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

and Dr. Vladimir I. Babanin

East Coal-Chemical Institute, 14 the 8th Mart St, Ekaterenburg 620001, Russia

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 0.4925Km0.027(3)

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 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.

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 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 – surface heat transfer coefficient from coke to coal burden, watt/(m2K). 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).

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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