CN106422732A - Thermal power plant W type boiler SNCR denitration system and control method thereof - Google Patents

Abstract

The invention discloses a thermal power plant W type boiler SNCR denitration system and a control method thereof. The system comprises long spray guns, a plurality of short spray guns, a laser detection system, a metering module and distribution modules, wherein the long spray guns are arranged in a W type boiler horizontal flue area, the short spray guns are arranged in a W type boiler furnace arch area in layers, and the metering module and the distribution module are sequentially connected. The method includes the steps that a CO concentration signal obtained through the laser detection system adjusts the concentration of a urea solution through the metering module; a temperature distribution signal obtained through the laser detection system adjusts the flow of the urea solution sprayed by each long spray gun through a long spray gun distribution module; the number of operation layers of the short spray guns and the total flow of the urea solution of each layer are controlled according to a unit load interval and an NSR value. The long spray guns provided with multiple nozzles extend into a flue, the sprayed urea solution can completely cover the section of the flue, it is guaranteed that the urea solution and flue gas are sufficiently and evenly mixed, denitration efficiency is improved, and a control mode is simple and easy to implement.

Description

A thermal power plant W-type boiler SNCR denitrification system and its control method

technical field

The invention relates to SNCR denitrification technology of a thermal power plant, in particular to an SNCR denitrification system of a W-type boiler in a thermal power plant and a control method thereof.

Background technique

When the W flame boiler is fired with low volatile coal, it has the characteristics of strong low-load stable combustion capability, good combustion stability, strong load performance, and reliable operation. The main furnace type of low-volatile coal such as coal, but there is a problem of high NOx emissions in actual operation. Faced with the ultra-clean emission requirement of NOx emission concentration of 50mg/m ³ , simply transforming the SCR denitrification system not only has high investment and operating costs, but also affects the safety of the unit. Considering many aspects such as technology and economy, adding SNCR denitrification device on the basis of making full use of the original SCR device is a reasonable choice to achieve ultra-low emission of nitrogen oxides from W-type boilers.

Selective non-catalytic reduction (SNCR) flue gas denitrification technology is the mainstream technology for power plant boilers, fluidized bed boilers, cement kilns and waste incineration flue gas denitrification. In the temperature range of 880°C-1050°C, under the condition of no catalyst, ammonia or urea and other amino reducing agents are injected, and the NOx in the flue gas can be selectively reduced to harmless nitrogen and water. The SNCR process uses the furnace as the reactor, which can be realized through the transformation of the boiler. The construction period is short, and the investment cost and operation cost are relatively low compared with other flue gas denitrification technologies. It is suitable for the transformation of small and medium-sized boilers. Modern SNCR technology can control NOx emissions to reduce by 20-50%. With the increase of unit capacity, the range of furnace size and unit load changes increases, which increases the difficulty of controlling the reaction temperature window and uniform mixing of reducing agents, resulting in lower denitrification efficiency. For a 600MW unit, the denitrification efficiency is only about 30% under the condition that the ammonia escape concentration is controlled to be less than 10 μL/L. Since the initial NOx concentration of W-type boilers burning anthracite is generally high, in order to ensure that NOx emissions reach 50mg/m ³ , the denitrification efficiency of the SNCR section must reach more than 45%. Therefore, it is imminent to research and develop efficient W-type boiler SNCR denitration systems .

The denitrification efficiency of SNCR is affected by factors such as temperature, CO concentration, initial value of NOx, NSR, combustion conditions, coal type, furnace type, and ammonia escape, among which temperature and CO concentration are the two main influencing factors. In order to improve the denitrification efficiency of the SNCR process, related research proposes to adjust the reducing agent flow rate by controlling the ratio of ammonia nitrogen under different loads, such as the SNCR-SCR combined denitrification system and method based on the detection and regulation of ammonia nitrogen molar ratio disclosed in Chinese patent CN105169917A. Chinese patent CN201520543068.4 discloses a selective non-catalytic reduction SNCR reaction system, and Chinese patent CN201510188180.5 discloses a method for controlling the amount of ammonia injection in the SNCR flue gas denitrification system in cement production, but this control method is very complicated. Difficult to implement in engineering. In addition, there are studies that measure the temperature distribution to control the spray gun to spray the reducing agent into the temperature region suitable for SNCR reaction, so as to realize the dynamic tracking of the temperature window of each SNCR spray gun, such as a high-efficiency SNCR point-to-point injection system disclosed in Chinese patent CN104307347A. Another example is a power plant boiler SNCR denitrification control system and its control method disclosed in Chinese patent CN104117279A. The difficulty of this control method lies in the large number of spray guns, and precise control of each spray gun will significantly increase the system cost. The concentration of CO in the flue gas is an important factor affecting the denitration efficiency of SNCR. The research results show that when the concentration of CO is lower than 1000ppm, the denitrification efficiency of SNCR increases with the increase of CO concentration; when the concentration of CO exceeds 1000ppm, the denitration efficiency of SNCR increases with the concentration of CO increase and decrease. Because it is difficult to measure the CO concentration in the flue gas online, the influence of the CO concentration is generally ignored in the current SNCR control system, which has also become an important reason restricting the denitrification efficiency of the SNCR.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a W-type boiler SNCR denitrification system of a thermal power plant and a control method thereof, which have high denitrification efficiency, simple control and convenient modification.

The present invention is achieved through the following technical solutions:

A W-shaped boiler SNCR denitrification system in a thermal power plant, including a long spray gun installed in the horizontal flue area of the W-shaped boiler, a plurality of short spray guns arranged in multiple layers in the deflection angle area of the W-shaped boiler, and a laser detection system and sequentially connected The metering module and distribution module; the distribution module includes a long spray gun distribution module whose output end is connected to a long spray gun and a short spray gun distribution module whose output end is connected to a short spray gun; the input ends of the metering module used to control the concentration of urea solution are respectively connected to the original urea solution storage tank and a desalinated water storage tank, the output ends of which are respectively connected to the long spray gun distribution module and the short spray gun distribution module; the laser detection system includes a central control cabinet, a diode laser, an optical fiber multiplexer, an optical fiber and multiple groups of lasers connected in sequence; The central control cabinet is used to detect the flue gas temperature distribution signal and CO concentration signal through the laser; its output end is respectively connected to the long spray gun distribution module and the metering module through the engineer station; multiple long spray guns are evenly distributed in the cross section of the horizontal flue. Layer layout, the long spray gun distribution module controls the flow of urea solution sprayed by each long spray gun according to the control signal of the engineer station; an electric valve is set at the entrance of the urea solution pipeline of each short spray gun, and the short spray gun distribution module is based on the unit load of the W-type boiler and NSR value to control the electric valve opening of each floor.

Preferably, there are six long spray guns, and they are evenly arranged in three layers on the cross section of the horizontal flue, and four groups of lasers are evenly arranged on the section where the long spray guns are located; the lasers are arranged at intervals from the long spray guns; each group of lasers includes a The transmitting end and a receiving end, the transmitting end is connected to the optical fiber, and the receiving end is connected to the central control cabinet.

Preferably, the inlet of the cooling end of the long lance is connected to the output end of the desalinated water storage tank, and the outlet of the cooling end is connected to the input end of the desalinated water storage tank.

Preferably, a compressed air storage tank is also included, and the output ends of the compressed air storage tanks are respectively used for cooling air to be connected to the inlet of the cooling end of the short spray gun, and for atomizing air to be connected between the metering module and the distribution module.

Preferably, the metering module includes a mixer, and control valves and flowmeters respectively arranged at the two inlets of the mixer; the output ends of the original urea solution storage tank and the desalted water storage tank are respectively mixed with the corresponding Inlet connection to the device.

Preferably, each short spray gun is provided with a manual valve, and the openings of all manual valves are consistent.

A thermal power plant W-type boiler SNCR denitrification control method, based on a thermal power plant W-type boiler SNCR denitrification system of the present invention, comprising:

A step of adjusting the concentration of the urea solution through the metering module according to the CO concentration signal obtained by the laser detection system;

The step of adjusting the flow rate of the urea solution sprayed by each long spray gun through the long spray gun distribution module according to the temperature distribution signal obtained by the laser detection system;

Steps for controlling the number of layers of short spray guns in operation and the total flow rate of each layer of urea solution according to the unit load range and NSR value.

Preferably, the step of adjusting the concentration of urea solution is as follows,

The laser detection system uses the TDLAS measurement method to obtain the CO concentration signal in the horizontal flue. The CO concentration signal is converted into a valve opening signal in the engineer station and sent to the metering module to adjust the opening of the control valve of the desalinated water circuit. Control the concentration of urea solution sprayed by the long spray gun;

As the CO concentration increases, the desalinated water flow increases; as the CO concentration decreases, the desalinated water flow decreases.

Preferably, the steps of adjusting the flow rate of the urea solution sprayed by each long spray gun are as follows,

The laser detection system uses the TDLAS measurement method to obtain the temperature distribution signal of the flue gas in the horizontal flue. The temperature distribution signal is converted into a multi-way valve opening signal in the engineer station and sent to the long spray gun distribution module to adjust the control valve of each long spray gun. The opening degree, thereby controlling the flow of urea solution sprayed by each long spray gun.

Preferably, the steps of controlling the number of layers of the short spray gun to be put into operation and the total flow rate of each layer of urea solution are as follows,

The short spray guns are arranged in two layers in the deflection angle area of the W-shaped boiler, from bottom to top there are the first layer of short spray guns and the second layer of short spray guns;

When the unit of the W-type boiler is under low load, the first layer of short spray guns is put into operation, the second layer of short spray guns is closed, and the opening of the first layer of valves is adjusted according to the NSR value;

When the unit of the W-type boiler is at medium load, put into operation two layers of spray guns at the same time, and adjust the opening of the two layers of valves according to the NSR value;

When the unit of the W-type boiler is under high load, the second layer of spray guns is put into operation, the first layer of short spray guns is closed, and the opening of the second layer of valves is adjusted according to the NSR value.

Compared with the prior art, the present invention has the following beneficial technical effects:

In the present invention, a long spray gun with a plurality of nozzles extends into the middle of the flue, and the urea solution sprayed by the long spray gun can completely cover the cross section of the flue, ensuring that the urea solution and the flue gas are fully and uniformly mixed, and the denitrification efficiency is improved; Cooling, cooling water can be recycled to reduce operating costs. At the same time, multiple sets of laser detectors are arranged in the area where the long spray gun is located, and the flue gas temperature distribution and CO concentration are measured at the same time, and the urea solution flow rate of each long spray gun is adjusted in real time according to the temperature distribution signal, and the desalted water flow is adjusted in real time according to the CO concentration signal, so as to ensure The sprayed denitrification reducing agent is in the best reaction condition, which improves the denitrification efficiency of the SNCR system. The urea solution flow rate of the short spray gun is controlled centrally on each floor, and the number of layers in operation and the total flow rate of each layer of urea solution are controlled according to the load range of the unit, and are evenly distributed to each spray gun. The control method is simple and easy to implement.

Description of drawings

Fig. 1 is a W-type boiler SNCR denitrification system according to the present invention.

Fig. 2 is the control circuit of the long spray gun in the denitrification system of the present invention.

In the figure: long spray gun 1, short spray gun 2, urea solution storage tank 3, demineralized water storage tank 4, metering module 6, mixer 61, distribution module 7, long spray gun distribution module 71, central control cabinet 81, diode laser 82, Optical fiber multiplexer 83, optical fiber 84, transmitting end 85, receiving end 86, engineer station 9, W-type boiler 10.

detailed description

The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

A kind of W-type boiler SNCR denitrification system of the present invention, as shown in Figure 1, it comprises the long spray gun 1 that is arranged on W-type boiler 10 horizontal flue areas, divides multi-layer arrangement in W-type boiler 10 flame angle areas A plurality of short spray guns 2, and a laser detection system and a metering module 6 and a distribution module 7 connected in sequence; the distribution module 7 includes a long spray gun distribution module 71 whose output end is connected to the long spray gun 1 and a short spray gun distribution module whose output end is connected to the short spray gun 2 The input end of the metering module 6 used to control the concentration of urea solution is respectively connected to the original urea solution storage tank 3 and the desalted water storage tank 4, and the output end is respectively connected to the long spray gun distribution module 71 and the short spray gun distribution module 72; the laser detection system It includes a central control cabinet 81, a diode laser 82, an optical fiber multiplexer 83, an optical fiber 84 and multiple sets of lasers connected in sequence; the central control cabinet 81 is used to detect the flue gas temperature distribution signal and CO concentration signal through the laser; its output terminal The long spray gun distribution module 71 and the metering module 6 are respectively connected via the engineer station 9; a plurality of long spray guns 1 are uniformly arranged in multiple layers on the cross section of the horizontal flue, and the long spray gun distribution modules 71 are respectively controlled according to the control signals of the engineer station 9 The flow of urea solution sprayed by each long spray gun 1; an electric valve is set at the inlet of the urea solution pipeline of each short spray gun 2, and the short spray gun distribution module 72 controls the electric valve of each layer according to the unit load and NSR value of the W-type boiler 10. Among them, a compressed air storage tank 5 is also included, and the output ends of the compressed air storage tank 5 are respectively used for cooling air to be connected to the inlet of the cooling end of the short spray gun 2, and for atomizing air to be connected between the metering module 6 and the distribution module 7. The central control cabinet 81 is used for detecting and processing the laser signal; the optical fiber multiplexer 83 is used for the coupling of the laser signals of two bands; the diode laser 82 generates the laser signal; the optical fiber 84 transmits the laser signal; the preferred laser detection device also includes Protective device for purging and pneumatic decoking.

In this preferred example, as shown in Figure 2, six long spray guns 1 are arranged in total, and are arranged in three layers evenly on the cross section of the horizontal flue, and four groups of lasers are evenly arranged on the cross section where the long spray gun 1 is located; The long spray guns 1 are arranged at intervals; each group of lasers includes a transmitting end 85 and a receiving end 86, the transmitting end 85 is connected to the optical fiber 84, and the receiving end 86 is connected to the central control cabinet 81.

In this preferred example, the inlet of the cooling end of the long lance 1 is connected to the output end of the desalted water storage tank 4 , and the outlet of the cooling end is connected to the input end of the desalinated water storage tank 4 . The metering module 6 includes a mixer 61, and control valves and flowmeters respectively arranged at two inlets of the mixer 61; the output ends of the original urea solution storage tank 3 and the desalted water storage tank 4 are connected to the corresponding mixer through a liquid addition pump respectively. 61 entrance connections.

A method for controlling SNCR denitrification of a W-type boiler in a thermal power plant according to the present invention includes the steps of adjusting the concentration of urea solution through the metering module 6 according to the CO concentration signal obtained by the laser detection system; the temperature distribution signal obtained by the laser detection system is passed through the long spray gun distribution module 71 A step of adjusting the flow rate of urea solution sprayed by each long spray gun 1; a step of controlling the number of layers of the short spray gun 2 in operation and the total flow rate of each layer of urea solution according to the load range of the unit and the NSR value. Preferably, the short spray guns 2 are arranged in two layers in the folded flame area of the W-shaped boiler 10, and there are the first layer of short spray guns and the second layer of short spray guns from bottom to top.

Among them, the laser detection system uses the TDLAS measurement method to obtain the CO concentration signal in the horizontal flue. The CO concentration signal is converted into a valve opening signal in the engineer station 9 and sent to the metering module 6 to adjust the control valve of the desalinated water circuit. Opening, thereby controlling the concentration of the urea solution sprayed by the long spray gun 1.

Among them, the laser detection system adopts the TDLAS measurement method to obtain the temperature distribution signal of the flue gas in the horizontal flue, and the temperature distribution signal is converted into a multi-way valve opening signal in the engineer station 9 and sent to the long spray gun distribution module 71 to adjust each The opening of the long spray gun 1 controls the valve, thereby controlling the flow rate of the urea solution sprayed by each long spray gun 1 .

The specific arrangement and control in the present invention are as follows.

1) As shown in Figure 1, six long spray guns are arranged in three layers in the horizontal flue area of the W-shaped boiler, spraying urea solution into the flue gas. The long spray gun extends into the center of the flue and contains multiple nozzles, and the sprayed urea solution can cover the entire flue section. The long spray gun is cooled by demineralized water, and the cooling water is recycled.

2) As shown in Figure 1, multiple short spray guns are arranged in two layers in the refraction angle area of the W-type boiler, and spray urea solution about 1 meter into the furnace. The short lance is cooled with compressed air, which is blown directly into the furnace.

3) As shown in Figure 2, four sets of lasers are arranged on the section where the long spray gun is located, and each set of lasers includes a transmitting end and a receiving end. The laser light of a specific wavelength emitted by the transmitter passes through the boiler and is collected by the receiver, and then sent to the central control cabinet, where the ratio of unabsorbed light to absorbed light is measured by the central control cabinet to determine the flue gas temperature distribution and CO concentration. The flue gas temperature distribution signal is converted into a six-way valve opening signal in the engineer station and sent to the long spray gun distribution module to adjust the opening of the electric valve in each long spray gun circuit, thereby controlling the flow of urea solution sprayed by each long spray gun. The CO concentration signal is converted into a valve opening signal in the engineer station and sent to the metering module to adjust the opening of the electric valve of the desalinated water circuit, thereby controlling the concentration of the urea solution sprayed by the long spray gun. Specifically, as the CO concentration increases, Increase the flow rate of desalinated water; decrease the flow rate of desalinated water as the CO concentration decreases.

4) The urea solution flow rate of the short spray guns is centrally controlled on each floor, and the number of layers in operation and the total flow rate of each layer of urea solution are controlled according to the unit load interval, and are evenly distributed to each short spray gun. Specifically, an electric valve is provided for the inlet of the urea solution pipeline of each short spray gun, and the opening of the valve is adjusted according to the load of the unit. When the unit is under low load, for example reaching 50% of full load, the first layer of short spray guns is put into operation, the second layer of short spray guns is closed, and the opening of the first layer valve is adjusted according to the NSR value; when the unit is under medium load, For example, when the unit reaches 75% of full load, put into operation two layers of short spray guns at the same time, and adjust the opening of the two layers of valves according to the NSR value; , the short spray gun of the first layer is closed, and the opening of the valve of the second layer is adjusted according to the NSR value. A manual valve is set at each short spray gun, and the openings of all manual valves are consistent.

Among them, the laser detection system adopts TDLAS (Tunable Diode Laser Absorption Spectroscopy, Tunable Diode Laser Absorption Spectroscopy) technology, which integrates two wavelengths of laser light into one optical fiber, and then makes the emitted light pass through the horizontal flue section of the W-type boiler in sequence. The receiver collects the light and transmits it back to the central control cabinet, and the central control cabinet compares the ratio between the reference light quantity of a specific wavelength passing through the boiler and the light quantity absorbed by the measured substance molecules, so as to determine the Concentration, gas temperature is measured according to the ratio of two CO ₂ characteristic absorption lines. The emitter and receiver can be automatically calibrated to ensure the best light transmission even when the boiler is disturbed. At the same time, it is equipped with an instrument gas purging device and a pneumatic decoking device to ensure the smooth flow of the detection hole. In the present invention, a transmitting end 85 and a receiving end 86 are installed at both ends of the horizontal flue. When the laser light is emitted from one side, after the receiving end 86 of the corresponding end receives it, a measuring path is formed in the horizontal flue. These paths can be Simultaneously measure CO concentration and furnace temperature in the furnace.

The principle of TDLAS measurement is that gas molecules absorb light of a specific frequency (wavelength), and the absorption rate is related to temperature, pressure, path length and gas concentration. For a known path length and gas pressure, the temperature and component concentration of the flue gas can be determined by collecting and analyzing the absorption rate of the laser light in a characteristic absorption frequency range.

Claims (10)

1. A W-type boiler SNCR denitrification system in a thermal power plant is characterized in that it comprises a long spray gun (1) arranged on the W-type boiler (10) horizontal flue area, and there are many points in the W-type boiler (10) refraction angle area. A plurality of short spray guns (2) arranged in layers, as well as a laser detection system and sequentially connected metering modules (6) and distribution modules (7); The distribution module (7) includes a long spray gun distribution module (71) whose output end is connected to the long spray gun (1) and a short spray gun distribution module whose output end is connected to the short spray gun (2); The input end of the metering module (6) for controlling the concentration of the urea solution is respectively connected to the original urea solution storage tank (3) and the demineralized water storage tank (4), and the output end is respectively connected to the long spray gun distribution module (71) and the short spray gun distribution module; Described laser detection system comprises central control cabinet (81), diode laser (82), optical fiber multiplexer (83), optical fiber (84) and multiple groups of lasers connected in sequence; central control cabinet (81) is used for The flue gas temperature distribution signal and the CO concentration signal are detected by a laser; the output end is respectively connected to the long spray gun distribution module (71) and the metering module (6) through the engineer station (9); Multiple long spray guns (1) are uniformly arranged in multiple layers on the cross-section of the horizontal flue, and the long spray gun distribution module (71) controls the urea sprayed by each long spray gun (1) respectively according to the control signal of the engineer station (9) Solution flow rate; the urea solution pipeline inlet of each layer of short spray guns (2) is provided with an electric valve, and the short spray gun distribution module (72) controls the opening of each layer of electric valves according to the unit load and NSR value of the W-type boiler (10). 2. The W-type boiler SNCR denitrification system of a thermal power plant according to claim 1, wherein six long spray guns (1) are arranged in three layers evenly on the cross section of the horizontal flue , four groups of lasers are evenly arranged on the section where the long spray gun (1) is located; the lasers are arranged at intervals with the long spray gun (1); each group of lasers includes a transmitting end (85) and a receiving end (86), and the transmitting end (85) is connected to an optical fiber (84), the receiving end (86) is connected to the central control cabinet (81). 3. The W-type boiler SNCR denitrification system of a thermal power plant according to claim 1, wherein the inlet of the cooling end of the long spray gun (1) is connected to the output end of the desalted water storage tank (4), and the outlet of the cooling end is connected to the desalted water The input end of the storage tank (4). 4. A kind of thermal power plant W type boiler SNCR denitrification system according to claim 1, is characterized in that, also comprises compressed air storage tank (5), and the output end of compressed air storage tank (5) is respectively used for cooling air connection At the cooling end inlet of the short lance (2) for atomizing air is connected between the metering module (6) and the distribution module (7). 5. A kind of thermal power plant W-type boiler SNCR denitrification system according to claim 1, characterized in that, the metering module (6) includes a mixer (61), and two The control valve and flow meter at the inlet; the output ends of the original urea solution storage tank (3) and the desalted water storage tank (4) are respectively connected to the inlet of the corresponding mixer (61) through a filling pump. 6. The W-type boiler SNCR denitrification system of a thermal power plant according to claim 1, wherein each short spray gun (2) is provided with a manual valve, and the openings of all manual valves are consistent. 7. A W-type boiler SNCR denitrification control method in a thermal power plant, characterized in that, based on the SNCR denitrification system of a W-type boiler in a thermal power plant according to claim 1, comprising: A step of adjusting the concentration of the urea solution through the metering module (6) according to the CO concentration signal obtained by the laser detection system; The step of adjusting the flow rate of the urea solution sprayed by each long spray gun (1) through the long spray gun distribution module (71) according to the temperature distribution signal obtained by the laser detection system; The step of controlling the number of layers of the short spray gun (2) in operation and the total flow rate of each layer of urea solution according to the unit load interval and the NSR value. 8. a kind of thermal power plant W type boiler SNCR denitrification control method according to claim 7, is characterized in that, the step of adjusting urea solution concentration is specifically as follows, The laser detection system uses the TDLAS measurement method to obtain the CO concentration signal in the horizontal flue. The CO concentration signal is converted into a valve opening signal in the engineer station (9) and sent to the metering module (6) to adjust the control of the desalinated water circuit. The degree of opening of the valve, thereby controlling the concentration of the urea solution sprayed by the long spray gun (1); As the CO concentration increases, the desalinated water flow increases; as the CO concentration decreases, the desalinated water flow decreases. 9. a kind of thermal power plant W type boiler SNCR denitrification control method according to claim 7, is characterized in that, the step of regulating the urea solution flow rate that each long spray gun (1) sprays is specifically as follows, The laser detection system adopts the TDLAS measurement method to obtain the temperature distribution signal of the flue gas in the horizontal flue, and the temperature distribution signal is converted into a multi-way valve opening signal in the engineer station (9) and sent to the long spray gun distribution module (71) for adjustment. Each long spray gun (1) controls the opening degree of the valve, thereby controlling the flow rate of the urea solution sprayed by each long spray gun (1). 10. a kind of thermal power plant W type boiler SNCR denitrification control method according to claim 7, is characterized in that, the step of controlling short spray gun (2) to put into operation layers and every layer of urea solution total flow is specifically as follows, The short spray guns (2) are arranged in two layers in the folded flame area of the W-shaped boiler (10), from bottom to top there are the first layer of short spray guns and the second layer of short spray guns; When the unit of the W-type boiler (10) is under low load, the first layer of short spray guns is put into operation, the second layer of short spray guns is closed, and the opening of the first layer of valves is adjusted according to the NSR value; When the unit of the W-type boiler (10) is under medium load, put into operation two layers of spray guns at the same time, and adjust the opening of the two layers of valves according to the NSR value; When the unit of the W-type boiler (10) is under high load, the second layer of spray guns is put into operation, the first layer of short spray guns is closed, and the opening degree of the second layer of valves is adjusted according to the NSR value.