Consistency of Waste Feed should be considered in developing sampling
plans and systems. The feed make up process will generally require accurate
measurement of all species significant to melter and possibly waste form
behavior. The feed make-up, as discussed above, is generally a batch
process; the vessel in which the feed is being prepared should be well mixed
to avoid composition errors that could damage the melter.
Feed Make-up and Chemical Addition . Feed make-up and chemical
addition may require concentration and then addition of chemicals needed to
meet target melter feed compositions. If the feed material is very well
characterized and homogeneous, the chemicals can be added in advance and
provided in the form of glass frit. If there is potential for variation, a chemical
batching system that can handle specific recipes is required. The system may
need to handle solids, liquids, and slurries, depending on the target feed
composition. Generally, the chemical additions should be made up in a
separate tank and batch-transferred into the feed tank. This recommendation
derives from unique requirements for contamination control and batch quality
control for high-level waste vitrification. There may be more innovative
approaches for other waste types.
Accurate measurements of tank volumes and fluid density have proven very
important in the feed make-up process. Special attention should be given to
these areas for batch make-up tanks.
Feed Holding . Melters generally perform longer and best when operated as
close to steady-state as possible. Enough feed should be prepared to support
that objective while the next batch of feed is being prepared. Vessel sizing
should consider the potential throughput, as well as the time necessary to
prepare batches. In estimating those times, analytical turnaround times for
process samples should not be discounted. They can and have been a large
part of the time required to make feed.
Mixing the feed holding tank is a necessary design feature to maintain
consistent feed material to the melter.
Re-suspension should be considered when developing the mixing system.