JPH0751540A - Denitration apparatus - Google Patents

Abstract

PURPOSE:To prevent the rising of an SO2 oxidation rate due to the adhesion and accumulation of vanadium to a catalyst bed. CONSTITUTION:The catalyst bed 12 employed in a denitration apparatus is constituted of the catalyst elements 18 placed on a catalyst receiving material 16 and the divided catalyst elements 17 provided on the catalyst elements 18 so as to leave a definite interval 'B' and a catalyst packing frame 15 distributing exhaust gas and preventing the abrasion of the catalyst bed due to dust is provided in the uppermost part of the catalyst bed 12. The catalyst elements 18 and the divided catalyst elements 17 have a honeycomb structure with a pore size pitch of 7mm and the length 'A' of the divided catalyst elements 17 is set to 300mm or less and the interval 'B' from the catalyst elements 18 arranged on the downstream side from the catalyst elements 17 is set to 50mm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry flue gas denitration device for a boiler which uses heavy and crude oil as a main fuel.

[0002]

2. Description of the Related Art FIG. 2 is a system diagram of a denitration device for removing nitrogen oxides in exhaust gas discharged from a boiler using heavy and crude oil as a main fuel, and FIGS. A structure and a catalyst pack are shown, and a conventional denitration device will be described with reference to these drawings. Fuel 7 such as heavy oil and crude oil and preheated air 9 are injected into the boiler 1 through the air preheater 3 by the forced draft blower 4 and burned. The exhaust gas generated in the boiler 1 is guided to the dry type denitration device 2 by the gas duct 8 to be denitrified, then heat-exchanged in the air preheater 3 and dust-removed in the electric precipitator 5 to a desulfurization device and a chimney (not shown). Sent. In addition, the code | symbol 6 is an induction fan.

Needless to say, NH ₃ is introduced upstream of the dry denitration device 2, and as shown in FIG. 3, the catalyst layers 12 are provided in multiple stages in the denitration reactor 13 constituting the denitration device 2 downstream thereof. Are arranged. As shown in FIG. 5, the catalyst layer 12 is composed of a catalyst element 14 placed on a catalyst receiving member 16 and a catalyst pack frame 15 placed above the catalyst element 14.

With the above-described structure, when the exhaust gas produced by burning heavy and crude oil, especially high-sulfur heavy oil in the boiler 1 is processed by the dry denitration device 2, the vanadium component contained in the fuel 7 reaches the catalyst layer 12 and the catalyst S of the denitration equipment by adhering to
The O ₂ oxidation rate increases, and the SO ₃ concentration at the denitration device outlet increases. If the SO ₃ concentration at the outlet of the denitration device increases, the air preheater 3 arranged thereafter will be corroded and the amount of soot and dust at the inlet of the electrostatic precipitator 5 will increase, which will be an obstacle. As a countermeasure for this, other than replacing the catalyst, there is currently no policy and enormous expense is involved.

The "SO ₂ oxidation" is the reaction (oxidation) of sulfur dioxide (SO ₂ ) and oxygen (O ₂ ), and the reaction formula is SO ₂ + 1 / 2O ₂ → SO _3. . The “SO ₂ oxidation rate” indicates the ratio of the SO ₃ concentration at the inlet and outlet of the denitration catalyst, which is (outlet SO ₃ −inlet S
O ₃ ) / inlet SO ₂ × 100.

[0006]

[Problems to be Solved by the Invention] Heavy and crude oil, which is the main fuel of a boiler, contains sulfur and vanadium.
Since this vanadium is also contained in the exhaust gas and discharged as it is, it is concentrated and adheres to the entrance of the denitration catalyst, and the SO ₂ oxidation rate in this part increases, which increases the SO ₂ oxidation rate of the entire denitration device. It is the main factor.

The current denitration equipment has a catalyst element length of 5
One unit is 00 to 1000 mm, but concentrated on the entrance side
Even if vanadium adheres, there is no way to remove it, so
SO ₂If the oxidation rate rises, replace the catalyst or
How to take out the catalyst and cut the catalyst inlet to reuse it
However, the former requires huge cost for replacement,
Also, the latter is better than the former in terms of cost, but is better for cutting / refilling.
It takes time and neither is realistic.

[0008]

In order to solve the problems described in the preceding paragraph, in the present invention, it becomes possible to replace the catalyst only with the gas inlet side portion of the catalyst to which vanadium easily adheres, or replace the catalyst and replace the ceramic body with the gas inlet side. It adopts a configuration in which it is divided as follows.

That is, according to the first aspect of the present invention, a dry method is used in which nitrogen oxides in exhaust gas discharged from a combustion facility using heavy and crude oil as a main fuel are removed by using a catalyst having a large number of holes in the gas flow direction. In the denitration device, the catalyst to be filled in the exhaust gas flow path to be denitrated should be 300
Divide into parts within mm, and the space between the divided catalysts is 50 mm
A denitration device with a catalyst arranged so that it is within the range is adopted.

In the second aspect of the present invention, instead of dividing the catalyst, a ceramic component having a specific surface area of 10 m ² / g or more is formed on the catalyst inlet side within a cross-sectional shape similar to that of the catalyst within a length of 300 mm. A denitration device having a structure in which the formed ceramic body is arranged on the upstream side of the catalyst so that the distance between the ceramic body and the catalyst is within 50 mm is adopted.

[0011]

As described above, according to the present invention, the catalyst to be filled in the gas flow path is divided into portions within 300 mm from the inlet side in the gas flow direction, and the catalyst is divided so that the distance between the divided catalysts is within 50 mm. In addition to the arrangement of the catalyst, instead of dividing the catalyst, a ceramic body having a specific surface area of 10 m ² / g or more is formed at the catalyst inlet side within a length of 300 mm with a cross-sectional shape similar to that of the catalyst, and By arranging the ceramic bodies so that the distance between them is within 50 mm, vanadium in the exhaust gas discharged from the boiler is concentrated and attached to the inlet portion of the inlet side catalyst or the simulated catalyst (ceramic body), Only this part can be replaced when the SO ₂ oxidation rate rises.

[0012]

EXAMPLE In the present invention, as described above, the catalyst layer 12 installed in the reactor 13 of the denitration device 2 shown in FIGS.
In advance, only the gas inlet side of the catalyst to which vanadium in the exhaust gas is likely to adhere is divided and replaceable. The dividing length is preferably within 300 mm where vanadium is easily attached. The reason is that if the thickness is 300 mm or more, it becomes difficult to use the catalyst after 300 mm where the adhesion of vanadium is relatively small.

Further, the distance between the divided portion and the catalyst layer in the subsequent flow is set to 50 mm or less. The reason is that vanadium tends to adhere to the catalyst inlet side because the test results show that the gas collision with the catalyst wall due to the turbulence of the gas when the exhaust gas enters the catalyst pores has a large effect. And
If the distance between the catalyst and the catalyst divided portion is set too large, the rectified gas flow is disturbed in the catalyst pores, and the turbulent portion of the gas is again formed on the inlet side of the catalyst pores in the downstream flow, and the vanadium content is reduced. It is not preferable because it promotes adhesion.

An example of the catalyst layers 12 provided in a plurality of stages in the denitration reactor 13 used in the denitration apparatus according to the present invention is shown in FIG. 1, which will be described. The catalyst layer 12 has a catalyst element 18 placed on a catalyst receiving material 16 and a divided catalyst element 17 above the catalyst element 18 with a constant interval "B". The catalyst layer 12 serves to rectify the exhaust gas 11 and prevent abrasion due to dust. A catalyst pack frame 15 is provided. The catalytic element 18 and the divided catalytic element 17 have a honeycomb structure with a hole diameter of 7 mm pitch, the length "A" of the divided element 17 is within 300 mm, and the distance "B" between the catalytic element 18 and the catalytic element 18 installed downstream thereof is Within 50 mm.
This may be set at an interval "B" at which the exhaust gas exiting the split catalytic element 17 does not cause turbulent flow, and the smaller the number, the better the contact.

Exhaust gas 11 is supplied to the divided catalytic element 17.
Vanadium in the inside tends to adhere, and a large amount adheres, so that it does not adhere to the catalytic element 18 in the downstream. For this reason, the divided catalyst element 17 is replaced with a ceramic body having a similar cross-sectional shape and a specific surface area of 10 m ² / g or more so that vanadium can be easily attached, and this portion can be manufactured at low cost. be able to.

[Experimental Example 1] In the denitration apparatus of the system shown in FIG. 2 having the catalyst layer shown in FIG. 5, a boiler 1 burning a fuel 7 containing a sulfur content of 2 to 3 wt% has a honeycomb having a hole diameter of 7 mm. A denitration catalyst 2 filled with a structured catalyst was installed and operated for about 2 years, and then a catalyst sample was taken out and the denitration performance, the SO ₂ oxidation rate and the state of vanadium adhesion were confirmed.

As a result, the denitration rate, SO₂About oxidation rate
As shown in Table 1, the denitrification rate is 96% when fresh and 2 years
It was 95.8% after that, almost unchanged,
SO ₂About 0.5% freshness after 2 years
It turned out to have risen to 1.5%. Catalyst moth
As a result of confirming the adhesion concentration of vanadium in the flow direction, Table 2
As shown in, in the part within 300 mm of the gas inlet side of the catalyst,
Base value (indicating initial value) + 2 to 1 wt%, after that
Since the base value is +0.1 to 0.2 wt%,
More vanadium is deposited on the gas inlet side of the catalyst.
It was confirmed that

[0018]

[Table 1]

[0019]

[Table 2]

[Experimental Example 2] Approximately 20 gas inlet side of the above catalyst
0 mm (total length of 800 mm per piece) was cut out, and the denitration rate and SO ₂ oxidation rate of only this portion were measured. As a result, as shown in Table 3, it was found that the SO ₂ oxidation rate was 0.5% when fresh and 4% after 2 years, showing a significantly high value. However, it was found that the denitration rate was 96%, which was almost unchanged.

[0021]

[Table 3]

[Experimental Example 3] Catalyst (800 mm per unit)
Is divided at a position of 200 mm from the entrance side, and the distance "B" between the divided portions is 10 mm, 30 mm, 50 mm, 80 mm, 100 m
m, 200 mm and arranged (see FIG. 4), Experimental Example 1
The same reactor was charged for about 1 year, and after operating, it was taken out and the adhering condition of the vanadium component on each part was confirmed. As a result, as shown in Table 4, it was confirmed that when the interval "B" between the divided portions exceeds 50 mm, vanadium begins to significantly accumulate on the inlet side of the downstream catalyst 18. The reason why the length of the divided catalyst 17 is 200 mm is that vanadium adheres within 300 mm, as is clear in Experimental Examples 1 and 2.
Since only a little adheres to the wake, in this experimental example, 200 mm was used in order to confirm how vanadium flows on the wake side and how it adheres.

[0023]

[Table 4]

[Experimental Example 4] Instead of a split catalyst, a ceramic made of silica-alumina having a specific surface area of 2 m ² / g, 5 m ² / g, 10 m ² / g, 50 m ² / g, 100 m ² / g was used as a catalyst. The same cross-sectional shape was formed to a length of 200 mm, and a catalyst of 600 mm was placed on the downstream side with a distance of 25 mm between the ceramic and the catalyst.
After being operated for about 1 year in the same boiler exhaust gas as in Experimental Example 1, the adhesion state of vanadium in the ceramics portion and the catalyst inlet portion was confirmed. As a result, Table 5
As shown in (1), when the specific surface area was 10 m ² / g or less, the adhesion of vanadium to the ceramic portion was not sufficient, and the accumulation of vanadium at the catalyst inlet was confirmed.

[0025]

[Table 5]

Further, it was found that vanadium adheres to the ceramic portion having a specific surface area of 10 m ² / g or more in the same manner as the catalyst, and vanadium is hardly seen to flow into the subsequent flow. As a result, it was found that ceramics could be used instead of the split catalyst 17 shown in FIG.

[0027]

In the denitration apparatus of the present invention, only the gas inlet portion of the catalyst to which vanadium in the exhaust gas is likely to adhere is divided and replaced, so that the SO ₂ oxidation rate increases due to the accumulation and accumulation of vanadium. Only the divided catalyst can be easily replaced at the time. Therefore, the catalyst is not wasted and the cost is low.

Further, in the denitration apparatus of the present invention, in which the ceramic body is placed in front of the catalyst layer instead of the split catalyst, the denitration rate is somewhat lower, but it is a cheaper ceramic product than the catalyst, Overall cost savings.

[Brief description of drawings]

FIG. 1 is a structural diagram of a catalyst layer housed in a denitration reactor in a denitration device according to the present invention.

FIG. 2 is a system diagram of a denitration device for a boiler that uses heavy and crude oil as a main fuel.

FIG. 3 is a structural diagram of a denitration reactor.

FIG. 4 is a layout diagram of catalysts in Experimental Example 3.

FIG. 5 is a structural diagram of a conventional catalyst layer housed in a denitration reactor.

[Explanation of symbols]

 1 Boiler 2 Dry flue gas denitration device 3 Air preheater 4 Push blower 5 Electric dust collector 6 Induction draft fan 7 Fuel 8 Gas duct 9 Air 11 Exhaust gas 12 Catalyst layer 13 Denitration reactor 14, 17, 18 Catalytic element 15 Catalyst pack frame 16 Catalyst Receiving material

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location 7704-3K F23J 15/00 ZAB A

Claims (2)

[Claims] 1. A dry denitration apparatus for removing nitrogen oxides in exhaust gas discharged from a combustion facility using heavy and crude oil as a main fuel by using a catalyst having a large number of holes in the gas flow direction, and denitrification should be performed. The catalyst to be filled in the flow path of the exhaust gas is divided in a portion within 300 mm from the inlet side in the gas flow direction,
A denitration device characterized in that the catalysts are arranged so that the distance between the divided catalysts is within 50 mm. 2. A dry denitration device for removing nitrogen oxides in exhaust gas discharged from a combustion facility using heavy and crude oil as a main fuel by using a catalyst having a large number of holes in the gas flow direction. A ceramic body having a cross-sectional shape similar to that of the catalyst and having a length of 300 mm or less and having a specific surface area of 10 m ² / g or more is arranged on the upstream side of the catalyst so that the distance from the catalyst is 50 mm or less. Denitration equipment.