Patent Application
20230340628
The present disclosure generally relates to a method for operating a blast furnace installation as well as to such a blast furnace installation.
Despite alternative methods, like scrap melting or direct reduction within an electric arc furnace, the blast furnace (BF) today still represents the most widely used process for steel production. One of the concerns of a blast furnace installation is the blast furnace gas (BFG) exiting the blast furnace. Since this gas exits the blast furnace at its top it is commonly also referred to as “top gas”. While, in the early days, this blast furnace gas may have been allowed to simply escape into the atmosphere, this has later been avoided by using it in BFG fed power plants in order not to waste the energy content of the gas and cause undue burden on the environment. One component in the blast furnace gas is CO2, which is environmentally harmful and is mainly useless for industrial applications. Indeed, the waste gas exiting the power plant fed with the blast furnace gas typically comprises a concentration of CO2 as high as 20 vol % to 40 vol %. The blast furnace gas being combusted usually comprises besides the before mentioned CO2 considerable amounts of N2, CO, H2O and H2. The N2 content, however, largely depends on whether hot air or (pure) oxygen is used for the blast furnace.
Mainly in order to reduce the amount of coke or other carbon sources used, a suggestion was made to recover the blast furnace gas from the blast furnace, treat it to improve its reduction potential and to inject it back into the blast furnace to aid the reduction process. One method for doing this is reducing the CO2 content in the blast furnace gas by Pressure Swing Adsorption (PSA) or Vacuum Pressure Swing Adsorption (VPSA), such as disclosed in patent application EP 2 886 666 A1. PSA/VPSA installations produce a first stream of gas which is rich in CO and H2 and a second stream of gas rich in CO2 and H2O. The first stream of gas can be used as reduction gas and fed back into the blast furnace. One example for this approach is the ULCOS (Ultra Low CO2 Steelmaking) process, where apart from the recycled first stream of gas, pulverized coal and cold oxygen are fed into the blast furnace. This type of furnace is also referred to as “top gas recycling OBF” (oxygen blast furnace).
The second stream of gas can be removed from the installation and, after extraction of the remaining calorific value, disposed of. This disposal controversially consists in pumping the CO2 rich gas into pockets underground for storage. Furthermore, although PSA/VPSA installations allow a considerable reduction of CO2 content in the blast furnace gas from about 35% to about 5%, they are very expensive to acquire, to maintain and to operate and further they need a lot of space.
It has also been proposed to use the blast furnace gas as a reforming agent for hydrocarbons in order to obtain a synthesis gas (also referred to as syngas) that can be used for several industrial purposes. According to a common reforming process, the blast furnace gas is mixed with a fuel gas that contains at least one hydrocarbon (e.g. lower alkanes). In a so-called dry reforming reaction, the hydrocarbons of the fuel gas react with the CO2 in the blast furnace gas to produce H2 and CO. At the same time the hydrocarbons react with the H2O in the blast furnace gas also producing H2 and CO by so-called steam reforming reaction. Either way, a synthesis gas is obtained that has a significantly increased concentration of H2 and CO.
The problems with the above-mentioned solutions are that they require expensive and technically complex equipment.
The present disclosure therefore provides a new method for operating a blast furnace installation, i.e. a blast furnace and its ancillary equipment, as well as a corresponding blast furnace installation, allowing for at least partially overcoming said problems.
In order to achieve this advantage, the present disclosure proposes, in a first aspect, a method for operating a blast furnace for producing pig iron by smelting, comprising the steps of
In a second aspect, the disclosure proposes a blast furnace installation for producing pig iron comprising a blast furnace provided with gas inlets in the shaft arranged for feeding a stream of syngas to the blast furnace. The blast furnace installation further comprises a first heater in fluidic downstream connection with a stream of steam and in fluidic downstream or upstream connection with an oxygen source providing oxygen or oxygen-enriched air, said first heater being arranged for heating said stream of steam to provide a first heated stream of oxygen-enriched steam; a second heater in fluidic connection with the top of the blast furnace arranged for conveying a first stream of blast furnace gas and with a source of a first stream of natural gas, said second heater being arranged for heating said first stream of blast furnace gas and said first stream of natural gas either separately or mixed to provide a heated carbon feed stream, wherein said first and second heater are in fluidic downstream connection with one or more reactor inlets of a catalytic partial oxidation reactor arranged for producing a stream of syngas, either directly for feeding the first heated stream of oxygen-enriched steam and the heated carbon feed stream separately to said one or more reactor inlets or through a mixing unit arranged for first joining the first heated stream of oxygen-enriched steam with the heated carbon feed stream to provide a combined stream and for feeding said combined stream to said one or more reactor inlets. Furthermore, said catalytic partial oxidation reactor is further in fluidic downstream connection with the gas inlets in the shaft of the blast furnace. Advantageously, said blast furnace installation can be operated by implementing a method according to the first aspect and as described more in detail below.
Catalytic partial oxidation reactors are known in the art of synthetic gas (syngas) production. Advantageously the catalytic partial oxidation reactor is a Short Contact Time Catalytic Partial Oxidation reactor. The process of Catalytic Partial Oxidation (CPO) is based on the following reaction, where oxygen can also come from air or oxygen-enriched air or a combination of oxygen and nitrogen:
CH4+½O2χCO+H2
conducted by colliding for few milliseconds, gaseous premixed reactant flows through extremely hot catalytic surfaces. The fast and selective chemistry that is originated is confined inside a thin solid-gas inter-phase zone surrounding the catalyst particles. Here, the molecules typically spend very short time at temperatures variable between 600 and 1200° C. A key issue for the technological exploitation is in the possibility of avoiding the propagation of reactions into the gas phase, which has to remain at a “relatively low” temperature. This condition favours the formation of primary reaction products (namely CO and H2) inhibiting chain reactions.
Experimental studies indicate that partial oxidation products are directly produced through parallel and competing surface reactions and that the formation of partial oxidation products is favoured under the CPO conditions due to the very high surface temperatures. The occurrence of the reactions in these local environments determines in some cases conversion and selectivity values higher than those predicted by the thermodynamic equilibrium at the reactor exit temperatures.
Catalytic Partial Oxidation, and in particular Short Contact Time Catalytic Partial Oxidation (SCT-CPO), combine heterogeneous catalysis characteristics and flameless combustion in porous media and is known for example from WO2011072877, WO2011151082, and L. E. Basini and A. Guarinoni, “Short Contact Time Catalytic Partial Oxidation (SCT-CPO) for Synthesis Gas Processes and Olefins Production”, Ind. Eng. Chem. Res. 2013, 52, 17023-17037. While SCT-CPO is known, the main advantages of catalytic partial oxidation applied for the production of syngas to be injected in a blast furnace can be summarized as follows:
Indeed, the present inventors have found that this syngas production technology may advantageously be applied to a mix of natural gas and blast furnace gas, thereby providing a syngas with compositions which are particularly suitable to the feeding within the shaft of the blast furnace. In fact, natural gas fed to CPO reactor is subjected to partial oxidation reaction producing CO and H2 and delivering heat. The latter is used within the system to sustain the endothermic reforming reaction (conversion of hydrocarbon by steam or CO2) that leads to the production of CO and H2. However, the blast furnace gas has a reduced content of carbon compared to natural gas. Thus, the behavior within the reactor is quite different. Increasing the percentage of blast furnace gas in the feeding gas stream is possible but values like critical ratios e.g. steam to carbon ratio or oxygen to carbon ratio and maximum acceptable component concentration in the syngas should be kept. For this reason, it may be advantageous to limit the proportion of blast furnace gas being mixed with the natural gas stream. The maximum proportion of the blast furnace gas in the feed gas mix with NG ranges generally is from 15 to 30% depending on the actual composition and temperature of the fed blast furnace gas to the reactor.
Indeed the inventors determined that a particularly advantageous syngas quality can be obtained by controlling the Oxygen/Carbon ratio at values from 0.58 to 0.68 mol/mol, preferably from 0.60 to 0.66 mol/mol, more preferably from 0.62 to 0.64 mol/mol, most preferably about 0.63 mol/mol, while Steam/Carbon ratio is preferably controlled at values from 0.10 to 0.40 mol/mol, preferably from 0.15 to 0.35 mol/mol, more preferably from 0.20 to 0.30 mol/mol, most preferably at about 0.25 mol/mol.
The behavior of the blast furnace gas within the catalytic partial oxidation reactor is strictly linked to reactions involved within the catalytic partial oxidation reactor. Beyond the components involved in the partial oxidation, the Water Gas Shift Reaction further determines the final composition of the syngas. It has been found that the presence of CO2, through the blast furnace gas stream, involves a readjustment of the equilibrium composition, which leads the excess of CO2 to react with the hydrogen, thus increasing the CO and H2O content.
In addition to the benefits mentioned above, one of the major advantages of the present method and installation is the substantially reduced CO2 production of the blast furnace operation by reconditioning part of the blast furnace gas for re-use in order to decrease the carbon input to the blast furnace.
Furthermore, the shaft injection of the resulting syngas allows a significantly reduction of the amount of coke per ton of pig iron produced, also called coke rate. Additionally, the injection of syngas partially from natural gas is not only compatible with tuyere injection of pulverized coal or natural gas, but can advantageously allow to replace further amounts of coke with natural gas, i.e. natural gas converted in the presence of blast furnace gas to a syngas. These and further advantages of the present method for operating a blast furnace, as well as the presently disclosed blast furnace installation will be further detailed below.
Blast furnace gas, which may also be referred to as top gas or BFG, is collected from the top of the blast furnace and is a gas containing mainly CO2 and other components like CO, H2O, H2 or other. It may also contain some N2 depending on the hot blast feeding. For conventionally operated blast furnaces, the N2 concentration in the blast furnace gas is generally between 35 and 50 vol % (% by volume), whereas for blast furnace gas operated according to the present disclosure, i.e. using syngas produced as described herein, the N2 concentration is generally lower, for example below 20 vol %, below 10 vol % or even below 5 vol %. Normally, the blast furnace gas needs to be cleaned in order to reduce e.g. its dust content. Hence, the first stream of blast furnace gas is further subjected to a gas cleaning step, preferably a dust removal step, metals removal step and/or HCl removal step, usually before being mixed with the first stream of natural gas. Accordingly, in a preferred blast furnace installation, the fluidic connection conveying the first stream of blast furnace gas from the blast furnace comprises a gas cleaning plant. This gas cleaning part preferably comprises a dust removal unit, such as one or more cyclones, scrubbers and/or bag filters, a metals removal unit, such as active carbon fixed bed reactor and/or a HCl removal unit, such as scrubbers with reactant injection. If required to bring the blast furnace gas at the required pressure in order to generate syngas suitable for injection in the shaft of the blast furnace, it may be compressed, e.g. at 0.3-0.5 MPa through a dedicated system provided downstream the blast furnace gas network.
The feed streams to the catalytic partial oxidation reactor, e.g. the carbon feed stream and the stream of oxygen-enriched steam, generally need to reach a temperature from 300 to 450° C. after having been combined for an appropriate operation of said reactor. Therefore, in preferred embodiments of the method, the heated carbon feed stream of step (b) is further heated within a third heater before step (c). In preferred embodiments of the blast furnace installation, the second heater is thus in fluidic downstream connection with a third heater arranged for further heating the carbon feed stream upstream of mixing unit.
The heat for the heaters may be produced by any appropriate means and energy source. Advantageously in the present method, a second stream of blast furnace gas is burned in a burner in the presence of combustion air or oxygen-enriched air within the first and/or second heater and/or third heater to provide the heat within said heaters. In particularly preferred embodiments, the first, second and/or third heaters are configured as corresponding heat exchangers and one burner is used for heating the first, second and third heat exchangers.
In advantageous embodiments, the off-gas from the burner(s) can be fed to the first stream of blast furnace gas from the blast furnace, to the first stream of natural gas or to the already (partially) heated carbon feed stream. Thereby not only the residual heat of the burner off-gas can be utilized, but also the CO2 produced in the burner added to that already contained in the blast furnace gas.
In other preferred embodiments, the first, second and/or third heaters are configured as heat exchangers using process heat from other processes within the blast furnace installation or plant.
Depending on their origin (or composition), it may be advantageous or necessary to subject the first stream of blast furnace gas and/or the first stream of natural gas and/or the heated carbon feed stream to a further treatment, such as a desulphurization step. In preferred embodiments, the heated carbon feed stream is subjected to a desulphurization step. Hence, the blast furnace installation may further comprise a desulphurization unit arranged within the fluidic connection of the first stream of blast furnace gas and/or the first stream of natural gas and/or the heated carbon feed stream, preferably within the fluidic connection of the heated carbon feed stream.
According to the disclosure, the first stream of steam is heated in a first heater, before or after having been enriched with oxygen, to provide a first heated stream of oxygen-enriched steam. Preferably the oxygen/oxygen-enriched air for enriching the first heated stream of steam is heated to a temperature from 100 to 350° C., preferably from 120 to 280° C. Advantageously, the oxygen/oxygen-enriched air for enriching the first heated stream of steam is heated to a temperature within (i.e. differing by not more than) 100° C., preferably within 50° C., of that of said first heated stream of steam before enrichment.
In particularly advantageous embodiments of the disclosure, the first heated stream of oxygen-enriched steam, the stream of natural gas and the stream of blast furnace gas are fed in amounts such that the stream of syngas of step (d) has a chemical composition fulfilling the following constraints:
Preferably the stream of syngas of step (d) has temperatures between 800 and 1100° C., more preferably between 900° C. and 1000° C.
It has been found that it may be desirable or beneficial for the operation of the blast furnace to add hydrogen, in particular so-called renewable or “green” hydrogen at an appropriate location of the process stream. In this context, renewable or “green” hydrogen is hydrogen (H2) produced by electrolysis of water using electricity coming from renewable sources such as wind, solar or hydropower. In particular, it may be advantageous to add hydrogen to the stream of syngas after the catalytic partial oxidation reactor before step (d) to adapt its temperature to the required temperature level of syngas for the shaft injection or if the hydrogen is preheated to the same temperature level. The preheating of the hydrogen generally is realized e.g. in an appropriate further heater or heat exchanger, which is preferably heated within the same enclosure as the first, second and third heaters, more preferably heated by one common burner.
The expression “natural gas” in the context of the present disclosure does not only designate natural gas as such, i.e. a naturally occurring hydrocarbon gas mixture of fossil origin consisting primarily of methane and commonly including varying amounts of other higher alkanes, but also gases with similar hydrocarbon constituents, such as biogas or coke oven gas, where the impurities content (if necessary after purification) make them compatible with the contact of catalysis in the CPO reactor.
“About” in the present context, means that a given numeric value covers a range of values form −10% to +10% of said numeric value, preferably a range of values form −5% to +5% of said numeric value.
“Shaft feeding”, “feeding . . . to the shaft of a blast furnace” or “gas inlets in the shaft” implies the injection of a material above the hot blast (tuyere) level, i.e. above the bosh, preferably within the gas solid reduction zone of ferrous oxide above the cohesive zone.
The expression “oxygen-enriched air” means air to which oxygen gas (O2) has been added, such that the proportion of oxygen within said gas is from 23 to 85 vol % or above, preferably from 60 to 75 vol %. The expression “oxygen-enriched steam” means steam (gaseous water) comprising oxygen, generally from 10 to 85 vol % or above, preferably from 25 to 75 vol % of oxygen gas (O2).
The expression “in fluidic connection” means that two devices are connected by conducts or pipes such that a fluid, e.g. a gas, can flow from one device to another. This expression includes means for changing this flow, e.g. valves or fans for regulating the mass flow, compressors for regulating the pressure, etc., as well as control elements, such as sensors, actuators, etc. necessary or desirable for an appropriate control of the blast furnace operation as a whole or the operation of each of the elements within the blast furnace installation.
Preferred embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings in which:
Further details and advantages of the present disclosure will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawing.
The requirements for the syngas and its utilization in the blast furnace are different to the applications already used today:
Reduction degree and temperature level of the syngas:
In other industries normally the syngas is produced and then cooled to separate the excess of steam from the syngas. Thereby only cooled gas is used in the downstream processes. In existing industrial applications beside the steel industry, a high reduction degree is not important. In steel industry however a high reduction degree, preferably above 7, is preferable, whereas the reduction degree is defined by the following molar ratio:(cCO+cH2)/(cH2O+cCO2).
Furthermore, high temperatures of syngas are favored compatible to the temperature level required for shaft injection in order to allow maximum thermal efficiency. Thus the temperature should be in the order of 900 to 1100° C. to allow its injection in the shaft of a blast furnace.
Ratio H2/CO
In the other industries, beside steel industry, the syngas is used for specific applications, such as pure hydrogen production, ammonia or the production of other chemical components. Thereby a specific ratio of hydrogen to CO is generally required.
In comparison, an advantage by using syngas in the blast furnace is reduction of ore, which is achieved with both reducing components, CO and hydrogen. While there is a difference between the reduction of ore with CO or hydrogen, this difference is relatively marginal considering that syngas is only part of the reducing gas used within the blast furnace.
CO2 Emissions
Coke is the main energy input in the blast furnace iron making. From the economic and CO2 point of view, this is the less favorable energy source. Substitution of coke by other energy sources, mostly injected at tuyere level, is widely employed. Due to cost reasons mostly pulverized coal is injected, however in countries with low natural gas price, this energy is used. Often residues like waste plastics are also injected in the blast furnace.
These auxiliary fuels may have a positive impact on the CO2 emissions from the blast furnace steel making, meanwhile their utilization is limited to process reasons and very often these limits are already attained today. The blast furnace produces blast furnace gas (BFG), which contains up to approximately 40% of the energy input to the blast furnace. This gas is generally used for internal heat requirements in the steel plant, but also for electric energy production. For the advantage of reducing the CO2 footprint of a blast furnace based steel production, one important strategy is thus to use this BFG for metallurgical reasons and apply other CO2 lean energies such as green electric energy for the remaining energy requirement of the steel plant.
Hence, the synthesis gas production should, beside the utilization of a CO2 lean hydrocarbon, also integrate blast furnace gas as much as possible in order to improve the CO2 emission reduction potential from the blast furnace iron making.
Impurities
Due to the utilization of coal and coke as well as often cheap secondary fuels as waste plastics or tar being used in the blast furnace, the typical and detrimental chemical components, such as chlorine and sulfur containing molecules, are part of the blast furnace gas. When using this gas for the production of syngas, these components may lead to quick poisoning of the reforming catalyst if not properly and pre-treated.
Pressure
Reforming reactions are favored by low pressure due to the Le Chatelier principle. However because compression of syngas downstream the reformer is costly (due to the increased flow rate) and smaller dimensions of equipment and catalyst bed, common syngas processes are operated at high pressure. In case of blast furnace application, low pressure levels are required only. Therefore, the syngas is injected in the shaft of the blast furnace, with a pressure typically between 1 and 4 barg.
Reforming and auxiliary technologies for syngas production:
These two last reactions are strongly endothermic and require a lot of heat.
Reforming technologies and its adaptation to blast furnace shaft injection
The thermodynamic equilibrium at the desired best reduction potential of the gas, leads to a temperature of the syngas, which is still too low for its injection in the shaft. In fact, increasing the temperature further result in higher requirement of higher oxygen and decreased reduction potential of the syngas, which is not favorable for the intended use.
Pre-Heating of the Feed Gases
The inventors found that to improve the situation a pre-heating of the feed gases could be applied to a CPO. In fact, with such a pre-heating, not only the reduction potential of the syngas can be increased, but the desired syngas temperature of about 1000° C. can also be obtained.
In
Concurrently, a first stream of steam [4] is heated in a first heater, before or after having been mixed with an oxygen source, selected from oxygen (oxygen gas 02) and oxygen-enriched air, to obtain a first heated stream of oxygen-enriched steam [6]. Preferably the oxygen source is first heated in an oxygen heater, e.g. a heat exchanger heated by a second stream of steam to obtain a heated oxygen stream [5], condensed water resulting from the heat exchange of this second stream of steam being thereafter discharged from the heat exchanger (condensation discharge). The heated oxygen stream [5] is preferably heated in a fourth heater (oxygen heater) to temperatures approaching/closely matching those of the heated carbon feed stream [4] (i.e. temperatures differing e.g. by no more than 100° C., preferably by no more than 50° C., from the temperatures of the heated carbon feed stream).
The first, second and third heaters are advantageously heat exchangers, preferably within the same enclosure (Fired heater), more preferably heated by one common burner. Said burner is preferably operated by burning a second stream of blast furnace gas in the presence of air, oxygen-enriched air or even oxygen. In some embodiments, the exhaust gas resulting from the combustion of the second stream of blast furnace gas in the presence of air, oxygen-enriched air or oxygen can be added to the first stream of blast furnace gas [2] or to the first stream of natural gas [1] or to the carbon feed stream [3], preferably to the first stream of blast furnace gas [2] upstream of the above-mentioned cleaning step(s).
If useful or necessary, a stream of nitrogen from a nitrogen source can be added to the heated carbon feed stream [4], to the heated oxygen stream [5] or to the combined stream [6], preferably after having been heated in a further (nitrogen) heater to temperatures approaching/closely matching those of the stream to which it is added (i.e. temperatures differing e.g. by no more than 100° C., preferably by no more than 50° C., from the temperatures of the stream to which it is added).
The first heated stream of steam [4] is then mixed to the heated oxygen source stream [5] to obtain a first heated stream of oxygen-enriched steam [6] which will be fed to the CPO reactor through one or more CPO reactor inlets.
The heated carbon feed stream is also fed to the CPO reactor through one or more reactor inlets. The combined stream of first heated stream of oxygen-enriched steam and carbon feed [7], optionally after having been mixed in a mixer, e.g. a CPO static mixer, is then allowed to react on the catalyst surface within the CPO reactor to form a stream of syngas [8] having temperatures in the range of 900 to 1100° C.
If desired or beneficial a stream of hydrogen, preferably renewable or so-called “green” hydrogen, can be added to the stream of syngas [8], if necessary after having preheated in an appropriate heater (hydrogen heater).
The (optionally further compressed) stream of syngas [8], optionally with added hydrogen, preferably renewable hydrogen, is thereafter fed to gas inlets within the shaft of the blast furnace, i.e. above the bosh, preferably within the gas solid reduction zone of ferrous oxide above the cohesive zone.
| Number | Date | Country | Kind |
|---|---|---|---|
| LU102057 | Sep 2020 | LU | national |
This application is a 35 U.S.C. § 371 National Stage patent application of PCT/EP2021/074749 filed 9 Sep. 2021, which claims the benefit of Luxembourg patent application 102 057 filed 9 Sep. 2020, the disclosures of which are incorporated herein by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/074749 | 9/9/2021 | WO |
