Circulating fluidized bed boiler for burning high-alkali coal

Abstract

The utility model discloses a circulating fluidized bed boiler for burning high-alkali coal, which comprises a hearth, a cyclone separator, a middle flue and a tail flue which are connected in sequence, and the lower end of the cyclone separator is connected with the hearth through a material returning device; a high-temperature superheater is arranged in the hearth; the middle flue is divided into a downstream flue and an upstream flue through a longitudinal water-cooling partition wall connected with the top of the middle flue, and water-cooling heat exchange tube bundles are arranged on the two side faces of the longitudinal water-cooling partition wall; a water cooling screen is arranged in the downstream flue, and a water cooling tube bundle is arranged in the upstream flue; the utility model can solve the problem of contamination and corrosion of the heating surface of the boiler, is suitable for coal types with fluctuating alkali metal content, is not influenced by the source of mixed combustion fuel or modified substances, does not increase the manufacturing and operating cost of the boiler, and can stably and efficiently operate for a long time.

Description

Technical Field

[0001] The utility model relates to a circulating fluidized bed boiler, in particular to a circulating fluidized bed boiler burning high-alkali coal. Background Art

[0002] The vast Gobi Desert stretching 220 kilometers from east to west in Xinjiang Zhundong Coalfield contains 390 billion tons of coal resources, which is very rich. According to my country's annual coal consumption, the Zhundong Coalfield alone is enough for the whole country to use for 100 years, which can provide a strong guarantee for my country's energy security. However, the overall content of Na2O and K2O in its coal ash is more than 6%, which is much higher than that of conventional power coal. The boiler will have serious contamination problems during the combustion process, which restricts the safe, efficient and clean use of Zhundong coal.

[0003] At present, in order to solve the contamination problem of burning high-alkali coal, CN105805736B proposes a circulating fluidized bed boiler and a method for preventing the contamination of its heating surface by alkali metal compounds. A high-temperature evaporation heating surface is arranged in the tail flue to reduce the flue gas temperature, so that a small part of the alkali metal compounds in the flue gas solidifies into a solid state. However, the contamination blocks condensed on the wall are easy to fall and clog the tail heating surface, affecting the stable operation of the boiler.

[0004] Another patent CN217004446U proposes a circulating fluidized bed boiler that prevents high-alkali coal from slagging. It uses the empty flue to reduce the high-temperature flue gas at the boiler outlet, and then cools it through the slag condensing pipe to reduce the risk of contamination on the tail heating surface. However, the flue gas enters the empty flue with uneven flow field, and the heat exchange capacity decreases. It cannot effectively reduce the flue gas temperature, and the effect of preventing contamination and corrosion is limited, affecting the stable operation of the boiler. As a result, the existing circulating fluidized bed boilers burning high-alkali coal have not completely solved the contamination and corrosion problem, affecting the long-term stable operation of the boiler. Summary of the invention

[0005] The purpose of the utility model is to provide a circulating fluidized bed boiler burning high-alkali coal in view of the above-mentioned deficiencies in the prior art, which can solve the problem of contamination and corrosion of the boiler heating surface, is suitable for coal types with fluctuating alkali metal content, is not affected by the source of blended fuel or modified substances, does not increase the manufacturing and operating costs of the boiler, and can operate stably and efficiently for a long time.

[0006] In order to achieve the above-mentioned purpose, the utility model discloses a circulating fluidized bed boiler burning high-alkali coal, comprising a furnace, a cyclone separator, an intermediate flue and a tail flue connected in sequence, wherein the lower end of the cyclone separator is connected to the furnace through a return device; the utility model is characterized in that a high-temperature superheater is arranged in the furnace; the intermediate flue is divided into a descending flue and an ascending flue by a longitudinal water-cooled partition wall connected to the top thereof, and water-cooled heat exchange tube bundles are arranged on both sides of the longitudinal water-cooled partition wall; a water-cooled screen is arranged in the descending flue, and a water-cooled tube bundle is arranged in the ascending flue.

[0007] In use, the high-temperature superheater is arranged in the furnace. By utilizing the scouring of a large amount of fluidized circulating materials in the furnace, corrosion caused by alkali metal contamination on the heating surface can be avoided. The flue gas first flows through the downward flue of the intermediate flue, and the temperature of the flue gas is rapidly reduced through the water-cooled heat exchange tube bundles and water-cooled screens of the longitudinal water-cooled partition wall. The temperature of the working medium flowing in the water-cooled screen is not higher than its saturation temperature. Therefore, the wall temperature of the heating surface is relatively low. Even though the flue gas temperature is high, gaseous alkali metal and alkaline earth metal compounds in the flue gas rapidly cool and solidify during the process of approaching the wall surface of the heating surface, rather than adhering to the heating surface in a liquid form, thus avoiding the contamination problem of the heating surface. Moreover, the water-cooled screen can make the flue gas flow field in the downward flue more uniform, which is beneficial to the heat exchange between the heating surface and the flue gas and better reduces the flue gas temperature. Then, the flue gas is further cooled by the water-cooled tube bundles, causing the alkali metal compounds therein to cool and solidify into a solid state, completely solving the problem of contamination and corrosion of the downstream heating surface. It is not affected by the blended fuel or the source of the modified substance, and does not increase the manufacturing and operating costs of the boiler, and can operate stably and efficiently for a long time.

[0008] As a further improvement of the present utility model, the side walls of the downward flue and the upward flue are both steam-cooled casings, and steam heat exchange tube bundles are provided on both steam-cooled casings. The temperature of the flue gas can be further reduced through the steam heat exchange tube bundles. Even for coal types with fluctuating alkali metal content, the downstream heating surface can be avoided from the contamination-sensitive temperature range and prevent contamination and corrosion.

[0009] As a further improvement of the present utility model, a medium-temperature superheater and a low-temperature superheater are sequentially arranged in the upward flue behind the water-cooled tube bundles. Heat can be exchanged with the flue gas step by step to further improve the thermal efficiency.

[0010] As a further improvement of the present utility model, an economizer and an air preheater are sequentially arranged in the tail flue. Heat can be exchanged with the flue gas step by step to further improve the thermal efficiency.

[0011] In summary, the present utility model can solve the problem of contamination and corrosion of the boiler heating surface, is applicable to coal types with fluctuating alkali metal content, is not affected by the blended fuel or the source of the modified substance, and does not increase the manufacturing and operating costs of the boiler, and can operate stably and efficiently for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic structural diagram of an embodiment of the present utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] The present utility model will be further described below with reference to the drawings.

[0014] As shown in Figure 1As shown in the figure, a circulating fluidized bed boiler burning high-alkali coal in this embodiment includes a furnace 1, a cyclone separator 2, an intermediate flue 3, and a tail flue 4 connected in sequence. The lower end of the cyclone separator 2 is connected to the furnace through a loop seal 5; a high-temperature superheater 6 is provided in the furnace 1; the intermediate flue 3 is divided into a downward flue 8 and an upward flue 9 by a longitudinal water-cooled partition wall 7 connected to its top. The side walls of the downward flue 8 and the upward flue 9 are both steam-cooled casings, and steam heat exchange tube bundles 10 are provided on the steam-cooled casings. A water-cooled panel 11 is provided in the downward flue 8, and water-cooled heat exchange tube bundles 12 are provided on both sides of the longitudinal water-cooled partition wall 7; in the upward flue 9, a water-cooled tube bundle 13, an intermediate-temperature superheater 14, and a low-temperature superheater 15 are provided in sequence from bottom to top; in the tail flue 4, an economizer 16 and an air preheater 17 are provided in sequence.

[0015] During use, the high-temperature superheater 6 is arranged in the furnace 1. By using the erosion of a large amount of fluidized circulating materials in the furnace, the corrosion caused by the contamination of alkali metals on the heating surface can be avoided; the flue gas first flows through the downward flue 8 of the intermediate flue 3, and the temperature of the flue gas is quickly reduced by the steam heat exchange tube bundle 10 on the side wall of the downward flue 8, the water-cooled heat exchange tube bundle 12 of the longitudinal water-cooled partition wall 7, and the water-cooled panel 11. The temperature of the working medium flowing in the water-cooled panel 11 is not higher than its saturation temperature, so the wall temperature of the heating surface is relatively low. Even though the flue gas temperature is relatively high, the gaseous alkali metals and alkaline earth metal compounds in the flue gas quickly cool and solidify during the process of approaching the wall surface of the heating surface, rather than adhering to the heating surface in a liquid state, thus avoiding the problems of contamination and corrosion of the heating surface; moreover, the water-cooled panel can make the flue gas flow field in the downward flue more uniform, which is beneficial to the heat exchange between the heating surface and the flue gas and better reduces the flue gas temperature; then the flue gas is further cooled by the water-cooled tube bundle 13, so that the alkali metal compounds in it cool and solidify into a solid state. Even for coal types with fluctuating alkali metal contents, the downstream heating surfaces can be avoided from the contamination-sensitive temperature range, completely solving the problems of contamination and corrosion of the downstream heating surfaces. It is not affected by the blended fuel or the source of the modified substance, and does not increase the boiler manufacturing and operation costs, and can operate stably and efficiently for a long time;

[0016] The intermediate-temperature superheater 14, the low-temperature superheater 15, the economizer 16, and the air preheater 17 can exchange heat with the flue gas step by step to further improve the thermal efficiency;

[0017] The above embodiments have been described, but it should be understood that the above embodiments are only for the purpose of illustration and example, and are not intended to limit the present invention to the scope of the described embodiments.

Claims

1. A circulating fluidized bed boiler burning high-alkali coal, comprising a furnace, a cyclone separator, an intermediate flue and a tail flue connected in sequence, wherein the lower end of the cyclone separator is connected to the furnace through a return device; characterized in that: A high-temperature superheater is arranged in the furnace; the middle flue is divided into a descending flue and an ascending flue by a longitudinal water-cooled partition wall connected to the top thereof, and water-cooled heat exchange tube bundles are arranged on both sides of the longitudinal water-cooled partition wall; a water-cooled screen is arranged in the descending flue, and a water-cooled tube bundle is arranged in the ascending flue.

2. A circulating fluidized bed boiler burning high-alkali coal as claimed in claim 1, characterized in that: The side walls of the descending flue and the ascending flue are both steam-cooled walls, and the steam-cooled walls are provided with steam heat exchange tube bundles.

3. A circulating fluidized bed boiler burning high-alkali coal as claimed in claim 1 or 2, characterized in that: A medium-temperature superheater and a low-temperature superheater are arranged in sequence in the ascending flue at the rear side of the water-cooled tube bundle.

4. A circulating fluidized bed boiler burning high-alkali coal as claimed in claim 3, characterized in that: Economizer and air preheater are arranged in the tail flue in sequence.

Images