METHOD FOR DIRECT REDUCTION IN A FLUIDIZED BED

Abstract

The invention relates to a method for the direct reduction of oxidic iron carrier particles to a reduction product in a fluidized bed through which a reduction gas containing 30-100 mol % hydrogen H.sub.2 flows in crossflow. At least 90% by mass of oxidic iron carrier particles introduced into the fluidized bed have a particle size of less than or equal to 200 micrometers. The superficial velocity U of the reduction gas flowing through the fluidized bed is set between 0.05 m/s and 1 m/s such that, for the particle size d equal to d.sub.30 of the oxidic iron carrier particles introduced into the fluidized bed, it is above the theoretical suspension velocity U.sub.t and is less than or equal to U.sub.max.

Claims

1-15. (canceled)

16. A process of direct reduction of oxidic iron-bearing particles to a reduction product in a fluidized bed, comprising: flowing in crosscurrent a reduction gas containing 30-100 mol % of hydrogen H.sub.2 through the fluidized bed; wherein the oxidic iron-bearing particles introduced into the fluidized bed have a grain size of not more than 200 micrometers to an extent of at least 90% by mass; wherein a superficial velocity U of the reduction gas flowing through the fluidized bed is set between 0.05 m/s and 1 m/s such that it is above the theoretical fluidization velocity U.sub.t and not more than U.sub.max for the grain size d=d.sub.30 of the oxidic iron-bearing particles introduced into the fluidized bed; wherein a theoretically predicted value U.sub.t for a grain size d is found from: $U_t=\surd \left(\frac{4}{3}*\frac{\left(\rho p-\rho g\right)}{\rho g}*\frac{d*g}{\mathrm{Cw}}\right)$ $\mathrm{with}\mathrm{Cw}=\frac{24}{\mathrm{Re}}+\frac{4}{\sqrt{\mathrm{Re}}}+0.4$ and with $\mathrm{Re}=\frac{\rho g*U_t*d}{\mu };$ and wherein U.sub.max is calculated from an actual correlation found between particle size and fluidization velocity for a particle size d=d.sub.30:
U.sub.max=(40000*d){circumflex over ( )}2.78.

17. The process as claimed in claim 16, wherein the process is conducted at a temperature between 773 K and 1123 K.

18. The process as claimed in claim 16, wherein the process is conducted under a slightly elevated pressure compared to the environment.

19. The process as claimed in claim 16, wherein d.sub.30 is not more than 110 micrometers for the oxidic iron-bearing particles introduced into the fluidized bed.

20. The process as claimed in claim 16, wherein the oxidic iron-bearing particles introduced into the fluidized bed are between 15 micrometers and 100 micrometers to an extent of at least 50% by mass.

21. The process as claimed in claim 16, wherein the oxidic iron-bearing particles are present at smaller than 10 micrometers μm with fractions of not more than 30% by mass.

22. The process as claimed in claim 16, wherein the fluidized bed has different zones with different bed heights.

23. The process as claimed in claim 16, wherein the bed height in the fluidized bed is 0.1-0.5 m.

24. The process as claimed in claim 23, wherein the bed height in the fluidized bed is 0.3-0.4 m.

25. The process as claimed in claim 16, wherein a gas dwell time of the reduction gas in the fluidized bed is 0.1 second to 10 seconds.

26. The process as claimed in claim 25, wherein the gas dwell time of the reduction gas in the fluidized bed is 1 second to 2 seconds.

27. The process as claimed in claim 16, wherein spent reduction gas exiting from the fluidized bed, after processing, is recirculated again into the fluidized bed as a component of the reduction gas.

28. The process as claimed in claim 16, wherein the fluidized bed is supplied with the same reduction gas throughout.

29. The process as claimed in claim 16, wherein different zones of the fluidized bed are supplied with different reduction gases.

30. A signal processing device with a machine-readable program code, wherein the signal processing device has control commands for performance of the process as claimed in claim 16.

31. A machine-readable program code for a signal processing device, wherein the program code has control commands that cause the signal processing device to perform the process as claimed in claim 16.

32. A storage medium having a machine-readable program code as claimed in claim 31 stored thereon.

33. A process of direct reduction of oxidic iron-bearing particles to a reduction product in a fluidized bed, comprising: flowing in crosscurrent a reduction gas containing 30-100 mol % of hydrogen H.sub.2 through the fluidized bed; limiting a grain size of the oxidic iron-bearing particles introduced into the fluidized bed to not more than 200 micrometers to an extent of at least 90% by mass; and setting a superficial velocity U of the reduction gas flowing through the fluidized bed to between 0.05 m/s and 1 m/s such that it is above the theoretical fluidization velocity U.sub.t and not more than U.sub.max for the grain size d=d.sub.30 of the oxidic iron-bearing particles introduced into the fluidized bed; wherein a theoretically predicted value U.sub.t for a grain size d is found from: $U_t=\surd \left(\frac{4}{3}*\frac{\left(\rho p-\rho g\right)}{\rho g}*\frac{d*g}{\mathrm{Cw}}\right)$ $\mathrm{with}\mathrm{Cw}=\frac{24}{\mathrm{Re}}+\frac{4}{\sqrt{\mathrm{Re}}}+0.4$ and with $\mathrm{Re}=\frac{\rho g*U_t*d}{\mu };$ and wherein U.sub.max is calculated from an actual correlation found between particle size and fluidization velocity for a particle size d=d.sub.30:
U.sub.max=(40000*d){circumflex over ( )}2.78.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] The present invention is described by way of example hereinafter with reference to multiple schematic figures.

[0096] FIG. 1 shows the performance of a process of the invention in a section through a schematic reaction chamber.

[0097] FIG. 2 shows a schematic of an arrangement with multiple subreactors.

[0098] FIG. 3 shows the theoretical correlation of the prevailing teaching and the correlation discovered by the inventors between superficial velocity U and particle size d.

DETAILED DESCRIPTION

[0099] FIG. 1 shows a schematic of one embodiment of the process of the invention. The process is performed in the apparatus 1. Oxidic iron-bearing particles 2 having a particle size of not more than 200 μm to an extent of at least 90% by mass, at input site A, are introduced continuously through input opening 3 into a fluidized bed 4 in the reactor space 5 of a fluidized bed reactor 6, which is indicated by an arrow. In one variant, up to 30% by mass of the oxidic iron-bearing particles may be smaller than 15 μm. The fluidized bed 4 is formed in the reactor space 5 in that particles are lifted counter to gravity by a reduction gas 8 that flows in from the bottom through a distributor tray 7—illustrated by unfilled block arrows. In the example shown, the same reduction gas 8 is supplied throughout. The distributor tray 7 is indicated by gaps in the lower outline of the reactor space 5; for better clarity, not every gap has its own block arrow, and not all block arrows have been given the reference numeral 8. Iron oxides in the oxidic iron-bearing particles 2 are reduced to the reduction product 9 by the reduction gas 8. Reduction gas 10 consumed by the reduction of the iron oxides in the oxidic iron-bearing particles—represented by filled block arrows—exits from the fluidized bed 4 at the top. The reduction gas 8 consists, for example, of hydrogen H.sub.2 of technical grade purity; correspondingly, the spent reduction gas 10 will contain, for example, water H.sub.2O and hydrogen, since not all the hydrogen flowing in at the bottom will be converted. Particles entrained upward out of the fluidized bed by the spent reduction gas 10 are not shown separately. At a withdrawal point B, the particles of the reduction product 9 are withdrawn continuously from the fluidized bed 4 in the reactor space 5, which is indicated by an arrow. The reduction gas 8 is guided through the fluidized bed 4 in crosscurrent from the top downward at a velocity of more than 0.05 m/s. The temperature of the oxidic iron-bearing particles 2 introduced is 1173 K, for example, and the temperature of the incoming reduction gas 8 is 1023 K throughout. The reduction product 9 has a temperature, for example, of 853 K.

[0100] In the fluidized bed reactor 6 shown in schematic form in FIG. 1, there is preferably a slightly elevated pressure of 200 000 Pa relative to the environment.

[0101] The process shown can be conducted, for example, such that the bed height in the fluid bed 4 is 0.1-0.5 m, and/or the gas dwell time is 0.1-10 s, preferably 1-2 s.

[0102] The reduction gas 8 is supplied to the distributor tray 7 via the reduction gas feed conduit 11. The reduction gas feed conduit 12 serves to remove spent reduction gas 10 from the reactor space 5.

[0103] FIG. 2 shows a schematic of an embodiment in which a fluidized bed reactor 13 comprises multiple subreactors 14, 16, 18, 20. The subreactors are connected sequentially to one another; subreactor 14 is connected at its end 15 to subreactor 16, which is itself connected at its end 17 to subreactor 18. Subreactor 18 is connected at its end 19 to subreactor 20. The connections are effected via transfer devices 21a, 21b, 21c. The input opening A for oxidic iron-bearing particles 22 is present at the start 23 of the subreactor 14; the withdrawal opening B for reaction product 24 is present at the end 25 of the subreactor 20. The intermediates from the reduction of the oxidic iron-bearing particles 22 to the reduction product 24 are transferred by the transfer devices 21a, 21b, 21c in each case from an upstream subreactor viewed in the direction from the input opening A along the fluid bed to the withdrawal opening B into the downstream subreactor. While the solid material within the fluid bed (not shown separately)—i.e. oxidic iron-bearing particles, particles of intermediates, and particles of reduction product —flows from the input opening A to the withdrawal opening B in the fluidized bed reactor 13 through the successive, i.e. sequentially interconnected, subreactors 14, 16, 18, 20, within the fluid bed (not shown separately)—i.e. oxidic iron-bearing particles, particles of intermediates, and particles of reduction product—it is subjected to a crossflow of reduction gas (not shown separately).

[0104] In the diagram of FIG. 2, the subreactors 14, 16, 18, 20 are stacked vertically one on top of another. They are executed with a slightly sloped base. Dedicated reduction gas feed conduits 26a, 26b, 26c, 26d open into each of the various subreactors 14, 16, 18, 20, all of which come from a central conduit 27—for better clarity, the connections thereof to central conduits 27 are not shown separately. Respective dedicated reduction gas removal conduits 28a, 28b, 28c, 28d exit from the various subreactors 14, 16, 18, 20, all of which open into a collective removal conduit 29—for better clarity, the connections thereof to the collective removal conduit 29 are not shown separately. The collective removal conduit 29 opens into a gas processing plant 30 in which spent reduction gas, for example, is dedusted and dried. By a recirculation conduit 31, the processing product—dedusted and dried hydrogen in the case of the example from FIG. 1—is sent to the central conduit 27, and hence recirculated into the process as a component of the reduction gas together with fresh hydrogen H.sub.2 from other sources.

[0105] The fluidized bed in the fluidized bed reactor 13 has multiple zones—there is one zone in each subreactor 14, 16, 18, 20. By means of different dimensions of the subreactors 14, 16, 18, 20, shown schematically in FIG. 2 by different heights, the different zones of the fluidized bed each have different bed heights in a continuous process regime.

[0106] In one variant of the process of the invention, it would be possible to supply the different zones with different reduction gas; this variant is not shown separately.

[0107] For better clarity, there is no detailed description of the supply and production of fresh hydrogen H.sub.2 from other sources.

[0108] Overall, temperature, pressure and composition of the reduction gas influence the reaction kinetics, which results in demands on gas dwell time and particle dwell time, and also bed height. The velocity of the reduction gas affects the extent of discharge from the fluidized bed and the amount of circulating reduction gas volume. Reaction kinetics and reduction gas velocity in turn affect the specific reaction area required.

[0109] FIG. 3 shows, with a solid line, the value expected according to prevailing teaching for the theoretical fluidization velocity U.sub.t for various grain sizes d of spherical DRI/iron ore particles at 1023 K with hydrogen H.sub.2 as reduction gas and an elevated pressure of 200 000 Pa:

[00003]$\mathrm{Ut}=\surd \left(\frac{4}{3}*\frac{\left(\rho p-\rho g\right)}{\rho g}*\frac{d*g}{\mathrm{Cw}}\right)$$\mathrm{with}\mathrm{Cw}=\frac{24}{\mathrm{Re}}+\frac{4}{\sqrt{\mathrm{Re}}}+0.4$

and with

[00004]$\mathrm{Re}=\frac{\rho g*U_t*d}{\mu }$

[0110] Likewise shown, by a dotted line, is the correlation between grain size d and fluidization velocity U.sub.max that is at variance with the prevailing teaching and follows U.sub.max=(40000*d){circumflex over ( )}2.78.

[0111] The description of advantageous configurations of the invention given so far contains numerous features that are in some cases expressed with two or more together in the individual subsidiary claims. However, these features may appropriately also be considered individually and combined to give viable further combinations. More particularly, these features are each individually combinable, in any suitable combination, in a process of the invention.

[0112] Even if the description or the claims use some terms respectively in the singular or in conjunction with a numerical word, the scope of the invention for these terms shall not be limited to the singular or the respective numerical word. Moreover, the word “a” shall not be understood as “one”, but as the indefinite article.

[0113] The properties, features and advantages of the invention as described, and the manner in which they are achieved, are elucidated in a clearer and more distinctly comprehensible manner in connection with the description of the working example(s) of the invention that are elucidated in detail in association with the drawings. The working example(s) serve(s) to elucidate the invention and do not limit the invention to the combinations of features specified therein, not even in relation to functional features. Moreover, suitable features for the purpose from any working example considered explicitly in isolation, removed from any working example, may be introduced into another working example for augmentation thereof and be combined with any of the claims.

[0114] Even though the invention has been elucidated in detail and described in detail by the preferred working example(s), the invention is not limited by the example(s) disclosed, and other variants may be derived therefrom without leaving the scope of protection of the invention.

LIST OF REFERENCE NUMERALS

[0115] 1 Apparatus for performance of a process of the invention [0116] 2 Oxidic iron-bearing particles [0117] 3 Input opening [0118] 4 Fluidized bed [0119] 5 Reactor space [0120] 6 Fluidized bed reactor [0121] 7 Distributor tray [0122] 8 Reduction gas [0123] 9 Reduction product [0124] 10 Spent reduction gas [0125] 11 Reduction gas feed conduit [0126] 12 Reduction gas removal conduit [0127] 13 Fluidized bed reactor [0128] 14 Subreactor [0129] 15 End [0130] 16 Subreactor [0131] 17 End [0132] 18 Subreactor [0133] 19 End [0134] 20 Subreactor [0135] 21a,21b,21c Transfer devices [0136] 22 Iron-bearing particles [0137] 23 Start [0138] 24 Reaction product [0139] 25 End [0140] 26a,26b,26c,26d Reduction gas feed conduits [0141] 27 Central conduit [0142] 28a,28b,28c,28d Reduction gas removal conduits [0143] 29 Collective removal conduit [0144] 30 Gas processing plant [0145] 31 Recirculation conduit