SYMBAT ALIKHANOVNA BOLEGENOVA Simulation of ... - kaznu.kz

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22 févr. 2014 (il y a 3 années et 6 mois)

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SYMBAT ALIKHANOVNA BOLEGENOVA


Simulation

of Physical
-
Chemical Processes
in the
Combustion
of
Coal
-
Dust Fuel


SUMMARY


Dissertation for the scientific degree of the doctor of philosophy (Ph.D)

in specialty “6D040400


physicist”



Actuality
.
Today

an inc
reasing
attention is paid to

the study of heat
-
and
-
mass transfer in
the presence of physical and chemical transformations. Study
ing

of the
mechanisms

of such
flows is

of

fundamental
importance for

constructing
physical

theor
ies

of combustion and
explosion
and
has a high practical potential in the development of
new physical and chemical
technologies, in particular, in the development of processes and systems with the rational use of
energy resources.

To solve the problems of modern power engineering and ec
ology
i
t is especially important

to
study
the
processes of
heat
-
and
-
mass
transfer in
the
high
-
temperature
reacting media and
to
simulate

physical and chemical processes that occur during
the
combustion of pulverized coal.
These problems are related,
on the

one hand
,

to

the concept of

energy s
afe
ty


of the country
and
, on the other hand,

to
the development of processes of

clean


fuel combustion under strict
standards
of emission of harmful substances into the environment.

The complex processes of heat
-
and
-
mass transfer in the presence of physical and chemical
reactions and combustion are non
-
stationary

and

highly nonisothermal with permanent change in
the physical and chemical state of the environment, which complicates their experimental
stud
ies
.

No a
nal
ytical solutions of this complex system of equations ha
ve

been found
,
and they can
be solved
only
numerically.
In the recent years

the main methods
used to

study

such processes,
particularly in the areas of real geometry,
we
re the methods of numerical mode
ling and
numerical experiments that adequately
describe

actual physical processes in the combustion
chambers.

Therefore,

it is important to carry out

a comprehensive study

of
physical and chemical
processes
of heat transfer in
the
high
-
temperature environ
ment. This study will
be based

on the
achievements of modern thermal physics, the use of new numerical methods
o
f 3
-
D modeling,
construction of

eff
icient

computational algorithms and new computational models
that enable
scientists to
describe
with high deg
ree of accuracy

real

physical processes that occur during
combustion of
power
-
plant

fuels
in the combustion chambers
of operating power stations.


Objective

of
the
research
.

Investigation of heat
-
and
-
mass transfer in the areas of real
geometry (the combust
ion chamber) during
combustion

of
power
-
plant

fuels
and determination
of
the basic laws of aerodynamics
and

mechanisms

of formation of
aerodynamics of
flow,
velocity, temperature and concentration fields
.


Object of
the
research
.

Heat
-
and
-
mass transfer pro
cesses occurring during combustion of
pulverized coal flame in the combustion chamber of the real
power

facility (boiler BKZ
-
160
,

Almaty
HP
P).

Subject of
the
research
.

Aerodynamics
of
flow, turbulence and thermal characteristics and
concentration fields t
hroughout the space
of
the combustion chamber during combustion of
the
pulverized coal
-
dust

flame
.

Scientific novelty
:
Usage of

advanced 3
-
D computer modeling
technology
for

the

comprehensive study of turbulent combustion of pulverized coal flame
i
n
the
r
eal combustion
power boiler BKZ
-
160 with
the

tangential feed
of the air
-
fuel mixture.

Mathematical
, physical and geometric model
s

were developed
and initial and boundary
conditions
,

that adequately describe turbulent heat
-
and
-
mass transfer processes in th
e real
geometry
conditions
and correspond
to the
real process flow
of
fuel combustion
with a
tangential
supply to
the

combustion chamber
,

were determined
.

The
main characteristics and
peculiarities

of the
flow
aerodynamics

in the

combustion power
boiler B
KZ
-
160
with
the
tangential feed of
the
solid fuel (coal)
were determin
ed:
the field of the
total
vector speed and pressure P, and turbulent components of the process



the turbulent
kinetic
energy k and the dissipation of
the
turbulent
kinetic
energy


.

The main characteristics of the turbulent heat transfer

were determin
ed
, the temperature
fields and the distribution of the chemical energy
Q
chem

in the
tangential
furnace of the
boiler
BKZ
-
160

were studied
.

The regularities and
specif
ic features

of
the
concentration fields of carbon oxides (CO,
CO2), nitrogen oxides (
NO
х
)
), and
О
2

throughout

the volume of the tangential furnace
of the
boiler BKZ
-
160 and
at its
exit

were established
.

No
investigations

in the areas of real geometry (boiler BKZ
-
160) for the selected
configuration of the combustion chamber with a tangential

feed
of the
pulverized coal have been
c
arried out
, they are
new and
original.

The results to be
defended
:



The n
ew data on the
investigation of

heat
-
and
-
mass transfer in
the
combustion of solid
fuels in the areas of real geometry (combustion chamber
s

o
f
operating industrial power plants.)


The n
ew results of the 3
-
D computer modeling of
heat
-
and
-
mass
transfer in turbulent
combustion of pulverized coal flame in the combustion chamber of the boiler BKZ
-
160
,

Almaty
H
P
P
, with

tangential feed
of the air
-
fu
el
mixture.

• The
established

aerodynamics
of
solid fuel
combustion in the
tangential
combustion
chamber
s

and
specific

features of formation of velocity

and

pressure
fields
and turbulence
characteristics in the combustion
space
.

• The established regular
ities and specific features of the fields and isosurfaces of
temperature and concentrations of the reacting mixture, the reaction products of combustion,
especially of hazardous substances throughout the volume of the combustion chamber and
its

exit.


Th
e n
ew
results of
computational experiments
that
enable
us

to get

such
characteristics of

turbulent combustion of pulverized coal flame as speed
,

its
direction, temperature, pressure,
turbulent kinetic energy, energy dissipation, the concentration of carbon

oxides (CO and
СО
2
)
,
nitrogen oxides (NOx),
О
2

and the energy released in chemical reactions at any point in the
combustion chamber
of the
boiler BKZ
-
160 with
the
tangential feed
of
fuel and oxidizer, which
allows us to estimate the emissions of harmful substances into t
he atmosphere.

The structure and
volume

of the
dissertation
: The
dissertation

consists of
the

introduction,
four chapters
,

the
conclusion,
and
the
bibliography
including

180 titles. The
number of pages is

118 includ
ing

56 figures and 3 tables.

Conclusion
:

1.
The n
umerical 3
-
D
modeling of
the
combustion of pulverized coal flame
was made based on
the Navier
-
Stokes equations
and

heat
-
and
-
mass transfer
equations taking into account

the
influence of nonlinear effects of thermal radiation, turbulent flow, inte
rfacial interaction, multi
-
stage chemical reactions,
and the two
-
phase media with
the
given initial and boundary conditions
correspond
ing

to
the
real technology
of the
solid fuel (coal) combustion
in the
combustion
chambers of
the HPP
boilers.

Physic
al
-
ma
thematical and geometric models of the
studied
problem adequately describe
turbulent heat
-
and
-
mass transfer processes in the combustion chamber with
the
tangential feed
of
fuel and oxidizer. The models have been tested on
the

experimental
fire
model of
the

combustion
chamber, and the results of numerical simulation and
calculations

(velocity and temperature

fields
)
were
compared with the data
of the
f
ull
-
scale

experiment and showed good agreement.
The difference
between

the calculated and experimental value
s of the average temperature T

along

the height of the combustion chamber is less than 5% except for the area where the flame
ignites and these processes are unstable.

2.
Physical
-
mathematical and geometric models of the combustion chamber of Kazakhstan's

power boiler BKZ
-
160
at
Almaty
HP
P with
the
tangential feed
of the
pulverized coal, which
adequately
presents

the basic elements, the configuration of the combustion chamber, the
location of its burners and the actual process of burning
of
high
-
ash coal
,

were developed
.

The c
omputational experiments on 3
-
D modeling of the combustion of pulverized coal flame in
the combustion chamber of the power boiler BKZ
-
160

were carried out
, and the main
characteristics of
the
aerodynamic flow

were obtained
:
the

field
of the
full speed
2
2
2
w
v
u
V



and pressure P, and turbulent flow characteristics determined by the
fluctuating velocity components: the kinetic turbulent energy k and its dissipation
ε
. The
obtained results of numerical simulation of the aerodyna
mics of the process correctly reflect the
real picture of the flow in the combustion chambers of
the
existing industrial boilers with
the
tangential feed
of the
dust
-
gas mixture.

3. The
obtained

aerodynamic

flow pattern confirm
s

the experimental fact that

in

the center of the
combustion chamber
a conventional
tangential circle with a diameter
usually

equal to 0.1
-
0.3 of
the depth of the furnace
with burners
at a

tangent to
it is formed
.
The results of our c
alculat
ions
of

vector fields
of the total

speed fo
r the boiler BKZ
-
160
also
give the diameter of the
conventional
circle about 0.2 o
f

the depth of the combustion chamber.

The results of numerical simulation of aerodynamics
of
the
BKZ
-
160

furnace

showed that
in
the
combustion chambers with
the
tangential
feed
of
fuel and oxidizer
a

vertical
ly directed

rotational
motion of flue gases

is formed
.
The t
hree
-
dimensional picture of the velocity field confirms the
experimental fact that in the area below the waist
of
burners (k <32, h <4.61m), one can see the
for
mation of
the
reverse flow, when part of the stream
goes down
at a s
mall

angle breaking into
two vortices
,
which

is typical

of all types of combustion chambers and is
caused by the
air

inflow

from

the bottom of the c
hamber
, made in the form of a funnel to
remove the slag.


4.
The
dependencies

and specific features of
formation of
te
mperature

fields and isosurfaces
correc
tly

reflect the process of turbulent heat transfer in
the

pulverized
-
coal flame.
In the center
of the flare
in the area of the burners


bel
t there are
temperature

maximums and

minimums
caused by
the
inflammation
of the
dust
-
gas mixture when the temperature rises sharply
(
Т
max
≈1681
0
C

) and low temperature
of the air mixture inflowing

into this area through
the
burners (
Т
а
=250
0
С
).

5. As we m
ove toward the exit of the process
,

such
characteristics
of
the
mass transfer
process
as
concentrations of
carbon monoxide CO, nitrogen oxide NO,
and oxygen
О
2

decrease,
which is
caused by

the
decrease in
the temperature T, the decrease
in

the
amount of
th
e
gas mixture of
fuel and oxidant

in the upper layers
, and
hence
,
the
decrease in
the concentration of pure carbon
and nitrogen

and
slowing down of

chemical processes.

At
the
exit

of the combustion chamber (h
= 20.96m), we have the average temperature equ
al to
Т
aver
≈1093
0
С
, and its maximum value

is

Т
max
=1152
0
С
. Here, the average value of the energy released by chemical reactions

is

Q
chem
ср
=1.052
kw
/
m
3
,

which is much less than its value
in the vicinity
of the burner where
Q
chem
ср
=1550
kw
/
m
3
.

6. The results obtai
ned
by the
3
-
D computer modeling of
the
heat
-
and
-
mass transfer in
combustion chambers of real
HP
P boilers have high
er information density than

the data of f
ull
-
scale

experiments.
The

full
-
scale experimental data cannot be obtained
at HPPs as it is
technica
lly

impossible to
make

such measurements.

7.
The
physical
-
mathematical and geometric models
presented in the dissertation
and the method
of their construction can be used
in

the
study of heat
-
and
-
mass
transfer in the combustion
of
any
coal fuel in the com
bustion chamber
s of the other HPP
boilers.
The r
esults can be used
in

developing
of
new technical solutions
aimed at

optimiz
ation of

combustion of solid fuels
at

existing power plants or creati
o
n

of

new burners.

Approbation and publications
:


The material
s of the dissertation were
published
in
42 p
apers
, including 14
papers in the editions
recommended by the Committee for Control of Education and Science,

RK MES,

3 in
the
international scientific journals (Scopus

database



2, the database
of
the
Republic
an Information
Center



1 )
,

1 article
was published
in the
foreign
scientific journal, 22
articles were published
in
the p
roceedings of international conferences, including 17
in the proceedings of
international

conferences
held
in other countries.