FI126078B - Method for utilizing lignin in black liquor - Google Patents

Description

A method for utilizing lignin contained in black liquor

Technical field

The present invention relates to a process for utilizing black liquor lignin according to the preamble of claim 1.

In this process, at least some of the lignin contained in the black liquor is carbonized after possible separation to carbon.

The invention also relates to the use according to claim 19.

background

A method for separating lignin from black liquor by precipitation and the use of the lignin product thus obtained as a fuel is known in the art. In this regard, the state of the art is described in WO2006 / 031175 and WO2006 / 038863.

In the prior art, lignin precipitation occurs by acidifying black liquor in a two-step process, first feeding carbon dioxide to at least partially precipitate the lignin, and then using sulfuric acid to wash the lignin.

The use of sulfuric acid involves e.g. the problem is that sulfur compounds are transported to the lignin washing solutions together with sulfuric acid, and if these waste solutions are recycled, the sulfur compounds will end up in the ash of the recovery boiler. This, in turn, affects the sulfur balance of the pulp mill, which requires an increase in the supply of fresh chemicals.

The use of lignin as a fuel, in turn, is associated with poor heat resistance and a relatively low carbon content.

Summary of the Invention

Problem to be solved

The object of the present invention is to eliminate at least some of the above problems and to provide a completely new solution for utilizing the lignin contained in black liquor.

Characteristics of the Invention

The invention is based on the idea that the spent cooking liquor lignin is subjected to a heat treatment to convert the lignin into substantially organic material free carbon. The heat treatment is preferably carried out by carbonation, for example by wet pyrolysis (hydrothermal carbonization process). The product thus obtained, hereinafter also referred to as "lignin carbon", is separated at least from the part which is incinerated in which the energy contained in this energy carrier is released.

Lignin carbon can be particularly advantageously used as a fuel for a lime kiln, where it partially or completely replaces conventional fuel.

Use in powder form is particularly preferred.

More specifically, the method according to the invention is essentially characterized by what is stated in the characterizing part of claim 1.

The use according to the invention, in turn, is characterized by what is claimed in claim 19.

Advantages of the Invention

The invention provides significant advantages. According to the invention, carbonization from black liquor can produce lignin carbon either 1) solely for the lime kiln or similar combustion boiler needs or 2) and for the lime kiln or similar incineration boiler and filler use, for example in the rubber market. The coal plant can be run all the time with a good basic load for the needs of the lime kiln. Market coal is produced according to sales.

The calorific value of coal is generally at the level of 30-33 GJ / t or 8.3-9.2 MWh / t. This is clearly higher than that of doped lignin, which has a calorific value in the range of 25-26, or about 7.1 MWh / t.

The lignin carbon used in the present technology is more advantageous than the black liquor lignin described above, which, after drying, is used, for example, as a fuel. The latter is chemically equivalent to the lignin in the black liquor, i.e. it has the same chemical composition. Lignin carbon, on the other hand, has a different composition: the organic matter is charred into carbon. The carbon content of the product is therefore higher than that of black liquor lignin (typically in the order of 75% by weight vs. about 60% by weight of lignin) and furthermore the lignin carbon has a higher heat resistance than black liquor lignin. Therefore, the present lignin carbon is suitable as such both as a fuel and as a filler or pigment. For the latter applications, lignin cannot be used, but its possible applications are adhesives.

In the following, preferred embodiments will be further explored with reference to the accompanying drawing. Figure 1 is a simplified process diagram of one embodiment of a new technology.

Application examples

As stated above, in the present solution, to utilize the lignin contained in black liquor or a corresponding lignin-containing solution or suspension, the lignin is carbonized to carbon.

Accordingly, the drawing process comprises treating the spent cooking liquor in pulp cooking so that lignin dissolved or dispersed in the cooking liquor produces lignin carbon (reference numeral 10 in the figure), at least some of which can be used to produce energy, especially thermal energy 14, 15. Reference numeral 10 generally refers to operations related to the treatment of the starting material, e.g., by lignin precipitation, HTC treatment and drying.

As can be seen from the drawing, for example, a spent cooking liquor of sulphate soup, sulphate black liquor, can be used as a feed for the process. The black liquor may have a dry solids content of 25-45%. However, these are only exemplary dry matter limits.

Preferably, the black liquor lignin is first precipitated from the black liquor and then the resulting lignin is carbonized to carbon 10.

In one embodiment, 1 to 50% by weight, typically 5 to 30% by weight, especially about 10 to 20% by weight, of the lignin contained in the black liquor is carbonized after any precipitation.

The carbonation in unit 10 is preferably carried out by a hydrothermal carbonization process, which will be described in more detail below.

In the first embodiment, the carbonization process uses black liquor or the equivalent lignin-containing dispersion as such starting material.

In another embodiment, the lignin isolated from the black liquor or the corresponding lignin-containing dispersion, particularly preferably from the black liquor by precipitation, is used as starting material in the carbonation process. An example of such lignin is lignin produced by acid precipitation. This type of lignin is obtained by the LignoBoost ™ method.

The precipitation may be one or more stages.

Carbonation 10 may be fed with material after the first or only stage of acid precipitation.

Typically, the treatment for separating the lignin from the black liquor or the corresponding lignin-containing dispersion comprises at least two steps. First, the lignin is precipitated by a gaseous substance, such as carbon dioxide, in the first stage of the precipitation and then by a mineral acid, such as sulfuric acid, in the second stage of the precipitation. For these process steps, reference is made to what is disclosed in the aforementioned WO2006 / 031175 and WO2006 / 038863, the contents of which are incorporated herein by reference.

In the present solution, where the lignin is carbonated, considerably less acid can be used in the two-stage acid precipitation in the second stage of the precipitation than in the prior art where the lignin is recovered and used as such after separation. Experimentally, it has been found that in the present solution, the amount of acid can be up to half the amount normally required for lignin production by precipitation.

It is preferable to feed the carbonization 10 precipitated lignin which has been treated with a mineral acid such as sulfuric acid. This solution is particularly advantageous if it is desired to separate metals in lignin, especially alkali metal ions such as sodium, which interfere with the use of lignin carbon as a fuel.

In a third embodiment, black liquor or the equivalent lignin-containing dispersion and isolated lignin, for example precipitated by the methods described above, are alternately used for carbonation.

It is, of course, possible to use a raw material containing both black liquor (or equivalent lignin-containing dispersion) and lignin isolated. In particular, mixtures of black liquor and acid precipitated lignin are used. In these mixtures, the ratios of lignin in black liquor to lignin precipitated by acids are usually in the range of 1: 100 to 100: 1, especially about 1:50 to .50: 1.

A particularly interesting method for carbonizing lignin carbon is hydrothermal carbonization (HTC). This process is also called wet pyrolysis. The hydrothermal carbonization process processes the pyrolyzable material in an acidic environment at elevated temperature and pressure. In the HTC process, lignin undergoes chemical changes. It removes some hydrogen and oxygen and breaks the bonds at the same time.

In one embodiment, the HTC process is carried out by lowering the pH of the liquid or dispersion to be pyrolysed to less than 7, preferably lowering the pH to a clearly acidic level (e.g., pH 1-6 or even below). In another embodiment, which may be combined with the former, the temperature is raised to about 150-300 ° C, especially about 180-250 ° C. In the above applications, the pressure is higher than normal atmospheric pressure, typically about 1.5 to 50 bar (a), preferably about 2 to 30 bar (a), especially about 3 to 25 bar (a), for example about 18 to 22 bar (a). . Under the conditions described, the organic material is decomposed and at least about 50% by weight, typically at least about 60% by weight, particularly at least about 70% by weight, preferably up to 80% by weight, is converted to carbon.

In addition to converting the organic pyrolysable material into carbon, the hydrothermal carbonization process comprises a small amount of gas (0.1-5% by weight of the organic material) and the rest, typically 5-20% by weight, of the liquid components. One of the special advantages of Hydrothermal carbonization is that it can handle moist feed without time-consuming and energy-wasting drying.

Black liquor can be subjected to carbonation as such. The isolated lignin, if available as a solid, is typically slurried in water or acid. The lignin content of the dispersion or solution to be treated is preferably about 0.1 to 50% by weight, especially about 1 to 30% by weight.

Based on the foregoing, in one embodiment of the present technology: - lignin carbon is produced either directly from black liquor (or a solution or suspension containing dissolved lignin) or from lignin separated from it, - black liquor (or equivalent solution or suspension) or lignin is fed to a hydrothermal carbonization process. in the carbonation process, where appropriate, the solid is slurried or dissolved, if necessary, - the pH of the lignin-containing liquid stage is lowered, if necessary, by addition of acid, and the temperature is raised immediately or gradually to about 180-250 ° C, to about 20 bar (absolute pressure), and - temperature and pressure are maintained until the desired amount of lignin has been converted to carbon, after which - the resulting lignin carbon is recovered.

After processing, the lignin carbon is dried, in particular, to a moisture content of less than 20% by weight, in particular less than about 10% by weight.

Regardless of what kind of starting material is fed to the carbonation, the product typically produces lignin carbon having a carbon content greater than 50% by weight, in particular about 60-95% by weight, for example about 65-85% by weight.

The resulting lignin carbon is similar to carbon black. Preferably, the carbon is finely divided.

In one embodiment, the product has a particle size of less than or equal to 50 mesh.

The product can be granulated or used as such, either as a fuel or in filler or pigment applications. In the drawing, reference numeral 11 shows the granular carbon stores of reference 12, the carbon granulation unit, and reference numeral 13 the carbon granular storage.

In one embodiment, the lignin carbon used as the powder fuel contains, in addition to the above, particles smaller than or equal to 50 mesh, but also particles smaller than about 80 mesh, e.g., less than about 200 mesh, e.g., less than 325 mesh, e.g. .400 mesh.

The term "particle size" above refers to the average particle size, often denoted by "0".

The carbonization product has a calorific value of about 28-35 GJ / t, especially about 30-33 GJ / t, making it suitable for use as a fuel. On the basis of particle size, lignin carbon can also be used, after any further processing, as a filler or pigment.

The lignin carbon (soot / carbon black) has better heat resistance than the black liquor lignin product does not melt at temperatures of 200 ° C or lower.

Lignin carbon is easy to transport in the pipeline even at high temperatures. Lignite coal cannot be agglomerated near combustion, nor does it burn itself, but dust combustion is possible.

Reference numeral 14 refers to the combustion of lignin carbon. Local combustion can be performed in a lime kiln or in a power boiler.

In one embodiment, the fuel, which is in powder form, is transferred from the un Granulated carbon storage 11 by conveyors 17, preferably pneumatically, to the storage. According to a preferred embodiment, the combustion 14 is carried out as a dust incineration.

Reference numeral 15 denotes a combustion unit located separately from the coal production site. For example, from a granular carbon storage 13, the product may be transferred to that combustion 15 in bulk (bulk) or sacking 20. The combustion 15 may be carried out in a lime kiln or power boiler.

In one embodiment, the incineration is performed as a dust incineration. In another embodiment, the combustion is effected in a bubbling bed or twisting bed.

This processing 15 may also include, on a case-by-case basis, storage of fuel prior to combustion as well as refining thereof.

In all of the above cases, the carbon from the carbonation can be blended with other fuel before being fed to the combustion boiler.

In addition to burning lignin carbon as described above, some of it can also be used as a filler or pigment. In Fig. 1, this use is designated by reference numeral 16.

From the storage of un Granulated carbon 11 or from the storage of granulated carbon 13, respectively, the carbon can be derived for other uses in bulk transport 18, 19, e.g. pneumatically. Alternatively, the granulated carbon can also be transferred in sacks 20 from the granular carbon stock 13 to other uses 16.

The easy handling of lignin coal and its combustion, for example as a dust burner, represent important advantages.

In filler or pigment applications, lignin carbon is used e.g. industrial rubber and other elastomeric products, such as conveyor belts, or vehicles or rubber tires for machines, or thermoplastic plastic products.

In the exemplary case, the process according to the drawing supplies carbon 1) only for the lime kiln or 2) both for the lime kiln and the rubber market, ie for the rubber industry. The latter case is suitable for situations where the aim is to target the rubber market, but where market entry is slower than what the plant can produce. In this case, the correct dimensioning of the precipitation and treatment plant will provide process engineering support during the time it goes to market. The coal plant can be run all the time with a good base load for the needs of the lime kiln and can be produced according to sales.

In one embodiment, lignin is isolated and carbonized during the first period for use solely as a boiler fuel, and in the second period lignin is isolated and carbonized both for use as a boiler fuel and for the production of value-added products.

At the pulp mill, the need for a lime kiln (for example, 200 GWh / a) and an equal amount for the rubber market can be distinguished. In this case, the furnace is still fully controllable in terms of superheat. The potential vapor shortage is easily filled by raising production if needed.

In view of the above, in a preferred embodiment, lignin is precipitated from the black liquor of the pulp mill by at least sufficient carbonation after carburization to meet the fuel requirements of the lime kiln during - the continuous operation of the pulp mill or - during a preselected run or

In one embodiment, at least 5% by weight of all carbon produced is used as fuel, in particular at least 10% by weight, for example at least 15% by weight. On a case-by-case basis, even all lignin carbon is used as fuel, but typically up to 95% by weight is used as fuel.

Industrial Applicability

The invention can be applied to objects where solutions containing dissolved lignin are available. The invention is particularly suitable for pulp mills and the like, in which lignin is leached from a lignocellulosic feedstock, in particular a fibrous feedstock, by dissolving it (cooking) in a liquid. The cooking liquid can be alkaline, neutral or acidic. Particularly preferably, the invention is applied to a sulphate mill which uses a spent cooking liquor, a black liquor containing about 10-100 g / l of dissolved lignin.

Part of the lignin carbon from the carbonization is used as fuel for the recovery boiler (lime kiln) of the same or another mill or another combustion boiler, such as a power boiler, for example a boiler. The part is also used as such, i.e. in applications where particles of lignin carbon or granules made therefrom are utilized without burning, preferably unmodified, e.g. to utilize their absorption capacity, e.g. as activated carbon, or as filler or pigments, e.g., in polymer or rubber products.

Reference Number List 10 Unit for lignin precipitation, HTC treatment and any drying 11 Granulated carbon storage 12 Carbon granulation 13 Granulated carbon storage 14 Local combustion furnace or power boiler.

15 Combustion at a site other than coal production.

16 Industrial use of coal other than for combustion in a furnace or power boiler 17 Transfer of coal to a burner by various conveyors, eg pneumatically, typically in bulk 18 Transfer of coal in bulk 19 Transfer of carbon in sack or bulk 20 Transfer of carbon in bulk or in bulk

Reference List of Publications

Patent Literature WO2006 / 031175 WO2006 / 038863.

Claims (20)

A process for utilizing the lignin in black liquor, according to which the process - the lignin is carbonized into finely divided carbon, characterized in that - at least a portion of the carbon is fed to a combustion boiler where it is incinerated. 2. A process according to claim 1, characterized by a combination, in which: - the lignin is precipitated from the black liquor, - the lignin thus obtained is carbonized to charcoal and - at least part of the carbon is fed to a combustion boiler where it is incinerated. Process according to Claim 1 or 2, characterized in that a portion of the carbon obtained from the carbonization is separated for use in the production of value-added products while a portion is fed to a combustion boiler. Process according to any one of claims 1-3, characterized in that 5-30% by weight, in particular about 10-20% by weight of the lignin containing the black liquor is carbonized after a possible precipitation. Process according to any one of claims 1-4, characterized in that at least 10% by weight of the carbon generated in the carbonization is fed to a combustion boiler where it is incinerated. Process according to one of the preceding claims, characterized in that the carbon obtained from the carbonization is combusted as powder combustion. Process according to any one of the preceding claims, characterized in that the carbon obtained from the carbonization is incinerated in a blast furnace or a boiler. Process according to one of the preceding claims, characterized in that the carbon obtained from the carbonization is mixed with other fuel before it is fed into a combustion boiler. Process according to one of the preceding claims, characterized in that at least a part of the carbon obtained from the carbonization is used as active carbon or filler, e.g. in polymer or rubber products or in both. Process according to claim 9, characterized in that the carbon is used as a filler in industrial rubber products, such as conveyor belts, or in vehicles or in rubber tires of working machines, or in thermoplastic plastic products. Process according to any one of the preceding claims, characterized in that the carbon content of the product obtained by carbonization from the lignin is> 50% by weight, in particular about 60-95% by weight, for example about 65-85% by weight. %. Method according to one of the preceding claims, characterized in that the carbon is carbon black. Process according to any one of the preceding claims, characterized in that the heat value of the product obtained from the carbonization amounts to about 28-35 GJ / h, in particular about 30-33 GJ / h. Process according to any one of the preceding claims, characterized in that the black liquor of a cellulose factory is separated by precipitation at least so much lignin that after the carbonization it fills the fuel needs of the blast furnace - during the continuous operation of the cellulose factory or - during a preselected period of time or - during stationary operation. Process according to one of the preceding claims, characterized in that - during a first period of time lignin is separated and carbonized only for use as fuel for a combustion boiler and - for a second period of time lignin is separated and carbonized for use both as fuel for a combustion boiler and for use in the production of value-added products. Process according to one of the preceding claims, characterized in that the lignin is precipitated from the black liquor with acid, e.g. mineral acid, or with a mixture of gas and mineral acid, most preferably by means of carbon dioxide and sulfuric acid. Process according to any of the preceding claims, characterized in that the metal content of the carbon produced by carbonization is lowered by precipitation of the lignin from the black liquor with a mineral acid, especially sulfuric acid, or by washing the precipitated lignin from the black liquor with a mineral acid, especially sulfuric acid. . Process according to any one of the preceding claims, characterized in that the lignin is carbonized by a wet pyrolysis process. 19. The use of the atomized carbon obtained by wet pyrolysis from lignin in black liquor as fuel for a lime kiln. The use according to claim 19, characterized in that the lignin coal is produced by a process according to any one of claims 1-18.