Reducing agent in powder form, its use and procedure for producing that reducing agent

Abstract

The invention relates to a powdered reducing agent, its use, and a method for producing it from biomass, preferably as a raw material. The method comprises the following steps in the order indicated: compression of the biomass at a pressure ≥ 150 MPa, pyrolysis of the compressed biomass at a temperature ≥ 280 °C, and grinding of the pyrolyzed biomass into a powder. The powder grains obtained from the reducing agent have a sphericity S50.3, measured by dynamic image analysis according to ISO 13322-2:2021, greater than 0.7, preferably greater than 0.8.

Description

Technical field

[0001] The invention relates to a reducing agent in powder form, its use and a method for producing this reducing agent from biomass, preferably provided as a starting material. State of the art

[0002] The steel industry is considered one of the most energy-intensive sectors. The blast furnace process accounts for the largest share of energy consumption. The possibilities for reducing this energy demand from traditional energy sources, and thus CO2 emissions, are largely exhausted.

[0003] A reduction in CO2 emissions can be achieved in the long term by using hydrogen or electrical energy instead of carbon.

[0004] In the short and medium term, and possibly also during the transition phase, the use of CO2-neutral energy carriers as a replacement for fossil coal and coke in blast furnaces is conceivable in order to further reduce CO2 emissions. Renewable biomass products, such as wood in the form of waste or residual wood, etc., from industry and from agricultural and forestry products, etc., are considered such.

[0005] It is known that thermochemical treatment of biomass can alter its chemical and physical properties. This treatment removes, for example, water, oxygen, and organic substances from the biomass, thereby increasing its gravimetric energy density to values ​​comparable with coal.

[0006] From US patent 2014 / 0306386 A1, a process is known in which wood is dried to < 10% moisture content, heat-treated at 150°C and sorted by size before being fed directly into the blast furnace from above.

[0007] WO 2018 / 229720 A1 discloses a process for treating carbonaceous waste in which the waste is first dried at > 70 °C and then roasted at 200 to 320 °C. After grinding, particles with a size of < 10 µm are produced, comprising at least 4% of the solids blown into the blast furnace.

[0008] US patent 2018 / 0179448 A1 discloses another process in which a biogenic coke substitute for use in blast furnaces is produced by means of pretreatment and carbonization in the temperature range of approximately 350–750 °C. Optionally, compaction and / or comminution are also mentioned during pretreatment to achieve specific sizes and shapes. After pyrolysis, the material can be used for steel production.

[0009] Phanphanich M and Mani S report in Bioresource Technology 102 (2011), 1246-1253 on the torrefaction of pine chips and logging residues, also providing sphericities for the torrefied materials. The highest value achieved is 0.62.

[0010] The known state of the art in reducing agents derived from biomass presents problems with their introduction using existing conveying systems, which limits their use as a substitute for coal, especially hard coal. Further reasons against such use include their low density and the resulting low volumetric calorific value. Description of the invention

[0011] The object of the present invention is to provide a process by which a reducing agent with comparable gravimetric and volumetric energy density and comparable pumpability to that known, for example, from pulverized hard coal can be produced from biomass. This object is achieved by a process with the features of claim 1.

[0012] According to the invention, in the process for producing the reducing agent from biomass, preferably provided as a starting material, the following process steps are carried out in the order mentioned: a. Compacting the biomass at a pressure ≥ 150 MPa, b. Pyrolyzing the compacted biomass at a pyrolysis temperature ≥ 280 °C and c. Grinding the pyrolyzed biomass into powder.

[0013] Regarding compaction: Compacting the biomass at a pressure ≥ 150 MPa according to the invention enables the biomass, after pyrolysis, to exhibit a similar volumetric energy density to that of pulverized hard coal. Furthermore, this process step also favorably influences flowability, fluidizability, and conveyability. It also allows for a smaller storage and transport volume than is known for pyrolyzed biomass without prior compaction. The specified pressure ≥ 150 MPa leads to the formation of various bonding mechanisms, resulting in the formation of solid particles. In addition to interlocking bonds, such as those formed by the entanglement of individual particles, chemical and / or physical reactions result in bonds through adsorption and / or bridging.Furthermore, the selected pressure renders the lignin contained in the biomass plastic, allowing it to penetrate the pores of the biomass and subsequently bind individual biomass particles together. This results in the required sphericity of the powder particles after pyrolysis and pulverization. This compaction also leads to an increase in the product's strength after pyrolysis.

[0014] Ad. Pyrolysis: By pyrolyzing the compacted biomass at a pyrolysis temperature ≥ 280 °C, the chemical and physical properties of the biological reducing agent can be influenced. Using the pyrolysis process according to the invention, the gravimetric energy density and thus the calorific value are increased, while oxygen, water, and low-boiling-point organic substances are reduced. Furthermore, this pyrolysis process according to the invention leads to the desired decomposition reactions of the various biomass components (carbonization), which consist mainly of cellulose, lignin, and hemicellulose. This prevents insufficient decomposition of the biomass components and thus also prevents the granules from remaining fibrous even after comminution.The pyrolysis temperature according to the invention, ≥ 280 °C, in combination with the preceding compaction, destroys the otherwise fibrous structure of the biomass, thus preventing the formation of elongated grains in the subsequent comminution step. A suitable pyrolysis reactor is, for example, a fluidized bed, rotary kiln, or screw reactor. Other reactor types are conceivable.

[0015] Ad. Comminution: After pyrolysis, the pyrolyzed biomass is comminuted into powder. Various comminution methods are conceivable, particularly those that result in a particle shape that is as spherical as possible. Compaction, pyrolysis, and comminution prevent rod-shaped particles, which can lead to clogging during pneumatic conveying and also make fluidizing the powder difficult. According to the invention, the biomass powder particles exhibit a high sphericity after comminution, namely s 50.3 > 0.7, in particular > 0.8, as measured by dynamic image analysis according to ISO 13322-2:2021. A QICPIC device from SYMPATEC GmbH System-Partikel-Technik, Germany, also known as "Sympatec-QICPIC," can be used for this purpose. The index "3" at s 50.3 specifies that the sphericity s 50.3 refers to a volume distribution; accordingly, 50 vol.-% of the particle collective has a higher respective particle sphericity than the specified value.

[0016] To achieve this sphericity, in addition to grinding into powder, compaction (rearrangement of the lignin) and pyrolysis (destruction of the cellulose fiber structure) are necessary.

[0017] This allows the biological reducing agent in powder form to be conveyed with a level of ease comparable to that of hard coal. Therefore, unlike with conventional powdered biomass, no further countermeasures are necessary to prevent conveying disruptions, such as higher conveying gas volumes for pneumatic conveying or mechanical discharge aids for the conveying vessels, which require more complex processes or, in existing plants, are only feasible through modification or new construction.

[0018] Preferably, compaction takes place at a pressure in the range of 150 to 350 MPa and preferably with a residence time under this pressure in the range of 3 to 6 seconds. This allows the aforementioned bonding mechanisms to develop more effectively through lignin rearrangement, which, after pyrolysis and comminution into powder, can further increase the required sphericity. For example, at the pressure according to the invention in the range of 150 to 350 MPa with a residence time in the range of 3 to 6 seconds, heating to 60 to 135 °C also occurs due to friction, which can further improve compaction.

[0019] It is conceivable that compaction could increase the bulk density of the biomass to between 1000 and 1300 kg / m³. Possible compaction methods include pressing processes such as pelleting or briquetting.

[0020] Preferably, pyrolysis is carried out at a pyrolysis temperature in the range of 280 °C to 600 °C, in particular from 300 °C to 450 °C and / or with a residence time at the pyrolysis temperature in the range of 1 minute to 3 hours, in particular from 20 minutes to 3 hours.

[0021] By limiting the pyrolysis temperature to ≤ 600 °C, a reduction in the solids-based yield due to mass loss can be avoided, for example. Furthermore, it can be prevented that the pyrolyzed biomass becomes so brittle that a comparatively high proportion of fines forms during subsequent comminution, which can adversely affect the fluidizability and thus the pneumatic conveyability of the reducing agent. The effects according to the invention can be further improved if the pyrolysis is carried out at a pyrolysis temperature in the range of 300 °C to 450 °C.

[0022] It can be advantageous if pyrolysis is carried out with a residence time in the range of 1 minute to 3 hours, especially from 20 minutes to 3 hours.

[0023] In the case of using a fluidized bed reactor for pyrolysis, for example, a pyrolysis temperature in the range of 300 to 360 °C and a residence time at this pyrolysis temperature in the range of 1 to 10 minutes may be sufficient to achieve an optimum in yield and energy density on the one hand and in grain size and grain shape on the other.

[0024] In a preferred embodiment, the compacted biomass can be heated to the pyrolysis temperature at a heating rate in the range of 0.01 to 2 K / s during pyrolysis in order to further improve the process.

[0025] Preferably, the pyrolysis is carried out essentially in the absence of air. For example, this pyrolysis can be carried out without the supply of oxygen.

[0026] For example, comminution can be achieved by grinding. A suitable method of comminution is, for instance, grinding the biomass using an impact or roller mill. Impact milling, for example, has the advantage of minimizing shear stress on the biomass. It is conceivable that screening could take place during or after grinding to avoid a comparatively high proportion of powder particles with a diameter < 10 µm, which could lead to detrimental cohesive behavior of the reactant.

[0027] Preferably, the biomass is reduced to a mean particle size x 50 in the range of 40 to 90 µm, which can further improve the conveyability of the powder. The method according to ISO 13320-1 using Sympatec-HELOS is suitable for measuring the mean particle size x 50.

[0028] Preferably, the biomass is dried to a moisture content of 8 to 20%, particularly 8 to 13% by weight, before compaction. The moisture content of different biomasses can vary considerably, depending, for example, on the type of biomass, storage duration, external influences, and any prior use. Drying can therefore be advantageous to homogenize the moisture content of the biomasses used. The moisture content of fresh biomass can be as high as 60% before drying. The moisture content can be adjusted by drying the biomass in a drying oven. For this purpose, the biomass or a sample thereof can be weighed and then dried in an oven until no further mass loss occurs. Afterward, the biomass or a sample thereof is weighed again, and the moisture content is determined from the weight loss.For example, one economically advantageous method of drying biomass is drying biomass in the form of atmospheric air drying.

[0029] The determination of the water content in the biomass can be carried out in particular according to DIN EN ISO 18134-3.

[0030] The biomass is preferably dried before compaction at a drying temperature in the range of 40 to 130 °C using a drying process under atmospheric pressure. Vacuum drying is also possible. It is also conceivable that the biomass is pre-shredded before compaction – for example, to a medium size in the range of 4 to 6 mm (millimeters). Depending on the origin of the biomass, or if it has already been shredded for drying, the required size range may already be met, thus eliminating the need for further shredding. For example, biomass from the wood processing industry generally does not require shredding. Shredding is preferably carried out by chopping, shredding, grinding, or other suitable size reduction methods to achieve the most homogeneous size distribution possible.

[0031] Preferably, the biomass provided for compaction has an average lignin content of >10% by weight (wt%) in order to further improve the formation of solid particles during compaction. This is particularly relevant if the biomass provided has an average lignin content of >13%.

[0032] Depending on the lignin content of the biomass provided, an additional binder may be required. This is the case, for example, if the biomass provided has an average lignin content of ≤ 10% by weight.

[0033] It is also conceivable to add a lignin-containing additive to adjust biomass to a desired or required lignin content. A lignin-containing additive, or the lignin for such an additive, could, for example, originate from paper production, where it is generated in relatively large quantities.

[0034] Biomass with a medium lignin content of >15% is particularly suitable for the process according to the invention, as this leads to a further improvement in particle properties. This also advantageously increases the energy content of the particles.

[0035] ASTM E1758-01 (Standard Test Method for Determination of Carbohydrates in Biomass by High Performance Liquid Chromatography) combined with ASTM D1106-21 (Standard Test Method for Acid-Insoluble Lignin in Wood) can be used to determine the lignin content. The values ​​obtained from this determination are given as weight percent.

[0036] For the process according to the invention, biomass, preferably provided as a starting material, is particularly suitable: Plant biomass, preferably purely plant biomass, which may optionally be treated with lignin as a binding agent, or woody biomass, namely short-rotation coppice including bark.

[0037] Furthermore, suitable biomass options include: short-rotation coppice including bark, and other woody materials such as waste wood, sawmill residues, and forest cuttings. This is due, among other things, to the sustainable supply made possible by plantation-like cultivation or the utilization of unused or low-quality material streams.

[0038] The aforementioned biomass(s) may be particularly suitable because the lignin content not only provides carbon but also significantly improves the formation of solid particles during compaction. For example, the biomass contains lignin.

[0039] The invention also aims to create a reducing agent from biomass, preferably provided as a starting material, which can be used reliably as a replacement for coal in plants. Furthermore, this reducing agent should exhibit a high gravimetric and volumetric energy density.

[0040] The invention solves the stated problem through claim 14.

[0041] A reducing agent in powder form produced by the process according to the invention can, unlike other reducing agents produced from biomass, exhibit a special sphericity. According to the invention, these powder granules have a sphericity s 50.3 > 0.7, in particular > 0.8, as measured by dynamic image analysis according to ISO 13322-2:2021. "Sympatec-QICPIC" can be used for this purpose.

[0042] This allows the biomass powder to be easily conveyed. This reduces disruptions to the conveying system and also enables higher conveying volumes. The biomass-based reducing agent according to the invention can therefore readily replace coal from mining.

[0043] Preferably, the calorific value of the reducing agent from biomass is in the range of 20 to 30 MJ / kg, measured according to DIN EN ISO 18125:2017-08.

[0044] For example, the carbon content of the reducing agent from biomass is in the range of 50 to 85 percent by weight, measured according to DIN 51732:2014-07. This means that this reducing agent has a sufficient energy density for a wide variety of reduction processes.

[0045] The bulk density of the reducing agent from biomass can be > 450 kg / m 3< , measured according to DIN EN ISO 60:2000-01.

[0046] The above can be further improved if the reducing agent has a mean particle size x 50 in the range of 40 to 90 µm, measured according to ISO 13320-1. For this purpose, a HELOS instrument from SYMPATEC GmbH System-Partikel-Technik, Germany, also known as "Sympatec-HELOS", can be used.

[0047] The reducing agent according to the invention is particularly suitable for steel production, especially as at least a partial replacement for bituminous coal, small-diameter coke, lump coke, or coke dust. Further applications include, for example, the replacement of coke dust in sinter production or its use as an additive in other metallurgical processes, such as the electric arc melting process. Method for implementing the invention

[0048] To demonstrate the achieved technical effects, the reducing agent from biomass was produced several times using different methods. Example 1:

[0049] Woody biomass, namely short-rotation coppice including bark, was pre-shredded into wood chips with particle sizes G30-G50 using a shredder or chipper, dried to a moisture content of 14%, and processed into shavings using a hammer mill. The average particle size was 4-6 mm.

[0050] The biomass provided in this way has an average lignin content of 23%.

[0051] This supplied biomass was then compressed into pellets (6-12 mm in diameter) using a pellet press at a pressure of 320 MPa, a residence time of 5 seconds, and a temperature of 90 to 110 °C, and subsequently cooled until hardened. This increased the bulk density to over 600 kg / m³ and the raw density to approximately 1100 kg / m³.

[0052] The pellets were then pyrolyzed in a torrefaction reactor (rotary reactor with an oxygen-depleted atmosphere) by heating them to 330–340 °C for 60 minutes and degassing them. Cooling followed. This resulted in a carbon content of approximately 65–75% by weight and a calorific value of approximately 25–28 MJ / kg in the finished reducing agent.

[0053] The pyrolyzed biomass was then pulverized for use as a reducing agent for iron ore by means of a roller mill to a particle size of 95 percent by weight less than 300 µm and an x ​​50 (corresponding to the particle size value at which 50 percent by weight of the ground material is below or above) of 40 to 90 µm (measured according to ISO 13320-1 with Sympatec-HELOS).

[0054] The finished reducing agent in powder form was blown into the blast furnace with inert gas via the existing coal-fired furnace technology as a test.

[0055] The following characteristic values ​​were recorded for this reducing agent according to embodiment 1: Carbon content = 73.1% according to DIN 51732:2014-07, calorific value = 25.78 MJ / kg, measured according to DIN EN ISO 18125:2017-08, sphericity s 50.3 = 0.85, measured by dynamic image analysis according to ISO 13322-2:2021 with Sympatec-QICPIC, bulk density = 500 kg / m 3< , measured according to DIN EN ISO 60:2000-01 and mean particle size x 50 = 42.4 µm, measured according to ISO 13320-1 with Sympatec-HELOS. Example 2:

[0056] Woody biomass was conveyed to a shredding plant and pre-shredded to the appropriate particle size (as in example 1). The moisture content was then adjusted to approximately 14%.

[0057] The biomass provided in this way has an average lignin content of 23%.

[0058] The compaction was carried out as described in Example 1, except that the pellets were fragmented. This biomass was pyrolyzed in a fluidized bed reactor at 330–340 °C for 6 minutes and subsequently cooled by active and direct air cooling. The comminution and use as a reducing agent were carried out as described in Example 1.

[0059] The following characteristic values ​​were recorded for this reducing agent according to embodiment 2: Carbon content = 72% according to DIN 51732:2014-07, calorific value = 25.4 MJ / kg, measured according to DIN EN ISO 18125:2017-08, sphericity s 50.3 = 0.83, measured by dynamic image analysis according to ISO 13322-2:2021 with Sympatec QICPIC, bulk density = 490 kg / m 3< , measured according to DIN EN ISO 60:2000-01 and mean particle size x 50 = 50 µm, measured according to ISO 13320-1 with Sympatec-HELOS. Example 3:

[0060] For the compaction step, a briquetting device was used instead of a pellet press. The remaining process steps were carried out analogously to embodiments 1 and 2.

[0061] The following characteristic values ​​were recorded for this reducing agent according to embodiment 3: Carbon content = 72.9% according to DIN 51732:2014-07, calorific value = 25.6 MJ / kg, measured according to DIN EN ISO 18125:2017-08, sphericity s 50.3 = 0.8, measured by dynamic image analysis according to ISO 13322-2:2021 with Sympatec-QICPIC, bulk density = 450 kg / m 3< , measured according to DIN EN ISO 60:2000-01 and mean particle size x 50 = 70 µm, measured according to ISO 13320-1 with Sympatec-HELOS. Example 4:

[0062] In contrast to embodiments 1, 2, and 3, other woody materials, such as waste wood, sawmill residues, and forest cuttings, were added to the biomass, which also included short-rotation coppice with bark. The resulting biomass had an average lignin content of 23%.

[0063] The following characteristic values ​​were recorded for this reducing agent according to embodiment 4: Carbon content = 74.6% according to DIN 51732:2014-07, calorific value = 26 MJ / kg, measured according to DIN EN ISO 18125:2017-08, sphericity s 50.3 = 0.82, measured by dynamic image analysis according to ISO 13322-2:2021 with Sympatec-QICPIC, bulk density = 490 kg / m 3< , measured according to DIN EN ISO 60:2000-01 and mean particle size x 50 = 60 µm, measured according to ISO 13320-1 with Sympatec-HELOS.

[0064] Thus, all reducing agents of the aforementioned embodiments 1 to 4 meet the conditions with a carbon content of > 65 wt%, measured with an elemental analyzer according to DIN 51732:2014-07, a calorific value of > 25 MJ / kg, measured according to DIN EN ISO 18125:2017-08, a sphericity of s 50.3 > 0.8, measured by dynamic image analysis according to ISO 13322-2:2021 with Sympatec-QICPIC, a bulk density of > 450 kg / m 3< , measured according to DIN EN ISO 60:2000-01 and a mean particle size x 50 in the range of 40 to 90 µm, measured according to ISO 13320-1 with Sympatec-HELOS.

[0065] It is generally accepted that "in particular" can be translated into English as "more particularly". A feature preceded by "in particular" is to be considered an optional feature that can be omitted and therefore does not represent a limitation, for example, of claims. The same applies to "preferably", which is translated into English as "preferably".

Claims

1. Method for producing a powdered reducing agent from biomass, preferably provided as a starting material, wherein the powder grains of the reducing agent have a sphericity s50,3 > 0.7, more particularly > 0.8, measured by dynamic image analysis according to ISO 13322-2:2021, comprising the following steps in the order stated: compacting the biomass at a pressure ≥ 150 MPa, pyrolyzing the compacted biomass at a pyrolysis temperature ≥ 280°C, and grinding the pyrolyzed biomass into powder.

2. Method according to claim 1, characterized in that the compaction takes place at a pressure in the range of 150 to 350 MPa and preferably at a dwell time under this pressure in the range of 3 to 6 seconds.

3. Method according to claim 1 or 2, characterized in that the compaction increases the bulk density of the biomass to 1000 to 1300 kg / m3.

4. Method according to one of the preceding claims, characterized in that the pyrolysis is carried out at a pyrolysis temperature in the range from 280°C to 600°C, more particularly from 300°C to 450°C, and / or with a dwell time at the pyrolysis temperature in the range from 1 minute to 3 hours, more particularly from 20 minutes to 3 hours.

5. Method according to one of the preceding claims, characterized in that the pyrolysis is carried out in a fluidized bed reactor at a pyrolysis temperature in the range of 300 to 360°C and with a dwell time at this pyrolysis temperature in the range of 1 to 10 minutes.

6. Method according to one of the preceding claims, characterized in that during pyrolysis, the compacted biomass is treated with a heating rate in the range of 0.01 to 2 K / s to the pyrolysis temperature and / or in that the pyrolysis is carried out essentially in the absence of air.

7. Method according to one of the preceding claims, characterized in that the comminution is carried out by grinding, more particularly by means of an impact or roller bowl mill.

8. Method according to one of the preceding claims, characterized in that the biomass is comminuted to a mean particle size x50 in the range from 40 to 90 µm, measured according to the method according to ISO 13320-1.

9. Method according to one of the preceding claims, characterized in that the biomass is dried to a water content in the range of 8 to 20%, more particularly 8 to 13% by weight, before compaction.

10. Method according to one of the preceding claims, characterized in that the biomass is dried at a drying temperature in the range of 40 to 130°C prior to compaction and / or in that the biomass is pre-crushed prior to compaction, more particularly to a medium size in the range of 4 to 6 mm.

11. Method according to one of the preceding claims, characterized in that for production from biomass, preferably provided as a starting material, the following is used: - plant biomass, preferably pure plant biomass, which may be treated with a binding agent or lignin-containing additive, or - wood-based biomass, or - wood-based biomass, namely short-rotation wood including bark, or - short-rotation wood including bark, other woody feedstocks, such as waste wood, sawmill residues, and forest cuttings added.

12. Method according to one of the preceding claims, characterized in that the biomass contains lignin and / or in that the biomass provided for compaction has an average lignin content, determined according to ASTM E1758-01 with ASTM D1106-21, of > 10 percent by weight, more particularly > 13 percent by weight.

13. Powdered reducing agent whose powder grains have a sphericity s50,3 > 0.7, more particularly > 0.8, measured by dynamic image analysis according to ISO 13322-2:2021, produced from biomass according to the method according to one of claims 1 to 12.

14. Reducing agent according to claim 13, characterized in that the calorific value of the reducing agent is in the range of 20 to 30 MJ / kg, measured in accordance with DIN EN ISO 18125:2017-08, and / or in that the carbon content of the reducing agent is in the range of 50 to 85 percent by weight, measured in accordance with DIN 51732:2014-07.

15. Reducing agent according to one of claims 13 to 14, characterized in that the bulk density is > 450 kg / m3, measured in accordance with DIN EN ISO 60:2000-01, and / or in that the reducing agent has a mean particle size x50 in the range from 40 to 90 µm, measured in accordance with ISO 13320-1.

16. Use of a reducing agent according to one of claims 13 to 15 in steel production, more particularly as at least a partial substitute for hard coal, small coke, lump coke, or coke breeze.