Nitrogen gas and its usage in Steel Plant...

Nitrogen gas and its usage in Steel Plant Nitrogen is a non-reactive component of the atmosphere which is not life supporting. The percentage of nitrogen in air is 78.06 % by volume or 77 % by weight of the air. The composition of air is shown in Fig 1. Fig 1 Composition of air The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air. Nitrogen is produced in large quantities and at high purity as a gas or liquid through the liquefaction and distillation of ambient air at the cryogenic air separation plants. It is also produced on commercial scales as a lower purity gas by adsorption technologies (pressure swing adsorption, PSA), or diffusion separation processes (permeation through specially designed hollow fibers). Gaseous nitrogen is called in short as GAN while the liquid nitrogen is called in short as LIN. Liquid nitrogen is a cryogenic liquid. Cryogenic liquids are liquefied gases that have a normal boiling point below – 150 deg C. Liquid nitrogen has a boiling point of -195.8 deg C. Because the temperature difference between the product and the surrounding environment is substantial, it is necessary to keep the liquid nitrogen insulated from the surrounding heat. Nitrogen is often stored as a liquid, although it is used primarily as a gas. Liquid storage is less bulky and less costly than the equivalent capacity of high-pressure gaseous storage. A typical storage system consists of a cryogenic storage tank, one or more vaporizers and a pressure control system. The cryogenic tank is constructed, in principle, like a vacuum flask. There is an inner vessel...

Nitrogen and Steels

Nitrogen and Steels Nitrogen (N) (atomic number 7 and atomic weight 14.008) has density of 1.25 gm/litre at standard temperature and pressure. Melting point of N is -210 deg C and boiling point is -195.8 deg C. The phase diagram of the Fe-N binary system is at Fig 1. Fig 1 Fe-N phase diagram N is present in all commercial steels. Since the of concerns of presence of N in steels are normally small and its analysis being complex and expensive, its existence is generally ignored even in steel specifications in various standards. However, whether present as a residual element or added deliberately as an alloying element, the effects of N in steel are significant.  N is an important and inexpensive alloying addition to steels. In recent years there has been an increasing demand to reduce and control the amount of dissolved gases in steel. N is one of the important gas which when dissolved in liquid steel affect its properties significantly. Hence control of N content of steels during steelmaking is important. N in steel can be in its uncombined form as free N or in the form of a compound or nitride. Steel from an electric arc furnace (EAF) normally has higher N levels (70-110 ppm) compared to that produced in a basic oxygen furnace (BOF) where N varies between 30 and 70 ppm. Hence, N is of particular importance in an EAF plant. In certain stainless steel grades the amount of N can be at the level of 3000 ppm. N levels in degassed steels can be below 10 ppm.  N exists in steel as an interstitial quite similar to, but much more soluble than, carbon (C) and as nitrides of iron (Fe), aluminum (Al), vanadium (V), niobium (Nb), titanium (Ti),...

Industrial gases used in steel industry...

Industrial gases used in steel industry The term “Industrial gas” refers to a group of gases (Fig 1) which are specifically produced for use in a variety of industrial processes. They are distinct from the fuel gases. Speciality gases such as neon, krypton, xenon and helium are sometimes considered under the category of industrial gases.  Industrial gases are produced and supplied in both gas and liquid form and transported in cylinder, as bulk liquid or in pipelines as gas. Industrial gases usually used in steel industry are oxygen, nitrogen, argon and hydrogen. Fig 1 Industrial gases Oxygen Oxygen (O2) is an active component of the atmosphere making up 20.94 % by volume or 23 % by weight of the air. It is colorless, odorless and tasteless. Oxygen is highly oxidizing.  Oxygen reacts vigorously with combustible materials, especially in its pure state, releasing heat in the reaction process. Many reactions require the presence of water or are accelerated by a catalyst. Oxygen has a low boiling/ condensing point which is -183 deg C. The gas is approximately 1.1 times heavier than air and is slightly soluble in water and alcohol.  Below its boiling point, oxygen is a pale blue liquid slightly heavier than water. Properties of oxygen are at Tab 1. Oxygen is produced in large quantities and at high purity as a gas or liquid by cryogenic distillation and in smaller quantities as a lower purity gas (typically about 93%) by adsorption technologies such as pressure swing adsorption (PSA) or vacuum pressure swing adsorption (VPSA or VSA). Oxygen is the second largest consumed industrial gas.  Aside from its chemical name O2 oxygen is also referred to as GOX or GO when produced and delivered in gaseous form, or as LOX or LO when in its cryogenic liquid form. Oxygen is...

Use of Hot Metal in Electrical Arc Furnace Jun04

Use of Hot Metal in Electrical Arc Furnace...

Use of Hot Metal in Electrical Arc Furnace Steel making by the electric arc furnace (EAF) has very good flexibility with respect to the selection of charge materials. The traditional charge material for the EAF process has been 100 percent cold scrap but as the issues regarding scrap such as its availability and quality, market price fluctuations and restrictions imposed by scrap in making some steel grades due to residual elements and nitrogen level etc. have increased, EAF operators intensified the search for alternative iron materials. Direct reduced iron (DRI), hot briquetted iron (HBI), pig iron (PI) and hot metal (HM) are the alternative iron materials which have been used in varying percentage successfully by EAF operators. The use of hot metal is more popular in those areas where there is shortage of scrap and/or electric power. The source of hot metal is blast furnace hence hot metal can be used in those EAFs which are in close proximity of the blast furnace, otherwise the EAF operator has to use pig iron. Pig iron will need extra energy for its melting. Presently EAF can be designed for using up to 80 percent of hot metal in the charge. Influence of HM on key parameters of EAF process In recent times the main emphasis in EAF steel making has been related to achieving maximum energy efficiency. Further the feed charge materials are influencing the design of the EAFs and their operation practices. The influence of HM as a charge material on various key parameters of an EAF process of steel making is detailed below. Residual elements – Residual elements also known as tramp elements cannot be removed from the steel during processing. Therefore, the amount of these elements in the product is a direct function...

Nitrogen in Steels May23

Nitrogen in Steels

Nitrogen in Steels All steels contain some nitrogen which can enter the steel as an impurity or as an intentional alloying addition. The quantity of nitrogen in steels normally depends on the residual level arising from the steelmaking processes or the amount aimed in case of deliberate addition. There are significant differences in residual levels of nitrogen in steels produced from the two main steelmaking processes. Basic oxygen furnace (BOF) process generally results into lower residual nitrogen in steels, typically in the range of 30 to 70 ppm while electric arc furnace (EAF) process results into higher residual nitrogen, typically in the range of 70 to 110 ppm. Nitrogen is added to some steels (e.g. steels containing vanadium) to provide sufficient nitrogen for formation of nitride to achieve higher strength. In such steels nitrogen levels can increase to 200 ppm or higher. Nitrogen in the liquid steel is present in the form of solution. During the solidification of steel in continuous casting, three nitrogen related phenomena can happen. These are Formation of blow holes Precipitation of one or more nitride compounds Solidification of nitrogen in interstitial solid solution. The maximum solubility of nitrogen in liquid iron is around 450 ppm, and less than 10 ppm at ambient temperature (Fig 1). The presence of significant quantities of other elements in liquid iron affects the solubility of nitrogen. Mainly the presence of dissolved sulfur and oxygen limit the absorption of nitrogen because they are surface active elements. Fig 1 Solubility of nitrogen in iron Nitrogen is generally considered as undesirable impurity which causes embrittlement in steels and affects strain aging. However nitrogen produces a marked (intersititial solid solution) strengthening when diffused into the surface of the steel, similar to the strengthening observed during case hardening (Nitriding)....