EP0704518A1 - Process and installation for thermal valorisation of waste products - Google Patents

Abstract

Waste substances, e.g. household refuse, sewage sludge, are pyrolysed in a rotary kiln and the resultant pyrolysis coke is, after mechanical processing, converted into a synthesis gas in a gasification cyclone using oxygen. The gas generated in the pyrolysis stage is fed directly into the gasification cyclone whilst still hot, and the C in the coke and the H2 in the pyrolysis gas are converted into a CO/H2 rich synthesis gas at above 1400 degrees C. Also claimed is a plant for utilising waste materials, having a rotary kiln whose outlet for the pyrolysis coke is connected to a liq. phase gasification cyclone via a mechanical prepn. stage; the pyrolysis gas outlet being connected to the cyclone via a dust separator.

Description

The invention relates to a method and a plant for the thermal utilization of waste materials containing organic and inorganic constituents, such as household waste, sewage sludge or the like, the waste materials being carbonized in a rotary kiln to form pyrolysis gas and the pyrolysis coke obtained during the smoldering after its mechanical processing in one Gasification cyclone is gasified with the addition of oxygen to a synthesis gas.

In the process for the thermal utilization of waste materials (domestic waste, sewage sludge or the like) containing organic and inorganic constituents of the older but not prepublished patent application P 43 38 927.9, from which the invention is based, the shredded waste materials are carbonized in a rotary kiln with the formation of pyrolysis gas and The pyrolysis coke obtained during the smoldering is gasified after its mechanical processing with separation of metals and other valuable substances in a gasification cyclone with the addition of oxygen to a synthesis gas, which is then used for its intended purpose. The ingredients that cannot be gasified in high-temperature gasification are withdrawn from the gasification cyclone as molten slag, which after solidification can be deposited in a leach-resistant manner or used as a building material. The hot pyrolysis gas drawn off from the rotary tube furnace as a smoldering reactor is thermally utilized in that it is burned in a waste heat boiler for the purpose of generating steam.

Since the hot pyrolysis gases drawn off from the rotary kiln as a smoldering reactor mainly consist of gaseous hydrocarbons and water vapor and small amounts of nitrogen, carbon monoxide, carbon dioxide and other gaseous pollutants, it cannot be avoided that the vaporous components of the hot pyrolysis gas cool down on the way condense in the waste heat boiler or afterwards in the flue gas duct. However, the condensable pyrolysis gas constituents result in a mixture of water and liquid and solid hydrocarbons at room temperature, this mixture in turn resulting in a residue which has to be disposed of in a relatively complex manner.

In the process for the production of flammable gases from waste materials of EP-B 0 152 912, the waste materials are carbonized in a rotary reactor, and the pyrolysis gas obtained during the smoldering is partially burned after gas cleaning at temperatures of 800 to 1200 ° C. and then by a red-hot one Layer of chunky foreign coke passed for the purpose of cracking crackable gas components. The pyrolysis coke that is produced during the smoldering process is deposited after mechanical processing, i.e. the carbon contained in the pyrolysis coke is not used to generate energy.

Finally, from DE-Z _" Rubbish and Waste" 8/1993, pages 569 to 572 a _" smoldering process" for the thermal disposal of waste such as household waste and sewage sludge is known, in which the waste in a rotary drum at about 450 ° C become smeared. The resulting solid smoldering residue is then burned in a combustion chamber at a temperature of approx. 1300 ° C, using the combustible pyrolysis gas drawn off from the smoldering drum, which is burned in the same combustion chamber. In this known method, only flue gases are produced as gaseous products, in no case a synthesis gas or fuel gas.

The invention has for its object the thermal utilization of waste materials, such as household waste, sewage sludge, etc., described above, with organic and inorganic constituents with smoldering of the waste materials and to design high-temperature gasification of the pyrolysis coke in a gasification cyclone in such a way that, in addition to a leach-resistant slag, not a flue gas, but only a high-quality CO + H₂-rich synthesis gas is produced without the risk of undesired formation of condensate during gas cooling.

In terms of method, this object is achieved with the measures of claim 1 and in terms of the device with the measures of claim 4. Advantageous refinements are specified in the subclaims.

als auch der im Pyrolysegas enthaltenen Kohlenwasserstoffe nach der Bruttoreaktion $${\text{C}}_{\text{n}}{\text{H}}_{\text{m}}\text{+ H₂O → CO + H₂}$$

zur Bildung des hochwertigen CO + H₂-reichen Synthesegases. Weil das heiße Pyrolysegas nicht abgekühlt wird und sein H₂O-Dampfanteil direkt im Hochtemperatur-Vergasungszyklon gemäß der Bruttoreaktion $${\text{C}}_{\text{n}}{\text{H}}_{\text{m}}\text{+ H₂O → CO + H₂}$$

umgesetzt wird, ist die Gefahr einer unerwünschten Kondensatbildung nicht gegeben, und auf diese Weise entsteht auch bei der Abkühlung des gewonnenen Synthesegases kein Gemisch mehr aus Wasser sowie flüssigen und festen Kohlenwasserstoffen, wobei dieses Gemisch ein zu entsorgender Reststoff wäre. Die Hochtemperaturvergasung im Vergasungszyklon erfolgt bei unterstöchiometrischer Sauerstoffzufuhr, das heißt mit einem Sauerstoffunterschuß bei einem Lamda-Wert von zum Beispiel 0,4 bis 0,8. Aus dem Vergasungszyklon werden das CO + H₂-reiche Synthesegas sowie eine schmelzflüssige laugungsresistente Schlacke abgezogen, wobei Synthesegas und Schlackenschmelze in einem dem Vergasungszyklon nachgeschalteten Unterofen voneinander getrennt werden. Die abgekühlte schmelzflüssige Schlacke kann beispielsweise als Baustoff verwendet oder zu Steinwolle verarbeitet werden, und das nahezu stickstoffreie und wasserdampffreie CO + H₂-reiche Synthesegas kann nach seiner Abkühlung und Reinigung seiner Verwendung zugeführt werden.It is characteristic of the process according to the invention that the pyrolysis gas obtained during the smoldering is introduced directly into the gasification cyclone in a hot, non-cooled state of, for example, approximately 400 to 650 ° C., in which the carbon of the pyrolysis coke and the hydrocarbons of the pyrolysis gas at temperatures above 1400 ° C to be converted to a CO + H₂-rich synthesis gas. In the high-temperature gasification cyclone, as much as possible of both the carbon contained in the pyrolysis coke is used after the gross reaction $$\text{C + 1/2 O₂ → CO}$$

as well as the hydrocarbons contained in the pyrolysis gas after the gross reaction $${\text{C.}}_{\text{n}}{\text{H}}_{\text{m}}\text{+ H₂O → CO + H₂}$$

to form the high-quality CO + H₂-rich synthesis gas. Because the hot pyrolysis gas is not cooled and its H₂O vapor content directly in the high-temperature gasification cyclone according to the gross reaction $${\text{C.}}_{\text{n}}{\text{H}}_{\text{m}}\text{+ H₂O → CO + H₂}$$

is implemented, there is no risk of undesired formation of condensate, and in this way, even when the synthesis gas obtained is cooled, there is no longer a mixture of water and liquid and solid hydrocarbons, this mixture being a residue to be disposed of. The high-temperature gasification in the gasification cyclone takes place with substoichiometric oxygen supply, that is with an oxygen deficit at a lambda value of, for example, 0.4 to 0.8. The CO + H₂-rich synthesis gas and a molten lye-resistant slag are withdrawn from the gasification cyclone, the synthesis gas and molten slag being separated from one another in a lower furnace downstream of the gasification cyclone. The cooled, molten slag can be used, for example, as a building material or processed into rock wool, and the almost nitrogen-free and steam-free CO + H₂-rich synthesis gas can be used after cooling and cleaning.

According to a further feature of the invention, the hot pyrolysis gas drawn off from the rotary tube furnace can be dedusted before introduction into the gasification cyclone and the dust can be introduced into the gasification cyclone. It is a dry pyrolysis gas dedusting at a temperature above the condensation temperature of the hydrocarbons carried in vapor form with the pyrolysis gas and of the water vapor.

The pyrolysis rotary kiln can be indirectly heated. According to a further feature of the invention, the pyrolysis rotary kiln can also be heated directly by branching off a portion of the processed smoldering residue or pyrolysis coke before its introduction into the gasification cyclone and recirculating it to the directly heated rotary kiln to form a hot immersion bed lying in the rotary kiln of which the waste materials introduced into the rotary kiln are carbonized. The energy required to maintain the smoldering in the pyrolysis rotary kiln is introduced into the rotary kiln through the hot immersion bed from the recirculated uncooled smoldering residues, as well as through combustion of fuel, for example a part of the synthesis gas generated in the rotary kiln.

A plant according to the invention for the thermal utilization of waste materials containing organic and inorganic constituents with a pyrolysis rotary kiln and a high-temperature gasification cyclone is characterized in that the discharge of the pyrolysis rotary kiln for the pyrolysis coke is over a mechanical preparation is connected to the gasification cyclone, and the pyrolysis gas discharge from the rotary kiln is also connected to the gasification cyclone via a dust separator.

The invention and its further features and advantages are explained in more detail with reference to the exemplary embodiment shown schematically in the drawing.

According to the illustrative embodiment, comminuted organic and inorganic constituents containing waste materials (10) such as household waste, sewage sludge or the like are introduced into a rotary pyrolysis furnace (11) and carbonized there to form pyrolysis gas (12), and the pyrolysis coke (13) obtained during the smoldering process is fed to its mechanical processing (14) with comminution, separation of metals and in inert substances (15) and, if necessary, further sorting stages.

After its mechanical preparation (14), the pyrolysis coke (16), brought to a grain size of <3 mm, is introduced into a high-temperature gasification cyclone (17) and there with substoichiometrically introduced oxygen (18) or oxygen-enriched air at a temperature above 1400 ° C converted to a slag melt and to a synthesis gas, both phases (19) leaving the gasification cyclone or melting cyclone (17) downwards. The pyrolysis gas (12) obtained during the smoldering in the rotary tube furnace (11) is also introduced into the same gasification cyclone (17) after its dust separation (20) in a hot, not cooled state via line (21), in which both the carbon of the pyrolysis coke (16 ) and the hydrocarbons of the pyrolysis gas (21) can be converted to a CO + H₂-rich synthesis gas according to the gross reaction equations given above. The water vapor contained in the pyrolysis gas (21) is consumed, so that when the synthesis gas cools, undesired condensates can no longer form, which in turn would mean a residual material which is difficult to dispose of.

The dust separated from the hot pyrolysis gas (12) in the dust separator (20) is introduced into the gasification cyclone (17) via line (22) and line (16). The emerging from the gasification cyclone (17) phases (19) melt slag on the one hand and gas phase on the other hand are then separated from one another in a sub-furnace (23) into a slag (24) and into the high-quality CO + H₂-rich synthesis gas (25). The slag (24) is molten, which can be used for further processing, for example for the production of rock wool. After it has cooled, any existing pollutants, such as heavy metals, are incorporated in the slag so that they are resistant to leaching, so that the slag (24) can also be deposited without problems or used as a building material.

As indicated by the dashed line in the drawing, a subset (26) of the processed smoldering residues can be branched off and recirculated to the rotary kiln (11), which is directly heated in this case, to form a hot immersion bed in the rotary kiln (11), within which the rotary kiln imported waste materials (10) are carbonized. The processed fine-grained smoldering residues (26) forming the immersion bed are recirculated uncooled into the rotary kiln (11), and part of the smoldering gases or pyrolysis gases released by the smoldering burns above the immersion bed in the rotary kiln (11) and maintains an almost self-sufficient operation of the smoldering process upright, which, if necessary, can be supported by burning additional fuel, for example a partial flow of the synthesis gas (25). Inside the pyrolysis rotary kiln (11), the existing immersion bed ensures that only carbonized gas components burn, while the waste materials (10) remain largely protected from contact with combustion oxygen by the immersion bed.

Claims (4)

Process for the thermal utilization of waste materials containing organic and inorganic constituents, such as domestic waste, sewage sludge or the like, the waste materials (10) being carbonized in a rotary tube furnace (11) to form pyrolysis gas (12) and the pyrolysis coke (13) obtained during the smoldering after its mechanical processing (14) is gasified in a gasification cyclone (17) with the addition of oxygen (18) to a synthesis gas, characterized in that the pyrolysis gas (12, 21) obtained during the smoldering is hot directly into the gasification cyclone (17) is introduced in which the carbon of the pyrolysis coke (16) and the hydrocarbons of the pyrolysis gas (21) are reacted at temperatures above 1400 ° C to a CO + H₂-rich synthesis gas (25). A method according to claim 1, characterized in that the hot pyrolysis gas (12) before introduction into the gasification cyclone (17) at a temperature above the condensation temperature of the hydrocarbons entrained in vapor and of the steam removes dust (20) and the dust (22) in the gasification cyclone ( 17) is introduced. A method according to claim 1, characterized in that a partial quantity (26) of the processed smoldering residues is branched off and recirculated to the directly heated rotary kiln (11) in order to form a hot immersion bed located in the rotary kiln (11), within which the waste materials (10 ) to be scorched. Plant for the thermal utilization of waste materials containing organic and inorganic constituents, in particular for carrying out the method according to one or more of claims 1 to 3, characterized by a pyrolysis rotary kiln (11), the discharge (13) for the pyrolysis coke via mechanical processing ( 14) is connected to a gasification melting cyclone (17), and the pyrolysis gas discharge (12) of the rotary kiln (11) is also connected to the gasification melting cyclone (17) via a dust separator (20).

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