FI20245494A1

FI20245494A1 - Synthesis gas production

Info

Publication number: FI20245494A1
Application number: FI20245494A
Authority: FI
Inventors: Eemeli Tsupari; Sampsa Vuori; Juho Kauppinen; Cyril Bajamundi; Esko Salo; Aki Hämäläinen
Original assignee: Teknologian Tutkimuskeskus Vtt Oy
Priority date: 2024-04-18
Filing date: 2024-04-18
Publication date: 2025-10-19
Also published as: WO2025219656A1; FI131724B1

Abstract

Esillä olevan keksinnön mukaan on tuotu esille prosessi synteesikaasun tuottamiseksi ensin tuottamalla hiilimonoksidia (CO) hiilidioksidia (CO2) sisältävästä virrasta, joka on saatu karbonaattia sisältävän raaka-aineen kalsinoinnista ja seuraavaksi saatetaan saatu CO:a sisältävä tuotekaasu edelleen kosketuksiin vetyä sisältävän kaasun kanssa synteesikaasun tuottamiseksi.According to the present invention, a process for producing synthesis gas is disclosed by first producing carbon monoxide (CO) from a carbon dioxide (CO2)-containing stream obtained from the calcination of a carbonate-containing feedstock and subsequently further contacting the resulting CO-containing product gas with a hydrogen-containing gas to produce synthesis gas.

Description

PRODUCING SYNTHESIS GAS

FIELD

[0001] The present invention relates to a process for producing synthesis gas by utilizing the carbon dioxide (CO2)-containing stream obtained from a calcination of a carbonate-containing raw material, and to the further uses of said synthesis gas.

BACKGROUND

[0002] Conventional calcinations and other similar high-temperature processes are — known to require large inputs of thermal energy, as well as to produce large amounts of carbon dioxide (CO>), both of which cause environmental hazards. Carbon capture has thus become an important technology area to be developed, for alleviating climate change.

However, many known processes for utilizing the CO? produced in such processes are expensive and thus far from efficient. — [0003] As a conseguence, there is a constant need for new alternatives for both energy production and for utilizing the formed carbon dioxide to prevent it from ending up in the atmosphere. Utilization of carbon dioxide formed in a calcination process has been described for example in WO 2015015161 Al. However, said document fails to utilize the full potential of the carbon dioxide. — [0004] Particularly carbon neutral processes for utilizing this gas stream are sought s after, thus providing more environmentally friendly solutions for these processes, and the & present invention provides a further alternative in this area.

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E SUMMARY OF THE INVENTION

+ . . . . .

S 25 — [0005] The invention is defined by the features of the independent claims. Some

LO a specific embodiments are defined in the dependent claims.

O

N

[0006] According to a first aspect of the present invention, there is provided a process that utilizes the gas stream containing carbon dioxide (CO) that is formed during calcinations of carbonate-containing raw materials.

[0007] According to a second aspect of the present invention, there is provided a — process that utilizes said CO? to produce synthesis gas.

[0008] According to a third aspect of the invention, there is provided alternatives for further use of said synthesis gas.

[0009] According to a further aspect, there is provided a more environmental alternative for supplying thermal energy to said process.

[0010] The present invention thus relates to a process for producing synthesis gas, by first producing carbon monoxide (CO) or a CO-containing gas mixture from a stream containing carbon dioxide (CO?) obtained from the calcination of a carbonate-containing raw material, among others, by utilizing Reactions (1) and (2) 2C0O; > 2CO + 0, (1)

CO, + C>2Cc0o (2) and subseguently contacting the CO-containing gas mixture further with a hydrogen- containing gas to produce synthesis gas.

[0011] Several advantages are achieved using the present process. Among others, carbon dioxide (CO?) emissions generated from the calcinations described herein and/or

S other high-temperature treatments can be utilized to provide efficient fuel sources for x combustion processes. The produced CO has a high energy content, with almost twice the © 25 — energy content compared to utilized carbonaceous material. Thus, the new process decreases = the consumption of conventional fuels, and it cuts down the carbon emissions of fuel 3 combustion. Further, the process provides a new technology, wherein limestone can be x utilized in the production of synthesis gas.

N

I [0012] The process also eliminates the need for high pressures and extreme temperatures in the production of carbon monoxide and synthesis gas.

[0013] Further, the optional electric calcination offers a cost-effective solution for the calcination and for capturing CO; by decreasing the consumption of energy from burning fossil fuels, while eliminating emissions of e.g. carbon and carbon dioxide from thermal energy production.

[0014] Particularly for cement production, the new process provides new resource efficient alternatives and enhances the process sustainability by decreasing the need for external energy supply.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIGURES 1 and 2 illustrate process configurations encompassed by the present invention; Fig. 1 illustrating the alternative of combining the reduction with the calcination, and Fig. 2 illustrating the alternative of carrying out a separate reduction of the

CO2-containing gas stream obtained from a heat treatment step. — [0016] FIGURE 3 illustrates a process configuration incorporating some preferred embodiments of the below description, showing for example the optional addition of further reagents (e.g. Oz, Hz, CH4, and steam) to either the calcination or the reduction step, or both, as well as using dotted lines to show the optional recovery of the CO2-containing gas stream, and to show the optional use of the CO-containing gas stream as dilution gas to enhance calcination. s [0017] FIGURE 4 illustrates a process configuration according to an embodiment of & the invention, where the synthesis gas is further converted into hydrocarbons. <t

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© [0018] FIGURE 5 illustrates the high CO; concentrations which can be achieved by r electrically heated calcination reactor, as a function of the pressure. [an a 3 25 [0019] FIGURE 6 is a graph showing the contents of a typical CO-containing gas 5 stream obtained in a reduction reaction carried out in accordance with the invention by using

N . . . ea.

Q three different carbonaceous materials having different reactivities.

EMBODIMENTS

[0020] DEFINITIONS

In the present context, the term “synthesis gas” encompasses a mixture of gaseous and possibly liquid components including carbon monoxide (CO) and hydrogen (Hz). Typically, it contains also carbon dioxide (CO;) and methane (CHa).

When “gas streams” or “gas mixtures” are mentioned, it is typically referred to wet gas or humid gas saturated with liquid vapor. — [0021] The present invention thus relates to a process for producing synthesis gas, by first producing a carbon monoxide (CO)-containing gas mixture by - calcining a raw material containing carbonates, to produce carbon dioxide (CO2), - obtaining a gas stream containing carbon dioxide (CO2) from the calcination, and - reacting the CO2-containing gas stream with a carbonaceous material to cause a reduction of the CO? into CO, the process being characterized by subseguently contacting an obtained CO-containing gas mixture with a hydrogen-containing gas to produce synthesis gas.

[0022] Typical process configurations are shown in Figs. 1 and 2, with detailed

N embodiments in Figs. 3 and 4. a

S [0023] The raw material is typically a material containing carbonates, preferably - 25 — containing the carbonates in the form of calcium carbonate (CaCOs3), calcium magnesium

E carbonate (CaMg(CO3)2), magnesium carbonate (MgCO3), lithium carbonate (Li2CO3),

S potassium carbonate (K2CO3), or sodium carbonate (Na2CO3), or a mixture of two or more 5 of these, most suitably being a mineral raw material, such as limestone or dolomite, or a

O calcium carbonate -containing fraction obtained from chemical pulping of wood materials.

[0024] Any known calcination eguipment can be used in the process, such as a fluidized bed reactor, shaft furnace, flash calciner or rotary kiln, but a preferred option is to carry out the calcination described herein in a rotary kiln. Thus, the calcination is typically carried out in a hollow cylindrical device with two ends. The hollow cylindrical device is 5 configured to be rotated around an axis of rotation. The axis of rotation is typically orientated horizontally or substantially horizontally. The term “axis orientated horizontally” means an axis that is orientated perpendicular to a gravity vector or perpendicular to the normal on the surface of the Earth. Similarly, the term “axis orientated substantially horizontally” means an axis that is tilted a few degrees, for example less than — 10 degrees, from the axis that is orientated perpendicular to a gravity vector or perpendicular to the normal on the surface of the Earth. In other words, when the rotary kiln is positioned substantially horizontally, a feed end is fixed at a higher level than a discharge end. Thus, the material carried through the kiln will gradually move from the feed end to the discharge end when the device is rotated. Additionally, the material is — distributed over an inner surface of the cylindrical device by the rotation. The rotational speed of the hollow cylindrical device may be, for example, in the range between 0.1 and 10 revolutions per minute (rpm). The rotational speed may be adjustable. When the rotary kiln is positioned substantially horizontally, the feed inlet is positioned at the feed end of the device that is fixed at a higher level than the discharge end at which the outlet for the — solid product is positioned. The calcination step carried out in said rotary kiln will thus take place during a time interval that is determined by the time it takes for the material to move from the feed end of the hollow cylindrical device to the discharge end. The heating can be applied using electrical heating equipment or a fuel-powered burner, or a < combination of these, the heating equipment preferably positioned by the discharge end of

S 25 — the substantially horizontal rotary kiln. Heating of the cavity within the hollow cylindrical 3 device typically takes place by increasing a wall temperature of the rotatable hollow © cylindrical device. The heating system may be capable of adjusting the temperature within

I the cavity, for example in a range between 150 °C and 1600 °C. a

S 30 [0025] Thus, in an embodiment, the calcination is at least partly achieved via v electrical heating. It may, however, also be carried out entirely by electrical heating.

O

N

[0026] Said calcination step can optionally be followed by one or more further heat treatment steps, preferably one or two. Such a further heat treatment step might be e.g. a sintering step or a clinkering step. Such subsequent heat treatment steps are typically heated at least partly by combustion.

[0027] The temperature used in the calcination step is typically >750 °C, preferably 750-1100 °C, more preferably 900 — 1100 °C, and, generally, the calcinations are operated at a pressure that is close to atmospheric pressure, typically at a slight overpressure level of 0.0001 to 0.5 bar, but electric calcination can also be operated at a slight vacuum, which facilitates the calcination reaction. In practice, the calcination reaction occurs within the range of -0.5 to 2 bar pressure, preferably 0.0001 — 0.5 bar. In — case the calcination is followed by one or more further heat treatment steps, their temperatures can naturally be different from the temperatures of the other heat treatment steps, such as achieved by operating each heat treatment step at a higher temperature than the previous one.. Thus, a preferred alternative is to operate a further heat treatment step at a temperature of 1000 — 1600 *C, more preferably 1200 — 1500 *C, and most suitably 1300 — 1450 °C. An optional intermediate step could thus be carried out at a temperature of 850 — 1200 °C. The duration of each of the calcination and other heat treatment steps typically ranges from few seconds to days, e.g. from 2 seconds to 20 days, or from 5 seconds to 10 days, partly based on the temperature and on the rate of energy transfer, which are significantly influenced by the type of eguipment and process. Further, the selected raw — material has an influence. Typically, the residence time in a rotary kiln could be 1 — 30 h, or 6 — 24 h, while the residence time in a fluid bed reactor could be as low as seconds, and the residence time in a shaft kiln could be as long as 12 — 50 h, or 16 — 48 h.

[0028] The scope of this description also includes the alternative, wherein a pre- a 25 heating step is carried out, e.g. to pre-dry the raw material before the above-described

N calcination, which pre-heating step can be carried out at a lower temperature than the

S calcination, such as a temperature of 150 — 800 °C, preferably 200 — 750 °C, and more - preferably 600 — 750 °C.

T

= < 30 [0029] No further additives are required in the calcination, but in an embodiment, it 3 may be carried out in the presence of steam (see the further reagents of Figs. 3 and 4), ja preferably in the form of superheated steam. This steam (H2O) will have the further effect

N of adjusting the temperature required for the calcination, which will further increase the durability of the process equipment and the wear resistance of the materials of the equipment, as well as improve the structural strength of the equipment structures. Further,

it will improve both the energy efficiency of the process and the quality of the products.

Further, the steam (as H2O) provides both hydrogen and oxygen to the calcination, other heat treatment step(s) or the reduction step. The amount of steam and other components can be adjusted to optimize the specific contents of the gas stream containing CO; or the — gas mixture containing carbon monoxide (CO).

[0030] In another embodiment, the calcination is carried out in the presence of oxygen (see the further reagents of Figs. 3 and 4), preferably in the form of oxygen gas (02), thus resulting in a higher quality for the CO; in the resulting gas stream, among — others reducing the concentration of nitrogen (N3) in the calcination, while also lowering the CO; content in the reaction zone, thus favouring the production of products in the calcination reaction. Further, the higher oxygen levels facilitate a more efficient burning in high-temperature heat-treatments, also allowing an adjustment of the temperatures used in such steps, thus providing further variety in the choice of fuel as the requirements for the — energy content are reduced. The oxygen can for example be oxygen produced by electrolysis from water using Reaction (3), 2H,0 > 2H2 + 02 (3) — Thus, the oxygen can optionally be produced at the same site of the present process.

[0031] A further option is to recirculate a fraction of the CO-containing gas mixture to the calcination, which will also reduce the CO2-content in the calcination zone, thus favouring the production of products in the calcination reaction, as mentioned above for x 25 the additional oxygen supply. & 3 [0032] In a preferred embodiment, a mixture of oxygen gas and steam is used in the o calcination. 7

[0033] The calcination produces both a calcined solid product, e.g. in the form of 3 calcium oxide (CaO) and a gas stream containing CO» and further off-gases. The gas 3 stream is utilized in the following reduction step, although a fraction thereof can be

N separated and utilized elsewhere, such as in other processes or in other steps of the herein described process. One preferred alternative is to utilize the separated fraction of off-gases — by recirculating it back to the calcination. This gas stream obtained as an intermediate product from the calcination is rich in CO), typically containing >50 vol-% CO,, preferably 85 — 95 vol-% COs. Further, it may contain carbon monoxide (CO), oxygen (02), hydrogen (Hz), nitrogen (Nz), and/or steam (H2O), and traces of other gases.

[0034] The gas stream containing carbon dioxide (CO>), obtained from the calcination, can be recovered (see Figs. 2-4) before reacting it with the carbonaceous material in a separate process step, i.e. a separate reduction step. This recovery may take place e.g. by separating the gaseous fraction from the solid product via a gas outlet in the — heat treatment unit. However, even if the reduction may be carried out in a reduction unit that is separate from the heat treatment unit(s), these units form an integrated seguence of units. If the gas stream is recovered, it is preferably fed to the reduction step directly, or it may be purified or concentrated before taking part in the reduction step. However, even if the reduction may be carried out in a reduction unit that is separate from the heat treatment unit(s), these units form an integrated sequence of units.

[0035] The temperature of the stream containing CO2 may even be sufficient to provide an optimal reduction step without further heating, particularly if no separate step for concentrating the CO? of the stream has been carried out. As an alternative, the stream containing CO; can be heated separately, preferably to a temperature of >900 °C, more preferably 900 — 1500 °C, before taking part in any further reactions, such as the reduction step. This alternative may also be applied when a low temperature has been applied in the calcination, such as a temperature below 900 °C, or a temperature below 800 °C. Also the reduction step can be carried out at a pressure that is close to atmospheric pressure, or at a 25 slightly adjusted pressure, more typically at a pressure in the range of -1 — 10 bar,

N preferably 0 — 2 bar. Further, the gas stream can be contacted with one or more catalysts,

S such as nickel, calcium oxide, magnesium oxide, zinc oxide, or aluminium oxide, - preferably in catalytic amounts, before further reactions. 7 < 30 [0036] In an embodiment, either the CO2-containing gas stream, or a fraction of off x gases separated therefrom, or a combination of one of these streams with added gaseous

N streams, is purified to increase the CO; content of this gas stream, and/or to remove

N undesired components, such as excess oxygen, nitrogen or sulphur dioxide. This purification can take place e.g. by washing, scrubbing, cooling or drying the gas stream, or by a combination of two or more such techniques, and preferably results in a CO» concentration of >85 vol-%.

[0037] In another alternative, the gas stream containing carbon dioxide (CO), obtained from the calcination, can be used as such in the reduction step, without recovery (see Fig. 1). Thus, the heat generated in the calcination can be utilized also for this reduction reaction. As a consequence, also the heat of the reduction reaction may be at least partly achieved by electrical heating, or alternatively entirely by electrical heating. — Further, also in said reduction step, a temperature of 900 — 1500 °C may be used, more preferably 900 — 1100 °C, and most suitably 950-1050 °C. Preferably, the reduction reaction will begin immediately in the solid material feed end of the heat treatment unit, or in the area of the heat treatment unit that is close to the feed end/area. Depending on the efficiency of the process and the selected heat treatment unit, the reduction reaction might be complete or essentially complete by the time the solid material reaches the discharge end, or the reaction might be completed or essentially completed at the discharge end, where the heating possibly is most efficient. This alternative is particularly suitable for embodiments, where the heating takes place by electric heating.

[0038] To achieve the reduction, the CO2-containing stream is reacted to produce a

CO-containing gas mixture, optionally generating also activated carbon. This reduction step utilizes a carbonaceous reagent, which preferably is in the form of char, charcoal, coke, petroleum coke or biochar, or a hydrocarbon, preferably in the form of methanol (CH30H), methane (CH4), ethylene (C2H4), propylene (C3Hc), butenes (C4Hs), or formic a 25 — acid, or a mixture of hydrocarbons. Alternatively, a mixture of carbon and hydrocarbon(s)

N can be used in the reduction reaction, or a biomass, such as wood chips, or a combination

S of any of these. The optional biomass is preferably formed of wood chips or other crude or - dried biomass, thus preferably excluding refined carbon products. 7 < 30 [0039] The term *biochar” is intended to cover all carbon materials obtained from x biomaterials, i.e. conventional biochar, as well as biocoke and biocharcoal, and torrefied

N biomass. The potential sources of the include both fresh biomass and waste materials, with

N waste materials being a preferred option particularly when aiming for an ecological improvement.

[0040] The stream containing COz can be used in the reduction step with only the carbonaceous reagent, and thus without further additives, but can, in an embodiment, also be reacted in the presence of steam (see the further reagents of Figs. 3 and 4), preferably in the form of superheated steam, thus providing a further means for heating, while also resulting in a gas stream containing hydrogen.

[0041] In another embodiment, the stream containing CO; is reacted in the presence of oxygen gas (02) (see the further reagents of Figs. 3 and 4), for example oxygen produced by electrolysis, e.g., at the same site of the present process. The oxygen will facilitate the heating of the reduction step, but will also take part in the reactions to produce carbon monoxide, via Reaction (4) 0, +2C > 2CO (4) — [0042] A further alternative is again to use a mixture of oxygen gas and steam.

[0043] In a further embodiment, the stream containing CO; is reacted in the presence of a hydrogen-containing gas (see the further reagents of Figs. 3 and 4), which can be either separately added hydrogen, or hydrogen carried to the reaction with the gas stream — or with another added stream, such as the above-mentioned steam, or it can be hydrogen produced by electrolysis (see Reaction (3)), e.g., at the same site of the present process.

The hydrogen in the reduction reaction will provide among others the further advantage of lowering the CO pressure in the reduction, whereby production of CO will be favoured in

Reactions (1) and (2). Further, the hydrogen will adjust the CO/H ratio to favour the a 25 — production of a desired synthesis gas, or to produce methane or methanol, as specified

N below.

S o [0044] In yet a further embodiment, the stream containing CO; is reacted with the

E carbonaceous material in the presence of added CO? e.g. used to initiate the reduction 3 30 reaction.

X [0045] To further facilitate the reaction, it is possible to contact the CO2-containing

N gas stream with one or more catalysts, such as nickel, calcium oxide, magnesium oxide, zinc oxide, or aluminium oxide, to the reduction reaction. The catalyst is typically added as —asolid material, e.g. a fixed bed or a coating, in the reduction unit, or it may be added to the carbonaceous material or the stream containing CO; before reacting into a CO- containing product gas mixture.

[0046] The above-described optional reagents can either be added separately to the reduction mixture in the reduction unit, or they can be premixed with the carbonaceous material or the CO2-containing gas stream before taking part in the reduction reaction.

Preferably, any solid reagents and materials are premixed with the carbonaceous material before the reduction reaction takes place, while any gaseous reagents and materials are premixed with the CO2-containing gas stream.

[0047] Thus a CO-containing gas mixture is obtained as an intermediate product.

This gas mixture may, in addition to carbon monoxide, contain e.g. unreacted carbon dioxide, as well as hydrogen and other common gaseous components, such as oxygen (02), nitrogen (Nz), hydrogen (Hz), ethylene (C2Hz4), methane (CHa), ethane (C2Hg) and/or sulphur dioxide (SO2), typically in trace amounts (see Fig. 6). When a biomass has been used as a carbon source in the reduction reaction, the CO-containing gas mixture will typically contain a more complex mixture of components, such as the mentioned ethylene, methane and ethane. When an excess of carbon is used in the reduction, and the reduction is carried out in a unit that is separate from the heat treatment unit, also activated carbon — can be generated.

[0048] The obtained CO-containing gas mixture is optionally recovered.

[0049] A fraction of this intermediate product can be used further, e.g., as a fuel in x 25 — energy production or in other high-temperature processes, such as calcinations, and it may < be utilized as a carbon source in such processes, or in the manufacture of synthetic fuels, 3 chemicals or plastics, or alternatively as a diluting gas for calcination (see Fig. 3), to adjust o the contents of materials during calcination, e.g. to reduce recarbonization, to facilitate

E calcination at lower temperatures, and to adjust the guality of the calcined product. Thus, a < 30 — further option is to return the synthesis gas or a fraction thereof, containing unreacted CO,, 3 or unreacted CO; separated from this fraction, to the reduction step.

S

N [0050] However, at least a fraction of the CO-containing gas mixture is contacted further with a hydrogen-containing gas to produce synthesis gas. The hydrogen-containing gas can, again, be either separately added hydrogen, or hydrogen carried to the reaction with the gas stream or with another added stream, such as the above-mentioned steam or a methane stream or a mixture of these, or it can be hydrogen produced by electrolysis, e.g., at the same site of the present process.

[0051] In a preferred embodiment, the step of producing synthesis gas takes place on the same site as the calcination step and the reduction step, merely in a separate reaction unit or reaction zone. Thus, also the hydrogen production can take place at the same site, e.g. by electrolysis.

[0052] The herein described process thus results in synthesis gas, which typically contains carbon monoxide (CO), hydrogen (Hz), unreacted carbon dioxide (CO), and methane (CH4), and traces of other unreacted components from the CO-containing gas mixture.

[0053] The synthesis gas can be further used as a fuel in energy production or in other high-temperature processes, or as a hydrogen or carbon source in such processes, or in the manufacture of synthetic fuels, chemicals or plastics. Further, it can be used as a reducing agent to convert iron ore into sponge iron. The iron ore for this optional conversion is typically in the form of hematite (Fe2O3) or magnetite (Fe304).

[0054] The particular suitability of the product in fuel applications and in high- temperature processes is achieved with the help of the advantageous chemistry of the product. — [0055] The invention, however, also relates to the further conversion of the synthesis

N gas into hydrocarbon products (see Fig. 4), wherein the synthesis gas or the remaining 5 unreacted CO-containing gas mixture with the hydrogen-containing gas mixture is reacted = further in conditions that produce hydrocarbons, such as methanol (CH3OH), methane = (CHa), ethylene (C2H4), propylene (C3H6), butenes (C4Hs), or formic acid (HCOOH), or

E 30 higher alkanes, higher olefins, synthetic gasoline, diesel fuel, kerosene or waxes and 3 lubricants. For example, for methane production, suitable conditions include using a x pressure of 1 — 10 bar and a temperature of 300 — 400 *C, and for methanol production,

N suitable conditions include a pressure of 50 — 80 bar and a temperature of 200 — 300 °C.

[0056] Said higher alkanes and higher olefins may include for example nonane, nonene, decane, decene, or further alkanes or olefins having > 10 carbon atoms. The waxes may, in turn, be polyethylene waxes, or paraffin waxes, or other commonly used waxes, while the lubricants may be polyolefin-based lubricants or similarly other commonly used lubricants.

[0057] In a preferred embodiment, the further conversion of the synthesis gas into hydrocarbons is optimized to obtain a product rich in methane and/or methanol. This is preferably achieved by utilizing conditions of methanation (3H; + CO > CH. + HO) — and/or methanol formation (CO + 2H, > CH3OF), respectively. The methanation reaction utilizes a H2/CO molecular ratio of 3:1 and is typically catalyzed by a nickel catalyst, while the methanol synthesis utilizes a H2/CO ratio of 2:1 and is typically catalyzed by a copper catalyst.

[0058] The conditions that produce hydrocarbons may, for example, involve varying the temperature or the pressure of the conversion reaction, or using one or more catalysts, such as iron, cobalt, nickel, and ruthenium-based catalysts, such as Ru/TiO2 or Ni/A1203, or alternatively biocatalysts.

[0059] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

N 25

N [0060] Reference throughout this specification to “one embodiment” or “an

S embodiment” means that a particular feature, structure, or characteristic described in - connection with the embodiment is included in at least one embodiment of the present

E invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” 5 30 in various places throughout this specification are not necessarily all referring to the same : embodiment.

N [0061] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0062] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous — specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring — aspects of the invention.

[0063] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles — and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0064] The verbs “to comprise” and “to include” are used in this document as open < limitations that neither exclude nor require the existence of also un-recited features. The

S features recited in depending claims are mutually freely combinable unless otherwise 3 25 explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular o form, throughout this document does not exclude a plurality. 7 3 3 EXAMPLE — Gas products formed by calcination followed by reduction 2

N

N [0065] A calcination of a calcium carbonate (CaCO3) material (limestone, containing 97%CaCO3) was carried out in electrically heated rotary kiln at 1000 °C, and a solid product of calcium oxide (CaO) was obtained, as well as a gaseous product containing mainly carbon dioxide (CO2), obtained from the carbonate and released as its own gas stream. Fig. 5 illustrates the CO; content in an offgas from calcination reactor operated as described herein, as a function of the pressure.

[0066] The gaseous product was collected, purified and carried to a reduction unit.

[0067] In the reduction unit, the carbon dioxide in the gaseous product was reduced with the help of a carbonaceous material fed into the reaction. The reaction reguires energy, which can be transferred to the reaction with the heat of the gaseous product fed into it, but in the present example, the reduction unit was further heated by resistors. The CO2- containing gaseous stream was combined with various carbon materials, providing different — test results. The contents of gaseous products were continually measured. Three different carbon materials were used, being char coal produced from different natural raw materials, char coal 1 being obtained by pyrolysis from wood chips and having the highest reactivity, char coal 2 being obtained by pyrolysis from bark waste, and char coal 3 being obtained by pyrolysis from a digestate originating from biowaste. Thus, different reduction products — were obtained (CO-containing gas mixture), having different gas contents. The results are shown in Fig. 6, providing the contents of carbon monoxide (CO), carbon dioxide (CO), water (or steam, i.e. H2O), and other components, which generally may include oxygen (Oz), nitrogen (Nz), hydrogen (Hz), ethylene (C2H4), methane (CHa), ethane (C2He) and/or sulphur dioxide (SO2), and in the present example the specific content of this fraction was disregarded due to the small size of the fraction.

[0068] As the results show, high CO contents were achieved for the CO-containing gas mixtures, thus providing gas mixtures which can be adjusted for desired synthesis by 3 adding hydrogen.

S

2 25 x 3 INDUSTRIAL APPLICABILITY

S

0 [0069] The present invention is useful for producing synthesis gas, which can be

O further converted into hydrocarbon products. Further, the synthesis gas can be used e.g. as a fuel in energy production or in other high-temperature processes, such as calcinations, and it may also be utilized as a carbon source in such processes.

[0070] Alternatively, the synthesis gas can be used as a reducing agent to convert iron ore into sponge iron.

CITATION LIST

Patent Literature

WO 2015015161 Al i

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Claims

CLAIMS:

1. Process for producing synthesis gas, by first producing a carbon monoxide (CO)- containing gas mixture by - calcining a raw material containing carbonates, to produce carbon dioxide (CO), - obtaining a gas stream containing carbon dioxide (CO;) from the calcination, and - reacting the CO2-containing gas stream with a carbonaceous material to cause a reduction of the CO? into CO, the process being characterized by subseguently recovering an obtained CO-containing gas mixture and contacting it with a hydrogen-containing gas to produce synthesis gas.

2. The process of claim 1, wherein the raw material containing carbonates is a material containing calcium carbonate (CaCQO3), calcium magnesium carbonate (CaMg(CO3)2), magnesium carbonate (MgCQ3), lithium carbonate (Li2CO3), potassium carbonate (K2CO3) or sodium carbonate (Na2CO3), preferably a mineral raw material, such as limestone or dolomite.

3. The process of claim 1 or 2, wherein the calcination is carried out at a calcining temperature of >750 preferably 750 — 1100 °C, more preferably 900 — 1000 °C.

4. The process of any preceding claim, wherein the calcination is carried out at least partly using electric heating. N 25

N 5. The process of any preceding claim, wherein the calcination is carried out in the S presence of oxygen, e.g. as oxygen gas (02). co

E 6. The process of any preceding claim, wherein the calcination is carried out in the x 30 presence of steam, preferably in the form of superheated steam. 5

N 7. The process of any preceding claim, wherein the carbonaceous material is carbon, N preferably in the form of char, charcoal, coke, petroleum coke, or biochar, or spent activated carbon, or it is a hydrocarbon, a mixture of carbon and a hydrocarbon, or a biomass, such as wood chips, or a combination of any of these.

8. The process of any preceding claim, wherein the gas stream containing CO; is reacted with the carbonaceous material in the presence of added COs.

9 The process of any preceding claim, wherein the gas stream containing carbon dioxide (CO?) is recovered before reacting it with the carbonaceous material in a separate reduction step, and optionally activated carbon is separated from the gas stream.

10. The process of claim 9, wherein the CO2-containing stream is purified to increase its COz content and/or to remove undesired components, such as oxygen, nitrogen or sulphur dioxide.

11. The process of any preceding claim, wherein the gas stream containing COz 1s reacted in the presence of steam, preferably in the form of superheated steam

12. The process of any preceding claim, wherein the gas stream containing CO is reacted in the presence of oxygen, e.g. as oxygen gas (02).

13. The process of any preceding claim, wherein the gas stream containing CO is reacted in the presence of hydrogen, e.g. as hydrogen gas (Ha).

14. The process of any of claims 1 to 8, wherein the gas stream containing carbon dioxide (CO?) is reacted with the carbonaceous material without preceding separation of the gas stream, the reduction reaction preferably taking place simultaneously with the calcination.

= . . . . om N 15. The process of any preceding claim, wherein the reduction of the carbon dioxide to

N . + carbon monoxide is carried out with heating, preferably at least partly achieved by o . . O electrical heating. I 30 = 16. Theprocess of any preceding claim, wherein the reduction of the carbon dioxide to S carbon monoxide is carried out by heating the gas stream and/or the reduction mixture to a <t 2 temperature of >900 °C, preferably 900 — 1200 °C, more preferably 1000 — 1200 °C O N

17. The process of any preceding claim, wherein the CO2-containing stream is fed with carbon, preferably in the form of char, charcoal, coke, petroleum coke, or biochar, to the reduction reaction, and is reacted to produce a CO-containing gas mixture, and optionally activated carbon.

18. The process of any of claims 1 - 16, wherein the CO2-containing stream is fed with one or more hydrocarbons to the reduction reaction, and is reacted to produce a CO- containing gas mixture.

19. The process of any preceding claim, wherein the stream containing CO is contacted with one or more catalysts, such as nickel, calcium oxide, magnesium oxide, zinc oxide, or aluminium oxide, before the reduction reaction.

20. The process of any preceding claim, wherein at least a fraction of the CO-containing gas mixture, containing unreacted CO», is returned to one or more heat treatment step(s),

e.g. for use as dilution gas.

21. Theprocess of any preceding claim, wherein at least a fraction of the CO-containing gas mixture, containing unreacted CO», or unreacted CO; separated from this fraction, is returned to the reduction step.

22. Process for converting the synthesis gas obtained from the process of any of claims 1 — 21 into hydrocarbon products, wherein the synthesis gas is reacted further in conditions that produce hydrocarbons, such as methanol (CH3;OH), methane (CHa), ethylene (C2H4), propylene (C3Hs), butenes (C4Hg), or formic acid (HCOOH), or higher alkanes, higher olefins, synthetic gasoline, diesel fuel, kerosene or waxes and lubricants. N

23. Theprocess of claim 22, wherein a catalyst is used in the reaction, preferably N selected from iron, cobalt, nickel, and ruthenium-based catalysts, such as Ru/TiO2 or S Ni/A1203, or alternatively a biocatalyst. D I 30

24. Use of synthesis gas obtained from the process of any of claims 1 — 21 as a reducing 3 agent to convert iron ore into sponge iron, or as a fuel in energy production or in other x high-temperature processes. N &