JPH0428039B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for reducing NOx in coal gasified fuel. More specifically, the present invention relates to a dry continuous method for removing ammonia contained in coal gasified fuel as an impurity.

(Conventional technology) In recent years, coal gasification combined cycle power generation has been attracting attention both domestically and internationally as a new coal utilization technology that is highly efficient and environmentally friendly. Combined coal gasification combined power generation is a system that gasifies coal in a gasifier, desulfurizes and dedusts it in a gas purifier, and then combusts it in a gas turbine combustor to generate electricity in the gas turbine and at the same time generate steam using the exhaust heat. This method also generates electricity using a steam turbine.

By the way, combustion in such gas turbines, etc. involves the production of nitrogen oxides (NOx), but since nitrogen oxides are environmental pollutants that cause photochemical smog, etc., the amount and concentration that can be released into the environment is limited. is strictly regulated.

Therefore, conventional NOx prevention measures include the adoption of combustion technology that suppresses NOx generation, and
It is common to use denitrification technology to remove NOx.
However, the fuel itself has not been considered a problem, and the fuel itself has not contained enough ammonia, which causes NOx, to become a problem.

However, when coal is gasified in a gasifier, part of the nitrogen content in the coal is converted to ammonia (NH ₃ ), so NH ₃ is included as an impurity in the coal gasified fuel. Since NH ₃ is easily absorbed by water, NH ₃ is easily removed when gas purification is performed using a wet method such as a scrubber.
However, in that case, the temperature of the coal gasification fuel decreases, resulting in a decrease in thermal efficiency in the coal gasification combined cycle power generation system. For this reason, there is a demand for a method in which gas purification in a coal gasification combined cycle power generation system is performed in a dry state. However, in that case, the NH ₃ produced in the coal gasifier will be supplied to the gas turbine combustor with almost the same concentration. The NH ₃ contained in this fuel is easily converted into nitrogen oxides (NOx) during the combustion process.

The concentration of ammonia produced in a coal gasifier varies depending on the coal type and gasification conditions, but is estimated to range from several hundred ppm _to several thousand ppm. The proportion is high. Therefore, there is a need for low NOx technology in coal gasification combined cycle power generation systems to reduce nitrogen oxides caused by NH ₃ in coal gasification fuel.

(Problem to be solved by the invention) However, coal gasified fuel is an extremely low-calorie gas (less than 2000 kcal) and difficult to burn compared to normal gaseous fuels, and its combustion in a gas turbine combustor exceeds the flame propagation speed. Because the fuel flows at such a high speed, it becomes increasingly difficult to ignite, creating combustion conditions that lack flame stability. For this reason, it is extremely difficult to establish combustion technology to reduce nitrogen oxides caused by _NH3 in the fuel in gas turbine combustors, and although research and development is currently underway, it has not yet been realized. It's not working. In addition, in the combustion exhaust gas
Catalytic exhaust gas denitrification equipment using ammonia injection, which is a common method for removing NOx, can be said to be an established technology, but it uses an expensive catalyst and requires replacing the catalyst approximately every 30,000 hours. Therefore, installing it in a coal gasification combined cycle power generation system poses a large burden both from the operational and economic standpoints of the system.

Therefore, an object of the present invention is to improve the fuel itself, that is, to provide a method for reducing NOx in coal gasified fuel. Specifically, the purpose of the present invention is to provide a method for continuously removing ammonia from coal gasified fuel in a dry manner.

(Means for Solving the Problems) In order to achieve the above object, the NOx reduction treatment of coal gasified fuel of the present invention includes
Oxygen, a gas containing oxygen, or a compound that evaporates to produce oxygen is mixed as uniformly as possible in a temperature range of 700°C or higher.

In addition, the NOx reduction treatment of coal gasified fuel of the present invention can be applied to coal gasified fuel containing ammonia.
Nitrogen oxide is injected together with oxygen, a gas containing oxygen, or a compound that evaporates to produce oxygen in a temperature range of .degree. C. or higher.

In the present invention, the gas containing oxygen is generally air, but is not limited to this, and any gas containing oxygen can be used as long as it does not adversely affect fuel components or combustion. be. Compounds that evaporate to produce oxygen include hydrogen peroxide and the like. In this specification, unless otherwise specified, when expressed as oxygen, it includes oxygen obtained from a gas containing oxygen or a compound that evaporates to produce oxygen gas.

Further, as the nitrogen oxide, NO, N ₂ O, NO ₂ and the like are suitable. This nitrogen oxide injection lowers the lower limit temperature for ammonia decomposition.

The amount of these injected gases is preferably such that the ratio of oxygen concentration to ammonia, _O2 / _NH3 , is in the range of 1 to 3, and the ratio of nitrogen oxide concentration to ammonia, NO/ _NH3 , is in the range of 0.5 to 1. It is preferable. This is because when the O ₂ /NH ₃ ratio is larger than 1, it is effective in decomposing ammonia, but when it exceeds 3, the amount of NO produced increases to a non-negligible extent, and the ratio becomes ineffective in reducing NOx as a whole. Also,
If it is less than 1, much ammonia will remain without being decomposed.

Additionally, at the same time as oxygen injection with the above concentration ratio, NOx
Injecting NO has the effect of lowering the lower limit temperature for decomposing NH ₃ , but if the NOx/NH ₃ ratio is less than 0.5, the effect is small, and if it exceeds 1, the amount of residual NO becomes non-negligible.

Further, in the present invention, oxygen and nitrogen oxides are preferably partially extracted from the coal gasification combined cycle power generation system between the coal gasifier and the gas cooler of the coal gasification combined cycle power generation system or within the gas cooler. The method is characterized in that the mixed gas diluted with the desulfurized and dedusted coal gasified fuel is most preferably diluted with the extracted coal gasified fuel, and then injected into the coal gasified fuel in a cooled state.

(Operation) Therefore, NH ₃ in the coal gasified fuel reacts with oxygen and nitrogen oxides and is decomposed into nitrogen (N ₂ ) and water (H ₂ O).

In other words, NH ₃ in the fuel becomes HCN, CN, and NHi (NH ₂ , NH, etc.) at high temperatures where O ₂ is present.
After that, some reacts with O ₂ to produce NO or is reduced to N ₂ .

The present invention aims to decompose NH ₃ in coal gasified fuel by utilizing the decomposition of NH ₃ by O ₂ and the reaction of NO with NH ₃ accompanying the reaction process. This reaction takes place in the gas phase and does not require a catalyst. Furthermore, since the reaction between NH ₃ and NO takes place only in the coexistence of O ₂ , if oxygen is mixed with nitrogen oxides and injected into coal gasified fuel, NH ₃ will be converted into O ₂ and nitrogen oxides. It is then decomposed. In addition, the injected oxygen and nitrogen oxides are _NH3 in the coal gasified fuel.
Since the amount is so small as to be several times the concentration, the effect on other compositional changes of the coal gasified fuel is so small that it does not pose a problem.

(Examples) Hereinafter, the present invention will be described in detail based on Examples.

First, FIG. 11 shows an outline of a coal gasification combined cycle power generation system implementing the present invention. In the figure,
11 is a coal gasification furnace; 12 is a gas cooler heat exchanger such as a heat exchanger that cools the coal gasification fuel to a temperature at which it can be desulfurized and dedusted; and 13 is a coal gasifier contained in the coal gasification fuel ( 14 is a cyclone dust collector that collects soot), and 14 is a clean-up (desulfurization/dust removal) device that removes H ₂ S in the coal gasified fuel and char that cannot be collected by the cyclone 13.
5 is a gas turbine, and 16 is a steam turbine.
In this system, a part of the coal gasified fuel purified through the clean-up device 13 is extracted, cooled to near room temperature in the cooling device 17, and then the coal collected by the cyclone 13 is returned to the gasifier. used as a carrier gas for At the same time, a part of the extracted coal gasified fuel is used as a gas for diluting oxygen or nitrogen oxides to be injected into the coal gasified fuel just generated in the gasifier 11. After the bleed coal gasified fuel and air are mixed and diffused, they are preferably further cooled to a low temperature in a cooler 18 and injected into the fuel stream upstream of the gas cooler 12 or within the gas cooler 12 . In this example, air is used as the injected oxygen. The mixed gas of the extracted coal gasified fuel and air is injected into the coal gasified fuel and diffuses at the same time, resulting in a uniform mixed state. Immediately after injection, the high concentration region does not react because the temperature is low, forming a reaction freezing region. As the diffusion progresses, the mixed gas is heated and reaches the reaction temperature. Therefore, the reaction starts when the coal gasified fuel and oxygen are mixed as uniformly as possible.

Note that when a liquid such as a hydrogen peroxide solution is used as the oxygen to be injected, the reaction temperature will not be reached unless diffusion progresses to a certain extent because it is cooled by the heat of vaporization. Moreover, since it is sprayed in the form of droplets, it has a strong penetrating force and good dispersion. In this case, extracted coal gasified fuel as diluent gas is not required.

Next, FIG. 10 shows an example of an apparatus for carrying out NOx reduction treatment of coal gasified fuel according to the present invention. In the figure, 1 is a storage tank for storing O ₂ or a gas containing O ₂ or a compound that evaporates to produce O ₂ ;
2 is a storage tank for storing nitrogen oxides such as NO, N ₂ O, and NO ₂ or compounds that evaporate to produce nitrogen oxides; 3 is a storage tank that controls the flow rate of oxygen and nitrogen oxides according to a control signal from the NH ₃ concentration monitoring device 6; A valve 4 controls extracted fuel obtained by extracting a part of the desulfurized and dedusted coal gasified fuel supplied to the gas turbine 15 and O ₂ and/or nitrogen oxides supplied from the storage tank 1 or 2. A mixer for mixing, 5 is a temperature monitoring device 9 for measuring and monitoring the temperature of coal gasified fuel.
A valve 6 opens and closes a supply flow path for a mixed gas of oxygen and/or nitrogen oxides and extracted gasified fuel in response to a signal from the valve, and 6 supplies the mixed gas uniformly dispersed in the coal gasified fuel. The injector, such as a nozzle, 7 monitors the _NH3 concentration in the coal gasified fuel.
A device that outputs an instruction signal of the O ₂ concentration and nitrogen oxide concentration to be injected from the measured value of the NH ₃ concentration to the control valve 3; 8 is a gas sampling pipe that collects the coal gasified fuel in the flow path; 9 is a thermoelectric The gas temperature measuring device 10 is a temperature monitoring device and a device that determines the optimum injection position from the measurement results of the gas temperature at each position and outputs an opening/closing signal for the valve 5. Since coal gasified fuel leaving the gasifier usually has a temperature of 1000°C or higher, ammonia can be decomposed simply by injecting oxygen, etc. into it.

Decomposition of NH ₃ by oxygen (O ₂ ) Figure 1 shows the concentration of NH ₃ in coal gasified fuel.
The relationship between the injected O ₂ concentration and the NH ₃ concentration after a reaction time of 0.1 sec at 1000 ppm-v and a gas temperature of 1000° C. is shown. From the figure, if the O ₂ concentration is 1500 ppm or more, the NH ₃ concentration in the coal gasified fuel is
It can be understood that 1000ppm is decomposed to less than 1ppm. When the O ₂ concentration to be injected is 1500 ppm or less, the decomposition rate of NH ₃ deteriorates, and in particular, when the O ₂ concentration is 1000 ppm or less, it deteriorates rapidly. For example, for an O 2 concentration of 500 ppm, the NH ₃ concentration is decomposed only to 600 ppm. At this time, the concentration ratio of O ₂ to NH ₃ is 1.5.

Figure 2 shows that the reaction temperature is 1000℃ and the NH ₃ concentration is
1500ppm _O2 in 1000ppm coal gasified fuel
This figure shows the relationship between the reaction time and the NH ₃ concentration when NH 3 is injected. As is clear from the figure
NH ₃ is decomposed in about 0.01 seconds.

Furthermore, Figure 3 shows the relationship between the decomposition of ammonia by oxygen in the reaction after 0.1 seconds and the concentration of produced nitrogen oxides when the NH ₃ concentration in the coal gasified fuel is 1000 ppm-v and the gas temperature is 1000°C. It is a graph. According to this, when the O ₂ /NH ₃ molar ratio is less than 1, the ammonia decomposition rate drops sharply below 90%, and when it exceeds 4.5, the concentration of nitrogen oxides produced exceeds 150 ppm, which can be considered a tentative guideline. Put it away. However, in actual reactions, the
Since NH ₃ and O ₂ are not completely and uniformly mixed at a predetermined molar ratio, there is a risk that there will be local excess oxygen and NO will be produced.
It is preferable to keep it within the range of 1 to 3.

Moreover, FIG. 4 is a graph showing the relationship between the reaction temperature after 0.1 seconds and the ammonia decomposition rate when O ₂ is injected at a molar ratio of 1.5 times that of NH ₃ . As is clear from the figure, the ammonia decomposition rate is 700
When the temperature drops below ℃, the decomposition rate begins to decrease, and when the temperature drops below about 670℃, the decomposition rate deteriorates rapidly.

From the above results, it is clear that at a certain temperature, NH ₃ in coal gasified fuel is decomposed by O ₂ injection. When the reaction temperature is 1000℃ and the NH ₃ concentration in the coal gasified fuel is 1000ppm,
If the O ₂ concentration to be injected is 1500 ppm or more, the NH ₃ concentration can theoretically be reduced to 1 ppm or less.
_NH3 and _O2 for injections of _O2 above 1500ppm
The production of NO due to the reaction becomes visible. However, if only a small amount of NO is produced, NH ₃
The benefits of being decomposed are far greater.

(2) Decomposition of NH ₃ by nitrogen oxides and O ₂ Even if only nitrogen oxides are injected into coal gasified fuel, NH ₃ in the gasified fuel is not decomposed. NO.
causes an ammonia decomposition reaction only in the coexistence of O ₂ and lowers the lower limit temperature for decomposing NH ₃ .
For example, Figure 5 shows that _NH3 is present in coal gasified fuel.
This graph shows the concentration changes of various chemical species over the course of reaction time when 1000 ppm of NO is injected as nitrogen oxide at a reaction temperature of 1000°C. Even after the reaction time is 1.0 seconds, NH ₃ remains at the initial concentration of 1000 ppm.

However, when 1000 ppm O ₂ is injected together with NO, NH ₃ is rapidly decomposed. Figure 6 shows the respective concentrations of NH ₃ , NO and O ₂ after a reaction time of 0.1 seconds when 1000 ppm of NO and O ₂ are injected each when the NH ₃ concentration in the coal gasified fuel is 1000 ppm. This is what is shown for. From the figure, if the reaction temperature is 770℃ or higher,
It is clear that _NH3 is mostly decomposed. For example, when the reaction temperature is 770℃, the NH ₃ concentration is reduced to about 0.02ppm, and when the reaction temperature is 1200℃
It is also broken down to about 0.2ppm.

However, in this case, as the reaction temperature increases, NO
As the NO concentration increases and the reaction temperature exceeds 1000°C, the NO concentration in the coal gasified fuel becomes over 100 ppm.

Also, what should be noted in Figure 6 is that even if O ₂ and NO are injected together into coal gasified fuel containing NH ₃ , the decomposition reaction of NH ₃ will progress slowly below a certain temperature. That's true. Under the conditions shown in Figure 6, the temperature most suitable for decomposition is
It is judged to be 770℃.

Figure 7 shows NH ₃ , NO, O after a reaction time of 0.1 sec when 1500 ppm of O ₂ alone was injected into coal gasified fuel containing 1000 ppm NH ₃ and when 500 ppm NO was injected with the same concentration of O ₂ . Each concentration of ₂ is shown relative to the reaction temperature. In Figure 7, the reaction temperature that maximizes the decomposition of NH ₃ is 840°C when only O ₂ is injected;
When 500ppm was added, the temperature dropped to 750℃. In other words, the effect of injecting NO together with O ₂ is that NH ₃
The goal is to reduce the reaction temperature range that enables the decomposition of . In addition, if the reaction temperature is about 700℃,
When 500ppmNO is added at the same time, _NH3
The concentration is 2ppm (without NO addition, the dotted line
NH ₃ ), and the decomposition rate of NH ₃ is 99.8%,
Even though the optimum temperature for the reaction is 850°C, 700°C is sufficient from the viewpoint of the decomposition effect of NH ₃ . However, 700
In the temperature range around 0.degree. C., if the temperature is lowered even slightly, the decomposition of NH ₃ becomes worse, so it is practically preferable that the reaction temperature range is 700.degree. C. or higher.

Figure 8 shows the NO concentration injected at the same time and the reaction time after 0.1 seconds when 1000 ppm of O ₂ is injected into coal gasified fuel containing 1000 ppm of NH ₃ .
This shows the relationship between NH ₃ concentration and NO concentration. The reaction temperature is 1000°C. NO concentration is
If it is 700ppm or more, NH ₃ will decompose to 1ppm or less. However, as the NO concentration to be injected increases, the NO concentration remaining in the coal gasified fuel also increases rapidly. When 2000 ppm of NO is injected, in Figure 6, the NO in the coal gasified fuel is
The concentration will be approximately 1000ppm.

Further, FIG. 9 is a graph showing the relationship between the ammonia decomposition promoting effect due to the addition of nitrogen oxides and the NO concentration. As is clear from the figure, NO/
It can be seen that when the molar ratio of NH ₃ is less than 0.5, the ammonia decomposition rate deteriorates rapidly, and when it exceeds 1.0, the NO production concentration exceeds the allowable concentration.

In this way, by appropriately selecting the O ₂ concentration and NO concentration to be injected and injecting them in the optimal temperature range, ammonia can be decomposed within a range where the generated NO and other remaining components do not have a significant effect. It is important to For example, the optimum temperature range for decomposing NH ₃ is determined by the concentration of O ₂ and NO injected with respect to the NH ₃ concentration contained in the coal gasified fuel. Furthermore, once the reaction temperature is determined, the O ₂ concentration and NO concentration to be injected to the NH ₃ concentration in the coal gasified fuel are determined from the NH ₃ decomposition rate and the NO concentration remaining in the gasified fuel. .

In addition, when calculating the reaction to confirm the ammonia decomposition effect of the present invention, the injected
It was assumed that O ₂ and nitrogen oxides were uniformly mixed in the coal gasified fuel, and the reaction temperature was kept constant at the set initial temperature.

(Effects of the Invention) As is clear from the above explanation, the present invention involves injecting oxygen, an oxygen-containing gas, or a compound that evaporates to produce oxygen into coal gasified fuel in a temperature range of 700°C or higher. Because
NH ₃ in coal gasified fuel reacts with O ₂ and NO accompanying the reaction process of decomposition of NH ₃ by O ₂ to form nitrogen (N ₂ ).
and water (H ₂ O) and removed.

Furthermore, by simultaneously injecting nitrogen oxides with O ₂ , the decomposition reaction temperature of NH ₃ is lowered, so that the decomposition of NH ₃ is promoted more effectively.

Therefore, according to the present invention, NH ₃ in coal gasified fuel can be removed in a dry manner without causing a decrease in the thermal efficiency of the entire system, and moreover, it is possible to remove NH ₃ from coal gasified fuel in a dry manner. to cause
Since NOx is eliminated, it is possible to significantly reduce the amount of NOx generated. In addition, a catalytic exhaust gas denitrification device is not required, reducing equipment costs and making the system easier to operate.

[Brief explanation of drawings]

Figure 1 shows the NH ₃ concentration versus the added O ₂ concentration,
A graph showing the relationship between NO concentration and O _2. Figure 2 is a graph showing changes in the concentration of each chemical species with respect to reaction time.
Figure 3 is a graph showing the relationship between the decomposition of O ₂ and NH ₃ and the NO concentration produced, Figure 4 is a graph showing the relationship between reaction temperature and NH ₃ decomposition rate, and Figure 5 is when only NO is added. Graph showing the behavior of NH ₃ in O ₂
Figure 7 is a graph showing the relationship between reaction temperature and the behavior of NH _{3 and} NO. Figure 8 is a graph showing the effect of NO on the decomposition of NH ₃ .
Figure 9 is a graph showing the effect of NO addition on NH ₃ decomposition and the relationship between NO concentration, and Figure 10 is a graph showing the effect of NO addition on NH 3
FIG. 11 is a schematic explanatory diagram showing one embodiment of an apparatus for carrying out NOx conversion treatment, and FIG. 11 is a block diagram showing an outline of a coal gasification combined cycle power generation system implementing the present invention. 11...Gasifier, 12...Gas cooler, 14
...Clean up device, 18...Cooler.

Claims (1)

[Claims] 1. In coal gasified fuel containing ammonia, 700
A coal gasification fuel-lowering method characterized by injecting oxygen, a gas containing oxygen, or a compound that evaporates to produce oxygen gas in a temperature range of ℃ or higher.
NOx treatment method. 2 The amount of oxygen injected is the concentration ratio to ammonia.
The coal gasification fuel NOx reduction treatment method according to claim 1, wherein the _O2 / _NH3 ratio is 1 to 3. 3 600℃ in coal gasified fuel containing ammonia
A coal gasification fuel NOx reduction treatment method characterized by injecting nitrogen oxides together with oxygen, a gas containing oxygen, or a compound that evaporates to produce oxygen gas in the above temperature range. 4 The amount of oxygen injected is the concentration ratio to ammonia.
O ₂ /NH ₃ is 1 to 3, and the injection amount of nitrogen oxide is 0.5 in concentration ratio NO / NH ₃ to ammonia.
4. The coal gasification fuel NOx reduction treatment method according to claim 3, wherein the NOx reduction treatment method is in the range of 1 to 1. 5. The coal according to claim 1, wherein the oxygen and nitrogen oxides are injected between a coal gasification furnace and a gas cooler or within a gas cooler of a coal gasification combined cycle power generation system. Gasified fuel low NOx treatment method. 6. The low NOx coal gasification fuel according to claim 5, wherein the oxygen and nitrogen oxides are diluted with desulfurized and dedusted coal gasification fuel extracted from a coal gasification combined cycle system and then injected. processing method. 7. The oxygen and nitrogen oxides according to claim 5, wherein the oxygen and nitrogen oxides are diluted with desulfurized and dedusted coal gasified fuel partially extracted from a coal gasification combined cycle power generation system, cooled, and then injected. Coal gasification fuel NOx reduction treatment method. 8. The coal gasification fuel NOx reduction treatment method according to any one of claims 1 to 5, wherein the compound that evaporates to produce oxygen gas is a hydrogen peroxide solution.