EP2451898A1

EP2451898A1 - Method for thermal treatment of organic matter of low calorific value

Info

Publication number: EP2451898A1
Application number: EP10796780A
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: FI20095781A0; WO2011004075A1; CN101943411A; CA2767629A1

Abstract

A method for thermal treatment of organic matter (x) of a low calorific value, in which method matter to be processed 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 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 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. For improving the calorific value of the matter to be processed, matter of a low calorific value (x) is fed into the process space (2) by the conveyor arrangement (3) together with at least one organic matter (w) of a better calorific value.

Description

METHOD FOR THERMAL TREATMENT OF ORGANIC MATTER OF LOW CALORIFIC VALUE

[0001] The invention relates to a method for thermal treatment of organic matter of a low calorific value, in which method the 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, flue gas thereby formed being discharged from the process space by means of a discharge arrangement, and thermally treated matter is discharged 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 pyroly- sis 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] The processing of organic matter of a low calorific value in particular by a method such as the one described above is not economically justifiable, because the calorific value of the matter to be processed is insufficient for a positive thermal balance to be obtained from the combustion process in the first place. In the processing of wet matter, for example, the lower limit for dry matter content is typically 28 to 30%. At present the major incon- venience 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 organic matter of a low calorific value to be made use of by thermal processing at reasonable investment and operating costs in particular.

[0006] An object of the invention is to provide a decisive improvement 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 for improving the calorific value of the matter to be processed, matter of a low calorific value is fed into the process space through the conveyor arrangement together with at least one organic matter of a better calorific value.

[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 thermal treatment of organic matter of a low calorific value 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 countercurrent flow principle is efficiently cooled as the heat contained therein is transferred into matter to be processed travelling to the opposite direction and heating/drying it at the same time as it is being fed into the process space, thus allowing the 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 exceeding 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 according 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 and the walls of the combustion space (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 signifi- cantly 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.

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 apparatus whose operation is based on the method of the invention;

Figure 2 shows a longitudinal section illustrating the operating prin- ciple of a similar apparatus; and Figures 3a and 3b show examples of two alternative Pl diagrams of an apparatus in which the method of the invention is applied.

[0010] 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 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 y' thereby formed is 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. To im- prove the calorific value of the matter to be processed, the matter of a low calorific value x is fed into the process space 2 through the conveyor arrangement 3 together with at least one organic matter w of a better calorific value.

[0011] 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 directly to the gas burner arrangement 7 for further processing, as shown for example in the exemplary Pl diagram of Figure 3a, or to a heat exchanger 13 and/or small separation arrangement 6, as shown in Figure 3b, for separating the tar contained therein before the combustion of the pyrolysis gas. As a further preferred embodiment, the pyrolysis gas y is conveyed to the conveyor arrangement 3 for further processing through a flow arrangement 8 connected to the outside of the process space 1.

[0012] As a further preferred embodiment, for the best 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.

[0013] As a further preferred embodiment of the method of the in- vention, the matter to be processed x, w 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 processed, firstly, in a continuous manner and, secondly, according to the principle of the Pl diagrams of Figure 3a and 3b, for example, in such a way that proc- ess gases are prevented from escaping from the conveyor arrangement or the process space into the environment in an uncontrolled manner.

[0015] Still as shown in the accompanying drawings, when particularly wet matter x is being processed, drier matter w is preferably mixed therein in the longitudinal direction of the conveyor arrangement by two successive feeders 1 ; 1 a , for example as shown in the accompanying drawings 1 and 2, the matter fed by which then becomes mixed as the screw conveyor 3a pushes them towards the process space. In this connection it is naturally also possible to use e.g. the solution of the Pl diagram shown in Figure 3b, the wet and dry matter x, w being mixed in a separate mixing space and conveyed by one con- veyor to the conveyor arrangement 3.

[0016] As a further preferred embodiment of the method of the invention, the calorific value of the matter to be processed is improved by adding to the wet matter x drier matter and/or matter of a better calorific value, the matter being substantially fluid, such as grease waste, glycerol and/or the like.

[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 arrange- ment 3 for sucking pyrolysis gas y through an ejector nozzle 11 into the gas burner.

[0018] With a particular reference to the Pl diagram of Figure 3b provided as an example, the tar p contained in the pyrolysis gas y is separated according to a preferred embodiment by an electrostatic precipitator (ESP).

[0019] With a further reference to the preferred implementation of

Figure 3b, thermally treated carbonized matter x', w' is removed from the proc- ess space 2 and then ground in step A by mixing therein tar p obtained from the small separation arrangement 6. As a further preferred embodiment, the ground, carbonized matter x', w' and the tar p mixed together are compressed into briquettes in step B by one or more briquette pressers.

[0020] 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 con- tinuous excess air is maintained in the combustion.

[0021] As a yet further preferred embodiment, the pyrolysis gas y is cooled to about 30⁰C before being fed to the small separation arrangement 6. Correspondingly, thermally treated carbonized matter x' is removed from the process space 2 preferably at a temperature of 450°.

[0022] As a further preferred embodiment and with a particular reference to the principle disclosed in Figure 2, 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 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 provided with one or more lower pitches at the front end thereof and one or more higher pitches at the rear end thereof.

[0023] It is obvious that the invention is not restricted to the em- bodiments 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 diagrams of Figure 3a and 3b, for example, may be utilized in the combustion process. Similarly, a screw conveyor arrangement pro- vided 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 diagrams of Figures 3a and 3b, the torch tube thus serving as a relief valve enabling rapid emergency switch- off of the apparatus.

Claims

1. A method for thermal treatment of organic matter (x) of a low calorific value, in which method matter to be processed 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 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 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 for improving the calorific value of the matter to be processed, matter of a low calorific value (x) is fed into the process space (2) by the conveyor arrangement (3) together with at least one organic matter (w) of a better calorific value.

2. A method according to claim ^ characterized in that the pyrolysis gas (y) is conveyed within the conveyor arrangement (3) as counter- current towards a feed end (I) of the conveyor arrangement for transferring the heat contained in the pyrolysis gas into matter to be processed (x, w) that is travelling to the opposite direction (s) and for feeding the cooled pyrolysis gas (y) to further processing, such as to the gas burner arrangement (7) or to a heat exchanger (13) and/or to a small separation arrangement (6).

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

4. A method according to any one the preceding claims 1 to 3, characterized in that the matter to be processed (x, w) 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 the materials to be processed (x, w) is brought to the conveyor arrangement (3) by two feeders successive in the longitudinal direction 8s) thereof, the materials thus conveyed becoming mixed as they travel in the conveyor system (3) towards the process space.

7. A method according to any one of the preceding claims 1 to 5, characterized in that the materials to be processed (x, w) are mixed in a separate mixing space and then conveyed on one feeder to the conveyor ar- rangement (3).

8. A method according to any one of the preceding claims 1 to 7, characterized in that the calorific value of the matter to be processed is improved by adding to the matter (x) of a low calorific value, such as wet matter, drier matter and/or matter of a better calorific value which is substantially liquid matter, such as grease waste, glycerol and/or the like.

9. A method according to any one of the preceding claims 1 to 7, characterized in that 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 con- nection 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).