Process and device for improving low-ash-content fire coal combustion of circulating fluidized bed boiler

Abstract

The invention provides a low-ash-content fire coal combustion process and device for lifting a circulating fluidized bed boiler, and the process comprises the following steps: S1, conveying fire coal into a hearth of the circulating fluidized bed boiler through a conveyor for combustion, conveying slag at the bottom of the circulating fluidized bed boiler to a feeding hole of a bucket elevator through a slag cooler and a scraper machine after combustion, and feeding the slag into a furnace; then, the slag is divided into two paths by an electric tee joint, one path of slag enters a slag bin through a discharging articulated chute I, and the other path of slag passes through a discharging articulated chute II, then sequentially passes through a large-dip-angle conveyor and a belt conveyor to be conveyed to a level gage and then enters a surge bin; and S2, the furnace slag is divided into furnace slag I and furnace slag II through a discharging pipe I and a discharging pipe II at the bottom of the surge bin, and the furnace slag I and the furnace slag II enter a hearth of the circulating fluidized bed boiler. The device is designed when the ash content in the fire coal of the circulating fluidized bed boiler is 5.8-6.0%, the bed temperature of the boiler can be effectively reduced during fire coal combustion, the boiler is made to operate at the temperature of 850-950 DEG C, the risks of high-temperature shutdown and high-temperature coking are avoided, and meanwhile energy can be saved.

Description

Technical Field

[0001] The invention relates to the technical field of circulating fluidized bed boiler combustion, and in particular to a process and a device for improving the low-ash coal combustion of a circulating fluidized bed boiler. Background Art

[0002] Circulating fluidized bed boiler is an advanced, efficient and clean combustion technology that has been widely used at home and abroad.

[0003] The circulating fluidized bed coal-fired boiler organizes the combustion process of coal based on the principle of circulating fluidization, and its main feature is the circulating combustion of a large amount of high-temperature solid particulate materials carrying fuel. The circulating fluidized bed boiler system usually consists of a fluidized bed combustion chamber (furnace), a circulating ash separator, a fly ash returner, a tail heating surface and auxiliary equipment. The basic working principle of a traditional circulating fluidized bed coal-fired boiler is as follows: the coal is crushed and sent to the furnace for combustion reaction. A large number of particles flowing out of the furnace with the flue gas are separated from the flue gas in the cyclone separator. The separated particles are directly returned to the furnace with the returner connected to the bottom of the separator to participate in the combustion process. The flue gas separated by the cyclone separator is introduced into the tail flue of the boiler to heat the superheater, economizer and air preheater in the tail flue. Then, the flue gas flowing out of the air preheater outlet is dedusted by the bag filter and discharged into the chimney by the induced draft fan, and finally discharged into the atmosphere.

[0004] Circulating fluidized bed coal-fired boiler has the following significant features:

[0005] 1) Strong fuel adaptability. It can efficiently burn a variety of fuels, such as coal gangue, lignite, anthracite, bituminous coal, etc., including medium and low sulfur coal, biomass mixed combustion and pure combustion, coal sludge mixed combustion, urban waste incineration, etc.; it can burn low calorific value of low-quality fuels, these low-quality fuels can achieve higher combustion efficiency in circulating fluidized bed boilers, and its efficiency is better than that of pulverized coal furnaces.

[0006] 2) High environmental performance. It has high efficiency desulfurization (up to 80% to 95%), can reduce NOX emissions by more than 50%, and has low combustion temperature. When the temperature is controlled between about (880℃ to 920℃), the NOX generated is relatively low, reducing the consumption of denitrification ammonia water and reducing environmental pollution.

[0007] 3) Load adjustment is relatively large. The load adjustment range is wide, and the load can be controlled from 30% to 100%, and even stable operation can be maintained at lower loads.

[0008] 4) Ash has wide comprehensive utilization. Ash has low carbon content and can be used to make cement and other building materials.

[0009] In addition, circulating fluidized bed boilers also have corresponding requirements for the circulation ratio of the cyclone separator. If the ash content of the coal entering the furnace is low, the circulation ratio of the cyclone separator will be low, resulting in high bed temperature, difficulty in carrying load, and the risk of high-temperature coking.

[0010] When the inventor used a circulating fluidized bed boiler to burn coal with a low ash content of 5.8-6% by weight, he found that the low ash content of the coal entering the furnace would cause a low circulation rate of the cyclone separator, resulting in a high bed temperature that often exceeded 960°C, making it difficult to carry load, and causing the high temperature in the furnace to produce a risk of coking, which may cause unplanned shutdowns. At the same time, the nitrogen oxide content also increased, and the power consumption of the primary fan and the induced draft fan also increased, posing a risk of environmental pollution, increasing operating costs, and being detrimental to the safe operation of the circulating fluidized bed boiler. Summary of the invention

[0011] In view of this, the present invention proposes a process and device for improving the combustion of low-ash coal in a circulating fluidized bed boiler. The present invention is designed and developed for low-ash (ash weight content of 5.8-6%) coal entering the circulating fluidized bed boiler fuel, and the return device of the present invention is added to the original circulating fluidized bed boiler equipment. According to the ash content ratio and the amount of coal entering the furnace, the amount of slag or river sand entering the furnace is adjusted according to the corresponding proportion, the return amount is increased, the circulation rate of the cyclone separator is increased, the boiler bed temperature is reduced, the generation of nitrogen oxides is reduced, the power consumption of the primary fan and the induced draft fan is reduced, and the risk of high-temperature coking of the boiler is reduced, thereby improving the boiler efficiency.

[0012] The technical solution of the present invention is achieved in this way:

[0013] A low-ash coal combustion process for a circulating fluidized bed boiler comprises the following steps:

[0014] S1. The coal is conveyed into the furnace of the circulating fluidized bed boiler through a conveyor for combustion. After combustion, the slag at the bottom of the circulating fluidized bed boiler is conveyed to the feeding port of the bucket elevator through a slag cooler and a scraper. Then, the slag is divided into two paths through the electric tee at the outlet of the bucket elevator. One path of slag passes through the discharge chute I and enters the slag bin. The other path of slag passes through the discharge chute II and then passes through the high-angle conveyor and the belt conveyor in sequence to the material level meter and then enters the buffer bin.

[0015] S2. The feed pipes I and II at the bottom of the buffer bin separate the slag into slag I and slag II. Slag I passes through the feed pipe I and then enters the return pipe I through the pipeline I and then enters the furnace of the circulating fluidized bed boiler. Slag II passes through the feed pipe II and then enters the furnace of the circulating fluidized bed boiler through the return pipe II and then the pipeline II.

[0016] S3. The flow rate of slag I into the furnace is controlled by adjusting the regulating valve I on the discharge pipe I, and the flow rate of slag II into the furnace is controlled by adjusting the regulating valve II on the discharge pipe II.

[0017] Furthermore, the ash weight content of the coal used in the circulating fluidized bed boiler is 5.8-6.0%.

[0018] Furthermore, during the entire combustion process, the ratio of the total mass of slag I and slag II to the total mass of coal is 24-32:1.

[0019] Furthermore, the volume of the buffer bin is 50-60 cubic meters.

[0020] A device for improving the low-ash coal combustion process of a circulating fluidized bed boiler, the device comprising a circulating fluidized bed boiler, a slag cooler, a scraper, a bucket elevator, a high-angle conveyor, a belt conveyor, a buffer bin, a cyclone separation system I, and a cyclone separation system II; the cyclone separation system I comprises a cyclone separator I, a tail flue I, a return feeder I, a plurality of return feed pipes I, and a smoke pipe I; the top of the cyclone separator I is connected to the tail flue I, the upper end of the cyclone separator I is connected to the upper end of the circulating fluidized bed boiler through the smoke pipe I, the lower end of the cyclone separator I is connected to the return feeder I, and the return feeder I is connected to the lower end of the circulating fluidized bed boiler through a plurality of return feed pipes I; the cyclone separation system II comprises a cyclone separator II, a tail flue II, a return feeder II, a plurality of return feed pipes II, and a smoke pipe II; the top of the cyclone separator II is connected to the tail flue II, the cyclone separator The upper end of the cyclone separator II is connected to the upper end of the circulating fluidized bed boiler through the smoke pipe II, and the lower end of the cyclone separator II is connected to the return device II, and the return device II is connected to the lower end of the circulating fluidized bed boiler through a plurality of return pipes II; the slag discharge port at the bottom of the circulating fluidized bed boiler is connected to the scraper, the scraper discharge port is connected to the feed port of the bucket elevator, and the bucket elevator discharge port is respectively connected to the discharge chute I and the discharge chute II, and an electric tee is provided at the connection; the discharge port of the discharge chute II is connected to the feed port of the slag bin, and the discharge port of the discharge chute I is connected to the feed port of the high-angle conveyor, the belt conveyor and the buffer bin top in sequence; the bottom of the buffer bin is respectively provided with a discharge pipe I and a discharge pipe II, the discharge pipe I is provided with a regulating valve I and the discharge pipe I is connected to the return pipe I through the pipeline I, the discharge pipe II is provided with a regulating valve II and the discharge pipe II is connected to the return pipe II through the pipeline II.

[0021] Furthermore, a dust collector is provided on the top of the buffer bin.

[0022] Furthermore, a material level meter is provided in the buffer bin.

[0023] Furthermore, both the regulating valve I and the regulating valve II are electric regulating valves.

[0024] Furthermore, the diameter of the pipeline I is 100-120 mm, and the diameter of the pipeline II is 100-120 mm.

[0025] Furthermore, the smoke pipe I and the smoke pipe II are arranged in parallel.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The process and device of the present invention are designed for circulating fluidized bed boilers with an ash content of 5.8-6.0% by weight. By adopting the process and device of the present invention, when low ash (ash content of 5.8-6.0% by weight) is burned, the boiler bed temperature can be effectively reduced, the boiler can be operated between 850°C and 950°C, the circulation rate of the cyclone separator can be effectively increased, the risk of high-temperature tripping and high-temperature coking can be avoided, and unplanned shutdown accidents can be avoided.

[0028] 2. The process of the present invention can also reduce the generation of nitrogen oxides in the furnace, while reducing the consumption of denitrification ammonia water and avoiding the risk of environmental accidents.

[0029] 3. In addition, by lowering the bed temperature of the circulating fluidized bed boiler, the power consumption of the primary air, the power consumption of the induced draft fan, the power consumption of the booster fan, etc. can be reduced, which is beneficial to saving energy and at the same time can alleviate the wear cycle of the furnace hood hole. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the structure of a device for improving a low-ash coal combustion process in a circulating fluidized bed boiler according to the present invention.

[0031] In the figure, 1-circulating fluidized bed boiler, 2-slag cooler, 3-scraper, 4-bucket elevator, 401-discharging chute Ⅰ, 402-discharging chute Ⅱ, 5-electric tee, 6-large angle conveyor, 7-belt conveyor, 8-buffer bin, 801-discharging pipe Ⅰ, 802-discharging pipe Ⅱ, 9-dust collector, 10-regulating valve Ⅰ, 11-pipeline Ⅰ, 12-regulating valve Ⅱ, 13-pipeline Ⅱ, 14-cyclone separator Ⅱ, 15-rear flue Ⅱ, 16-returner Ⅱ, 17-returner pipe Ⅱ, 18-smoke pipe Ⅱ, 19-cyclone separator Ⅰ, 20-rear flue Ⅰ, 21-returner Ⅰ, 22-returner pipe Ⅰ, 23-slag bin. DETAILED DESCRIPTION

[0032] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0033] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0034] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0035] See also Figure 1The present invention is a device for improving the low-ash coal combustion process of a circulating fluidized bed boiler, the device comprising a circulating fluidized bed boiler 1, a slag cooler 2, a scraper 3, a bucket elevator 4, a large-angle conveyor 6, a belt conveyor 7, a buffer bin 8, a cyclone separation system I, and a cyclone separation system II; the cyclone separation system I comprises a cyclone separator I 19, a tail flue I 20, a return device I 21, a plurality of return pipes I 22, and a smoke pipe I; the top of the cyclone separator I 19 is connected to the tail flue I 20, and the upper end of the cyclone separator I 19 is connected to the upper end of the circulating fluidized bed boiler 1 through the smoke pipe I The lower end of the cyclone separator Ⅰ19 is connected to the return device Ⅰ21, and the return device Ⅰ21 is connected to the lower end of the circulating fluidized bed boiler 1 through a plurality of return pipes Ⅰ22; the cyclone separation system Ⅱ includes a cyclone separator Ⅱ14, a tail flue Ⅱ15, a return device Ⅱ16, a plurality of return pipes Ⅱ17, and a smoke pipe Ⅱ18; the top of the cyclone separator Ⅱ14 is connected to the tail flue Ⅱ15, the upper end of the cyclone separator Ⅱ14 is connected to the upper end of the circulating fluidized bed boiler 1 through the smoke pipe Ⅱ18, and the lower end of the cyclone separator Ⅱ14 is connected to the return device Ⅱ16, and the return device Ⅱ16 is connected to the lower end of the circulating fluidized bed boiler 1 through a plurality of return pipes Ⅱ18.

[0036] Ⅱ17 is connected to the lower end of the circulating fluidized bed boiler 1; the slag discharge port at the bottom of the circulating fluidized bed boiler 1 is connected to the scraper 3, the scraper 3 discharge port is connected to the feed port of the bucket elevator 4, the bucket elevator 4 discharge port is respectively connected to the discharge chute Ⅰ401 and the discharge chute Ⅱ402 and an electric tee is provided at the connection; the discharge port of the discharge chute Ⅱ402 is connected to the feed port of the slag bin 23, and the discharge port of the discharge chute Ⅰ401 is connected to the feed port of the high-angle conveyor 6, the belt conveyor 7 and the top of the buffer bin 8 in sequence; the bottom of the buffer bin 8 is respectively provided with a discharge pipe Ⅰ801 and a discharge pipe Ⅱ802, the discharge pipe Ⅰ801 is provided with a regulating valve Ⅰ10 and the discharge pipe Ⅰ801 is connected to the return pipe Ⅰ22 through the pipeline Ⅰ11, the discharge pipe Ⅱ802 is provided with a regulating valve Ⅱ12 and the discharge pipe Ⅱ802 is connected to the return pipe Ⅱ17 through the pipeline Ⅱ13.

[0037] Specifically, a dust collector is also provided on the top of the buffer bin 8; a material level meter is provided in the buffer bin 8; the regulating valve I10 and the regulating valve II12 are both electric regulating valves; the diameter of the pipeline I11 is 100 mm, and the diameter of the pipeline II13 is 100 mm; the smoke pipe I and the smoke pipe II18 are arranged in parallel.

[0038] When the coal ash weight content is between 5.8-6.0%, the low ash coal combustion process of the circulating fluidized bed boiler is improved, including the following steps:

[0039] S1. The coal is conveyed into the furnace of the circulating fluidized bed boiler 1 through a conveyor for combustion. After combustion, the slag at the bottom of the circulating fluidized bed boiler 1 is conveyed to the feeding port of the bucket elevator 4 through a slag cooler 2 and a scraper 3. Then, the slag is divided into two paths through the electric tee at the discharge port of the bucket elevator 4. One path of slag passes through the discharge chute Ⅰ401 and enters the slag bin 23. The other path of slag passes through the discharge chute Ⅱ402 and then is conveyed to the buffer bin 8 through the high-angle conveyor 6 and the belt conveyor 7 in sequence. During the combustion process, the total mass ratio of slag Ⅰ and slag Ⅱ to the total mass of coal is 32:1.

[0040] S2, the feed pipe I801 and the feed pipe II802 at the bottom of the buffer bin 8 separate the slag into slag I and slag II. Slag I passes through the feed pipe I801 and enters the return pipe I22 through the pipe I11, and then enters the furnace of the circulating fluidized bed boiler 1 together with the particles separated from the cyclone separator I19 to continue burning. Slag II passes through the feed pipe II802 and enters the return pipe II17 through the pipe II13, and then enters the furnace of the circulating fluidized bed boiler 1 together with the particles separated from the cyclone separator I19 to continue burning. The pipe I11 can be connected to one of the return pipes I22, and the pipe II13 can be connected to one of the return pipes II17.

[0041] S3. The flow rate of slag I entering the furnace is controlled by adjusting the regulating valve I10 on the discharge pipe I801, and the flow rate of slag II entering the furnace is controlled by adjusting the regulating valve II12 on the discharge pipe II802. The flow rate of slag I entering the furnace is regulated by monitoring the return pressure difference A between the cyclone separator I19 and the return device I21, and the flow rate of slag II entering the furnace is regulated by monitoring the return pressure difference B between the cyclone separator II14 and the return device II16. During the combustion process, the return pressure difference A and the return pressure difference B are both maintained ≥15mbar.

[0042] For the combustion of coal with an ash weight content between 5.8-6.0%, the above process and device were added to the MB3 circulating fluidized bed boiler to compare the effects before and after the improvement. The monitoring system was used to monitor the changes in the furnace temperature of the circulating fluidized bed boiler, the average denitrification liquid nitrogen consumption, the primary air current, and the induced draft fan current. The results are shown in Table 1 below.

[0043] Table 1 Changes in the combustion performance of low-ash coal in circulating fluidized bed boilers before and after improvement

[0044]

[0045]

[0046] Calculated based on the denitrification liquid nitrogen price of 4,831 yuan / ton, from July 2022 to June 2023, the liquid nitrogen consumption that can be saved after the improvement is: (5.9-3.5)*4831*350 days=4,058,040 (yuan / year).

[0047] Calculated from July 2022 to June 2023, the fan power consumption is reduced during normal operation: the fan current before improvement is 208.5A, and the induced draft fan current is 178A; the fan current after improvement is 169.5A, and the induced draft fan current is 167.5A; the rated current of the primary fan is 218A, the load is 100%, and the power is 2000KW; the rated current of the induced draft fan is 220A, the load is 100%, and the power is 1900KW. The electricity fee is calculated at 635 yuan / MW. The total cost that the fan can save in one year is: electricity fee 635*{(208.5-169.5) / 218*100%*2000+(178-167.5) / 220*100%*1900} / 1000*24*350=2392192 yuan / year.

[0048] In addition, the annual loss costs caused by boiler coking can be reduced: water consumption costs are 1,774 yuan, electricity consumption costs are 478,851 yuan, oil consumption costs are 470,405 yuan, and coke cleaning costs are 200,000 yuan.

[0049] The total cost of boiler coking is: 1774+478851+470405+200000=1151030 (yuan / year).

[0050] The total cost of the above is: 4058040+2392192+1151030=7601262 (yuan / year).

[0051] The above results show that the circulating fluidized bed boiler is improved by the process and device of the present invention, and the bed temperature of the circulating fluidized bed boiler can be effectively reduced when the ash weight content is 5.8-6.0% during combustion. After the improvement, the temperatures on the left, middle and right sides of the furnace are all ≤950°C, so that the boiler can operate between 850°C and 950°C, avoiding the risks of high-temperature tripping and high-temperature coking. At the same time, it can also effectively reduce the generation of nitrogen oxides in the furnace, reduce the consumption of denitrification ammonia water, avoid the risk of environmental accidents, and also reduce the primary wind power consumption, induced draft fan power consumption, booster fan power consumption, etc., and at the same time alleviate the wear cycle of the furnace hood hole.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for improving the combustion of low-ash coal in a circulating fluidized bed boiler, characterized in that: The following steps are involved: S1. The coal is conveyed into the furnace of the circulating fluidized bed boiler through a conveyor for combustion. After combustion, the slag at the bottom of the circulating fluidized bed boiler is conveyed to the feeding port of the bucket elevator through a slag cooler and a scraper. Then, the slag is divided into two paths through the electric tee at the discharge port of the bucket elevator. One path of slag passes through the discharge chute I and enters the slag bin. The other path of slag passes through the discharge chute II and then is conveyed to the buffer bin through a high-angle conveyor and a belt conveyor in sequence. S2. The feed pipes I and II at the bottom of the buffer bin separate the slag into slag I and slag II. Slag I passes through the feed pipe I and the pipe I into the return pipe I and then enters the furnace of the circulating fluidized bed boiler. Slag II passes through the feed pipe II and the pipe II into the return pipe II and then enters the furnace of the circulating fluidized bed boiler. S3. The flow rate of slag I into the furnace is controlled by adjusting the regulating valve I on the discharge pipe I, and the flow rate of slag II into the furnace is controlled by adjusting the regulating valve II on the discharge pipe II.

2. The low-ash coal combustion process for a circulating fluidized bed boiler according to claim 1, characterized in that: The ash content of the coal used in the circulating fluidized bed boiler is 5.8-6.0% by weight.

3. The low-ash coal combustion process for a circulating fluidized bed boiler according to claim 1, characterized in that: During the entire combustion process, the ratio of the total mass of slag I and slag II to the total mass of coal is 24-32:

1.

4. The low-ash coal combustion process for a circulating fluidized bed boiler according to claim 1, characterized in that: The volume of the buffer bin is 50-60 cubic meters.

5. The device for improving the low-ash coal combustion process of a circulating fluidized bed boiler according to any one of claims 1 to 4, characterized in that: The device includes a circulating fluidized bed boiler, a slag cooler, a scraper, a bucket elevator, a high-angle conveyor, a belt conveyor, a buffer bin, a cyclone separation system I, and a cyclone separation system II; The cyclone separation system I comprises a cyclone separator I, a tail flue I, a return material device I, a plurality of return material pipes I, and a flue pipe I; the top of the cyclone separator I is connected to the tail flue I, the upper end of the cyclone separator I is connected to the upper end of the circulating fluidized bed boiler through the flue pipe I, the lower end of the cyclone separator I is connected to the return material device I, and the return material device I is connected to the lower end of the circulating fluidized bed boiler through a plurality of return material pipes I; The cyclone separation system II comprises a cyclone separator II, a tail flue II, a return device II, a plurality of return pipes II, and a smoke pipe II; the top of the cyclone separator II is connected to the tail flue II, the upper end of the cyclone separator II is connected to the upper end of the circulating fluidized bed boiler through the smoke pipe II, the lower end of the cyclone separator II is connected to the return device II, and the return device II is connected to the lower end of the circulating fluidized bed boiler through a plurality of return pipes II; The slag discharge port at the furnace bottom of the circulating fluidized bed boiler is connected to several slag coolers and scrapers in sequence, the scraper discharge port is connected to the feed port of the bucket elevator, the bucket elevator discharge port is respectively connected to the discharge chute I and the discharge chute II and an electric tee is provided at the connection; the discharge port of the discharge chute II is connected to the feed port of the slag bin, and the discharge port of the discharge chute I is connected to the feed port of the high-angle conveyor, the belt conveyor and the buffer bin top in sequence; the bottom of the buffer bin is respectively provided with a discharge pipe I and a discharge pipe II, the discharge pipe I is provided with a regulating valve I and the discharge pipe I is connected to the return pipe I through the pipeline I, the discharge pipe II is provided with a regulating valve II and the discharge pipe II is connected to the return pipe II through the pipeline II.

6. The device according to claim 5, characterized in that A dust collector is also provided on the top of the buffer bin.

7. The device according to claim 5, characterized in that A material level meter is arranged in the buffer bin.

8. The device according to claim 5, characterized in that The regulating valve I and regulating valve II are both electric regulating valves.

9. The device according to claim 5, characterized in that The diameter of the pipeline I is 100-120 mm, and the diameter of the pipeline II is 100-120 mm.

10. The device according to claim 5, characterized in that The smoke pipe I and the smoke pipe II are arranged in parallel.

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