JP2008169338A - Method of reducing unburned coal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reducing unburned coal which does not need additional capital investment, reduces the amount of unburned coal in coal ash at a low cost and enhances the electric power generation efficiency. <P>SOLUTION: The method for reducing unburned coal reduces the amount of unburned coal after the coal used for fuel in coal-fired power generation systems is burned by adding a coal-adding unburned coal reducing agent. Metal oxides or compounds serving as the raw material for the metal oxides are used for the coal-adding unburned coal reducing agent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for reducing unburned coal for reducing unburned coal in coal ash.

  There are various methods for burning coal in a coal-fired power generation system. Among them, so-called pulverized coal combustion in which particles obtained by finely pulverizing coal are blown into a furnace and burned is mainly employed. And the coal ash which becomes the residue after combustion is partially used as civil engineering and building materials, such as concrete and a soil improvement material, from a viewpoint of effective utilization of resources.

  Depending on the coal combustion conditions, unburned carbon may remain in the coal ash, and this may cause harmful effects in the effective use of coal ash as unburned coal. For example, when coal ash is used as a cement admixture, the air entraining agent added to the cement is absorbed by the unburned coal, which reduces the construction softness of concrete and the resistance to freezing and thawing. It was known to do. In such a case, a method of increasing the amount of the air entrainment agent added to the cement, a method of adding a large amount of unburned fraction from the coal ash, and the method of adding it to the cement were performed. None of these methods is expensive and could not be suitably implemented.

In order to solve such a problem, Patent Document 1 includes a hydrophobizing step of hydrophobizing the unburned coal by adding a collecting agent to the water slurry of coal ash, and adding a foaming agent to the water slurry. In the method for treating coal ash, which includes a flotation process in which bubbles are generated and the unburned coal is attached to the bubbles and floats, the cation collector and the nonpolar reagent are used in combination as a collector. A method for treating coal ash is disclosed. According to this coal ash treatment method, a cation scavenger is used in combination with a non-polar reagent as a scavenger, so that more unburned coal is attached to the bubbles compared to the conventional example. The For this reason, it is said that the unburned coal content in coal ash can be separated very efficiently.
JP-A-5-339094

  However, in the invention described in Patent Document 1, after collecting the coal ash generated in the combustion furnace, a process for treating the coal ash is separately required. By providing such a treatment process, There was a problem that the processing cost was increased. In addition, in the invention described in Patent Document 1, equipment for treating coal ash is also necessary, and new equipment investment is required to implement the method.

  In addition, the remaining unburned matter in the coal ash is a problem related to the power generation efficiency of the coal-fired power generation system, and there is also a problem that the power generation cost is increased because the coal does not completely burn in the combustion furnace. It was. Here, the invention described in Patent Document 1 does not show any solution to such a problem.

  The present invention has been made in view of the above-described problems, and is a method that does not require new capital investment, can reduce unburned components in coal ash at low cost, and can further generate power. An object of the present invention is to provide a method for reducing unburned coal that can increase efficiency.

  The present inventors have found that when an unburned coal reducing agent for coal addition consisting of a metal oxide or a compound that is a raw material of the metal oxide is added to coal, the unburned content in coal ash can be reduced, The present invention has been completed.

  Specifically, the present invention provides the following.

  (1) A method for reducing unburned coal by reducing unburned coal after combustion of coal by adding an unburned coal reducing agent for coal addition to coal as fuel in a coal-fired power generation system. A coal unburned matter reducing method using a metal oxide or a compound serving as a raw material for the metal oxide as the coal-added unburned matter reducing agent.

  According to the invention described in (1), since a metal oxide or a compound serving as a raw material of the metal oxide is added to coal, the metal oxide oxidizes unburned coal in a high-temperature combustion furnace, Unburned matter in coal ash can be reduced. Thereby, since coal is fully burned in a combustion furnace, power generation efficiency can also be improved.

  Here, the “metal oxide” refers to a metal oxide having an oxidizing power for oxidizing carbon in coal in an environment ranging from 1300 ° C. to 1500 ° C. in a combustion furnace. The “compound that becomes” refers to a compound that forms such a metal oxide in the environment. That is, the “compound as a raw material for the metal oxide” is a compound that generates the metal oxide by thermal decomposition.

  (2) The metal oxide or the compound that is a raw material of the metal oxide is an oxide of at least one metal selected from the group consisting of calcium, magnesium, iron, and copper, or a compound that is a raw material of the oxide The method for reducing unburned coal according to (1).

  Calcium, magnesium, iron, and copper oxides have oxidizing power, and can sufficiently oxidize unburned components in coal ash in a combustion furnace ranging from 1300 ° C to 1500 ° C. Therefore, according to the invention described in (2), it is possible to effectively reduce the unburned content in the coal ash. In addition, if calcium, magnesium, iron, and copper are added in a reduced amount, they will not adversely affect the combustion furnace even if added to the combustion furnace. Moreover, even under such conditions, the unburned content in the coal ash can be effectively reduced. Therefore, according to the invention described in (2), it is possible to safely implement the method for reducing unburned coal.

  (3) The unburned coal according to (1) or (2), wherein the metal oxide or the compound that is a raw material of the metal oxide is at least one selected from the group consisting of quicklime, slaked lime, and limestone. Reduction method.

  According to the invention described in (3), in addition to the effect described in (2), there is an effect that the method for reducing unburned coal can be implemented at low cost. That is, quick lime, slaked lime, and limestone are inexpensive and can be easily obtained, so that the cost required for the method for reducing unburned coal can be kept low.

  (4) The unburned matter reducing agent for coal addition is added in a range of 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the coal according to any one of (1) to (3). Coal unburned matter reduction method.

  According to the invention described in (4), since 0.1 parts by mass or more of the unburned coal reducing agent for coal addition is added to 100 parts by mass of coal, the unburned content in coal ash is effectively reduced. Can do. Further, since 10 parts by mass or less of the unburned coal reducing agent for coal addition is added to 100 parts by mass of coal, the influence on the combustion furnace can be minimized.

  (5) The coal-fired power generation system is a power generation system of a pulverized coal combustion system, and the coal according to any one of (1) to (4), in which the coal-added unburned content reducing agent is added into a combustion boiler. Unburned content reduction method.

  According to the invention described in (5), the unburned fuel reducing agent for coal addition can be added into the combustion boiler. When such an addition is performed, the addition of new equipment can be minimized, so that the unburned content in the coal ash can be kept low while effectively using the existing equipment.

  (6) The coal-fired power generation system is a power generation system of a pulverized coal combustion system, and the coal-added unburned content reducing agent is added upstream of the combustion boiler according to any one of (1) to (4) Coal unburned matter reduction method.

  According to the invention as described in (6), the unburned content reducing agent for coal addition can be added upstream from the combustion boiler. When such an addition is performed, the addition of new equipment can be minimized, so that the unburned content in the coal ash can be kept low while effectively using the existing equipment.

  According to the present invention, since an unburned component reducing agent for coal addition is added to coal, no new capital investment is required to reduce the unburned amount of coal ash, and unburned coal ash in coal ash can be reduced at low cost. Minutes can be reduced. Furthermore, the method for reducing unburned coal according to the present invention increases the efficiency of coal combustion at the stage of combustion of coal in the combustion furnace, and thus can contribute to the improvement of power generation efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a pulverized coal combustion facility that is an example of a coal-fired power generation system will be described as an example.

<A: Configuration of pulverized coal combustion facility in coal-fired power generation system>
FIG. 1 is a block diagram showing a pulverized coal combustion facility 1 in a coal-fired power generation system. Here, as shown in FIG. 1, the pulverized coal combustion facility 1 includes a coal supply unit 12 that supplies coal, a pulverized coal generation unit 14 that converts the supplied coal into pulverized coal, and a pulverized coal that burns pulverized coal. The combustion part 16 and the coal ash process part 18 which processes the coal ash produced | generated by combustion of pulverized coal are provided. FIG. 2 is an enlarged view of the vicinity of the combustion furnace 161 in the pulverized coal combustion section 16.

<A-1: Coal supply section>
The coal supply unit 12 includes a coal bunker 121 that stores coal, and a coal feeder 122 that supplies the coal stored in the coal bunker 121. The coal bunker 121 stores coal to be supplied to the coal feeder 122. The coal feeder 122 continuously supplies the coal supplied from the coal bunker 121 to the coal pulverized coal machine 141. Moreover, this coal feeder 122 is provided with the apparatus which adjusts the supply_amount | feed_rate of coal, and, thereby, the amount of coal supplied to the coal pulverizer 141 is adjusted. Further, a coal gate is provided at the boundary between the coal bunker 121 and the coal feeder 122, thereby preventing air from the coal feeder from flowing into the coal bunker.

<A-2: Pulverized coal generation unit>
The pulverized coal generation unit 14 includes a coal pulverized coal machine 141 (mil) that converts coal into pulverized coal capable of pulverized coal combustion, and an air supply unit 142 that supplies air to the coal pulverized coal machine 141.

  The coal pulverized coal machine 141 pulverizes the coal supplied from the coal feeder 122 through the coal supply pipe to form fine pulverized coal, and is supplied from the pulverized coal and the air supply unit 142. Mix with fresh air. Thus, by mixing pulverized coal and air, the pulverized coal is preheated and dried to facilitate combustion. Air is blown onto the formed pulverized coal, thereby supplying the pulverized coal to the pulverized coal combustion unit 16.

  Examples of the type of the coal pulverized coal machine 141 include a roller mill, a tube mill, a ball mill, a beater mill, an impeller mill, and the like. However, the type of the coal pulverized coal machine 141 is not limited to these and may be any mill used in pulverized coal combustion.

<A-3: Pulverized coal combustion section>
The pulverized coal combustion unit 16 supplies air to the combustion furnace 161 that burns the pulverized coal generated by the pulverized coal generation unit 14, a heater 162 (heat exchange unit) that heats the combustion furnace 161, and the combustion furnace 161. And an air supply machine 163 for carrying out the operation.

  The combustion furnace 161 is heated by the heater 162 (heat exchange unit), and combusts the pulverized coal supplied from the coal pulverized coal machine 141 via the pulverized coal pipe together with the air supplied from the air supply unit 163. By burning pulverized coal, coal ash is generated and discharged to the coal ash treatment unit 18 together with the exhaust gas.

  The combustion furnace 161 will be described in detail with reference to FIG. 2. In FIG. 2, the combustion furnace 161 has a generally inverted U shape as a whole, and the combustion gas moves in an inverted U shape along the arrow in the figure. After that, it is inverted again into a small U shape, and the outlet of the combustion furnace 161 (the last arrow in FIG. 2) is connected to the denitration device 181 and the dust collector 182 in FIG. In the pulverized coal combustion facility 1 according to this embodiment, the height of the combustion furnace 161 is 30 m to 70 m, and the total length of the exhaust gas flow path ranges from 300 m to 1000 m.

  Below the combustion furnace 161, a burner 161a for burning pulverized coal is disposed in the vicinity of the burner zone 161a 'in the combustion furnace 161. Also, near the top of the U-shape in the combustion furnace 161, a furnace upper dividing wall 161b, a final superheater 161b ′, and a first reheater 161f (all of which are heat exchange units) are arranged, and further from there A standing primary superheater 161c (heat exchange unit) is subsequently arranged. Further, a second reheater 161f ′ is provided in parallel with the horizontal primary superheater 161c, and from the vicinity of the terminal end of the horizontal primary superheater 161c, the primary economizer 161d (heat exchange unit). A secondary economizer 161e (heat exchange unit) is provided in two stages. Here, the economizer (also referred to as ECO) is a heat transfer surface group provided for preheating boiler feedwater using the heat held by the combustion gas. In the present embodiment, in the combustion furnace 161, the primary economizer 161d and the secondary economizer 161e are installed separately in two stages, but the present invention is not limited to such a form. That is, the combustion furnace 161 may have only a single economizer.

<A-4: Coal ash treatment unit>
The coal ash treatment unit 18 includes a denitration device 181 that removes nitrogen oxides in the exhaust gas discharged from the pulverized coal combustion unit 16, a dust collector 182 that removes soot in the exhaust gas, and coal ash collected by the dust collector 182. A coal ash recovery silo 183 for primary storage.

  The denitration device 181 removes nitrogen oxides in the exhaust gas. That is, ammonia gas is injected as a reducing agent into exhaust gas at a relatively high temperature (300 to 400 ° C.), and nitrogen oxides in the exhaust gas are decomposed into harmless nitrogen and water vapor by the action of a denitration catalyst, so-called dry ammonia contact. A reduction method is preferably used.

  The dust collector 182 is a device that collects coal ash in the exhaust gas with an electrode. The coal ash collected by the dust collector 182 is conveyed to the coal ash collection silo 183. Further, the exhaust gas from which the coal ash has been removed is discharged from the chimney after passing through a desulfurization device (not shown).

  The coal ash collection silo 183 is a facility that primarily stores the coal ash collected by the dust collector 182.

<B: Coal unburned matter reduction method of the present invention>
The method for reducing unburned coal according to the present invention comprises adding unburned coal reducing agent for coal addition to coal as fuel in a coal-fired power generation system, thereby reducing unburned coal after combustion of coal. A method for reducing unburned coal, comprising using a metal oxide or a compound that is a raw material for the metal oxide as an unburned amount reducing agent for coal addition. A description will be given using the pulverized coal combustion facility 1.

  The coal unburned matter reducing method of the present invention includes a coal supply step S10 for supplying coal, a pulverized coal generation step S20 for pulverizing the supplied coal to generate pulverized coal, and burning the pulverized coal to produce coal ash. A pulverized coal combustion step S30 and a coal ash treatment step S40 that collects and stores the coal ash, each of which includes a coal supply unit 12 of the above-described pulverized coal combustion facility 1, It is performed in the pulverized coal generation unit 14, the pulverized coal combustion unit 16, and the coal ash treatment unit 18. The unburned coal reduction step S50, which is a feature of the present invention, is preferably performed in any one of the coal supply unit 12, the pulverized coal generation unit 14, and the pulverized coal combustion unit 16.

<Coal supply process S10>
First, in the coal supply step S <b> 10, the coal stored in the coal bunker 121 is supplied to the coal pulverized coal machine 141 by the coal feeder 122. The coal supplied to the coal pulverized coal machine 141 is specifically bituminous coal, subbituminous coal, lignite, or the like, but is not limited to these coals and can be pulverized coal combustion. Good.

<Pulverized coal production process S20>
Next, in the pulverized coal generation step S20, the coal supplied from the coal feeder 122 is pulverized by the coal pulverized coal machine 141, thereby generating pulverized coal. The generated pulverized coal is supplied to the combustion furnace 161. At this time, the average particle size of the pulverized coal formed in the pulverized coal generation step may be a particle size range generally used in pulverized coal combustion, and generally 74 μm under 80 wt% or more. The degree of pulverization. This range can also be applied when an unburned coal reducing agent for coal addition is added.

<Pulverized coal combustion process S30>
Next, in the pulverized coal combustion step S <b> 30, the pulverized coal generated by the coal pulverized coal machine 141 is burned by the combustion furnace 161. As shown in FIG. 2, the pulverized coal is burned in the burner zone 161a ′, and the temperature at this time ranges from 1300 ° C. to 1500 ° C., and the coal ash generated by the combustion rises in the direction of the arrow. And the exhaust gas through the furnace upper partition wall 161b, the final superheater 161b ', the first reheater 161f, the second reheater 161f', and the horizontal primary superheater 161c (all of which are heat exchange units). The primary economizer 161d (heat exchange unit) and the secondary economizer 161e (heat exchange unit) are sequentially passed. The vicinity of the heat exchange unit is an area where the temperature is maintained at about 450 ° C. to about 900 ° C., and passes through a heat transfer surface group provided for preheating boiler feedwater using the heat held by the combustion gas. As a result, heat exchange occurs and the temperature decreases. The time required for the exhaust gas to reach from the burner zone 161a ′ to the vicinity of the economizer is approximately 5 to 10 seconds. Then, it is sent to a denitration device 181 and a dust collector 182 at the subsequent stage. The coal ash produced in the pulverized coal combustion step S30 is usually in the form of a powder having an average particle size in the range of 1 μm to 100 μm.

<Coal ash treatment process S40>
Thereafter, the coal ash generated by burning pulverized coal is discharged to the denitration device 181 together with the exhaust gas, and sent to the coal ash recovery silo 183 through the dust collector 182. The dust collector 182 is preferably provided in a plurality of stages.

<Coal unburned matter reduction process S50>
As shown in FIG. 1, the coal unburned matter reducing step S50, which is a step of adding the coal-added unburned amount reducing agent, which is a feature of the present invention, is preferably the above-described coal supply unit 12 and pulverized coal generating unit 14 This is performed for any of the pulverized coal combustion sections 16 (S51, S52, S53 in FIG. 1 respectively).

  In addition, the addition place of the unburnt reducing agent for coal addition will not be specifically limited if it is a state of coal, For example, the transfer path between the coal supply part 12 and the pulverized coal production | generation part 14, or a pulverized coal production | generation part 14 and the pulverized coal combustion unit 16 may be used.

  Specifically, for example, a method of supplying and mixing the coal-added unburned content reducing agent on the belt conveyor being transferred when transporting from the coal feeder 122 to the coal pulverized coal machine 141, and coal-added unburned A method of directly supplying a minute reducing agent to a coal hopper (not shown) of the coal pulverized coal machine 141, a method of supplying an agent charging port in a pipe between the coal pulverized coal machine 141 and the combustion furnace 161, and a combustion furnace 161 Examples of such a method include direct injection with combustion air, but are not limited thereto. As described above, the method of the present invention does not require a new facility, and can be applied by a slight improvement of the existing facility. Therefore, the existing facility can be used effectively, which is advantageous in terms of cost.

  Examples of the metal constituting the metal oxide used in the unburned coal reducing agent for coal addition and the raw material of the metal oxide of the present invention include calcium, magnesium, iron, and copper. Among these, calcium can be preferably used.

When calcium is used as the metal, examples of calcium oxides and compounds used as raw materials for the oxides include limestone (CaCO ₃ ), slaked stone (Ca (OH) ₂ ), and quicklime (CaO). Can do. As for limestone and slaked lime, since calcium oxide is generated by thermal decomposition in an environment ranging from 1300 ° C. to 1500 ° C. in the combustion furnace 161, it can be used as a compound as a raw material of the metal oxide of the present invention. Is.

  The unburned coal reducing agent for coal addition is preferably granular or powdery, specifically, the average particle size is preferably 10 μm to 100 μm, more preferably 10 μm to 80 μm, and more preferably 10 μm to 60 μm. More preferably. When the average particle size is less than 10 μm, the average particle size is too fine and is not practical as an unburned content reducing agent for coal addition. When the average particle size exceeds 100 μm, the effect of adjusting the average particle size can hardly be obtained. Moreover, when making an average particle diameter into 80 micrometers or less, the particle size of the unburned content reducing agent for coal addition can be adjusted using the coal pulverized coal machine 141, and it is efficient.

  As for the addition amount to coal of the unburned content reducing agent for coal addition, it is preferable to add 0.1 mass part or more of the unburned content reducing agent for coal addition to 100 parts by mass of coal. When the amount is less than 0.1 parts by mass, the effect of adding the unburned coal reducing agent for coal addition cannot be substantially obtained. On the other hand, depending on the type of metal oxide to be used, the coal-unburned unburnt reducing agent may be added at less than 10 parts by mass from the viewpoint of preventing slugging and fouling in order to lower the melting point of coal ash. Preferably, it is more preferably added at 6.0 parts by mass or less, and further preferably at 1.0 parts by mass or less.

<Example 1>
In a coal-fired power generation facility using a pulverized coal combustion system, 1 part by mass of limestone was added to 100 parts by mass of coal, and pulverized and mixed with a coal pulverizer. This was sent to a combustion furnace together with air to burn coal. The dust contained in the exhaust gas after combustion was collected at each stage (from the first stage to the fourth stage) of the electric dust collector to obtain fly ash. The above test was performed twice independently to obtain two series of fly ash.

<Comparative Example 1>
In a coal-fired power generation facility using a pulverized coal combustion method, pulverized coal was pulverized without adding limestone to the coal. This was sent to a combustion furnace together with air to burn coal. The dust contained in the exhaust gas after combustion was collected at each stage (from the first stage to the fourth stage) of the electric dust collector to obtain fly ash. The above test was performed twice independently to obtain two series of fly ash.

<Measurement of unburned coal>
About the fly ash obtained in Example 1 and Comparative Example 1, the unburned content in coal ash as defined in JIS M8815 based on the ash content and moisture value in coal ash determined by the method defined in JIS M8812 The content (ratio of the mass of unburned carbon in coal ash) was determined. The results are shown in Table 1.

  As is clear from Table 1, it can be seen that the unburned amount in the coal ash of Example 1 is smaller than the unburned amount in the coal ash of Comparative Example 1. From the above results, it was found that by adding limestone to coal and burning it, the unburned content in the coal ash decreased.

It is a schematic block diagram of the pulverized coal combustion facility in the coal thermal power generation system which shows one Embodiment of this invention. FIG. 2 is an enlarged view of the vicinity of a combustion furnace in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pulverized coal combustion facility 12 Coal supply part 121 Coal bunker 122 Coal feeder 14 Pulverized coal production | generation part 141 Coal pulverized coal machine 142 Air supply machine 16 Pulverized coal combustion part 161 Combustion furnace 161a Burner 161a 'Burner zone 161b Furnace upper division wall 161b 'Final superheater 161c Horizontal primary superheater 161d Primary economizer 161e Secondary economizer 161f First reheater 161f' Second reheater 162 Heater 163 Air supply unit 18 Coal ash treatment unit 181 Denitration Equipment 182 Dust collector 183 Coal ash recovery silo S10 Coal supply process S20 Pulverized coal generation process S30 Pulverized coal combustion process S40 Coal ash treatment process S50 Coal unburned matter reduction process

Claims (6)

An unburned coal reduction method for reducing unburned coal after burning the coal by adding an unburned coal reducing agent for coal addition to the coal that serves as fuel in the coal-fired power generation system,
A coal unburned matter reducing method using a metal oxide or a compound as a raw material of the metal oxide as the coal-unburned burnout reducing agent.   The metal oxide or the compound that is a raw material of the metal oxide is an oxide of at least one metal selected from the group consisting of calcium, magnesium, iron, and copper, or a compound that is a raw material of the oxide. Item 4. The method for reducing unburned coal according to Item 1.   The method for reducing unburned coal according to claim 1 or 2, wherein the metal oxide or the compound that is a raw material of the metal oxide is at least one selected from the group consisting of quicklime, slaked lime, and limestone.   The unburned coal reduction according to any one of claims 1 to 3, wherein the unburned coal reducing agent for coal addition is added in a range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the coal. Method.   The coal unburned coal power generation system according to any one of claims 1 to 4, wherein the coal thermal power generation system is a power generation system of a pulverized coal combustion system, and the coal unburned fuel reducing agent is added to a combustion boiler. .   The coal coal power generation system is a pulverized coal combustion type power generation system, and the coal unburned component reducing agent is added upstream from a combustion boiler. Method.

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