JPS5820234A - Method for washing catalyst - Google Patents

Abstract

PURPOSE:To reactivate catalytic properties, by a method wherein the gas passing surface of a catalyst layer is divided into plural sections to wash the same successively as well as waste water with low contamination degree is utilized as washing water of the next section to carry out economical washing. CONSTITUTION:The gas passing surface of a catalyst layer 4 is divided into plural sections 4-a, 4-b, 4-c and a washing nozzle 5 is provided so as to be opposed to the gas passing surface as well as a washing liquid receiving tray 6 is provided at every sections below the catalyst layer 4. In this structure, fresh washing water 14 is sprayed toward the catalyst layer 4 from the upper part of said layer 4 through a valve 15-a, a washing nozzle 5-a to wash out and elute the alkali metal component contained in the catalyst composition. After this treatment, the receiving tray 6 receives waste water but waste water 7 containing contaminating substances at high concn. is discarded and a liquid after washing with low contamination degree is supplied to the next section to be succeedingly used in washing. As referred above, the catalyst composition is washed by water in an apparatus to reactivate catalitic properties by a small amount of water within a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for revitalizing the performance of a catalyst packed in an actual device due to accumulation of poisonous substances during use when its performance is lowered by washing with water, and a method for carrying out water washing more economically. 0 A denitrification reaction in which exhaust gas from burning coal or oil is passed through a catalyst to reduce and detoxify nitrogen oxides in the exhaust gas.
- When alkali or alkaline earth metals (potassium, sodium, magnesium, etc.) contained in dust in combustion exhaust gas accumulate in various catalysts used in reactions that oxidize and burn carbon oxides or hydrocarbons, resulting in a decrease in performance. This is a particularly effective means.

Alkali metals such as potassium and sodium are poisonous substances that inhibit catalyst active sites in catalytic reactions targeting combustion exhaust gas, such as denitrification catalysts and combustion catalysts, so it is desirable to reduce their content as much as possible, but they are not used in synthesis reactions. Unlike conventional catalysts, the main purpose of exhaust gas treatment catalysts is to improve the environment, and there is no consideration given to pre-treating the exhaust gas to protect catalyst activity and lifespan. Increasingly, dust is becoming a source of exhaust gas that has negative effects on catalysts depending on its amount and composition, and the catalysts used there are now required to be resistant to dust poisoning.

The present inventors have also developed a denitrification catalyst that is optimal for reducing and removing nitrogen oxides contained in the above exhaust gas with ammonia,
By changing the catalyst composition, shape, and manufacturing method to suit each exhaust gas source,
We provide highly active and long-lasting denitrification equipment, and many commercial machines are already in smooth operation in boilers at thermal power plants and various chemical plants.

That is, with a clean gas that does not contain dust or SOx, such as an LNG-fired boiler, there is no concern about SOx resistance or dust blockage resistance, so At, 0. There is no practical problem with carriers with insufficient SOX resistance, such as At20, because they are inexpensive.
3 to y20. , WO3, Fe, 03, MoO
Catalysts are used in combination with active ingredients such as s, and there is no concern about dust clogging, so catalysts shaped into granules, cylinders, ellipses, etc. are used in fixed beds. And there is almost no dust in the exhaust gas (it is no exaggeration to say that there is no deterioration in performance due to dust).

On the other hand, for dirty gas containing dust and SOx, such as heavy oil-fired boilers and coal-fired boilers, the optimal catalyst specifications are selected by considering SOx resistance, dust toxicity resistance, dust clogging resistance, dust abrasion resistance, etc. TiO2
Since it has sufficient SOx resistance by using T as a carrier, T
A catalyst is used in which 1O2 is combined with active components such as ■203, WO3, 20g of Fe, and MoO3. In addition, as catalyst shapes that do not become clogged with dust, catalysts shaped into granules, cylinders, ellipsoids, etc. as mentioned above are used in the moving method, catalyst structures such as plates, pipes, honeycombs, etc. are used as fixed bed catalysts. A method of passing exhaust gas in a parallel flow was compared and studied, and now honeycomb catalysts, which are economical and easy to maintain, are the mainstream. High-efficiency honeycomb catalysts have been developed, and there are virtually no problems in practical use.

However, the only way to prevent dust components from entering the catalyst and reducing catalyst performance is to soften the effect as much as possible by creating a catalyst composition that allows dust to enter the catalyst (a). However, potassium (K) and sodium (
It is important to select active ingredients that are resistant to alkali or alkaline earth metals such as Na), magnesium (Mg), etc.
The present inventors have also discovered optimal catalyst compositions compatible with various gas sources. The %Na1Mg content of heavy oil and coal varies greatly depending on where it is extracted, and the higher the content of these metals, the more alkali dust resistance is required of the catalyst. However, most of these metals exist in the form of sulfates in exhaust gas, so they are soluble in water, so they can be wetted with water with dust attached to the catalyst surface, boiler evaporator pipes, etc.
Economizer - If a water supply pipe breakage causes dust-laden steam in the furnace or the catalyst to become wet, poisonous substances such as Na and Mg will rapidly increase inside the catalyst, resulting in an unexpected drop in performance. , the boiler may not be operational.

If the denitrification equipment no longer performs as expected due to such an emergency accident, in the worst case scenario, the boiler may have to be shut down, so we provide a method to restore performance in a short period of time. There is a need.

As mentioned above, it is known that if the DAS (Dus)/Z catalyst mainly consists of alkali or alkaline earth metals such as Na and Mg, it can be washed thoroughly by taking advantage of its water solubility. However, this is a treatment method after removing the catalyst from the denitrification equipment and removing it from the bank where the catalysts are grouped together. It can be said that it is completely impractical as a method of activating with water in between. In other words, stopping the bamboo boiler for a long period of time in order to recover the catalyst performance in an emergency is not allowed due to its mission as an exhaust gas treatment catalyst, as mentioned above, and it is necessary to activate the activity as quickly and inexpensively as possible. Must be.

Based on this idea, the present inventors developed a vertical reaction bed using a water washing nozzle as a method to restore the catalyst performance by washing with water in as short a time as possible with a large amount of catalyst packed in an actual device. proposes a method in which poisoning components are eluted and the catalyst performance is restored by installing the above-mentioned water washing nozzle at the gas inlet, or in the gas inlet or outlet of a horizontal reaction bed to wash the catalyst. However, the present invention makes this water washing more economical.

That is, the present invention is a method for restoring the performance of a catalyst by washing with water while the catalyst is still packed in the device when the performance of the catalyst deteriorates. Immediately after washing, the wastewater with high pollutant concentration is disposed of in a treatment pit, and the subsequent wastewater with low pollutant concentration is used as washing water for the next catalyst section, and subsequent sections are washed in sequence by repeating the same operation. This invention relates to a method for washing a catalyst with water.

The present invention is not limited to denitrification catalysts only, but can also be applied to desulfurization methods that use oxidation catalysts such as combustion catalysts and adsorbents, when catalyst performance deteriorates due to poisoning of the catalyst by alkali metals. Needless to say, it is applicable.

Hereinafter, the present invention will be explained in detail with reference to FIG.

Normally, ammonia gas 18 is injected as a reducing agent into the combustion exhaust gas 1 containing nitrogen oxides to form a catalyst layer 4 (4a, 4 in the figure).
b, 4c), the nitrogen oxides are decomposed into harmless nitrogen and water, and the denitrified exhaust gas 2 is led to downstream equipment.

On the other hand, if the catalytic performance of the catalytic converter filled in the denitration equipment main body 3 decreases during use due to the accumulation of poisonous substances such as alkali metal components in the exhaust gas, the boiler will stop with the catalyst still being filled in the denitrification equipment. Sometimes, in a method of restoring performance by washing with water, a plurality of gas passage surfaces of the catalyst layer 4 are
, 4-b, and 4-c, and a washing nozzle 5° is installed in each section facing the gas passage surface, and a washing liquid receiving tray 6 is provided in each section under the catalyst layer.

New washing water (e.g. aqua regia) 14 switching valves + 5-
It is supplied to the water washing nozzle 5-a through the catalyst layer 4-a, and is sprayed from above the partitioned catalyst layer 4-a.

After the alkali metal components contained within the catalyst are washed and eluted, they are temporarily received in the washing tray 6-a and drained out of the apparatus as a washing liquid.

Here, the washing liquid immediately after washing is waste water with a high concentration of pollutants, and is collected in the first waste water cypress 8 as high concentration waste water 7 by turning the switching valve 17-a and disposed of in the waste water treatment pit 11.

On the other hand, since the concentration of pollutants in wastewater after washing for a certain period of time is low, disposing of this washing liquid directly into the wastewater treatment pit will not only increase the amount of washing water but also cause the capacity of the wastewater treatment pit to be exceeded. It could happen. Therefore, after a certain period of time has elapsed, the washed liquid whose pollutant concentration has become low is discharged to the second drainage tank 10 as low concentration wastewater 9 via the switching valve 17-d. The low-concentration wastewater collected here is supplied to the washing nozzle 5-b as washing water 15 for the next section through the switching valve 16-b using the pump 12 to wash the catalyst 4-b. Here, too, the initial washing liquid is discarded, and the washing liquid, which has a low concentration of contaminants, is passed to the next compartment, and subsequent compartments are similarly washed sequentially.

In addition, by operating the switching valve, it is possible to wash with water in either the pan sensei or continuous type.

Furthermore, the timing of switching the wastewater to the second drainage tank cannot be determined unambiguously because it depends on the accumulation of poisonous substances on the catalyst and the water washing conditions, but the concentration of pollutants can be determined by sampling the wastewater over time. to analyze, or ll1pH
Decrease in contamination concentration shall be recognized and switched by a method such as judgment based on the value.

In addition, removing dust adhering to the catalyst layer by air blowing etc. before washing has the effect of reducing the amount of washing water, and by performing a final washing with fresh washing water, the washing The effect can be further enhanced.

After washing, the catalyst is drained and dried before combustion in the boiler. As a drying method, a conventional method such as driving a ventilation blower and supplying air to the catalyst layer via a boiler is used.

Therefore, compared to the conventional method of taking the catalyst out of the prefecture and washing it with water, the present invention allows washing with water within the actual equipment, and is effective as a method of activating the catalyst with water in a short time.
Furthermore, the amount of water used for washing can be greatly reduced, making a significant contribution to practical use.

Example 1 In FIG. 1, part of the gas passage surface of the catalyst layer 4 of the denitrification device 5 for exhaust gas from a stopped heavy oil-fired boiler is partitioned off with a partition plate 19, and a full-cone spray nozzle 5 is installed above the partition plate 19, and a full-cone spray nozzle 5 is installed on the top of the partition plate 19. was sprayed onto the catalyst to wash the catalyst with water.

The washing conditions are shown in Table 1.

Table 1 Washing conditions: Wash the catalyst with water by spraying with the spray nozzle 5a,
The first 10 minutes of washing water flows into the first drainage tank 8, and then the 50 minutes wash water flows into the second drainage tank 411o. The wastewater flowing into each drainage tank was sampled over time and the concentration of pollutants (K, Na) was analyzed, as shown by the solid line in Figure 2.

Next, the above-mentioned second drainage tank 10 is placed in the catalyst layer of section 4-b.
The waste water having a low concentration of pollutants flowing into the tank is sprayed from the spray nozzle 5-b using the pump 1-2. As in the case of section 4-a, the first 10 minutes of washing water was drained into the first drainage tank, and the subsequent 50 minutes of washing water was drained into the second drainage tank.

The concentration analysis value of the contaminant is shown by the broken line in FIG.

Similarly, after washing the 4-b section catalyst with water, the 4-C section catalyst is washed with water flowing out to the second drainage tank, and the above steps are repeated in sequence.

After drying the catalyst that had been washed with water in this manner, the denitrification performance was measured under the conditions shown in Table 2. Table 5: Denitrification Performance Measurement Results As is clear even from this result, the concentration of pollutants was high immediately after washing with water. By disposing of wastewater in a wastewater treatment pit and using the subsequent wastewater with a low concentration of pollutants as flushing water for the next section, the amount of flushing water can be reduced without significantly changing the denitrification performance of activated carbon. For example, as shown in Table 4, the amount of washing water required to wash the catalyst in five sections is less than half that of the method of discarding the washing water for each section.
This not only saves washing water, but also facilitates wastewater treatment.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing one embodiment of the method of the present invention applied to a boiler flue gas denitrification device;
The figure is a graph showing the change over time of contaminants in the washing liquid when the catalyst is washed with water using the method shown in Fig. 1. Sub-agents 1) Meifuku agent Ryo Hagiwara -

Claims (1)

[Claims] In a method of restoring the performance of a catalyst by washing with water while the catalyst remains in the device when its performance deteriorates, the catalyst bed gas passage surface is divided into a plurality of parts and washed with water in sequence, and at that time, the first catalyst section is washed with water. Catalyst washing with water, characterized in that immediately after, wastewater with a high pollutant concentration is discarded, and subsequent wastewater with a low pollutant concentration is used as washing water for the second catalyst section, and subsequent washings are carried out sequentially in the same manner. Method.