EP0282880B1 - Process for the pollution-free destruction of polychlorinated waste products - Google Patents

Abstract

1. A process for the pollution-free destruction of polychlorinated waste materials such as dibenzodioxines (PCCD), polychlorinated dibenzofuranes (PCDF) and polychlorinated biphenyls (PCB), characterized in that these substances or combustible residual materials contaminated with said substances are subjected to combustion together with waste sulfuric acids, acid tars and similar sulfur- and carbon-containing waste products of different composition and consistency in a multistage combustion furnace, wherein a) in a first stage, the mixture, optionally in combination with elemental sulfur, is fed onto a coke bed in a rotary furnace at a temperature of at least 400 degrees C and an amount of air equal to about 25 to 55% of the total amount of air required for the whole process is introduced as primary air, so that the resultant reducing mixture and the rear portion of the coke bed are heated to about 800 degrees C to 1100 degrees C, whereby any excess coke if formed is discharged at the end of the rotary furnace ; b) in a second stage, the gas mixture in an intermediate chamber is admixed with about 10 to 15% of the amount of air required for the whole process, while a space velocity per hour of about 200 to 400 Nm**3 of gas/m**3 of combustion space is maintained and the temperature of the gas mixture increases to about 1150 degrees C to 1350 degrees C ; c) in a third stage, the gas is fed into the forward combustion space of a secondary combustion chamber and mixed with another 20 to 45% of the amount of air required for the whole process, while a space velocity per hour of about 50 to 180 Nm**3 of gas/m**3 of combustion space is maintained and the gas mixture is being cooled to about 1000 degrees C to 1200 degrees C : and d) in a fourth stage, the remaining portion of the total air required in the overall process is fed into about the center portion of the secondary combustion chamber and mixed with the separation gas so that in the rear part of the secondary combustion chamber a temperature of about 1000 degrees C to 1200 degrees C is obtained and a space velocity per hour of about 150 to 400 Nm**3 of gas per m**3 of combustion space is maintained, whereupon, after completion of the reaction, the resulting gas mixture is cooled in a waste heat boiler and is reprocessed, preferably by way of a sulfuric acid contact process to form sulfuric acid.

Description

The present invention relates to a process for the environmentally friendly destruction of polychlorinated waste materials, in particular dibenzodioxins (PCDD), polychlorinated dibenzofurans (PCDF) and polychlorinated biphenyls (PCB). Today, polychlorinated waste is one of the particularly problematic waste, because some of it is extremely toxic even in small quantities and leads to long-lasting damage. It is known that these waste materials are only partially destroyed in simple incineration plants or waste incineration plants and therefore represent an unacceptable pollution and danger to the environment.

• a) in einer ersten Stufe das Gemisch, gegebenenfalls zusammen mit elementarem Schwefel, in einem Drehrohrofen auf ein Koksbett von mindestens 400_°C aufgibt und 25 bis 55% der insgesamt für das Verfahren erforderlichen Luft als Primärluft einbläst, so daß das entstehende reduzierende Gemisch und der hintere Teil des Koksbettes sich auf 800 bis 1100_°C erwärmen, wobei der gegebenenfalls sich bildende überschüssige Koks am Ende des Drehrohrofens ausgetragen wird, das Gasgemisch
• b) in einer zweiten Stufe in einer Zwischenkammer mit weiteren 10 bis 15% der erforderlichen Luft versetzt, wobei eine Raumgeschwindigkeit von 200 bis 400 Nmⁿ Gas/mⁿ Brennraum eingehalten wird und sich die Temperatur des Gasgemisches auf 1150 bis 1350_°C erhöht,
• c) in einer dritten Stufe am Anfang einer Nachbrennkammer weitere 20 bis 45% der erforderlichen Luft zugibt, wobei eine Raumgeschwindigkeit von 50 bis 180 Nmⁿ Gas/mⁿ Brennraum eingehalten wird und sich das Gasgemisch auf 1000 bis 1200_°C abkühlt, und schließlich
• d) in einer vierten Stufe etwa in der Mitte der Nachbrennkammer den Rest der erforderlichen Luft zugibt, wobei sich im hinteren Teil der Nachbrennkammer Temperaturen von 1000 bis 1200_°C einstellen und eine Raumgeschwindigkeit von 150 bis 400 Nmⁿ Gas/mⁿ Brennraum eingehalten wird,
  woraufhin man das durchreagierte Gasgemisch in an sich bekannter Weise in einem Abhitzekessel abkühlt und vorzugsweise in einem Schwefelsäure-Kontaktverfahren zu Schwefelsäure aufarbeitet.

Through detailed investigations it has now been found that it is possible to destroy these waste materials easily and safely if one combines these substances or flammable residues contaminated with these substances together with waste sulfuric acids, acid tars and similar sulfur and carbon containing waste products of different composition and consistency in one multi-stage incinerator burns where one

• a) in a first stage, the mixture, optionally together with elemental sulfur, in a rotary kiln on a coke bed of at least 400 _° C and blows 25 to 55% of the total air required for the process as primary air, so that the resulting reducing mixture and the rear part of the coke bed heats up to 800 to 1100 _° C, the excess coke which may form is discharged at the end of the rotary kiln, the gas mixture
• b) in a second stage in an intermediate chamber with a further 10 to 15% of the required air, a space velocity of 200 to 400 Nm ⁿ gas / m ⁿ combustion chamber being maintained and the temperature of the gas mixture increasing to 1150 to 1350 _° C,
• c) in a third stage at the beginning of a post-combustion chamber, a further 20 to 45% of the required air is added, a space velocity of 50 to 180 Nm ⁿ gas / m ⁿ combustion chamber being maintained and the gas mixture cooling to 1000 to 1200 _° C, and finally
• d) in a fourth stage, approximately in the middle of the afterburning chamber, the rest of the required air is added, temperatures in the rear part of the afterburning chamber being set at 1000 to 1200 _° C. and a space velocity of 150 to 400 Nm ⁿ gas / m ⁿ combustion chamber being maintained ,
  whereupon the gas mixture which has reacted through is cooled in a manner known per se in a waste heat boiler and preferably worked up to sulfuric acid in a sulfuric acid contact process.

The process for working up waste sulfuric acids, acid tars and similar sulfur and carbon-containing waste products of different compositions and consistencies is the subject of DE-A 29 47 497 (corresponds to EP-A 29 583).

In practice, this process has proven to be reliable and economical, so that it has an essential prerequisite for the environmentally friendly destruction of polychlorinated waste materials. However, it was completely unclear how the polychlorinated waste would behave under the process conditions of the known process for processing waste sulfuric acids, so that no predictions could be made as to whether the polychlorinated waste would burn completely and whether the resulting chlorine-containing products would disrupt the course of the reaction.

Surprisingly, it has been shown that no faults occur and that unburned residues of the polychlorinated waste materials are not formed in the cracked gas or in the solid combustion residues.

In order to determine this, extensive investigations and measurements were necessary, whereby the measurement methods had to be checked first to see whether they lead to reliable values under the process conditions. Finally, it was necessary to vary the process conditions in order to determine whether a variation in the process conditions would nevertheless result in the inadmissible leakage of large amounts of formed or unburned polychlorinated waste. Furthermore, it was necessary to determine the polychlorinated content in the waste materials to be used.

The results have finally shown that even with the substantial addition of polychlorinated waste materials, these can neither be found in the cracked gas nor in the pure gases, that is to say they have been reduced at least to amounts which are below the detection limit.

For example, the detection limit of approx. 0.02 gg / m ⁿ currently applies to 2,3,7,8-TCDD in cracked gas ^. The method according to DE-OS 29 47 497 can therefore also be used without problems for the destruction of polychlorinated waste materials .

The process according to the invention is explained in more detail in the example below:

example

The existing plant for splitting waste sulfuric acids in the applicant's house was used. It consists of two identical rotary kilns, each with an intermediate and two post-combustion chambers and a downstream waste heat boiler. The process gases from both furnaces are combined behind the waste heat boilers and cleaned in two washing systems and an electrostatic filter. The sulfur dioxide is removed from the exhaust gas in a washing battery consisting of four absorbers connected in series and then sent to a further processing plant. After an alkaline wash, the exhaust gas is discharged into the open via a chimney.

A coke bed temperature of around 1000 ° C is maintained in the rotary kiln. The coke breeze is continuously drawn off at the end of the rotary kiln. The gas mixture generated in the rotary kiln in a reducing atmosphere, the Schwe Field steam, hydrogen sulfide, carbon oxide sulfide, carbon monoxide and hydrocarbons, leaves the rotary kiln at a temperature of 900 to 1000 _° C and enters an intermediate chamber. At 1200 to 1300 _° C, the remaining H ₂ S0 ₄ vapors and sulfur trioxide are completely reduced to S0 ₂ , and higher hydrocarbons are cracked and converted into low-molecular compounds, which can burn more quickly in the afterburning chambers. All combustible gases and vapors are completely combusted in the afterburning chamber, an oxygen excess of 1 to 2% being aimed for and the end gas leaving the afterburning chamber at a temperature of 1080 to 1200 _° C.

The process gas is then cooled to about 350 _° C to obtain steam. The gas is then fed to the exhaust gas cleaning system.

The combustion temperatures are monitored at a total of seven temperature measuring points using thermocouples.

The pressure conditions are measured and registered at the gas inlet of the intermediate chamber, at the gas outlet of the waste heat boiler and in the gas line after the hot gas blower. There is a probe in the waste heat boiler for the extraction of sample gas to determine the content of oxygen, sulfur dioxide, carbon dioxide and carbon monoxide. The concentrations are continuously measured, displayed and registered.

A total of four series of measurements were created, namely a zero measurement without waste oil, measurement I with 100 kg / h and furnace waste oil containing 500 ppm PCB, measurement II with 100 kg / h and furnace waste oil containing 1000 ppm PCB, and the measurement III with 250 kg / h and furnace waste oil, containing 1000 ppm PCB.

In addition to the usual measurements of the gas constituents, gas samples were taken and examined using the method of the Rheinisch-Westfälischen Technical Monitoring Association. For this purpose, representative samples of the exhaust gas are taken at temperatures up to 773 K and cooled to temperatures below 323 K. Here, vaporous compounds condense out and are partially absorbed by existing solid particles. The particles contained in the mixed gas are separated on appropriate filters and the very fine particles and volatile compounds are absorbed in a downstream solid bed. Sorbent was used in the zero measurement and the measurement series and 111 Florisil and in the measurement series II XAD-2. Comparative measurements with the sorbents Parapak PS, XAD-2 and Florisil showed that the sorptive separation of PCDD and PCDF is the same size and therefore provides equivalent results. The volume flows in the exhaust gas and the cooling air were controlled by a computer, with electronic measured value acquisition and evaluation of the filter temperature, the probe cross section and the exhaust gas state, so that isokinetic partial flow withdrawals were ensured. In the clean gas measurement, filter temperatures of 301 K were maintained, with a partial gas quantity extracted of 3.5 m ³ / h and a dilution factor of about 1: 5. The filter temperature for the raw gas measurement was 313 K, the extracted partial gas volume on average 2.2 m3 / h with a dilution factor of 1:10. The cooling air was pre-cooled by water in a countercurrent heat exchanger. After the measurement, the sampling fractions, filters and solid sorbents were packed and protected against heat and light radiation and sent for analysis.

A mixture of the following 13C-labeled PCDD was added to all samples before extraction: 5 ng 2,3,7,8-TCDD, 5 ng 1,2,3,7,8-PentaCDD, 5 ng 1,2,3,6 , 7,8-HexaCDD, 10ng 1,2,3,4,6,7,8-HeptaCDD and 10ng OCDD. The filters of the raw and clean gas samples were extracted and analyzed chromatographically. The analysis results showed that no polychlorinated waste materials could be found in the pure gases and were therefore significantly below the detection limit. The detection limit of the analytical methods for 2,3,7,8-TCDD was approx. 0.02 ng / m ^3. The environmental authority currently authorizes emissions as 0.1 ng / m3.

Claims (1)

1. A process for the pollution-free destruction of polychlorinated waste materials such as dibenzodi- oxines (PCCD), polychlorinated dibenzofuranes (PCDF) and polychlorinated biphenyls (PCB), characterized in that these substances or combustible residual materials contaminated with said substances are subjected to combustion together with waste sulfuric acids, acid tars and similar sulfur- and carbon-containing waste products of different composition and consistency in a multistage combustion furnace, wherein

   a) in a first stage, the mixture, optionally in combination with elemental sulfur, is fed onto a coke bed in a rotary furnace at a temperature of at least 400_°C and an amount of air equal to about 25 to 55% of the total amount of air required for the whole process is introduced as primary air, so that the resultant reducing mixture and the rear portion of the coke bed are heated to about 800_°C to 1100_°C, whereby any excess coke if formed is discharged at the end of the rotary furnace;

   b) in a second stage, the gas mixture in an intermediate chamber is admixed with about 10 to 15% of the amount of air required for the whole process, while a space velocity per hour of about 200 to 400 Nm3 of gas/m3 of combustion space is maintained and the temperature of the gas mixture increases to about 1150_°C to 1350_°C;

   c) in a third stage, the gas is fed into the forward combustion space of a secondary combustion chamber and mixed with another 20 to 45% of the amount of air required for the whole process, while a space velocity per hour of about 50 to 180 Nm3 of gas/m³ of combustion space is maintained and the gas mixture is being cooled to about 1000_°C to 1200_°C: and

   d) in a fourth stage, the remaining portion of the total air required in the overall process is fed into about the center portion of the secondary combustion chamber and mixed with the separation gas so that in the rear part of the secondary combustion chamber a temperature of about 1000°C to 1200°C is obtained and a space velocity per hour of about 150 to 400 Nm³ of gas per m3 of combustion space is maintained,
   whereupon, after completion of the reaction, the resulting gas mixture is cooled in a waste heat boiler and is reprocessed, preferably by way of a sulfuric acid contact process to form sulfuric acid.