CA2108677A1 - Process for melting down combustion residues in slag - Google Patents

Abstract

Instead of a complete incineration of waste, such as has hitherto been sought, firstly in a low temperature unit there is only a carbonization of the process material and sub-sequently concomitantly using carbonization materials or gases in a high temperature unit the temperatures necessary for melting the slag and complete combustion are obtained. In this way extraneous materials, heavy metals are received in the slag and can be permanently bound in. The conventional combustion zone is replaced by a generator for producing flammable carbonization gases, so that instead of an incinera-tion there is only a gasification of the charge. The gasification or carbonization can be randomly controlled. The residues left behind from carbonization contain more combustion energy than conventional, burnt-out residues and can be supplied to a slag fluidization process in the high temperature unit - a revolving cylindrical furnace being proposed here. The end product is completely burnt-out, fluidized slag, which can be left to solidify in random form.

Description

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-PROCESS FOR MELTING DAWN COMBUSTION RESIDUES IN SLAG
The invention relates to a process and to an apparatus for degassing (degasifying), gassing (gasifying), burning (incinerating and melting down waste, as well as solid residual materials, e.g. from domestic refuse incinerators using the refuse as the energy carrier.
The fly ash, filter cake and slag from conventional incinerators, apart from unburnt carbon, contain heavy metal compounds and organic hydrocarbons which can be washed out. Legislation throughout the world is tending to require significant reductions in the quantity of such pollutants over a relatively short time scale, so as to reduce the eco-toxic potential of the slag and allow a safe storage and/or reutilizatian.
There are also ever more stringent demands on other solid residues (flue dust and flue gas cleaning residues) and those residues which cannot be reused are to be processable into inert residual materials.
As a rule the aim is at present to reduce the volume of the non-reusable constituents with a view to keeping as small as possible the unavoidable residual material dumps.
In the case of highly toxic residues a space-intensive, environmentally safe residual .
material dumping proves to be very expensive, particularly if it is necessary to comply with legal requirements concerning long-term safety.
In the standard grate furnaces for domestic refuse it has not hitherto been possible to burn or incinerate with such a high temperature, quite apart from undesired local heating, that during burning there is a process melting down of the combustion slag for the permanent binding of heavy metals and burning off of organic and in part highly toxic compounds. Experience is such that during slag fluidization the grates tend to become stuck during combustion or the fluidized slag flows through the gaps in the grates. In other words, neither the presently known combustion process, nor the plants which are in operation are suitable for such a procedure. 1n the few plants comprising a combination of a grate furnace and a revolving cylindrical furnace, it has hitherto been impossible to meltdown slag, because in the half area usually a total combustion of the waste is sought and obtained and in the revolving cylindrical furnace sufficient combustion energy is no longer available for melting down the slag.
In addition, these revolving cylindrical furnaces do not have the necessary characteristics and equipment for drawing off the molten slag. Such furnaces are only _, , ? ~ p ~ ~'~'~

used for the complete burning off of the slag. In the case of special refuse disposal, the waste materials are burned in the special refuse revolving cylindrical furnaces at very high temperatures and using extraneous energy. The slag problem is here of a minor nature.
The aim of the invention is to reduce the burden on the environment. The problem of the invention is to provide a process for effectively rendering inert slag, flue dust, potash and similar toxic substances and to provide an apparatus for performing this process. The material effectively binding according to the inventive process condensed, environmentally prejudicial substances must offer an environmentally harmless dump form (e.g. as a TVA inert residue according to the requirements of the regulations governing waste materials in Switzerland) or instead of being dumped must be suppliable for a useful purpose.
The process according to the invention makes it possible to melt down slag, flue dust and potash through the energy content of the waste materials. The heavy metal compounds are immobilized, the ignition loss is reduced to a minimum, the organic hydrocarbon compounds are lowered to below the present detection limit and the specific volumes are greatly reduced. The fundamental idea of the invention is, in place of a complete combustion of waste such as has hitherto been sought, to initially carry out in a low temperature unit a substoichiometric carbonization of the process material and then, using the carbonization substances or gases obtained to perform in a high temperature unit a complete combustion or incineration (e.g. in a revolving cylindrical furnace) with subsequent slag fluidization. The material left behind from the carbonization process (residues) contains more combustion energy than the standard, burnt off residues and can be supplied to a slag fluidization process in the high temperature unit, e.g. a revolving cylindrical furnace. Of the energy recovered by gasification all or part can be supplied to slag fluidization in gaseous form, so that the process can be controlled or regulated in a relatively simple manner. The end product of the process is then a completely burned off, fluidized slag, which can be allowed to solidify in random form.
The invention is described in greater detail hereinafter relative to the attached drawings, wherein show:
Fig. 1 Diagrammatically an overall plant according to the invention, the reactor operable with waste materials with the boiler and flue gas ~~ ~~~7'~

cleaning, whereby the process and essential parts of an apparatus according to the invention can be discussed relative to said reactor.
Fig. 2 The temperature gradient in the reactor, measured in a test plant.
Fig. 3 A diagram of the course of an extraneous material addition for melting down in slag, in the form of recirculated filter dust, but it could also be in the form of extraneous materials from other plants.
Fig. 4 A diagram representing an exemplified composition of the residual materials from one tonne of waste (Vehlow literature reference).
The reactor according to Fig. 1 is constructed with commercially available, tried and tested plant components. From the process engineering standpoint the components are so coupled and connected in series that the desired process can be performed.
The reactor shows in the process direction, i.e. from left to right, the essential apparatus parts, namely a feed or charging station 1 for receiving the process material with means for charging the same on the carbonization grate (e.g. a feed grate), a generator 2 in which with substoichiometric air supply refuse can be carbonized or gasified as the energy carrier. In said generator are present as essential equipment parts a feed grate 3, nozzles or jets 4 and feed means 5, 6. This is followed by a revolving cylindrical furnace 7 with a gas/air collecting hood 8, for the combustion of the generator gases produced and for the burning off and melting of the slag. This is followed by an afterburning chamber 9 with a feed device 10, e.g. air supply for the afterburning of still flammable constituents and subsequently an empty flue for the flue gases to be removed and which leads into a battery of boilers 11 for reducing the temperature and the heat utilization of the flue gases. This is followed by an electro-static precipitator 12 and a flue gas cleaning installation 13 for cleaning the flue gases and finally the stack 14 for leading off the cleaned flue gases into the atmosphere.
Numerous process paths designated by groups of letters are involved at different process points in the sequence whose significance will be explained in conjunction with the discussion of the operation.
Initially the waste material is fed via a charging means into a generator on a feed grate. In a substoichiometric medium there is a partial degasification and gasification, as well as a partial combustion. The refuse is consequently carbonized and preheated.
Since, as opposed to the most widely used grate systems, the processes in the gener-ator (grate) take place with much smaller air quantities and in particular with a lower undergrate quantity; respectively a lower, substoichiometric air excess, far fewer hot spots are formed in the micro or local area, which greatly reduces the NOx emissions (probably 50 to 70 % ).
To the generator is connected the revolving cylindrical furnace for melting down the internal and extraneous substances in the slag. At the transition from the generator to the revolving cylindrical furnace and under well controlled conditions air is jetted in well distributed manner into said furnace. In the same region it is also possible to charge extraneous materials, recirculated flue dust, flue dust and slag from external plants, etc. At this location there is a combustion of the carbonization gases produced in the generator and a burning off of the solid charge. As a result of the liberated energy the temperature in the revolving circulating furnace is raised to above the slag melting point and all the solids (internal slag and extraneous materials) are fluidized.
The revolving of the slag in the revolving cylindrical furnace leads to a good thorough mixing, a homogenization and a good burn-off. The slag flows out of the slightly inclined revolving cylindrical furnace into a precooler and then into a deslagging means.
For the complete combustion of the flue gases secondary air is supplied-to the latter in the afterburning chamber and throughout the residence time this leads to a completely satisfactory burning off of the gases. In place of secondary air additionally also flue gases could be recirculated or vapours jetted in. The boiler of the present reactor must be designed for the higher flue gas temperatures of this process. By means of large radiation surfaces and a long gas path the flue gas temperature up to the first convection part is lowered to below the flue dust softening point.
Following the boiler the reactor can be equipped with the presently commercially available gas cleaning components such as dust filters, washers/scrubbers, denox and dioxin separators, etc. Compared with conventional refuse incinerators these com-ponents can be designed for must lower gas volume flows. As in a conventional standard plant the end temperatures of the combustion process are lower than in the presently discussed process, this leads to higher gas quantities. Thus, in the process according to the invention the plant efficiency is higher than in conventional refuse incinerators.
Tests on a modified plant Plants of this size cannot readily be constructed on a trial basis or on the same basis existing plants cannot be converted. However, it is also an aim of the invention to direct the process at the use of proven, commercially available plant or incinerator parts.
For testing out the process a specially selected plant was matched to a reactor accord-ing to the invention. Various deficiencies were accepted. Thus, the waste charging quantity, i.e. the energy carrier necessary for slag fluidization, was difficult to regulate. The ratio between the carbonization and combustion air can only be approximately regulated. The jetting in of combustion and burn-off air could only take place in part in the correct quantity and in well distributed form. It was also necessary to ensure the operational safety of the plant.
Despite these limitations it was possible during several tests to achieve in the revolving cylindrical furnace the temperatures necessary for slag melting. The calorific value was measured on average as H~ = 10,890 kJ/kg. On the basis of these findings for reactors according to the invention with controllable air supply the process can be operated with a minimum calorific value of about 7,500 kJ/kg.
Through a preheating of the combustion air and the addition of fluxes, which reduce the slag melting point and increase the binding of heavy metals, it is possible to process refuse with still lower calorific values. A presorting and comminution of domestic refuse did not take place. However, it would be advisable to eliminate certain fractions, such as e.g. metals.
Something further must be taken into specific consideration. It is possible with the process according to the invention to melt down in the same process e.g.
extraneous slag, i.e. slag from combustion plants or incinerators where melting down is not possible, or flue dust, ash, etc. from other installations. It is necessary to supply to the melting reactor, extraneous slag, ash, dust, etc. using refuse as the energy carrier the energy quantity necessary for its maintenance, but this preferably takes place in the form of refuse.
The extraneous material charging and melting down was tested by means of a recirculated material test. After during a test domestic refuse slag alone was melted down and this test gave positive results, in a further test investigations took place on the melting down of filter dust from the electrostatic precipitators of the plant. There ' was no addition of residue from flue gas cleaning (filter cake). However, it is _, .
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possible to process such residues in the reactor according to the invention.
1t is assumed that if the essential fraction of heavy metals occurring during refuse incineration can permanently be melted down into slag (the basis being e.g. an eluate test), this reduces the dumps and their capacities provided for this purpose.
Harmful materials could be disposed of by melting down according to the invention by binding them in slag.
The addition of filter dust as recirculated material takes place by means of a specially produced, water-cooled lock construction fitted close to the revolving cylindrical furnace (charging point 6 in Fig. 1). The filter dust was introduced into the plant in charge form. For a specific time period on average about 10 % and then 20 % of the refuse quantity was fed into the plant and melted down (cf. Fig. 3).
Due to an excessively large charging of waste material during the test there was a slight rise in the dust quantity upstream of the electrostatic precipitator.
Even if, which is improbable, the entire rise in the flue dust concentration in the flue gas could be attributed to the recirculated material, as a function of the temperature at least 91 thereof would be bound in the molten slag. This corresponds to approximately 82 to 182 kg of filter dust per tonne of incinerated refuse. As compared with this there is an "inherent" flue dust proportion during the incineration of a tonne of waste of approximately 33 kg, which is approximately 3 % . In other words considerable quantities of toxic refuse from other plants and which would otherwise have to be expensively dumped, can be additionally disposed of with the aid of refuse in the melting down process according to the invention. Fig. 6 shows the approximate composition of the residual material quantity during the incineration of 1 tonne of waste material.
With regards to the pollutant emissions in the process according to the invention the following remarks can be made. Several samples of melted refuse slag were tested with an eluate test (CH-TVA test) with and without the addition of recirculated material, respectively with and without filter dust addition. The melted refuse slag without recirculated material addition not only fulfilled the TVA eluate test with respect to an inert material, it also only had an ignition loss of < 0.1 % .
All the highly harmful hydrocarbon compounds such as dioxins, furans, etc. were below the detection limit. Evaluations show that the TVA limits for inert materials (eluate test) were not exceeded in all the samples tested. In both eluates (tests 1 and 2) the TVA

_7_ limits for inert materials were not exceeded. Thus, with respect to the tested parameters, the slags comply with the official requirements.
During the test with filter dust addition, in addition to the regular measurements on the plant, in addition to the temperatures and moisture contents, the concentrations of the most important waste gas emittents were determined.
The dust concentration in the crude gas following the boiler, which in normal operation is in the centre of the standard range, increased somewhat during the testing phase. This can be attributed to an increased charging of waste material due to inadequate control possibilities. However, the clean gas fulfils the TVA
requirements of 17 BImSchV.
The nitrogen oxide or NOx emission during the test with filter dust addition was 2.5 times lower than in normal operation and below the level specified in Switzerland.
The daily average value was approximately 141 mg/m3o, based on 11 % Oz. The sulphur oxide or SOx concentration in the clean gas rose during the test, which is probably due to the temperature-caused decomposition of metal sulphates.
The process according to the invention offers the possibility, without any energy supply from the outside, to melt down slag, ash and flue dust. As is shown by the eluate tests, the heavy metal compounds are insolubly bound into the slag. The melted slag also has a very low ignition loss and the dioxin values are below the detection limits. Melting not only takes place without any energy supply from the outside, but there is also a higher plant efficiency than in conventional incinerating plants. The plant offers the possibility of removing the waste incineration residues in a form not prejudicial to the environment and at the same time reduce disposal costs.
The diagram of Fig. 2 shows the temperature gradient in the reactor measured during the test. It is possible to see the low temperature range of the generator of 600 to 1000°C and the high temperature range of the revolving cylindrical furnace of 1000 to 1400°C. In the afterburning chamber and the empty flue the temperature is controlled back to lower levels, in order to completely lower it in a following battery of boilers for heat recovery and return. The continuous line indicates the thermal path of a theoretical (ideal) combustion and the broken line the temperature path of the plant in standard operation. The dotted line path indicates the melting operation.

r. ,~y _ g _ Figs. 3 and 4 are two flow diagrams related to the process essentially showing the mass passage and the associated energy passage. It is clear that these diagrams give with absolute figures a specific course and composition dependent on the plant and the combustion material, but still demonstrate the effectiveness of the process according to the invention.
Discussion The present reactor essentially comprises a combination of a closed gas producing generator 2 with a mechanical feed grate 3 and a following revolving cylindrical furnace 7 and a plurality of process-influencing connections (e.g. additions, feedbacks, etc.). This is followed by the standard flue gas cleaners and an apparatus for discharging the molten slag. These components also have process-influencing feedbacks to the generator/revoiving cylindrical furnace.
According to Fig. 1 the process path starts at the charging intake 1, into which are introduced solid and liquid waste RG, additives AD, recycled riddlings RD and extraneous materials FR (e.g. slag from other refuse incinerators for. melting down).
These substances pass onto the feed grate 3 where, accompanied by the addition of further materials such as grate air RL, vapours BR, carbonization air VL, extraneous substances FR and oxygen-containing gases 02, are carbonized, gasified, but are nat incinerated. This is brought about in that following the initial heating through the grate a substoichiornetric quantity of grate air RL is very slowly blown in.
It is possible to add through a plurality of air nozzles or jets 4 recirculated flue gas RR, vapours BR and carbonization air VL. Through two further addition means 5, 6, namely a charging device for solids 5, in order to introduce solid residual materials such as potash KA, filter dust FS and extraneous materials FR, and an addition device 6, in order to add a preheated gas/air mixture VV from the area of the collecting hood g via the revolving cylindrical furnace, vapours BR, combustion air (better gasification or carbonization air) VL and oxygen-containing gas O2, e.g. air.
In this plant no additional energy supply is required for the actual process besides that through the solid waste, air supply and for the drive units. By means of the additional feed device 5 the solid residues potash KA and filter dust FS as recirculated material RZ or from refuse incinerators as extraneous material FR can be fed into the plant close to the revolving cylindrical furnace and melted down with the generator residual materials. Such extraneous and residual materials can also be added as ballast _,,. . . ,~,~~r~~
materials for the planned modification of the composition of the carbonized product at the time of charging. Through the melting down of the residual materials and the re-circulated material, together with the extraneous materials FR it is possible to immobilize its pollutants, particularly the heavy metals. For this purpose the means has on the side walls of the generator feed points 4 for the supply of the combustion air VL, vapours VR or recirculated flue gas RR. In tl7e vicinity of the transition from the grate hearth zone to the revolving cylindrical furnace is provided a device 6, which is used for feeding in preheated gas/air mixture from the vicinity of a hood S
above the furnace, as well as combustion air VL, vapours BR or oxygen 02. In the afterburning chamber 9 following the revolving cylindrical furnace there is a further device 10 for feeding in combustion air VL or vapours BR. Apart from bringing about a process control, these measures minimize the heat losses, particularly in the vacuum-operated revolving cylindrical furnace, which almost always has leaks.
A
very high process efficiency can be obtained with the planned recycling of un-processed energy-containing materials and thermal energy.
In the vicinity of the transition from the generator to the revolving cylindrical furnace by means of the device 5 it is possible to add potash KA and filter dust FS
from the plant, as well as extraneous refuse incinerating plants FR. An addition is appropriate at this point, so that the flue dust is not immediately discharged into the flue gas by the generator air passing through the grate.
The preheated and partly degasified, solid residual materials of the generator pass into the revolving cylindrical furnace. As a result of the air VL,02 introduced in the vicinity of the transition from the generator to the revolving cylindrical furnace, there is a combustion in the latter of the generator gases. The resulting temperature in said furnace leads to a complete burn-off and to the melting of the solid reaction products, which are discharged from the furnace in molten form. As a result of melting down all the organic compounds are destroyed at 1300 to 1400°C and heavy metals are permanently bound into the glass structure of the slag. The vitrified slag only gives off a little of the bound heavy metals at the surface.
In the afterburning chamber 9 behind the revolving cylindrical furnace, it is possible to supply combustion air VL or vapours. The combustion air leads to a very sub-stantial final combustion of the burnable materials of the flue gas, as well as the temperature regulation thereof. From the battery of boilers 11 following the after-- to burning chamber it is possible to recover thermal energy by utilizing the energy content of the flue gases in the form of steam (electricity) and long-distance heat.
Most of the known slag and residual material melting processes require an energy supply from the outside, e.g. using fossil energy carriers or electricity.
This is unnecessary in the process according to the invention. As a result of the special construction and special air circulation of the plant, the energy content of the solid waste is adequate in order to melt down the reaction products of the generator and the other residual materials, which are additionally added. Compared with conventional domestic refuse incinerators without slag melting, more and not less energy is led off for other purposes (such as e.g. electric power, long-distance heat). However, maxi-mum significance is attached to the fact that the energy for melting down is obtained from waste materials, which would otherwise have had to be burned or incinerated and would have produced slag and residual substances. The process according to the invention not only melts its inherent slag and residual substances, but also has a capacity to process extraneous substances.
As domestic refuse and similar waste materials forming most of the product charged in this apparatus constitutes a very inhomogeneous mixture, the described reaction sequences in the generator are not to be spatially defined. The supply of the different gases to the different points should be adapeed as satisfactorily as possible thereto, so as to correspond to the different calorific value of the charged material and its composition.
Fig. 2 shows the approximate temperature gradient of the process in the reactor, which starts at the charging intake 1, where the ambient temperature still applies.
Considered in the process direction, at the start of the grate in the generator, the temperature is a few 100°C and rises with increajing carbonization (gasification) at the end of the grate to approximately 1000°C, but without forming significant hot spots.
The carbonization temperature is controlled by planned additions of grate air RL
below the grate and by adding vapours BR and/or carbonization air'dL. At the start of the revolving cylindrical furnace, in which burn-out and slag fluidization take place, the temperature rises as a result of the ignition of the carbonization gases rapidly into the high temperature range between 1200 and 1400°C. Burn-out and melt-down take place at this temperature. At the transition point to the afterburning chamber the temperature remains substantially the same due to the action of furthee supplied combustion air and then drops towards the low temperature range of 1100°C

by the planned addition of further, cooling combustion air VL and/or vapours BR. In the boiler 11 the flue gases are cooled to 200°C.
This diagram makes it clear that the very high temperatures above 1000°C, at which the slag starts to melt and at which plant parts not designed for this temperature start to suffer damage, can be displaced e.g. from the grate into a revolving cylindrical furnace designed for these temperatures. These high temperatures at the suitable location and only achievable in planned manner through the inventive process, are transferred to the better designed revolving cylindrical furnace and this not only applies with regards to the combustion at a different location, but also the transfer of the energy carrier to said location. In this case it is flammable gases which emanate from the carbonization on the grate and which in the revolving cylindrical furnace, together with the still burnable, but degasified residues, permit the desired high temperatures. The substoichiometric carbonization is largely or even completely supported by the recovered, recycled thermal energy from the revolving cylindrical furnace (hood 8).
Fig. 3 is a diagram for filter dust supply within the test series discussed hereinbefore.
For somewhat more than two hours the fractions were charged in two quantity ratios, at the start approximately 10% based on the refuse quantity and then approximately 20%. With an automated addition finer charging steps can be obtained.
Fig. 4 shows in the form of a Vehlow diagram an exemplified composition of the residual material quantities from one tonne of waste. This composition is naturally largely dependent on the starting composition of the waste. The following references are used: A = incinerated and vaporized fraction, B = material thrown off grate, C
= flue gas cleaning gas residues, salts, D = filter dust, E = potash, F =
riddlings.

Claims (22)

1. Process for melting down residual substances in slag, characterized in that waste materials are used as the energy carrier and the thermal material conversion process is subdivided into a low temperature process (carbonization process) and into a follow-ing high temperature process (incineration process), flammable gases obtained in the low temperature process (carbonization process) are supplied to the high temperature process (incineration process).

2. Process according to claim 1, characterized in that the low temperature process is a substoichiometric carbonization process on a combustion grate with a substoichio-metric grate air quantity, which is forced as undergrate air with limited pressure through the carbonization material, or is sucked by a vacuum over the grate through the carbonization material.

3. Process according to claim 1, characterized in that the high temperature process is an incineration process, in which the residues from the carbonization process are burned together with carbonization gases and accompanied by the supply of combustion air, in order to reach the melting temperature of the slag and so as to be able to branch the fluidized slag off from the process.

4. Process according to any one of the claims 1 to 3, characterized in that an afterburning process, accompanied by the supply of combustion air, follows the high temperature process.

5. Process according to either of the claims 2 and 3, characterized in that extraneous materials are supplied to the low or high temperature process for melting down into slag.

6. Process according to claim 5, characterized in that the extraneous materials are recirculated materials or emanate from extraneous plants and are either jetted into the carbonization process as ballast material or directly supplied to the high temperature process.

7. Process according to claim 2, characterized in that the thermal energy becoming free in process stages following the carbonization process is returned to the same.

8. Process according to claim 7, characterized in that for assisting the low temperature process waste heat from the high temperature process (incineration process) is supplied to the low temperature process (carbonization process) for heating the conversion product.

9. Process according to claim 2, characterized in that combustion air for maintaining the combustion of carbonization gases passed into the high temperature part are admixed upstream of the latter, where the mixture is ignited.

10. Process according to claim 4, characterized in that combustion air is introduced into an afterburning zone, in order to burn the flammable residual gases from the flue gas.

11. Process according to either of the claims 4 and 10, characterized in that for temperature control purposes (cooling) an extra quantity of combustion air or vapours is introduced into the afterburning zone.

12. Process according to claims 2 or 3, characterized in that for controlling the process in the phase of carbonization and/or the phase of afterburning vapours are introduced.

13. Process according to any one of the claims 1 to 12, characterized in that by means of nozzles on the generator side walls air (VL), vapours (BR) from the sewage sludge combustion for nitrogen oxide reduction and/or recirculated flue gases are added.

14. Process according to any one of the claims 1 to 12, characterized in that by means of a special charging device (5) there is an addition of potash and filter dust from the actual process and from extraneous processes, particularly refuse incin-erators, so as on the one hand to melt down the same together with the solid reaction products of the generator and on the other to use same as a ballast material for regulating the process.

15. Process according to any one of the claims 1 to 5, characterized in that there can be an addition of air (VL) and vapours (BR) to the afterburning zone between the revolving cylindrical furnace and the boiler, in order to bring about an afterburning and temperature regulation of the flue gases.

16. Process according to any one of the claims 1 to 15, characterized in that gas is produced in a generator and is heated in a following revolving cylindrical furnace by the supply of air to approximately 1400°C and the refuse on the grate during degasi-fication is preheated to approximately 1000°C at the transition to the revolving cylindrical furnace, before said slag, mixed with extraneous substances, is melted in the revolving cylindrical furnace by the combustion of carbonization gases.

17. Apparatus for melting down combustion residues such as slag, ash, etc., characterized in that it comprises a low temperature section (carbonization generator) and a following, high temperature section (revolving cylindrical furnace), whereby in said low temperature section (carbonization generator) the combustible substances are converted into flammable gases and residues, in order, together with the flammable gases, to assist the combustion process in the high temperature section (revolving cylindrical furnace), so that the slag becomes molten and means are provided for returning waste heat from the high temperature section to the low temperature section, in order to assist there the conversion of the combustible materials.

18. Apparatus according to claim 17, characterized in that the low temperature section comprises a carbonization generator, which has a feed grate on which the process material is substoichiometrically carbonized and that it has supply means for adding process materials controlling carbonization.

19. Apparatus according to claim 17, characterized in that the high temperature section comprises a revolving cylindrical furnace, at whose intake are provided means for adding combustion air and extraneous materials and at whose outlet are provided means for drawing off the molten slag.

20. Apparatus according to claim 17, characterized in that the high temperature section is followed by an afterburning chamber with feeds for means for controlling the burning off and/or cooling the flue gas.

21. Apparatus according to claims 17 to 20, characterized in that the reactor has feedbacks for thermal energy and solid materials from the process to permit a re-circulation of energy and residual materials.

22. Apparatus according to any one of the claims 17 to 21, characterized in that the revolving cylindrical furnace (7) and afterburning chamber are followed by a boiler (11) so that, if necessary, the heat content of the flue gases can be used in the carbonization process.