JP4300351B2 - Denitration catalyst regeneration method - Google Patents

Description

  The present invention treats exhaust gas in which sulfur oxides coexist, such as waste incinerator exhaust gas, at a relatively low temperature (150 ° C. to 300 ° C.) and catalytically reduces nitrogen oxides in the exhaust gas using an ammonia reducing agent. The present invention relates to a method for regenerating a denitration catalyst that has been poisoned by the accumulation of sulfur oxides and sulfates in the catalyst.

  A denitration catalyst that treats exhaust gas in which sulfur oxides coexist at a temperature in the range of 150 ° C. to 300 ° C. and catalytically reduces nitrogen oxides in the exhaust gas using an ammonia reducing agent. Many methods for regenerating a poisoned catalyst have been proposed (see Patent Documents 1 to 4).

Among these conventional techniques, there are a method in which a deteriorated catalyst is regenerated by washing with an alkaline aqueous solution, a method in which the deteriorated catalyst is regenerated by washing with an acid aqueous solution, a method of regenerating by heating, and a method of regenerating by water washing.
JP 2000-102737 A JP 2000-107612 A JP 2001-113131 A JP-A-8-229402

When sulfur oxides coexist in the exhaust gas, they are strongly adsorbed on the catalyst and the denitration performance is lowered. In particular, this phenomenon appears remarkably in exhaust gas of 250 ° C. or lower such as a garbage incinerator. In the proposed regeneration method, the deteriorated catalyst is regenerated by washing with an alkaline aqueous solution or an acid aqueous solution. The management of the cleaning solution is complicated, and the catalyst component and binder component are eluted in the cleaning solution, resulting in a decrease in catalyst strength. There is a problem to do. In addition, the method for regenerating the deteriorated catalyst by heating requires a high temperature of 500 ° C. or higher to completely desorb the sulfur oxide, and requires equipment for allowing NH ₃ to coexist in the heated gas. Furthermore, since the heating temperature is high, there is a concern about catalyst sintering. In addition, in the method of regenerating a deteriorated catalyst by washing with water, the washing of sulfur oxides and sulfates cannot be sufficiently performed by washing alone, and remains in the catalyst. Therefore, although the initial performance is restored, the degree of performance deterioration with use time is large. I hate being.

  A denitration catalyst that treats exhaust gas in which sulfur oxides coexist, such as waste incinerator exhaust gas, at a relatively low temperature to catalytically reduce nitrogen oxides in the exhaust gas. In order to regenerate, it is important to completely remove sulfur oxides and sulfates accumulated in the catalyst from the viewpoint of initial performance and durability.

  In view of the above, the present invention provides a method for effectively regenerating a poisoned catalyst by accumulating sulfur oxide and sulfate in the catalyst by a simple and simple method.

When sulfur oxides coexist in the exhaust gas at a temperature of 250 ° C. or lower, the NOx removal performance is generally reduced by sulfur oxide (SOx), moisture (H ₂ O), and ammonia (NH ₃ ) as a reducing agent. This is thought to be due to precipitation of ammonium sulfate, acidic ammonium sulfate, etc. produced by the reaction with the catalyst surface.

  In order to solve the above problems, the present inventors have paid attention to the following.

(1) Ammonium sulfate, acidic ammonium sulfate, and sulfur oxide are water-soluble compounds, but cannot be completely removed from the catalyst by washing with water alone.

(2) In order to remove sulfur compounds accumulated in the catalyst by washing with water, the pH of the washing solution is preferably as high as possible.

(3) In the regeneration method with only washing, the catalyst components are also eluted, so the performance is lowered.

  Focusing on this knowledge, it is possible to completely dissolve and remove sulfur oxides and sulfates accumulated in the catalyst by washing with an aqueous solution containing ammonia roots and containing vanadium and / or tungsten. A recycling method that can also re-support the components has been completed.

That is, the present invention is a playback method of denitration catalyst for catalytic reduction with ammonia reducing agent of nitrogen oxides in an exhaust gas sulfur oxides coexist at a temperature ranging from 0.99 ° C. to 300 ° C., ammonia roots This is a method for regenerating a denitration catalyst, characterized in that, by washing with an aqueous solution containing vanadium and / or tungsten, sulfur oxides and sulfate accumulated in the catalyst are mainly removed by elution and then calcined.

In the present invention, ammonia roots serves to keep relatively high pH in an aqueous solution, vanadium and / or tungsten elution of the sulfur compounds that have accumulated in the catalyst relatively easily allowed to proceed further coexist in the aqueous solution The sulfur compound can be more completely eluted by promoting the exchange reaction between the sulfur compound and the sulfur compound. At the same time, elution of the catalyst components vanadium and tungsten is partly caused, leading to performance degradation. However, since vanadium and / or tungsten coexist in the aqueous solution, the elution occurs in the aqueous solution. Vanadium and / or tungsten can be re-supported, and there is no fear of performance degradation.

  By the regeneration method of the present invention, sulfur oxides and sulfates accumulated in the catalyst can be completely eluted and removed, and the regenerated catalyst exhibits the same performance as the fresh catalyst in both initial performance and durability performance.

Next, in order to specifically explain the present invention, some examples of the present invention and comparative examples for showing comparison with the examples will be given. However, Example 2 does not belong to the present invention and is shown as a reference example.

Example 1
(1) Preparation of catalyst Ceramic paper composed of ceramic fibers (thickness: 0.5 mm) was impregnated with a titania colloid solution (solid content: 32% by weight) obtained by the nitrate hydrolysis method. After drying at 0 ° C., it was calcined at 400 ° C. for 3 hours to obtain a plate-like carrier holding anatase-type titania at 120 g / m ² .

This plate-like carrier was immersed in a saturated aqueous solution of ammonium metavanadate at room temperature and baked at 250 ° C. for 1 hour. Next, this was immersed in a 0.5 mol / l aqueous solution of WO ₃ and calcined at 400 ° C. for 1 hour to obtain a denitration catalyst. The initial performance of this catalyst was measured.

(2) Denitration performance The performance of the catalyst is based on the assumption that the denitration reaction is the primary reaction of NOx, and the reaction rate constant “K” (K = − (AV) ln (1-x) when NOx / NH ₃ ratio = 1.0. , AV is defined as the ratio “K / K ₀ ” of the amount of exhaust gas per geometric surface area of the catalyst, x: denitration rate) and the initial reaction rate constant “K ₀ ” without any deterioration treatment. Therefore, K / K ₀ = 1 in the initial state.

(3) Preparation of deteriorated catalyst First, the reactor was charged with the above-mentioned denitration catalyst so that the area velocity AV in the catalyst bed was 50 Nm / hour. here,
Next, these gases are injected into the reactor so that the exhaust gas temperature on the catalyst bed is 180 ° C., SO ₃ 20 ppm in the exhaust gas, O ₂ 15%, H ₂ O 10%, NO _X 80 ppm, NH ₃ 80 ppm. The denitration reaction was performed for a long time. Under these conditions, ammonium sulfate seems to be depositing on the catalyst, and the denitration performance gradually decreases with time, and the performance was measured for a certain period of time. Performance and SO ₃ storage amount at that time is shown in Table 1.

(4) Catalyst regeneration After measuring the performance, the deteriorated catalyst was removed from the reactor, washed with an aqueous solution containing ammonium metavanadate (4.5 g / l) for 1 hour, dried and calcined, and regenerated. The performance of this regenerated catalyst was measured. The results are shown in Table 1 (initial). The performance of the initial regeneration catalyst almost recovered, and almost no SO ₃ accumulation was observed.

Further, using this regenerated catalyst, a denitration reaction was performed under the same conditions as in the above step (3) “Preparation of deteriorated catalyst”, and performance was measured in the same manner as described above after a certain period of time. The results are shown in Table 1 (endurance).

As can be seen from Table 1, the performance of the durable regenerated catalyst and the accumulated amount of SO ₃ are similar to the performance of the initially regenerated catalyst and the accumulated amount of SO ₃ , and the regenerated catalyst has the same initial performance and durability as the fresh catalyst. Showed the performance.

Example 2
Catalyst regeneration In step (4) catalyst regeneration in Example 1, the degraded catalyst prepared in step (3) “Preparation of degraded catalyst” was first washed with water, and then ammonium metavanadate (4.5 g / l) was added. The operation was performed in the same manner as in step (4) of Example 1, except that the aqueous solution was washed for 1 hour, dried and fired. The results are shown in Table 2.

  From Table 2, it was confirmed that the regenerated catalyst showed the same performance as the fresh catalyst in both initial performance and durability performance.

Comparative Example 1
Catalyst regeneration In step (4) catalyst regeneration of Example 1, the degraded catalyst prepared in step (3) “Preparation of degraded catalyst” is washed with water and then contains ammonium metavanadate (4.5 g / l). The operation was carried out in the same manner as in step (4) of Example 1 except that it was dried without washing with an aqueous solution. The results are shown in Table 3.

From Table 3, it was found that the regenerated catalyst had lower performance than the fresh catalyst in both initial performance and durability performance. As this factor, only washing with water is considered to be due to not fully eluted S0 ₃ which has accumulated in the catalyst, it is a large difference in the particular durability.

Compressive strength Table 4 shows the compressive strength ratio before and after catalyst regeneration shown in step (4) “Catalyst regeneration” in Example 1. From Table 4, it can be seen that no decrease in compressive strength is observed due to catalyst regeneration. In Table 4, compression strength ratio = compression strength after reproduction / compression strength before reproduction.

Claims (1)

A reproducing method of denitration catalyst sulfur oxide is catalytically reduced with ammonia reducing agent in a range of nitrogen oxides temperature 0.99 ° C. to 300 ° C. in an exhaust gas coexisting include ammonia roots, vanadium and / or A method for regenerating a denitration catalyst, characterized in that the sulfur oxide and sulfate accumulated in the catalyst are eluted and removed mainly by washing with an aqueous solution containing tungsten, followed by calcination.