A PROCESS FOR LOW TEMPERATURE GAS CLEANING AND A CATALYST FOR USE IN THE PROCESS

Abstract

A process for the cleaning of a lean gas stream contaminated with volatile organic compounds and/or sulfur-containing compounds comprises the steps of adding ozone to the contaminated lean gas stream and contacting the resulting ozone-containing gas stream with a catalytic device at a temperature down to room temperature. Depending on the content of particulates in the lean gas stream, the catalytic device is either a monolithic catalyst or a catalytic bag filter, both impregnated with a catalyst containing one or more metal oxides, in which the metal is selected from vanadium, tungsten, palladium and platinum.

Claims

1. A process for the cleaning of a lean gas stream contaminated with volatile organic compounds and/or sulfur-containing compounds, said process comprising adding ozone to the contaminated lean gas stream, and contacting the resulting ozone-containing gas stream with a catalytic device at a temperature down to room temperature, wherein, depending on the content of particulates in the lean gas stream, the catalytic device is either a monolithic catalyst or a catalytic bag filter, both impregnated with a catalyst containing one or more metal oxides, in which the metal is selected from vanadium, tungsten, palladium and platinum.

2. Process according to claim 1, wherein the catalytic device is a monolithic catalyst.

3. Process according to claim 1, wherein the catalytic device is a catalytic bag filter.

4. Process according to claim 1, wherein the catalyst carrier is titanium dioxide.

5. Process according to claim 1, wherein the metal of the catalyst is vanadium.

6. Process according to claim 1, wherein the temperature is between 20 and 200 C.

7. Process according to claim 6, wherein the temperature is lower than 50 C.

8. Process according to claim 1, wherein particulates are removed from the lean gas stream by passing the gas stream through a non-catalytic bag filter.

9. Process according to claim 1, wherein particulates are removed from the lean gas stream by electrostatic precipitation (ESP).

10. Process according to claim 3, wherein the catalytic bag filter comprises two or three layers of filter fabric, of which the outer layer captures particulates, while the inner layer is impregnated with the selected catalyst substance.

11. Process according to claim 10, wherein the inner layer of the catalytic bag filter contains a catalytic substance which is especially efficient in removing ozone, while the other layers contain catalytic substances which are more efficient for VOC removal.

Description

[0032] The invention is illustrated in more detail with reference to the appended Figures.

[0033] FIG. 1 shows the simple layout of the process according to the invention. Pure O.sub.2 is fed to an ozone generator A, in which the O.sub.2 stream is converted into a mixture of O.sub.2 and O.sub.3. For instance, in a 30 kW ozone generator, a 30 kg/h stream of pure O.sub.2 is converted to 2.7 kg/h O.sub.3 and 27.3 kg/h O.sub.2. An 8 kW air-water cooling unit B is coupled to the ozone generator A. Instead of pure O.sub.2, it is possible to use air as feed to the ozone generator.

[0034] To the gas stream g, which is to be cleaned, for instance 18000 kg/h, the mixture of 2.7 kg/h O.sub.3 and 27.3 kg/h O.sub.2 is added, and the resultant gas stream is passed over the ozone catalyst C. The result is 18030 kg/h of cleaned effluent gas.

[0035] FIG. 2 illustrates a working example of performance, as described in detail in the example which follows.

EXAMPLE

[0036] The tested catalyst was a catalyst normally used for DeNOx and VOC removal purposes (TiO.sub.2 carrier with V, W and Pd). The idea of the invention is to add ozone to this specific catalyst.

[0037] The feed to the 9 kW heater (see FIG. 2) is 600-1000 m.sup.3/hr air, and xylene is injected into the heater as an exemplary VOC (pollutant), the removal of which is measured. After the heater, ozone (O.sub.3) is injected.

[0038] The table below shows the results, which were found:

TABLE-US-00001 Flow X.sub.in X.sub.out T.sub.in XO.sub.3 m.sup.3/hr ppm ppm C. ppm RE O.sub.3/VOC 150 80 32 21.5 90 60% 1.125 150 29.8 12.2 21.2 48 59% 1.611 150 32 7 21.2 60 78% 1.875 150 33 3 74 100 90% 3.03

[0039] In the table, X.sub.in and X.sub.out are the concentrations in ppm of VOCs into and out of the catalyst, respectively. XO.sub.3 is the concentration of ozone (O.sub.3) into the catalyst, O.sub.3/VOC is the ratio between ozone and VOC into the catalyst, calculated from the concentrations, and RE is the removal efficiency of VOC calculated from the calculations.

[0040] Efficient removal of the VOC was seen even at room temperature. Ozone was destroyed by the catalyst, resulting in a gas with a reduced VOC content and no ozone.