CN105169917A - SNCR-SCR combined denitration system and method based on ammonia nitrogen molar ratio detection and regulation - Google Patents

Abstract

The invention belongs to the technical field of controlling air pollutants discharged from coal-fired boilers, and in particular relates to an SNCR-SCR combined denitrification system and method based on ammonia nitrogen molar ratio detection and regulation. The system includes an ammonia storage tank, an air preheater, an SNCR reaction zone, an SCR reaction zone, a first detection system, a second detection system, a third detection system and a control system. The SNCR reaction zone is set in the boiler furnace, and the SCR The reaction zone is set in the boiler flue, and the first detection system, the second detection system and the third detection system are respectively connected to the control system. The combined denitrification system of the present invention can realize full-load denitrification operation, and the denitration efficiency is high, eliminating the need for ammonium bisulfate in the follow-up Corrosion and deposition problems in equipment.

Description

A SNCR-SCR combined denitrification system and method based on ammonia nitrogen molar ratio detection and regulation

technical field

The invention belongs to the technical field of controlling air pollutants discharged from coal-fired boilers, and in particular relates to an SNCR-SCR combined denitrification system and method based on ammonia nitrogen molar ratio detection and regulation.

Background technique

In order to meet the NOx emission standards of GB13223-2011 "Emission Standards of Air Pollutants for Thermal Power Plants", coal-fired units of thermal power plants, especially to meet the "ultra-clean" emission requirements of coal-fired units proposed by the National Development and Reform Energy 2014 (2093), the coal-fired units Coal units must be equipped with a denitrification system to meet the emission requirements of flue gas nitrogen oxides. In the denitrification process, selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), and SNCR+SCR combined technology are widely used denitrification technologies.

The SCR process uses NH ₃ as a reducing agent to reduce _NOx in the flue gas to N ₂ at the action line of the catalyst, and the denitration rate can reach more than 90%. It is the most mature denitration technology with the highest denitration efficiency, but SCR is in the The following problems exist in the operation process: 1) With the change of social power consumption structure, coal-fired thermal power units have a large area and long-term low-load operation. The denitrification system stops ammonia injection, which affects the normal operation of the thermal power plant denitrification system, affects flue gas NO _x emissions and denitrification price compensation for power plants, and cannot meet the recent National Energy Administration's full-load denitrification requirements for power plants; 2) SO ₂ in flue gas Under the action of the SCR catalyst, it is transformed into SO ₃ , which reacts with excess ammonia escape to generate ammonium bisulfate ABS, a by-product of denitrification, which leads to new problems such as corrosion and blockage of the air preheater and subsequent equipment, and bag dust in the bag filter. In many units, the pressure difference of the air preheater increased to varying degrees, the operating current of the electrostatic precipitator was low, the pressure difference of the bag filter increased significantly, and the flue was torn; 3) The catalyst was easily poisoned, and the operation and maintenance costs were high.

The SNCR process is to spray the reducing agent containing amino groups such as ammonia or urea into the boiler furnace at about 800 ° C ~ 1250 ° C. Under the condition of no catalyst, the reducing agent quickly pyrolyzes into NH ₃ and selectively reacts with the NH3 in the flue gas. _NOx reacts and is reduced to _N2 and _H2O . The incomplete reaction of NH ₃ and NO _x will cause a large amount of ammonia slip. The denitrification efficiency of SNCR is low, and the denitrification efficiency is between 30% and 75%. For large coal-fired power plant boilers, the denitrification efficiency of the SNCR process is usually below 40%. It is difficult to meet the strict denitrification requirements by using SNCR alone. Due to the small footprint of SNCR, low operation and maintenance costs, ammonia injection and denitrification under low boiler load conditions, and easy combination with other processes, it is especially suitable for the transformation of old power plants.

The SNCR+SCR combination method is a new denitrification technology in recent years. Chinese patent CN103007707B discloses a high-load adaptable SNCR and SCR combination system and method for industrial boilers. The upper part of the furnace is equipped with furnace nozzles; SCR reaction The inlet flue of the furnace is connected to the tail of the flue, and an SCR nozzle is installed at the connection; the reductant storage tank outside the furnace is connected to the nozzle in the furnace and the SCR nozzle. By combining the SNCR denitrification process in the furnace with the SCR denitrification process at the tail, the efficient removal of NOx in the flue gas is achieved, and the load adaptability of the entire denitrification system is improved. However, the SNCR and SCR in this patent cannot be operated at the same time, and the denitrification efficiency cannot be achieved. The highest range, and the ammonia nitrogen molar ratio is difficult to be reasonable, timely, accurate, continuous control and equipment blockage and corrosion problems caused by ammonium bisulfate.

Chinese patent CN104147912A discloses a selective non-catalytic reduction SNCR and selective catalytic reduction SCR mixed flue gas denitrification method and device to improve the denitrification efficiency of small and medium-sized units, while reducing the amount of SCR catalyst and saving costs. The flue gas denitrification method includes the SNCR reaction step and the SCR reaction step carried out in sequence, and the ammoniacal solution is only sprayed into the SNCR reaction step, and the addition amount of the ammoniacal solution is 1/2 of the molar amount of nitrogen oxides in the original flue gas. 1 to 3 times; in the SCR reaction step, the ammonia that does not participate in the SNCR reaction continues to react with the remaining nitrogen oxides in the flue gas. However, its disadvantage is that the amount of ammonia escaping through the SNCR reaction section does not have a linear relationship with the injection amount, it is difficult to control the amount of ammonia escaping, and it is impossible to accurately measure the consumption of reducing agent required by the SCR reactor in the subsequent stage, and the amount of ammonia solution added is high , there are still problems of fouling and corrosion caused by ammonium bisulfate to subsequent equipment.

Chinese patent CN102861511A discloses a coal-fired boiler flue gas SNCR and SCR combined denitrification method and device. The reducing agent ammonia solution is added to the temperature window of 800-1050°C in the furnace, and part of the ammonia reacts with NOx in the flue gas for SNCR, and the rest escapes. Ammonia goes to the flue with the flue gas and performs heat exchange to cool down; add a supplementary reducing agent in the temperature range of 500-650°C in the boiler outlet flue and decompose ammonia, and the active substances are V ₂ O ₅ and WO ₃ at 300-420°C In the presence of a catalyst, ammonia and NOx undergo SCR reaction to remove the remaining NOx in the flue gas. However, this patent still has the problems of difficulty in reasonable, timely, accurate and continuous control of ammonia escape and equipment blockage and corrosion caused by ammonium bisulfate.

Contents of the invention

In order to overcome the above defects, the object of the present invention is to provide an SNCR-SCR combined denitrification system based on the detection and regulation of the ammonia nitrogen molar ratio.

To achieve the above object, the present invention adopts the following technical solutions:

An SNCR-SCR combined denitrification system based on ammonia nitrogen molar ratio detection and regulation, including ammonia storage tank, air preheater, SNCR reaction zone and SCR reaction zone. One nozzle, the ammonia-containing storage tank is connected to the first nozzle through the first flowmeter; the SCR reaction zone is set in the boiler flue, and the entrance of the SCR reaction zone is provided with a second nozzle, and the ammonia-containing storage tank is connected to the second nozzle through the second flowmeter connection, the air preheater is respectively connected to the lower part of the furnace and the outlet of the flue, and also includes the first detection system, the second detection system, the third detection system and the control system, the first detection system is set on the upper part of the furnace, and the second detection system is set At the inlet of the second nozzle, the third detection system is set at the outlet of the SCR reaction zone, and the first detection system, the second detection system, the third detection system, the first flow meter and the second flow meter are respectively connected to the control system.

According to the SNCR-SCR combined denitrification system based on the detection and regulation of the ammonia-nitrogen molar ratio, the first nozzle is set in the area where the flue gas temperature in the boiler is 800-1100°C.

According to the SNCR-SCR combined denitrification system based on the detection and regulation of the ammonia-nitrogen molar ratio, the second nozzle is set in the area where the temperature of the flue gas in the flue is 300-410°C.

Another object of the present invention is to provide a SNCR-SCR combined denitrification method based on ammonia nitrogen molar ratio detection and regulation, with less investment in equipment, full-load denitrification operation, high denitrification efficiency, reduced SCR catalyst consumption, and extended catalyst service life , reduce the escape of ammonia, and eliminate the corrosion and deposition of ammonium bisulfate in subsequent equipment.

A SNCR-SCR combined denitrification method based on ammonia nitrogen molar ratio detection and regulation, comprising the following steps:

When the boiler load is ≤50%, only the SNCR reaction zone works,

(1) The ammonia-containing storage tank adjusts the first nozzle to spray ammonia-containing solution into the SCNR reaction zone through the first flow meter, so that the ammonia-nitrogen molar ratio at the entrance of the SNCR reaction zone is 0.5-0.9:1;

(2) The first detection system detects the flue gas temperature in the furnace, and adjusts the ammonia injection position of the first nozzle through the control system, and the ammonia injection position of the first nozzle is in the area where the flue gas temperature is 800-1100°C;

(3) The third detection system detects the content of ammonia and NO _x at the outlet of the SCR reaction zone, and fine-tunes the amount of ammonia entering the SCNR reaction zone through the control system to make the denitrification efficiency of the SNCR reaction zone ≥ 50%;

When the boiler load is >50%, the SNCR reaction zone and the SCR reaction zone act simultaneously,

(1) The ammonia-containing storage tank adjusts the first nozzle to spray ammonia-containing solution into the SCNR reaction zone through the first flow meter, so that the ammonia-nitrogen molar ratio at the entrance of the SNCR reaction zone is 0.5-0.9:1; at the same time, the ammonia-containing storage tank passes the second flow rate Adjust the second nozzle to spray ammonia-containing solution into the SCR reaction zone, so that the second detection system detects that the ammonia-nitrogen molar ratio at the entrance of the SCR reaction zone is 0.9-0.95:1;

(2) The first detection system detects the flue gas temperature in the furnace, and adjusts the ammonia injection position of the first nozzle through the control system. The ammonia injection position of the first nozzle is in the area where the flue gas temperature is 800-1100 ° C. The second detection system detects the SCR The ammonia and NO _x content at the entrance of the reaction zone is obtained to obtain the ammonia nitrogen molar ratio, and the second flow meter is adjusted through the control system to make the ammonia nitrogen molar ratio 0.9 to 0.95:1. The third detection system detects the ammonia and NO _x content at the outlet of the SCR reaction zone, and passes The control system fine-tunes the amount of ammonia entering the SCR reaction zone by the second flowmeter, so that the NO _x content at the outlet of the SCR reaction zone is ≤50mg/m ³ .

According to the above SNCR-SCR combined denitrification method, the ammonia-containing solution is urea solution or ammonia water.

According to the above SNCR-SCR combined denitrification method, the mass percent concentration of the ammonia-containing solution is 5-15%.

According to the above SNCR-SCR combined denitrification method, the catalyst in the SCR reaction zone is V ₂ O ₅ or WO ₃ .

Positive beneficial effect of the present invention

1. The present invention can realize full-load denitrification operation. When the load is less than or equal to 50%, the ammonia solution is only sprayed in the SNCR reaction zone, and the SNCR reaction zone operates, and the denitrification efficiency can reach more than 50%. Both the SNCR reaction zone and the SCR reaction zone are sprayed with ammonia solution, and the SNCR reaction zone and the SCR reaction zone are running, and the denitrification efficiency can reach more than 90%. The whole system has flexible operation and high denitrification efficiency.

2. The combined denitrification system of the present invention includes a first detection system, a second detection system, a third detection system and a control system. The first detection system is located on the upper part of the furnace to detect the flue gas temperature in the furnace and feed back the signal to the control system to adjust The ammonia injection position of the first nozzle; the second detection system is set at the inlet of the second nozzle. When the boiler load is >50%, the ammonia and _NOx content at the inlet of the SCR reaction zone is detected to obtain the ammonia nitrogen molar ratio, and the signal is fed back to the control system. The second flow meter adjusts the amount of ammonia-containing solution sprayed into the SCR reaction zone; the third detection system is set at the outlet of the SCR reaction zone to detect the ammonia and _NOx content at the outlet of the SCR reaction zone, and feed back the signal to the control system. The boiler load is ≤ At 50%, fine-tune the amount of ammonia-containing solution entering the SNCR reaction zone through the control system; when the boiler load is >50%, fine-tune the amount of ammonia-containing solution entering the SCR reaction zone through the second flowmeter through the control system; the whole system can Timely, accurate and continuous control of the amount of ammonia-containing solution, with a high degree of automation.

3. When the boiler load of the present invention is > 50%, most of the _NOx in the flue gas is removed by SNCR in the furnace, and the escape ammonia produced in the front-end SNCR reaction zone is used as the reducing agent in the rear-end SCR reaction zone. In the process of channel flow, it is further mixed with flue gas evenly. Compared with the single SCR reaction, it solves the problem of a large amount of ammonia injection in the SCR reaction zone, and the reductant has a long residence time, which reduces the amount of catalyst in the SCR reaction zone and prolongs the service life of the catalyst. Catalyst cost.

4. The first flowmeter of the present invention adjusts the molar ratio of ammonia nitrogen in the SNCR reaction zone to 0.5-0.9:1, the second detection system adjusts the molar ratio of ammonia nitrogen in the SCR reaction zone to 0.9-0.95:1, and when the boiler load is >50%, the third detection The _NOx content controlled by the system meets the national GB13223-2011 "Emission Standards of Air Pollutants for Thermal Power Plants" or the "ultra-clean" emission requirements of the National Development and Reform Energy 2014 (2093), and consumes less ammonia, realizing denitrification at full load of the unit and improving denitrification Efficiency, eliminating the corrosion and deposition of ammonium bisulfate ABS in subsequent equipment.

Description of drawings

Fig. 1 is the schematic flow chart of the SNCR-SCR combined denitrification method based on ammonia nitrogen molar ratio detection and regulation of the present invention;

In the figure: 1-Ammonia storage tank, 2-First flow meter, 3-Second flow meter, 4-SNCR reaction zone, 5-Air preheater, 6-SCR reaction zone, 7-First nozzle, 8 - the second nozzle, 9 - the first detection system, 10 - the second detection system, 11 - the third detection system, 12 - the control system.

Detailed ways

The present invention will be further described below in conjunction with some specific embodiments.

Referring to Figure 1, an SNCR-SCR combined denitrification system based on ammonia-nitrogen molar ratio detection and regulation, including ammonia storage tank 1, air preheater 5, SNCR reaction zone 4 and SCR reaction zone 6, SNCR reaction zone 4 is set in In the furnace of the boiler, the first nozzle 7 is arranged on the upper part of the furnace, the ammonia storage tank 1 is connected to the first nozzle 7 through the first flow meter 2, the SCR reaction zone 6 is set in the boiler flue, and the entrance of the SCR reaction zone 6 is provided with a second The nozzle 8, the ammonia-containing storage tank 1 is connected to the second nozzle 8 through the second flowmeter 3, and the air preheater 5 is respectively connected to the lower part of the furnace and the outlet of the flue; it also includes a first detection system 9, a second detection system 10, The third detection system 11 and the control system 12, the first detection system 9 is arranged on the upper part of the boiler furnace, the first detection system 10 detects the flue gas temperature in the furnace, feeds back the signal to the control system 12, and adjusts the ammonia injection position of the first nozzle 7; The second detection system 10 is set at the entrance of the second nozzle 3, and when the boiler load is > 50%, it detects the ammonia and NO _x content at the entrance of the SCR reaction zone 6 to obtain the ammonia-nitrogen molar ratio, and feeds back the signal to the control system 12, through the second The flow meter adjusts the amount of ammonia-containing solution sprayed into the SCR reaction zone; the third detection system 11 is set at the outlet of the SCR reaction zone 6, detects the ammonia and _NOx content at the outlet of the SCR reaction zone 6, and feeds back the signal to the control system 12, and the boiler load When ≤50%, fine-tune the first flow meter 2 through the control system; when the boiler load is >50%, fine-tune the second flow meter 3 through the control system, the first detection system 9, the second detection system 10, the third detection system 11, The first flow meter 2 and the second flow meter 3 are respectively connected to the control system 12 .

The data acquisition and transformation of the SNCR-SCR combined denitrification system are undertaken and realized by the first detection system 9, the second detection system 10 and the third detection system 11, and the first detection system 9 controls each layer of the first nozzle 7 in the furnace. The temperature value at the position is detected, and the radiation thermometer high-temperature detection equipment is used. The flue gas parameters detected by the second detection system 10 and the third detection system 11 include the following items: flue gas temperature, flue gas pressure, flue gas flow, NOx concentration, _SO2 concentration, ammonia concentration. Among them, double platinum thermal resistance and stainless steel protective sleeve can be used for flue gas temperature measurement, and pressure transmitter can be used for flue gas pressure measurement, and primary instrument valve, secondary instrument valve, blowdown valve and pipe joints should be installed. Orifice throttling mode flow measurement sensor, NOx, SO ₂ , NH ₃ gases in the flue gas are continuously monitored online by the flue gas analyzer. All the above monitoring data are sent to the control system 12 with 4~20mADC or pulse signal for monitoring and analysis, and control and adjust the ammonia injection volume of the first nozzle 7 and the second nozzle 8, so that the ammonia-nitrogen molar ratio of the SNCR reaction zone and the SCR reaction zone The requirements of the present invention are met, and the optimal distribution of the SNCR-SCR combined denitrification system is realized.

Example 1

The device of this embodiment is as described above, and will not be repeated here, wherein the first nozzle 7 is a 4-layer atomization spray gun, 10 are arranged in each layer, the first nozzle 7 is arranged on the inner wall of the boiler, and the temperature of the flue gas is 800-1100°C within the area.

This embodiment is a 600MW unit, the boiler load is 50%, the flue gas volume is about 75×10 ⁴ m ³ /h, and the NOx concentration in the flue gas is about 320 mg/m ³ .

A SNCR-SCR combined denitrification method based on the detection and regulation of the ammonia nitrogen molar ratio, including the sequential SNCR reaction step and SCR reaction step, the specific steps are as follows:

(1) The ammonia-containing storage tank 1 adjusts the first nozzle 7 to spray the ammonia-containing solution into the SCNR reaction zone 4 through the first flow meter 2. The ammonia-containing solution is a urea solution with a concentration of 5% to 10% by mass, so that the SNCR can react The ammonia-nitrogen molar ratio at the entrance of Zone 4 is 0.85:1;

(2) The first detection system 9 detects the flue gas temperature in the furnace, and adjusts the ammonia injection position of the first nozzle 7 through the control system 12, and the ammonia injection position of the first nozzle is in the area where the flue gas temperature is 800-1100°C;

(3) The third detection system 11 detects the content of ammonia and NO _x at the outlet of the SCR reaction zone 6, and fine-tunes the amount of ammonia entering the SCNR reaction zone 4 through the control system 12 to make the denitrification efficiency of the SNCR reaction zone ≥ 50%.

Example 2

The device of this embodiment is as described above, and will not be repeated here, wherein the first nozzle 7 is a 4-layer atomization spray gun, 10 are arranged in each layer, the first nozzle 7 is arranged on the inner wall of the boiler, and the temperature of the flue gas is 800-1100°C within the area.

The second nozzle 8 is a 3-layer atomization spray gun, and each layer is provided with 3 nozzles. The second nozzle 8 is arranged on the rear wall of the diversion chamber in the flue, in the area where the temperature of the flue gas is 300-410°C.

In this example, the boiler load is 60%, the flue gas volume is about 120×10 ⁴ m ³ /h, and the NOx concentration in the flue gas is 560 mg/m ³ .

A SNCR-SCR combined denitrification method based on ammonia nitrogen molar ratio detection and regulation, the specific steps are as follows:

(1) The ammonia-containing storage tank 1 adjusts the first nozzle 7 to spray the ammonia-containing solution into the SCNR reaction zone 4 through the first flowmeter 2. The ammonia-containing solution is an ammonia solution with a concentration of 5% to 10% by mass, so that the SNCR can react The ammonia-nitrogen molar ratio at the entrance of zone 4 is 0.5:1; at the same time, the ammonia-containing storage tank 1 adjusts the second nozzle 8 to spray ammonia-containing solution into the SCR reaction zone 6 through the second flowmeter 3, so that the second detection system 10 detects the SCR reaction zone 6 The ammonia nitrogen molar ratio at the entrance is 0.9:1; the catalyst in the SCR reaction zone 6 is V ₂ O ₅ ;

(2) The first detection system 9 detects the flue gas temperature in the furnace, and adjusts the ammonia injection position of the first nozzle 7 through the control system 12. The detection system 11 detects the ammonia and NO _x content at the entrance of the SCR reaction zone 6 to obtain the ammonia nitrogen molar ratio, adjusts the second flowmeter 3 through the control system 12 to make the ammonia nitrogen molar ratio 0.9:1, and the third detection system 11 detects the SCR reaction zone 6 Ammonia and _NOx content at the outlet, fine-tune the amount of ammonia entering the SCR reaction zone 6 through the control system 12 through the second flowmeter 3, so that the _NOx content at the outlet of the SCR reaction zone 6 is ≤ 50 mg/m ³ .

Example 3

The device of this embodiment is as described in Embodiment 2, and will not be repeated here.

In this example, the boiler load is 80%, the flue gas volume is about 160×10 ⁴ m ³ /h, and the NOx concentration in the flue gas is 620 mg/m ³ .

A SNCR-SCR combined denitrification method based on ammonia nitrogen molar ratio detection and regulation, the specific steps are as follows:

(1) The ammonia-containing storage tank 1 adjusts the first nozzle 7 to spray the ammonia-containing solution into the SCNR reaction zone 4 through the first flowmeter 2. The ammonia-containing solution is a urea solution with a mass percentage concentration of 10-15% to make the SNCR reaction The ammonia-nitrogen molar ratio at the entrance of zone 4 is 0.8:1; at the same time, the ammonia-containing storage tank 1 adjusts the second nozzle 8 to spray ammonia-containing solution into the SCR reaction zone 6 through the second flow meter 2, so that the second detection system 10 detects the SCR reaction zone 6. The ammonia nitrogen molar ratio at the entrance is 0.92:1; the catalyst in the SCR reaction zone 6 is WO ₃ ;

(2) The first detection system 9 detects the flue gas temperature in the furnace, and adjusts the position of the first nozzle ammonia injection 7 through the control system 12. The detection system 10 detects the ammonia and NO _x content at the entrance of the SCR reaction zone 6 to obtain the ammonia nitrogen molar ratio, adjusts the second flow meter 3 through the control system 12, so that the ammonia nitrogen molar ratio is 0.92:1, and the third detection system 11 detects the SCR reaction zone For the ammonia and NO _x content at the outlet, fine-tune the amount of ammonia entering the SCR reaction zone 6 through the second flow meter 3 through the control system 12, so that the NO _x content at the outlet of the SCR reaction zone 6 is ≤50 mg/m ³ .

Example 4

The device of this embodiment is as described in Embodiment 2, and will not be repeated here.

In this embodiment, the boiler load is 100%, the flue gas volume is about 210×10 ⁴ m ³ /h, and the NOx concentration in the flue gas is 600 mg/m ³ .

A SNCR-SCR combined denitrification method based on ammonia nitrogen molar ratio detection and regulation, the specific steps are as follows:

(1) The ammonia-containing storage tank 1 adjusts the first nozzle 7 to spray the ammonia-containing solution into the SCNR reaction zone 4 through the first flowmeter 2. The ammonia-containing solution is an ammonia solution with a concentration of 5% to 10% by mass, so that the SNCR can react The ammonia-nitrogen molar ratio at the entrance of zone 4 is 0.9:1; at the same time, the ammonia-containing storage tank 1 adjusts the second nozzle 8 to spray ammonia-containing solution into the SCR reaction zone 6 through the second flowmeter 2, so that the second detection system 10 can detect the SCR reaction zone The ammonia nitrogen molar ratio at the entrance is 0.95:1; the catalyst in the SCR reaction zone 6 is V ₂ O ₅ ;

(2) The first detection system 9 detects the flue gas temperature in the furnace, and adjusts the ammonia injection position of the first nozzle 7 through the control system 12. The detection system 10 detects the content of ammonia and NO _x at the entrance of the SCR reaction zone 4 to obtain the ammonia nitrogen molar ratio, adjusts the second flow meter 3 through the control system 12 to make the ammonia nitrogen molar ratio 0.95:1, and the third detection system 11 detects the SCR reaction zone 6 Ammonia and _NOx content at the outlet, fine-tune the amount of ammonia entering the SCR reaction zone 6 through the control system 12 through the second flowmeter 3, so that the _NOx content at the outlet of the SCR reaction zone 6 is ≤ 50 mg/m ³ .

Table 1 shows the denitration treatment results of the SNCR-SCR combined denitrification system and method based on the ammonia nitrogen molar ratio detection and regulation in Examples 1 to 4 of the present invention.

Table 1 The denitrification results of Examples 1 to 4 of the present invention

.

As can be seen from Table 1, the combined denitrification systems and methods of Examples 1 to 4 of the present invention have removal rates of nitrogen oxides NOx in flue gas of 72%, 93%, 95%, and 96%, respectively, and the entire system can timely , Accurate and continuous control of the amount of ammonia-containing solution, high degree of automation, high denitrification efficiency, and no corrosion and deposition of ammonium bisulfate ABS in subsequent equipment.

Claims (7)

1. An SNCR-SCR combined denitrification system based on ammonia nitrogen molar ratio detection and regulation, including ammonia storage tank, air preheater, SNCR reaction zone and SCR reaction zone, the SNCR reaction zone is set in the furnace of the boiler, the upper part of the furnace The first nozzle is set, and the ammonia storage tank is connected to the first nozzle through the first flowmeter; the SCR reaction zone is set in the boiler flue, and the second nozzle is installed at the entrance of the SCR reaction zone, and the ammonia storage tank is connected to the first nozzle through the second flowmeter. The two nozzles are connected, and the air preheater is respectively connected to the lower part of the furnace and the outlet of the flue. It is characterized in that it also includes a first detection system, a second detection system, a third detection system and a control system. The first detection system is set on the upper part of the furnace. , the second detection system is set at the inlet of the second nozzle, the third detection system is set at the exit of the SCR reaction zone, the first detection system, the second detection system, the third detection system, the first flowmeter and the second flowmeter respectively Connect the control system. 2. The combined SNCR-SCR denitrification system based on ammonia nitrogen molar ratio detection and regulation according to claim 1, characterized in that the first nozzle is set in the area where the flue gas temperature in the boiler is 800-1100°C. 3. The combined SNCR-SCR denitrification system based on ammonia nitrogen molar ratio detection and regulation according to claim 1, wherein the second nozzle is set in the flue gas temperature range of 300-410°C. 4. A SNCR-SCR combined denitrification method based on ammonia nitrogen molar ratio detection and regulation based on the combined denitrification system described in any one of claims 1 to 3, characterized in that it comprises the following steps: When the boiler load is ≤50%, only the SNCR reaction zone works, (1) The ammonia-containing storage tank adjusts the first nozzle to spray ammonia-containing solution into the SCNR reaction zone through the first flow meter, so that the ammonia-nitrogen molar ratio at the entrance of the SNCR reaction zone is 0.5-0.9:1; (2) The first detection system detects the flue gas temperature in the furnace, and adjusts the ammonia injection position of the first nozzle through the control system, so that the ammonia injection position of the first nozzle is in the area where the flue gas temperature is 800-1100°C; (3) The third detection system detects the content of ammonia and NO _x at the outlet of the SCR reaction zone, and fine-tunes the amount of ammonia entering the SCNR reaction zone through the control system to make the denitrification efficiency of the SNCR reaction zone ≥ 50%; When the boiler load is >50%, the SNCR reaction zone and the SCR reaction zone act simultaneously, (1) The ammonia-containing storage tank adjusts the first nozzle to spray ammonia-containing solution into the SCNR reaction zone through the first flowmeter, so that the ammonia-nitrogen molar ratio at the entrance of the SNCR reaction zone is 0.5-0.9:1; at the same time, the ammonia-containing storage tank passes the second flow rate Adjust the second nozzle to spray ammonia-containing solution into the SCR reaction zone, so that the second detection system detects that the ammonia-nitrogen molar ratio at the entrance of the SCR reaction zone is 0.9-0.95:1; (2) The first detection system detects the flue gas temperature in the furnace, adjusts the ammonia injection position of the first nozzle through the control system, so that the ammonia injection position of the first nozzle is in the area where the flue gas temperature is 800-1100°C, and the second detection system detects The content of ammonia and NO _x at the inlet of the SCR reaction zone is obtained to obtain the molar ratio of ammonia nitrogen, and the second flow meter is adjusted through the control system to make the molar ratio of ammonia nitrogen to 0.9-0.95:1, and the third detection system detects the content of ammonia and NO _x at the outlet of the SCR reaction zone, Finely adjust the amount of ammonia entering the SCR reaction zone through the control system to make the NO _x content at the outlet of the SCR reaction zone ≤ 50 mg/m ³ . 5. The SNCR-SCR combined denitrification method according to claim 4, characterized in that the ammonia-containing solution is urea solution or ammonia water. 6. The SNCR-SCR combined denitrification method according to claim 5, characterized in that the mass percent concentration of the ammonia-containing solution is 5-15%. 7. The SNCR-SCR combined denitrification method according to claim 4, characterized in that the catalyst in the SCR reaction zone is V ₂ O ₅ or WO ₃ .