JPS5824367B2 - Manufacturing method of ammonium nitrite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is a method of absorbing NOx gas containing nitrogen oxides (hereinafter sometimes abbreviated as NOx) in a multistage absorption tower.
Contact with an absorption liquid of ammonium water at 10 to 10°C to sequentially absorb NOx in NOx gas to form ammonium nitrite (liquid).
The invention relates to an improvement in the method of manufacturing.

US Pat. No. 2,797,144 discloses that in a multi-stage absorption tower, NOx gas is brought into contact with an absorption liquid of ammonium water at -lO to 10°C to sequentially absorb NOx in the NOx gas.
A method for producing ammonium nitrite liquid is described.

However, in the above-mentioned known method, the molar yield of the generated ammonium nitrite (sometimes simply abbreviated as NH4NO2 yield) with respect to the total amount of NOx (NHs equivalent moles) supplied to the absorption tower is not sufficiently high. There was a drawback.

The nitrogen oxides (NOx) mentioned above are N02NO2°N2
It refers to one or more nitrogen oxides selected from the group consisting of O3 and N2O4, and NOx gas is
This refers to a gas containing the above-mentioned NOx.

Generally, it is known that NOx gas reacts mainly in accordance with the following reaction formula or equilibrium formula in the absorption liquid contact area of the absorption tower where it comes into contact with the carbon dioxide absorption liquid.

[Liquid phase reaction]

N2O3+H20→ 2HNO□ (1)N
204+H20→ HNO2+HNO3 (2) HNO2
+NH41→NH4NO2+H” (3) HNO
3+NH4→ NH4NO3+H+ (4)4H
NO-→ 2NO+2HO10N O(5)2
2 2 [Gas phase / liquid phase reaction] N2O3 + 2NH3 → N2 + NH4NO2 + H20 (6
)N204+2NH3→N2+NH4NO3+H20(
7) [Gas phase reaction] 2NO+0 → 2N02 (8)N
O+NO→ N O(9) 2 ← 23 2N02g N20. αO) In this specification, in NOx gas, mixed gas, auxiliary NO
The nitrogen monoxide equivalent component (hereinafter sometimes abbreviated as eNO) in x gas corresponds to NO and N2O3, and the nitrogen dioxide equivalent component (hereinafter sometimes abbreviated as eN02) corresponds to NO□p N2O3 and N2O4.

In addition, in this specification, NOx, eNO and e
The number of moles of NO2 converted to NH3 and the total number of moles of NOx are values calculated using the following formula.

NH of NOx, converted mole number (eNOx) = eNO+
eN02 (Number of moles of mono eNO converted to NH3 = NO1N
203 (mol) Number of moles of eNO2 converted to NH3 = N02+
N2O3 + 2N204 (mol) Total number of moles of NOx = NO + N02 + N203 ten N20
4 (Mole) In this specification, the molar ratio of NOx gas (eNO/e NO2) is the ratio of the number of moles of eNO in terms of NH3 and the number of moles of eNO□ in terms of NH3.

Now, according to the above-mentioned reaction equation and equilibrium equation, in the method of producing ammonium nitrite by absorbing NOx into ammonium water through contact between NOx gas and the absorption liquid of ammonium water, eNO (1 ), (3) and (9), reactions in the right direction occur selectively at a high rate, and eN
(2), (4) and a1 formula related to O2, and N
If the reactions in equations (6) and (7) related to the reaction between H3 and NOx, and the reaction in equation (5) related to the decomposition of HNO2 are prevented from proceeding, the amount of nitrogen produced relative to the number of moles of supplied NOx converted to NH3 will be reduced. Molar yield of ammonium nitrate (NH4N
It is clear that this increases the O2 yield).

However, the above-mentioned known method involves a reaction in which ammonium nitrate and N2 are produced (2).

(4), (5), (6), (7) and (
10) The reaction of formula (1) cannot be suppressed sufficiently effectively or is related to the reaction in which ammonium nitrite is produced.
, it was not possible to selectively carry out the reactions of formulas (3) and (9) at a high rate, so a high NH4NO2
Ammonium nitrite could not be obtained in terms of yield, and NOx remained, deteriorating the surrounding environment.

In this invention, NOx gas is brought into contact with ammonium water to reduce NOx.
The present invention relates to a method for producing ammonium nitrite by absorbing ammonium nitrite, which improves all at once the drawbacks of the above-mentioned known techniques regarding the NH4NO2 yield and the amount of NOx in the waste gas.

That is, this invention uses a multi-stage absorption tower to absorb NOx gas containing NOx into a
NOx in NOx gas by contacting with absorption liquid at ~10℃
(a) In the method of manufacturing ammonium nitrite liquid by sequentially absorbing
About 5% of NOx with a composition of 1.5 to 7 (O/eNO2)
Supplying NOx gas containing ~20 molar ratio, the molar ratio of ammonia equivalent component (abbreviated as eNH3) and carbon dioxide equivalent component (abbreviated as eCO2) (eNH3/eCO
2) is adjusted to 1.5 to 2.2, and ammonium carbonate is converted into ammonium; 50 to 100 ji/
1-containing ammonium water is added to the circulating absorption liquid of the first absorption tower, the absorption liquid and the NOx gas are brought into contact with each other, and a portion of the NOx in the NOx gas is absorbed; (b) Next, the first absorption tower An auxiliary NOx gas is added to the residual NOx gas that has passed through the absorption liquid contact zone, and the molar ratio of NOx in the resulting mixed gas (eNo/eN02) is set to approximately 1.5 to 5, and the mixed gas is transferred to the second absorption liquid. A part of the circulating absorption liquid from the first absorption tower is brought into contact with the absorption liquid mixed with the circulating absorption liquid from the second absorption tower.

(c)
Thereafter, auxiliary NOx gas is added to each residual NOx gas that has passed through the absorption liquid contact zone of the absorption tower at each stage, and the molar ratio of NOx in the resulting mixed gas (eNO/eNO,) is approximately 0.9.
~4, each mixed gas thereof.

(d) The remaining NOx gas and the auxiliary NOx gas are sequentially supplied to the next-stage absorption tower, and the NOx in the mixed gas is sequentially absorbed in the same manner as the second absorption tower. Supply a mixed gas in which the molar ratio of NOx in the mixed gas (eNO/eNO2) is approximately 0.9 to 1.1, and absorb NOx in the mixed gas in the same manner as in each stage. The present invention relates to a method for producing ammonium nitrite, characterized by the following.

According to the method of this invention, NOx gas and auxiliary NOx
Molar yield of generated ammonium nitrite relative to the total number of moles of NOx in the gas converted to NH3 (NH4NO2 yield)
is much higher than that of conventionally known methods, and the amount of NOx in the waste gas discharged from the final stage absorption tower can be reduced compared to known methods.

Further, according to the method of the present invention, the yield of ammonium nitrite per unit volume of the total internal volume of the multi-stage absorption tower (per unit time) is considerably higher than in a conventional method using a multi-stage absorption tower.

Also commonly used in the production of ammonium nitrite.

The absorption liquid in the absorption tower contains an ammonia-equivalent component (hereinafter e
NH4+ combined with CO3'- and HCO3-, molecular NH3, NH2 (sometimes abbreviated as NH3)
It contains carbon dioxide equivalent components (hereinafter referred to as eC
(sometimes abbreviated as O2).

THCO3-2CO3"-, etc., and further contains various reaction products shown in the reaction formula and equilibrium formula. According to the method of the present invention, ammonium carbonate (ammonium carbonate) in the absorption liquid is ) molar ratio (e NHa /e
C02) can be lowered than conventionally known methods,
Moreover, the increase in NH4NO2 yield due to the lower molar ratio (eNH3/eCO2) was greater than expected, and the amount of ammonia equivalent component (NH3) required to produce 1 mole of ammonium nitrite was also less than expected. Even less is required.

Hereinafter, the method of the present invention will be explained in more detail using flow sheets shown in the drawings.

FIGS. 1 and 2 are flow sheets outlining the process for carrying out this invention.

In FIG. 1, a cocurrent absorption tower having a liquid column section and a packed bed section is used, and in FIG. 2, a bubble tower absorption tower is used.

In the method of this invention, the NOx gas supplied to the first absorption tower 2a through the NOx gas feed line 1 may be produced by any industrial method, and may contain a certain amount of NOx. However, since the NOx content of industrially produced NOx gas is generally about 5 to 20 mol, the present invention uses NOx of 5 to 20 mol, particularly 5.5 mol. With a NOx gas containing ~15 molar ratio (calculated based on the total number of moles of NOx), eNO/eN02 (molar ratio) in NOx is ~1.5
7, particularly those having a composition of 2 to 6 are preferred.

It is preferable that the value of eNO/eNO□ is large because it can suppress the reaction in equation (2) and reduce the amount of NO3- by-product, but if the value of eNO/eNO2 is too large, the
The O2 component is too small and the equilibrium component of NO and NO2 is N2O.
Since the partial pressure of 3 is low and the reaction of equation (1) hardly occurs, the absorption reaction of NOx gas does not proceed, and eNO/eNO
If the value of 2 is too small, the NO2 partial pressure will be high, and the N2O4 partial pressure that exists in equilibrium with NO2 will also be high, the reaction of equation (2) will occur, the amount of NO3- by-product will increase, and the NH4N0□ yield will increase. Therefore, eNO/eNO□ is preferably within the above range.

Note that NOx contains oxygen in considerable excess compared to NOx.
It may be gas.

As this NOx gas, for example, NOx gas obtained by catalytically oxidizing ammonia with a platinum catalyst or a platinum-rhodium catalyst in the presence of oxygen is suitable.

In the method of the present invention, the multi-stage absorption tower 2 may be any known absorption tower in terms of the type of each absorption tower and the type and type of the entire absorption tower, and each absorption tower 2 may have the following characteristics: An absorption tower with a large source-side physical transfer coefficient KL measured in a physical absorption experiment (0°C) in a pure CO2 gas-water system in which gas phase diffusion resistance can be ignored is used to absorb HNO generated in the liquid phase.
This is preferable because it suppresses the decomposition of 2 (formula 5) and increases the yield of NH and NO□.

The absorption tower 2 has a value of the source side mass transfer coefficient KL of at least 5 x 10-3C7FL/sec or more, particularly 5 x 10-2 cIrL/sec or more, more preferably 1 x 10-1 to 3 x Absorption towers of the type 1O-1cIrL/sec are preferred.

This absorption tower 2 may be, for example, an absorption tower such as a countercurrent packed tower, a cocurrent packed tower, a wet wall tower, a liquid column tower, a perforated plate bubble tower, a bubble bell type bubble tower, or a combination of the above absorption towers. Absorption columns can be mentioned, and in particular, co-current packed columns, liquid column columns, bubble bell-type bubble columns, and absorption columns combining co-current packed columns and liquid column columns have the above-mentioned source-side mass transfer coefficient. The value of KL is 1O-2cIr
This is preferable because it can increase the yield of N)(4NO2) or higher.

In addition, in the method of the present invention, each absorption tower 2 is of a type in which the gas side mass transfer coefficient KG is a small value, in particular, the ratio of the gas side mass transfer coefficient KG to the source side mass transfer coefficient KL (KL /KG) is at least 200 or more, and more preferably 300 or more.

That is, an absorption tower having a large ratio (KL/KO) is suitable because the decomposition reaction of HNO□ in the above-mentioned formula (5) can be suppressed.

Note that the superficial flow velocity of all the gases passing through each absorption tower 2 may be generally 1 to 50 CrfL/sec, more preferably 5 to 30 cm/sec.

Generally, as the superficial flow velocity of all gases (in the absorption tower 2) decreases, the aforementioned gas side mass transfer coefficient KG decreases, which is preferable from this point of view, but conversely, the amount of NOx absorbed tends to decrease. So, the superficial flow rate of the total gas mentioned above is the same for various types of absorption towers.

Therefore, it is best to act as appropriate.

In the method of the present invention, the multi-stage absorption tower 2 is preferably such that the total number of stages in each absorption tower is at least two or more, particularly preferably 3 to 10 stages, and most preferably 4 to 6 stages.

In the method of this invention, each absorption liquid in the multi-stage absorption tower 2 contains ammonium carbonate (charcoal chamber), and -10 to
The temperature is adjusted to 10°C, preferably -5 to 5°C.

In the method of this invention, the suction of the first absorption tower 2a.

The coal chamber water that is newly mixed through the fresh coal ammonium water supply line 7 into the circulating absorption liquid circulating through the collecting liquid circulation line 3a has a molar ratio (eNH
3/ecO2) is 1.5 to 2.2, especially 1.6 to 2,
It is preferable that the content of ammonium carbonate is 50 to IoOg/A', particularly 60 to 90 g/l in terms of ammonia.

If the molar ratio (eNH3/ecO2) of coal chamber water is smaller than 1.5, the NH4HCO3 component will increase and crystallization will occur easily, and if it is larger than 2.2, the molecular NH3 component will increase and NH3 will be diffused into the gas phase. Not only is it easy to do, but also (6)
It reacts with the NOx component in the reaction of formula (7) and becomes N2.

In addition, the content of ammonium carbonate is 10% in terms of ammonia.
If it is more than 0 g//l, the NH fraction will be supplied in excess of the required amount, resulting in the dissipation of NH3 vapor and the N2 production reaction of equations (6) and (7), which will result in a reduction of 50!9/1 in terms of ammonia.
If the amount is less than 1, not only will the absorption of NOx deteriorate, but also HNO□ will be generated, which will further become HNO, and N
This is not preferable because H4N03 is generated.

In addition, the circulating absorption liquid supplied to each absorption tower 2 from each absorption liquid circulation line 3 has a molar ratio (eNH3
/ecO2) is 1.3 to 2. Ol especially 1.4-1.
9, and the content in the charcoal chamber is 10 to 80 in terms of antakunia.
g/13. Especially 12-70f! # is preferable.

The circulation amount of the above-mentioned circulating absorption liquid in each absorption tower 2 is maintained by sequentially supplying a part of each circulation liquid of each absorption tower 2 to each absorption tower 2.

Therefore, as each circulating absorption liquid goes from the first absorption tower 2a to the final stage absorption tower 2d, the molar ratio of the coal chamber (e NH
s/e CO2) and the content in the coal chamber gradually decreases, but in this invention, the circulating absorption liquid (to which fresh coal chamber water is added) of the first absorption tower 2a molar ratio of chambers (
eNH3/ecO2) from 1.5 to 2.0, especially from 1.6 to
1.9, and the content in the charcoal chamber is 35 in terms of ammonia.
~80g#! ,% is 40 to 70 g/l, and furthermore, the circulating absorption liquid of the final stage absorption tower 2d has a molar ratio (eNH3/ecO2) of 1.3 to 1.3 in the nitrous chamber liquid extraction line 6.
1.6, and the content in the charcoal chamber is 10 in terms of ammonia.
~25&#, especially 12~21 g/11 is optimal.

The circulation amount of the circulating absorption liquid in each absorption tower 2 is about 10 to 80 times the amount of newly supplied coal chamber water, especially about 10 to 80 times the amount of newly supplied coal chamber water.
It is enough if it is about double.

Moreover, in this invention, if necessary, coal chamber water similar to that newly mixed with the circulating absorbent of the first absorption tower 2a is newly supplied to the circulating absorbent of each absorption tower 2. It's okay.

The circulating absorption liquid may be cooled by each cooler 8 attached to each absorption tower 2.

In the method of this invention, NOx gas is brought into contact with an absorption liquid containing a charcoal chamber at -10 to 10°C in a multi-stage absorption tower 2, and NOx in the NOx gas is sequentially absorbed, thereby converting the nitrous chamber liquid into In this case, each auxiliary NOx gas containing more eNO2 than eNO is added to the residual NOx gas A containing residual NOx that has passed through the contact zone between the gas and absorption liquid in the absorption tower 2 of each stage. of each mixed gas B obtained.
The molar ratio (eNO/eNO2) of Let it absorb.

The contact zone 12 of each absorption tower 2 mentioned above is an area where gas and absorption liquid come into contact and NOx in the gas can move to the source side. For example, as shown in FIG. The liquid column section 9 and the packed bed section 10 of the column 2, or the bubble bell shape of each absorption column 2 as shown in FIG.

This refers to the absorption liquid contact area 12 such as the shelf section 11.

Further, the residual NOx gas A is the gas that has just passed through the absorption liquid contact area of each absorption tower 2 and is about to be supplied to the next absorption tower 2. , absorbed in the absorption liquid contact area.

NOx, which is mainly composed of NO, was reduced to about 0.05 to 1
Contains 0 moles.

Furthermore, the above-mentioned auxiliary NOx gas refers to each of the above-mentioned absorption towers 2.
The molar ratio of NOx (eNO/eNO2) of the resulting mixed gas B is mixed with the remaining NOx gas.

eNO2, such that it can range from 0.9 to 5.
It is a gas containing more eNO than eNO.

This auxiliary NOx gas has a molar ratio of NOx (eNO/eN
O2) is about 0.05 to 0.8, especially 0.07 to 0.5, and NOx is about 5 to 20 molar, especially 5.5 to 15
It is preferable that the molar content is contained.

As shown in the figure, the auxiliary NOx gas is mixed with the residual NOx gas A of each absorption tower 2 through the auxiliary NOx gas supply line 4 to form a mixed gas B, which is then mixed into the absorption liquid contact area of the next absorption tower 2. supplied to

In this invention, the mixed gas B supplied to the absorption liquid contact area of the second absorption tower 2b has a molar ratio (eNO/eNO2) of 1.
5 to 5, especially 2.0 to 4.0, and the mixed gas B supplied to the other intermediate absorption tower 2c has a molar ratio (eNO
/eNO□) is about 0.9 to 4, especially 0.95 to 3, and the mixed gas B supplied to the final stage absorption tower 2d has a molar ratio (eNO/eNO□) of about 0. .9~1.
Optimally, it should be 1.

If the value of the molar ratio (eNO/eNO
NO3 + HNO2) is likely to occur, and eNO2 is
The molar ratio (
If e NO/e NO2) is set to an excessively large value, N
Since the absorption reaction of Ox gas does not proceed, the mixed gas B supplied to these absorption towers has the molar ratio (eNO/eN
02).

Furthermore, the molar ratio (eNO/eNO2) of the mixed gas B supplied to the absorption tower 2d in the final stage is set so that eNO and eNO2 are approximately equimolar based on the reactions of equations (1) and (9).

Next, embodiments of the present invention will be described in detail according to the drawings.

That is, in one embodiment, (a) NOx having a composition with a molar ratio (eNO/eNO2) of 1.5 to 7 is added to the first absorption tower 2a of the multistage absorption tower 2.
is supplied through the NOx gas supply line 1, and the molar ratio (e NH3/
Coal chamber water whose CO2) has been adjusted to 1.5 to 2.2 and which contains 50 to 100 g/l in terms of ammonia is passed through the fresh coal ammonium water supply line 7 to the absorption liquid circulation line 3a. The NOx gas is brought into contact with the absorption liquid mixed with the circulating absorption liquid in the absorption liquid contact area consisting of the liquid column part 9 and the packed bed part 10, or the bubble bell-shaped shelf part 11, so that the NOx gas in the NOx gas is brought into contact with the NOx gas. (b) Then, the residual NOx gas A immediately after passing through the absorption liquid contact zone of the first absorption tower 2a has a molar ratio (eNO/eNO2) of about 0.
．． 05 to 0.8 is added through the auxiliary NOx gas supply line 4a, and the molar ratio of NOx in the resulting mixed gas (eNO/eNO□) is about 1.5 to 5, and the mixed gas B is supplied to the absorption liquid contact area of the second absorption tower 2b, and is brought into contact with the absorption liquid mixed with a part of the circulating absorption liquid of the first absorption tower 2a to partially absorb NOx in the mixed gas, (c ) Thereafter, an auxiliary gas is mixed with each residual NOx gas A that has passed through the absorption liquid contact zone of the absorption tower 2 of each stage, and the molar ratio of NOx in each mixed gas (eNo/eNO2) is adjusted to about 0.9. - 4, each mixed gas B is sequentially supplied to the next stage absorption tower, and in the same manner as the second absorption tower 2b, NOx in the mixed gas is sequentially absorbed, (d) Finally, the final stage absorption To tower 2d, residual NOx
A mixed gas B of gas and auxiliary NOx gas having a NOx molar ratio (eNO/eN02) of about 0.9 to 1.1 is supplied and mixed in the same manner as in the absorption tower of each stage. NOx in the gas is absorbed, and the ammonium nitrite solution is extracted from the ammonium nitrite solution extraction line 6.

*“In the method of this invention, the residence time of the gas in each absorption tower 2 is approximately 0.8
~3 seconds, particularly about 1-2 seconds is preferred.

Next, examples and comparative examples will be shown.

Embodiment 1 A four-piece structure having the format shown in FIG. 1 and each part size shown in Table 1, with each absorption liquid contact area consisting of a liquid column part and a packed bed part.
Using the absorption towers in stages, according to the flow sheet shown in Figure 1, NOx gas is supplied to the first absorption tower, and while adding auxiliary NOx gas from the second absorption tower onward, NOx gas and NOx in each mixed gas are is absorbed into the absorption liquid at an absorption temperature of 0℃,
Ammonium nitrite was produced.

The operation of absorbing NOx gas and NOx in each mixed gas using the four-stage absorption tower described above will be described in detail below.

First, in the first absorption tower, a NOx gas (molecular (contains approximately 6.57 moles of oxygen)
is supplied to the absorption liquid contact zone of the first absorption tower, and coal chamber water with the composition shown in Table 2 is newly added at a feed rate of 5.461/hr. Circulating absorption liquid about 2
501! While circulating at a circulation rate of /hr, the NOx gas and the absorption liquid are brought into contact with each other at about 0° C. in the absorption liquid contact zone, so that a part of the NOx is absorbed by the absorption liquid, and then in the second absorption tower, the NOx gas and the absorption liquid are 1 The residual NOx gas that has passed through the absorption contact zone of the absorption tower is supplemented with auxiliary NOx gas (NOx content: 7.06 mol, eNO/
A mixed gas having the composition shown in Table 2, which was formed by adding eNO2 molar ratio: 0.11), was supplied to the absorption liquid contact area, while the circulating absorption liquid of the first absorption tower was added at a rate of 5.461/hr. While circulating a certain circulating absorption liquid at a rate of about 2501/hr, the mixed gas and the absorption liquid are brought into contact at about 0° C. in the absorption liquid contact area to absorb some of the NOx into the absorption liquid, and then a third In the absorption tower, the residual NOx gas that has passed through the absorption liquid contact zone of the second absorption tower is added with auxiliary NOx gas (same composition as the second absorption tower) in the amount shown in Table 2 to form the gas shown in Table 2. A mixed gas of the same composition is supplied to the absorption liquid contact zone, and the circulating absorption liquid of the second absorption tower is added at a rate of 5.46 l/hr.While the circulating absorption liquid is being circulated at about 250 #/hr, the absorption The mixed gas and the absorption liquid are brought into contact with each other at about 0°C in the liquid contact zone, and a portion of the NOx is absorbed into the absorption liquid.Finally, in the fourth absorption tower, the gas passes through the absorption liquid contact zone of the third absorption tower. A mixed gas having the composition shown in Table 2, which is formed by adding the amount of auxiliary NOx gas (same composition as the second absorption tower) shown in Table 2 to the remaining NOx gas, is supplied to the absorption liquid contact area, The mixed gas and absorption liquid were heated to about 0°C in the absorption liquid contact zone while circulating the circulation absorption liquid at about 250 l/hr, which was being added to the circulating absorption liquid in the third absorption tower at a rate of 5.461/hr. contact, and NOx was absorbed into the absorption liquid.

The ammonium nitrite liquid taken out at a rate of 5.46 l/hr from the circulating absorption liquid of the fourth absorption tower contains the second
Ammonium nitrite was produced in the amount shown in the table.

Total NOx from the first absorption tower to the fourth absorption tower. Supply amount (N
Molar yield of ammonium nitrite (N
H4N02 yield) are shown in Table 2.

Table 2 also shows the NOx content in the waste gas discharged from the fourth absorption tower.

Example 2 The composition of the coal chamber water newly added to the circulating absorption liquid of the first absorption tower was changed as shown in Table 2, and the supply amount of each auxiliary NOx gas and the NOx composition of the mixed gas were shown in Table 2. Ammonium nitrite was produced in a multi-stage absorption tower in the same manner as in Example 1, except for the following changes.

The results are shown in Table 2. Comparative Example l The same procedure as in Example 1 was carried out, except that the supply amount of NOx gas and fresh coal ammonium water and the circulation amount of circulating absorption liquid were the same as in Example 1, and each auxiliary NOx gas was not supplied at all. Ammonium nitrite was produced in a multistage absorption tower.

The results are shown in Table 2. Example 3 Using an apparatus in which the liquid column part of each absorption tower in Example 1 was eliminated and the place corresponding to this liquid part was a packed bed, the supply amount of each auxiliary NOx gas and the NOx composition in the mixed gas were determined. Ammonium nitrite was produced in a multistage absorption tower in the same manner as in Example 1, except for the changes shown in Table 2.

The results are shown in Table 2.

[Brief explanation of the drawing]

FIGS. 1 and 2 are flow sheets outlining the process for carrying out this invention. 1: NOx gas feed line, 2: Absorption tower (2a: first absorption tower, 2b: second absorption tower, 2c; third absorption tower, 2d
; 4th absorption tower), 3; Absorption liquid circulation line, 4; Auxiliary NO
x gas feed line, 5: waste gas line, 6; ammonium nitrous liquid extraction line, 7; fresh coal ammonium water supply line, 8; cooler, 9; liquid column section, 10: packed bed section, 11; bubble bell shape Shelf section.

Claims (1)

[Claims] 1. NO containing nitrogen oxides (abbreviated as NOx)
x gas is brought into contact with an absorption liquid containing ammonium carbonate at -10 to 10°C in a multi-stage absorption tower to sequentially absorb NOx in the NOx gas to produce an ammonium nitrite liquid, ) A NOx gas containing approximately 5 to 20 moles of NOx having a molar ratio (eNO/eNO2) of 1.5 to 7 is supplied to the first absorption tower of the multi-stage absorption tower, and ammonia equivalent component NH3 is molar ratio of carbon dioxide equivalent component (abbreviated as ecO2)
e NHs/e C02) is adjusted to 1.5 to 2.2, and ammonium carbonate is 50% in terms of ammonia.
Adding ammonium water containing ~100 g/71 to the circulating absorption liquid of the first absorption tower and bringing this absorption liquid into contact with the NOx gas to partially absorb NOx in the NOx gas, (b) then, The molar ratio of NOx in the mixed gas obtained by adding auxiliary NOx gas to the residual NOx gas that has passed through the absorption liquid contact zone of the first absorption tower (, eNO/eNo 2 )
is about 1.5 to 5, the mixed gas is supplied to the second absorption tower, and a part of the circulating absorption liquid of the first absorption tower is brought into contact with the absorption liquid mixed with the circulating absorption liquid of the second absorption tower. (C) After that, auxiliary NOx is added to each remaining NOx gas that has passed through the absorption liquid contact zone of each absorption tower in each stage.
The molar ratio of NOx in the resulting mixed gas (e
No/eNo2) is set to about 0.9 to 4, each of the mixed gases is sequentially supplied to the next absorption tower, and NOx in the mixed gas is sequentially absorbed in the same manner as the second absorption tower, (d) The molar ratio of NOx (eNOx
A method for producing ammonium nitrite, which comprises supplying a mixed gas having a ratio of about 0.9 to 1.1 (/eN02) and absorbing NOx in the mixed gas in the same manner as in each stage.