JP4511282B2 - Dry ammonia decomposition method - Google Patents

Description

The present invention relates to a dry ammonia decomposition method for an ammonia-containing fuel containing at least carbon monoxide as a compound containing at least a compound containing carbon atoms and H ₂ , such as a gasified fuel. More specifically, the present invention relates to dry decomposition of ammonia contained in an ammonia- containing fuel containing at least carbon monoxide as a compound containing at least carbon and a compound containing carbon atoms typified by gasified fuel and H _2. The present invention relates to a method for decomposing ammonia.

  In recent years, it has been demanded that coal or biomass fuel be used efficiently and cleanly as a fuel to replace oil. In addition, since nitrogen oxides (NOx) in the atmosphere continue to increase particularly in urban areas, there is a strong demand to suppress the generation of NOx. There are two types of nitrogen oxides: fuel NOx due to nitrogen compounds in fuel and thermal NOx due to reaction of nitrogen and oxygen in air in the high temperature combustion zone. The former removes nitrogen compounds in fuel. By doing so, the latter can be reduced by not generating a local high temperature region during combustion.

  By the way, in order to use coal, heavy oil, biomass, municipal waste, etc. with high efficiency, there is a method of gasifying them at high temperatures to make them gasified fuels containing hydrogen, carbon monoxide, etc. Therefore, ammonia is generated when the fuel is gasified and mixed into the fuel. When the gasified fuel mixed with ammonia is burned as it is, nitrogen and oxygen in the ammonia react to generate fuel NOx.

  Therefore, as a method for efficiently suppressing the generation of fuel NOx without lowering the thermal efficiency of the gasification plant, a dry treatment method in which ammonia is decomposed into harmless nitrogen and hydrogen by the reaction promoting action of the catalyst has been studied. Yes.

  As this type of method, (a) a method using a catalyst having high ammonia decomposition activity and decomposing ammonia by heating the catalyst layer to a temperature at which high decomposition efficiency is obtained (Patent Document 1), (b) gasification In the process, a method of disposing the catalyst at a position where the temperature of the gasified fuel is high (Patent Document 2), (c) mixing oxygen or air into the gasified fuel and burning part of the gasified fuel, A method of decomposing ammonia by heating the catalyst to a high temperature by the heat generation (Patent Document 3) has been proposed.

  As the method of (a), a composite comprising a carrier substantially consisting of carbon and at least one element selected from the group consisting of alkaline earth metals and transition metals supported on the carrier is used as a catalyst. Thus, ammonia gas is decomposed into nitrogen gas under a temperature condition of 500 to 1200 ° C.

In addition, as the method (b), a part of the fuel pumped by a pump selected from liquid hydrocarbon fuels or liquid emulsions thereof, petroleum slurries of petroleum coke, or mixtures thereof containing sulfur, nitrogen, etc. Oxidize to produce a hot raw gas stream having a temperature of about 980 ° C. to 1650 ° C. and containing NH ₃ , H ₂ S, etc., and cooling the gas stream to a temperature of about 800 ° C. to 980 ° C. , And disproportionate by the catalyst to produce a process gas stream substantially free of NH ₃ .

  Further, as the method (c), oxygen-enriched air or oxygen is added to a combustible gas containing ammonia generated by gasifying a hydrocarbon, and a part of the combustible gas is combusted to set the temperature. After raising the temperature, the catalyst is brought into contact with a catalyst containing at least one of nickel, chromium and iron at a temperature of 800 ° C. or higher to decompose ammonia into nitrogen and water.

JP 2001-261302 A JP 7-10502 A JP-A-2-276890

  However, the above method (a) requires external heat to heat the catalyst to 500 to 1200 ° C. For this reason, in order to heat a catalyst, installation of a heating apparatus and new energy are needed, and an increase in equipment cost and energy cost is caused. In addition, although the heating minimum temperature of the catalyst is 500 ° C., only the ammonia decomposition treatment at 750 ° C. or more is disclosed in the examples, and further, the reaction at 750 ° C. causes a decrease in activity, but the reaction at 850 ° C. Discloses experimental data in which no decrease in activity occurs, and does not mention a reaction at 600 ° C. or lower.

  Moreover, even in the method using heat exchange, an increase in equipment costs due to the installation of a heat exchanger and energy loss accompanying heat exchange occur, and the thermal efficiency of the entire plant decreases. Furthermore, in order to make it react at high temperature, an expensive apparatus material with high heat resistance is required. In addition, the deterioration of the catalyst due to heat is accelerated. On the other hand, when the reaction is carried out at a low temperature, the ammonia decomposition rate is lowered and carbon is deposited on the catalyst, so that the catalyst performance is rapidly lowered.

  Further, when an ammonia decomposition apparatus is disposed at the outlet of a high-temperature gasification furnace as in the method (b), hydrogen sulfide and dust contained in the gasification fuel are directly supplied to the catalyst. For this reason, the catalyst performance is rapidly deteriorated due to poisoning or wear. Furthermore, in order to make it react at high temperature, an expensive apparatus material with high heat resistance is required. In addition, the deterioration of the catalyst due to heat is accelerated.

  Further, when the reaction is performed at a temperature of 800 ° C. or more as in the method (c), an expensive device material having high heat resistance is required, and the heat resistance of a device such as a flow rate adjusting valve installed downstream is required. The problem is that a heat exchanger must be installed to lower the temperature of the gas after decomposition, resulting in increased equipment costs and energy loss associated with heat exchange. Furthermore, deterioration of the catalyst due to heat is accelerated. Further, since this method is simply reacted with a catalyst containing at least one of nickel, chromium and iron, only a low decomposition rate can be obtained at a temperature of 800 ° C. or lower.

  All of the above conventional ammonia decomposition methods and apparatuses are premised on a reaction at a high temperature exceeding 600 ° C. However, in an actual machine incorporating an apparatus for carrying out the ammonia decomposition treatment method of the present invention, for example, an apparatus for decomposing ammonia in gasified fuel supplied to a gas turbine combustor, it is necessary to adjust the fuel flow rate with a flow control valve. However, the upper limit of the heat-resistant temperature of the flow control valve for gasification fuel applicable to an actual machine is 600 ° C. Since gasified fuels often contain hydrogen, steel is prone to hydrogen embrittlement, and use at high temperatures and pressures is an extremely severe condition for steel. The flow rate control valve is difficult to obtain, and even if it is available, it is extremely expensive and has low reliability, and is difficult to apply to an actual machine. For this reason, when the catalyst is heated to a temperature exceeding 600 ° C., it is necessary to lower the temperature to 600 ° C. or less with a heat exchanger. However, installing an expensive heat exchanger in the downstream of the ammonia decomposing apparatus in this way increases the equipment cost as described above and impairs the thermal efficiency of the entire plant due to energy loss due to the heat exchanger. A technique capable of efficiently decomposing ammonia at 600 ° C. or lower is desired.

The present invention can heat the catalyst to 600 ° C. or less without using external heat or heat exchange, eliminates the need for cooling of the cracked gas, maintains the performance of the catalyst for a long time, and reduces energy loss. It is an object of the present invention to provide an ammonia decomposition treatment method for an ammonia- containing fuel containing at least carbon monoxide as a compound containing at least a compound containing carbon atoms and H ₂ , such as a gasified fuel, which is easy to maintain.

In order to achieve this object, the dry ammonia decomposition method of the present invention comprises a carrier containing an ammonia-containing fuel containing at least carbon monoxide as a compound containing at least a compound containing carbon atoms and H ₂ and containing at least carbon. Necessary for heating the catalyst to 600 ° C. or lower and 200 ° C. or higher by catalytic combustion on the surface of the catalyst when supplied to the catalyst in an amount that prevents the fuel from being vapor-phase burned upstream of the catalyst containing nickel A large amount of oxygen is added to the fuel so that the molar ratio exceeds 0.0008, and the oxygen supplied to the surface of the catalyst causes the catalyst to be heated to 600 ° C. or lower by catalytic combustion on the catalyst surface. simultaneous reactions carbon monoxide with the catalyst surface is decomposed into carbon with a decomposition reaction of ℃ before while heated above the ammonia nitrogen and water in Ki燃 charges selectively advancing It is to suppress. Here, in order to distinguish between normal combustion and catalytic combustion, which shows that heat is generated when the fuel is oxidized by the oxidation promotion action of the catalyst on the catalyst surface, normal combustion is expressed as gas phase combustion. Yes.

  Therefore, when oxygen or a small amount of gas containing oxygen is supplied to the catalyst, a part of the fuel containing ammonia and a compound containing carbon atoms, for example, a part of gasified fuel is oxidized and catalytically burned on the catalyst surface. Without heating from the outside, the temperature of the whole fuel supplied to the catalyst rises and the catalyst is heated to 600 ° C. or lower. At the same time, even in a low temperature of 600 ° C. or lower, hydrogen in the ammonia molecules selectively reacts with oxygen on the catalyst surface and decomposes into nitrogen and water. Further, the added oxygen prevents carbon from being deposited on the catalyst, and since it is at a low temperature of 600 ° C., the catalyst is not deteriorated by heat and the activity of the catalyst is maintained for a long time.

Here, as the ammonia decomposition catalyst, a catalyst capable of efficiently decomposing ammonia in the presence of oxygen at 600 ° C. or lower is used. Examples of such a catalyst include a catalyst supported on a carrier and containing nickel. This catalyst has a low oxidation activity for combustible components other than ammonia, and a high activity for selectively reacting hydrogen in the ammonia molecule with oxygen to decompose it into nitrogen and water.

Therefore, when a small amount of oxygen is supplied to the catalyst, in addition to the reaction in which ammonia contained in the fuel is decomposed into nitrogen and hydrogen even at a low temperature of 600 ° C. or lower, the decomposition reaction of ammonia into nitrogen and water by oxygen is a catalyst. Selectively proceed on the surface. Further, when oxygen is supplied to the catalyst surface, the reaction of decomposing carbon monoxide or the like into carbon does not proceed on the catalyst surface, and carbon deposition is prevented. Here, in the present invention, it is preferable that the molar ratio of the oxygen to the fuel is at least 0.004, and the catalyst is heated to 600 ° C. or lower and 400 ° C. or higher. The fuel is preferably a gasified fuel.

  Accordingly, in the ammonia decomposition treatment method of the present invention, oxygen or a gas containing oxygen in an amount necessary for the catalyst to be heated to 600 ° C. or less by the oxidation heat of the fuel containing ammonia and a compound containing carbon atoms. Since the catalyst is supplied to the catalyst, the catalyst can be heated to 600 ° C. or less by the oxidation heat of the fuel without heating from the outside. That is, installation of an expensive heating device and supply of energy necessary for heating from the outside are not required, and ammonia can be efficiently decomposed at low cost equipment costs and operating costs. Further, the added oxygen prevents carbon from being deposited on the catalyst, and since the temperature is low at 600 ° C., the catalyst is not deteriorated by heat, and the activity of the catalyst is maintained for a long time. Accordingly, stable ammonia decomposition treatment can be performed, and the operating cost can be reduced by using the catalyst for a long time.

  Moreover, since ammonia contained in the fuel can be efficiently decomposed at a low temperature of 600 ° C. or less, it is not necessary to install an expensive heat exchanger in the downstream of the ammonia decomposition treatment apparatus, and energy loss due to the heat exchanger is eliminated. Ammonia can be efficiently decomposed without impairing the overall thermal efficiency. In addition, since an inexpensive low-temperature reactor can be used, it is not necessary to configure equipment with expensive heat-resistant materials, and equipment costs can be reduced.

In addition to the reaction in which ammonia contained in fuel decomposes into nitrogen and hydrogen even at a low temperature of 600 ° C. or lower, high ammonia decomposition is achieved by the selective decomposition of ammonia into nitrogen and water by oxygen. The rate is realized. In addition, the catalytically active component is supported in a highly dispersed manner on the carrier, the surface area where the fuel and the catalytically active component are in contact with each other is increased, and a high ammonia decomposition activity is obtained with a small amount of the catalytically active component. Can be manufactured. Furthermore, since the catalyst can be produced at a lower cost than the catalyst of the element number of platinum group, lanthanoid, and actinoid or higher, the cost of ammonia decomposition treatment can be reduced.

Hereinafter, the configuration of the present invention will be described in detail based on the best mode shown in the drawings.
The ammonia decomposing treatment method of the present invention decomposes ammonia contained in an ammonia-containing fuel containing at least a compound containing carbon atoms and H ₂ by contacting the catalyst with a catalyst, which is supported on a carrier and contains nickel. Necessary for heating the catalyst to 600 ° C or lower and 200 ° C or higher by catalytic combustion on the surface of the catalyst when supplied to the catalyst in such an amount that the fuel cannot be vapor-phase combusted upstream of the catalyst. A large amount of oxygen is added to the fuel so that the molar ratio exceeds 0.0008 , and the catalyst is heated to 600 ° C. or lower and 200 ° C. or higher by catalytic combustion on the catalyst surface by oxygen supplied to the catalyst surface. While heating, the decomposition reaction of ammonia in the fuel into nitrogen and water is selectively advanced, and at the same time, the reaction in which carbon monoxide or the like is decomposed into carbon on the catalyst surface is suppressed at the same time. The ammonia-containing fuel containing at least a compound containing carbon atoms and H ₂ is more preferably a fuel containing ammonia containing 10 vol% or more of combustible components excluding ammonia and a compound containing carbon atoms, Since gasified fuel is representative, in this embodiment, gasified fuel will be mainly described.

  Here, as the ammonia decomposition catalyst, a catalyst capable of efficiently decomposing ammonia in the presence of oxygen at 600 ° C. or lower is used. Such catalysts include transition elements and some elements other than transition elements.

According to research on oxidative decomposition of ammonia in water, the order of decomposition activity of ammonia into nitrogen in the absence of fuel components other than ammonia is Pt>Ru>Pd> Rh >> Cu, Co, Ni (Supervised by Masakazu Iwamoto, “Environmental Catalyst Handbook”, NTS, p. 69, November 20, 2001). In other studies on the decomposition rate of ammonia, Ru, Pd>Rh> Mo >>Co>Pt> Mn / CeO ₂ > Cr, Ni> Fe (supervised by Masakazu Iwamoto, “Environmental Catalyst Handbook” , NTS, p. 74 Table 1, November 20, 2001). As described above, many of the elements exhibiting the oxidation activity of ammonia are transition elements. The reason for this is that, as shown in the example of the reaction below, the transition element easily changes the oxidation number, pulls electrons from ammonia (NH ₃ ), changes the oxidation number of the transition element itself, and H ⁺ and This is thought to be due to the ability to decompose into NH ₂ and N ₂ and to combine H ⁺ and O ₂ with H ₂ O.
NH ₃ + M ^{n +} → NH ₂ + M ^{(n-1) +} + H ⁺
2NH ₂ → N ₂ H ₄
N ₂ H ₄ + 4M ^{n +} → N ₂ + 4M ^{(n-1) +} + 4H ⁺
2M ^{(n-1) +} + 2H ⁺ + 1/2 O ₂ → 2M ^{n +} + H ₂ O
M; transition element

The transition elements also have hydrogen oxidation activity, and the order is PdO> PtO ₂ > RuO ₂ > Ag ₂ O> Co ₃ O ₄ , Au>NiO> CuO, MnO ₂ > Fe ₂ O ₃ > Cr ₂ O ₃ > V ₂ O ₅ (Matsuta Haruta, catalyst, vol.29, No.4, p.299 (1987)), and high oxidation activity of platinum group hydrogen.

However, the ammonia-containing fuel serving gasified fuel ammonia cracking process is the subject of the present invention contains hydrogen. Therefore, when the oxidation activity of hydrogen is high, ammonia cannot be selectively oxidized. In addition to hydrogen, flammable components such as carbon monoxide and methane are often contained, and even when their oxidation activity is high, ammonia cannot be selectively oxidized. The platinum group element catalyst has an excellent ammonia decomposition activity at a high temperature of 600 ° C. or higher, but at a temperature of 600 ° C. or lower, the ammonia decomposition activity is low because the oxidation reaction of hydrogen or the like proceeds preferentially. On the other hand, transition metals other than the platinum group have low oxidation activity such as hydrogen at a temperature of 600 ° C. or lower, and excellent ammonia decomposition activity in order to selectively advance the oxidation reaction of ammonia to nitrogen and water. Indicates. Moreover, when the transition metal reacts with the gasified fuel without adding oxygen at a temperature of 600 ° C. or lower, carbon is deposited on the catalyst and the catalytic performance is rapidly deteriorated. And the catalyst performance can be maintained for a long time. Although fuel NOx may be generated by the addition of oxygen, this fuel NOx is reduced and decomposed by ammonia, hydrogen, etc. in the gasified fuel, thus preventing the discharge of fuel NOx from the catalyst outlet. be able to. Therefore, among transition elements, transition elements excluding the platinum group with high oxidation activity such as hydrogen, carbon monoxide, and methane have the ability to selectively oxidize ammonia in the presence of these combustible components. It is thought to have.

  Also. All elements with element numbers higher than promethium and actinoids are radioactive elements, and elements with element numbers 104 and higher do not exist in nature and are practically difficult to use. It can be used, but is preferably excluded as a suitable catalytically active component. Moreover, it is expensive.

  Furthermore, lanthanoids (element numbers 57 to 60, 62 to 71) excluding promethium are not radioactive elements, are naturally available and can be used because they have ammonia decomposition activity. Expensive. For this reason, it can be used as a catalytically active component if economic reasons do not matter.

  For these reasons, transition elements preferable as the catalytically active component are transition elements excluding elements having an element number equal to or higher than that of the platinum group, promethium, and actinoid (that is, element numbers 21 to 29, 39 to 43, 47, 57 to 60, 62). ~ 71, 72-75, 79), more preferably at least one element of transition elements excluding elements having element numbers equal to or higher than platinum group, lanthanoid and actinoid. . Considering ease of availability at low cost, it is preferable to include, for example, iron, cobalt, nickel, copper, and the like.

  These catalytically active components can be used without using a carrier, but are more preferably used by being supported on a carrier. When the catalyst active component is supported on the support, the active component particles can be supported on the support in a highly dispersed manner, so that the contact area with the reaction gas is increased, and the ammonia decomposition reaction can be accelerated at a temperature of 600 ° C. or less with a small amount of the active component. It becomes. There is no limitation on the shape and composition of the carrier, and for example, it may be a particle having a particle size of several centimeters or a honeycomb having a cell density of several hundred cells / square inch. Further, a carrier may be carried on the surface of the honeycomb, and a catalyst may be carried thereon. Also, the composition of the carrier is not limited, and for example, γ-alumina, titania, zirconia may be used.

  In addition, as a catalytically active component, a catalyst other than an inexpensive transition element although its performance is inferior, for example, typical metal elements such as magnesium, calcium, strontium, barium, gallium, indium, germanium, and tin can be used. One element selected from these typical metal elements may constitute a catalytically active component by itself, or at least one of transition elements excluding elements having an element number equal to or higher than platinum group, promethium, and actinoids. It may be included at the same time as the element.

  The oxygen supplied to the catalyst mixed with the gasified fuel is so small that the gasified fuel cannot be vapor-phase combusted upstream of the catalyst, and gas is supplied to the catalyst surface when supplied to the catalyst. This is the amount necessary to heat the catalyst to 600 ° C. or lower and 200 ° C. or higher by catalytic combustion. Thereby, oxygen is supplied to the catalyst surface together with gasified fuel, and a high ammonia decomposition rate at 600 ° C. or less is achieved by a catalyst capable of selectively advancing the decomposition reaction of ammonia into nitrogen and water by oxygen. In addition, when oxygen is supplied to the catalyst surface, the reaction of decomposing carbon monoxide or the like into carbon does not proceed on the catalyst surface, and carbon deposition is prevented. Note that oxygen may be injected into the gasified fuel in a state of pure oxygen, or may be supplied as a gas containing oxygen. That is, oxygen or a gas containing oxygen is, for example, oxygen, air, a gas in which oxygen is mixed and oxygen concentration is increased.

  Here, the heating temperature of the catalyst may be any temperature as long as it is 600 ° C. or less and at least the temperature at which the ammonia decomposition reaction occurs or more, preferably 600 ° C. or less and 200 ° C. or more, more preferably fuel. It is a temperature range in which ammonia decomposition reaction easily occurs depending on the composition. For example, the composition of gasified fuel is about 11 mol% hydrogen, about 28 mol% carbon monoxide, about 4 mol% carbon dioxide, about 54 mol% nitrogen, about 3 mol% water vapor, and transition elements represented by Ni and the like In the case of this catalyst, it is preferably 400 ° C to 600 ° C, more preferably 400 ° C to 550 ° C, and most preferably about 500 ° C. When the temperature exceeds 600 ° C., a heat exchanger that lowers the temperature to 600 ° C. or less is required. When the temperature is less than 100 ° C., ammonia is hardly decomposed, and the fuel remains in a gaseous state at about 200 ° C. to cause a stable decomposition reaction. It seems to be. Furthermore, the higher the temperature, the more active component particles agglomerate and the surface area decreases due to sintering, resulting in a decrease in catalyst performance. However, since the catalyst can be used at a low temperature of 600 ° C. or lower, sintering of the active component is prevented, The catalyst performance can be maintained for a long time.

  The supply amount of oxygen or oxygen-containing gas varies depending on the gas temperature, the fuel flow rate, the fuel composition and temperature, the oxygen concentration in the gas, the heat release amount of the ammonia decomposition apparatus, etc. It is determined appropriately in consideration of these. In addition, in the case of a small amount of oxygen having a ratio of fuel and oxygen that cannot cause self-ignition, even if mixed in the fuel upstream of the catalyst, the fuel does not undergo gas phase combustion. The amount varies depending on the fuel composition, pressure, inlet temperature, residence time, heat release, etc., but if it is less than the amount of oxygen required to heat the catalyst to 600 ° C. or less by the oxidation heat of the fuel on the catalyst surface. In general, it seems to include the range in which gas phase combustion does not occur upstream of the catalyst.

  FIG. 1 shows an example of an embodiment of an ammonia decomposition treatment apparatus for gasified fuel to which the present invention is applied. This ammonia decomposition treatment apparatus 2 is a device that decomposes ammonia contained in the gasified fuel by bringing the gasified fuel into contact with the catalyst 3, and supplies the catalyst 3 with the gasified fuel F and oxygen or a gas O containing oxygen. A part of the fuel is oxidized by bringing the fuel into contact with the catalyst 3, and the catalyst 3 is heated to 600 ° C. or less by the heat, and the ammonia in the fuel is decomposed by the catalyst 3.

  In the present embodiment, the ammonia decomposition treatment device 2 is disposed downstream of the dry desulfurization device 1, and after the gasification fuel F is desulfurized by the dry desulfurization device 1, the catalyst inside the ammonia decomposition treatment device 2 together with the gas O containing oxygen. 3 is supplied to oxidize a part of the gasified fuel F. By installing the ammonia decomposition treatment apparatus 2 downstream of the dry desulfurization apparatus 1, ammonia contained in the gasified fuel desulfurized by the dry desulfurization apparatus is decomposed, so that catalyst poisoning by hydrogen sulfide is prevented. The activity of the catalyst is sustained for a long time.

  The gas O is oxygen or a gas containing oxygen, such as oxygen, air, or a gas in which oxygen concentration is increased by mixing oxygen into the air. The flow rate of the gas O containing oxygen may be a flow rate necessary for heating the catalyst to 600 ° C. or less by the heat of oxidation of the gasified fuel F. When a flow rate higher than that is supplied, the gasification fuel that has been subjected to ammonia decomposition treatment needs to be cooled in order to exceed the heat resistance temperature of downstream equipment, leading to a decrease in plant thermal efficiency and an increase in equipment costs.

  The flow rate of the gas O containing oxygen is adjusted to a flow rate necessary for heating the catalyst to 600 ° C. or less by the oxidation heat of the gas O. For this reason, the flow rate is determined in accordance with the concentration of oxygen in the gas O, the temperature of the gas O, the flow rate, composition and temperature of the gasified fuel F, the heat radiation of the ammonia decomposition treatment apparatus 2, and the like. In an oxygen-enriched air-blown coal gasification plant, when the ammonia decomposition treatment device 2 is disposed downstream of the dry desulfurization device 1, as an example of assumed conditions, the composition of the gasification fuel F is 10.5 mol% hydrogen, Carbon monoxide is 28.4 mol%, carbon dioxide is 3.6 mol%, nitrogen is 54.3 mol%, water vapor is 3.1 mol%, ammonia is 1040 ppm, the temperature of gasification fuel F is 420 ° C, and the composition of gas O is The temperature of 100% oxygen and gas O is 100 ° C. In this case, the flow rate of the gas O is, for example, that the ammonia decomposition treatment device 2 has a heat insulating structure and does not dissipate heat, and oxygen is completely consumed. About 0.01 mol is required.

  A gas turbine combustor 4 is disposed downstream of the ammonia decomposition processing device 2 and supplied with gasified fuel obtained by decomposing ammonia. As a result, the generation of fuel NOx in the combustor 4 is suppressed. By installing the ammonia decomposing apparatus 2 upstream of the combustor 4, the ammonia contained in the gasified fuel can be decomposed and supplied to the combustor 4, so that fuel NOx generated in the combustor 4 is reduced. This makes it possible to clean the combustion exhaust gas.

  Further, a denitration device is disposed downstream of the combustor 4, NOx is further reduced, and clean exhaust gas is emitted from the chimney 14. By installing a denitration device downstream of the combustor, thermal NOx is reduced in addition to fuel NOx generated in the combustor due to ammonia supplied to the combustor without being decomposed by the ammonia decomposition treatment device. This makes it possible to further clean the combustion exhaust gas.

  Next, FIG. 2 shows a schematic configuration of an apparatus in which ammonia decomposition treatment apparatuses are arranged in parallel. In this apparatus, two ammonia decomposition treatment apparatuses 2 are installed in parallel, the ammonia decomposition treatment apparatuses 2 can be operated independently, and the ammonia decomposition treatment apparatuses 2 to be operated are sequentially switched to gasify fuel. The maintenance of the ammonia decomposition treatment apparatus 2 in a dormant state is enabled while the decomposition treatment of ammonia contained in F is continuously performed. Thereby, maintenance of the other ammonia decomposition processing apparatus, for example, replacement or regeneration of the catalyst can be performed while continuing the decomposition process of ammonia contained in the gasified fuel by one ammonia decomposition processing apparatus.

  In the present embodiment, two ammonia decomposition treatment apparatuses 2 are arranged in parallel upstream of a combustor (not shown). Of the two ammonia decomposition treatment apparatuses 2, one ammonia decomposition treatment apparatus 2 and related members will be denoted by reference symbol A, and the other ammonia decomposition treatment apparatus 2 and related members will be denoted by reference numeral B.

  The supply of the gasified fuel F to each ammonia decomposition treatment device 2 is controlled by opening and closing the fuel inlet valve 15, and the supply of the gas O containing oxygen is controlled by opening and closing the oxygen inlet valve 17. In addition, outlet valves 16 and 18 are provided at the outlet of each ammonia decomposition treatment apparatus 2.

  Now, when one ammonia decomposing apparatus 2A is operated, one ammonia decomposing apparatus is closed with the outlet valve 18A and the fuel inlet valve 15B and the outlet valves 16B, 18B of the other ammonia decomposing apparatus 2B being closed. The 2A fuel inlet valve 15A, oxygen inlet valve 17A and outlet valve 16A are opened. As a result, the gas containing fuel and oxygen-containing gas flows to one ammonia decomposition treatment apparatus 2A, undergoes ammonia decomposition treatment, and is then supplied to a combustor (not shown). That is, one ammonia decomposition processing apparatus 2A is operated. In this state, the other ammonia decomposition treatment apparatus 2B is in a dormant state, and maintenance work such as replacement of the deteriorated catalyst 3B can be performed.

  When the cause of deterioration is a combustible substance such as carbon, the oxygen inlet valve 17B and the outlet valve 18B are opened with the catalyst 3B filled, and the substance causing the deterioration is gasified by oxidation treatment and discharged. It can be regenerated without exchanging the catalyst. Here, the discharged gas may be supplied to the combustor outlet, the exhaust heat recovery boiler inlet, the denitration equipment inlet, or the like.

  Then, after operating for a predetermined period, the operation is switched from one ammonia decomposition treatment apparatus 2A to the other ammonia decomposition treatment apparatus 2B. That is, the fuel inlet valve 15A, the oxygen inlet valve 17A, and the outlet valves 16A, 18A of one ammonia decomposition processing apparatus 2A are closed, and the fuel inlet valve 15B, the oxygen inlet valve 17B, and the outlet of the other ammonia decomposition processing apparatus 2B are closed. The valve 16B is opened and the outlet valve 18B is closed. As a result, the gasified fuel flows to the other ammonia decomposition treatment apparatus 2B and is subjected to ammonia decomposition treatment. In this state, one ammonia decomposition treatment apparatus 2A is in a dormant state, so that maintenance work such as regeneration and replacement of the deteriorated catalyst 3A can be performed. That is, it is possible to regenerate or replace the deteriorated catalyst 3 while continuously operating the plant fuel gasifier and the combustor.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in the above description, a catalyst that is supported on a carrier and contains at least one element among transition elements excluding elements having an element number of platinum group, lanthanoid, and actinoid is used. Other inexpensive catalysts such as magnesium, calcium, strontium, barium, gallium, indium, germanium, and tin may be used. Moreover, although the ammonia decomposition processing apparatus 2 was arrange | positioned downstream of the dry-type desulfurization apparatus 1, when there are few hydrogen sulfides in gasification fuel, you may omit the dry-type desulfurization apparatus 1. FIG. Further, although the gas turbine combustor 3 is disposed downstream, a combustor other than the gas turbine may be used, and an apparatus other than the combustor such as a chemical product synthesis apparatus may be used. Further, although the denitration device 12 is disposed at the combustor outlet, the denitration device may be omitted.

  Further, it goes without saying that the ammonia decomposing method of the present invention can be applied to fuels other than gasification gas as long as it is a fuel containing ammonia and a compound containing carbon atoms. More specifically, the present invention can be implemented as long as the fuel contains 10 vol% or more of combustible components excluding ammonia, contains a compound containing carbon atoms, and contains ammonia. Moreover, even in the fuel containing H2, which is easy to react with oxygen, among other fuels, ammonia can be selectively decomposed by using the above-mentioned catalyst. Therefore, in the case of other fuels that are more difficult to react with oxygen than H2, It is thought that ammonia can be selectively decomposed further. In order to exhibit the effect of preventing carbon deposition, it is necessary to include a compound containing carbon atoms (carbon monoxide, carbon dioxide, hydrocarbon, alcohol, phenol, ether, ketone, etc.) in the fuel. Further, a fuel that is vaporized at least by the time when the fuel comes into contact with the catalyst surface is preferable. If heavy oil or coal is supplied directly to the catalyst, it will not be vaporized upstream of the catalyst and will contact the catalyst in a liquid or solid state. Therefore, the decomposition reaction of ammonia in the part that does not contact the catalyst, that is, inside the droplets or solid particles However, there is a possibility that sufficient decomposition rate cannot be obtained.

  Furthermore, this ammonia decomposition treatment method is not limited to the case of decomposing ammonia contained in the fuel itself, and can be applied to, for example, ammonia decomposition in sewage treatment or wastewater treatment. That is, sewage and waste water containing ammonia is vaporized to mix fuel, and when the fuel is supplied to the catalyst in an amount that cannot be vapor-phase combusted, the catalyst is burned on the surface of the catalyst to cause the catalyst to reach 600 ° C. The amount of oxygen required for heating to 200 ° C. or higher is added, and the catalyst is heated to 600 ° C. or lower and 200 ° C. or higher by catalytic combustion on the catalyst surface by oxygen supplied to the surface of the catalyst. The ammonia is decomposed by selectively advancing the decomposition reaction of ammonia in the sewage and waste water into nitrogen and water, and simultaneously suppressing the reaction of carbon monoxide and the like to be decomposed into carbon on the catalyst surface. Burn to complete the process.

Example 1
In the present invention, the possibility of decomposing ammonia in the gasified fuel was examined using commercially available chemical equilibrium calculation software (HSC Chemistry) developed based on the Gibbs energy minimization method. FIG. 3 shows an oxygen-enriched air-blown gasified fuel, in which hydrogen is 10.5 mol%, carbon monoxide is 28.4 mol%, carbon dioxide is 3.6 mol%, nitrogen is 54.3 mol%, and water vapor is 3 The chemical equilibrium composition of ammonia in a gas having a composition of 1 mol% and 1040 ppm of ammonia is shown. As is clear from FIG. 3, if the chemical equilibrium concentration of ammonia is relatively low at a temperature of about 600 ° C. or lower and the decomposition rate of ammonia is high, ammonia may be decomposed to a low concentration. FIG. 4 shows the results obtained by chemical equilibrium calculation of the effect of oxygen addition on carbon deposition in a gasified fuel having the above gas composition. As the amount of oxygen to be added increases, the temperature at which carbon does not precipitate shifts to the low temperature side, and carbon deposition may become difficult.

(Example 2)
A catalyst was produced by the following method, and the ability to decompose ammonia in the simulated coal gasification fuel into nitrogen was investigated. TA-1301 manufactured by Sumitomo Chemical Co., Ltd. was used as the alumina powder as the carrier. Distilled water was added to nickel nitrate hexahydrate and alumina powder and stirred sufficiently. Subsequently, evaporation to dryness was performed on a hot plate, and after evaporating the solvent, a powder was collected. The obtained powder was heated in a dry air stream using silica gel at 10 ° C./min, baked at 800 ° C. for 2 hours, and allowed to cool naturally. Ni was supported so that the amount supported was 15 wt%. The obtained Ni / Al ₂ O ₃ catalyst was sized to 9 to 16 mesh after press molding. Next, an experimental method is shown. N ₂ , H ₂ , CO, CO ₂ , O ₂ , ₂ vol% NH ₃ / N ₂ are supplied to the mixer while adjusting the flow rate from the cylinder with a mass flow controller, and distilled water is sprayed using a metering pump Were injected into the mixer. The mixed gas was supplied to the reaction tube, and the reaction gas was analyzed. The reaction tube had a triple tube structure of an Inconel outer tube, a quartz inner tube, and an Inconel sheath tube, and the temperature distribution in the axial direction of the catalyst layer was measured at three points with a K-type thermocouple inserted into the sheath tube. The quartz tube had an inner diameter of 16 mm, and the sheath tube had an outer diameter of 3.2 mm. Quartz wool was spread on a quartz plate and filled with a catalyst. The reaction tube was heated in a muffle furnace. Part of the gas was introduced into the FT-730G Fourier transform infrared spectrophotometer manufactured by HORIBA, Ltd. through a sample tube made of Teflon (trademark of DuPont) heated to 130 ° C., and NH ₃ , HCN, NO, NO ₂ and N ₂ O was quantitatively analyzed. At the same time, after dehumidifying with calcium chloride at room temperature, it was introduced into CP2002 Micro Gas Chromatography manufactured by Crompack, and H ₂ , CH ₄ , CO, CO ₂ , N ₂ and O ₂ were measured. The pressure in the reactor was controlled by a pressure regulating valve at the reactor outlet. Table 1 shows the standard experimental conditions. It is a composition simulating oxygen-enriched air-blown coal gasification fuel. The amount of carbon deposited on the catalyst after the experiment was measured using a quadrupole mass spectrometry / thermogravimetric / differential thermal analyzer TG-DTA2000S manufactured by Mac Science. The alumina cell was filled with 50 mg of catalyst and set on a balance. While supplying a mixed gas of O ₂ and He having a O ₂ concentration of 21 vol% at a flow rate of 100 ml / min, 10 ° C./min from room temperature to 1000 ° C. The weight loss was measured in the temperature range where a peak intensity of m / z corresponding to CO ₂ yielded a peak intensity of 44. From this value, the amount of deposited carbon was calculated by subtracting the weight increase due to oxidation of the catalyst in the temperature range.

  FIG. 5 shows the effect of addition of oxygen when the reaction is performed under atmospheric pressure using 3.0 ml of catalyst. When the oxygen / fuel was 0.0008 mol / mol or less, the decomposition of ammonia hardly progressed at a catalyst temperature of 600 ° C. or less. However, the decomposition in the temperature range of 400 ° C. to 600 ° C. when the oxygen / fuel was 0.004 mol / mol or more. In particular, the conversion rate of ammonia to nitrogen was 44% under the conditions of oxygen / fuel of 0.008 mol / mol and catalyst temperature of 500 ° C. The amount of carbon deposited on the catalyst after the end of the experiment is shown in FIG. The catalyst was taken out of the reactor after 7 hours of experiments at approximately the same temperature history from 200 ° C. to 875 ° C. under each fuel / oxygen condition, and the amount of carbon deposited was measured. As is apparent from FIG. 6, when oxygen was not added, carbon deposition of about 3 wt% with respect to the catalyst weight occurred. However, the amount of carbon deposition rapidly decreased when oxygen / fuel was 0.0008 mol / mol. The amount of deposited carbon was suppressed to 0.06 wt% or less, which is 1/50 or less at 0.004 mol / mol.

(Example 3)
A Ru / Al ₂ O ₃ catalyst was produced by the same production method as the Ni / Al ₂ O ₃ catalyst. Ru source material used was ruthenium nitrate hexahydrate. Supply oxygen of 0.008 mol / mol of oxygen / fuel under the conditions shown in Table 1 using 3.6 ml of the Ni / Al ₂ O ₃ catalyst and 3.6 ml of the Ru / Al ₂ O ₃ catalyst. The conversion rate of ammonia into nitrogen when reacted at a pressure of 0.9 MPa is shown in FIG. In the case of an empty cylinder, the decomposition of ammonia hardly progressed at a reaction temperature of 700 ° C. or lower. In the case of the Ru / Al ₂ O ₃ catalyst, a conversion rate of about 10% was shown at a catalyst temperature of about 300 ° C., but the conversion rate decreased to 600 ° C. as the temperature increased. In addition, the conversion rate rose rapidly above 600 degreeC. In contrast, the Ni / Al ₂ O ₃ catalyst showed a high ammonia conversion rate from about 400 ° C. to 550 ° C.

It is a schematic block diagram which shows one Embodiment of the electric power generation system incorporating the ammonia decomposition processing apparatus which enforces the ammonia decomposition processing method of this invention. It is a schematic block diagram which shows 2nd Embodiment of the apparatus which implements the ammonia decomposition processing method concerning this invention. It is a graph which shows the chemical equilibrium composition and temperature relationship of ammonia in various pressures of the coal gasification simulation fuel containing ammonia. It is the graph which calculated | required the influence of the oxygen / fuel ratio in various pressures by the chemical equilibrium calculation regarding the carbon deposition / non-deposition temperature range of the coal gasification simulation fuel containing ammonia. In the experiment of Example 2, the influence of the oxygen / fuel ratio on the conversion rate of ammonia is shown when a coal gasification simulated fuel containing ammonia is reacted under atmospheric pressure using a Ni / Al ₂ O ₃ catalyst. It is a graph. In the experiment of Example 2, it is the graph which measured the carbon deposition amount of the catalyst after performing the reaction experiment of each oxygen / fuel ratio, and investigated the influence which the oxygen / fuel ratio at the time of reaction has on the carbon deposition amount. In the experiment of Example 3, for the empty cylinder, the Ni / Al ₂ O ₃ catalyst, and the Ru / Al ₂ O ₃ catalyst, oxygen / fuel was supplied with 0.008 mol / mol of oxygen to the coal gasification simulated fuel containing ammonia. And it is a graph which shows the conversion rate of ammonia at the time of making it react by the pressure of 0.9 Mpa.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dry-type desulfurization apparatus 2 Ammonia decomposition processing apparatus 3 Catalyst 4 Combustor 5 Air compressor 6 Gas turbine 7 Generator 8 Waste heat recovery boiler 9 Steam turbine 10 Generator 11 Condenser 12 Pressure pump 13 Denitration apparatus 14 Chimney 15 Fuel inlet valve 16 Outlet valve 17 Oxygen inlet valve 18 Outlet valve A Air F Gasified fuel O Gas including oxygen G Gasified fuel obtained by decomposing ammonia H Gas generated during catalyst regeneration

Claims (3)

An ammonia-containing fuel containing at least carbon monoxide as a compound containing at least a carbon atom-containing compound and H ₂ cannot be vapor-phase combusted upstream of a catalyst supported on a carrier and containing nickel. The amount of oxygen required to heat the catalyst to 600 ° C. or lower and 200 ° C. or higher in a molar ratio with respect to the fuel is 0.0008 in a quantity and when supplied to the catalyst. The oxygen added to the surface of the catalyst is heated to 600 ° C. or lower and 200 ° C. or higher by catalytic combustion on the catalyst surface while oxygen is supplied to the surface of the catalyst, to ammonia nitrogen and water in the fuel at the same time suppressing dry ammonia cracking process reaction of compounds containing pre-SL carbon atoms in the catalyst surface with the decomposition reaction selectively proceeds is decomposed into carbon in. The dry ammonia decomposition method according to claim 1, wherein the molar ratio of the oxygen to the fuel is at least 0.004, and the catalyst is heated to 600 ° C or lower and 400 ° C or higher. The dry ammonia decomposition method according to claim 1, wherein the fuel is a gasified fuel.

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