KR20210068878A - pulverized coal-fired boiler Combustion system of low-combustibility fuel and combustion method using same. - Google Patents

Abstract

The present invention relates to a pulverized coal-fired boiler combustion system of low-combustion fuel and a combustion method using the same, and more particularly, a low-combustion pulverized coal-fired boiler comprising a combustion unit in which combustion occurs and a windbox unit through which a first fuel and a second fuel different from each other and air are injected into the combustion unit, wherein the windbox unit includes an upper layer part, a middle layer part and a lower layer part, and the upper layer part, the middle layer part and the lower layer part include a fuel supply unit for supplying the first fuel and the second fuel. The pulverized coal-fired boiler combustion system according to the present invention can effectively co-fire low-combustion fuel through simple remodeling of existing facilities without building a new boiler.

Description

Pulverized coal boiler combustion system of low-combustibility fuel and combustion method using same.

The present invention relates to a pulverized coal boiler combustion system for low-combustion fuel and a combustion method using the same.

Pecoke (petcoke, petroleum coke) is a by-product generated in the refining process of crude oil. In the heavy oil pyrolysis process (delated coker), atmospheric/reduced heavy oil is pyrolyzed at high temperature at 490℃ to make curdled flour (LPG, naphtha, kerosene, diesel). By calculation, when waste coke is burned, the same amount of electricity can be produced in an amount of about 80% (1/1.24) of bituminous coal.

Waste coke for fuel has a high sulfur content, low volatile matter content compared to general fuel, and has problems such as reducing corrosion of sulfur oxides and high-temperature oxidation corrosion on the surface of heat transfer parts, so it is classified as a low-grade fuel and has a lower price than sub-bituminous coal. There is a characteristic. In addition, the combustion in the boiler is relatively poor, so there are cases where it is generally used as a power generation fuel using a fluidized bed boiler (CFBC).

Boilers that burn solid fuel are largely divided into pulverized coal boilers and fluidized bed boilers. Unlike pulverized coal boilers, fluidized bed boilers do not require pulverization of fuel, facilitate mixing of various fuels, and allow recirculation of unburned fuel in the boiler. Boiler temperature is low, so efficiency is low and capacity is limited.

On the other hand, pulverized coal boilers are used in most coal-fired power plants in Korea in a way that the fuel is pulverized to less than 200mesh (75㎛) and burned after being put into a moiler. In addition, in order to burn waste coke, expensive fuels such as bunker C oil, LPG, and biogas are burned in a boiler like waste coke, or waste coke that has not yet been burned is collected by facilities such as a multi-cyclone and returned to the boiler. A method of re-combustion by input is also used.

However, in the case of a coal-fired power plant using a large-capacity boiler of 500 to 1000 MW or more, when the expensive fuel is used in parallel, it may cause an increase in fuel cost, and the method of reburning unburned fuel is various, such as sorting and transporting unburned fuel. It can be applied only to small combustion systems because it requires a review from the viewpoint.

Therefore, it is absolutely necessary to develop a combustion method and system capable of co-firing waste coke for fuel into pulverized coal boilers in domestic coal-fired power plants without modifying or remodeling existing facilities and without additional co-firing of fuel.

SUMMARY OF THE INVENTION The present invention aims to solve the above and other problems.

Another object of the present invention is to provide a pulverized coal boiler combustion system for low-combustion fuel and a combustion method using the same.

In addition, it aims to effectively co-fire low-combustion fuel through simple remodeling of existing facilities without constructing a new boiler.

However, these problems are exemplary, and the scope of the present invention is not limited thereto.

According to one aspect of the present invention, in a low-combustion pulverized coal boiler, comprising: a combustion unit in which combustion is performed; and a windbox unit in which different first fuel, second fuel, and air are injected into the combustion unit, the windbox unit It includes an upper layer part, a middle layer part and a lower layer part, and the upper layer part, the middle layer part and the lower layer part provide a low combustion pulverized coal boiler system that includes a fuel supply part for supplying the first fuel and the second fuel. do.

According to an embodiment of the present invention, the fuel supply unit includes a first supply unit to which different first and second fuels are supplied to the upper layer, and different first and second fuels are supplied to the middle layer. It may include a second supply unit supplied to the unit, and a third supply unit through which different first and second fuels are supplied to the lower layer unit.

According to an embodiment of the present invention, the first supply unit, the second supply unit, and the third supply unit receive the first fuel from the first fuel storage unit and the first fuel storage unit and differentiate the first fuel. It may include a primary fuel pulverizer, a pulverized first fuel storage unit for storing the pulverized first fuel, and a second fuel storage unit for storing the second fuel.

According to an embodiment of the present invention, the first supply unit, the second supply unit, and the third supply unit may be connected to each of the four burners.

According to an embodiment of the present invention, the burner is a swirl burner, the swirl burner is disposed at four corners of the boiler, and the angle of the swirl burner disposed at the four corners is 30± It may be 5°.

According to an embodiment of the present invention, the air temperature of the pulverized first fuel storage unit may be maintained at 230°C to 260°C.

According to an embodiment of the present invention, the second fuel storage unit is stored in a pulverized second fuel, and the air temperature of the second fuel storage unit including the pulverized second fuel is maintained at 300°C to 350°C. it could be

According to an embodiment of the present invention, the upper layer portion, the stop layer portion and the lower layer portion are stacked and disposed, and a windbox gap is formed between the stacked upper layer portion, the stop layer portion and the lower layer portion. have.

According to one embodiment of the present invention, the upper layer portion, the middle layer portion and the lower layer portion are auxiliary air nozzles (aux. air nozzle), pulverized coal insufficient nozzle (weak. coal nozzle), pulverized coal excessive nozzle (conc. coal nozzle) , an oil nozzle, and a bottom air nozzle may be included.

According to an embodiment of the present invention, the upper layer portion may further include an over fire air nozzle (OFA nozzle), and the over fire air nozzle (OFA nozzle) may be disposed on the upper portion of the upper layer portion.

According to another aspect of the present invention, there is provided a combustion method using a low combustion pulverized coal boiler system, the method comprising: pulverizing a first fuel; storing the pulverized first fuel in a pulverized first fuel storage unit; and supplying the pulverized first fuel stored in the pulverized first fuel storage unit into a boiler through a windbox, wherein supplying the pulverized second fuel into the boiler includes the pulverized second fuel through the windbox unit. It provides a combustion method of a low combustion pulverized coal boiler to be supplied together with the first fuel.

According to an embodiment of the present invention, the step of storing the pulverized first fuel in the pulverized first fuel storage unit comprises mixing the pulverized first fuel with the primary air having an increased temperature exchanged through a heat exchanger. and may be stored.

According to an embodiment of the present invention, the pulverized first fuel may be pulverized by 90% or more to 325 mesh or less.

According to an embodiment of the present invention, in the step of supplying into the boiler through the windbox unit, the pulverized first fuel is distributed using a distributor, and the pulverized first fuel for which the distribution is completed is transferred to the windbox unit. weak. coal nozzle and conc. It may be supplied through a coal nozzle.

According to an embodiment of the present invention, the windbox part includes an upper layer part, a middle layer part, and a lower layer part, and the pulverized first fuel is the weak. coal nozzle and the conc. It may be uniformly supplied through a coal nozzle.

According to an embodiment of the present invention, the pulverized first fuel is distributed according to a ratio of primary air included in the pulverized first fuel, and a ratio of primary air included in the pulverized first fuel. If is high, weak. If it is supplied through a coal nozzle, and the ratio of primary air contained in the pulverized first fuel is low, conc. It may be supplied through a coal nozzle.

According to an embodiment of the present invention, the pulverized secondary fuel is weak. It may be supplied together with the pulverized first fuel through a coal nozzle.

According to an embodiment of the present invention, the pulverized secondary fuel includes the weak. It may be uniformly supplied through a coal nozzle.

According to an embodiment of the present invention, the amount of excess air injected into the upper layer portion, the middle layer portion, and the lower layer portion may be 5% or less.

According to an embodiment of the present invention, the middle layer portion may be injected by increasing the amount of excess air compared to the upper layer portion and the lower layer portion.

According to an embodiment of the present invention, the middle layer portion may be one in which 1.0 to 1.5 times of excess air is injected as compared to the upper layer portion and the lower layer portion.

According to an embodiment of the present invention, the pulverized secondary fuel may include waste coke, the sulfur content of the waste coke may be 3 wt% to 9 wt%, and the waste coke may be pulverized to 325 mesh or less.

The effects of the low-burning fuel pulverized coal boiler combustion system and the combustion method using the same according to the present invention will be described as follows.

According to at least one of the embodiments of the present invention, there is an effect that it is not necessary to construct a new boiler and can effectively mix low-combustion fuel through simple remodeling of existing equipment.

In addition, there is an effect of improving the efficiency of the coal-fired power plant and lowering the power generation unit cost by using the existing facilities.

In addition, in the case of waste coke, the ash content is low, which is effective in reducing the emission of fine dust.

Further scope of applicability of the present invention will become apparent from the following detailed description. However, it should be understood that the detailed description and specific embodiments such as the preferred embodiments of the present invention are given by way of illustration only, since various changes and modifications within the spirit and scope of the present invention may be clearly understood by those skilled in the art.

1 is a schematic diagram showing the configuration and location of a windbox of a 500MW class pulverized coal boiler according to the present invention.
Figure 2 is a schematic view showing the arrangement of the air injection nozzle of the windbox unit according to the present invention.
3 is a schematic diagram showing a fuel supply unit according to the present invention.
4 is a schematic diagram showing the principle of combustion according to the injection of raw materials into the boiler according to the present invention.
5 shows a combustion simulation result of a 500MW class pulverized coal boiler according to the present invention.
6 shows the results of TGA analysis and measurement of the reaction rate constant according to the present invention.
7 to 9 show changes in the temperature field in the longitudinal direction in the boiler furnace according to the injection of the second raw material according to the height of the windbox according to the present invention.
9 to 10 show the change in the temperature field of the cross section in the weboiler furnace according to the injection of the second raw material according to the height of the windshield according to the present invention.
11 shows changes in LOI content and combustion efficiency according to the present invention.

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings of the present invention. These examples are only illustratively indicated to explain the present invention in more detail, and it will be apparent to those of ordinary skill in the art that the scope of the present invention is not limited by these examples. will be.

Further, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and in case of conflict, this specification, including definitions description will take precedence.

In order to clearly explain the invention proposed in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification. And, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated. In addition, as described in the specification, “subordinate” refers to one unit or block that performs a specific function.

In each step, the identification number (first, second, etc.) is used for convenience of description, and the identification number does not describe the order of each step, and each step does not clearly describe a specific order in context. It may be performed differently from the order specified above.

That is, each step may be performed in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art to which the present invention pertains can easily practice the present invention.

In addition, the standard coal used in the present invention means coal of a standard recommended to be used when designing a boiler for a coal-fired power plant, and the main coal means coal mainly used in a coal-fired power plant.

1 is a schematic diagram showing the configuration and location of a windbox of a 500MW class pulverized coal boiler according to the present invention.

Referring to FIG. 1 , a 500MW class pulverized coal boiler is configured to include a combustion unit in which combustion is performed, and a windbox unit for injecting other first fuel, secondary fuel and air into the combustion unit, wherein the The combustion part means a furnace. In this case, the windbox part is characterized in that it is located at each of the four corners of the boiler.

Figure 2 is a schematic diagram showing the arrangement of the air injection nozzles in the windbox according to the present invention, Table 1 shows the names according to the arrangement of the air injection nozzles.

No. Nozzle name upper part of windbox One OFA nozzle 2 OFA nozzle 3 OFA nozzle 4 OFA nozzle 5 Aux. air nozzle 6 Weak.coal nozzle 7 Conc. coal nozzle 8 Aux. air nozzle 9 Oil nozzle 10 Aux. air nozzle 11 Conc. coal nozzle 12 Weak.coal nozzle 13 Bottom air nozzle windbox gap windbox middle floor 14 Aux. air nozzle 15 Aux. air nozzle 16 Weak.coal nozzle 17 Conc. coal nozzle 18 Aux. air nozzle 19 Oil nozzle 20 Aux. air nozzle 21 Conc. coal nozzle 22 Weak.coal nozzle 23 Bottom air nozzle windbox gap the lower part of the windbox 24 Aux. air nozzle 25 Aux. air nozzle 26 Weak.coal nozzle 27 Conc. coal nozzle 28 Aux. air nozzle 29 Oil nozzle 30 Aux. air nozzle 31 Conc. coal nozzle 32 Weak.coal nozzle 33 Bottom air nozzle

2 and Table 1, the windbox portion is characterized in that it includes an upper layer portion, a middle layer portion and a lower layer portion. Specifically, it is preferable that the windbox portion is disposed by stacking the upper layer portion, the middle layer portion and the lower layer portion, and a windbox gap is formed between the stacked upper layer portion, the stop layer portion and the lower layer portion. .

In addition, the upper layer portion, the middle layer portion, and the lower layer portion are auxiliary air nozzles (aux. air nozzle), pulverized coal insufficient nozzle (weak. coal nozzle), pulverized coal excessive nozzle (conc. coal nozzle), oil nozzle (oil nozzle) , to include a lower air nozzle (bottom air nozzle), the combustion air supplied for pulverized coal combustion can be largely divided into over fire air, primary air, secondary air.

At this time, the over fire air is introduced into the combustion part through the OFA nozzle, and the secondary air is Aux. The air is divided into air nozzle, oil nozzle, and bottom air nozzle, and the primary air is Weak.coal nozzle and Conc. It is introduced together with the pulverized coal through the coal nozzle.

Furthermore, the upper layer portion further includes an over fire air nozzle (OFA nozzle), and the over fire air nozzle (OFA nozzle) is preferably disposed at the top of the nozzle included in the upper layer portion.

In addition, the windbox part including the upper layer part, the middle layer part, and the lower layer part is characterized in that it is divided into 1 to 6 stages.

Specifically, the upper part is divided into first and second stages based on the oil nozzle, and the first stage is a Weak.coal nozzle, Conc. coal nozzle, and Aux. It includes an air nozzle, and the second stage is an Aux. It may include an air nozzle, a coal nozzle, a Weak.coal nozzle, and a Bottom air nozzle.

In addition, the upper part of the middle layer part is divided into 3 stages and 4 stages based on the oil nozzle, and the 3 stages are Weak.coal nozzle, Conc. coal nozzle, and Aux. It includes an air nozzle, and the 4th stage is an Aux. It may include an air nozzle, a coal nozzle, a Weak.coal nozzle, and a Bottom air nozzle.

In addition, the upper part of the lower layer is divided into 5 stages and 6 stages based on the oil nozzle, and the 5 stages are Weak.coal nozzle, Conc. coal nozzle, and Aux. It includes an air nozzle, and the 6th stage is an Aux. It may include an air nozzle, a coal nozzle, a Weak.coal nozzle, and a Bottom air nozzle.

That is, the windbox part, except for the OFA nozzle part, has a weak coal nozzle and a conc. Position the coal nozzles in pairs to aux. As there are six nozzle groups in which the air nozzles are located, it is preferable that the above-mentioned nozzle groups enter two each at the top, the middle, and the bottom of the windbox.

3 is a schematic view showing the fuel supply unit 100 injected into the combustion unit according to the present invention.

The upper layer portion, the middle layer portion and the lower layer portion may include a fuel supply unit 100 for supplying the first fuel and the second fuel.

In detail, the fuel supply unit 100 includes a first supply unit to which different first and second fuels are supplied to the upper layer, and different first and second fuels are supplied to the middle layer. and a second supply unit, and a third supply unit to which different first and second fuels are supplied to the lower layer.

Referring to FIG. 3 , the first supply unit, the second supply unit, and the third supply unit, which are the fuel supply unit 100 , receive the first fuel from the first fuel storage unit 110 and the first fuel storage unit. A first fuel pulverizer 120 for differentiating a first fuel, a pulverized first fuel storage unit 150 for storing the pulverized first fuel, and a second fuel storage unit 160 for storing the second fuel It is characterized in that it includes.

In addition, the first supply unit, the second supply unit, and the third supply unit is characterized in that it is connected to each of the four burners arranged for combustion of the combustion unit. In this case, the burner is a swirl burner, the swirl burner is located at each corner of the combustion unit, and the angle of the swirl burner disposed at each corner is 30±5°.

The first fuel storage unit 110 is a storage unit in which a first fuel is stored, and the first fuel preferably includes raw coal. For example, the first fuel preferably includes bituminous coal and sub-bituminous coal, and may be selected from kideco coal, suek coal, and flame-I coal.

The first fuel differentiator 120 receives the first fuel from the first fuel storage unit 110 and differentiates the first fuel. At this time, in order to increase the combustion efficiency by differentiating the first fuel, it is preferable that the first fuel is finely divided to 325 mesh or less, and specifically, it is preferably 200 mesh or less.

The pulverized first fuel storage unit 150 stores the first fuel pulverized from the first fuel pulverizer 120 , and the air temperature of the pulverized first fuel storing unit 150 is 230° C. to 260° C. It is preferable to keep it at ℃. In this case, when the air temperature is lower than 230°C, the combustion efficiency may be lowered, and when the air temperature is higher than 260°C, the pulverized primary fuel may be ignited. Accordingly, it is preferable to set the air temperature so that combustion efficiency can be maintained without ignition.

The second fuel storage unit 160 stores the second fuel, and the second fuel is pulverized and stored. In this case, the second fuel includes pecoque, and the pecoque has an ash content of 1 wt% or less and a sulfur content of 3 wt% to 9 wt%. In addition, in order to increase the combustion efficiency, it is preferable that the secondary fuel be finely divided to 325 mesh or less, and specifically, it is preferably 200 mesh or less.

In this case, the second fuel storage unit 160 may be separately configured for each stage, but is not limited thereto, and may not be configured separately by performing bunker blending with the first fuel. That is, if the second fuel is injected into the boiler through a weak coal nozzle, the configuration of the second fuel storage unit 160 may not be limited.

In addition, in general, in the case of the pecoque, the activation energy is about twice as high as that of coal. Accordingly, in order to increase combustion efficiency, it is preferable that the air temperature of the second fuel storage unit 160 including the pulverized second fuel is maintained at 300°C to 350°C. At this time, when the air temperature is 350° C. or higher, the pulverized secondary fuel may be ignited. Accordingly, it is preferable to set the air temperature so that combustion efficiency can be maintained without ignition.

According to an embodiment of the present invention, the combustion method using the low-combustion pulverized coal boiler system includes the steps of pulverizing a first fuel, and storing the pulverized first fuel in the pulverized first fuel storage unit 150 . , supplying the pulverized first fuel stored in the pulverized first fuel storage unit 150 to the combustion unit through the windbox unit 180 .

The step of differentiating the first fuel is characterized in that the first fuel is supplied from the first fuel storage unit 110 (1) and the first fuel is differentiated in the first fuel differentiator 120 .

The step of storing the pulverized first fuel storage unit 150 is a first step in which the pulverized first fuel is heat-exchanged from the heat exchanger 140 through the first fuel pulverizer 120 (2) and the temperature is increased. It is characterized in that it is mixed with air and stored (3) in the pulverized first fuel storage unit (150). At this time, it is preferable that the air temperature of the pulverized first fuel storage unit 150 is maintained at 230°C to 260°C by mixing with the primary air having the increased temperature.

In addition, the step of supplying to the combustion unit through the windbox unit 180 is characterized in that while supplying the pulverized first fuel (4), the pulverized second fuel is also supplied (5).

4 is a schematic diagram showing the principle of combustion according to the injection of raw materials into the boiler according to the present invention.

Referring to FIG. 4 , the fuel supply unit 200 includes a distributor 290 , and the distributor 290 distributes the pulverized first fuel and supplies it to the combustion unit.

In detail, in the step of supplying to the combustion unit through the windbox unit 180, the pulverized first fuel is supplied (4) and the supplied first fuel is distributed using the distributor 290, and the The pulverized first fuel, which has been distributed, is weak in the windbox unit 290 . coal nozzle(7-1) and conc. It is characterized in that it is supplied through the coal nozzle (7-2).

In this case, the windbox part 290 includes the upper layer part, the middle layer part, and the lower layer part, and the pulverized first fuel is the weak. coal nozzle (7-1) and the conc. It is preferable to uniformly supply through the coal nozzle (7-2).

At this time, it is preferable to increase the ratio of the primary air to the first fuel to be supplied. In other words, the conc. coal nozzle(7-2) and weak. It is distributed to the coal nozzle (7-1) and injected into the combustion unit, the conc. The pulverized first fuel injected through the coal nozzle has an insufficient amount of air, so the incomplete combustion region 11 is generated, and the unburned pulverized first fuel remains.

In this case, the weak. The pulverized first fuel injected through the coal nozzle has a higher air ratio than the coal ratio, so that the complete combustion region 10 is achieved, but the amount of the pulverized first fuel (the amount of coal) itself is small, leaving a large amount of air. . Thus, the conc. As the pulverized first fuel remaining after incomplete combustion in the coal nozzle rises to the upper part of the combustion unit, the weak. It meets with the excess air remaining in the coal nozzle and restarts the combustion reaction to form a complete combustion region 12 above the position of the burner.

Accordingly, in order to co-fire the finely divided secondary fuel, the weak. It is preferable to supply (5) together with the pulverized primary fuel through a coal nozzle.

That is, the pulverized first fuel and the pulverized second fuel are supplied to the combustion unit at a predetermined ratio to pass through the region 10 in which a large amount of excess air exists, so that the combustibility is somewhat lower than that of the pulverized first fuel. Incomplete combustion of the pulverized secondary fuel can be prevented.

In addition, excess air may be further injected into the combustion unit for complete combustion of the pulverized secondary fuel.

Specifically, the weak. Excess air may be injected through the coal nozzle, and the amount of the injected excess air is preferably 5% or less.

In addition, it is preferable to inject by increasing the amount of excess air in the middle layer portion compared to the upper layer portion and the lower layer portion.

Specifically, the range of the excess air ratio to the secondary fuel injected from the weak coal nozzle is preferably 1.0 to 1.5 times.

Hereinafter, the present invention will be described in detail through Examples and Experimental Examples. However, the following Examples and Experimental Examples only illustrate the present invention, and the present invention is not limited by the following Examples and Experimental Examples.

5 shows a combustion simulation result of a 500MW class pulverized coal boiler according to the present invention.

Referring to FIG. 5(a), in the velocity distribution of the cross section where z=1m, the air injected from the air nozzle flows from left to right, and most of the air injected from the upper nozzle rises obliquely to the right of the upper part of the combustion unit. and the air injected from the remaining lower nozzle descends to the hopper area under the combustion unit to form a recirculation area. Afterwards, it becomes clear that it rises along the spiral upward flow formed at the center of the combustion unit, and it can be seen that the distribution rises obliquely from the left to the right side of the wall. In the vicinity of the air injection nozzle, a high-speed flow field is formed according to the inflow of air, and the upper left It can be seen that the flow is biased toward and rising.

In addition, referring to FIG. 5(b), in the velocity distribution of the z=8.064m section, the air flow toward the center of the combustion unit and the flow at the bottom meet at the center of the furnace and start to rise, and rise along the center of the furnace to the top of the boiler. and a relatively high-speed flow is formed in the region near the right.

Also, referring to FIG. 5-1(c), the velocity distribution of the cross section when y=21.6m is aux. With the flow in the air nozzle, it can be seen that this part tends to rise mainly vertically. In addition, it can be confirmed that a clockwise rotation is formed when a little deviates from the center. At this time, the rotational direction of the swirling flow appears in the order of the front, right side, rear side, and left side directions, and a small vortex is formed by the flow injected near each nozzle and the flow formed near the wall surface.

5-2 (a), in the temperature distribution, the low-temperature air injected from the nozzle flows along the flow field from right to left along the wall to form a low-temperature region of less than 900K near the nozzle and the wall, and combustion It can be seen that it is distributed as if forming a layer from low to high temperature according to the height in the lower part of the part.

In addition, under the influence of CC OFA and SOFA, a low-temperature region appears obliquely along the flow of the internal gas, and as a whole, a high temperature is formed in the re-burn region after OFA through the vicinity of the windbox part and the upper part of the combustion part, and the temperature as it progresses to the exit is lowered, and in particular, it can be seen that the temperature change is abruptly caused by the superheater panels located on the upper part.

In addition, referring to FIG. 5-2(b), a convex temperature distribution is shown from the bottom of the boiler to the top of the windbox and then to the furnace outlet. In the vicinity of the windbox, the temperature at the center of the furnace is relatively low compared to the temperature near the surrounding wall. is showing

This tendency is due to the flow characteristics described above, and appears convex upward because the flow that descends to the lower part of the combustion unit rises along the center of the vortex, and the air and pulverized coal injected from each nozzle are biased toward the wall due to the vortex. As a result of the flow, the flame is also formed in a circle around the wall, so that the temperature near the wall tends to appear higher.

In addition, referring to FIG. 5-2(c), a low-temperature region of less than 900K is shown near each corner nozzle, and the flame is formed along the swirling flow and has a circular shape in cross section, and the temperature gradient near the wall and the center It can be seen that the temperature gradient is large.

Example 1. Evaluation of fuel characteristics of pecoque.

In order to evaluate the fuel characteristics of pecoque and compare it with general coal to evaluate the possibility that it can be mixed and used in existing coal-fired power plants, industrial analysis and elemental analysis of 8 pecoque samples by particle size were conducted.

Table 2 shows the industrial analysis results of pecoque by particle size, and Table 3 shows the elemental analysis results of pecoque by particle size.

Sample name granularity Industry analysis (wt%) fuel cost
(Fixed carbon / volatile matter) moisture volatile matter ash fixing
carbon Pekok
6.5 100mesh or more 1.02 11.66 1.50 85.82 7.36 140mesh or less 1.19 12.42 1.12 85.33 6.87 200mesh or more 1.12 13.63 0.92 84.33 6.19 200mesh or less 1.13 14.24 0.84 83.79 5.88 Pekok
7.0 100mesh or more 0.87 9.48 1.11 88.53 9.34 140mesh or less 0.65 9.50 1.00 88.825 9.35 200mesh or more 0.55 10.56 0.82 88.06 8.34 200mesh or less 0.68 12.35 0.54 86.43 7.00

Sample name granularity Elemental analysis (wt%) calorific value
(kcal/kg) carbon Hydrogen nitrogen Oxygen sulfur content eminence low rank Pekok
6.5 100mesh or more 86.50 3.68 1.61 0.65 6.08 8,417 8,213 140mesh or less 86.28 3.76 1.60 0.92 6.32 8,443 8,237 200mesh or more 86.62 3.74 1.66 0.75 6.31 8,463 8,253 200mesh or less 86.73 3.78 1.66 0.70 6.28 8,457 8,247 Pekok
7.0 100mesh or more 87.94 3.46 1.47 0.33 5.35 8,400 8,223 140mesh or less 88.08 3.50 1.63 0.20 5.65 8,460 8,267 200mesh or more 88.27 3.54 1.64 0.12 5.62 8,490 8,293 200mesh or less 88.92 3.44 1.63 0.07 5.41 8,533 8,343

Referring to Tables 2 and 3, as the particle size of pecoque decreased, the moisture content and fuel ratio decreased and the volatile matter increased. In addition, it can be confirmed that the fuel characteristics of the semi-anthracite grade are shown in the range of 0.6 to 3.9% moisture, 82 to 92% fixed carbon, 5 to 15% volatile matter, and 6 to 17 fuel ratio, and the fixed carbon content is 86wt% to 96wt %, it can be confirmed that most of the pecoque samples are carbon components. In addition, the calorific value is 8,400 ~ 8,803 kcal/kg at the high level and 8,213 ~ 8,567 kcal/kg at the low level, confirming that it has a higher calorific value than general bituminous coal.

Example 2. Evaluation of fuel properties of mixed coal.

In order to evaluate the fuel properties and usability of the mixed coal mixed with pecoque and bituminous coal (FLAME-1), the sample was prepared by sieving and mixing pecoque and bituminous coal to a size of 200 mesh (75㎛) or less. Industrial analysis and elemental analysis were carried out according to the content of dupe coke and bituminous coal.

Sample name Content ratio (wt%)
Pekok: bituminous coal Industry analysis (wt%) fuel cost
(Fixed carbon / volatile matter) moisture volatile matter ash fixing
carbon Pekok
6.5 5:95 16.55 36.08 6.48 40.89 1.13 10:90 15.66 34.25 6.13 43.96 1.28 15:85 14.60 33.26 6.09 46.05 1.38 20:80 14.03 32.64 5.82 47.81 1.46 Pekok
7.0 5:95 16.90 36.19 6.49 40.42 1.12 10:90 15.81 34.58 6.29 43.32 1.25 15:85 15.47 33.26 6.00 45.27 1.36 20:80 14.96 32.83 5.73 46.48 1.42

Sample name Content ratio (wt%)
Pekok: bituminous coal Elemental analysis (wt%) calorific value
(kcal/kg) carbon Hydrogen nitrogen Oxygen sulfur content eminence low rank Pekok
6.5 5:95 69.60 4.85 1.54 16.40 1.13 6,420 6,060 10:90 71.95 4.92 1.51 13.97 1.52 6,580 6,220 15:85 74.75 4.78 1.58 12.80 1.82 6,730 6,380 20:80 74.45 7.84 1.51 11.31 2.04 6,840 6,490 Pekok
7.0 5:95 70.95 5.02 1.55 14.98 1.01 6,420 6,050 10:90 73.35 4.86 1.52 12.56 1.42 6,580 6,220 15:85 73.60 4.82 1.48 12.42 1.68 6,690 6,340 20:80 75.10 4.80 1.55 11.06 1.76 6,810 6,460

As a result of the fuel characteristic evaluation, it can be confirmed that the fixed carbon, fuel cost, and calorific value increase as the content of pecoque increases, and the volatile matter and ash content decrease.

In addition, it can be seen that the nitrogen content is about 1.5 wt%, and the change in the content is not large. Through this, it is judged that the amount of flue NOx generated by mixing pecoque is almost not even when pecoque is mixed and burned.

Example 3. Kinetic evaluation of pecoque and bituminous coal

Thermogravimetric analysis (TGA) was performed to evaluate the combustibility of fuel containing pecoque in a boiler.

6 shows the results of TGA analysis and measurement of the reaction rate constant according to the present invention. In addition, Table 6 below shows the activation energy and frequency constant for each sample, and a coat redfern model was used to calculate the activation energy and frequency constant.

At this time, the activation energy is the minimum energy required for the activation (combustion_) reaction, and the larger the value, the lower the reaction, and the frequency constant is the collision frequency at the molecular level where the reaction can occur. The higher the value, the better the reactivity.

Accordingly, referring to FIGS. 6 and 6, it can be seen that pecoque has higher activation energy and frequency constant values compared to bituminous coal. In pecoque, the combustion reaction takes place in a relatively high temperature range, and the activation energy is in bituminous coal. It is about 2 times higher than that of bituminous coal, but the frequency constant is 50 to 100 times higher, so that the reaction rate constant (k, temperature range 1,100~1,400℃) is higher than that of bituminous coal. That is, it can be predicted that the combustibility in the boiler of pekok will be superior to that in the boiler of bituminous coal.

activation energy
(E, Kj/mol) frequency constant
(A, s ^-1 ) R ² Bituminous Coal (FLAME-I) 49.98 1.0E+01 0.970 Pecoque 6.5 86.40 5.0E+02 0.946 Pecoque 7.0 92.80 9.0E+02 0.957

Example 4. Combustion kinetic evaluation of pekok-bituminous coal mixed coal

In order to evaluate the combustibility of the pecoque-bituminous coal mixed coal in the boiler, the sample was analyzed in the same manner as in Example 3 except that the sample was used according to the pecoque-bituminous coal mixing ratio, and the results are shown in Table 7.

Pecoque content
(Pecoque: bituminous coal) Pecoque 7.0 activation energy
(E, Kj/mol) frequency constant
(A, s ^-1 ) R ² 5wt% (5:95) 46.67 6.0E+01 0.886 10wt% (10:90) 49.59 8.0E+02 0.933 15wt% (15:85) 30.69 3.0E-01 0.653 20wt% (20:80) 21.26 2.0E-02 0.601

Referring to Table 7, it can be seen that the activation energy and frequency constant are lowered as the content of pecoque is increased. Specifically, when the content of pecoque is 10 wt% or less, changes in combustion and reactivity in the boiler can be predicted to be good without it.

Example 5. Evaluation according to the degree of pulverization of Pekok.

The hardgrove index (HGI) was evaluated by pre-treating pecoque used as a high-calorie auxiliary fuel, and the results are shown in Table 8.

Sample pretreatment 200mesh passing amount
(Based on sample 50g) HGI Pecoque 6.5 No sample drying 10.36g 84.79 Pecoque 7.0 14.75g 115.22 Pecoque 6.5 dry naturally
(37℃, 3hr, cooling 20hr) 9.94g 81.88 Pecoque 7.0 8.65g 72.94 Pecoque 6.5 completely dry
(100℃, 3hr, cooling 20hr) 10.89g 88.47 Pecoque 7.0 12.02g 96.30

The grindability index (HGI index) can be calculated through Equation 1 below.

Calculation 1

HGI=(6.93 * standard 200 mesh passing amount) + 13

The grindability index (HGI index) is an index indicating the degree of pulverization of coal, and a higher value means better pulverization. Generally, the pulverization index of coal is 59 to 80, and the pulverization index of domestic anthracite is 120 . In comparison, it can be seen that the pulverization index of pecoque according to the sample pretreatment method is 73 to 120, which is higher than that of general coal. Through this, it can be predicted that when pekok is pulverized for co-firing of a pulverized coal boiler in a coal-fired power plant, the pulverization energy required to increase the pulverization degree is low.

Example 6. DTF evaluation of pecoque and bituminous coal.

This was carried out to derive the optimal combustion conditions for the co-firing of pecoque in the pulverized coal boiler of a coal-fired power plant. The combustion characteristics were evaluated by measuring the amount of ash generation and loss on ignition (LOI) according to the conditions using a drop tube furnace (DTF) for a sample sieved with pecoque and bituminous coal under 200 mesh as a standard sieve. compared. At this time, the furnace temperature, excess air flow rate, and residence time (replaced by furnace length) of DTF were varied according to the degree of fineness of the pecoque.

In general, fuel input to boilers in coal-fired power plants is pulverized so that particles of 200 mesh or less occupy 90% or more through the pulverizer. Therefore, in the case of pecoque, since it is known that the combustibility is relatively low compared to coal, the DTF combustibility was reviewed by adjusting the fineness of pecoque to 325mesh or less, and the results are shown in Tables 9 and 10.

DTF variable result division Temperature
(℃) residence time
(length, cm) excess air volume
(Oxygen, L/min) ash generation
(wt%) LOI
(wt%) bituminous coal 1,300 90 5.45 8.03 3.65 1,100 90 5.45 10.82 7.85 1,300 50 5.45 12.09 12.64 1,300 90 6.00 11.05 2.84 1,300 90 4.80 (+3.10air) 9.91 12.54 Pekok 1,300 90 5.45 4.80 - 1,100 90 5.45 4.32 - 1,300 50 5.45 8.19 - 1,300 90 6.00 2.94 - 1,300 90 4.80 (+3.10 air) 11.06 -

DTF variable result granularity
(mesh) Temperature
(℃) residence time
(length, cm) excess air volume
(Oxygen, L/min) ash generation
(wt%) LOI
(wt%) 200 or less 1,300 90 5.45 4.80 - 275 or less 1,300 90 5.45 4.10 - 325 or less 1,300 50 5.45 3.81 -

Referring to Table 9, as the amount of ash generated and the LOI content decreases, it approaches complete combustion, and it can be confirmed that the change in the amount of ash and the LOI content according to the variables is conspicuous when an experiment using bituminous coal is used. However, in the case of testing using FEKO, it can be confirmed that the amount of ash generated varies depending on the residence time and the flow condition of excess air, but there is no change in the amount of ash generated depending on the furnace temperature. In particular, in the case of Pecoque, it can be seen that the amount of ash generated varies according to the flow rate of excess air.

In general, coal-fired power plants are operated by maintaining the excess air amount at 1.18 of the theoretical oxygen amount. Accordingly, even in the DTF furnace, when the excess air amount was maintained at the same condition as the excess air amount of the coal-fired power plant, the higher the ratio of oxygen to air, the closer to complete combustion was obtained. Through this, it was confirmed that nitrogen in the air was an obstacle to the combustion of bituminous coal and pecoque.

In addition, in the case of the experiment in which the excess air flow rate was set to about 1.3 times the theoretical oxygen amount (excess air flow rate, oxygen 6.0 L/min), it was confirmed that the LOI content and the amount of pecoque ash generated in bituminous coal ash were significantly lower. In other words, it can be confirmed that it is desirable to mix the pecock under the conditions of sufficient excess air, such as in the weak and coal nozzles of the windbox part, and it is possible to confirm that a lot of excess air exists in the upper part through the OFA nozzle like the upper layer of the windbox part. In this area, it can be predicted that the combustion of pecoque will become more active.

In addition, by injecting a certain amount of oxygen into the weak, coal nozzle, it is possible to promote the combustion of the pecoque and increase the combustion efficiency.

Referring to Table 10, it can be seen that the higher the fineness, the lower the amount of ash generated in Pecoque. Compared with the case of changing the excess air amount, the change in the amount of ash generation was not relatively large, but it can be confirmed that it can affect the LOI content in the ash during co-firing of pecoque, and the width increases as the co-firing rate of pecoque increases. is expected to increase. Therefore, it can be confirmed that the combustion efficiency can be increased by injecting an excess amount of air and at the same time increasing the degree of pulverization to improve the combustion in the pulverized coal boiler of Pekok.

Example 6. Computational analysis of 500MW gold pulverized coal boiler Pekok co-firing

Computational analysis was carried out to create shape and boundary conditions based on a 500MW-class boiler, and to compare the diameter of mixing and spraying pecoque into the existing coal nozzle. Conc.coal nozzle, weak. After mixing and spraying pecoque into the coal nozzle, a computational analysis was performed to compare and analyze the unburnt content in the coal ash. The conditions according to the computational analysis case are shown in Table 11, and the unburned content thereof is shown in Table 12.

case No. Condition case 1 design coal combustion case 2-1 Mix design bullet + pecoque and inject it into the entire nozzle case 2-2 Total secondary air volume increased in case 2-1 condition case 2-3 In case 2-1 condition, 1st and 2nd stage 2nd air amount increased case 2-4 In case 2-1 condition, 3rd and 4th stage secondary air volume increased case 2-5 4, 5eks 2ck air volume increase in case2-1 condition case 3-1 Injection of the lower part of the pecock (5 steps) case 3-2 Injection of the lower part of the pecock (5 steps) case 3-3 In case 3-1 condition, pecoque injection primary air temperature increased case 3-4 In case 3-1 condition, pecoque injection primary air flow rate / temperature increase case 4-1 Pecock Interrupted (3rd Stage) Injection case 4-2 In case 4-1 condition, pecoque injection primary air temperature increased case 4-3 In case 4-1 condition, Pecoque's differential degree increased

Analysis conditions case No. Unburnt content (wt%) Co-fired effect of Pekok compared to design rounds case 1 2.3 case 2-1 6.9 In the case of mixed injection of design coal/pekok
Effect of Secondary Air Volume Change case 2-1 6.9 case 2-2 2.8 case 2-3 4.5 case 2-4 1.4 case 2-5 2.1 Effect of primary air condition change in the case of injecting the lower end of the pecock (5 stages) case 3-1 35.2 case 3-2 32.3 case 3-3 34.9 case 3-4 31.8 Effect of primary air and fineness change in the case of pecock interruption (3rd stage) injection case 4-1 30.8 case 4-2 31.2 case 4-3 28.3

Referring to Tables 11 and 12, it can be seen that when the pecoque is mixed and injected into all nozzles of the windbox unit (case 2-1), the content of the unburned portion is increased by about 4.6% compared to the design coal. In addition, it can be seen that the unburned powder content is significantly increased in the method of injecting the pecoque injection position individually for each stage (case 3-1, case 4-1). In this case, it can be seen that the unburned content is relatively low.

When pecoque was mixed with design coal and the effect of the change in the secondary air amount for each stage was examined, when the secondary air quantity of the 3rd and 4th stage, which is the middle layer of the windbox part, was increased, the unburnt content was the lowest at 1.4wt%. . In addition, when the primary air temperature was increased by 15°C and the fineness was increased, it was confirmed that the unburned powder content decreased by about 3% compared to the existing one. Accordingly, in the case of co-firing the pecoque, bunker blending is carried out, the amount of secondary air in the 3rd and 4th stages, which are the middle layers of the windbox part, is increased, and the unburned content is minimized when a relatively small amount of air from other nozzles is injected. It can be confirmed that the .

7 to 8 show the change of the temperature field in the longitudinal direction in the boiler furnace according to the injection of the second raw material according to the height of the windbox part according to the present invention, and FIGS. 9 to 10 are the windbox parts according to the height of the windbox according to the present invention. 2This shows the change in the temperature field of the section of the boiler furnace according to the injection of raw materials.

Specifically, Figs. 7 and 8 show z=12.5m, 8.25m. The temperature distribution at 15.25m is shown, and FIGS. 9 and 10 show the temperature distribution at the cross sections at y=17.41, 24.54m, 34.05m, and 51.52m positions. 7 to 10, depending on the injection positions of the conc, coal nozzle, and weak, coal nozzle, there is a section in which the temperature range is slightly higher than that of the designed coal, but this is because the gas temperature is slightly increased as the pecock is burned. As it rises, it can be confirmed that the overall distribution of gas temperature in the furnace does not change significantly because the co-burning ratio of pekok does not significantly affect the fixed carbon ratio of the total coal.

Example 7. Evaluation of co-firing characteristics of Pecoque using a large-capacity test combustion furnace

The co-firing characteristics of pecoque were evaluated using a test combustion furnace of 200 kg-coal/hr (owned by Korea Electric Power Research Institute). To evaluate this, two types of main coal (bituminous coal) (kideco, suek) and 1 type (flame-I) of auxiliary coal (sub-bituminous coal) were prepared, and when the above three types of coal were burned 100%, Each combustion characteristic was evaluated by dividing it into the case of 10% co-firing (based on the total calorific value of fuel). At this time, according to the results of Examples 5 and 6, the excess air amount was set to 5% in order to make the nozzle part into which the fuel is injected with combustion air into a weak condition with a large excess air amount, and for secondary air injection into the test combustion The co-firing characteristics of the pecoque were evaluated by setting the angle of the swirl burner to 30°. The combustion efficiency for this is shown in Table 13. In addition, FIG. 11 shows changes in LOI content and combustion efficiency according to the present embodiment.

coal fire Pekok 5% mixed firing Pecoque 10% mixed firing kideco shot 99.90 99.79 99.72 suek shot 99.78 99.51 99.49 flame-I shot 99.68 99.22 99.02

Referring to FIGS. 11 and 13, when the pecoque is co-fired to 10% or less (based on calorific value), the total fuel amount is reduced by 3%, and the contact probability with excess air is increased. It can be confirmed that the combustion efficiency similar to that of standard coal is produced by co-firing the pecoque. That is, it can be confirmed that the combustion efficiency of 99% or more is achieved by mixing and injecting the pecoque in the range of 5% of excess air and the angle of the swarf burner in the range of 30±5°.

In this specification, only a few examples among the various embodiments performed by the present inventors will be described, but the technical spirit of the present invention is not limited or limited thereto, and it is of course that it may be modified and variously implemented by those skilled in the art.

100, 200: fuel supply unit
110: first fuel storage unit
120: primary fuel pulverizer
140: heat exchanger
150: pulverized first fuel storage unit
160: second fuel storage unit
180: windbox unit
290: divider

Claims (22)

In the low combustion pulverized coal boiler,
a combustion unit in which combustion occurs; and
and a windbox unit in which different first fuel, second fuel, and air are injected into the combustion unit.
The windbox part includes an upper layer part, a middle layer part and a lower layer part,
The upper layer portion, the middle layer portion and the lower layer portion will include a fuel supply unit for supplying the first fuel and the second fuel,
Low combustion pulverized coal boiler system. According to claim 1,
The fuel supply unit,
Including; a first supply unit to which different first and second fuels are supplied to the upper layer portion;
It includes; a second supply unit to which different first fuel and second fuel are supplied to the interruption layer unit;
Which includes; a third supply unit to which different first and second fuels are supplied to the lower layer portion;
Low combustion pulverized coal boiler system. 3. The method of claim 2,
The first supply unit, the second supply unit and the third supply unit
a first fuel storage unit;
a first fuel pulverizer for receiving the first fuel from the first fuel storage unit and differentiating the first fuel;
a pulverized first fuel storage unit for storing the pulverized first fuel; and
A second fuel storage unit for storing the second fuel;
Low combustion pulverized coal boiler system. 4. The method of claim 3,
The first supply part, the second supply part and the third supply part will be connected to each of the four burners,
Low combustion pulverized coal boiler system. 5. The method of claim 4,
The burner is a swirl burner,
The swirl burner is disposed at the four corners of the boiler,
The angle of the swirl burner disposed at the corner is 30 ± 5 °,
Low combustion pulverized coal boiler system. 4. The method of claim 3,
The air temperature of the pulverized first fuel storage unit is to be maintained at 230 ℃ to 260 ℃,
Low combustion pulverized coal boiler system. 4. The method of claim 3,
In the second fuel storage unit, the second fuel is pulverized and stored,
The air temperature of the second fuel storage unit including the pulverized second fuel is maintained at 300°C to 350°C,
Low combustion pulverized coal boiler system. According to claim 1,
The upper layer portion, the middle layer portion and the lower layer portion
stacked and placed,
A windbox gap is formed between the stacked upper layer part, the middle layer part, and the lower layer part,
Low combustion pulverized coal boiler system. According to claim 1,
The upper layer portion, the middle layer portion and the lower layer portion
Auxiliary air nozzle (aux. air nozzle), pulverized coal insufficient nozzle (weak. coal nozzle), pulverized coal excessive nozzle (conc. coal nozzle), oil nozzle (oil nozzle), to include a bottom air nozzle (bottom air nozzle) ,
Low combustion pulverized coal boiler system. 10. The method of claim 9,
The upper layer further comprises an over fire air nozzle (OFA nozzle),
The over fire air nozzle (OFA nozzle) will be disposed on the upper portion of the upper layer,
Low combustion pulverized coal boiler system. It relates to a combustion method using the low combustion pulverized coal boiler system of claim 1,
pulverizing the first fuel;
storing the pulverized first fuel in a pulverized first fuel storage unit;
and supplying the pulverized first fuel stored in the pulverized first fuel storage unit to the combustion unit through a windbox unit;
The supplying to the combustion unit is to supply the pulverized second fuel together with the pulverized first fuel through the windbox unit,
Combustion method of low-combustion pulverized coal boiler. 12. The method of claim 11,
Storing the pulverized first fuel in the pulverized first fuel storage unit,
The primary air having an increased temperature exchanged through a heat exchanger and the pulverized primary fuel are mixed and stored,
Combustion method of low-combustion pulverized coal boiler. 13. The method of claim 12,
That the pulverized first fuel is pulverized more than 90% to 325 mesh or less,
Combustion method of low-combustion pulverized coal boiler. 12. The method of claim 11,
The step of supplying to the combustion unit through the windbox unit,
The pulverized first fuel is distributed using a distributor,
The pulverized first fuel for which the distribution is completed is weak. coal nozzle and conc. which is supplied through a coal nozzle,
Combustion method of low-combustion pulverized coal boiler. 15. The method of claim 14,
The windbox part includes an upper layer part, a middle layer part and a lower layer part,
The pulverized primary fuel is the weak. coal nozzle and the conc. It is uniformly supplied through the coal nozzle,
Combustion method of low-combustion pulverized coal boiler. 16. The method of claim 15,
The pulverized first fuel is distributed according to the ratio of primary air contained in the pulverized first fuel,
If the ratio of primary air included in the pulverized primary fuel is high, weak. It is supplied through a coal nozzle,
If the ratio of primary air contained in the pulverized first fuel is low, conc. which is supplied through a coal nozzle,
Combustion method of low combustion pulverized coal boiler 12. The method of claim 11,
The pulverized secondary fuel is weak. It will be supplied together with the pulverized first fuel through a coal nozzle,
Combustion method of low-combustion pulverized coal boiler. 18. The method of claim 17,
The windbox part includes an upper layer part, a middle layer part and a lower layer part,
The pulverized secondary fuel includes the weak. It is uniformly supplied through the coal nozzle,
Combustion method of low-combustion pulverized coal boiler. 19. The method of claim 18,
The amount of excess air injected into the upper layer portion, the middle layer portion and the lower layer portion is 5% or less,
Combustion method of low-combustion pulverized coal boiler. 19. The method of claim 18,
The interruption layer portion is injected by increasing the amount of excess air compared to the upper layer portion and the lower layer portion,
Combustion method of low-combustion pulverized coal boiler. 21. The method of claim 20,
The interruption layer portion is that 1.0 to 1.5 times the excess air is injected compared to the upper layer portion and the lower layer portion,
Combustion method of low-combustion pulverized coal boiler. 18. The method of claim 17,
The pulverized secondary fuel includes waste coke,
The sulfur content of the waste coke is 3wt% to 9wt%,
The waste coke will be finely divided to 325 mesh or less,
Combustion method of low-combustion pulverized coal boiler.

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