FI20245345A1 - Preparation of fossil-free coke from lignin - Google Patents

Abstract

The invention relates to a method for producing fossil-free coke from lignin, which method comprises the steps of obtaining lignin, subjecting the lignin to elevated pressure, subjecting the lignin to elevated temperature, whereby the combination of elevated pressure and temperature releases volatile organic compounds (VOCs), and recovering the coke. The invention also relates to an apparatus (1000) for producing fossil-free coke from lignin, the use of the apparatus (1000), and the coke obtainable by the method.

Description

PREPARATION OF FOSSIL-FREE COKE FROM LIGNIN

TECHNICAL FIELD

[0001] The present invention relates to a method of preparing coke. Further, the present invention relates to an apparatus for the production of fossil-free coke from lignin. Still further, the present invention relates to coke obtainable by said method.

BACKGROUND

[0002] Metallurgical coke is a high-carbon fuel that is primarily used in the iron and steel-making industries to provide heat and reduce the iron oxide in iron ore. It is made by heating coal in the absence of air, a process called "carbonization," to remove volatile components and leave behind a solid, porous material rich in carbon.

[0003] The process of making metallurgical coke involves the following steps: e — Selection and preparation of coal: The coal used to make metallurgical coke is usually a high-guality bituminous coal with low sulfur and ash content. The coal is crushed and screened to remove any impurities. e Charging: The coal is charged into a coke oven, which is a large, refractory-lined chamber. The oven is sealed, and the temperature is gradually raised to around 2000°F (1093°C) using natural gas or coke oven gas as fuel. e Carbonization: The coal is carbonized for around 18 to 24 hours, during which time the volatile components are driven off, leaving behind solid coke. e Quenching: After the carbonization process is complete, the coke is quenched with water or air to cool it down and prevent it from continuing to react. e Recovery: The volatile components that were driven off during carbonization are + 25 collected and used as fuel or chemical feedstocks.

S [0004] There are several drawbacks to this method of making metallurgical coke. The carbonization

O process releases large amounts of greenhouse gases such as carbon dioxide, as well as other pollutants

I into the atmosphere contributing to climate change and air pollution. Additionally, workers in a coke

N plant may be exposed to potentially hazardous gases such as benzene and ammonia, which could cause & 30 health issues. Further, coal is a non-renewable resource, upon which traditional methods of coke 2 manufacture rely. The production of coke requires a large quantity of energy, often derived from fossil

O fuels, further contributing to emissions of greenhouse gases and to climate change.

O [0005] Overall, the production of metallurgical coke is an important process for the iron and steel industry, but it comes with several significant drawbacks that need to be addressed to make the process more sustainable and environmentally friendly.

[0006] Making coke from biomass involves a similar process to that used in traditional coal-based coke production, but instead of using coal, biomass such as wood chips or agricultural waste is used as the raw material. The process involves heating the biomass in an oxygen-free environment to produce a solid, high-carbon fuel.

[0007] The process of making biomass coke involves the following steps: e — Selection and preparation of biomass: The biomass used to make coke must be of high quality, free from contaminants such as sand, stones, or metals. The biomass is crushed, screened, and dried to remove any moisture. e Charging: The prepared biomass is charged into a coke oven, which is similar to those used in traditional coke production. e Carbonization: The biomass is carbonized at high temperatures of around 1200°C to 1500°C, with the process taking several hours. During carbonization, volatile components are removed, leaving behind a solid, porous material rich in carbon. e Quenching: After the carbonization process is complete, the coke is cooled down using water or air to prevent further reactions. e Recovery: The volatile components that were removed during carbonization can be collected and used as a fuel or chemical feedstock.

[0008] The availability of biomass for coke production is limited and the production of biomass coke is more expensive than traditional coke due to the higher costs of the feedstock and the technology used. Biomass coke has a lower energy density than traditional coke which rules it unsuitable for some industrial process. There is the additional concern that the production of biomass coke may contribute to deforestation and the loss of natural habitats.

[0009] Compared to traditional coal-based coke, biomass coke has the potential to be a more sustainable and environmentally friendly option. Biomass is a renewable resource, and its use for coke production could reduce reliance on non-renewable coal. However, the higher cost and lower energy density of biomass coke may limit its potential for widespread adoption in industrial applications.

Additionally, further research and development are needed to optimize the production process and

N reduce environmental impacts.

N

& 5 30 SUMMARY z [0010] It is an aim of the present invention to overcome at least some of the problems described o above and provide a method for the production of fossil-free coke from lignin. Aspects of the invention 3 are defined in the independent claims. According to a first aspect of the invention there is provided a

N method for the production of fossil-free coke from lignin as defined in claim 1. According to a second

N 35 aspect of the invention there is provided an apparatus for the production of fossil-free coke from lignin as defined in claim 11. According to a third aspect of the present invention there is provided a use of the apparatus of the second aspect, defined in claim 15. According to a fourth aspect of the invention there is provided coke obtainable by the method of the first aspect, defined in claim 16.

[0011] It has surprisingly been found that a high-quality lignin coke having a high energy density, similar to that of traditional metallurgical coke and containing more fossil-free carbon than biomass coke can be prepared by means of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the following, the invention will be described in more detail with reference to the appended drawing which illustrates an apparatus for production of fossil-free coke from lignin.

EMBODIMENTS

[0013] The present invention relates to a method of manufacturing fossil-free coke from lignin in which method lignin is subjected to elevated temperature and increased pressure, whereby volatile organic compounds (VOCs) are released from the lignin during the coking process. The volatile organic compounds may be recovered for further processing. After the release of VOCs coke is recovered having a hardness in the range of 30 to 90 on the Hardgrove grindability index (HGI) and a porosity in the range of 35 to 55%. The high-quality coke recovered is suitable for replacing all or at least a part of coke e.g. in metallurgical processes. The present invention further relates to an apparatus for carrying out the method. One embodiment of the apparatus is illustrated in FIGURE 1.

[0014] FIGURE 1 illustrates an apparatus1000 according to at least some embodiments. In one embodiment the apparatus comprises a storage silo 20 for storing lignin which is fed from the storage silo 20 to a solid base 30. The lignin is fed from the silo 20 into a coking oven 120 to the solid base 30 with a feeding conveyor 40 suitable for the transfer of a lignin raw material from the storage silo 20 to the solid base 30. The solid base 30 is adapted to convey lignin through the coking oven to a first calendar <+ 25 60 to which heat 50 for heating the lignin and intermediates in the coking process is applied. The first

N

< calendar 60 is equipped with a device 70 for the application of pressure onto the lignin and intermediates & in the coking process. As the lignin and intermediates are heated 50 and pressurised 70 with the first

N calendar 60, VOCs are released which are optionally directed to recovery 80 for further use. A further

I calendar or calendars 65 similarly adapted to apply heat 55 and pressure 75 to lignin and intermediates [an “30 are optionally provided. After pressure 70 and heat 55 treatment with a first calendar 60 and optionally

LO . . . .

S further calendars 65 coke is formed. The coke is conveyed from the coking oven 120, optionally on a 3 conveyor 100 to coke storage 110 after optional cooling and heat recovery 90.

O

N [0015] As described above, the present technology relates to a method for the production of fossil- free coke from lignin. In an embodiment the method comprises the steps of providing lignin, subjecting the lignin to increased pressure, subjecting the lignin to increased temperature, whereby a combination of increased pressure and temperature releases volatile organic compounds (VOCs), and recovering coke. The lignin is typically provided in the form of lignin chips, however in some embodiments the lignin is provided in the form of an aqueous slurry e.g. in an embodiment lignin precipitated from black liquor such as in a pulp mill is the source of lignin.

[0016] Lignin is a complex organic polymer found in the cell walls of many plant species. In one embodiment the lignin is obtained from softwood. Softwoods are commonly used in a variety of application such as construction, furniture, paper and packaging materials. The specific properties and characteristics of each wood might be dependent on where and how the wood is grown and how it is processed. All softwoods, however, contain lignin. In an embodiment the lignin is obtained from softwood selected from the group consisting of pine, spruce, fir, cedar, hemlock, douglas fir, redwood, yew cypress, juniper, larch, tamarack, western red cedar, eastern white pine, white cedar, and a mixture thereof.

[0017] In a further embodiment the lignin is obtained from hardwood. Hardwoods are often used in the manufacture of e.g. fumiture and flooring. The properties of hardwoods, too, may be dependent on the conditions in which they are grown and processed as with softwoods. In a further embodiment the lignin is obtained from hardwood selected from the group consisting of oak, maple, cherry, walnut, ash, birch, hickory, mahogany, teak, poplar, beech, sycamore, elm, alder, ebony, eucalyptus, and a mixture thereof.

[0018] Further sources of lignin are used in embodiments. In an embodiment the lignin is obtained from agricultural residues. Upcycling of agricultural residues that would normally be left to decompose or be burned provides a valuable renewable source of lignin. In an embodiment the lignin is obtained from an agricultural residue selected from the group consisting of wheat straw, rice straw, bagasse and a mixture thereof. In one embodiment the lignin is obtained from energy crops, which are typically grown for bioenergy production. In an embodiment the lignin is obtained from at least one energy crop selected from the group consisting of willow, miscanthus, and switchgrass.

[0019] It has been found that lignin from various sources may be mixed and used together. For

N example, lignin obtained from hardwood may be mixed with lignin obtained from softwood. Similarly, a lignin contained with hardwood may be mixed with lignin obtained from agricultural residues. Further,

I lignin obtained from softwood may be mixed with lignin obtained from agricultural residues. In one

N 30 embodiment the lignin is obtained from the group consisting of hardwood, softwood, agricultural

E: residues and a mixture thereof. s [0020] As mentioned above lignin can be obtained from industrial residues such as black liguor. In 3 the past, black liquor has been evaporated to increase its solid content and has then been sprayed into a x furnace and burned whereby valuable process chemicals for the pulp mill can be recovered. Because lignin recovered from black liquor stinks it was typically burned. Lignin, however, has become a valuable resource and may be recovered from the black liquor by various methods. Typically, lignin is recovered from black liguor in a precipitation process, for example an acid precipitation process. Thus, in an embodiment the lignin is obtained from black liguor from a pulp mill. In one embodiment the lignin is recovered from black liquor in a precipitation process. In a further embodiment, the lignin is recovered from black liguor in an acid precipitation process. 5 [0021] As described above the lignin is provided and subjected to an increase in pressure. In an embodiment the increased pressure is provided by contacting lignin with an external surface of a first calendar and a planar surface of a bed, whereby the calendar is adapted to move perpendicular to the bed. The pressure is provided by the mechanical load exerted by the calendar onto the lignin which is on the planar surface of the bed.

[0022] In a further embodiment the pressure is provided by contacting lignin with the external surface of the first calendar and an external surface of a lower calendar, whereby at least one of the first and lower calendars is adapted to move perpendicular to the lower or first calendar. The perpendicular movement of the first and/or lower calendar with respect to the lower and first calendar exerts a mechanical load onto the lignin contacted by the calendars. For the purpose of embodiments the term “lower” with respect to lower calendar means that the calendar is positioned below or beneath the first calendar. In one embodiment the pressure the lignin is subjected to is increased to a pressure in the range of 0.5 — 5 kg/cm”, suitably 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 12, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 19, 2.0, 2.1, 22, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8. 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7,4.8, or 4.9 kg/cm?

[0023] In order to release VOCs, in addition to subjecting the lignin to pressure the lignin is heated.

In an embodiment the lignin is heated by at least one of the surfaces contacting the lignin e.g. at least the planar surface or the first calendar is heated. In a further embodiment the lignin is heated by more than one of the surfaces contacting the lignin, e.g., both the planar surface and first calendar or both the first and the lower calendars are heated.

[0024] The heated surfaces may be heated in a variety of ways. For example, in an embodiment the surface or surfaces are heated with steam. In a further embodiment the surface or surfaces are heated

S with electricity. In one embodiment the surface or surfaces are heated with combustible gases. & [0025] In one embodiment the lignin is subjected to a temperature in the range of 50 — 600 °C,

S preferably 100 — 500 °C, suitably 200 — 400 °C, particularly 250 — 350 °C, e.g., about 260, 270, 280,

I 30 290, 300, 310, 320, 330 or 340 °C. > [0026] As mentioned above the combination of heating and pressing causes the release of VOCs. 3 In an embodiment the VOCs are recovered for further processing. VOCs are all those organic

N compounds that exist in a gas or very volatile liguid state at ordinary room temperature. VOCS are all

N those organic compounds that have a vapour pressure egual to or higher than 0.01 kPa or an eguivalent volatility in the particular conditions of use at 20*C. VOCs usually have less then twelve carbon atoms in their chain and contain other elements such as oxygen, fluoride, chlorine, bromine, sulphur or nitrogen. In a particular embodiment. In one embodiment the recovered VOCs are burned to provide at least a portion of the heat for heating the surfaces of the planar surface and/or the surface of the first calendar or the surface of the first calendar and/or the surface of the lower calendar. The increased temperature and increased temperature are applied until the coke to be recovered has a desired porosity and desired hardness.

[0027] The ideal porosity and hardness of metallurgical coke can vary depending on the specific requirements of the steelmaking process and the particular blast furnace in which the coke will be used.

However, generally speaking, there are certain ranges of porosity and hardness that are considered suitable for metallurgical coke used in the steelmaking process.

[0028] Porosity refers to the amount of empty space or voids within the coke. In the context of metallurgical coke, porosity is an important factor as it affects the permeability of the coke in a blast fumace. the higher the porosity, the easier it is for gases to flow through the coke bed and the reaction between the coke and the hot gases proceeds faster. Porosity of the coke can be measured using a variety of methods, e.g., the mercury intrusion porosimetry (MIP) method (ISO 15901-1:2016) or the gas adsorption method (ISO 15901-2:2022). In MIP, mercury is forced into the pores of the coke under high pressure and the volume of mercury that is absorbed is measured. In gas adsorption, coke is exposed to a gas, typically nitrogen or sometimes carbon dioxide and the amount of gas that is absorbed by the coke is measured.

[0029] The porosity of metallurgical coke used in the steelmaking process typically falls in the range of 25% to 35%. This level of porosity allows for adeguate gas flow through the coke bed in the blast furnace, which is essential for the reduction of iron oxide and the production of steel.

[0030] Thus, in one embodiment the increased pressure and increased temperature to which the lignin is subjected to is maintained until the coke produced has a porosity in the range of 20% to 40 %, preferably 25% to 35%, e.g. 26 %, 27%, 28%, 29%, 30%, 31%, 32%, 33% or 34% when measured by

MIP in accordance with ISO 15901-1:2016 and/or when measured by gas adsorption in accordance with

ISO 15901-2:2022. x < [0031] Hardness refers to the resistance of a material to deformation, indentation, or scratching. In & the context of metallurgical coke, hardness is important as it affects the strength of the coke and its

S ability to withstand the weight of the material above it in a blast furnace.

E 30 [0032] Typically, the hardness of coke is measured according to ASTM D409-17. A sample of coke

LO is crushed and screened to a size range suitable for the test, typically 0.6 — 1.8 mm. A weighed sample 3 of coke, typically 50g is placed in a ball and race mill, which is rotated at a speed of 60 revolutions per

N minute (rpm). After a specified grinding time, e.g. 600 revolutions or 10 minutes, the mill is stopped

N and the ground material is sieved through a standard mesh size of 75 microns. The undersize fraction, expressed as a percentage of the total sample is used to calculate HGI using the formula HGI = 100 (-

undersize % x 1.7), where 1.7 is a constant to convert the undersize percentage to the HGI scale. The test is repeated at least twice to provide an average HGI value.

[0033] The hardness of metallurgical coke used in the steelmaking process is typically in the range of 60 to 90 HGI (Hardgrove Grindability Index). This level of hardness ensures that the coke can withstand the weight of the material above it in a blast furnace and maintain its structural integrity during the steelmaking process.

[0034] Thus, in an embodiment the increased pressure and increased temperature to which the lignin is subjected to is maintained until the coke produced has a hardness in the range of 50 to 100 HGI, preferably 60 to 90 HGI, e.g. 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72,73, 74,75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88 or 89 HGI measured in accordance with ASTM D409-17.

[0035] The exact porosity and hardness requirements for coke depend very much on the application the coke will be used in. As such the porosity and hardness can be adjusted as required by varying the time that increased pressure and temperature are applied.

[0036] Further embodiments relate to an apparatus for manufacturing fossil-free coke from lignin.

In an embodiment the apparatus comprises an inlet for lignin, a first calendar, a lower calendar or moving bed (provided at the frame), whereby the first calendar and the lower calendar or moving bed are configured to press against each other, a surface for receiving the lignin from the inlet at one of the calendars or at the moving bed, a heating device for heating at least one of the surface for receiving the lignin, the first calendar, and the moving bed or the second calendar, an outlet for discharging VOCs released in the pressing and heating of the lignin from the apparatus, and an outlet for recovering coke.

[0037] In one embodiment the surface for receiving the lignin is the moving bed or the lower calendar. In a further embodiment the first calendar and the lower calendar or moving bed are configured to press against each other to exert pressure on the lignin, preferably increasing the pressure on the lignin to a pressure in the range of 0.5 — 5 kg/cm2, suitably 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, < 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, or 4.9 kg/cm?2. Exerting pressure on the lignin in combination with

S heat releases of VOCs from lignin leaving coke that is fossil free and that has a hardness and porosity & suitable for use in particular as metallurgical coke. Thus, in one embodiment the apparatus is used to

S carry out the method.

E 30 [0038] As described above, fossil free coke having a hardness and porosity rendering it suitable for

LO use as metallurgical coke is obtainable by the method. Similarly, fossil free coke suitable for use as 3 metallurgical coke is obtainable using the apparatus. Thus, one embodiment relates to fossil-free coke

N obtainable by the method described hereinabove.

N

INDUSTRIAL APPLICABILITY

[0039] Embodiments of the present invention find use in the production of fossil-free coke from lignin, e.g., lignin recovered as a by-product from pulp-mill processes. The method and apparatus are also suitable for coking lignin from a diverse range of sources ranging from hardwood and softwood to agricultural residues and energy crops. i

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Claims (1)

1. A method for the production of fossil-free coke from lignin comprising the steps of e providing lignin, e subjecting the lignin to increased pressure, e subjecting the lignin to increased temperature, whereby a combination of increased pressure and temperature releases volatile organic compounds, and e recovering coke.

2. The method according to claim 1, wherein the lignin is obtained from softwood, preferably from softwood selected from the group consisting of pine, spruce, fir, cedar, hemlock, douglas fir, redwood, yew cypress, juniper, larch, tamarack, western red cedar, eastern white pine, white cedar, and a mixture thereof.

3. The method according to claim 1, wherein the lignin is obtained from hardwood, preferably from hardwood selected from the group consisting of oak, maple, cherry, walnut, ash, birch, hickory, mahogany, teak, poplar, beech, sycamore, elm, alder, ebony, eucalyptus and a mixture thereof.

4. The method according to any of the preceding claims, wherein the lignin is obtained from a pulp mill, particularly the lignin is obtained from black liquor from a pulp mill, preferably by precipitation.

5. The method according to any of the preceding claims wherein, the increased pressure is provided by contacting lignin with an external surface of a first calendar (6a) and a planar surface of a bed, whereby the calendar is adapted to move perpendicular to the bed.

6. The method according to any of claims 1 to 4, wherein the pressure is provided by contacting lignin with — the external surface of the first calendar and an external surface of a lower calendar, whereby at least one of the first (6a) and lower calendars is adapted to move perpendicular to the lower or first calendar (6a). :

> 7. The method according to any of the preceding claims, wherein at least one of the surfaces contacting the ? lignin is heated. N

E 8. The method according to any of the preceding claims, wherein more than one of the surfaces contacting o 25 — the lignin are heated. 0

N 9. The method according to any of the preceding claims, wherein the pressure the lignin is subjected to is N increased to a pressure in the range of 0.5 — 5 kg/cm?, suitably 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5,

1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9,

4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, or 4.9 kg/cm?.

10. The method according to any of the preceding claims, wherein the temperature the lignin is subjected to is in the range of 50 — 600 °C.

11. The method according to any of the preceding claims, wherein the VOCs are recovered for further processing.

12. An apparatus (1000) for the production of fossil-free coke from lignin comprising e a frame, e an inlet for lignin, e a first calendar (6a), e a lower calendar or moving bed (3) provided at the frame, whereby the first calendar (6a) and the lower calendar or moving bed (3) are configured to press against each other, e a surface for receiving the lignin from the inlet at one of the calendars or at the moving bed, e a heating device (5) for heating at least one of the surfaces for receiving the lignin, the first calendar (6a), and the moving bed (3) or the second calendar(6b), e an outlet (8) for discharging VOCs released in the pressing and heating of the lignin from the apparatus, and e an outlet for recovering coke.

13. The apparatus (1000) according to claim 12, wherein the surface for receiving the lignin is the moving bed (3) or the lower calendar.

14. The apparatus (1000) according to claim 12 or 13, wherein the first calendar (6a) and the lower calendar or moving bed (3) are configured to press against each other to exert pressure on the lignin, preferably increasing the pressure on the lignin to a pressure in the range of 0.5 — 5 kg/cm”, suitably 0.6, 0.7, 0.8, 0.9,

1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3,

+ 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, or 4.9 kg/cm”. S N A 15. A use of the apparatus (1000) according to any of claims 12 to 14 in a method according to any of K 25 claims 1to 11. N = a 16. Coke obtainable by the method according to any of claims 1 to 11. Lo <t 0 Lo + N O N