Pressurized fluidized-bed combustion part-load behavior. Volume I. Summary report Page: 83 of 122
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- 36 -
(2) decrepitation of the incoming particles due to the sudden
evolution of carbon dioxide and to shock heating of the
particle
(3) attrition and abrasion of particles in the bed, enhanced by
the fact that calcination converts the hard stone into soft,
easily breakable material, but hindered by sulphaticn which
hardens the particle.
It is reasonable to suppose that mechanism (2) will be proportional
to the rate of feed of dolomite and to same function of the rate of
calcination in the bed. Mechanism (3) will depend on the amount of
dolomite material in the bed and on seme function of the velocities in
the bed. (This function is often assumed to be U - Uj . The data
from the 25 test conditions are reproduced in Appendix^, where it is
shown that the amount of fines produced by mechanism (2) is small in
PFBC and can be neglected. It is also shown .that the "best fit"
to mechanism (3) requires a function (U - Uj" where n = 3. However,
a simpler relationship is shown in Fig. 35 (mere r is the rate of
production of fines in the bed (defined as the difference between the
observed elutriatian and the elutriable quantity in the feed and W is
the weight of dolomite material in the bed. It would appear that
attrition and abrasion are negligible at values of (U - U _) lower
than about 2.5 ft/s. It must be remembered that becausemtost of the
elutriated dolomite arises from the elutriable part of the dolomite
feed, almost any correlation to account for fines production in the bed
will be effective.
Using Fig. 35 together with the amount of elutriable material in the
dolomite feed produces a calculated value of elutriatian which is in
close agreement with the observed value, as shewn in Fig. 34(b).
6.4.2 Elutriatian of coal ash. Fig. 36 plots the amount of coal ash
elutriated against the elutriable amount in the feed, using- the data
given in Table A3 of Appendix 2. The upper diagram plots the amount
fo coal ash elutriated against the amount elutriable in the coal feed -
assuming that the ash size distribution is the same as the coal size
distribution. It is clear from Fig. 36(a) that there is no real
correlation between the two parameters, with 40 to 70% more being
elutriated than would be expected from the coal size distribution.
It is well-known that the size distribution of the coal ash is finer
than that of the coal and that the extent of the difference depends
on hew much "stone" is included in the material. The relationship
between the size of the coal and the ash particles for Glen Brock coal
is shewn in Fig. 37. This was oroduced by ashing a sample of coal in
in a laboratory furnace at l650°F and determining the resulting size
distribution. Fig 36(b) shows the revised relationship for Glen Brook
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Roberts, A. G.; Pillai, K. K.; Raven, P. & Wood, P. Pressurized fluidized-bed combustion part-load behavior. Volume I. Summary report, report, September 1, 1981; United States. (https://digital.library.unt.edu/ark:/67531/metadc1088075/m1/83/: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.