JPH0194925A - Apparatus for removing nitrogen oxides in flue gas - Google Patents

Abstract

PURPOSE:To minimize a poisoning of a catalyst by attaching an injection equipment of an inorganic oxide, which captures heavy metal components in a flue gas, to a flue gas passage between a combustion equipment and a denitration equipment and also arranging an equipment for removing the inorganic oxide. CONSTITUTION:An inorganic oxide powder and ammonia are introduced into an upstream position of a denitration equipment 2 through an inorganic oxide injection line 16 and an ammonia injection line 15, respectively. The inorganic oxide powder absorbs heavy metal compounds such as As etc., so as to lower their concentrations in a flue gas. The flue gas, denitrated by the denitration equipment 2, is led through an air heater 3 and introduced into an electrostatic precipitator 4, wherein the ash and inorganic oxide powder in the flue gas are collected. The collected ash and inorganic oxide powder are returned to the boiler 1 by way of an ash recycle line 19, The inorganic oxide powder is discharged out of the system through a line 12 as a clinker together with part of recycled coal ash.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a device for removing nitrogen oxides from exhaust gas, and is particularly suitable for treating exhaust gas containing heavy metal elements, which are catalyst poisoning components, in fuel. The present invention relates to a suitable device for removing nitrogen oxides from exhaust gas.

[Conventional technology]

FIG. 3 shows a main exhaust gas system diagram of a boiler plant incorporating the most common flue gas denitrification device according to the prior art. For example, in order to treat nitrogen oxides (hereinafter referred to as NOx) in the exhaust gas discharged from the exhaust gas generator (hereinafter referred to as boiler) 1, ammonia is injected into the exhaust gas flue 18 of the boiler 1 from the ammonia injection line 15. A denitrification device (denitrification reactor) 2 is provided, which is injected as a reducing agent and contains a catalyst for promoting the reaction between NOx and NH3. This denitrification device 2 is provided between the boiler economizer 24 and the air heater 3 because denitrification is generally performed most efficiently in a temperature range of about 300 to 400°C. on the other hand,
Exhaust gas from the boiler 1 passes through an air heater 3, is removed by a dust removal device (for example, an electrostatic precipitator, etc.) 4, and then passes through a desulfurization device 5 and is released into the atmosphere from a chimney 6. On the other hand, the ash content in the exhaust gas is approximately 15% in the furnace 25 of boiler 1.
A certain amount of ash is discharged from the bottom of the furnace 25 as clinker, and the remaining 84% is removed by the dust collector 4.

Some types of fuel (coal) burned in the boiler 1 are difficult to burn; for example, the ash collected by the dust collector 4 may contain a large amount of unburned matter. For example, about 5 to 10% of the fuel supplied to the boiler 1 may be included as unburned fuel. Therefore, this unburned content is
As shown in the figure, if the ash was disposed of directly from the ash discharge line 20', the combustion efficiency of the boiler 1 would be lowered, leading to a reduction in boiler efficiency and causing problems in terms of heat balance. In this case, as an example, if the fuel supply line 10 is 100, the mass balance of ash is 85 at the outlet of the boiler 1, 15 at the ash discharge line 20' of the boiler 1, and 15 at the ash caught in the dust collector 4. 84, becomes 1 at the inlet line of the desulfurizer 5.

Therefore, as shown in Fig. 4, the ash removed by the dust collector 4 is recycled back to the boiler 1 using the ash recycling line 19 and re-burned in the boiler 1, thereby reducing the amount of unburned matter and increasing the combustion efficiency. In some cases, a system is adopted to increase the ash mass balance, but in this case, if the fuel supply line 10 is 100, the ash mass balance is 65 at the outlet of the boiler 1, and the ash recycling line of the dust collector 4 is 65 at the outlet of the boiler 1. 19 and 63
, 98 at the ash discharge line 20' of the boiler 1, and 2 at the inlet line of the desulfurizer 5. Therefore, in terms of the ash mass balance, the ash separated and removed in the furnace 25 of the boiler 1 is discharged to the outside of the system via the ash discharge line 20'. There's no big difference.

However, some of the trace amounts of heavy metal elements contained in the fuel burned in the boiler 1 are gasified in the high-temperature gas atmosphere in the furnace 25 of the boiler 1. Over time, some particles condense and solidify in a low temperature range, enter the ash, and are removed together with the ash by the dust collector 4. Therefore, since the ash containing the trace amount of heavy metal elements in the ash is supplied to the boiler 1 again from the ash recycling line 19 and burned again, the heavy metal elements are concentrated by the circulation by the ash recycling line 19. Become. - As an example, if the content of the heavy metal elements is not recycled (as shown in Figure 3), and if the exhaust gas in the exhaust gas flue 18 contains 30 ppm of heavy metal elements, then in the case of Figure 4, the boiler system Due to the balance between the amount supplied from outside and the amount discharged from the dust collector 4 to the outside of the system, the ash recycle line 19 is theoretically concentrated 50 times, and the heavy metal elements in the exhaust gas reach a high concentration of 1500 ppm. It will be concentrated.

The trace heavy metal elements include As, Cd, Cu, Pb5SbsSes, from the relationship between the exhaust gas temperature of each part of the boiler plant shown in Fig. 5 and the vaporization temperature of the heavy metal element.
Tls Zn is considered.

Figure 6 shows the decrease in denitrification performance when denitrification bags WL2 are installed in plant A, which does not recycle ash, as shown in Figure 3, and plant B, which recycles ash, as shown in Figure 4. It shows the situation. In the case of Plant A, a slight decrease in denitrification performance was observed immediately after the start of initial operation, but thereafter stable denitrification reactions were performed. On the other hand, in the case of Plant B, the denitrification performance significantly decreased in the early stages of operation, and thereafter, the catalyst activity decreased significantly as the operation time progressed.

The difference in the system between plants A and B is whether or not ash is recycled, and it can be seen that the poisoning of the catalyst in the denitrification device 2 due to the concentration effect of the trace heavy metal elements is a direct cause.

Therefore, to solve the problem of trace amounts of heavy metal elements, it has been considered to adopt a so-called after-DesOx type denitrification device 2, in which the denitrification device 2 is installed downstream of the desulfurization device 5, as shown in Fig. 7. ing. However, the temperature of the treated gas at the outlet of the desulfurization device 5 is too low to perform denitrification (usually around 150°C at the DeSOx output log gas outlet).
, a gas heating furnace 22 etc. is provided to transfer the exhaust gas to the fuel supply line 2.
The temperature suitable for denitration (approximately 300 to 4
It is necessary to take measures such as raising the temperature to 00°C. Therefore, there is a problem in that the cost of fuel supplied to the gas heating furnace 22 and the cost of equipment such as the gas-gas heater 21, which is a heat recovery device, increase, resulting in high construction and operating costs.

Alternatively, as shown in Figure 9, a part of the collected ash is extracted out of the system via line 14 to reduce the concentration of heavy metal components (
Partial recycling method) is also being considered. If the ash recycling rate is lowered, the concentration ratio of heavy metal components will also be lowered, and catalyst poisoning will be alleviated. leads to a decrease in thermal efficiency.

However, if this point is compromised, the advantage of reducing catalyst poisoning can be obtained with a simple system.

[Problem that the invention seeks to solve]

As described above, when the general flow shown in FIG. 3 is adopted, there is a problem that when the combustion efficiency of the boiler 1 is low, the thermal efficiency of the boiler decreases due to this. Furthermore, the fourth
When adopting the method shown in the figure that recycles combustion ash containing unburned content, the thermal efficiency of the boiler can be improved compared to the method shown in Figure 3, but the denitrification catalyst becomes poisoned due to the concentration of catalyst poisoning components. There was a problem with being exposed.

As a countermeasure against these problems, a denitrification device 2 is installed downstream of the desulfurization device 5 as shown in FIG.
The SOx method is being considered, but if this method is adopted, construction costs and operating costs will be high, leading to higher costs. There is also a method (partial recycling method) that sacrifices some thermal efficiency and removes a portion of the collected ash from the system as shown in Figure 9, but although catalyst poisoning is reduced, unburned ash is removed. Since the ash contained therein is discharged outside the system, the problem of reduced thermal efficiency still remains.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, install a denitrification device at the most economical boiler outlet, and minimize catalyst poisoning in the partial recycling method without significantly reducing thermal efficiency. An object of the present invention is to provide a device for removing nitrogen oxides from exhaust gas.

[Means for solving problems]

The present invention provides a path for guiding combustion exhaust gas from a combustion device, a denitration device installed in the path, a dust removal device for treating the exhaust gas from the denitration device and separating contained ash, and directing the separated ash to the combustion device. In a device for removing nitrogen oxides from exhaust gas, which is equipped with a recirculation device, an inorganic oxide injection device for capturing heavy metal components in the combustion exhaust gas is provided in a passageway that leads the combustion exhaust gas from the combustion device to the denitrification device. With,
The combustion apparatus is characterized in that a device for removing inorganic oxides recycled together with ash is provided.

The inorganic oxide used in the present invention has a specific surface area of 10 by the BET method (one of the methods for measuring specific surface area).
There is no particular limitation as long as it is rrf/g or more,
For example, anatase titania, γ-alumina, silica,
Magnesia, manganese oxide, etc. are used. Alkali metal oxides are not preferred because they can become catalyst poison components.

Further, the amount of inorganic oxide to be injected into the exhaust gas INnf is preferably about 0.1 to 100 g. If it exceeds 100 g, catalyst abrasion may be accelerated.

[Effect]

By injecting inorganic oxide powder into the flue between the boiler outlet and the denitrification equipment, heavy metal volatiles in the exhaust gas are adsorbed on the surface of the inorganic oxide powder, reducing the concentration of heavy metal volatiles in the exhaust gas. be able to. The powder that has adsorbed heavy metals is collected by a dust collector located downstream of the denitrification equipment, and sent to the boiler combustion equipment along with the coal ash via the ash recycling line. It falls to the bottom of the boiler together with some of the recycled coal ash and is discharged as clinker. Therefore, there is almost no increase in ash content due to the injection of inorganic oxide powder (1) Ash can be recycled stably.

〔Example〕

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

FIG. 1 is a system diagram of an apparatus for removing nitrogen oxides from exhaust gas according to the present invention. The exhaust gas generated in the combustion device (boiler) 1 is introduced into the denitrification device 2 through the exhaust gas flue 18.

Upstream of the denitrification device 2, inorganic oxide powder is injected from an inorganic oxide injection line 16 and ammonia is injected from an ammonia injection line 15. The powder adsorbs heavy metal components such as A3 present as volatile components in the exhaust gas, thereby reducing the concentration of heavy metal components in the exhaust gas. The exhaust gas denitrified by the denitrification device 2 is introduced into an electrostatic precipitator 4 via an air heater 3, where ash and inorganic oxide powder in the exhaust gas are collected. The collected ash and inorganic oxide powder are returned to the boiler 1 via the ash recycling line 19. Here, the inorganic oxide powder is discharged to the outside of the yarn from the ash and inorganic oxide discharge line 12 as clinker together with a portion of the recycled coal ash.

On the other hand, the dust-removed exhaust gas is desulfurized by the desulfurizer 5 and then discharged from the chimney 6 to the outside.

Example 1 In the apparatus shown in FIG.
Accordingly, powder of anatase type titania having a specific surface area of 110 of/g by the BET method was
0 g was injected and the operation was performed for about 1000 hours. The effect of denitrification over the course of operation time was investigated, and the results are shown in Figure 2 (solid line C).

Comparative Example 1 Operation for about 1000 hours was carried out in the same manner as in Example 1 except that the inorganic oxide was not injected. The effect of denitrification over the course of operation time was investigated, and the results are shown in Figure 2 (dashed line D).
)It was shown to.

From the results shown in FIG. 2, it is clear that catalyst deterioration can be suppressed by injecting inorganic oxides.

Examples 2 and 3 The anatase-type titania powder used in Example 1 was heat-treated and the operation was performed in the same manner as in Example 1, except that the specific surface area by the BET method was set to 10rd/g and 50nf/g. Ta.

Examples 4 and 5 The same procedure as in Example 1 was carried out except that the injection amount of the anatase titania powder in Example 1 was changed to 0.1 g and 100 g per exhaust gas INnr.

Examples 6 to 9 Instead of anatase titania in Example 1, γ-alumina, silica, magnesia and manganese oxide were used,
The operation was otherwise carried out in the same manner as in Example 1.

The catalyst deterioration rates (initial activity 60% - activity after 1000 hours) of Examples 2 to 9 and Comparative Example 1 after 1000 hours of operation were investigated, and the results are shown in Table 1.

Table 1 [Effects of the Invention] According to the present invention, it is possible to reduce the concentration of heavy metal components in exhaust gas and prevent deterioration of denitrification catalyst activity, and also to reburn unburned ash to improve fuel efficiency. It is possible to maintain high combustion efficiency7.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of the exhaust gas nitrogen oxide removal device according to the present invention, Fig. 2 is a diagram showing the deterioration of denitrification activity depending on operating time, and Figs. 3 and 4 are diagrams according to the prior art. Figure 5 is a system diagram of the exhaust gas nitrogen oxide removal device, and Figure 6 is a diagram showing the gas temperature distribution in each part of the combustion equipment.
7, 8, and 9 are system diagrams of other nitrogen oxide removal devices according to the prior art. DESCRIPTION OF SYMBOLS 1... Combustion device, 2... Denitration device, 3... Air heater, 4... Dust removal device, 5... Desulfurization device, 6...
Chimney, 10... Fuel supply line, 12... Ash and inorganic oxide discharge line, 15... Ammonia injection line, 16... Inorganic oxide injection line, 19... Collected ash recycling line . Agent Patent Attorney Takenaga Kawakita Figure 1 1: Combustion device 2: Denitration device 3: Air heater 4: Dust removal device 5: Welfare removal device 6
: Chimney 1o: Fuel supply line 12: Ash and inorganic oxide discharge line 15: Ammonia i7A line 1
6: Inorganic oxide injection fin 19: Collected ash recycling line operating time (hr) Figure 5 Figure 6 Operating time (hr)

Claims (1)

[Claims] A passage for guiding combustion exhaust gas from the combustion device, a denitrification device installed in the passage, a dust removal device for treating the exhaust gas from the denitration device and separating contained ash, and a device for recirculating the separated ash to the combustion device. In an apparatus for removing nitrogen oxides from exhaust gas, an inorganic oxide injection device for capturing heavy metal components in the combustion exhaust gas is provided in a passage leading the combustion exhaust gas from the combustion apparatus to the denitrification apparatus, and A device for removing nitrogen oxides from exhaust gas, characterized in that the device is equipped with a device for removing inorganic oxides recycled together with ash.