JPH04136602A - Method of reducing nox - Google Patents

Abstract

PURPOSE:To reduce thermal NOx and, at the same time, achieve the reduction of the unburned carbon in the reduction zone of flame by blowing in carbon powder of a specific quantity to the fuel near the burner flame of a combustion furnace that employs petroleum fuel. CONSTITUTION:It is possible to reduce NOx in the exhaust gas by blowing in carbon powder or aqueous slurry near the burner flame of a combustion furnace. And, at least one kind of compounds that contain Fe or Ca is mixed. The compounds that contain Fe or Ca are, for instance for Fe, Fe2O3, FeOOH, Fed, and for Ca, Ca(OH)2, CaCO3, (CH3COO)2Ca, Ca(NO3) and they are chosen from these compounds. The carbon powder is in the ratio of 0.1-1.0wt.% of the fuel, the quantity of compounds that contain Fe or Ca is preferably 5-100ppm in total. When the carbon is added in the aqueous slurry that which contains carbon in 1.0-5.0wt.% is used. The particle diameter of a compound that contains carbon and Fe or Ca is preferably that of powder passing 350 mesh. If it is used in slurry, diameter below 2.0mu is preferable.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for reducing nitrogen oxides (hereinafter referred to as NOx) contained in the exhaust gas of combustion equipment such as boilers and combustion furnaces that use fossil fuels. .

(Conventional technology) In recent years, the number of factories, hospitals, buildings, etc. that are equipped with boilers and various furnaces for private power generation or supply of heat and steam has been increasing. Fossil fuels such as asphalt, oil coke, and coal are used, and NOx is always generated during combustion.

Large facilities such as commercial boilers are usually equipped with a denitrification device to reduce NOx in exhaust gas, and in particular, an ammonia reduction denitrification device is well known. This ammonia reduction denitrification method is a method in which ammonia is injected and mixed into the exhaust gas, and then reacted at 30 to 500'C in a denitration catalyst layer to reduce it to harmless nitrogen and water.

(Problems to be Solved by the Invention) However, the above-mentioned denitrification equipment requires a large space, requires a huge amount of equipment cost, and has to be replaced at regular intervals because the catalyst wears out. . Furthermore, lining costs are high because ammonia is consumed as a denitrification agent.

On the other hand, a method of reducing NOx in exhaust gas without using the above-mentioned denitrification catalyst is known. One of the methods is to inject ammonia into the high temperature range of about 800 to 1100'C in the exhaust gas to directly reduce NOx. However, when this method is adopted, the amount of ammonia injected is NO.
This is several times the stoichiometric amount required to reduce NH, )H5Q4 is produced. Since this substance has a low melting point of approximately 150"C, it adheres to downstream equipment such as air preheaters, reducing equipment performance and causing corrosion. Also, ammonia is a highly toxic substance and a high-pressure gas. Therefore, it is difficult to handle.

The present invention solves the above problems and aims to provide a NOx reduction method suitable for small-scale equipment that does not require a large space and can be operated at low running costs.

(Means for Solving the Problems) As a result of extensive research in order to solve the above problems, the present inventor has devised a method for reducing NO in exhaust gas by injecting carbon powder or aqueous slurry into the vicinity of the burner frame of a combustion furnace.
It has been found that x can be reduced. It has also been found that the amount of dust particles can be significantly reduced by mixing and injecting at least one compound containing Fe or Ca into the above-mentioned carbon.

The carbon used in the present invention includes ordinary carbon powder,
It is economical because electrode carbon and dust collected from an electrostatic precipitator can be used sufficiently. Capone turns into CO in the high-temperature combustion gas and acts as a strong reducing agent. It is also considered that NOx, such as No and No□, generated in the flame when carbon is burned is directly reduced to N2, and its effect is estimated to be based on the following formula.

2C+0□→2CO 2CO+ 2NO-+ Nz + 2CO□C
+2NO→N2+Co□ 2C+ 2NO□ → N, + 2CO□NOx is generated in the combustion flame, especially at oxidation points (true spots). Therefore, NOx can be reduced by blowing in carbon from the air inlet near the frame.

The reason why dust particles are reduced when Fe or Ca is added together with carbon is that, for example, Fe changes to FeO and then FezO3 in the combustion gas, and Fe2O3 acts as an oxidation catalyst in the high temperature gas, accelerating the dust particles. It is thought to be burned. Similarly, Ca also forms peroxide (Ca) in high-temperature combustion gas.
O□), which is thought to release atomic oxygen and promote the combustion of the dust.

The above-mentioned compounds containing Fe or Ca are not particularly limited, and for example, Fe can be
From among eO, or Ca is Ca (OH) z, C
aC0=(C)13cOo)zCa, Ca(No:+
) z and mixed with carbon in the form of powder or aqueous slurry.

Fe5Oa and Ca(NO:+)z may be added as an aqueous solution.

The amount of carbon and compounds containing Fe or Ca used is:
Carbon powder is 0.1 to 1.0w relative to fuel
The amount of the compound containing Fe or Ca is preferably 5 to 1 oopp+m in total amount as Fe20= or CaO based on the fuel. When these are added as an aqueous slurry, the carbon aqueous slurry is used in an amount of 1.0 to 5.0 wt%, and the compound containing Fe or Ca is mixed into the aqueous slurry in the range of 5 to 100 ppI11.

The particle size of the compound containing carbon and Fe or Ca is 3
A powder with a 50 mesh pass is preferable, and when used as a slurry, a particle size of 2.0 μm or less is preferable to prevent sedimentation.

Next, the injection point for these additives must be located close to the burner for the reasons mentioned above, and may be divided into more than one point. A screw feeder extracts a fixed amount of powder, and an injector sends it to the burner along with conveying air.

(Examples) Hereinafter, the present invention will be explained in more detail by examples with reference to the drawings.

・Test boiler specifications 2 Mitsubishi CB-VU-60 type Evaporation amount: 150'/H ・Fuel composition Carbon 86-1% Hydrogen 11 Sulfur 2-3" Nitrogen 0.2" Residual carbon 11-12" Ash content 0 .02~0.03' In the figure, 1 is a heavy oil tank, 2 is an additive tank, and 3 is a metering pump, and the additive is injected together with air from an air inlet 5 close to the fuel injection port of the burner 4.Air Stream 12 has been preheated in air preheater 10 and combustion gas stream 1
1 from the combustion chamber 6 to the superheater 7, low temperature superheater 8, energy saver 9,
The air is discharged via an air preheater 10.

Example 1 Carbon powder was added to the fuel at Q, 5wt% and 1.0wt
The reduction in NOx was measured at the smoke inlet for the case where % was added and compared with the case when no addition was made. The concentration of NOx is JIS
- to -0104 Measured by PDS method.

Note that NOx is shown in terms of N02% conversion value.

Example 2 The amount of dust and N when 1100 pp of a compound containing Fe or Ca was added alone or in combination to carbon powder
Measured 0xf14 degrees, and the concentration of dust was JIS-2880.
8 Cylindrical f Paper Cylinder Climb was measured.

Table 1 From the above results, it was confirmed that the concentration of dust as well as the NOX concentration could be reduced.

(Effects of the Invention) The method of the present invention can simultaneously achieve a reduction in thermal NOx in the oxidation zone of the burner flame and a reduction in unburned carbon in the reduction zone.

There is no need for a denitrification catalyst as a fixed bed, and the additives injected into the exhaust gas do not need to be molded, so they can be supplied at low cost. Since there is no problem of catalyst deterioration, lining costs are low.

[Brief explanation of the drawing]

The figure shows a combustion process diagram of a heavy oil-fired boiler to which the method of the present invention is applied, and in the figure, 1: heavy oil tank 2: additive tank 3: pump
4: Burner 5; Air and additive inlet 6: Combustion chamber 7: Superheater 8, low temperature superheater 9: Economizer 10: Air preheater 11: Combustion gas flow 12: Air flow

Claims (1)

[Claims] 1. A combustion furnace using petroleum-based fuel, characterized in that 0.1 to 1.0% by weight of carbon is injected as powder into the vicinity of the burner frame of the combustion furnace based on the fuel. Method for reducing NOx in exhaust gas. 2. Along with carbon, Fe_2O_3, FeOOH, F
eO, FeSO_4, CaO, Ca(OH)_2, Ca
CO_3, (CH_3COO)_2Ca, Ca(NO_
3) A method for reducing NOx and dust in combustion furnace exhaust gas, characterized by injecting one or more compounds selected from the group consisting of _2 in a mixture of 5 to 100 ppm relative to the fuel. 3. The method according to claim 1 or 2, wherein 1.0 to 5.0% by weight of carbon relative to the fuel is injected as an aqueous slurry. 4. The method according to any one of claims 1 to 3, wherein the particle size of the compound containing carbon and Fe or Ca is 350 mesh pass when used as a powder, and 2.0 μ or less when used as an aqueous slurry. .