Slag discharge system and control method for improving circulating fluidized bed boiler bed quality

Abstract

The present invention discloses a slag discharge system and a control method for improving the bed quality of a circulating fluidized bed boiler, and solves the problem of how to keep the bed quality of a circulating fluidized bed boiler in an optimal state. A fine bottom slag discharge port is set at the center of the boiler furnace bottom, and a coarse bottom slag discharge port is set at the boiler furnace bottom close to the furnace wall. A fine bottom slag discharger is connected to the fine bottom slag discharge port, and a coarse bottom slag discharger is connected to the coarse bottom slag discharge port. The carbon content of the fine bottom slag discharged by the fine bottom slag discharger is detected, and the obtained value is compared with the design value of the carbon content of the boiler circulating ash, thereby dynamically increasing or decreasing the fine bottom slag discharge amount. The carbon content of the coarse bottom slag discharged by the coarse bottom slag discharger is detected, and the obtained value is compared with the design value of the carbon content of the boiler bottom ash, thereby dynamically increasing or decreasing the coarse bottom slag discharge amount; the purpose of maintaining or improving the bed quality is achieved by adjusting the discharge amount ratio of the coarse and fine slag discharged from the furnace body.

Description

Technical Field

[0001] The invention relates to a circulating fluidized bed boiler, and in particular to a slag discharge system and a control method thereof which can improve the bed quality of the circulating fluidized bed boiler. Background Art

[0002] The design of the furnace structure and parameters of a circulating fluidized bed boiler is generally determined based on the coal quality characteristics of the coal burned in the boiler. During boiler operation, this type of coal is continuously added to the furnace through a coal feeder in front of the furnace. Large-particle slag after full combustion falls to the bottom of the furnace, and small-particle ash rises and enters the cyclone separator. The ash is separated in the cyclone separator, and larger ash particles return to the furnace through a return pipe, and continue to burn after mixing with the newly entered coal. During the combustion process, large-particle slag falls to the bottom of the furnace again, and small-particle ash rises again and enters the cyclone separator again for separation, and this cycle is repeated. In this process, bottom ash with basically uniform size particles will be formed at the bottom of the furnace of the circulating fluidized bed boiler, and circulating ash of circulating fluidization will be formed on the bottom ash, that is, the bottom ash constitutes the lower bubbling bed of the circulating fluidized bed boiler, and the circulating ash constitutes the upper fast bed of the circulating fluidized bed boiler. During the above-mentioned operation of the circulating fluidized bed boiler, a slag discharge system is arranged at the bottom of the boiler, and the slag discharge system continuously discharges the bottom slag out of the furnace, and realizes the full combustion of the coal-quality fuel in the furnace of the circulating fluidized bed boiler by adjusting the combustion control quantities such as the primary air intake and secondary air intake of the furnace. The boiler is generally equipped with a distributed control system, and the operator uses the distributed control system to control the coal feeding, primary air intake, secondary air intake, induced draft and slag discharge system of the boiler in real time.

[0003] In the normal operation of a circulating fluidized bed boiler, the distribution pattern of the boiler bottom ash is generally as follows: the bottom ash particles near the edge of the furnace are larger, while the bottom ash particles near the center of the furnace are smaller. Therefore, in the traditional design of the boiler, the slag discharge port of the boiler is generally designed to be arranged in the middle position between the edge of the furnace and the center of the furnace, in order to achieve the purpose of discharging large particles of bottom ash and small particles of bottom ash as much as possible in equal amounts, so that the circulating ash in the furnace of the circulating fluidized bed boiler can maintain a basically stable state. In a sense, the carbon content of the discharged large particles of bottom ash can basically represent the unburned carbon content of the furnace bottom ash. The carbon content of the discharged small-particle bottom ash can basically represent the unburned carbon content in the circulating ash in the furnace. The boiler designed according to the coal quality characteristics of the coal burned in the boiler generally makes the coal burn as much as possible to keep the bed quality in a better state. At this time, the corresponding unburned carbon content of the furnace bottom ash and the unburned carbon content of the circulating ash in the furnace are the ideal carbon content values. That is to say, if the carbon content of the large-particle bottom ash discharged from the furnace and the carbon content of the small-particle bottom ash discharged from the furnace are measured, when the two indicators are close to the ideal design values, it can be basically judged that the bed quality of the boiler is in a better working condition. However, in the actual operation of the boiler, various control factors may affect the bed quality. In particular, the type of coal supplied to the boiler cannot remain constant. When the coal quality characteristics of the coal change significantly, its ash-forming characteristics will also change significantly, and the ash particle size in the furnace will change significantly. The furnace bottom slag discharge system of existing equipment does not have the function of timely changing the slag discharge amount with the change of coal type. When the coal type characteristics change significantly, it is easy to discharge too much large bottom ash or too much fine bottom ash, causing the circulating fluidized bed ash in the furnace to deviate greatly from its ideal working state, resulting in a significant reduction in the combustion efficiency of the circulating fluidized bed boiler. How to keep the bed quality of the working boiler in a better working state when the coal characteristics change significantly has become a technical problem that needs to be solved on site. Summary of the invention

[0004] The present invention provides a slag discharge system for improving the bed quality of a circulating fluidized bed boiler and a control method thereof, which solves the technical problem of how to keep the bed quality of the circulating fluidized bed boiler in a better state.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] The overall concept of the present invention is: a fine bottom slag discharge port is set at the center of the boiler bottom, a coarse bottom slag discharge port is set at the boiler bottom close to the furnace wall, a fine bottom slag discharge port is connected to the fine bottom slag discharge port, and a coarse bottom slag discharge port is connected to the coarse bottom slag discharge port, the carbon content of the fine bottom slag discharged by the fine bottom slag discharger is detected, and the obtained value is compared with the design value of the carbon content of the boiler circulating ash, so as to dynamically increase or decrease the fine bottom slag discharge amount, the carbon content of the coarse bottom slag discharged by the coarse bottom slag discharger is detected, and the obtained value is compared with the design value of the carbon content of the boiler bottom ash, so as to dynamically increase or decrease the coarse bottom slag discharge amount; and, by limiting the distance between the return port for the circulating ash to enter the furnace and the fine bottom slag discharge port, and by limiting the distance between the furnace coal feeding port and the coarse bottom slag discharge port, the carbon content of the bottom slag and fly ash discharged from the furnace body is further reduced; by adjusting the slag discharge amount ratio of the coarse and fine slag discharged from the furnace body, the purpose of maintaining or improving the bed quality is achieved.

[0007] A slag discharge system for improving the bed quality of a circulating fluidized bed boiler comprises a furnace, a coal feeder, a cyclone separator and a cold slag discharger, a return box and a return pipe are connected to the lower end of the cyclone separator, the lower section of the return pipe is connected to the furnace through a return port, a front coal feeding pipe and a rear coal feeding pipe are respectively connected to the coal feeder, the front coal feeding pipe is connected to the furnace through the front coal feeding port, the rear coal feeding pipe is connected to the furnace through the rear coal feeding port, a fine slag discharge port is provided at the central position of the furnace bottom, and a fine slag discharge port is provided between the fine slag discharge port and the front inner wall of the furnace A front coarse slag discharge port is provided on the front side of the midpoint position, and a rear coarse slag discharge port is provided on the rear side of the midpoint position between the fine slag discharge port and the rear inner wall of the furnace, a fine slag discharge port is connected with a fine slag discharge pipe, and the other end of the fine slag discharge pipe is connected with a fine slag cooler discharger, a front coarse slag discharge port is connected with a front coarse slag discharge pipe, and the other end of the front coarse slag discharge pipe is connected with a front coarse slag cooler discharger, a rear coarse slag discharge port is connected with a rear coarse slag discharge pipe, and the other end of the rear coarse slag discharge pipe is connected with a rear coarse slag cooler discharger.

[0008] The line passing through the center point of the return material port and perpendicular to the plane where the return material port is located is defined as the median vertical line of the return material port; the line passing through the center point of the fine slag discharge port and perpendicular to the plane where the fine slag discharge port is located is defined as the median vertical line of the fine slag discharge port; the distance between the median vertical line of the return material port and the median vertical line of the fine slag discharge port is less than 300 mm; the line passing through the center point of the front side coal feeding port and perpendicular to the plane where the front side coal feeding port is located is defined as the median vertical line of the front side coal feeding port; the line passing through the center point of the front side coarse slag discharge port and perpendicular to the plane where the front coarse slag discharge port is located is defined as the median vertical line of the front side coal feeding port; The line perpendicular to the plane is defined as the median vertical line of the front coarse slag discharge port, and the distance between the median vertical line of the front coarse slag discharge port and the median vertical line of the front coal feeding port is greater than 600 mm; the line passing through the center point of the rear coal feeding port and perpendicular to the plane where the rear coal feeding port is located is defined as the median vertical line of the rear coal feeding port, and the line passing through the center point of the rear coarse slag discharge port and perpendicular to the plane where the rear coarse slag discharge port is located is defined as the median vertical line of the rear coarse slag discharge port, and the distance between the median vertical line of the rear coarse slag discharge port and the median vertical line of the rear coal feeding port is greater than 600 mm.

[0009] A control method for a slag discharge system for improving the bed quality of a circulating fluidized bed boiler, characterized by the following steps:

[0010] Retrieve the design value of the coarse slag carbon content and the design value of the fine slag carbon content designed for the circulating fluidized bed boiler, and detect the detection value of the coarse slag carbon content and the detection value of the fine slag carbon content discharged from the furnace body;

[0011] Compare the coarse slag carbon content detection value with the coarse slag carbon content design value. If the coarse slag carbon content detection value is greater than the coarse slag carbon content design value, the coarse slag discharge amount is reduced through the front coarse slag cold slag discharger and the rear coarse slag cold slag discharger; if the coarse slag carbon content detection value is less than the coarse slag carbon content design value, the coarse slag discharge amount is increased through the front coarse slag cold slag discharger and the rear coarse slag cold slag discharger;

[0012] The detected value of fine slag carbon content is compared with the designed value of fine slag carbon content. If the detected value of fine slag carbon content is greater than the designed value of fine slag carbon content, the fine slag discharge amount is reduced through the fine slag cold slag discharger. If the detected value of fine slag carbon content is less than the designed value of fine slag carbon content, the fine slag discharge amount is increased through the fine slag cold slag discharger.

[0013] The present invention changes the traditional method of increasing furnace temperature and oxygen supply when the combustion efficiency of the circulating fluidized bed boiler becomes low and the bed quality becomes poor. By changing the ratio of coarse slag and fine slag discharged from the furnace body, the quality of the bubbling bed and the fast bed is adjusted, thereby achieving the purpose of improving the bed quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of a circulating fluidized bed of the present invention;

[0015] Figure 2It is a schematic structural diagram of the furnace of the present invention in a side view direction;

[0016] Figure 3 It is a structural schematic diagram of the furnace bottom slag discharge port of the present invention. DETAILED DESCRIPTION

[0017] The present invention is described in detail below in conjunction with the accompanying drawings:

[0018] A slag discharge system for improving the bed quality of a circulating fluidized bed boiler, comprising a furnace 1, a coal feeder 6, a cyclone separator 2 and a cold slag discharger, wherein a return box 3 and a return pipe 4 are connected to the lower end of the cyclone separator 2, and the lower section of the return pipe 4 is connected to the furnace 1 through a return port 5, and a front coal feeding pipe 20 and a rear coal feeding pipe 19 are respectively connected to the coal feeder 6, the front coal feeding pipe 20 is connected to the furnace 1 through a front coal feeding port 7, and the rear coal feeding pipe 19 is connected to the furnace 1 through a rear coal feeding port 18, and a fine slag discharge port 9 is provided at the central position of a furnace bottom 8 of the furnace 1, and a fine slag discharge port 9 is provided between the fine slag discharge port 9 and the front inner wall of the furnace 1 A front coarse slag discharge port 12 is provided on the front side of the midpoint position, and a rear coarse slag discharge port 15 is provided on the rear side of the midpoint position between the fine slag discharge port 9 and the rear inner wall of the furnace 1. A fine slag discharge pipe 10 is connected to the fine slag discharge port 9, and a fine slag cooler 11 is connected to the other end of the fine slag discharge pipe 10. A front coarse slag discharge port 12 is connected to a front coarse slag discharge pipe 13, and a front coarse slag cooler 14 is connected to the other end of the front coarse slag discharge pipe 13. A rear coarse slag discharge port 15 is connected to a rear coarse slag discharge pipe 16, and a rear coarse slag cooler 17 is connected to the other end of the rear coarse slag discharge pipe 16.

[0019] The line passing through the center point of the return material port 5 and being perpendicular to the plane where the return material port 5 is located is defined as the mid-perpendicular line of the return material port; the line passing through the center point of the fine slag discharge port 9 and being perpendicular to the plane where the fine slag discharge port 9 is located is defined as the mid-perpendicular line of the fine slag discharge port; the distance between the mid-perpendicular line of the return material port and the mid-perpendicular line of the fine slag discharge port is less than 300 mm; the line passing through the center point of the front side coal feeding port 7 and being perpendicular to the plane where the front side coal feeding port 7 is located is defined as the mid-perpendicular line of the front side coal feeding port; the line passing through the center point of the front side coarse slag discharge port 12 and being perpendicular to the front side coarse slag discharge port 12 is defined as the mid-perpendicular line of the front side coal feeding port; The line perpendicular to the plane where the rear coal feeding port 18 is located is defined as the median vertical line of the front coarse slag discharge port, and the distance between the median vertical line of the front coarse slag discharge port and the median vertical line of the front coal feeding port is greater than 600 mm; the line passing through the center point of the rear coal feeding port 18 and perpendicular to the plane where the rear coal feeding port 18 is located is defined as the median vertical line of the rear coal feeding port, and the line passing through the center point of the rear coarse slag discharge port 15 and perpendicular to the plane where the rear coarse slag discharge port 15 is located is defined as the median vertical line of the rear coarse slag discharge port, and the distance between the median vertical line of the rear coarse slag discharge port and the median vertical line of the rear coal feeding port is greater than 600 mm.

[0020] A control method for a slag discharge system for improving the bed quality of a circulating fluidized bed boiler, characterized by the following steps:

[0021] Retrieve the design value of the coarse slag carbon content and the design value of the fine slag carbon content designed for the circulating fluidized bed boiler, and detect the detection value of the coarse slag carbon content and the detection value of the fine slag carbon content discharged from the furnace body;

[0022] The coarse slag carbon content detection value is compared with the coarse slag carbon content design value. If the coarse slag carbon content detection value is greater than the coarse slag carbon content design value, the coarse slag discharge amount is reduced through the front coarse slag cold slag discharger 14 and the rear coarse slag cold slag discharger 17; if the coarse slag carbon content detection value is less than the coarse slag carbon content design value, the coarse slag discharge amount is increased through the front coarse slag cold slag discharger 14 and the rear coarse slag cold slag discharger 17;

[0023] The detected value of the fine slag carbon content is compared with the designed value of the fine slag carbon content. If the detected value of the fine slag carbon content is greater than the designed value of the fine slag carbon content, the fine slag discharge amount is reduced through the fine slag cold slag discharger 11. If the detected value of the fine slag carbon content is less than the designed value of the fine slag carbon content, the fine slag discharge amount is increased through the fine slag cold slag discharger 11.

Claims

1. A control method for a slag discharge system for improving the bed quality of a circulating fluidized bed boiler, which is carried out by using the slag discharge system for improving the bed quality of a circulating fluidized bed boiler. The slag discharge system for improving the bed quality of a circulating fluidized bed boiler comprises a furnace (1), a coal feeder (6), a cyclone separator (2) and a cold slag discharger. A return box (3) and a return pipe (4) are connected to the lower end of the cyclone separator (2). The lower section of the return pipe (4) is connected to the furnace (1) through a return port (5). A front coal feeding pipe (20) and a rear coal feeding pipe (19) are respectively connected to the coal feeder (6). The front coal feeding pipe (20) is connected to the furnace (1) through the front coal feeding port (7). The rear coal feeding pipe (19) is connected to the furnace (1) through the rear coal feeding port (8). The coal port (18) is connected to the furnace (1). A fine slag discharge port (9) is provided at the central position of the furnace bottom (8) of the furnace (1). A front coarse slag discharge port (12) is provided at the front side of the midpoint between the fine slag discharge port (9) and the front inner wall of the furnace (1). A rear coarse slag discharge port (15) is provided at the rear side of the midpoint between the fine slag discharge port (9) and the rear inner wall of the furnace (1). A fine slag discharge pipe (10) is connected to the fine slag discharge port (9). A fine slag cooler (11) is connected to the other end of the fine slag discharge pipe (10). A front coarse slag discharge pipe (13) is connected to the front coarse slag discharge port (12). One end is connected to a front coarse slag cooling slag discharger (14), a rear coarse slag discharge port (15) is connected to a rear coarse slag discharge pipe (16), and the other end of the rear coarse slag discharge pipe (16) is connected to a rear coarse slag cooling slag discharger (17); a line passing through the center point of the return port (5) and perpendicular to the plane where the return port (5) is located is defined as the return port mid-vertical line; a line passing through the center point of the fine slag discharge port (9) and perpendicular to the plane where the fine slag discharge port (9) is located is defined as the fine slag discharge port mid-vertical line; the distance between the return port mid-vertical line and the fine slag discharge port mid-vertical line is less than 300 mm; a line passing through the center point of the front coal feeding port (7) and perpendicular to the plane where the front coal feeding port (7) is located is defined as is the mid-vertical line of the front coal feeding port; a line passing through the center point of the front coarse slag discharge port (12) and perpendicular to the plane where the front coarse slag discharge port (12) is located is defined as the mid-vertical line of the front coarse slag discharge port, and the distance between the mid-vertical line of the front coarse slag discharge port and the mid-vertical line of the front coal feeding port is greater than 600 mm; a line passing through the center point of the rear coal feeding port (18) and perpendicular to the plane where the rear coal feeding port (18) is located is defined as the mid-vertical line of the rear coal feeding port, a line passing through the center point of the rear coarse slag discharge port (15) and perpendicular to the plane where the rear coarse slag discharge port (15) is located is defined as the mid-vertical line of the rear coarse slag discharge port, and the distance between the mid-vertical line of the rear coarse slag discharge port and the mid-vertical line of the rear coal feeding port is greater than 600 mm; it is characterized in that Follow these steps: Retrieve the design value of the coarse slag carbon content and the design value of the fine slag carbon content designed for the circulating fluidized bed boiler, and detect the detection value of the coarse slag carbon content and the detection value of the fine slag carbon content discharged from the furnace body; Comparing the coarse slag carbon content detection value with the coarse slag carbon content design value, if the coarse slag carbon content detection value is greater than the coarse slag carbon content design value, reducing the coarse slag discharge amount through the front coarse slag cooling slag discharger (14) and the rear coarse slag cooling slag discharger (17); if the coarse slag carbon content detection value is less than the coarse slag carbon content design value, increasing the coarse slag discharge amount through the front coarse slag cooling slag discharger (14) and the rear coarse slag cooling slag discharger (17); The fine slag carbon content detection value is compared with the fine slag carbon content design value. If the fine slag carbon content detection value is greater than the fine slag carbon content design value, the fine slag discharge amount is reduced through the fine slag cooling slag discharger (11). If the fine slag carbon content detection value is less than the fine slag carbon content design value, the fine slag discharge amount is increased through the fine slag cooling slag discharger (11).

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