DE102020120741A1 - Process for the production of activated charcoal and the activated charcoal produced therewith - Google Patents

Abstract

The invention relates to a method for producing an activated charcoal, characterized in that the starting material used is wood gasification charcoal, which occurs as a residue in the pyrolysis and gasification of wood and other organic fuels in a wood gasification process and is enlarged by refining steps using at least a second gasification stage of the specific BET surface area and a reduction in the PAH values.

Description

The invention relates to a method for producing activated charcoal and the activated charcoal produced therewith.

Activated carbon is a fine-grained carbon in the form of a microcrystalline, heavily disturbed graphite with a large internal surface area, thanks to which it is used as an adsorbent in chemistry, medicine, water and waste water treatment, and ventilation and air conditioning technology. It is used as granules, as a powder, in pellet form or pressed into tablets (charcoal compacts).

Activated carbon consists mainly of carbon (usually > 90%) with a highly porous structure. Like a sponge, the pores are connected to each other with open pores. The inner surface area is between 300 and 2000 m ² /g carbon, so the inner surface area of four grams of activated carbon roughly corresponds to the area of a soccer field. The density of activated carbon is in the range of 0.2 to 0.6 g/m ³ . The pore size distribution of the micropores (<2 nm), mesopores (2 - 50 nm) and macropores (>50 nm) determines the adsorption properties.

Macropores are access routes for fluids into the interior of the coals and play a key role in diffusion and mass transport processes into deeper-lying areas of the grain. Most of the adsorption takes place on the surface of the micropores. The size of this area determines the effective surface and thus the adsorption properties of an activated carbon.

The size of the effective surface is characterized by the so-called BET measurement, named after the inventors Stephen Brunauer, Paul Hugh Emmett and Edward Teller. In this analysis method, a gas (adsorptive), often liquid nitrogen, is passed over the material to be examined (adsorbent) and due to the cooling of the liquid nitrogen, the adsorbed quantity is determined using a normal pressure device below the saturation vapor pressure of the measuring gas (adsorption). The saturation vapor pressure of the sample gas must not be reached during the analysis process, otherwise condensation would occur, which would falsify the measurement result. Subsequent heating of the sample releases part of the adsorbed amount of gas from the surface, allowing an adsorption-desorption isotherm to be determined. The measured amount of adsorbed or released gas is proportional to the surface.

Activated carbon is obtained from plant, animal, mineral or petrochemical substances. Wood, peat, nut shells, coconut fibre, lignite or hard coal are used as the starting material.

When the activated carbon is extracted, so-called polycyclic aromatic hydrocarbons (PAHs) are produced as a result of the incomplete combustion processes of the starting material. These are solid, mostly colorless, lipophilic compounds that are carcinogenic. Accordingly, it is of interest to keep these values low in the activated carbon.

Three methods can be used for the production and activation of activated carbon. Chemical activation by acid, a strong base, or a salt. The physical activation by heating the material to high temperatures in an oxidizing or partially oxidizing environment, which is steam or carbon dioxide, in a heated rotary kiln or fluidized bed reactor. Or a process method that is a combination of the first two.

From the WO 2019 104 382 A1 discloses a method for producing activated carbon in which the starting material of wood, coconut shell or coal is placed in a first reactor and pyrolytically carbonized material and volatile gas are produced. Part of the volatile gas is diverted to a first combustor to provide heat for the first reactor. Part of the resulting fuel gas from the first combustion chamber is diverted to a second reactor in order to provide the fuel gas for converting carbonizing material into activated carbon.

From the CN109569512 a method for the production of a modified activated carbon adsorbent is known, in which the starting material of wood, apricot shells, coconut shells and palm shells is crushed, ground, sieved, washed with deionized water and then dried. The material is then treated with microwave radiation under a nitrogen atmosphere and finally impregnated with an aqueous 1-5% citric acid solution to obtain modified activated carbon.

In the U.S. 2016 005 92 11 describes a method for improving, characterizing and testing activated carbon. Activated carbon based on coconut shells is used as the starting material and activated by various treatments to become more mesoporous. The starting material used has 95% micropores and 5% mesopores. A catalyzed impregnated activated carbon is produced by treatment with an aqueous calcium-based catalyst, which is heated at a pyrolysis temperature until a structure of 10% mesopores is formed.

Known manufacturing processes have the disadvantage that the starting material consists of coconut shells, which are usually transported to the production site from the Philippines and thus the production of activated carbon creates a large CO ₂ footprint.

The object of the invention is to provide a method for producing activated carbon, the starting materials of which are available locally and are produced from a residue.

The object is achieved with the method having the features of claim 1.

Advantageous developments are characterized in the subclaims dependent thereon.

Another object of the invention is to produce a corresponding activated carbon that is produced more effectively and sustainably and has an increased BET surface area and low PAH values.

The object is achieved with the features of claim 15.

The inventors have recognized that a residual material from the wood gasification process, namely the residual carbon, which is normally mixed with water at the end of the process to avoid dust and filled into big bags, can be used as a starting material for the production of activated carbon and thus this residual material can be upgraded can be supplied.

Instead of being used to produce briquettes, the Holvergaser charcoal is refined into activated charcoal through a refining process. Thus, two processes that are already known, such as the wood gasification process and the activation of activated carbon, are used and an intermediate step according to the invention is introduced.

In this intermediate step, the wood gasifier coal is not mixed with water and filled, but the residual heat of the coal is dissipated in a raw shell heat exchanger. In addition, this residual heat is at least partially used to preheat the activation means and the reactors, thus ensuring thermal feedback. This intermediate step makes available a new starting material for the production of activated carbon, which is available locally and is not burdened with high transport costs.

The coconut shells, which are usually used for the large-scale industrial production of activated carbon, are delivered to the production site from southern countries, often from the Philippines, which leads to long transport routes and a high CO ₂ load. The inventor has recognized that the locally present residue from the wood gasification is suitable if it is subjected to a modification. Since today value is placed on sustainable products that have a lower environmental impact during production, the inventor has created an additional benefit in addition to the technically outstanding suitability of the modified residue. Thus, the starting material of this invention does not cover enormous transport distances, instead the residual product of a wood gasification plant is recycled through a coal upgrading process.

In addition, the invention envisages treating the waste water in some process steps and feeding it back into the process, which also leads to a reduction in the burden on the environment.

The invention provides for converting organic plant material such as wood chips, shrubbery, forest residues and waste wood in a wood gasification process and dissipating the residual heat of the resulting coal in a raw shell heat exchanger and thereby modifying it for further processing into activated carbon.

The invention thus relates in particular to a method for producing an activated charcoal, characterized in that the starting material used is wood gasification charcoal, which occurs as a residue in the pyrolysis and gasification of wood and other organic fuels in a wood gasification process and through refining steps using a second gasification stage Enlargement of the specific BET surface and a reduction of the PAH values is generated.

A further advantageous embodiment provides that the wood gasification coal is filtered out of the raw gas flow by a gas filter at the end of the wood gasification process and is cooled via a lock system, which at the same time represents a transition container, and is rendered inert with an inert fluid, in particular an inert gas such as nitrogen .

In another advantageous embodiment, the wood gasifier charcoal is fed through another lock at the beginning of the refining process as an intermediate step to activate the charcoal, which at the same time represents a raw shell heat exchanger in which the residual heat present is dissipated instead of mixing the wood gasifier charcoal with water and filling it.

The waste heat obtained in the raw shell heat exchanger is advantageously fed to subsequent or previous process steps of the method, in particular for preheating the activating means and the reactors.

Advantageously, a certain reserve of coal is created in a reservoir, which is continuously fed through the refining process and can be rendered inert by the fluid, such as nitrogen.

In a further embodiment, a maximum particle size of 3 mm is preferably refined by means of a screening or classifying system by separating the upper belt, or else different fractions are classified. Oversizes can be crushed to the required particle sizes using a milling plant.

It is also advantageous if the carbon in a component is chemically activated by means of ultrasound or vacuum using an impregnating agent, the impregnating agent being phosphoric acid, potassium hydroxide, potassium carbonate or zinc chloride.

Another advantageous embodiment provides that a measured mixture of impregnating agent and deionized water enables the impregnation rate to be set precisely and, after a certain treatment period, the treated coal is filtered off through a filter and dried in the dryer, with the waste water being processed either in the treatment system and returned to the process or discharged into the sewage system.

Depending on the type of activation, the coal can advantageously either be pretreated or fed directly into the gasification reactor. The activating agent is also added to the reactor and preheated by means of the heat exchanger.

In addition, it is advantageous if the activating agent is N ₂ /H ₂ O(g), CO ₂ or CO ₂ /H ₂ O(g).

Advantageously, the activation process is followed by exhaust gas aftertreatment, which represents a filter, catalytic converter or post-combustion and in which the steam part contained in the exhaust gas is separated in the exhaust gas condensation.

A further advantageous embodiment provides that the coal is passed through a tube-shell heat exchanger in order to dissipate the residual heat after activation and to cool the product below the self-ignition temperature. The waste heat obtained in the raw shell heat exchanger is advantageously fed to subsequent or previous process steps of the method, in particular for preheating the activating means and the reactors. The coal is then stored in a transfer container and, depending on the filling level of this transfer container, is periodically discharged and the container is flooded with nitrogen to avoid self-ignition in the event of a malfunction.

Another advantageous embodiment with chemical activation provides that the chemicals are washed out with water after the actual activation process in the washer, the water is separated in the filter and the residual moisture is removed from the coal in the downstream dryer or in a corresponding drying zone in the actual activation reactor.

Advantageously, a physically activated charcoal is applied directly. Both the chemically activated and the physically activated charcoal are passed through a screening plant to sort out the granules or are optionally mixed with water to form a powder in the mixer or processed into pellets in the pelletizing process.

The invention also relates to an activated charcoal which is produced from wood gasification charcoal by the above-mentioned method.

• 1: Stand der Technik und erfindungsgemäßer Verfahrensweg

The invention is explained by way of example using a drawing. They show:

• 1 : State of the art and process route according to the invention

1 lists the current state of the art at the beginning of the process, in Section S1, in which the combustible material such as wood chips, forest residues, waste wood and plant material is converted into coal and pyrolysis gas in a wood gasification process in a pyrolysis and downstream gasification reactor.

In a gas filter 1, the coal is filtered out of the raw gas. The product gas is then transported to a gas scrubber and the coal left over from the gasification process is rendered inert with nitrogen in a lock or transfer container 2 and partially cooled. As soon as it leaves the filter, the carbon has a specific BET surface area of between 200 and 300 m ² /g.

In the known state of the art, the coal is usually mixed with water in a downstream mixer 28 . The wet coal powder is then filled into big bags 29 and used as fertilizer/soil treatment.

In section 2 the process path according to the invention is given, in which the coal left over from the fuels preferably passes through a further lock. A raw shell heat exchanger 3 is integrated in this lock, through which the existing residual heat of the wood gasification coal is dissipated.

The barrier 23 in front of the raw shell heat exchanger 3 and the barrier 24 after the raw shell heat exchanger 3 serve as safety aspects and enable a separation between the gasification and refining process. This area can be flooded with an inert gas, such as nitrogen, on the one hand to prevent the development of fire and on the other hand to provide a liquid heat transfer medium for dissipating and passing on the thermal energy. This now modified residue is now fed into a coal refinement process.

A certain supply of coal is created in storage tank 4 and this is continuously fed through the refining process. Here, too, it is possible to render the system section inert with an inert gas such as nitrogen.

The resulting coal is in powder form with an existing particle size range and an existing particle size distribution. It has been found that a maximum particle size of 3 mm should preferably be used in the refining stage. In order to ensure this, the upper band can be separated by means of a screening or sifting system 5 or different fractions can also be classified. In order to enable a complete processing of the feed material, oversizes can be crushed to the required particle sizes with a grinding plant 6 . Conventional grinding systems such as ball mills, impact mills or the like can be used for this. If grain size classification is not necessary, the coal stream can be transported directly.

Alternatively, preparation for chemical activation is possible in the further section. The wood gasifier carbon is chemically impregnated in component 7 by ultrasound or vacuum (e.g. with phosphoric acid, potassium hydroxide, potassium carbonate, zinc chloride). Metered additions of saturant and deionized water allow precise adjustment of the saturation rate. After a certain treatment period, the treated coal is filtered through a filter 8 and dried in a separate dryer 9 or directly in a drying zone in the activation reactor 12. The waste water is either treated in a treatment system 10 and returned to the process or fed into the waste water system.

Depending on the type of activation, the coal is either pretreated or introduced directly into the gasification reactor 12 (e.g. rotary kiln, fluidized bed, fixed bed pulsation reactor). The activating agent is also added in the reactor (e.g. N ₂ H ₂ O ( _g ), CO ₂ , CO _{2 /} H ₂ O _(g) ), which is preheated by means of a heat exchanger 11 . Depending on the different process parameters, activated carbon with a wide variety of BET surface areas and pore sizes can be produced. In addition, the second gasification stage (activation) reduces the PAH values, which makes it possible to use the activated carbon produced in the food and animal feed sector. In order to avoid uncontrolled burning in the reactor or to ensure safety technology, nitrogen can be supplied for complete inerting. The activated charcoal is discharged via a lock system rendered inert with nitrogen (shutoff 25 in front of the raw-shell heat exchanger 13 and the shut-off 26), with residual heat being dissipated here by means of a raw-shell heat exchanger 13 in order to avoid self-ignition. Depending on the filling level in the transfer container 14, the product is discharged periodically by opening the barrier 27.

With a chemical activation method, the product can be suitably upgraded by washing the chemicals from the carbon in the scrubber 15 with water. The washing water is separated off in the filter 16, and the residual moisture that remains in the coal is removed by a downstream dryer 17. Physically activated charcoal is applied directly. A subsequent screening plant 18 enables separation into different products. With this screening plant, 18 activated carbons can be produced in granulate and powder form. To reduce dust and facilitate handling, the carbon powder is optionally mixed with water in a mixer 19 . In a pelletizer 20, activated carbon pellets are produced from the powdered carbon dust.

Due to the fact that volatile components escape from the coal during the activation process, dust can also be discharged and certain gas-forming reactions take place, exhaust gas aftertreatment 21 is required (e.g. filter, catalytic converter, post-combustion). The proportion of steam contained in the exhaust gas is separated off in the downstream exhaust gas condensation unit 22 . The waste heat obtained from this as well as that from the raw shell heat exchanger 3 and raw shell heat exchanger 13 is used to partially preheat the activator as well as the reactor.

The advantage of the invention is that the method is more environmentally friendly than conventional methods. No coconut shells are used as raw material for the production of the activated charcoal, which have to be delivered from southern countries such as the Philippines, which leads to a reduction of the carbon _footprint of this activated charcoal. In addition, a residual product, which is usually only used with a low value, is upgraded to a valuable and versatile raw material.

Furthermore, the process is preferably operated in a network in such a way that improved energy efficiency of the overall process is achieved, since in particular all waste heat can be used for the energy-requiring processes in the method. In addition, the invention provides for treating the waste water in some process steps and feeding it back into the process, which also leads to a relief of the environment.

Reference List

1

gas filter

2

transition tank

3

raw shell heat exchanger

4

template store

5

screening plant

6

mill plant

7

component

8th

filter

9

dryer

10

treatment system

11

heat exchanger

12

gasification reactor

13

tubular shell heat exchanger

14

transfer container

15

washer

16

filter

17

dryer

18

screening plant

19

mixer

20

pelleting

21

exhaust aftertreatment

22

exhaust condensation

23

Shut-off in front of the raw shell heat exchanger 3

24

Shut-off after the raw shell heat exchanger 3

25

Shut-off in front of the raw shell heat exchanger 13

26

Shut-off after the raw shell heat exchanger 13

27

Barrier after the transfer container

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2019104382 A1 [0009]
• CN109569512 [0010]
• US20160059211 [0011]

Claims (15)

Method for producing an activated carbon, characterized in that the starting material used is wood gasification carbon, which occurs as a residue in the pyrolysis and gasification of wood and other organic fuels in a wood gasification process, and an increase in the specific BET surface area through refining steps by means of at least a second gasification stage and a reduction in PAH levels is produced. procedure after claim 1 , characterized in that at the end of the wood gasification process, the wood gasification charcoal is filtered out of the raw gas flow by a gas filter (1) and is cooled via a lock system, which at the same time represents a transition tank (2), and is mixed with an inert fluid, in particular an inert gas such as Nitrogen is rendered inert. Method according to one of the preceding claims, characterized in that the wood gasifier coal at the beginning of the refining process as an intermediate step for charcoal activation is guided through a further lock, which at the same time represents a raw shell heat exchanger (3) in which the residual heat present is dissipated instead of the wood gasifier - Mix coal with water and fill. Process according to one of the preceding claims, characterized in that the waste heat obtained in the raw shell heat exchanger (3) is fed to subsequent or previous process steps of the process, in particular for preheating the activation means and the reactors. Method according to one of the preceding claims, characterized in that a certain supply of coal is created in a reservoir (4), which is continuously conducted through the refining process and can be rendered inert by the fluid, such as nitrogen. Method according to one of the preceding claims, characterized in that preferably a maximum particle size of 3 mm is refined by means of a screening or sifting plant (5) by separating the upper belt, or different fractions are also classified. Oversized particles can be crushed to the required particle sizes using a milling plant (6). Method according to one of the preceding claims, characterized in that the carbon in the component (7) is chemically activated by means of ultrasound or vacuum using an impregnating agent, the impregnating agent being phosphoric acid, potassium hydroxide, potassium carbonate or zinc chloride. Method according to one of the preceding claims, characterized in that a measured mixture of impregnating agent and deionized water enables the impregnation rate to be set precisely and, after a certain treatment period, the treated carbon is filtered off through a filter (8) and dried in the dryer (9). , wherein the waste water is either treated in the treatment system (10) and fed back into the process or is fed into the waste water system. Method according to one of the preceding claims, characterized in that, depending on the type of activation, the coal is either pretreated or fed directly into the gasification reactor (12). The activating agent is also added to the reactor and preheated by means of the heat exchanger (11). Method according to one of the preceding claims, characterized in that the activating agent can be N ₂ /H ₂ O( ₉ ), CO ₂ or CO _2/ H ₂ O( ₉ ). Method according to one of the preceding claims, characterized in that the activation process is followed by exhaust gas aftertreatment (21), which represents a filter, catalytic converter or post-combustion and in which the vapor part contained in the exhaust gas is separated in the exhaust gas condensation (22). Method according to one of the preceding claims, characterized in that the coal is passed through a tube-shell heat exchanger (13) in order to remove the residual heat after activation and to cool the product below the self-ignition temperature. The waste heat obtained in the raw shell heat exchanger is advantageously fed to subsequent or previous process steps of the method, in particular for preheating the activating means and the reactors. The coal is then stored in a transfer container (14) and is periodically discharged depending on the filling level of this transfer container (14) and the container is flooded with nitrogen in order to avoid self-ignition in the event of a malfunction. Method according to one of the preceding claims, characterized in that with chemical activation the chemicals after the actual activation process in the washer (15) are washed out with water, the water is separated off in the filter (16) and the residual moisture is removed from the coal in the downstream dryer (17) or in a corresponding drying zone in the actual activation reactor. Method according to one of the preceding claims, characterized in that a physically activated charcoal is applied directly. Both the chemically activated and the physically activated carbon are passed through a screening plant (18) in order to sort out the granules or are optionally mixed with water in the mixer (19) to form a powder or processed into pellets in the pelletizer (20). Activated carbon produced by a process according to claims 1 until 14 from wood charcoal.

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