Heat Transfer during Continuous Casting of Steel Jun19

Heat Transfer during Continuous Casting of Steel...

Heat Transfer during Continuous Casting of Steel During continuous casting (CC) of steel, careful control of the strand cooling and growth of the shell along the CC machine is of great importance. These factors play an important role on the formation of cracks and other defects which can be formed in the cast steel product. To ensure defect free cast steel products, the strand is to be cooled down according to a pattern which depends on steel grade, steel product dimensions, casting speed, and CC machine design. On the other hand, the control of the liquid pool length is a key element in optimizing the casting speed with respect to good productivity. So, the heat transfer plays a very important role in the operation of the CC machines, especially when casting crack sensitive steel grades. In fact, many diverse phenomena simultaneously control the complex sequence of events which govern heat transfer in the CC process. The temperature of liquid steel in the tundish is typically 30 deg C to 50 deg C higher than the liquidus temperature. At the beginning of the continuous casting process, the liquid steel is cooled in a water cooled mould to form a solidified shell which can support the liquid pool at the mould exit. Typical temperature at the end of the mould is1100 deg C and that in the center of the strand is 1550 deg C. Since steel does not solidify at a fixed temperature, but over a range of temperature, there is a mushy region where the steel is neither completely solid nor completely liquid. Steel grades used in continuous casting are completely solid below a temperature ranging from 1350 deg C to 1500 deg C, and the solidification starts at a temperature ranging from 1450...

Process Steam and its use in a Steel Plant...

Process Steam and its use in a Steel Plant Process steam is the general term used for steam which is used in process applications such as a source of energy for process heating, process cooling, pressure control and mechanical drives among others. Process steam is a popular mode of conveying energy and may come into contact with the final process or product. Like compressed air, steam is often thought of as a utility which is often generated at a central location and then distributed to various points-of-use throughout the steel plant. At atmospheric pressure the saturation temperature is 100 deg C. However, if the pressure is increased, this allows the addition of more heat and an increase in temperature without a change of phase. Therefore, increasing the pressure effectively increases both the enthalpy of water, and the saturation temperature. Water and steam can coexist at any pressure, both being at the saturation temperature. Steam at a condition above the saturation condition is known as superheated steam. Temperature above saturation temperature is called the degree of superheat of the steam and water at a condition below the saturation condition is called sub-saturated water. Steam used as process steam is usually of the following types. (Fig 1) Saturated steam – Steam is said to be ‘saturated’ with energy at a given and constant pressure when the addition of more heat to the generation system results in more steam, but no rise in steam temperature. In this state, the steam cannot hold more heat energy in a given volume unless pressure is allowed to rise. Dry steam – It is the steam that contains 100 % of water vapour in the gas phase. Dry saturated steam – Achieving the above states of dry and saturated steam simultaneously...

Energy Audit in an Integrated Iron and Steel Plant...

Energy Audit in an Integrated Iron and Steel Plant Energy audit is a key requirement for an integrated iron and steel plant which helps it to identify and realize energy efficiency improvements in a systematic way. It assists the steel plant management in understanding how it uses energy and helps to identify the areas where waste occurs and where opportunities for improvement exist. Energy audit is the inspection, examination, analysis and evaluation of the physical and financial processes of the steel plant relating to the use of the energy. The aim of the energy audit is to systematically identify the potential for saving energy and make recommendations for improvement. Energy audit is the key to a systematic approach for decision making in the area of energy management.It attempts to balance the total energy inputs with its use, and serves to identify all the energy streams in the steel plant. It quantifies energy usage according to its discrete functions. It is an effective tool in defining and pursuing comprehensive management of the energy usage in various processes of the steel plant. Energy audit helps to understand more about the ways energies and fuels are used in various processes of the steel plant. It helps in identifying the areas where waste of energy is occurring and where scope for improvement in energy consumption exists. It gives a positive orientation to the energy cost reduction and helps to keep focus on variations which occur in the availability and reliability of supply of energies and their costs, decide on appropriate energy mix, identify energy conservation technologies, retrofit for energy conservation equipment etc. It is the translation of conservation ideas into realities, by identifying technically feasible solutions with economic and other organizational considerations within a specified time frame. Energy...

Continuous Casting Machine and its Equipment Jun13

Continuous Casting Machine and its Equipment...

Continuous Casting Machine and its Equipment Continuous casting (CC) is a method of producing an infinite solid strand from liquid steel by continuously solidifying it as it moves through a CC machine. It is the predominant process route in a modern steel plant which links steelmaking and hot rolling. A typical section and plan view of a CC machine is shown in Fig 1. Fig 1 Typical section and plan view of a CC machine Types of continuous casting machines CC machines have evolved from the strictly vertical type of machine to curved machines in order to limit the installation height while still using high casting speeds. In recent years, CC machines of more sophisticated mechanical design are being constructed. These machines apply several techniques for achieving higher casting speeds and higher outputs and are with progressive straightening or progressive bending over a liquid core. The main types of the CC machines which are in operation these days are given below. Simple vertical CC machine with a straight mould and cutoff in the vertical position Vertical CC machine with a straight mould along with single point bending and straightening Vertical CC machine with a straight mould along with progressive bending and straightening Bow type machine with curved mould and straightening Bow type machine with curved mould and progressive straightening In all cases, the bending and straightening is usually carried out in one or several steps. Multistep bending and straightening reduces the mechanical stresses and reduces the risk of strand cracking. The first CC machine which was built up for CC of liquid steel was a simple vertical CC machine. Then later the development led to many kinds of CC machines with various ways of bending and straightening. The main objective for these developments have...

Liquid Fuels – Their Characteristics and Safety Requirements...

Liquid Fuels – Their Characteristics and Safety Requirements Liquid fuels are combustible or energy generating molecules that take the shape of their container. Most of the liquid fuels are derived from fossil fuels mainly from crude oil. Main liquid fuels used in iron and steel plant (Fig 1) are (i) furnace oil (FO), (ii) low sulphur heavy stock (LSHS), (iii) light diesel oil (LDO), and (iv) high speed diesel oil (HSD).  Coal tar fuel is a byproduct liquid fuel produced during the cleaning of the raw coke oven gas in the coke oven and byproduct plant. Liquid fuels are normally used in the steel plant for the production of steam for power generation, for heating purpose in various furnaces of the plant, for injection in blast furnace, and for the operation of locomotives and the mobile equipment. Fig 1 Liquid fuels used in a steel plant   Liquid fuels are chemically stable and incompatible with strong oxidizers. They do not react vigorously with common materials but can react with oxidizing agents. Liquid fuels are stored in a dry cool, well – ventilated area away from heat and flame. They are also kept away oxidizing agents. Furnace oil Furnace oil is a fuel oil which is dark and viscous. It is a residual fuel oil which is obtained by blending residual products from various refining processes with suitable diluent usually middle distillates to obtain the required fuel oil grades. The fuel oil grades are similar in nature and are being marketed under different specifications in various countries. Furnace oil is used mainly in different furnaces of the steel plant, in power plant boilers for raising steam and for injection in the blast furnace. It is also sometimes used in air preheaters. Furnace oil is having...