DE3317701A1 - Process and device for controlling the metallisation and cementation in the reduction of iron ore to sponge iron - Google Patents

Abstract

In a process for operating a vertical moving-bed reduction reactor for reducing iron ore to sponge iron, having a reduction zone in the upper part of the reactor and a cooling zone in the lower part of the reactor, the desired degree of metallisation of the reducing ore is obtained in the reduction zone and the desired degree of cementation is obtained in the cooling zone, the process being characterised in that a predetermined stream of a reducing gas consisting of carbon monoxide and hydrogen is fed to the reactor and the ratio of the reducing gas stream in the reduction zone to the reducing gas stream in the cooling zone is adjusted so that at least the metallisation taking place in the reduction zone and the cementation taking place in the cooling zone are modified, the carbon dioxide concentration in the reduction zone being adjusted to a value at which the desired degree of metallisation therein is achieved, and wherein the carbon dioxide content in the cooling zone is adjusted to a value at which the desired degree of cementation in the cooling zone is obtained.

Description

Method and device for checking the metal

ization and cementation in the reduction of iron ore to sponge iron The invention relates to the gaseous reduction of granular metal ore to metal in granular form in a moving bed reactor with a vertical shaft and in particular a method zur.Herstellung of a "balanced" sponge metal product with a pre-selected and controlled level of metallization and cementation. The invention consists of a process which allows greater process flexibility and control of the metallization and cementation (carbonization) of the sponge iron product achieved by regulating the amount of carbon dioxide in the process gas and by the distribution of the fresh reducing gas in the reducing and cooling loops regulated. Except for the balanced sponge metal product that obtained by the process according to the invention, the consumption of natural gas is and the overall energy efficiency of the reduction process is improved. Included It should be noted that although the following description is a method and a Device for reducing iron ore to sponge iron concerns it for the skilled person but it is clear that the invention also applies to the treatment of ores other than Metal ores is applicable.

Typically, the manufacture of sponge iron is carried out in a moving bed reactor carried out with a vertical shaft in two main stages: namely the reduction of the ore in a reduction zone through which a suitable hot reducing gas, which is composed mainly of carbon monoxide and hydrogen, in one Temperature in the range of 700 to 1.0000C and preferably 750 to 950 "C is, and the cooling of the reduced sponge iron in a cooling zone through which a gaseous coolant at a temperature below about 2000C and preferably is conducted below 1000C. Systems of this general type are described in U.S. Patents 3,765,872, 3,816,102, and 4,216,011, in which a vertical reactor used with a reduction zone in the upper part and a cooling zone in the lower part will. The ore to be treated is placed at the top of the reactor and then after down through the reduction zone let flow where it is hot Reducing gas is reduced and then the reduced ore flows into the Cooling zone down where it comes into contact with a stream of a suitable cooling gas is cooled and cemented. The cooled sponge iron is then placed on the bottom of the Taken from the reactor. Typically, both the reducing gas and the Cooling gas circulated, if desired in closed loops, to which Streams of fresh (so-called make-up) reducing gas is added and from which Streams of spent gas are withdrawn.

In a number of known direct reduction processes, the reducing gas required to reduce the iron is generated in a catalytic reforming unit by converting natural gas according to the following equations: In the reforming reactions of natural gas, which is mainly composed of methane, it is converted into hydrogen and carbon monoxide in the presence of an oxidizing agent from either water or carbon dioxide. As a result, a reforming gas is obtained which is composed essentially of hydrogen and carbon monoxide. More recently, with the decrease in availability and the increasing cost of natural gas, it has become extremely important and desirable to minimize the amount of natural gas required for a direct reduction process.

The reducing gas introduced into the reduction zone of the reactor is typically at a higher temperature and contacts the iron ore flowing downwards, whereby the iron oxide contained therein is reduced according to the following basic reactions: The used reducing gas leaving the reactor is cooled in order to remove the water formed by the reduction of the iron ore with hydrogen and then the dehydrated exhaust gas is recirculated into the reduction zone of the reactor. The recirculation or recycling of the exhaust gas can be done in different ways: For example, the gas can be fed back directly into the reactor, or the gas can first be fed through the reformer and a heating device, or the gas can only be circulated through the heating device . In any case, however, fresh reducing gas is added to the circulating exhaust gas before it is introduced into the reactor. Since the amount of carbon dioxide formed in the reactor during the reduction process is significant, some of the spent gas must be vented or cleaned in order to maintain a suitable overall carbon balance within the reduction zone.

As mentioned earlier, the fresh reducing gas, typically by catalytic conversion of methane in the natural gas fed into the process is generated, the net carbon input to the process due to the carbon content of the natural gas. To the reduction process under constant conditions and To be able to carry out continuously, it is necessary to remove the carbon from the System to be removed in such an amount that is essentially the net amount of the supplied amount of carbon is equivalent. Carbon can be in from the system combined form with the sponge iron in the form of iron carbide or in gaseous form Form as CO, CO2 and CH4, which comes out of the circulatory loop in the form of consumed Gas is vented, removed from the system.

A suitable balance between the amount of in the process Entering and exiting carbon is necessary to prevent excessive carbon deposition to avoid the sponge iron moving through the reactor. Although it can one can effectively eliminate carbon from the process by having at least one part of Exhaust gas vented from the reactor, however, goes with this Process also the hydrogen, which is also present in the exhaust gas and which is special is effective in reducing, lost.

There is thus a real need for a direct gaseous one Reduction process in which the carbon can be extracted from the process, without a loss of valuable reducing components, such as hydrogen or Methane, entering. There is also a need for a reduction process which is more flexible in terms of controlling the level of metallization and cementation of the sponge iron product.

Such procedural flexibility desirably becomes concurrent with an optimization of the total energy consumption of the direct reduction process achieved.

According to the invention, a method and a device are available provided, by means of which one has a greater procedural flexibility with regard to the degree of metallization and cementation of the sponge iron product and while minimizing the consumption of natural gas in the reduction process and the total energy demand - optimized.

It is an object of the invention to provide a new method and apparatus for the direct reduction of iron ore to sponge iron available, in which the desired level of metallization and cementation of the sponge iron product selected and regulated can be.

It is another object of the present invention to provide a direct reduction process and to provide an apparatus wherein natural gas consumption is minimized and the total energy consumption is optimized.

Another object of the invention is to provide a new method and a To provide a device for the direct reduction of iron ore to sponge iron, where the overall carbon balance can be effectively monitored. Other goals of the invention will emerge from the following description.

For a better understanding of the invention, it is shown that the reduction of FeO in the reduction zone of the reactor by conversion of the hot reducing gas, which is mainly composed of carbon monoxide and hydrogen, proceeds as follows: The cementation reactions that take place in the reactor at the same time as the reduction reactions can be expressed by the following equations: It is known that the above cementing reactions are favored at temperatures in the range from about 500 to 7000 ° C. and that the carbon deposition on the sponge iron therefore takes place to a much greater extent in the cooling zone of the reactor.

From equation (8) it is clear that the cementation rate in the reduction zone and in the cooling zone to a large extent due to the concentration is dependent on CO contained in the reducing or cooling gas. In the same way one can see from equation (6) that the rate of reduction is considerable Mass is determined by the concentration of CO in the reducing gas.

As previously mentioned, it is known to produce carbon from the reduction process to get the desired total carbon footprint by adding ventilates at least part of the used cycle gas. The present Invention provides an alternative method and apparatus for selective elimination of carbon from the reduction system available by controlling carbon dioxide absorbed from the spent gas circulating in the reactor. Through the Absorption of carbon dioxide from the cycle gas can be the required amount of carbon without loss of hydrogen taking place in the system.

As a result, one has to use less natural gas to compensate for the loss the reduction capacity in the cycle gas, compared to the known systems, where a significant part of the cycle gas is cleaned or is vented, add.

The invention relates to a method for operating a vertical Moving bed reduction reactor for reducing iron ore to sponge iron, around the desired level of metallization of the reduced ore and the desired level Achieve the cementation by running the reactor at a predetermined flow of the reducing gas, which is composed essentially of carbon monoxide and hydrogen is, supplied and the ratio of the reducing gas flow into the reduction zone the reducing gas flow in the cooling zone varies, thereby at least the amount of metallization and the amount of cementation while changing the Carbon dioxide concentration both in the reduction zone and in the cooling zone is maintained at a level that provides the desired level of metallization and cementing the sponge metal product.

The objects and advantages of the invention are best understood from the Drawings understood.

Figure 1 is a diagram of a system including a moving bed reactor with a vertical shaft according to a preferred embodiment of the invention Process, Fig. 2 shows a curve in which the percentage of metallization as a function of the relative gas flow in the reduction and Cooling zones Figure 3 shows a graph for the percentage of carbon on the Sponge iron, i.e. the cementation, as a function of the relative gas flow into the Reduction zones and cooling zones, and Figure 4 shows a graph for the total percentage of the carbon absorbed in the form of CO2 as a function of the relative gas flow in the reduction and cooling zones.

Referring to FIG. 1, a catalytic reforming unit 80 known type with natural gas through a line 78 and with steam through a line 79 is injected, supplied. The steam is generated from water that is passed through a Line 85 into a waste heat furnace 84 through the coils of line 79 into the shaft 81 is introduced. The natural gas and the steam mixture are preheated by it is passed through snakes in the shaft part 81 of the reformer 80, whereupon it then flow through a heated catalyst bed in the lower portion 82 of the reformer leaves, where it is converted into a gas mixture consisting mainly of carbon monoxide, Consists of hydrogen and water vapor.

The reformed gas leaves the reformer 80 through a line 83 and enters a quench cooler 90 where the gas is cooled and dewatered. Upon exiting the cooler 90, the gas flows through a conduit 92 which is a flow rate actuator 94 has at a flow rate referred to as Fg. Of the Gas stream F0 splits into two separate streams, namely F1, which flows through the Line 95 flows and is used as make-up reducing gas in the reduction loop is, and in F4, which flows through a line 96 and as supplementary cooling gas in the cooling loop is used.

With particular reference to the reduction loop as set out in Fig. 1 is shown, the gas stream F1 flows through a line 95 which is connected to a Flow rate actuator 97 is provided and is made with the spent gas the reactor which is returned to the reduction zone and which is designated as F3 is, combined and forms a reducing gas flow F2l through a line 98 in a heater 100 flows wherein the gas is raised to a temperature in a known manner is heated in the range of 700 to 1,100 "C, preferably about 9000C. The heated Reducing gas leaves the heater 100 through a line 101 and enters the Reduction zone 12 of the reactor designated 10 a.

The reducing gas entering the reducing zone 12 of the reactor 10 is allowed to flow upward therein in contact with the descending iron ore to thereby effect the reduction of the iron ore contained therein. The spent reducing gas leaves the reactor 10 through a line 18 and enters the cooler 20, where it is cooled and dewatered. The cooled and dewatered spent gas leaves the cooler 20 through a line 21, with part of the gas designated by F6 is, through a line 22, which is equipped with a flow rate actuator 24, vented or transported to a storage room. The gas flow denoted by F6 can also be used as fuel in the reformer 80 or in the heater 100.

The greater part of the used gas from the reactor flows through a line 25 into the suction side of the compressor 26. The compressed consumed Gas leaves the compressor 26 through a line 28 and flows into a carbon dioxide absorption unit 30, wherein the carbon dioxide contained in the spent gas is removed. To the removal of the carbon dioxide from the consumed gas flows that designated with F3 Gas flow through a conduit 32 provided with a flow rate actuator 34 is and is, as previously indicated, combined with the gas stream F1.

As mentioned, part of the gas flow Fg can be passed through a line 96 let flow into the cooling loop of the reduction system as supplementary cooling gas. The make-up cooling gas F4 flows through a line 96 connected to a flow-through actuator 98 is provided and combines with the cooling gas in the cooling loop of the reactor 10 is circulated, with the formation of a cooling gas flow denoted by F5. Gas streams F5 flow through a line 99 and are in the cooling zone 14 of the reactor 10 initiated. One lets the cooling gas through the cooling zone in contact with the descending one reduced sponge iron come to the sponge iron it contains to cool and cement. The cooling gas leaves the cooling zone 14 through a line 103 and enters a cooler 110 where it is cooled and drained. The chilled one and dewatered gas stream flows through line 112 into the suction side of the compressor 116, after which it is pumped back into the cooling zone 14 through a line 118 it was combined with the stream F4 to form the stream F5.

It should be noted that in the cooling zone the one described in FIG. 1 Embodiment no external cleaning is required.

Part of the make-up flow F4 is produced by the reduction and cementation reactions of the aforementioned type, which run in the cooling zone 14, consumed, while the rest Part of the supplemental cooling gas introduced into the cooling zone 14 into the reduction zone 12 flows within the reactor 10. By absorbing carbon dioxide in the used cycle gas, carbon can be selectively removed from the system, without the other reducing components being lost and thereby the The amount of natural gas to be added to the process is minimized. In practical operation the gas flows F01, F2 and F5 are preferably kept at a constant value, because these streams are the optimal execution of the reforming unit, the heating unit and the cooling loop compressor. A typical gas composition of the Stroms Fg is the following: Vol.% H2 73.0 CO 14.2 CO2 8.5 CH4 3.5 H2O 0.5 N2 0.3 The carbon monoxide contained in the stream Fg is used as a reducing agent according to equations (3), (4) and (5) or as a cementing agent according to Equation (8) is used. As already mentioned, it is known that with direct reduction Carbon monoxide from sponge iron tends to become iron oxide at higher temperatures while reducing the tendency for carbon to deposit on the sponge product exists at low temperatures. About both the metallization and the carbon content of the sponge iron product to ensure a "balanced" product with with either a higher metallization and a lower cementation or to achieve a lower metallization and a higher carbon content, become the relative amounts of make-up gas flow F4 to and from the cooling loop F1 to the reduction loop is variably controlled. In other words, that means that by keeping the gas flows F0 F2 and F5 constant and by varying the Gas flow ratio F4 / Fo a balanced sponge iron product is obtained.

Fig. 2 shows the effect of the metallization of sponge iron as a function the change in the F4 / FO ratio.

In the same way, Fig. 3 shows the effect on the percentage carbon content of the sponge iron product as a function of the F4 / F0 ratio. From FIGS. 2 and 3 it can be seen that as the F4 / F0 ratio approaches zero, there is a product with very high metallization and low carbon content is obtained while then as the F4 / F0 ratio approaches 1.0, lower metallization and a higher carbon content can be obtained. To the important effect which the change in the F4 / F0 ratio on the metallization and cementation of the sponge iron product should use the carbon dioxide content in the stream F3 will be close to zero. In order to achieve the desired control of the reduction and cementation reactions, which take place in the reduction and cooling zones, should be achieved little or even no carbon dioxide is present in the reducing or cooling gas supplied to the reactor be.

Fig. 4 shows the relationship between the percentage of carbon dioxide absorbed carbon, calculated on the basis of the total carbon contained in the system enters as natural gas, as a function of the F4 / F0 flow ratio. the Curve in Fig. 4 clearly shows that as the F4 / F0 ratio approaches zero, about 80% of the carbon introduced into the system as carbon dioxide in the absorber removed. This indicates that the amount of carbon in the product is proportionate is low. When the F4 / F0 ratio approaches 1.0 then about 62% of carbon introduced into the system is removed as carbon dioxide while the rest as carbon is deposited on the sponge iron. In both cases, the Overall carbon balance in the system is appropriately maintained without that there is a need to vent large amounts of gas and thereby becomes increases the overall efficiency of the reduction process.

The expressions and terms used here are in no way intended to be limiting be interpreted and it goes without saying that equivalent measures can perform to those shown.

Claims (10)

Method and device for checking metallization and cementation in the reduction of iron ore to sponge iron. PATENT CLAIMS Process for operating a moving bed reduction reactor with a vertical shaft for reducing iron ore to sponge iron with a reducing zone in the upper part and a cooling zone in the lower part Part of the reactor, to achieve the desired degree of metallization of the reducing agent th ore in the reduction zone and the desired level of cementation in the cooling zone, noting that one in introducing into the reactor a predetermined flow of a reducing gas resulting from Carbon monoxide and hydrogen are composed of 12 the ratio of the. In the reduction zone flow the reducing gas to the flowing into the cooling zone Reduction gas changed at least to the extent that the reduction in the Reduk-12 Metallization took place in the ionization zone and cementation took place in 14 of the cooling zone is changed that one has the carbon dioxide concentration in the 12 reduction zone holds at a value that gives the desired degree of metallization and that the carbon dioxide concentration in the cooling zone 14 is kept at a value at which the desired 14 degrees of cementation in the cooling zone are achieved. 2. The method according to claim 1, characterized in that g e k e n n -z e i c h-n e t that the carbon dioxide concentration in the reduction zone and in the cooling zone 14 is adjusted by essentially taking the total amount of carbon dioxide, which is contained in the reducing gas, removed before the reducing gas in introduces the reactor. 3. The method according to claim 2, characterized in that g e k e n n -z e i c h n e t that essentially the entire amount of the reducing-12 fed to the reactor gases is introduced into the reduction zone, to obtain a sponge iron with a metallization of at least 94% and a carbon content of less than 1.0%. 4. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that one passes the reducing gas 12 through the reduction zone to the therein to convert contained iron ore at least partially into sponge metal that one the exhaust gas from the reduction reactor to remove the water vapor contained therein cools that one removes the carbon dioxide contained in the exhaust gas that one preselected amount of fresh reducing gas in the exhaust gas that has been freed from carbon dioxide with the formation of a reducing gas mixture, the gas mixture is added again heated and through the 12 reduction zone with the formation of a reducing gas loop circulates and that you have a selected amount of fresh reducing gas into a closed cooling gas loop from a cooling gas fed into the cooling zone adds, with 14 the gas is passed through the cooling zone in order to be more controllable Way to monitor the cementation of the sponge iron contained in it and wherein a constant amount of the used cooling gas is withdrawn and the withdrawn gas Improved in its value 14 and goes through the cooling zone in the circuit under training a cooling gas loop, with the respective amounts of the fresh, the exhaust gas and the The reducing gas supplied to the cooling gas loop can be set in a controlled manner so that that the desired degree of metallization and cementation is achieved. 5. The method according to claim 4, characterized in that g e k e n n -z e i c h n e t that the combined amount of the fresh, the exhaust gas and the cooling gas loop supplied Reducing gas is kept at a constant value. 6. The method according to claim 5, characterized in that g e k e n n -z e i c h n e t that you do not add fresh reducing gas to the exhaust gas if you use a sponge iron with a metallization in the range of 80 to 84% and a carbon content wants to get in the range of 2.7 to 3.2%. 7. The method according to claim 5, characterized in that g e k e n n -14 z e i c h n e t that the cooling zone is not supplied with fresh reducing gas when a Sponge iron with a metallization of at least 94% and a carbon content would like to achieve less than 1.0%. 8. Device for reducing metal ore to sponge-10 metal in a vertical shaft reactor with a downward moving bed of Part-12 Chen of the metal, with a reduction zone in the upper part, in which the heated Reducing gas of carbon monoxide and hydrogen through part of the bed beneath Reduction of the metal ore contained therein to metal flows and whereby one the desired Degree of metallization of the reduced ore achieved, and a cooling zone in the lower 10 part of the reactor in which the cooling gas flow calmly is used to reduce the reduced metal ore and while getting the desired degree of cementation of the reduced ore receives a first service through 101, which is provided on the reactor in the vicinity of the bottom of the reduction zone, to introduce heated reducing gas into the zone, a second line, the 99 is connected to the reactor in the vicinity of 12 of the head of the reduction zone, a third power, which is arranged on the reactor near the bottom of the cooling zone, to introduce gas into the cooling zone, a fourth line connected to the reactor is connected near the head of the cooling zone, the first .12 and second lines form a reduction loop with the reduction zone, the third and aY fourth lines and the cooling zone form a cooling loop; one Carbon dioxide removal device .30 in the reduction loop, valves in the Loops to regulate the gas stream flowing through, as well as a source of fresh Reduc-95 tion gas, a fifth line to the source of the fresh reducing gas to connect to the reduction loop, a sixth. 96 Line for connecting the source of the fresh reduction 4 aes with the cooling loop, valve devices in the fifth and sixth lines, to regulate the gas flow through it, and ventilation devices in the reduction line, to vent some of the gas flowing through it. 9. The device according to claim 8, characterized in that it is -k e n n z e i c h n e t that the reduction and cooling loops cooling devices for cooling the flowing through it Gas have that 101 100 the first line heating devices for heating 10 of the gas passed to the reactor and flowing therethrough and wherein the reduction and cooling loops have pumping devices for pumping the gas through. 10. The device according to claim 8, characterized in that g e -k e n n z e ic h n e t that the fifth and sixth line 9n5 'measuring devices for measuring the have reducing gas fed to the reducing and cooling loops.