Scrap inventory management method

Abstract

To provide a scrap inventory management method enabling of better controlling a scrap stock.SOLUTION: A method comprises a step of calculating at least one combination of an action performed on a given scrap and an associated quantity, based on a characteristic of liquid steel to be produced and a property of the scrap.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a scrap inventory management method for producing liquid steel using different types of steel scrap.

Background Art

[0002] Today, steel scrap is commonly used in the steelmaking process for producing liquid steel. The scrap can be used at different stages along the steelmaking process and with different steelmaking tools. The converter, basic oxygen furnace (BOF), and electric arc furnace (EAF) are some of the tools that can be particularly used in steel production.

[0003] The scrap may be of different types, especially depending on their origin or their pretreatment. Steel scrap is classified into three main categories, namely, in-house generated scrap, new scrap, and old scrap, according to the time when it becomes scrap in its life cycle.

[0004] In-house generated scrap is scrap that is generated internally during the production of new steel products in a steel plant. It is also known as run-around scrap and is material in the form of trimmings or exclusions generated within the steel plant during the production process of iron and steel. This form of scrap hardly leaves the steel plant production area. Instead, it is returned to the on-site steelmaking furnace and melted again. This scrap has known physical properties and chemical compositions.

[0005] New scrap (also called prime or industrial scrap) is generated from manufacturing units involved in the manufacture and production of steel products. When steel is cut, drawn, extruded, or machined, scrap accumulates. The casting process also produces scrap as excess metal. New scrap includes items such as turnings, cuttings, and punchings that remain when parts are produced from iron and steel during the manufacturing process. It is usually quickly transported back to steel plants through scrap processors and dealers or returned directly to steel plants for remelting to avoid storage space and inventory management costs. The supply of new scrap is a function of industrial activity. When activity is high, a greater amount of new scrap is generated. The chemical composition and physical characteristics of new scrap are well known. This scrap is typically clean, meaning it is not mixed with other materials. In principle, new scrap does not require any major pretreatment process before being melted, although sizing cuts may be necessary in some cases.

[0006] Old scrap is also known as post-consumer scrap or obsolete scrap. It is steel that has been discarded when industrial and consumer steel products (such as automobiles, electrical appliances, machinery, buildings, bridges, ships, cans, and railway vehicles and wagons, etc.) have reached the end of their useful lives. Old scrap is collected separately or mixed after the consumption cycle and is often contaminated to some extent, depending greatly on its origin and collection system. Since the lifespan of many products (such as buildings and building products) can exceed 10 years and sometimes even 50 years, steel products in use have accumulated since large-scale steel production began. Old scrap is often a material that has been used over several years or decades, so its chemical composition and physical characteristics are usually not well known. It is also often mixed with other waste.

[0007] The type and available amount of scrap are important because they affect the process in which it is used, regardless of the quality of the manufactured product or the productivity of the process.

[0008] In a steel plant, scrap is stored in stockyards, one for each type of scrap to avoid their mixing. It is important to ensure that each stockyard has the required amount of a given type of scrap for the different steelmaking tools it is to be used for. However, with many stockyards on site, it is not easy to have a clear inventory and some scrap may be missing.

[0009] There are several ways to control the scrap stock in a plant. For example, Japanese Patent Laid-Open No. 2002-068478 describes a method of managing scrap inventory where each type of scrap is weighed before being stored in the stockyard. Then, a lot of information related to the scrap, such as quality, supplier, net weight, receipt date, and price, is collected. Then, the scrap is consumed and the consumption amount is used as an input to update the inventory. This method treats each stockyard individually and uses the scrap consumption amount as an input, which does not enable predicting any stockouts.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] The object of the present invention is to improve the drawbacks of the prior art by providing a scrap inventory management method that enables better control of a plurality of scrap stocks, particularly within a plurality of steelmaking plants. Furthermore, the method according to the present invention makes it possible to maintain the required levels of the quality and quantity of the liquid steel produced, regardless of the available amounts of the various types of scrap.

Means for Solving the Problems

[0012] This problem is solved by the method according to the present invention, wherein at least two different types of scrap, each having its own characteristics and stored in a stockyard, are used to produce liquid steel having the characteristics of liquid steel in at least one steelmaking plant. The method includes, for each plant, defining the characteristics of the liquid steel produced from among weight, composition, temperature, maximum scrap weight, minimum scrap weight, hot metal ratio, slag weight, slag composition, number of heats, and weight per heat; for each scrap, listing the characteristics of the scrap from among the available amount, type, density, size, contamination level, chemical composition, and enthalpy in a given stockyard; for each scrap, calculating at least one combination of operations to be performed from among transfers between stockyards, use in a steelmaking plant, replenishment of the stockyard, and the associated amounts of the scrap, based on the defined characteristics of the liquid steel produced and the listed characteristics of the scrap, and performing the calculated operations.

[0013] The method according to the present invention may also comprise any of the following optional features, considered individually or in all possible technical combinations. - The calculation is performed using a mass balance model. - The liquid steel is produced in at least two plants - The type of scrap is selected from among old scrap, new scrap, prime scrap, in-house generated scrap, pit scrap, shred, plate and structural scrap, heavy melting scrap, casting scrap, coil scrap, or bushelling scrap. - At least one type of scrap is major scrap. - The calculations are performed using a thermodynamic model. - The method is executed each time new steelmaking activities are initiated, and replenishment measures are executed at the end of the activities. - Liquid steel is produced in a converter. - Liquid steel is produced in an electric arc furnace.

[0014] Other features and advantages of the present invention will become apparent from the following description of the invention, which is given by way of example and with reference to the accompanying drawings and is in no way limiting.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0016] The elements in the figures are illustrative and may not be drawn to scale.

[0017] Figure 1 shows a network of steelmaking plants where the present invention can be implemented. The network of plants comprises a plurality of steelmaking plants P1, P2, P3, each of which comprises at least one steelmaking tool such as a converter 1, 2, or an electric arc furnace 3. Each of said steelmaking tools produces liquid steel LS1, LS2, LS3. Each steelmaking plant P1, P2, P3 further comprises at least one stockyard Y 1,1 , Y 1,2 , Y 2,1 , Y 3,1 , Y 3,2 , in which one type of scrap S1, S2, S3, S4 used in steelmaking production is stored. It will be understood that one steelmaking plant may comprise a plurality of steelmaking tools that each produce liquid steel while sharing the same stockyard. The method according to the present invention is equally applicable.

[0018] S1 may be in-house generated scrap such as pit scrap which is a by-product of, for example, the flat steel product manufacturing process, and S2 may be shredded scrap corresponding to old scrap that is usually fragmented into pieces not exceeding 200 mm in any direction with respect to 95% of the load, such as old scrap. S3 may be major scrap which is a by-product of the manufacture of steel-based products such as piping equipment, automobiles, or electronic devices. The type of scrap may also correspond to a given classification such as that used in Europe (see EU27 scrap specification published by the European Steel Recycling and Recycling Federation in May 2007).

[0019] Figure 2 shows a flowchart of the inventory method according to the present invention. The first step 100 of the present invention is for each plant P k to define the characteristics CLS k of the liquid steel LS k produced by the steelmaking tool. The characteristics are selected from the weight of the liquid steel produced, the composition of the liquid steel produced, the temperature of the liquid steel produced, the maximum scrap weight input into the steelmaking tool, the minimum scrap weight input into the steelmaking tool, the hot metal ratio, the slag weight, the slag composition, the number of heat sources, and the production weight per heat source. These characteristics are represented in units selected to match each other. The composition of the liquid steel may be selected from the maximum value, minimum value, or range of the weight percentage of a given component such as carbon, iron, sulfur, phosphorus, copper, titanium, tin, or nickel. The hot metal ratio is the ratio of hot metal to scrap used in the converter. The maximum and minimum scrap weights may be defined for each type of scrap Sn. The heat source corresponds to the production of liquid steel in one operation in the converter and depends on the capacity of the converter. A given liquid steel production activity may include a plurality of heat sources, and therefore, the number of heat sources and the weight of each heat source may be among the defined characteristics.

[0020] In the second step 110 which can be executed in parallel with the first step 100, different types of scrap S nand their characteristics SP n are listed. These characteristics are selected from the available amount, density, size, contamination level, chemical composition, enthalpy, type in a given stockyard Y k,t . The composition of the scrap may be selected from the maximum, minimum, or range of weight percentages of a given component such as carbon, iron, sulfur, phosphorus, copper, titanium, tin, or nickel. The type may be selected from prime scrap, old scrap, new scrap, shred, pit scrap, reuse scrap, plate and structural scrap, heavy melting scrap, coil scrap, cast iron scrap, or busheling scrap.

[0021] Iron scrap is basically classified according to several characteristics, most notably (i) chemical composition, (ii) the level of impurity elements, (iii) physical size and shape, and (iv) homogeneity, i.e., variation within a given specification. Thus, a list of characteristics may correspond to one type.

[0022] Plate and structural scrap, often referred to as P&S in the scrap industry, is a cut grade of iron scrap that is presumed to contain no contaminants. Plate and structural scrap consists of clean open-hearth steel plates, structural shapes, crop ends, shears, or damaged steel tires. Heavy melting steel (HMS) or heavy melting scrap is the name for recyclable steel and wrought iron. This is divided into two main categories, HMS1 and HMS2, where HMS1 does not contain zinc-plated and blackened steel, while HMS2 does. Both HMS1 and 2 consist of iron and steel recovered from items that have been destroyed or disassembled at the end of their life. Pit scrap is a by-product of the flat steel production process that contains only scale. Coil scrap contains discarded coils due to quality issues by example, or residues from coil cutting. Cast iron scrap is an alloy of iron that contains a large amount of carbon. The carbon content makes it susceptible to corrosion. As a result, cast iron scrap often rusts and wears. Cast iron scrap can be obtained from heating systems, vehicle parts, etc. Another type is bushelling scrap, composed of clean steel scrap, including new mill bushelling (e.g., sheet cutting, stamping, etc.).

[0023] When the first step 100 and the second step 110 are executed, the third step 120 is executed, which consists of calculating at least one combination of operations Xi with the associated quantity Qi for each type of scrap Sn. These operations are selected from the transfer from one stockyard Yk,t to another stockyard Yk,t, the use as raw material for the production of liquid steel LSk, and the replenishment of the stockyard Yk,t. This calculation is performed taking into account the characteristics of the liquid steel CLSk defined in the first step 100 and the scrap characteristics SPn listed in the second step 110. This may be performed using a mass balance model considering how each chemical component behaves in a converter or an electric furnace, and thus which part of each scrap becomes liquid steel or slag. This may also include a thermodynamic model considering in particular the enthalpy of each scrap, hot metal, and slag in order to ensure an appropriate temperature operating point for each liquid steel.

[0024] When all combinations are calculated, all the calculations X i are executed in the fourth step 130, and then liquid steel LSk k is produced.

[0025] By the method according to the present invention, it is possible to accurately control the scrap stock and guarantee the continuous production of liquid steel with the required levels of quality and productivity.

[0026] Furthermore, in the method according to the present invention, by calculating an appropriate scrap mixture from the available types of scrap, it is possible to maintain the required quality level and production level of liquid steel even when higher scrap grades such as prime scrap are not available.

[0027] Example Input data This method is applied to three plants P1, P2, P3. - Plant P1 equipped with a converter for producing liquid steel LS1. Plant P1 has three stockyards, namely Y1,1 for storing scrap S1, stockyard Y1,2 for storing scrap S2, and stockyard S2 for storing scrap S3. - Plant P2 equipped with a converter for producing liquid steel LS2. Plant P2 has three stockyards, namely Y2,1 for storing scrap S1, Y2,2 for storing scrap S2, and stockyard Y2,3 for storing scrap S4. - Plant 3 equipped with a converter for producing liquid steel LS3. Plant 3 has four stockyards, namely Y3,1 for storing scrap S1, Y3,2 for storing scrap S2, stockyard Y3,2 for storing scrap S3, and Y3,4 for storing scrap S4.

[0028] This is summarized in Table 1 below:

[0029]

Table 1

[0030] - Characteristics of liquid steel The characteristics CLS1, CL2, CLS3 of liquid steels LS1, LS2, and LS3 are listed in Table 2 below. N / A means not applicable, and there is no requirement for this parameter.

[0031] The percentages are percentages by weight %w.

[0032]

Table 2

[0033] - Characteristics of scrap The characteristics SP1, SP2, SP3, SP4 of various types of scrap S1, S2, S3, S4 are listed in Table 3 below.

[0034] The percentages shown are the average percentages by weight of each component in the scrap.

[0035] The amounts are expressed in tons.

[0036]

Table 3

[0037] Results Next, the calculation step (130) of the method according to the invention is performed based on the above-described liquid steel characteristics and scrap characteristics. The results are shown in Table 4 below.

[0038]

Table 4

[0039] Using the inventory method according to the invention, it was possible to produce liquid steel at three different plants using the available scrap and still have a scrap stock for the next production campaign.

Claims

1. A method for managing scrap inventory, each having its own characteristics (SP ｎ ), and at least two different types of scrap (S ｋ，ｔ ) stored in a stockyard (Y ｎ ) are used to produce liquid steel (LS ｋ ) having the characteristics of liquid steel (CLS ｋ ) in at least one steelmaking plant (P ｋ ). The method comprises the following steps: - Plant (P ｋ ) for each, characteristics of the liquid steel produced from among weight, composition, temperature, maximum scrap weight, minimum scrap weight, hot metal ratio, slag weight, slag composition, number of heat sources, and weight per heat source (CLS ｋ ) defining step (100), and - For each scrap (S ｎ ), a step (110) of listing scrap characteristics (SP ｋ，ｔ ) from the available amount, type, density, size, contamination level, chemical composition, and enthalpy in a given stockyard (Y ｎ ); - For each scrap (S ｎ ), a transfer between stockyards (Y ｋ，ｔ ), use in a steelmaking plant (P ｋ ), replenishment of the stockyard (Y ｋ，ｔ ), and at least one combination of operations (X ｉ ), from among the associated quantity (Q ｉ ), of said scrap, is calculated based on the defined characteristics (CLS ｋ ) of the liquid steel produced and the listed scrap characteristics (SP ｎ ), in step (120); - An operation (X ｉ ) calculated for a related quantity (Q ｉ ) and a step (130) of performing the operation, a method comprising the steps.

2. The calculation (120) is performed using a mass balance model, the method according to claim 1.

3. The liquid steel is produced in at least two plants P1, P2, the method according to claim 1 or 2.

4. The type of scrap is selected from old scrap, new scrap, prime scrap, in-house generated scrap, pit scrap, shredded material, plate and structural scrap, remelt scrap, casting scrap, coil scrap, or bushelling scrap, the method according to any one of claims 1 to 3.

5. At least one type of scrap (S ｎ ) is the main scrap, the method according to any one of claims 1 to 4.

6. The calculation (120) is performed using a thermodynamic model, the method according to any one of claims 1 to 5.

7. The method is performed each time a new steelmaking activity is started and replenishment measures are performed at the end of the activity, the method according to any one of claims 1 to 6.

8. The liquid steel is produced in a converter, the method according to any one of claims 1 to 7.

9. The liquid steel is produced in an electric arc furnace, the method according to any one of claims 1 to 8.

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