3. Results
The addition of kraft lignin in this test was 1.1%–4.2% on dry solids
(% ds). The running conditions used in the tests are summarized
below (see Table 2). The die pressure and the die temperature
showed small variations during all test series, namely, 78.9±8.8 Bar
(mean±standard deviation) and 113.7±8.1 °C for dry kraft lignin,
and 64.2±3.5 Bar and 104.2±5.4 °C for wet kraft lignin.
A stable environment implies that we can conclude that the tests
in which kraft lignin grades were used were performed during stable
conditions.
Fig. 2 presents the pellet length results when no cutting blade is
used. The length increased with an increasing amount of added kraft
lignin. There is no clear trend as to whether dry or wet kraft lignin is
more effective in producing long pellets. For dry kraft lignin, the pellet
length increase was significant with every addition of lignin except for
the increase from 3% to 4% (at which point the pellets had a more variable
length). For wet kraft lignin, the increase in length was significant
with the 0% to 1% addition of lignin, and alsowith the 1% to 2% increase.
The bulk density was not affected in any obvious manner by the
increased amount of added kraft lignin. There is a large uncertainty
in the measurements. There is a significant difference between the
two runs, but, as the difference is present at 0% of added kraft lignin,
it is likely that it is due to process variables rather than to a difference
between dry and wet kraft lignin (see Fig. 3).
The analysis of durability showed that both wet and dried kraft
lignin increased the durability of the pellets (see Fig. 4). Already at
the addition of 1% of kraft lignin, the amount of fines had decreased.