Research On Heat Transfer R-ULE Of Blast Furnace Slag During Fibe Ring Process

More attentions are currently paid to researches on how to achieve energy-saving production activities in iron & steel industry and utilize mineral resources in a high-quality and efficient manner. One of critical utilizing approaches is how to fully fiberize blast furnace slag, the main by-product of blooming process. Quenching & tempering is an essential part before fibering, and heat transfer directly affects addition of quenching & tempering agent and fibering performance of blast furnace slag. Traditional approach fully depends on classical theory and experience, especially it is difficult to accurately describe and simulate heat transfer of viscoelastic slag with second order partial differential equations. This paper creatively introduces fractional differential operator theory into research on micro heat transfer mechanism of slag fiber-forming process, further concludes general rules with a specific case, in order to provide meaningful support for practices or production.In order to investigate heat transfer rule of quenching & tempering agent in slag solution, the paper establishes invasive fractional differential heat transfer model for invasion of quenching & tempering agent into slag, according to diffusion properties during blast furnace slag melting process, by combining two heat transfer approaches: conduction heat transfer and radiation heat transfer, and introducing local fractional differential operator; it further concludes functional relations between slag temperature, height from quenching & tempering agent center to liquid surface, and melting time, with Young-Laplace transform. In order to analyze the melting process of quenching & tempering agent more effectively, from five stages herein the paper discusses heat transfer law of quenching & tempering agent during the process from contact with liquid surface to full immersion, and the calculated results are basically consistent with observational data from laboratory, thereby verifying the rationality of the heat transfer rule.For the purpose of studying the soaking rule of quenching & tempering agent in liquid slag, the paper makes analysis from the views of external heating only or chemical reactions only. Under the conditions where external heating is considered only, fractional soaking models for the temperature field of continuum is proposed, on basis of the energy conservation law, and then soaking time is calculated with Yang-Fourier successive approximation method. Under the conditions where chemical reaction is considered only, the paper comprehensively evaluates slag reaction, proposes main reaction equation, and establishes soaking physical model with unreacted model and diffusion model of homogeneous process, also further solves the direct relations between time and temperature during the soaking process. The calculated soaking time is basically consistent with repeated experimental data from laboratory, thus verifying the rationality of the soaking rule.The paper analyzes from the two processes: from liquid core to stream boundary, and from stream boundary to external air, respectively, in order to investigate the heat radiating rule of dumped liquid slag during free falling process. A model is established to solve convection heat exchange, radiation heat loss, influence of liquid slag radius on heat transfer under laminar flow conditions, as well as total loss ratio of stream column, thereby to conclude the optimal stream radius in laboratory experiments. The calculated total loss ratio is basically consistent with the data measured in laboratory, thus verifying the rationality of the heat radiating rule. For the purpose of investigating the heat radiating rule of liquid slag during its movement in slag tank, from the view of radiation heat transfer and conduction heat transfer, the paper establishes models to solve radiation heat transfer heat flux between slag and air, heat conduction flux between slag and tank, concludes the calculation equation of remaining heat of slag in tank, and concludes that the remaining heat is directly proportional to the depth of slag in tank. The calculated remaining heat of tank is basically consistent with the data observed in laboratory, thus verifying the rationality of the heat radiating rule.In order to analyze the heat transfer and radiating rules of slag during injection and fibering process, a heat radiating model is established, according to research on liquid slag crushing mechanism during injection and flowing process, by modifying the flow conditions of Reynolds number and Karman Vortex Street, thus to propose radiating rules of liquid slag thin line and liquid slag forming line. On basis of the convective heat transfer theory, the paper establishes a partial fractional radiating model of liquid slag pellets. Regarding liquid fiber’s cooling, it proposes liquid cooling law under gas- liquid heat exchange control; as well as solid phase cooling law under gas- solid heat exchange control; also the temperature field of cooling process is simulated. The data errors, between fiber coagulation time, heat loss after injection and fibering, and those results from experimental observation, are within the acceptable range, thereby verifying the rationality of the heat transfer and radiating rules.In short, the paper provides support for heat compensation and waste heat recovery in industrialization process, by research on heat transfer law during quenching & tempering, soaking, dumping, tank flowing, and injection for direct fibering of blast furnace slag, with a certain theoretical significance and practical value.