A precise ammonia spraying device applied to a SNCR+SCR combined denitration process of a circulating fluidized bed boiler

Abstract

The application belongs to the technical field of environmental protection, and discloses a precise ammonia spraying device applied to a SNCR+SCR combined denitration process of a circulating fluidized bed boiler.The device comprises an SNCR spraying gun, an SCR ammonia supplement spraying gun, a NOx rapid measurement system, a NOx and NH3 escape rapid measurement system, a partition control system and an SCR reactor; the SNCR spraying gun is arranged at the inlet of a cyclone separator; the SCR ammonia supplement spraying gun is arranged at the outlet of the cyclone separator; the SCR reactor is arranged at the tail flue of the circulating fluidized bed boiler; the NOx rapid measurement system is arranged at the front end of the SCR ammonia supplement spraying gun; the NOx and NH3 escape rapid measurement system is arranged at the outlet of the SCR reactor; and the partition control system is arranged at the adjacent position of the SCR ammonia supplement spraying gun.The device has the characteristics of simple process system, reliability, energy saving and the like, and can realize the control requirement of precise ammonia spraying.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, and more specifically to a precision ammonia injection device applied to the SNCR+SCR combined denitrification process of a circulating fluidized bed boiler. Background Technology

[0002] Traditional ammonia injection control relies primarily on NOx analyzers installed at the inlet and outlet of the denitrification unit, combined with a PID control system to guide the adjustment of ammonia injection volume. This type of ammonia injection control has the following drawbacks: 1) The NOx analyzer has a long response time, failing to provide real-time, rapid data, resulting in control lag, which is particularly pronounced when boiler load fluctuates rapidly. 2) NOx measurement is primarily done at a single point, and the values ​​cannot reflect the NOx distribution across the entire cross-section, as it is well known that NOx in flue gas has different distributions at different cross-sections. 3) Due to the measurement lag and lack of cross-sectional representativeness of NOx, automatic control is difficult to achieve, and a combination of automatic and manual methods is generally used. Because of these drawbacks, existing ammonia injection methods cannot achieve simultaneous control of NOx and ammonia slip. Often, in pursuit of denitrification efficiency, ammonia slip control is sacrificed, leading to air preheater blockage and posing a significant threat to stable boiler operation; furthermore, excessive ammonia slip also results in persistently high ammonia consumption. Recently, with the large-scale grid connection of intermittent renewable energy sources such as wind and solar power, coal-fired power plants require more frequent peak-shaving operations, resulting in drastic load fluctuations. This results in greater fluctuations in flue gas volume and NOx concentration, exacerbating the problems of slow response and insufficient control precision in traditional ammonia injection systems, and further intensifying the contradiction between ammonia escape and excessive emissions.

[0003] Precision ammonia injection devices can adjust the ammonia supply to the denitrification system in real time and quickly as needed, and can perform refined ammonia supply in different areas, thereby reducing ammonia consumption, controlling ammonia escape, achieving energy-saving and consumption-reducing economic benefits, and mitigating the side effects of excessive ammonia injection. Because it can solve the problems existing in traditional ammonia injection and truly achieve "fast, timely, precise, and automated" ammonia injection control, it has been increasingly used in newly built coal-fired power unit SCR denitrification devices in the past two years.

[0004] Small and medium-sized boilers, especially circulating fluidized bed boilers, primarily employ SNCR+SCR combined denitrification technology. However, current research and applications of precision ammonia injection are mainly limited to SCR denitrification and a small amount of SNCR denitrification. Therefore, inventing a precision ammonia injection device suitable for the SNCR+SCR combined denitrification process in circulating fluidized bed boilers would be of great significance. Summary of the Invention

[0005] In view of this, the present invention provides a precision ammonia injection device, which is suitable for the combined SNCR+SCR denitrification process of circulating fluidized bed boilers, and especially achieves precise, timely and automated control of ammonia injection with minimal modification to the existing system.

[0006] To achieve the above objectives, this invention provides a precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler, comprising an SNCR injection gun, an SCR ammonia replenishment injection gun, a NOx rapid measurement system, a NOx and NH3 escape rapid measurement system, a zone control system, and an SCR reactor; wherein... The SNCR spray gun is installed at the inlet of the cyclone separator of the circulating fluidized bed boiler; The SCR ammonia replenishment spray gun is installed at the outlet of the cyclone separator of the circulating fluidized bed boiler; The SCR reactor is located in the appropriate temperature range of the tail flue of the circulating fluidized bed boiler. The NOx rapid measurement system is installed at the outlet of the cyclone separator and located at the front end of the SCR ammonia replenishment spray gun. The rapid NOx and NH3 escape measurement system is installed at the outlet of the SCR reactor. The zonal control system is located near the SCR ammonia replenishment spray gun.

[0007] Preferably, the SNCR spray gun is located in the horizontal flue at the inlet of the cyclone separator.

[0008] Preferably, the SCR ammonia replenishment spray gun is installed in the outlet flue of the cyclone separator.

[0009] Preferably, the SCR reactor is located between two economizers in the tail flue or between the economizer and the air preheater.

[0010] Preferably, the circulating fluidized bed boiler is a newly built circulating fluidized bed boiler or an existing circulating fluidized bed boiler.

[0011] Preferably, the SCR ammonia replenishment spray gun is a short gun, a long gun, or a combination of long and short guns.

[0012] Preferably, the SCR reactor is arranged inside the tail flue or in a pull-out configuration.

[0013] Preferably, the NOx rapid measurement system and the NOx and NH3 escape rapid measurement system adopt a "zoned patrol measurement layout scheme" or a "zoned non-patrol measurement layout scheme".

[0014] This invention first removes NOx from boiler flue gas using SNCR spray guns positioned in the horizontal flue at the inlet of the cyclone separator in a circulating fluidized bed boiler or other suitable locations. Then, SCR ammonia replenishment spray guns are positioned in the flue at the outlet of the boiler cyclone separator. The injected reducing agent removes NOx under high-temperature conditions and simultaneously converts it into ammonia using the heat of the high-temperature flue gas, thus replenishing ammonia for the downstream SCR system. Flow field simulation is used to determine the division of SCR zones and the placement of the spray guns, achieving targeted and correlated zoning and ammonia replenishment, thereby achieving precise control of ammonia supply to each zone. A rapid NOx detector is installed at the cyclone separator outlet to assess the denitrification effect of the SNCR system and serve as the original design value for the NOx concentration at the SCR inlet. A rapid NOx detector and an ammonia slip analyzer can be installed in each zone at the SCR outlet to achieve precise control of the zones.

[0015] As can be seen from the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention are as follows: 1. For the precision ammonia injection retrofit of existing denitrification units, only the NOx / NH3 rapid measurement system, zoning control system and ammonia replenishment system need to be added according to the zoning requirements. No other modifications are required. The workload of the retrofit is small and the investment cost is low.

[0016] 2. The high-temperature flue gas from the boiler is used to evaporate or pyrolyze the injected reducing agent to supply ammonia to the downstream SCR unit. There is no need to add an ammonia evaporator or urea pyrolysis / hydrolysis unit, resulting in low system energy consumption.

[0017] 3. Precision ammonia injection retrofitting of existing denitrification units has become feasible, although the site space for retrofitting such units is generally limited. If the original SNCR unit is removed to add precision ammonia injection and ultra-low emission requirements are only achieved through the SCR unit, a single-layer catalyst is basically insufficient to meet the ultra-low emission requirements. Arranging two or more layers of catalyst reactors would require them to be moved out, which is difficult to meet on-site space requirements, making such retrofitting impossible.

[0018] 4. For newly built boilers, a precision ammonia injection device can be added simultaneously to the denitrification unit. This device can achieve precise ammonia injection in conjunction with the downstream SCR while having minimal impact on the denitrification efficiency of the circulating fluidized bed SNCR. This results in low investment and operating costs. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1This is a schematic diagram of a precision ammonia injection device used in a combined SNCR+SCR denitrification process for a circulating fluidized bed boiler, as described in this embodiment.

[0021] in: 1. SNCR spray gun; 2. SCR ammonia replenishment spray gun; 3. Inlet NOx rapid measurement system; 4. Outlet NOx and NH3 rapid measurement system; 5. SCR reactor; 6. Zone control system; 7. Cyclone separator. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The technical objective of this invention is to provide a precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler. It mainly consists of an SNCR injection gun 1, an SCR ammonia replenishment injection gun 2, a NOx rapid measurement system 3, a NOx and NH3 escape rapid measurement system 4, a zone control system 6, and an SCR reactor 5. The SNCR spray gun 1 is installed in the horizontal flue at the inlet of the cyclone separator 7 or other suitable locations; the SCR ammonia replenishment spray gun 2 is installed in a suitable location in the flue at the outlet of the cyclone separator 7. The injected reducing agent removes NOx under high temperature conditions and uses the heat of the high-temperature flue gas to convert it into ammonia, thereby replenishing ammonia for the downstream SCR; the SCR reactor 5 is installed in a suitable temperature zone in the flue at the tail of the boiler, generally between two economizers or between the economizer and the air preheater; the inlet NOx rapid measurement system 3 is installed at the outlet of the cyclone separator 7, located in front of the SCR ammonia replenishment spray gun 2, to determine the denitrification effect of the SNCR system and to serve as the original design value of the SCR inlet NOx concentration; the outlet NOx and NH3 escape rapid measurement system 4 is installed at the outlet of the SCR reactor 5. Its measurement value, combined with the value of the inlet NOx rapid measurement system 3, is used to control the zoning control system 6, thereby achieving rapid and precise injection of the reducing agent, i.e., precise ammonia injection; the zoning control system 6 is generally located on a platform near the location where the SCR ammonia replenishment spray gun 2 is installed.

[0024] Optionally, the reducing agent is liquid ammonia, ammonia water, urea, biological calcium denitrification agent, or polymeric denitrification agent.

[0025] Optionally, the catalyst selected in the SCR reactor 5 may be a honeycomb catalyst, a plate catalyst, a corrugated plate catalyst (depending on dust content), or a medium-high temperature catalyst, a wide-temperature catalyst, or a low-temperature catalyst (depending on flue gas temperature).

[0026] Optionally, the catalyst arrangement in the SCR reactor 5 can be a single layer, 1+1, 2+1, 3+1, or other arrangements.

[0027] like Figure 1 As shown, this embodiment provides a precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler. It mainly consists of an SNCR injection gun, an SCR ammonia replenishment injection gun, a NOx rapid measurement system, a NOx and NH3 escape rapid measurement system, a zone control system, and an SCR reaction system; wherein, NOx in the boiler flue gas is initially removed by SNCR spray guns 1 arranged in the horizontal flue at the inlet of the cyclone separator 7 of the circulating fluidized bed boiler or other suitable locations, using a method that does not involve excessive ammonia injection.

[0028] SCR ammonia injection gun 2 is arranged in the flue gas outlet of the boiler cyclone separator. The injected reducing agent removes NOx under high temperature conditions and uses the heat of the high temperature flue gas to turn it into ammonia gas to supplement ammonia for the downstream SCR. The division of SCR zones and the arrangement of the injection guns are determined by flow field simulation to ensure the accuracy and correlation of ammonia injection in each zone.

[0029] A NOx rapid detector 3 is installed at the outlet of the cyclone separator 7 to determine the denitrification effect of the SNCR system and to serve as the original design value for the NOx concentration at the SCR inlet. A set of NOx rapid detectors and ammonia slip analyzers can be installed in each zone at the SCR outlet to achieve precise control of the zone.

[0030] The specific application of the precision ammonia injection device includes the following steps: (1) The initial removal of NOx from flue gas is achieved by the SNCR spray gun 1; (2) The SCR ammonia replenishment spray gun 2 is used to spray a reducing agent into the flue gas. While removing NOx under high temperature conditions, it uses the heat of the high temperature flue gas to turn it into ammonia gas, thereby replenishing ammonia for the downstream SCR. (3) Ammonia gas passes through the SCR reactor 5 and reacts with NOx in the flue gas to achieve its deep removal; (4) The number of outlet zones of SCR reactor 5 is determined according to the relevant requirements such as flow field.

[0031] The technical solution of the present invention will be further described below with reference to specific embodiments. Example 1

[0032] There is currently one 340t / h circulating fluidized bed boiler, which uses SNCR+SCR combined denitrification technology with 20% ammonia water as the reducing agent. SNCR spray guns are arranged in the inlet flue of the cyclone separators, with 5 spray guns at each cyclone separator inlet, for a total of 10 spray guns across the two cyclone separators. The SCR reactor is located inside the furnace, with a single layer of honeycomb catalyst. A separate ammonia injection grid is provided for ammonia replenishment during SCR. Ammonia water is heated and diluted by hot air before being injected above the SCR reactor through the ammonia injection grid. One NOx analyzer and one NH3 analyzer are installed at the SCR reactor outlet, and their readings are used to control the ammonia injection rate. Because the existing detection instruments cannot detect NOx in real time, quickly, and accurately, and single-point measurements cannot reflect the NOx distribution across the entire cross-section, the ammonia injection rate cannot be adjusted promptly when operating conditions change. The ammonia levels in different areas do not match actual needs, and to prevent exceeding the limits, operators have to lower the target values. This results in problems such as high ammonia consumption, high ammonia escape, and inability to achieve automatic control. Therefore, it is necessary to carry out a precise ammonia injection modification to achieve "fast, timely, accurate, and automated" ammonia injection control.

[0033] like Figure 1 As shown, the original SNCR spray gun 1 is retained, and ammonia injection is not excessive, which still serves the purpose of initially removing NOx from the flue gas. Given that the original ammonia injection grid is close to the catalyst, the ammonia injection cannot be effectively mixed, and the energy consumption of evaporating ammonia water with external heat is high; therefore, the original ammonia injection grid and ammonia water evaporation device are discarded, and ammonia supplement spray gun 2 is arranged in the horizontal flue of the cyclone separator 7 outlet. It can utilize the high-temperature flue gas for denitrification while evaporating ammonia water into ammonia gas to supply ammonia to the downstream SCR; 10 ammonia supplement spray guns are set, with a combination of 2 long guns and 8 short guns, which are respectively arranged at the top and side of the horizontal flue of the outlet to correspond to the outlet zone of SCR reactor 5. Based on the flow field simulation, SCR reactor 5 is proposed to be divided into 4 zones. Precision ammonia injection adopts a "total quantity + zoned non-monitoring" scheme; each of the two cyclone separators 7 outlets is equipped with a NOx rapid measurement system 3 to detect the denitrification effect of the SNCR system and the NOx concentration at the SCR inlet; 4 sets of NOx / NH3 slip rapid measurement systems are installed at the outlet of the SCR reactor 4 to detect the NOx concentration and NH3 slip value of each zone; these systems act on the zoned control system 6, thereby achieving precise ammonia injection. Example 2

[0034] A self-owned power plant is constructing a new 320t / h circulating fluidized bed boiler, equipped with a denitrification system. The denitrification adopts SNCR+SCR combined denitrification technology. The SCR reactor is arranged between the two economizers in the tail flue. The catalyst adopts a "1+1" arrangement and uses plate catalyst. Urea is used as the reducing agent. A precision ammonia injection device is required to be added to the denitrification system simultaneously.

[0035] like Figure 1As shown, SNCR spray guns are arranged in the horizontal flue at the inlet of cyclone separator 7, with 5 guns in each cyclone separator and 10 guns in total for the two cyclone separators. Ammonia injection is not excessive, achieving preliminary removal of NOx from the flue gas, with an expected denitrification efficiency of approximately 50%. Ammonia supplementation spray guns 2 are arranged in the horizontal flue at the outlet of cyclone separator 7. These guns utilize the high-temperature flue gas for denitrification while simultaneously pyrolyzing urea into ammonia to supply ammonia for the downstream SCR process. Eight ammonia supplementation spray guns are arranged in a combination of 2 long guns and 6 short guns, positioned at the top and sides of the outlet horizontal flue to correspond to the outlet zones of SCR reactor 5. Based on flow field simulation, SCR reactor 5 is planned to be divided into 3 zones. Precision ammonia injection adopts a "total quantity + zoned non-monitoring" scheme; each of the two cyclone separators 7 outlets is equipped with a NOx rapid measurement system 3 to detect the denitrification effect of the SNCR system and the NOx concentration at the SCR inlet; 3 NOx / NH3 slip rapid measurement systems are installed at the outlet of the SCR reactor 4 to detect the NOx concentration and NH3 slip value of each zone; these systems act on the zoned control system 6, thereby achieving precise ammonia injection.

[0036] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler, characterized in that, This includes an SNCR spray gun, an SCR ammonia replenishment spray gun, a NOx rapid measurement system, a NOx and NH3 slip rapid measurement system, a zone control system, and an SCR reactor; among which, The SNCR spray gun is installed at the inlet of the cyclone separator of the circulating fluidized bed boiler; The SCR ammonia replenishment spray gun is installed at the outlet of the cyclone separator of the circulating fluidized bed boiler; The SCR reactor is located in the tail flue of the circulating fluidized bed boiler; The NOx rapid measurement system is installed at the front end of the SCR ammonia replenishment spray gun; The rapid NOx and NH3 escape measurement system is installed at the outlet of the SCR reactor. The zonal control system is located near the SCR ammonia replenishment spray gun.

2. The precision ammonia injection device for the SNCR+SCR combined denitrification process in a circulating fluidized bed boiler according to claim 1, characterized in that, The SNCR spray gun is installed in the horizontal flue at the inlet of the cyclone separator.

3. The precision ammonia injection device for the combined SNCR+SCR denitrification process in a circulating fluidized bed boiler according to claim 1, characterized in that, The SCR ammonia replenishment spray gun is installed in the outlet flue of the cyclone separator.

4. A precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler according to claim 1, characterized in that, The SCR reactor is located between two economizers or between the economizer and the air preheater in the tail flue.

5. A precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler according to claim 1, characterized in that, The circulating fluidized bed boiler can be a newly built circulating fluidized bed boiler or an existing circulating fluidized bed boiler.

6. A precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler according to claim 1, characterized in that, The SCR ammonia replenishment spray gun can be a short gun, a long gun, or a combination of long and short guns.

7. A precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler according to claim 1, characterized in that, The SCR reactor is arranged either inside the tail flue or in a pull-out configuration.

8. A precision ammonia injection device for a combined SNCR+SCR denitrification process in a circulating fluidized bed boiler according to claim 1, characterized in that, The NOx rapid measurement system and the NOx and NH3 escape rapid measurement system adopt a "zoned patrol measurement layout scheme" or a "zoned non-patrol measurement layout scheme".

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