"Process and plant for obtaining a carbon-containing valuable substance fraction"
The invention relates to a process for obtaining a granular valuable substance fraction with a high carbon content by pyrolysis of a feedstock containing inert constituents and organic constituents, in which at least an inert fraction is separated off from the pyrolysis solids outgassed during the pyrolysis and in which a pyrolysis gas is removed from the pyrolysis. The invention further relates to a plant for carrying out this process.
A large number of different processes are known for the pyrolysis of carbon-containing waste materials. In a pyrolysis plant in practical operation, intended for the processing of domestic reflise and other waste materials, an indirectly heated drum-type furnace is employed as the pyrolysis unit. The pyrolysis solids outgassed at the discharge end of the drum-type furnace are passed into a water lute and cooled in a water bath, before being discharged from the water lute. The steam produced during the cooling is removed together with the pyrolysis gas produced during the pyrolysis. To prevent the pyrolysis gas from burning in the offtake region, the pyrolysis system is sealed off from the outside atmosphere by the water lute. Besides materials which are inert (with respect to pyrolysis), such as metals, glass and stones, the pyrolysis solids removed from the rotary tubular furnace also contain in particular carbon. The term pyrolysis coke is therefore also employed. This pyrolysis coke is a valuable substance which can be used as a fuel for subsequent combustion. Normally, at least the metallic constituents of the outgassed, cooled pyrolysis solids are separated off before the combustion is carried out.
Owing to the fact that the pyrolysis solids are cooled in a water bath, the pyrolysis coke contains amounts of moisture which adversely affect its calorific value. For this reason, the pyrolysis coke produced in this way is subjected to drying before the combustion, this involving corresponding costs and expenditure of energy.
Tlie object of the invention is to improve a process of the generic type such that a valuable substance fraction with a high carbon content is obtained which no longer requires costly

drying before the combustion. Furthermore, a plant for carrying out this process is to be proposed.
This object is achieved with regard to the process by means of the characterizing features of Claim I. Advantageous developments of the process according to the invention emerge from Subclaims 2 to 9. A plant according to the invention for carrying out this process has the features specified in Claim 10 and is refined in an advantageous manner by the characterizing features of Subclaims 11 to 18.
The basic concept of the present invention consists in the fact that the granular valuable substance fraction with a high carbon content which is to be obtained is not passed through a water bath for cooling, but rather is removed from the pyrolysis plant by a dry route. The carbon-containing valuable substance fraction here constitutes merely part of the entire solids removed from the pyrolysis. According to the invention, this fraction is obtained as a fme fraction rich in carbon by screening the pyrolysis sohds at the end of the pyrolysis in the hot state and out of contact with air. The fme fraction constitutes the screen undersize. The largest particle of this fine fraction should expediently be about 12 mm. It has been shown that such a treatment of the pyrolysis solids allows the carbon-containing proportion to be largely concentrated in the fme fraction. On screening with a mesh width of about 12 mm, the proportion of the fme fraction accounts for about 60% of the total amount of pyrolysis sohds if normal unsorted domestic refuse is chosen as the feedstock. The coarse fraction separated as the screen oversize, which consists essentially of inert materials such as metals, glass and stones, makes up a proportion of about 40% and contains only small amounts of the carbon remaining in the pyrolysis solids. Like the fine fraction, this separated coarse fraction is, out of contact with air, removed in order to prevent combustion air from getting into the pyrolysis gas generated or combustible pyrolysis gas from getting to the outside. The cooling of the coarse fraction is expediently effected in a known manner in a water bath. The steam produced during the cooling of the coarse fraction is, as happens in the case of the process of the generic type as well, preferably removed together with the pyrolysis gas. It is recommended to subject the coarse fraction obtained also to metal separation at the end, in order to recover any recyclable substances.

In a preferred embodiment of the invention, the fine fi-action removed fi-om the pyrolysis is cooled, in the dry state and out of contact with air, to below the ignition temperature of the fine fraction. In the cooled form, this finely divided valuable substance fraction can be stored. In order to ensure the exclusion of air during the discharge of the fine fracfion, an expedient development of the invention provides for a filling, which acts as a plug, of the fine fi-action to be employed for sealing off, the height of the filling being maintained at a preset minimum height. The maintenance of the minimum filhng height should advantageously be ensured by a control with which the filling height is measured, for example, by y-radiation,
It is not essential to store the fine fraction after coohng; rather, an advantageous development of the invention provides for the fine fraction obtained to be subjected directly to combustion. In this case, it is possible to supply the fine fi-action, while still at elevated temperature, directly to the combustion unit.
The invention is employed with particular advantage for the pyrolysis of domestic refuse and wastes similar to domestic reiuse- It is however also possible to treat other waste materials containing inert constituents and a significant proportion of organic constituents using the process according to the invention, in order to obtain therefi-om a valuable substance fi-action with a high carbon content.
The invention is explained in more detail below with the aid of the exemplary embodiment illustrated in the single figure as a plant diagram.
The plant according to the invention includes a dmm-type furnace 1 which rotates about its longitudinal axis and is provided with indirect heating of its outer shell. This drum-type furnace 1 can be charged with the feedstock at its left end face by way of a sluice device (not shown specifically). The said feedstock travels through the drum-type furnace 1 from left to right owing to the constant rotation and a corresponding slight inclination of the ftimace axis. A screening drum 3 is flanged to the discharge end of the drum-type furnace 1, so that a rotationalty fixed coimection exists between the two. It is however also readily possible to equip the drum-type furnace 1 and the screening dmm 3 with separate rotary drives and to provide appropriate transporting equipment for transferring the pyrolysis solid discharged

from the drum-type furnace 1 to the screening drum 3. The screening drum 3 expediently has an aperture width of about 12 mm, so that only correspondingly coarse-grained material can escape, as the screen oversize, at the right end face of the screening drum 3 into the discharge device 8 for the coarse fraction. The discharge device 8 is sealed off from the outside to prevent the admission of air. The fine fi-action obtained as the screen undersize, which has a largestparticle, depending on the aperture width of the screening drum 3, of less than 12 mm for example, falls into a catching device 5 arranged beneath the screening drum 3. The catching device 5 is of funnel-shaped design like the discharge device 8 and is connected at its underside to a pipe piece 6 running substantially vertically. This pipe piece 6 constitutes a conveying connection to a discharge-conveying unit 7 for a granular material. The catching device 5, like the discharge device 8, is sealed off to the admission of combustion air. This sealing-off of the catching device 5 is preferably ensured by a filling of the fine fraction in the pipe piece 6, the filling being maintained at a preset height as indicated by the arrow shown in the drawing. A control employing, for example, a y-probe 10 for the detection of the filling height is expediently provided for this purpose. It is of course also readily possible to employ other measuring methods for the determination of the filling height. In the exemplary embodimenv illustrated, the discharge-conveying unit 7 for the fine fraction is designed as a screw conveyor which has a drive motor M. The control influences the drive motor M in accordancewith the value of the actual filling height measured by the y-probe 10. As the fine fraction passes through the conveying unit 7, it is able to give offbeat to the outside and thus cool down. If required, the cooling effect can be increased, for example, by intensifying the cooling of the shell of the discharge-conveying unit. The dry fine fi-action, once it has cooled down to below its ignition temperature, can be emptied, for example, into a transport container 11 and taken to an intermediate storage area. It would of course also be possible to connect the discharge-conveying unit 7 directly to a combustion installation for direct thermal utilization of the fine fraction while still hot if possible.
Expediently, the discharge device 8, the catching device 5 and the offtake device 2 for the pyrolysis gas form a common housing which externally surrounds the screening drum 3. Beneath the discharge device 8 there is arranged a water lute 4 which is leaktightly connected to the housing of the discharge device 8 and has a solids-conveying member 9 in its lower region, so that the coarse fraction falling into the water bath in the water lute 4 from the

screening drum 3 can be removed from the water lute 4 in moist form. It is also possible, in principle, to provide dry cooling for the coarse fraction. The use of a water lute is recommended, however, especially for cost reasons. The steam produced during the cooling of the coarse fraction is carried off together with the pyrolysis gas by the offtake device 2. Ii recommended to provide in addition a metal-separating facility downstream of the solids-conveying member 9, in order to recover metallic constituents of the coarse fraction. All that then remains in the inert coarse fraction is moist residual material, which can be dumped.

We claim
1. Process for obtaining a granular valuable substance fraction with a high carbon content
by pyrolysis of a feedstock containing inert constituents and at least 10% by weight of
organic constituents, in which at least an inert fraction is separated off from the
outgassed pyrolysis solids and a pyrolysis gas is removed from the pyrolysis,
characterized
in that the pyrolysis solids emerging from the pyrolysis are separated at the end
of the pyrolysis, in the hot state and out of contact with air, by screening, into a
fine fraction rich in carbon and a coarse fraction poor in carbon,
in that the fine fraction is discharged in the dry state and
in that the coarse fraction is removed separately and likewise out of contact
with air and cooled.
2. Process according to Claim I,
characterized
in that the coarse fraction is cooled in a water bath and in that the steam produced during this is removed together with the pyrolysis gas.
3. Process according to either of Claims 1 and 2,
characterized
in that the fine fraction is cooled, in the dry state and out of contact with air, to below the ignition temperature of the fine fraction.
4. Process according to any of Claims 1 to 3,
characterized
in that the exclusion of air during the discharge of the fine fraction is effected by a filling, which acts as a plug, of the fine fraction, the height of the filling being maintained at a preset minimum height.

5. Process according lo Claim 4,
characterized
in that, for the maintenance of the minimum filling height, a control is provided with which the filling height is measured by y-radiation,
6. Process according to any of Claims 1 to 5,
characterized
in that sorted or unsorted domestic refuse is used as the feedstock.
7. Process according to any of Claims 1 to 6,
characterized
in that the fraction obtained is subjected to combustion.
8. Process according to any of Claims 1 to 7,
characterized
in that the coarse fi'action is subjected to metal separation.
9. Process according to any of Claims 1 to 8,
characterized
in that the largest particle of the fme fraction in the screening is set at a maximum of 12 mm.
10. Plant for carrying out the process according to Claim 1, comprising
an indirectly heated rotary tubuEar furnace (l) for the pyrolysis, a discharge device for pyrolysis solids, which is sealed to the admission of air, an offtake device (2) for pyrolysis gases,
a separating unit for separating off an inert fraction from the pyrolysis solids and
a cooling device for the pyrolysis solids, characterized

in that the separating unit is designed as a screening drum (3), the charging
opening of which, out of contact with air, is in direct transport communication
with the rotary tubular furnace (I),
in that a catching device (5) for the screen undersize obtained as the fine
fraction is arranged under the screening drum (3), the catching device (5) being
connected to a pipe piece (6) arranged under the latter and running substantially
vertically, which pipe piece for its part is connected to a discharge-conveying
unit (7), and
in that an air-sealed discharge device (8) for the screen oversize obtained as the
coarse fi-action is connected at the end of the screening drum (3).
11. Plant according to Claim 10,
characterized
in that the discharge device (8) for the coarse fraction comprises, as cooling device, a water lute (4) having a solids-conveying member (9).
12. Plant according to either of Claims 10 and II,
characterized
in that the discharge-conveying unit (7) for the fine fraction is designed as a screw conveyor.
13. Plant according to any of Claims 10 to 12,
characterized
in that a control is provided which maintains the filling height of the fine fraction in the pipe piece (6) at a preset minimum height.
14. Plant according to Claim 13,
characterized
in that ay-probe (10) is provided for the detection of the filling height.

15. Plant according to any of Claims 10 to 14,
characterized
in that the discharge device (8) and the offtake device (2) have a common housing.
16. Plant according to any of Claims 10 to 15,
characterized
in that a metal-separating facility is connected downstream of the solids-conveying member (9) for the coarse fraction.
17. Plant according to any of Claims lOto 16,
characterized
in that the screening drum (3) is connected in a rotationally fixed mamier to the rotary tubular flimace(l).
18. Plant according to any of Claims 10 to 17,
characterized
in that the discharge-conveying unit (7) for the fine fraction is connected to a combustion plant.