Heterogeneous condensation of water
vapor on coal-fired fine particles
was investigated in a growth tube. The influence of operating parameters
and wetting agent addition on vapor condensation enlargement for three
coal-fired fine particles from different power plants were tested.
The results show that all the three coal-fired fine particles induce
heterogeneous condensation and the process is favored by increasing
the water temperature and residence time and decreasing particles
initial number concentration; wetting agent addition highly facilitates
the effect of vapor condensation on fine particles and the performance
is increased with the increase of wetting agent addition. It is also
found that excessive addition encourages the performance of final
mean size of particles but discourages the performance of finer particles
enlargement. With wetting agent addition, the mean diameter of fine
particles can be enlarged above 3 μm while the mean diameter
can only be enlarged above 2 μm without wetting agent addition
(the original mean diameter of particles is about 0.15 μm).
The
supersaturation profiles in the one-/multi-section growth tube
were predicted under the conditions of different carrier gases for
two kinds of typical supersaturation-achieving methods. The results
show that Lewis number (Le) of the carrier gas is an important factor
affecting the supersaturation profiles. For the one-section growth
tube, the carrier gas with a smaller Le is beneficial to a higher
level and flatter trend of supersaturation profiles for method 1,
where the supersaturated environment is achieved by a cool saturated
flow into a warm-walled growth tube. However, for the carrier gas
of a larger Le, the higher level but less stable supersaturation profiles
are presented from method 2, with a warm saturated flow into a cold-walled
growth tube. With the carrier gas of large Le (>1) from method
1 and
the carrier gas of small Le (<0.5) from method 2, an efficient
supersaturated environment cannot be achieved under the ordinary conditions.
In the multi-section growth tube, the more minimum number of the sections
is selected for stable supersaturation profiles with the carrier gas
of larger Le. Additionally, the sections of a flatter supersaturated
environment are closely related to the achieving methods of a supersaturation
environment, the whole length of the growth tube, and radial positions.
Alkaline K poisoned and Co-modified catalysts were prepared using Fe and Mn as active components, nickel foam as a carrier, and Co as a trace additive.
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