MODELING OF MOVEMENT AND DIRECT HEAT AND MASS TRANSFER
BETWEEN FLOWS OF GRANULAR MATERIALS IN MIXING HEAT
EXCHANGER, APPLIED FOR METALLURGICAL COKE PRODUCTION.
by Dr. Boris Sh. Statnikov
P.O.Box 8255, Nazareth Illit 17571, Israel
statnikov@bezeqint.net
and Dr. Vladimir I. Babanin
East Coal-Chemical Institute, 14 the 8th Mart St, Ekaterenburg 620001, Russia
babanin@nexcom.ru
In modern coke production before coking a coal burden of - 6 mm is dried and
heated up to 150oC in gas flow of burned fuel while a hot coke of +25 mm is
cooled by inert gas flow which is used for following steam production in
boilers with low coefficient of heat utilization. Therefore, there is sense to join
two above stages of one technological process in order to decrease capital cost
of industrial equipment and energetic consumption.
According to our proposal (see Fig.1), the joint process of coke cooling and
coal burden thermal preparation is created in horizontal rotated cylindrical
mixing (drum) heat exchanger with direct heat transfer between the coke and
the coal. The coal isn’t overheated due to an effect of formation of steam
covering with the first contact to the cooled coke. In the end of rotated heat
exchanger the coal-coke composite is disintegrated on grid separator because of
different sizes of the components. Speed of the component move and the period
of the heat transfer are controlled by gradient of cylinder axis, speed of drum
rotation, diameter of locking diaphragm between the heat transfer and
separation zones, angle of a swerve of special grid trowels regarding the
cylinder axis. These trowels are located inside cylinder and used for regulation
of the coke move regarding the coal move.
In order to create optimal technology and design of equipment the above
process was researched, regarding main varied parameters, with analytic and
experimental modeling methods, and then tested in industrial plant.
With application of theory of dimensions and physical modeling the following
criteria equations were fond through experiments for describing of the drum
filling and materials move:
1. Move of coke: ntk=0.9287(D1/D2)1.381(L/D1)0.762 Fr 0.184 P -0.204
(1)
2. Move of coal burden: ntb=1.225(D1/D2)0.325(L/D1)1.797 Fr 0.629 P -0.224 (2)
3. Drum filling coefficient:
B=2012(D1/D2)0.55(L/D1)0.143 Fr -0.335P 0.4925Km 0.027
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(3)
9
12
7
10
11
2
13
14
6
5
4
3
1
Small coke of –25 mm
7
8
Quality cooled coke
Figure 1. Schema of joint process of coke cooling and coal burden thermal
preparation: 1-Hot coke storage and pusher. 2- Small coke separating grid.
3- Rotated drum heat exchanger. 4- Regulated grid trowels of coke move.
5- Locking diaphragm. 6- Separating part of the heat exchanger.
7- Conveyers of the heated coal burden. 8, 9 - Circular pneumonic system of
heated coal transportation. 10 – Storage of wet coal burden. 11, 12 – Dust
cleaning system. 13, 14 - Outlets of cooled coke and heated coal burden.
In equations (1)–(3) are applied following parameters: n - speed of the drum
rotation, 1/sec. tk,, tb – time of coke and coal burden move through the drum,
sec. L, D1 – length and diameter of drum heat exchanger, m. D2 - opened
diameter of locking diaphragm, m. Fr = (nD1)2/gdk – Frude index characterize
the ratio of inertia and gravitation affecting on moved materials. g – gravity
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acceleration, m/sec2. fk, fb – virtual density of coke and coal burden, kg/m2.
dk, db – mean diameters of coke and coal burden particles, m. Gk , Gb - coke
and coal burden mass-flows in drum, kg/sec. P = nGb /gfkD1L – index
characterize the loading of drum moving surface. Km = (Gk fb) /(Gb fk) – ratio
of coke and coal burden volumes on dram inlet. B – coefficient of drum filling:
B=4( Mm /fm+ Mb /fb) /πL(D1)2
(4)
Here: Mm , Mb – absolute masses of coke and coal burden in rotated drum heat
exchanger with constant condition of materials move.
The materials move in rotated drum was searched within of following intervals:
D1/D2 = 1.85–3.0, L/D1 = 4.1–4.8, Fr = (3–8.2)*10-2, P = (0.715–1.725)*10-6,
Km = 0.3 – 0.7.
L, m
7.0
1
2
3
7.5
1
A
6.5
2
A
3
7.0
1
6.0
2
B
3
6.5
1
2
3
5.5
5.0
2
3
4
5
Drum rotation speed, 1/min
Figure 2.
B
6.0
1.1
1.7
2.3
Locking diaphragm opened diameter, m
Active length (L) of Rotated Heat Exchanger as functions of the
Drum rotation speed and the Locking diaphragm diameter and:
A, B – Coke beginning temperature of 650 C & 1000 C.
1, 2, 3 – Drum diameter of 3.0 m, 3.2 m & 3.4 m.
For calculation of thermal processes and application of width used methods for
parallel material flows, there is a need to consider a virtual coefficient of heat
exchange between thermal massive granules of the coke and thermal thin
particles of the coal. With using of known heat theories and experimental data
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of physical modeling, got in laboratory and on industrial pilot, we obtained
following criteria equation of the heat transfer intensiveness:
Nu=0.186 Fr -0.235(Pe*10 -4) 1.189W 0.027
(5)
In equation (5): Nu=Kdk/lb - Nucelt index of heat transfer. Pe=nD1dk/ab –
Pecle index characterize the ratio of conductive and convective heat transfer.
W=(Gk /fk)/(Gk / fk+Gb / fb) – volume part of coke in total materials flow.
K
2
– surface heat transfer coefficient from coke to coal burden, watt/(m K). ab –
thermo-conductivity coefficient of coal burden, m2/sec. lb – heat-conductivity
coefficient of coal burden, watt/(m K).
Achieved results allowed calculate and analyze the proposed joint process of
coke cooling and coal burden drying and thermal preparation in rotated mixing
drum heat exchanger with direct heat transfer between the coke and the coal
(see Fig. 2&3).
t, min
5.5
1
2
3
4.5
A
3.5
2
Figure 3.
1
2
3
B
2.5
3
4
Drum rotation speed, 1/min
5
Time of coal burden heating up to 150 C as function of
the Dram rotation speed with following conditions:
A, B – Coke beginning temperature of 650 C & 1000 C.
1, 2, 3 – Drum diameter of 3.0 m, 3.2 m & 3.4 m.
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On base of extensive calculations of design and technological parameters were
selected the optimal geometrical sizes and conditions of application of dram
heat exchanger in one Coke Furnace Battery of Krivoy Rog Coke-Chemical
Enterprise (Ukraine), that was tested as industrial pilot.
Conclusion
The application of described technology allows to increase the total coefficient
of heat utilization in the coke production by 20...25 % regarding the modern
technological scheme and decrease capital cost of industrial equipment within a
cost of thermal preparation plant of coal burden.
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