JP2017180157A - Denitration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a denitration system enabled to suppress the deterioration of a catalyst by lowering the precipitation speed of an acid ammonium sulfate into a catalyst.SOLUTION: A denitration system comprises: a first NOx removal catalyst 104 and a second NOx removal catalyst 107 for causing a nitrogen oxide and a reducer to react; and a first reducer feed section 105 and a second reducer feed section 108 arranged upstream of the first NOx removal catalyst 104 and the second NOx removal catalyst 107 for injecting a reducer into exhaust gases. The first NOx removal catalyst 104 and the second NOx removal catalyst 107 are arranged in series, and the injection rates of the reducer from first reducer feed section 105 and the second reducer feed section 108 are restricted to an ordinary injection rate less than 0.8 to the nitrogen oxides of the individual exhaust gases.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a denitration system.

  Research and development of Selective Catalytic Reduction (SCR) has become active as one of the means for meeting the tertiary regulation of nitrogen oxides (NOx) for ship engines by the International Maritime Organization (IMO).

As a denitration method, a titanium / vanadium catalyst provided in the exhaust gas passage is reacted with nitrogen oxide (NOx) by supplying ammonia as a reducing agent, and decomposed into water and nitrogen as shown in chemical formula (1). Ammonia selective catalytic reduction is known. In addition, a method is employed in which urea is injected into the exhaust gas passage and ammonia is supplied to the catalyst by decomposing urea as in chemical formula (2).
[Chemical 1]
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O
[Chemical formula 2]
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

  In the dry ammonia selective catalytic reduction method, a mixing device is arranged between the first denitration device and the second denitration device to agitate the combustion gas discharged from the first denitration device and make the nitrogen oxide concentration distribution uniform. A configuration is disclosed (Patent Document 1). Also, a configuration is disclosed in which a plurality of stages of catalyst filling sections are arranged in series, a reducing agent addition pipe is provided upstream of each stage, and a cooler is provided to prevent a temperature rise in the catalyst filling section (Patent Document). 2). Further, in this configuration, in order to regenerate the catalyst in the catalyst filling portion, the amount of the reducing agent added is increased as it goes upstream of the catalyst filling portion, and the exhaust gas temperature is temporarily raised to 300 to 400 ° C. Is disclosed (Patent Document 3). In addition, for exhaust gas containing nitrogen oxides of 500 ° C. or higher, the first-stage catalyst layer and the second-stage catalyst layer are connected in series, and ammonia as a reducing agent is divided and injected into each stage. The structure which does is disclosed (patent document 4).

Japanese Patent No. 3002452 Japanese Patent Laid-Open No. 10-323538 Japanese Patent No. 3248166 JP 2003-144854 A

By the way, in diesel fuel, especially C heavy oil used in ships, etc., the sulfur component in the fuel is high, and sulfur dioxide (SO ₂ ) is generated in the exhaust gas. It is known that it is deposited and deteriorated. Therefore, a denitration system that can suppress deterioration of the catalyst due to precipitation of acidic ammonium sulfate without reducing the reduction effect of nitrogen oxide (NOx) as much as possible is desired.

  A denitration system corresponding to claim 1 is a denitration system for treating nitrogen oxides in exhaust gas of a combustion engine that burns heavy oil having a sulfur content in fuel exceeding 0.1%, wherein the nitrogen oxides and reduction A plurality of denitration units arranged upstream of the denitration catalyst and having a reducing agent injection means for injecting the reducing agent into the exhaust gas, and the plurality of denitration units are arranged in series. In addition, the injection amount of the reducing agent injected from each of the reducing agent injection means is limited to a normal injection amount of less than 0.8 in terms of the equivalent ratio of the exhaust gas passing through each of the denitration catalysts to the nitrogen oxides. . Thereby, in each denitration unit, the precipitation rate of the acidic ammonium sulfate to a catalyst can be reduced, and deterioration of a catalyst can be suppressed significantly.

  Here, when the denitration catalyst is regenerated, injection of the reducing agent by the reducing agent injection means in the denitration unit to be regenerated is stopped, and the denitration catalyst is regenerated by the exhaust gas passing through the denitration catalyst. Is preferred.

  Further, at the time of the regeneration, it is preferable that the amount of the reducing agent injected by the reducing agent injection means in at least one of the denitration units other than the regeneration target is an equivalent ratio that exceeds the normal injection amount. . For example, when the normal injection amount is less than 0.8 in terms of equivalent ratio, the injection amount during regeneration is set to 0.8 or more in terms of equivalent ratio.

  In addition, it is preferable that three or more denitration units are provided, and at least two of the denitration units are arranged in parallel.

  In addition, it is preferable that a pipe connecting each of the plurality of denitration units and a pipe switching unit that switches connection between the pipes are provided, and the passage of the exhaust gas is changed by the pipe switching unit. For example, three denitration units connected to tandem, two denitration units connected in parallel, one denitration unit connected to tandem, two denitration units connected to tandem, and one denitration The state in which the unit is disconnected can be switched.

  Further, it is preferable that the denitration unit has a nitrogen oxide concentration detection means for detecting the concentration of the nitrogen oxide, and the normal injection amount is determined based on a detection result of the nitrogen oxide concentration detection means. Further, it is preferable that the combustion engine is an internal combustion engine, provided with a rotation speed detection means for detecting a rotation speed of the internal combustion engine, and determining the normal injection amount based on a detection result of the rotation speed detection means.

  Further, it is preferable that the denitration system is mounted on a moving body together with the combustion engine, and the normal injection amount is changed according to an environmental regulation condition of a geographical position of the moving body. In addition, it is preferable that the denitration system is mounted on a moving body together with the combustion engine, and a combination used by the plurality of denitration units is changed according to an environmental regulation condition of a geographical position of the moving body. Further, it is preferable that the denitration system is mounted on the moving body together with the combustion engine, and the regeneration is performed at a position where the environmental regulation condition of the geographical position of the moving body is relaxed.

  According to the denitration system of the present invention, there is provided a denitration system for treating nitrogen oxides of exhaust gas of a combustion engine that burns heavy oil having a sulfur content exceeding 0.1%, wherein the nitrogen oxides and the reducing agent A plurality of denitration units, and a plurality of denitration units arranged in series, each having a denitration catalyst that reacts with the catalyst and a reducing agent injection means that is disposed upstream of the denitration catalyst and injects the reducing agent into the exhaust gas. In addition, the injection amount of the reducing agent injected from each of the reducing agent injection means is limited to a normal injection amount of less than 0.8 in terms of the equivalent ratio of the exhaust gas passing through each of the denitration catalysts to the nitrogen oxides. As a result, the rate of precipitation of acidic ammonium sulfate on the catalyst can be reduced to greatly suppress the deterioration of the catalyst.

  Here, when the denitration catalyst is regenerated, injection of the reducing agent by the reducing agent injection means in the denitration unit to be regenerated is stopped, and the denitration catalyst is regenerated by the exhaust gas passing through the denitration catalyst. The denitration process can be continued by at least one of the plurality of denitration units, and the remaining denitration units can be regenerated. Further, since the exhaust gas temperature is used for regeneration, it is not necessary to have an extra heating device.

  Further, at the time of regeneration, a denitration catalyst is obtained by setting the injection amount of the reducing agent by the reducing agent injection means in at least one of the denitration units other than the regeneration target to an equivalent ratio exceeding the normal injection amount. In the regeneration process, the regeneration process can be performed at the same time while maintaining the normal denitration rate.

  Further, by providing three or more denitration units and arranging at least two of the denitration units in parallel, it is possible to reduce the ventilation resistance as a whole denitration system and to suppress the degradation of the denitration catalyst.

  In addition, there are provided pipes for connecting the plurality of denitration units, and pipe switching means for switching the connection of the pipes. By changing the exhaust gas passage by the pipe switching means, denitration can be performed according to various situations. It is possible to perform denitration processing, regeneration processing, maintenance, etc. while changing the system configuration.

  Further, the denitration unit has a nitrogen oxide concentration detection means for detecting the concentration of the nitrogen oxide, and the normal injection amount is determined based on the detection result of the nitrogen oxide concentration detection means, thereby In accordance with the concentration of nitrogen oxide, an appropriate amount of normal reducing agent can be adaptively set, and appropriate denitration treatment can be performed. Further, the combustion engine is an internal combustion engine, and includes a rotation speed detection means for detecting the rotation speed of the internal combustion engine, and the internal injection engine is determined by determining the normal injection amount based on a detection result of the rotation speed detection means. An appropriate normal injection amount of the reducing agent can be set adaptively according to the exhaust state of the exhaust gas, and appropriate denitration treatment can be performed.

  In addition, the denitration system is mounted on a moving body together with the combustion engine, and the normal injection amount is changed according to the environmental regulation condition of the geographical position of the moving body, so that it is adaptive according to the geographical environmental regulations. Therefore, it is possible to set a normal injection amount of an appropriate reducing agent and perform an appropriate denitration treatment. Further, the denitration system is mounted on a moving body together with the combustion engine, and a geographical environment regulation is performed by changing a combination used by the plurality of denitration units according to an environmental regulation condition of a geographical position of the moving body. Accordingly, it is possible to adaptively change the connection state of the plurality of denitration units and perform an appropriate denitration process. Further, the denitration system is mounted on the moving body together with the combustion engine, and the regeneration is performed at a position where the environmental regulation condition of the geographical position of the moving body is relaxed, so that only the other denitration units that do not perform the regeneration are used. It can respond to environmental regulations and can regenerate the denitration catalyst over time.

It is a figure which shows the structure of the denitration system in embodiment of this invention. It is a figure which shows the reaction system of a nitrogen oxide and a reducing agent. It is a figure which shows the reaction system of a sulfur oxide and a reducing agent. It is a figure which shows the structure of the denitration system in the modification 1. It is a figure which shows another example of a structure of the denitration system in the modification 1. It is a figure which shows the connection state 1 of the denitration system in the modification 2. It is a figure which shows the connection state 2 of the denitration system in the modification 2. It is a figure which shows the connection state 3 of the denitration system in the modification 2. It is a figure which shows the connection state 4 of the denitration system in the modification 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a main configuration of an exhaust gas denitration system 100 according to an embodiment of the present invention. As shown in FIG. 1, the denitration system 100 includes a combustion engine 102, a first gas passage 103, a first denitration catalyst 104, a first reducing agent supply unit 105, a second gas passage 106, a second denitration catalyst 107, a second denitration catalyst 107, and a second denitration catalyst 107. A reducing agent supply unit 108 and a control unit 109 are included. Here, the set of the first denitration catalyst 104 and the first reducing agent supply unit 105 and the set of the second denitration catalyst 107 and the second reducing agent supply unit 108 are respectively connected to the first denitration unit 100a and the second denitration unit 100b. Configure.

  The combustion engine 102 is an internal combustion engine such as an engine or a gas turbine, for example, a marine diesel engine. The denitration system 100 is used to remove nitrogen oxides contained in exhaust gas exhausted from the combustion engine 102. Since the marine combustion engine 102 has high thermal efficiency, the temperature of the exhaust gas is in the temperature range of 200 ° C. or higher and 280 ° C. or lower.

The first denitration catalyst 104 and the second denitration catalyst 107 are catalysts for decomposing nitrogen oxide (NOx) contained in the exhaust gas by reacting with ammonia. The first denitration catalyst 104 and the second denitration catalyst 107 may be made of titanium / vanadium metal. For example, a titanium oxide TiO ₂ -based catalyst containing vanadium (V), molybdenum (Mo), or tungsten (W) as an active component is used. In particular, in the present embodiment, it is preferable that the first denitration catalyst 104 and the second denitration catalyst 107 contain niobium (Nb) as an additive. The content of niobium (Nb) is preferably 0.001 wt% or more and 10 wt% or less with respect to the first denitration catalyst 104 and the second denitration catalyst 107. By setting the content in this range, the heat resistance of the first denitration catalyst 104 and the second denitration catalyst 107 can be improved, and a regeneration process at a higher temperature and a faster temperature increase rate can be applied. That is, the addition of niobium (Nb) suppresses sintering (sintering) of titania particles and other components contained in the first denitration catalyst 104 and the second denitration catalyst 107, and the first denitration catalyst 104 and the second denitration catalyst. It is assumed that the fine structure of the pores of the catalyst 107 is maintained and the corrosion resistance, heat resistance, and impact resistance can be improved. In particular, by containing niobium (Nb) in an amount of 0.01 wt% or more, higher heat resistance can be exhibited. On the other hand, when the content of niobium (Nb) exceeds 5 wt%, the effect of improving heat resistance is saturated, and there is a risk of causing economic disadvantage. Since the denitration catalyst containing niobium (Nb) as an additive is particularly effective at a temperature exceeding 300 ° C., it rapidly exceeds the temperature range of 200 ° C. to 280 ° C. of the normal exhaust gas temperature and rapidly exceeds 300 ° C. Effective when playing.

  The first denitration catalyst 104 and the second denitration catalyst 107 are arranged in series in the first gas passage 103 and the second gas passage 106, respectively. The first denitration catalyst 104 and the second denitration catalyst 107 preferably have a structure in which flat plates and catalyst thin tubes are bundled in order to increase the reaction area. For example, a honeycomb structure is preferable.

The first denitration catalyst 104 promotes the reaction between a reducing agent such as ammonia represented by the chemical reaction system shown in FIG. 2 and a nitride compound (NOx) in the exhaust gas. The exhaust gas contains nitrogen oxides (NOx) such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ), and is generated by reaction with urea and water supplied from the first reducing agent supply unit 105. It reacts with ammonia and is reduced to water and nitrogen by the reaction represented by chemical formula (1). The reaction in the second denitration catalyst 107 is the same.

When the exhaust gas contains a sulfur oxide such as SO ₂ , the first denitration catalyst 104 promotes the reaction represented by the chemical reaction system shown in FIG. Sulfur dioxide (SO ₂ ) contained in the exhaust gas reacts with ammonia generated by the reaction with urea and water supplied from the first reducing agent supply unit 105, and is represented by chemical formulas (3) and (4). By the reaction, sulfur trioxide (SO ₃ ) and acidic ammonium sulfate ((NH ₄ ) HSO ₄ ) are generated. The reaction represented by the chemical formula (4) is an equilibrium reaction in which the reaction from the left to the right easily proceeds as the temperature decreases, and the reaction from the right to the left easily proceeds as the temperature increases. The reaction in the second denitration catalyst 107 is the same.
[Chemical formula 3]
2SO ₂ + O ₂ → 2SO ₃
[Chemical formula 4]
SO ₃ + NH ₃ + H ₂ O ← → (NH ₄ ) HSO ₄

The first reducing agent supply unit 105 and the second reducing agent supply unit 108 can each include a urea tank, a pump, a urea valve, a compressor, an air valve, an injection nozzle, and piping. Among these components, those that can be shared may be used in the first reducing agent supply unit 105 and the second reducing agent supply unit 108. The 1st reducing agent supply part 105 and the 2nd reducing agent supply part 108 are provided in order to supply urea (urea water) and air to the 1st gas passage 103 and the 2nd gas passage 106 via an injection nozzle, respectively. . For example, urea (urea water) is injected as a reducing agent into the first gas passage 103 and the second gas passage 106, and ammonia generated by the decomposition reaction represented by the chemical formula (2) is converted into the first denitration catalyst 104 and the second denitration catalyst. It is configured to supply the surface of the catalyst 107. The urea tank is a tank that stores urea water ((NH ₂ ) ₂ CO + H ₂ O). A pump is provided in the middle of piping which connects a urea tank and an injection nozzle. The pump applies pressure to the urea water stored in the urea tank, and supplies the urea water to the first gas passage 103 and the second gas passage 106 via the piping and the injection nozzle. The urea valve is provided downstream of the pump of the piping, and supplies / blocks urea water pressurized by the pump to the injection nozzle. A compressor is provided in the middle of piping connected to an injection nozzle. A compressor pressurizes air and supplies it to an injection nozzle through piping. Note that when the denitration system 100 is mounted on a ship, air in an air pipe provided in the ship may be used instead of the compressor. The air valve is provided downstream of the compressor of the pipe, and supplies and blocks air pressurized by the compressor to the injection nozzle. The injection nozzle is a nozzle for injecting urea water from the first reducing agent supply unit 105 and the second reducing agent supply unit 108 to the first gas passage 103 and the second gas passage 106. The injection nozzle is formed by processing the tip of the pipe, or is configured by connecting another member to the tip of the pipe. The injection nozzles are disposed upstream of the first denitration catalyst 104 in the first gas passage 103 and upstream of the second denitration catalyst 107 in the second gas passage 106, respectively. The injection nozzle mixes urea water and air, and injects urea water mixed in advance with air into the first gas passage 103 and the second gas passage 106 with an appropriate supply pressure. However, the reducing agent is not limited to urea (urea water).

  The control unit 109 controls the denitration system 100 in an integrated manner. The control unit 109 can be configured by a general computer including a CPU, a memory, an input device, an output device, an external interface, and the like. The control unit 109 controls the injection timing and the injection amount of the reducing agent in the denitration system 100 by reading and executing a control program stored in the memory in advance by the CPU. Further, the control unit 109 incorporates a clock (timer) for measuring the regeneration start timing and regeneration processing time of the first denitration catalyst 104 and the second denitration catalyst 107.

  A nitrogen oxide sensor 10 is provided in the first gas passage 103, and the concentration of nitrogen oxide (NOx) contained in the exhaust gas flowing through the first gas passage 103 is input to the control unit 109. The nitrogen oxide sensor 12 is also provided in the second gas passage 106, and the concentration of nitrogen oxide (NOx) contained in the exhaust gas flowing through the second gas passage 106 is input to the control unit 109. As the nitrogen oxide sensors 10 and 12, a chemiluminescent NOx meter, a constant voltage electrolytic NOx meter, a general sensor using a zirconia solid electrolyte, or the like can be used.

  The combustion engine 102 is provided with a rotation speed sensor 14, and the rotation speed of the combustion engine 102 is input to the control unit 109.

  The control unit 109 estimates the exhaust gas emission amount from the rotational speed of the combustion engine 102 measured by the rotational speed sensor 14. For example, the control unit 109 stores a discharge amount database of the rotation speed and the exhaust gas discharge amount measured in advance, and corresponds to the rotation speed measured by the rotation speed sensor 14 with reference to the discharge amount database. Estimate emissions. Then, the control unit 109 responds to the estimated exhaust gas emission amount and the amount of nitrogen oxide (NOx) in the first gas passage 103 and the second gas passage 106 measured by the nitrogen oxide sensors 10 and 12. The amount of reducing agent (urea) injected from the first reducing agent supply unit 105 and the second reducing agent supply unit 108 is controlled.

  In the present embodiment, the control unit 109 sets the injection equivalent ratio of the reducing agent in each stage of the first denitration catalyst 104 and the second denitration catalyst 107 to the nitrogen oxide (NOx) required for the denitration system 100 as a whole. Set smaller than the value corresponding to the reduction rate. For example, when the reduction rate of nitrogen oxide (NOx) required for the entire denitration system 100 is 80% (0.8 in terms of equivalent ratio), each of the first denitration catalyst 104 and the second denitration catalyst 107 The injection equivalent ratio of the reducing agent in the stage is set to less than 0.8.

  Here, the equivalence ratio is the amount of reducing agent that is just necessary to reduce 100% of the nitrogen oxide (NOx) contained in the inflowing exhaust gas in each of the first denitration catalyst 104 and the second denitration catalyst 107. It means the ratio of the injection amount of the reducing agent that is actually injected to the injection amount. That is, when the equivalent ratio of the reducing agent injected from the first reducing agent supply unit 105 is 1, the nitrogen oxide (NOx) in the exhaust gas flowing into the first denitration catalyst 104 is the first denitration catalyst 104. Is ideally reduced by 100%. Therefore, in this case, the exhaust gas flowing into the second denitration catalyst 107 ideally does not contain nitrogen oxides (NOx). Further, when the equivalent ratio of the reducing agent injected from the first reducing agent supply unit 105 is 0.6, the nitrogen oxide (NOx) in the exhaust gas flowing into the first denitration catalyst 104 is the first denitration. The catalyst 104 reduces 60%. Therefore, in this case, the exhaust gas flowing into the second denitration catalyst 107 contains 40% nitrogen oxide (NOx) before flowing into the first denitration catalyst 104.

  In the present embodiment, the injection equivalent ratio of the reducing agent in each stage of the first denitration catalyst 104 and the second denitration catalyst 107 corresponds to the nitrogen oxide (NOx) reduction rate required for the denitration system 100 as a whole. By setting the value smaller than the value, the deposition rate of acidic ammonium sulfate on the first denitration catalyst 104 and the second denitration catalyst 107 can be reduced, and the progress of deterioration of the first denitration catalyst 104 and the second denitration catalyst 107 can be delayed. it can. For example, even in an emission control area (ECA) in which a reduction rate of 80% or more with respect to nitrogen oxides (NOx) is required, in each stage of the first denitration catalyst 104 and the second denitration catalyst 107. The injection equivalent ratio of the reducing agent can be set to less than 0.8, whereby the progress of deterioration of the first denitration catalyst 104 and the second denitration catalyst 107 can be delayed.

  If the equivalence ratio of the injection amount of the reducing agent in each stage of the first denitration catalyst 104 and the second denitration catalyst 107 is low, the first denitration catalyst 104 and the second ammonium nitrate solution exceed the ratio of the absolute amount of reducing agent to be injected. The deposition rate on the denitration catalyst 107 decreases. For example, when the equivalence ratio is 0.2 compared to when the equivalence ratio is 0.8, the deposition rate of acidic ammonium sulfate in each stage of the first denitration catalyst 104 and the second denitration catalyst 107 does not become ¼. Almost close to zero. Further, when the equivalent ratio is 0.6 as compared to when the equivalent ratio is 0.8, the deposition rate of acidic ammonium sulfate in each stage of the first denitration catalyst 104 and the second denitration catalyst 107 does not become 3/4. 1/6.

The reason is as follows. Acidic ammonium sulfate, sulfur dioxide in the exhaust gas (SO ₂₎ is first denitration catalyst 104, after oxidizing the sulfur trioxide on the second denitration catalyst 107 (SO _3), the sulfur trioxide (SO ₃₎ ammonia In this case, the oxidation reaction of sulfur dioxide (SO ₂ ) is slower than the denitration reaction. When the equivalent ratio of the reducing agent is small, a small amount of the generated ammonia is first spent in the denitration reaction, and almost all ammonia is denitrated before sulfur dioxide (SO ₂ ) is oxidized to sulfur trioxide (SO ₃ ). It is spent on the reaction and hardly produces acidic ammonium sulfate. When the equivalent ratio of the reducing agent is large, it takes time for all of the generated ammonia to be spent on the denitration reaction, so that a part of the ammonia reacts with sulfur trioxide (SO ₃ ) to produce acidic ammonium sulfate. become. For this reason, when the equivalent ratio of the reducing agent is small, the deposition rate of the acidic ammonium sulfate on the first denitration catalyst 104 and the second denitration catalyst 107 is lower than the ratio of the absolute amount of the spray amount of the reducing agent.

  In particular, when the equivalence ratio is less than 0.8, the precipitation rate of acidic ammonium sulfate rapidly decreases, so the injection equivalent ratio of the reducing agent in each stage of the first denitration catalyst 104 and the second denitration catalyst 107 is less than 0.8. By doing so, the deposition rate of acidic ammonium sulfate on the first denitration catalyst 104 and the second denitration catalyst 107 can be reduced.

  On the other hand, if the equivalent ratio of the reducing agent is too low, the reduction of nitrogen oxides (NOx) in the denitration system 100 becomes insufficient. It is preferable to determine the equivalence ratio. For example, in order to satisfy the regulation of removing 80% or more of nitrogen oxide (NOx) contained in the exhaust gas and discharging it, the reducing agent injected from the first reducing agent supply unit 105 and the second reducing agent supply unit 108 It is preferable that the equivalent ratio of is 0.56 or more. As a result, 56% of the nitrogen oxide (NOx) in the initial exhaust gas is reduced by the first denitration catalyst 104, and the remaining 44% of nitrogen oxide (NOx) flows into the second denitration catalyst 107. The second denitration catalyst 107 further reduces 56% of the nitrogen oxides (NOx) in the exhaust gas, thereby reducing 80.64% of the nitrogen oxides (NOx) contained in the original exhaust gas. Can be removed. Similarly, in order to satisfy the regulation that, for example, 60% or more of nitrogen oxides (NOx) contained in the exhaust gas are removed and discharged, injection is performed from the first reducing agent supply unit 105 and the second reducing agent supply unit 108. It is preferable that the equivalent ratio of the reducing agent is 0.37 or more. As a result, 37% of the nitrogen oxide (NOx) in the initial exhaust gas is reduced by the first denitration catalyst 104, and the remaining 63% of nitrogen oxide (NOx) flows into the second denitration catalyst 107. Further, 37% of the nitrogen oxide (NOx) in the exhaust gas is further reduced by the second denitration catalyst 107, so that 60.31% of the nitrogen oxide (NOx) contained in the original exhaust gas is reduced. Can be removed.

  Further, if the equivalent ratio is too small, it is necessary to increase the areas of the first denitration catalyst 104 and the second denitration catalyst 107 in order to ensure the reduction of nitrogen oxides (NOx). In the case of the two-stage configuration of the 104 and the second denitration catalyst 107, in order to remove 60% to 80% of the nitrogen oxide (NOx) in the exhaust gas, the equivalent ratio of the reducing agent injected in each stage is set to 0. It is preferable to make it about 4 to 0.7.

  For example, 80% or more of denitration is required in an emission control area (ECA) and less than 80% may be used in a general sea area. Therefore, the first reducing agent supply unit 105 and the second reduction may be performed depending on the sea area. The equivalent ratio of the reducing agent supplied from the agent supply unit 108 may be changed, or the supply of the reducing agent may be stopped.

  Judgment of the emission control sea area is done by detecting the geographical position of the ship using the global positioning system GPS or GLONASS of the satellite system, the Loran C of the ground system, etc., and collating it with the emission control sea area information. Determine whether the area is restricted or general.

  In the present embodiment, the aspect in which the equivalent ratios of the reducing agents injected upstream of the first denitration catalyst 104 and the second denitration catalyst 107 are equalized has been described. However, the present invention is not limited to this. That is, the equivalent ratio of the reducing agents injected from the first reducing agent supply unit 105 and the second reducing agent supply unit 108 is such that the concentration of nitrogen oxide (NOx) discharged from the denitration system 100 is one stage of the denitration catalyst. The amount should be less than the equivalent ratio of the reducing agent that must be injected upstream of the one-stage denitration catalyst.

  As described above, according to the denitration system 100 of the present embodiment, the first denitration catalyst 104 and the second denitration catalyst 107 are connected in tandem to use the nitrogen oxide (NOx) as the entire denitration system 100. ), The acid ammonium sulfate precipitation rate can be decreased, and deterioration of the first denitration catalyst 104 and the second denitration catalyst 107 can be suppressed.

  In particular, when the denitration system 100 is applied to a marine combustion engine 102, the temperature of the exhaust gas is about 200 ° C. to 280 ° C., which is lower than the combustion engine 102 mounted on a vehicle or the like, and the first denitration catalyst 104. In addition, since the acidic ammonium sulfate is easily deposited on the second denitration catalyst 107, the application effect of the present invention is remarkable.

  Further, since the marine combustion engine 102 often uses heavy oil with a sulfur component exceeding 0.1%, particularly C heavy oil with more than 0.5%, the first denitration compared to the case of using other fuels. Since acidic ammonium sulfate is easily deposited on the catalyst 104 and the second denitration catalyst 107, the application effect of the present invention is remarkable.

[Catalyst regeneration]
In the denitration system 100, the deposition rate of acidic ammonium sulfate on the first denitration catalyst 104 and the second denitration catalyst 107 can be reduced, but even so, acidic ammonium sulfate is still applied to the first denitration catalyst 104 and the second denitration catalyst 107. Accumulate and deteriorate. Therefore, the denitration system 100 can regenerate the first denitration catalyst 104 and the second denitration catalyst 107.

  The control unit 109 determines whether or not to start the regeneration process of the first denitration catalyst 104 and the second denitration catalyst 107. For example, the control unit 109 may start the regeneration process when the elapsed time from the previous regeneration process of the first denitration catalyst 104 and the second denitration catalyst 107 exceeds a predetermined time. In addition, since denitration at a high rate is required in the emission control area (ECA), regeneration processing is not performed, and denitration at a low rate is acceptable in general sea areas, so that regeneration processing is started in the sea area. It may be. Specifically, first, the geographical position of the ship is detected by GPS or the like, and the detected position is collated with the emission control sea area information to determine whether it is an emission control sea area or a general sea area. When it is detected that the ship is located in the general sea area, for example, the first denitration catalyst 104 is regenerated with the exhaust gas while the second denitration catalyst 107 denitrates the exhaust gas. In general sea areas, denitration can be performed at a low rate, so only the second denitration catalyst 107 that does not perform regeneration can meet environmental regulations, and even if the exhaust gas is at an intermediate temperature, the navigation time of the ship is long, so the regeneration of the first denitration catalyst 104 is possible. Can be done over time. Further, when regeneration of the first denitration catalyst 104 is completed, switching is performed so that denitration is performed by the first denitration catalyst 104 and regeneration of the second denitration catalyst 107 is performed. Alternatively, standby may be made in preparation for entering the next emission control sea area.

  When regeneration is required in this way, the denitration system 100 does not regenerate the first denitration catalyst 104 and the second denitration catalyst 107 at the same time. It is preferable to continue the reduction treatment of NOx).

Specifically, when the first denitration catalyst 104 is regenerated, by stopping the injection of the reducing agent from the first reducing agent supply unit 105 and continuing to supply the exhaust gas to the first denitration catalyst 104, the heat of the exhaust gas The first denitration catalyst 104 is regenerated. That is, by supplying exhaust gas having a medium temperature (about 220 ° C. to 280 ° C. in the case of a ship) to the first denitration catalyst 104, the temperature of the first denitration catalyst 104 is raised, and the balance equation (4) is changed from the right side to the left side. The acidic ammonium sulfate ((NH ₄ ) HSO ₄ ) deposited on the first denitration catalyst 104 is discharged as sulfur trioxide (SO ₃ ) gas. The sulfur trioxide (SO ₃ ) gas is effectively discharged from the first denitration catalyst 104 together with the exhaust gas.

Usually, in order to regenerate the catalyst to which acidic ammonium sulfate is adhered, it is often regenerated by applying a high temperature of 300 ° C. or more, but it can be regenerated if it takes a long time even at an intermediate temperature (about 220 ° C. to 280 ° C.). In the case of acidic ammonium sulfate, for example, the vapor pressure exists even when the temperature is low as in the case of indoor water (H ₂ O). Therefore, the exhaust gas does not contain acidic ammonium sulfate, that is, the intermediate temperature exhaust gas in which the reducing agent is not injected. By flowing for a long time, acidic ammonium sulfate can be removed.

  At this time, more reducing agent is injected from the second reducing agent supply unit 108 than the equivalent ratio during normal operation. For example, in order to satisfy the regulation of removing 80% or more of nitrogen oxide (NOx) contained in the exhaust gas and discharging it, the reducing agent may be injected at an equivalent ratio of 0.56 during normal operation. When the first denitration catalyst 104 is regenerated, the reducing agent is injected at an equivalence ratio of 0.8 or more. Thus, the first denitration catalyst 104 can be regenerated while maintaining the same nitrogen oxide (NOx) removal rate as that during normal operation by the second denitration catalyst 107.

  Further, when the second denitration catalyst 107 is regenerated, by stopping the injection of the reducing agent from the second reducing agent supply unit 108 and continuing to supply exhaust gas to the second denitration catalyst 107, the second denitration catalyst is heated by the heat of the exhaust gas. The catalyst 107 is regenerated. At this time, more reducing agent is injected from the first reducing agent supply unit 105 than the equivalent ratio during normal operation. For example, in order to satisfy the regulation of removing 80% or more of nitrogen oxide (NOx) contained in the exhaust gas and discharging it, the reducing agent may be injected at an equivalent ratio of 0.56 during normal operation. When the second denitration catalyst 107 is regenerated, the reducing agent is injected at an equivalence ratio of 0.8 or more. Thus, the second denitration catalyst 107 can be regenerated while maintaining the same nitrogen oxide (NOx) removal rate as that during normal operation by the first denitration catalyst 104.

  An exhaust gas heating means (not shown) may be provided on the downstream side of the combustion engine 102 so that the exhaust gas can be heated. The exhaust gas heating means can include a reheating burner and an electric reheater. The exhaust gas heating means is provided for heating the exhaust gas flowing through the first gas passage 103 in response to a control signal from the control unit 109. The reheat burner mixes fuel by diffusing into the gas and burns it at a high temperature to raise the temperature of the exhaust gas. The electric reheater raises the temperature of exhaust gas by energizing a resistance heater or the like with electricity.

  Further, a heater (not shown) may be provided for the first denitration catalyst 104 and the second denitration catalyst 107. The heater is provided to directly heat the first denitration catalyst 104 and the second denitration catalyst 107 during regeneration upon receiving a control signal from the control unit 109. As the heater, for example, an electric induction heater is suitable.

  Further, the control unit 109 may control the amount of reducing agent injected into the first denitration catalyst 104 and the second denitration catalyst 107 according to the environmental regulation conditions at the geographical location. Emission control area (ECA) requires denitration at a high rate, so the amount of reducing agent injected into the first denitration catalyst 104 and the second denitration catalyst 107 is increased. Since denitration is sufficient, the amount of reducing agent injected into the first denitration catalyst 104 and the second denitration catalyst 107 may be reduced. Specifically, the geographical position of the ship is detected by GPS or the like, and the detected position is collated with the emission control sea area information to determine whether it is an emission control sea area or a general sea area. When it is detected that the ship is located in the general sea area, the amount of reducing agent injected into the first denitration catalyst 104 and the second denitration catalyst 107 is decreased. When it is detected that the ship is located in an emission control area (ECA), the amount of reducing agent injected into the first denitration catalyst 104 and the second denitration catalyst 107 is increased.

  Moreover, the control part 109 may change the connection state of the 1st denitration catalyst 104 and the 2nd denitration catalyst 107 according to the environmental regulation conditions of a geographical position. For example, in an emission-regulated sea area, it is preferable to connect the first denitration catalyst 104 and the second denitration catalyst 107 in tandem to suppress catalyst deterioration while maintaining a high nitrogen oxide (NOx) reduction rate. is there. On the other hand, in the general sea area, it is preferable to connect the first denitration catalyst 104 and the second denitration catalyst 107 in parallel to suppress the deterioration of the catalyst while keeping the ventilation resistance as a whole denitration system low. Further, as described above, only one of the first denitration catalyst 104 and the second denitration catalyst 107 may be used and the other may be regenerated.

[Modification 1]
In the above embodiment, the first denitration catalyst 104 and the second denitration catalyst 107 are connected in tandem. However, the present invention is not limited to this as long as it includes a configuration in which a plurality of denitration catalysts can be connected in tandem. Absent.

  For example, as shown in FIG. 4, the third denitration catalyst 111 may be connected in parallel to the second denitration catalyst 107. Here, the first denitration catalyst 104 and the first reducing agent supply unit 105, the second denitration catalyst 107 and the second reducing agent supply unit 108, and the third denitration catalyst 111 and the third reducing agent supply unit 112. Each set constitutes a first denitration unit 100a, a second denitration unit 100b, and a third denitration unit 100c.

  The second gas passage 106 and the third gas passage 110 are branched from the first denitration catalyst 104, the second gas passage 106 is provided with a second denitration catalyst 107, and the third gas passage 110 is provided with a third denitration catalyst 111. . A second reducing agent supply unit 108 is provided on the upstream side of the second denitration catalyst 107 in the second gas passage 106, and a third reducing agent supply unit is provided on the upstream side of the third denitration catalyst 111 in the third gas passage 110. 112 is provided.

  In this configuration, for example, in order to satisfy the regulation that nitrogen oxide (NOx) contained in the exhaust gas is removed by 80% or more and discharged, the first reducing agent supply unit 105, the second reducing agent supply unit 108, and It is preferable that the equivalent ratio of the reducing agent injected from the third reducing agent supply unit 112 is 0.56 or more. As a result, 56% of the nitrogen oxides (NOx) in the initial exhaust gas are reduced by the first denitration catalyst 104, and the remaining 44% of the nitrogen oxidation is performed in the second denitration catalyst 107 and the third denitration catalyst 111, respectively. Half of the product (NOx) flows in, and 56% of the nitrogen oxides (NOx) in the exhaust gas are further reduced by the second denitration catalyst 107 and the third denitration catalyst 111, so that the original exhaust gas 80.64% of the nitrogen oxide (NOx) contained therein can be removed.

  According to the said structure, compared with the structure of FIG. 1, the ventilation resistance of the whole denitration system can be made into 3/4. Further, the second denitration catalyst 107 and the third denitration catalyst 111 can be regenerated alternately by stopping the injection of the reducing agent alternately in the second reducing agent supply unit 108 and the third reducing agent supply unit 112. Further, when the first denitration catalyst 104 is regenerated, the injection of the reducing agent from the first reducing agent supply unit 105 is stopped, and the reduction ratio of 0.8 or more from the second reducing agent supply unit 108 and the third reducing agent supply unit 112 is reduced. What is necessary is just to inject an agent.

  In addition, as shown in FIG. 5, it is good also as a structure which connected the 1st denitration catalyst 104 and the 3rd denitration catalyst 111 in parallel. In this configuration, the same operation as that of the configuration of FIG. 4 can be obtained.

[Modification 2]
Moreover, it is good also as a structure which can switch the interconnection of a some denitration catalyst. For example, what is necessary is just to set it as the structure which provided piping switching means, such as a valve which switches the piping between the 1st denitration catalyst 104, the 2nd denitration catalyst 107, and the 3rd denitration catalyst 111.

  FIGS. 6A to 6D show examples of configurations in which the connection of the three first denitration catalysts 104, the second denitration catalyst 107, and the third denitration catalyst 111 can be switched. FIG. 6A shows a state in which the first denitration catalyst 104 and the second denitration catalyst 107 are connected in tandem, and the third denitration catalyst 111 is disconnected. FIG. 6B shows a state in which the second denitration catalyst 107 and the third denitration catalyst 111 are connected in parallel, and the first denitration catalyst 104 is connected in tandem. FIG. 6C shows a state in which the first denitration catalyst 104 and the third denitration catalyst 111 are connected in parallel, and the second denitration catalyst 107 is connected in tandem. FIG. 6D shows a state where the first denitration catalyst 104, the third denitration catalyst 111, and the second denitration catalyst 107 are connected in tandem. Switching can be realized by appropriately providing piping satisfying these four states and piping switching means. 6A to 6D, these are omitted. For example, in FIG. 6D, the third reducing agent supply unit 112 branches from between the combustion engine 102 and the first reducing agent supply unit 105. And four pipes connected to the downstream side of the second denitration catalyst 107 and connected to the downstream side of the second denitration catalyst 111, and appropriately provided with a switching valve at each branching part or merging part. Can be switched.

  The connection state of the first denitration catalyst 104, the second denitration catalyst 107, and the third denitration catalyst 111 is preferably changed according to the situation. For example, in an emission-regulated sea area, as shown in FIG. 6D, three first denitration catalysts 104, a third denitration catalyst 111, and a second denitration catalyst 107 are connected in tandem to reduce high nitrogen oxides (NOx). It is preferable to suppress deterioration of the catalyst while maintaining the rate. For example, when three stages of catalysts are used connected in tandem, the equivalent ratio of reducing agents in each stage should reduce 80% or more of the nitrogen oxides (NOx) as a whole even if the equivalent ratio is set to 0.42 or more. Can do. The ability to set the equivalence ratio as low as possible is suitable for greatly suppressing the deterioration of the catalyst. On the other hand, in general sea areas other than emission restricted sea areas, two catalysts are connected in parallel as shown in FIGS. 6 (b) and (c), and the remaining one catalyst is connected to the tandem so that denitration is achieved. It is preferable to suppress deterioration of the catalyst while keeping the ventilation resistance of the entire system low. When maintenance such as cleaning of the catalyst is necessary, as shown in FIG. 6A, two catalysts are connected in tandem to reduce nitrogen oxides (NOx), and one catalyst is Maintenance is preferred.

  In this modification, the connection state of the three first denitration catalysts 104, the second denitration catalyst 107, and the third denitration catalyst 111 is switched. However, the connection state of four or more catalysts may be switched. In addition to changing the combination of multiple denitration units, it is possible to select a denitration unit to be used for control, or to remove some denitration units, in addition to providing pipes and pipe switching means as appropriate. It can also be realized by adding.

  The above embodiment can be applied to the exhaust gas treatment of marine diesel engines, but is not limited to this, and can also be applied to other mobile objects such as rail vehicles and automobiles. . Further, the present invention can also be applied to engines (boilers, gas turbines, etc.) that perform combustion other than diesel engines. Furthermore, the present invention can be applied to general combustion engines such as garbage incinerators and thermal power generation facilities.

  10, 12 Nitrogen oxide sensor, 14 Rotational speed sensor, 100 Denitration system, 100a First denitration unit, 100b Second denitration unit, 100c Third denitration unit, 102 Combustion engine, 103 First gas passage, 104 First denitration catalyst , 105 First reducing agent supply unit, 106 Second gas passage, 107 Second denitration catalyst, 108 Second reducing agent supply unit, 109 Control unit, 110 Third gas passage, 111 Third denitration catalyst, 112 Third reducing agent Supply section.

Claims (10)

A denitration system for treating nitrogen oxides in exhaust gas of a combustion engine that burns heavy oil in which the sulfur content in the fuel exceeds 0.1%,
A denitration catalyst for reacting the nitrogen oxide with a reducing agent;
A plurality of denitration units disposed upstream of the denitration catalyst and having a reducing agent injection means for injecting the reducing agent into the exhaust gas;
While arranging a plurality of the denitration units in series,
Limiting the injection amount of the reducing agent injected from each of the reducing agent injection means to a normal injection amount of less than 0.8 in an equivalent ratio of the exhaust gas passing through each of the denitration catalysts to the nitrogen oxides A denitration system that is characterized. The denitration system according to claim 1,
When the denitration catalyst is regenerated, injection of the reducing agent by the reducing agent injection means in the denitration unit to be regenerated is stopped, and the denitration catalyst is regenerated by the exhaust gas passing through the denitration catalyst. Denitration system. A denitration system according to claim 2,
A denitration system characterized in that, during the regeneration, the amount of the reducing agent injected by the reducing agent injection means in at least one of the denitration units other than the regeneration target is an equivalent ratio that exceeds the normal injection amount. . A denitration system according to any one of claims 1 to 3,
Including three or more denitration units,
A denitration system, wherein at least two of the denitration units are arranged in parallel. The denitration system according to any one of claims 1 to 4,
Piping connecting each of the plurality of denitration units;
Provided with a pipe switching means for switching the connection of the respective pipes;
A denitration system, wherein the exhaust gas passage is changed by the pipe switching means. A denitration system according to any one of claims 1 to 5,
The denitration system, wherein the denitration unit has nitrogen oxide concentration detection means for detecting the concentration of nitrogen oxide, and the normal injection amount is determined based on a detection result of the nitrogen oxide concentration detection means. A denitration system according to any one of claims 1 to 6,
The denitration system according to claim 1, wherein the combustion engine is an internal combustion engine, and includes a rotation speed detection means for detecting a rotation speed of the internal combustion engine, and the normal injection amount is determined based on a detection result of the rotation speed detection means. A denitration system according to any one of claims 1 to 7,
It is mounted on a moving body together with the combustion engine,
The denitration system, wherein the normal injection amount is changed according to an environmental regulation condition of a geographical position of the mobile body. A denitration system according to any one of claims 1 to 7,
It is mounted on a moving body together with the combustion engine,
A denitration system, wherein a combination used by a plurality of the denitration units is changed according to an environmental regulation condition of a geographical position of the mobile body. The denitration system according to claim 2 or 3,
A denitration system which is mounted on a moving body together with the combustion engine and performs the regeneration at a position where an environmental regulation condition of a geographical position of the moving body is relaxed.