SCR denitration system and method based on ammonia produced by catalytic hydrolysis of urea water using flue gas waste heat

Abstract

The present application relates to the field of gas turbine SCR denitration technology, and discloses an SCR denitration system and method based on flue gas waste heat catalytic urea hydrolysis for ammonia production. The system comprises a urea hydrolysis ammonia production reactor, an ammonia gas and flue gas mixer, and an ammonia injection grid, an ammonia mixing device and a denitration device arranged in sequence along the flue gas flow direction in the waste heat boiler. The urea hydrolysis ammonia production reactor has a urea solution inlet and is internally provided with a heat exchange tube. The inlet end of the heat exchange tube inputs high-temperature flue gas from the inlet of the waste heat boiler, and the outlet end outputs flue gas after heat exchange and delivers it to the ammonia gas and flue gas mixer. The ammonia gas outlet of the urea hydrolysis ammonia production reactor delivers ammonia-containing mixed gas to the ammonia gas and flue gas mixer, which is mixed with the flue gas input through the heat exchange tube and injected into the ammonia injection grid. The SCR denitration system can make full use of the waste heat of high-temperature flue gas to provide energy for urea hydrolysis ammonia production, save system energy consumption and reduce costs.

Description

Technical Field

[0001] This invention relates to the field of SCR denitrification technology for gas turbines, specifically to an SCR denitrification system and method based on the catalytic hydrolysis of urea to produce ammonia using waste heat from flue gas. Background Technology

[0002] Selective catalytic reduction (SCR) flue gas denitrification is widely used in the field of gas turbine denitrification at home and abroad due to its advantages such as high efficiency, stable performance and strong load adaptability. It is currently the mainstream technology for oxide emission reduction in gas turbines.

[0003] SCR (Sequencing Catalytic Reduction) denitrification systems refer to a process in which nitrogen oxides in flue gas undergo a redox reaction with injected ammonia under the action of a denitrification catalyst to produce nitrogen and water. An SCR denitrification system mainly includes a denitrification unit, an ammonia injection unit, a reducing agent (i.e., ammonia) preparation system, and other auxiliary devices. The reducing agent can be liquid ammonia, ammonia water, or urea. Currently, using urea to produce ammonia has become the preferred technology in the field of gas turbine SCR denitrification due to its better safety performance. Urea hydrolysis and urea pyrolysis are the most common methods for producing ammonia. However, uneven flow field and temperature distribution within the urea pyrolysis furnace lead to low urea conversion rates, complex side reactions, and high urea consumption. Therefore, urea hydrolysis ammonia production technology is currently one of the more suitable technical solutions.

[0004] However, conventional urea hydrolysis ammonia production technology requires a large amount of high-quality steam to power it and maintain the stable operation of the urea hydrolysis ammonia production reaction, resulting in high energy consumption for the entire urea hydrolysis ammonia production process. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide an SCR denitrification system and method based on waste heat from flue gas to catalytically hydrolyze urea to produce ammonia. This SCR denitrification system can fully utilize the high-temperature flue gas generated by the combustion of the gas turbine unit to replace high-quality steam for powering the hydrolysis of urea to produce ammonia, thus saving system energy consumption. In addition, it can avoid problems such as corrosion, blockage, and deformation of high-temperature fans caused by urea pyrolysis to produce ammonia, and also reduce the risk of blockage in the product gas pipeline.

[0006] To achieve the above objectives, the present invention provides an SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production. The system includes a urea hydrolysis to ammonia production reactor, an ammonia and flue gas mixer, and an ammonia injection grid, an ammonia mixing device, and a denitrification device arranged sequentially in the waste heat boiler along the flue gas flow direction.

[0007] The urea hydrolysis ammonia production reactor has a urea solution inlet and is equipped with a heat exchange tube inside. The inlet end of the heat exchange tube receives high-temperature flue gas from the inlet of the waste heat boiler, and the outlet end outputs the flue gas after heat exchange and delivers it to the ammonia-containing mixed gas and flue gas mixer.

[0008] The ammonia outlet of the urea hydrolysis ammonia production reactor delivers ammonia-containing mixed gas to the ammonia and flue gas mixer, which mixes with the flue gas input through the heat exchange tube and then injects it into the ammonia injection grid.

[0009] Preferably, the system further includes a urea solution preparation system for preparing a urea solution and injecting the urea solution into the urea hydrolysis ammonia production reactor through the urea solution inlet.

[0010] Preferably, the urea solution preparation system includes a urea unpacking machine, a bucket elevator, a urea storage silo, a urea dissolving tank, a urea solution delivery pump, and a urea solution storage tank connected in sequence.

[0011] Preferably, the system further includes a high-temperature fan, which injects high-temperature flue gas from the inlet of the waste heat boiler into the heat exchange tube.

[0012] Preferably, the heat exchange tube is a multi-layer coil.

[0013] Preferably, the multilayer coil has 3-6 layers.

[0014] Preferably, the ammonia injection grid includes a plurality of nozzles, and the nozzles are spaced 400-500mm apart.

[0015] Preferably, the ammonia mixing device is equipped with a static mixer that corresponds one-to-one with the nozzles of the ammonia injection grid.

[0016] Preferably, the denitrification device is filled with a honeycomb denitrification catalyst.

[0017] Preferably, the honeycomb denitrification catalyst has 40-75 pores.

[0018] Preferably, the urea hydrolysis ammonia production reactor is equipped with a sewage discharge pipe, which is used to discharge the wastewater generated by the urea hydrolysis ammonia production reactor during the urea hydrolysis ammonia production process.

[0019] A second aspect of the present invention also provides an SCR denitrification method based on the catalytic hydrolysis of urea to produce ammonia using waste heat from flue gas. This method is implemented in the aforementioned system and includes:

[0020] High-temperature flue gas from the waste heat boiler inlet is transported to the heat exchange tubes in the urea hydrolysis ammonia production reactor. Urea solution is injected into the urea hydrolysis ammonia production reactor through the urea solution inlet. The urea solution undergoes a hydrolysis reaction under the heating action of the heat exchange tubes. The resulting ammonia-containing mixed gas and the flue gas after heat exchange in the heat exchange tubes are mixed in the ammonia gas and flue gas mixer and then injected into the ammonia injection grid.

[0021] In the waste heat boiler, the flue gas is denitrified by passing through an ammonia injection grid, an ammonia mixing device, and a denitrification device in sequence.

[0022] The SCR denitrification system of this invention features a multi-layered coil for flue gas heat exchange in its urea hydrolysis ammonia production reactor. High-temperature flue gas from the waste heat boiler inlet is introduced to replace high-quality steam, powering the urea hydrolysis process. The ammonia-containing mixed gas produced by urea hydrolysis mixes with the heat-exchanged flue gas and enters the waste heat boiler, where it mixes with the high-temperature flue gas for denitrification treatment. The high-temperature flue gas generated by the gas turbine unit is characterized by virtually no soot, low sulfur dioxide concentration, and high temperature, eliminating the risk of clogging equipment such as the ammonia injection grid in the SCR denitrification system. Utilizing the waste heat of the high-temperature flue gas to power the urea hydrolysis ammonia production reaction saves system energy and simultaneously improves the efficiency of the reaction. Meanwhile, in the SCR denitrification system described in this invention, the flue gas after heat exchange is mixed with the ammonia-containing mixed gas produced by urea hydrolysis before being conveyed to the ammonia injection grid. The flue gas after heat exchange dilutes the ammonia-containing mixed gas produced by urea hydrolysis, reducing the risk of blockage in the product gas pipeline. The SCR denitrification system described in this invention does not require an additional dilution fan to dilute the obtained ammonia-containing mixed gas, further simplifying the entire process. It also increases the temperature of the ammonia-containing mixed gas, eliminating the need for additional heating. In addition, in the SCR denitrification system described in this invention, an ammonia injection grid and an ammonia mixing device are installed in the waste heat boiler along the flue gas flow direction to further mix the flue gas and product gas before sending them to the denitrification device for denitrification treatment. This increases the temperature of the product gas and avoids problems such as blockage of the ammonia injection grid pipeline caused by the precipitation of solids from the reverse reaction of urea hydrolysis, ensuring the stable operation of the entire SCR denitrification system, making it very suitable for large-scale promotion. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the SCR denitrification system described in this invention.

[0024] Explanation of reference numerals in the attached figures

[0025] 1. Urea unpacking machine; 2. Bucket elevator; 3. Urea storage silo; 4. Urea dissolving tank; 5. Urea solution storage tank; 6. Urea solution transfer pump; 7. Urea hydrolysis ammonia production reactor; 8. Sewage pipe; 9. High-temperature fan; 10. Ammonia and flue gas mixer; 11. Ammonia injection grid; 12. Ammonia mixer; 13. Denitrification device; 14. Flue gas online monitoring device; 15. Waste heat boiler; Ⅰ. Urea solution preparation system. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] Furthermore, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0029] In this article, "ammonia-containing mixed gas" refers to a mixed gas containing ammonia and carbon dioxide obtained through urea hydrolysis.

[0030] In this document, "product gas" refers to the gas obtained by mixing the ammonia-containing mixed gas obtained in the urea hydrolysis ammonia production reaction with the heat-exchanged flue gas in the ammonia and flue gas mixer 10.

[0031] like Figure 1 As shown, the SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to produce ammonia according to the present invention includes a urea hydrolysis ammonia production reactor 7, an ammonia and flue gas mixer 10, and an ammonia injection grid 11, an ammonia mixing device 12, and a denitrification device 13 arranged sequentially in the waste heat boiler 15 along the flue gas flow direction.

[0032] In the SCR denitrification system of the present invention, the urea hydrolysis ammonia production reactor 7 is used to hydrolyze urea solution to prepare an ammonia-containing mixed gas, and the ammonia-containing mixed gas is used as the feed gas for subsequent denitrification treatment of flue gas. The heat source for the urea hydrolysis ammonia production reaction is provided by high-temperature flue gas from the inlet of the waste heat boiler 15. Specifically, the urea hydrolysis ammonia production reactor 7 has a urea solution inlet for introducing an aqueous urea solution into the reactor. The reactor 7 is equipped with heat exchange tubes. The inlet end of the heat exchange tubes receives high-temperature flue gas from the inlet of the waste heat boiler 15, and the outlet end outputs the heat-exchanged flue gas, which is then transported to the ammonia and flue gas mixer 10.

[0033] In this invention, the "high temperature" in "high temperature flue gas" refers to the flue gas temperature relative to the temperature of the flue gas after heat exchange and cooling through the heat exchange tubes. Typically, the temperature of the high temperature flue gas from the inlet of the waste heat boiler 15 is 560℃-600℃, and the temperature of the flue gas after heat exchange is 200-300℃.

[0034] In this invention, the high-temperature flue gas is generated by combustion of a gas turbine unit. When the high-temperature flue gas generated by the gas turbine unit is transported to the waste heat boiler 15, a small portion of the high-temperature flue gas is extracted at the inlet of the waste heat boiler 15 and enters the heat exchange tube in the urea hydrolysis ammonia production reactor 7 through the high-temperature fan 9 to supply energy for the urea hydrolysis ammonia production reaction. After heat exchange, the flue gas is mixed with the ammonia-containing mixed gas generated by urea hydrolysis and then enters the ammonia injection grid 11. The remaining high-temperature flue gas enters the waste heat boiler 15 and mixes with the product gas injected from the ammonia injection grid 11 before entering the denitrification device 13 for denitrification treatment.

[0035] In the SCR denitrification system of the present invention, the ammonia outlet of the urea hydrolysis ammonia production reactor 7 delivers ammonia-containing mixed gas to the ammonia and flue gas mixer 10, which mixes with the flue gas input through the heat exchange tube and is then injected into the ammonia injection grid 11.

[0036] In the SCR denitrification system of the present invention, the system further includes a urea solution preparation system I, which is used to prepare an aqueous urea solution and inject the urea solution into the urea hydrolysis ammonia production reactor through the urea solution inlet.

[0037] In this invention, the urea solution used for the urea hydrolysis to ammonia production reaction can be a directly provided aqueous urea solution, or it can be prepared by the urea solution preparation system I and injected into the urea hydrolysis to ammonia production reactor 7 for reaction.

[0038] In a preferred embodiment, the urea solution preparation system I includes a urea unpacking machine 1, a bucket elevator 2, a urea storage silo 3, a urea dissolving tank 4, a urea solution transfer pump 6, and a urea solution storage tank 5, which are connected in sequence.

[0039] Specifically, the urea unpacking machine 1 is used to remove the packaging bags of commercially available urea in a dust-free manner and remove urea packaging bag residue; it can be a common instrument in the prior art. The bucket elevator 2 is used to transport the urea obtained after being unpacked by the urea unpacking machine to the urea storage silo 3. The urea storage silo 3 is used to store urea and to transport urea to the urea dissolving tank 4 according to production needs. The urea dissolving tank 4 is used to mix urea with water, and after stirring, the urea and water are fully dissolved to obtain a urea aqueous solution. The urea solution transfer pump 6 is used to transport the urea aqueous solution in the urea dissolving tank 4 to the urea solution storage tank 5. The urea solution storage tank 5 is used to store the urea aqueous solution and to provide the urea aqueous solution to the urea hydrolysis ammonia production reactor 7 for ammonia production reaction.

[0040] In the SCR denitrification system of the present invention, a stirrer is provided at the bottom of the urea dissolving tank 4 to prevent urea and residue from depositing and stratifying.

[0041] In the SCR denitrification system described in this invention, the system further includes a high-temperature fan 9. High-temperature flue gas from the inlet of the waste heat boiler 15 is injected into the heat exchange tube through the high-temperature fan 9 to supply energy for the urea hydrolysis ammonia production reaction. The high-temperature fan 9 can be a common type of fan in the art that operates at high temperatures and can be used to transport gas, such as a Roots blower or a centrifugal blower.

[0042] In a specific embodiment, the heat exchange tube is a multi-layer coil, with 3-6 layers. The multi-layer coil is located at the bottom of the urea hydrolysis ammonia production reactor 7. During the urea hydrolysis ammonia production process, high-temperature flue gas is introduced into the multi-layer coil by a high-temperature fan 9, transferring heat to the urea hydrolysis reaction system. The flue gas after heat exchange enters the ammonia and flue gas mixer 10 through the outlet end of the multi-layer coil.

[0043] In this invention, the urea hydrolysis ammonia production reactor 7 provides a site for carrying out the urea hydrolysis ammonia production reaction, and the chemical reaction equation occurring in the urea hydrolysis ammonia production reactor 7 is as follows:

[0044] CO(NH2)2+H2O=2NH3+CO2↑.

[0045] In the SCR denitrification system of the present invention, the ammonia-containing mixed gas obtained from the urea hydrolysis ammonia production reactor 7 contains ammonia and carbon dioxide. The gas output from the ammonia outlet of the urea hydrolysis ammonia production reactor 7 is an ammonia-containing mixed gas containing ammonia and carbon dioxide. The carbon dioxide generated in the urea hydrolysis ammonia production reaction enters the ammonia and flue gas mixer 10 along with the ammonia-containing mixed gas, and mixes with the cooled flue gas before entering the ammonia injection grid 11, ammonia mixing device 12, and denitrification device 13 of the SCR denitrification system. Finally, it is discharged with the tail gas after the denitrification treatment is completed.

[0046] In this invention, the urea hydrolysis ammonia production reactor 7 is equipped with a sewage discharge pipe 8, which is used to discharge the waste liquid generated by the urea hydrolysis ammonia production reactor 7 during the urea hydrolysis ammonia production process.

[0047] In a specific implementation, the urea hydrolysis ammonia production reactor 7 can be set close to the waste heat boiler 15 to reduce the heat consumption caused by high-temperature flue gas during transmission.

[0048] In this invention, the flue gas cooled by heat exchange in the heat exchange tube is transported to the ammonia and flue gas mixer 10. The ammonia-containing mixed gas produced by urea hydrolysis is also transported to the ammonia and flue gas mixer 10 and mixed with the heat-exchanged flue gas. The ammonia-containing mixed gas is diluted with the heat-exchanged flue gas to a certain extent to obtain product gas. Then, the product gas is transported to the ammonia injection grid 11. The heat-exchanged flue gas and the ammonia-containing mixed gas can dilute and heat the obtained ammonia-containing mixed gas, reducing the risk of blockage in the product gas pipeline. Furthermore, in this system, there is no need to use a dilution fan and heater to treat the product gas, which simplifies the denitrification process, saves energy consumption of urea hydrolysis, and reduces equipment costs.

[0049] In this invention, the ammonia spraying grid 11 includes a plurality of nozzles, and the spacing between the nozzles is 400-500mm.

[0050] In a specific embodiment, the ammonia injection grid 11 is also provided with a gas regulating valve for adjusting the flow rate of the product gas delivered by the ammonia injection grid.

[0051] In this invention, the nozzle diameter of the ammonia injection grid 11 is 6-15mm. Using nozzles within this diameter range can better mix the ammonia mixture with the flue gas, achieving a better mixing effect.

[0052] In a specific embodiment, the gas velocity of the product gas ejected from the nozzle at the nozzle opening is ≥15m / s.

[0053] In this invention, the ammonia mixing device 12 is equipped with static mixers that correspond one-to-one with the nozzles of the ammonia injection grid 11. The static mixers have an impeller-shaped structure and are located downstream of the nozzles. The static mixers can perform sufficient turbulence and mixing within the region, fully mixing the product gas from the ammonia injection grid 11 with the high-temperature flue gas in the waste heat boiler 15. The mixed gas then flows into the denitrification device 13 for denitrification treatment.

[0054] In a specific embodiment, the denitrification device 13 is filled with a honeycomb denitrification catalyst.

[0055] In a preferred embodiment, the honeycomb denitrification catalyst has 40-75 pores.

[0056] In this invention, the SCR denitrification system further includes a flue gas online monitoring device 14 located downstream of the denitrification device 13. The flue gas online monitoring device 14 is located at the gas emission outlet of the waste heat boiler 15 chimney and is used to monitor the concentration of nitrogen oxides in the emitted gas after denitrification treatment. The flow rate of the gas delivered by the nozzle in the ammonia injection grid 11 can be adjusted according to the concentration of nitrogen oxides in the emitted gas, thereby ensuring the removal rate of nitrogen oxides in the flue gas.

[0057] In the SCR denitrification system described in this invention, the product gas entering the ammonia injection grid 11 is sprayed out through the nozzle and fully mixed with the high-temperature flue gas in the waste heat boiler 15 under the action of the ammonia mixing device 12. The mixed gas enters the denitrification device 13 to remove nitrogen oxides from the flue gas.

[0058] In the SCR denitrification system of the present invention, the ammonia and flue gas mixer 10 is provided with an ammonia inlet for inputting the ammonia-containing mixed gas generated by urea hydrolysis, and the ammonia and flue gas mixer 10 is also provided with a flue gas inlet for inputting the flue gas after heat exchange. The flue gas after heat exchange in the heat exchange tube is transported to the ammonia and flue gas mixer 10 through the flue gas inlet on the ammonia and flue gas mixer 10. The ammonia-containing mixed gas generated by urea hydrolysis in the urea hydrolysis ammonia production reactor 7 is transported to the ammonia and flue gas mixer 10 through the ammonia inlet on the ammonia and flue gas mixer 10 and mixed with the flue gas after heat exchange to obtain product gas.

[0059] In the SCR denitrification system of the present invention, the urea solution preparation system I is connected to the urea solution inlet of the urea hydrolysis ammonia production reactor 7, and the ammonia outlet of the urea hydrolysis ammonia production reactor 7 is connected to the ammonia inlet of the ammonia and flue gas mixer 10; the inlet of the heat exchange tube in the urea hydrolysis ammonia production reactor 7 is connected to the outlet of the high-temperature fan 9, and the outlet of the heat exchange tube in the urea hydrolysis ammonia production reactor 7 is connected to the flue gas inlet of the ammonia and flue gas mixer 10; the outlet of the ammonia and flue gas mixer 10 is connected to the inlet of the ammonia injection grid 11; the waste heat boiler 15 is provided with the ammonia injection grid 11, the ammonia mixing device 12 and the denitrification device 13 connected in sequence; the flue gas online monitoring device 14 is installed at the gas emission outlet of the waste heat boiler 15 chimney.

[0060] In a specific implementation, the outlet of the urea solution storage tank 5 in the urea solution preparation system I is connected to the urea solution inlet of the urea hydrolysis ammonia production reactor 7.

[0061] According to a first specific embodiment of the SCR denitrification system of the present invention, the SCR denitrification system includes a urea hydrolysis ammonia production reactor 7, an ammonia and flue gas mixer 10, and an ammonia injection grid 11, an ammonia mixing device 12, and a denitrification device 13 arranged sequentially in a waste heat boiler 15 along the flue gas flow direction. The urea hydrolysis ammonia production reactor 7 has a urea solution inlet and is equipped with a heat exchange tube inside. The inlet end of the heat exchange tube receives high-temperature flue gas from the inlet of the waste heat boiler 15, and the outlet end outputs the heat-exchanged flue gas and delivers it to the ammonia and flue gas mixer 10. The ammonia outlet of the urea hydrolysis ammonia production reactor 7 delivers ammonia-containing mixed gas to the ammonia and flue gas mixer 10, which is mixed with the flue gas input through the heat exchange tube and then injected into the ammonia injection grid 11. The SCR denitrification system can use the high-temperature flue gas from the inlet of the waste heat boiler 15 to power the urea hydrolysis ammonia production process, thereby saving energy consumption in the urea hydrolysis ammonia production reaction.

[0062] According to another embodiment of the SCR denitrification system of the present invention, the SCR denitrification system includes a urea solution preparation system I, a urea hydrolysis ammonia production reactor 7, an ammonia and flue gas mixer 10, and an ammonia injection grid 11, an ammonia mixing device 12, and a denitrification device 13 arranged sequentially along the flue gas flow direction within a waste heat boiler 15; the urea hydrolysis ammonia production reactor 7 has a urea solution inlet and is internally equipped with heat exchange tubes, the inlet end of which receives high-temperature flue gas from the inlet of the waste heat boiler 15, and the outlet end outputs the heat-exchanged flue gas and delivers it to the ammonia and flue gas mixer 10; The ammonia outlet of the urea hydrolysis ammonia production reactor 7 delivers an ammonia-containing mixed gas to the ammonia and flue gas mixer 10, which mixes with the flue gas input through the heat exchange tube and is then injected into the ammonia injection grid 11. The urea solution preparation system I includes a urea unpacking machine 1, a bucket elevator 2, a urea storage silo 3, a urea dissolving tank 4, a urea solution delivery pump 6, and a urea solution storage tank 5 connected in sequence. The SCR denitrification system can utilize the high-temperature flue gas from the inlet of the waste heat boiler 15 to power the urea hydrolysis ammonia production process, which can save energy consumption in the urea hydrolysis ammonia production reaction and reduce the risk of blockage in the product gas pipeline.

[0063] According to another embodiment of the SCR denitrification system of the present invention, the SCR denitrification system includes a urea solution preparation system I, a urea hydrolysis ammonia production reactor 7, an ammonia and flue gas mixer 10, and an ammonia injection grid 11, an ammonia mixing device 12, and a denitrification device 13 arranged sequentially in a waste heat boiler 15 along the flue gas flow direction; the urea hydrolysis ammonia production reactor 7 has a urea solution inlet and is internally equipped with multi-layer coils, the inlet end of which receives high-temperature flue gas from the inlet of the waste heat boiler 15, and the outlet end outputs the heat-exchanged flue gas and is transported to the ammonia and flue gas mixer 10. In the gas mixer 10, the ammonia outlet of the urea hydrolysis ammonia production reactor 7 supplies ammonia-containing mixed gas to the ammonia and flue gas mixer 10, which is then mixed with the flue gas input through the heat exchange tube and injected into the ammonia injection grid 11. The urea solution preparation system I includes a urea unpacking machine 1, a bucket elevator 2, a urea storage silo 3, a urea dissolving tank 4, a urea solution delivery pump 6, and a urea solution storage tank 5 connected in sequence. The SCR denitrification system can utilize the high-temperature flue gas from the inlet of the waste heat boiler 15 to power the urea hydrolysis ammonia production process, which can further save energy consumption in the urea hydrolysis ammonia production reaction.

[0064] According to another embodiment of the SCR denitrification system of the present invention, the SCR denitrification system includes a urea solution preparation system I, a urea hydrolysis ammonia production reactor 7, an ammonia and flue gas mixer 10, and an ammonia injection grid 11, an ammonia mixing device 12, and a denitrification device 13 arranged sequentially in a waste heat boiler 15 along the flue gas flow direction; the urea hydrolysis ammonia production reactor 7 has a urea solution inlet and is internally equipped with multi-layer coils, the inlet end of which receives high-temperature flue gas from the inlet of the waste heat boiler 15, and the outlet end outputs... The flue gas after heat exchange is then conveyed to the ammonia and flue gas mixer 10; the ammonia outlet of the urea hydrolysis ammonia production reactor 7 delivers an ammonia-containing mixed gas to the ammonia and flue gas mixer 10, which mixes with the flue gas input through the heat exchange tubes and is then injected into the ammonia injection grid 11; the urea solution preparation system I includes a urea unpacking machine 1, a bucket elevator 2, a urea storage silo 3, a urea dissolving tank 4, a urea solution delivery pump 6, and a urea solution storage tank 5 connected in sequence; the heat exchange tubes are multi-layer coils, with 3-6 layers. The SCR denitrification system can utilize the high-temperature flue gas from the inlet of the waste heat boiler 15 to power the urea hydrolysis ammonia production process, further saving energy consumption in the urea hydrolysis ammonia production reaction.

[0065] This invention further provides an SCR denitrification method based on the catalytic hydrolysis of urea to produce ammonia using waste heat from flue gas. This method is implemented in the aforementioned system and includes:

[0066] The high-temperature flue gas at the inlet of the waste heat boiler 15 is transported to the heat exchange tube in the urea hydrolysis ammonia production reactor 7. Urea solution is injected into the urea hydrolysis ammonia production reactor 7 through the urea solution inlet. The urea solution undergoes a hydrolysis reaction under the heating action of the heat exchange tube. The resulting ammonia-containing mixed gas and the flue gas after heat exchange in the heat exchange tube are mixed in the ammonia gas and flue gas mixer 10, and then injected into the ammonia injection grid 11.

[0067] In the waste heat boiler 15, the flue gas is denitrified by passing through the ammonia injection grid 11, the ammonia mixing device 12 and the denitrification device 13 in sequence.

[0068] The working principle of the SCR denitrification system described in this invention is as follows: After the commercially available urea is unpacked by the urea unpacking machine 1, the urea is transported to the urea storage silo 3 by the bucket elevator 2. Then, the urea in the urea storage silo 3 is transported to the urea dissolving tank 4. In the urea dissolving tank 4, the urea and water are thoroughly stirred and mixed to obtain a urea aqueous solution. Then, the urea aqueous solution is transported to the urea solution storage tank 5 by the urea solution transfer pump 6 for storage. Then, the urea aqueous solution in the urea solution storage tank 5 is transported to the urea hydrolysis ammonia production reactor 7 for urea hydrolysis to prepare an ammonia-containing mixed gas. The ammonia-containing mixed gas obtained during the urea hydrolysis process is transported to the ammonia and flue gas mixer 10 through the ammonia outlet.

[0069] A portion of the high-temperature flue gas from the inlet of the waste heat boiler 15 is transported by the high-temperature fan 9 to the heat exchange tubes in the urea hydrolysis ammonia production reactor 7. The heat from the high-temperature flue gas in the heat exchange tubes powers the urea hydrolysis ammonia production reaction. After heat exchange, the flue gas is transported to the ammonia and flue gas mixer 10. The ammonia-containing mixed gas prepared in the urea hydrolysis ammonia production reactor 7 is transported through the ammonia outlet to the ammonia and flue gas mixer 10 and mixed with the heat-exchanged flue gas to obtain product gas. The product gas is then transported through the outlet of the ammonia and flue gas mixer 10 to the ammonia injection grid 11, where it is ejected through the nozzles of the ammonia injection grid 11. The injected product gas is further mixed with the remaining high-temperature flue gas in the waste heat boiler 15 by the static mixer in the ammonia mixing device 12. The uniformly mixed gas is then transported to the denitrification device 13, where the flue gas is denitrified by the honeycomb denitrification catalyst to remove nitrogen oxides. The gas after denitrification can be discharged. The flue gas online monitoring device 14, located downstream of the denitrification device 13, controls the flow rate of the product gas in the ammonia injection grid 11 by real-time testing of the nitrogen oxide content in the discharged gas, so as to ensure that nitrogen oxides in the flue gas are removed as much as possible.

[0070] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0071] Example 1

[0072] The following examples use the following SCR denitrification system for treatment, such as... Figure 1 As shown, the SCR denitrification system includes a urea unpacking machine 1, a bucket elevator 2, a urea storage silo 3, a urea dissolving tank 4, a urea solution transfer pump 6, and a urea solution storage tank 5 connected in sequence; it also includes a urea hydrolysis ammonia production reactor 7, a sewage pipe 8, a high-temperature fan 9, and an ammonia and flue gas mixer 10, an ammonia injection grid 11, an ammonia mixing device 12, and a denitrification device 13 arranged in the waste heat boiler 15 along the flue gas flow direction; the flue gas online monitoring device 14 is located downstream of the denitrification device 13 and is installed at the gas emission outlet of the waste heat boiler 15 chimney;

[0073] The outlet of the urea solution storage tank 5 is connected to the urea solution inlet of the urea hydrolysis ammonia production reactor 7, and the ammonia outlet of the urea hydrolysis ammonia production reactor 7 is connected to the ammonia inlet of the ammonia and flue gas mixer 10; the inlet of the heat exchange tube in the urea hydrolysis ammonia production reactor 7 is connected to the outlet of the high-temperature fan 9, and the outlet of the heat exchange tube in the urea hydrolysis ammonia production reactor 7 is connected to the flue gas inlet of the ammonia and flue gas mixer 10; the outlet of the ammonia and flue gas mixer 10 is connected to the inlet of the ammonia injection grid 11.

[0074] The urea hydrolysis ammonia production reactor 7 is equipped with a sewage discharge pipe 8.

[0075] The specific process of using the SCR denitrification system is as follows:

[0076] Commercially available urea is unpacked by a urea unpacking machine 1, and then transported to a urea storage silo 3 via a bucket elevator 2. The urea in the storage silo 3 is then transferred to a urea dissolving tank 4, where it is thoroughly mixed with water to obtain a urea aqueous solution. This solution is then pumped by a urea solution transfer pump 6 to a urea solution storage tank 5 for storage. The urea solution in the storage tank 5 is then transferred to a urea hydrolysis ammonia production reactor 7 for urea hydrolysis to prepare an ammonia-containing mixed gas. The ammonia-containing mixed gas obtained during the urea hydrolysis process enters an ammonia and flue gas mixer 10.

[0077] A portion of the high-temperature flue gas (approximately 580°C, with a nitrogen oxide concentration of 10-25 ppm) from the inlet of the waste heat boiler 15 is transported by a high-temperature fan 9 to the multi-layer coils within the urea hydrolysis ammonia production reactor 7 to power the urea hydrolysis process. After heat exchange (approximately 250°C), the flue gas enters the ammonia and flue gas mixer 10 and mixes with the ammonia-containing mixed gas obtained from urea hydrolysis to produce product gas. This product gas is then transported to the ammonia injection grid 11 and ejected through nozzles (10mm) between the nozzles. The product gas, with a spacing of 400mm, is further mixed with the remaining high-temperature flue gas in the waste heat boiler 15 under the action of the static mixer in the ammonia mixing device 12. Then, the mixed gas is sent to the denitrification device 13, where the flue gas is denitrified under the action of the honeycomb denitrification catalyst (with 45 pores) to remove nitrogen oxides from the flue gas. Then, the content of nitrogen oxides in the denitrified gas is monitored in real time by the flue gas online monitoring device 14. This system can realize the denitrification treatment of high-temperature flue gas and can also save the energy consumption of urea hydrolysis to produce ammonia.

[0078] Comparative Example 1

[0079] The method described in Example 1 is implemented, except that the ammonia and flue gas mixer 10 is not set up, and a high-temperature fan 9 is used to transport high-quality water steam to the multi-layer coil to supply energy for urea hydrolysis to produce ammonia. All the high-temperature flue gas generated by the gas turbine unit enters the waste heat boiler 15, and the ammonia-containing mixed gas generated by urea hydrolysis directly enters the ammonia injection grid 11. Under the action of the static mixer in the ammonia mixing device 12, it is mixed with the high-temperature flue gas in the waste heat boiler 15, and then transported to the denitrification device 13 for denitrification treatment.

[0080] Using the systems of Example 1 and Comparative Example 1 to denitrify the same weight of high-temperature flue gas, the system of Example 1 can save 30% of energy and also save water resources. This shows that the SCR denitrification system of the present invention can make full use of the waste heat of high-temperature flue gas to power the urea hydrolysis ammonia production reaction, which can not only save system energy consumption, but also make full use of the heat of flue gas, and can also remove nitrogen oxides in flue gas. In addition, the SCR denitrification system of the present invention can further prevent pipeline blockage and maintain the stable operation of the system, which has great industrial application prospects.

[0081] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production, characterized in that, The system includes a urea hydrolysis ammonia production reactor (7), an ammonia and flue gas mixer (10), and an ammonia injection grid (11), an ammonia mixing device (12), and a denitrification device (13) arranged sequentially in the waste heat boiler (15) along the flue gas flow direction. The urea hydrolysis ammonia production reactor (7) has a urea solution inlet and is equipped with a heat exchange tube inside. The inlet end of the heat exchange tube is fed from the high-temperature flue gas at the inlet of the waste heat boiler (15), and the outlet end outputs the flue gas after heat exchange and delivers it to the ammonia and flue gas mixer (10). The ammonia outlet of the urea hydrolysis ammonia production reactor (7) delivers ammonia-containing mixed gas to the ammonia and flue gas mixer (10), which mixes with the flue gas input through the heat exchange tube to obtain product gas, and then injects the product gas into the ammonia injection grid (11). The remaining high-temperature flue gas enters the waste heat boiler (15) and mixes with the product gas injected by the ammonia injection grid (11) before entering the denitrification device (13) for denitrification treatment; The system also includes a urea solution preparation system (Ⅰ) for preparing urea solution and injecting urea solution into the urea hydrolysis ammonia production reactor (7) through the urea solution inlet. The system also includes a high-temperature fan (9) that injects high-temperature flue gas from the inlet of the waste heat boiler (15) into the heat exchange tube.

2. The SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production according to claim 1, characterized in that, The urea solution preparation system (Ⅰ) includes a urea unpacking machine (1), a bucket elevator (2), a urea storage silo (3), a urea dissolving tank (4), a urea solution transfer pump (6), and a urea solution storage tank (5) connected in sequence.

3. The SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production according to claim 1, characterized in that, The heat exchange tube is a multi-layer coil.

4. The SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production according to claim 3, characterized in that, The multilayer coil has 3-6 layers.

5. The SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production according to claim 1, characterized in that, The ammonia spraying grid (11) includes several nozzles, and the spacing between the nozzles is 400-500mm.

6. The SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production according to claim 5, characterized in that, The ammonia mixing device (12) is equipped with a static mixer that corresponds one-to-one with the nozzles of the ammonia injection grid (11).

7. The SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production according to claim 1, characterized in that, The denitrification device (13) is filled with a honeycomb denitrification catalyst.

8. The SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production according to claim 7, characterized in that, The honeycomb denitrification catalyst has 40-75 pores.

9. The SCR denitrification system based on flue gas waste heat catalytic urea hydrolysis to ammonia production according to claim 1, characterized in that, The urea hydrolysis ammonia production reactor (7) is equipped with a sewage discharge pipe (8), which is used to discharge the waste liquid generated by the urea hydrolysis ammonia production reactor (7) during the urea hydrolysis ammonia production process.

10. A method for SCR denitrification based on the catalytic hydrolysis of urea to produce ammonia using waste heat from flue gas, characterized in that, The method is implemented in the system according to any one of claims 1-9, the method comprising: High-temperature flue gas from the inlet of the waste heat boiler (15) is transported to the heat exchange tube in the urea hydrolysis ammonia production reactor (7). Urea solution is injected into the urea hydrolysis ammonia production reactor (7) through the urea solution inlet. The urea solution undergoes hydrolysis under the heating action of the heat exchange tube. The resulting ammonia-containing mixed gas and the flue gas after heat exchange in the heat exchange tube are mixed in the ammonia gas and flue gas mixer (10) and then injected into the ammonia injection grid (11). In the waste heat boiler (15), the flue gas is denitrified by passing through the ammonia injection grid (11), the ammonia mixing device (12) and the denitrification device (13) in sequence.

Images