DE19642294C1 - Process for the thermal treatment of fly ash and kettle ash - Google Patents

Description

The invention relates to a method for the thermal treatment of flight and boiler rule according to the preamble of claim 1, as from Kley, G .; Köcher, P .; I'm happy denberg, A .; Faulstich, M .: RedMelt process for oxidic residues from combustion und Industrieanlagen, in: Reimann, D. O. (ed.): Disposal of slags and other Residual materials, Booklet 31 on garbage and waste, Erich Schmidt Verlag, Berlin 1994, pp. 146-149, is known.

Thermal waste treatment has now become a tried and tested and reliable one Waste recycling process developed. Nevertheless, the environment is affected by emissions and residues, as with other disposal methods.

The solid residues consist of ecologically relatively harmless silicates and others Oxides, however, contaminated with inorganic and organic pollutants are that they can harm the environment. The inorganic pollutants are concerned mostly heavy metals, with organic pollutants around halogenated coals Hydrogen such as dibenzodioxins and dibenzofurans.

The solid residues of thermal waste treatment can be treated as follows be subjected to:

Mechanical processes (metal deposition, aging, offset processes)

(Reimer, H .: Slag processing, in Hösel, G .; Schenkel, W .; Schnurer, H. (ed.): Garbage manual, chap. 7630, line 29 III / 76, Erich Schmidt Verlag Berlin)  

Physico-chemical processes (solidification, washing)

(Vehlow, J .; Braun, H .; Horch, K .; Merz, A .; Stieglitz, L .; Vogg, H .: Semi-technical demonstration of the 3 R process, in: Thome'-Kozmiensky, K.J. (Ed.): Waste incineration and Environment 3, EF publishing house for energy and environmental technology, Berlin 1989, pp. 687-700)

Thermal processes (low temperature processes, melting processes)

(Hagenmaier, H .; Schetter, G .: Decontamination of PCDD and PCDF-loaded activated coke, VGB power plant technology 72 (1992) No. 6, pp. 536-539)

Melting process

The currently offered melting processes are in Faulstich, M .: Treatment processes for solid residues from waste incineration; Garbage Handbook, Hösel, G .; Schenkel, W .; Bilitewski, B .; Schnurer, H .; (Ed.); Erich Schmidt Verlag MuA Lfg. 3 / (1996) together composed.

The proportions of silicon and aluminum oxide as well as alkali and alkaline earth compounds possible that the solid residues above about 1250 ° C as aluminosilicate melt zen are present, which form a glass-like matrix after cooling, into the existing one Heavy metals are firmly integrated and largely rendered inert.

The melting can be integrated into the thermal waste treatment or downstream will. Integrated melting processes are those in which melting  is integrated into the waste treatment process. It doesn't have to be in the course of the backlog treatment cooled and then heated again.

Processes with downstream melts are understood to be those in which behind a conventional thermal waste treatment plant is connected downstream that the waste incineration plant and the melting plant independently can be operated with each other.

There are two main categories of glazing processes:
Processes from glass technology: Furnaces heated with fossil fuels or electrically with molybdenum electrodes are used. The objective is to integrate the heavy metals and possibly also the salts in the glass matrix as completely as possible. (Oxidizing process conditions)

Metallurgical processes: Metallurgical electric furnaces with graphite electrodes used. In these processes, the depletion of heavy metals from the Melt attached particular importance. By reducing conditions in the Melt (graphite electrodes, residual carbon in the residues, possibly adding the loaded NEN activated carbon residues) heavy metal oxides are reduced so that iron, copper and Nickel settles and zinc, lead and cadmium are evaporated.

None of the glazing processes - almost all of which are still in the experimental stage - succeeds in fully integrating all heavy metals. Evaporation is also never completely so that you can not get a pollutant-free glass.

The invention has the task of fly and boiler ash largely from volatile Heavy metals and clean and the non-volatile heavy metals in a glass matrix to involve.  

This problem is solved by the characterizing features of claim 1. Die Subclaims describe advantageous embodiments of the invention.

A particular advantage of the process resides in the fact that none during the process PCDD / PCDF arise and the already existing PCDD / PCDF is completely destroyed. PCDD / PCDF are completely decomposed at temperatures above 800 ° C at the latest. PCDD / PCDF can also cool down in the "education window" in the range of approx. 500 ° C up to 250 ° C will not be formed again, because the carbon required for the new formation is no longer is available.

Another advantage of the method is that the reducing and oxidizing Treatment conditions in an oven without cooling the fly and kettle ash follow each other.

The novelty of the invention is further that the solid residues in a gas-tight oven chamber, which is ideally heated from the outside, first with the addition of koh Material containing lengen (e.g. plastic waste, activated carbon waste) in an inert atmosphere (e.g. Nitrogen atmosphere) just below the melting point for some time. The resulting reducing conditions result in more volatile Me metals such as As, Cd, Pb, and Zn evaporated more easily from the residues (Table 1). The right reducing inerting conditions can instead of adding carbon-containing Material and introduction of nitrogen into the furnace chamber; even just by introducing CO be placed in the oven chamber.

The evaporating metals can optionally be collected and recycled be fed. The metals that often evaporate as aerosols can e.g. B. with stainless steel fa sermatten can be caught with microfine fibers.

Sintering under reducing conditions is more favorable for evaporating metals as a treatment in the melt, because a larger surface during the sintering process  is available for the expulsion of metals. The effect of metal evaporation is The greater the more homogeneous and fine-grained the mixture of residual material and added Is carbon. Sintering in an inert atmosphere also results in the residues contained, polychlorinated hydrocarbons completely destroyed.

After the extensive evaporation of the more volatile metals is in the enamel device without the intermediate cooling or pouring of the residues an oxidizing atmosphere is necessary by introducing oxygen or air. The excess carbon not used to reduce heavy metals burns completely and thereby supplies energy that is used as melting energy that can. The oxidizing conditions in the melt still contain them NEN metals oxidized and can better in the resulting when the melt cools Glass matrix can be installed. During the melt, or at the beginning of the thermal loading additive can be added to the quality of the resulting glass improve matrix, e.g. B. also waste glass.

The additives and the process of the melt under oxidic conditions orientie industrial glass manufacturing.

The process described here can be used as a downstream melting process for solid Residues from conventional incineration and pyrolysis processes can be carried out and is therefore also suitable for retrofitting in old systems. Downstream enamel Procedures also have some advantages for new systems because they are more flexible and Offer independence from the upstream combustion and pyrolysis processes.

When carrying out the procedure, care must be taken to ensure that the flight and Kettle ashes are ground small. The added carbon must be fine and even be mixed thoroughly with the fly and kettle ash. The finer the reaction mixture is grinding and the better the mixing with carbon, the more reaction surface  is available during sintering to evaporate the metals and the larger the Er follow the procedure.

If the reducing conditions during sintering are set by introducing CO the addition of carbon to the fly and boiler ash can be dispensed with.

The invention is explained in more detail below using examples with the aid of the figure. The figure shows the diagram of an oven with gas metering for performing the Ver driving.

The furnace, a tube furnace with a reactor insert, consists of a furnace housing 10 with heating rods and a ceramic tube with various inserts. The ceramic tube is sealed gas-tight on both sides with flanges 3 , 7 . On one side of the tube, gas is introduced into the furnace through a ceramic tube 2 , which is inserted in an opening of the flange, and on the other side 8 is discharged through a tube in the same way. On the gas inlet side of the reactor tube, a thermocouple 1 can be inserted into the reaction space 6 of the reactor through an additional opening in the flange. A ceramic container 4 , which contains the reaction mixtures, is located in the reaction space. On the gas outlet side of the reactor tube, a water-cooled cooling finger 9 made of VA steel can be introduced into the vicinity of the reaction space through an opening in the flange. A ceramic cap 5 , on which evaporating metals can precipitate, sits on this cooling finger. These metals can be analyzed in more detail later.

Through the furnace at a maximum temperature of 1600 ° C, oxygen, carbon mon oxide, carbon dioxide and nitrogen can be mixed continuously, with a volume flow of 0.6-600 l / h be directed.

For the large-scale application of this thermal treatment process for flight and boiler ash, a rotary kiln can be used.  

The new process can be used for all common heavy and fly ash and boiler ash, as in Thome'-Kozmiensky, K.J .; Borchers, H.-W .; Faulstich, M .: Measures to damage material reduction in waste incineration, in: Thome'-Kozmiensky, K.J. (Ed.): Müllver burning and environment 2, EF publishing house for energy and environmental technology, Berlin 1987, S. 1-143 described, are used.

In order to achieve the clearest possible effects in the investigations, filters were used dust and kettle ash from waste incineration plants, an artificial filter dust without Carbon content and manufactured with relatively high heavy metal contents.

Table 1 shows the concentrations of some heavy metals in artificially produced ther mixed treated filter dust.

In several test series, artificially produced filter dust was first thermally heated at temperatures of 600 ° C, 800 ° C, 1000 ° C, 1200 ° C, 1400 ° C and 1600 ° C in a gas-tight tube furnace in a nitrogen, oxygen and carbon dioxide atmosphere for two hours treated (experiments N ₂ , O ₂ , CO ₂ ). The filter dust has melted from a treatment temperature of 1400 ° C. Taking into account the resulting weight loss (Tab. 2), there are no decisive differences in the evaporation behavior of metals in the different reducing and oxidizing atmospheres.

Then 2/1 polyethylene was added to the artificial filter dust, mixed well and thermally treated under the same conditions as above. (Try N ₂ / PE, O ₂ / PE, CO ₂ / PE). In the case of an inert atmosphere (nitrogen atmosphere) there is a clear depletion in some metals due to the reducing conditions. The depletion is particularly evident in Zn, As, Pb, Cd and Sb. This depletion was determined by comparing the heavy metal contents in the thermally treated and untreated filter dusts.

The heavy metal evaporation could also "on line "with LIBS (laser-induced breakdown spectrometry) heavy metal aerosols were evaporated from the furnace chamber via an exhaust pipe, continuously analyzed with LIBS.

The greatest depletion rates are generally at temperatures just below half the melting point of the artificial filter dust. For sintered loosely Products have a larger surface area that is available for metal evaporation stands.

After sintering under reducing conditions, oxygen is introduced or air in the oven creates an oxidizing atmosphere and the temperature is 20 ° C to 50 ° C above the melting point of the filter dust.

The remaining carbon burns completely and provides energy. In the fil Metals remaining in the dust are oxidized. The oxidized metals can do very well are built into the glassy matrix that forms after cooling and are rendered inert.

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Claims (4)

1. A process for the thermal treatment of fly ash and kettle ash, heavy metals being evaporated under reducing conditions and the fly ash and kettle ash treated in this way being vitrified, characterized by the following process steps:

• a) adding up to 20% additives to the fly and kettle ash,
• b) Setting a temperature of 20 ° C to 400 ° C below the melting point of the fly and kettle ash and maintaining the temperature over a period of at least 15 minutes under reducing conditions,
• c) establishing an oxidizing atmosphere by introducing oxygen and oxygen-containing gas mixtures,
• d) increasing the temperature to values of at least 20 ° C. above the melting point of the reduced fly and boiler ash and maintaining this temperature for a period of at least 15 minutes and
• e) incorporating the remaining heavy metals in a glass-like matrix by rapidly cooling the melt.

2. The method according to claim 1, characterized in that the reducing conditions by adjusting the carbon content of the flight and kettle ash to at least 10% and is generated by a non-oxidizing gas atmosphere.   3. The method according to claim 1, characterized in that the reducing conditions generated by a CO atmosphere. 4. The method according to any one of claims 1 or 2, characterized in that the flight and Kettle ashes are crushed and homogenized with the added carbon.