EP0295454B1 - Process and apparatus for the purposeful destruction (cracking) of polychlorodibenzodioxines and/or polychlorinated dibenzofuranes and for the low-pollution processing of the cracked matter - Google Patents

Abstract

In the combustion of chlorinated organic compounds, small quantities of polychlorinated dibenzo-p-dioxines (PCDD) and dibenzofurans (PCDF) can be formed in addition to the comparatively highly concentrated gaseous and particulate combustion products such as, for example, carbon monoxide, nitrogen monoxide, sulphur dioxide, sulphur trioxide, hydrogen chloride, hydrogen fluoride, soot and solids. PCDD and PCDF have a considerable potential for polluting the environment. According to the invention, organic-chemical substances can be decomposed under defined conditions, so that, for example, toxic substances can be processed without polluting the environment. This is effected in an anaerobic atmosphere by means of a fluidised bed 3 and/or piston compressor 11, in which, for example, PCDD and PCDF are cracked. Such a process with the respective equipment can be used on site wherever polluting substances from the group indicated are formed. <IMAGE>

Description

The invention relates to a method for the targeted decomposition (cracking) of polychlorodibentodioxins (PCDD) and / or polychlorinated dibenzofurans (PCDF) and for the conversion of these substances into new environmentally friendly substances according to the preamble of claim 1. A further embodiment of the method is specified in claim 2 . Devices for carrying out the method are characterized in the subclaims.

Polychlorodibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF) play a special role here, and the problem at hand is to be explained using the example of this group of substances, which has given rise to several current incidents. PCDD and PCDF have proven to be extremely unpopular substances. There is broad agreement in science, business and politics to stop trading these substances themselves and to prevent them from being produced. Such a resolution will of course only be effective if the problem of "legacy issues" can be overcome. This means that the already existing "contaminated sites" or their producers, e.g. polychlorinated biphenyls (PCB), must be destroyed. It makes more sense financially to remove the legacy PCDD and PCDF than to manage and care for them.

PCDD and PCDF arise as trace products in the chemical synthesis of chlorinated hydrocarbons, especially in the synthesis of more chlorinated aromatic hydrocarbons, and can also arise when aromatic chlorinated hydrocarbons are used as intermediates in chemical syntheses.

Preferred reaction conditions for the formation of PCDD and PCDF are high temperatures and alkaline medium.

Furthermore, PCDD and PCDF can also arise in all types of combustion processes if organic chlorine compounds are present. Waste incineration plants are a well-known example. But even when burning wood and fuel, small amounts of PCDD and PCDF can be expected.

The formation of large quantities of PCDF has been reported in several cases in smoldering fires from transformers filled with PCB.

A number of accidents in the past 40 years have exposed PCDD and PCDF to the environment. The best known of these accidents was in Seveso, Italy in 1976, when approximately 2,5 kg 2,3,7,8-TCDD was released into the environment during the production of 2,4,5-trichlorophenol.

The group of PCDD and PCDF can be detected as a predominantly anthropogenic environmental contamination practically everywhere in nature. The identification and especially the quantification of this class of substances, which is characterized by a large number of isomers - often referred to simply as "dioxins" in the public eye - was only made possible by modern instrumental analysis.

The main requirement in the disposal of waste containing PCDD and PCDF is the removal of this material from the natural cycle. However, the conditions of the applicable laws must be observed. The yardstick for assessing which disposal path to take is the content of PCDD and PCDF in the waste, and the level of the disposal facilities.

The previous methods of environmentally friendly disposal of waste containing PCDF, such as landfilling, incineration, or chemical-physical treatment, proved to be very problematic.

The invention is therefore based on the object of finding a method which makes it possible to carry out an environmentally friendly removal of PCDD- and PCDF-containing wastes and to provide an apparatus for using this method.

This object is achieved according to the invention by the method outlined with the characterizing features of claim 1 and a device specified in the subclaims.

A further embodiment of the method is specified in claim 2, for which a device is specified in subclaims.

The main advantage of the method described in claims 1 and 2 is the treatment of PCDD and / or PCDF under defined reductive conditions with a very constant temperature over the entire reaction scheme. This means e.g. created the possibility of eliminating waste containing PCDD and PCDF in an anaerobic atmosphere. A high reduction potential is built up through a high hydrogen content. The reaction temperature can be kept very precisely at better than +/- 2 ° C for a long period of time. Technical and chemical parameters are chosen so that e.g. the formation or destruction of PCDD and PCDF is not only influenced kinetically, but also via the existing reaction partners.

Advantageous components of a device that works according to the method of claim 1 are characterized in subclaims 9 to 11, while advantageous components of a device that works according to claim 2 are described in claims 16 and 17.

• 1. Nach der Benetzung der aufgeheizten Partikel wird die Wärmeenergie schlagartig auf die zu zerlegenden Stoffe übertragen.
• 2. Die Partikel transportieren die zu zerlegenden Stoffe durch das Fluidbett hindurch und erhalten den Kontakt mit frischem Reaktionsgas.
• 3. Durch das Niederdruckfluidisieren ist die Verweilzeit besonders lang.
• 4. Der dünne Film der zu zerlegenden Stoffe zeigt an der Oberfläche der Aluminiumoxidkügelchen eine besondere Reaktionsbereitschaft.

The special feature of the device is that the temperature of the devices can be set homogeneously and constantly over the entire reaction volume. In addition, the gas atmosphere can be specifically selected for the reaction period. The aluminum oxide spheres have several functions, especially in the fluidized bed:

• 1. After wetting the heated particles, the thermal energy is suddenly transferred to the substances to be dismantled.
• 2. The particles transport the substances to be dismantled through the fluid bed and maintain contact with fresh reaction gas.
• 3. Because of the low-pressure fluidization, the dwell time is particularly long.
• 4. The thin film of the substances to be dismantled shows a special willingness to react on the surface of the aluminum oxide spheres.

• Fig. 1 eine Vorrichtung mit einem Fluidbett.
• Fig. 2 eine weitere Vorrichtung mit einem Kolbenverdichter.

Embodiments of the invention are shown in drawings and are explained in more detail below. Show it

• Fig. 1 shows a device with a fluid bed.
• Fig. 2 shows another device with a piston compressor.

1 and 2, the first part of the device is used to generate an anaerobic atmosphere. For this purpose, a fluid mixture of nitrogen, hydrogen and residual gases is generated in a gas cracking system 1 by partial combustion of natural gas or propane with atmospheric air and subsequent removal of unwanted combustion gases. The fluid mixture prepared in this way is further refined in a device for fine control 2 downstream of the gas cracking system 1 with the aid of hydrogen and / or nitrogen, a computer-controlled gas analysis laboratory 6 making it possible to influence the fine control by means of determined data after the cracking process in the fluid bed.

1, the fluid mixture is preheated and enters the fluid bed 3 through gas inlet nozzles 32 below a nozzle plate 31. There are aluminum oxide particles 34 in the fluid bed 3. Below the fluid bed there is a container 4 for the substances to be dismantled, which are injected into the fluid bed 3 via an injection pump 5 through injection nozzles 33. By constantly swirling the fluid mass, a fluid mixture that is always prepared is guided past the surfaces of the aluminum oxide particles 34. Here, chlorine and any oxygen present are bound by the hydrogen in the fluid mixture. The cracked low molecular weight substances are carried out of the fluid bed 3 according to the flow rate of the fluid mixture and sucked off or blown out.

2, the fluid mixture can also be fed to a piston compressor 11 via a charger 10. The loader has the task of compressing and conveying the fluid mixture from a low initial pressure to a higher final pressure. The piston compressor consists of a cylindrical compression chamber 12 as a working space with a piston reciprocating in a straight line. The substances to be dismantled in liquid form are initially in a container 4, from which they are injected into the piston compressor by means of an injection pump 5. The fluid mixture passes from the loader 10 via inlet valves 14 into the piston compressor 11. Via outlet valves 15, the mixture consisting of the fluid mixture and the cracking products leaves the piston compressor 11, previously passing through a catalytic converter 16.

1 and 2, the mixture consisting of the fluid mixture and the cracking products is then analyzed in the gas analysis laboratory 6. This laboratory essentially consists of a gas chromatograph and further analysis devices, from which data are transmitted to the device for fine control 2 for the supply of water and / or nitrogen. Subsequent filtering of the mixture consisting of fluid mixture and cracking products in a washing system 7 has the result that the hydrochloric acid contained in the mixture is washed out. A decision is then made as to whether the remainder is washed back to new substances 9 by recycling measures or is fed to thermal post-combustion 8.

In this case too, data from the gas analysis laboratory 6 can influence the process sequence in the final stage. 2, the loader is influenced by data from the gas analysis laboratory 6.

Claims (15)

1. Process for the purposeful destruction (cracking) of polychlorodibenzodioxins and/or polychlorinated dibenzofurans and for converting these substances into new low-polluting substances in a cracking unit by the fluidized bed process, characterized in that

1.1 an anaerobic, preheated fluid mixture of nitrogen and hydrogen is generated,

1.2 preheated aluminium oxide beads (34) are fluidized in the fluidized bed (3),

1.3 the fluid mixture is blown into the fluidized bed (3),

1.4 the substances to be destroyed, such as halogenohydrocarbons, are injected into the fluidized bed (3), where they wet the surfaces of the aluminium oxide particles (34), and at the same time

1.5 a constantly processed fluid mixture is passed over the surfaces of the aluminium oxide particles (34) by perpetual swirling of the fluid mass, elements such as e.g. chlorine and any oxygen present being bonded by the hydrogen of the fluid mixture,

1.6 the cracked low molecular weight substances are discharged from the fluidized bed (3) according to the flow rate of the fluid mixture and are sucked off,

1.7 the mixture consisting of the fluid mixture and the cracked products is analysed, and

1.8 this mixture is filtered such that reactions products, such as e.g. hydrochloric acid, are recovered by absorption or passed to a thermal after-combustion (8).

2. Process for the purposeful destruction (cracking) of polychlorodibenzodioxins and/or polychlorinated dibenzofurans and for converting these substances into new low-polluting substances in a cracking unit, characterized in that

2.1 an anaerobic, preheated fluid mixture is generated,

2.2 the fluid mixture is sucked through the inlet valves (14) of a piston compressor (11),

2.3 the hydrocarbon-containing substances to be destroyed are injected, if appropriate in solution, into the compressed fluid mixture at a temperature of 350°C to 550°C,

2.4 the temperature over the entire volume region is kept at a defined constant value by regulation of the suction pressure, the suction temperature, the piston speed and the preheating of the hydrocarbon-containing substances to be destroyed,

2.5 the mixture of the cracked products and the fluid mixture is passed, after discharge from the compression chamber (12), through a catalyst (16), and

2.6 is sucked off through a pipe by opening the discharge valves (15),

2.7 this mixture then being analysed and

2.8 filtered such that reaction products, such as e.g. hydrochloric acid, are absorbed, the residue being recovered by recycling measures or fed to a thermal after-combustion (8).

3. Process according to claims 1 or 2, characterized in that the anaerobic fluid mixture of nitrogen containing 4 to 12% hydrogen is generated by partial combustion of natural gas or propane with air from the atmosphere and subsequent removal of undesirable combustion gases, the fluid mixture containing a residual gas of the original constituents of 0.1 %.

4. Process according to claims 1 and 3, characterized in that the anaerobic fluid mixture is blown in through a nozzle plate (31) at the bottom of the fluidized bed (3), the distances of the constituents of the aluminium oxide beads (34) being increased or reduced, depending on the blowing- in pressure.

5. Process according to claims 1 or 2, characterized in that the hydrocarbon-containing substances to be destroyed are fed in continuously or discontinuously.

6. Process according to one of claims 1 to 5, characterized in that samples of the mixture of the cracked products and the fluid mixture are taken continuously above the fluidized bath and are analysed in a gas chromatograph with the aid of previously standardized substances.

7. Process according to one of claims 1 to 6, characterized in that data such as the composition of the fluid mixture, temperature and flow rate are measured and determined in a gas analysis laboratory (6) using a computer program, and in that the data are passed on, in the form of signals, to the device for fine regulation (2) and to the output of a washing unit (7) for influencing the fluid mixture or the cracked substances.

8. Process according to claim 6, characterized in that if critical substances (e.g. dioxin) are present, the samples are fed to the thermal after-combustion (8), the temperature of the after-combustion being increased to 1,000°C for a short time.

9. Device for carrying out the process according to one of claims 1 to 8, characterized in that the fluidized bed (3) consists of the reaction vessel which is filled with aluminium oxide beads (34) and contains in the lower region a nozzle plate (31), under which are provided injection nozzles (33) for entry of the substances to be destroyed, and in that gas inlet nozzles (32) are located in the region of the injection nozzles (33).

10. Device according to claim 9, characterized in that the fluidized bed (3) is connected via a pipeline for the fluid mixture to a gas cracking unit (1) for generating the fluid mixture.

11. Device according to one of claims 8 or 9, characterized in that a device for fine regulation (2) for the hydrogen and/or nitrogen feed is included in the pipeline between the fluidized bed (3) and the gas cracking unit (1), the device being connected to a gas analysis laboratory (6) connected to the fluidized bed (3) and being influenceable.

12. Device according to one of claims 9 to 11, characterized in that an injection pump (5) is included at the entry into the fluidized bed (3) for the hydrocarbon-containing substances to be destroyed.

13. Device according to one of claims 9 to 12, characterized in that the entire unit (1 to 9) is constructed as a stationary unit.

14. Device according to one of claims 9 to 12, characterized in that the entire unit (1 to 9) is accommodated in mobile units.

15. Device according to claim 14, characterized in that the unit (1 to 9) is located in containers, in each case one container being provided for the gas processing, the cracking operation and the gas analysis laboratory, including the regulating unit and the remote monitoring.

Images