EP2346600A2

EP2346600A2 - Energy-efficient system for generating carbon black, preferably in energetic cooperation with systems for generating silicon dioxide and/or silicon

Info

Publication number: EP2346600A2
Application number: EP09747848A
Authority: EP
Inventors: Jürgen Erwin LANG; Hartwig Rauleder; Bodo Frings; Mustafa Siray; Rudolf Schmitz; Dietmar Wewers; Peter Nagler; Rainer Wendt; Georg Markowz
Original assignee: Evonik Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2008-11-10
Filing date: 2009-11-05
Publication date: 2011-07-27
Also published as: EA201100742A1; WO2010052285A3; AU2009312760A1; CA2743231A1; US20110214425A1; WO2010052285A2; DE102008043606A1; TW201033297A; CN102209586A; KR20110093784A; BRPI0921349A2; JP2012508101A

Abstract

The object of the invention is a more energy-efficient system for utilizing waste heat and residual gases from the engineered generation of carbon compounds, such as carbon black, graphite or from sugar pyrolysis, using a coupling of energy-heat or a thermal heat-generating plant for generating electrical energy, in particular for operating melt furnaces, and/or for utilizing the waste heat in endothermal processes. The invention also relates to the use of waste heat.

Description

Energy-efficient plant for the production of carbon black, preferably as an energetic composite with plants for the production of silicon dioxide and / or silicon

The invention relates to the provision of a more energy-efficient plant for the utilization of waste heat and residual gases from the industrial production of carbon compounds, such as carbon black, graphite or from the sugar pyrolysis, by means of a combined heat and power plant or a thermal power plant for the production of electrical energy, in particular for the operation of melting furnaces, and / or the use of waste heat in endothermic processes and the corresponding use of waste heat.

The plant according to the invention can achieve a considerable process intensification in the production of silicon, which leads to a significant reduction of climate-damaging carbon dioxide and / or carbon monoxide and to a significantly reduced demand for electrical energy. In addition, by recycling of silicon oxide, which is formed in the reduction of silicon dioxide to silicon in the electric arc furnace, the material balance of the silicon used in the overall process can be significantly increased.

So far, the waste heat, ie the thermal energy that accumulates in the production of carbon black (carbon black), not technically and economically made available for other processes. The waste heat of the carbon black process is usually currently used for preheating or preheating of the educts, such as combustion air and oil, the same process. Accordingly, so far, the waste heat of the production of silicon, especially in the form of hot process gases, only quenched with air and directed to the separation of silicon dioxide through hot gas filter. The resulting tail gas in these processes is exuded. A utilization of the significant amounts of thermal energy from the carbon black or silicon production to save energy in other processes has not been possible. Especially in the production of high purity carbon blacks or of silicon, which is suitable for the production of solar silicon or for the production of semiconductor silicon, the transfer of excess thermal energy due to the necessary spatial separation of certain processes for producing high purity products was unthinkable. The extremely high demands on the respective purity of the products and the possibility of a mutual contamination categorically excluded this possibility.

As a method for producing carbon blacks, the gas black method (DRP 29261, DE-PS 2931907, DE-PS 671739, Carbon Black, Prof. Donnet, 1993 by MARCEL DECCER, INC, New York, page 57 et seq.) Is known a hydrogen-containing carrier gas laden with oil vapors is burned at numerous outlet openings in excess air. The flames strike against water-cooled rolls, which stops the combustion reaction. A part of the soot formed inside the flame is deposited on the rollers and is scraped off by them. The soot remaining in the exhaust stream is separated in filters. Further, the Channel Black method (Carbon Black, Prof. Donnet, 1993 by MARCEL DECCER, INC., New York, page 57 et seq.) Is known in which a plurality of natural gas-fed small flames burn against water-cooled iron channels. The soot deposited on the iron chutes is scraped off and collected in a funnel.

In the processes mentioned produces a large amount of waste heat, especially in the form of hot residual gases with temperatures below 200 ⁰ C, such as hot steam. The furnace carbon black process produces tail gas as residual gas.

So far, the waste heat is partially removed from the gases, for example via capacitors, then the gases are purified and blown into the environment. The extracted waste heat is not yet widely used. Due to the finely particulate structure of the soot, contamination of other parts of the system with soot can not be ruled out. For this reason, such plants have not been combined at a production facility with other facilities that have also been used to produce high purity compounds.

On the other hand, for example, in the production of silica, especially silica such as precipitated silica or silica which has been ion-exchanged, the drying step requires extra energy to dry the wet silicas.

The object of the present invention was to develop an energy-efficient plant and to provide an efficient use of the thermal energy in the production of carbon black, and in particular of silicon dioxide. Another task was to develop an overall system that makes it possible to use the thermal energy with a high degree of efficiency for an overall process or the overall use in the production of silicon.

The objects are achieved by the system according to the invention, in particular as a total or partial system, and the use according to the invention according to the features of the independent claims, in the subclaims and in the description, preferred embodiments are disclosed.

According to the invention, an object is a complete plant 2 with a reactor 4.1 for the thermal conversion of carbon-containing compounds, wherein the reactor is connected to a combined heat and power 5.1, decoupled via the part of the waste heat 5.3 from the thermal conversion and another part of the Waste heat is converted into electrical energy 5.2, wherein the decoupled waste heat 5.3 in the process for producing silicon oxide, in particular in a process step in the production of silicon dioxide, in the device 7.1 is being used. Particularly preferably, the waste heat is used directly or indirectly for heating or Temperarturregelung the precipitation vessel to form precipitated silicas or silica gels and / or for drying of silica, in particular of silica, such as precipitated silica or silica gels, which has been purified by ion exchanger, used in the device 7.1, in particular the waste heat is 5.3 guided via heat exchanger 8, preferably in a secondary circuit. According to a preferred alternative, a direct drying of SiO ₂ with superheated steam 5.3 can take place, as shown in FIG. ₂ b or 2 c. With low temperature steam 5.3, contact dryers as described below can be operated.

The recovered electrical energy from the combined heat and power 5.2 can be used to power a reactor 6.1 for the reduction of metallic compounds, for the production of silica, particularly preferably in the production of precipitated silica, fumed silica or silica gels and / or preferably for drying and / or for temperature control during precipitation, are used in the device 7.1. Likewise, the use of electrical energy for the operation of a device in the production of pyrogenic oxides, such as fumed silica, is possible. In a possible embodiment, the electrical energy can be used in the desorption for HCI recovery in this process. The overall system allows the silica and the soot production to be provided at one site and, if appropriate, to provide the reactor 6.1 for the reduction of metallic compounds via a power grid at another location.

For power-heat coupling, the person skilled in the well-known devices 5.1 or 5.1 systems can be used. The combined heat and power has a much better efficiency than the pure power generation of thermal thermal power plants. The total efficiency of combined heat and power can be up to 90 percent in particularly preferred cases. there can the combined heat and power according to the invention not only flow and heat, but also exclusively flow or heat operated operated. A combined heat and power plant usually works with hot steam, which drives steam turbines, which then takes power generation. The decoupling of water vapor and feed into a heat exchanger, preferably in processes for the production of silicon dioxide, such as for temperature control or for drying of silicon oxide, in a device 7.1, usually takes place before the last turbine stage. In the system according to the invention, the decoupling can be carried out expediently also after the last turbine stage. Usually, for example, the temperature control of a precipitation vessel or the drying of the silicon oxide, such as precipitated silica or a silica gel, via heat exchangers, ie via a secondary circuit. Likewise, an immediate use of the waste heat for drying is possible, as described above. Cogeneration may relate the waste heat from carbon black production, such as preferably after the quench zone or other hot reactor parts, for example via heat exchangers or direct use of the process vapors and / or combustion of the tail gases, which in turn may serve to produce steam , Preferably, the cogeneration is operated with steam. The tail gases include water vapor, hydrogen, nitrogen, Cx, carbon monoxide, argon, hydrogen sulfide, methane, ethane, ethene, ethyne, amides, nitrogen-containing compounds, metal oxides such as aluminum oxides and / or carbon dioxide. Preferably, the cogeneration operates in the back pressure, whereby no thermal losses occur in the steam cycle. As a result, there is usually no need for fresh cooling water.

According to the invention, a carrier gas after the preheating zone of the combustion air and / or the waste heat from the combustion of the tail gases in 5.1 can be used as waste heat 5.3. With particular preference, superheated steam 5.3 from 4.1 or above 5.1 can also be used directly in a process for producing silicon dioxide as shown in Figures 2b and 2c, in particular for the direct drying of silica, such as silica gel or precipitated silica. Additionally or alternatively, a contact dryer (device 7.1), for example plate dryer or preferably a rotary tube dryer can be operated with low-temperature steam. With the current obtained from 5.1, preferably primary dryers, in particular nozzle tower dryers or spinflash dryers for drying silicon dioxide can also be operated.

According to the invention, it is possible to provide the soot production and the production of silicon oxide, in particular the precipitated silica or of the silica gel, in a production plant or in a common plant, because a possible mutual contamination of soot and silicon oxide for the production of silicon, in particular solar silicon in the reactor 6.1 is irrelevant for this overall process. This combination was hitherto unthinkable because contamination of carbon black with silica or silicon dioxide with carbon black was to be avoided. In the underlying processes for producing silicon from silicon oxide, in particular silicon dioxide, and carbon black and / or pyrolyzed carbohydrates, the silicon oxide in the reactor 6.1 is reduced to silicon, so that for this particular application the mutual contamination of high-purity soot, high-purity pyrolyzed carbohydrates or high purity silica does not bother.

Likewise preferred is the use of waste heat from the individual parts of the system or from the combustion of tail gas soot production by means of heat exchanger 8 via a secondary circuit to contamination of the high-purity carbon blacks containing compounds or high-purity silicon oxide, in particular silica, with other impurities such to prevent other metals. Another object of the invention is an overall system, such as Oa or Ob, in which a reactor 4.1 is connected to the thermal conversion of carbon-containing compounds with a combined heat and power 5.1, on the part of the waste heat 5.3, from the thermal reaction in 4.1, decoupled and another part of the waste heat can be converted into electrical energy 5.2, wherein the decoupled waste heat 5.3, in particular in processes for the production of silicon dioxide, is used in a device 7.1. In this case, the device 7.1 can be part of a plant for the production of silicon dioxide. Preferably, the waste heat 5.3 or the waste heat stream 5.3 for temperature control of a precipitation vessel and / or for drying of silica, in particular of silica, such as precipitated silica, silica gel or silica, which has been purified over ion exchanger, are used in the device 7.1. In this case, the decoupled waste heat in particular directly (see Figure 2b / 2c) or by means of heat exchanger 8, as in Figures 4a and 4b, and the electrical energy 5.2 to power a reactor 6.1 for the reduction of metallic compounds or in processes for the production of silicon dioxide, in particular used for the device 7.1 and optionally, in addition, the waste heat 6.2 from the reactor 6.1 for the reduction of metallic compounds in a process for the production of silicon dioxide, for example, for controlling the temperature or drying of silica in the device 7.1 are used. In alternatives, the combined heat and power can also be pure flow or heat.

For further optimization of the energy balance, it is preferred if the waste heat 6.2 of the reactor is used for the reduction of metallic compounds in the device 7.1, in particular the waste heat is 6.2 transferred via heat exchanger 8 from the reactor 6.1 in the device 7.1. This can be done by the waste heat, in particular a waste heat stream 6.2, the reactor 6.1 is connected to the device 7.1. In addition, the hot process gases from the reactor 6.1 for the reduction of metallic compounds via a hot gas line 6.3 are preferably introduced into the reactor 4.1 for the thermal conversion of carbon. A hot gas line 6.3 preferably connects the reactor 6.1 for the reduction of metallic compounds and the reactor 4.1 for the thermal conversion of carbon, in particular for the transfer of the hot process gases from the reactor 6.1 into the reactor 4.1.

Additionally or alternatively, the hot process gases from the reactor 6.1 for the reduction of metallic compounds via a hot gas line 6.3 in the combined heat and power 5.1 or in the thermal power plant 5.1 are conducted. Preferably, a hot gas line 6.3 connects the reactor 6.1 for the reduction of metallic compounds with the combined heat and power 5.1 or a thermal power plant 5.1, in particular for transferring the hot process gases from the reactor 6.1 in 5.1 for steam generation. This design of the system is shown by way of example in Appendix Oc in Figure 4c for all conceivable total or partial systems.

The hot gas line 6.3 of the systems Oa, Ob or 1 c according to the invention is designed so that it largely prevents condensation of the gaseous silicon oxide of the hot process gases, which arise in the production of silicon. The hot process gases usually include carbon monoxide, silica and / or carbon dioxide. The condensation of silicon oxide poses a considerable risk of detonation. Therefore, the hot gas line is provided on its inner surface with a so-called Beschleierung which reduces this condensation on the inner surface of the hot gas line, preferably prevented. As an alternative to the fogging, the hot gas line can be equipped with a tracing heater and / or have an air gas addition over the surface for temperature control, in particular for a reactive temperature increase, preferably in the wall area. By recycling the hot process gases the reduction step to molten silicon in 6.1 in the reactor 4.1, the yield of silicon by up to 20 mol .-% can be increased because the formed gaseous silica remains in the process. Thus, the overall process by the inventive system can also lead to an increase in yield of silicon in relation to the silicon oxide used. Due to the introduced heat of reaction of the hot gases also reduces the amount of natural gas in the production of soot.

The Beschleierung can be done for example via the generation of Votrex vertebrae. As a further constituent of the hot process gases, among other things carbon monoxide is transferred to the reactor 4.1. In the underlying process, the introduction of silica into the reactor does not interfere with the production of soot or pyrolysis of carbohydrates when the reaction products are used to produce silicon. In addition, the introduction of carbon monoxide in the hot process gases via the hot gas line into the reactor 4.1 there allows a favorable shift of the equilibrium of the hot gas in the combustion or thermal decomposition of the Rußrohstoffe or carbohydrate-containing compounds. As a result of the process procedure which is enabled in the system according to the invention, a significant reduction of carbon oxides, in particular of carbon dioxide, in the overall process for the production of silicon is accompanied.

Stream 7.2 schematically represents the stream again, directly or indirectly a product from the device 7.1, for example, a precipitation vessel or reactor for the drying of silicon dioxide, transferred to the reactor 6.1. In this case, the immediate product from 7.1 can still be fed to further processing, such as drying, grinding, granulation, tabletting, reaction or mixing with carbon black, carbohydrate or carbohydrate-containing compounds, or other processing or process steps, before the indirect product is fed to the reactor 6.1 , According to one alternative, the subject matter of the invention is a plant-part system according to the invention - 1 a with a reactor 4.1 for the thermal conversion of carbon-containing compounds, wherein the reactor is connected to a combined heat and power coupling 5.1, on the part of the waste heat from the 5.3 decoupled thermal conversion and / or another part of the waste heat is converted into mechanical or electrical energy 5.2, or, wherein the reactor 4.1 is connected to a thermal power plant 5.1, via which the waste heat is converted into mechanical or electrical energy 5.2. The electrical energy obtained can be fed into the public power grid, internally to the power supply or according to the invention for the operation of the electric arc furnaces in the production of silicon or for the production of silica, preferably precipitated silica or fumed silica or silica gels in precipitated silicas and silica gels particularly preferred for drying or heating of the precipitation tank.

In a possible embodiment, the electrical energy in the process for producing fumed silica, for example, in the desorption for HCI recovery can be used in this process. The decoupled waste heat can be fed into a district heating network, it being preferred to use the waste heat via heat exchangers in the process for the production of silicon dioxide, such as temperature control or drying of silica, in particular of silica for further use in the production of silicon.

As a reactor for the thermal conversion of carbon-containing compounds, all reactors for the production of carbon black, graphite, carbon or generally a carbon matrix-containing compound, for example, silicon carbide-containing carbons and other skilled in the art corresponding compounds. According to the invention, the reactor 4.1 for the thermal conversion of carbon-containing compounds is a reactor or furnace for the production of carbon black or for the combustion and / or pyrolysis of carbohydrates, For example, the pyrolysis of sugar, optionally in the presence of silica, for the preparation of carbon-containing matrices, for example in the presence of high-purity silica. Conventional reactors for the production of soot are operated at process temperatures of 1200 to over 2200 ⁰ C in the combustion chamber. The best known methods of producing carbon black are the Lamp Black process, the Furnace Black process, the Gas Black process, the flame black, acetylene black or thermal black process. Accordingly, the reactor 4.1 is preferably designed for carrying out the said processes. For the system according to the invention, a reactor known from the prior art is preferably used for the production of carbon black or for the thermal conversion of carbon-containing compounds. Such reactors are well known to those skilled in the art.

Common reactor types generally include all furnaces suitable for carbon black production. These in turn can be equipped with different burner technologies. An example of this is the Hüls ^' arc furnace (arc). For the selection of the burner, it is crucial whether a high temperature in the flame or a fat flame should be generated. As aggregates, the reactors may include the following burners: gas burners with integrated combustion air blower, gas burners for wired air flow, combination gas burners with gas injection via peripheral lances, high-speed burners, Schoppe impulse burners, parallel diffusion burners, combined oil-gas burners, burst furnace burners, evaporative oil burners, burners with air or steam atomization, flat flame burners, gas-heated radiant tube, and all burners and reactors, which are suitable for the production of carbon black or pyrolysis of carbohydrates, such as sugar, optionally in the presence of silica. As the reactor 4.1, the entire reactor or even parts of the reactor is understood, for example, the reactor comprises the reaction chamber, a combustion zone, a mixing zone, reaction zone and / or quench zone. According to the invention recuperators are used in the quench zone, such as radiation recuperator with a ring of steel pipes.

A further alternative embodiment provides for a combination in which the system 1 b or 1 b. 1 according to the invention comprises, as a unit, a reactor 4.1 for the thermal conversion of carbon-containing compounds, the reactor being connected to a cogeneration 5.1 can be decoupled over the part of the waste heat 5.3 from the thermal conversion and / or another part of the waste heat can be converted into mechanical or electrical energy 5.2, or, the reactor 4.1 with a thermal power plant

5.1 is connected, via which the waste heat into mechanical or electrical energy

5.2 is converted and the electrical energy 5.2 for supplying energy to a reactor 6.1 for the reduction of metallic compounds, in particular an electric arc furnace 6.1 electric melting furnace, thermal reactor, induction furnace, melt reactor or blast furnace, preferably for the production of silicon, or for the power supply of a device 7.1 in the Production of silicon dioxide, such as for controlling the temperature of a precipitation tank, for drying of silicon oxide, such as SiO 2, or for the operation of a device in the process for the production of fumed silica is used.

The person skilled in the art knows that 5.1 can also be operated in such a way that only the waste heat 5.3 or electrical energy 5.2 or any mixed forms are used. In this case, the decoupled waste heat 5.3 is conducted to the device 7.1, in particular the waste heat is transferred via a heat exchanger 5.3 5.3 or used directly as superheated steam (Figure 2b and 2c), preferably the device 7.1 part of a plant for the production of silica.

In all variants of the systems according to the invention, the produced carbon black, the pyrolyzed carbohydrate, can be indirectly or directly above the electric arc furnace via 4.2 6.1 are supplied. Indirect means that the compounds prepared in the reactor 4.1 can be further processed before they are fed to the reactor 6.1. By way of example, but not limitation, the carbon black or carbon-containing compound may be pelleted or briquetted.

It is particularly preferred according to the invention, if the system has a supply line 6.3 of the hot process gases from the reactor 6.1 for the reduction of metallic compounds via a hot gas line 6.3 in the reactor 4.1 for the thermal conversion of carbon, as exemplified for the systems 1 c and Ob is shown. According to a preferred embodiment, the plant, in particular the entire plant Oa allows the use of the waste heat 6.2 of the reactor 6.1 for the reduction of metallic compounds in processes for the production of silicon dioxide, such as for temperature control of precipitation tanks or in the drying of silica in the device 7.1, in particular the waste heat is 6.2 transferred via heat exchanger 8 from the reactor 6.1 in the device 7.1.

The device 7.1 may be a precipitation vessel for precipitation or gelation of SiO ₂ or a dryer, a tunnel kiln, rotary kiln, rotary grate furnace, fluidized bed, rotary kiln, circulating fluidized bed apparatus, continuous furnace and / or an oven for pyrolysis in all systems. Thus, directly superheated steam 5.3, which is obtained directly or indirectly in 4.1, for example by quenching with water, from the waste heat of 4.1 or via the combustion of the tail gases from 4.1, can be used for a drying of silicon dioxide (FIGS. 2b and 2c). ,

With low-temperature steam 5.3, the operation of contact dryers 7.1, for example, plate dryers or particularly preferably rotary kiln dryers offers. The current obtained via 5.1 5.2 can be used directly for the operation of primary driers. These are preferably nozzle tower dryers or Spin flash dryer. It is clear to the person skilled in the art that the abovementioned enumeration is only to be understood as an example and that other conventional dryers can also be used.

For the reactors 4.1 or 6.1 applies that the whole or parts of the waste heat produced there, such as the reaction zone, the hot reactor parts, steam by quenching with water in 4.1 or the waste heat of the reaction products, such as gases or other streams as used waste heat should be detected according to the invention. According to the invention, in particular the residual gas (tail gas) is burned and the waste heat generated is used in the plant according to the invention.

Preferably, the system operates continuously 24 hours a day, 7 days a week, so that the use of waste heat, directly or via the heat exchanger 8, in a continuous cycle, in particular via primary and / or secondary circuits occurs. The savings in energy that can be achieved per kilogram of dried silicon dioxide between 0.01 to 10 kWh, preferably 2 to 6 kWh, more preferably by 2 kWh. It is clear to the person skilled in the art that the respectively achieved energy balance depends directly on the residual moisture and the used drying device as well as other process parameters, so that the stated values are to be understood as indicative only. When using the obtained electrical energy of about 0.01 to 10 kWh, preferably between 0.1 to 5 kWh per kilogram of soot for the reduction of one kilogram of silicon dioxide to molten silicon, there is a potential savings of 1 to 10 kWh, in particular of 4 up to 9 kWh involving the process for the production of silicon dioxide. For the production of about one kilogram of molten silicon, the energy savings can increase to 5 kWh to 20 kWh, in particular, it can, considering the overall process, comprising the production of silicon dioxide and carbon black and their conversion to silicon, in the range of 17 kWh. According to a further preferred embodiment, the waste heat 6.2 can be used together with the waste heat 5.3 in a method for producing silicon dioxide for the device 7.1, preferably for temperature control or for drying of silica, in particular of precipitated silica or silica gel or precipitated silica or silica gel which (s ) Was purified by ion exchange. Preferably, the use of the waste heat 6.2 and / or 5.3 for drying the silica via one or more heat exchangers 8. The device 7.1 may be part of a system for the production of silicon dioxide in all systems.

Heat exchangers 8 are preferably used to prevent contamination of the silicon dioxide, in particular of high-purity silicon dioxide. In these heat exchangers, the waste heat from the reactor 6.1 is used by means of a secondary circuit in a process for the production of silicon dioxide, such as for drying of silicon dioxide or temperature control of a precipitation tank. Usually, in the heat exchangers and / or in the supply and discharge of the waste heat as a medium water, a conventional coolant or other media well-known to the skilled person used.

An expedient system 3 also provides for the sole use of the waste heat 6.2 from the reactor 6.1 for the reduction of metallic compounds 5.3 in processes for producing silicon dioxide in the device 7.1, in particular for controlling the temperature of a precipitation tank 7.1 or dryer 7.1 for drying silicon oxide, in particular the system 3 with the system 1 a connectable, preferably the waste heat 6.2 is passed from the reactor 6.1 in the device 7.1 by means of heat exchanger 8.

It goes without saying that the device 7.1, which may in particular be a reactor, precipitation vessel and / or dryer, is only part of a partial or complete plant for the production of silicon oxide and upstream and / or downstream other equipment or devices is connected or connectable, for example, to produce high-purity silica from contaminated silicates.

In particular, the supply line 7.2 in all systems is to be regarded as a direct or indirect supply line into the reactor or as a material flow into the reactor 6.1. Thus, the silica dried in 7.1 can be subjected to further processing steps before it is fed to the reactor 6.1. These are in particular grinding, formulating, briquetting. Also in these steps the electric energy flow according to 5.2 can be used.

According to the invention, the waste heat of the reactor 4.1 is used for the thermal conversion of carbon-containing compounds for the production of electrical energy, in particular by means of a combined heat and power or thermal thermal power plant. Waste heat is also the waste heat of the tail gases and the waste heat, which is produced by combustion of the tail gas. It is particularly preferred if the waste heat is used in whole or in part, in particular directly or indirectly, in processes for the production of silicon dioxide, such as for temperature control or for drying. Preferably, superheated steam from 4.1 and / or 5.1 in 7.1 can be used for drying or temperature control (FIGS. 2b / 2c).

This combined use of the waste heat according to the invention has hitherto been unthinkable for the person skilled in the art because the possible mutual contamination would have led to considerable problems in the process control. Only the combined use of silicon dioxide purified in or from aqueous systems and carbon black or pyrolyzed carbohydrates for the production of high-purity silicon makes this combined synergistic use of waste heat or thermal energy possible. The electrical energy obtained can preferably be used to operate a reactor 6.1 for the reduction of metallic compounds or for the operation of devices 7.1, in processes for the production of silicon dioxide, preferably for the operation of dryers, such as primary dryers, furnaces for the production of fumed silica for the production of silicon or for the temperature control of precipitation tanks or for the operation of other process steps, which work with electric current. As stated at the outset, the energy balance of the overall process, including the production of carbon black, the production of silicon oxide and / or the reduction of the silicon dioxide, improves considerably compared with known plants and the known use from the prior art.

Thus, the energy balance of the silicon dioxide process can be considerably improved in the particularly energy-intensive steps, such as, for example, the heating of the precipitation vessel or in drying steps of the silicon dioxide and further process steps, to which energy has to be supplied. By the combined process management, the consistent use of waste heat, combustible residual gases and / or the return of the hot gas from 6.1 all material cycles can be driven in the system with an improved energy balance over known methods of the prior art. Thus, the recirculation of the hot gases, which comprise carbon monoxide and silicon oxide, in particular gaseous SiO, into the reactor 4.1 leads to a process intensification, in particular the formation of carbon oxides COx during the process for producing carbon black in the overall balance can be reduced. The overall process in the overall plant according to the invention or in the subsystems leads to a considerable reduction of the carbon dioxide and / or carbon monoxide formed over the entire process in the production of silicon, in particular compounds containing silicon dioxide and carbon, such as carbon black or pyrolyzed sugar. According to the invention, the hot process gases from the reactor 6.1 for the reduction of metallic compounds in the reactor 4.1 are used for the thermal conversion of carbon in the reactor 4.1, in particular by being introduced via a hot gas line 6.3 from the reactor 6.1 in the reactor 4.1.

Also according to the invention, the hot process gases from the reactor 6.1 for the reduction of metallic compounds in the combined heat and power 5.1 or in the thermal power plant 5.1 can be used for steam and / or energy generation, in particular by a hot gas line 6.3 from the reactor 6.1 in 5.1.

According to a further aspect of the invention, the waste heat of a reactor 6.1 can be used for the reduction of metallic compounds in processes for the production of silicon dioxide, in particular in the device 7.1, such as temperature control vessel or dryer. In addition, the reactors 4.1 and / or 6.1 and the device 7.1 are usually in turn part of a plant for the respective process strands, d. H. 7.1 is, for example, a part of the silicon dioxide production, 4.1 is part of a plant for the production of carbon black or pyrolyzed carbohydrates, etc., and 6.1 can be part of a plant for the production of solar grade silicon with upstream and / or downstream further process stages.

It is clear to the person skilled in the art that the said systems can also have a multiplicity of reactors instead of in each case one reactor in the respective process stage; this can in particular permit continuous and / or uniform and uninterrupted execution of the overall process. The reactors can be operated continuously or discontinuously.

In general, as reactors 4.1 for the thermal conversion of carbon, in particular for the production of carbon black, preferably reactors of the analog type, as described in said patent, can be installed in the system. With regard to the disclosure content, reference is made in full to the disclosure of the reactors and their mode of operation of US Pat. Nos. 5,651,945, 6,391, 274 B1, EP 0 184 819 B1, EP 0 209 908 B1, EP 0 232 461 B1, EP 0 102 072 A2, EP 1 236 509 A1, EP 0 206 315 A1, EP 0 136 629 A2, US 4,970,059 and US 4,904,454.

The following figures illustrate the system according to the invention in more detail, without limiting the invention to this example.

References:

0a, Ob, 0c 1 a, 1 b, 1 c, 2, 2 a, 2 b, 2 c, 3: Alternative investments or

Plant combinations, total plant;

4.1: Reactor for the thermal conversion of carbon-containing

Compounds, for example reactors for the production of carbon black or for the pyrolysis of carbohydrate, such as the pyrolysis of sugar optionally in the presence of silicon dioxide;

5.1: Combined heat and power, thermal heat and power plant,

6.1: reactor, for example, electric furnace, induction furnace, electric arc furnace;

7.1: Apparatus for use for the production of silicon dioxide, for example in a drying stage, preferably a dryer, for example fluidized bed reactor or other reactor for drying substrates, a reactor, an apparatus in the process for producing fumed silica, or a precipitation vessel;

8: heat exchangers, preferably they have a secondary circuit and allow the dissipation of waste heat (thermal energy) of processes, in 4.1 and / or 6.1, and the supply of thermal energy in endothermic processes, in particular in 7.1 for drying;

4.2: Material flow, for example, supply line (s), the direct or indirect supply of the product from 4.1, which previously one Further processing, such as briquetting, can be fed into the reactor 6.1 allows;

5.2: electrical energy flow, for example, line for conducting electrical energy;

6.2: thermal energy flow, for example, line (s), in particular with connected heat exchangers 8, to use the waste heat from 6.1 in 7.1, preferably as a secondary circuit;

7.2: Material flow, for example supply line (s) and, if necessary

Production levels over which directly or indirectly the product from 7.1 into the reactor 6.1 can be converted, wherein the immediate product of 7.1 nor a further processing, such as drying, grinding, granulation, tabletting, reaction or mixing with carbon black, carbohydrate or carbohydrate-containing compounds, or other processing or process steps can be supplied before the indirect product is fed to the reactor 6.1;

5.3 thermal energy flow or energy flow, such as superheated steam or

Low-temperature steam, which is used for example by pipes, optionally with connected heat exchangers 8, to use the waste heat from 4.1, which is decoupled over 5.1, for drying or tempering in 7.1;

6.3: Hot gas line.

The figures show:

Figure 1 a, 1 b, 1 b.1, 1 c: Alternative plant combinations or sub-combinations of reactors for the production of carbon black together with a combined heat and power, optionally together with reactors for the production of solar grade silicon.

FIGS. 2, 2a, 2b and 2c show combinations according to the invention of installations in which a tempering step or drying step is involved in the production of

Silicon dioxide via a combined heat and power (5.1, 5.3 and 5.2) energetically Waste heat from the production of soot (4.1) uses. According to Figure 2c, steam from the

Quench zone be introduced by 5.1 in 7.1 as superheated steam.

Figure 3 shows the use of waste heat from a melting furnace for the production of

Silicon in the production of silicon dioxide.

FIGS. 4a, 4b and 4c each show possible overall systems (Oa, Ob or Oc) for

Production of silicon with production stages from the silicon dioxide and the

Carbon black production.

FIG. 1 a shows a system 1 a with a reactor 4.1 for the thermal conversion of carbon-containing compounds, the reactor being connected to a combined heat and power system 5.1 via which part of the waste heat 5.3 is decoupled from the thermal conversion and another part is converted into mechanical or electrical energy 5.2. Via the line 5.3, the decoupled heat is dissipated. Depending on the process, the entire waste heat or a portion of the waste heat for temperature control of the device can be used 7.1 or for energy. With the waste heat, a precipitation tank can be tempered or dryer 7.1 can be operated. About 5.2, the generated electrical energy can be forwarded. The electrical energy can be fed into the public power grid, used in the process for the production of silicon dioxide or directly in an overall process for the production of silicon in an electric furnace, for example an electric arc furnace 6.1. According to Appendix 1 b 5.1 can be used exclusively for power generation, whereby the power can also be used to operate 7.1 or other parts of the system. FIG. 1 c illustrates the combination of system 1a with a reactor 6.1. System 1 c can be part of an overall system and additionally has a hot gas line 6.3 between 4.1 and 6.1.

The plants 2 and 2a represent combinations according to the invention, the use of waste heat (5.3) and the generated electrical energy (5.2) in the process for the production of silicon dioxide, which via a combined heat and power (5.1) is particularly suitable for the production of silicon, in particular of solar silicon, allow. Alternatives show the systems 2b and 2c, in which no heat exchangers are used in 7.1. The process is operated directly with superheated steam.

The plants - total plants - Oa, Ob and Oc also show plants according to the invention, which are in particular part of an overall plant for the production of silicon, in particular of solar silicon, in which the waste heat from the reactors 4.1 and 6.1 in a device 7.1, for example, precipitation tank or dryer , in the production of silicon dioxide, for example from wet chemical processes, such as the precipitation of silica from water glass or the purification of water glass over lonentauschersäulen used. The heat exchangers 8 are optional. In the system 0c, the hot gas stream 6.3 is returned to 5.1 and in the plant Ob in 4.1. It is clear to the person skilled in the art that 6.3 can also be converted to 5.1 and 4.1.

Alternative systems according to the invention, as shown schematically in FIG. 10b or 0c, and their energy and material flows are explained in more detail below.

In these alternatives, the electrical energy 5.2 obtained in 5.1 is used to operate 7.1, while the reactor 6.1 is fed by additional power. Starting from 4.1, the burner is fed with natural gas in order to achieve the required temperatures of up to 2000 ⁰ C can. For the production of about one kilogram of carbon black, about 0.2 kilograms of natural gas are currently required, which contribute about 2 kWh. The choke feeds another 1.5 kg of feedstock, which contributes about 15 kWh / kg. In a further process stage, air is introduced into the carbon black reactor, in particular for preheating the combustion air of the quench zone, the reactions which occur during soot production are quenched with water. Per kilogram of produced soot becomes one Tail gas with an energy content of about 1 to 10 kWh / kg of carbon black, preferably obtained from about up to 5 kWh / kg of carbon black. With this tail gas can be generated by combustion in 5.1 steam, which is converted into 7.1, to be used there as an example for the drying of SiO ₂ . The energy content of this steam can be about 1 to 8 kWh, preferably up to 4 kWh. To illustrate the energy needs of 7.1, it has to be taken into account that between 2 to 5 kilograms of water, usually around 4 kilograms of water per kilogram of dried carbon dioxide, have to be evaporated. The evaporated water from 7.1 can be used as residual heat, for the operation of greenhouses or be drained via the roof. A preferred alternative provides for the use of steam for energy. The energy content of about 4 kilograms of steam of about 102 ⁰ C is in the range of about 4 kWh in addition to the usable heat of condensation. For all given kWh, a wide fluctuation range of at least plus / minus 50% of the specified value in kWh must be taken into account, as the energy balances of the respective material and energy flows influence each other. In addition, the expert knows that in such a complex network of processes only approximate values can be determined.

For the operation of, for example, an electric arc furnace 6.1 approximately 14 kWh of electricity are needed to produce about one kilogram of silicon from about 1 kg of soot and 3 kg of silica. This form in the Möllerzusammensetzung under the reaction conditions at up to 2000 ⁰ C gaseous silica, which has been quenched together with likewise formed carbon monoxide as hot gases at 600 to 700 ⁰ C with air, oxidized and filtered. In the system according to the invention, these hot gases can be introduced alternatively or simultaneously in 4.1, in particular in the region of the burner or choke. The hot gases per kilogram of silicon produced about 0.4 kg of silica and about 2.3 kg of carbon monoxide, the energy content can be up to 9 kWh per kilogram of silicon. By this measure, about 0.5 l of oil / kg of carbon black or 1 to 6 kWh / kg, preferably up to 5 kWh / kg of carbon black can be saved. In addition, about 0.2 kg of silicon per kilogram of silicon can be recovered by the recycle. This can mean an increase in yield of from 1 to 25% by weight, preferably from 5 to 20% by weight, particularly preferably from 15 to 22% by weight, based on the silicon used in the starting product SiO 2 with respect to the end product silicon.

Alternatively or additionally, the hot gas stream 6.3 can also be introduced in 5.1, for example in order to generate steam there, via which in turn electricity can be generated. Thus, in 5.1 per kilogram of produced silicon 1 up to 11 kWh, in particular 5 to 10 kWh, preferably 9 kWh of heat can be used for the production of steam and / or electricity. At the same time, the entrained silica can be deposited as silica and added to the process in 5.1 or the method of making silica. The described use of the material and / or energy flows or the process control in a system according to the invention allows a considerable improvement in the energy balance of the overall process for the production of silicon and at the same time an increase in the yield of silicon.

Claims

claims

1. Plant (1a), characterized in that it comprises a reactor (4.1) for the thermal conversion of carbon-containing compounds, wherein the reactor (4.1) is connected to a combined heat and power (5.1) through which a part of Waste heat (5.3) decoupled from the thermal conversion and another part of the waste heat in mechanical or electrical energy (5.2) is converted, or, wherein the reactor (4.1) with a thermal power plant (5.1) is connected via the waste heat in mechanical or electrical energy (5.2) is converted.

2. Plant (2) according to claim 1, characterized in that the decoupled waste heat (5.3) to the device (7.1) is guided, in particular the waste heat (5.3) via a heat exchanger (8), preferably by means of a secondary circuit in the device 7.1 Preferably, the device 7.1 is part of a plant for the production of silicon dioxide, more preferably the device is a precipitation vessel, reactor and / or a dryer.

3. Plant (1 b) according to any one of claims 1 or 2, characterized in that the electrical energy (5.2) for powering a reactor (6.1) for the reduction of metallic compounds, in particular an electric arc furnace (6.1) melt reactor or blast furnace, preferably for Production of silicon, preferably solar silicon, is used.

4. Plant (1 c) according to any one of claims 1 to 3, characterized in that hot process gases from the reactor (6.1) for the reduction of metallic compounds via a hot gas line (6.3) in the reactor (4.1) for the thermal conversion of carbon and / or in the cogeneration (5.1) or in the thermal power plant (5.1) are initiated.

5. Plant (1 c) according to any one of claims 1 to 4, characterized in that a hot gas line (6.3) the reactor (6.1) for the reduction of metallic compounds and the reactor (4.1) for the thermal conversion of carbon or the reactor (6.1 ) with the combined heat and power plant or the thermal power plant (5.1) connects, in particular for transferring the hot process gases from the reactor (6.1) in the reactor (4.1) or in (5.1).

6. Plant (Oa) according to one of claims 1 to 5, characterized in that the waste heat (6.2) of the reactor (6.1) for the reduction of metallic compounds in the device (7.1) is used, in particular, the waste heat (6.2) Heat exchanger (8) from the reactor (6.1) in the device (7.1) transferred.

7. Plant (Oa) according to any one of claims 1 to 6, characterized in that the waste heat, in particular a waste heat stream, (6.2) of the reactor (6.1) with the device (7.1) is connected.

8. Plant (Ob) according to claim 6 or 7, characterized in that the hot process gases from the reactor (6.1) for the reduction of metallic compounds via a hot gas line (6.3) in the reactor (4.1) for the thermal conversion of carbon or in the combined heat and power (5.1) or the thermal power plant (5.1) initiated become.

9. Plant (Ob) according to claim 6 or 7, characterized in that a hot gas line (6.3) for the introduction of hot process gases from the reactor (6.1) for the reduction of metallic compounds, this reactor with the reactor 4.1 for the thermal conversion of carbon or the Hot gas line connects the reactor (6.1) with the combined heat and power (5.1) or the thermal thermal power plant (5.1).

10. Plant (3), characterized in that the waste heat (6.2) of the reactor (6.1) for the reduction of metallic

Compounds (5.3) to the device (7.1) is transferred, in particular in

Combination with the system (1 a), preferably the waste heat (6.2) from the

Reactor (6.1) transferred to the reactor (7.1) by means of heat exchangers (8), preferably the waste heat stream 6.2 of the reactor 6.1 is connected to the device 7.1.

11. Use of the waste heat of a reactor (4.1) for the thermal conversion of carbon-containing compounds for the production of electrical energy, in particular by means of a cogeneration or thermal thermal power plant.

12. Use of the waste heat according to claim 11 in the production of silicon oxide, in particular silicon dioxide.

13. Use of electrical energy according to claim 11 for operating a reactor (6.1) for the reduction of metallic compounds or a device (7.1).

14. Use, in particular according to one of claims 11 to 13, the hot process gases (6.3) from the reactor (6.1) for the reduction of metallic compounds in the reactor (4.1) for the thermal conversion of carbon in the reactor (4.1), in particular by over a hot gas line (6.3) from the reactor (6.1) in the reactor (4.1) are introduced, or use of the process gases (6.3) in the combined heat and power (5.1) or the thermal power plant (5.1) for steam generation.

15. Use of the waste heat of a reactor (6.1) for the reduction of metallic compounds in the production of silicon oxide, in particular in the tempering or drying of silicon dioxide.