EP0710799B1 - Thermal oxidation method for liquid waste material - Google Patents

Description

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

Such methods are known and e.g. in Chem. Ing. Tech. 63 (1991) pp. 621-622 described. An essential step is the utilization of the thermal Energy from a flue gas stream coming from an incinerator for thermal oxidation and thus disposal of liquid waste. The oxygen required for this oxidation process is called hot Flue gas stream delivered; i.e. the flue gas flow must be sufficient Contain oxygen. Is the hot flue gas e.g. through a waste incineration plant generated, must be burned with an excess of oxygen be worked so that part of the unused oxygen with the hot flue gas is discharged.

In terms of plant technology, this is an incineration plant with a Afterburning chamber, which is supplied with the liquid waste to be disposed of become. According to the prior art, one or installed several special burners, which applied the liquid waste fuel become. The liquid waste fuel is in the burner flame atomized finely. The swarm of drops generated forms a full cone. Each Burner is also used in sufficient quantities of combustion air Atomization of the liquid waste material required compressed air. 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. Between the single drop flows out of the nozzle at the speed of sound Atomizing air. This two-phase mixture is initially relatively cold Combustion air enveloped. This initially prevents combustion, since there is no one between the lower and upper explosion limits The fuel gas / air mixture still has the required ignition temperature is. By cross-mixing into the outside of the combustion air penetrating tiny drops of fuel evaporate quickly because there is one Mixture of combustion air and hot flue gas is present. With that the Combustion one. Because of the heat now released and further progressive mixture of the two-phase mixture present in the core Liquid drops and atomizing air with hot flue gases become one self-accelerating process more and more fuel burned. The The combustion process becomes strong due to this mixing behavior in the flame influenced. There has therefore been no shortage of attempts to implement constructive measures better mixing of the hot flue gas into the spray of the burner to meet. In any case, the aim is to burn as completely as possible the injected waste materials; i.e. the most complete burnout possible.

The combustion of flammable liquid waste in an afterburning chamber is always problematic if due to the geometrical Arrangement of the burner in the combustion chamber and that in the combustion chamber Flow conditions not the flame formed with the waste fuel burns constantly, but flickers. Such instabilities can occur when the Substance composition fluctuates over time and / or if it comes into contact with the wall unburned drops cannot be avoided. Are multiple burners on one Level exists, so the problem of mutual arises in a special way Influencing the flames and the interference of those of the individual Burners generated flue gas flows in the total flue gas flow.

The invention has for its object also poorly combustible liquid waste fuels to be introduced into the afterburning chamber in such a way that even with unfavorable ones Burning conditions a complete burnout is guaranteed.

Based on the method described in the introduction, this object is achieved according to the invention 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 using one or more two-substance nozzles, which pulsate at a frequency of 5 s ^-1 to 70 s ^-1 , preferably 10 s ^-1 to 20 s ^{-1 are} operated, a fan-shaped spray carpet with relatively coarse drops of long range and a flat spray carpet with relatively fine drops of short range being generated in alternation at each two-component nozzle, 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 its oxygen content at least is so high that complete oxidation of the combustible materials is guaranteed is.

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-fluid nozzles is adjusted so that the time average flow ratio of air and liquid flows at each Two-component nozzle is in the range of 0.01 to 0.2, while the instantaneous value of the Flow ratio fluctuates according to the pulsation frequency.

The pulsating mode of operation can be caused by periodic exposure to the Two-substance nozzle with compressed gas or liquid. Alternatively, the pulsating operation even when compressed air and Fluid generated in the two-fluid nozzle itself.

• 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.

In Fig. 1 is a main combustion chamber 1 with a burner 2 and a main flame 3 shown. The main flame 3 becomes so much combustion air or oxygen that the flowing out of the main combustion chamber 1 Flue gas 4 still has a considerable residual oxygen content (more than 6%). The Oxygen content of the flue gas can be varied by the main flame 3 more or less in excess oxygen or combustion air supplied becomes

The oxygen-containing flue gas 4 leaves the main combustion chamber 1 with a Temperature from 1000 ° C to 1400 ° C and then flows into the afterburner 5. Liquid is injected into the afterburning chamber 5 Waste fuels, which are then in the hot flue gas stream with the residual oxygen are thermally oxidized and thus disposed of Technology), one or more burners are installed in the afterburning chamber are equipped with their own burner air supply. The ones to be treated liquid waste 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 made with the help of special Two-substance nozzle lances 6 are injected into the flue gas stream in a fan shape. The fan-shaped Spray carpet 7 is shown in Fig. 2. Its transverse extent is b much larger than its thickness a (see Fig. 1). The main difference compared to conventional nozzle lances is that the used here Two-fluid nozzle lances 6 alternate with a fan-shaped spray carpet relatively coarse drops with a long range and a fan-shaped spray carpet generate with relatively fine drops of small range, so that the flue gas flow 4 alternating with finely sprayed drops of short range and rough that Flue gas with a relatively large throw penetrating drops becomes. This pulsating operation is hereinafter referred to as "bimodal operation" designated.

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 m ³ / 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, the quantity ratio of steam to oxygen-containing flue gas 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 oxidation takes place with or without a flame, regardless of the fuel, its evaporation and the mixing of flue gas. 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 is shown below described for bimodal operation. These two-substance nozzle lances make one special pulsation nozzle use.

The pulsation nozzle forms the front part of the one shown in FIGS. 1 to 3 4 and consists of a in a welding sleeve 9th screwed-in commercially available flat jet nozzle 10, one with the welding sleeve 9 firmly connected cladding tube 11, one axially displaceable in the cladding tube Inner tube 12, and a liquid distributor 13 attached to the inner tube. The inner tube 12 with the liquid distributor 13 attached is via centering webs 14 axially displaceably mounted in the cladding tube 11. The required seal of the slidable inner tube 12 relative to the cladding tube 9 is not shown here.

The liquid to be oxidized flows through the inner tube 12 and through the Annular gap 15 between the inner tube 12 and the cladding tube 11 as compressed air gaseous atomizing medium The liquid distributor 13 consists of a frontally sealed, placed on the inner tube 12 pipe piece with Exit bores 16 oriented perpendicular to the axis and offset from one another. The liquid to be oxidized exits the inner tube 12 through the outlet bores 16 into a first resonance chamber adjoining the distributor 13 17 a while the compressed air through the annular gap between the inner tube 12th and cladding tube 11 is supplied. The compressed air flows through the groove-like Open spaces 18 between the centering webs 14. The outlet bores 16 are in the Distributor 13 attached so that they are each in the axial extension of the annular gap cross section partially closing centering webs 14; i.e. the exit holes 16 are in the dead space or in the flow shadow behind the Centering webs 14. In this way, a mixing of the liquid phase and the gaseous phase (compressed air) in the resonance chamber 17 largely excluded.

The resonance chamber 17 is on the long side through the cladding tube 11, on the front side Entry through the liquid distributor 13 and at the outlet through a throttle or Aperture 19 with an inner diameter of the resonance chamber 17 greatly reduced cross-section limited. If the inner tube moves 12 in the cladding tube 11 changes the effective length a and thus also the volume the resonance chamber 17.

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

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 because practically pure liquid ejection takes place in this phase, while the substantially 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.

5 is the instantaneous value K of the mass flow ratio in a pulsating operation of the two-substance nozzle according to FIG. 4 as Function of time plotted. In an extreme case, flow through the throttle 19 alternating liquid and compressed air, while in the other extreme case Flow rate ratio K of those flowing through the throttle at the same time gaseous and liquid phase practically does not change. From the atomization room 20 (last resonance chamber) the liquid-gas mixture enters periodically variable composition through the flat jet nozzle exit surface 21 in the flue gas duct. As shown in Fig. 5, the mass flow ratio tends K from an upper limit - this corresponds to a high proportion of gaseous atomizing medium all through the nozzle slot 21 flowing mass - to a lower limit value, in order to then return to the To increase the maximum value. The upper limit corresponds to the state of the Fine atomization with a short range and the lower limit of education of coarse drops with a long range. This process is repeated periodically. The repetition frequency or pulsation frequency can be increased or reducing the volume of the resonance chamber 17 to be changed. If the volume is e.g. by increasing the distance a increases, the frequency decreases (lower field in Fig. 5), while as the volume decreases, the pulsation frequency increases (upper Partial image in FIG. 5) The one measured on a two-component nozzle according to FIGS. 3 and 4 Dependence of the pulsation frequency on the length a of the resonance chamber 17 shown in Fig. 6. The volume of the resonance chamber 17 could also be the result be changed that secondary chambers are provided, which are switched on if necessary become.

The pulsation mode arises with the resonance chamber two-substance nozzle described above by itself (autopulsation). Instead of the auto pulsation mode Forced pulsation can also be induced if one Compressed air or liquid is periodically applied to the two-substance nozzle. This can e.g. done by so-called flutter valves, which are in the supply lines for the Compressed air or the liquid are installed.

Examples

1. Versuch Flüssigrückstand Kresol Druck flüssigkeitsseitig mit Luft und Produkt 2,5 bar Durchsatz Produkt 1500 l/h Verdüsungsluftstrom 115 m³/h Verbrennungsluftstrom 4200 m³/h Brennkammertemperatur 1100°C O₂-Gehalt im Rauchgas 10,2 % CO-Gehalt im Rauchgas 5 mg/m³ Flamme: Teppichförmig, Zündung ca. 500 mm von Düse entfernt, hell.

2. Versuch Flüssigrückstand Kresol Druck flüssigkeitsseitig mit Luft und Produkt 2,5 bar Durchsatz Produkt 2000 l/h Verdüsungsluftstrom 100 m³/h Verbrennungsluftstrom 4200 m³/h Brennkammertemperatur 1120°C O₂-Gehalt im Rauchgas 8,5 % CO-Gehalt im Rauchgas 5 mg/m³ Flamme: wie vor.

3. Versuch Flüssigrückstand Kresol Druck flüssigkeitsseitig mit Luft und Produkt 2,0 bar Durchsatz Produkt 700 l/h Verdüsungsluftstrom 80 m³/h Verbrennungsluftstrom 4500 m³/h Brennkammertemperatur 1120°C O₂-Gehalt im Rauchgas 7,2 % CO-Gehalt im Rauchgas 5 mg/m³ Flamme: Beginn ca. 400 mm von Düse, sehr hell, fast weißer Teppich

4. Versuch Flüssigrückstand Kresol Druck flüssigkeitsseitig mit Luft und Produkt 2,5 bar Durchsatz Produkt 1200 l/h Verdüsungsluftstrom 115 m³/h Verbrennungsluftstrom 4400 m³/h Brennkammertemperatur 1100°C O₂-Gehalt im Rauchgas 9,5 % CO-Gehalt im Rauchgas 5 mg/m³ Flamme: Etwas voluminöser als zuvor.

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 m ³ / h Combustion air flow 4200 m ³ / h Firing chamber temperature 1100 ° C O ₂ content in the flue gas 10.2% CO content in the flue gas 5 mg / m ³ 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 m ³ / h Combustion air flow 4200 m ³ / h Firing chamber temperature 1120 ° C O ₂ content in the flue gas 8.5% CO content in the flue gas 5 mg / m ³ 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 m ³ / h Combustion air flow 4500 m ³ / h Firing chamber temperature 1120 ° C O ₂ content in the flue gas 7.2% CO content in the flue gas 5 mg / m ³ 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 m ³ / h Combustion air flow 4400 m ³ / h Firing chamber temperature 1100 ° C O ₂ content in the flue gas 9.5% CO content in the flue gas 5 mg / m ³ Flame: A little more voluminous than before.

Claims (6)

1. Method for complete thermal oxidation of liquid waste substances in which the waste substance is vaporized and oxidized in a stream of hot flue gas (4) which also contains the oxygen necessary for oxidation, characterized in that the liquid waste combustible substance is sprayed into the stream of hot flue gas (4) as a fan-shaped flat jet with a component which is perpendicular to the main direction of flow, by means of one or more two-fluid nozzles (6) which are operated in a pulsed mode at a frequency of 5 s^-1 to 70 s^-1, preferably 10 s^-1 to 20 s^-1, a fan-shaped spray carpet with relatively large droplets of large range and a fan-shaped spray carpet (7) with relatively fine droplets of small range being generated in an alternating cycle at each two-fluid nozzle (6), so that the stream of flue gas (4) is supplied alternately with finely sprayed droplets of small range and coarse droplets which penetrate the flue gas with a relatively large range of throw.
2. Method according to Claim 1, characterized in that the liquid waste substance is sprayed into a stream of flue gas (4) which has a temperature of at least 800°C and an oxygen content which is at least sufficiently high to ensure complete oxidation of the combustible substances.
3. Method according to Claim 1 or 2, characterized in that the included angle of the fan-shaped spray carpet (7) is 60° to 160°.
4. Method according to Claims 1 to 3, characterized in that the atomizing gas throughput and the liquid throughput are set so that the time-averaged volumetric flow ratio of the air and liquid streams at each two-fluid nozzle (6) lies within the range from 0.01 to 0.2, while the instantaneous value of the volumetric flow ratio varies according to the pulsation frequency.
5. Method according to Claims 1 to 4, characterized in that the pulsed operation is effected through a periodic admission of compressed gas or liquid to the two-fluid nozzle (6).
6. Method according to Claims 1 to 4, characterized in that the pulsed operation is generated fluidically within the two-fluid nozzle (6) itself when the admission of compressed gas and liquid is constant in respect of time.

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