EP0607210B1 - Process for incinerating solids - Google Patents

Abstract

PCT No. PCT/EP92/02280 Sec. 371 Date Aug. 15, 1994 Sec. 102(e) Date Aug. 15, 1994 PCT Filed Oct. 2, 1992 PCT Pub. No. WO93/07422 PCT Pub. Date Apr. 15, 1993A process for incinerating solids, especially for burning rubbish in a combustion vessel comprising at least one combustion chamber and an after-burner chamber. Here, instead of secondary or tertiary air, water vapor under increased pressure is sprayed into the combustion vessel after the combustion gases have left the combustion chamber. Only primary air is supplied as the combustion air. In this manner and with the use of minimum quantities of combustion air, it is possible to increase the effectiveness of the overall process while at the same time reducing the emission of pollutants. It is also possible to feed back flue gas together with the water vapor, so that, for example, the maximum temperatures, the temperature reduction and the dwell times in the 1st and 2nd flue of the vessel can be easily set to the optima.

Description

The present invention relates to a method for the combustion of solids, in particular for waste incineration, in a combustion boiler which comprises at least one combustion chamber and an afterburning chamber, water vapor being introduced into the combustion boiler.

Such a method is known from documents DE-A-3 125 429 and EP-A-0 487 052.

When burning solid energy sources, such as. B. waste or coal, pollutant-containing exhaust gases. For ecological and economic reasons, the combustion should be carried out with an optimal air excess in order to minimize the amount of exhaust gas and pollutants. However, for procedural and technical reasons, the ecologically and economically optimal mode of operation often contradicts.

A sufficient burnout of the flue gases with the oxygen in the air is only guaranteed if there is an excess of air and corresponding turbulence in or directly above the combustion chamber. To generate this turbulence, part of the combustion air is usually blown in as secondary air at low pressure and moderate speeds. The aim is to reduce the formation of carbon monoxide and nitrogen oxides. In order to simultaneously ensure the necessary turbulence and thus adequate mixing, the amount of secondary air blown in must be selected to be correspondingly high. However, this excess air significantly increases the amount of exhaust gas and thus the loss of usable energy.

The adiabatic combustion temperatures decrease considerably with increasing air excess. If there is a large excess of air, additional CO formation can be caused by supercooling the fuel gases by adding the secondary air. However, high temperature peaks can occur in the edge region of the secondary air flow, which in conjunction with the locally high oxygen concentrations contribute to the formation of NO _x .

When incinerating waste, the oxygen concentration in the moist flue gas after the incineration boiler is usually around 10% by volume. The excess air in this case is about 150%, corresponding to an air ratio of 2.5. Between 20 and 40% of the combustion air is usually blown in as secondary air. A reduction in the secondary air leads to poorer combustion of the fuel gases, a reduction in the primary air leads to poorer combustion of the slag.

Another task of the secondary air is to achieve a certain flame control. This is intended to break the thermals in the 1st draft of the combustion boiler (afterburning chamber) and thus create a narrow range of dwell times in the 1st draft. This goal has so far been achieved incompletely. The use of tertiary air to break the thermal is only of limited use due to the additional air volume, since cooling results in additional CO formation and additional flue gas volumes.

A major disadvantage of the previous methods is the high amount of secondary or tertiary air required to burn out the exhaust gases safely and to break the thermals. These high air volumes can only be added if the primary air volume is reduced at the same time, although the burnout result on the grate is endangered. Increasing the amount of flue gas also leads to a shorter average residence time in the first train. Optimal pollutant degradation is therefore not guaranteed. Furthermore, the adiabatic combustion temperature is reduced by the increased amount of air. The temperature reduction in the area of the steam generator is accordingly flat. This significantly reduces the use of heat.

The object of the present invention is to develop a method for the combustion of solids with which it is possible to reduce the amounts of pollutants in the flue gas. Either the amount of flue gas should be significantly reduced while maintaining the same heat output, or vice versa the fuel throughput should be increased significantly. The process should be able to operate with as little excess air as possible. At the same time, the disadvantages of the known methods are to be largely avoided. The method is said to be particularly suitable for use in waste power plants.

This object is achieved according to the invention by a method with the features of the main claim. Advantageous refinements and developments of the new method result from the subclaims.

The solids, such as. B. garbage or coal, are charged in a combustion boiler and burned on a grate in the combustion chamber. The primary combustion air is blown through the grate from below. Flow through the hot flue gases generated in the combustion chamber First, an afterburner chamber (1st draft of the boiler) and then fed to the convective part of the boiler via further radiation. The flue gas is then freed of dust and pollutants in a flue gas cleaning system and released into the atmosphere via a chimney.

According to the method according to the invention, no further combustion air, such as e.g. Secondary or tertiary air, introduced into the combustion boiler. The exclusive use of primary air would, however, lead to poor combustion of the flue gases due to inadequate mixing in the afterburning chamber (after-reaction or combustion chamber) and accordingly to high CO and pollutant contents in the exhaust gas. Therefore, according to the invention, a gas and / or superheated, vaporous medium is injected into the combustion boiler 1 as a fluid medium above the combustion chamber 2 and in the lower region of the afterburning chamber 4. The injection of water vapor does not promote the formation of carbon monoxide and nitrogen oxide in the flue gas. The mixing energy required to generate the turbulence necessary for optimal combustion conditions of the fuel gases is applied via the water vapor. In this way, the total amount of air and the oxygen content of the flue gas can be significantly reduced. The main advantages of this method of operation are a reduction in the amount of flue gas with the same net heat output and lower fuel consumption, or an increase in heat output by increasing the fuel throughput with the same amount of flue gas.

Determining the mixing energy, which according to the invention is introduced into the combustion boiler via water vapor the set pressure and the volume flow of the water vapor. A value of at least 1 bar should be selected as the minimum overpressure for the water vapor. Below this value, the volume flow of the water vapor must be set very high to ensure sufficient mixing energy. The amount of flue gas can then be reduced slightly at most. In addition, undesirably high water contents in the flue gas can result. In principle, the highest possible excess pressure of the water vapor should therefore be provided. The upper limit is only determined by the justifiable expenditure on equipment.

The volume flow of the water vapor to be set depends on the overpressure, with a higher volume requiring a lower volume flow and vice versa. At a given pressure of the water vapor, the volume flow is preferably selected so that a mixing energy in the range between 0.1 and 30 kW per m³ of turbulence space is introduced.

wobei a Werte zwischen 0,2 und 0,5 annehmen kann. Dabei sind für a mit zunehmender Anzahl an Düsenebenen für den Wasserdampf kleinere Werte des genannten Bereiches anzusetzen. Die charakteristische Länge d_hydr. (hydraulischer Durchmesser) errechnet sich hier wie folgt: $${\text{d}}_{\text{hydr.}}\text{= 4 F / U}$$

Dabei entspricht F dem von den Verbrennungsgasen durchströmten Querschnitt (z. B. geringster Querschnitt nach Austritt aus dem Feuerraum) und U bezeichnet dessen Umfang.The area in the combustion boiler that is directly detected by the blown-in water vapor is referred to as the turbulence space. The volume V _{T of} the turbulence space can, for. B. can be determined using the following formula: $${\text{V}}_{\text{T}}\text{= (}\frac{\text{π}}{\text{4th}}{\text{* d}}_{\text{hydr.}}{}^{\text{2nd}}{\text{) * (a * d}}_{\text{hydr.}}\text{)}$$

where a can have values between 0.2 and 0.5. Here, for a with increasing number of nozzle levels for water vapor, smaller values of the range mentioned are start. The characteristic length d _hydr. (hydraulic diameter) is calculated as follows: $${\text{d}}_{\text{hydr.}}\text{= 4 F / U}$$

F corresponds to the cross-section through which the combustion gases flow (e.g. smallest cross-section after exiting the combustion chamber) and U denotes its circumference.

The mixing energy to be introduced can also be related to the exhaust gas volume. In this case, mixing energies in the range between 0.03 and 3 W per Nm³ / h exhaust gas should preferably be set.

Below a mixing energy of 0.1 kW / m³ turbulence space or 0.03 W per Nm³ / h exhaust gas, the turbulence generated is not sufficient to guarantee optimal combustion conditions, while above 30 kW / m³ turbulence space or 3 W per Nm³ / h h Exhaust gas uneconomically high pressures and / or volume flows of the water vapor are required. A narrow range of dwell times within the afterburning chamber (afterreaction or burnout chamber) of the combustion boiler is achieved if the pressure and the volume flow of the water vapor are selected such that a uniform piston flow of the flue gas is achieved in the afterburning chamber. In this way, an optimal thermal degradation of pollutants can be guaranteed.

With the method according to the invention, comparatively high temperatures can be achieved in the afterburning chamber, since there is no cooling of the flue gases by high amounts of excess air. The The temperature when entering the afterburning chamber should preferably be in the range between 1273 and 1673 K in order to ensure adequate combustion of the pollutants. Above 1673 K there is a risk of increased NO _x formation even with lower oxygen levels in the flue gas. By controlling the injection parameters of the water vapor, the mean residence time of the flue gases in the afterburning chamber at temperatures ≥ 1123 K can be increased to such an extent that the degradation of pollutants is considerably promoted.

A conventional incinerator for solids according to the prior art is shown schematically in FIG. 1. In the lower area of the combustion boiler 1, the grate 3 is arranged, on which the solids, such as garbage or coal, are burned with the addition of primary air 9. Immediately above the grate 3 is the combustion chamber 2, which merges upwards into the afterburning chamber 4, corresponding to the 1st draft of the boiler. The hot flue gases generated during combustion in the combustion chamber 2 first flow through the afterburning chamber 4. They are then conducted via the second train 5 of the boiler 1 to the evaporators and superheaters 6 and the ECO 7. Dust and pollutants are then removed in a flue gas cleaning system 8. If secondary air is used in such a combustion system, the supply takes place via secondary air nozzles 10, which are arranged in the combustion chamber 2 in the region of the transition to the afterburning chamber 4. Optionally, additional tertiary air can be blown in via tertiary air nozzles 11, which are installed in the afterburning chamber 4.

According to the method of the invention, only primary air is used as combustion air. Secondary or tertiary air is completely replaced by water vapor. The water vapor is blown in with a volume flow that is far below the commonly used secondary or tertiary air volume flow. In order to nevertheless introduce a sufficiently high mixing energy into the boiler 1, the water vapor is introduced at an overpressure which is clearly above the usual secondary or tertiary air pressure (approx. 40 mbar). In this way, it is possible to introduce high mixing energies into the boiler without having to accept the disadvantages of a high excess of air. Since the combustion temperature rises and the exhaust gas losses decrease under the conditions according to the invention, the amount of fuel and the amount of primary air can be reduced with the same steam output when the secondary or tertiary air is fully replaced. The primary air volume and the fuel volume can be reduced by 10%, for example. The amount of primary air is preferably reduced to such an extent that the excess air is between the value of 150% customary for such combustion plants and a lower limit value of 20%. With an air excess of 20%, the oxygen content in the flue gas is approx. 2%. If this value is undershot, the pollutants in the flue gases have a very aggressive effect on the boiler wall.

The steam is blown in via nozzles designed for supersonic operation, since this enables a particularly good conversion of pressure energy into kinetic energy.

The nozzles are installed in the area where the combustion gases exit from the combustion chamber 2 and / or directly in the area of the afterburning chamber 4. They are preferably arranged in one or more nozzle levels. Existing systems can be converted to the method according to the invention in a simple manner by directly installing the nozzles for the water vapor instead of already existing secondary and / or tertiary air nozzles.

By blowing in the water vapor in the area where the combustion gases emerge from the combustion chamber 2, the combustion and mixing conditions in the combustion chamber 2 and in the inlet to the afterburning chamber 4 are optimized in particular. If, in addition or as an alternative, the water vapor is blown directly into the afterburning chamber 4, z. B. of smoke streaks favors the formation of a uniform piston flow. In this way, it is possible to generate a uniformly narrow residence time spectrum in the afterburning chamber 4 and to significantly increase the pollutant burnup.

In particular, the formation of CO and NO _x in the flue gas is not promoted by the use of water vapor according to the method according to the invention. At the same time, water vapor is produced in the steam generators 6, 7 of the incineration plant and is therefore available inexpensively and in sufficient quantities. There are also a number of other advantages. The radiation properties of the flue gases are improved by the higher water vapor partial pressure. So that increases the heat transfer by radiation and thus the heat utilization in the radiation part of the boiler considerably. In connection with the higher flue gas temperatures and higher CO₂ partial pressures achieved under the conditions according to the invention, the increase in heat transfer due to radiation proceeds disproportionately. The heat transfer increases z. B. with a temperature increase from 1073 to 1273 K by twice the value and with a temperature increase to 1473 K by 3.5 times the value. As a result of the higher heat utilization achieved and the faster temperature reduction, the exhaust gas temperature after the steam generators 6, 7 is reduced below the usual values.

Surprisingly, it has also been found that when water vapor is used according to the invention, presumably due to the higher water vapor partial pressure, the dust content of the exhaust gas can be separated with exceptionally high efficiency in the electrical flue gas cleaning. The dust concentration in the exhaust gas after the electrostatic precipitator can be reduced to about 10 mg / Nm³.

In theory, gases or gas mixtures could also be used instead of water vapor, which are also composed in such a way that they do not promote the formation of CO and NO _x in the flue gas, such as, for. B. recycled flue gas or nitrogen and other inert gases or mixtures thereof. However, these gases are usually present under normal pressure or only a slight excess pressure, so that an extraordinarily high outlay on equipment would be necessary to set the high pressures required for the process according to the invention. When blowing in such media with the usual overprints 40 mbar, the amount to be supplied is so high that the advantages of the process according to the invention cannot be achieved.

The return of flue gases to the combustion area of the boiler to reduce nitrogen oxide formation is generally known. Since the flue gas is recirculated cold, it cannot be ruled out that streaks of low temperature will form locally within the combustion gas stream, which will result in additional CO formation. Under the special conditions of the process according to the invention, however, hot flue gas at temperatures above 873 K can be returned to the combustion boiler together with the water vapor. In this way, local hypothermia with corresponding CO formation can be completely avoided.

The hot flue gas can e.g. B. can be returned via one or more connecting channels from the 2nd train to the 1st train of the boiler. The water vapor nozzles are preferably arranged concentrically in the connecting channels for the recirculated flue gas. Due to the injector effect of the steam injected under high pressure, some of the hot flue gases are sucked out of the 2nd draft of the boiler and injected into the combustion boiler together with the water vapor without complex measures. Since the pressure conditions to be overcome for this flue gas recirculation are very low, only a correspondingly small amount of steam is required for this. If the total water vapor introduced is fed into the boiler via several nozzles or nozzle levels, it is sufficient to supply only a part of these nozzles for the flue gas recirculation use. The proportion of recirculated flue gas is set to values between 5 and 50%, preferably around 30%, of the total flue gas quantity. The maximum temperatures, the temperature reduction and the dwell times in the 1st and 2nd draft of the boiler can thus be easily adjusted to optimal values.

In the same way, nitrogen or other inert gases or their mixtures can be injected into the combustion boiler together with the high-pressure water vapor by the process according to the invention.

• Die Rauchgasmenge wird bei gleicher Nettowärmeleistung erheblich reduziert, bei vollem Ersatz der Sekundär- bzw. Tertiärluft und Rücknahme der Primärluft (entsprechend dem geringeren Brennstoffdurchsatz) um etwa 20 bis 40 %.
• Bei gleichbleibender Rauchgasmenge kann der Brennstoffdurchsatz um bis zu 40 % gesteigert werden, ohne die Notwendigkeit besonderer Maßnahmen im Rauchgasweg, insbesondere in der Rauchgasreinigungsanlage.
• Die Wärmenutzung wird um bis zu 15 % gesteigert.
• Die Staubbelastung der Heizflächen im gesamten Kessel sowie die Belastung der Rauchgasreinigung fällt zumindest entsprechend der verringerten Rauchgasmenge, wobei u. a. die Ofenreisezeit deutlich verlängert wird.
• Die Verbrennungstemperaturen im Eintritt zur Nachbrennkammer werden wesentlich erhöht, steuerbar über die zugeführte Primärluftmenge, wodurch ein besserer Ausbrand sichergestellt ist.
• Die Schadstoffmengen und -konzentrationen im Abgas werden wesentlich reduziert, insbesondere CO und NO_x.
• Unverhältnismäßig hohe Staubabscheidung in der elektrischen Gasreinigung durch Einsatz von Wasserdampf.
• Durch den Einsatz von Wasserdampf wird der Wärmeübergang durch Strahlung deutlich erhöht, wobei ein schnellerer Temperaturabbau in der Kesselanlage sowie eine geringere Abgastemperatur erzielt wird.
• Die erforderlichen Antriebsleistungen der Luftventilatoren und des Saugzugs können entsprechend der verringerten Luftmenge vermindert werden.
• Nachgeschaltete Rauchgasreinigungsanlagen können entsprechend kleiner ausgelegt werden.
• Bei nachgeschalteten "low dust"-Entstickungsanlagen sinkt der Aufwand an Energie zur Wiederaufwärmung des Rauchgases bei gleicher Grädigkeit entsprechend der geringeren Rauchgasmenge.
• Bestehende Anlagen lassen sich in einfacher Weise an das erfindungsgemäße Verfahren anpassen.

The main advantages of the method according to the invention can be summarized as follows:

• The amount of flue gas is significantly reduced with the same net heat output, with full replacement of the secondary or tertiary air and withdrawal of the primary air (corresponding to the lower fuel throughput) by about 20 to 40%.
• With the same amount of flue gas, the fuel throughput can be increased by up to 40% without the need for special measures in the flue gas path, especially in the flue gas cleaning system.
• The use of heat is increased by up to 15%.
• The dust pollution of the heating surfaces in the entire boiler as well as the pollution of the flue gas cleaning falls at least in accordance with the reduced amount of flue gas, whereby, among other things, the furnace travel time is significantly extended.
• The combustion temperatures in the inlet to the afterburning chamber are significantly increased, controllable via the amount of primary air supplied, which ensures better burnout.
• The amounts and concentrations of pollutants in the exhaust gas are significantly reduced, especially CO and NO _x .
• Unreasonably high dust separation in electrical gas cleaning through the use of water vapor.
• Through the use of water vapor, the heat transfer through radiation is significantly increased, whereby a faster temperature reduction in the boiler system and a lower flue gas temperature is achieved.
• The required drive power of the air fans and the suction can be reduced in accordance with the reduced amount of air.
• Downstream flue gas cleaning systems can be designed accordingly smaller.
• In the case of downstream "low dust" denitrification plants, the amount of energy required to reheat the flue gas decreases with the same degree of correspondence in accordance with the lower flue gas quantity.
• Existing systems can be easily adapted to the method according to the invention.

The method according to the invention is explained in more detail below on the basis of a few exemplary embodiments.

Blow in water vapor

In this process example, an existing incineration plant of a waste power plant was converted for blowing in steam. The steam nozzles were designed for supersonic operation. The supply of primary air and water vapor was set up to be infinitely variable.

An investigation of the combustion in the waste power plant showed that the addition of secondary air for the combustion is not necessary, but rather disadvantageous for the overall process. In normal operation, the system works with a total air volume of approx. 80,000 Nm³ / h, with a secondary air share of 27,000 Nm³ / h. The excess air is around 150%, corresponding to an air ratio of 2.5. Under these conditions, the oxygen content of the flue gas is approx. 10% by volume. The secondary air is supplied under a slight excess pressure of approx. 40 mbar. When the secondary air is released, a mixing energy of around 30 kW is released.

In the system converted to the process according to the invention, a steam quantity of approx. 2,000 kg / h with an overpressure of 5 bar was blown into the combustion boiler in the area where the combustion gases exit from the combustion chamber. The total air volume was reduced by approximately 30% while maintaining the nominal load of steam generation, whereby the secondary air was completely replaced by steam and the primary air volume was also reduced.

Under these conditions according to the invention, the oxygen content of the flue gas dropped to approximately 6% by volume (moist). With comparable fuel, the air ratio dropped from 2.5 to 1.8. The amount of flue gas decreased from 100,000 Nm³ / h to 72,500 Nm³ / h and was thus reduced by a total of approx. 27%. The NO _x content of the flue gas was reduced by approx. 25%. At the same time, the CO content of the flue gas dropped from 20 mg / Nm³ to values below 10 mg / Nm³.

The exhaust gas temperature after the steam generators was reduced from approx. 500 K to approx. 470 K. This increased the chloride separation in the flue gas cleaning system and reduced the HCl emission concentration from 50 to 80 mg / Nm³ to values below 30 mg / Nm³.

The dust carried in the flue gas and the hydrated lime used for dry flue gas cleaning, as well as the corresponding reaction products, can be separated out excellently in the electrical flue gas cleaning due to the higher water vapor partial pressure. This behavior is favored by the lower flue gas temperatures. Dust emissions are also positively influenced by the significantly lower gas speeds in the electrical flue gas cleaning system. The dust content in the flue gas after the electrostatic precipitator was reduced from 40 to 60 mg / Nm³ to approx. 10 mg / Nm³.

The combustion temperature in the entrance to the afterburner was increased by approx. 200 K. However, the flue gas temperature at the end of the afterburner rose only slightly by 30 to 50 K.

At 5.4 MW, the exhaust gas losses for a comparable travel time (idle time between cleaning cycles) are much lower than before the conversion with 9.3 MW. While maintaining the nominal load of steam generation, the fuel throughput (= waste throughput) was reduced by more than 10%.

Injection of water vapor with return of hot flue gas

For this purpose, investigations were carried out in the same plant under essentially the same conditions as described above.

Via one or more connecting channels from the 2nd train to the 1st train of the boiler, hot flue gas with a temperature of approx. 900 K was returned to the 1st train of the boiler together with part of the water vapor. Some of the nozzles for the steam were installed concentrically in the individual flue gas return channels. Due to the suction effect of the water vapor injected under a pressure of approx. 6 bar, part of the flue gases was withdrawn from the second draft (convective part) and injected into the 1st draft of the boiler. The proportion of the returned flue gas was 30% of the total flue gas amount. The pressure conditions to be overcome were very low with a maximum of 1 to 5 mbar, so that only a little steam was required to return the flue gases. During the tests it was found that between 4 and 40 g of water vapor are required per Nm³ of recirculated flue gas. When using slightly superheated steam under a pressure of 6 bar with a temperature of approx. 440 K, the temperature of the returned flue gas (approx. 900 K) practically did not drop.

Under these conditions the temperature in the hot zone could e.g. from approximately 1473 K (without flue gas recirculation) to approximately 1308 K. In this way, the temperature in the transition to the 1st train could be reduced while maintaining a minimal amount of combustion air. The temperature reduction in the 1st and 2nd draft was somewhat flatter in this case, while the temperature and heat reduction in the convective part of the boiler practically matched the corresponding values without flue gas recirculation. Even under these conditions, a minimum dwell time of 2 s at temperatures above 1123 K could easily be maintained. In addition, the other advantages as described when using water vapor without flue gas recirculation are retained.

Claims (14)

1. A process of incinerating solid substances, especially of incinerating refuse in an incineration tank (1) which comprises at least one combustion space (2) with primary air generating means (9) and a reincineration chamber (4), with gas and/or water vapour being blown above the combustion space (2) and in the lower region of the reincineration chamber (4) into the incineration tank (1) at a supersonic speed generated by excess pressure, without any further incineration air being supplied apart from the primary air.
2. A process according to claim 1,
   charactersied in
   that water vapour and inert gases as well as flue gases or their mixtures are used.
3. A process according to any one of the preceding claims, characterised in
   that the pressure and volume flow of the blown-in water vapour are set in such a way that a mixed energy ranging between 0.1 and 30 kW pro m³ turbulence space is introduced.
4. A process according to any one of the preceding claims, characterised in
   that the pressure and volume flow of the blown-in water vapour are set in such a way that a mixed energy ranging between 0.03 and 3 W per Nm³/h exhaust gas is introduced.
5. A process according to any one of the preceding claims, characterised in
   that in the region where the incineration gases enter the reincineration chamber (4), the temperature is set between 1273 and 1673 K.
6. A process according to any one of the preceding claims, characterised in
   that the volume flow of the primary incineration air is set in such a way that the excess air amounts to 20 to 150%.
7. A process according to any one of the preceding claims, characterised in
   that part of the water vapour is used to return part of the flue gas into the region between the combustion space (2) and the reincineration chamber (4) and/or directly into the reincineration chamber (4).
8. A process according to claim 7,
   characterised in
   that the percentage of returned flue gas amounts to 50%, preferably 30%, of the entire quantity of flue gas.
9. A process according to any one of claims 7 or 8,
   characterised in
   that the flue gas is returned with a temperature of at least 873 K.
10. A process according to any one of claims 7 to 9,
    characterised in
    that for the purpose of returning the flue gas, a quantity of water vapour ranging between 4 and 40 g per Nm³ of returned flue gas is used.
11. A process according to any one of the preceding claims, characterised in
    that part of the water vapour is used to introduce nitrogen or other inert gases into the incinceration tank (1).
12. A process according to any one of the preceding claims, characterised in
    that for blowing in the water vapour, use is made of nozzles arranged in one or a plurality of planes in the tank wall in the region where the incineration gases emerge from the combustion space (2) and/or in the region of the reincineration chamber (4).
13. A process according to any one of the preceding claims, characterised in
    that supersonic nozzles are used for blowing in the water vapour.
14. A process according to any one of claims 7 to 13, characterised in
    that the flue gas is returned through one or a plurality of channels and that one water vapour nozzle is arranged concentrically in each channel.

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