Circulating fluidized bed boiler suitable for high-alkali high-chlorine coal

Abstract

The utility model discloses a circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal. The circulating fluidized bed boiler comprises a hearth, a cyclone separator, a steam cooling flue and a tail flue which are connected in sequence, a water cooling screen is arranged in the hearth; the lower end of the cyclone separator is connected with a material returning device, the material returning device is connected with the lower part of the hearth through a first-stage material returning pipe and connected with an external bed through a connecting pipe, a high-temperature superheater is arranged in the external bed, and the external bed is connected with the lower part of the hearth through a second-stage material returning pipe; the steam cooling flue is divided into a steam cooling down flue and a steam cooling up flue through a longitudinal partition wall connected with the top of the steam cooling flue, and a water cooling tube bundle is arranged in the steam cooling up flue; according to the utility model, contamination and corrosion of high-alkali and high-chlorine coal for combustion to a heating surface can be prevented, damage to equipment in the boiler is avoided, and long-period stable operation of the boiler is realized.

Description

Technical Field

[0001] The utility model relates to a circulating fluidized bed boiler, in particular to a circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal. Background Technique

[0002] The content of sodium oxide (calculated by ash) in Shahu coal is generally above 4%, and the content of chlorine element is generally above 0.3%. It is typical high-alkali and high-chlorine coal. The problems of coking, fouling, corrosion and chlorine-containing pollutant emission during the utilization of this coal are extremely serious, restricting the safe, efficient and clean utilization of Shahu coal.

[0003] The existing patent CN204328985U proposes a CFB-U type radiant boiler for reducing the fouling of high-alkali coal types, which uses the combination of the furnace of a traditional CFB boiler and a U-type radiant boiler. To a certain extent, it reduces the fouling problem caused by the combustion of high-alkali metal coal types, but does not completely solve the problem of high-alkali fouling of the fuel.

[0004] Another patent CN217004446U proposes a circulating fluidized bed boiler for preventing slagging of high-alkali coal. The high-temperature flue gas generated by the furnace enters the empty flue through the cyclone separator, exchanges heat with the evaporative heating surface in the empty flue, and then is cooled by the slag screen tube to reduce the risk of fouling of the tail heating surface. However, the problem of high-chlorine corrosion has not been solved yet. As a result, the current circulating fluidized bed boiler burning Shahu coal still fails to effectively prevent fouling and corrosion problems, affecting the long-term stable operation of the boiler. Summary of the Invention

[0005] The purpose of the utility model is to aim at the above deficiencies of the prior art and provide a circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal, which can prevent the fouling and corrosion of the heating surface caused by burning high-alkali and high-chlorine coal, avoid damage to the equipment in the furnace, and realize the long-term stable operation of the boiler.

[0006] In order to achieve the above purpose, a circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal of the utility model includes a furnace, a cyclone separator, a steam-cooled flue and a tail flue connected in sequence. The lower end of the cyclone separator is connected to a loop seal; its characteristics are: a water-cooled screen is arranged in the furnace; the loop seal is connected to the lower part of the furnace through a primary return pipe, the loop seal is connected to an external bed through a connecting pipe, a high-temperature superheater is arranged in the external bed, and the external bed is connected to the lower part of the furnace through a secondary return pipe; the steam-cooled flue is divided into a steam-cooled downward flue and a steam-cooled upward flue by a longitudinal partition wall connected to its top, and a water-cooled tube bundle is arranged in the steam-cooled upward flue.

[0007] During operation, the water-cooled screen arranged in the furnace can control the bed temperature at 850 - 880 °C, effectively suppressing the release of alkali metals and chlorine elements during combustion and reducing the alkali-chlorine content in the flue gas. The high-temperature superheater is arranged in the external bed, which can avoid fouling corrosion caused by the contact of alkali-chlorine-containing flue gas with the high-temperature heating surface. The flue gas separated by the cyclone separator first enters the steam-cooled downcomer flue. The steam-cooled downcomer flue is an empty flue, which can effectively reduce the flue gas temperature and provide a basis for the downstream heating surface to avoid the fouling-sensitive interval. Subsequently, the flue gas flows into the steam-cooled upcomer flue, and the flue gas temperature is further reduced to <650 °C through the water-cooled tube bundle, completely solving the fouling corrosion problem, avoiding damage to the furnace equipment, and realizing the long-term stable operation of the boiler.

[0008] As a further improvement of the present invention, a low-temperature superheater is arranged in the steam-cooled upcomer flue at the rear side of the water-cooled tube bundle; it can exchange heat with the flue gas to improve the thermal efficiency.

[0009] As a further improvement of the present invention, an intermediate-temperature superheater can be arranged between the water-cooled tube bundle and the low-temperature superheater; an intermediate-temperature superheater can also be arranged in the external bed.

[0010] As a further improvement of the present invention, a high-stage economizer, a denitration device, a low-stage economizer, and an air preheater are successively arranged in the tail flue; the downstream heating surfaces exchange heat with the flue gas step by step to further improve the thermal efficiency.

[0011] As a further improvement of the present invention, the pitch of the water-cooled tube bundle is greater than 200 mm; this enables the water-cooled tube bundle to maintain a relatively low wall temperature, which is beneficial for reducing the flue gas temperature.

[0012] In summary, the present invention can prevent the fouling corrosion of the heating surface caused by burning high-alkali and high-chlorine coal, avoid damage to the furnace equipment, and realize the long-term stable operation of the boiler. Description of the Drawings

[0013] Figure 1 It is a schematic structural diagram of Embodiment 1 of the present invention.

[0014] Figure 2 It is a schematic structural diagram of Embodiment 2 of the present invention. Detailed Embodiments

[0015] The present invention will be further described below with reference to the drawings.

[0016] Embodiment 1

[0017] As Figure 1As shown in the figure, a circulating fluidized bed boiler applicable to high-alkali and high-chlorine coal in this embodiment includes a furnace 1, a cyclone separator 2, a steam-cooled flue 3, and a tail flue 4 connected in sequence; a single-layer or multi-layer water-cooled screen 5 is provided in the furnace 1; the lower end of the cyclone separator 2 is connected to a return feeder 6, the return feeder 6 is connected to the lower part of the furnace through a primary return pipe 7, the return feeder 6 is also connected to an external bed 9 through a connecting pipe 8, a high-temperature superheater 10 is provided in the external bed 9, and the external bed 10 is connected to the lower part of the furnace through a secondary return pipe 11; the steam-cooled flue 3 is divided into a steam-cooled downcomer flue 13 and a steam-cooled upcomer flue 14 by a longitudinal partition wall 12 connected to its top, and a water-cooled tube bundle 15 with a large pitch, an intermediate-temperature superheater 16, and a low-temperature superheater 17 are arranged in sequence in the steam-cooled upcomer flue 14, and the pitch of the water-cooled tube bundle 15 is greater than 200 mm; a upper-stage economizer 18, a denitration device 19, a lower-stage economizer 20, and an air preheater 21 are arranged in sequence in the tail flue 4;

[0018] A heat exchange tube bundle is provided on the side wall of the steam-cooled flue 3, and low-temperature steam is introduced into the heat exchange tube bundle to exchange heat with the flue gas; the boiler feed water sequentially passes through the lower-stage economizer 20, the upper-stage economizer 18, the water-cooled wall in the furnace 1, and the water-cooled screen 5 to absorb heat. After the saturated steam is sequentially heat-exchanged through the cyclone separator 2, the steam-cooled flue 3, the low-temperature superheater 17, and the intermediate-temperature superheater 16, it is sent to the high-temperature superheater 10; during use, the bed temperature can be controlled at 850-880 °C through the water-cooled screen 5 in the furnace 1, effectively inhibiting the precipitation of alkali metals and chlorine elements in the high-alkali and high-chlorine coal during the combustion process and reducing the alkali and chlorine content in the flue gas; the high-temperature dusty flue gas at the outlet of the furnace 1 is separated by the cyclone separator 2, and the circulating ash enters the return feeder 6. In the return feeder 6, it is divided into two parts. One part of the circulating ash exchanges heat with the high-temperature superheater 10 in the external bed 9 and then returns to the furnace, and the other part directly returns to the furnace; the high-temperature superheater 10 is arranged in the external bed 9, which can avoid fouling corrosion caused by the contact of the alkali and chlorine-containing flue gas with the high-temperature heating surface; the flue gas separated by the cyclone separator 2 first enters the steam-cooled downcomer flue 13. The steam-cooled downcomer flue 13 is an empty flue. After the flue gas exchanges heat with the warm steam in the heat exchange tube bundle on its side wall, the flue gas temperature can be effectively reduced, providing a basis for the downstream heating surface to avoid the fouling-sensitive interval. Subsequently, the flue gas turns and flows into the steam-cooled upcomer flue 14, and the flue gas temperature is further reduced to <650 °C through the water-cooled tube bundle 15, completely deviating from the fouling-sensitive temperature interval, thoroughly solving the fouling corrosion problem of the downstream heating surface, avoiding damage to the equipment in the furnace, and realizing the long-term stable operation of the boiler;

[0019] The downstream intermediate-temperature superheater 16, low-temperature superheater 17, upper-stage economizer 18, lower-stage economizer 20, and air preheater 21 exchange heat with the flue gas step by step to further improve the thermal efficiency;

[0020] Embodiment 2

[0021] As Figure 2As shown, the difference between this embodiment and the first embodiment is only that the medium-temperature superheater 16 is arranged in the external bed 9, and the same technical effect can be achieved.

[0022] The above embodiments have been described, but it should be understood that the above embodiments are only for illustrative and explanatory purposes, and are not intended to limit the present invention to the scope of the described embodiments.

Claims

1. A circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal, comprising a furnace, a cyclone separator, a steam cooling flue and a tail flue connected in sequence, wherein the lower end of the cyclone separator is connected to a return device; characterized in that: A water-cooling screen is provided in the furnace; the returner is connected to the lower part of the furnace through a first-level return pipe, the returner is connected to the external bed through a connecting pipe, a high-temperature superheater is provided in the external bed, and the external bed is connected to the lower part of the furnace through a second-level return pipe; the steam-cooled flue is divided into a steam-cooled descending flue and a steam-cooled ascending flue by a longitudinal partition wall connected to the top thereof, and a water-cooled tube bundle is provided in the steam-cooled ascending flue.

2. A circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal as claimed in claim 1, characterized in that: A low-temperature superheater is arranged in the steam-cooled ascending flue at the rear side of the water-cooled tube bundle.

3. A circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal as claimed in claim 2, characterized in that: A medium-temperature superheater is arranged between the water-cooled tube bundle and the low-temperature superheater.

4. A circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal as claimed in claim 2, characterized in that: A medium-temperature superheater is arranged in the external bed.

5. A circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal according to any one of claims 1 to 4, characterized in that: In the tail flue, an upper economizer, a denitrification device, a lower economizer and an air preheater are arranged in sequence.

6. A circulating fluidized bed boiler suitable for high-alkali and high-chlorine coal as claimed in claim 5, characterized in that: The pitch of the water-cooling tube bundle is greater than 200 mm.

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