WO1991019819A1

WO1991019819A1 - Method and apparatus for steel making

Info

Publication number: WO1991019819A1
Application number: PCT/CA1991/000188
Authority: WO
Inventors: Ghulam Nabi
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-06-14
Filing date: 1991-06-05
Publication date: 1991-12-26
Anticipated expiration: 1992-12-14
Also published as: JPH04231409A; CA2019050C; CA2019050A1

Abstract

This invention provides a method and apparatus whereby steel of various compositions may be produced from iron ore and coal through a series of stages without the intermediate production of liquid iron. A reforming reactor receives top gases from the steel making reactors, and converts them to high reduction potential gases which are returned to the steel making reactors. The iron ore and reductants, such as coal, are charged to a controlled atmosphere reactor which may be an inclined rotary cylindrical shaft. From the controlled atmosphere reactor the charge is moved to a potential shift reactor which is inclined or vertical and encounters increasing heat and rising gases for converting the carbonized sponge into a semi-molten state. The charge then passes to a high temperature reactor where it encounters the reducing gases from the reforming reactor and preheated oxygen to create temperature in which steel is made. Hot gases from the high temperature reactor pass through the PSR and the CAR and are returned to the reforming reactors to complete the cycle.

Description

METHOD & APPARATUS FOR STEEL MAKING

TECHNICAL FIELD

This invention relates to a method and apparatus for steel making. In particular, it relates to a process by which liquid steel of various compositions can be produced without the separate stage of hot iron production. Furthermore, steel may be made from raw materials comprising iron ore and coal without the need to use coke, pellets or sinter.

BACKGROUND ART

Steel has been manufactured for many years using variations of a conventional process in which iron ore and limestone are combined with coke and added continuously to a blast furnace where preheated air is added to facilitate combustion and create high heat. From the blast furnace, impurities are removed as slag and iron with a high carbon content is removed as molten metal. The molten iron is then further refined in a bessemer furnace, basic oxygen furnace, open hearth furnace or electric arc furnace (depending on the newness of the plant and the quality of steel required)

SUBSTITUTE SHEET where excess carbon is removed and additives which effect the quality of steel are combined with the molten iron. The molten steel is drawn off in batches and thereafter processed by rolling it into bars, pipes, plates, sheets, rails or structural shapes.

Although variations of this process are used to handle different types of ore or to produce different types of steel, the basic process has remained substantially unchanged for many years. DISCLOSURE OF THE INVENTION

It is, therefore, the purpose of this invention to provide a method and apparatus whereby steel of various compositions may be produced from iron ore and coal, through a series of stages without the intermediate production of liquid iron.

It is also the purpose of this invention to provide a method and apparatus which is more efficient and contributes less to pollution because of it's ability to recycle hot gases and other by-products.

SUBSTITUTE SHEET These objectives are achieved by four interrelated reactors. A reforming reactor (RR) which receives top gases from the steel making reactors, after dust removal and purification and converts them to high reduction potential gases which are returned to the steel making reactors to be burnt with preheated oxygen so as to produce the required intense heat and controlled reaction.

In the steel making portion of the plant, the iron ore and reductants, such as coal, are charged to a controlled atmosphere reactor (CAR) which may be an inclined, rotary, cylindrical shaft or a vertical shaft. From the CAR the charge moves into a hood or conduit which serves as a potential shift reactor (PSR) which may be an inclined or preferably vertical conduit where it encounters increasing heat from rising gases and a reduction atmosphere, thus converting the carbonised sponge iron into a semi-molten state.

The charge then passes into the high temperature reactor (HTR) which is similar to a basic oxygen furnace (BOF) where it encounters highly reducing gases from the reforming reactor (RR) and preheated oxygen to create a temperature in the order of 1,500 to 2,200 degrees C in which the steel is made and removed, either in batches or continuously.

SUBSTITUTE SHEET The hot gases of the HTR rise and pass through the PSR and the CAR to provide heat. Any oxygen potential in the rising gases combine with carbon to provide additional heat and maintain the reduction atmosphere. The top gases from the top end of the CAR are cleaned and conveyed to the RR for conversion to create additional fuel to the HTR.

The invention may more easily be understood by a description of one embodiment thereof with reference to the attached drawings. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic diagram of a steel making plant incorporating the principles of the present invention.

Figure 2 is an enlarged, more detailed, schematic diagram of the steel making portions of the plant in Figure 1. BEST MODE OF CARRYING OUT THE INVENTION

In the plant illustrated in Figure 1, the hopper 2 is provided to receive and discharge crushed or granular iron ore in the form of magnetite (FE-O.) or hematite (FE-O^) or any other economically exploitable iron ore.

SUBSTITUTE The hopper 4 is provided to receive and discharge granular or powdered coal to provide the basic reducing ingredient to the feed. The hopper 6 is provided to receive and discharge sludge containing principally iron ore particles and coal and liquid condensates of coal. It may also handle other constituents necessary to refine the process or determine the type of steel ultimately produced.

The contents of these hoppers are discharged to a pan mixer 8 which mixes the ingredients and provides to the conveyor 10 the basic charge to the reactors.

The conveyor 10 deposits the charge to a pair of sealed charging chambers 12 and 14 which are established in series and are capable of being sealed from the atmosphere to avoid escape of fumes from the reactors which will be discussed later. The upper chamber 12 is adapted to receive a charge of ore and other ingredients and has a purging line 16 which will convey nitrogen to eliminate fumes from the chamber which can be conveyed to a flare as indicated. A controllable seal is provided at 18 which will close to prevent the upward flow of gases from the lower chamber 14 and will open to allow the charge to travel down to the chamber 14.

SUBSTITUTE SHEET The chamber 14 is also connected with the source of nitrogen 20 by means of a line 22 to equalize pressure in chambers 12 and 14 before the sealed closure 18 is opened and to avoid pressure surges. A chute 24 is provided to allow the release of the charge from the lower chamber 14 into the upper inlet 26 of the controlled atmosphere reactor (CAR) 30.

In the embodiment illustrated, the CAR is a substantially horizontal but inclined, hollow, cylindrical drum, adapted to rotate about it's axis. The rotation and inclination of the drum causes the charge to tumble and process from the entrance 26 through the drum to the outlet end 32 while undergoing exposure to heat and the reducing atmosphere of the CAR.

As with the charging chambers, the CAR is provided with instruments to measure, analyze, record and control temperatures, flow rates and to activate alarms where necessary at various points in the reactor. The CAR may also be provided with a source of oxygen to provide additional heat to the charge at an early stage.

The charge reaches the outlet end 32 of the CAR at a red hot temperature of about 1,100 degrees C, depending on the type of ore, and is monitored by a sampling apparatus 34 to monitor the iron, oxygen and carbon contents.

SUBSTITUTE SHEET To regulate the process and reaction in the CAR appropriate monitors and control devices will be required and these instruments are indicated in Figure 1 by the symbols TCR (meaning temperature control and recording), ACR (meaning analysis control and recording of gases and coal input), FOR (meaning flow rate control and recording), 0 C (indicating oxygen input control) .

At this point, the charge enters the hood 36 which is connected by means of seals to the end of the rotary drum and connects by means of a seal 38 to a conduit 40 which leads to the high temperature reactor (HTR) 50. The conduit 40 acts as a potential shift reactor (PSR). It is lined with refractories and cooled by stave type coolers or by external means. It has an elaborate monitoring system to record and control the composition of rising gases and falling materials, temperature, carbon, C0₂, H₂0, CO, H_, FE, C as indicated at 42 in the drawings.

These instruments are indicated by the symbols ARSAH (meaning analysis recording switch alarm high) for CO- and H₂0 and ARSAL (meaning analysis recording switch alarm low) for CO and H₂. At this point temperature control and recording is provided. A small open circle with Fe, C and 0 shows that on the line analysis is not performed.

SUBSTITUTE SHEET Oxygen which is available from the source 44 can be conducted to the PSR by means of the line 46 which is provided with lime injection 47 and an oxygen preheater 48 before it is conducted to a coil structure within the high temperature zone of the PSR to further preheat the oxygen. In an alternative configuration, oxygen may be heated in an external furnace.

Gaseous hydrocarbons (natural gas) and coal fines may be introduced by the pipeline 51 (seen in Figure 2) to balance or create more reducing potential as required, as indicated by the instrument QCR (indicating quantity control and recording) .

The PSR conveys the charge to. he high temperature reactor (HTR) 50 which is similar to a basic oxygen furnace. It comprises a vessel with a refractory lining and has means to tap or pour off the molten slag and the molten steel and a hole to draw steel samples for analysis.

The HTR is a more or less conventional reactor except that it may be modified to cope with the high temperatures which may be encountered in this process. hese modifications might include the provision of internal cooling plates or external coils and the lining of the reactor may be acid or basic refractory material.

SUBSTITUTE SHEET The HTR has a pair of charging chambers in series 52 to allow for the addition of solid and gaseous ingredients or alloying material in order to produce different types of steel. The sealed charging chambers allow the additives to be inserted into the HTR in the gaseous, slag, or liquid metal phase of the reactor while maintaining the system substantially closed to the atmosphere. The alloying materials may be in the form of particulate ores or pure substances. The necessary heat and the reducing atmosphere of the HTR are provided by reducing gas conveyed by line 54 from the gas reforming reactors (RR) 60 which are shown only in Figure 1. As in a basic oxygen furnace, the oxygen of combustion is provided through the line 46, preheated as mentioned above, to the HTR at the inlet 56 of which there are several spaced around the periphery of the vessel. The multiple inlets for reduction gases are kept separate from oxygen inlets.

Ideally, tuyers for the admission of reformed gas or oxygen may be of the water cooled plasma arc design. Iron oxides will be reduced to iron which, with alloys, will produce steel and silica will form slag with other ingredients.

SUBSTITUTE SHEET Typical reactions in the HTR are represented by the following equations. The gaseous combustion reactions are similar to those given under reformer furnace.

Metal (solid) + Heat ^■> metal (molten)

Carbon (Dissolved in Fe) + 0 (remaining in Fe) ^■> CO (gaseous)

The oxydizing conditions in the reactor plus CaO which can be inserted into the 0 line 46 at 47 shown in Figure 1, will remove phosphorous from the molten metal while reducing conditions and CaO additive will remove sulphur.

Oxides^{^}sϋchTas Nϊθ7^"MnO, Cr₂0₃, ₂0₅, will be directly reduced and combine with molten Fe to form alloys. Complex high melting ores like titaniferous magnetite can be treated in the reactor. Iron will go to the liquid metal phase leaving the titanium rich slag which can be separated for titanium recovery. As nitrogen is excluded from the furnace, titanium nitride will not be formed.

Because temperatures in excess of 1,600°C can be achieved, reduction of highly stable oxides like^" MgO and CaO should be possible. A typical reaction in the formation of slag is represented by the following equation.

2⁽MgO.CaO⁾ + fs£._FE ^2Mg ₍σ₎ ^{+ Ca}2^Si04 ^(sla9⁾«

SUBSTITUTE The actual slag composition depends upon the ore and coal composition, the lining of the furnace, and the working atmosphere in the HTR.

If the combustion production gases in the middle of the HTR have an oxidizing potential, then as they rise in the hood or PSR, they will meet with downward falling carbon and carbonized sponge so that the oxygen is first consumed producing higher temperatures but subsequently will lose heat in the counter falling sponge, iron, solid carbon and in chemical heat to the endother ic reaction, thus producing high reduction potential gases. When the HTR has a reduction atmosphere, the reduction potential of the rising gases will be further increased.

The hot gases of the HTR will rise through the PSR until they reach the outlet end 32 of the CAR where they will encounter hot iron oxides, at which point most of the oxygen in the rising gases will have been consumed. As they rise through the CAR the CO will combine with the ore to form some native iron and carbon dioxide while hydrogen will combine with oxygen to form iron and vapour. Typical reactions in the CAR may be described as follows;

SUBSTITUTE SHEET At the outlet end;

FeO + Co = Fe + CO.

FeO + H, = Fe + H₂0

Carbon dissolved in sponge iron

Fe₃0₄ + CO = 3Fe0 + C0₂ Fe₃0₄ + H₂ = 3Fe0 + H₂0 C0₂ + C = 2C0 H₂0 + C = CO + H₂ In the upstream end;

3Fe₂0₃ + CO = 2Fe₃0₄ + CO, 3Fe₂0₃ + H₂ = 2Fe₃0₄ + H₂0 30₂ + 4C = 2C0 + 2C0₂ C0₂ + H₂ =C0 + H₂0

SUBSTITUTE SHEET The gases travel up the inclined rotary drum of the CAR in counter current relationship to the ore and coal mixture, but because the charge is delivered to the CAR by a sealed chamber system, the gases will reach the upper end of the CAR at a temperature in the order of 600-800 degreesC.

The "top gas" is treated in a cyclone apparatus (which includes a heat exchanger to recover heat energy which can be used in steam electric generation) 70 to remove dust, which includes iron ore, coal and gasified metals (which are recycled to the CAR by line 71 in Figure 1) or the dust can be treated for the recovery of volatile metals if economically feasible. The gas is then conveyed to a gas scrubber 72 where it is treated with a water spray to remove any additional dust which is collected as sludge in the settling tank 74 and eventually returned to the hopper 6. The gas is then processed through an electro-static precipitator 76, a sulphur recovery apparatus 78, and a C0₂ recovery apparatus 80.

The clean gas is then conveyed to one of a pair of gas reforming reactors 60 shown only in Figure 1.

TE SHEET It should be realized that some of the gas will be used and combined with natural gas to heat the reforming reactors, or if necessary, the gas may be conveyed to an emergency flare. The other part of the gas which is not freed of C0₂ can be used in the reforming reactor with natural gas. Reformer Reactor can be a single unit tubular reformer or multiple units working in sequence as shown in the present embodiment.

In the reforming reactors, natural gas reacts with carbon dioxide and water vapours to produce high temperature, high reduction potential gases. This reforming reaction is carried on at 700-1,500 degrees C, the temperature of the exit gases being adjusted to 600-1,200 degrees C. This is done by mixing clean gas or gasified hydro carbon in the exit pipe of the high temperature reformed gas. The reformed gas is then conveyed by means of line 54 where it is used in controlled quantities as part of the fuel and reducing gas in the HTR 50.

SUBSTITUTE SHEET Typical reactions in the RR are represented by the following equations:

CnH + n H Δ0 = nCO + (n+m/2) H 2.

CO + 1/2 0₂ = C0₂

H₂+ 1/2 0₂ = H₂0

2C0 = C0₂ + C

H₂ + CO = H₂0 + C

C0₂ + H₂ = CO + H₂0

The extent of any reaction and the direction of these reactions depends on the thermo dynamics, kinetics and catalysts employed but the main product of the reforming reactors will be CO and H 2~ with some CO2-, H2_0 and CH4. left over.

In the reformer, heat is created in the reformer furnace as represented by the following reaction equations;

CnHm + (n+m/4) 0 Δ- = nCO Δ- + m/2 H Δ-0

CO + 1/2 o₂ ■ α>₂ H₂ + 1/2 0₂ = H₂0

SUBSTITUTE SHEET As seen in Figure 1, the output of the reforming reactors is provided with the necessary controls 62, 64, 66, 68 and 69 to monitor CO, H₂, C0₂, CH₄ and temperature. INDUSTRIAL APPLICABILITY

Thus, by means of the present invention, a steel plant may be constructed in which various types of iron ore are charged to the reactors with a controlled and variable amount of coal and other ingredients so that they are exposed to a controlled atmosphere reactor, a potential shift reactor and a high temperature reactor in continuous sequence and result in the desired steel product while gases from the reforming reactors are added to oxygen, which is pre-heated with other ingredients such as lime to the high temperature reactor and travel upwards through the PSR to the CAR to cause the heating and reduction of the incoming charge. The top gases from the CAR are then recycled through dust cleaners, precipitators, sulphur recovery, C0₂ recovery and are passed through the RR to regenerate with the addition of variable and controlled amounts of natural gas, coal, oxygen, etc. to form the fuel of the high temperature reactor.

SUBSTITUTE SHEET The four reactors referred to are intended to provide a closed loop, substantially sealed system and it is contemplated that the pressures within the system will be positive and will amount to approximately four to five atmospheres in the reformers and the reformed gas and oxygen feed to the high temperature furnace, approximately three atmospheres in the PSR and approximately two to three atmospheres in the CAR.

Of course, it will be realized that variations and modifications of the illustrated embodiment might be employed without departing from the inventive concept herein.

SUBSTITUTE SHEET

Claims

1. A steel making plant comprising:

- a controlled atmosphere reactor adapted to receive a charge comprising iron ore and reductants and to pass said charge through a heating and reducing atmosphere;

- a potential shift reactor adapted to receive said charge from said controlled atmosphere reactor and to pass it through an atmosphere of increasing heat and reduction potential;

- a high temperature reactor adapted to receive the charge from the shift reactor and to treat said charge with reducing gases and preheated oxygen and added ingredients to make steel;

- a reforming reactor adapted to receive top gases from the controlled atmosphere reactor and convert them to reducing gases suitable for use in the high temperature reactor to make steel.

SUBSTITUTE SHEET

2. A steel making plant as claimed in claim 1 in which said controlled atmosphere reactor, said potential shift reactor, and said high temperature reactor are inter¬ connected so that the charge may pass through each in the aforesaid sequence, substantially continuously.

3. A steel making plant as claimed in claim 2 in which the high temperature reactor has a sealed connection to the outlet end of the potential shift reactor and the potential shift reactor has a sealed connection to the outlet end of the controlled atmosphere reactor so that hot gases may flow from the high temperature reactor to the potential shift reactor to the controlled atmosphere reactor counter-current,to the passage of the charge.

4. A steel making plant as claimed in claims 1,

2 and 3, including means to remove top gas from the controlled atmosphere reactor, means to remove contaminants from said top gas, and means to convey said gas to said reforming reactor.

SUBSTITUTE SHEET

5. A steel making plant as claimed in claims 1,

2 and 3, in which said controlled atmosphere reactor comprises an inclined rotary drum, sealed charging chambers to control and convey the charge to said controlled atmosphere reactor, and means to measure, analyze, and control the temperatures flow rates and compositions in the controlled atmosphere reactor, and means to provide oxygen to said controlled atmosphere reactor.

6. A steel making plant as claimed in claims 1,

2 and 3, in which said potential shift reactor comprises an upright conduit adapted to convey a charge from the controlled atmosphere reactor to the high temperature ^" reactor and having means to monitor the temperature and composition of rising gases therein and means to preheat oxygen for injection in the high temperature reactor.

SUBSTITUTE SHEET

7. A steel making plant as claimed in claims 1, 2 and 3, in which said high temperature reactor comprises a vessel adapted by refractory lining and cooling means for high temperature steel making and having means to inject reducing gases from the reforming reactor, means to inject preheated oxygen, means to inject alloying ingredients, means to inject lime in said oxygen, means to remove molten slag, and means to remove molten steel.

8. A steel making plant as claimed in claims 1,

2 and 3, in which the means to convey top gas to the reforming reactors includes means to remove dust, means to remove sulphur, means to remove carbon dioxide.

9. A steel making plant as claimed in claims 1, 2 and 3, in which said reforming reactor is adapted to combine natural gas with carbon dioxide and water to create a high temperature, high reduction potential gases.

SUBSTITUTE SHEET