Exhaust gas treatment system and exhaust gas treatment method

Abstract

Even when the exhaust gas composition fluctuates, it is possible to reduce nitrogen oxides while suppressing the leakage of ammonia components. [Solution] The invention includes a first catalyst arranged in the piping to promote the reaction between nitrogen oxides and ammonia, a second catalyst which is an oxidation catalyst arranged in the piping downstream of the first catalyst in the exhaust gas flow direction, a reducing agent supply unit which supplies a reducing agent that becomes ammonia when it reaches the first catalyst to the piping upstream of the first catalyst, a first catalyst outlet sensor which measures the nitrogen oxide concentration of the exhaust gas downstream of the first catalyst and upstream of the second catalyst, a second catalyst outlet sensor which measures the oxide concentration of the exhaust gas downstream of the second catalyst, and a control device which controls the amount of reducing agent supplied from the reducing agent supply unit to the piping based on the detection results of the first catalyst outlet sensor and the second catalyst outlet sensor.

Description

[Technical Field]

[0001] This disclosure relates to an exhaust gas treatment system and an exhaust gas treatment method for treating nitrogen oxides contained in exhaust gas. [Background technology]

[0002] Combustion plants such as gas turbines and boilers that burn fossil fuels such as natural gas, oil, and coal, or fuels such as biomass, are equipped with exhaust gas treatment equipment to treat the exhaust gas generated by combustion. The exhaust gas treatment equipment has an exhaust gas treatment system that reduces nitrogen oxides contained in the exhaust gas. The exhaust gas treatment system supplies urea or ammonia to the exhaust gas and reacts the ammonia with nitrogen oxides to reduce the nitrogen oxides. The denitrification equipment is equipped with a catalyst that promotes the reaction between ammonia and nitrogen oxides.

[0003] As a denitrification catalyst (exhaust gas treatment catalyst), Patent Document 1 describes a catalyst for removing nitrogen oxides from exhaust gas where the NO2 / NO molar ratio is 1 or higher, wherein the catalyst is made of TiO2-V2O5-WO3 to which at least one of Cr, Cu, Mn, and Co is added in an amount of 0.1 to 10 wt% in terms of its oxide equivalent. Furthermore, as an exhaust gas treatment system, Patent Document 2 describes an exhaust gas flow path containing an oxidation catalyst, a urea supply device, and NO x An exhaust gas treatment system in which reduction-selective catalysts are arranged in a specific order is described. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 04-18932 [Patent Document 2] International Publication No. 2007 / 102607 [Overview of the project] [Problems that the invention aims to solve]

[0005] The catalyst described in Patent Document 1 can accelerate the reduction treatment of nitrogen oxides. The exhaust gas treatment system described in Patent Document 2 oxidizes the exhaust gas with an oxidation catalyst, then supplies urea (ammonia), and uses a NOx reduction selective catalyst to accelerate the reaction between ammonia and nitrogen oxides, thereby treating the nitrogen oxides.

[0006] For example, gas turbines and boilers used in power generators may operate under variable load conditions, adjusting the amount of power generated according to the overall power output. When operating with varying loads, or when operating at low loads versus above a specified load, the composition of the exhaust gas changes. The same applies to engines and other equipment where combustion conditions fluctuate. If the amount of reducing agent supplied is not appropriate for the nitrogen oxides in the emitted exhaust gas, the amount of nitrogen oxides, ammonia, and ammonia components in the emitted gas will increase.

[0007] Here, ammonia components are those containing nitrogen (N) and hydrogen (H), and are components that can produce NH3, in addition to NH3 itself. Components that can produce NH3 are those that can react with substances in the exhaust gas atmosphere to produce ammonia. For example, HCN can react with water in the exhaust gas as follows: HCN + 2H2O → CO2 + NH3 + H2. Therefore, HCN is included in the components that can produce NH3. Also, HCONH2 can react as follows: HCONH2 → CO + NH3. Therefore, HCONH2 is included in the components that can produce NH3.

[0008] This disclosure aims to solve the aforementioned problems and to provide an exhaust gas treatment system and exhaust gas treatment method that can reduce nitrogen oxides while suppressing the leakage of ammonia components, even when the composition of the exhaust gas fluctuates. [Means for solving the problem]

[0009] To achieve the above objectives, the exhaust gas treatment system of the present disclosure is an exhaust gas treatment system that promotes the reaction between nitrogen oxides and ammonia in a fluid in which ammonia is mixed with exhaust gas containing nitrogen oxides, and treats nitrogen oxides in the exhaust gas, and includes a pipe through which the exhaust gas flows, a first catalyst disposed in the pipe and promoting the reaction between nitrogen oxides and ammonia, a second catalyst which is an oxidation catalyst disposed in the pipe downstream of the first catalyst in the direction of exhaust gas flow, a reducing agent supply unit that supplies a reducing agent which becomes ammonia when it reaches the first catalyst to the pipe upstream of the first catalyst, a first catalyst outlet sensor which measures the nitrogen oxide concentration of the exhaust gas downstream of the first catalyst and upstream of the second catalyst, a second catalyst outlet sensor which measures the nitrogen oxide concentration of the exhaust gas downstream of the second catalyst, and a control device which controls the amount of reducing agent supplied from the reducing agent supply unit to the pipe based on the detection results of the first catalyst outlet sensor and the second catalyst outlet sensor.

[0010] Furthermore, the exhaust gas treatment method of the present disclosure is an exhaust gas treatment method that promotes the reaction between nitrogen oxides and ammonia in a fluid in which ammonia is mixed with exhaust gas containing nitrogen oxides, and treats nitrogen oxides in the exhaust gas, comprising: a pipe through which the exhaust gas flows; a first catalyst disposed in the pipe and promoting the reaction between nitrogen oxides and ammonia; a second catalyst which is an oxidation catalyst disposed in the pipe downstream of the first catalyst in the direction of exhaust gas flow; a reducing agent supply unit which supplies a reducing agent that becomes ammonia when it reaches the first catalyst to the pipe upstream of the first catalyst; a first catalyst outlet sensor which measures the nitrogen oxide concentration of the exhaust gas downstream of the first catalyst and upstream of the second catalyst; and a second catalyst outlet sensor which measures the nitrogen oxide concentration of the exhaust gas downstream of the second catalyst, comprising the steps of: measuring the nitrogen oxide concentration with the first catalyst outlet sensor and the second catalyst outlet sensor; determining the amount of reducing agent to be supplied from the reducing agent supply unit to the pipe based on the detection results of the first catalyst outlet sensor and the second catalyst outlet sensor; and supplying the determined amount from the reducing agent supply unit to the pipe. [Effects of the Invention]

[0011] According to the present disclosure, even when the components of exhaust gas fluctuate, nitrogen oxides can be reduced while suppressing leakage of ammonia components. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] [Figure 1] Figure 1 is a schematic configuration diagram illustrating a combustion plant to which the exhaust gas treatment system of the present embodiment is applied. [Figure 2] Figure 2 is a flowchart showing an example of processing of the exhaust gas treatment system. [Figure 3] Figure 3 is a flowchart showing an example of processing of the exhaust gas treatment system. [Figure 4] Figure 4 is an explanatory diagram for explaining a catalyst replacement method for the exhaust gas treatment system. [Figure 5] Figure 5 is an explanatory diagram for explaining a catalyst replacement method for the exhaust gas treatment system. [Figure 6] Figure 6 is an explanatory diagram for explaining a catalyst replacement method for the exhaust gas treatment system. DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by these embodiments, and in the case where there are a plurality of embodiments, configurations formed by combining the respective embodiments are also included. In addition, the constituent elements in the embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent scope.

[0014] Figure 1 is a schematic diagram showing a combustion plant to which the exhaust gas treatment catalyst of this embodiment is applied. The combustion plant to which the exhaust gas treatment system of this embodiment is applied is a gas turbine that rotates a turbine with combustion gas produced by burning gaseous fuel in a combustion chamber. In this embodiment, the combustion device is a gas turbine, but the combustion device is not particularly limited and can be used as an exhaust gas treatment system for various combustion devices that burn fuel and emit exhaust gas containing nitrogen oxides. For example, the combustion device may be a boiler that burns fuel with a combustion burner and recovers the heat generated by this combustion. The exhaust gas treatment system can also be used as a treatment facility for exhaust gas discharged from a mixed-burning type combustion device that burns a mixture of coal, liquid fuel, and gaseous fuel as fuel. The exhaust gas treatment system can also be used as a treatment device for exhaust gas discharged from a combustion device that burns biomass or the like. The exhaust gas treatment system of this disclosure can be suitably used for treating exhaust gas produced by burning carbon-containing fuels.

[0015] The combustion plant 10 of this embodiment includes a fuel supply unit 12, an air supply unit 14, a combustion device 20, a flue (piping) 30, and an exhaust gas treatment system 40. The combustion plant 10 may also include a heat exchanger that performs heat exchange with the exhaust gas discharged from the combustion device 20, and exhaust gas treatment devices other than the exhaust gas treatment system 40. The combustion supply unit 12 supplies fuel, such as LNG or shale gas, to the combustion device 20. The air supply unit 14 supplies air to the combustion device 20.

[0016] The combustion device 20 is a gas turbine. The combustion device 20 has a combustor, a compressor, and a turbine, with the compressor and turbine connected by a shaft.

[0017] The combustion device 20 compresses air supplied from the air supply unit 14 using a compressor, mixes the compressed air with fuel supplied from the fuel supply unit 12, and burns it in a combustor to produce high-temperature, high-pressure combustion gas. The combustion device 20 uses the energy of the combustion gas to rotate a turbine, and exhaust gas generated from rotating the turbine is discharged.

[0018] The flue 30 is connected to the combustion equipment 20, and exhaust gas that has passed through the turbine of the combustion equipment 20 flows into it.

[0019] The exhaust gas treatment system 40 supplies a reducing agent, such as ammonia or urea solution, into the flue 30, and removes and reduces nitrogen oxides in the exhaust gas by passing the exhaust gas, to which the reducing agent has been supplied, through a selective reduction catalyst that promotes the reaction between nitrogen oxides and the reducing agent. The exhaust gas treatment system 40 includes a reducing agent supply device 42, a denitrification catalyst layer 50, an oxidation catalyst layer 52, a control device 60, a first concentration sensor 72, a second concentration sensor 74, and a third concentration sensor 76. The exhaust gas treatment system 40 also includes a portion of the flue (piping) 30 through which the exhaust gas flows.

[0020] The reducing agent supply device 42 has a reducing agent storage section 42a and an injection section 42b. The reducing agent storage section 42a is a tank for storing the reducing agent. As the reducing agent, ammonia water, gaseous ammonia, urea water, etc., can be used. The injection section 42b is connected to the reducing agent storage section 42a and has a supply port located inside the flue 30. The reducing agent supply device 42 supplies the reducing agent from the reducing agent storage section 42a to the injection section 42b and supplies the reducing agent into the flue 30 by discharging (injecting) the reducing agent from the supply port of the injection section 42b located inside the flue 40. The reducing agent supplied from the reducing agent supply device 42 moves with the exhaust gas and diffuses within the path through which the exhaust gas flows.

[0021] The denitrification catalyst layer 50 is located downstream of the reducing agent supply device 42 in the direction of exhaust gas flow. The denitrification catalyst layer 50 comprises a catalyst and a support mechanism for fixing the catalyst to the flue 30. The shape of the catalyst is not particularly limited and may be plate-shaped or honeycomb-shaped. The components of the catalyst will be described later. The support mechanism can be any mechanism capable of supporting the catalyst, and its structure is not particularly limited.

[0022] The oxidation catalyst layer 52 is positioned downstream of the denitrification catalyst layer 50 in the direction of exhaust gas flow. The oxidation catalyst layer 52 includes a catalyst and a support mechanism for fixing the catalyst to the flue 30.

[0023] Next, the catalysts of the denitrification catalyst layer 50 and the oxidation medium layer 52, that is, the exhaust gas treatment catalyst unit of this embodiment, will be described. The exhaust gas treatment catalyst unit of this embodiment has a first catalyst and a second catalyst. The second catalyst is positioned downstream of the first catalyst. In this embodiment, the catalyst of the denitrification catalyst device 50 is the first catalyst, and the catalyst of the oxidation catalyst device 52 is the second catalyst. The shapes of the first catalyst and the second catalyst can be various shapes, such as plate-shaped or honeycomb-shaped.

[0024] The first catalyst is a denitrification catalyst that promotes the reaction between ammonia and nitrogen oxides, and is mainly composed of titanium oxide. The first catalyst preferably contains vanadium, tungsten, etc. as active components. In other words, the exhaust gas treatment catalyst is a binary TiO2-WO3 catalyst, a TiO2-V2O5 catalyst, or a ternary TiO2-V2O5-WO3 catalyst, and the amount of manganese (Mn) added is preferably 1.0 mass% (wt.%) or less in terms of Mn2O3 relative to the total amount of catalyst. The exhaust gas treatment catalyst may also contain molybdenum (Mo) as an active component. In other words, it may be a TiO2-MoO3 catalyst, a TiO2-V2O5-MoO3 catalyst, etc.

[0025] The second catalyst is an oxidation catalyst that promotes the oxidation reaction of exhaust gas. The second catalyst is a catalyst containing zeolite or platinum (Pt). The second catalyst is a catalyst in which zeolite is coated on the surface of a substrate. Instead of a catalyst containing zeolite or platinum (Pt), the second catalyst can be a catalyst in which at least one of TiO2, SiO2, or Al2O3 is coated on the surface of a substrate, and further contains at least one of platinum or ruthenium.

[0026] In the exhaust gas treatment catalyst unit, the first catalyst is positioned upstream of the second catalyst, so that the exhaust gas supplied with the reducing agent NH3 passes through the first catalyst, which is a denitrification catalyst, and then the second catalyst, which is an oxidation catalyst. In this embodiment, the exhaust gas treatment system 40 has two catalyst layers, each containing a first catalyst and a second catalyst, but the total number is not particularly limited and may be three or more layers or just one layer. The catalyst layer may consist of two layers of the first catalyst (denitrification catalyst) or two or more layers of the second catalyst (oxidation catalyst). In addition, the exhaust gas treatment system 40 may have a flow straightening layer upstream of the catalyst layer.

[0027] The control device 60 controls the amount of reducing agent supplied from the reducing agent supply device 42 to the flue 30. The control device 60 can be implemented, for example, by a CPU (Central Processing Unit) or MPU (Micro Processing Unit) executing a stored program using RAM or the like as a working area. The control device 60 may also be implemented by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). The control device 60 may also be implemented by a combination of hardware and software. The control device 60 controls the amount of reducing agent supplied based on the nitrogen oxide concentration at each location detected by the first concentration sensor 72, the second concentration sensor 74, and the third concentration sensor 76. The control device 60 may also acquire information on the combustion conditions of the combustion device 20 that generates exhaust gas, such as the amount of fuel supplied and the type of fuel.

[0028] The first concentration sensor 72, the second concentration sensor 74, and the third concentration sensor 76 are positioned in the flue 30 and measure the nitrogen oxide concentration at their respective positions. The first concentration sensor 72 is positioned upstream of the first denitrification catalyst layer 50 (first catalyst), specifically downstream of the reducing agent supply device 42 and upstream of the first catalyst. The second concentration sensor 74 is positioned downstream of the first denitrification catalyst layer 50 (first catalyst) and upstream of the second denitrification catalyst layer 52 (second catalyst). The third concentration sensor 76 is positioned downstream of the second denitrification catalyst layer 52 (second catalyst). The first concentration sensor (first catalyst inlet sensor) 72 measures the nitrogen oxides in the exhaust gas before it passes through the first catalyst. The second concentration sensor (first catalyst outlet sensor) 74 measures the nitrogen oxides in the exhaust gas after it has passed through the first catalyst and before it passes through the second catalyst. The third concentration sensor (second catalyst outlet sensor) 76 measures nitrogen oxides in the exhaust gas after it has passed through the second catalyst.

[0029] In the exhaust gas treatment system 40, a reducing agent supply device 42 supplies a reducing agent to the flue 30, and the exhaust gas mixed with the reducing agent passes through the first denitrification catalyst layer 50 and the second denitrification catalyst layer 52. The exhaust gas treatment system 40 removes nitrogen oxides from the exhaust gas by promoting the reaction between nitrogen oxides and the reducing agent in the first denitrification catalyst layer 50 and the second denitrification catalyst layer 52.

[0030] Figure 2 is a flowchart illustrating an example of the exhaust gas treatment system's process. Next, Figure 2 will be used to explain the control of the reducing agent supply in the exhaust gas treatment system 40. The process in Figure 2 shows an example of the control device 60 controlling the supply of the reducing agent based on the nitrogen oxide concentration detected at each position.

[0031] The control device 60 measures the nitrogen oxide concentration at the first catalyst outlet and the second catalyst outlet (step S12). In other words, the control device 60 acquires the nitrogen oxide concentration detected by the second concentration sensor 74 and the third concentration sensor 76.

[0032] The control device 60 detects the difference in nitrogen oxide concentrations between the first catalyst outlet and the second catalyst outlet (step S14). The control device 60 subtracts the nitrogen oxide concentration at the second catalyst outlet from the nitrogen oxide concentration at the first catalyst outlet and takes the calculated value as the difference.

[0033] The control device 60 determines the supply amount based on the current supply amount and the calculated difference (step S16). The control device 60 maintains the supply amount if the calculated difference in nitrogen oxide concentrations between the first catalyst outlet and the second catalyst outlet is less than a threshold, and decreases the supply amount if the difference is greater than the threshold. Here, the threshold for the concentration difference is 3 ppm or less.

[0034] The control device 60 supplies the determined amount of reducing agent (step S18). The control device 60 injects the determined amount of reducing agent from the reducing agent supply device 42 into the flue 30.

[0035] Figure 3 is a flowchart illustrating an example of the exhaust gas treatment system's process. Using Figure 3, another example of controlling the supply amount of reducing agent in the exhaust gas treatment system 40 will be explained. The process in Figure 3 shows an example of the control device 60 calculating the denitrification rate based on the nitrogen oxide concentration detected at each position and controlling the supply amount of reducing agent.

[0036] The control device 60 measures the nitrogen oxide concentrations at the first catalyst inlet, the first catalyst outlet, and the second catalyst outlet (step S22). In other words, the control device 60 acquires the nitrogen oxide concentrations detected by the first concentration sensor 72, the second concentration sensor 74, and the third concentration sensor 76.

[0037] The control device 60 calculates the denitrification rate at the first catalyst outlet and the second catalyst outlet (step S24). The denitrification rate is calculated using the measurement result of the nitrogen oxide concentration at the inlet of the first catalyst. For example, the denitrification rate can be calculated by using the measurement result of the nitrogen oxide concentration at the inlet of the first catalyst as the denominator and the measurement results of the nitrogen oxide concentrations at the first catalyst outlet and the second catalyst outlet as the numerators (if it is a percentage, multiply the value by 100).

[0038] The control device 60 detects the difference in denitrification rates between the first catalyst outlet and the second catalyst outlet (step S26). The control device 60 subtracts the denitrification rate at the second catalyst outlet from the denitrification rate at the first catalyst outlet and takes the calculated value as the difference.

[0039] The control device 60 determines the supply amount based on the difference between the current supply amount and the calculated denitrification rate (step S28). The control device 60 maintains the supply amount if the difference between the calculated denitrification rates at the first catalyst outlet and the second catalyst outlet is less than a threshold, and decreases the supply amount if the difference is greater than the threshold. Here, the threshold for the difference in denitrification rates is 1% or more and 3% or less.

[0040] The control device 60 supplies the determined amount of reducing agent (step S30). The control device 60 injects the determined amount of reducing agent from the reducing agent supply device 42 into the flue 30.

[0041] The exhaust gas treatment system 40 arranges a second oxidation catalyst downstream of a first reduction catalyst, and controls the supply amount of the reducing agent based on the nitrogen oxide concentration measured by a second concentration sensor 72 upstream of the second catalyst and a third concentration sensor 74 downstream of the second catalyst, thereby effectively reducing nitrogen oxides while reducing the outlet ammonia (NH3) component.

[0042] Here, ammonia components are those containing nitrogen (N) and hydrogen (H), and are components that can produce NH3, in addition to NH3 itself. Components that can produce NH3 are those that can react with substances in the exhaust gas atmosphere to produce ammonia. For example, HCN can react with water in the exhaust gas as follows: HCN + 2H2O → CO2 + NH3 + H2. Therefore, HCN is included in the components that can produce NH3. Also, HCONH2 can react as follows: HCONH2 → CO + NH3. Therefore, HCONH2 is included in the components that can produce NH3.

[0043] Furthermore, the exhaust gas treatment system 40 can reduce ammonia components while maintaining a high denitrification rate under NO2-rich conditions and in the presence of HCHO at NO2 concentrations or higher. This allows, for example, the generation of ammonia outlet components from HCHO to be suppressed and nitrogen oxide reduction treatment to be performed effectively, even when an oxidation catalyst for removing CO and VOCs is not installed upstream of the exhaust gas treatment system and HCHO (formaldehyde) emitted from the gas turbine flows directly into the system. The same applies when an oxidation catalyst is present but the removal of HCHO by the oxidation catalyst is insufficient. Specifically, the exhaust gas treatment catalyst unit can reduce outlet ammonia components through the following reaction even when HCHO is present in the exhaust gas. NH3 + HCHO + 1 / 2O2 → HCONH2 + H2O HCONH2 → CO + NH3 NH3 + O2 → N2 + H2O

[0044] Furthermore, the exhaust gas treatment system 40 can reduce nitrogen oxides in the exhaust gas and also reduce the ammonia component at the outlet, even when the exhaust gas does not contain HCHO.

[0045] The following will be explained using a specific example. For example, the second catalyst of an exhaust gas treatment system is a catalyst containing V2O5-WO3-MnO3-TiO2, and the second catalyst is a catalyst containing platinum and zeolite. In the first catalyst, the mass percentages of TiO2 are 60% or more, V2O5 is 2.5%, WO3 is 5.3%, and MnO3 is 0.53%. In addition to the above components, binders and unavoidable contaminants are also included. Furthermore, chromium, copper, and cobalt are not included as active ingredients. Here, "not including the target component" means that the amount is below the amount of unavoidable contaminants. The zeolite in the second catalyst is of the MFI type, and the platinum is 0.1% by mass (wt.%) of the total catalyst amount.

[0046] The first condition is that the composition is NOx = 98 ppm, NO2 / NO x=0.85, NH3=125ppm, HCHO=179ppm, CO=0.3%, C2H4=230ppm, CH4=0.66%, O2=14%, H2O=9%, CO2=4%, with the balance being N2, at a temperature of 317°C, the treated gas flow rate per catalyst gas-contact area of the first catalyst AV12Nm 3 / m 2 / hr, and the treated gas flow rate per catalyst gas-contact area of the exhaust gas treatment catalyst unit (first catalyst + second catalyst) AV10Nm 3 / m 2 / hr, a reducing agent was supplied to the catalyst, the amount of nitrogen oxides after passing through the catalyst and the ammonia component at the outlet were measured, and the denitration rate which is the reduction ratio of nitrogen oxides before and after the catalyst, and the amount of nitrogen oxides after passing through the catalyst (outlet NO x ), and the outlet ammonia component after passing through the catalyst were calculated. AV is the gas flow rate / the gas-contact area of the catalyst.

[0047] Under the first condition, the ratio of NH3 / NO at the inlet of the first catalyst X is 1.28, the denitration rate at the outlet of the first catalyst is 96%, the outlet ammonia component is 7ppm, the ammonia slip is 1ppm, the denitration rate at the outlet of the second catalyst is 93%, the outlet ammonia component is 2ppm, and the ammonia slip is 1ppm.

[0048] Next, as the second condition, an exhaust gas having a composition of NOx=40ppm, NO2 / NO x =0.85, NH3=61ppm, HCHO=179ppm, CO=0.3%, C2H4=230ppm, CH4=0.66%, O2=14%, H2O=9%, CO2=4%, with the balance being N2, at a temperature of 317°C, the treated gas flow rate per catalyst gas-contact area of the first catalyst AV12Nm 3 / m 2 / hr, and the treated gas flow rate per catalyst gas-contact area of the exhaust gas treatment catalyst unit (first catalyst + second catalyst) AV11Nm 3 / m 2 / hr, a reducing agent was supplied to the catalyst, the amount of nitrogen oxides after passing through the catalyst and the ammonia component at the outlet were measured, and the denitration rate which is the reduction ratio of nitrogen oxides before and after the catalyst, and the amount of nitrogen oxides after passing through the catalyst (outlet NO xThe ammonia component at the outlet after passing through the catalyst was calculated. AV is the gas flow rate divided by the gas contact area of ​​the catalyst.

[0049] Under the second condition, NH3 / NO3 at the inlet of the second catalyst X The ratio was 1.53, the denitrification rate at the first catalyst outlet was over 99%, the ammonia component at the outlet was 22 ppm, and the ammonia was 8 ppm. At the second catalyst outlet, the denitrification rate was 77%, the ammonia component at the outlet was 5 ppm, and the ammonia was 1 ppm.

[0050] The third condition is that the composition is NOx = 98 ppm, NO2 / NO x Exhaust gas with the following composition: =0.85, NH3=100ppm, HCHO=179ppm, CO=0.3%, C2H4=230ppm, CH4=0.66%, O2=14%, H2O=9%, CO2=4%, with the remainder being N2, at a temperature of 317°C, with a treatment gas flow rate of AV12Nm per catalyst contact area of ​​the first catalyst. 3 / m 2 / hr, exhaust gas treatment catalytic converter unit (first catalyst + second catalyst) treatment gas flow rate per catalytic gas contact area AV10Nm 3 / m 2 At a rate of / hr, a reducing agent is supplied to the catalyst, and the amount of nitrogen oxides after passing through the catalyst and the amount of ammonia at the outlet are measured. The denitrification rate, which is the percentage reduction in nitrogen oxides before and after the catalyst, and the amount of nitrogen oxides after passing through the catalyst (outlet NO) are measured. x The ammonia component at the outlet after passing through the catalyst was calculated. AV is the gas flow rate divided by the gas contact area of ​​the catalyst.

[0051] Under the third condition, NH3 / NO3 is present at the inlet of the first catalyst. X The ratio is 1.02, the denitrification rate at the first catalyst outlet is 93%, the ammonia component at the outlet is 5 ppm, and the ammonia is 1 ppm.

[0052] It can be seen that when the amount of reducing agent supplied to nitrogen oxides at the inlet changes from the first condition to the second condition, and the amount of ammonia supplied under the above conditions changes, the denitrification rate at the outlet of the second catalyst and the amount of ammonia at the outlet change. By placing the second oxidation catalyst, the ammonia component contained in the exhaust gas that has passed through the first denitrification catalyst can be converted into nitrogen oxides. As a result, by measuring the nitrogen oxide concentration with both the second and third concentration sensors, it is possible to understand the denitrification rate and the amount of ammonia component remaining at the outlet after passing through the first catalyst.

[0053] Therefore, the exhaust gas treatment system 40 can determine the amount of reducing agent to supply based on both the denitrification rate and the ammonia component at the outlet by measuring the nitrogen oxide concentration with both the second and third concentration sensors in addition to the first concentration sensor, and controlling the amount of reducing agent to supply based on these values. Furthermore, by placing an oxidation catalyst downstream of the denitrification catalyst, the amount of ammonia leaking from the exhaust gas treatment system 40 can be reduced. It should be noted that the exhaust gas treatment system 40 can also control the amount of reducing agent to supply based on the inflow nitrogen oxide concentration using the denitrification rate, but is not limited to this. The exhaust gas treatment system 40 may also measure the nitrogen oxide concentration with both the second and third concentration sensors and control the amount of reducing agent to supply based on the nitrogen oxide concentration and the amount of nitrogen oxides.

[0054] The exhaust gas treatment system 40 can reduce the difference in denitrification rates between the second concentration sensor and the third concentration sensor, as in the first condition, thereby increasing the denitrification rate at the outlet of the second catalyst and reducing the amount of ammonia at the outlet compared to the second and third conditions.

[0055] Furthermore, as described above, it is preferable that the control device 60 controls the supply amount of the reducing agent so that the difference in nitrogen oxide concentration between the first catalyst outlet sensor 74 and the second catalyst outlet sensor 76 is 3 ppm or less. By keeping the difference in nitrogen oxide concentration within the above range, the denitrification rate at the second catalyst outlet can be increased and the amount of ammonia at the outlet can be reduced.

[0056] In the process shown in Figure 2, the process is based on the detection results of the first catalyst outlet sensor 74 and the second catalyst outlet sensor 76. However, as shown in Figure 3, it is preferable to also use the detection results of the first catalyst inlet sensor 72 for control. For example, the control device 60 can calculate the denitrification rate by using the nitrogen oxide concentration of the first catalyst inlet sensor 72 as the denominator and the nitrogen oxide concentrations of the first catalyst outlet sensor 74 and the second catalyst outlet sensor 76 as the numerator. This allows the control device 60 to perform control based on the denitrification rate. Furthermore, the control device 60 can improve the accuracy of control by also using the nitrogen oxide concentration of the exhaust gas flowing into the first catalyst, as measured by the first catalyst inlet sensor.

[0057] The control device 60 may correct the amount of reducing agent supplied, which was determined based on the difference, based on the nitrogen oxide concentration and denitrification rate values ​​(detected value, calculated value) of at least one of the first catalytic converter outlet sensor 74 and the second catalytic converter outlet sensor 76. Specifically, the amount of reducing agent supplied may be corrected so that the nitrogen oxide concentration is high, or so that the nitrogen oxide concentration does not exceed a threshold. For example, if the nitrogen oxide concentration exceeds a threshold, the amount of reducing agent supplied may be increased. This improves the accuracy of the control and reduces both ammonia and nitrogen oxides emitted from the exhaust gas treatment system.

[0058] The control device 60 may acquire combustion conditions of the combustion device 20, such as fuel supply amount, fuel composition, air-fuel ratio, etc., and estimate the exhaust gas flow rate, composition, etc., based on the acquired results, and correct the amount of reducing agent supplied based on the estimation results. This can improve the accuracy of the control and reduce both ammonia and nitrogen oxides emitted from the exhaust gas treatment system.

[0059] Here, it is preferable that the second catalyst has a smaller surface area in contact with the exhaust gas than the first catalyst. Specifically, it is preferable that 1 / 30 ≤ (surface area of ​​the second catalyst) / (surface area of ​​the first catalyst) ≤ 1. For example, (surface area of ​​the second catalyst) / (surface area of ​​the first catalyst) = 1 / 12. By making the second catalyst smaller than the first catalyst, it is possible to reduce the outlet ammonia component and outlet ammonia while maintaining denitrification performance.

[0060] Here, the first catalyst preferably contains titanium oxide at 60% by mass or more of the total amount, and more preferably at 70% by mass or more, in terms of TiO2. It is preferable to use TiO2 as the titanium oxide. By setting the main component titanium oxide within the above range, the denitrification rate can be increased.

[0061] The first catalyst preferably contains at least one of tungsten oxide and vanadium oxide as an active component, as described above. This allows for a higher denitrification rate. The active component may also contain molybdenum.

[0062] The first catalyst preferably contains vanadium oxide in an amount of 0.1% to 10% by mass of the total amount, and more preferably 2% to 5% by mass of the total amount, based on V2O5. This allows for a higher denitrification rate.

[0063] The first catalyst preferably contains tungsten oxide in an amount of 0.1% to 20% by mass of the total amount, and more preferably 4% to 8% by mass, based on WO3. This allows for a higher denitrification rate.

[0064] The first catalyst preferably contains manganese as an active ingredient. The amount of manganese (Mn) added to the first catalyst is preferably 1.0% by mass (wt.%) or less in terms of Mn2O3 relative to the total amount of catalyst, and more preferably 0.2% by mass or more and 1.0% by mass or less of the total amount. By setting the manganese content of the second catalyst within the above range, catalytic activity can be maintained under NO2-rich conditions, enabling high denitrification performance, and catalytic activity can also be maintained under conditions of coexistence with high concentration HCHO (formaldehyde), enabling high denitrification performance.

[0065] The first catalyst mainly consists of titanium dioxide and contains manganese as an active ingredient. By limiting the amount of manganese (Mn) added to 1.0% by mass (wt.%) or less in terms of Mn2O3 relative to the total amount of catalyst, nitrogen oxides in exhaust gas containing a high amount of nitrogen dioxide can be removed at a high rate, regardless of the presence or absence of HCHO. The second catalyst is a catalyst containing zeolite or platinum (Pt). The second catalyst is a catalyst in which zeolite is coated on the surface of a substrate.

[0066] Furthermore, the exhaust gas treatment catalyst unit of this disclosure can perform treatment with a nitrogen oxide removal rate comparable to that of the comparative example, even when HCHO is not present, that is, when a natural gas-fired gas turbine is burning under suitable conditions. In other words, the exhaust gas treatment method using the exhaust gas treatment catalyst unit of this disclosure can remove NO2 / NO2 from the exhaust gas. x However, even when exhaust gas is treated in a plant where the concentration of HCHO fluctuates from 0.5 or higher and the concentration of HCHO is equal to or higher than the concentration of NO2, to conditions where the concentration of HCHO is not present, a high denitrification rate can be maintained, and even if HCHO is generated, it can be effectively removed.

[0067] The first catalyst preferably further contains 0.1 wt% to 2% of the total amount of sulfur trioxide, and more preferably 0.2 wt% to 2% of the total amount of sulfur trioxide. This allows for a higher denitrification rate.

[0068] The first catalyst preferably does not contain chromium, copper, or cobalt as active ingredients. This simplifies the catalyst's composition and prevents a reduction in the proportion of the main components.

[0069] Furthermore, it is preferable that the exhaust gas treatment system 60 replaces the catalyst of an existing exhaust gas treatment system with the first and second catalysts of this disclosure and performs the control of this disclosure. Figures 4 to 6 are explanatory diagrams illustrating the method of replacing the catalyst of an exhaust gas treatment system. The exhaust gas treatment system 100 shown in Figure 4 is an existing facility, in which a denitrification catalyst 150 and a preliminary layer 152 are arranged in the flue 130. In the exhaust gas treatment system 100, the preliminary layer 152 is arranged downstream of the denitrification catalyst 150. The preliminary layer 152 is an area in which no catalyst is installed, and a catalyst can be added when the denitrification performance of the denitrification catalyst 150 deteriorates.

[0070] When the denitrification catalyst 150 in the exhaust gas treatment system 100 shown in Figure 4 is due for replacement, it is replaced with a denitrification catalyst 160, as shown in the exhaust gas treatment system 100a shown in Figure 5. Here, the denitrification catalyst 160 is a catalyst pack formed of a honeycomb with a higher density than the denitrification catalyst 150. Furthermore, the catalyst pack of the denitrification catalyst 160 is inclined with respect to the exhaust gas flow direction and is inclined in a different direction from adjacent catalyst packs. As a result, the catalyst pack is in contact with one adjacent catalyst pack on the upstream side in the flow direction and with the other adjacent catalyst pack on the downstream side in the flow direction. The denitrification catalyst 160 has the same denitrification performance as the denitrification catalyst 150, but with a shorter installation area in the exhaust gas flow direction.

[0071] In the exhaust gas treatment system 100a shown in Figure 5, an oxidation catalyst is placed in the preliminary layer 152. As a result, in the exhaust gas treatment system 100b shown in Figure 6, the oxidation catalyst (second catalyst) 162 is placed downstream of the denitrification catalyst (first catalyst) 160. Furthermore, in the exhaust gas treatment system 100b, the oxidation catalyst 162 can be placed not only in the preliminary layer 152 region but also in the space created by replacing the denitrification catalyst 150 with the denitrification catalyst 160. This allows the time for the exhaust gas to pass through the oxidation catalyst 162 to be increased, thereby promoting the reaction.

[0072] Furthermore, as shown in Figures 4 to 6, the oxidation catalyst can be suitably positioned in an exhaust gas treatment system in which a preliminary layer is provided downstream of the denitrification catalyst 150, allowing for the suitability of modifying existing exhaust gas treatment systems and improving denitrification performance. In addition, the exhaust gas treatment system 100b can achieve high denitrification performance while suppressing the leakage of ammonia components even when treating exhaust gas with a higher concentration of impurities. Therefore, it can treat exhaust gas under operating conditions that could not be treated by the existing exhaust gas treatment system 100, thereby expanding the operating range of the upstream combustion device 20.

[0073] [Effects of this embodiment] This disclosure has the following characteristics. However, this disclosure is not limited to the following. (1) An exhaust gas treatment system that promotes the reaction between nitrogen oxides and ammonia in a fluid in which ammonia is mixed with exhaust gas containing nitrogen oxides, and treats the nitrogen oxides in the exhaust gas, comprising: a pipe through which the exhaust gas flows; a first catalyst disposed in the pipe and promoting the reaction between nitrogen oxides and ammonia; a second catalyst, which is an oxidation catalyst, disposed in the pipe downstream of the first catalyst in the direction of exhaust gas flow; a reducing agent supply unit that supplies a reducing agent that becomes ammonia when it reaches the first catalyst to the pipe upstream of the first catalyst; a first catalyst outlet sensor that measures the nitrogen oxide concentration of the exhaust gas downstream of the first catalyst and upstream of the second catalyst; a second catalyst outlet sensor that measures the nitrogen oxide concentration of the exhaust gas downstream of the second catalyst; and a control device that controls the amount of reducing agent supplied from the reducing agent supply unit to the pipe based on the detection results of the first catalyst outlet sensor and the second catalyst outlet sensor. This allows exhaust gas to be treated with a high denitrification rate and also reduces the amount of ammonia at the outlet.

[0074] (2) The exhaust gas treatment system according to (1), wherein the control device controls the amount of reducing agent supplied based on the difference in nitrogen oxide concentrations between the first catalyst outlet sensor and the second catalyst outlet sensor. This allows exhaust gas to be treated with a high denitrification rate and also reduces outlet ammonia.

[0075] (3) The exhaust gas treatment system according to (2), wherein the control device controls the amount of reducing agent supplied so that the difference in nitrogen oxide concentration between the first catalyst outlet sensor and the second catalyst outlet sensor is 3 ppm or less.

[0076] (4) An exhaust gas treatment system according to any one of (1) to (3), wherein the system has a first catalyst inlet sensor upstream of the first catalyst that measures the nitrogen oxide concentration of the exhaust gas, and the control device calculates the denitrification rate based on the nitrogen oxide concentrations of the first catalyst inlet sensor and the first catalyst outlet sensor and controls the amount of reducing agent supplied.

[0077] (5) The exhaust gas treatment system according to any one of (1) to (4), wherein the first catalyst is a catalyst containing titanium oxide as its main component.

[0078] (6) The exhaust gas treatment system according to (5), wherein the first catalyst contains 60% by mass or more of the titanium oxide in terms of TiO2. This makes it possible to increase the denitrification rate.

[0079] (7) The exhaust gas treatment system according to (5) or (6), wherein the active ingredient is at least one of tungsten oxide and vanadium oxide. This makes it possible to increase the denitrification rate.

[0080] (8) The exhaust gas treatment system described in (7), wherein the vanadium oxide is 0.1% by mass or more and 10% by mass or less of the total amount on a V2O5 basis. This makes it possible to increase the denitrification rate.

[0081] (9) The exhaust gas treatment system according to (7) or (8), wherein tungsten oxide is 0.1% by mass or more and 20% by mass or less of the total amount on a WO3 basis. This makes it possible to increase the denitrification rate.

[0082] (10) The exhaust gas treatment system according to any one of (5) to (9), wherein the first catalyst contains manganese as an active ingredient, which is 1.0% by mass or less of the total amount in terms of Mn2O3. This makes it possible to increase the denitrification rate even when the exhaust gas contains VOC components.

[0083] (11) The exhaust gas treatment system according to any one of (5) to (9), wherein the first catalyst contains manganese as an active ingredient in an amount of 0.2% by mass or more and 1.0% by mass or less of the total amount in terms of Mn2O3. This makes it possible to increase the denitrification rate even when the exhaust gas contains VOC components.

[0084] (12) The exhaust gas treatment system according to any one of (5) to (11), wherein the first catalyst further comprises 0.1 wt% to 2% of the total amount of sulfur trioxide. This makes it possible to increase the denitrification rate.

[0085] (13) An exhaust gas treatment system according to any one of (5) to (12) that does not contain chromium, copper, or cobalt as an active ingredient. This makes it possible to increase the denitrification rate.

[0086] (14) The exhaust gas treatment system according to any one of (1) to (13), wherein the second catalyst is a catalyst containing zeolite or platinum. This makes it possible to increase the denitrification rate.

[0087] (15) An exhaust gas treatment method for treating nitrogen oxides in an exhaust gas containing nitrogen oxides, wherein the reaction between nitrogen oxides and ammonia in a fluid is promoted, and nitrogen oxides in the exhaust gas are treated, An exhaust gas treatment method comprising: a pipe through which the exhaust gas flows; a first catalyst disposed in the pipe for promoting the reaction between nitrogen oxides and ammonia; a second catalyst, which is an oxidation catalyst, disposed in the pipe downstream of the first catalyst in the exhaust gas flow direction; a reducing agent supply unit for supplying a reducing agent that becomes ammonia when it reaches the first catalyst to the pipe upstream of the first catalyst; a first catalyst outlet sensor for measuring the nitrogen oxide concentration of the exhaust gas downstream of the first catalyst and upstream of the second catalyst; and a second catalyst outlet sensor for measuring the nitrogen oxide concentration of the exhaust gas downstream of the second catalyst, comprising the steps of: measuring the nitrogen oxide concentration using the first catalyst outlet sensor and the second catalyst outlet sensor; determining the amount of reducing agent to be supplied from the reducing agent supply unit to the pipe based on the detection results of the first catalyst outlet sensor and the second catalyst outlet sensor; and supplying the determined amount from the reducing agent supply unit to the pipe. This method enables exhaust gas treatment with a high denitrification rate and also reduces outlet ammonia.

[0088] (16) The exhaust gas treatment method according to (15), wherein the amount of reducing agent supplied is such that the difference in nitrogen oxide concentration between the first catalyst outlet sensor and the second catalyst outlet sensor is 3 ppm or less. This allows exhaust gas to be treated with a high denitrification rate and also reduces outlet ammonia. [Explanation of Symbols]

[0089] 10 Combustion Plant 12 Fuel supply section 14 Air supply unit 20 Combustion device 30 Flue (exhaust gas passage) 40 Exhaust gas treatment system 42 Reducing agent supply device 50 Denitration catalyst layer 52 Oxidation catalyst layer 60 Control device 72. First concentration sensor (first catalyst inlet sensor) 74. Second concentration sensor (first catalyst outlet sensor) 76. Third concentration sensor (second catalyst outlet sensor)

Claims

1. An exhaust gas treatment system that promotes the reaction between nitrogen oxides and ammonia in a fluid in which ammonia is mixed with exhaust gas containing nitrogen oxides, and treats the nitrogen oxides in the exhaust gas, The aforementioned piping through which the exhaust gas flows, The piping is arranged to include a first catalyst that promotes the reaction between nitrogen oxides and ammonia, The piping includes a second catalyst, which is an oxidation catalyst, positioned downstream of the first catalyst in the exhaust gas flow direction, A reducing agent supply unit is provided in the piping upstream of the first catalyst to supply a reducing agent that becomes ammonia when it reaches the first catalyst, A first catalyst outlet sensor measures the nitrogen oxide concentration of the exhaust gas downstream of the first catalyst and upstream of the second catalyst, A second catalyst outlet sensor for measuring the nitrogen oxide concentration of the exhaust gas downstream of the second catalyst, An exhaust gas treatment system including a control device that controls the amount of reducing agent supplied from the reducing agent supply unit to the piping based on the detection results of the first catalyst outlet sensor and the second catalyst outlet sensor.

2. The exhaust gas treatment system according to claim 1, wherein the control device controls the amount of reducing agent supplied based on the difference in nitrogen oxide concentrations between the first catalyst outlet sensor and the second catalyst outlet sensor.

3. The exhaust gas treatment system according to claim 2, wherein the control device controls the amount of reducing agent supplied so that the difference in nitrogen oxide concentration between the first catalyst outlet sensor and the second catalyst outlet sensor is 3 ppm or less.

4. The first catalyst has a first catalyst inlet sensor that measures the nitrogen oxide concentration of the exhaust gas upstream of the first catalyst, The exhaust gas treatment system according to claim 1, wherein the control device calculates the denitrification rate based on the nitrogen oxide concentrations of the first catalyst inlet sensor and the first catalyst outlet sensor, and controls the amount of reducing agent supplied.

5. The exhaust gas treatment system according to claim 1, wherein the first catalyst is a catalyst containing titanium oxide as its main component.

6. The first catalyst is a titanium oxide TiO ２ The exhaust gas treatment system according to claim 5, wherein the converted amount is 60% by mass or more of the total amount.

7. The exhaust gas treatment system according to claim 5, wherein the first catalyst has at least one of tungsten oxide and vanadium oxide as an active component.

8. The first catalyst is a vanadium oxide, V ２ O ５ The exhaust gas treatment system according to claim 5, wherein the converted amount is 0.1% by mass or more and 10% by mass or less of the total amount.

9. The first catalyst is a tungsten oxide, WO ３ The exhaust gas treatment system according to claim 5, wherein the amount is 0.1% by mass or more and 20% by mass or less of the total amount when converted.

10. The first catalyst contains manganese as an active ingredient, Mn ２ O ３ The exhaust gas treatment system according to claim 5, wherein the converted amount is 1.0% by mass or less of the total amount.

11. The first catalyst contains manganese as an active ingredient, Mn ２ O ３ The exhaust gas treatment system according to claim 5, wherein the converted amount is 0.2% by mass or more and 1.0% by mass or less of the total amount.

12. The exhaust gas treatment system according to claim 5, wherein the first catalyst further comprises 0.1 wt% to 2% of the total amount of sulfur trioxide.

13. The exhaust gas treatment system according to claim 5, wherein the first catalyst does not contain chromium, copper, or cobalt as an active ingredient.

14. The exhaust gas treatment system according to claim 5, wherein the second catalyst is a catalyst containing zeolite or platinum.

15. An exhaust gas treatment method for treating nitrogen oxides in exhaust gas containing nitrogen oxides, wherein the reaction between nitrogen oxides and ammonia in a fluid is promoted, and nitrogen oxides in the exhaust gas are treated, The system comprises: a pipe through which the exhaust gas flows; a first catalyst disposed in the pipe for promoting the reaction between nitrogen oxides and ammonia; a second catalyst, which is an oxidation catalyst, disposed downstream of the first catalyst in the exhaust gas flow direction in the pipe; a reducing agent supply unit that supplies a reducing agent that becomes ammonia when it reaches the first catalyst to the pipe upstream of the first catalyst; a first catalyst outlet sensor that measures the nitrogen oxide concentration of the exhaust gas downstream of the first catalyst and upstream of the second catalyst; and a second catalyst outlet sensor that measures the nitrogen oxide concentration of the exhaust gas downstream of the second catalyst. The first catalyst outlet sensor and the second catalyst outlet sensor measure the nitrogen oxide concentration, The steps include determining the amount of reducing agent to be supplied from the reducing agent supply unit to the piping based on the detection results of the first catalyst outlet sensor and the second catalyst outlet sensor, An exhaust gas treatment method comprising the step of supplying a determined amount of reducing agent from the reducing agent supply unit to the piping.

16. The exhaust gas treatment method according to claim 15, wherein the amount of reducing agent supplied is such that the difference in nitrogen oxide concentration between the first catalyst outlet sensor and the second catalyst outlet sensor is 3 ppm or less.

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