Hearth structure of circulating fluidized bed boiler for purely burning furfural residues

Abstract

The invention discloses a hearth structure of a circulating fluidized bed boiler for purely burning furfural residues, and solves the problems of how to ensure sufficient burning of burning materials and how to avoid smoke return and fire channeling phenomena when the furfural residues enter the hearth, and how to ensure that slag is easy to form on a heating surface in the hearth and how to avoid the occurrence of the phenomena of smoke return and fire channeling when the furfural residues enter the hearth. A secondary air lower annular air bellow (13) and a secondary air upper annular air bellow (14) are respectively arranged on the outer side wall of the hearth (2) at the dense-phase area (11); the air distribution quantity of a secondary air lower branch air pipe (15) is equal to that of the secondary air upper annular air bellow (14); the ratio of the secondary air distribution quantity to the primary air distribution quantity in the hearth is 55: 45; a furfural residue feeding port (17) is arranged on the outer side wall of the hearth (2) between the secondary air lower annular air bellow and the secondary air upper annular air bellow, the shrinkage ratio of the hearth on the dense-phase area (11) is 40%, and the pressure intensity at the furfural residue feeding port in the dense-phase area of the hearth is zero by setting the air inducing capacity of an induced draft fan (19).

Description

Technical Field

[0001] The invention relates to a circulating fluidized bed boiler, in particular to a furnace structure of a circulating fluidized bed boiler for burning pure furfural slag. Background Art

[0002] Furfural slag, as a biomass material, is a biomass waste produced after the furfural is extracted. Acid, sulfur and chlorine components remain in the furfural slag, and it is rich in alkali metals. It has the characteristics of high moisture content and low calorific value. How to treat furfural slag in an environmentally friendly way is a difficult problem that relevant enterprises and environmental protection departments urgently need to solve. In the existing technology, furfural slag is burned by a small-capacity chain furnace, but this treatment method has the defect of limited furfural slag treatment capacity, which cannot meet the market requirements for large-scale treatment of furfural slag. At the same time, due to the characteristics of furfural slag, there is also the problem of easy slagging in the furnace. How to develop a circulating fluidized bed boiler suitable for pure burning of furfural slag through the circulating fluidized bed boiler technology with fluid state reconstruction, and the treatment of furfural slag covers 10-62 tons per hour (based on 45% moisture content), so as to achieve the ability to digest furfural slag in large quantities and turn waste into treasure to produce steam with a steam pressure of 3.82-13.73MPa, has become a problem that needs to be solved on site.

[0003] Furfural slag has the characteristics of small particle size and light specific gravity. When burning in the furnace, there is no large particle material to stabilize the bed pressure and bed temperature, and the suspended combustion share in the upper part of the furnace is relatively large. The conventional flow rate design of 5 meters per second in the circulating fluidized bed furnace is completely unsuitable for the combustion and heat transfer of furfural slag fuel. The fuel has a high alkali metal content, and K in the ash 2 O content is about 15%, the melting point of fuel ash is low, and it is easy to produce adhesion in the furnace, resulting in poor circulation and fluidization of the fuel in the furnace; the primary air ratio of conventional circulating fluidized bed boilers is designed to be about 50-60%. The function of the primary air is mainly to ensure fluidization, and the function of the secondary air is mainly to strengthen the mixed combustion of the fuel. However, for the circulating fluidization of furfural slag, due to the fine particle size and small specific gravity of furfural slag, there are very few coarse particles in the lower part, and the proportion of upper combustion is bound to increase. How to design the primary and secondary air ratio to meet the characteristics of furfural slag combustion requires exploration and experimentation; in addition, in the process of transporting a large amount of furfural slag into the furnace, it is necessary to ensure normal circulation and fluidization in the furnace. At the same time, it is also a difficult problem to avoid the occurrence of smoke return and fire when the light furfural slag enters the furnace to the greatest extent. Summary of the invention

[0004] The invention provides a furnace structure of a circulating fluidized bed boiler for burning pure furfural slag, solving the technical problems of how to ensure full combustion of fuel and no slagging on the heating surface in the furnace, and how to avoid smoke return and crossfire when furfural slag enters the furnace.

[0005] The present invention solves the above technical problems through the following technical solutions: A furnace structure of a circulating fluidized bed boiler for pure burning furfural slag comprises a steel frame, on which a furnace and a cyclone separator are respectively arranged, the furnace is connected with the upper cylinder of the cyclone separator through an upper furnace outlet flue, the lower end of the upper cylinder is connected with the lower cone of the cyclone separator, the lower end of the lower cone is connected with the furnace through a material returning device, a separator central outlet cylinder is arranged at the top of the upper cylinder, a tail flue is connected to the other end of the separator central outlet cylinder, and an induced draft fan is connected to the outlet of the tail flue; a water-cooled air chamber is arranged at the lower end of the furnace, and an air distribution plate is arranged at the connection between the water-cooled air chamber and the furnace; a primary air box and an ignition device are connected to the water-cooled air chamber; the lower part of the furnace is a dense phase zone, and the upper part of the furnace is a dilute phase zone; a secondary air lower annular wind box and a secondary air upper annular wind box are respectively arranged on the outer side wall of the furnace in the dense phase zone, and the secondary air lower annular wind box and the secondary air upper annular wind box are The secondary air lower annular bellows are arranged parallel to each other and at intervals, and are connected to the dense phase zone through the secondary air lower branch duct, and the secondary air upper annular bellows are connected to the dense phase zone through the secondary air upper branch duct, and the air distribution volume of the secondary air lower branch duct is equal to the air distribution volume of the secondary air upper annular bellows; the ratio of the secondary air distribution volume to the primary air distribution volume in the furnace is 55:45; a furfural slag feeding port is arranged on the outer wall of the furnace between the secondary air lower annular bellows and the secondary air upper annular bellows, the distance H2 between the furfural slag feeding port and the air distribution plate is 4.5 meters, the distance H1 between the entrance of the secondary air lower branch duct on the furnace and the air distribution plate is 2.5 meters, and the distance H3 between the secondary air upper branch duct and the air distribution plate is 5.5-6 meters; the contraction ratio of the furnace in the dense phase zone is 40%, and the height of the dense phase zone is 9-11 meters; by setting the induced draft capacity of the induced draft fan, the pressure at the furfural slag feeding port in the dense phase zone of the furnace is made to be 0.

[0006] The cross-sectional flue gas velocity in the furnace is 3.6-4.2 meters per second; the design temperature of the furnace is 740-780℃; dense pins are arranged in the dense phase area, and a wear-resistant layer is coated on the dense pins; an online bottom material adding system is arranged on the furnace to add coarser particle bottom material to the dense phase area of ​​the furnace.

[0007] An anti-corrosion coating is provided on the inner wall of the upper furnace in the dilute phase zone; a high-temperature superheating screen and a medium-temperature superheating screen are provided in the dilute phase zone; and a cyclone separator realizes the circulation of flue gas particles with a particle size greater than 50 microns.

[0008] The present invention realizes the full combustion of a large amount of furfural slag, solves the problem that the furfural slag feeding port is too low, resulting in high furnace back pressure and difficulty in entering the furnace, while the feeding port is too high, resulting in no combustible materials in the lower part of the circulating fluidized bed, and the coarse particles on the bed lose the function of stabilizing the bed temperature, which is not conducive to combustion; the secondary air of the present invention is arranged in two layers, upper and lower, and an additional layer of secondary air is arranged above the feeding port, which can ensure that after the furfural slag fuel enters the furnace, the gas quickly parsed out can be completely burned. In addition, since the position of the feeding port cannot be too low and the height from the air distribution plate is higher than that of a conventional coal-fired boiler, it is necessary to arrange a layer of secondary air at the lower part of the feeding port to ensure effective connection with the primary air, and the height of the secondary air lower inlet must ensure the normal operation of the circulating combustion system; the present invention increases the pressure head of the induced draft fan, creatively expands the negative pressure area in the furnace, and lowers the zero pressure area to the furfural slag feeding port, which completely solves the occurrence of smoke return and fire crossover when the furfural slag enters the furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the structure of the present invention; Figure 2 Schematic diagram of the structure from a top view. DETAILED DESCRIPTION

[0010] The present invention is described in detail below in conjunction with the accompanying drawings: A furnace structure of a circulating fluidized bed boiler for pure furfural slag combustion, comprising a steel frame 1, a furnace 2 and a cyclone separator are arranged on the steel frame 1, the furnace 2 is connected to an upper cylinder 3 of the cyclone separator through an upper furnace outlet flue 4, a lower cone 5 of the cyclone separator is connected to the lower end of the upper cylinder 3, the lower end of the lower cone 5 is connected to the furnace 2 through a return device 6, a separator center outlet tube 18 is arranged at the top of the upper cylinder 3, a tail flue is connected to the other end of the separator center outlet tube 18, and a tail flue is connected to the outlet of the tail flue. A draft fan 19 is connected; a water-cooled air chamber 7 is arranged at the lower end of the furnace 2, and an air distribution plate 8 is arranged at the connection between the water-cooled air chamber 7 and the furnace 2; a primary air box 9 and an ignition device 10 are connected to the water-cooled air chamber 7; the lower part of the furnace 2 is a dense phase area 11, and the upper part of the furnace 2 is a dilute phase area 12; a secondary air lower annular wind box 13 and a secondary air upper annular wind box 14 are respectively arranged on the outer side wall of the furnace 2 at the dense phase area 11, and the secondary air lower annular wind box 13 and the secondary air upper annular wind box 14 are parallel to each other and spaced apart, and the secondary air lower annular wind box 13 passes through the secondary The lower branch duct 15 is connected to the dense phase area 11, and the secondary air upper annular wind box 14 is connected to the dense phase area 11 through the secondary air upper branch duct 16. The air distribution volume of the secondary air lower branch duct 15 is equal to the air distribution volume of the secondary air upper annular wind box 14, or the air distribution volume of the secondary air lower branch duct 15 is 51.2% of the total secondary air volume, and the air distribution volume of the secondary air upper branch duct 16 is 48.8% of the total secondary air volume. This secondary air distribution method in the furnace is designed for the characteristics of the lighter furfural slag having a higher upper combustion share in the furnace. The strategy can ensure that the gas that is quickly parsed after the fuel enters the furnace can be completely burned; the ratio of the secondary air distribution volume to the primary air distribution volume in the furnace is 55:45; a furfural slag feeding port 17 is provided on the outer wall of the furnace 2 between the secondary air lower annular wind box 13 and the secondary air upper annular wind box 14, and the distance H2 between the furfural slag feeding port 17 and the air distribution plate 8 is 4.5 meters, the distance H1 between the entrance of the secondary air lower branch duct 15 on the furnace 2 and the air distribution plate 8 is 2.5 meters, and the distance H3 between the secondary air upper branch duct 16 and the air distribution plate 8 is 5.5-6 meters; the contraction ratio of the furnace 2 on the dense phase area 11 is 40%, the ratio of the designed boiler bed section B1 to the furnace section B2 is 40:100, and the height of the dense phase area 11 is 9-11 meters. The above indicators are all explored through repeated on-site tests; by setting the induced draft capacity of the induced draft fan 19, the pressure at the furfural slag feeding port 17 in the dense phase area 11 of the furnace 2 is 0. Since the exhaust of flue gas in the entire boiler system mainly relies on the induced draft suction of the tail induced draft fan 19, the power of the existing circulating fluidized bed induced draft fan 19 is based on setting the negative pressure area after the upper outlet of the furnace, that is, the 0 pressure setting is generally set at the top position of the furnace. The present invention expands the negative pressure area and lowers the 0 pressure area to the furfural slag feeding port on the furnace, creatively solving the problem that the furfural slag with light specific gravity and small particle size is easy to return smoke and crossfire in the direction of the feeding device when entering the furnace. .

[0011] The flue gas cross-sectional velocity in the furnace 2 is 3.6-4.2 meters per second; the furnace design temperature is 740-780℃; dense pins are arranged in the dense phase area 11, and a wear-resistant layer is coated on the dense pins; the high-temperature superheating screen and the medium-temperature superheating screen 20 are arranged in the furnace, and the pipe material is TP347H with better corrosion resistance: according to the characteristics of the fuel, its fly ash is easy to adhere to the heating surface pipe with a wall temperature of 500-600℃ and cause under-scale corrosion, while the medium temperature of the high-temperature superheater is as high as 540℃, and the wall temperature is above 550-580℃. Therefore, the high-temperature superheater is arranged in the furnace, and a large amount of reflux material attached to the wall flushes the heating surface to avoid corrosion caused by ash accumulation. This arrangement solves the corrosion problem of the high-temperature heating surface.

[0012] An anti-corrosion coating layer is provided on the inner side wall of the furnace 2 at the upper part of the dilute phase zone 12; the cyclone separator realizes the circulating fluidization of flue gas particles with a particle size greater than 50 microns, and the furnace 2 is connected to the upper cylinder 3 of the cyclone separator through the furnace upper outlet flue 4, and the separator throat C where the furnace upper outlet flue 4 enters the upper cylinder 3 of the cyclone separator is reduced, and the diameter QD of the upper cylinder 3 of the cyclone separator is increased, so that the speed of the flue gas carrying the circulating particles in the furnace 2 increases from 3.6-4.2 meters per second to 30 meters per second, so that the ash particles entering the cyclone separator from the dilute phase zone 12 will not enter the separator center outlet tube 18 to escape, and the separator efficiency is improved through the above effective means, so that the ability of the separator to capture fine particles is greatly improved, ensuring the bed quality in the furnace, thereby creating favorable conditions for the stability and environmental protection of the boiler, and prolonging the residence time of the particles in the furnace, which is beneficial to the combustion of furfural slag and fine fuel. At the same time, the limestone desulfurization system is put into use in front of the furnace, which is beneficial to the effective utilization of limestone, improves the desulfurization efficiency in the furnace, and controls the SO2 emissions at the furnace outlet.

[0013] For existing circulating fluidized bed boilers, the furnace requires both fine particles for heat transfer and coarse particles for stabilizing the bed pressure and bed temperature. However, when burning furfural slag, the fuel basically does not have coarser particles. Therefore, an online bottom material adding system is set on the furnace to add coarser bottom material particles to the dense phase area of ​​the furnace to ensure that the boiler can operate stably and reliably.

Claims

1. A furnace structure of a circulating fluidized bed boiler for burning pure furfural slag, comprising a steel frame (1), a furnace (2) and a cyclone separator are arranged on the steel frame (1), the furnace (2) is connected to an upper cylinder (3) of the cyclone separator through an upper furnace outlet flue (4), a lower cone (5) of the cyclone separator is connected to the lower end of the upper cylinder (3), the lower end of the lower cone (5) is connected to the furnace (2) through a material return device (6), and a separator is arranged at the top of the upper cylinder (3). A central outlet tube (18) is provided at the other end of the separator central outlet tube (18), a tail flue is connected to the other end of the tail flue, and an induced draft fan (19) is connected to the outlet of the tail flue; a water-cooled air chamber (7) is provided at the lower end of the furnace (2), and an air distribution plate (8) is provided at the connection between the water-cooled air chamber (7) and the furnace (2); a primary wind box (9) and an ignition device (10) are connected to the water-cooled air chamber (7); the lower part of the furnace (2) is a dense phase zone (11), and the upper part of the furnace (2) is a dilute phase zone (12); the characteristics are as follows: A secondary air lower annular wind box (13) and a secondary air upper annular wind box (14) are respectively arranged on the outer side wall of the furnace (2) at the dense phase zone (11). The secondary air lower annular wind box (13) and the secondary air upper annular wind box (14) are parallel to each other and arranged at intervals. The secondary air lower annular wind box (13) is connected to the dense phase zone (11) through a secondary air lower branch air duct (15). The secondary air upper annular wind box (14) is connected to the dense phase zone (11) through a secondary air upper branch air duct (16). The air distribution volume of the secondary air lower branch air duct (15) is equal to the air distribution volume of the secondary air upper annular wind box (14). The ratio of the secondary air distribution volume to the primary air distribution volume in the furnace is 55:

45. The secondary air lower annular wind box (13) is connected to the dense phase zone (11) through a secondary air lower branch air duct (16). A furfural slag feeding port (17) is arranged on the outer wall of the furnace (2) between the secondary air upper annular wind box (14) and the furnace (2); a distance H2 between the furfural slag feeding port (17) and the air distribution plate (8) is 4.5 meters; a distance H1 between an entrance of the secondary air lower branch duct (15) on the furnace (2) and the air distribution plate (8) is 2.5 meters; a distance H3 between the secondary air upper branch duct (16) and the air distribution plate (8) is 5.5-6 meters; a contraction ratio of the furnace (2) on the dense phase zone (11) is 40%, and a height of the dense phase zone (11) is 9-11 meters; and by setting the induced draft capacity of the induced draft fan (19), the pressure at the furfural slag feeding port (17) in the dense phase zone (11) of the furnace (2) is made zero.

2. The furnace structure of a circulating fluidized bed boiler for pure burning of furfural slag according to claim 1, characterized in that: The cross-sectional flue gas velocity in the furnace (2) is 3.6-4.2 meters per second; the furnace design temperature is 740-780°C; dense pins are arranged in the dense phase area (11), and a wear-resistant layer is coated on the dense pins; an online bottom material adding system is arranged on the furnace to add coarser particle bottom material to the dense phase area (11) of the furnace (2).

3. The furnace structure of a circulating fluidized bed boiler for pure burning of furfural slag according to claim 1 or 2, characterized in that: An anti-corrosion coating layer is provided on the inner side wall of the upper furnace (2) of the dilute phase zone (12); a high-temperature superheating screen and a medium-temperature superheating screen (20) are provided in the dilute phase zone (12); and a cyclone separator realizes the circulation of flue gas particles with a particle size greater than 50 micrometers.

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