DE4026104C1 - Nitrogen oxide(s) removal from waste gases - by using and carbon-contg. catalyst treated with e.g. hydrochloric acid - Google Patents

Abstract

NOx is removed from waste gases with the aid of NH3 using as catalyst a C-contg. material which has (A) been treated with a mixt. of 5-20 pref. 5-15% HCl and 1-8, pref. 2-4% HNO3 for 5-60 min. and (B) been dried at 200 deg.C or above in a stream of N2 after removal of the acid mixt.. The waste gas from the drying is condensed and recycled. ADVANTAGE - More active catalyst than known ones reducing previously experienced losses of NH3 to a min..

Description

The invention relates to a method for producing a Catalyst for removing nitrogen oxides from exhaust gases with the addition of ammonia, the catalyst consists of a carbon-containing material that with is treated with a hydrogen chloride solution. Such one The method is known from DE-PS 23 50 498. Doing so a carbonaceous adsorbent such. B. activated carbon, with aqueous hydrogen halide solution, e.g. B. Hydrogen chloride solution, impregnated. Through the halogen treatment becomes the catalytic activity of the carbonaceous Materials increased in the presence of Ammonia gas at temperatures of 60-150 ° C with nitrogen oxides is brought into contact. In the manufactured Catalyst is disadvantageous in that the resistance to H₂O steam is comparatively low.  

Furthermore, it is known from DE-OS 38 42 527, gaseous Hydrogen halide, e.g. B. hydrogen bromide, for doping of carbonaceous material. Here the halogen is applied from an inert gas stream, an improved catalyst for separation to obtain nitrogen oxides with the addition of ammonia. The disadvantage of these catalysts is that a higher Ammonia slip occurs.

The invention is based on a method for Production of a catalyst of the type mentioned at the beginning, based on the task of taking this procedure Avoiding the disadvantages of the aforementioned state of the Technology continues to improve to the effectiveness of afterwards produced catalyst to increase.

This task is characterized by the in the characterizing part of the claim resolved characteristics.

Experiments have surprisingly shown that by the treatment of carbon-containing Adsorbents with a mixed solution considerably more effective catalysts for the reduction of nitrogen oxides can be generated by means of NH₃.

In addition, these catalysts have a high resistance towards water vapor. The NH₃ content of the exhaust gas significantly reduced. At the same time, a burden of Environment avoided.

The contact time can be adapted to the starting material will. With lighter material - e.g. B. 540 g / l - can Contact time may be less than with denser material - e.g. B. 560 g / l.  

Test results are shown in Tables 1 to 3 listed the improved effectiveness of the invention manufactured catalysts over conventional Catalysts for the reduction of nitrogen oxides by means of NH₃ from the levies of coal-fired power plants, from Have waste-to-energy plants and earth remediation plants.

In detail, Table 1 shows that the NO- Removal from exhaust gases from coal-fired power plants by means of catalysts, which are treated with different mixed solutions compared to untreated activated carbons Sales increase of approx. 43 to approx. 66 to 69% in one simultaneous ammonia slip of zero% has been achieved is. Compared to catalysts treated with bromine vapor has been, there is still an increase in NO sales approx. 61% to 66 to 69% have been achieved.

As can be seen from Table 2, in which the denitrification of Exhaust gases from waste heat and power plants represented by catalysts  is, when using mixed solutions treated catalysts over untreated Activated carbons NO sales increases at the same Bulk height in the reactor from 76 to 98.5% and opposite bromide-steamed catalysts of approx. 96 to 98.5% be achieved.

When using the catalysts treated with mixed solutions were able to do more with reduced dumping heights relative improvements in NO sales are determined.

It was also surprisingly found that with Mixed solution treated catalysts after 800 hours of operation an increase in activation occurred while at bromide treated catalysts deactivation already started at 100 h operating time.

The increase in activation took place, although in waste-to-energy plants compared to a high water vapor content of 28% 9.8% is the rule for coal-fired power plants.

It should also be noted that the more favorable values for the ammonia slip in soaked with mixed solution Catalysts.

As Table 3 shows, the denitrification of the exhaust gases of soil remediation plants, could use catalysts, that have been treated with mixed solutions, NO conversion rate of 75% compared to approx. 22% for activated carbons and approx. 70% for steam-treated catalysts can be achieved.  

Special mention should be made of the strong deactivation experience the untreated activated coke after 100 hours of operation has only 8.5% NO conversion rate compared to 55.5% for those treated with bromine and 63% for those treated with mixed solution Catalysts.

There are also considerable differences with regard to the ammonia slip, which is more favorable in the case of catalysts treated with mixed solutions than in the case of bromide-steamed and much more favorable than in the case of untreated activated carbons.

Claims (1)

A process for producing a catalyst for removing nitrogen oxides from waste gases under addition of ammonia, wherein the catalyst comprises a carbon-containing material which is treated with a solution of hydrogen chloride, characterized in that the carbonaceous material with a mixed solution of 5 to 20%, in particular 5 to 15% HCl and 1 to 8%, in particular 2 to 4% HNO₃ treated with a contact time of 5 to 60 min and after draining the mixed solution at 200 ° C or higher in a stream of N₂, the Exhaust gas from the N₂ treatment is condensed and recycled.