Page 65 - Wastewater Solids Incineration Systems

34 Wastewater Solids Incineration Systems

• Ash ultimate analysis—up to 14 significant constituents.
• Ash fusion temperature—performed in oxidizing and reducing atmospheres.

The ASTM proximate and ultimate analysis tests were originally developed
for coal.
When applied to fuels such as WWTP residuals or biomass, modifications to
these procedures are sometimes necessary. One study resulted in the recommenda-
tion to reduce the temperature used when determining the ash ultimate analysis in
order to eliminate erroneous results because of the volatilization of some of the alkali
fractions (Miles et al., 1996). Unfortunately, no similar study exists for WWTP resid-
uals. Until additional data are developed, the modified biomass analysis procedure
is recommended.
Because of the wide variability between incoming streams of WWTPs and differ-
ences between wastewater processes, actual equipment designs or modifications
based on values published in the literature are generally not worthwhile. In many
cases, this practice can lead to inaccurate conclusions. WWTPs should take an ade-
quate number of samples to cover seasonal variations and use a sampling technique
that ensures a good composite. These practices are almost as important as obtaining
a proper laboratory analysis on feed cake from a particular site. When wet weather
flows are known to cause a variation in the ratio of ash to volatiles, fuel analysis
during both wet and dry periods is recommended. Because of daily variations due to
stratification in tanks or other changes in operation, taking a series of samples
throughout the week or on different days over a multi-week period for analysis is
recommended. Typically, analysis of the volatiles (moisture, ash-free basis) varies
much less than one would expect, and multiple samples can yield a composite
number by averaging the results for the volatile fraction of the feed cake.
Most WWTPs routinely perform basic analyses for fixed and volatile solids, often
on a daily basis, which can be used to develop a powerful database of historical infor-
mation. The WWTP can use these data with the more comprehensive analyses per-
formed as a part of the incineration system design or operations process, or both.
This invaluable information can help pinpoint the true range of operation that the
incineration system will experience and can guide the designer in making provisions
for the degree of process flexibility needed in the incineration system. The sampling
program should be customized to reflect the characteristics of the specific plant.