JPH09220436A - Decomposition of nitrogen oxides in combustion gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decomposed nitrogen oxides in a combustion gas by adding a carbon recovered from the combustion of a petroleous fuel and substantially containing no ammonium sulfate into the combustion gas containing the nitrogen oxides at a specified temp. or above thereby to utilizing unburnt carbon in a petroleous combustion ash. SOLUTION: The carbon substantially containing no ammonium sulfate is added into the combustion gas containing the nitrogen oxides at >=800 deg.C. The quantity of the carbon to be added is properly decided while considering to the quantity of combustion gas, the concentration of the nitronge oxide in the combustion gas, oxygen balance in the combustion gas, a desired nitrogen oxide concentration or the like. In this case, the quantity of air to be fed is properly selected so as to well burn the carbon to be added. As the carbon substantially containing no ammonium sulfate, the combustion ash itself recovered from a low sulfur oil boiler or a carbon obtained by recovering from a high sulfur oil boiler and then removing ammonium sulfate by a wet process exemplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing nitrogen oxides in combustion gas, and more specifically, an industrially advantageous method for decomposing nitrogen oxides in combustion gas using industrial waste. It is about.

[0002]

2. Description of the Related Art For example, NO and NO, which are abbreviated as NO _x , are contained in combustion gas generated from a boiler of an oil-fired power plant.
Nitrogen oxides such as ₂ are contained, but they are harmful to the human body and cause photochemical smog, so they must be removed from the exhaust gas. As a method for removing nitrogen oxides in exhaust gas, a catalytic method using an expensive catalyst such as cerium oxide and a non-catalytic method using ammonia as a reducing agent have been established, each of which is used depending on the type of exhaust gas. There is.

By the way, for example, coal and petroleum-based fuels are used as fuels for boilers of thermal power plants. When petroleum-based fuels are used, combustion ash containing a relatively high proportion of unburned carbon is generated. . As a method for treating such combustion ash, a technique called a wet process has been established in order to recover valuable components such as vanadium contained therein. However, regarding carbon in petroleum-based combustion ash, although its effective use is being studied, at this stage, it has no choice but to treat it as waste,
The processing cost including the distribution cost cannot be ignored.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to industrially utilize unburned carbon in petroleum-based combustion ash, which is regarded as industrial waste at present. Another object of the present invention is to provide a method for decomposing nitrogen oxides in combustion gas, which is advantageous to the above.

[0005]

SUMMARY OF THE INVENTION The present invention is, surprisingly, if the unburned carbon in the petroleum-based combustion ash is added to the combustion gas containing nitrogen oxides and burned, Achieved based on the novel finding by the present inventors that the concentration of nitrogen oxides is reduced, and therefore, unburned carbon as waste can be incinerated simultaneously with decomposition of nitrogen oxides in combustion gas. The summary is
A method for decomposing nitrogen oxides in combustion gas, comprising adding carbon recovered from a petroleum-based fuel combustion furnace and substantially not containing ammonium sulfate to combustion gas containing nitrogen oxides at 800 ° C. or higher. Exist in.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
In the present invention, the combustion gas containing nitrogen oxides is not particularly limited, and the combustion gas of various combustion furnaces (combustion devices) that uses coal, petroleum-based fuel (for example, heavy oil, orimulsion, etc.) as fuel. Is mentioned. Specific examples include boilers such as thermal power plants and garbage incinerators.

In each of the above facilities, an electrostatic precipitator is arranged on the downstream side of the flue to collect the combustion ash. Then, for example, in the case of a high-sulfur heavy oil-fired boiler, ammonia is added to the combustion gas in order to prevent corrosion due to sulfuric acid gas (SO ₃ ) generated in the combustion gas, so the combustion ash in the exhaust gas is In addition to unburned carbon and heavy metal ash, it also contains ammonium sulfate.

In the present invention, it is necessary to use carbon that does not substantially contain ammonium sulfate as carbon recovered from the petroleum fuel combustion furnace. That is, in the present invention, the above-mentioned carbon is added to a combustion gas containing nitrogen oxides and burned as described below, but when carbon containing a large amount of ammonium sulfate is used, Ammonia must be added again due to the acid gas re-generated.

Carbons that are substantially free of ammonium sulfate typically include, for example, the combustion ash itself recovered from a low-sulfur heavy oil-fired boiler or a high-sulfur heavy oil-fired boiler followed by a wet process. An example is carbon (combustion ash) from which ammonium sulfate has been removed.

The above-mentioned wet process includes a step of performing solid-liquid separation after mixing combustion ash and water, and various steps of recovering various valuable metals, gypsum and the like from the aqueous solution separated in the step. Various wet processes have been proposed due to differences in methods of recovering valuable metals and gypsum (for example, JP-A-60-19086 and JP-A-60-4).
No. 6930, Japanese Patent Publication No. 4-61709, and No. 5-
9157 and 5-13718).

In the solid-liquid separation step in the above-mentioned wet process, carbon in which ammonium sulfate is substantially removed is recovered from the combustion ash recovered from the high-sulfur heavy oil-fired boiler. That is, one example of the composition analysis of the combustion ash recovered from the high-sulfur heavy oil burning boiler is shown in Table 1, but most of the ammonium sulfate component in the table is removed.

[0012]

[Table 1] ──────────────────────────────────── Component C NH ₄ SO ₄ V Ni Fe Mg SiO ₂  Weight% 10-80 0.5-20 20-60 1-5 0.3-2 0.3-2 0.1-8 0.1 ────────────────────────── ──────────

The solid-liquid separation step described above may be carried out under acidic conditions in order to positively dissolve the valuable metal and increase the recovery rate thereof, and as a result, it is mixed into the recovered carbon. The amount of ash content (metal component) varies depending on the wet process used.

In the present invention, ammonium sulfate need not be completely removed from carbon (combustion ash). That is, ammonium sulfate may be contained in carbon within a range in which the amount of sulfuric acid gas (SO ₃ ) generated in the combustion gas of carbon is not so large as to require addition of ammonia.

In the present invention, carbon which does not substantially contain ammonium sulfate is added to the combustion gas at 800 ° C. or higher, preferably 1000 to 1300 ° C. Then, from the viewpoint of improving the combustion efficiency of carbon, the addition of carbon is preferably performed during the flame of the combustion furnace. The addition of carbon is usually carried out by pneumatic transportation, and the amount of air supplied at that time is appropriately selected so that the carbon to be added is satisfactorily combusted. The amount of carbon added is not particularly limited, considering the amount of combustion gas, the concentration of nitrogen oxides in the combustion gas, the oxygen balance in the combustion gas, the concentration of nitrogen oxides in the target exhaust gas, etc. It is decided as appropriate.

The method for decomposing nitrogen oxides of the present invention using carbon (combustion ash) recovered from a combustion furnace for petroleum-based fuels is not limited to the combustion gas of the combustion furnace for recovering carbon described above, Applied to the combustion gas of the combustion furnace of
When applied to the combustion gas of a combustion furnace that recovers carbon, the physical distribution cost of carbon as waste can be significantly reduced, which is the most industrial advantage.

The method for decomposing nitrogen oxides of the present invention is
There are also the following advantages over the non-catalytic method using ammonia as the reducing agent. That is, in the non-catalytic method using ammonia, ammonium sulfate produced from ammonia supplied in excess with respect to nitrogen oxides and sulfuric acid gas (SO ₃ ) in the combustion gas precipitates as the temperature of the combustion gas decreases, There is a problem that it adheres to the piping group arranged in the boiler flue. However, in the method for decomposing nitrogen oxides of the present invention, carbon (combustion ash) is used instead of ammonia, and therefore the above-mentioned problems are not present. The decomposition mechanism of nitrogen oxides in the present invention is not necessarily clear, but it is presumed that some reduction action of carbon is involved.

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In the following examples, "%" means "% by weight".

Example 1 As a test facility, a heating furnace was equipped with 20 burners of a heavy oil and by-product oil / gas co-firing tangential corner firing system, and its flue had a second heater pipe and a first heating system. Boiler equipment of a thermal power plant (Mitsubishi CE single-body radiating type natural) equipped with sequential piping, economizer (ECO), air preheater, electrostatic precipitator (EP), flue gas desulfurizer A circulating boiler) was used.

The ammonium sulphate-containing combustion ash recovered from the electrostatic precipitator of the above equipment was mixed with 5 times by weight of water and sulfuric acid in an amount necessary to adjust the pH to 3 or less, and solid-liquid separation was performed to separate The carbon sludge was dried. The obtained carbon sludge had a bulk specific gravity of 0.44 T / m ³ , and elemental analysis values of C: 60.3%, H: 1.5%, N: 5.2.
%, S: 9.0%, V: 1.24%, Ni: 1.32
%, Fe: 0.90, Mg: 0.78%.

The above carbon sludge is transferred to a hopper, and is supplied to the inside of the heating furnace (in flame) of the boiler equipment by air conveyance by air supplied from a roots blower through a rotary valve provided at the lower part of the carbon sludge. Burned. The amount of carrier air is 4 m ³ / min (blowing velocity:
80m / sec) Carbon sludge supply rate (combustion rate)
Was 400 kg / hr. The amount of exhaust gas is 260000 Nm ³ / hr at the ECO outlet and 330000 N at the EP inlet.
m ³ / hr.

The NOx concentration in the exhaust gas at the chimney was measured as a result of continuous operation for about two months, and the average concentration was 115 ppm. In addition, as a result of calculating the combustion rate (incineration rate) of carbon sludge by mass balance calculation, 8
7%. For comparison, the supply of carbon sludge into the heating furnace was stopped, and continuous operation was performed as above,
As a result of measuring the NOx concentration in the exhaust gas at the chimney, the average concentration was 145 ppm. From the above results,
It was confirmed that about 20% of NOx in the exhaust gas was decomposed by the combustion of carbon sludge.

[0023]

INDUSTRIAL APPLICABILITY The present invention described above has great industrial value because it is possible to decompose nitrogen oxides in combustion gas and incinerate unburned carbon as waste.

Front page continuation (72) Inventor Tatsuyuki Kimura 16 Towada, Kamisu-cho, Kashima-gun, Ibaraki Kashima Kita Kyodo Power Co., Ltd.

Claims (1)

[Claims] 1. Nitrogen in a combustion gas containing nitrogen oxide, wherein carbon recovered from a petroleum fuel combustion furnace and containing substantially no ammonium sulfate is added to the combustion gas containing nitrogen oxides at 800 ° C. or higher. Oxide decomposition method.