A method and automatic blending system for blending low-quality coal in coal-fired power plants

Abstract

This invention provides an automatic blending system for low-quality coal in coal-fired power plants, comprising several charging devices. A first coal conveyor belt is positioned below each charging device, and each first coal conveyor belt is equipped with a belt scale. A second coal conveyor belt is positioned below the first coal conveyor belt, and a mixing coal bin is positioned below the second coal conveyor belt. The mixing coal bin has three coal outlets at its bottom, each with a corresponding unloading valve. A third coal conveyor belt is positioned corresponding to each coal outlet, and a coal storage bin is positioned corresponding to each third coal conveyor belt. By setting up the mixing coal storage bins and the coal hopper compartments, different fuel ratios can be freely switched. The system switches to different fuel ratios according to the actual power generation load of the unit, thereby achieving the purpose of economical coal blending and combustion.

Description

Technical Field

[0001] This invention relates to the field of coal blending equipment technology, and in particular to a method for blending low-quality coal in coal-fired power plants and an automatic blending system. Background Technology

[0002] High coal prices have increased fuel costs for coal-fired power plants, severely impacting their profitability. Therefore, seeking low-cost fuels has become crucial for increasing profits. This constant search for various low-priced, low-quality coals has led to frequent changes in boiler fuels. To ensure stable combustion and safe operation, different types of coal are typically blended in specific proportions before being fed into the boiler. Low-quality coal is inexpensive, but it has low calorific value and is difficult to burn. If only low-quality coal is used, even at maximum feeder output, the combustion heat will not reach the design value, limiting the unit's load and preventing it from reaching its rated capacity. At lower loads, the difficulty in combustion can cause unstable combustion, affecting the safe and stable operation of the unit. Therefore, low-quality coal needs to be blended with a certain proportion of high-quality coal before being fed into the boiler. Determining the blending ratio is a critical factor affecting the fuel economy of the power plant and also a crucial factor affecting stable combustion and safe operation of the boiler.

[0003] CN115682023A discloses a Zhundong coal blending system and method. It mainly uses simulation to determine the maximum blending ratio of a particular coal type.

[0004] CN114529114A discloses a precise coal blending method and system for coal-fired power plants. It primarily relies on precisely selecting coal based on the target coal quality to ensure accurate coal blending.

[0005] CN115325558A discloses a coal blending method and system for furnace feed. The method mainly controls the moisture content of the coal fed into the furnace by adjusting the amount of ash and slag blended, and controls the calorific value of the coal fed into the furnace by adjusting the amount of gangue and coal slime blended, thereby achieving a high proportion of coal slime and gangue blended for combustion.

[0006] CN104724479A discloses a power calorific value coal blending system and method. It mainly utilizes the calorific value of each raw coal to adjust the conveying speed of the raw coal regulating conveyor, thereby achieving closed-loop control of calorific value coal blending and closed-loop control of calorific value.

[0007] None of the aforementioned patents considered the economics of coal blending or its adaptability to power generation load. Summary of the Invention

[0008] The present invention aims to provide a method for blending low-quality coal in coal-fired power plants to overcome the shortcomings of the existing technology.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for blending low-quality coal in a coal-fired power plant, comprising the following steps:

[0010] Step 1, according to coal type C i The calorific value per unit mass is Q. i The market price per unit mass is P. i The calculation yielded coal type C. i unit price of calorific value C i =P i / Q i Based on the n types of coal purchased by the coal-fired power plant, C i Comparison, C i The smallest coal type is the lowest cost coal type. Using this coal type as the main fuel can achieve the lowest power generation cost. The lowest cost coal type is C1, which is the lowest cost low-quality coal.

[0011] Step 2: Based on coal type C1, blend other coal types, controlling the volatile matter (V) and ash fusion point (T) after blending. While ensuring stable combustion at medium loads and preventing boiler coking after blending, control the minimum blending ratio, i.e., ensure the highest possible proportion of coal type C1. Let this ratio be r. m1 ;

[0012] Step 3, with a ratio of r m1 Under the specified coal blending method, determine the maximum load that the coal-fired power unit can achieve by burning this blended coal. At this point, the unit's power generation load reaches the maximum value P under this coal blending method. m1 Assume the maximum rated load of the generating unit under the design coal type is P. max Then P m1 <P max ; at a ratio of r m1 Under this coal blending method, the minimum load that a coal-fired power unit can achieve when burning this blended coal is P. m2 When the unit load is lower than P m2 At that time, assuming the lowest deep-adjustment load that the unit's power generation load can reach under the design coal type of the retrofit is P min Then P m2 >P min .

[0013] As an improvement to the low-quality coal blending method and automatic blending system for coal-fired power plants of the present invention, in step 3, the load can be divided into three load intervals based on the four load points: low load P min ~P m2 Medium load P m2 ~P m1 High load P m1 ~P max Three types of coal blending are implemented in these three load ranges.

[0014] As an improvement to the method and automatic blending system for blending low-quality coal in a coal-fired power plant according to the present invention, the medium-load P m2 ~P m1 The interval uses coal type C1 with a proportion of r. m1 The coal blending method, while blending 1-r m1 The proportion of other high-quality coal types is used to ensure stable boiler combustion and prevent coking.

[0015] As an improvement to the low-quality coal blending method and automatic blending system for coal-fired power plants of the present invention, low-load P min ~P m2 The interval, with a proportion of coal type C1 of r m1 The coal blending method was adjusted to reduce the proportion of coal type C1 and increase the proportion of high-volatile V high-quality coal. At this time, the proportion of coal type C1 was rm2.

[0016] 5. A method for blending low-quality coal in a coal-fired power plant according to claim 2, characterized in that, during high-load P... m1 ~P max The interval, with a proportion of coal type C1 of r m1 The coal blending method is adjusted, reducing the proportion of coal type C1 and increasing the proportion of high-calorific-value (Q) high-quality coal. At this point, the proportion of coal type C1 is r. m3 .

[0017] The present invention aims to provide an automatic blending system for low-quality coal in coal-fired power plants to overcome the shortcomings of the existing technology.

[0018] To solve the above-mentioned technical problems, the technical solution of the present invention is: an automatic blending system for low-quality coal in coal-fired power plants, comprising several loading devices, a first coal conveying belt correspondingly arranged below the loading devices, each first coal conveying belt equipped with a belt scale, a second coal conveying belt arranged below the first coal conveying belt, a mixing coal bin arranged below the second coal conveying belt, three coal outlets at the bottom of the mixing coal bin, each coal outlet equipped with a corresponding unloading valve, a third coal conveying belt corresponding to each coal outlet, and a coal storage bin corresponding to each third coal conveying belt.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] By calculating the coal type with the lowest power generation cost and using it as the primary fuel, combined with blending of other coal types, low-cost power generation can be achieved. This also ensures the stability and safety of boiler combustion, preventing issues such as boiler water-cooled wall overheating and coking. Furthermore, by setting up blended coal storage bins and separate coal hopper compartments, different fuel ratios can be freely switched, allowing for adaptation to the unit's actual power generation load and achieving economical coal blending. This method considers both the economic cost of fuel and the stability and safety of boiler combustion, making it significant for fuel cost control and safe, stable operation of coal-fired power plants. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic diagram of an automatic blending system for low-quality coal in a coal-fired power plant.

[0023] Figure 2 for Figure 1 A schematic diagram of the fuel switcher structure.

[0024] The components include: 1. Raw coal pile; 2. Loading device; 3. First coal conveyor belt; 4. Belt scale; 5. Second coal conveyor belt; 6. Mixed coal bunker; 7. Coal outlet; 8. Coal unloading valve; 9. Third coal conveyor belt; 10. Coal storage bunker; 11. Fourth coal conveyor belt; 12. Three-part coal drop hopper; 13. Fuel switcher; 14. Motor; 15. Coal feeder. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] A method for blending low-quality coal in coal-fired power plants is proposed. The blending method comprehensively considers three dimensions of coal quality: calorific value Q, volatile matter V, and ash fusion point T. The calorific value Q determines the heat load of the boiler, the volatile matter V determines the ease of combustion of the coal, and the ash fusion point T affects the coking situation of the boiler.

[0027] First, based on coal type C i The calorific value per unit mass is Q.i The market price per unit mass is P. i The calculation yielded coal type C. i unit price of calorific value c i =P i / Q i Then, based on the n types of coal (usually 3-4 types) purchased by the coal-fired power plant, c... i Comparison, c i The smallest coal type is the lowest cost coal type. Using this coal type as the main fuel can achieve the lowest power generation cost. Let's assume that the lowest cost coal type is C1, which is the lowest quality coal with the lowest cost.

[0028] Using coal type C1 as the base, other coal types are blended. The volatile matter (V) and ash fusion point (T) of the blended coal are controlled. While ensuring stable combustion at medium loads and preventing boiler coking after blending, the minimum blending ratio is controlled, i.e., ensuring the highest possible proportion of coal type C1. Let this ratio be r. m1 .

[0029] When the ratio is r m1 Under the specified coal blending method, determine the maximum load that the coal-fired unit can achieve by burning this blended coal, that is, when the coal feeder output is at its maximum, the coal feed rate reaches its maximum, and at this time the unit's power generation load reaches the maximum value P under this coal blending method. m1 Assume that the maximum rated load that the generating unit can achieve under the design coal type is P. max Then P m1 <P max .

[0030] During deep peak shaving of coal-fired power units, it is difficult for the boiler to burn low-quality coal, therefore, at a ratio of r m1 Under this coal blending method, the minimum load that a coal-fired power unit can achieve by burning this blended coal is P. m2 When the unit load is lower than P m2 At that time, the mixed coal could not guarantee stable combustion in the boiler. Assume the lowest achievable deep-adjustment load for the unit's power generation load under the modified coal type is P. min Then P m2 >P min .

[0031] Based on the above four load points, three load zones can be defined: low load P min ~P m2 Medium load P m2 ~P m1 High load P m1 ~P max Three coal blending strategies are implemented in these three load ranges.

[0032] Medium load P m2 ~Pm1 The interval uses coal type C1 with a proportion of r. m1 The purpose of this coal blending method is to use as much C1 coal as possible for power generation, while also blending in (1-r) m1 Other high-quality coal types are used in proportion to ensure stable boiler combustion and prevent coking.

[0033] Low load P min ~P m2 The interval, with a proportion of coal type C1 of r m1 The coal blending method was adjusted to reduce the proportion of C1 coal and increase the proportion of high-volatile V high-quality coal, with the aim of ensuring that the minimum load P is maintained. min At this time, the boiler can burn stably, and the proportion of C1 in the coal is r. m2 .

[0034] High load P m1 ~P max The interval, with a proportion of coal type C1 of r m1 The coal blending method is adjusted to reduce the proportion of coal type C1 and increase the proportion of high-calorific-value (Q) high-quality coal. The purpose is to ensure that the boiler can reach its rated load when the coal feeder is at maximum output, and that coking does not occur during combustion. At this time, the proportion of coal type C1 is r. m3 .

[0035] Based on the above three scenarios, the blending methods for low-quality coal C1 are as follows: low-load blending ratio r m2 Medium load blending ratio r m1 High load blending ratio r m3 .

[0036] Due to the structural characteristics of the boiler, a certain amount of coal is stored in the coal hopper. Therefore, fuel switching often requires waiting until all the coal in the coal hopper is completely exhausted before switching to another fuel. The unit load changes frequently according to the grid regulation. Therefore, the traditional coal blending system and coal feeding system cannot adapt to the real-time fuel switching under changing loads. A corresponding automatic blending system needs to be designed.

[0037] See automatic blending system Figure 1 :

[0038] Different types of coal are sorted and piled into raw coal piles 1 in the coal yard. Each raw coal pile 1 is equipped with a loading device 2, and each loading device 2 is equipped with a first coal conveyor belt 3. The loading device 2 loads the coal from the raw coal pile 1 onto the first coal conveyor belt 3. Each first coal conveyor belt 3 is equipped with a belt scale 4, which can weigh the conveyed raw coal. The transmission speed of the first coal conveyor belt 3 is controlled according to the weighing results of the belt scale 4, thereby controlling the coal conveying amount of each first coal conveyor belt 3. The coal conveying amount is determined according to the blending ratio of each type of coal. Each first coal conveyor belt 3 will transport the raw coal to the second coal conveyor belt 5 for collection according to its blending ratio. The second coal conveyor belt 5 will transport the raw coal to the mixing coal bunker 6 for mixing. The mixing coal bunker 6 has three coal outlets 7 at the bottom, each coal outlet 7 is equipped with a coal unloading valve 8, each coal outlet 7 corresponds to a third coal conveyor belt 9, and each third coal conveyor belt 9 corresponds to a coal storage bunker 10. The third coal conveyor belt 9 transports the mixed coal unloaded from the coal outlet 7 to the coal storage silo 10. The three coal outlets 7, three unloading valves 8, three third coal conveyor belts 9, and three coal storage silos 10 correspond to the mixed coal configured for the high, medium, and low load sections, respectively.

[0039] The blending process is as follows: First, coal is blended according to a certain load range, such as the high load range. Each first conveyor belt 3 transports raw coal to the second conveyor belt 5 according to the proportion. After mixing in the mixing coal bunker 6, the coal is discharged through one of the outlets 7 to the corresponding third conveyor belt 9. During discharge, the discharge valve 8 corresponding to that outlet 7 is open, while the other discharge valves 8 are closed. The third conveyor belt 9 transports the blended coal from the high load range to the storage silo 10 for storage. At this time, the other third conveyor belts 9 are not in operation. When the blended coal from the high load range meets the storage requirements of the storage silo 10, the discharge valve 8 is closed, and the corresponding third conveyor belt 9 stops working. At this time, the blending and storage of the high load range is completed. Next, the blending of coal for the medium load range continues. Each first conveyor belt 3 transports raw coal to the second conveyor belt 5 according to the blending ratio for the medium load range, and the blending and storage of the medium load range continues according to the above process. After completing the coal blending for the medium-load section, the coal blending for the low-load section is completed, and this cycle is repeated to continuously store mixed coal in the three coal storage silos.

[0040] Each coal storage bin 10 is equipped with a fourth coal conveyor belt 11, which transports the mixed coal in the coal storage bin 10 to the three-compartment coal hopper 12. Compared to a conventional coal hopper, the three-compartment coal hopper 12 has three internal partitions, dividing it into three independent compartments. Each compartment stores one type of mixed coal, sourced from the three coal storage bins 10. A fuel switcher 13 is installed below the three-compartment coal hopper 12; the structure of the fuel switcher 13 is described below. Figure 2The upper notch corresponds to the lower channel section of the three-compartment coal hopper 12. The motor 14 can drive the fuel switcher 13 to rotate. When the notch corresponds to a certain compartment, the mixed coal in that compartment falls into the coal feeder 15 and is sent to the boiler for combustion. When the unit load switches between high, medium, and low load ranges, the fuel switcher 13 can switch to the corresponding blended coal, achieving rapid fuel switching. Compared with the traditional method, it is not necessary to wait for all the coal in the coal hopper to be exhausted before switching coal types.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0042] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for blending low-quality coal in a coal-fired power plant, characterized in that, Includes the following steps, Step 1, according to coal type C i The calorific value per unit mass is Q. i The market price per unit mass is P. i The calculation yielded coal type C. i unit price of calorific value C i =P i / Q i Based on the n types of coal purchased by the coal-fired power plant, C i Comparison, C i The smallest coal type is the lowest cost coal type. Using this coal type as the main fuel will achieve the lowest power generation cost. The lowest cost coal type is C1, which is the lowest cost low-quality coal. Step 2: Based on coal type C1, blend other coal types, controlling the volatile matter (V) and ash fusion point (T) after blending. While ensuring stable combustion at medium loads and preventing boiler coking after blending coal type C1, control the minimum blending ratio, i.e., ensure the highest possible proportion of coal type C1. Let this ratio be r. m1 ; Step 3, with a ratio of r m1 Under the specified coal blending method, determine the maximum load achieved by the coal-fired unit burning this blended coal. At this point, the unit's power generation load reaches the maximum value P under this coal blending method. m1 Assume the maximum rated load of the generating unit under the design coal type is P. max Then P m1 <P max ; at a ratio of r m1 Under this coal blending method, the minimum load that a coal-fired power unit can achieve when burning this blended coal is P. m2 When the unit load is lower than P m2 At that time, it is assumed that the minimum rated load reached by the generating unit when burning this type of designed coal is P. min Then P m2 >P min ; In step 3, the load is divided into three load zones based on the four load points: low load P min ~P m2 Medium load P m2 ~P m1 High load P m1 ~P max Three types of coal blending are implemented in these three load ranges; Medium load P m2 ~P m1 The interval uses coal type C1 with a proportion of r. m1 The coal blending method, while blending 1-r m1 The proportion of other high-quality coal types is used to ensure stable boiler combustion and prevent coking. Low load P min ~P m2 The interval, with a proportion of coal type C1 of r m1 The coal blending method is adjusted to reduce the proportion of coal type C1 and increase the proportion of high-volatile, high-quality coal. At this time, the proportion of coal type C1 is r. m2 ; High load P m1 ~P max The interval, with a proportion of coal type C1 of r m1 The coal blending method is adjusted to reduce the proportion of coal type C1 and increase the proportion of high-calorific-value (Q) high-quality coal. At this time, the proportion of coal type C1 is r. m3 .

2. The method for blending low-quality coal in a coal-fired power plant according to claim 1, characterized in that, The coal blending method employs an automatic blending system for low-quality coal in coal-fired power plants. This system includes several loading devices, with a first conveyor belt positioned below each loading device. Each first conveyor belt is equipped with a belt scale. A second conveyor belt is positioned below the first conveyor belt, collecting coal from the coal. A mixing coal bin is positioned below the second conveyor belt, with three coal outlets at the bottom of the mixing coal bin. Each coal outlet is equipped with a corresponding unloading valve. A third conveyor belt is positioned corresponding to each coal outlet, and a coal storage bin is positioned corresponding to each third conveyor belt. The three coal outlets, three unloading valves, three third conveyor belts, and three coal storage bins correspond to the mixed coal configured for high, medium, and low load ranges, respectively.

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