Apparatus and method for the treatment of hydrocarbon- containing sludges for the production of a recyclable product

The invention relates to a device and a method for treating hydrocarbon-containing and optionally oxide-containing, in particular scale-containing, sludge for the production of a recyclable product, the sludge being heated in a first process step and freed from volatile components, in particular water, and in a second process step heated by indirect heating and removed from other volatile components, in particular of hydrocarbons, exhaust gas from the first and / or second process step being subjected to a suitable exhaust gas treatment.

In the steel processing industry, the crude steel, such as it is delivered in slab form from the casting plant, is formed in rolling mills into the respective end product.

During this forming process, the tiniest chips and abrasion occur or, in particular, oxide-containing substances arise on surfaces, which, in accordance with the high production output of such systems, soon add up to those quantities that make regular recycling appear sensible. This waste in the form of iron-containing particles is also called mill scale by the person skilled in the art. In addition, scale is also produced in the operation of continuous casting plants.

Due to other operating materials, in particular fats and oils, such as are preferably used as friction-reducing additives, the scale is contaminated, which makes recycling significantly more difficult or even impossible.

Various methods are known in the prior art for recycling mill scale sludge, as this mixture of mill scale, oil, fats and water is called. The mill scale sludge that occurs in the course of the waste water treatment of the steelworks or rolling mill is made usable through special processes and devices.

In EP 0373577 A1, for example, a device and a method for processing sewage or industrial sludge with organic components by means of a conversion process are taught. As part of this conversion process, the sludge is mechanically pre-dewatered, conveyed into the interior of an indirectly heated continuous conveyor and there exposed to heating while the volatile components are expelled at the same time.In a subsequent second stage, the sludge is left at the conversion temperature to expel the remaining volatile components from the solid product. In practice, this procedure turns out to be comparatively inefficient, since the required low hydrocarbon contents cannot be achieved by the device shown and the procedure under economic circumstances.

DE 19715839 A1 deals with a method and a device for cleaning oil- and water-containing mill scale sludge, the sludge being subjected to vacuum drying in a second drying step. Again, practice shows a relative inefficiency of this system, as well as the associated high construction and operating costs.

The present invention is therefore based on the object of overcoming the disadvantages of the prior art, and of developing a simple and economical method and a suitable device for carrying out the method mentioned, and thus of producing a recyclable product.

This object is achieved according to a method according to the invention according to the characterizing part of claim 1 and according to a device according to the invention according to the characterizing part of claim 17.

The fact that the second process step, that is to say the further heating of the sludge to drive off the remaining volatile components, takes place with the addition of oxygen, brings about a considerable acceleration of this process step compared to the prior art. The oxygen acts specifically on the hydrocarbons contained in the mill scale sludge, thus lowering the reduction temperature and causing the hydrocarbons to evaporate more quickly.

According to various embodiments of the invention, the oxygen can be provided, for example, as pure oxygen or as a component of a gas mixture, in particular in the form of air.

By separating the hydrocarbons from the mill scale sludge according to the invention, the end product of the mill scale sludge treatment can also be used in sintering plants or other facilities which require a low content of hydrocarbons

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According to the invention, in the first process step, the dryer is heated, in particular indirectly, whereupon the water contained in the mill scale sludge evaporates at an internal temperature of 100 to 120 ° C, preferably about 105 ° C. Once the water has evaporated, a further rise in temperature is brought about in the second process step, with volatile hydrocarbons leaving the sludge and changing into their respective gas phases. By introducing oxygen, which in particular accelerates the ongoing reactions from 140 ° C, a partially exothermic oxidation of the hydrocarbons to carbon monoxide and / or carbon dioxide takes place, and furthermore an exothermic, partial oxidation of the iron oxide, in particular from wüstite to haematite and / or Magnetite, and the associated acceleration of the heating and the cracking processes, whereby more short-chain hydrocarbons are formed. At least part of the oxygen introduced is consumed as a result of these reactions.

In contrast to the prior art, the exhaust gas of the present process according to the invention contains a large proportion of short-chain hydrocarbons, which significantly simplifies the further exhaust gas treatment.

The oxidation of the wustite to haematite and / or magnetite is basically not intended, since reduction work has to be applied, especially when used in a reduction unit in the iron and steel industry, but this oxidation takes place in a strongly exothermic reaction, which means that the temperature in the interior of the Dryer increases quickly and without additional heating. In addition, the oxidation of the hydrocarbons also contributes to the further heating of the mill scale sludge. From a temperature of 180-200 ° C., the conversion of the liquid phases is essentially complete, whereupon there is a sharp rise in temperature due to the course of exothermic reactions, in particular the oxidation of the wustite to haematite and / or magnetite.

According to a preferred embodiment of the invention, the second process step takes place at a temperature, based on the feedstock, of 130-250.degree. C., particularly preferably in a temperature range of 140-200.degree.

The partial oxidation of the iron contained in the mill scale sludge in the process results in a cooling effect when the end product is added, for example in an electric furnace, as is desired in some metallurgical processes. On the one hand, the heat of the exothermic oxidation of the iron is used in the mill scale sludge treatment and, on the other hand, the cooling effect of the processed mill scale sludge is used in the metallurgical process.

Since the supply of oxygen in the second process step of the process according to the invention brings about a sharp increase in temperature, the supply of oxygen can be limited by supplying nitrogen to the dryer and the temperature can thus be adjusted.

Compared to the prior art, in particular a shortened treatment time of the sludge, a lower process temperature and more economical operation of such a device and such a process are achieved.

The use of the method and the device is not limited to the application for treating a mill scale sludge, but is most extensively documented for this case. The subject matter of the invention can also be used for the treatment of other hydrocarbon-containing sludges in the metalworking industry, such as those obtained, for example, in the production and processing of aluminum, titanium or copper. Furthermore, hydrocarbon-containing sludges from the non-metalworking industry can also be treated according to the inventive method and / or the inventive device.

According to further embodiments of the invention, the dryer according to the invention also fulfills the function of a mixer and / or granulator.

The parameters, in particular the treatment temperature, of the first process step can in principle be selected independently of the parameters of the second process step, but it is expedient to adapt the process parameters.

According to a feature of the invention, the treatment of the sludge, in particular the second process step, takes place essentially quasi-continuously.

Systems and methods according to the preamble of claim 1 or 17, insofar as the subject 3

AT 409 096 B known from the prior art, are characterized by discontinuous or batch operation. Compared to these modes of operation, a quasi-continuous or continuous process is characterized by increased economic efficiency, and more efficient recycling of the exhaust gases can also be achieved.

In a quasi-continuous mode of operation, a smaller part of the treated material than the total material in the dryer is discharged from the dryer, while untreated material is introduced into the dryer. In contrast to the continuous mode of operation, this exchange does not necessarily take place continuously, but rather, for example, at different times. The sludge can preferably be introduced into the dryer via an intermediate bunker with a corresponding metering device.

Compared to a continuous mode of operation, the quasi-continuous operation is characterized by its high process reliability.

The method according to the invention and the device according to the invention are also suitable for a continuous mode of operation.

According to an additional feature of the invention, the exhaust gases, which mainly consist of CO, CO₂, O₂, as well as gaseous hydrocarbons, withdrawn from the reaction chamber and subjected to recycling.

According to a further feature of the invention, the sludge is mechanically pre-dewatered and / or pre-dried before the thermal treatment. The pre-drying or pre-dewatering already removes a high percentage of the water from the mill scale sludge, which significantly reduces the throughput and treatment times in the dryer.

According to an additional inventive feature, the temperature of the sludge is measured indirectly or directly, and / or the carbon monoxide and / or the carbon dioxide and / or the oxygen content of the exhaust gas from the thermal treatment of the sludge, and on the basis of the measured variables determined, a control of the Parameters of the process carried out.

By evaluating these different measured variables, precise conclusions can be drawn about the progress of the reaction, for example in a dryer. In this way, a product can be manufactured that has a consistent composition and meets the high quality standards of the iron and steel industry. In particular when utilizing the end product of the process according to the invention in a sintering plant and / or a blast furnace and / or another facility of a steelworks, the treated mill scale sludge must not exceed a maximum hydrocarbon content in the range from 0.1 to 0.2% by mass.

The temperature measurement is preferably carried out with thermocouples, which are guided into the working area of ​​the dryer in a protective jacket tube.

According to a preferred embodiment, the treatment of the mill scale sludge in a dryer can be controlled by means of several recorded measured variables, for example by the, preferably indirect, heating of the dryer and by the amount of oxygen supplied.

The consideration of further regulating and control variables, such as the setting of the treatment time of the material in the dryer, preferably as a function of the product temperature reached, in particular when designing a quasi-continuous process, are the subject of further preferred embodiments of the invention.

According to a particularly preferred embodiment of the invention, the first and the second process step according to the invention are carried out in a single dryer, in which case the installation of a further dryer is omitted, and thus considerable investment and operating costs are saved. Such a dryer is operated discontinuously, that is, in batches.

According to a further feature of the invention, the first method step is carried out in a first dryer and the second method step is carried out in a second dryer. This enables a particularly reliable and safe mode of operation of the inventive method.

In this case, a batch operation or a quasi-continuous operation, at least the second process step, is possible. A continuous development of the entire process can also be considered.

According to a further preferred embodiment of the invention, the thermal and optionally mechanical dewatering and / or drying to be subjected,

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Sludge taken from the last stage of a multi-stage sedimentation and filtration process.

According to the prior art, this sludge represents a considerable disposal problem, since it has a particularly high content of hydrocarbons. The process according to the invention also enables these sludges to be reused.

According to a feature of the invention, the exhaust gas from the dryer is passed into a dedusting device. The dedusting device is preferably operated at a temperature which essentially corresponds to the temperature of the dryer. According to further features of the invention, the dedusting device is thermally insulated and / or additionally, for example indirectly, heated, so that precipitation of the hydrocarbons, in particular of higher-boiling fractions, on cold surfaces is prevented. The temperature of the dedusting device is set at least as high as the process temperature for the expulsion of the hydrocarbons in the dryer.

According to a further feature of the invention, the exhaust gas, optionally from the dedusting device, is introduced into a condenser, where it is depressurized and / or cooled, and also partially freed from impurities.

According to a further embodiment of the invention, at least one pipe, which is used to conduct the exhaust gas from the dryer, in particular into the dedusting device and / or from the dedusting device into the condenser, is additionally, preferably indirectly, heated. This prevents hydrocarbons, in particular higher-boiling fractions, from precipitating in the pipe. The set temperature is at least as high as the process temperature for evaporating the hydrocarbons from the sludge.

According to an additional feature of the invention, the exhaust gas, preferably pre-dedusted, is filtered in an activated carbon filter and freed of residual hydrocarbons, such as those that cannot be separated in a condenser, for example.

According to a further feature, the exhaust gas, preferably pre-dedusted, is particularly preferably burned in incinerators in the iron and steel industry, for example in a pusher furnace. In this way, it may be possible to dispense with the attachment of a condenser or the condensation of the hydrocarbons.

The method according to the invention preferably produces a substance in which the metallurgical substance, in particular the mill scale sludge or the sludge from the water treatment of a continuous casting plant, which has been treated according to the method according to the invention, has a hydrocarbon content of less than 0.2% by mass, preferably less than 0.1 mass⁰/), and an iron oxide content of at least 80% by mass, preferably of at least 84% by mass, is characterized.

According to a further characteristic, the metallurgical material has a content of essentially 60-80 mass⁰/ »Iron, in particular 63-72% by mass of iron, of which about 50-60% by mass of FeO and about 30-40% by mass of Fe₂O₃ on.

Due to its composition, the product according to the invention is particularly suitable for use in the EAF, in the blast furnace, or other, preferably metallurgical , aggregates. The quality of the composition of the rolled steel scale treated by the method according to the invention corresponds to that of fine iron ore of good quality.

The invention is further characterized by a device for carrying out the method according to the invention, which provides a number of, preferably indirectly, heatable dryers, on each of which one or more lines are provided for the targeted supply of oxygen and optionally nitrogen.

It has been shown that, due to environmental considerations, indirect heating has various advantages over direct heating of the dryer. With indirect heating, for example, the waste heat from other areas of a steelworks can be used. According to a particularly preferred embodiment of the invention, the heat from the combustion of the exhaust gas of the process is used.

According to a preferred embodiment of the device according to the invention, at least one heat-insulated and / or, preferably indirectly, heatable dedusting device is provided after the dryer.

The dedusting device removes coarse particles and dust from the hot exhaust gas.

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According to a further preferred embodiment of the invention, a number of condensers are provided after the dryer, optionally after the dedusting device. The condenser, as known from the prior art, expands the exhaust gas and cools it down, with higher-boiling constituents of the gas, in particular hydrocarbons, being separated out.

According to one feature of the invention, a number of heat-insulated and / or, in particular indirectly, heatable tubes are provided, which serve to conduct the exhaust gas from the dryer, in particular into the dedusting device and / or from the dedusting device into the condenser.

The tubes are heated in order to prevent the tubes from clogging by hydrocarbons, which have a particularly high evaporation temperature and are therefore preferentially deposited on cold surfaces.

According to a further feature of the invention, an activated carbon filter is attached after the dryer, optionally after the dedusting device, particularly preferably after the condenser. The exhaust gas is further freed of hydrocarbon residues through the activated carbon filter.

According to an additional feature of the invention, one or more lines are provided for at least partial return of the gas from the condenser and / or the dedusting device and / or the activated carbon filter into the dryer.

This enables the exhaust gas to be recycled in the dryer.

According to a further feature of the invention, two condensers are attached after the dryer, optionally after the dedusting device, a first condenser for condensing the water vapor and a second condenser for condensing the hydrocarbons. Via an attached control device, for example when using a single dryer to carry out both process steps of the process according to the invention, the exhaust gas can be introduced into a first condenser for separating the water during the first process step and into a second condenser for separating the hydrocarbons during the second process step . In this way, the supply of the gas to be condensed into the respective condenser can be regulated via the regulating device.

According to a further feature of the device according to the invention, a number of probes and / or sensors are attached to the line for the targeted supply of oxygen into the dryer and / or to at least one exhaust gas line, the oxygen and / or carbon monoxide and / or content of the gas being or carbon dioxide, and / or the temperature of the gas can be determined. Exhaust pipes are defined as all pipes for discharging the exhaust gases from the dryer.

The method according to the invention and the device according to the invention are explained in more detail below with the aid of non-restrictive drawings.

1 shows an apparatus for carrying out the first method step of the method according to the invention.

2 shows an apparatus for carrying out the second method step of the method according to the invention according to a quasi-continuous mode of operation.

Fig. 3 shows a device for performing the first and second method step of the method according to the invention.

4 shows a device for carrying out the second method step of the method according to the invention with at least partial recirculation of the process exhaust gas.

In FIG. 1 it can be seen: backwash water 1 from a sand filter is fed to a thickener 2. A flocculant 3 may be added to the backwash water 1 in order to promote the settling or separation of solids contained in the backwash water 1. The sand filter, not shown in the drawing, represents the last stage of the multi-stage separation and / or filtration process.

In the thickener 2, scale sludge with a high hydrocarbon content is deposited, overflow water 4 from the thickener 2 can be circulated and thus, for example, be used again as a flushing medium for loaded sand filters.

The thickener 2 is connected to an intermediate sludge container 6 via a sludge line 5

AT 409 096 B connected, the intermediate sludge container 6 being provided with a stirring device 7 in order to avoid further settling of the sludge and to keep the sludge pumpable.

The intermediate sludge container 6 is connected to a combined dryer / mixer / granulator 9 via a further sludge line 8. The dryer / mixer / granulator 9 is designed in a simple embodiment as a variable-speed ploughshare or paddle mixer and operates in batch mode in the embodiment shown in FIG. 1.

Since scale sludge is continuously fed to the thickener 2, there are several embodiments for the transition from the continuously operated thickener 2 to the dryer / mixer / granulator 9 operated in batches. As shown in FIG. 1, an intermediate sludge container 6 can be provided; furthermore, as also shown in FIG. 1, a return line 10 branches off from the sludge line 5, through which sludge is circulated via the thickener 2. Finally, it is also possible to dimension the thickener 2 in such a way that, under the given operating conditions, it is always capable of supplying the dryer / mixer / granulator 9 with a batch of scale sludge. Each of these three embodiments can be used alone or in combination with one or both of the others.

The dryer / mixer / granulator 9 is provided with a heating jacket 11 through which a heating medium 12 flows. The heating medium 12 can be liquid or gaseous, heat transfer oil preferably being used as the liquid heating medium, but superheated, pressurized water can also be used. As a gaseous heating medium, for example, one of the process or exhaust gases occurring in a steelworks can be used, for example Exhaust gas from an electric furnace, a converter or a walking beam furnace or top gas from the reduction shaft of a COREX system. Saturated steam, superheated steam or technical nitrogen can also be used as the gaseous heating medium.

The dryer / mixer / granulator 9 can be heated directly or indirectly, with a heat transfer system being provided with indirect heating, by means of which heat from one of the process or exhaust gases to the heating medium 12, which with indirect heating preferably heat transfer oil, superheated steam, saturated steam or Nitrogen is transferred.

The water vapor 13 emerging from the dryer / mixer / granulator 9 is condensed in a condenser 14 (with cooling water lines 18 and 19) and can be used as make-up water 15 for the closed circuits of a water treatment plant.

According to one possible embodiment, the dryer / mixer / granulator 9 is connected to a container 16 for binding agent 17, wherein binding agent 17 is added to the dryer / mixer / granulator 9 after a batch of scale sludge has been dried. A low moisture content of the binder can also be tolerated, since this moisture is also removed. The dryer / mixer / granulator 9 is then switched to the “granulating” operating mode by increasing the speed.

If no binder is added, the dry product 20 is finally in powder form with a particle size of approximately 1 to 200 μm, with binder addition and granulation as granules with a particle size of approximately 1 to 10 mm.

The plant according to the exemplary embodiment from FIG. 1 is able to process scale sludge from a hot rolling mill - with a capacity of around 3 million tonnes broad band per year.

In such a hot rolling mill, for example, about 420 kg / h of scale and about 12 kg / h of hydrocarbons are produced in the sand filters - the last stage of the multi-stage sedimentation and / or filtration process. The sand filters are backwashed with water and this backwashing water, which is laden with scale and hydrocarbons, is fed to a thickener 2. In the thickener 2, the hydrocarbon-containing scale sludge is dewatered to such an extent that it has a dry substance of approximately 35%. This dewatered scale sludge is transferred in batches to the combined dryer / mixer / granulator 9, where it is dried at about 110 ° C. to a residual moisture content of <3%. The dryer / mixer / granulator 9 is heated with saturated steam (5 bar, 1000 kg / h). The steam 13 evaporated from the scale sludge is stored in a condenser 14 (cooling water requirement approx. 16 m³/ h, 25 ° C) and the condensate (about 800 kg / h, 40 ° C) used as make-up water 15 in a water treatment plant.

The finished granulate 20 can then be further processed in a suitable manner (see FIG. 2).

According to Fig. 2, a device for performing the second method step of the invention

AT 409 096 B illustrated method according to the invention, wherein a dryer 21 is charged via a conveying line 22 with, preferably pre-dewatered and pre-dried mill scale sludge. The mill scale sludge has already been treated by thermal treatment in accordance with the first process step of the process according to the invention (see FIG. 1) and has a low water content and a high content of hydrocarbons.

Oxygen is fed to the dryer 21 via a number of lines 23. In addition to oxygen, other gases, preferably nitrogen, can be introduced into the dryer. A quasi-continuous process is shown in FIG. 2, the mill scale sludge being conveyed through a dryer and finally transported away through a line 24 for further use. The exhaust gases produced in the dryer are introduced via a heated line 25 into a heat-insulated and heated gas dedusting device 26, the gas being separated from dust which is discharged via a line 27. The gas is conveyed further via a heated line 28 into a condenser 29, expanded and cooled in this condenser, and the condensed liquid is discharged via a drain 30. A number of cooling lines 31, 32 are provided for cooling the condenser.

Finally, the gas reaches an activated carbon filter, for example, and is freed from further impurities, for example residual hydrocarbons. According to another embodiment of the invention, the exhaust gas is fed to an afterburning.

The dryer in FIG. 2 is preferably heated indirectly, with a heating medium 33 flowing through the jacket of the dryer. A number of valves and sensors or probes are provided on the various lines for transporting the, in particular gaseous, media, through which the flow rate, the composition or other measured variables are recorded or controlled. In this case, sensors for recording the oxygen content 34, as well as flow meters / valves 35 for controlling the flow rate are attached to the line 23 for supplying the reaction gas, in particular the oxygen. A sensor 36 for determining the temperature of the heating medium is attached to the line for supplying the heating medium 33 and to the line 37 for discharging the heating medium. The pressure drop in the exhaust gas is determined at the gas dedusting device via a sensor 38. Finally, after the condenser, a probe 40 for determining the carbon monoxide, carbon dioxide and oxygen content is provided on a line 39 for discharging the residual gas.

The process temperature is recorded by temperature measuring sensors 48 and represents a guide value for the process control.

3 shows a further preferred, non-limiting embodiment of a device for carrying out the method according to the invention, the first and the second method step being carried out in a single dryer.

The device differs from the embodiment shown in FIG. 2 in that two capacitors 41, 42 are provided. In this case, a condenser 41, corresponding to the condenser 14 in FIG. 1, serves to condense water vapor, and a second condenser 42, corresponding to the condenser 29 in FIG. 2, serves to condense the hydrocarbons.

The device shown is operated in batches (batch operation), the path to the first condenser 41 being closed by means of a slide after the water has evaporated and the path to the second condenser 42 being opened.

4 shows a device for carrying out the second method step of the method according to the invention with at least partial recirculation of the process exhaust gas.

In this case, a dryer 21 'is charged with preferably pre-dewatered and pre-dried mill scale sludge via a conveying line 22'. The mill scale sludge has already been treated by thermal treatment in accordance with the first process step of the process according to the invention (see FIG. 1) and has a low water content and a high content of hydrocarbons.

Oxygen is fed to the dryer 21 'via a number of lines 23'. In addition to oxygen, other gases, preferably nitrogen, can be introduced into the dryer. A quasi-continuous process is shown in FIG. 4, the mill scale sludge being conveyed through a continuous dryer and finally transported away through a line 24 'for further use. The exhaust gases produced in the dryer are introduced into a heat-insulated and heated gas dedusting device 26 'via a heated line 25', the gas being released from

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Dust, which is discharged via a line 27 ', is separated. The gas is conveyed further via a heated line 28 'into a condenser 29', expanded and cooled in this condenser, and the condensed liquid is discharged via a drain 30 '. A number of cooling lines are preferably provided for cooling the condenser.

Finally, the gas reaches an activated carbon filter 43 'and is freed from further impurities, for example residual hydrocarbons.

The cleaned gas is now suitable for further use as a process gas, and at least part of the gas is introduced into a gas mixing device 45 'via a line 44'. Residual gas which is not suitable for further use as a process gas is discharged via a residual gas line 46 '.

In the gas mixing device 45 ', the recirculated gas is prepared with fresh gas 47', if necessary, before it is introduced into the mixer via the line 23 '.