JP2013091056A - System for removing nitrogen oxide in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system for removing nitrogen oxide in an exhaust gas of a combustion gas at a lower temperature with a smaller size than a conventional urea SCR system.SOLUTION: Water containing active hydrogen is made to react with a combustion exhaust gas to reduce and remove the nitrogen oxide in the combustion exhaust gas. The method for generating the active hydrogen comprises using magnesium and an acid.

Description

  The present invention relates to an exhaust gas treatment system for removing nitrogen oxides from exhaust gas discharged from an internal combustion engine such as a vehicle or a ship, a combustion apparatus such as a thermal power plant or a garbage incineration facility.

In recent years, nitrogen oxides (NO + NO ₂ ) emitted from thermal power plants, garbage incineration facilities, vehicles, marine diesel engines, etc., cause acid rain and smog. is important. In particular, the suppression of nitrogen oxides is a major problem in diesel engines.

For example, in the case of a diesel engine, as a method for suppressing nitrogen oxides in exhaust gas,
(1) Exhaust gas treatment technology suppresses the generation of nitrogen oxides by burning at a low temperature and low pressure as much as possible, and treats PM, CO, HC with an oxidation catalyst or DPF (Diesel particulate filter),
(2) There are two main types of urea SCR (Selective Catalytic Reduction) system that suppresses the generation of CO and HC by completely burning at as high a temperature as possible and reduces the resulting nitrogen oxides with urea water.

  The principle of the urea SCR system applies that ammonia and nitrogen oxides are reduced to nitrogen and water by reaction. However, it is dangerous to load ammonia in a vehicle. Instead, it is loaded with urea water in a tank and injected into exhaust gas to hydrolyze it at a high temperature to obtain ammonia gas. Nitrogen oxide is reduced to obtain nitrogen gas and water. Currently, this system is the mainstream of exhaust gas systems for large vehicles equipped with diesel engines.

JP 2000-230414 A JP-A-2005-334681

However, this system has the following four problems.
(1) In addition to the urea water tank and the injection system, it is necessary to equip the front and rear stages of the system with an oxidation catalyst, which increases the weight.
(2) Since the crystallized urea coagulates and the injector is clogged, it must be cleaned regularly.
(3) A device for preventing ammonia leakage is necessary.
(4) If the temperature of the exhaust gas is low, the catalyst will not work sufficiently.
There are problems such as.

  The present invention was made to solve the various problems (1) to (4) described above, and is a system for efficiently reducing and removing nitrogen oxides in non-gas generated from various facilities such as diesel engines. The purpose is to provide.

  In order to solve the above problems, first, the first invention is an exhaust gas treatment method characterized by reacting water containing active hydrogen with combustion exhaust gas to remove nitrogen oxides in the combustion exhaust gas.

  Further, according to a second aspect of the present invention, the method for generating active hydrogen is based on magnesium and an acid. The exhaust gas according to claim 1, wherein nitrogen oxides in the combustion exhaust gas are removed. It is a processing method.

  Further, according to a third aspect of the present invention, there is provided an exhaust gas characterized by removing nitrogen oxides from the combustion exhaust gas according to the second aspect of the present invention, wherein the method for generating active hydrogen is based on magnesium and acid. It is a processing method.

  In the present invention, the exhaust gas is selected from a gas discharged from a combustion apparatus such as an internal combustion engine such as a vehicle or a ship, a thermal power plant or a garbage incineration facility.

In the present invention, active hydrogen is atomic hydrogen (hydrogen radical, H.) or hydride ion (H ⁻ ). For example, it is generated from a cathode during electrolysis or an acid is allowed to act on a metal. Can be generated when The method of generating active hydrogen by electrolysis requires large facilities and high running costs. A method in which an acid is allowed to act on a metal to generate active hydrogen is more preferable because it can be carried out using a general-purpose material and a simple method.

  Analysis of active hydrogen in an aqueous solution should be performed by an electron spin resonance apparatus (ESR) or a method using the absorbance of a colored product by a reaction between a radical and a wrapping agent, for example, a known method such as registered patent No. 3657535. Can do.

  In addition, the metal in the present invention is selected from group 2 elements having particularly strong reducibility, and calcium and magnesium are preferable as versatile materials. Further, magnesium is more preferable from the viewpoint of stability in air and ease of handling.

The acid in the present invention can be an inorganic acid such as hydrochloric acid or sulfuric acid, or an organic acid such as citric acid, gluconic acid, lactic acid, ascorbic acid, or acetic acid.
In particular, citric acid is more preferable because of its high solubility in the oxide film of magnesium when combined with magnesium and high effect of preventing iron corrosion when combined with magnesium even in the acidic region. Magnesium can be reacted alone with water to generate a small amount of generated hydrogen, but it is not practical to adapt in the present invention.

  The amount of magnesium added may be any unreacted metallic magnesium remaining during the production of the active hydrogen of the present invention. There is no problem even if it exists in excess.

  The amount of inorganic acid and organic acid added is sufficient to dissolve the oxide film on the metal surface and react with the metal to generate hydrogen. For example, in the case of magnesium and citric acid, hydrogen gas is generated from the surface of magnesium. A method of adding citric acid in small portions while confirming the above is preferable. The reaction temperature of the aqueous solution is not particularly limited. According to the method of the present invention, the reaction proceeds sufficiently even at room temperature.

  The mechanism of removal of nitrogen oxides by active hydrogen according to the present invention is not clear, but it is thought that nitrogen oxides were reduced by hydrogen radicals and changed into nitrogen gas and water.

  In the present invention, the nitrogen oxide-containing gas to be treated includes an internal combustion engine such as a diesel engine vehicle or ship, an exhaust gas of a gasoline engine, an exhaust gas discharged from a combustion apparatus such as a thermal power plant or a garbage incineration facility, and the like. It is done. The water containing the active hydrogen of the present invention can also be used in place of the urea water of the urea SCR system used in combination with the catalyst.

(1) Urea (ammonia), which requires care, is not used, and the material (drug) used is extremely safe. Moreover, the reaction is sufficiently possible at a low temperature.
(2) Since the aqueous solution containing active hydrogen of the present invention is a non-corrosive reducing aqueous solution, there is no fear of metal corrosion in the reaction vessel and piping.
(3) As a lightweight and compact system, a reduction in the loading capacity of vehicles and ships can be avoided, and it can be applied to small cars and ships.

Schematic of NO ₂ removal performance test apparatus of an embodiment of the present invention Graph showing the NO ₂ removal performance of embodiments of the present invention

Hereinafter, an embodiment of a method for removing nitrogen oxides in exhaust gas according to the present invention will be specifically described with reference to the drawings. In addition, this invention is not limited at all by these embodiment. The concentration analysis of NOX of the present invention used a HORIBA Ltd. _NO X -A / F spectrometer MEXA-720NO _X.

In the present invention, as shown in FIG. 1, the cylinder 1 is filled with a nitrogen balance simulated exhaust gas containing about 1000 ppm (v / v) NO ₂ gas, and a 15 L reaction vessel 5 is filled with 10 L of tap water and reducing metal. 9, 200 g of flaky magnesium and 150 g of citric acid were placed in the reaction vessel 5 respectively. The pressure reducing valve connected to the cylinder 1 was adjusted so that the simulated exhaust gas flowed at 40 L / min, the gas supply valve 3 was opened, and the simulated gas was allowed to flow to react.

    The open end inserted into the reaction vessel 5 of the gas supply pipe 4 was first taken out from the active hydrogen-containing aqueous solution 8, and the above reaction was performed after the upper space of the active hydrogen-containing aqueous solution 8 was completely replaced with simulated exhaust gas. Moreover, the reaction container 5 was provided with a cover 10 at the opening so that the gas could be released freely.

About 50 seconds after confirming complete replacement of the upper space of the active hydrogen-containing aqueous solution 8 with the simulated exhaust gas, the open end in the reaction vessel 5 of the gas supply pipe 4 was inserted into the active hydrogen-containing aqueous solution 8. In order to measure the NO ₂ gas concentration after the simulated exhaust gas treatment, the NOX gas sensor 6 was attached to the upper space of the aqueous solution 8 containing active hydrogen, and the measured value was read with a NOX concentration analyzer.

  The pH of the sex hydrogen-containing aqueous solution 8 during the active reaction was about 3 to 5, and the oxidation-reduction potential (ORP) was between -250 mV to -500 mV. The liquid temperature was 22 ° C to 23 ° C. During the reaction, the active hydrogen-containing aqueous solution 8 became cloudy with extremely small bubbles of hydrogen gas generated from magnesium.

FIG. 2 shows the change over time in the NO ₂ gas concentration after the simulated exhaust gas treatment. At the start, the concentration of the NO ₂ gas concentration analyzer was 1041 ppm (v / v), and decreased to 290 ppm (v / v) about 3 minutes after the start of the exhaust gas treatment. It can be seen from FIG. 2 that the aqueous solution containing active hydrogen is effective for the decomposition and removal of NO ₂ gas.

  INDUSTRIAL APPLICABILITY The present invention is widely applicable to industrial exhaust gas treatment as an exhaust gas treatment system that removes nitrogen oxides from exhaust gas emitted from internal combustion engines such as vehicles and ships, thermal power plants, and garbage incineration equipment. is there.

DESCRIPTION OF SYMBOLS 1 ... Cylinder 2 ... Pressure reducing valve 3 ... Gas supply valve 4 ... Gas supply piping 5 ... Reaction container 6 ... NOX gas sensor 7 ... Bubble (exhaust gas)
8 ... Active hydrogen-containing aqueous solution 9 ... Reducing metal 10, ... Cover 11, ... NOX concentration analyzer

Claims (3)

  A method for treating exhaust gas, comprising: reacting water containing active hydrogen with combustion exhaust gas to remove nitrogen oxides in the combustion exhaust gas   2. The exhaust gas treatment method according to claim 1, wherein the method for generating active hydrogen is based on magnesium and acid.   3. The exhaust gas treatment method according to claim 2, wherein the method for generating active hydrogen is magnesium and citric acid.

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