Boiler slag falling monitoring method based on optical fiber vibration signals

Abstract

The invention discloses a boiler slag falling monitoring method based on optical fiber vibration signals. The method comprises the following steps that (1) optical fiber vibration sensing devices are arranged on the front wall inclined face and the rear wall inclined face of a boiler dry bottom hopper respectively; each optical fiber vibration sensing device is composed of two sets of optical fibers of the same kind, main body parts of the two sets of optical fibers are vertically arranged in a crossed mode, and the same light source and the same signal receiver are adopted. (2) continuously recording vibration signals of all the optical fiber vibration sensing devices in the operation process of the boiler; and (3) calculating the slag falling area, the slag block height and the mass according to the position information, the signal duration and the amplitude characteristic of the optical fiber vibration in the same inclined plane optical fiber vibration sensing device. By monitoring the vibration signals in the optical fibers arranged on the inclined surface of the boiler dry bottom hopper, the slag falling position and the height and mass of slag blocks can be accurately calculated, and guidance is provided for use and combustion optimization of a boiler soot blower.

Description

Technical Field

[0001] The invention relates to the technical field of pulverized coal boiler combustion, and in particular to a boiler slag monitoring method based on optical fiber vibration signals. Background Art

[0002] As a key equipment in industrial production and energy supply, the operating efficiency and safety of boilers are of vital importance. However, during operation, boilers will inevitably encounter slagging problems, that is, the ash produced after coal powder combustion accumulates in the furnace.

[0003] The formation of slag is mainly due to the fuel combustion process, in which the ash is melted or semi-melted under high temperature. As the flue gas flows, when these molten ashes encounter the heating surface with a lower temperature, they will adhere to the heating surface due to rapid cooling to form slag. Slag will lead to a decrease in the heat transfer efficiency of the heating surface, an increase in the heat loss of flue gas, and a reduction in boiler efficiency; at the same time, uneven heating in the slag area may also cause water circulation failures and reduce boiler output; the risk of high-temperature corrosion and heating surface tube bursts will increase accordingly, and in severe cases, it may even lead to boiler extinguishing and shutdown.

[0004] Therefore, monitoring the boiler slagging state is of great significance for the safe and stable operation of the boiler. At present, the monitoring methods for boiler heating surface pollution mainly include direct diagnosis, indirect diagnosis using heat flow meter, indirect diagnosis using the temperature difference on the back of the water-cooled wall, and indirect diagnosis based on the change of flue gas temperature at the furnace outlet.

[0005] Direct diagnosis is to monitor furnace contamination by directly observing the slagging condition of the heating surface in the furnace through instruments and equipment. Due to the limits of complex environments such as high temperature and fly ash in the furnace, and the lack of suitable equipment and information evaluation methods, there are not many methods that can be used for direct diagnosis.

[0006] Indirect diagnosis using heat flow meter is to use the heat flow meter installed on the water wall as a diagnostic sensor, use the contamination on the surface of the heat flow meter to simulate the generation and development process of slagging on the water wall nearby, and diagnose the slagging according to the heat flow change caused by the slagging. However, it has the disadvantages of high cost, difficult maintenance, and insufficient product reliability.

[0007] Indirect diagnosis using the temperature difference on the back of the water-cooled wall is to use the temperature difference measurement point on the back of the water-cooled wall to measure the local heat load of the water-cooled wall online, that is, the dust heat load. The clean heat load under normal conditions is obtained by directly measuring the clean heat flow or calculating the furnace section. By comparing the dust heat load and the clean heat load, the slagging location and severity can be determined. However, this method is limited to laboratory research and has not been further promoted and applied.

[0008] The principle of indirect diagnosis based on the change of furnace outlet flue gas temperature is that when contamination and slagging occur in the furnace, the heat absorption of the water-cooled wall decreases and the furnace outlet flue gas temperature increases. After the furnace soot is blown, the furnace outlet flue gas temperature drops significantly, and then gradually increases with the increase of contamination until the next soot is blown. Therefore, the change of furnace outlet flue gas temperature can reflect the characteristics of the slagging condition in the furnace as a whole. However, this method can only judge the overall slagging condition of the furnace, and it is difficult to locate the slagging. Summary of the invention

[0009] The present invention provides a boiler slag falling monitoring method based on optical fiber vibration signals. By monitoring the vibration signals in the optical fiber arranged on the inclined surface of the boiler cold ash hopper, the slag falling position, the height and the quality of the slag block can be accurately calculated, providing guidance for the use of the boiler soot blower and combustion optimization.

[0010] A boiler slag monitoring method based on optical fiber vibration signals comprises the following steps:

[0011] (1) An optical fiber vibration sensor device is arranged on the inclined surface of the front wall and the inclined surface of the rear wall of the boiler cold ash hopper respectively; each optical fiber vibration sensor device is composed of two groups of optical fibers of the same type, the main parts of the two groups of optical fibers are arranged vertically and crosswise, and the same light source and signal receiver are used;

[0012] (2) Continuously record the vibration signals of all optical fiber vibration sensing devices during boiler operation;

[0013] (3) The slag falling area, slag block height and mass are calculated based on the position information, signal duration and amplitude characteristics of the optical fiber vibration in the same inclined optical fiber vibration sensing device.

[0014] In step (1), the optical fiber in the optical fiber vibration sensing device can withstand a temperature greater than or equal to 400°C.

[0015] The specific process of step (3) is as follows:

[0016] (3-1) Based on the optical fiber vibration signal characteristics of the front and rear wall slopes of the cold ash hopper, it is preliminarily determined whether the slag falling area is located on the front wall or the rear wall;

[0017] (3-2) calculating the specific position where the slag hits the cold ash hopper slope according to the position information of the optical fiber vibration corresponding to the slope and the arrangement of the optical fiber on the slope, and then calculating the initial position of the slag in the furnace according to the slag hitting position;

[0018] (3-3) transforming and analyzing the vibration signal received by the signal receiver in the optical fiber vibration sensor device, and obtaining the height of the slag according to the duration of the optical fiber vibration signal;

[0019] (3-4) After calculating the slag height, the slag mass is calculated based on the maximum amplitude of the vibration signal.

[0020] In order to improve the accuracy of calculating the slag position, preferably, in step (3-1), whether the slag is close to the front wall or the rear wall is determined by comparing the average values ​​of the jump amplitudes of the optical fiber vibration signals of the front and rear walls. The larger the average value, the slag is located on that side.

[0021] In order to improve the accuracy of calculating the slag position, preferably, in step (3-2), the main parts of the two groups of optical fibers are arranged vertically and crosswise, and the accurate position of the slag is determined according to the intersection of the slag ranges calculated by the two groups of optical fibers. Since there is a certain error in the position information determined by the vibration signal of a single group of optical fibers, a more accurate slag position is determined by arranging two groups of optical fibers vertically and crosswise.

[0022] In step (3-3), the signal duration of the optical fiber vibration is the time it takes for a single signal amplitude to decay from the maximum value to the average amplitude of the background signal.

[0023] In order to improve the accuracy of calculating the slag height, preferably, in step (3-3), the longer the duration of the optical fiber vibration signal, the higher the slag height. Since the duration of the optical fiber vibration signal is related to the hardness of the slag block, that is, the higher the hardness of the slag block, the shorter the duration of the vibration; the higher the temperature of the slag block in the furnace, the greater its hardness; only considering the area above the furnace flame, for a certain slag range, the higher the height, the lower the temperature. The specific formula for obtaining the slag height based on the duration of the optical fiber vibration signal is:

[0024] h=(k 2 k 3 / k 1 )t

[0025] Where, h is the slag height, in meters; t is the duration of the optical fiber vibration signal, in seconds; k 1 is a constant determined by the relationship between the duration of the optical fiber vibration signal and the hardness of the slag block; k 2 is a constant determined by the relationship between the hardness of the slag and the temperature; k 3 It is a constant determined by the temperature distribution in the furnace.

[0026] In step (3-4), the maximum amplitude of the optical fiber vibration is related to the mass of the slag block, the collision speed, the hardness of the slag block and the physical parameters of the slope of the cold ash hopper;

[0027] When the slope of the cold ash hopper remains unchanged, the collision speed is related to the slag falling height, and the hardness of the slag block is related to the slag falling height, so the mass of the slag block can be calculated based on the maximum amplitude.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention provides a boiler slag monitoring method based on optical fiber vibration signals. By monitoring the optical fiber vibration signals in the boiler cold ash hopper, the slag position, slag block height and quality are calculated, and guidance is provided for the use of the boiler soot blower and combustion optimization. The method only requires arranging optical fibers in the boiler cold ash hopper to monitor the boiler slag status, which is easy to implement and promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0031] Figure 1 The figure is a schematic diagram of the arrangement of the optical fiber vibration sensor device in the boiler slag monitoring method based on the optical fiber vibration signal of the present invention.

[0032] Figure 2 Schematic diagram of the optical fiber vibration sensing device.

[0033] Figure 3 This is the time domain diagram of the characteristic signal of the collision between slag of different hardness in the furnace and the inclined surface of the cold ash hopper.

[0034] Figure 4 This is the time domain diagram of the optical fiber vibration signal generated during the operation of the system. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] It should be noted that, in the absence of conflict, the features in the following embodiments and implementations may be combined with each other.

[0037] A boiler slag monitoring method based on optical fiber vibration signals comprises the following steps:

[0038] Step 1: arrange an optical fiber vibration sensor device on the front wall slope and the rear wall slope of the boiler cold ash hopper respectively.

[0039] Specifically, Figure 1 As shown, the measuring system used in this embodiment includes a boiler body 1, a light source 2, an optical fiber 3, a signal receiver 4, and a computer 5.

[0040] like Figure 2 As shown, an optical fiber vibration sensing device includes two groups of optical fibers arranged on the same inclined plane, the interval between the main bodies of the same group of optical fibers is 0.2 m, and the two groups of optical fibers are arranged vertically and crosswise. The optical fiber can withstand high temperatures of at least 400°C.

[0041] Step 2, using a signal receiver to continuously record vibration signals of all optical fiber vibration sensing devices during the operation of the boiler;

[0042] Step 3: The computer transforms and analyzes the received vibration signal, and calculates the slag falling area, slag block height and mass according to the position information, signal duration and amplitude characteristics of the optical fiber vibration sensor device on the same slope. The specific steps are as follows:

[0043] 3-1. Based on the characteristics of the optical fiber vibration signal of the front and rear wall slopes of the cold ash hopper, it is preliminarily determined whether the slag falling area is located on the front wall or the rear wall;

[0044] 3-2. The specific position where the slag hits the cold ash hopper slope is calculated based on the position information of the optical fiber vibration corresponding to the slope and the arrangement of the optical fiber on the slope, and then the initial position of the slag in the furnace is calculated based on the slag impact position; since the position signal of the optical fiber vibration sensor device has a certain error range, the accurate position of the slag is determined based on the intersection of the slag ranges calculated by the two groups of optical fibers;

[0045] 3-3. The vibration signal received by the signal receiver in the optical fiber vibration sensor device is transformed and analyzed, and the height of the slag is obtained according to the duration of the vibration signal. In the early stage, the temperature distribution field of the longitudinal section of the furnace is calculated through numerical simulation, and the relationship between the height and temperature distribution inside the furnace is obtained. Then, slag blocks in different temperature zones are taken for collision experiments to obtain the relationship between the duration of the vibration signal and the temperature of the slag blocks. Finally, the slag height is determined based on the duration of the vibration signal. Figure 3 It is a time domain diagram of the characteristic signal of the collision between slag of different hardness and the inclined surface of the cold ash hopper in the furnace. It consists of two pictures, the upper and lower pictures, which are the characteristic signal of the collision between the soft body (slag with smaller hardness) and the inclined surface of the cold ash hopper and the characteristic signal of the collision between the rigid body (slag with larger hardness) and the inclined surface of the cold ash hopper. The results show that the hardness of the slag is inversely proportional to the duration of its collision characteristic signal.

[0046] The height of the slag is obtained according to the duration of the optical fiber vibration signal. The specific formula is:

[0047] h=(k 2 k 3 / k 1 )t

[0048] Where, h is the slag height, in meters; t is the duration of the optical fiber vibration signal, in seconds; k 1is a constant determined by the relationship between the duration of the optical fiber vibration signal and the hardness of the slag block, k 1 =20.0~210.0; k 2 is a constant determined by the relationship between the hardness of the slag and the temperature, k 2 =0.2~0.7; k 3 is a constant determined by the temperature distribution in the furnace

[0049] k 3 =3.0×10 3 ~6.0×10 3 .

[0050] 3-4. After calculating the slag height, calculate the slag weight according to the maximum amplitude of the vibration signal; the maximum amplitude of the optical fiber vibration is related to the mass of the slag block, the collision speed, and the physical parameters of the slag block and the slope of the cold ash hopper, among which the physical parameters of the slag block are mainly the hardness of the slag block. When the slope of the cold ash hopper remains unchanged, the collision speed and the hardness of the slag block are related to the slag height, and the mass of the slag block can be calculated according to the maximum amplitude and the slag height.

[0051] Step 4: monitor the boiler slagging status for a long time and guide the use of soot blowers. For areas with high slagging frequency and large slagging amount, increase the frequency of soot blowers. Conversely, for areas with low slagging frequency and small slagging amount, reduce the frequency of soot blowers. Figure 4 This is the time domain diagram of the optical fiber vibration signal generated during the operation of the system. Under the premise of excluding the influence of the background noise signal of the boiler cold ash hopper water-cooled wall, each single vibration signal corresponds to a slag falling, and the more vibration signals, the higher the slag falling frequency.

[0052] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A boiler slag monitoring method based on optical fiber vibration signal, characterized in that: The following steps are involved: (1) Arrange an optical fiber vibration sensor device on the front wall slope and the rear wall slope of the boiler cold ash hopper respectively; Each optical fiber vibration sensor device is composed of two groups of optical fibers of the same type, the main parts of the two groups of optical fibers are arranged vertically and crosswise, and use the same light source and signal receiver; (2) Continuously record the vibration signals of all optical fiber vibration sensing devices during boiler operation; (3) The slag falling area, slag block height and mass are calculated based on the position information, signal duration and amplitude characteristics of the optical fiber vibration in the same inclined optical fiber vibration sensing device.

2. The boiler slag monitoring method based on optical fiber vibration signal according to claim 1 is characterized in that: In step (1), the optical fiber in the optical fiber vibration sensing device can withstand a temperature greater than or equal to 400°C.

3. The boiler slag monitoring method based on optical fiber vibration signal according to claim 1 is characterized in that: The specific process of step (3) is as follows: (3-1) Based on the optical fiber vibration signal characteristics of the front and rear wall slopes of the cold ash hopper, it is preliminarily determined whether the slag falling area is located on the front wall or the rear wall; (3-2) calculating the specific position where the slag hits the cold ash hopper slope according to the position information of the optical fiber vibration corresponding to the slope and the arrangement of the optical fiber on the slope, and then calculating the initial position of the slag in the furnace according to the slag impact position; (3-3) transforming and analyzing the vibration signal received by the signal receiver in the optical fiber vibration sensor device, and obtaining the height of the slag according to the duration of the optical fiber vibration signal; (3-4) After calculating the slag height, the slag mass is calculated based on the maximum amplitude of the vibration signal.

4. The boiler slag monitoring method based on optical fiber vibration signal according to claim 3 is characterized in that: In step (3-1), whether the slag is close to the front wall or the rear wall is determined by comparing the average values ​​of the jump amplitudes of the optical fiber vibration signals of the front and rear walls. The larger the average value, the slag is located on that side.

5. The boiler slag monitoring method based on optical fiber vibration signal according to claim 3 is characterized in that: In step (3-2), the main parts of the two groups of optical fibers are arranged vertically and crosswise, and the exact position of the slag is determined according to the intersection of the slag ranges calculated by the two groups of optical fibers.

6. The boiler slag monitoring method based on optical fiber vibration signal according to claim 3 is characterized in that: In step (3-3), the signal duration of the optical fiber vibration is the time it takes for a single signal amplitude to decay from the maximum value to the average amplitude of the background signal.

7. The boiler slag monitoring method based on optical fiber vibration signal according to claim 3 is characterized in that: In step (3-3), the height of the slag is obtained according to the duration of the optical fiber vibration signal. The specific formula is: h=(k2k3 / k1)t Where, h is the slag height, in m; t is the duration of the optical fiber vibration signal, in seconds; k1 is a constant determined by the relationship between the duration of the optical fiber vibration signal and the hardness of the slag block; k2 is a constant determined by the relationship between the hardness of the slag block and the temperature; k3 is a constant determined by the temperature distribution in the furnace.

8. The method for monitoring boiler slag based on optical fiber vibration signals according to claim 3 is characterized in that: In step (3-4), the maximum amplitude of the optical fiber vibration is related to the mass of the slag block, the collision speed, the hardness of the slag block and the physical parameters of the slope of the cold ash hopper; When the slope of the cold ash hopper remains unchanged, the collision speed is related to the slag falling height, and the hardness of the slag block is related to the slag falling height, so the mass of the slag block can be calculated based on the maximum amplitude.

Images