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Title:
PROCESS AND PLANT FOR THE HEAT TREATMENT OF SOLIDS CONTAINING TITANIUM
Document Type and Number:
WIPO Patent Application WO/2005/026397
Kind Code:
A2
Abstract:
This invention relates to a process and a plant for the heat treatment of solids contain­ing titanium. For this purpose, the fine-grained solids are heated to a temperature of 700 to 1000 °C in a reactor (4) with circulating fluidized bed and are partly discharged from the reactor (4) together with waste gases into a downstream separator (9). In the same, the solids are separated from the waste gases and are recirculated to the reactor (4) at least partly and/or phase by phase. Downstream of the reactor (4) and/or the separator (9) an injection cooler (13) is provided, in which the solids are cooled to below 250 °C by injecting a coolant. Downstream of the injection cooler (13) a fluidized-bed cooler (16) can be provided for the further cooling of the solids.

Inventors:
STOCKHAUSEN WERNER (DE)
BEYZAVI ALI-NAGHI (DE)
NUBER DIRK (DE)
Application Number:
PCT/EP2004/010276
Publication Date:
March 24, 2005
Filing Date:
September 15, 2004
Export Citation:
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Assignee:
OUTOKUMPU OY (FI)
STOCKHAUSEN WERNER (DE)
BEYZAVI ALI-NAGHI (DE)
NUBER DIRK (DE)
International Classes:
B01J8/00; B01J8/18; B01J8/38; C01G23/00; C22B1/10; C22B34/12; (IPC1-7): C22B1/10
Foreign References:
US4076796A1978-02-28
US5714113A1998-02-03
GB1312765A1973-04-04
Other References:
DATABASE INSPEC THE INSTITUTION OF ELECTRICAL ENGINEERS, STEVENAGE, GB; 26 July 2002 (2002-07-26), SUNG WON KIM, JUNG YEUL AHN, SANG DONE KIM, DONG HYUN LEE: "Heat transfer and bubble characteristics in a fluidized bed with immersed horizontal tube bundle" XP008047046
Attorney, Agent or Firm:
KEIL & SCHAAFHAUSEN (Frankfurt am Main, DE)
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Claims:
Claims :
1. A process for the heat treatment of solids containing titanium, in which fine grained solids are heated to a temperature of 700 to 1000°C in a reactor (4) with circu lating fluidized bed and are partly discharged from the reactor (4) together with waste gases into a downstream separator (9), in which the solids are separated from the waste gases and are recirculated to the reactor (4) at least partly and/or phase by phase, characterized in that downstream of the reactor (4) and/or the separator (9) a fluidizedbed injection cooler (13) is provided, in which the solids are cooled to below 250°C by injecting a coolant, and that fluidizing gas is introduced into the injection cooler (13) with such a gas velocity that the ParticleFroudeNumber in the fluidized bed is between 0.01 and 10, in particular between 0.1 and 1.
2. The process as claimed in claim 1, characterized in that the ParticleFroude Number at the bottom of the injection cooler (13) is between 0.1 and 0.25, in particular about 0. 17.
3. The process as claimed in claim 1 or 2, characterized in that the Particle FroudeNumber at the top of the injection cooler (13) is between 0.35 and 0.55, in particular about 0.47.
4. The process as claimed in any of the preceding claims, characterized in that the gas content of the fluidized bed in the injection cooler (13) includes 50 to 70%, in particular about 60% steam.
5. The process as claimed in any of the preceding claims, characterized in that downstream of the injection cooler (13) a fluidizedbed cooler (16) is provided.
6. The process as claimed in any of the preceding claims, characterized in that ilmenite is used as starting material.
7. The process as claimed in any of the preceding claims, characterized in that the solids supplied to the reactor (4) have a mean grain size (d_50) between 75 and 250 um, in particular between 100 and 150 um.
8. The process as claimed in claim 7, characterized in that the solids supplied to the reactor (4) have a maximum grain size of 2 mm, in particular of less than 250 urn.
9. The process as claimed in any of the preceding claims, characterized in that fuel is supplied to the reactor (4), by whose combustion in the reactor (4) with an oxy gencontaining gas at least part of the amount of heat required for the thermal treat ment is generated.
10. The process as claimed in claim 9, characterized in that into the reactor (4) gaseous fuel, preferably natural gas, is introduced through lances (6) and/or through bottom tuyeres, and air is introduced as fluidizing gas.
11. The process as claimed in claim 10, characterized in that the waste gas dis charged from the reactor (4) into the separator (9) has an oxygen content between 3 and 10%, in particular about 5%.
12. The process as claimed in any of the preceding claims, characterized in that the average retention time of the solids in the reactor (4) is between 10 and 30 min, in particular about 20 min.
13. The process as claimed in any of the preceding claims, characterized in that at least part of the waste gas of the reactor (4) is largely separated from solids in the separator (9) and supplied to a preheating stage (2,3) with a drier (2) and a separator (3) upstream of the reactor (4) for drying and preheating the solids to be supplied to the reactor (4).
14. The process as claimed in claim 13, characterized in that the waste gases of the reactor (4) together with the steamloaded waste gases of the injection cooler (13) are cleaned in a waste gas cleaning stage (20) downstream of the preheating stage (2, 3).
15. The process as claimed in any of the preceding claims, characterized in that the recirculation of solids from the separator (9) into the reactor (4) is effected in a self regulating manner.
16. A plant for performing a process for the heat treatment of solids containing titanium as claimed in any of the preceding claims, comprising a reactor (4) with circu lating fluidized bed, downstream of which a separator (9) is provided, characterized in that downstream of the reactor (4) and/or the separator (9) an injection cooler (13) is provided and downstream of the same a separate fluidizedbed cooler (16).
17. The plant as claimed in claim 16, characterized in that the fluidizedbed cooler (16) has cooling coils through which a coolant is passed countercurrently.
18. The plant as claimed in claim 17, characterized in that the fluidizedbed cooler (16) has two or more chambers (16a, 16b) through whose bottom fluidizing gas is introduced by means of a blower (18).
19. The plant as claimed in any of claims 16 to 18, characterized in that the reac tor (4) has a lance assembly (6) opening into the same and/or bottom tuyeres, which are connected with a supply conduit (7) for especially gaseous fuel.
20. The plant as claimed in any of claims 16 to 19, characterized in that between the reactor (4) and the separator (9) a selfregulating Ushaped seal (11) is provided for controlling the supply of solids from the separator into the reactor.
21. The plant as claimed in any of claims 16 to 20, characterized in that upstream of the reactor (4) a preheating stage (2,3) for the solids is provided, whose drier (2) is connected with the waste gas conduit of the separator (9) downstream of the reactor (4).
Description:
Process and Plant for the Heat Treatment of Solids Containing Titanium The present invention relates to a process for the heat treatment of solids containing titanium, in which fine-grained solids are heated to a temperature of 700 to 1000°C in a reactor with circulating fluidized bed and are in part discharged from the reactor to- gether with waste gases into a downstream separator, in which the solids are sepa- rated from the waste gases and are recirculated to the reactor at least partly and/or phase by phase. Furthermore, the invention relates to a corresponding plant.

Such processes and plants are used for instance for the magnetizing calcination of ilmenite (X*Ti02Y*FeOZ*Fe203). In the past, a reactor with stationary fluidized bed was used for the magnetizing calcination of ilmenite, which reactor has, however, only a small control range and a low reaction density. In addition, when using a reactor with stationary fluidized bed, only a comparatively low flow rate is possible with respect to the container volume. The temperature and retention time control also frequently is unfavorable in the case of such reactors with stationary fluidized bed.

Therefore, it is also known to effect a magnetizing calcination of ilmenite in reactors with a circulating fluidized bed. For this purpose, hot air is introduced into the reactor through a tuyere bottom (gas distributor) for fluidizing the solids. This hot air is mostly generated in an external burner, in which e. g. propane and ambient air are burnt. The solids discharged from the reactor together with the waste gases are separated from the waste gases in a separator and at least partly recirculated to the reactor. For con- trolling the recirculation of solids from the separator into the reactor a so-called"L- valve"is used, which can be controlled by supplying gas.

Before the further processing of the ilmenite calcined in the reactor, the same must be cooled. To this end it is known, for instance, to use a fluidized-bed cooler, in which the

product heat is dissipated. In these known processes and plants it is, however, possible that changes in the magnetizingly calcined ilmenite occur during the cooling period, so that the positive magnetic properties achieved beforehand are deteriorated again.

Therefore, it is the object of the present invention to provide a process as mentioned above, in which the product quality is improved and changes of the product after the heat treatment are largely avoided.

In accordance with the invention, this object substantially is solved in that downstream of the reactor and/or the separator an injection cooler is provided, in which the solids are cooled to below 250°C by injecting a coolant and possibly are cooled further in another cooler, for instance a fluidized-bed cooler, downstream of the injection cooler, fluidizing gas being introduced into the injection cooler with such a gas velocity that the Particle-Froude-Number in the fluidized bed is between 0.01 and 10, in particular be- tween 0.1 and 1. Preferred ranges of the Particle-Froude-Number in the fluidized bed also lie between 0.01 and 0.1, between 0.05 and 0.7 or between 0.5 and 4. Preferably, the Particle-Froude-Number at the bottom of the fluidized-bed cooler is between 0.1 and 0.25, in particular about 0.17. At the top of the fluidized-bed cooler, the Particle- Froude-Number preferably is between 0.35 and 0.55, in particular about 0.47.

The Particle-Froude-Numbers are each defined by the following equation: with u effective velocity of the gas flow in m/s pf = effective density of the fluidizing gas in kg/m3 pus-density of a solid particle in kg/m3 (apparent density) dp = mean diameter in m of the particles of the reactor inventory (or the secon- dary agglomerates formed) during operation of the reactor g = gravitational constantin m/s2.

When using this equation it should be considered that dp does not designate the mean diameter (d50) of the material used, but the mean diameter of the reactor inventory formed during operation of the reactor, which can differ significantly from the mean diameter of the material used (primary particles).

In this process in accordance with the invention, the product withdrawn from the reactor or the separator first of all is cooled very much in the injection cooler to e. g. about 100 to 200°C within a very short time. Changes in the magnetizingly calcined ilmenite during the cooling period largely can be avoided in this way. Due to the rapid cooling, a particularly high product quality of the magnetizingly calcined ilmenite thus can be achieved. This high product quality ensures a high degree of separation during a sub- sequent magnetic separation. Due to the large temperature range during cooling it is necessary to not only take care of changes in the product, but to also properly adjust the quantity and velocity of the gas introduced into the injection cooler for fluidization, so that the fluidized bed does not expand too much when the injected coolant is evapo- rated. In accordance with the invention, the gas velocity of the fluidizing gas in the injection cooler therefore is chosen such that a comparatively dense fluidized bed is obtained. The fluidized bed is denser at the bottom of the injection cooler than at the top of the injection cooler, as the coolant injected is evaporated there. In the fluidized- bed cooler downstream of the injection cooler, the product heat no longer usable in the process is dissipated.

Preferably, water is injected into the injection cooler as coolant. The gas content in the fluidized bed of the injection cooler then can include between 50 and 70%, in particular about 60% steam.

With the process in accordance with the invention, all kinds of ores containing titanium, in particular those which additionally contain iron oxides, can be heat-treated effec- tively. In particular, the process is suited for the magnetizing calcination of ilmenite. The mean particle size (d50) of the solids supplied to the reactor preferably is between 75 and 250 um, in particular between about 100 and 150 um. The maximum grain size of the solids supplied to the reactor is about 2 mm, preferably less than 250 um. The grain

size of the ilmenite magnetizingly calcined in the reactor preferably lies in the same ranges indicated above.

The generation of the amount of heat necessary for the operation of the reactor can be effected in any way known to the expert for this purpose. In accordance with a pre- ferred embodiment of the invention it is provided to supply fuel to the reactor, by whose combustion with an oxygen-containing gas inside the reactor the amount of heat re- quired for the heat treatment is completely or at least partly generated. In the last- mentioned alternative, the other part of the required amount of heat then can be cov- ered by supplying hot gases or preheated solids. It is preferred when a gaseous fuel, preferably natural gas, is introduced into the reactor through e. g. lateral lances and/or bottom tuyeres, and air is introduced into the reactor as fluidizing gas. In this magnetiz- ing calcination with air, the product quality is influenced by the oxygen content. There- fore, the waste gas discharged from the reactor into the separator should preferably have an oxygen content between 3 and 10%, in particular about 5%.

In the process in accordance with the invention, a particularly high product quality can be achieved when the retention time of the solids in the reactor is between 10 and 30 minutes, in particular about 20 minutes. The Particle-Froude-Number in the reactor can lie in a range from about 0.3 to 30, in particular between 0.5 and 15.

The energy consumption of the process can be reduced in that in the separator at least part of the waste gas of the reactor is separated from solids and supplied to a preheat- ing stage upstream of the reactor. The preheating stage can, for instance, comprise a heat exchanger such as a Venturi drier, and a separator such as a cyclone or the like.

In this way, the solids supplied to the reactor are dried and preheated, whereby the heat treatment in the reactor is facilitated. A multi-stage preheating of solids is also possible, the waste gas of the reactor being cooled step by step.

In accordance with a development of this invention it is provided that the waste gases of the reactor together with the e. g. steam-loaded waste gases of the injection cooler are cleaned in a waste gas cleaning stage downstream of the preheating stage. The gases then can possibly be recirculated to the process.

In accordance with a preferred embodiment of the invention it is provided that the recirculation of solids from the separator into the reactor is effected in a self-regulating manner. In this way, an intensive internal and external re-mixing of the solids treated in the reactor can be effected, so that a uniform temperature and reaction profile is achieved in the reactor.

A plant in accordance with the invention, which is in particular suited for performing the process described above, includes a reactor with circulating fluidized bed, downstream of which a separator is provided. Downstream of the reactor and/or the separator there is furthermore provided an injection cooler and downstream of the same a separate fluidized-bed cooler. In the injection cooler, the product can be cooled quickly, i. e. within few seconds, to temperatures between e. g. 100 and 200°C by injecting for in- stance water. This rapid first cooling is decisive for the product quality, as for instance during the magnetizing calcination of ilmenite changes in the product are possible during a too long cooling time. The final cooling of the product then is effected in the separate fluidized-bed cooler, which is provided downstream of the injection cooler.

Preferably, cooling coils are provided in the fluidized-bed cooler, through which a coolant is passed countercurrently. These cooling coils can for instance be combined to form cooling bundles.

In the fluidized-bed cooler, the product heat no longer usable in the process can be dissipated particularly effectively, when the same has two or more chambers through whose bottom fluidizing gas is introduced by means of a blower. The fluidizing gas on the one hand is used for cooling the product and at the same time effects an intensive intermixing of the solids to be cooled.

For adjusting the temperatures necessary for the heat treatment of the solids, the reactor preferably has a lance assembly and/or bottom tuyeres opening into the same, e. g. disposed laterally, which are connected with a supply conduit for especially gase- ous fuel. In this way, the fuel is directly burnt inside the reactor in the presence of the solids.

In accordance with a preferred embodiment of the invention, a self-regulating U-shaped seal is provided between the reactor and the separator, by means of which the supply of solids from the separator into the reactor is controlled. An expensive control system, for instance by using an L-valve known from the prior art, thus can be omitted.

To decrease the energy consumption of the plant, a preheating stage can be provided upstream of the reactor, in which the solids are dried and preheated. The preheating stage includes a drier, which is connected with the waste gas conduit of the separator downstream of the reactor, so that the heat generated in the reactor by internal com- bustion of the fuel can be utilized for predrying the solids.

Further developments, advantages and possible applications of the invention can also be taken from the following description of an embodiment and the drawing. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

The only Figure shows a process diagram of a process and a plant in accordance with an embodiment of the present invention.

In the process as shown in the Figure, which is suited in particular for the magnetizing calcination of solids containing titanium, such as ilmenite, moist solids are introduced into a preheating stage via a screw conveyor 1. This preheating stage comprises a Venturi drier 2, in which the raw material is suspended, dried and preheated, and a separator 3, e. g. a cyclone, downstream of the Venturi drier 2. The solids separated from waste gases in the separator 3 are charged into a reactor 4.

The reactor 4 constitutes a fluidized-bed reactor with circulating fluidized bed. For fluidizing the solids, bottom tuyeres are provided in the reactor 4, through which air is introduced by means of a blower 5. Via lateral lances 6, natural gas is supplied to the reactor 4, which is burnt inside the reactor together with the fluidizing air. Alternatively or in addition, fuel can be introduced into the reactor 4 via a conduit 7 by means of bottom tuyeres.

In the fluidized-bed reactor 4, the solids are carried upwards by the fluidizing gas. Part of the solids separate out in the reactor and are thereby recirculated to the circulating fluidized bed, in order to be carried upwards again by the fluidizing gas. Together with a waste gas stream from the reactor 4, the other part of the solids is discharged upwards through a conduit 8 and in a downstream separator 9, for instance a cyclone, separated from the gas stream for the most part. Through a conduit 10, the solids from the sepa- rator 9 are recirculated to the fluidized-bed reactor 4. By means of this intensive inter- nal and external remixing a particularly uniform temperature and reaction profile is achieved inside the fluidized-bed reactor 4.

The control of the amount of solids recirculated from the separator 9 into the fluidized- bed reactor 4 is effected via a self-regulating U-shaped seal 11 which is provided in the conduit 10. As a result, a control and regulating unit for metering the amount of solids recirculated into the fluidized-bed reactor 4 can be omitted.

The gases which leave the fluidized-bed reactor 4 together with solids through conduit 8 are heated by the internal combustion of fuel in the reactor 4. The gas stream sepa- rated from the solids in the separator 9 is supplied to the Venturi drier 2, so that the heat content of the gas stream leaving the separator 9 is utilized for drying and pre- heating the solids.

From the fluidized-bed reactor 4 and/or the separator 9 hot solids are withdrawn and supplied to an injection cooler 13 via conduits 12a and 12b, respectively. In the injec- tion cooler 13, the hot solids are fluidized in a stationary fluidized bed. For this purpose, air is introduced into the injection cooler 13 as fluidizing air via a blower 14. The gas velocity of the fluidizing gas is chosen such that the fluidization in the injection cooler 13 is low, so that the stationary fluidized bed expands only little. At the same time, water is injected into the injection cooler 13 as coolant via conduit 15. The water is evaporated in the injection cooler 13, so that the stationary fluidized bed in the upper region of the injection cooler 13 expands more than in the bottom region of the injection cooler. By injecting water, the hot product is quickly cooled to temperatures of e. g. below 200°C.

Downstream of the injection cooler 13 a separate fluidized-bed cooler 16 is provided, in which the product heat no longer usable in the process is dissipated. In the illustrated embodiment, the fluidized-bed cooler has two chambers 16a and 16b, into which e. g. water is countercurrently introduced as coolant through schematically illustrated cooling coils 17, whereby the product is further cooled to the temperature necessary for the further processing, such as the magnetic separation. Via a blower 18, air is introduced into the two chambers 16a and 16b of the fluidized-bed cooler 16, in order to fluidize and cool the product. The cooled product then is supplied to the further processing via a conduit 19.

Via conduits, the separator 3 of the preheating stage, the injection cooler 13 as well as the fluidized-bed cooler 16 are connected with a waste gas cleaning stage 20, which for instance has a bag filter. In this waste gas cleaning stage 20, the gas streams partly containing solids and/or steam are cleaned. Via conduit 21, the solids can be charged frorn the waste gas cleaning stage 20 into the fluidized-bed cooler 16.

Example (magnetizing calcination of ilmenite) In a plant for the magnetizing calcination of ilmenite as shown in the Figure, 43 t/h of moist ilmenite from a storage tank are charged via the screw conveyor 1 into the Ven- turi drier 2. In the Venturi drier 2, the moist ilmenite was suspended, dried and pre- heated by hot waste gases from the separator 9. In the cyclone 3, which is provided downstream of the Venturi drier 2, the dried and preheated ilmenite was separated from the gas stream and introduced into the reactor 4 with circulating fluidized bed.

The waste gas of the cyclone 3 was supplied to the waste gas cleaning stage 20, therein liberated from solids and supplied to a chimney. The dry ilmenite dust separated in the waste gas cleaning stage 20 was passed through conduit 21 into the fluidized- bed cooler 16.

Via the blower 5,13, 000 Nm3/h of air were introduced into the fluidized-bed reactor 4 for fluidization. At the same time, about 700 Nm3/h of natural gas were supplied to the

reactor 4 via the lateral lances 6 as well as conduit 7 and were burnt in the fluidized bed together with air. The hot gas obtained heated the ilmenite charged into the fluid- ized-bed reactor 4 to about 900°C, the Particle-Froude-Number in the reactor being about 1.2. By an excess of oxygen in the reactor 4, a partial calcination of the ilmenite was achieved with retention times of the solids between 10 and 30 minutes. After the calcination, the oxygen content in the top of the reactor 4 was between 3 and 10%.

Together with the waste gases of the reactor 4, the solids were transported into the separator 9, separated there and for the most part recirculated to the reactor 4 through conduit 10. An amount of ilmenite product, which corresponds to the amount charged into the reactor 4, was supplied to the injection cooler 13 through conduits 12a and 12b, respectively. The average particle size (d_50) both of the ilmenite charged into the reactor 4 and of the calcined ilmenite was about 100 to 150 um with a maximum grain size of about 250 um.

The injection cooler 13 was operated as stationary fluidized bed by supplying about 6300 Nm3/h of fluidizing air into the injection cooler 13 via the blower 14. At the same time, about 8 m3/h of water were introduced into the injection cooler 13 via conduit 15, so that the hot ilmenite was cooled to about 150°C within few seconds. Due to the evaporating water, the steam was about 60% of the total amount of gas in the fluidized bed of the injection cooler 13. The gas velocity of the fluidizing air introduced via the blower 14 was chosen such that the Particle-Froude-Number at the bottom of the injection cooler 13 was about 0.17 and at the top of the injection cooler about 0.47.

The final cooling of the product was effected in the two chambers 16a and 16b of the fluidized-bed cooler 16. For fluidization, about 6000 Nm3/h of air were introduced into the fluidized-bed cooler 16 via the blower 18. At the same time, cooling water was countercurrently passed through the chambers 16a and 16b via conduit 17. In the chambers 16a and 16b, the conduit 17 had cooling bundles.

In this way, a magnetizing calcination of ilmenite could be effected, and due to the rapid cooling no changes were detected during the cooling period, so that the calcined ilmen- ite had a high product quality.

List of Reference Numerals 1 screw conveyor 2 Venturi drier 3 cyclone 4 fluidized-bed reactor 5 blower 6 lance 7 conduit 8 conduit 9 separator 10 conduit 11 U-shaped seal 12a, 12b conduit 13 injection cooler 14 blower 15 conduit 16 fluidized-bed cooler 16a, 16b chamber 17 conduit 18 blower 19 conduit 20 waste gas cleaning stage 21 conduit