Agriculture Reference
In-Depth Information
Table 27. Potassium content of Fuels tested
Fuel
Ash (%) dry basis
K (% of Ash)
K (% of Fuel, AR)
Raffinate
40
32.5
6.5
Vinasse
23
30.4
2.94
Pulp
7
10.7
0.21
Coal
5.2
1.16
0.03
Table 28. Potassium calculations on Fuels tested
Fuel fed
(kg)
K fed with
fuel (kg)
Potassium flow
(g/h)
Sand to K
ratio
K in sand (kg),
SEM
Coal-PP Tests
(56 hours)
96 + 96
0.23
4.1
32
0.08
Coal-Raffinace
Test
4.2+2.2
0.14
245.6
52
0.58
Natural gas-
Raffinate Test
0.5
0.03
176.5
231
0.35
Coal-Vinasse
Test
3.9+1.3
0.04
65.6
185
0.75
During 56 hours testing of coal-PP co-firing, almost 96 kg of PP was burned with an
equivalent amount of coal in the bed. Amount of potassium introduced into the bed during
this period is calculated to be 0.23 kg which equates to sand to potassium ratio of around
32.4. Results of calculations for all the experiments are given in Table 28. It is inte resting to
note that potassium introduced into the bed is the highest and sand to potassium ratio is the
lowest in coal-PP test as compared to raffinate and vinasse tests. This shows that potassium
feed-rate into the bed is very important. During vinasse and raffinate tests potassium feed-rate
was higher than PP test as raffinate and vinasse contain considerably higher amounts of
potassium. Thus higher the amount of alkali per unit time fed into the bed higher the chances
of agglomeration to occur, for explanation see column 4 of Table 28. It also indicates that
introduction of small amount of alkali for a longer time is better than introducing larger
amount in a shorter time.
The table also shows, in the right column, calculated value of potassium based on SEM
results, in the bed after each experiment. It can be observed that, for coal -PP test, potassium
found in the bed, by SEM results, after the test is a lot lower than the potassium introduced
into the bed. This could be due to evaporation of part of the potassium during the combustion
process. Wu et al. (1999) observed that 13 - 20% potassium was evaporated with flue gas or
deposited in the combustor. It can be observed that the amount of potassium accumulated in
the bed, for raffinate and vinasse tests, is very much higher than the amount of potassium
introduced into the bed. This shows discrepancy in the SEM results. However, it is possible
that the distribution of potassium in the bed was not even. As the samples were taken from the
top of the bed it is possible that this has higher potassium content as compared to the bottom.
However, this theory violates the inherent nature of fluidized bed to distribute material fed
into the bed equally throughout the bed. The results indicate that, in order to devise suitable
energy recovery systems, more research is needed to fully understand the behaviour of
potassium in the by-products of sugar process combusted in fluidized beds.
