Environmental Engineering Reference
In-Depth Information
Fig. 3.10 Size distribution
of PM 2.5 flying ash
collected from the stack of a
thermal power plant in
California (USA) [ 47 ]
waste incineration plants. This category includes the point sources of the residential
heating sector [ 40 - 44 ].
3.3.1.1 Thermal Energy and Power Generation Systems
Thermal power plants release PM in different ways: flying ash escaping from the
electric filters mounted on the stack, bottom ash extraction, fine dust scattering and
final ash storage, if ash is not dried and sprayed permanently [ 45 , 46 ].
Studies on the PM 2.5 fraction of flying ash in a fluidised bed coal-fired thermal
power plant have revealed the particle distribution shown in Fig. 3.10 [ 47 ].
The data presented so far indicate that about 50 % of the ash collected from the
electrostatic filter bags is 100-1000 nm in size.
For the bottom ash resulted from fluidised bed combustion of crushed coal in
several thermal power plants in Poland, the size distribution of nano- and
microparticle-containing fractions is given in Fig. 3.11 [ 46 ].
The comparison of the size distribution of flying ash and bottom ash in modern
thermal power plants in Poland and the USA indicates that PM 1-2.5 in the bottom
ash are less than a quarter of the whole amount and half of the nanoparticle
concentration in the flying ash.
The two types of ash differ very slightly in their chemical composition. The
difference lies in the origin of the coal [ 46 , 47 ]. Their typical chemical composition
is given in Table 3.7 [ 47 ].
The composition was determined by high-resolution methods:
- Ion chromatography
- AAS spectrophotometry
- Total organic carbon
- X-ray spectroscopy
The current trend of the studies dealing with the recovery of unburnt carbon from
coal ash, as well as the encouragement of renewable fuels in the energetic produc-
tion require the use of vegetal pellet or dust (straw, wood) in combination with
bottom ash [ 48 ].
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