Method for compacting a material

Abstract

The invention relates to a method for compacting a material which comprises or consists of the combustion residue obtained from the combustion of black liquor, wherein, during the compaction process, the material has a water content of at least 0.001 wt.%, preferably at least 0.01 wt.%. The invention also relates, inter alia, to a system, the material as such and to uses of the material.

Description

[0001] Process for compacting a material

[0002] The present invention relates, among other things, to a method for compacting a material, to a material as such, and to uses of this material. In particular, the present invention relates to various aspects relating to a combustion residue obtained from the combustion of black liquor.

[0003] For paper production, cellulose must be extracted from wood fibers through chemical pulping. In kraft pulping, also known as the sulfate process, wood is treated in a reactor with a mixture of chemicals, usually sodium sulfide and sodium hydroxide. These chemicals separate lignin, resins, and other non-cellulosic components from the cellulose fibers. The fibers obtained after separating the liquid components, i.e., the pulp, are subsequently used in paper production. Kraft pulping is one of the most common processes for producing cellulose for the paper industry because of its high efficiency and the ability to process a wide range of wood species.

[0004] The liquid residue from kraft pulping is called black liquor. It is a complex mixture of organic wood derivatives and alkaline pulping chemicals, primarily containing degraded lignin, organic acid salts, resins, and large amounts of sodium salts such as hydroxide, carbonate, sulfide, sulfate, and sulfite. Furthermore, black liquor typically contains certain amounts of potassium salts. Black liquor obtained directly from kraft pulping typically contains around 15% dissolved and suspended solids by weight, of which typically about 80% is organic compounds and the remainder is inorganic compounds.

[0005] Further treatment of black liquor is an essential step in modern power generation processes. The organic component of the black liquor can serve as an energy source, while the inorganic component can be used to recover process chemicals.

[0006] For further treatment, the black liquor is typically concentrated to a solids content of around 85 wt.%, which is usually done in several concentration steps.

[0007] The concentrated black liquor is burned in recovery boilers. The released energy can be recycled into a process step, for example, for the digestion itself or for the concentration of black liquor. The black liquor is burned under predominantly reducing conditions. What typically remains is a liquid molten bed at the bottom of the boiler and a solid combustion residue in the form of fly ash, which typically contains significant amounts of sodium and potassium, primarily present as carbonates or sulfates or as corresponding double or multiple salts. The high sodium content is due to the process chemicals used in the digestion. The potassium content typically comes from the wood material and varies depending on the type of wood used.

[0008] The combustion residue is typically present as a white powder, with the bulk density of the residue usually being around 300 kg / m 3 and / or the average particle size is below 100 pm, usually between 2 and 20 pm. It is known in the art to recycle the resulting combustion residue back into the process to balance the material balance. If necessary, a treatment step, such as leaching, is carried out before recirculation to remove undesirable substances from the combustion residue.

[0009] In conventional power generation processes, however, the combustion residue is usually not fully recycled. Instead, surpluses are generated, which are typically disposed of, which is disadvantageous from both an ecological and economic perspective. Due to the generally small quantities of combustion residue to be disposed of, no significant efforts have yet been made to repurpose the excess combustion residue, which could potentially increase value creation.

[0010] However, since the combustion residue typically has low bulk densities and tends to form dust due to the small particle diameters, further use of the combustion residue is problematic and commercialization has so far proven difficult.

[0011] One object of the present invention can be seen in overcoming the disadvantages of the prior art and in being able to reuse excess combustion residue. In particular, one object can be seen in enabling cost-effective transport and / or simple metering of the combustion residue.

[0012] It has now surprisingly been discovered that the combustion residue is compactable, allowing pellets, briquettes, or other compacted aggregates of the combustion residue to be obtained. These pellets have a higher bulk density than native combustion residue, thus enabling better processability and transportability. In particular, the compactability is enabled by the fact that the material comprising or consisting of the combustion residue has a water content of at least 0.001 wt.% upon compaction.

[0013] In the context of this description, the water content refers in particular to the content of chemically unbound water in a material. It may be possible to compact the combustion residue without adding a binder or other additive, in which case the water is not considered a binder.

[0014] However, the incineration residue can also be mixed with other substances before compaction to form a material that is subsequently compacted. It should be noted that the water content can also be adjusted by adding a binder or other additive.

[0015] For example, starch, which typically has a water content between 3 and 15 wt.%, can be added to the combustion residue as a binder. When added, the starch simultaneously increases the water content of the mixture.

[0016] The combustion residue can also be given the desired water content by mixing it with liquid or gaseous water. Treatment with gaseous water, i.e., steam, is advantageous.

[0017] The incineration residue can be compacted without further treatment after the black liquor incineration. Typically, the incineration residue is essentially anhydrous immediately after the black liquor incineration. It is also possible to perform a treatment step prior to compaction, such as purification or leaching, to remove certain components from the incineration residue.

[0018] The material, which contains the combustion residue and any additives, is compacted, especially with a predetermined water content. Compaction can be carried out using various methods suitable for forming solidified or compacted material aggregates. For example, a matrix press or an extrusion device can be used for compaction.

[0019] In particular, the compacted material has a density of more than 550 kg / m 3, possibly more than 700 kg / m 3 . Densities of more than 900 kg / m are preferred 3 or even more than 1000 kg / m 3 . In the context of this description, unless otherwise stated, density refers to the bulk density of a material, in particular the compacted material.

[0020] When compacted, compacted aggregates of the material can be formed, which, for example, have the form of pellets or briquettes.

[0021] In the context of this description, compaction refers in particular to the increase in the density of a substance or mixture of substances during a process step, so that the density after this process step is higher than before.

[0022] Typically, the combustion residue is present in the material to be compacted at a concentration of at least 30 wt.%. However, it is possible for the material to contain larger amounts of combustion residue. If necessary, the material can also consist entirely of the combustion residue and the added water, i.e., without any further additives.

[0023] If a binder, i.e., a solid binding agent, is present in the material, this can typically be present in a concentration of up to 10% by weight. Alternatively or additionally, the material can also contain one or more other additives that do not act as binders, such as aluminum salts or gypsum.

[0024] The combustion residue typically consists of large amounts of potassium, sodium, sulfate, and carbonate, or particularly mixed compounds containing these ions. Smaller amounts of chloride may also be present. The combustion residue may contain at least 10 wt.% sodium as Na2O and / or at least 0.3 wt.% potassium as K2O. In the context of this description, these figures generally refer to calculated equivalents of the corresponding oxides. The combustion residue therefore does not necessarily have to contain the aforementioned oxides.

[0025] The components of the combustion residue are present in particular as aphthitalite and / or burkeite. Aphthitalite refers to a sodium potassium sulfate with the formula KsNa(SO4)2. Burkeite refers to a mixed sodium carbonate sulfate with the formula Na4(SO4)i.39(003)0.61. The combined proportion of aphthitalite and burkeite in the combustion residue is typically more than 50 wt.%, optionally more than 80 wt.%, in particular more than 90 wt.%. The combustion residue may also contain sodium chloride. Other elements, such as calcium, magnesium, or silicon, may typically be present in traces in the combustion residue.

[0026] The material compaction process can be used in a process for the recovery of inorganic compounds during the kraft pulping of lignin-containing plant material. The process is carried out after the combustion of concentrated black liquor obtained from the pulping of plant material and the subsequent separation of the liquid components.

[0027] The present description also discloses a plant with which such a process can be carried out or with which a compacted material can be produced. This plant can comprise a water supply device for adjusting the desired water content prior to compaction and a compacting device for producing the compacted material.

[0028] Furthermore, a material, in particular a compacted material, is described as such, which comprises a combustion residue obtained from the combustion of black liquor. The material can have a density, i.e. a bulk density, of more than 550 kg / m 3 possibly more than 700 kg / m 3 , preferred densities are more than 900 kg / m 3 or even more than 1000 kg / m 3 .

[0029] The material may contain at least 30% by weight of the combustion residue. However, it is possible for the material to contain larger amounts of the combustion residue. If necessary, the material may also consist entirely of the combustion residue and the added water, thus containing no additives.

[0030] Regarding the material, it should be noted that the water content of the material after compaction does not necessarily correspond to the water content the material has or had during compaction. It is possible that the water content of the material may be higher, lower, or the same as before compaction, for example, due to changes in the water content during storage.

[0031] Various uses of a material comprising or consisting of the combustion residue obtained from the combustion of black liquor are also described. In these uses, the material may exhibit characteristics described in connection with the manufacturing process or the material itself. However, it should be noted that the material does not necessarily have to be compacted.

[0032] If appropriate, the material can be used as an aggregate for cementitious or hydraulically hardening building materials such as concrete and / or cement, particularly as a hardening accelerator. The combustion residue contained in the material may trigger an earlier crystallization / hardening reaction in cementitious building materials. If appropriate, the material can be used as an aggregate in a proportion of up to 4% by weight based on the amount of cementitious building material.

[0033] Surprisingly, it was discovered that the material described here can be used as a replacement for currently common curing accelerators. If appropriate, the material can be used as an aggregate, particularly as a curing accelerator, for the curing of gypsum. An example application is the curing of plasterboard. If appropriate, the material can be used as an aggregate in a proportion of up to 3 wt.% based on the amount of gypsum.

[0034] Surprisingly, it was found that the material can initiate crystallization earlier than conventional accelerators. For example, a proportion of the material of about 0.4 wt.% relative to the amount of gypsum can lead to an approximately 20% earlier onset of crystallization and an approximately 27% earlier end of crystallization.

[0035] If necessary, the material can be used as a flux in the production of glass.

[0036] It was surprisingly discovered that the material can at least partially replace the sodium sulfate and sodium carbonate commonly used in glass production. By adding the material, which also contains certain amounts of potassium, an accelerated melting of the glass mass can be achieved, resulting in energy savings. Furthermore, the refining, i.e., the settling of solids or the purification, of the glass can be improved. It is expected that using the material will result in fewer gas bubbles in the molten or cooled glass. Furthermore, the potassium present in the material can have a strengthening effect, making the glass more mechanically resistant.

[0037] If necessary, the material can be used as an anti-swelling agent for starch.

[0038] Typically, sodium sulfate or sodium chloride is used in the processing of starch powder to minimize swelling of the gel prior to drying, thus achieving energy savings. Surprisingly, the use of this material leads to a reduction in the swelling of the starch and thus a reduction in the drying requirements for the starch powder. For this purpose, it is advantageous to use material containing purified combustion residue.

[0039] If necessary, the material can be used as a fixative for dyes.

[0040] The material can be used as an additive in various types of textile dyeing, such as direct dyeing or reactive dyeing. In particular, the material can neutralize an inherent negative charge in textile materials (such as cotton) to enable improved absorption of the dye into the fibers.

[0041] If necessary, the material can be used as an additive for surfactants and / or as an alkali source for batteries.

[0042] A process is described for compacting a material comprising or consisting of the combustion residue obtained from the combustion of black liquor.

[0043] Optionally, it is provided that the material has a water content of at least 0.001 wt.%, preferably of at least 0.01 wt.%, during compaction.

[0044] Optionally, it is provided that the material has a water content of between 0.001 wt.% and 25 wt.%, preferably between 0.01 wt.% and 10 wt.%, more preferably between 0.01 wt.% and 5.0 wt.%, during compaction.

[0045] Where appropriate, the compacted material shall have a density of at least 550 kg / m 3 , preferably at least 800 kg / m 3 , has.

[0046] If necessary, it is intended that the material for compaction is subjected to a pressure of at least 0.5 N / mm 2 , preferably of at least 1.0 N / mm 2 , is applied. Where appropriate, the compaction process may result in pellets or briquettes of the material being formed, which in particular have a cylindrical shape with a diameter of between 2 and 150 mm.

[0047] Optionally, it is provided that the combustion residue contains sodium, wherein sodium is contained as sodium oxide Na2O in an amount of at least 10 wt.%, in particular at least 30 wt.%, preferably at least 50 wt.%.

[0048] Optionally, it is provided that the combustion residue further contains potassium, wherein potassium is contained as potassium oxide K2O in an amount of at least 0.3 wt.%, in particular at least 2.0 wt.%, preferably at least 15 wt.%.

[0049] Where appropriate, it is provided that the combustion residue is present to at least 50 wt.%, in particular to at least 60 wt.%, as burkeite and / or aphthitalite.

[0050] Optionally, it is provided that the material comprises at least 30 wt.%, preferably at least 50 wt.%, more preferably at least 70 wt.%, of the combustion residue.

[0051] Where appropriate, the material shall be binder-free,

[0052] Optionally, it is provided that the material comprises a solid binder in addition to the combustion residue, wherein the binder is contained in the mixture in a content of up to 10 wt.%, preferably up to 5 wt.%, more preferably up to 2 wt.%.

[0053] Optionally, the binder is selected from starch, for example native starch from maize, potato, wheat, rice or tapioca; sucrose; or a mixture of two or more of these binders.

[0054] Where appropriate, the combustion residue is included in the material without further treatment. Where appropriate, the combustion residue is included in the material in purified, in particular leached and / or recrystallized, form.

[0055] A process for the recovery of inorganic compounds during the kraft pulping of lignin-containing plant material, in particular wood, is also described.

[0056] Optionally, the process comprises the following steps: (a) digesting the plant material, (b) separating cellulose obtained by digestion and black liquor, (c) concentrating the black liquor, (d) combusting the concentrated black liquor to obtain a combustion residue, and (e) compacting a material containing the combustion residue as described herein.

[0057] Where appropriate, the concentrated black liquor shall have a solids content of at least 60% by weight.

[0058] Where appropriate, the combustion temperature in step (d) is more than 700°C.

[0059] If necessary, the combustion residue is purified, in particular leached and / or recrystallized, before compaction.

[0060] A system, in particular for carrying out a method as described here, is also disclosed.

[0061] Optionally, the plant comprises the plant components arranged in the following order: a digestion cooker; a separation device for separating cellulose and black liquor from the digestion cooker; a concentration device for partially removing, in particular evaporating, water from the black liquor; an incineration device for burning the concentrated black liquor; optionally a purification device for purifying the combustion residue obtained in the incineration device; and a compaction device for compacting a material containing the optionally purified combustion residue from the incineration device, wherein the compaction device comprises a water supply device.

[0062] If necessary, it is provided that the compacting device is designed as a pelletizing plant, in particular with a piston or matrix press.

[0063] A material comprising or consisting of the combustion residue obtained from the combustion of black liquor is also described.

[0064] Where appropriate, it is intended that material in compacted form, in particular with a density of more than 550 kg / m 3 , is present.

[0065] Optionally, it is provided that the material comprises at least 30 wt.%, preferably at least 50 wt.%, more preferably at least 70 wt.%, of the combustion residue.

[0066] Optionally, it is provided that the combustion residue is present to at least 50 wt.%, in particular to at least 60 wt.%, in the crystal form of burkeite and / or aphthitalite.

[0067] Uses of a material comprising or consisting of the combustion residue obtained from the combustion of black liquor are also described. The uses include at least one of the following applications: hardening accelerating additive for concrete, cement, and / or gypsum; flux for glass production; anti-swelling agent for starch; fixative for dyes; additive for surfactants; alkali source for batteries.

[0068] Where appropriate, the combustion residue for these uses is in compacted form, preferably with a density of more than 550 kg / m 3 , before.

[0069] Further features emerge from the patent claims and the description of the embodiments. Certain aspects of the present disclosure are explained in detail below using exemplary embodiments. These are intended to serve as illustrations and do not limit the scope of the patent claims.

[0070] The starting material used in the embodiments described below and in the comparative example was a combustion residue obtained from the combustion of black liquor produced in a pulp mill.

[0071] The elemental composition of this combustion residue was determined by X-ray fluorescence analysis and is listed in Table 1.

[0072] Table 1: Elemental composition of the combustion residue

[0073] In a phase analysis using X-ray diffraction, the phases listed in Table 2 were also determined in the combustion residue.

[0074] Table 2: Phases in the combustion residue

[0075] The combustion residue was a white powder with a bulk density of about 300 kg / m 3 The residue was processed without further purification in the working examples 1-3 described here, as well as in the comparative example. Materials were produced in which the combustion residue had different water contents. The water content was adjusted by storing the combustion residue in a climate-controlled atmosphere until constant weight (working examples 1 and 2) or by vaporizing the combustion residue (working example 3). The water contents during compaction of these materials are given in Table 3.

[0076] Table 3: Water content of the materials during compaction

[0077] Neither in Examples 1-3 nor in the comparative example was a solid binder or aggregate added to the combustion residue. The compacted materials therefore consisted essentially entirely of the combustion residue with the corresponding water content.

[0078] The materials according to the four examples described above were compacted in a pelletizing mold with a cylindrical recess with a diameter of approximately 10 mm. Individual pellets were produced for experimental purposes, but production can be carried out in a comparable manner in commercially available pelletizing systems. In these experiments, 30 pellets were produced per example.

[0079] Compaction was performed using a TIRATEST 2850 press with a compression speed of approximately 20 mm / min, a maximum compression force of approximately 310 N, and a holding time at the maximum compression force of approximately 60 s. No pellets could be obtained from the material according to the comparative example. However, the materials of working examples 1-3 were pelletizable. The bulk density of the compacted materials was determined by measuring the resulting pellets. The resulting bulk densities are listed in Table 4.

[0080] Table 4: Bulk densities of the compacted materials

[0081] In comparison with the data in Table 3, the measured densities show that a higher density than the bulk density of the combustion residue (about 300 kg / m 3 ) a density that is increased many times over can be achieved even at low water contents during compaction.

[0082] A further increase in density is possible by increasing the water content, with the results showing that the highest densities can be achieved at water contents between 2.5 and 3.0 wt%.

[0083] The water content cannot be increased indefinitely if the material is to be pelletized. However, for very high water contents, other compaction methods can be used, such as forming a slurry and subsequent drying.

[0084] In Example 4, the combustion residue described above was subjected to a leaching step with water, with approximately 20 wt.% water being added to the residue. After removal of the liquid phase, the remaining solid was dried. This had a bulk density of approximately 1,800 kg / m³. 3 This method also made it possible to obtain a compacted material.

Claims

Patent claims 1 . A method for compacting a material comprising or consisting of the combustion residue obtained from the combustion of black liquor, characterized in that the material has a water content of at least 0.001 wt.%, preferably of at least 0.01 wt.%, during compaction.

2. Process according to claim 1, characterized in that the material has a water content of between 0.001 wt.% and 25 wt.%, preferably between 0.01 wt.% and 10 wt.%, more preferably between 0.01 wt.% and 5.0 wt.% during compaction.

3. A method according to claim 1 or 2, characterized in that the compacted material has a density of at least 550 kg / m 3 , preferably at least 800 kg / m 3 , has.

4. Method according to one of claims 1 to 3, characterized in that the material for compacting is subjected to a pressure of at least 0.5 N / mm 2, preferably of at least 1.0 N / mm 2 , is applied.

5. Method according to one of claims 1 to 4, characterized in that during compaction pellets or briquettes of the material are formed, which in particular have a cylindrical shape with a diameter between 2 and 150 mm.

6. Process according to one of claims 1 to 5, characterized in that the combustion residue contains sodium, wherein sodium is present as sodium oxide Na2O in an amount of at least 10 wt.%, in particular at least 30 wt.%, preferably at least 50 wt.%.

7. The method according to claim 6, characterized in that the combustion residue further contains potassium, wherein potassium is present as potassium oxide K2O in an amount of at least 0.3 wt.%, in particular at least 2.0 wt.%, preferably at least 15 wt.%.

8. Process according to one of claims 1 to 7, characterized in that the combustion residue is present to an extent of at least 50% by weight, in particular to an extent of at least 60% by weight, as burkeite and / or aphthitalite.

9. Process according to one of claims 1 to 8, characterized in that the material comprises at least 30 wt.%, preferably at least 50 wt.%, more preferably at least 70 wt.%, of the combustion residue.

10. Method according to one of claims 1 to 9, characterized in that - that the material is binder-free, - or that the material comprises, in addition to the combustion residue, a solid binder, wherein the binder is present in the mixture in a content of up to 10 wt.%, preferably up to 5 wt.%, more preferably up to 2 wt.%.

11. A method according to claim 10, characterized in that the binder is selected from starch, for example native starch from corn, potato, wheat, rice or tapioca; sucrose; or a mixture of two or more of these binders.

12. Method according to one of claims 1 to 11, characterized in that - that the combustion residue is contained in the material without further treatment, or - that the combustion residue is contained in the material in purified, in particular leached and / or recrystallised, form.

13. A process for the recovery of inorganic compounds during the kraft pulping of lignin-containing plant material, in particular wood, comprising the following steps: a. pulping of the plant material, b. separating cellulose and black liquor obtained by pulping, c. concentrating the black liquor, d. Combustion of the concentrated black liquor to obtain a combustion residue, and e. Compacting a material containing the combustion residue by a process according to any one of claims 1 to 12.

14. Process according to claim 13, characterized in that the concentrated black liquor has a solids content of at least 60% by weight.

15. The method according to claim 13 or 14, characterized in that the combustion temperature in step (d) is more than 700°C.

16. A process according to any one of claims 13 to 15, characterized in that the combustion residue is purified, in particular leached and / or recrystallized, before being compacted.

17. Plant, in particular for carrying out a method according to one of claims 13 to 16, comprising the plant components arranged in the following order: - a digestion cooker, - a separation device for separating cellulose and black liquor from the digestion cooker, - a concentrating device for the partial removal, in particular evaporation, of water from the black liquor, - a combustion facility for burning the concentrated black liquor, - if necessary, a purification device for purifying the combustion residue obtained in the incineration device, and - a compacting device for compacting a material containing the optionally purified combustion residue from the combustion device, wherein the compacting device comprises a water supply device.

18. Plant according to claim 17, characterized in that the compacting device is designed as a pelletizing plant, in particular with a piston or matrix press.

19. Material comprising or consisting of the combustion residue obtained from the combustion of black liquor, characterized in that the material is in compacted form, in particular with a density of more than 550 kg / m 3 , is present.

20. Material according to claim 19, characterized in that the material comprises at least 30 wt.%, preferably at least 50 wt.%, more preferably at least 70 wt.%, of the combustion residue.

21. Material according to claim 19 or 20, characterized in that the combustion residue is present to at least 50 wt.%, in particular to at least 60 wt.%, in the crystal form of burkeite and / or aphthitalite.

22. Use of a material comprising or consisting of the combustion residue obtained from the combustion of black liquor for at least one of the following applications: hardening accelerating additive for concrete, cement and / or gypsum, flux for glass production, swelling inhibitor for starch, fixative for dyes, Additive for surfactants, Alkali source for batteries, wherein the combustion residue is in particular in compacted form, preferably with a density of more than 550 kg / m 3 , is used.

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