Device for the thermal-gas reduction of metal oxides utilizing hydrogen as the process gas

Abstract

A device for the direct reduction of metal oxides, in particular iron oxides (DRI), constituting a bell-type furnace unit 18 in connection with a process plant utilising hydrogen (H2) as process gas, whereby the plant is a set of the following functional blocks: process gas cooler 19, steam condenser 20, process gas dehumidifier 21, mechanical filter unit 22, process blower 23, vacuum pump unit 24, post-process gas ejection system 25, process gas station (H2 and N2) 26, closed-circuit cooling water system 27, loading and unloading unit 28 and condensate container tank 29, while the bell-type furnace 18, located vertically in a two-part separable casing 1, contains, in its lower part lb, a stationary thermally insulated hearth 10, on which the loaded charge basket with an open-work bottom 3 is placed, whereby the upper part of the furnace in the casing la, which serves as a movable bell, is equipped with an internally placed ceramic thermal insulation 2 with a process temperature control system: a set of electric high- power heating elements 4 and a process gas flow system 11, 12, whereby the two parts of the casing la and lb, equipped with contact flanges 5 and 16 respectively, are tightly connected with each other and, moreover, a torus-shaped process gas manifold 7, with circumferentially external outlet nozzles 9, is placed between the hearth 10 and the basket 3, integrated in function with the support of the basket 3, whereby the manifold 7 is supplied with process gas via an inlet channel 12 located off-axially in the hearth 10, while in the hearth 10, below the manifold 7, an outlet duct 11 for the used process gas is axially located.

Description

[0001] Device for the thermal-gas reduction of metal oxides utilizing hydrogen as the process gas

[0002] The subject of the invention is a device for the thermal-gas reduction of metal oxides, particularly iron oxides [direct reduced iron (DRI)], utilising hydrogen as the process gas.

[0003] There are numerous patent publications describing solutions for gaseous reduction of metal oxides, such as those of the US company Midrex Technologies Inc. US 11,499,201 B2 and WO 2020 / 247328 Al, as well as the Mexican company ’HYL Technologies, S.A. de C.V.' By analysing these publications, it is evident that there is an important feature concerning the nature of the technical processes performed with the proposed equipment and plants. The vast majority of publications deal with solutions for running continuous processes, and only a few are based on intermittent work. In fact, this feature is related to the flow of the processed material in the course in the processes, which, in the case of the former, takes place continuously, unlike the latter, where specific portions of the input are available in well-defined time windows. Each of these modes allows the solution to be properly tailored to individual operating conditions, including the type of raw material, its form, availability, expected plant performance, infrastructure constraints, etc.

[0004] This application presents design solutions aimed at improving the features of batch operation equipment only.

[0005] Known batch devices for DRI are presented, among others, in the Swedish patent publication of Greeniron H2 AB No. SE 543 341 C2, in the publications of patent applications of the same company Greeniron H2 AB at the European Patent Office (EPO) no.: EP3947757, EP3947758, EP3947749, EP4034685, EP4172374 and

[0006] WO2022191754.

[0007] There are several problems with the state of the art, including performance in terms of heat loss as well as gaseous hydrogen consumption. A control problem also exists, as post-process measurements are required. It would, therefore, be desirable to design a thermally and energy-efficient direct metal oxide reduction (pellet) equipment that would allow for increased production scale, easier scaling, a flexible and robust way to achieve direct metal material reduction, so as to handle ever-changing productivity and environmental requirements at low cost.

[0008] In the Greeniron H2 AB patents and patent applications cited above, the configured heating elements are located at the top of the process chamber, and this location of the process heat source may result in a reduction in furnace performance.

[0009] By building the heating system exclusively under the surface of the process chamber top, for certain process time assumptions, the amount of charge will have to be limited, which means that the process capacity of the plant, for a given size, cannot be optimally utilised.

[0010] The essence of the device of the invention, which is a bell-type furnace unit in combination with a process plant, consists in that in the bell-type furnace, positioned vertically in a two-piece detachable casing, between the hearth and the basket, there is a torus-shaped process gas manifold with circumferential outer outlet nozzles, integrated in function with the basket support, whereby the manifold is supplied with process gas, which is hydrogen (H2), via an off-axis inlet duct located in the hearth, with the spent process gas outlet duct located axially in the hearth below the manifold.

[0011] It is advantageous if, between the manifold and the ceramic thermal insulation of the bell, at the height of the outlet nozzles, there are guide vanes to force vertical upward movement of the process gas.

[0012] It is also advantageous if two gaskets are positioned coaxially between the contact flanges of the two casing parts, while the tightness of the connection is achieved via a multi-segment vacuum-pressure quick-releasc clamp.

[0013] It is further advantageous if the thermal insulation of the upper part of the furnace in the casing is made of lightweight refractory material based on ceramic fibre, having an appropriate density and built up in a modular way, whereby the material may contain a binder, be mouldable and / or be installed at the destination with appropriate compression.

[0014] It is also advantageous if the ceramic thermal insulation of the upper part of the furnace in the casing is made up of structured ceramic fibre modules set on an internal system-integrated frame, which is built in such a way that all its components are contained within it, thus remaining separate from the process environment.

[0015] At the same time, it is advantageous if the furnace is equipped with an arbitrary temperature control system for the internal thermal insulation.

[0016] Furthermore, it is advantageous if the heating elements are large-size, high-power resistors which, thanks to a suspension system, are securely and stably mounted on the furnace wall made of light thermal insulation.

[0017] Note that the internal equipment of the bell-type furnace, i.e. the thermal insulation and the heating elements, have properties that enable the processes, directly in the process environment, to run correctly, thus eliminating the need for separating elements such as a retort or muffle.

[0018] Moreover, the geometry of the torus manifold used in the bell-type furnace makes it possible to achieve an even distribution of the process gas jet to all the nozzles located around its perimeter when the process gas is fed to it through a single inlet.

[0019] The invention will be illustrated by an example of the implementation shown in the drawing, in which the individual figures represent:

[0020] Fig. 1 - bell-type furnace in vertical section;

[0021] Fig. 2 - vacuum-pressure connection of the bell-type furnace in vertical section; and

[0022] Fig. 3 - block diagram of the process plant of the bell-type furnace.

[0023] In the process plant shown in Fig. 3, the output and input of the mating loading and unloading unit 28 of the bell-type furnace 18 are interconnected via a process loop comprising: process gas coolers 19, steam condenser 20, process gas dehumidifier 21, mechanical filter unit 22, process blower 23 and process gas cooler 19, are interconnected, whereby the output of the process blower 23 is also connected, to the input of the process gas stations (H2 and N2) 26 and, via the vacuum pump unit 24, with the post-process gas outlet system 25, while the second output of the steam condenser 20, which works with the closed-circuit cooling water system 27, is connected to the condensate tank 29.

[0024] In the example implementation, the iron oxide reduction process was carried out while maintaining the following parameters:

[0025] Charge weight (Fe^Ch): 5 tonnes

[0026] Height of material bed: approx. 0.7 m

[0027] Reduction temperature: approx. 600°C

[0028] Hydrogen gas: 75% vol.

[0029] Steam: 25% vol.

[0030] A dedicated loading and unloading device 28 delivers the steel basket 3 with the granulated charge into it and positions it on the hearth 10 of the furnace 18. To make this possible, the furnace 18 is prepared accordingly by lifting the bell la. When the loading device is withdrawn, the bell la of the furnace 18 is sealed and the processing begins.

[0031] After all the auxiliary phases, i.e. evacuation by the vacuum pump unit 24, inerting with nitrogen from the process gas station 26 and preheating by means of the furnace 18 built-in heating elements 4, the hydrogen reduction phase follows. The hydrogen, fed into the furnace 18 under high pressure, starts to circulate and, flowing through the volume of the charge, located in the basket 3 with the openwork bottom, reacts with it. This reaction results in the gradual reduction of metal oxides to metallic form. The product of this process is a mixture of hydrogen, which was not involved in the reaction, and steam. This gas flows out of the furnace 18 and is directed to the process gas cooler 19. In the cooler, the mixture is cooled to a temperature close to that necessary for the condensation of steam. The cooling medium is the unreacted hydrogen that is returned to the process and is thus preheated, allowing part of the circulating heat to be recovered. The cooled process gas goes to the steam condenser 20, where more steam is removed. In this case, the cooling medium is circulating water protected by a closed-circuit system 27. Condensed water in the form of condensate is removed from the system and accumulates in a dedicated condensate tank 29. In this way, the mixture has significantly increased share of hydrogen, but, in order to finally determine the composition of the process gas, it is passed through the dehumidifier 21. After leaving the dehumidifier 21, the gas is directed to the filter unit 22 and then enters the suction manifold of the process blower 23 intended to provide the required mass flow of hydrogen during the reduction process, under pressurised conditions. The blower 23 pressurises the hydrogen to the appropriate pressure through the secondary cooler circuit 19 of the process gas from where, after the station 26 has compensated for the used hydrogen mass, the gas enters the furnace inlet port for reduction 18. According to the scheme described above, the reduction process is carried out at temperature and pressure until the required degree of metallisation (reduction) is achieved. This condition is determined by a control and measurement equipment installed on furnace 18. After notification that the reduction is complete, the charge is cooled to the outlet temperature and the hydrogen remaining in the system is flushed out with nitrogen from station 26, with the resulting mixture being discharged to the environment via the post-process gas outlet system 25 .

[0032] List of items shown in the drawing (Fig. 1 - 3)

[0033] 1. two-part separable casing la. bell casing (upper part of the furnace) lb. hearth casing (lower part of the furnace)

[0034] 2. ceramic thermal insulation of the bell

[0035] 3. basket with an openwork bottom filled with the charge

[0036] 4. electric high-power heating elements

[0037] 5. bell casing flange

[0038] 6. vacuum-pressure quick-release clamp

[0039] 7. torus-shaped process gas manifold with outlet nozzles (integrated in the basket support function)

[0040] 8. process gas guide vane

[0041] 9. process gas outlet nozzle, located on the outer jacket of the manifold

[0042] 10. furnace heart in the ceramic thermal insulation

[0043] 11. post-process gas outlet duct

[0044] 12. process gas inlet duct (to the distributor)

[0045] 13. bell casing wall

[0046] 14. internal quick-connect gasket

[0047] 15. external quick release gasket

Claims

Claims1. A device for the direct reduction of metal oxides, in particular iron oxides (DRI), constituting a bell-type furnace unit 18 in connection with a process plant utilising hydrogen (H2) as process gas, whereby the plant is a set of the following functional blocks: process gas cooler 19, steam condenser 20, process gas dehumidifier 21, mechanical filter unit 22, process blower 23, vacuum pump unit 24, post-process gas ejection system 25, process gas station (H2 and N2) 26, closed-circuit cooling water system 27, loading and unloading unit 28 and condensate container tank 29, while the bell-type furnace 18, located vertically in a two-part separable casing 1, contains, in its lower part lb, a stationary thermally insulated hearth 10, on which the loaded charge basket with an open-work bottom 3 is placed, whereby the upper part of the furnace in the casing la, which serves as a movable bell, is equipped with an internally placed ceramic thermal insulation 2 with a process temperature control system: a set of electric high-power heating elements 4 and a process gas flow system 11, 12, whereby the two parts of the casing la and lb, equipped with contact flanges 5 and 16 respectively, are tightly connected with each other, characterised in that a torus-shaped process gas manifold 7, with circumferentially external outlet nozzles 9, is placed between the hearth 10 and the basket 3, integrated in function with the support of the basket 3, whereby the manifold 7 is supplied with process gas via an inlet channel 12 located off-axially in the hearth 10, while in the hearth 10, below the manifold 7, an outlet duct 11 for the used process gas is axially located.

2. Device according to claim 1, wherein, between the manifold 7 and the ceramic thermal insulation 2 of the bell, at the height of the outlet nozzles 9, there are guide vanes 8 to force vertical upward movement of the process gas.

3. Device according to claim 1 or 2, wherein, two gaskets 14 and 15 are coaxially positioned between the contact flanges 5 and 16 of both casing parts la and lb, while the tightness of the connection is achieved by means of a multi-segment clamp 6 of the vacuum-pressure quick connector.

4. Device according to one of the claims 1 or 2 or 3, wherein the thermal insulation 2 of the upper part of the furnace in the casing la is made of lightweight refractory material based on ceramic fibre, having an appropriate density and built up in a modular way, whereby the material may contain a binder, be mouldable and / or be installed at the destination with appropriate compression.

5. Device according to claim 4, wherein the ceramic thermal insulation 2 of the upper part of the furnace in the casing la is made up of structured ceramic fibre modules set on an internal system-integrated frame, which is built in such a way that all its components are contained within it, thus remaining separate from the process environment.

6. Device according to claim 4 or 5, wherein the bell-type furnace 18 is provided with an arbitrary temperature control system for the internal thermal insulation 2.

7. Device according to one of the claims 1 to 6, wherein the heating elements 4 are large-sized, high-power resistors which, thanks to a suspension system, are securely and stably mounted on the furnace wall made of lightweight thermal insulation 2.

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