JP6605934B2 - Coal fired boiler and low-grade coal drying method - Google Patents

Description

  Embodiments of the present invention relate to a coal fired boiler and a method for drying low-grade coal.

In a thermal power plant using coal as fuel, finely pulverized coal is burned in a coal fired boiler, and power is generated by rotating a steam turbine with the generated steam.
In conventional coal-fired boilers for thermal power generation, high-grade coal such as bituminous coal has been used as fuel coal, but in recent years, as fuel costs have risen, there have been few opportunities to use it as fuel. The use of low-grade coal (sub-bituminous coal, lignite, etc.) is being studied. As a prior art which concerns on this kind of coal fired boiler, what is described in patent document 1 can be mentioned, for example.

  Low-grade coal such as sub-bituminous coal has a low degree of coalification compared to high-grade coal, and therefore not only has a low carbon content but also contains a lot of moisture. Moreover, depending on the type of coal, there are some that contain about 20% of water, and about 45% of water when there are many.

  Conventionally, when low-grade coal containing a lot of moisture is used as fuel in coal fired boilers for thermal power generation, it is used by mixing with high-grade coal with low moisture and high calorific value, or when moisture is about 35% or less In the case of coal, there was a method of exclusively burning low-grade coal by increasing the number of pulverized coal machines capable of drying coal and increasing the size.

  Here, FIG. 3 is a diagram schematically showing an outline of a conventional general coal fired boiler for thermal power generation.

  The coal fired boiler 10 includes a furnace 12 that generates a high-temperature combustion gas by burning coal, and a rear heat transfer section 14.

  A plurality of burners 15 are installed in the lower part of the furnace 12 at different installation heights. Each of these burners 15 is connected to a vertical roller / lace type pulverized coal machine 17 through a pulverized coal pipe 16, and the finely pulverized coal from these vertical type roller / lace type pulverized coal machine 16 is used as fuel. It comes to be supplied.

  Inside the furnace 12, a superheater 18 is installed above, and in the rear heat transfer unit 14, reheaters 19 and 20 and a heat exchanger such as a economizer 22 are installed. The combustion gas that has exchanged heat with these heat exchangers is sent from the outlet of the rear heat transfer section 14 to the air preheater 24.

  The air preheater 24 uses the combustion gas extracted from the outlet of the economizer 22 to exchange heat with the primary air introduced using the primary air fan 25 to preheat the primary air. The primary air is heated to about 330 ° C. by the air preheater 24 and then sent to the pulverized coal machine 17 through the primary air duct 26 to be used as a heat source for drying the low-grade coal.

  In such a conventional coal-fired boiler drying system, a low-grade coal with a moisture content of about 20% is practically used to adjust the moisture, even if it is not mixed with a high-grade coal, a low-grade coal is used. Charcoal can be burned exclusively.

JP 2008-304178 A

  However, in the coal drying system used in the conventional coal fired boiler, the combustion gas extracted from the outlet of the rear heat transfer section 14 is used as a heat source for drying low-grade coal, and the air preheater 24 uses the pulverized coal machine. The primary air sent to 17 is preheated.

  In the coal fired boiler 10 for power generation, the temperature of the combustion gas discharged from the rear heat transfer section 14 is usually about 350 ° C. When the combustion gas temperature is about this level, a drying effect sufficient for practical use can be obtained for low-grade coal having a moisture content of about 20%. However, depending on the type of coal, the moisture content may be 30 to 45%, which is insufficient as a heat source for such low-grade coal, and supplying pulverized coal with sufficient combustion conditions to the burner 15. There is a problem that it cannot be done.

  The present invention has been made in view of the above-described problems of the prior art, and is a coal fired boiler and a low-grade coal that can be fired exclusively in a boiler even with a low-grade coal having a high water content. It aims to provide a method.

In order to achieve the above object, the present invention provides a furnace having a plurality of burners for burning pulverized coal, and a coal fired boiler having a rear heat transfer section continuous to the furnace, and pulverizing coal into pulverized coal. An air preheater that preheats the primary air by exchanging heat between the pulverized coal machine that supplies the burner, the combustion gas introduced from the outlet of the rear heat transfer section, and primary air at room temperature, and the air preheating A primary air duct for supplying primary air preheated by a gas generator to the pulverized coal machine, and a combustion gas duct for extracting combustion gas from the rear heat transfer section, wherein the primary air duct transmits the combustion gas to the primary air. It is connected to the combustion gas duct via a combustion gas injection device for injecting into the duct, and the rear heat transfer section includes a reheater and a economizer installed downstream of the reheater, The combustion gas duct is It is characterized in that to extract the combustion gases from the intermediate position between the vessel and the economizer.

  According to the present invention, even low-grade coal with a high water content can be sufficiently dried and sent to a burner and can be burned exclusively with a boiler.

It is a mimetic diagram showing a coal fired boiler by a 1st embodiment of the present invention. It is a schematic diagram which shows the coal fired boiler by 2nd Embodiment of this invention. It is a schematic diagram which shows the coal fired boiler which concerns on a prior art.

Hereinafter, an embodiment of a method for drying a coal fired boiler and low-grade coal according to the present invention will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a diagram schematically showing an outline of a coal fired boiler according to the present embodiment. This coal-fired boiler 10 is installed in a thermal power plant and uses high-grade coal such as bituminous coal as fuel, and also uses low-grade coal such as sub-bituminous coal and lignite with a low degree of coalification other than bituminous coal. A boiler that can.

  The coal fired boiler 10 is roughly composed of a furnace 12 that generates high-temperature combustion gas by burning coal and a rear heat transfer section 14 that is disposed downstream from the outlet of the furnace 12.

  First, in the lower part of the furnace 12, three burners 15a to 15c are installed at different installation heights as burners for burning pulverized coal. The furnace 12 is a rectangular tube-like structure, and four burners at each stage of the burners 15a to 15c are installed on a diagonal line. By burning the burners at all stages of these burners 15a to 15c, the coal fired boiler 10 can generate steam necessary for rated load operation with a power generation amount of 100% of the thermal power plant.

  Next, in FIG. 1, the code | symbol 17 has shown the pulverized coal machine which grind | pulverizes the coal thrown in from the coal feeder which is not shown in figure, and processes it into pulverized coal. In this embodiment, a vertical roller race type pulverized coal machine is used as the pulverized coal machine. This vertical roller lace type pulverized coal machine is a pulverized coal machine having a structure in which coal supplied from a coal feeder is crushed by a roller tire that rolls on a table. From the bottom of the table, primary air preheated by an air preheater, which will be described later, is introduced, and the pulverized pulverized coal is dried by mixing with primary air, and passes through the pulverized coal pipe 16. It is supplied to the stage burners 15a to 15c.

Next, arrangement | positioning of heat exchangers, such as a superheater, in the coal fired boiler 10 is demonstrated.
The coal fired boiler 10 of this embodiment is a boiler that supplies steam to a turbine in which a reheat cycle is configured. Inside the furnace 12, a superheater 18 that generates high-temperature and high-pressure steam to be sent to a high-pressure turbine is installed above. In the rear heat transfer section 14, a first reheater 19 that reheats the steam returned from the high pressure turbine and sends it to the intermediate pressure turbine is disposed on the downstream side of the outlet of the furnace 12.

  Further, a second reheater 20 is disposed downstream of the first reheater 19. On the downstream side of the second reheater 20, a economizer 22 for heating the boiler feed water is installed. A gas duct 26 for introducing combustion gas into the air preheater 24 is connected to the outlet 23 of the rear heat transfer section 14. The combustion gas that has exchanged heat with the economizer 22 flows through the gas duct 26 and is sent to the air preheater 24.

  The air preheater 24 exchanges heat between the combustion gas extracted from the outlet 23 of the rear heat transfer section 14 through the gas duct 26 and the primary air introduced using the primary air fan 25 to perform primary air. Preheat. The air preheater 24 and the pulverized coal machine 17 are connected by a primary air duct 27, and the preheated primary air is supplied to the pulverized coal machine 17 through the primary air duct 27.

  In the coal fired boiler 10 of the present embodiment, the primary air preheated by the air preheater 24 is further heated with combustion gas and used as an effective drying heat source for low-grade coal as a fuel. A combustion gas duct 30 is provided as a gas extraction pipe.

  In the rear heat transfer section 14, a combustion gas extraction port 28 is provided at a position upstream of the economizer 22, and a combustion gas duct 30 extends from the extraction port 28 to the primary air duct 27. A combustion gas injection device 32 for injecting combustion gas into the primary air duct 27 is provided in the middle of the primary air duct 27. The combustion gas injection device 32 is connected to the end of the combustion gas duct 30.

  In this embodiment, the combustion gas duct 30 is provided with a gas extraction fan 33 in order to efficiently extract the combustion gas from the rear heat transfer section 14. On the upstream side of the gas extraction fan 33, a dust collecting device 34 is provided to protect the gas extraction fan 33 from slag remaining after burning pulverized coal.

The coal fired boiler 10 according to the present embodiment is configured as described above. Next, the operation and effect thereof will be described.
First, the flow of combustion gas in the coal fired boiler 10 will be described.

  The combustion gas generated by the combustion of the pulverized coal in the burners 15a to 15c becomes a jet and flows upward in the furnace 12. The superheater 18 disposed at the top of the furnace 12 is heated mainly by the radiant heat of the flame to generate high-temperature and high-pressure steam.

  The downstream side of the superheater 18 is the outlet of the furnace 12, and the temperature of the combustion gas decreases as it flows downstream. However, in normal operation, the amount of pulverized coal to burn is large, so the outlet of the furnace 12 The temperature of the combustion gas at is kept high.

  Further, the combustion gas flows into the rear heat transfer section 14 from the outlet of the furnace 12, exchanges heat with the first reheater 19, and reheats the steam returned from the high pressure turbine. After that, the combustion gas exchanges heat with the second reheater 20 and the economizer 22, and then flows through the gas duct 26 and is sent to the air preheater 24.

  In the air preheater 24, heat exchange is performed between normal temperature primary air taken in by the primary air fan 25 and combustion gas of about 360 ° C. sent through the gas duct 25, and the primary air is The temperature is raised to about 330 ° C.

  The primary air that has exited the air preheater 24 is further heated by the high-temperature combustion gas extracted from the rear heat transfer section 14 via the combustion gas duct 30 as follows.

  That is, the combustion gas extracted from the rear heat transfer section 14 is injected from the combustion gas injection device 32 into the pipe of the primary air duct 26. When the combustion gas injected into the primary air duct 27 joins the flow of the primary air, the combustion gas and the primary air are mixed and supplied to the pulverized coal machine 17.

  In the case of boiler operation at the rated load, the temperature of the combustion gas upstream of the economizer 22 is normally maintained at a high temperature of about 500 to 600 ° C. in the rear heat transfer section 14. If the primary air is heated to about 330 ° C. by preheating in the air preheater 24, the primary air can be further heated to about 400 to 450 ° C. by injecting high-temperature combustion gas.

  Thus, the primary air is subjected to a process for raising the temperature in two stages, such as heat exchange with the combustion gas in the air preheater 24 and injection of the combustion gas by the combustion gas injection device 32, and then the primary air is supplied to the pulverized coal machine 17. It is sent and used as a heat source for drying low-grade coal.

  In the pulverized coal machine 17, primary air heated to a high temperature is blown out from under a table on which a roller tire that pulverizes a coal lump, and the pulverized low-grade coal is separated from high-temperature primary air. Are dried and pulverized to be supplied to the burners 15a to 15c.

  According to the above-mentioned coal fired boiler drying system, even low-grade coal with a moisture content of about 45% is dried to, for example, about 10% and mixed with high-grade coal to adjust moisture. Even if not, it becomes possible to burn exclusively in the boiler.

(Second Embodiment)
Next, 2nd Embodiment of the coal fired boiler 10 which concerns on this invention is described with reference to FIG.

  In the second embodiment, a combustion gas duct 30 provided with a gas extraction fan 33 and a dust collector 34 that protects the gas extraction fan 33 is connected to the air preheater 24 via a combustion gas injection device 32. The point connected to the primary air duct 27 downstream is the same as in the first embodiment, and the same components are denoted by the same reference numerals and detailed description thereof is omitted.

  The difference from the first embodiment is that a temperature detector 40 for detecting the gas temperature is provided on the outlet side of the pulverized coal machine 17, and the combustion gas flow rate of the combustion gas is provided upstream of the combustion gas injection device 32 in the combustion gas duct 30. This is in that a combustion gas flow rate adjusting mechanism 42 for adjusting the above is provided.

The fuel gas flow rate adjusting mechanism 42 includes a valve mechanism portion 43 that has a variable valve opening degree, and a valve drive portion 44 that drives the valve mechanism portion 43. A servo mechanism is configured in which the opening degree of the valve mechanism 43 is adjusted so that the difference between the gas temperature detected by the temperature detector 40 and a preset target gas temperature is eliminated. ing.
Next, the operation of the coal fired boiler system of the second embodiment as described above will be described.
Also in the second embodiment, the primary air is heated in two stages in which the temperature is raised by heat exchange with the combustion gas in the air preheater 24 and further raised by the injection of the combustion gas from the combustion gas injector 32. Temperature treatment is performed. For this reason, the high-temperature combustion gas is supplied to the pulverized coal machine 17 as in the first embodiment.

  On the other hand, the gas temperature on the outlet side of the pulverized coal machine 17 is considered to correlate with the moisture content and the dry state of the pulverized coal. The fact that the gas temperature on the outlet side of the pulverized coal machine 17 is high is a case where moisture is sufficiently evaporated from the pulverized coal and drying is sufficiently advanced. On the other hand, when this gas temperature is lower than the planned temperature, it is assumed that the amount of water in the pulverized coal is large and drying is insufficient.

  Therefore, for the low-grade coal used as fuel, the condition of the gas temperature at the outlet side of the pulverized coal machine 17 necessary for drying to pulverized coal suitable for exclusive firing is determined experimentally in advance corresponding to the moisture content. . Based on these data, for example, the gas temperature at the outlet side of the pulverized coal machine 17 necessary for drying low grade coal having a moisture content of about 45% to about 10% is set.

  During operation of the boiler, the temperature detector 40 detects the gas temperature on the outlet side of the pulverized coal machine 17, and the primary air is supplied from the combustion gas injection device 32 so that this gas temperature becomes a preset target gas temperature. The flow rate of the combustion gas injected into the duct 26 is adjusted. That is, when the gas temperature at the outlet side of the pulverized coal machine 17 does not reach the target temperature, the opening degree of the valve mechanism 43 is increased and injected into the primary air duct 26 via the combustion gas injection device 32. The gas flow rate increases. In this way, the gas temperature on the outlet side of the pulverized coal machine 17 is finally maintained at the target temperature, so that the pulverized coal can be dried without excess or deficiency.

  As described above, according to the second embodiment, even low-grade coal having a moisture content of about 45% can be reliably dried to, for example, about 10%. Even many low-grade coals can be made into pulverized coal in a state suitable for exclusive firing.

  As mentioned above, although the preferred embodiment was mentioned and demonstrated about the drying method of the coal fired boiler and low grade coal which concern on this invention, these embodiment was mentioned as an illustration and intends the restriction | limiting of the scope of the invention. It is not a thing. Of course, the novel apparatus, method and system described in the specification can be implemented in various forms, and various omissions, substitutions and changes can be made without departing from the spirit of the present invention. is there. The claims and their equivalents are intended to cover the embodiments or improvements thereof within the spirit of the invention.

DESCRIPTION OF SYMBOLS 10 ... Coal fired boiler, 12 ... Furnace, 14 ... Rear heat transfer part, 15a-15c ... Burner, 16 ... Pulverized coal pipe, 17 ... Pulverized coal machine, 18 ... Superheater, 19 ... 1st reheater, 20 ... 2nd reheater, 22 ... economizer, 24 ... air preheater, 25 ... gas duct, 26 ... gas duct, 27 ... primary air duct, 28 ... extraction port, 30 ... combustion gas duct, 32 ... combustion gas injection device, 33 DESCRIPTION OF SYMBOLS ... Gas extraction fan, 34 ... Dust collector, 40 ... Temperature detector, 42 ... Fuel gas flow rate adjustment mechanism, 43 ... Valve mechanism part, 44 ... Valve drive part

Claims (7)

In a furnace having a plurality of burners for burning pulverized coal, and a coal fired boiler having a rear heat transfer section continuous to the furnace,
A pulverized coal machine for pulverizing coal into pulverized coal and supplying the burner;
An air preheater that preheats the primary air by exchanging heat between the combustion gas introduced from the outlet of the rear heat transfer section and primary air at normal temperature
A primary air duct for supplying primary air preheated by the air preheater to the pulverized coal machine;
A combustion gas duct for extracting combustion gas from the rear heat transfer section,
The primary air duct is connected to the combustion gas duct via a combustion gas injection device for injecting combustion gas into the primary air duct ;
The rear heat transfer section includes a reheater and a economizer installed downstream of the reheater, and the combustion gas duct burns from an intermediate position between the reheater and the economizer. A coal fired boiler characterized by extracting gas . A temperature detector for detecting the gas temperature on the outlet side of the pulverized coal machine;
Gas flow rate adjusting means provided in the combustion gas duct, for adjusting the gas flow rate introduced into the combustion gas injection device so that the gas temperature on the outlet side of the pulverized coal machine becomes a target temperature. The coal fired boiler according to claim 1. The said combustion gas duct, a combustion gas fan for air the combustion gases, according to the combustion gas fan to claim 1, characterized in that a dust collector for protecting from the combustion residue of coal, is provided Coal fired boiler. The pulverized coal machine, vertical coal-fired boiler according to any one of claims 1 to 3, characterized in that it consists of rollers Race type coal pulverizer of. A furnace having a plurality of burners for burning pulverized coal of a low-grade coal, and the heat recovery unit and an economizer continuous to the furnace which is located downstream of the reheater and the reheater, the In a coal fired boiler having a combustion gas duct for extracting combustion gas of the rear heat transfer section from an intermediate position between a reheater and a economizer, a method of drying the low-grade coal when pulverizing with a pulverized coal machine Because
Combustion gas extracted from the outlet of the rear heat transfer section is introduced into an air preheater, normal temperature primary air is preheated by the air preheater, and preheated primary air is sent to the pulverized coal machine through a primary air duct. And
Combustion gas extracted by the combustion gas duct from the rear heat transfer section is joined and mixed in the primary air duct to further raise the temperature of the primary air and introduce it into the pulverized coal machine,
A method for drying coal in a coal fired boiler, wherein the low-grade coal is dried. The gas temperature on the outlet side of the pulverized coal machine is monitored, and the combustion gas injection flow rate injected into the primary air duct is adjusted so that the gas temperature on the outlet side of the pulverized coal machine becomes a target temperature. The method for drying coal in the coal fired boiler according to claim 5 . The method for drying coal in a coal fired boiler according to claim 5 , wherein low-grade coal having a moisture content of 30 to 40 (wt%) less than sub-bituminous coal is introduced into the pulverized coal machine.

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