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1.
强化预热带对流换热是降低套筒窑排烟温度的有效途径。为了在强化换热的同时不使气流阻力增加,提出了以适当缩小上内套筒的直径来加大预热带中单位高度石灰石换热面积和热容量的设计思路。以500 t/d的套筒窑为例对预热带的对流换热进行了估算,并给出了料层截面积与热流量的关系。计算结果表明,适当缩小套筒窑上内套筒直径能够在一定范围内解决使用低热值煤气后带来的排烟温度过高的问题。 相似文献
2.
V. I. Matyukhin Yu. G. Yaroshenko A. V. Matyukhina V. A. Dudko S. E. Punenkov 《Steel in Translation》2017,47(8):528-533
Natural gas is employed to reduce coke consumption in cupola furnaces with an open or closed top. The usual approach here is combustion of the natural gas by means of burners in external chambers at the perimeter of the furnace housing. Depending on their design, the burners ensure partial or complete preliminary mixing of the gas and air, with an air excess of 1.2–1.5. Then the combustion products are sent directly to the batch bed. In this system, the coke consumption amounts to 8–9% of the metal charge, while the consumption of gaseous fuel is 30–40 m3/t of melt. In these conditions, the melt temperature rises slightly (by 10–20°C); the productivity is increased by 15–20%; and the harmful gas emissions (mainly CO) are reduced by 20–25%. The gas dynamics of the cupola furnace is periodically disrupted, with suspension of the batch bed, cooling of the melt produced, less complete chemical combustion, and damage to the furnace lining. When using this method, the gas–air mixture is supplied to the hot bed with an air excess no lower than 2.5–3.0. A high-temperature zone (1350–1380°C) of width 60–70 mm is formed and moves through the bed at a speed of 15–20 mm/min. This calls for uniform mixing of the gas and air, specific gas-dynamic conditions, and the creation of the required gas–air ratio, with an air excess of more than 2.5–3.0. If cold gas–air mixture is supplied to the furnace bed through a tuyere, the combustion zone divides the whole bed into two stages: the initial and final stages. The high temperature of the combustion zone ensures fast cooling of the material at ignition of the gas–air mixture. That prevents ignition in the space above the bed. The lack of direct contact between the high-temperature zone and the furnace’s working space improves the reliability and economic indices of this process (no heat losses). Bed combustion of natural gas in the heating of such cupola furnaces increases the productivity from 10 to 13.6 t/h (by 36%), with reduction in coke consumption by 80 kg/t (33.3%) and decrease in heat consumption by 25 kW (18.78%). The heat losses with the exhaust gases are reduced by 25.32 kW (16.2%). The total thermal efficiency of the system is increased from 35.58 to 42.26% (by 15.81%, rel.). 相似文献
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The distribution of gas fraction and the flow field of gas-stirred liquid metal in steel ladles at eccentric injection of the stirring gas through the bottom of the vessel were measured in melts of 437 kg liquid Wood's metal. The melts had a temperature of 100°C. The bath height was 37 cm and the vessel diameter 40 cm. The blowing nozzle was positioned at half of the vessel radius. Gas flow rates were between 100 and 800 cm3(STP)/s. The gas fractions were measured by electrical resistance probes. The flow velocity of the liquid metal was determined by magnet-probes. The gas fraction and the velocity distribution in the plume were found to have a Gaussian shape. The cross-section of the plume is ellipsoid, as the plume width in the direction of the radius was a little smaller than the width in the direction perpendicular to it. Moreover the plume was inclined to the wall. The results which were found for the plume are mathematically described. The flow field at eccentric gas-stirring consists of one great loop, which fills almost the entire vessel. This is contrary to centric blowing, where for aspect ratios of the ladle in the order of 1, a toroid is formed in the upper and a dead zone exists in the lower part of the vessel. The consequences of this behaviour, especially for mixing in the melt, are discussed. 相似文献
5.
CHU Man-sheng YANG Xue-feng SHEN Feng-man YAGI jun-ichiro NOGAMI Hiroshi 《钢铁研究学报(英文版)》2006,13(6):8-15
To date ,blast furnace operators have a relative-ly good understanding of internal mechanisms ,andno longer treat blast furnace as a“black box”. Forthe blast furnace , however , one of the most com-plex metallurgical units inthe field of chemical engi-neering,the complexity keeps proliferating with theadoption of newtechnologies ,such as high rate in-jection of pulverized coal ,effective use of carbona-ceous andferrous materials ,and so on.If merely bydirect instrumentation and empirical kno… 相似文献
6.
通过对铜浮渣转炉进行热工综合测试,获取了转炉关键位置的温度、压力、烟气组分等炉况参数,分析了转炉能量利用状况和能质流路径。通过数值模拟技术,基于热工测试数据,模拟了炉膛内天然气的富氧燃烧过程。结果表明:铜浮渣转炉的热效率为19.96%,转炉漏风量过大、壁面散热量过大是转炉热效率较低的主要原因。此外,转炉粒煤用量在反应热理论计算中过量较多。根据热工诊断结果,提出的节能优化建议如下:调整粒煤用量,达成最优配料;采取保温措施,减少表面散热;增强转炉密闭性,减少漏风量;调整烧嘴布置方式,强化烟气与熔体换热。 相似文献
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The absorption of gas through the plume eye and of an injected gas in a steelmaking ladle process was investigated, using
a physical model of CO2 absorption into a NaOH solution. The results show that the inert gas escaping through the plume eye is ineffective in protecting
the bath from the atmosphere, and placing an oil layer (simulated slag) decreases the absorption rate significantly. Increasing
the flow rate of the inert gas not only exposes more of the liquid surface to the CO2 atmosphere, but also increases the mass transfer coefficient at the surface. The overall mass transfer between an injected
CO2 gas and NaOH solution includes the mass transfer through the surface of the bath as well as the mass transfer in the bubble
dispersion zone. The difference between the mass transfer in the bubble dispersion zone and the overall mass transfer was
found to be significant for relatively low gas flow rates. The mass transfer coefficient of CO2 in the bubble dispersion zone was estimated using available information regarding the bubble size and velocity. Mass transfer
coefficient estimated for the constant bubble frequency regime shows a dependence on gas flow rate. However, if a constant
characteristic size of bubbles is assumed as an alternative approach, the mass transfer coefficient is independent of the
gas flow rate. 相似文献
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Tobias Vogt Artur Andruszkiewicz Sven Eckert Kerstin Eckert Stefan Odenbach Gunter Gerbeth 《Metallurgical and Materials Transactions B》2012,43(6):1454-1464
A model experiment of a submerged gas injection system in a cylindrical vessel under the influence of a rotating magnetic field and its effect on liquid metal mixing is presented. Argon gas is injected through a nozzle into a column of the eutectic alloy GaInSn, which is liquid at room temperature. Without a magnetic field, the bubble plume in the center region of the cylindrical vessel produces a recirculation zone with high fluid velocities near the free surface, while the fluid velocities in the bottom region are rather low. Our measurements revealed the potential of rotating magnetic fields to control both the amplitude of the meridional flow and the bubble distribution and to provide an effective mixing in the whole fluid volume. Various periodic flow patterns were observed in a certain parameter range with respect to variations of the magnetic field strength and the gas flow rate. 相似文献
11.
Heat transfer from flames in a rotary kiln 总被引:3,自引:0,他引:3
J. P. Gorog T. N. Adams J. K. Brimacombe 《Metallurgical and Materials Transactions B》1983,14(3):411-424
Heat flow in the flame zone of a direct-fired rotary kiln has been modeled mathematically. The flame has been assumed to be
cylindrical in shape, backmixed radially, and moving axially in plug flow. The length of the flame and the rate of entrainment
of secondary air have been characterized by empirical equations reported in the literature. It has been shown that the axial
component of radiation can be reasonably neglected since it is relatively small compared to the radial component. The resulting
one-dimensional model is capable of predicting the axial temperature profiles of the flame and wall and the axial profiles
of heat flux to the solids bed and refractory wall. The model has been employed to study the influence on heat flow to the
bed of the following variables: fuel type (fuel oil, natural gas, producer gas), firing rate, temperature of secondary air,
pct primary air, and oxygen enrichment. Of the three fuels, combustion of fuel oil gives the longest flame and the greatest
heat input to the solids in the flame zone. Raising the secondary-air temperature increases the flame length significantly
but has a small effect on the maximum flame temperature and heat flux to the solids. Increasing percent primary air decreases
the flame length and increases the peak values of flame temperature and solids heat flux but reduces the quantity of heat
received by the solids in the flame zone. Oxygen enrichment results in a shorter flame, higher maximum flame temperature,
and increase in the heat transferred to the solids in the flame zone.
Formerly Graduate Student, University of British Columbia 相似文献
12.
George Kaptay 《Metallurgical and Materials Transactions A》2012,43(2):531-543
The rule of Lupis and Elliott (LE rule) proposed for the first time in 1966 is reformulated in this article as, “Real solid,
liquid and gaseous solutions (and pure gases) gradually approach the state of an ideal solution (perfect gas) as temperature
increases at any fixed pressure and composition.” This rule is rationalized through the heat expansion of phases and loss
of any interaction with increased separation between the atoms. It is shown that the rule is valid only if the standard state
is selected properly, i.e., if mixing does not involve any hidden phase changes, such as melting. It is shown that the necessary and sufficient practical
conditions to obey the LE rule is the equality of signs of the heat of mixing and excess entropy of mixing and the nonequality
of signs of heat of mixing and excess heat capacity of mixing of the same solution. It is shown that these two conditions
are fulfilled for most of the experimentally measured high-temperature solutions. The LE rule is compared with the existing
laws of thermodynamics. It is shown that the LE rule can be considered as a potential fourth law of materials thermodynamics. 相似文献
13.
In densely populated coastal cities in Asia, wastewater outfalls are often located not far from sensitive areas such as beaches or shellfisheries. The impact and risk assessment of effluent discharges poses particular technical challenges, as pollutant concentration needs to be accurately predicted both in the near field and intermediate field. The active mixing close to the discharge can be modeled by proven plume models, while the fate and transport far beyond the mixing zone can be well-predicted by three-dimensional (3D) circulation models based on the hydrostatic pressure approximation. These models are usually applied separately with essentially one-way coupling; the action of the plume mixing on the external flow is neglected. Important phenomena such as surface buoyant spread or source-induced changes in ambient stratification cannot be satisfactorily addressed by such an approach. A Distributed Entrainment Sink Approach is proposed to model effluent mixing and transport in the intermediate field by dynamic coupling of a 3D far field shallow water circulation model with a Lagrangian near-field plume model. The action of the plume on the surrounding flow is modeled by a distribution of sinks along the plume trajectory and an equivalent diluted source flow at the predicted terminal height of rise. In this way, a two-way dynamic link can be established at grid cell level between the near and far-field models. The method is demonstrated for a number of complex flows including the interaction of a confined rising plume with ambient stratification, and the mixing of a line plume in cross flow. Numerical predictions are in excellent agreement with basic laboratory data. The general method can be readily incorporated in existing circulation models to yield accurate predictions of mixing and transport in the intermediate/far field. 相似文献
14.
《钢铁冶炼》2013,40(5):348-354
AbstractThe influence of post-combustion, heat transfer efficiency, and the degree of metallisation is studied with regard to coal saving and export gas in the COREX process using a thermochemical model. An increase in post-combustion ratio decreases the coal rate and the amount of reduction gas, which influences the achievable degree of metallisation, when no additional reduction gas is added to the system. Further post-combustion with oxygen generates a higher temperature than that with air at all post-combustion ratios. A higher heat transfer rate is necessary to keep the temperature of the gas within the refractoriness limits of the lining material. It is asserted that the post-combustion ratio, the degree of metallisation, and the medium for post-combustion must be adjusted according to the refractoriness of the lining material of the melter–gasifier, the efficiency of heat transfer mechanisms from the post-combustion zone to the bath, the gas handling efficiency, and the thermal energy requirement of the surplus gas, when considering the use of post-combustion in the COREX process. 相似文献
15.
C. Nelson Neale Anthony W. Holder C. H. Ward Joseph B. Hughes 《Canadian Metallurgical Quarterly》2002,128(1):40-50
A series of three-dimensional numerical modeling experiments was conducted to determine the impacts of reaeration on the bioattenuation of petroleum hydrocarbon contaminants in groundwater systems. The influence of reaeration on plume length and mass loss was affected by four mechanisms including the groundwater mass transfer coefficient KL,GW, the concentration on partial pressure of O2 in the overlying soil gas PO2, the aquifer vertical dispersivity αv, and the reaeration zone Z or region of mixing between contaminated ground water and O2 supplied from the vadose zone. Results from this study showed that reaeration may reduce steady-state hydrocarbon plume length and mass by up to 87% as compared to the case in which reaeration is not considered. Among the four mechanisms, αv exerted the greatest influence on plume length followed by KL,GW, PO2, and Z. Comparisons between plume length and the ratio of reaeration transport KL,GW to hydraulic conductivity K indicated that appreciable reductions in steady-state plume length were possible when KL,GW/K ≥ 10?3. 相似文献
16.
G. M. Druzhinin L. A. Zainullin A. V. Kushnarev Yu. N. Ovchinnikov S. V. Filatov A. A. Shalyagin 《Steel in Translation》2010,40(3):252-255
There is a pressing need to replace natural gas in blast-furnace smelting by other fuels. One option is carbon-bearing emulsion
(coal dust + fuel oil + water). The temperature in the tuyere zone is calculated, and the change in reductive potential of
the tuyere gas and the heat transfer processes in the upper part of the furnace are estimated. The feasibility of replacing
natural gas with carbon-bearing emulsion is explored. 相似文献
17.
Averaged and turbulent fluctuating liquid velocities in the gas/liquid plume zone of a gas-stirred water model ladle were
measured with a combined laser Doppler anemometer (LDA) and elec-trical probe technique. The measured turbulence fields, void
fraction distribution, and gas and liquid velocities in the plume zone were used for evaluation of various turbulence models.
It was found that, among all of the turbulence models tested, only a modified k-ε model, with extra source terms to take into
account the generation and dissipation resulting from the inter-action of the bubbles with the liquid, yielded good agreement
with both the mean liquid flow field and the turbulent kinetic energy distribution. However, the values of the coefficients
orig-inally proposed by their authors were found inapplicable to the bubbly plume situation; more appropriate values of the
coefficients were determined based on comparison with experimental measurement. 相似文献
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19.
Aniruddha Mukhopadhyay Prashanta Deb Ahindra Ghosh Biswajit Basu Rupa Dutta Pabitra Kumar Mukhopadhyay 《国际钢铁研究》2001,72(5-6):192-199
As a first step towards prediction of temperatures in secondary steelmaking, mathematical modelling of fluid flow and heat transfer in ladle furnace was undertaken. A two‐dimensional quasi‐single phase model has been developed for turbulent recirculating flow by solving Reynolds averaged Navier‐Stokes equations along with a two‐equation k‐? model. The model was then extended to include thermal transport in a conjugate domain (i.e., molten steel + refractory shell + steel shell). The flow model was validated with water model data reported in literature by different researchers. Good agreement for velocity field and satisfactory agreement for turbulent kinetic energy field were obtained. The thermal model showed good agreement with results predicted in literature. The paper also presents findings of tests for sensitivity of flow on modelling and process parameters. By comparison with water model experiments, it has been demonstrated that the flow field in a ladle with a porous plug can be represented using a gas voidage fraction in the plume obtained from experiments with nozzles for axial gas injection from the bottom. Flow and thermal fields were insensitive to initial turbulence level at nozzle. Maximum temperature inhomogeneity in the melt was 2 °C after 1.5 min and negligible after 3 min of onset of gas purging. 相似文献