DE102011103452A1 - Carbonizing cellulose fibers, comprises introducing cellulose fibers in inert gas atmosphere, pre-heating cellulose fibers and drying, treating dried cellulose fibers to temperature, at which they carbonize, and cooling cellulose fibers - Google Patents

Abstract

Carbonizing cellulose fibers, comprises (a) introducing the cellulose fibers in an inert gas atmosphere, (b) pre-heating the cellulose fibers and drying, (c) treating the dried cellulose fibers to a temperature, at which they carbonize under evolution of pyrolysis gas, (d) cooling the carbonized cellulose fibers, (e) obtaining the heat required for carrying out the steps (b) and/or (c) by burning a fuel gas, where the pyrolysis gas obtained in step (c) is used as combustion gas. An independent claim is also included for a plant for carbonizing the cellulose fibers, comprising (i) a furnace (2), whose inner chamber is filled with an inert gas, exhibiting (ia) a preheating section, in which the cellulose fibers are introduced into the inert gas atmosphere, and dried by heating, (ib) a carbonization section (10), in which the cellulose fibers are treated to a temperature, at which the carbonization takes place under the evolution of pyrolysis gas, (ic) a cooling section, in which the carbonized cellulose fibers are cooled to a temperature, at which self-ignition is prevented, and (id) a conveyor system, with which the cellulose fibers are passed through the preheating section, carbonization section and the cooling section, (ii) a heating device (16), which is fired with combustion gas, and provides the heat required in the preheating section and/or in the carbonization section, where the carbonization section of the furnace is connected with a combustion gas supply of the heating device such that the evolving pyrolysis gas can be used as combustion gas.

Description

The invention relates to a method for carbonizing cellulose fibers according to the preamble of claim 1 and to a system for carbonizing cellulose fibers according to the preamble of claim 4.

Carbon fibers or components produced therefrom are increasingly gaining importance in a very wide variety of industrial sectors, especially in vehicle construction or as insulating material, because of their very good mechanical and thermal properties and low weight. However, the cost of these devices is still relatively high compared to those made of conventional materials. As a result, the cost situation is receiving increasing attention to make the use of carbon fibers attractive.

In known from the market methods and systems of the type mentioned, the cellulose fibers, whose length is generally a few millimeters to centimeters, first suitably formed, placed in an inerting atmosphere and heated from the outside in temperature stages. This produces pyrolysis gases which are flared off or at least only insufficiently recycled into the process.

Object of the present invention is to provide a method or a plant of the type mentioned, in which or which the cellulose fibers with as little external energy dried in the shortest possible time, carbonized and ultimately can be cooled.

• e) die im Schritt c) gewonnenen Pyrolysegase im Schritt e) als Brenngase genutzt werden.

This task is, as far as the method is concerned, solved by

• e) the pyrolysis gases obtained in step c) are used as fuel gases in step e).

According to the invention, it was recognized that the energy requirement in the carbonization of cellulose fibers can be significantly reduced if the gases produced during the pyrolysis are used as fuel gases. The pyrolysis gases consist to a considerable extent of CO and hydrogen and are therefore suitable as fuel gas. The achievable with the method according to the invention reduction of the need for external fuel gas, for which, for example, natural gas is used so far, can be so large that at least during operation under full load no external fuel gas must be used. The resulting cost advantages need not be explained in detail.

It is expedient if natural gas is used as fuel gas in the initial phase, since the pyrolysis gas is only available as fuel gas when the cellulose fibers have reached the temperature required here. However, if the development of pyrolysis gas has begun, the feed of natural gas as fuel gas can be increasingly reduced.

A further energy saving for the overall process results when the heat of the flue gas generated in the combustion of the pyrolysis gas and / or natural gas is used to operate an adsorption refrigeration system, with the help of the final cooling of the cellulose fibers is performed.

• c) der Karbonisierungsabschnitt des Ofens derart mit einem Brenngasanschluss der Heizeinrichtung verbunden ist, dass das sich entwickelnde Pyrolysegas als Brenngas genutzt werden kann.

The above object is, as far as the plant is concerned, solved by

• c) the carbonizing portion of the furnace is connected to a fuel gas port of the heater so that the developing pyrolysis gas can be used as the fuel gas.

The advantages of the system according to the invention correspond mutatis mutandis to the described advantages of the method according to the invention.

In an expedient embodiment of the system according to the invention, the heating device is designed as Mehrstoffheizeinrichtung that can be fed with both an externally supplied fuel gas and with pyrolysis gas. Above, attention has already been drawn to the fact that when starting up the system, first of all the necessary temperatures must be brought into the furnace, which are necessary for the development of pyrolysis gas. This initial heating is carried out in the multi-fuel heater by means of the externally supplied fuel gas, and then with increasing evolution of pyrolysis gas, the supply of external fuel gas can be reduced.

The removal point of the pyrolysis gas from the Karbonisierungsabschnitt is advantageously the point at which the highest temperature prevails during operation. The higher the temperature of the pyrolysis gases supplied to the heater, the better the energy utilization.

In the flow path of the flue gases generated by the heater may be an adsorption refrigeration system, which communicates via a refrigerant circuit with a cooling body arranged in the cooling section in combination. The associated further energy savings have already been mentioned above in explaining the advantages of the method according to the invention.

A particularly advantageous embodiment of the invention is characterized in that for heating the preheating section and / or the Karbonisierungsabschnittes at least one jet pipe is provided, which is traversed by the flue gas of the heater. The heat generated in the heater is thus introduced via the flue gases in the oven.

It is particularly advantageous if the jet pipe is coated with ceramic material. It is known that there are ceramic materials that emit heat radiation at a wavelength that is particularly suitable for heating hydrogen molecules when heated to 120 ° C to 500 ° C. Such a ceramic material is also particularly suitable for the inventive purposes.

If a jet pipe is used as the heat source in the preheating section and / or the carbonizing section, it is recommended that the jet blast be guided in a serpentine manner through the preheating section and / or the carbonating section and that the distances between the serpentines are different, adapted to the local heat requirement.

An embodiment of the invention will be explained in more detail with reference to the drawing; the single FIGURE shows schematically a plant for the carbonization of cellulose fibers with a tunnel furnace shown in vertical longitudinal section.

In the drawing, the plant for the carbonation of cellulose fibers is denoted by the reference numeral 1 characterized. It comprises a continuous furnace as the main component 2 with a suitably thermally insulated housing 3 , The carbon fibers to be carbonized, which have a length of usually only a few millimeters to centimeters, are in the illustrated embodiment in cassettes 4 filled, in turn, by means of a conveyor belt, not shown, of an inlet 5 of the continuous furnace 2 in a first end wall to an outlet 6 in the opposite end wall of the continuous furnace 2 be transported. The inlet 5 and the outlet 6 may be designed as sluices that allow an exchange of the atmospheres inside and outside the continuous furnace 2 prevent as far as possible. Details of these locks are not relevant in the present context.

The continuous furnace 2 is by means of two vertical, transverse to the conveying direction extending partitions 7 . 8th divided into three sections: the inlet 5 nearest are a preheating section 9 , in the direction of movement of the cassettes 4 seen, the actual Karbonisierungsabschnitt 10 follows. The outlet 6 adjacent is a cooling section 11 intended. The partitions 7 . 8th have in the lower area not specially provided with reference numerals passages just large enough to the passage of cassettes 4 allow, but the exchange of gas between the different areas 9 . 10 . 11 of the continuous furnace 2 prevent as much as possible.

The preheating section 9 and the carbonation section 10 are heated by means of radiant tubes, which are provided with a ceramic coating. The ceramic material used is chosen in a known manner so that it radiates at a temperature between 120 ° C and 500 ° C thermal radiation at wavelengths that are particularly suitable for heating water molecules.

In the illustrated embodiment, a single radiation tube 12 represented, which serpentine through the Karbonisierungsabschnitt 10 and the preheating section 9 from an inlet 13 to an outlet 14 extends. By selecting the distance between the individual serpentines of the jet pipe 12 For example, the local heat output can be adapted to the requirements of the passage of cellulose fiber filled cassettes 4 through the continuous furnace 3 locally quite varied.

A flue gas inlet 13 of the continuous furnace 2 is over a line 15 with a multi-fuel heater 16 connected. By "multi-substance heating device" is meant such a heating device which can be fired with different fuels simultaneously or in succession. In the present case, the Mehrstoffheizeinrichtung 16 operate with natural gas via a pipe 17 is fed while on a line 18 the associated combustion air is fed. As the second fuel for the multi-fuel heater 16 Pyrolysis gas is used, which via a line 19 in which a throttle 20 lies, the Karbonisierungsabschnitt 10 of the continuous furnace 2 is removed. The removal of the pyrolysis gas takes place at the hottest point of the interior of the continuous furnace 2 instead, generally seen in the direction of travel, in the end region of the carbonation section 10 lies.

The combustion air, with which the over the line 19 fed pyrolysis gases are burned over a pipe 21 , in the sake of redundancy, two blowers 22 . 23 lie, taken from the outside atmosphere. The Mehrstoffheizeinrichtung used in the illustrated embodiment 16 has two different inputs for the combustion air of the pyrolysis gases, one for starting and a second for continuous operation, via branch lines 21a . 21b be fed. In the branch lines 21a . 21b each is a throttle 25 respectively. 26 so the division of over the line 21 supplied combustion air the two branch line 21a . 21b or the corresponding inlets on the Mehrstoffheizeinrichtung 16 can be adjusted.

The over a flue gas outlet 14 from the continuous furnace 3 Exiting, to a certain extent cooled flue gases are via a line 27 partly a fireplace 28 fed. For this serve two blowers 29 . 30 in the pipe 27 , which in turn are connected in parallel for redundancy reasons. The use of another part of the flue gases will be explained below.

The carbonization of the cellulose fibers takes place in an inert gas atmosphere. In the illustrated embodiment, nitrogen is used as the inert gas. This becomes the continuous furnace 2 over a line 31 supplied with a heat exchanger 32 connected is. In the heat exchanger 32 finds a heating of the nitrogen supplied by the continuous furnace 2 leaving flue gas instead. At the outlet of the heat exchanger 32 in this one with the preheating section 9 connecting line 33 , the nitrogen then has a temperature of about 200 ° C.

Above it was mentioned that only part of the line 27 flowing flue gases to the fireplace 28 arrives. Another part of these flue gases is circulated in the system. For this branches of the line 27 a line 34 starting with an adsorption refrigeration system 35 connected is. The purpose of this adsorption refrigeration system 35 will be explained below. The outlet of the adsorption refrigeration system 35 is over another line 36 in which, if necessary, another cooling device 37 can lie with the combustion chamber of Mehrstoffheizeinrichtung 16 connected.

In the direction of movement of the cassettes 4 last section of the continuous furnace 3 , in the cooling section 11 , is a heat sink 38 provided, which is also shown in the illustrated embodiment as a serpentine-shaped tube. The heat sink 38 is traversed by a refrigerant, which him over a line 39 from the outlet of the adsorption refrigeration system 35 is fed and that from the outlet of the heat sink 38 over another line 40 is recirculated to the inlet of the adsorption refrigeration system.

The plant described above for the carbonation of cellulose fibers works as follows:
Since initially no pyrolysis gas is available when starting, the Mehrstoffheizeinrichtung 16 initially fired exclusively with natural gas, which via the line 17 is supplied. The flue gases that are produced during combustion are transferred via the pipe 15 the flue gas inlet 13 of the continuous furnace 2 supplied and flow, contrary to the direction of movement in the cassettes 4 located cellulose fibers, through the jet pipe 12 to the flue gas outlet 14 therethrough. Of course, in the start-up phase of the continuous furnace 2 First, wait for the correct operating temperatures within the sections 9 . 10 and also 11 are reached before the conveyor belt on which the cellulose fiber filled cassettes 4 are set in motion: Typical values for these operating temperatures are in the preheat section 9 about 200-300 ° C, in the carbonation section 10 900 ° C and in the cooling section 11 below about 300 ° C.

When the required temperatures are reached, the cassettes become 4 with the cellulose fibers first in the preheating section 9 largely free of entrained external atmosphere; the moisture entrained by the cellulose fibers is evaporated so that the cellulose fibers pass into the carbonation section 10 of the continuous furnace 2 are largely dry and preheated.

Passing through the carbonation section 10 finds, as there prevail the required temperatures, the per se known pyrolysis process, in which the cellulose fibers are converted into carbon fibers. The resulting pyrolysis gas is passed over the line 19 removed and the Mehrstoffheizeinrichtung 16 fed. Accordingly, the supply of natural gas can now be reduced. Is sufficient pyrolysis gas, it is u. U. possible, the supply of natural gas via the line 17 shut down completely and make the heating exclusively with pyrolysis gas.

Already before the first pass of cellulose fiber loaded cassettes 4 through the continuous furnace 2 Of course, the different sections have to 10 . 11 be filled with nitrogen gas. This happens on the one hand via the above-mentioned lines 31 . 33 between which the heat exchanger 32 lies. On the other hand is not preheated nitrogen via a pipe 41 directly into the cooling section 11 of the continuous furnace 2 brought in.

The case of combustion in the multi-fuel heater 16 resulting flue gases, which the continuous furnace 2 have flowed through, warm, as already indicated, the nitrogen before, in the preheating section 9 is introduced. With the help of the heat in the from the pipe 27 over the line 34 the flue gas is still in circulation, the adsorption refrigeration plant will 35 practically "free" operated. This adsorption refrigeration system 35 is regulated so that the circulating through them refrigerant in heat sink 38 of the cooling section 11 of the continuous furnace 3 provides the necessary cooling capacity. The carbonized fibers must be cooled to a maximum temperature of 300 ° C before exiting to the outside atmosphere to avoid self-ignition.

About the fireplace 28 As much flue gas is removed in terms of quantity as is supplied to the circulating gas circulation of nitrogen and combustion air from the outside and to pyrolysis gas in the Karbonisierungskammer 10 arises, so that the circulating total amount of gases remains constant over time.

In the drawing is still a bypass line 42 recognizable, in which a throttle 43 lies. This bypass line 42 connects the multi-fuel heater 26 directly to the fireplace 28 leading line 27 when the emission of flue gases from the Mehrstoffheizeinrichtung 26 greater than the demand in the continuous furnace 2 is. About another line 44 in which another throttle 45 can, if necessary, from the Vorerwämungsabschnitt 9 Water vapor in the bypass line 42 be delivered.

Claims (10)

A method of carbonizing cellulose fibers, comprising: a) introducing the cellulose fibers into an inert gas atmosphere; b) the cellulose fibers are preheated and dried; c) the dried cellulose fibers are brought to a temperature at which they carbonize to form pyrolysis gas; d) cooling the carbonized cellulose fibers; wherein e) the heat required to carry out steps b) and / or c) is obtained by burning a fuel gas; characterized in that f) the pyrolysis gases obtained in step c) are used as fuel gases in step e). A method according to claim 1, characterized in that at least in the initial phase in step e) natural gas is used as the fuel gas. A method according to claim 1 or 2, characterized in that the heat of the flue gases generated in step b) is used to operate an adsorption refrigeration system, with the aid of the step d) is performed. Plant for carbonizing cellulose fibers with a) a furnace, in the interior of which an inert gas atmosphere prevails and which comprises: aa) a preheating section, in which the cellulose fibers are introduced into the inert gas atmosphere and dried by heating; ab) a Karbonisierungsabschnitt in which the cellulose fibers can be brought to a temperature at which with the development of pyrolysis, the carbonization takes place; ac) a cooling section in which the carbonized cellulose fibers are cooled to a temperature excluding auto-ignition; ad) a conveyor system for guiding the cellulose fibers through the preheating section, the carbonizing section and the cooling section; b) a heater that is fired with fuel gas and that provides the heat required in the preheat section and / or in the carbonation section; characterized in that c) the carbonation section ( 10 ) of the furnace ( 2 ) in such a way with a fuel gas connection of the heating device ( 16 ) is connected, that the developing pyrolysis gas can be used as fuel gas. Plant according to claim 4, characterized in that the heating device ( 16 ) is designed as Mehrstoffheizeinrichtung that can be fed with both an externally supplied fuel gas and with pyrolysis gas. Plant according to claim 4 or 5, characterized in that the removal point of the pyrolysis gas from the Karbonisierungsabschnitt ( 10 ) is the point at which the highest temperature prevails during operation. Installation according to one of claims 4 to 6, characterized in that in the flow path of the heating device ( 16 ) produced flue gases an adsorption refrigeration system ( 35 ), which via a refrigerant circuit with a in the cooling section ( 11 ) arranged heat sink ( 38 ). Installation according to one of claims 4 to 7, characterized in that for heating the preheating section ( 9 ) and / or the carbonation section ( 10 ) at least one jet pipe ( 12 ) provided by the flue gases of the heating device ( 16 ) can be flowed through. Plant according to claim 8, characterized in that the jet pipe ( 12 ) is coated with ceramic material. Plant according to claim 8 or 9, characterized in that the jet pipe ( 12 ) serpentine through the preheating section ( 9 ) and / or the carbonation section ( 10 ) is guided and that the distances between the serpentines, adapted to the local heat demand, are different.

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