DE102011103452B4 - Process and plant for carbonizing cellulose fibers - Google Patents

Abstract

Process for carbonizing cellulose fibers, in which a) the cellulose fibers are placed in 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 are developed carbonizing of pyrolysis gas; d) the carbonized cellulose fibers are cooled; wobeie) the heat required to carry out steps b) and / or c) is obtained by burning a fuel gas; f) the pyrolysis gases obtained in step c) are used as fuel gases in step e), characterized in thatg) the heat of the flue gases produced in step e) is partly used to heat the inert gas atmosphere, and h) a further part of the heat of the flue gases produced in step e) is used to cool the carbonized cellulose fibers according to step d) by using in step e) resulting flue gases are passed through an adsorption refrigeration system (35).

Description

The invention relates to a method for carbonizing cellulose fibers according to the preamble of claim 1 and an installation for carbonizing cellulose fibers according to the preamble of claim 3.

Carbon fibers or components made from them are becoming increasingly important in a wide variety of industries, including particularly in vehicle construction or as insulating material, due to their very good mechanical and thermal properties and low weight. However, the cost of these components is still relatively high compared to those made from conventional materials. As a result, increasing attention is being paid to the cost situation in order to make the use of carbon fibers attractive.

In methods and systems of the type mentioned above known from the market, the cellulose fibers, the length of which is generally a few millimeters to centimeters, are first suitably shaped, placed in an inerting atmosphere and heated from the outside in temperature stages. This creates pyrolysis gases that are flared or at least insufficiently returned to the process.

The recycling of composite material also produces pyrolysis gases, for example from the DE 43 04 294 A1 has become known. There, a low-temperature pyrolysis is carried out under an inert gas atmosphere, the combustion of the pyrolysis gas being provided to generate the required temperature. The same applies to the EP 0 682 099 A1 as well as the DE 689 07 052 T2 which, however, uses a high temperature pyrolysis process.

The object of the present invention is to create a method or a system of the type mentioned at the outset in which the cellulose fibers can be dried, carbonized and ultimately cooled with as little external energy as possible in the shortest possible time.

As far as the method is concerned, this object is achieved by the features specified in claim 1.

In the prior art it is known per se 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 quite suitable as fuel gas. The reduction in the need for external fuel gas that can be achieved in this way, for which, for example, natural gas has previously been used, can be so great that no external fuel gas has to be used at all during operation under full load. The resulting cost advantages do not need to be explained in more detail.

According to the invention, it was recognized that there is a further energy saving for the entire process if the heat of the flue gas generated during the combustion of the pyrolysis gas and / or natural gas is used to operate an adsorption refrigeration system, with the help of which the final cooling of the cellulose fibers is carried out becomes. As a result, the heat of the flue gas is used in two ways.

It is useful 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, once the development of pyrolysis gas has started, the supply of natural gas as fuel gas can be increasingly reduced.

As far as the system is concerned, the above-mentioned object is achieved by the features specified in claim 3.

The advantages of the plant according to the invention correspond accordingly to the explained 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 a multi-fuel heating device which can be fed both with an externally supplied fuel gas and with pyrolysis gas. Above, attention was drawn to the fact that when the system is started up, the temperatures required for the development of pyrolysis gas must first be brought about in the furnace. This initial heating is carried out in the multi-fuel heating device by means of the fuel gas supplied from the outside, and the supply of external fuel gas can then be reduced as the pyrolysis gas develops.

The point at which the pyrolysis gas is taken from the carbonation section is advantageously the point at which the highest temperature prevails during operation. The higher the temperature of the pyrolysis gases that are fed to the heating device, the better the energy use.

In the flow path of the flue gases generated by the heating device, there can be an adsorption refrigeration system which is arranged in the cooling section via a refrigerant circuit Heat sink is in communication. The further energy savings associated with this have already been addressed above when explaining the advantages of the method according to the invention.

A particularly advantageous embodiment of the invention is characterized in that at least one jet pipe is provided for heating the preheating section and / or the carbonation section, through which the flue gas of the heating device can flow. The heat generated in the heating device is thus introduced into the furnace via the flue gases.

It is particularly advantageous if the jet pipe is coated with ceramic material. It is known that there are ceramic materials which, when heated to 120 ° C to 500 ° C, emit thermal radiation with a wavelength that is particularly suitable for heating water molecules. Such a ceramic material is also particularly suitable for the purposes of the invention.

If a radiant tube is used as a heat source in the preheating section and / or the carbonizing section, it is recommended that the radiant tube is guided in a serpentine manner through the preheating section and / or the carbonizing section and that the distances between the serpentines are different, adapted to the local heat demand.

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

In the drawing, the system for carbonizing cellulose fibers is identified as a whole with the reference number 1 marked. The main component is a continuous furnace 2 with a suitably thermally insulated housing 3 . The cellulose fibers to be carbonized, which usually have a length of only a few millimeters to centimeters, are in the illustrated embodiment in cassettes 4th Filled, in turn by means of a conveyor belt, not shown, from an inlet 5 of the conveyor oven 2 in a first end wall to an outlet 6th in the opposite end wall of the continuous furnace 2 be transported. The inlet 5 and the outlet 6th can be designed as locks that allow an exchange of atmospheres inside and outside the continuous furnace 2 prevent as much as possible. Details of these locks are not relevant in the present context.

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

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

In the illustrated embodiment, there is a single radiation tube 12 shown, which serpentine-like through the carbonation section 10 and the preheating section 9 from an inlet 13 to an outlet 14th extends. By choosing the distance between the individual serpentines of the jet pipe 12 the local heat emission can be adapted to the requirements when passing through the cassettes filled with cellulose fibers 4th through the conveyor oven 2 varies locally.

A smoke inlet 13 of the conveyor oven 2 is over a line 15th with a multi-fuel heater 16 connected. The term xMulti-fuel heating device x is understood to mean a heating device that can be fired with different fuels simultaneously or in succession. In the present case, the multi-fuel heating device 16 operate with natural gas via a pipe 17th is fed while via a line 18th the associated combustion air is fed in. As a second fuel for the multi-fuel heater 16 pyrolysis gas is used, which is via a pipe 19th , in which a throttle valve 20th is located, the carbonation section 10 of the conveyor oven 2 is removed. The pyrolysis gas is withdrawn from the hottest point in the interior of the continuous furnace 2 instead, generally, viewed in the direction of passage, in the end area of the carbonation section 10 lies.

The combustion air with which the pipe 19th pyrolysis gases supplied are burned via a pipe 21st , in which two fans for redundancy reasons 22nd , 23 are taken from the outside atmosphere. The one at that illustrated embodiment used multi-fuel heater 16 has two different inputs for the combustion air of the pyrolysis gases, one for start-up and a second for continuous operation via branch lines 21a , 21b be fed. In the branch lines 21a , 21b there is a throttle valve each 25th or. 26th so that the division of over the line 21st supplied combustion air to the two branch lines 21a , 21b or the corresponding inlets on the multi-fuel heating device 16 can be adjusted.

The via a smoke outlet 14th from the conveyor oven 3 Exiting flue gases that have been cooled to a certain extent are passed through a pipe 27 partly a chimney 28 fed. Two fans are used for this 29 , 30th on the line 27 which in turn are connected in parallel for redundancy reasons. The use of a further part of the flue gases is explained further 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 fed with a heat exchanger 32 connected is. In the heat exchanger 32 the nitrogen supplied is heated by the continuous furnace 2 leaving flue gas instead. At the outlet of the heat exchanger 32 , in one of these with the preheating section 9 connecting line 33 , the nitrogen then has a temperature of around 200 ° C.

It was mentioned above that only part of the line 27 flue gases flowing through to the chimney 28 got. Another part of these flue gases is circulated in the system. To do this, branches off the line 27 one line 34 starting with an adsorption refrigeration system 35 connected is. The purpose of this adsorption refrigeration system 35 is explained below. The outlet of the adsorption refrigeration system 35 is via another line 36 , in which an additional cooling device if required 37 can lie with the combustion chamber of the multi-fuel heater 16 connected.

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

• Da beim Anfahren zunächst noch kein Pyrolysegas verfügbar ist, wird die Mehrstoffheizeinrichtung 16 zunächst ausschließlich mit Erdgas befeuert, welches über die Leitung 17 zugeführt wird. Die Rauchgase, die bei der Verbrennung entstehen, werden über die Leitung 15 dem Rauchgaseinlass 13 des Durchlaufofens 2 zugeführt und strömen, entgegen der Bewegungsrichtung der in den Kassetten 4 befindlichen Zellulose-Fasern, durch das Strahlrohr 12 bis zum Rauchgasauslass 14 hindurch. Selbstverständlich muss in der Anlaufphase des Durchlaufofens 2 zunächst zugewartet werden, bis die richtigen Betriebstemperaturen innerhalb der Abschnitte 9, 10 und auch 11 erreicht sind, bevor das Transportband, auf dem die mit Zellulose-Fasern gefüllten Kassetten 4 angebracht sind, in Bewegung gesetzt wird: Typische Werte für diese Betriebstemperaturen sind im Vorerwärmungsabachnitt 9 etwa 200-300 °C, im Karbonisierungsabschnitt 10 900 °C und im Kühlabschnitt 11 unter etwa 300 °C.

The plant described above for the carbonization of cellulose fibers works as follows:

• Since no pyrolysis gas is initially available when starting up, the multi-fuel heater 16 initially fired exclusively with natural gas, which is via the line 17th is fed. The flue gases that arise during combustion are passed through the pipe 15th the flue gas inlet 13 of the conveyor oven 2 fed and flow in the opposite direction to the direction of movement in the cassettes 4th cellulose fibers, through the nozzle 12 to the smoke outlet 14th through. Of course, it must be in the start-up phase of the continuous furnace 2 first wait until the correct operating temperatures within the sections 9 , 10 and also 11 are reached before the conveyor belt on which the cassettes filled with cellulose fibers 4th are attached, is set in motion: Typical values for these operating temperatures are in the preheating section 9 about 200-300 ° C, in the carbonation section 10 900 ° C and in the cooling section 11 below about 300 ° C.

Once the required temperatures are reached, the cassettes 4th with the cellulose fibers first in the preheating section 9 largely freed from external atmosphere carried along; the moisture carried along by the cellulose fibers is evaporated, so that the cellulose fibers pass into the carbonation section 10 of the conveyor oven 2 are largely dry and preheated.

When passing through the carbonation section 10 As the required temperatures prevail there, the known pyrolysis process takes place, in which the cellulose fibers are converted into carbon fibers. The resulting pyrolysis gas is over the line 19th removed and the multi-fuel heater 16 fed. The supply of natural gas can now be reduced accordingly. If sufficient pyrolysis gas is produced, it may be possible to supply natural gas via the pipe 17th shut down completely and only use pyrolysis gas for heating.

Cassettes already loaded with cellulose fibers before the first passage 4th through the conveyor oven 2 need of course the different sections 10 , 11 filled with nitrogen gas. This is done on the one hand via the lines already mentioned above 31 , 33 , between which the heat exchanger 32 lies. On the other hand, nitrogen that has not been preheated is fed through a pipe 41 directly into the cooling section 11 of the conveyor oven 2 brought in.

During the combustion in the multi-fuel heating device 16 resulting flue gases, which the continuous furnace 2 have flowed through, preheat, as already indicated, the nitrogen, which in the preheating section 9 is introduced. With the help of the heat that is in that from the pipe 27 over the line 34 led flue gas is still stuck, the adsorption refrigeration system 35 operated practically "free of charge". This adsorption refrigeration system 35 is regulated in such a way that the refrigerant circulating through it in the heat sink 38 of the cooling section 11 of the conveyor oven 3 provides the necessary cooling capacity. In order to avoid self-ignition, the carbonized fibers must be cooled to a temperature of no more than 300 ° C before they are released into the outside atmosphere.

Over the fireplace 28 the same amount of flue gas is removed as the amount of nitrogen and combustion air that is supplied to the circulating gas circuit and of pyrolysis gas in the carbonation chamber 10 arises so that the total amount of gases circulating remains constant over time.

In the drawing there is also a bypass line 42 recognizable in which a throttle valve 43 lies. This bypass line 42 connects the multi-fuel heating device 16 directly to the fireplace 28 leading line 27 when the emission of flue gases from the multi-fuel heater 26th greater than the demand in the continuous furnace 2 is. Via another line 44 , in which another throttle valve 45 can, if necessary, from the pre-heating section 9 Water vapor in the bypass line 42 be handed in.

Claims (10)

Process for carbonizing cellulose fibers, in which a) the cellulose fibers are introduced 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 with the development of pyrolysis gas; d) the carbonized cellulose fibers are cooled; wherein e) the heat required to carry out steps b) and / or c) is obtained by burning a fuel gas; f) the pyrolysis gases obtained in step c) are used as fuel gases in step e), characterized in that g) the heat of the flue gases produced in step e) is partially used to heat the inert gas atmosphere, and h) a further part of the heat of the Flue gases generated in step e) are used to cool the carbonized cellulose fibers according to step d) by passing flue gases generated in step e) over an adsorption refrigeration system (35). Procedure according to Claim 1 , characterized in that at least in the initial phase in step e) natural gas is used as fuel gas. Plant for carbonizing cellulose fibers with a) an oven (2) in the interior of which there is an inert gas atmosphere and which has: aa) a preheating section (9) in which the cellulose fibers are introduced into the inert gas atmosphere and are dried by heating; ab) a carbonization section (10) in which the cellulose fibers can be brought to a temperature at which the carbonization takes place with the development of pyrolysis gas; ac) a cooling section (11) in which the carbonized cellulose fibers are cooled to a temperature at which spontaneous combustion is excluded; ad) a conveyor system with which the cellulose fibers are guided through the preheating section (9), the carbonizing section (10) and the cooling section (11); b) a heating device (16) which is fired with fuel gas and which provides the heat required in the preheating section (9) and / or in the carbonation section (10); wherein c) the carbonation section (10) of the furnace (2) is connected to a fuel gas connection of the heating device (16) in such a way that the developing pyrolysis gas can be used as fuel gas, characterized in that d) in the flow path of the heating device (16 ) there is a heat exchanger (32) which is designed to heat the inert gas supplied, and e) there is an adsorption refrigeration system (35) in the flow path of the smoke gases generated by the heating device (16). Plant after Claim 3 , characterized in that the heating device (16) is designed as a multi-fuel heating device which can be fed both with an externally supplied fuel gas and with pyrolysis gas. Plant after Claim 3 or 4th , characterized in that the point at which the pyrolysis gas is taken from the carbonation section (10) is the point at which the highest temperature prevails during operation. Plant according to one of the Claims 3 to 5 , characterized in that the adsorption refrigeration system (35) is connected to a cooling body (38) arranged in the cooling section (11) via a refrigerant circuit. Plant according to one of the Claims 3 to 6th , characterized in that at least one jet pipe (12) through which the flue gases from the heating device (16) can flow is provided for heating the preheating section (9) and / or the carbonation section (10). Plant after Claim 7 , characterized in that the jet pipe (12) is coated with ceramic material. Plant after Claim 7 or 8th , characterized in that the jet pipe (12) is guided in a serpentine manner through the preheating section (9) and / or the carbonation section (10) and that the distances between the serpentines are different, adapted to the local heat requirement. Plant according to one of the Claims 3 to 9 , characterized in that the adsorption refrigeration system (35) is connected to a line (34) which branches off from a line (27) through which flue gases flow.

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