DE102016008915A1 - CO2 emission-free blast furnace process - Google Patents

Abstract

The invention relates to a blast furnace method for operating a CO2-emission-free blast furnace. Here are the necessary measures: 1. The blast furnace is operated with pure oxygen. 2. Top gas recycling with CO2 capture increases the indirect reduction and lowers the carbon input. 3. CO2 capture, which converts the carbon dioxide emitted to methane using environmentally friendly hydrogen, gives a low-carbon fuel which, in blast furnace operation, replaces the coal dust injection proportionately and is used as fuel in the integrated DRI plant. Further advantages: 1. The HBI produced by means of the direct reduction plant integrated into the blast furnace complex lowers as an iron carrier used in existing blast furnaces, their reduction work and thus the use of carbon and CO2 emissions. 2. Incorporation and methanation of external low-carbon combustion gases 3. Increasing production through top gas recycling with an increase in indirect reduction 4. Increasing production through methane combustion - Hydrogen reduction Summary: The presented blast furnace process fully complies with the system of a circular economy, in which all recyclable substances in the process be returned and used.

Description

1. State of the art

The blast furnace process is the main process worldwide for pig iron production, more than 95% of the pig iron is produced in the blast furnace. The biggest disadvantage of the blast furnace, however, is the high emission of carbon dioxide, since over 1500 kg of carbon dioxide are produced in the production of pig iron in a blast furnace at the melting of 1000 kg of RE.

2. HO process for CO ₂ reduction

• – Im ULCOS-TGRBF Programm ist es vorgesehen das vom CO₂ befreite, durch die Sauerstoffverbrennung im wesentlichen aus CO und H₂ bestehende, Topgas dem Hochofen als Reduktionsgas zu zuführen. So sollen bei der Version 1 ca. 20% der Recyclinggase bei Umgebungstemperatur mit Hilfe der Herdblasformen und die restlichen 80% auf 900°C erhitzt durch Düsen in den unteren Schachtbereich eingeblasen werden. Die notwendige Prozesswärme wird durch die Verbrennung von Koks und eingeblasenem Kohlenstaub im Unterofen erzeugt.
• – Das japanische CO₂-Minderungsprogramm COURSE50 nutzt auch von CO₂ befreites Gichtgas und zusätzlich Wasserstoff als Reduktionsgas. Durch Recycling des von CO₂ befreiten Gichtgases und dem Einblasen und Verbrennen von reformiertem Kokereigas [H₂-Gehalt > 60%] mit Hilfe der Herdblasformen und reformiertem auf 800°C erhitzten Kokereigas durch Schachtdüsen vermindert sich der Kohlenstoffeinsatz und der CO₂-Ausstoss. Die notwendige Prozesswärme wird durch die Verbrennung von Koks und des mit Hilfe der Herdblasformen eingeblasenen Wasserstoffs generiert.

To reduce these CO ₂ emissions, European and Japanese steelmakers have launched the ULCOS and COURSE50 initiatives to investigate improved blast furnace processes.

• - In ULCOS TGRBF program it is provided freed from CO _2, top gas to carry out the blast furnace as reduction gas consisting of oxygen by the combustion essentially of CO and H _2. For example, in version 1, about 20% of the recycled gases are blown through the nozzles into the lower shaft area at ambient temperature using the hearth blow molds and the remaining 80% heated to 900 ° C. The necessary process heat is generated by the combustion of coke and injected coal dust in the lower furnace.
• - The Japanese CO ₂ -Minderungsprogramm COURSE50 also uses CO ₂ liberated blast furnace gas and also hydrogen as a reducing gas. The carbon input and the CO ₂ emissions are reduced by recycling CO ₂ -fired blast-furnace gas and injecting and burning reformed coking gas [H ₂ content> 60%] with the help of the furnace blow molding and reformed coking gas heated to 800 ° C. The necessary process heat is generated by the combustion of coke and the hydrogen blown in with the help of the hearth blow molds.

Both modifications of the blast furnace process use carbon monoxide or carbon monoxide and hydrogen to increase the indirect reduction of the iron carriers and thus proportionally replace the fuel intensive direct reduction and thereby significantly reduce the carbon input and CO ₂ formation and by depositing the separated carbon dioxide is only to a small extent CO ₂ emitted.

3. Blast furnace process with minimal CO ₂ emissions

A further reduction in the use of carbon in the blast furnace process would be possible by recycling the top gas freed from CO ₂ and the blowing of environmentally friendly generated to ~ 2300 ° C heated hydrogen as a reducing gas. The fact that no oxygen is supplied to the blast furnace, carbon dioxide is produced only as a product of the equilibrium reactions of the ore oxygen with the coking coal. With this modification of the known and proven blast furnace process, it would be possible to limit carbon dioxide emissions to the minimum possible. However, with the available technical means and materials it is not possible to heat hydrogen indirectly to 2300 ° C, for this reason, the H ₂ as CH ₄ as shown in the following process description on the way of methanation of the deposited carbon dioxide by oxidation directly to be heated.

4. Modified blast furnace process to avoid CO ₂ emissions

Complete avoidance of CO ₂ emissions in pig iron production is achieved by means of the in 1 As the two abovementioned CO ₂ reduction programs, the process utilizes the indirect carbon monoxide by recycling the top gas freed from CO ₂ and, analogously to the COURSE 50 project, enhances the environmentally friendly hydrogen reduction to reduce CO ₂ formation and avoid them altogether CO ₂ emissions convert the separated carbon dioxide into methane with hydrogen and use it as a gaseous substitute fuel in the blast furnace process and as a process gas for operating a direct-reduction plant. That is by merging the DRI offgas stream to the primary gas stream prior to the CO ₂ capture separated accumulating CO ₂ in the DRI production, methanated and is thus usable as a process or fuel gas. In addition, additional combustion gases produced in an integrated steelworks can be fed to CO ₂ separation and methanated to form CH ₄ . By using the above-mentioned blast furnace process using hydrogen produced by means of renewable energies and by integrating a direct reduction plant, a virtually CO ₂ emission-free steel plant is conceivable.

Conventional blast furnaces require approximately 500 kg of coke and single-shot coal to melt 1000 kg of pig iron at an indirect reduction rate of approx. 60%. The operation of a blast furnace according to the presented process with Topgasrecycling achieved with a reduced to 200 kg coke consumption and 160 kg injection coal indirect pre-reduction of over 90% combined with a significant decrease in CO ₂ emissions and parallel increases the iron production to AM Gent the pre-reduction by more than 45%.

In hot blast furnaces, the carbon monoxide necessary to reduce the iron oxides is produced by the combustion of the coke, the spar and other carbon carriers in the blast furnace. The recycling of carbon monoxide reduces the amount of carbon to be supplied to the blast furnace, since the carbon essentially only needs to be burned or needed for heating, for melting the iron carriers, for the direct reduction of the iron oxides and for the regeneration of the combustion products.

In the presented HO-method, as from the flowchart 1 can be seen, blown the substitute fuels CH ₄ and coal dust with the oxygen through the outer channel of the blowing in the coke bed, in which then the gas mixture is heated with the coal dust in the glowing coke by radiation and convection at 100 to 1000 K / ms. The tangential injection of methane into the outer channel, see cross section 2 , causes intensive mixing of the CH ₄ / O ₂ gas mixture, so that burns spontaneously after adequate heating at ~ 2800 ° C. Through the central channel, the depleted of CO ₂ and hydrogen-enriched top gas is fed as a reducing gas at room temperature to the blast furnace and heated in this by the combustion of the substitute fuels to T <2800 ° C.

The adiabatic combustion temperature of 2300 ° C, see ULCOS - Example of flow sheet version 1, is exceeded by ~ 500 ° C in pure methane combustion. To reduce the combustion temperature, CO _{2 is} added to the CH ₄ / O ₂ gas stream, which reacts with the reactions: CO ₂ + C → 2CO, ΔH = +172.5 kJ / mol, CO + H ₂ O → H ₂ + CO ₂ , ΔH = -41.2 kJ / mol and H ₂ O + C →CO + H ₂ , ΔH = +131.3 kJ / mol the combustion enthalpy of CH ₄ , ΔH = -802.4 kJ / mol counteracts and thus allows by the added amount of CO ₂ lowering the adiabatic combustion temperature to T = 2300 ° C, wherein the carbon necessary for the reaction is the Char of the injection coal is. Depending on the state of aggregation of the substitute fuels, the combustion of the fuels blown into the blast furnace takes place in a homogeneous or heterogeneous state. In the homogeneous combustion, the reactants methane and oxygen are gaseous and the coal burns in a heterogeneous gas-solid reaction in which the degassed coal by the boundary layer and the pore diffusion, which may be 80 to 90% of the total reaction time must be digested before it oxidized to CO ₂ in a chemical reaction with oxygen. From this, the homogeneous methane combustion requires only 10 to 20% of the total combustion time of a coal grain. In the combustion gas stream, the methane is mixed in a stoichiometric ratio [1 mol CH ₄ + 2 mol O ₂ ]. After entering the blast furnace, the methane burns by the homogeneous reaction before the much slower "heterogeneous" gas-solid reaction of the coal dust to H ₂ O and CO ₂ . Due to the degassing of the injection coal there is an excess of fuel at the time of the gas combustion, so that the oxygen is bound in the combustion products CO ₂ and H ₂ O before the slower carbon oxidation. As the CH ₄ combustion increases, the H ₂ O and CO ₂ partial pressures in the envelope jet increase in proportion to the decrease in oxygen. The carbon conversion is then carried out according to the Boudouard reaction [CO ₂ + C → 2CO] and the heterogeneous water gas reaction [H ₂ O + C → H ₂ + CO] with the reduction of the combustion products by the Char of the injection coal.

• 1. Oxidation des Methans – CH₄ +2O₂ → CO₂ +2H₂O – homogene Reaktion
• 2. Reduktion der Verbrennungsprodukte – CO₂ + C_PCI → 2CO – heterogene Reaktion H₂O + C_PCI → CO + H₂ – heterogene Reaktion

ist eine Absenkung der adiabaten Verbrennungstemperatur auf 2300°C durch Einblasen von CO₂ mit Kohlenstaub gewährleistet. Die nicht oxidierten Kohlenwasserstoffverbindungen, erzeugt durch die Entgasung der Einblaskohle, dissoziieren über 1250°C in C und H₂ und erhöhen durch das H₂ die Reduktionsgasmenge und der Kohlenstoff reduziert vorrangig durch seine geringe Partikelgröße die Produkte CO₂ und H₂O zu CO und H₂.Through the reaction sequence:

• 1. Oxidation of methane - CH ₄ + 2O ₂ → CO ₂ + 2H ₂ O - homogeneous reaction
• 2. Reduction of combustion products - CO ₂ + C _PCI → 2CO - heterogeneous reaction H ₂ O + C _PCI → CO + H ₂ - heterogeneous reaction

is a lowering of the adiabatic combustion temperature to 2300 ° C by blowing CO ₂ with coal dust guaranteed. The non-oxidized hydrocarbon compounds produced by the degassing of Injected carbon, dissociate over 1250 ° C in C and H ₂ and increase the amount of reducing gas through the H ₂ and the carbon reduced primarily by its small particle size, the products CO ₂ and H ₂ O to CO and H ₂ .

The flow picture 1 shows the process path and the components for CO ₂ -industrial pig iron smelting with the help of a blast furnace. Due to the oxygen combustion, the blast furnace gas consists primarily of CO, CO ₂ and H ₂ . After separation of the carbon dioxide from the purified top gas this is injected as a reducing gas in two levels in the blast furnace. The supply of about 75% of the reducing gas is heated to 900 ° C in the lower HO-shaft and in the blow mold level, the remaining 25% of the reducing gases at ambient temperature by means of the blowing device, 2 , introduced into the blast furnace. The reduction gas for pre-reduction, injected into the HO-shaft, can be indirectly heated only to 350 ° C because of the "metal dusting" in a metallic heater and therefore only before entering the blast furnace by means of plasma torch from 350 ° C to 900 ° C heated. To increase the raceway and increase the reduction power, hydrogen is added to the lower CO recycling gas stream.

The methanation of the removed from the top gas of the blast furnace carbon dioxide with hydrogen z. B. using a combined high-temperature electrolysis with CO ₂ methanation, efficiency η = 0.87, produces a gaseous, highly reactive low-carbon in the blast furnace process usable substitute fuel. High-temperature electrolysis uses the exothermicity of CO ₂ methanation to vaporize the water to be split.

A portion of the methane is injected into the outer annular space of the injector, mixed with the previously injected into the annulus of the injector oxygen, as a gaseous substitute fuel and produced by the combustion of the necessary operating temperature in the blast furnace. As mentioned previously, the methane stream is mixed with carbon dioxide to lower the adiabatic combustion temperature in the raceway, and a portion of the CH ₄ / CO ₂ gas stream serves as a propellant assisting the HO process to introduce the coal dust into the rotary mixing chamber.

For the complete utilization of the methane produced with the separated carbon dioxide and hydrogen, a direct reduction plant is integrated into the blast furnace plant. The product of the direct reduction plant - Hot Briquetted Iron (HBI) - as feedstock in existing blast furnaces reduces the reduction work by the Fe content of 90-95% and thus reduces the CO ₂ emission and the methane blown into the hot blast replaces proportionally during combustion the injection coal and with the use of HBI reduces the carbon dioxide production in existing blast furnaces. The use of HBI increases the productivity of a blast furnace, because if the iron content of the blast furnace charge increases by 10%, the blast furnace capacity increases by about 8% in parallel. In addition, increasing the hydrogen content by 10% in the reducing gas increases the reduction rate three times.

Im Vergleich das Reaktionsschema Kohlenstoff - gegenüber Methanverbrennung

Stoffmengen Kohlenstoffverbrennung - ULCOS gegenüber Methanverbrennung

This procedure makes it possible to increase the production of pig iron in existing blast furnaces despite reduced carbon input and reduced CO ₂ emissions! According to the ULCOS-TGRBF program, according to the flow chart - version 1 - it is planned to charge 209 kg of coke to the blast furnace for the melting of 1000 kg pig iron ore and to blow in 180 kg coal dust as a substitute fuel. The quantities detailed:

In comparison, the reaction scheme carbon - to methane combustion

Quantities of carbon burning - ULCOS versus methane combustion

Compared to ULCOS version 1, the carbon input, according to Table 2, in the blast furnace process presented by the methane combustion of 27454 mol C decreases by ~6% to 26000 mol C and the reduction gas amount, Table 1, increases to 1.5 times of 4CO on 4CO + 2H ₂ .

Conclusion:

The application of the aforementioned blast furnace process with top gas recycling using hydrogen produced with the aid of renewable energies and the integration of a direct reduction plant, in 1 allows a CO ₂ emission-free pig iron melting.

The advantages of the presented blast furnace process:

• 1. CO ₂ emission-free blast furnace process.
• 2. Only modification of an established procedure, not new development.
• 3. Hydrogen produced by renewable energy means methanation of the separated carbon dioxide, instead of landfill.
• 4. Using HBI and SNG to improve the CO ₂ balance and increase the production of existing blast furnaces.
• 5. Integration of CO ₂ -containing exhaust gases of existing plants.
• 6. Reduction of the carbon input.
• 7. Production increase through top gas recycling with pre-reduction to AM-Gent> 45%.
• 8. Increase in productivity due to methane combustion = hydrogen reduction by ~ 50%.

Stoffströme und Bereiche: a Kohlenmonoxid und Wasserstoff b Kohlenstaub mit Methan und Kohlendioxid als Treibgas c Sauerstoff d CH₄, und CO₂ e Kernbereich, Kernstrahl f CO – Kernstrahl g Gesamtstrahl h Koks Key to Fig. 1: Components Pos. designation A blast furnace B CO ₂ capture C CO-heater D HT electrolysis e bubbler F DRI plant G Prev. blast furnace H plasma torch J methanation material flows Pos. description 1 Solids - ore, coke ... 2 top gas 3 carbon dioxide 4 CO ₂ - waste gas 5 Carbon monoxide 6 Carbon monoxide, T = 350 ° C 7 coal dust 8th oxygen 9 Carbon monoxide, T = 900 ° C 10 hydrogen 11 HBI 12 methane 13 water Key to Fig. 2:

Material flows and areas: a Carbon monoxide and hydrogen b Coal dust with methane and carbon dioxide as propellant c oxygen d CH ₄ , and CO ₂ e Core area, core beam f CO - core beam G total beam H coke

Claims (10)

CO ₂ emission-free blast furnace process by Topgasrecycling with CO ₂ capture, the use of renewable energy and integration of a direct reduction plant, characterized in that recycled discharged from CO ₂ blast furnace gas is fed as a reducing gas to the blast furnace in two levels as described above. A method according to claim 1, characterized in that the reducing gases are injected through the central channel and the oxidizing and reducing agents, oxygen, methane, carbon dioxide and pulverized coal through the outer annular channel of the device in the blast furnace and that in the rotary mixing chamber of the coal. Dust is injected by means of tangentially arranged nozzles offset by the propellant methane with carbon dioxide. Method according to one of the preceding claims, characterized in that the separated carbon dioxide is converted in a conversion plant with the help of, from renewable energy or biotechnologically generated, hydrogen to methane. Method according to one of the preceding claims, characterized in that the reduction of the adiabatic flame temperature in the homogeneous methane combustion by the delayed compared to the homogeneous oxidation heterogeneous reduction takes place with the injected pulverized coal to carbon monoxide. Method according to one of the preceding claims, characterized in that with the synthetic methane and with the help of renewable energy produced hydrogen Direct reduction plant is operated. The CO ₂ -containing offgas of the DRI plant is added to the crude gas stream before the CO ₂ separation. Method according to one of the preceding claims, characterized in that the product of the DRI plant, the sponge iron as Hot Briquetted Iron existing blast furnaces is supplied as a prereduced, iron-containing material. Method according to one of the preceding claims, characterized in that a partial stream of the synthetic methane to reduce the CO ₂ emissions is blown into existing blast furnaces as a hydrogen-containing fuel. Method according to one of the preceding claims, characterized in that further obtained in an integrated steel plant, low-nitrogen combustion gases for the purpose of decarbonization of the steel mill exhaust gases of the CO ₂ separation are fed and synthesized to CH ₄ . Method according to one of the preceding claims, characterized in that the hydrogen used in the process is generated by means of electricity generated from renewable energies or hydrogen produced by other means or hydrogen-containing gases or mixtures thereof are used. Method according to one of the preceding claims, characterized in that instead of the methane produced by conversion of the carbon dioxide with the hydrogen, natural gas is used as the fuel.

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