2. Idea of Mass Balance Model
The principle of creating a mathematical mass balance model in a
supercritical CFB boiler under steady-state operation is shown in Fig. 1.
The essence of this approach is balancing of optional parameters by
division of particle size distribution into classes. A spherical shape of
particles was assumed. The division of particle distribution into classes
with respect to their mean size was performed. The span of particles
size is characteristic of the each class. The class is represented by the
mean particles size, which is located in the middle of the classes. This
division is necessary to obtain balance formulae for a given particle
class. It should assume, that in each class shrinking core model, i.e. the
particles found in the class reduce its own size under the influence
of chemical reaction (i.e. fuel combustion) and physical processes
(e.g.: attrition, fragmentation, coagulation etc.). It is possible for particles
to migrate from the class with greater span to a class with smaller
span. Generally an increase of particle size is also possible, i.e. the migration
fromthe classes about smaller span to the classeswith larger spans.
All processes occurring in the CFB combustion system can divide in
three groups: feeding, internal and external processes respectively.
Among external processes and characteristic of external devices following
elements can be distinguished: (i) carry away of bed material as a
result of air interaction on the bed inventory in the bottom zone of
the furnace chamber; (ii) separator characteristic curve, separating
device in which coarse particles are recirculated to the combustion
chamber; (iii) ash remover characteristic curve (i.e. drainage constant),
drainage system of bottom ash; (iv) characteristic of return leg which
circulatingbed material feeding into the furnace chamber; (v) characteristic
of fly ash recirculation system which fine particles as additional
bed material are feeding into the combustion chamber. Moreover, the
internal processes connected with the migration of particles between
classes can be distinguished: (i) fuel combustion; (ii) fragmentation
i.e. size reduction of particle classes; (iii) abrasion i.e. the migration of
particles from the classes having larger diameters to the classes with
smaller diameters. Additionally, the accumulation of fine particles
about sizes less than 50 microns was assumed.
An example of a general scheme of the mass balance of the “k”-th
particle class is shown in Fig. 2.
According to the above idea the mass balance equation of general
mass flow for the particle
2. Idea of Mass Balance Model
The principle of creating a mathematical mass balance model in a
supercritical CFB boiler under steady-state operation is shown in Fig. 1.
The essence of this approach is balancing of optional parameters by
division of particle size distribution into classes. A spherical shape of
particles was assumed. The division of particle distribution into classes
with respect to their mean size was performed. The span of particles
size is characteristic of the each class. The class is represented by the
mean particles size, which is located in the middle of the classes. This
division is necessary to obtain balance formulae for a given particle
class. It should assume, that in each class shrinking core model, i.e. the
particles found in the class reduce its own size under the influence
of chemical reaction (i.e. fuel combustion) and physical processes
(e.g.: attrition, fragmentation, coagulation etc.). It is possible for particles
to migrate from the class with greater span to a class with smaller
span. Generally an increase of particle size is also possible, i.e. the migration
fromthe classes about smaller span to the classeswith larger spans.
All processes occurring in the CFB combustion system can divide in
three groups: feeding, internal and external processes respectively.
Among external processes and characteristic of external devices following
elements can be distinguished: (i) carry away of bed material as a
result of air interaction on the bed inventory in the bottom zone of
the furnace chamber; (ii) separator characteristic curve, separating
device in which coarse particles are recirculated to the combustion
chamber; (iii) ash remover characteristic curve (i.e. drainage constant),
drainage system of bottom ash; (iv) characteristic of return leg which
circulatingbed material feeding into the furnace chamber; (v) characteristic
of fly ash recirculation system which fine particles as additional
bed material are feeding into the combustion chamber. Moreover, the
internal processes connected with the migration of particles between
classes can be distinguished: (i) fuel combustion; (ii) fragmentation
i.e. size reduction of particle classes; (iii) abrasion i.e. the migration of
particles from the classes having larger diameters to the classes with
smaller diameters. Additionally, the accumulation of fine particles
about sizes less than 50 microns was assumed.
An example of a general scheme of the mass balance of the “k”-th
particle class is shown in Fig. 2.
According to the above idea the mass balance equation of general
mass flow for the particle
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