JP3172304B2 - Method and apparatus for removing ammonia in carbon dioxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for removing ammonia by-produced when nitrogen oxides (NO _x ) in carbon dioxide are reduced and decomposed with hydrogen in the presence of a catalyst.

[0002]

2. Description of the Related Art In recent years, as part of the prevention of global warming, interest in a technology for recovering carbon dioxide from combustion exhaust gas has been increasing. For example, in the steel industry, a combustion gas having a high concentration of carbon dioxide (CO ₂ ) has been used. Pressure swing adsorption (Pr
essure Swing Adoption: P
It is commercially recovered by the SA) method.

[0003] During the combustion exhaust gas contains typically NO _x, NO during the recovery of the CO ₂ by PSA at present _x
Since it is difficult to remove, it is necessary to remove the NO _x in the PSA of the post-treatment step.

Although there are various methods for removing NO _x, the reductive decomposition method using H ₂ using a noble metal catalyst is advantageous because of its high removal rate and easy operation. For example,
According to the method disclosed in Japanese Patent Application Laid-Open No. 219309/1992, NO _x is reductively decomposed and removed at a low temperature of 50 to 60 ° C. with H _{2 in} the presence of a platinum (P _t ) catalyst. At that time, there is no generation of NH ₃ as a side reaction, and it is known that this is a suitable removal method.

[0005] While the de-NO _x by the precious metal catalyst are known on pollution control technology, raise the activity of the catalyst in recent years, has become more capable so the reaction at low temperatures. For example,
In P _t / Al ₂ O ₃ based catalyst in the removal method described above of the NO _x can be disassembled more than 99% of the NO _x at 50-60 ° C., is practically suitable catalyst in terms of energy consumption.

However, these catalysts having a high activity at a low temperature are affected by the effect that poisonous components such as dust block the pores of the porous catalyst and reduce the contact surface area after long-term use. Is reduced. In addition, there is also a side reaction in which a part of NH ₃ is generated together with a main reaction of reductively decomposing NO _x by H ₂ , and there is a problem that the selectivity for determining the degree of the main reaction and the side reaction is reduced. .

[0007] In the P _t / Al ₂ O ₃ catalyst, the generation of NH ₃ as a by-reaction components becomes a non-negligible amounts over its use time was found newly. P _t / Al ₂ O ₃ as known is an expensive catalyst,
Cannot be replaced frequently. Therefore, it is necessary to exclude NH ₃ as a side reaction product from the recovered carbon dioxide gas due to long-term use of the catalyst.

[0008] The concentration of NH ₃ generation increases to about 5 to 10 ppm over about half a year, depending on the conditions of use of the catalyst. Therefore, NH ₃ has been conventionally removed using an appropriate removing apparatus. .

[0009]

As a general method of removing NH ₃ , there are methods such as adsorption and removal using activated carbon impregnated with a strongly acidic substance such as sulfuric acid, or installation of a washing tower. The adsorption capacity is small, the required replacement amount of activated carbon is large, and the processing cost is high. In the latter case, of course, it is necessary to take measures such as manufacturing the apparatus from stainless steel in consideration of carbon dioxide corrosion, and it is difficult to remove NH ₃ with an inexpensive apparatus.

The present invention solves the above-mentioned problems of the conventional apparatus in removing NH ₃ and makes it possible to easily and inexpensively reduce CO 3.
And to provide a method and apparatus capable of removing NH ₃ in _2.

[0011]

According to the present invention, the above-mentioned object relates to a method thereof, wherein a nitrogen oxide contained in carbon dioxide gas is reduced and decomposed by hydrogen in the presence of a catalyst as a side reaction in the gas. In the method for removing the produced ammonia, oxygen is added together with excess hydrogen in an amount more than necessary for the decomposition of nitrogen oxides to a dew point of -5 to -20 in the presence of the catalyst.
A first step of reducing and decomposing nitrogen oxides and synthesizing water by supplying the gas into the gas while maintaining the temperature at 0 ° C., a second step of pressurizing the gas to a pressure of 10 kg / cm ² or more at a gauge pressure, This is achieved by passing through a third step in which the gas thus produced is cooled to produce a carbonate mist and a drain, which absorbs ammonia and discharges the ammonia out of the system.

Further, with respect to an apparatus for carrying out such a method, ammonia produced as a side reaction in a gas when nitrogen oxides contained in carbon dioxide gas are reductively decomposed with hydrogen in the presence of a catalyst is removed. In the apparatus, a reducing device that receives the supply of the carbon dioxide gas and has a catalyst therein, a hydrogen supplying device that supplies hydrogen to the reducing device, an oxygen supplying device that supplies oxygen to the reducing device, and a reducing device are connected to the reducing device. A compression device for compressing gas from the reduction device;
A drain separation device connected to the compression device and having cooling means for cooling the compressed gas and separating a drain liquefied by cooling.

[0013]

In the present invention having the above structure, NH _{3 in} CO ₂ is removed by the following principle.

The main reaction of NO _x removal by H ₂ on the catalyst is NO + H ₂ → 1 / 2N ₂ + H ₂ O. In the present invention, since H ₂ is supplied in an amount equal to or more than the amount required for the main reaction and O ₂ is also supplied, excess H ₂ and O ₂ are converted into H ₂ + 1 / 2O ₂ → H ₂ O. Cause a reaction. That it is, in the present invention by supplying of H ₂ of the weight together with O _2, to produce a perform and water de-NO _x. As a result, a desired amount of moisture is contained in CO _{2 as} the processing gas.

[0015] Carbon dioxide as a product is usually distributed on the market as a liquefied gas. Even in the present invention, CO ₂ as the processing gas also passes through a liquefaction step for commercialization.
In the liquefaction step, the gas is compressed. At this time, when the water content in the gas exceeds the saturated vapor pressure due to the compression, the gas first precipitates in the form of a mist and further grows into droplets.

Since the mist or droplet water in the pressurized state is acidic, NH ₃ present in CO ₂ is well absorbed by the water. By discharging the water having absorbed NH ₃ as drain water, NH ₃ is removed from CO ₂ .

[0017]

Embodiments of the present invention will be described below.

FIG. 1 is a diagram showing the steps of this embodiment. In FIG. 1, carbon dioxide (CO ₂ ) in the combustion exhaust gas is PSA.
The gas is collected by the device 1 and sent to the reduction device 2. The reducing device 2 has a built-in catalyst for removing nitrogen oxides (NO _x ) contained in the CO ₂ . A hydrogen supply device 3 and an oxygen supply device 4 are connected to the reduction device ₂ , respectively, so that hydrogen (H ₂ ) and oxygen (O ₂ ) are supplied to the reduction device under the catalyst. . H
The supply amount of ₂ is determined such that the excess over the amount required for reduction of the NO _x. Accordingly, in the reducer 2, with NO _x contained in the CO ₂ is reduced and decomposed with H ₂ as a main reaction, partly produces NH ₃ by side reactions. An excess amount of H ₂ is supplied from the hydrogen supply unit 3 to the reduction unit 2 in excess of the amount required for the main reaction. O ₂ supplied from the oxygen supply unit 4 reacts with the excess H ₂ Generates water in the form of a mist or water droplets.

Thus, the main reaction between NO _x and H ₂ causes NO _x
Is reduced and CO ₂ containing NH ₃ by a side reaction is sent to the compression device 5 in a state where it contains moisture, and is compressed. This compression is performed, for example, at a gauge pressure of 10 kg / cm ² or more. The compressed gas is then brought to the drain separation device 6, where it is cooled and the water in the gas becomes drain water. In the drain separation device 6, the NH ₃ is well absorbed by the drain water because the gas is in a compressed state. N
The drain water having absorbed H ₃ is discharged from the separation device 6.

A drying device 7 is connected to the drain separation device 6, and CO ₂ from which NH ₃ has been removed together with drain water.
Is dried here, liquefied by the next liquefaction device 8, and filled in the storage tank 9 as a product.

Table 1 shows an example of the state of the gas in the stream between each step in the apparatus of this embodiment.

[0022]

[Table 1]

Table 1 shows the process and the N in the stream.
It shows the concentrations of O _x , NH ₃ and H ₂ O and the gas pressure. As an example, the pressure in the compression step is set to 20 kg / cm ²
(Gauge pressure), since the cooling temperature after compression was 32 ° C., the H ₂ O concentration for generating a drain required a dew point of −12 ° C. or higher, whereas the actual H ₂ O concentration was about −7 ° C. As described above.

NO_xIn the catalyst, 6 ppm of NH_ThreeBut
By-product, CO after drain separation _TwoInside, the detection tube method
Was not detected. Drain amount and
NH contained in this _Four ⁺I actually measured ions,
NH in carbon dioxide_ThreeThe whole amount is removed from the drain
Confirmed that it had been.

[0025]

The present invention relates to a method for removing ammonia from carbon dioxide gas, by supplying more than the amount of hydrogen necessary for the reductive decomposition of nitrogen oxides and further supplying oxygen to absorb the ammonia in the generated water. As a result, drain water can be discharged, and ammonia can be removed by a very simple process. In addition, the device can be simply added to the hydrogen and oxygen supply device and the compression device, so that the above-described method can be performed with an inexpensive device.

[Brief description of the drawings]

FIG. 1 is a process chart showing one embodiment of the present invention.

[Explanation of symbols]

 2 reduction device 3 hydrogen supply device 4 oxygen supply device 5 compression device 6 drain separation device

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takamasa Takahashi 1-3-3 Kudankita, Chiyoda-ku, Tokyo Adchemco Co., Ltd. (56) References JP-A-4-123523 (JP, A) JP-A-5 -124808 (JP, A) JP-A-4-219309 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 31/20 B01D 53/94 CA (STN)

Claims (2)

(57) [Claims] 1. A method for removing ammonia generated as a side reaction in a gas when reductively decomposing nitrogen oxides contained in carbon dioxide gas with hydrogen in the presence of a catalyst, the method comprising the steps of: A first step of supplying oxygen into the gas while maintaining the dew point at -5 to -20 ° C in the presence of the catalyst with excess hydrogen in excess of the amount to reduce and decompose nitrogen oxides and synthesize water; , The above gas at a gauge pressure of 1
A second step of pressurizing to 0 kg / cm ² or more, and a third step of cooling the pressurized gas to generate a carbonate mist and a drain, to absorb ammonia into the mist and discharge it to the outside of the system. A method for removing ammonia in carbon dioxide gas. 2. An apparatus for removing ammonia produced as a side reaction in a gas when a nitrogen oxide contained in carbon dioxide is reductively decomposed by hydrogen in the presence of a catalyst. A reduction device having a catalyst, a hydrogen supply device for supplying hydrogen to the reduction device,
An oxygen supply device for supplying oxygen to the reduction device, a compression device connected to the reduction device for compressing gas from the reduction device, and cooling means connected to the compression device for cooling the compressed gas; An apparatus for removing ammonia in carbon dioxide gas, comprising: