Patent Application
20190017143
The invention relates to a process and a plant for thermal treatment of a sulfur-containing ore in which the ore is calcined at temperatures of between 600 and 1200° C. in the presence of oxygen in a reactor so that between 1 and 90% by weight of the sulfur contained in the ore is burned to sulfur dioxide and impurities contained are driven off in gaseous form, in which exhaust gas being produced and containing the sulfur dioxide is fed into a gas purification comprising at least one component and/or in which the calcined ore is fed into at least one further process stage.
With the increasing demand for raw materials metallic resources, in particularly also copper-, cobalt-, gold- and nickel-containing ores, are exploited more and more. This results in the fact that resources which can be exploited without large effort or which provide highly pure raw materials meanwhile are nearly exhausted. So today exploited resources of ores are characterized by a higher proportion of impurities, in particularly it is known that copper-, cobalt- and/or nickel-containing ores also comprise arsenic and antimony. Before melting the ore, the content of these impurities has to be reduced strongly.
For that, normally, the ore is heated at a temperature of between 600 and 1200° C., preferably 600 to 900° C. This operation is also referred to as calcining. By this heating also sulfur contained in the ore is burned to sulfur dioxide (SO2), by which again heat is produced. Therefore, preferably, this process, after ignition with externally fed fuel, can be conducted in an autothermic manner.
Due to the higher amounts of impurities in the ore used and, connected therewith, the requirement of evaporating higher proportions, the energy demand of this process increases with the amounts of impurities in the ore. So the sulfur contained is either no longer capable of allowing an autothermic process control or a very large proportion of the sulfur contained is already consumed during this calcining process, so that into the later melt of the ore more fuel has to be fed from outside.
Therefore, it is an object of the present invention to provide a process with which the energy demand for the removal of impurities during the calcining step can be reduced.
This object is solved by a process with the features of patent claim 1.
For that a sulfur-containing ore is fed into an autothermal operated reactor and there it is thermally treated at a temperature of between 600 and 1200° C., preferably 600 and 900° C., particularly preferably 650 and 750° C. in the presence of oxygen. So 1 to 90% by weight, preferably 10 to 60% by weight of the sulfur contained in the ore is burned to sulfur dioxide and impurities contained are driven off in gaseous form. Such a process is referred to as partial calcination.
In such a case, a typical ore is characterized by the following composition:
By the thermal treatment an exhaust gas is produced which contains both, the sulfur dioxide and also gaseous impurities, and which is fed into a gas purification comprising at least one component. In an alternative or in addition, it is possible to feed the calcined ore into at least one further process stage.
For autothermal conditions the energy demand in this process, either an exhaust gas from one component of the gas purification and/or an exhaust gas from the further process stage are fed into the reactor as recycling gas. During unstable process conditions, it is also possible to use a gas used for cooling before, during and/or after the gas purification and/or a gas used for cooling before, during and/or after a process stage as recycling gas or, in an even more preferred embodiment, to use coils in the reactor for a heat transfer medium. But in any case, the recycling gas must have a temperature of higher than 100° C. and thus reduce the energy demand for operating in the given temperature range by feeding it into the reactor.
Using a gas with high inlet temperature, the energy demand in the reactor is reduced so that a lower amount of sulfur being contained in the ore has to be burned. So also ores being characterized by lower contents of sulfur can be calcined more easily. When the ore in deed has a sufficient sulfur demand for the calcination, then the procedure according to the present invention is also preferable, because so the calcined ore is characterized by a higher content of sulfur which in turn can act as an internal energy supplier in downstream processing stages.
However, it is essential that the reactor is operated in an autothermic manner, i.e. that during steady operation no fuel has to be fed in or the reactor has to be cooled. This considerably reduces the effort in connection with the required equipment, because in this manner no fuel has to be fed into the reactor. The autothermic operation is realized by burning a sufficient amount of sulfur which is also contained in the ore to SO2:
S+O2 --->SO2, ΔHR=−297.03 kJ.
Preferably, in this case the temperature in the reactor is controlled by the amount of oxygen which is fed in, because the amount of sulfur which can be burned depends on the oxygen being available.
Preferably, the driven off impurities contain arsenic and/or antimony in amounts of between 0.1 and 10% by weight, preferably 0.5 and 5% by weight, based on the composition of the ore being fed into the reactor. Arsenic and antimony are compounds which in particularly at temperatures of between 650 and 750° C. evaporate and thus can be discharged in gaseous form. At the same time, arsenic and antimony are highly toxic and thus have to be removed from the ore as early as possible.
Preferably, the ore contains in addition at least 20% by weight of copper, cobalt, gold and/or nickel, whereby the conduction of the process according to the present invention is particularly cost-effective.
Furthermore, it was shown to be advantageous, when the reactor is operated as a fluid bed reactor. In this case it is particularly favorable, when the recycling gas is fed into the fluid bed as fluidization gas. On the one hand, so the gas amount for the fluid bed is created in advance, and on the other hand, the problem that the reactor is cooled down by cold fluidization air does not exist.
Preferably, the recycling gas has a temperature of between 200 and 500° C., particularly preferably between 300 and 450° C., because in this manner as much as possible heat is introduced into the reactor. At the same time, the temperature of the gas is not so high that the required equipment would be subjected to temperatures which are too high and thus correspondingly would be more cost-intensive to purchase.
Furthermore, it was shown to be advantageous, when the recycling gas has a proportion of oxygen of between 3 and 20% by weight. When the reaction procedure is conducted according to the present invention, then such a proportion of oxygen is sufficient for operating the reactor at the required temperatures in an autothermic manner. A further advantage of the invention is that due to the fact that now a lower amount of sulfur has to be burned for achieving the required temperatures also the amount of oxygen which has to be provided for the reaction is lower. However, by a decrease of the oxygen content it is possible to reliably avoid the formation of arsenic and/or antimony oxides, which cannot be removed from the ore in gaseous state any longer and thus remain in it and reduce the quality thereof.
Furthermore, it was shown to be advantageous, when the recycling gas is a mixture of several exhaust gases and/or gases which are used for cooling. In particular a mixture in which the oxygen content is adjusted in a targeted manner to the desired temperature in the reactor due to the burning of sulfur is a mixture which is of advantage.
In addition, it was shown to be favorable, when after the reactor the ore is fed into a process stage being designed as a melt and gases from this melt and/or from a downstream cooling are returned back into the reactor as recycling gas or constituent of the recycling gas. In particular, the advantage is that the melt is realized at very high temperatures (>1200° C.) so that also cooling and/or exhaust gases from the melt are characterized by correspondingly high temperatures and a total gas flow which is smaller has to be returned back, since it is already characterized by a very high content of energy. Here it is also imaginable that small amounts of very hot cooling and/or exhaust gases from the melt are fed in before the reactor and there are mixed with fresh air so that the temperature of the gas is not an unnecessary burden for the parts of the plant, but the returned gas flow is smaller and thus the design of the required equipment may be characterized by smaller dimensions.
A preferable design of the invention is characterized by a gas purification which comprises a process for producing sulfuric acid from sulfur dioxide being contained in the exhaust gas. Such a process for producing sulfuric acid is, for example, described in DE 10 2005 008109 A1. Such a process releases relatively much energy, so that it is of advantage to reuse this energy for calcination in the form of the recycling gas.
Preferably, in such a process under heterogeneous catalysis with addition of air at first SO2 is reacted to SO3. In this case, the source of oxygen is air. Besides SO3, from this reaction also a gas which is poor in oxygen results, wherein poor in oxygen in the sense of the invention means a proportion of oxygen which is lower than 21% by volume, preferably lower than 18% by volume. This gas which is poor in oxygen, according to the present invention, can then be returned back into the reactor as recycling gas or as constituent of the recycling gas, so that here the provision of oxygen is minimized and therefore the risk of forming arsenic and/or antimony oxides is considerably reduced.
When the gas purification comprises a process for producing sulfuric acid from SO2, then, furthermore, it was shown to be favorable that the SO3 is absorbed with sulfuric acid in at least two stages and that between two adjacent stages the sulfuric acid is guided through a heat exchanger. Such a recovery process is also described in DE 10 2005 008109 A1. According to the present invention, the heat exchanger uses air or another gas, preferably with an oxygen content of <20% by volume, so that the cooling gas of the heat exchanger is returned back into the reactor as recycling gas or constituent of the recycling gas.
According to the present invention, it is particularly preferable, when the sulfur dioxide is at first reacted to sulfur trioxide and subsequently the sulfur trioxide is absorbed in sulfuric acid. In this case, both, the gas which is poor in oxygen from the heterogeneous reaction of SO2 to SO3 and also the heated air from the at least one heat exchanger between both absorbers in the absorption stage are mixed with air so that a specific oxygen content of between 3 and 20% by weight is adjusted, whereby the temperature in the reactor can be regulated or controlled by regulating or controlling the amount of sulfur to be burned and thus the additional energy amount through the oxygen content.
In addition, it is also imaginable to burn sulfur yet in addition during the production of sulfuric acid. The heat resulting from this burning can also be used for the partial calcination, either directly in the form of the exhaust gas or indirectly as vapor.
Furthermore, the invention also comprises a facility with the features of patent claim 13. Preferably, such a plant is designed for conducting a process with the features of patent claims 1 to 12.
Such a facility for thermal treatment of a sulfur-containing ore comprises an autothermal reactor in which the ore is calcined at temperatures of between 600 and 1200° C., preferably 600 and 900° C., particularly preferably 650 to 750° C. in the presence of oxygen. Furthermore, such a facility comprises at least one component of a gas purification and/or a further process stage for treating the ore.
Furthermore, according to the present invention, the facility comprises a return line from at least one component of the gas purification and/or the further process stage and/or a return line from a cooling within the gas purification and/or a cooling for the further process stage. So heated gas as recycling gas can be returned back into the reactor for calcining, whereby, in addition to the burning of sulfur, the required energy input is reduced. So, on the one hand, the oxygen content in the calcining reactor can be reduced which decreases the risk of forming oxides which can be removed only with high effort, and, on the other hand, so a lower amount of sulfur has to be burned. Therefore, it is possible to process ore with a sulfur content which is not sufficient for achieving the required temperature at all, or the sulfur content of the calcined ore remains higher so that the ore in downstream process stages can be processed better due to the inherent energy content.
It is particularly preferable, when the reactor is designed as a fluidized bed reactor, because such a fluidized bed reactor results in very homogenous conditions throughout the whole fluidized bed.
However, in principle, it is also imaginable to conduct the reaction in a rotary kiln or a multiple-hearth furnace.
In a preferred embodiment, cooling coils are foreseen. This is particular preferred for a fluidized bed reactor wherein the coils at least partly are immersed into the fluidized bed during operation, but it is not restricted to this reactor type. With these cooling coils, instable process conditions as well as start-up and shut down of the plant can be handled.
In the following, the invention is explained in more detail by means of a FIGURE. Here, all described and/or depicted features form on its own or in arbitrary combination the subject matter of the invention, independently from their summary in the patent claims or their back reference.
In
But similarly the described process is also possible for each ore composition mentioned in table 1.
In reactor 1 the ore is thermally treated in a so-called calcining process at temperatures of between 550 and 1000° C., preferably 680 and 720° C. under autothermal conditions. Here, on the one hand, sulfur contained in the ore is burned so that SO2 and heat are formed. On the other hand, at the prevailing reaction temperatures impurities, in particularly arsenic and/or antimony, are evaporated which is an energy consuming process. Exhaust gases consisting of the introduced air, the produced SO2 and gaseous impurities are subsequently drawn off via line 11 and are fed into a cyclone 20.
In this cyclone 20 the particles entrained by the exhaust gas flow are separated from the gas flow. The so purified gas from which dusts and small particles (<20 μm) have been removed is then fed into a gas purification 22.
The gas purification 22, preferably, comprises a hot filtration and/or a quench, preferably with water, and/or a wet filtration and/or a mercury removal and/or a gas drying, particularly preferably in this arrangement. Exhaust gases which are produced so and/or a gas which is used for cooling of one of the mentioned gas components or between the mentioned gas purification components can then be returned back into the reactor 10 via lines 23, 41 and 40 as recycling gas, wherein this recycling gas has a temperature of higher than 100° C., preferably 300 to 450° C.
Furthermore, the gas from the gas purification facility 22 or also directly from line 21 is fed into a sulfur trioxide reactor 30 via line 23 for reacting SO2 to SO3 in a heterogeneously catalyzed reaction. The oxygen required for this reaction is introduced via line 31. Similarly, also an introduction into lines 22 or 23 would be imaginable. The exhaust gas which is produced and which is oxygen-depleted, since oxygen from air has been used for the reaction of SO2 to SO3, is fed as recycling gas into reactor 10 via line 42 and line 40.
Via line 32 the produced SO3 is fed into at least one absorption stage 33. Into this absorption stage 33 via line 34 sulfuric acid is introduced and via line 35 drawn off again. In the sulfuric acid SO3 and H2SO4 form disulfuric acid H2S2O7 which in contact with water decomposes into two molecules of sulfuric acid. This product is drawn off via line 35.
Preferably, as shown, the absorption is characterized by a design of at least two stages so that line 35 does not immediately withdraw the end product, but does it fed into a second absorption stage 36 from which then the end product is drawn off via line 37. In line 35 a heat exchanger 39 is located which also uses a gas, preferably air, as a heat carrier medium. So the air fed via line 38 into the heat exchanger 39 can be heated and it can be fed into recycling line 40 via line 44, 43. Similarly, also the use of a process gas which is poor in oxygen instead of air would be imaginable.
Preferably, gas which is poor in oxygen, thus gas with an oxygen content of between 5 and 20% by weight, preferably 8 to 14% by weight is drawn off from the sulfur trioxide reactor 30 via line 42. This step of drawing off can also be realized via a chimney (not shown), thus after passing both absorption stages. By mixing the gases in lines 42 and 44 the oxygen content in lines 43, 40, optionally also by further admixing via line 41, can be controlled or regulated. A definition of the oxygen content also results in the stoichiometrically possible conversion of sulfur in reactor 10, whereby in this manner also the amount of heat generated by the burning of sulfur and thus finally the temperature in reactor 10 can be controlled.
The ore is drawn off from reactor 10 via line 12. Preferably, into it the particles and fine dusts separated in cyclone 20 are fed by means of line 24. Then, the ore can be used elsewhere or it can be directly further processed in a cluster of production plants.
In an alternative or in addition to the described recycling gas guidance from the gas purification, when the further processing is conducted on-site, it is possible to recover recycling gas also in a downstream ore processing stage. Preferably, in this case, the ore is fed into a melting furnace 50 via line 51 in which the ore is further purified. Exhaust gases which are produced here and originate either directly from the melting furnace 50 or also from a cooling downstream of the melting furnace 50 (not shown) can be fed into reactor 10 via a recycling gas line 60.
Similarly, also other stages for further processing the ore are imaginable from which either directly gas and/or cooling gas used in a corresponding cooling can be used as recycling gas or as constituent of the recycling gas. In the shown process, at the same time, the melting furnace is cooled and via the same recycling gas line in its function as a heat carrier medium also heated gas is returned back into reactor 10.
Furthermore, generally, it is also imaginable to mix the recycling gas from recycling gas line 60 independently from its origin with the recycling gas from line 40.
Preferably, reactor 10 is designed as a fluidized bed reactor so that the recycling gas is used completely or partially as fluidization gas. In this case, both, a stationary fluidized bed and also a circulating fluid bed are possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 105 574.3 | Mar 2016 | DE | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2017/057087 | Mar 2017 | US |
| Child | 16133057 | US |
