The Impact of the Source of Alkali on Sludge Batch 3 Melt Rate (U)
Previous Savannah River National Laboratory (SRNL) melt rate tests in support of the Defense Waste Processing Facility (DWPF) have indicated that improvements in melt rate can be achieved through an increase in the total alkali of the melter feed. Higher alkali can be attained by the use of an ''underwashed'' sludge, a high alkali frit, or a combination of the two. Although the general trend between melt rate and total alkali (in particular Na{sub 2}O content) has been demonstrated, the question of ''does the source of alkali (SOA) matter?'' still exists. Therefore the purpose of this set of tests was to determine if the source of alkali (frit versus sludge) can impact melt rate. The general test concept was to transition from a Na{sub 2}O-rich frit to a Na{sub 2}O-deficient frit while compensating the Na{sub 2}O content in the sludge to maintain the same overall Na{sub 2}O content in the melter feed. Specifically, the strategy was to vary the amount of alkali in frits and in the sludge batch 3 (SB3) sludge simulant (midpoint or baseline feed was SB3/Frit 418 at 35% waste loading) so that the resultant feeds had the same final glass composition when vitrified. A set of SOA feeds using frits ranging from 0 to 16 weight % Na{sub 2}O (in 4% increments) was first tested in the Melt Rate Furnace (MRF) to determine if indeed there was an impact. The dry-fed MRF tests indicated that if the alkali is too depleted from either the sludge (16% Na{sub 2}O feed) or the frit (the 0% Na{sub 2}O feed), then melt rate was negatively impacted when compared to the baseline SB3/Frit 418 feed currently being processed at DWPF. The MRF melt rates for the 4 and 12% SOA feeds were similar to the baseline SB3/Frit 418 (8% SOA) feed. Due to this finding, a smaller subset of SOA feeds that could be processed in the DWPF (4 and 12% SOA feeds) was then tested in the Slurry-fed Melt Rate Furnace (SMRF). The results from a previous SMRF test with SB3/Frit 418 (Smith et al. 2004) were used as the SMRF melt rate of the baseline feed. The SOA SMRF test results agreed with those of the MRF tests for these two feeds as the melt rates were similar to the baseline SB3/Frit 418 feed. In other words, the source of alkali was close enough to the baseline feed as to not negatively impact melt rate. Based on these results, there appears to be an acceptable range of the source of alkali that results in the highest melt rate for a particular sludge batch. If, however, the alkali is too depleted from either the sludge or the frit, then melt rate will be lower. Although SB3 simulant sludge and Frit 418 were used for these tests, it was not the intent of these tests to determine an optimum source of alkali range for SB3. Rather, the findings of these tests should be used to help in the decision process for future sludge batch washing and/or blending strategies. The results, however, do confirm that the current processing of SB3 is being performed in the proper source of alkali range. Because all of this testing was performed on small-scale equipment with slurried, non-radioactive simulant, the exact impact of the source of alkali with SB3 in the DWPF melter could not be fully evaluated.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-96SR18500
- OSTI ID:
- 890167
- Report Number(s):
- WSRC-TR-2005-00177; TRN: US0604653
- Country of Publication:
- United States
- Language:
- English
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