Blast Furnace Design

Contents

Introduction

Section 1. Theoretical part

1.1. Methods of producing alumina clinker

1.2. Blast Furnace Profile

1.3. Physical and chemical processes in blast furnace

Section 2. Practical part

2.1. Determination of consumption of blast furnace smelting charge materials

2.1.1. The initial conditions are

2.1.2. Calculation of blast furnace charge composition (excluding coke)

2.1.2.1. Determination of average composition of iron ore materials

2.1.2.2. Exit of cast iron from charge components

2.1.2.3. Balance of manganese in charge components

2.1.2.4. Balance of basic and acidic oxides at specified basicity of slag

2.1.3. Coke Flow Calculation

2.1.3.1. Concept of thermal equivalents

2.1.3.2. Calculation of thermal equivalents of elements and connections

2.1.3.3. Calculation of thermal equivalents of blast furnace charge components and additional fuel

2.1.4. Determination of specific consumption of charge components and slag composition, checking of cast iron composition and slag basicity

2.1.4.1. Consumption of charge components

2.1.5. Determination of blast furnace smelting gas composition

2.2. Calculation of material and heat balances of melting

2.2.1. Material balance of the domain process

2.2.2. Heat balance of blast furnace smelting

2.3.1. Heat performance of blast furnace

Bibliographic list

Introduction

Blast furnace - a continuous metallurgical unit of the mine type for smelting cast iron from iron ore materials (agglomerate, pellets, iron ore) using solid fuel - coke (Fig. 1). The whole complex of complex interconnected phenomena of the blast furnace process is carried out in countercurrent conditions: charge materials fall down, and hot gases move from bottom to top. The furnace is huge: the volume of working space reaches 5000m ³, the height of the metal structures reaches 100m (Fig. 2). Such a furnace smelts about 25,000 tons of charge materials every day, consumes 200,000 tons of oxygen-enriched air, smelts 13,000 tons of cast iron and 4,000 tons of slag, and delivers 28,000 tons of flue gas.

The guarantee of normal operation of the furnace is reliable and efficient equipment, ensuring the continuity of operation of the unit, safety and ease of maintenance. When selecting the operating mode of the equipment, the process requirements of the furnace maintenance process are taken into account. The capacity of the equipment, and in some areas its quantity is determined taking into account the reserve from 50 to 100%. The modern furnace is equipped with the latest means of monitoring the progress of the blast furnace process, mechanization and automation of all production processes. Working on such a furnace places high demands on technological personnel in terms of theoretical knowledge, practical experience and skill, responsibility and independence in making decisions on the management of such a complex unit.

Section 1. Theoretical part

1.1. Methods of producing alumina clinker

Two methods for producing alumina cement have been developed: sintering, which involves the formation of a clinker due to reactions in the solid phase, and the complete melting of the entire raw material mixture.

When choosing a particular method, a number of factors must be taken into account, and above all the chemical composition of bauxite of a certain grade, and in particular the content of silicic acid and iron oxide in it.

On the basis of experimental studies, the sintering and melting temperature and the interval between them are determined, as well as the quality of the resulting melt or clinker. Technical and economic analysis allows you to identify which method of production in these conditions is more rational. At the same time, the presence and cost of electricity, the quality of coke, etc., are taken into account .

Melting. Alumina cement can be produced by melting in watercolor furnaces (wargans with water cooling). Bauxite, limestone and coke in the calculated ratio are loaded into the upper part of the furnace. Air heated in recuperators is blown through lances; melt formed at the bottom of the furnace at 17731873K is discharged through a spout; metal iron melt is discharged from furnace separately. Experiments were conducted on the use of oxygen-enriched air for these furnaces. Their productivity reached 50 tons per day at a specific fuel consumption of about 500 kg per 1 ton of melt.

This production requires high quality bauxites with a low silica content, since the reduction of silica to silicon and the production of simultaneously siliceous iron or ferrosilicon occurs at high temperatures, which are difficult to create in these furnaces. The melt (slag) is cooled in special molds and chilled in crushers and then finely ground in multi-chamber pipe mills.

There is a method of electrofusion of alumina cement, in which the product is not contaminated with silicic acid contained in coke ash, since ferrosyl is simultaneously melted.

There is experience in the use of arc furnaces operating mainly on alternating current. To intensify the melting process, the raw materials were pre-dried, crushed and briquetted or granulated after thorough mixing. To avoid emissions from the furnace, which are due to the rapid release of water and carbon dioxide from the raw material, bauxite is previously calcined and limestone calcined. The capacity of the furnaces reaches 3040t per day. Electricity consumption is about 43205040MJ per 1 ton of product. In these electric furnaces, high-quality alumina cement from high-silica bauxite is melted.

Due to the high temperature in such an electric furnace reaching 2273K, and the use of coke in the charge, the silica of the charge is reduced to silicon and ferrosilicon is formed as a result of interaction with metal iron. For example, when using bauxite containing 1517% SiO2, the amount of bauxite in the cement (melt) is reduced to 68%. The amount of ferrosilicon with 1315% Si is about 355 weight cement. The specific consumption of electricity is very high, reaching 900010800MJ per 1 ton of cement. A disadvantage of this method is the limited reduction limit of silica due to the formation of significant amounts of calcium carbide, which increases with increasing melting temperature.

When melting in a blast furnace, bauxite and limestone mixed with a certain amount of coke are charged onto a pile in the upper part of the furnace. A special filling apparatus loads the charge into a blast furnace, where it dries as it descends to the mountain, and the limestone contained in the charge is decarbonized. Iron oxides are reduced by gases containing CO as well as solid carbon. In the furnace rock, alumina slag is obtained from the slag-forming components, and iron is transferred to cast iron. In the furnace hearth, cast iron and slag do not mix with each other, forming two layers. Periodically, they are discharged from the furnace. Slag in slag buckets is taken to the slag field for cooling. Cast iron is poured at a special installation - an iron casting machine. Roasting in a blast furnace is economical, since the melting of the raw materials is due to the same fuel that is necessary for smelting cast iron.

According to the sintering method, a thoroughly ground and well-averaged mixture of bauxite and limestone is fired until sintering at a temperature of 115012500C. The obtained product is milled in ball mills. Both dry and wet production methods can be used. When firing in mine furnaces, the charge must be briquetted.

The raw materials used to produce alumina cement by this method are subject to increased requirements. This is particularly true of SiO2, Fe2O3, MgO because the sintering interval is reduced in their presence. The resulting fusible compounds lead to the formation of welds, lumps and rings in the furnace, which complicates the clinker formation process and the operation of the furnace. When producing alumina cement by sintering, the limestone should contain SiO2 and MgO not more than 2%. The amount of SiO2 in bauxite should not exceed 12%, while the ratio Al2O3: SiO2 should be more than 5, and the amount Fe2O3 - no more than 6%.

Preparation of clinker by melting method involves complete melting of raw mixture. In this case, the phase composition thereof depends more on the cooling rate than on the melting point.

When melting the charge, the method of cooling the melt determines the ratio between the vitreous and crystalline phases, which has a great influence on the physical and mechanical properties of the cement. There are various proposals for methods of cooling alumina slag, but most of them involve slow cooling. Rapid cooling adversely affects the properties of alumina cement, since in this case less CA is formed, which leads to a decrease in the strength of the cement. It is most expedient to cool the alumina slags in high-capacity molds, avoiding heat loss by the melt before it is cast.

Rapid cooling markedly reduces the rate of strength growth, but there is a wide limit to the rate of cooling at which the properties of the cement are almost unchanged. Increased strength of cement and improved crystallization of compounds are observed as melt cooling rate decreases. At that time, very slow cooling results in a quick-grasping cement.

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