CC BY
19Journal of Siberian Federal University. Engineering & Technologies 3 (2010 3) 264-271
УДК 536.24: 669.3
The Mathematical Model and Investigation of Influence of Design Characteristics on Heat Transfer in Vanyukov Smelting Energotechnological Complex
Alexander P. Skuratov* and Svetlana D. Skuratova
Siberian Federal University, 79 Svobodny, Krasnoyarsk, 660041 Russia 1
Received 3.09.2010, received in revised form 10.09.2010, accepted 17.09.2010
The polyzonal mathematical model of heat transfer in the furnace with a liquid bath of Vanyukov smelting energotechnological complex has been improved and its design-theoretical analysis has been made. The paper gives quantitative estimation of influence on thermal condition offurnace's design characteristics: shapes and size of over layer space, the situation of uptake and place of charge load.
Keywords: Vanyukov smelting, energotechnological complex, over layer space of the furnace, heat transfer mathematical model, design characteristics
Introduction
The melt of sulphide raw material containing heavy non-ferrous metals in a liquid bath (liquidphase melting or Vanyukov smelting) has got a wide application in Russia industry. It is a result of its following advantages: the possibility of melt both slime concentrate and lump raw material; recycling of secondary raw material; high specific furnace productivity; low dust taken-away from the furnace (no more than 1...2 % of charge's mass); the wide range of unit capacity (from ten to thousands tons of charge in 24 hours). The physicochemical basics of Vanyukov smelting (VS) have considerably been researched, the physical and mathematical models for investigation of material and heat balances, hydrodynamic and heat exchange in barbotage bath have been created [1-3]. At the same time, the lack of research of heat processes in Vanyukov smelting energotechnological complex «Vanyukov furnace -waste-heat boiler» (VS ETC) does not allow to design effective complex structure and composition of its elements and take into consideration their mutual influence on heat exchange indices.
To maintain effective and durable work of entire VS ETC and create means and methods for melt operation we need to know thermal physical features of the process taking place in melt bath, in over layer (gas) furnace space (GS) and in the work volume of waste-heat boiler (WHB) as well. In particular, the further improvement of VS requires the furnace construction optimization. Along with creation of efficient melt conditions in the bath the optimization will provide stable work of the complex, which depends mostly on work of gas disposal section (uptake). It will be
* Corresponding author E-mail address: [email protected]
1 © Siberian Federal University. All rights reserved
a " b
Fig. 1. Geometrical model of Vanyukov smelting energotechnologiacal complex: a - the division on volume zones and scheme of charge, gasses and melt motions; b - model side evaluation; I and II - central and wall boundary layer of the model; A-A - the cross-section of the surface defined the uptake effect from waste-heat boiler; B-B -the surface of melt bath
limited by skull formation on technological surfaces of WHB due to technological carry-over when melting.
In the paper the results of design-theoretical research of influence of furnace design characteristics on thermal condition of the GS are shown: situation of uptake and place of charge load, the shape and size of GS as well. The research has been conducted on the basis of previously developed three-dimensional mathematical polyzonal model of heat transfer in VS ETC (Fig. 1), which equation system binds GS VS, WHB and melt bath together in one complex [4, 5].
Experimantal
The mathematical model takes into account the GS geometry, the formation of liquid and hard layers of skull, presence of lining cooling system, flammable compounds combustion, heat and mass exchange between GS and WHB. Though when calculating heat and mass exchange in VS ETC the attention should be paid to the fact that intensive melt barbotage (intensive blast of gas or oxygen through a liquid phase bath) results in high spattering drop out of the furnace. The carry-over is in a liquid state and has high temperature that can essentially act on heat exchange indices in GS VS. Moreover, aggressive carry-over under high temperatures promotes increased GS's lining wear out and WHB heating surfaces soiling and slagging. Therefore the further improvement of the model is connected with accurate consideration of dusting and sputtering from the melt bath.
When describing the heat exchange process by the system of zonal heat exchange equations the mass and heat transfer between volume zones of over layer space and barbotage melt bath (bath gassing and sputtering) was additionally taken into account in the model.
For zonal calculation of carry-over indices in the GS VS model the technique [6] offered for barbotage type furnaces has been modified. At that the mass of carry-over from melting layer into GS VS volume zones is found as:
M = [cf pmuf (1 - <pffSc f, ] / <Pf. (1)
Here, cf - the coefficient depended on the gas concentration on gas-liquid flow axis, the distance from the stream and Schmidt number (Sc); pm - the density of the melt, kg/m3; uf - the speed of gasliquid flow near the axis of the stream, m/s; ^ef - the effective gas-bearing of the flow; % - the gas-bearing volume of the flow; Fi - the square of barbotage melt layer, m2. In conditions of barbotage melt: Sc = 0.75; 9ef = 0.3.0.4; % = 0,75. Note, that the values of cf and uf can be find from formulas [6].
When spray refining the variation of specific carry-over (kg/m3) with the model height of y can be described by following equation:
mz=mo exp(- 0.0412/^ - 0.45 y), (2)
where m, = M/Q - the specific carry-over near the layer surface, kg)m3; Q - the total gas consumption from all tuyere, m3/s; Ho = h/d, - the relative layer height (1^ - the liquid phase height under the tuyere axis when no blast, do - tuyere diameter, m ); y = y/Ssj - the dimensionless coordinate of the cross-section, where the carry-over volume needs to be cteternuned (5SJ - the radius of transition section of the stream, m).
To obtain the mass of carry-over wasted from the work zone we need to find the critical volue of separation zone height ycr. Then the mass of wasted carry-over Mtr and nne regained to the bath Mr are defined by formulas:
MyynQQ and My ye - ntr) Q, (3)
where mtr is determined by tine equation (2) at y = ycr.
Results and discussion
The design-theoretical analysis of heat exchange processes was made on the Balhashski MMC (BMMC) industry VS ETC example. The operating conditions of ETC have been taken accordingly furnace # 1 balance tests (VS-1) [7]. In the basic variant relatively to the project one the charge input was Go = 19.44 kg/s, where 15.3 kg/s were put through load windows at the melting side. The melt bath temperature was tn = 1350 °C, the gassing power was vo= 8.53 m3/s, the intensity of carry-over was determined according to formulas (1)-(3). It was considered that gassing and spattering from the melt went evenly on the whole bath surface except ones under load windows. The proportion of circulating technological gases in GS were as follows %: 40.5 SO2; 2.1 CO2; 14.2 H2O; 3.2 O2 h 40.0 N2. After calculating GS temperatures and dust and gas flow composition in basic variant the mathematical model estimation has shown good agreement with VS ETC practical operation [1, 7].
The situation of uptake and charge load. The technological spattering contains a great amount of charge with fine fraction. One of the possible design decisions for carry-over decrease is to move the charge load places away from uptake zones. Since the load of charge at VS-1 BMMC goes down from the furnace arch at the both sides of uptake zone, we can achieve the considerable removal of load place by designing the furnace construction with gas disposal at one of its side. It is offered to place the uptake zone near slag siphon which is the most removed away from the load zone. Later this design was embodied in the furnace # 2 BMMC (VS-2). This change results in increased time of charge processing and more favorable conditions for slag formation.
The research has been conducted on polyzonal GS VS-2 model with uptake shifted toward the slag siphon and places of charge load windows accordingly changed along the arch length (Fig. 2). The
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Fig. 2. The schemes of over layer space in Vanyukov furnace taken in consideration: a - the basic design of the furnace (VS-2); b and c - the first and the second modifications of the furnace GS. Roman numbers: I-IV and I-IX - the numbers of layers in height and sections in length of the furnace; 1 and 2 - outer and central layers; ^ - gasses; - charge; ^11 - melt
dimensions of the furnace and the character of dividing of its volume and bounding surfaces are the same as in GS VS-1 model. The model took into account the combustion of flammable compounds of technological carry-over which was located in uptake zone [8]. The power of heat output was distributed in uptake zones in proportion to their volume and reached 2000 kW [7].
The analysis shows that the change of uptake place and its distance from the optically density cold charge flow alters the volume and character of distribution of temperatures and heat flows in GS volume. The closed zone of high temperatures remains in the uptake and reaches 1300 °C (Fig. 3). At the same time the uptake shift leads to according shift of gas and dust stream temperature toward the slag siphon. It can be explained by the change of aerodynamics in gas and dust streams: one-way entering of relatively cold gases from GS and hot gases rise from the melt bath in shifted uptake zone (see Fig. 2).
The temperature level of gas and dust flow tg has been found to be higher than in the basic variant. The temperature of GS's side walls increased approximately on 20 °C in uptake zone as well. The temperature level of gasses and side walls on the melt side of the furnace decreased in average on
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40 °C, the temperature of arch - on 80 °C. Here, the cooling influence of charge flow has greater effect on heat exchange due to the distance decrease between load windows. At that the value of radiational flows falling on surfaces of side walls, furnace arch and uptake qs decreases in average on 50.150 kW/ m2. That proves that the furnace with shifted uptake has less heat-stressed work conditions of bounding surfaces and increased durability of GS's lining. It was established that in considered VS modification, as in the basic one, the uptake has almost no influence on the temperature of melt under it - «the cold spot» on the malt bath surface is absent. That can be explained by the fact that the uptake has the combustion zone of carry-over compounds which protects the melt bath from relatively cold volume of waste-heat boiler and its heating surfaces of radiational chamber.
The shape and dimensions of the furnace. The comparative analysis of heat exchange indices has been carried out in the GS with different geometry. The basic furnace construction and two its modifications differing with width and height of work space were taken into consideration (see Fig. 2). The basic VS-2 design with uptake shifted to the side of slag siphon has the work space width z = 2.5 m and GS height from the level of still bath y = 3.5 m. The first modification has z = 2.0 m and y = 5.0 m and the second one - z = 4.0 m and y = 2.5 m. Note, that on the figure 3 the height of GS is shown when melt barbotaging. Taking into account the barbotage layer the GS's volumes of basic design, the first and the second modifications was accordingly equal to 123.2; 144.9 and 128.8 m3. The calculation of heat exchange indices was lead with operating conditions of basic variant without technological sputtering combustion in uptake.
The alteration of shape and dimensions of the furnace do not act significantly on the distribution of temperatures and heat flows in GS's volume. Though the great increase of GS's volume and slight
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Fig. 4. The Vanyukov furnace geometry influence on heat exchange indices in over layer space: y and z - the height and width of over layer space. Temperatures: 1, 3 and 4 - maximums for gasses, walls and arch; 2 -gasses at the furnace outlet. The maximum density of falling radiational flows: 5, 6 and 7 - for walls, arch and uptake accordingly
decrease of its width in the first modification (relatively to the basic design the GS's volume has increased on 17.6 %) leads to the significant reduction of level of temperatures and heat flows (Fig. 4). Especially it's demonstrated in higher layer of GS. So in the lower layer the temperature tg reduces in average on 60 °C, the heat flow qs - on 46 kW/m2. In the higher layer the indices increase accordingly till 175 °C and 58 kW/m2. The increase of distance between uptake output window and melt results in temperature drop of output gasses of the furnace to on 106 °C.
The approaching of furnace arch to the melt with simultaneous increase of GS's width in the second modification (relatively to the basic design the GS's volume has rise on 4.5 %) leads to slight increase of level of temperatures and heat flows (see Fig. 4). So in the lower GS's layer the temperature tg rises in average on 20 °C, qs on the walls - on 8 kW/m2. In the higher layer the volumes increase accordingly till 39 °C and 14 kW/m2. The temperature of technological gasses to rises on 32 °C.
The comparison of the three GS designs shows that the first modification is more preferable in the way of improvement lining work conditions. Also the interaction between relatively cold shielded surfaces of lower part of WHB's radiational chamber with the melt bath surface reduces as well. The design of WHB for such construction should estimate the lower temperature of outlet technological gasses taking into account the furnace charge capacity. The reduction of GS's height in the second modification changes for the worse the lining work conditions. Though the carry-over of loaded charge particles is considered to be low, since the GS's cross-section and gas speed in all three constructions do not change.
Conclusions
The research of furnace design characteristics influence on the indices of VS ETC heat exchange has shown that:
- the increase of distance between the load place and the uptake (qs for walls, arch and uptake
decreases in average on 15...44 %) due to its shift toward slag siphon along with reduction of
reduction of dust and more preferable conditions of slag formation leads to improvement of temperature conditions of work of GS's bounding surfaces and uptake, that increases the durability of furnace lining;
- the form of GS has significant influence on the heat exchange in under-arch space: the increase of GS height reduces the level of temperatures and heat flows near the arch and in uptake (qs on bounding surfaces decreases in average on 14...17 % in height, to - on 106 oC), at the same time the interaction between relatively cold shielded surfaces of WHB's radiational chamber with melt bath surface decreases; the reduction of GS height changes for the worse the lining work conditions and increases the temperature of technological gasses before WHB on 32 oC.
Статья опубликована при поддержке Программы развития Сибирского федерального университета.
References
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2. A.V. Vanyukov. Physic-chemical basics of melt in liquid bath / A.V. Vanukov, A.D. Vaskevich // Non-ferrous metallurgy. - 1982/ - # 6. - Pp. 20-28.
3. A.V. Grechko. The development of melt processes in Vanyukov's furnace /A.V. Grechko, I.I. Kirilin // Non-ferrous metallurgy. - 1994. - # 7. - Pp. 19-22.
4. A.P. Skuratov. Mathematical modeling for investigation heat transfer in energotechnological complex smelting Vanyukov's / A.P. Skuratov, O.M. Grigireva, U. A. Guravlev // Non-ferrous metallurgy. - 1989. - # 4. - Pp. 100-106.
5. A.P. Skuratov. The research of thermal performance effectiveness of different waste-heat boiler designs for Vanyukov's furnaces / A.P. Skuratov, O.M. Grigoreva, U.A. Guravlev // Non-ferrous metallurgy. - 1990. - # 1. - Pp. 95-98.
6. N.K. Nikolaenko. The separation of carry-over in over layer space in the barbotage type furnaces / N.K. Nikolaenko, G.S. Sborshikov // Non-ferrous metallurgy. - 1987. - # 4. - Pp. 39-42.
7. V.V. Mechev. About improvements of furnace thermal performance with liquid bath melt / V.V. Mechev. G.M. Shvarcburg, A.Z. Zaharchuk, B.V. Meierovich // The integrated use of mineral raw material: The collection of scientific works. - 1988. - # 5. - Pp. 58-63.
8. A.P. Skuratov. The modeling and heat exchange analysis when sulphur reburning in under arch space of Vanyukov's furnace / A.P. Skuratov, A.V. Finkelshtain, A.M. Pticin, O.M. Grigoryeva // The production theory of heavy non-ferrous metals: The collection of scientific works of Gincvetmet. - M.: Vneshtorgizdat. - 1991. - Pp. 96-100.
Математическая модель и исследование влияния конструктивных характеристик печи на теплообмен в энерготехнологическом комплексе плавки Ванюкова
А.П. Скуратов, С.Д. Скуратова
Сибирский федеральный университет, Россия 660041, Красноярск, пр. Свободный, 79
Усовершенствована многозональная математическая модель и проведен расчетно-теоретический анализ теплообмена в печи в жидкой ванне энерготехнологического комплекса плавки Ванюкова. Количественно оценено влияние на тепловое состояние конструктивных характеристик печи: формы и размеров надслоевого пространства, местоположения аптейка и загрузки шихты.
Ключевые слова: плавка Ванюкова, энерготехнологический комплекс, надслоевое пространство печи, математическая модель теплообмена, конструктивные параметры.
