A method for regulating bed temperature of circulating fluidized bed boiler

Abstract

The present invention provides a method for regulating the bed temperature of a circulating fluidized bed boiler. The method comprises: in a circulating fluidized bed boiler, mixing an optional water-coal slurry and raw coal and performing a combustion reaction; during the combustion reaction, adjusting the proportion of the water-coal slurry relative to the raw coal according to the load value of the circulating fluidized bed boiler, and the load value of the circulating fluidized bed boiler is positively correlated with the proportion of the water-coal slurry relative to the raw coal, so that the bed temperature of the circulating fluidized bed boiler is maintained at 800-900°C. The present invention achieves flexible regulation of the bed temperature by adjusting the ratio of water-coal slurry and raw coal. The bed temperature can be generally controlled at 800-900°C within the range of full load to 25% load, which can reduce flue gas pollutant emissions and reduce costs while ensuring high combustion efficiency; in addition, the method of the present application is not restricted by the operating load of the circulating fluidized bed boiler, has good bed temperature regulation capability, and the method of the present application is simple and easy to implement, which can reduce operating risks.

Description

Technical Field

[0001] The invention relates to the technical field of clean coal power generation, and in particular to a method for regulating the bed temperature of a circulating fluidized bed boiler. Background Art

[0002] Circulating fluidized bed combustion technology has been rapidly promoted and applied in my country in recent years due to its wide fuel adaptability, high utilization rate, and low pollutant emissions. Bed temperature restriction is an important control parameter for the economic and environmental performance of circulating fluidized bed boilers. It is generally believed that the appropriate bed temperature of circulating fluidized bed boilers is in the range of 800-900°C, but affected by factors such as coal quality and regulation characteristics, the bed temperature of circulating fluidized bed boilers in actual operation is polarized - when the load is high, the bed temperature is high (up to 1050°C) and the combustion efficiency is high, but the pollutant emissions are also relatively high, and there is a risk of coking; when the load is low, the bed temperature is low (the lowest is even only 700°C), the combustion efficiency is low, and the consumption of limestone desulfurizer and denitrification reducing agent is large.

[0003] Engineering practice shows that combustion adjustments can only be made by optimizing bed pressure, optimizing the ratio of primary and secondary air, and other measures, and the bed temperature can generally be adjusted slightly, by only 5 to 10°C. If a higher degree of bed temperature reduction is to be achieved, an external heat exchanger must be used, which requires a huge investment. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for adjusting the bed temperature of a circulating fluidized bed boiler to solve the problem in the prior art that the bed temperature of the circulating fluidized bed boiler cannot be adjusted over a large range and more pollutants are generated.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for regulating the bed temperature of a circulating fluidized bed boiler is provided, the method comprising: in a circulating fluidized bed boiler, mixing optional water-coal slurry and raw coal and carrying out a combustion reaction; during the combustion reaction, adjusting the proportion of the water-coal slurry to the raw coal according to the load value of the circulating fluidized bed boiler, and the load value of the circulating fluidized bed boiler is positively correlated with the proportion of the water-coal slurry to the raw coal, so that the bed temperature of the circulating fluidized bed boiler is maintained at 800-900°C.

[0006] Furthermore, in the process of mixing the optional water-coal slurry and raw coal, the amount of water-coal slurry added is controlled to be 24% to 36% of the mass of the raw coal at full load, 18% to 24% of the mass of the raw coal at 75% to 100% load, 6% to 18% of the mass of the raw coal at 50% to 75% load, and 0% to 6% of the mass of the raw coal at 25% to 50% load, so that the bed temperature is 850 to 900°C from full load to 50% load, and 800 to 850°C from 50% load to 25% load.

[0007] Furthermore, the amount of water-coal slurry added at full load is 24% to 36% of the mass of the raw coal, the amount of water-coal slurry added at 75% load is 18% to 24% of the mass of the raw coal, the amount of water-coal slurry added at 50% load is 6% to 18% of the mass of the raw coal, and the amount of water-coal slurry added at 25% load is 0% to 6% of the mass of the raw coal.

[0008] Furthermore, the circulating fluidized bed boiler comprises: a furnace 1, a separator 2, a return feeder 3, a tail flue 4, a tail flue 4, an air distribution device 6, an air inlet is arranged at the bottom of the furnace 1, and a coal feeding port 5, a water-coal slurry feeding port 7, and a combustion flue gas outlet are arranged on the side wall; the coal feeding port 5 is used to add raw coal, the water-coal slurry feeding port 7 is used to add water-coal slurry, and the combustion flue gas outlet is used to discharge the combustion flue gas generated by the combustion reaction; wherein the water-coal slurry feeding port 7 is at the same height as the secondary air port of the upper layer of the circulating fluidized bed boiler; the secondary air port 7 is provided at the same height as the secondary air port of the upper layer of the circulating fluidized bed boiler; The inlet is arranged in the reverse zone at the lower part of the furnace 1; the separator 2 has a separator inlet, a separator gas phase outlet and a separator solid phase outlet, the separator inlet is connected to the combustion flue gas outlet, and the separator 2 is used for gas-solid separation of the combustion flue gas to obtain fuel and flue gas; the returner 3 is located below the separator 2 and is connected to the separator solid phase outlet; the returner 3 is also provided with a return port, which is connected to the lower part of the furnace 1 to return the fuel to the furnace 1; the tail flue 4 is connected to the separator gas phase outlet; the air distribution device 6 is arranged at the air inlet.

[0009] Furthermore, the circulating fluidized bed boiler further comprises a soot blower 8, which is arranged at one side of the tail flue 4 and is connected thereto; preferably, the soot blower 8 is a sonic soot blower.

[0010] Furthermore, the above method includes: storing the water-coal slurry in a slurry storage tank in front of the furnace, pumping the optional water-coal slurry into the furnace 1 through the front-of-furnace conveying system and the water-coal slurry spray gun, and simultaneously conveying the raw coal from the coal feeding port 5 into the furnace 1 by belt conveying for combustion reaction; preferably, the front-of-furnace conveying system includes a water-coal slurry preparation system, a finished product tank, a slurry conveying pump, a buffer tank, and a feed pump, and preferably the water-coal slurry spray gun is arranged in the water-coal slurry feeding port 7.

[0011] Furthermore, the number of water-coal slurry spray guns is 2 to 6; preferably, the water-coal slurry feed port 7 is formed by the first side wall, the second side wall, the third side wall and the fourth side wall connected and surrounded in sequence, and preferably, one water-coal slurry spray gun is arranged on each of the first side wall and the third side wall, and 0 to 4 water-coal slurry spray guns are arranged on the second side wall.

[0012] Furthermore, the delivery amount of the water-coal slurry is regulated by a water-coal slurry control system.

[0013] Furthermore, after adding the water-coal slurry, limestone is added to the circulating fluidized bed boiler for combustion desulfurization. Preferably, a wet method or a semi-dry method is used at the tail end for off-furnace desulfurization. The preferred method is to use selective non-catalytic reduction technology for denitrification.

[0014] Furthermore, the average particle size of the water-coal slurry is 15-75 μm, the total moisture content of the water-coal slurry is preferably 25-40%, and the received basis lower calorific value of the water-coal slurry is preferably 10-16 MJ / kg.

[0015] Furthermore, the raw coal is selected from one or two of anthracite, bituminous coal, lean coal and lignite; preferably, the average particle size of the raw coal is 0 to 13 mm, the median average particle size of the raw coal is 1.25 to 3 mm, the dry ash-free basis volatile matter content of the raw coal is 5 to 45%, the as-received basis ash content of the raw coal is 10 to 40%, and the as-received basis lower calorific value of the raw coal is 12 to 28 MJ / kg.

[0016] Furthermore, the apparent viscosity of the water-coal slurry is 950-1350 mPa·s, and the coal ash fusibility softening temperature of the water-coal slurry is preferably greater than 1250°C.

[0017] By applying the technical solution of the present invention, the bed temperature can be flexibly adjusted by adjusting the ratio of water-coal slurry and raw coal (i.e., slurry-coal ratio). The overall bed temperature can be controlled within the range of 800-900°C from full load to 25% load, which can reduce flue gas pollutant emissions and reduce costs while ensuring high combustion efficiency; in addition, the method of the present application is not restricted by the operating load of the circulating fluidized bed boiler, has good bed temperature adjustment capabilities, and the method of the present application is simple and easy to implement, which can reduce operating risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0019] Figure 1 A schematic diagram showing the relationship between the slurry-coal ratio, load and operating bed temperature in one embodiment of the present invention is shown;

[0020] Figure 2 A schematic diagram of a circulating fluidized bed boiler in one embodiment of the present invention is shown.

[0021] The above drawings include the following reference numerals:

[0022] 1. Furnace; 2. Separator; 3. Return device; 4. Tail flue; 5. Coal feeding port; 6. Air distribution device; 7. Water-coal slurry feeding port; 8. Additional soot blower. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] Full load means the maximum steam volume that the boiler can reach when operating safely and continuously at rated steam parameters, rated feed water temperature, using designed fuel, that is, 100% load; 75% load refers to 75% of the maximum steam volume, and other percentage loads have similar definitions.

[0025] As analyzed in the background technology of this application, when only raw coal is burned, the bed temperature of the circulating fluidized bed boiler at full load is 950-1000°C, the bed temperature at 75% load is 900-950°C, the bed temperature at 50% load is 850-900°C, and the bed temperature at 25% load is 800-850°C. The existing technology has the problem that the bed temperature of the circulating fluidized bed boiler cannot be adjusted over a large range and more pollutants are generated. In order to solve these problems, this application provides a method for adjusting the bed temperature of a circulating fluidized bed boiler.

[0026] In a typical embodiment of the present application, a method for regulating the bed temperature of a circulating fluidized bed boiler is provided, the method comprising: in a circulating fluidized bed boiler, mixing optional water-coal slurry and raw coal and carrying out a combustion reaction; during the combustion reaction, adjusting the proportion of the water-coal slurry to the raw coal according to the load value of the circulating fluidized bed boiler, and the load value of the circulating fluidized bed boiler is positively correlated with the proportion of the water-coal slurry to the raw coal, so that the bed temperature of the circulating fluidized bed boiler is maintained at 800-900°C.

[0027] In the present application, the water-coal slurry can complete the evaporation of water before burning, and there is a time difference between heat absorption and heat release. Therefore, the bed temperature can be flexibly adjusted by adjusting the ratio of water-coal slurry and raw coal (i.e., slurry-coal ratio). The overall bed temperature can be controlled at 800-900°C within the range of full load to 25% load, which can reduce flue gas pollutant emissions and reduce costs while ensuring high combustion efficiency; in addition, the method of the present application is not restricted by the operating load of the circulating fluidized bed boiler, has good bed temperature adjustment capabilities, and the method of the present application is simple and easy to implement, which can reduce operating risks.

[0028] According to the relationship diagram between boiler load and operating bed temperature ( Figure 1), the boiler load is reduced, and the amount of water-coal slurry added is also reduced accordingly. Too high or too low bed temperature is not conducive to reducing flue gas pollutant emissions. In order to reduce the bed temperature to a greater extent and avoid the bed temperature being too low to reduce flue gas emissions, the present application needs to adjust the amount of water-coal slurry added according to the load value of the circulating fluidized bed boiler. In order to avoid reducing the combustion efficiency while reducing the bed temperature, in some embodiments, in the process of mixing the optional water-coal slurry and raw coal, the amount of water-coal slurry added at full load is controlled to be 24% to 36% of the mass of the raw coal, the amount of water-coal slurry added at 75% to 100% load is 18% to 24% of the mass of the raw coal, the amount of water-coal slurry added at 50% to 75% load is 6% to 18% of the mass of the raw coal, and the amount of water-coal slurry added at 25% to 50% load is 0% to 6% of the mass of the raw coal, so that the bed temperature is 850 to 900°C when the full load is to 50% load, and the bed temperature is 800 to 850°C when the load is from 50% to 25%.

[0029] In order to improve combustion efficiency and prevent pollutant emissions and coking, in some embodiments, the amount of water-coal slurry added at full load is 24% to 36% of the mass of the raw coal, the amount of water-coal slurry added at 75% load is 18% to 24% of the mass of the raw coal, the amount of water-coal slurry added at 50% load is 6% to 18% of the mass of the raw coal, and the amount of water-coal slurry added at 25% load is 0% to 6% of the mass of the raw coal; so that the bed temperature is 850 to 900°C from full load to 50% load, and the bed temperature is 800 to 850°C from 50% load to 25% load.

[0030] The circulating fluidized bed boiler in this application needs to have the ability to burn raw coal and water-coal slurry at the same time, and be able to maintain good operating bed temperature regulation capabilities. In some embodiments, such as Figure 2 As shown, the circulating fluidized bed boiler comprises: a furnace 1, a separator 2, a return feeder 3, a tail flue 4, and an air distribution device 6. The bottom of the furnace 1 is provided with an air inlet, and the side wall is provided with a coal feeding port 5, a water-coal slurry feeding port 7, and a combustion flue gas outlet; the coal feeding port 5 is used to add raw coal, the water-coal slurry feeding port 7 is used to add water-coal slurry, and the combustion flue gas outlet is used to discharge the combustion flue gas generated by the combustion reaction; wherein the water-coal slurry feeding port 7 is at the same height as the secondary air port on the upper layer of the circulating fluidized bed boiler; the secondary air port is arranged In the reverse zone at the lower part of the furnace 1; the separator 2 has a separator inlet, a separator gas phase outlet and a separator solid phase outlet, the separator inlet is connected to the combustion flue gas outlet, and the separator 2 is used to perform gas-solid separation on the combustion flue gas to obtain fuel and flue gas; the returner 3 is located below the separator 2 and is connected to the separator solid phase outlet; the returner 3 is also provided with a return port, which is connected to the lower part of the furnace 1 to return the fuel to the furnace 1; the tail flue 4 is connected to the separator gas phase outlet; the air distribution device 6 is arranged at the air inlet.

[0031] In order to reduce the impact of increased flue gas volume and fly ash content, in some embodiments, the circulating fluidized bed boiler further includes a soot blower 8, which is arranged on one side of the tail flue 4 and connected thereto; preferably, the soot blower 8 is a sonic soot blower.

[0032] In order to improve the fuel delivery efficiency, in some embodiments, the method includes: storing the water-coal slurry in a slurry storage tank in front of the furnace, pumping the optional water-coal slurry into the furnace 1 through the furnace-front conveying system and the water-coal slurry spray gun, and simultaneously conveying the raw coal from the coal feeding port 5 into the furnace 1 by belt conveying for combustion reaction. The furnace-front conveying system of the present application can refer to the furnace-front conveying system commonly used in the prior art. Preferably, the furnace-front conveying system includes a water-coal slurry preparation system, a finished product tank, a slurry delivery pump, a buffer tank, and a feed pump, and preferably the water-coal slurry spray gun is arranged in the water-coal slurry feeding port 7.

[0033] In some embodiments, in order to reduce SO2 and NO in flue gas x Discharge, a water-coal slurry spray gun is arranged in the water-coal slurry feeding port 7, which can promote the reaction of calcium oxide and SO2. The number of water-coal slurry spray guns is 2 to 6; the water-coal slurry feeding port 7 is formed by the first side wall, the second side wall, the third side wall and the fourth side wall connected and surrounded in sequence. Preferably, the first side wall and the third side wall are each arranged with 1 water-coal slurry spray gun, and the second side wall is arranged with 0 to 4 water-coal slurry spray guns. The fourth side wall is arranged near the coal feeding port 5.

[0034] In some embodiments, the delivery rate of the water-coal slurry is regulated by a water-coal slurry control system so that the water-coal slurry can be fully burned in the furnace 1 .

[0035] In order to reduce SO2 and NO in flue gas x Emission concentration, after adding water-coal slurry, limestone is added to the circulating fluidized bed boiler for combustion desulfurization, preferably wet or semi-dry desulfurization is used at the tail end. Selective non-catalytic reduction (SNCR) technology is used for denitrification, so that the SO2 emission concentration is less than 30mg / m 3 , NO x Emission concentration is less than 45mg / m 3 .

[0036] In some embodiments, in order to ensure that the water-coal slurry has a certain concentration and fluidity, the average particle size of the water-coal slurry is controlled to be 15-75 μm. Since the water in the water-coal slurry is evaporated before combustion in the furnace 1, the total water content of the water-coal slurry should not be too low, and excessive water content should be avoided to affect the combustion efficiency. The total water content of the water-coal slurry is preferably 25-40%, and the received low calorific value of the water-coal slurry is preferably 10-16 MJ / kg.

[0037] The present application has no particular restrictions on raw coal, and the raw coal commonly used in the art can be applied to the present application, so the method of the present application also has better fuel adaptability. In some embodiments, in order to further improve the combustion efficiency, the raw coal is selected from one or two of anthracite, bituminous coal, lean coal, and lignite; the average particle size of the raw coal is preferably 0 to 13 mm, the median average particle size of the raw coal is preferably 1.25 to 3 mm, the dry ash-free volatile matter content of the raw coal is preferably 5 to 45%, the as-received ash content of the raw coal is preferably 10 to 40%, and the as-received low calorific value of the raw coal is preferably 12 to 28 MJ / kg.

[0038] The present application has no particular restrictions on the properties of the water-coal slurry, and any water-coal slurry commonly used in the art can be applied to the present application. In some embodiments, the apparent viscosity of the water-coal slurry is 950-1350 mPa·s, and the coal ash fusibility softening temperature of the water-coal slurry is preferably greater than 1250°C.

[0039] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0040] Example 1

[0041] Use Figure 2 The circulating fluidized bed boiler shown has a capacity rating of 135MW. During normal operation, the coal used is bituminous coal, with a low calorific value of 18MJ / kg on a received basis, an average particle size of 2mm, and a volatile matter content of 15% on a dry ash-free basis. The total moisture content of the water-coal slurry used is 30%, with a low calorific value of 12MJ / kg on a received basis, and an average particle size of 30μm. The water-coal slurry is stored in a slurry storage tank in front of the furnace, and the water-coal slurry is fed into the furnace 1 from the water-coal slurry feeding port 7 through the furnace conveying system in front of the furnace. At the same time, the raw coal is fed into the furnace 1 from the coal feeding port 5 by belt conveying for combustion reaction, and then limestone is added to the boiler for combustion and desulfurization. The delivery amount of the water-coal slurry is adjusted by the water-coal slurry control system. There are 4 water-coal slurry spray guns, including 1 for each of the first side wall and the third side wall, and 2 for the second side wall.

[0042] When the amount of water-coal slurry used is 25% of the mass of the raw coal, the bed temperature of the boiler is 890°C at full load, the molar ratio of desulfurization calcium to sulfur in the furnace is 3.2, and NO x Emission concentration 160mg / Nm 3 ; NO after denitrification x The emission concentration is 45mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 30mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 90.6-91.6%.

[0043] When the amount of water-coal slurry used is 30% of the mass of the raw coal, the bed temperature of the boiler is 865°C at full load, the molar ratio of desulfurization calcium to sulfur in the furnace is 2.8, and NO x Emission concentration 110mg / Nm 3 , NO after denitrification x The emission concentration is 40mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 30mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 87.5-89.5%.

[0044] When the amount of water-coal slurry used is 20% of the mass of raw coal, the bed temperature is 875°C when the boiler is 75% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 89.1-90.8%.

[0045] When the amount of water-coal slurry used is 10% of the mass of raw coal, the bed temperature is 890°C when the boiler is 50% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 86.5-88.5%.

[0046] Properly increasing the amount of water-coal slurry can reduce SO2 and NO x The emission reduction is about 3-8 mg / Nm 3 , but the corresponding boiler efficiency decreases by 0.1 to 0.2%.

[0047] Example 2

[0048] Use Figure 2 The circulating fluidized bed boiler shown has a capacity rating of 350MW. During normal operation, the coal used is bituminous coal, with a received base calorific value of 18MJ / kg. The total moisture content of the water-coal slurry used is 30%, and the received base calorific value is 12MJ / kg. The water-coal slurry is stored in a slurry storage tank in front of the furnace, and the water-coal slurry is fed into the furnace 1 from the water-coal slurry feeding port 7 through the furnace front conveying system and the water-coal slurry spray gun. At the same time, the raw coal is fed into the furnace 1 from the coal feeding port 5 by belt conveyor for combustion reaction, and then limestone is added to the boiler for combustion and desulfurization. The delivery amount of the water-coal slurry is adjusted by the water-coal slurry control system. There are 6 water-coal slurry spray guns, including 1 each for the first side wall and the third side wall, and 4 for the second side wall.

[0049] When the amount of water-coal slurry used is 30% of the mass of the raw coal, the bed temperature of the boiler is 895°C at full load; the molar ratio of calcium and sulfur in the furnace is 3.0, and the NO x Emission concentration 180mg / Nm 3 , NO after denitrification x The emission concentration is 40mg / Nm 3 After desulfurization, the SO2 emission concentration is 20mg / Nm 3At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 88-90%.

[0050] When the amount of water-coal slurry used is 20% of the mass of raw coal, the bed temperature is 880°C when the boiler is 75% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 87-89%.

[0051] When the amount of water-coal slurry used is 15% of the mass of raw coal, the bed temperature is 870°C when the boiler is 50% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 86-88%.

[0052] When the amount of water-coal slurry used is 3% of the mass of raw coal, the bed temperature is 850°C when the boiler is 25% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 85.5-88.5%.

[0053] Since the bed temperature of Example 2 is always within the optimal range, the boiler parameters can be flexibly adjusted and pollutant emissions are low.

[0054] Example 3

[0055] Use Figure 2 The circulating fluidized bed boiler shown has a capacity rating of 300MW. During normal operation, the coal used is bituminous coal, with a received base low calorific value of 18MJ / kg. The total moisture content of the water-coal slurry used is 30%, and the received base low calorific value is 12MJ / kg. The water-coal slurry is stored in a slurry storage tank in front of the furnace, and the water-coal slurry is fed into the furnace 1 from the water-coal slurry feeding port 7 through the furnace front conveying system and the water-coal slurry spray gun. At the same time, the raw coal is fed into the furnace 1 from the coal feeding port 5 by belt conveyor for combustion reaction. There are 6 water-coal slurry spray guns, including 1 each for the first side wall and the third side wall, and 4 for the second side wall. Then, limestone is added into the boiler for combustion and desulfurization. The delivery amount of the water-coal slurry is adjusted by the water-coal slurry control system.

[0056] When the amount of water-coal slurry used is 30% of the mass of the raw coal, the bed temperature of the boiler is 895°C at full load; the molar ratio of calcium and sulfur in the furnace is 3.0, and the NO x Emission concentration 170mg / Nm 3 , NO after denitrification x The emission concentration is 35mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 25mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 88-90%.

[0057] When the amount of water-coal slurry used is 20% of the mass of raw coal, the bed temperature is 880°C when the boiler is 75% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 87-89%.

[0058] When the amount of water-coal slurry used is 15% of the mass of raw coal, the bed temperature is 870°C when the boiler is 50% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 86-88%.

[0059] When the amount of water-coal slurry used is 3% of the mass of raw coal, the bed temperature is 850°C when the boiler is 25% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 85.5-88.5%.

[0060] Example 4

[0061] The difference from Example 2 is that when the amount of water-coal slurry used is 36% of the mass of the raw coal, the bed temperature is 880°C when the boiler is fully loaded; the molar ratio of desulfurization calcium to sulfur in the furnace is 2.8, and NO x Emission concentration 160mg / Nm 3 , NO after denitrification x The emission concentration is 38mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 22mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 87.5-89.5%.

[0062] When the amount of water-coal slurry used is 24% of the mass of raw coal, the bed temperature is 865°C when the boiler is 75% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 86.5-88.5%.

[0063] When the amount of water-coal slurry used is 18% of the mass of raw coal, the bed temperature is 850°C when the boiler is 50% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 85.5-88.5%.

[0064] When the amount of water-coal slurry used is 6% of the mass of raw coal, the bed temperature is 815°C when the boiler is 25% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 85-88%.

[0065] Example 5

[0066] The difference from Example 2 is that when the amount of water-coal slurry used is 24% of the mass of the raw coal, the bed temperature is 900°C when the boiler is fully loaded; the molar ratio of desulfurization calcium to sulfur in the furnace is 3.3, and NO x Emission concentration 220mg / Nm 3 , NO after denitrification x The emission concentration is 45mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 30mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 87.5% to 89.5%.

[0067] When the amount of water-coal slurry used is 18% of the mass of raw coal, the bed temperature is 890°C when the boiler is 75% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 86.5-88.5%;

[0068] When the amount of water-coal slurry used is 6% of the mass of raw coal, the bed temperature is 865°C when the boiler is 50% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 85.5-88.5%;

[0069] Without adding water-coal slurry, the bed temperature is 800°C when the boiler is at 25% load; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 85.5-88.5%.

[0070] Example 6

[0071] The difference from Example 2 is that when the amount of water-coal slurry used is 40% of the mass of the raw coal, the bed temperature is 865°C when the boiler is fully loaded; the molar ratio of desulfurization calcium to sulfur in the furnace is 3.0, and NO x Emission concentration 220mg / Nm 3 , NO after denitrification x The emission concentration is 45mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 30mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 86-88%;

[0072] When the amount of water-coal slurry used is 27% of the raw coal mass, the bed temperature of the boiler is 870°C at full load; the molar ratio of calcium and sulfur in the furnace is 2.8, and the NO x Emission concentration 220mg / Nm 3 , NO after denitrification x The emission concentration is 45mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 30mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 85-86%;

[0073] When the amount of water-coal slurry used is 23% of the mass of raw coal, the bed temperature is 850°C when the boiler is 50% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 84-87%;

[0074] When the amount of water-coal slurry used is 8% of the mass of raw coal, the bed temperature is 810°C when the boiler is 25% loaded; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 82-85%.

[0075] Properly increasing the amount of water-coal slurry can reduce SO2 and NO x The amount of emissions is reduced, but the corresponding boiler efficiency decreases by 0.1-0.2%. When the amount of water-coal slurry is too much, the boiler efficiency will be reduced.

[0076] Comparative Example 1

[0077] A circulating fluidized bed boiler with a capacity rating of 135MW is used, and only raw coal is used for combustion. The raw coal is bituminous coal, and the received basic low calorific value is 18MJ / kg.

[0078] When the circulating fluidized bed boiler is fully loaded, the bed temperature is 980℃, the molar ratio of desulfurization calcium to sulfur in the furnace is 4.5, and NO x The emission concentration is 280mg / Nm 3 , NO after denitrification x The emission concentration is 90mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 120mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 90.9-91.9%;

[0079] When the circulating fluidized bed boiler is 75% loaded, the bed temperature is 920℃; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 87.8-89.8%;

[0080] When the circulating fluidized bed boiler is 50% loaded, the bed temperature is 890°C; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 89.4-91.2%.

[0081] Compared with Example 1, Comparative Example 1 has a high calcium-sulfur molar ratio and cannot achieve ultra-low emissions. Compared with Comparative Example 1, when the boiler is fully loaded, when the bed temperature drops, the pollutant emission concentration and environmental protection investment decrease significantly, and at the same time, the boiler efficiency does not decrease significantly.

[0082] Comparative Example 2

[0083] A circulating fluidized bed boiler with a capacity rating of 350MW is used, which only uses raw coal for combustion. The raw coal is bituminous coal, and the received minimum calorific value is 18MJ / kg.

[0084] When the circulating fluidized bed boiler is fully loaded, the bed temperature is 1020℃; the molar ratio of desulfurization calcium to sulfur in the furnace is 5.0, and when no denitration is performed, NO x Emission concentration 320mg / Nm 3 , NO after denitrification x The emission concentration is 120mg / Nm 3 ; After desulfurization, the SO2 emission concentration is 150mg / Nm 3 At this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 88.5-90.5%;

[0085] When the circulating fluidized bed boiler is 75% loaded, the bed temperature is 960°C; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 87.5-89.5%;

[0086] When the circulating fluidized bed boiler is 50% loaded, the bed temperature is 920℃; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 86.5-88.5%;

[0087] When the circulating fluidized bed boiler is at 25% load, the bed temperature is 860°C; at this time, the thermal efficiency of the boiler burning water-coal slurry and raw coal is 86-89%.

[0088] Compared with comparative examples 1-2, since the bed temperature of Example 2 is always within the optimal range, the boiler parameters can be flexibly adjusted and the pollutant emissions are low.

[0089] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: In the present application, the water-coal slurry can complete the evaporation of water in the furnace 1 before burning, and there is a time difference between heat absorption and heat release, so the bed temperature can be flexibly adjusted by adjusting the ratio of water-coal slurry and raw coal (i.e., slurry-coal ratio). The overall bed temperature can be controlled at 800-900°C in the range of full load to 25% load, which can reduce flue gas pollutant emissions and reduce costs while ensuring high combustion efficiency; in addition, the method of the present application is not restricted by the operating load of the circulating fluidized bed boiler, has good bed temperature adjustment capabilities, and the method of the present application is simple and easy to implement, which can reduce operating risks.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for regulating the bed temperature of a circulating fluidized bed boiler, characterized in that: The method comprises: In a circulating fluidized bed boiler, water-coal slurry and raw coal are mixed and combustion reaction is carried out; During the combustion reaction, the ratio of the water-coal slurry to the raw coal is adjusted according to the load value of the circulating fluidized bed boiler, and the amount of the water-coal slurry added is adjusted according to the load value of the circulating fluidized bed boiler; the load value of the circulating fluidized bed boiler is positively correlated with the ratio of the water-coal slurry to the raw coal, so that the bed temperature of the circulating fluidized bed boiler is maintained at 800-900° C.; During the process of mixing the water-coal slurry and the raw coal, the amount of the water-coal slurry added is controlled to be 24%-36% of the mass of the raw coal at full load, 18%-24% of the mass of the raw coal at 75%-100% load, 6%-18% of the mass of the raw coal at 50%-75% load, and 0%-6% of the mass of the raw coal at 25%-50% load, so that the bed temperature is 850-900° C. from full load to 50% load, and 800-850° C. from 50% load to 25% load; The average particle size of the coal-water slurry is 15-75 μm, and the total moisture content of the coal-water slurry is 25-40%.

2. The method according to claim 1, characterized in that The circulating fluidized bed boiler comprises: A furnace (1), wherein the bottom of the furnace (1) is provided with an air inlet, and the side wall is provided with a coal feeding port (5), a water-coal slurry feeding port (7), and a combustion flue gas outlet; the coal feeding port (5) is used to add the raw coal, the water-coal slurry feeding port (7) is used to add the water-coal slurry, and the combustion flue gas outlet is used to discharge the combustion flue gas generated by the combustion reaction; wherein the water-coal slurry feeding port (7) and the secondary air port of the upper layer of the circulating fluidized bed boiler are at the same height; the secondary air port is provided in the reverse zone at the lower part of the furnace (1); A separator (2), the separator (2) having a separator inlet, a separator gas phase outlet, and a separator solid phase outlet, the separator inlet being connected to the combustion flue gas outlet, the separator (2) being used for performing gas-solid separation on the combustion flue gas to obtain fuel and flue gas; A return device (3) is located below the separator (2) and is connected to the solid phase outlet of the separator; the return device (3) is also provided with a return port, which is connected to the lower part of the furnace (1) to return the fuel to the furnace (1); A tail flue (4) connected to the gas phase outlet of the separator; An air distribution device (6) is arranged at the air inlet.

3. The method according to claim 2, characterized in that The circulating fluidized bed boiler further comprises a soot blower (8), which is arranged on one side of the tail flue (4) and is in communication with the tail flue (4).

4. The method according to claim 3, characterized in that The soot blower (8) is a sonic soot blower.

5. The method according to claim 4, characterized in that The method comprises: The water-coal slurry is stored in a slurry storage tank in front of the furnace, and the water-coal slurry is pumped into the furnace (1) through a furnace-front conveying system and a water-coal slurry spray gun, and the raw coal is simultaneously conveyed from the coal feeding port (5) into the furnace (1) by a belt conveyor to carry out the combustion reaction; The furnace front conveying system includes a water-coal slurry preparation system, a finished product tank, a slurry conveying pump, a buffer tank, and a feed pump.

6. The method according to claim 5, characterized in that The water-coal slurry spray gun is arranged in the water-coal slurry feed port (7).

7. The method according to claim 5, characterized in that The number of the water-coal slurry spray guns is 2 to 6; the water-coal slurry feed port (7) is formed by sequentially connecting and surrounding a first side wall, a second side wall, a third side wall, and a fourth side wall.

8. The method according to claim 7, characterized in that One coal-water slurry spray gun is disposed on each of the first side wall and the third side wall, and 0 to 4 coal-water slurry spray guns are disposed on the second side wall.

9. The method according to claim 8, characterized in that The delivery rate of the water-coal slurry is regulated by a water-coal slurry control system.

10. The method according to claim 9, characterized in that After the water-coal slurry is added, limestone is added to the circulating fluidized bed boiler for combustion and desulfurization.

11. The method according to claim 10, characterized in that After adding the water-coal slurry, a wet method or a semi-dry method is used at the tail end for off-furnace desulfurization, and the method uses a selective non-catalytic reduction technology for denitrification.

12. The method according to claim 11, characterized in that The received low calorific value of the water-coal slurry is 10-16 MJ / kg.

13. The method according to claim 12, characterized in that The raw coal is selected from one or two of anthracite, bituminous coal, lean coal and lignite.

14. The method according to claim 13, characterized in that The average particle size of the raw coal is 0~13mm, the median average particle size of the raw coal is 1.25~3mm, the dry ash-free volatile matter content of the raw coal is 5~45%, the as-received ash content of the raw coal is 10~40%, and the as-received lower calorific value of the raw coal is 12~28MJ / kg.

15. The method according to claim 14, characterized in that The apparent viscosity of the water-coal slurry is 950-1350 mPa·s, and the fusibility softening temperature of the coal ash of the water-coal slurry is greater than 1250°C.

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