Cohesive Zone Shape Research Articles

Numerical Simulation for the Influence of Cohesive Zone Shape on Distribution of Unburned Pulverized Coal in Blast Furnace

Numerical Simulation for the Influence of Cohesive Zone Shape on Distribution of Unburned Pulverized Coal in Blast Furnace

Soft-sensing method of cohesive zone shape and position in blast furnace shaft

The cohesive zone in a blast furnace has an important influence on its smooth operation by affecting the distribution of gas flow, the permeability of the charge, and the temperature distribution. And the online sensing of the cohesive zone is a key problem to realize optimal operation of the blast furnace. In the present study, the soft-sensing method of cohesive zone was put forward by integrating its off-line CFD calculation with the on-line measurement of the cooling water information. The database with shape and position of cohesive zone was established under different charging patterns and descending speeds of burden based on the CFD off-line calculation. The descending speed of the burden was derived from the root position of the cohesive zone which was determined by the cooling water information. Then, the shape and position of cohesive zone was matched with that in the database by means of the charging pattern and the descending speed. Thus, it is possible to obtain on-line the shape and position of cohesive zone of blast furnace based on the charging pattern and the cooling water information.

Revealing cohesive zone shape and location inside blast furnace

ABSTRACTIt is common practice in many blast furnaces to use the shape and position of the cohesive zone as a control guide for burden distribution. Knowledge of the location and shape of the cohesive zone will help to have better control over the blast furnace process and improve its thermal efficiency and productivity. Accurate estimation of the shape and location of the cohesive zone was believed to aid this objective. Hence for achieving better accuracy along with affordability to be used as a continuous monitoring method, a combined modelling approach of using furnace operating and probe data along with mathematical estimation model was attempted for estimating cohesive zone shape and location. Further, comparative evaluation was done with respect to current method adopted in Tata Steel based on process data analysis, for a given blast furnace.Both combined modelling approach and current method adopted in Tata Steel were found equally capable in predicting the cohesive zone root location but the combined modelling approach seemed to be better in predicting the overall shape of cohesive zone.

Modeling of Internal State and Performance of an Ironmaking Blast Furnace: Slot vs Sector Geometries

Mathematical modeling is a cost-effective method to understand internal state and predict performance of ironmaking blast furnace (BF) for improving productivity and maintaining stability. In the past studies, both slot and sector geometries were used for BF modeling. In this paper, a mathematical model is described for simulating the complex behaviors of solid, gas and liquid multiphase flow, heat and mass transfers, and chemical reactions in a BF. Then the model is used to compare different model configurations, viz. slot and sector geometries by investigating their effects on predicted behaviors, in terms of two aspects: (i) internal state including cohesive zone, velocity, temperature, components concentration, reduction degree, gas utilization, and (ii) performance indicators including liquid output at the bottom and gas utilization rate at the furnace top. The comparisons show that on one hand, predictions of internal state of the furnace such as fluid flow and thermo-chemical phenomena using the slot and sector geometries are qualitatively comparable but quantitatively different. Both sector and slot geometries give a similar cohesive zone shape but the sector geometry gives a higher cohesive zone near the wall and faster reduction. On the other hand, the two geometries can produce similar performance indicators including gas utilization at the furnace top and liquid output at the bottom. Such a study is useful in selecting geometry for numerically examining BF operation with respect to different needs.

Influence of Cohesive Zone Shape on Solid Flow in COREX Melter Gasifier by Discrete Element Method

Based on the principle of discrete element method (DEM), a 2D slot model of a COREX melter gasifier was established to analyze the influence of cohesive zone shape on solid flow, including mass distribution, velocity distribution, normal force distribution and porosity distribution at a microscopic level. The results show that the cohesive zone shape almost does not affect the particle movement in the upper shaft and deadman shape. The particles in the lower central bottom experience large normal force to support the particles above them, while particles around the raceway and in the fast flow zone exhibit weak force network. The porosity distribution was also examined under three kinds of cohesive zones. Like the velocity distribution, the whole packed bed can be divided into four main regions. With the increase of cohesive zone position, the low porosity region located in the root of cohesive zone increases. And the porosity distribution becomes asymmetric in the case of biased cohesive zone.

Influence of Shape of Cohesive Zone on Gas Flow and Permeability in the Blast Furnace Analyzed by DEM-CFD Model

Maintaining gas permeability is an important issue to realize low coke rate operation of blast furnace. In present study, the melting behavior of the iron ore and the layer structure in low coke rate operation were introduced in to the DEM-CFD model, and then behaviors of gas and moving bed in the blast furnace were simulated. Influence of shape of cohesive zone in low coke rate operation was investigated, and the effect of coke slit in the cohesive zone on gas flow was demonstrated in the calculation result. Surface area of cohesive zone and intersection angle between the burden layers and cohesive zone will determine the activity of coke slit.

Numerical analysis of isothermal flow in lower part of blast furnace considering effect of cohesive zone

The increasing interest in minimising fuel consumption and reducing environmental problems of the ironmaking industry has led to efforts to optimise the blast furnace process. One of the undeveloped fields generated from the adoption of new operating conditions is the internal phenomenon in the lower part of the furnace following the change of cohesive zone shape. The effective liquid flow in the dripping zone of a blast furnace is important for stable operation with high iron productivity. Study of the liquid flow behaviour in a packed bed needs to investigate the effect of various operational changes in the dripping zone. As a stepping stone toward the comprehensive modelling which includes chemical reaction and its associated heat transfer, isothermal flow for three phases is simulated with the variation of the shape of cohesive zone to see the effect of charging condition.

Transient Behavior of Burden Descending and Influence of Cohesive Zone Shape on Solid Flow and Stress Distribution in Blast Furnace by Discrete Element Method

The present investigation intends to elucidate the transient behavior of burden descending, the influence of cohesive zone shape on the solid flow and the stress field through three-dimensional analysis by discrete element method (DEM) in blast furnace. Although many continuum models were developed to analyze the in-furnace phenomena such as solid flow, DEM enables to analyze the unsteady state solid flow, the stress distribution and slip of burden in the three dimensional state. In this study, it was clarified that the solid flow in blast furnace was composed of steady flow and transient flow which caused by burden charge and slip around raceway. Burden charge instantaneously causes high stress region and high velocity region to spread from upper part to lower part. High velocity region caused by slip around raceway spreads upwards and mitigates the stress field in the vicinity of raceway. The cohesive zone shape almost does not affect on the particle movement in the upper part of shaft and deadman shape. However, the distribution of high stress region and high slipping region is affected by the cohesive zone shape. Asymmetric high stress and slipping distribution are formed in the case of biased cohesive zone, and high cohesive zone enlarges the region of high stress. Weak slipping region in the upper part of shaft tends to be mitigated by the stress field in upper part. Belly receives the maximum stress from burden. The normal stress acting on the bottom is concentrated on the center of bottom by the buoyancy effect of pig iron in the hearth.

Gas-powder flow in blast furnace with different shapes of cohesive zone

With high PCI rate operations, a large quantity of unburned coal/char fines will flow together with the gas into the blast furnace. Under some operating conditions, the holdup of fines results in deterioration of furnace permeability and lower production efficiency. Therefore, it is important to understand the behaviour of powder (unburnt coal/char) inside the blast furnace when operating with different cohesive zone (CZ) shapes. This work is mainly concerned with the effect of cohesive zone shape on the powder flow and accumulation in a blast furnace. A model is presented which is capable of simulating a clear and stable accumulation region in the lower central region of the furnace. The results indicate that powder is likely to accumulate at the lower part of W-shaped CZs and the upper part of V- and inverse V-shaped CZs. For the same CZ shape, a thick cohesive layer can result in a large pressure drop while the resistance of narrow cohesive layers to gas-powder flow is found to be relatively small. Implications of the findings to blast furnace operation are also discussed.

Gas–powder flow and powder accumulation in a packed bed: I. Experimental study

Gas–powder flow in a slot type packed bed is experimentally studied in order to understand the flow and accumulation behaviour of powder in systems like an ironmaking blast furnace (BF). A variety of variables including gas flow rate, powder flow rate and packing properties are considered. It is found that a clear and stable accumulation region, in which the voids among packed particles are fully filled with powder, can form in the low gas–powder velocity zone at the bottom of the bed. The accumulation region is stable and shows strong hysteresis. The distribution of softening-melting layers in the blast furnace known as the cohesive zone (CZ) is modelled by inserting solid blocks into the bed. The results indicate that the inverse-V cohesive zone shape leads to low powder accumulation within the CZ and at the corner of the bed.

Modeling nonlinear peeling of ductile thin films––critical assessment of analytical bending models using FE simulations

Three analytical double-parameter criteria based on a bending model and a two-dimensional finite element analysis model are presented for the modeling of ductile thin film undergoing a nonlinear peeling process. The bending model is based on different governing parameters: (1) the interfacial fracture toughness and the separation strength, (2) the interfacial fracture toughness and the crack tip slope angle, and (3) the interfacial fracture toughness and the critical Mises effective strain of the delaminated thin film at the crack tip. Thin film nonlinear peeling under steady-state condition is solved with the different governing parameters. In addition, the peeling test problem is simulated by using the elastic–plastic finite element analysis model. A critical assessment of the three analytical bending models is made by comparison of the bending model solutions with the finite element analysis model solutions. Furthermore, through analyses and comparisons for solutions based on both the bending model and the finite element analysis model, some connections between the bending model and the finite element analysis model are developed. Moreover, in the present research, the effect of different selections for cohesive zone shape on the ductile film peeling solutions is discussed.

Modelling the gas-liquid flow in an ironmaking blast furnace

A mathematical model is presented to describe the discrete flow of liquid within and below the blast furnace cohesive zone. The model is developed based on a force balance approach to describe the liquid flow and a stochastic treatment to take into account the complex packing structure. The interaction between gas and liquid flows has been included in the governing equations, so that the localised liquid flow in a packed bed can be modelled with or without gas flow. The validity is demonstrated by comparing model predictions and measurements obtained under different gas and/or liquid flow conditions. Application of the model to blast furnace is discussed with reference to the interaction between gas and liquid phases and the effect of cohesive zone shape.

Modelling of Gas-Powder Flow in a Blast Furnace

This paper presents a study of the gas-powder flow in a slot type packed bed in order to investigate the distribution of powder flow and accumulation in an ironmaking blast furnace. The effects of operational parameters such as gas flow rate, and cohesive zone shape are examined. It is shown that a distinct and stable accumulation region can be formed in the low gas-powder velocity zone in a bed with a lateral gas inlet. Also, the existence of a cohesive zone changes the powder accumulation pattern significantly. The inverse-V cohesive zone leads to low accumulation in the bed compared to other cohesive zone shapes. A mathematical model is developed to describe the gas-powder flow and powder accumulation. Its validity is verified by comparing the predicted and measured distributions of powder accumulation under various flow conditions.

New Method for Estimating Shape of Cohesive Zone in Blast Furnaces from Wall Temperature Distribution

New Method for Estimating Shape of Cohesive Zone in Blast Furnaces from Wall Temperature Distribution