle catalytic hydrogen generation and process chemistry was conducted by the Savannah River National Laboratory (SRNL) using a full-factorial experimental design. This test design can identify significant interactions between these three species in addition to individual effects. Statistical modeling of data from the Rh-Ru-Hg matrix study has been completed. Preliminary data and conclusions were given in an earlier report. This final report concludes the work on the Rh-Ru-Hg matrix study. Modeling results are summarized below. Rhodium was found to: Promote increased total hydrogen mass; Promote an increase in the maximum hydrogen generation rate; Promote an increase in the hydrogen generation rate shortly after acid addition; Shorten the elapsed time between acid addition and the maximum hydrogen generation rate; Increase formate loss; Inhibit NO{sub 2} and total NO{sub x} off-gas species formation; and Reduce nitrite-to-nitrate conversion. Ruthenium was found to: Promote increased total hydrogen mass; Promote an increase in the maximum hydrogen generation rate; Promote an increase in the hydrogen generation rate in the second half of the SRAT cycle; Promote an increase in total CO{sub 2} generated; Increase formate loss; Promote NO{sub 2} and total NO{sub x} off-gas species formation; and Reduce nitrite-to-nitrate conversion. Mercury was found to: Inhibit total hydrogen mass produced; Promote an increase in total CO{sub 2} generated; Promote NO{sub 2} off-gas species formation; and Inhibit total NO{sub x} off-gas species formation. Results confirmed qualitative observations that Rh was activating before Ru for hydrogen generation. An interaction between Rh and Ru was present in the model for the total hydrogen generated during the SRAT, perhaps because the total combined contributions from two separate episodes of hydrogen generation. The first episode was dominated by Rh and the second by Ru. Consequently, the linear statistical model was asked to explain more than one phenomenon and included more terms. Mercury did not significantly impact hydrogen generated by either Rh or Ru in models in this study (all tests had Hg {ge} 0.5 wt% in total solids), whereas tests in Sludge Batches 3 and 4 (SB3 and SB4) with and without Hg showed a very significant negative impact from adding Hg. The conclusion is that once a small quantity of Hg is present, the primary inhibiting effect of Hg is in place, and hydrogen generation is relatively insensitive to further increases in total Hg. Any secondary Hg effects were difficult to quantify and model. Mercury was found to be statistically significant, however, as an inhibiting factor for hydrogen generation when modeling was based on the logarithm of the hydrogen generation rate. Only limited statistical evidence was found for non-linearity and quadratic dependence of other SRAT process measures, such as formate loss or total NO{sub x} generation, on the three matrix variables. The interaction term for Ru with Hg, however, appeared in models for total CO{sub 2}, total NO{sub 2}, and total moles of nitrogen-derived off-gas species. A single interaction between Ru and Hg during nitrite destruction could explain all three of these effects in the observed responses. Catalytic decomposition of nitrite ion by formic acid produces CO{sub 2} plus either NO or N{sub 2}O. The vast majority of the NO produced is converted to NO{sub 2}, and NO{sub 2} is the major fraction of the total moles of nitrogen in the off-gas species. Future experimental work related to catalytic hydrogen generation control is expected with regard to minimizing formic acid use through alternative reductants as well as in pursuing mesoporous media for sequestering the catalytically active noble metals to inhibit catalytic hydrogen generation. Two alternative stoichiometric acid equations are also under development. A summary document is in draft form that provides an overview of progress made in understanding catalytic hydrogen generation as well as the progress made in resolving open issues from the one external and two internal reviews of the catalytic hydrogen generation program.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-08SR22470
- OSTI ID:
- 952445
- Report Number(s):
- SRNL-STI-2009-00084; TRN: US200913%%620
- Country of Publication:
- United States
- Language:
- English
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