# Patent

## Title
Recovery of UO.sub.2 /Pu O.sub.2 in IFR electrorefining process

## Abstract

A process for removing halogenated organic compounds from waste gases optionally containing NO.sub.x, in which the waste gas is optionally supplemented with SO.sub.2, optionally led through a fixed bed or fluidized bed of a solid and contacted with Caro's acid or one of its salts. The Caro's acid can be produced in situ by adding H.sub.2 O.sub.2 and optionally H.sub.2 SO.sub.4.

## Background
The present invention relates to a process for removing halogenated organic compounds from waste gases which, optionally, contain NO.sub.x, especially waste gases from refuse incineration plants.

Waste gases from refuse incineration plants contain, apart from NO.sub.x (200 ppm on average) and residual SO.sub.2 (10-20 mg/Nm.sup.3 on average, =ca. 3 to 7 ppm), chlorinated dibenzodioxins and chlorinated dibenzofurans in a concentration of the order of ca. 2 to 10 ng TE/m.sup.3 (toxicity equivalents).

In the 17th Statutory Regulation to the Federal Law on Protection from Noxious Substances, the legislature stipulates from 1996 a limit value of 0.1 ng TE/Nm.sup.3.

In public discussion, thermal treatment of waste (refuse incineration) is regarded as an emission source from which a disproportionately high environmental pollution originates, especially because of dioxin emissions.

The waste gases from refuse incineration are led through adsorption plants in which the environmentally harmful substances are removed from the waste gas.

It is known to use activated coal coke or activated carbon as an adsorbent in adsorption plants. When this is done, the waste gas is led through a bed of solid with a velocity of between 0.1 and 0.3 meters/second (VDI Textbook 780, page 12). Another possibility which, unfortunately, is limited to relatively low flow rates, consists of using an activated carbon filter according to the cross-flow principle (VDI Textbook 972, page 2).

There is a disadvantage associated with the use of activated carbon. The disadvantage is that, if oxygen is present in the waste gas, the activated carbon can ignite at elevated temperature, and the adsorption performance is reduced. In the extreme case, this can also lead to the complete combustion of the activated carbon filter.

The object of the present invention is to provide a process for removing halogenated organic compounds from waste gases which optionally containing NO.sub.x, especially waste gases from refuse incineration plants, which does not have these disadvantages.

The invention provides a process for removing halogenated organic compounds from waste gases optionally containing NO.sub.x, in which the waste gas is optionally led through a fixed bed or fluidized bed and contacted with Caro's acid or one of its salts.

In an embodiment of the invention the waste gas can optionally be supplemented with SO.sub.2, optionally led through a fixed bed or fluidized bed of a solid, and contacted with H.sub.2 O.sub.2. The SO.sub.2 component is added if the exit waste gas contains little or no SO.sub.2.

In an embodiment of the invention, apart from Hhd 2O.sub.2, Caro's acid can also be applied.

The waste gas can moreover be led through a fixed bed or fluidized bed of a solid while an aqueous mixture of H.sub.2 O.sub.2 and H2SO.sub.4 is sprayed onto the solid.

In an embodiment of the invention, before the solid is introduced into the waste gas stream, it can be impregnated with H.sub.2 SO.sub.4 and H.sub.2 O.sub.2 applied.

In a further embodiment of the invention, before the solid is introduced into the waste gas stream, it can be impregnated with H.sub.2 O.sub.2 and H.sub.2 SO.sub.4 applied.

In a further embodiment of the invention, before the solid is introduced into the waste gas stream, it can be impregnated with Caro's acid or with an aqueous solution of its salt. Likewise, before the solid is introduced into the waste gas stream, it can be sprayed with Caro's acid or with an aqueous solution of its salt.

As the solid, the following can be used as finely-divided, granulated or tabletted substances or as substances formed to any shaped articles, including honeycomb bodies, or applied to honeycomb-shaped supports, alone or in a mixture: hydrophobed form;

The following solids have been thoroughly checked experimentally:

Aerosil 200 (pyrogenic amorphous silicic acid), tablets 6.times.5.5 mm (development product from the commercial product Aerosil 200 of the Degussa company, Frankfurt);

Wide-pore 12-ring zeolite, dealuminized y-zeolite (pore width 7.4 .ANG., modulus 200 (Si/Al=100)).

The solids according to the invention have the advantage that they are not combustible. They are temperature-stable up to 900.degree. C. They are regenerable, so that remaining dioxins can be completely destroyed, for example by means of Fenton's reagent (H.sub.2 O.sub.2 +Fe(II) or Fe(III) salts) or by means of another known chemical reaction or thermally. In the process according to the invention, the preponderant part of the dioxins is destroyed directly on the solid.

The amount of H.sub.2 O.sub.2 or of Caro's acid depends on the quantity of dioxin that has to be destroyed. The destruction of dioxin should, to the extent possible, be quantitative.

The H.sub.2 O.sub.2 is added as an aqueous solution with an H.sub.2 O.sub.2 content of 30 to 90 wt %, preferably 50%.

If the waste gas contains no SO.sub.2, SO.sub.2 can be added to the waste gas in an amount of 0.01 to more than 10,000 ppm.

The fixed bed can be impregnated with H.sub.2 SO.sub.4 in an amount up to the saturation of the solid.

The fixed bed can be impregnated with H.sub.2 O.sub.2 at a concentration of 1 to 90 wt % and in an amount up to the saturation of the solid.

An aqueous solution of H.sub.2 SO.sub.4 can be introduced into the waste gas stream in a concentration of 10 to 98 wt % and in an amount of 0.01 to 10 g/m.sup.3 .times.s.sup.-1.

It appears to be essential according to the invention that, apart from H.sub.2 SO.sub.4, H.sub.2 O.sub.2 also is present in the reaction zone. The Caro's acid formed as an intermediate appears to be the effective agent. The waste gas temperature should optionally be above the dewpoint that results from the water content of the waste gas. This is necessary in order to prevent the condensation of water on the fixed bed, which would lead to undesired dilution of the acid.

The process according to the invention has the following advantages:

First, an incombustible catalyst or solid is used, second, the dioxins or the chlorinated organic compounds are not only adsorbed on the solid but also destroyed there substantially quantitatively.

In a continuous test for nitrogen oxide reduction of a waste gas from a refuse incineration plant, parallel dioxin measurements were carried out:

The object was to investigate the behavior of the poly-chlorinated dibenzodioxins and -furans under strongly oxidizing conditions (destruction or adsorption on the catalyst). To this end the experimental plant was operated continuously in 24-hour shift operation over a period of 10 days. After 7 days continuous operation, the actual dioxin measurement started. To this end, gas samples were taken on three successive days, in each case before contact with the catalyst and after contact with the catalyst, over a period of 6 hours. At the end of the test, samples of the catalyst also were taken.

SiO.sub.2 tablets that had been formed from the pyrogenically produced silicon dioxide Aerosil 200 were used as the solid.

In the course of this the following conditions were maintained: Reactor diameter   300 mm Bed height of the fixed bed 400 mm Material: Aerosil 200 tablets 6 .times. 5 mm Volume of the fixed bed 28-30 liters Bulk density ca.   0.5 kg/liter Temperature at the reactor inlet 69-70.degree. C. Temperature at the reactor outlet 69.degree. C. Dew point of the gas ca. 60.degree. C. Pressure drop ca.  110 mm water column Linear velocity    0.6-0.7 meters/second in the reactor Gas throughput ca. 160 m.sup.3 /h .apprxeq. ca. 130 Nm.sup.3 /h moist gas .apprxeq. ca. 104 Nm.sup.3 /h dry gas H.sub.2 O.sub.2 (50%) dosing rate 1 ml/min Average SO2 content ca. 5-15 mg/Nm3 in crude gas Test duration      10 days Mass balance ##STR1## ______________________________________ L = liquid streams G = gas streams I = inlet O = outlet xi = concentration of component i in the liquid phase yi = concentration of component i in the gas phase

The sampling points can be taken from FIG. 1

The results of the measurements are shown in Tables 1 to 9. Table 10 shows results of measurements obtained by a process according to the prior art.

The abbreviations used in the examples have the following meanings: degrees of substitution siloxane) Environment Conditions:

The reactor is operated for 240 hours with 130 Nm.sup.3 /h waste gas with a moisture content of ca. 20% from the refuse incineration plant. Calculation: d=31,200 Nm.sup.3 =Dioxin.sub.reacted +Dioxin.sub.accumulated Exemplary calculation for 1, 2, 3, 6, 7, 8-hexa CDF (TE=0.1) Average inlet concentration, absolute =     3.85 ng/Nm.sup.3 Average outlet concentration =     0.07 ng/Nm.sup.3 Max. concn. on the catalyst (top layer) =     1.1870 ng/g Average concn. on the catalyst =     0.099 ng/g (mixed sample) Dioxin.sub.in = 3.85 .times. 25,000 = 96,250 ng =     100% Dioxin.sub.out = 0.07 .times. 25,000 = 1,750 ng =     1.8% Dioxin.sub.acc. (max.) = 1.1870 .times. 1000 g/kg .times. 15 =     17,805 =     18.5% Dioxin.sub.acc. (average) = 0.099 .times. 1000 .times. 15 =     1,485 =     1.54% ______________________________________

From this, there follows a reaction of 80-97% for this component. The calculation was carried out for all components: see Table 09.

The crude gas stream has an average dioxin contamination of 4.19 ng TE (BGA)/Nm.sup.3 (3.9-4.61).

The average clean gas concentration is 0.014 ng TE(BGA)/Nm.sup.3 (0.010-0.017).

The average proportion of dioxin removed in the system is accordingly 99.67% (see also Table 08).

On the catalyst, there is on average 0.050 ng TE/g catalyst. Peak values in the top catalyst layer are about 0.635 ng TE/g catalyst.

Via the gas stream, ca. 104,750 ng TE are fed in. The amount discharged is ca. 350 ng TE. On the catalyst, ca. 750 ng TE are found. It follows from this that on average 99% of the dioxins are destroyed on the catalyst and ca. 0.7% accumulate over a period of 10 days.

In the period of the test, as well as in the continuous operation of the plant after the test, it is observed that sulphuric acid accumulates on the catalyst. This sulphuric acid comes from the reaction of the residual SO.sub.2 of the flue gas with hydrogen peroxide. It is present on the catalyst in highly concentrated form, since its vapor pressure is distinctly lower than that of water. It is assumed that the dioxins are not oxidized by the hydrogen peroxide but by Caro's acids formed as an intermediate from H.sub.2 O.sub.2 and H.sub.2 SO.sub.4. Mass balances are drawn up for all of the individual components. It is apparent that, by oxidation, the low-chlorinated dioxins and furans up to C.sub.16 are destroyed preferentially. The less poisonous highly chlorinated dioxins and furans up to C.sub.18 are somewhat more slowly oxidized. ______________________________________ Description of the Solid Sampling Conditions and of the Sampling Points Concerned Matrix or point Alloted of removal sample number Description ______________________________________ SiO.sub.2 P 1.1       The SiO.sub.2 tablets are taken by (reference            the operator from a stock bin. sample) SiO.sub.2 P 2.1       After the end of three waste (top layer)           gas sampling series, the catalyst is opened at the top, and the top layer of the SiO.sub.2 fixed bed is removed by the operator. SiO.sub.2 P 2.2       After completion of the above (mixed sample)        sampling and after removing the top layer, the whole catalyst charge is discharged into a vessel by the operator and thoroughly mixed. A sample is taken from the mixing vessel. ______________________________________ __________________________________________________________________________ Description of Measuring and Sampling Points (Technical Data) for Waste Gas Sampling Does the sampling Position of                          point meet the measuring  Duct          Length of Length of requirements of VDI point in Alloted cross- Edge     inflow outflow Guideline 2066, page flue gas sample section.sup.a lengths Diameter section section 1, regarding the path  number (m.sup.2) (m) (m)  (m)   (m)   measuring section? __________________________________________________________________________ Crude gas P 3.1-3 0.03     0.1  0.1   0.1   the sampling was before     (round)                   no not isokinetic; catalyst                             the waste gas samples were taken via a flanged glass tube. Clean gas P 4.1-3 0.03     0.1  0.2   0.2   the sampling was after      (round)                   no not isokinetic; catalyst                             the waste gas samples were taken via a flanged glass tube. __________________________________________________________________________ .sup.a round, square or rectangular __________________________________________________________________________ Survey of Samples and Analyses Sample O.sub.2 normaliz- Sampling Sampling Sample volume ing factor Matrix    date period no. (m.sup.3).sup.b (% O.sub.2 .fwdarw. 11% O.sub.2) PCDF/D __________________________________________________________________________ SiO.sub.2 19.09.91 a     P 1               x (reference sample) SiO.sub.2 19.09.91 a     P 2.1             x (top layer) SiO.sub.2 19.09.91 a     P 2.2             x (mixed sample) Crude gas 17.09.91 0900-1500 P 3.1 10.136 0.98      x before catalyst Clean gas 17.09.91 0900-1500 P 4.1 10.579 0.98      x after catalyst Crude gas 18.09.91 0830-1430 P 3.2 10.043 1.00      x before catalyst Clean gas 18.09.91 0830-1430 P 4.2 10.804 1.00      x after catalyst Crude gas 19.09.91 0730-1330 P 3.3 10.542 0.89      x before catalyst Clean gas 19.09.91 0730-1330 P 4.3 10.296 0.89      x after catalyst __________________________________________________________________________ .sup.a sampling by operator .sup.b referred to 0.degree. C., 1,013 hPa, dry ______________________________________ PCDF/D Concentration in the SiO.sub.2 (Reference Sample: P 1.3, Top Layer: P 2.1, Mixed Sample: P 2.2) Sample number P 1.3     P 2.1    2.2 PCDF/PCDD       ng/g      ng/g     ng/g ______________________________________ Total TetraCDF  b         3.52     0.22 Total PentaCDF  b         5.63     0.41 Total HexaCDF   b         8.16     0.64 Total HeptaCDF  0.004     6.13     0.51 OctaCDF         <0.004    1.54     <0.11 Total Tetra- to OctaCDF 0.004     24.98    1.78 2378-TetraCDF*  <0.0009   0.148    0.010 12378-/12348-PentaCDF.sup.a <0.0014   0.483    0.035 23478-PentaCDF* <0.0014   0.372    0.033 123478-/123479-HexaCDF.sup.a <0.0015   0.880    0.069 123678-HexaCDF* <0.0015   1.187    0.099 123789-HexaCDF  <0.0015   0.070    0.004 234678-HexaCDF  <0.0015   0.816    0.084 1234678-HeptaCDF 0.0038    5.202    0.450 1234789-HeptaCDF <0.0009   0.123    0.010 Total TetraCDD  b         0.14     b Total PentaCDD  b         0.49     0.03 Total HexaCDD   b         0.70     0.05 Total HeptaCDD  b         1.09     0.12 OctaCDD         0.008     1.45     0.18 Total Tetra- to OctaCDD 0.008     3.87     0.38 2378-TetraCDD*  <0.0008   0.011    <0.001 12378-PentaCDD* <0.0011   0.062    0.006 123478-HexaCDD* <0.0023   0.041    <0.004 123678-HexaCDD* <0.0023   0.069    <0.004 123789-HexaCDD* <0.0023   0.043    <0.004 1234678-HeptaCDD <0.0035   0.506    0.062 Total Tetra- to 0.012     23.85    2.16 OctaCDF/C Total PCDF/D according b         1.933    0.148 to GefStoffV* TE (BGA 1984)   <0.0001   0.635    0.050 TE (NATO/CCMS 1988) <0.0001   0.639    0.053 TE (NATO/CCMS incl. 0.0036    0.639    0.056 NWG) ______________________________________ if not specifically mentioned, undetected congeners or homologue groups are not taken into account in totals and toxicity equivalents (TE). .sup.a Congeners not separable chromatographically on SP2331. .sup.b Undetectable. ______________________________________ 2378-TetraCDD Toxicity Equivalent Factors (TEF) According to a Proposal of the BGA, Berlin, and NATO/CCMS BGA     NATO/CCMS PCDF/D           1984    1988 ______________________________________ 2378-TetraCDD    1.0     1.0 12378-PentaCDD   0.1     0.5 123478-HexaCDD   0.1     0.1 123678-HexaCDD   0.1     0.1 123789-HexaCDD   0.1     0.1 1234678-HeptaCDD  0.01    0.01 Octa-CDD          0.001   0.001 2378-TetraCDF    0.1     0.1 12378-PentaCDF   0.1      0.05 23478-PentaCDF   0.1     0.5 123478-HexaCDF   0.1     0.1 123678-HexaCDF   0.1     0.1 123789-HexaCDF   0.1     0.1 234678-HexaCDF   0.1     0.1 1234678-HeptaCDF  0.01    0.01 1234789-HeptaCDF  0.01    0.01 OctaCDF           0.001   0.001 .SIGMA. TetraCDD  0.01   0 .SIGMA. PentaCDD  0.01   0 .SIGMA. HexaCDD   0.01   0 .SIGMA. HeptaCDD  0.001  0 .SIGMA. TetraCDF  0.01   0 .SIGMA. PentaCDF  0.01   0 .SIGMA. HexaCDDF  0.01   0 .SIGMA. HeptaCDF  0.001  0 ______________________________________

The TE value of a sample is calculated by multiplying the concentration concerned by the corresponding TEF and adding the products. It should be taken into account that the calculated total values do not contain the 2378-Cl-substituted congeners of the homologue group concerned. ______________________________________ PCDF/D Concentration in the Crude Gas before the Catalyst (P 3.1-3) Reference state: 0.degree. C., 1,013 hPa, dry, normalized to 11% O.sub.2 Sample number P 3.1    P 3.2    P 3.3 PCDF/PCDD         ng/m.sup.3 ng/m.sup.3 ng/m.sup.3 ______________________________________ Total TetraCDF    58.3     42.0     50.3 Total PentaCDF    56.1     47.1     49.7 Total HexaCDF     27.5     27.0     37.0 Total HeptaCDF    15.9     16.1     17.4 OctaCDF           3.6      4.9      <1.8 Total Tetra- to OctaCDF 161.4    137.1    154.4 2378-TetraCDF     1.61     1.55     1.78 12378-/12348-PentaCDF.sup.a 5.13     4.28     4.30 23478-PentaCDF    2.21     2.38     2.84 123478-/123479-HexaCDF.sup.a 3.21     3.22     4.45 123678-HexaCDF    3.40     3.39     4.75 123789-HexaCDF    0.23     0.29     0.30 234678-HexaCDF    1.94     3.03     3.42 1234678-HeptaCDF  12.57    12.07    14.13 1234789-HeptaCDF  0.40     0.59     0.36 Total TetraCDD    3.8      4.9      5.8 Total PentaCDD    8.8      10.6     12.1 Total HexaCDD     7.2      9.3      9.5 Total HeptaCDD    9.2      8.8      10.0 OctaCDD           10.8     11.9     10.6 Total Tetra- to OctaCDD 39.8     45.5     48.0 2378-TetraCDD     0.39     0.37     0.44 12378-PentaCDD    1.19     1.21     1.61 123478-HexaCDD    0.40     0.45     0.53 123678-HexaCDD    0.67     0.84     0.87 123789-HexaCDD    0.59     0.77     0.85 1234678-HeptaCDD  4.45     4.49     4.89 Total Tetra- to   201.2    182.6    202.4 OctaCDF/D TE (BGA 1984)     4.05     3.90     4.61 TE (NATO/CCMS 1988) 3.74     3.92     4.78 TE (NATO/CCMS incl. NWG) 3.74     3.92     4.78 ______________________________________ If not specifically mentioned, undetected congeners or homologue groups are not taken into account in totals and toxicity equivalents (TE). .sup.a Congeners not separable chromatographically on SP2331. ______________________________________ PCDF/D Concentration in the Clean Gas after the Catalyst (P 4.1-3) Reference state: 0.degree. C., 1,013 hPa, dry, normalized to 11% O.sub.2 Sample number P 4.1     P 4.2   P 4.3 PCDF/PCDD        ng/m.sup.3 ng/m.sup.3 ng/m.sup.3 ______________________________________ Total TetraCDF   b         0.07    0.03 Total PentaCDF   0.05      0.07    0.03 Total HexaCDF    0.15      0.17    0.10 Total HeptaCDF   0.20      0.26    0.16 OctaCDF          0.32      0.36    0.09 Total Tetra- to  0.72      0.93    0.41 OctaCDF 2378-TetraCDF    <0.004    0.004   0.003 12378-/12348-PentaCDF.sup.a 0.008     0.008   0.005 23478-PentaCDF   0.008     0.007   0.004 123478-/123479-  0.028     0.021   0.014 HexaCDF.sup.a 123678-HexaCDF   0.017     0.019   0.012 123789-HexaCDF   <0.003    <0.007  <0.002 234678-HexaCDF   0.037     0.042   0.027 1234678-HeptaCDF 0.146     0.184   0.114 1234789-HeptaCDF 0.007     0.016   0.009 Total TetraCDD   b         b       b Total PentaCDD   b         b       b Total HexaCDD    b         b       b Total HeptaCDD   0.15      0.19    0.12 OctaCDD          0.68      0.84    0.52 Total Tetra- to  0.83      1.03    0.64 OctaCDD 2378-TetraCDD    <0.002    <0.003  <0.003 12378-PentaCDD   <0.004    <0.005  <0.004 123478-HexaCDD   <0.012    <0.005  <0.013 123678-HexaCDD   <0.012    <0.005  <0.013 123789-HexaCDD   <0.012    <0.005  <0.013 1234678-HeptaCDD 0.088     0.108   0.073 Total Tetra- to  1.55      1.96    1.05 OctaCDF/D TE (BGA 1984)    0.014     0.017   0.010 TE (NATO/CCMS 1988) 0.016     0.017   0.010 TE (NATO/CCMS incl. 0.024     0.024   0.020 NWG) ______________________________________ If not specifically mentioned, undetected congeners or homologue groups are not taken into account in totals and toxicity equivalents (TE). .sup.a Congeners not separable chromatographically on SP2331. .sup.b Undetectable ______________________________________ Proportions of PCDF/D Decomposed After the Catalyst (P 4.1-3) Sample number P 4.1     P 4.2     P 4.3 Proportion removed %         %         % ______________________________________ Total TetraCDF b         99.83     99.94 Total PentaCDF 99.91     99.85     99.94 Total HexaCDF  99.46     99.37     99.73 Total HeptaCDF 98.72     98.39     99.08 OctaCDF        91.11     92.65     <95.00 Total Tetra- to OctaCDF 99.56     99.32     99.73 2378-TetraCDF  >99.75    99.74     99.83 12378-/12348-PentaCDF.sup.a 99.84     99.81     99.88 23478-PentaCDF 99.64     99.71     99.85 123478-/123479-HexaCDF.sup.a 99.13     99.35     99.69 123678-HexaCDF 99.50     99.44     99.75 123789-HexaCDF >98.70    >97.59    >99.33 234678-HexaCDF 98.09     98.61     99.21 1234678-HeptaCDF 98.84     98.48     99.19 1234789-HeptaCDF 98.25     97.29     97.50 Total TetraCDD b         b         b Total PentaCDD b         b         b Total HexaCDD  b         b         b Total HeptaCDD 98.37     97.84     98.80 OctaCDD        93.70     92.94     95.09 Total Tetra- to OctaCDD 97.91     97.74     98.67 2378-TetraCDD  >99.49    >99.19    >99.32 12378-PentaCDD >99.66    >99.59    >99.75 123478-HexaCDD >97.00    >98.89    >97.55 123678-HexaCDD >98.21    >99.40    >98.51 123789-HexaCDD >97.97    >99.35    >98.47 1234678-HeptaCDD 98.02     97.59     91.80 Total Tetra- to OctaCDF 99.23     98.93     99.48 TE according to . . . BGA/UBA 1984   99.65     99.93     99.78 NATO/CCMS 1988 99.57     99.95     99.79 TE (NATO/CCMS incl. NWG) 99.36     99.89     99.58 ______________________________________ Undetected congeners or homologue groups are not taken into account in totals and toxicity equivalents (TE). .sup.a Congeners not separable chromatographically on SP2331. .sup.b Not calculable ______________________________________ Percentage Contents of the Individual Components and Conversions In the Top    middle % con- layer % average version %       %       max on % on   aver- Components inlet   outlet  catalyst catalyst age ______________________________________ Sum TetraCDF 100.00  0.07    4.21   0.26   99.67 Sum PentaCDF 100.00  0.10    6.63   0.48   99.42 Sum HexaCDF 100.00  0.46    16.05  1.26   98.28 Sum HeptaCDF 100.00  1.26    22.34  1.86   96.89 OctaCDF    100.00  9.06    32.61  0.00   90.94 Sum Tetra- 100.00  0.45    9.93   0.71   98.84 to OctaCDF 2378-TetraCDF 100.00  0.14    5.39   0.36   99.49 12378-/12348- 100.00  0.15    6.34   0.46   99.39 PentaCDF 23478-PentaCDF 100.00  0.26    9.01   0.80   98.94 123478-/123479- 100.00  0.58    14.56  1.14   98.28 HexaCDF 123678-HexaCDF 100.00  1.74    18.51  1.54   96.71 123789-HexaCDF 100.00  0.00    15.37  0.88   99.12 234678-HexaCDF 100.00  1.26    17.51  1.80   96.93 1234678-   100.00  1.15    24.15  2.09   96.77 HeptaCDF 1234789-   100.00  2.37    16.40  1.33   96.30 HeptaCDF Sum TetraCDD 100.00  0.00    1.74   0.00   100.00 Sum PentaCDD 100.00  0.00    2.80   0.17   99.83 Sum HexaCDD 100.00  0.00    4.85   0.35   99.65 Sum HeptaCDD 100.00  1.64    7.01   0.77   97.59 OctaCDD    100.00  6.13    7.84   0.97   92.90 Sum Tetra- to 100.00  1.88    5.23   0.51   97.61 OctaCDD 2378-TetraCDD 100.00  0.00    0.15   0.00   100.00 12378-PentaCDD 100.00  0.00    2.78   0.27   99.73 123478-HexaCDD 100.00  0.00    5.35   0.00   100.00 123678-HexaCDD 100.00  0.00    5.22   0.00   100.00 123789-HexaCDD 100.00  0.00    3.50   0.00   100.00 1234678-   100.00  1.95    6.59   0.81   97.25 HeptaCDD Sum Tetra- to 100.00  0.78    8.86   0.66   98.56 OctaCDF/D ______________________________________

It has been established that at a crude gas concentration of ca. 4.2 ng TE/m.sup.3 ca. 99.67% of the PCDD/F's are removed from the gas. Ca. 0.7% accumulates on the catalyst. On average, 98.95 is destroyed oxidatively. The individual component analyses showed that the lower-chlorinated (and with that, more poisonous) compounds up to C.sub.16 are oxidized preferentially. The so-called Seveso dioxin (2,3,7,8-TCDD) is completely destroyed. It is assumed that the residual SC content of the flue gas plays a decisive role for the oxidation reaction. In the course of this, SO.sub.2 is very probably converted with H.sub.2 O.sub.2 via the H.sub.2 SO.sub.4 stage to H.sub.2 SO.sub.5 (Caro's acid). It has further been established that sulphuric acid concentrates on the catalyst. This sulphuric acid can form Caro's acid with the hydrogen peroxide. The oxidizing action of Caro's acid is considerably greater than that of hydrogen peroxide alone, and is supposed to be sufficient to destroy dioxins.

The following methods were used in making the measurements: HRGC/LRMS system (MSD) was used; and for the analysis after the reactor the HRGC/HRMS system. The sample was taken with the XAD-z cartridges with C-1234 TetraCDD standard. __________________________________________________________________________ PCDD/CDF Waste Gas Cleaning in Refuse Incineration Plants PCDD/PCDF Concentration Waste Gas Incineration PCDD/PCDF Waste Gas in ng TE/m.sup.3 Amount, Plant     Cleaning     Crude Gas Clean Gas m.sup.3 /h __________________________________________________________________________ Pilot Plants MVA Dusseldorf Activated coke adsorber 2.4-2.7.sup.(1) 0.022-0.025 2,000 MVA Stapelfeld Activated coke adsorber 1.6-5.8.sup.(1) 0.026-0.079 100 MVA Flozersteig Activated coke adsorber 0.6-1.0.sup.(1) 0.03-0.05 200 SMVA Simmering Activated coke adsorber 1.0-9.3.sup.(1) 0.05  200 Operating Plants SMVA Schoneiche Dry additive process 0.34-1.74.sup.(2) 0.011-0.022 17,000 with addition of activated coke MVA Neufahrn Dry additive not measured 0.09  18,000 process.sup.(3) MVA Dusseldorf Hearth-type furnace 1-5.sup.(5) <0.1.sup.(4) 3 .times. 160,000 coke/activated coke adsorber RZR Herten Hearth-type furnace 1-5.sup.(5) <0.1.sup.(4) 70,000 coke/activated coke adsorber __________________________________________________________________________ .sup.(1) measured after the removal stages for dust, halogens and sulphur dioxide. .sup.(2) after steam generator .sup.(3) without special steps for cleaning PCDD/PCDF from waste gas .sup.(4) design value .sup.(5) after electrofilter MVA = refuse incineration plant SMVA = special waste incineration plant Source:Statutory regulations and measures for limiting dioxin and furan pollution, Prof. Dr. Ing, Michael Lange, VBA Berlin Lecture at VDA Meeting, 17-18/September/1991, Munich

## Claims

1. A process for removing halogenated organic compounds selected from the group consisting of polychlorinated dibenzodioxins and polychlorinated dibenzofurans from waste gases containing said halogenated organic compounds which comprises contacting said waste gases with Caro's acid or an aqueous solution of its salt.

2. A process as set forth in claim 1 in which the waste gases are led through a fixed bed or fluidized bed of a solid where it is contacted with Caro's acid.

3. A process according to claim 1 or claim 2 in which the waste gas is supplemented with SO.sub.2 and contacted with H.sub.2 O.sub.2, whereby Caro's acid is produced in situ.

4. A process according to claim 1 in which the waste gas is led through a fixed bed or fluidized bed of a solid and at the same time a mixture of H.sub.2 O.sub.2 and H.sub.2 SO.sub.4 is sprayed onto the solid.

5. A process according to claim 2 or claim 4 in which, before the solid is introduced into the waste gas stream, it is impregnated with H.sub.2 SO.sub.4 and H.sub.2 O.sub.2 is applied.

6. A process according to claim 2 or claim 4 in which, before the solid is introduced into the waste gas stream, it is impregnated with H.sub.2 O.sub.2 and H.sub.2 SO.sub.4 is applied.

7. A process according to claim 2 in which, before the solid is introduced into the waste gas stream, it is impregnated with Caro's acid or with an aqueous solution of its salt.

8. A process according to claim 2 in which, before the solid is introduced into the waste gas stream, it is sprayed with Caro's acid or with an aqueous solution of its salt.

9. A process as set forth in claim 1 in which said waste gas also contains NO.sub.x.