Coal based Direct Reduction Rotary Kiln Process Feb14

Coal based Direct Reduction Rotary Kiln Process...

Coal based Direct Reduction Rotary Kiln Process The coal based direct reduction rotary kiln process was developed for converting iron ore directly into metallic iron without the melting of the materials. The process has the advantage of low capital expenditure and no requirement of coking coal. The metallic iron in this process is produced by the reduction of iron oxide below the fusion temperature of iron ore (1535 deg C) by utilizing carbonaceous material present in the non-coking coal. As the iron ore is in direct contact with the reducing agent throughout the reduction process, it is often termed as direct reduced iron (DRI). The reduced product having high degree of metallization shows a ‘honeycomb structure’, due to which it is often called sponge iron. Coal based DRI plants are flexible with respect to plant location since non-coking coal is widely distributed in large deposits and is easy to transport. Most plants employ reduction process which is carried out in rotary kilns. These plants use wide variety of raw materials and non-coking coal. The quality of these materials has direct bearing on the process as well as the product. Some plants do not use iron ore directly. These plants use iron ore pellets in the rotary kiln. Raw material mix consisting of iron ore, dolomite and non-coking coal is fed at the one end of the rotary kiln and is heated by coal burners to produce DRI. The product DRI along with char (sometimes called dolo char) is taken out from the other end of the kiln. Apart from this, primary air and secondary air are supplied to the kiln to initiate the combustion and sustain the reaction process in the kiln. Raw materials The main raw materials for the production of DRI by...

Basic Shaped Refractories...

Basic Shaped Refractories  Basic shaped refractories are those refractories which have resistance to corrosive reactions with chemically basic slags, dusts and fumes at elevated temperatures. They are both MgO and CaO based refractories or in combination between them or in combination between MgO and Cr2O3. These refractories belong to MgO- CaO equilibrium system as shown in Fig 1. Fig 1 MgO-CaO equilibrium system  Broadly basic refractories falls into one of the following five compositional categories (Fig 2). Products based on dead burned magnesite (DBM) or magnesia. These products are known as magnesite bricks. Products based on DBM or magnesia in combination with chrome containing materials such as chrome ore. Chrome containing magnesite bricks with about 5 % to 15 % Cr2O3 are known as magnesite chrome bricks while those with 15 % to 30 % chromium are called chrome magnesite bricks. DBM or magnesia in combination with spinel. In these basic bricks magnesia-rich spinel (MgO.Al2O3) replaces chrome ore. These bricks are called magnesite spinel bricks. DBM or magnesia in combination with carbon. These bricks are known as magnesite carbon bricks. Dolomitic products. These bricks are known as sintered dolomite bricks. Fig 2 Categories of basic shaped refractories based on composition  Basic refractories are characterized by an extremely high refractoriness and good resistance to basic slags. Compared to fireclay bricks they do not have glassy phase. These refractories have low resistance both to thermal shocks and creep at temperatures close to 1500 deg C. The chemical-physical characteristics together with a very high thermal capacity and thermal conductivity make basic refractories ideal refractories for steel making processes. Hence basic refractories received increased importance with the introduction of basic oxygen steel making process. One of the more important types of magnesite bricks are those which have low...

Limestone and dolomite flux and their use in iron and steel plant...

Limestone and dolomite flux and their use in iron and steel plant Limestone is a naturally occurring mineral. The term limestone is applied to any calcareous sedimentary rock consisting essentially of carbonates.  The ore is widely available geographically all over the world. Earth’s crust contains more than 4 % of calcium carbonate. Limestone is basically calcite which is theoretically composed of exclusively calcium carbonate (CaCO3). When limestone contains a certain portion of magnesium, it is called dolomite or dolomitic limestone (CaCO3.MgCO3). Dolomite theoretically contains CaCO3 54.35 % and MgCO3 45.65 % or CaO 30.4 %, MgO 21.9 % and CO2 47.7 %. However, in nature, dolomite is not available in this exact proportion. Hence generally the rock containing 40-45 % MgCO3 is usually called dolomite. When MgCO3 is less than 40 % but more than 20 % then the limestone is called dolomitic limestone. The chemical composition of limestone and dolomite varies greatly from region to region as well as between different deposits in the same region. Therefore, the end product from each natural deposit is different.  Typically limestone and dolomite are composed of calcium carbonate (CaCO3), magnesium carbonate (MgCO3), silica (SiO2), alumina (Al2O3), iron (Fe), sulphur (S) and other trace elements. These minerals are shown in Fig 1 Fig 1 Limestone and dolomite The limestone from the various deposits differs in physical chemical properties and can be classified according to their chemical composition, texture and geological formation. Limestones from different sources differ considerably in chemical compositions and physical structures. The chemical reactivity of various limestones also shows a large variation due to the difference in crystalline structure and the nature of impurities such as silica, alumina and iron etc. The varying properties of the limestone have a big influence on the processing method....