Patent Application
20170130284
The field of this invention relates to recovery of steel alloys in an electric arc furnace using ferrous material, primarily low grade coal, cured and bound into solid pieces and a carbon fixing binder.
Hard or metallurgical coke is used in blast furnace production of steel. Metallurgical coke per se is not ordinarily used in electric arc furnace because, among other things, such is not cost effective. Electric arc furnace secondary steelmaking differs basically from primary steelmaking from iron ore in a blast furnace. Historically, soft coke is the carbon source for electric arc furnace secondary production of steel from pig iron, direct reduction iron and salvage or scrap steel and iron, but is still expensive and negatively impacts the environment.
In the past, little has been done to provide a less expensive but effective source of carbon for secondary steel production using electric arc furnaces.
The present invention meaningfully addresses the need to provide a less expensive but highly functional source of carbon for secondary steelmaking in electric arc furnaces. Carbon from different sources, primarily low grade coal, are combined, blended, formed and heat-treated into cured and bound solid electric arc furnace influent carbon pieces, which do not deteriorate or elutriate in an electric arc furnace. The solid pieces can also be customized, with certain additives, to meet the specific demands associated with the diverse operations of various electric arc furnaces.
In brief summary, the present invention addresses problems or shortcomings of the prior art. Cost-effective methods are providing for forming and using a composite carbon feedstock comprising small cured and bound solid pieces, such as pellets and briquettes, suitable for secondary steelmaking in electric arc furnaces. The composite carbon solid pieces primarily comprise low value crushed coal and a minor amount of coke breeze and/or petroleum coke. The cured and bound solid pieces comprise a first influent to an electric arc furnace and ferrous material a second influent. Flux may be a third influent.
The make-up of the solid pieces can be customized, using certain additives, to meet the specific demands associated with the diverse operations of various electric arc furnaces.
With the foregoing in mind, it is a primary object of the present invention to cost-effectively provide reliable carbon feedstock for secondary steelmaking in electric arc furnaces, which feedstock dominantly comprises low value coal formed, with other materials, into cured and bound solid pieces, and related methods.
A further important object is to provide solid cured and bound carbon-providing pieces for cost-effective and reliable use in electric arc furnaces, the solid pieces predominantly comprising low value coal combined with a lesser amount of coke breeze and/or petroleum coke, and related methods.
Another significant object of the invention is the provision of cost-effective and reliable bound and cured small solid pieces as carbon feedstock for secondary steelmaking in electric arc furnaces, such that the solid pieces comprise mostly low value coal augmented by some coke breeze and/or petroleum coke to obtain a composition comprising 75-90% by weight of nominal fixed carbon coke, supplemented by additives such as discarded revert materials to customize the solid pieces to meet specific demands associated with the diverse operations of various electric arc furnaces, and related methods.
These and other objects and features of the present invention will be apparent from the detailed description taken with reference to the accompanying drawing.
The Figure is a flow chart illustrating one presently preferred method according to the invention.
Steelmaking is an old technology and generally has heretofore combined carbon, in the form of coke and ferrous material in blast and electric arc furnaces (EAFs). Those with skill in the art declare that primary steelmaking in blast furnaces differs significantly and basically from secondary steelmaking in EAFs. Broadly, the differences, among others, include the need for iron ore as the primary ferrous source and metallurgical coke in blast furnaces compared to scrap metal and soft coke in EAFs.
The present invention is limited to EAF technology, to the exclusion of blast furnace technology. More specifically, the present invention substitutes small solid pieces, such as pellets and briquettes, for the soft coke of the past as the carbon source for secondary steelmaking. Surprisingly, the solid pieces have proven to be effective and far less costly. The makeup and methodology of the solid pieces are explained in detail below.
As used herein, the term EAF includes the basic furnace and any and all ladles used to first obtain pig iron and then steel, when such a system is used.
Typically, the basic EAF is refractory lined and charged at the top when open. The main and sometimes exclusive source of ferrous material is recycled scrap iron and steel, which is loaded into the top of the basic EAF essentially at the same time that the carbon source is also loaded into the top. The scrap iron and steel are preferably pre-heated, before introduction, to reduce costs. Off-gas from the EAF can be used to preheat the scrap.
Oxygen, in a very pure state, is supplied through a water-cooled lance, usually in three steps, i.e. (1) at the correct height well above the bath surface, (2) at a lower position once heat has somewhat melted the scrap metal and (3) finally substantial into the molten bath with a very high velocity discharge blow. Flux, such as burnt lime (CaO) and dolomitic lime (MgO), may be added while the lance is above the bath surface to increase slag production. Fluxes control the chemistry and sulfur and phosphorous capacity of the slag. Oxygen from the lance lowers the bath carbon content to the desired level for tapping. A reaction of oxygen with carbon in the bath produces carbon monoxide, which may burn in the EAF, if oxygen is available.
Phosphorus, sulfur, aluminum, silicon, manganese and carbon are removed by reaction with the oxygen to form oxides which become part of the slag. At the appropriate time, the slag is poured out of the furnace through a slag door.
Gaseous discharge by-products are processed as off-gas to reduce environmental contamination and to recover energy.
In one EAF system, the molten material produced in a basic furnace is transferred via a ladle to a ladle furnace, where additions are melted and blended into the liquid steel being produced, such that the resulting steel has the properties desired by the producer prior to forming the steel product into the desired shapes. The basic furnace and the ladle furnace are considered herein collectively as constituting a single EAF.
The traditional mode of secondary steelmaking in EAFs has become cost intensive. More specifically, the cost of traditional soft coke imposes some limitations on and higher costs for steel derived from EAFs.
The present invention meaningfully addresses the need to provide a less expensive but highly functional source of carbon for secondary steelmaking in EAFs. Carbon from different sources, primarily low grade coal, are combined, blended, formed and heat-treated into cured and bound small solid EAF influent carbon pieces, which do not deteriorate or elutriate when used in electric arc furnaces. The solid pieces, as explained here and after, can also be customized, with certain additives, to meet the specific demands associated with the diverse operations of various EAFs.
The reliability and cost effectiveness of the present invention centers on the use of low value crushed coal, to which a minor amount of coal breeze and/or petroleum coke is added. The composition is bound and cured in the form of small solid pieces which, when placed in an EAF do not deteriorate prior to functioning in their steelmaking capacity and do not elutriate. The solid pieces and the methodology by which the solid pieces are formed combine to define, in large measure, the present invention.
Since EAFs produce an array of steels having various properties, the present invention includes additives in the solid particles selected from discarded revert materials and other elective materials.
While not critical, in addition to scrap iron and steel as the ferrous material for EAFs, in accordance with the present invention, a lesser amount of iron ore may be used, as would be apparent to those skilled in the art.
Reference is now made to the drawing for purposes of providing greater detail concerning the present invention. The sources of carbon 10, comprises clean, crushed and sized low value coal having a low moisture content, typically in the range of 4-12% by weight, which is depicted at 12 in the drawing. This low value coal 12 is critically selected to comprise 72-75% by weight of the solid shapes being produced. Combined with the coal is a far lesser amount of coke breeze and/or petroleum coke 14 on the order of 10-17% by weight. Flux 16 of one or more types selected by those skilled in the art may also be added when appropriate for the steel selected to be produced. Also, in certain applications, leftover revert materials 18, comprised of carbon content, discarded from blast furnaces and/or EAFs may be added to the initial mix from which the solid shapes are derived.
The low value coal 12 preferably has a sieve size on the order of one-quarter inch minus, although that is not critical. The coal particles are derived from the bituminous, subbituminous, lignite and processed waste coal fines, as appropriate and available and as determined by those skilled in the art.
Low value coal is cleaned, unwanted debris is removed and the water content is lowered to an acceptable level for purposes of producing reliable and effective solid pieces. The washing, removal of debris and reduction in water content in the crushed low value coal are all accomplished using well known technologies. Accordingly, no further description of how the coal is cleaned, washed and reduced in moisture content is necessary. The use of a predominant amount of low value coal in creating a composite source of carbon in the form of bound and cured solid pieces to be used in EAFs provides reliability in secondary steelmaking and provokes a meaningful reduction in the cost of manufacturing steel in EAFs.
The low value coal 12 and the coke breeze and/or petroleum coke 14 are introduced essentially at the same time into a commercially available blender 20 together with a carbon fixing binder 22, such as coal tars, pitches derived from destructive coal distillation, partially reacted Styrene oligomers or any other binder capable of functioning as a carbon fixing binder. The binder 22 is introduced into the blender 20 during mixing. While the amount of binder 22 used in any batch varies with the quality of the coal, usually the binder will comprise 10-18% by weight of the mixture at 20. After the ingredients placed in the blender 20 have been thoroughly mixed so as to be essentially homogeneous, the resulting mixture is then formed into green solid shapes shown at 24. It has been found that the coke 14 acts as a spine to hold the green pieces together until they are fired. The coke 14 thus acts as a temporary adhering agent holding the coal and the binder together as a semi-solid conglomerate until the green solid pieces are fired. Techniques for forming green semi-solid material into green pellets and briquettes are well known and need not be further described here. The solid shapes may also be created using extruders and/or dies and presses. As a result, the blended composition constitutes separate small green solid pieces, which are next introduced into a furnace, preferably a muffle furnace having a moving bed on which the green solid pieces are transported through the calcining furnace 26 so as to be first pre-heated to a temperature of about 550° F. and then, in an anaerobic phase of the oven, to 1000° C., where volatile materials are evaporated. The volatile gases 28 are then condensed and distilled, at 30, create high value products, including coal tar, liquid hydrocarbons 32 and off gas 34 for use in the plant or elsewhere, as deemed appropriate. For example, the lighter gases can fuel equipment used to generate electricity for use in the plant. In the third phase of the muffle furnace, the solid pieces are anaerobically cooled. The time duration during which the green solid pieces are heat-treated in the muffle furnace should be on the order of one hour, but such is not precisely critical. In any event, the resulting cured and bound solid pieces produced should be amply heat-treated in the furnace so as to be reliable and not break down or elutriate during use in secondary steelmaking.
The resulting solid cured and bound pieces 36 comprise a composite form of fixed carbon composite coke having a 75-90% fixed carbon content to effectively function for the purpose intended. The cured and bound solid pieces 36 may be stored in inventory or may be directly used in an EAF, shown at location 38 in the drawing, to which ferrous material consisting primarily of scrap iron and steel 40 is also added as an influent to the EAF 38. Minerals, such as flux 42, may also be added in accordance with choices made by those skilled in the art in order to produce the desired type of steel from the EAF 38.
The resulting steel product is formed into the desired shape or shapes. The effluent 44 from the EAF 38 is molten steel.
The cured and bound solid pieces issuing from 36 are preferred to have the following characteristics: moisture not to exceed 2.5%; sulfur not to exceed 2.0%; volatile residue not to exceed 2.5%; ash not to exceed 8.0%; and carbon not less than 85.0%.
The solid piece carbon product 36, made in the foregoing manner, offers several important qualities to steel producers. First, the product can be manufactured to meet precise attributes specific to each producer's needs. The product can be customized or blended with fluxing agents and other materials specific to the needs of each individual mill.
During experimental testing, the cured and bound solid pieces were found to help protect vital mill components and to potentially increase the efficiency of mill operations by reducing individual batch melting times. The manufacturing process has the ability to produce variously sized materials, using extrusion, pelletizing or briquetting techniques, to customize the solid pieces for individual customer needs.
Experimental Testing examples are set forth below:
A supply of solid cured and bound pieces were prepared in accordance with the process set forth above and having the characteristics also set forth above. Approximately 300 lbs. of these solid pieces were introduced into an EAF together with scrap steel, in two heats. The resulting steel was of suitable high quality and no contra results took place.
Two one-thousand pound batches of solid carbon pieces were made for testing in an EAF, using the process and having the characteristics recited above. The solid pieces were utilized in several experimental tests. Test results were positive and solid pieces were deemed functional in the electric arc melt operation. The resulting steel was of high quality.
While this invention has been described with reference to certain specific embodiments and examples, it will be recognized by those skilled in the art that many variations are possible without departing from the scope and spirit of this invention, and that the invention, as set forth in the claims, is intended to cover all changes and modifications of the invention which do not depart from the spirit of the invention.
