EP2451896A1

EP2451896A1 - Method for separating carbon by thermal treatment

Info

Publication number: EP2451896A1
Application number: EP10796778A
Authority: EP
Inventors: Sampo Tukiainen
Original assignee: Preseco Oy
Current assignee: Preseco Oy
Priority date: 2009-07-08
Filing date: 2010-07-07
Publication date: 2012-05-16
Also published as: CN101943410A; CA2767626A1; FI20095778A0; WO2011004073A1

Abstract

The invention relates to a method for separating carbon by thermal treatment, in which method matter to be processed (x) is brought by a feed arrangement (1) to a conveyor arrangement (3) connected to a process space (2) that is substantially of a Thompson Converter type, the matter to be processed (x) being made to move in the process space (2) in longitudinal direction (s) thereof by means of a conveyor arrangement (3) closed in relation to the space, whereby pyrolysis gas (y) formed by heat transfer from the process space into the matter to be processed (x) contained in the conveyor system is conveyed into a combustion space (4) provided in the process space for combustion of the gas, flue gas (y') thereby formed being discharged from the process space by means of a discharge arrangement (5), and thermally treated matter (x') is discharged from the conveyor arrangement for further processing. The pyrolysis gas (y) is, firstly, burned by a continuous gas burner arrangement (7) and, secondly, heat transfer of the conveyor system (3) in the process space (2) is carried out substantially by direct radiation from the flame of the gas burner arrangement (7) and from the walls of the combustion space (4).

Description

METHOD FOR SEPARATING CARBON BY THERMAL TREATMENT

[0001] The invention relates to a method for separating carbon by thermal treatment, in which method matter to be processed is brought by a feed arrangement to a conveyor arrangement connected to a process space that is substantially of a Thompson Converter type. The matter to be processed is made to move in the process space in the longitudinal direction thereof by means of a conveyor arrangement closed in relation to the space. Pyrolysis gas formed by heat transfer from the process space into the matter to be processed contained in the conveyor system is conveyed into a combustion space provided in the process space for combustion of the gas, the flue gas thereby formed being discharged from the process space by means of a discharge arrangement, and the thermally treated matter is removed from the conveyor arrangement for further processing.

[0002] The use of a conventional Thompson Converter type apparatus for the above purpose is based on the feeding of the matter to be processed to one or more screw conveyors provided in the process space of the apparatus, by which conveyor/s the matter to be processed is transferred in the longitudinal direction of the process space while being heated indirectly at the same time. The matter carbonized inside the screw conveyors by heat transferred from the conveyors to the matter to be processed is discharged from one end of the conveyors to a collecting conveyor that transfers the carbonized matter out of the process space. In a solution such as this the pyrolysis gas created inside the screw conveyors is conventionally carried within the matter to be processed in the travel direction thereof from the discharge end of the screw conveyors to a collection chamber and further on a connecting conduit to a combustion furnace below the screw conveyor space, where it is burned. Fuel gas leaves the combustion furnace to enter a screw conveyor space, where the heat contained in the fuel gas is transferred by convective heat transfer into the screw conveyors before being discharged from the process space through a discharge assembly.

[0003] The activation of this type of apparatus requires the combustion furnace to be heated throughout to a sufficiently high temperature e.g. by means of solid fuel burned therein before the actual carbonization process is started to allow the pyrolysis gas to be burned and to make the system then work in what is known as a self-sustained manner. For this reason the solution in question is laborious and slow particularly as regards initial start-up.

[0004] There are also current solutions of the above type in which the combustion furnace is provided with a kerosene burner to maintain an aux- iliary flame, thus providing a further implementation in which pyrolysis gas conveyed to a direction opposite to the transfer direction of the screw conveyor arrangement is carried to the combustion furnace for combustion in the burner flame.

[0005] At present the major inconvenience in the apparatuses of the above type is their modest "volume efficiency [WIm³]" due to the indirect or convective heat transfer applied for heating the screw conveyors. On the one hand, this prolongs significantly the cold start of the apparatus before the actual continuous carbonization process can be started. On the other hand, an essential disadvantage is that the preheating of the furnace space requires using either solid fuel for a relatively long period of time or a continuous use of an auxiliary flame produced by separate fuel to allow pyrolysis gas to be burned. Hence current technology does not enable a carbon separation process of reasonable investment and operating costs to be implemented.

[0006] An object of the invention is to provide a decisive improve- ment to the above problems and thereby significantly raise the level of the art prevailing in the field. For this purpose the method of the invention is primarily characterized in that, firstly, the pyrolysis gas is burned using a continuous gas burner arrangement and that, secondly, heat transfer of the conveyor system in the process space is implemented substantially by direct radiation from the flame of the gas burner arrangement and the walls of the combustion space.

[0007] Among the most important advantages of the method of the invention to be mentioned are the simplicity and efficacy of its operating principle, of the equipment suitable thereto and the use thereof. The method of the invention enables to implement separation of carbon from matter to be proc- essed by thermal treatment in a technically extremely simple and efficient manner by using, firstly, a continuous conveyor arrangement provided with a feed and discharge member substantially gas tight in relation to the environment. This allows to prevent oxygen supply to the pyrolysis gas within the conveyor arrangement, whereby the gas travelling towards the feed end of the conveyor arrangement according to the principle of countercurrent flow is efficiently cooled as the heat contained therein is transferred into matter to be processed travelling to the opposite direction, thus enabling pyrolysis gas to be conveyed at an ideal temperature to the gas burner for combustion. As the method of the invention makes use of a large combustion space, the large inner volume enables, firstly, fuel gases to be burned at a temperature exceed- ing 850⁰C for a delay of two seconds, as required by the EU waste incineration directive. In addition, conditions favourable for an SNCR nitrogen reduction (Selective Non-catalytic Reduction), i.e. a temperature of 800 to 1100⁰C and an oxidizing atmosphere, prevail at the rear part of the combustion space.

[0008] The volume efficiency of the apparatus implemented accord- ing to the invention is optimal when heat transfer to the conveyor arrangement takes place in the process space by direct radiation heat from the flame of the gas burner/burners (the radiation heat transfer being proportional to the fourth order of the temperature), thus speeding up the initiation of the carbon separation process because direct radiation from the gas flame increases the surface temperatures of the conveyor system significantly more rapidly than convective heat transfer. The method of the invention thus enables to assemble an apparatus which is compact and significantly smaller than corresponding, currently available apparatuses and naturally also significantly more affordable in terms of investment, service and maintenance costs than prior art solutions.

[0009] Other preferred embodiments of the method of the invention are disclosed in the dependent claims drawn to the method.

[0010] In the following, the invention will be illustrated in detail with reference to the accompanying drawings, in which

Figure 1 shows, by way of an example, a perspective view of an ap- paratus whose operation is based on the method of the invention;

Figure 2 shows a longitudinal section illustrating the operating principle of a similar apparatus; and

Figure 3 shows a preferred Pl diagram of an apparatus in which the method of the invention is applied.

[0011] The invention relates to a method for separating carbon by thermal treatment, in which method matter to be processed x is brought by a feed arrangement 1 to a conveyor arrangement 3 connected to a process space 2 that is substantially of a Thompson Converter type. The matter to be processed x is made to move in the process space 2 in longitudinal direction s thereof by means of a conveyor arrangement 3 closed in relation to the space, whereby pyrolysis gas y formed by heat transfer from the process space into the matter to be processed x contained in the conveyor system is conveyed into a combustion space 4 provided in the process space for combustion of the gas, flue gas y' thereby formed being discharged from the process space by means of a discharge arrangement 5, and thermally treated matter x' is dis- charged from the conveyor arrangement for further processing. With a particular reference to the exemplary longitudinal section of Figure 2, pyrolysis gas y is, firstly, burned by a continuous gas burner arrangement 7. Secondly, heat transfer of the conveyor system 3 in the process space 2 is carried out substantially by direct radiation from the flame of the gas burner arrangement 7 and from the walls of the combustion space 4.

[0012] As a preferred embodiment of the method of the invention, pyrolysis gas y is conveyed within the conveyor arrangement 3 by countercur- rent towards feed end I of the conveyor arrangement for transferring heat contained in the pyrolysis gas into the matter to be processed x that is moving to the opposite direction s and for feeding cooled pyrolysis gas y into the gas burner arrangement 7. As a further preferred embodiment, the pyrolysis gas y is conveyed to the gas burner arrangement 7 through a flow arrangement 8 connected to the conveyor arrangement 3 on the outside of the process space 1.

[0013] As a further preferred embodiment of the method of the invention, the matter to be processed x is handled in connection with the process space 2 by a continuous conveyor arrangement 3 provided with feed and discharge members 1 a, 1 b that are substantially gas tight in relation to the environment, the arrangement being implemented by means of one or more screw conveyors 3a or the like that are driven by an electric motor o and steplessly regulated by means of a frequency converter, for example.

[0014] The matter to be processed may be fed to the conveyor system 3 by using the method and feed arrangement of Finnish Patent 119125, for example, particularly for implementing overfeed of the matter to be proc- essed, firstly, in a continuous manner and, secondly, according to the principle of the Pl diagram of Figure 3, for example, in such a way that process gases are prevented from escaping from the conveyor arrangement or the process space into the environment in an uncontrolled manner.

[0015] As a further preferred embodiment, for the best heating ef- feet the conveyor system 3 is heated immediately after its introduction into the process space 2 by one or more gas burners 7; 7a arranged to the entry wall 2a of the process space parallel with the conveyor arrangement.

[0016] As a further preferred embodiment and with a particular reference to the principle disclosed in Figure 2, the transfer power of the con- veyor arrangement 3, such as one or more screw conveyors 3a, is changed in the longitudinal direction s of the processing space so as to particularly reduce the layer thickness of the matter to be processed x from the feed end I of the conveyor arrangement 3 towards its discharge end II. In that case the conveyor arrangement 3 is preferably implemented by a screw conveyor 3a pro- vided with one or more lower pitches at the front end thereof and one or more higher pitches at the rear end thereof.

[0017] With a further reference to the implementation of Figure 2, air supply to the gas burner arrangement 7, such as one or more parallel gas burners 7a, is implemented by a separate combustion air blower 9. On the other hand, an ejector blower 10 is applied, also in a preferred manner, in connection with one or more gas burners 7 belonging to the gas burner arrangement 3 for sucking pyrolysis gas y through an ejector nozzle 11 into the gas burner.

[0018] Further, as shown in the accompanying drawings, the method of the invention allows also mutually different types of matter x, w to be processed simultaneously by introducing them into the conveyor system by two longitudinally successive feeders 1 ; 1a, as shown in the accompanying drawings, the matter transferred from the feeders being then mixed as the screw conveyor 3a pushes them towards the process space. In this connection it is naturally also possible to use e.g. a solution of the Pl diagram shown in Figure 3, the different materials being mixed in a separated mixing space and conveyed by one conveyor to the conveyor arrangement 3.

[0019] As a further preferred embodiment and with reference to the principle of Figures 2 and 3, a nitrogen reduction is carried out in the process space by feeding ammonia-containing medium, such as urea mist, ammonia- water solution or the like, into the combustion space 4 by an additional nozzle arrangement z. By placing the above-mentioned nozzle arrangement outside the reach of the combustion zone of the gas flame, the medium sprayed through the nozzle arrangement evaporates, whereby the remaining ammonia becomes mixed and has enough time to work on the flue gases so that a significant nitrogen reduction is achieved. Moreover, the method of the invention also preferably ensures by means of a Lambda sensor, for example, that continuous excess air is maintained in the combustion.

[0020] It is obvious that the invention is not restricted to the embodiments presented or explained above, but may be modified within the basic inventive idea according to each purpose of use and application. Hence it is evident, firstly, that in the method of the invention conventional control technology and automation known per se, such as oxygen analyzers and temperature sensors needed in the combustion of pyrolysis gas and/or a preheating burner as in the exemplary Pl diagram of Figure 3, for example, may be utilized in the combustion process. Similarly, a screw conveyor arrangement provided with necessary control arrangements for enabling optimal carbonization and final temperature by stepless regulation of the operation of the screw conveyor arrangement, for example, may be used in the processing of the matter to be processed. It is naturally preferred to provide an apparatus applying the method of the invention with optical flame monitoring analyzers, for example, and with a "torch tube" 12 connected to the conveyor arrangement, as in the drawings, to allow pyrolysis gas to be released, when necessary, by combustion in a separate burner, as shown in the Pl diagram of Figure 3, the torch tube thus serving as a relief valve enabling rapid emergency switch-off of the apparatus.

Claims

1. A method for separating carbon by thermal treatment, in which method matter to be processed (x) is brought by a feed arrangement (1 ) to a conveyor arrangement (3) connected to a process space (2) that is substan- tially of a Thompson Converter type, the matter to be processed (x) being made to move in the process space (2) in a longitudinal direction (s) thereof by means of a conveyor arrangement (3) closed in relation to the space, whereby pyrolysis gas (y) formed by heat transfer from the process space into the matter to be processed (x) contained in the conveyor system is conveyed into a combustion space (4) provided in the process space for combustion of the gas, flue gas (y¹) thereby formed being discharged from the process space by means of a discharge arrangement (5), and thermally treated matter (x¹) is discharged from the conveyor arrangement for further processing, characterized in that the pyrolysis gas (y) is, firstly, burned by a continuous gas burner arrangement (7) and, secondly, heat transfer of the conveyor system (3) in the process space (2) is carried out substantially by direct radiation from the flame of the gas burner arrangement (7) and from the walls of the combustion space (4).

2. A method according to claim ^ characterized in that the pyrolysis gas (y) is conveyed within the conveyor arrangement (3) by counter- current towards feed end (I) of the conveyor arrangement for transferring heat contained in the pyrolysis gas into matter to be processed (x) that is moving to the opposite direction (s) and for feeding the cooled pyrolysis gas (y) into the gas burner arrangement (7).

3. A method according to claim 1 or 2, characterized in that the pyrolysis gas (y) is conveyed to the gas burner arrangement (7) through a flow arrangement (8) connected to the conveyor arrangement (3) on the outside of the process space (1 ).

4. A method according to any one the preceding claims 1 to 3, characterized in that the matter to be processed (x) is handled in connection with the process space (2) by a continuous conveyor arrangement (3) provided with feed and discharge members (1a, 1b) that are substantially gas tight in relation to the environment.

5. A method according to claim 4, characterized in that the conveyor arrangement (3) is implemented by one or more screw conveyors (3a) or the like driven by an electric motor (o) and regulated steplessly by means of a frequency converter, for example.

6. A method according to any one of the preceding claims 1 to 5, characterized in that for the most efficient heating effect the conveyor system (3) is heated immediately after its introduction into the process space (2) by one or more gas burners (7; 7a) arranged to the entry wall (2a) of the process space parallel with the conveyor arrangement.

7. A method according to any one of the preceding claims 1 to 6, characterized in that the transfer power of the conveyor arrangement (3), such as one or more screw conveyors (3a), is changed in the longitudinal direction (s) of the processing space particularly for reducing the layer thickness of the matter to be processed (x) from the feed end (I) of the conveyor arrangement (3) towards the discharge end (II) thereof.

8. A method according to claim 7, characterized in that the conveyor arrangement (3) is implemented by one or more screw conveyors

(3a) provided with a lower pitch at the front end and a higher pitch at the rear end thereof.

9. A method according to any one of the preceding claims 1 to 8, characterized in that air supply to the gas burner arrangement (7), such as one or more parallel gas burners (7a), is implemented by means of a combustion air blower (9) and/or an ejector blower (10) is utilized in connection with one or more gas burners (7) belonging to the gas burner arrangement (3) for sucking the pyrolysis gas (y) through the ejector nozzle into the gas burner.

10. A method according to any one of the preceding claims 1 to 9, characterized in that a nitrogen reduction is carried out in the process space by feeding into the combustion space (4) ammonia-containing medium, such as urea mist, ammonia-water solution or the like, by means of an additional nozzle arrangement (z).