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Title:
METHOD FOR MANUFACTURING ACTIVATED CARBON
Document Type and Number:
WIPO Patent Application WO/2011/161314
Kind Code:
A1
Abstract:
In the method a carbonous fuel is carbonised at a high temperature to carbon and the carbon is activated physically with the aid of water vapour and/or carbon dioxide into activated carbon. Activated carbon is manufactured with a co-current gasifier meant for manufacturing product gas, which gasifier has a furnace (32). The fuel is carbonised into carbon and the carbon is activated into activated carbon in the furnace of the co- current gasifier. At least a part of the water vapour used in the activation of the carbon is formed by gasifying moist fuel, whereby water vapour is generated, which functions as an oxidising gas in the activation. Wood chips, which have a moisture content of 30-40 percent by weight, may be used as the fuel. In the same way at least a part of the carbon dioxide used in the activation of the carbon is formed in the gasification process of the fuel. The product gas generated in the gasification contains carbon dioxide, which functions in the activation process as an oxidising gas either on its own or together with water vapour. Activated carbon may be manufactured as a by-product of the manufacture of product gas. When gasifying solid fuel, fly ash, which is at least partly activated carbon, is generated as a by-product.

Inventors:
KANGASOJA EERO (FI)
Application Number:
PCT/FI2011/050588
Publication Date:
December 29, 2011
Filing Date:
June 20, 2011
Export Citation:
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Assignee:
GASEK OY (FI)
KANGASOJA EERO (FI)
International Classes:
C01B31/08; C01B32/336; C10J3/26
Foreign References:
US4883499A1989-11-28
US20020095866A12002-07-25
JP2007022831A2007-02-01
DE715874C1942-01-08
Other References:
See also references of EP 2588408A4
Attorney, Agent or Firm:
BERGGREN OY AB (Oulu, FI)
Download PDF:
Claims:
Claims

1. A method for manufacturing activated carbon, in which method a carbonous fuel is carbonised to carbon at a high temperature and the carbon is activated physically with the aid of water vapour and/or carbon dioxide into activated carbon, characterised in that the activated carbon is manufactured with a co-current gasifier meant for manufacturing product gas, which gasifier has a furnace (32).

2. The method according to claim 1 , characterised in that the fuel is carbonised into carbon and the carbon is activated into activated carbon in the furnace (32) of the co-current gasifier. 3. The method according to claim 1 or 2, characterised in that at least a part of the water vapour used in the activation of the carbon is formed by gasifying moist fuel with the co-current gasifier.

4. The method according to any of the claims 1-3, characterised in that at least a part of the carbon dioxide used in the activation of the carbon is formed in the fuel gasification process.

5. The method according to any of the claims 1-4, characterised in that the method uses a wood-based fuel, such as wood chips, the moisture content of which is 30-40 percent by weight.

6. The method according to any of the claims 1-5, characterised in that activated carbon is manufactured as a by-product of the manufacture of product gas.

Description:
Method for manufacturing activated carbon

A method for manufacturing activated carbon, in which method a carbonous fuel is carbonised at a high temperature to carbon and the carbon is activated physically with the aid of water vapour and/or carbon dioxide into activated carbon.

Activated carbon may be manufactured from several different raw materials, such as wood, sawdust, peat, brown coal or mineral coal, coconut shell or crude oil residue. The choice of raw material for the activated carbon can affect the structure, size and total area of the pores of the final product. In selecting the raw material, its price is often the deciding factor. A large part of the activated carbon is nowadays manufactured from mineral coal due to its low price.

In the manufacturing process of activated carbon the raw material is dried, carbonised and finally activated. In the drying the raw material is heated slowly to a desired temperature. The carbonisation is usually done in an oxygen-free environment in a furnace, the temperature of which is 800-1000 . During the carbonisation hydrocarbons and inorganic substances in the raw material are gasified and exit from it, whereby pores are generated in the carbon. At the end of the manufacturing process the carbon is activated in a process, where superfluous substances are removed from the carbon and the size and number of pores in the carbon grows significantly. Activation of the carbon can be done either chemically or physically. In chemical activation, the carbon is first dried with the aid of activation chemicals, whereafter the carbon is heated to a temperature of 400- 800 "C. Physical activation is done at a high tempe rature of 800-1 100 Ό with the aid of a suitable oxidising gas, such as water vapour and/or carbon dioxide. Chemical activation is usually used for activating carbon manufactured from wood- based raw materials. Manufacturing processes of activated carbon according to prior art are multiphase processes, which increases the manufacturing costs of the activated carbon. The raw materials of the manufacturing process and the chemicals used in the process increase the manufacturing costs of the activated carbon. It is an object of the invention to provide a new method for manufacturing activated carbon, with which the manufacturing costs of the activated carbon can be significantly lowered. The objects of the invention are obtained with a method, which is characterised by what is presented in the independent claim. Some advantageous embodiments of the invention are presented in the dependent claims.

In a method according to the invention for manufacturing activated carbon a carbonous fuel is carbonised at a high temperature to carbon and the carbon is activated physically with the aid of water vapour and/or carbon dioxide into activated carbon. In the method the activated carbon is manufactured with a co- current gasifier meant for manufacturing product gas, which gasifier has a furnace. The method does thus not need a separate apparatus meant especially for manufacturing activated carbon, but the carbonisation of the fuel and the activation of the generated carbon are done with the co-current gasifier in connection with the gasification of the fuel. Advantageously the fuel is carbonised into carbon and the carbon is activated into activated carbon in the furnace of the co-current gasifier. In an advantageous embodiment of the method according to the invention at least a part of the water vapour used in the activation of the carbon is formed by gasifying moist fuel with the co-current gasifier. The water in the moist fuel is vaporised in the gasification, whereby water vapour is generated, which functions as an oxidising gas in the activation. In a second advantageous embodiment of the method according to the invention at least a part of the carbon dioxide used in the activation of the carbon is formed in the gasification process of the fuel. Product gas is formed in the gasification of the fuel, which product gas contains among others carbon dioxide. The carbon dioxide of the product gas functions in the activation process as an oxidising gas either on its own or together with water vapour.

In a third advantageous embodiment of the method according to the invention a wood-based fuel, such as wood chips, which have a moisture content of 30-40 percent by weight, is used as the raw material for the activated carbon.

In a fourth advantageous embodiment of the method according to the invention activated carbon is manufactured as a by-product of the manufacture of product gas. The co-current gasifier used in the method is used to gasify solid fuel, whereby product gas containing carbon dioxide, carbon monoxide, hydrogen and methane is generated, which product gas may be used as fuel for example in engines or boilers. Fly ash, which is at least partly activated carbon, is generated as a by-product of the gasification.

It is an advantage of the invention that it does not require a separate apparatus for manufacturing the activated carbon, but the method can utilise a known co-current gasifier meant for gasifying solid fuel.

It is further an advantage of the invention that the manufacturing of activated carbon does in practice not involve any raw material costs, since the activated carbon is generated as a by-product of the manufacture of product gas.

It is still an advantage of the invention that it improves the profitability of manufacturing product gas, since the by-product generated in the gasification has a significant market value.

In the following, the invention will be described in detail. In the description, reference is made to the appended drawings, in which

Figure 1 shows as an example a co-current gasifier used in the method according to the invention as a vertical cross-section.

Figure 1 shows as an example a co-current gasifier used in the method according to the invention for manufacturing activated carbon as a vertical cross-sectional view. The gasifier has a cylindrical outer casing 10, the upwards pointing end of which has an airtight lid 12, which can be opened. Inside the outer casing there are two essentially parallel floors at a distance from each other, an upper floor 16a and a lower floor 16b, which between them delimit a ring-shaped air channel 18, through which gasification air needed in the gasification of fuel is led into the gasifier. The outer wall of the gasifier forms the outer wall of the air channel and an internal jacket 34 of the furnace 32 of the gasifier forms the inner wall of the air channel. Above the air channel 18 there is a cylindrical fuel silo 14, which is rotated with a rotation motor 24, into which silo fuel to be gasified is dispensed through the lid 12, which can be opened. The part below the air channel forms the gasification part of the co-current gasifier, where the actual gasification of the fuel occurs. The upper and lower floor has a hole 30, through which a connection opens from the fuel silo 14 to the gasification part. On the edge of the hole there is a catcher 28, which scrapes fuel from the fuel silo through the hole into the furnace when rotating the fuel silo. When using the co-current gasifier the air channel 18 between the fuel silo and the gasification part functions as a structural part, which reduces the transfer of heat from the gasification part to the fuel silo. In the gasification part there is a furnace 32, which has a triple wall structure comprising an internal jacket 34, an intermediate jacket 36 and an external jacket 38. At the level of the lower edge of the internal jacket there is a round grate 40. The grate is supported on two support rings 42, which are attached by a pin joint to round rods, which are in turn attached to a support flange 45. The support flange rests on the intermediate jacket, which extends below the grate. Through the central part of the grate runs a vertical axis 46, the first end of which extends above the grate and the second end of which extends through the wall of the furnace to the outside of the gasifier. A wing-like ash scraper 44 is attached to the first end of the axis. The axis can be rotated with an actuator (not shown in the figure), whereby the ash scraper rotates along the surface of the grate and ash drops through the grate.

On the inner surface of the internal jacket, a little below the height level of the lower floor 16b, there is a horizontal, ring-shaped fire ring 50, which forms in the upper part of the furnace a narrowing, which reduces its cross-section. The intermediate jacket 36 around the internal jacket forms a closed wall surface outside the cylindrical sidewall of the internal jacket and below the grate 40. Around the intermediate jacket there is an external jacket 38, which forms the outermost casing of the furnace. A space surrounding the furnace is formed between the external jacket and the intermediate jacket, which space functions as a preheating space for the gasification air. The gasification air can flow from the air channel 18 along an air duct 64 to the lower part of the preheating space. In the part between the lower floor and the upper edge of the intermediate jacket, the preheating space is limited by the internal jacket 34. This ring-shaped wall portion of the preheating space, limited by the internal jacket, is equipped with air nozzles 60, through which the gasification air is led from the preheating space to above the fire ring.

A product gas duct 62 leads from inside the furnace to outside the gasifier, the first end of which duct is attached tangentially to the intermediate jacket 36, passing through the wall of the intermediate jacket. The second end of the product gas duct is led via a hole passing through the external jacket 38 to outside the gasifier. At the through-hole of the external jacket and around the product gas duct there is a flexible bellows seal 66, which ensures the tightness of the through- hole also when thermal movements occur. The product gas exits the furnace through the grate 40 into the space between the internal jacket and the intermediate jacket and from there along the product gas duct further to the outside of the gasifier. The tangential attachment of the product gas duct to the intermediate jacket generates a turbulent flow of product gas below the grate, lifting the fine-grained fly ash generated in the furnace with it. The fly ash exits the furnace along with the product gas and it is separated from the product gas in a separate washer (the washer is not shown in the figures), where the product gas is cleaned also from other impurities. The co-current gasifier according to the invention further includes an ignition mechanism, with which the fuel to be gasified is ignited (the ignition mechanism is not shown in the figures).

In the method according to the invention activated carbon is manufactured in the following manner: The lid 12 of the fuel silo 14 is opened and a suitable amount of fuel is dispensed into the fuel silo, whereby a part of the fuel flows into the furnace 32. Thereafter the lid is closed. The co-current gasifier can also be equipped with an automatic filling mechanism comprising a lock feeder, with which the fuel is fed into the fuel silo. Thus it is not necessary to open the lid of the fuel silo for the duration of the fuel feeding. Pine, birch, fir, willow or other kinds of wood chipped with the bark can be used as fuel for the gasifier. The wood chips may be air- dried, whereby their moisture content can be even 30-40 percent by weight.

An exhauster connected to the product gas duct is started and the fuel in the furnace is ignited. Due to the negative pressure provided by the exhauster, gasification air flows into the air channel 18 and from the air channel along the air duct 64 further into the preheating space between the intermediate jacket 36 and the external jacket 38, from where it is led through air nozzles 60 above the fire ring 50 in the furnace. The co-current gasifier according to the invention reaches its normal use temperature about 3-5 minutes after the ignition, depending on the used fuel. It has through measuring been noted that in a use situation the temperature inside the furnace is about 1050 .

In the co-current gasifier an air channel 18 has been arranged between the fuel silo 14 and the furnace, which air channel decreases the conduction of heat from the furnace to the fuel silo. The gasification air is led into the gasifier through the air channel, whereby heat is transferred from the walls of the air channel to the gasification air, whereby the temperature of the gasification air rises. The air channel thus functions also as a pre-heater for the gasification air. In the co- current gasifier used in the method, attempts are made to actively prevent the transfer of heat from the furnace to the fuel silo and the heating up of the fuel. The fuel runs from the fuel silo through the hole 30 into the furnace, where it is gasified at a high temperature of about 1050 Ό. Si nee the temperature of the fuel in the fuel silo is low, pyrolysis does in practice not occur at all in the fuel silo. Drying of the fuel does also not significantly occur in the fuel silo, but the fuel is nearly at its original moisture state when it has passed the catcher. The pyrolysis thus occurs during a very short distance between the lower part of the fuel silo and the fire ring. In this are the temperature quickly rises to 1050 * C. It is even possible that the pyrolysis occurs mainly or completely below the fire ring in the furnace. Simultaneously with the pyrolysis a lot of water is evaporated from the moist fuel, so there is a lot of water vapour in the furnace. The carbon residue generated in the pyrolysis reacts with the carbon dioxide and water vapour, whereby gasification occurs, where product gas containing carbon dioxide, carbon monoxide, hydrogen and methane and fine-grained fly ash are generated. The fly ash and the product gas exit from the furnace through the product gas duct 62.

It has surprisingly been noted that the fly ash generated as a by-product of the gasification process is at least partly activated carbon, i.e. it has a very porous and fine-grained structure and a large effective surface area, which is typical for activated carbon. This surprising find can be explained by the fact that pyrolysis of the fuel, where carbon residue is generated, occurs first in the gasification. The pyrolysis process of the fuel is thus in fact the carbonisation of the fuel included in the manufacturing process of activated carbon. In the same pyrolysis process the fuel gives off a lot of water vapour and carbon dioxide. It is clear that the carbon residue in the furnace of the co-current gasifier, i.e. the carbonised fuel, reacts with the water vapour and carbon dioxide in the furnace and/or with a mixture of said gasses, whereby physical activation of the carbon residue occurs. The reaction is made possible by the very high temperature of about 1050 Ό in the furnace. In the method according to the invention activated carbon is generated directly as a by-product of the gasification of fuel, i.e. no "additional" ingredients or "additional" method phases in the gasification process are needed for manufacturing activated carbon.

The manufacturing process of activated carbon according to the invention is based on a fuel gasification process, where as opposed to known gasification methods moist carbonous fuel is used, such as wood chips. A lot of water vapour is thus freed in the fuel pyrolysis. The pyrolysis further occurs at a significantly higher temperature than in known gasification methods. The high temperature, water vapour and carbon dioxide in the product gas create circumstances in the furnace of the co-current gasifier, where physical activation of the carbon residue in the furnace to activated carbon occurs. Activated carbon is thus apparently not generated at all in gasification methods according to prior art, where dry fuel is used and where the pyrolysis occurs at a lower temperature. In the method according to the invention the gasification of the fuel occurs in the furnace, where combustion air is led from outside the gasifier. The pyrolysis of the fuel, i.e. the carbonisation, does thus not occur in at least completely oxygen-free circumstances, unlike in known manufacturing methods of activated carbon. For the above-mentioned reasons it is surprising that the carbon residue generated in the gasification has a sufficiently porous structure to enable activation. The physical activation of the carbon residue is surprising also because the activation of activated carbon manufactured from wooden raw materials is usually done by chemical activation.

Some advantageous embodiments of the manufacturing method of activated carbon according to the invention have been described above. The invention is not limited to the solutions described above, but the inventive idea can be applied in numerous ways within the scope of the claims.