EP0710799A2 - Thermal oxidation method for liquid waste material - Google Patents

Abstract

The liquid waste fuel is injected into the hot current (4) of flue gas using one or more two-component nozzles (6). The nozzles have a component in the form of a fan-shaped flat jet at right angles to the main direction of flow. At each two-component nozzle, in alternating rhythm, a fan-shaped spray with relatively large and far-range drops, and a fan-shaped spray (7) possessing a flare angle of 60 to 160 deg. with relatively fine, short-range drops, are produced. The temp. of the flue gas current is at least 800 deg. C, and its oxygen content sufficient for complete oxidation of the burnable products.

Description

The invention relates to a method for the complete thermal oxidation of liquid waste materials. The waste material is introduced into a hot flue gas stream, evaporated and thermally oxidized. For this purpose, the flue gas stream must contain the oxygen necessary for the oxidation.

Such methods are known and e.g. in Chem. Ing. Tech. 63 (1991) pp. 621-622. An essential step is the utilization of the thermal energy of a flue gas stream coming from an incineration plant for thermal oxidation and thus disposal of liquid waste. The oxygen required for this oxidation process is supplied with the hot flue gas stream; i.e. the flue gas flow must contain sufficient amounts of oxygen. Is the hot flue gas e.g. generated by a waste incineration plant, the combustion must be done with an excess of oxygen, so that part of the unused oxygen is removed with the hot flue gas.

In terms of plant technology, this is an incineration plant with an afterburning chamber to which the liquid waste materials to be disposed of are fed. According to the state of the art, one or more special burners are installed in the afterburning chamber, which are charged with the liquid waste fuel. The liquid waste fuel is atomized in the burner flame. The swarm of drops generated forms a full cone. A sufficient quantity of combustion air and the compressed air required to atomize the liquid waste material are also fed to each burner. The atomized liquid is initially available as a droplet collective that mixes with the Initial velocity of the atomization is moved into the combustion chamber. The atomizing air emerging from the nozzle at the speed of sound flows between the individual drops. This two-phase mixture is enveloped by the initially relatively cold combustion air. This initially prevents combustion, since there is no fuel gas / air mixture between the lower and upper explosion limits, and the required ignition temperature is not available. The smallest fuel droplets that penetrate into the outside area of the combustion air evaporate quickly because there is a mixture of combustion air and hot flue gas. With this, the combustion begins. Due to the heat now released and the progressive mixture of the two-phase mixture of liquid drops and atomizing air with hot flue gases present in the core, more and more fuel is burned in a self-accelerating process. The combustion process is strongly influenced by this mixing behavior in the flame. There has been no shortage of attempts to take constructive measures for better mixing of the hot flue gas into the spray mist of the burner. In any case, the aim is to burn the injected waste materials as completely as possible; ie the most complete burnout possible.

The combustion of combustible liquid waste materials in an afterburning chamber is always problematic if, due to the geometrically determined arrangement of the burner in the combustion chamber and the flow conditions prevailing in the combustion chamber, the flame formed with the waste fuel does not burn constantly, but flickers. Such instabilities can occur if the composition of the material fluctuates over time and / or if wall contact with unburned drops cannot be avoided. If there are several burners on one level, the problem of the mutual influencing of the flames and the mixing of the flue gas streams generated by the individual burners into the total flue gas stream arises in a special way.

The invention is based on the object of introducing poorly combustible liquid waste fuels into the afterburning chamber in such a way that complete burnout is ensured even under unfavorable combustion conditions.

This object is achieved on the basis of the method described in the introduction in that the liquid waste fuel is injected into the hot flue gas stream with a flow component perpendicular to the main flow direction as a fan-shaped flat jet with the help of one or more two-substance nozzles which pulsate at a frequency of 5 s von¹ to 70 s⁻¹, preferably 10 s⁻¹ to 20 s⁻¹ operated, with each two-component nozzle alternately a fan-shaped spray carpet with relatively large drops of long range and a flat-shaped spray carpet with relatively fine drops of short range is generated, so that the flue gas stream alternating with finely sprayed drops of short range and coarse that flue gas with a relatively large throw penetrating drops.

The liquid waste material is preferably injected into a flue gas stream whose temperature is at least 800 ° C. and whose oxygen content is at least so high that complete oxidation of the combustible substances is ensured.

The geometry of the two-component nozzles and the flow conditions (throughput and operating pressures) are chosen so that the opening angle of the fan-shaped spray carpets is 60 ° to 160 °.

According to a preferred embodiment, the atomizing gas throughput and the liquid throughput at the two-component nozzles are set such that the time-averaged mass flow ratio of the air and liquid streams at each two-component nozzle is in the range from 0.01 to 0.2, while the instantaneous value of the mass flow ratio fluctuates according to the pulsation frequency .

The pulsating mode of operation can be carried out by periodically applying compressed gas or liquid to the two-substance nozzle. Alternatively, the pulsating operation can also be generated in terms of flow technology in the two-component nozzle itself when the compressed air and liquid are kept constant over time.

• Es wird eine schnelle vollständige Oxidation aller oxidierbaren Flüssigabfall-Inhaltsstoffe erreicht.
• Auch bei niederkalorischen Flüssigabfällen, Abwässern und Schlämmen und auch bei stark schwankenden Heizwerten ist eine betriebssichere Oxidation gewährleistet.
• Im Gegensatz zu den herkömmlichen Brennern in der Nachbrennkammer sind keine zusätzliche Verbrennungsluft-Versorgungen und auch keine Zünd- oder Pilotbrenner erforderlich.
• Die Tropfenfeinheit, die Reichweite und der Sprühwinkel des verdüsten Tropfenschwarms können in weiten Grenzen variiert und damit an vorhandene Brennraumgeometrien angepaßt werden. Dadurch ist auch ein nachträglicher Einbau bzw. eine Nachrüstung bereits vorhandener Anlagen möglich.
• Selbst bei höchstem Flüssigabfalldurchsatz konnte keine Erhöhung des CO-Gehaltes in dem die Nachbrennkammer verlassenden Gasstrom festgestellt werden.

The following advantages are achieved with the invention:

• Rapid complete oxidation of all oxidizable liquid waste ingredients is achieved.
• Reliable oxidation is guaranteed even with low-calorific liquid waste, waste water and sludge and also with strongly fluctuating heating values.
• In contrast to the conventional burners in the afterburning chamber, no additional combustion air supplies and no pilot or pilot burners are required.
• The droplet fineness, the range and the spray angle of the atomized droplet swarm can be varied within wide limits and can thus be adapted to existing combustion chamber geometries. This also enables retrofitting or retrofitting of existing systems.
• Even with the highest liquid waste throughput, no increase in the CO content was found in the gas stream leaving the afterburner.

Fig. 1

schematisch einen Querschnitt durch eine Haupt- und Nachbrennkammer zur Verdüsung und Verbrennung eines flüssigen Abfallstoffes

Fig. 2

den fächerförmigen Sprühteppich der verdüsten Flüssigkeit

Fig. 3

einen Querschnitt durch die Nachbrennkammer aus dem die Anordnung der Zweistoffdüsen und die räumliche Konfiguration der Sprühteppiche in der Nachbrennkammer hervorgehen

Fig. 4

den Aufbau einer für den bimodalen Betrieb geeigneten Zweistoffdüse und

Fig. 5

den Momentanwert des Mengenstromverhältnisses von Luft- und Flüssigkeitsstrom beim bimodalen Betrieb der Zweistoffdüse

Fig. 6

Die Abhängigkeit der Pulsationsfrequenz von der Länge der ersten Resonanzkammer in der Zweistoffdüse.

The invention is described in more detail below with reference to drawings and exemplary embodiments. Show it:

Fig. 1

schematically shows a cross section through a main and post-combustion chamber for atomization and combustion of a liquid waste

Fig. 2

the fan-shaped spray of the atomized liquid

Fig. 3

a cross section through the afterburning chamber from which the arrangement of the two-substance nozzles and the spatial configuration of the spray carpets in the afterburning chamber emerge

Fig. 4

the construction of a two-substance nozzle suitable for bimodal operation and

Fig. 5

the instantaneous value of the mass flow ratio of air and liquid flow during bimodal operation of the two-component nozzle

Fig. 6

The dependence of the pulsation frequency on the length of the first resonance chamber in the two-substance nozzle.

A main combustion chamber 1 with a burner 2 and a main flame 3 is shown schematically in FIG. 1. So much combustion air or oxygen is fed to the main flame 3 that the flue gas 4 flowing out of the main combustion chamber 1 still has a considerable residual oxygen content (more than 6%). The oxygen content of the flue gas can be varied by supplying the main flame 3 more or less in excess oxygen or combustion air.

The oxygen-containing flue gas 4 leaves the main combustion chamber 1 at a temperature of 1000 ° C to 1400 ° C and then flows into the afterburning chamber 5. In the afterburning chamber 5, liquid waste fuels are injected, which then thermally oxidize with the residual oxygen in the hot flue gas stream and thus to be disposed of. Usually (prior art) one or more burners are installed in the afterburning chamber, which are equipped with their own burner air supply. The liquid waste to be treated is injected directly into the flames of these burners.

The new process eliminates the need for burners in the afterburner. The liquids to be oxidized are injected into the flue gas stream in a fan shape using special two-substance nozzle lances 6. The fan-shaped spray carpet 7 is shown in Fig. 2. Its transverse extent b is considerably larger than its thickness a (see FIG. 1). The main difference compared to conventional nozzle lances is that the two-substance nozzle lances 6 used here alternately produce a fan-shaped spray carpet with relatively large drops of long range and a fan-shaped spray carpet with relatively fine drops of short range, so that the flue gas stream 4 alternates with finely sprayed drops of short range and rough that flue gas with a relatively large throw penetrating drops. This pulsating operation is referred to below as "bimodal operation".

According to FIG. 3, four bimodal two-substance nozzle lances 6 are arranged in the afterburning chamber 5 in a rotationally symmetrical manner. The fan-shaped spray carpets 7 of the two-substance nozzle lances 6 partially overlap. The atomizing gas, for example air and the liquid to be disposed of, is fed to a bimodal two-substance nozzle lance 6. The opening angle of the fan-shaped spray carpets is approx. 120 °. The spray level is perpendicular to the main direction of flow of the hot flue gases. However, this condition need not be strictly observed. In the bimodal mode of operation, coarse and fine drops of different speeds and thus throwing distances replace each other. This prevents the formation of a closed vapor cloud, which would be difficult to penetrate from the hot surrounding smoke gases. Bimodal spraying is also characterized by a very wide range of drops. At a throughput of 1.5 m³ / h, coarse drops with a diameter of approx. 2 mm and a range of approx. 6 m were observed on the one hand and small drops of approx. 30 µm with a range of approx. 0.4 m on the other. An essential characteristic of this mode of operation is the rapid change in time between fine drops and coarse drops. The fine drops are generated when the two-substance nozzle lance works in the two-substance atomization mode. The coarse drops, on the other hand, arise in the subsequent mode of the pressure nozzle operation. The fine drops evaporate quickly and ignite quickly in the hot atmosphere. This results in a flame that stabilizes itself near the nozzle. The turbulence bales 8 formed on contact with the flue gas and formed from steam and flue gas are considerably smaller than in the usual post-combustion because neither significant drop collectives nor cold combustion air hinder the evaporation of the liquid and also do not delay the mixing with the hot flue gas. In the case of the coarse droplets in particular, a steam trail with spatially different flue gas-steam mixture ratios is generated along their trajectory, with the ratio of flue gas containing steam to oxygen becoming smaller over time. If there is a combustible mixture locally, a stable combustion takes place after an ignition delay time in the ms range. However, if the mixing processes fall below the lower ignition limit during the ignition delay time, combustion can no longer take place. Surprisingly, it was found that after further mixing with the flue gas, flameless oxidation takes place. This ensures that independent the fuel, its evaporation and the mixing of flue gas are oxidized with or without a flame. Due to the improvements described above, complete oxidation of all oxidizable liquid waste ingredients can be achieved.

The construction of the two-substance nozzle lances 6 used here for bimodal operation is described below. These two-substance nozzle lances use a special pulsation nozzle.

The pulsation nozzle forms the front part of the nozzle lance 6 shown in FIGS. 1 to 3 and, according to FIG. 4, consists of a commercially available flat jet nozzle 10 screwed into a weld-on sleeve 9, a cladding tube 11 firmly connected to the weld-on sleeve 9, and an inner tube 12 which can be displaced axially in the cladding tube. and a liquid distributor 13 attached to the inner tube. The inner tube 12 with the liquid distributor 13 attached is axially displaceably mounted in the cladding tube 11 via centering webs 14. The required sealing of the slidable inner tube 12 with respect to the cladding tube 9 is not shown here.

The liquid to be oxidized flows through the inner tube 12 and compressed air as a gaseous atomizing medium flows through the annular gap 15 between the inner tube 12 and the cladding tube 11. The liquid distributor 13 consists of a tube piece which is closed at the end and is placed on the inner tube 12 and has outlet bores 16 oriented perpendicular to the axis and offset from one another. The liquid to be oxidized enters the inner tube 12 through the outlet bores 16 and into a first resonance chamber 17 connected to the distributor 13 , while the compressed air is supplied via the annular gap between the inner tube 12 and the cladding tube 11. The compressed air flows through the groove-like open areas 18 between the centering webs 14. The outlet bores 16 are provided in the distributor 13 in such a way that they are each in the axial extension of the centering segments 14 partially closing the annular gap cross section; ie the outlet bores 16 lie in the dead space or in the flow shadow behind the centering webs 14. In this way, mixing of the liquid phase and the gaseous phase (compressed air) in the resonance chamber 17 is largely ruled out.

The resonance chamber 17 is delimited on the long side by the cladding tube 11, on the front end at the inlet by the liquid distributor 13 and at the outlet by a throttle or orifice 19 with a cross section which is greatly reduced in relation to the inner diameter of the resonance chamber 17. When the inner tube 12 is displaced in the cladding tube 11, the effective length a and thus also the volume of the resonance chamber 17 change.

Another resonance chamber 20 connects to the throttle 19. Through the actual nozzle opening on the nozzle head, which is designed here as a narrow rectangular slot 21, the two-phase mixture of compressed air / waste liquid located in the second resonance chamber 20 enters the flue gas duct. The second resonance chamber 20 can therefore also be regarded as a spray chamber. In principle, more than two resonance chambers could also be connected in series, each of which is separated from the other by orifices or chokes.

It has been shown that when this two-jet nozzle is operated with constant compressed air and liquid pre-pressure, the liquid is pulsed, the pulsation frequency being adjustable via the volume of the resonance chamber 17 and in a typical frequency range from 5 s⁻¹ to 70 s⁻¹ lies. Investigations have shown that with such pulsating operation, a spray fan with relatively coarse drops with a long range and a spray fan with relatively fine drops with a short range are generated alternately at each two-component nozzle. The pulsation frequencies of the nozzle lances 6 can be different. The relatively coarse drops come about in that in this phase practically pure liquid ejection takes place, while the much smaller drops produced in the subsequent fine spray phase are due to the atomization by the expanding compressed air. With this bimolar atomization, a very wide range of drops is generated, whereby the coarse drops are characterized by a particularly large throw distance. A particularly uniform and good heat and material exchange between little liquid and a relatively large amount of gas is achieved. The atomization takes place at a pre-pressure of 0.8 to 2.5 bar and with a compressed air / liquid flow ratio between 0.01 and 0.2.

In the diagram according to FIG. 5, the instantaneous value K of the mass flow ratio during pulsed operation of the two-substance nozzle according to FIG. 4 is plotted as a function of time. In one extreme case, liquid and compressed air alternately flow through the throttle 19, while in the other extreme case the mass flow ratio K of the gaseous and liquid phase flowing simultaneously through the throttle point practically does not change. From the atomization chamber 20 (last resonance chamber), the liquid-gas mixture enters the flue gas duct in a periodically variable composition through the flat jet nozzle exit surface 21. As shown in FIG. 5, the mass flow ratio K tends from an upper limit value - this corresponds to a high proportion of gaseous atomizing medium in the total mass flowing through the nozzle slot 21 - to a lower limit value in order to then rise again to the maximum value. The upper limit corresponds to the state of fine atomization with a short range and the lower limit to the formation of coarse drops with a long range. This process is repeated periodically. The repetition frequency or pulsation frequency can be specifically changed by increasing or decreasing the volume of the resonance chamber 17. If the volume is e.g. increased by increasing the distance a, the frequency decreases (lower field in FIG. 5), while when the volume is reduced the pulsation frequency increases (upper field in FIG. 5). The dependence of the pulsation frequency on the length a of the resonance chamber 17 measured on a two-substance nozzle according to FIGS. 3 and 4 is shown in FIG. 6. The volume of the resonance chamber 17 could also be changed in that secondary chambers are provided, which are switched on if necessary.

The pulsation mode occurs automatically with the resonance chamber two-component nozzle described above (autopulsation). Instead of the autopulsation mode, a forced pulsation can also be brought about if a two-component nozzle is periodically pressurized with compressed air or liquid. This can be done, for example, by so-called flutter valves, which are built into the supply lines for the compressed air or the liquid.

Examples

The following experiments were carried out with a cresol residue as a liquid waste. 1st attempt Liquid residue Cresol Pressure on the liquid side with air and product 2.5 bar Product throughput 1500 l / h Atomizing air flow 115 m³ / h Combustion air flow 4200 m³ / h Firing chamber temperature 1100 ° C O₂ content in the flue gas 10.2% CO content in the flue gas 5 mg / m³ Flame: carpet-shaped, ignition approx. 500 mm from the nozzle, bright. Second attempt Liquid residue Cresol Pressure on the liquid side with air and product 2.5 bar Product throughput 2000 l / h Atomizing air flow 100 m³ / h Combustion air flow 4200 m³ / h Firing chamber temperature 1120 ° C O₂ content in the flue gas 8.5% CO content in the flue gas 5 mg / m³ Flame: as before. 3. Attempt Liquid residue Cresol Pressure on the liquid side with air and product 2.0 bar Product throughput 700 l / h Atomizing air flow 80 m³ / h Combustion air flow 4500 m³ / h Firing chamber temperature 1120 ° C O₂ content in the flue gas 7.2% CO content in the flue gas 5 mg / m³ Flame: beginning about 400 mm from the nozzle, very bright, almost white carpet 4th try Liquid residue Cresol Pressure on the liquid side with air and product 2.5 bar Product throughput 1200 l / h Atomizing air flow 115 m³ / h Combustion air flow 4400 m³ / h Firing chamber temperature 1100 ° C O₂ content in the flue gas 9.5% CO content in the flue gas 5 mg / m³ Flame: A little more voluminous than before.

Claims (6)

Process for the complete thermal oxidation of liquid waste materials, in which the waste material is evaporated and oxidized in a hot flue gas stream (4), which also contains the oxygen required for the oxidation, characterized in that the liquid waste fuel is fed into the hot flue gas stream (4) with a Component perpendicular to the main flow direction is injected as a fan-shaped flat jet with the help of one or more two-substance nozzles (6) which are operated pulsating at a frequency of 5 s⁻¹ to 70 s⁻¹, preferably 10 s⁻¹ to 20 s⁻¹, with every two-substance nozzle (6) alternately creates a fan-shaped spray carpet with relatively large drops of long range and a fan-shaped spray carpet (7) with relatively fine drops of short range, so that the flue gas stream (4) alternates with finely sprayed drops of short range and coarse, the flue gas with relatively large throwing distance penetrating drops is opened. Method according to claim 1, characterized in that the liquid waste material is injected into a flue gas stream (4), the temperature of which is at least 800 ° C and the oxygen content is at least so high that a complete oxidation of the combustible materials is ensured. Method according to claims 1 to 2, characterized in that the opening angle of the fan-shaped spray carpet (7) is 60 ° to 160 °. Method according to claims 1 to 3, characterized in that the atomizing gas and liquid throughput are adjusted so that the time-averaged mass flow ratio of the air and liquid flows at each two-substance nozzle (6) is in the range of 0.01-0.2, while the instantaneous value of the mass flow ratio fluctuates according to the pulsation frequency. Method according to Claims 1 to 4, characterized in that the pulsating operation is carried out by periodically applying compressed gas or liquid to the two-substance nozzle (6). Method according to Claims 1 to 4, characterized in that the pulsating operation is generated in terms of flow technology itself in the two-component nozzle (6) when pressure gas and liquid are applied at a constant time.

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