JP2011122800A - Fluidized bed combustion furnace and method for operating the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluidized bed combustion furnace and a method for operating the fluidized bed combustion furnace, which controlls the temperature of the furnace and reduces the consumption of sand supplied to the furnace. <P>SOLUTION: A CFB boiler 1 includes the furnace 3 for burning a fuel, a bottom ash discharge port 3c for discharging the bottom ash from the furnace 3, a discharge-amount control unit 33 for controlling the discharge amount of the bottom ash from the bottom ash discharge port 3c on the basis of the temperature of the furnace 3, a crushing machine 31 for adjusting the grain sizes of sand and ash in the bottom ash discharged from the furnace 3, and lines L4, L3 for introducing the sand and ash into the furnace 3 again. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a fluidized bed combustion furnace and a method for operating the fluidized bed combustion furnace.

  Conventionally, an incineration facility described in Patent Document 1 below is known as a technology in such a field. This incineration equipment includes a fluidized bed combustion furnace, and uses sand such as silica sand as a circulating material in the furnace. In the furnace, if the components remaining after the incineration of fuel accumulate as salt, the fluidity of the circulating material sand will be hindered, so to prevent this, sand is removed from the bottom of the furnace together with incombustible material and the sand is washed. And return to the furnace.

Japanese Patent No. 4365256

  Even if the sand in the furnace is washed and reused, the sand wears out as it flows through the furnace as a circulating material and is eventually discharged out of the furnace together with the exhaust gas. Gradually decreases. Therefore, it is necessary to periodically supply new sand to the furnace. This type of sand is often expensive, and the increase in sand consumption hinders the reduction of equipment operating costs. In addition, when a water pipe is provided on the wall of the furnace and sand functions as a heat transfer medium to the water pipe, the sand temperature affects the temperature in the furnace. It was done.

An object of the present invention is to provide a fluidized bed combustion furnace capable of controlling the temperature of the furnace and reducing the consumption of sand supplied to the furnace and a method for operating the fluidized bed combustion furnace.

  The fluidized bed combustion furnace of the present invention includes a furnace for burning fuel, a bottom ash outlet for extracting bottom ash from the furnace, and an extraction for controlling the amount of bottom ash extracted from the bottom ash outlet based on the temperature of the furnace. It is characterized by comprising quantity control means and ash return means for adjusting the particle size of at least the ash contained in the bottom ash extracted from the furnace and returning it to the furnace.

  The fluidized bed combustion furnace operating method of the present invention is a fluidized bed combustion furnace comprising a furnace for burning fuel and a bottom ash discharge port for extracting the bottom ash from the furnace, based on the temperature of the furnace. An extraction amount control step for controlling the amount of bottom ash extracted from the outlet, and an ash return step for adjusting the particle size of at least the ash contained in the bottom ash among the bottom ash extracted from the furnace and returning it to the furnace, It is provided with.

  In this fluidized bed combustion furnace and operation method, the ash contained in the bottom ash is adjusted in particle size and returned to the furnace. The ash contained in the bottom ash functions as a circulating material by adjusting the particle size. Therefore, the amount of new sand to be introduced into the furnace as the circulating material is reduced, and the consumption of sand can be reduced. Further, by extracting the bottom ash from the furnace and introducing the ash having the adjusted particle size into the furnace, the particle size distribution of the circulating material in the furnace can be improved, and the temperature of the furnace can be adjusted. And the control which stabilizes the temperature of a furnace becomes possible by performing the extraction amount of such a bottom ash based on the temperature of a furnace.

  The extraction amount control means may increase the extraction amount of the bottom ash when the furnace temperature exceeds a predetermined threshold.

  Bottom ash tends to have a coarse particle size distribution by staying in the furnace. If the fluidity of the circulating material in the furnace decreases due to the transition of the bottom ash particle size distribution to the coarser side, heat transfer to the furnace wall is not smoothly performed, and the temperature in the furnace tends to increase. In such a case, the amount of the bottom ash extracted from the furnace is increased, the particle size is adjusted and returned to the furnace again, the particle size of the bottom ash staying in the furnace is adjusted, and the temperature of the furnace is lowered. Therefore, an excessive rise in the furnace temperature can be suppressed by such control.

  According to the fluidized bed combustion furnace and the operation method of the fluidized bed combustion furnace of the present invention, the temperature of the furnace can be controlled, and the consumption of sand supplied to the furnace can be reduced.

It is a figure showing a CFB boiler as one embodiment of a fluidized bed combustion furnace concerning the present invention. It is a flowchart which shows the process of the extraction amount control part of the boiler of FIG.

  Hereinafter, preferred embodiments of a fluidized bed combustion furnace according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a boiler 1 which is an embodiment of a fluidized bed combustion furnace of the present invention. The boiler 1 is of a type called a circulating fluidized bed boiler or a CFB (Circulating Fluidized Bed) boiler. In the boiler 1, not only fossil fuels such as coal, but also a wide range of fuels such as biomass, plastics, tires, sludge, RFP, and RDF can be used.

  The boiler 1 includes a fluidized bed furnace 3 for burning fuel. A fuel inlet for supplying fuel is provided on the side surface of the furnace 3, and a gas outlet 3 b for discharging exhaust gas generated by combustion is provided at the upper portion of the furnace 3. A cyclone 7 is connected to the gas outlet 3b. The cyclone 7 is also called a separator, a cyclone classifier, or a cyclone separator, and functions as a solid-gas separator. An inlet 7 a of the cyclone 7 is connected to the gas outlet 3 b, and an outlet 7 b of the cyclone 7 is connected to a downstream gas processing system via a back path 11. A return line 9 called a downcomer extends downward from the bottom outlet of the cyclone 7, and the lower end of the return line 9 is connected to the lower side surface of the furnace 3.

  In the furnace 3, the combustion / flowing air introduced from the lower air supply line causes the solid matter including the fuel introduced from the inlet to flow, and the fuel burns while flowing in the furnace 3. . Exhaust gas generated in the furnace 3 is introduced into the cyclone 7 with accompanying solid particles. The cyclone 7 generates a swirling flow of exhaust gas inside and separates solid particles and gas by a centrifugal separation action. The cyclone 7 returns the separated solid particles (circulated material) to the furnace 3 through the return line 9 and sends the exhaust gas from which the solid particles have been removed to the back path 11 from the discharge port 7b. The solid particles circulate in the furnace 3, the cyclone 7 and the return line 9.

  The back path 11 is a duct that conveys exhaust gas. In order to recover the heat of the exhaust gas for power generation, the back path 11 is provided with a heat recovery unit 17. The heat recovery unit 17 has a boiler tube that crosses the flow path of the exhaust gas, and water, steam, and air flow in the boiler tube. When the high-temperature exhaust gas sent from the cyclone 7 comes into contact with the boiler tube, the heat of the exhaust gas is recovered into water, steam and air in the tube, and the generated high-temperature steam is sent to the turbine for power generation through the pipe. .

  The exhaust gas discharged from the lower portion of the back path 11 is introduced into the exhaust gas purification device 13 through the line L13. The exhaust gas purification device 13 removes fine particles such as fly ash still accompanying the exhaust gas and desulfurizes the exhaust gas. The exhaust gas after being cleaned by the exhaust gas purification device 13 is discharged from the chimney 15 through the line L15.

  A water pipe through which water flows is provided on the outer wall of the furnace 3, and heat generated by combustion in the furnace 3 is recovered by heating the water in the water pipe. At this time, the solid particles (circulating material) flowing in the furnace 3 function as a heat transfer medium that transfers heat generated by the combustion to the water pipe. This circulating material includes ash generated by combustion of fuel in the furnace 3 and sand described later. As the circulating material stays in the furnace 3 for a long time, the circulating material having an appropriate particle size gradually becomes finer and decreases. As a result, the particle size distribution of the circulating material tends to become coarse. Then, when the particle size distribution of the circulating material is shifted to the coarser side, the fluidity of the circulating material in the furnace 3 is lowered, and it is easy to accumulate as bottom ash at the bottom of the furnace 3. And when the fluidity | liquidity of a circulating material falls, the heat transfer to a water pipe | tube will not be performed favorably, As a result, the combustion temperature of the furnace 3 rises and it may lead to the trouble of the boiler 1.

  Therefore, in the boiler 1, sand such as silica sand whose particle size distribution is controlled in advance is introduced into the furnace 3 as a circulating material. Specifically, the boiler 1 includes a sand storage unit 21 that stores sand whose particle size distribution is controlled. Sand supplied from the sand reservoir 21 is introduced into the furnace 3 by the blower 23 through the circulating material line L3. Furthermore, a bottom ash discharge port 3c is provided at the bottom of the furnace 3 for extracting the bottom ash (sometimes referred to as “furnace ash” or “bed ash”) accumulated at the bottom of the furnace downward. . The bottom ash to be extracted includes the above-mentioned sand, ash generated by combustion of fuel, foreign matter having a large particle size of about 30 mm or more, such as a stone lump, and a metal lump such as an iron lump. And valuables. As described above, the sand whose particle size is controlled is supplied to the furnace 3, and the bottom ash having a large particle size is discharged from the furnace 3, so that the particle size distribution of the circulating material in the furnace 3 can be kept at a good distribution.

  The boiler 1 includes a screw conveyor 25, a magnetic separator 27, a filter 29, and a crusher 31. The screw conveyor 25 can adjust the extraction amount of the bottom ash extracted from the bottom ash discharge port 3c by adjusting the rotation speed. The magnetic separator 27 removes valuable materials from the bottom ash and discharges them out of the system. The filter 29 removes foreign matter having a large particle diameter of, for example, about 30 mm or more from the bottom ash and discharges it out of the system. The crusher 31 is introduced with bottom ash from which valuables and foreign substances have been removed as described above. That is, a mixture of sand and ash is introduced into the crusher 31. The crusher 31 crushes the mixture of sand and ash to reduce the particle size. That is, the crusher 31 functions as a particle size adjusting means for adjusting the particle size of the mixture. The mixture of the particle-adjusted sand and ash joins the circulating material line L3 through the circulating material line L4, is returned again into the furnace 3 by the blower 23, and functions again as the circulating material.

  Moreover, the boiler 1 is provided with the extraction amount control part 33 which controls the extraction amount of bottom ash by drive control of the screw conveyor 25. FIG. The extraction amount control unit 33 can control the rotation speed of the screw conveyor 25 by a drive signal. The extraction amount control unit 33 is configured by, for example, a computer. Furthermore, a thermometer 35 for measuring the combustion temperature of the furnace 3 and a pressure gauge 37 for measuring the pressure in the furnace 3 are provided at the lower part of the furnace 3. The measurement values of the thermometer 35 and the pressure gauge 37 are transmitted to the extraction amount control unit 33 as electric signals.

  Hereinafter, processing in which the extraction amount control unit 33 controls the extraction amount of the bottom ash will be described. As illustrated in FIG. 2, the withdrawal amount control unit 33 acquires the measurement value of the pressure gauge 37 (S101). When the pressure measurement value of the pressure gauge 37 is larger than a predetermined upper limit pressure (for example, 6 kPa) (Yes in S103), the extraction amount control unit 33 increases the rotation speed of the screw conveyor 25 to increase the bottom. The amount of ash extracted is increased (S105). Further, when the measured pressure value is smaller than a predetermined lower limit pressure (for example, 5 kPa) (Yes in S107), the extraction amount control unit 33 reduces the rotation speed of the screw conveyor 25 to reduce the bottom ash. The extraction amount is decreased (S109). With the above control, the pressure in the furnace 3 is kept constant between the lower limit pressure and the upper limit pressure.

  Next, the extraction amount control part 33 acquires the measured value of the thermometer 35 (S111). And when the temperature measurement value of the thermometer 35 is larger than predetermined upper limit temperature (for example, 1000 degreeC) (it is Yes at S113), the extraction amount control part 33 raises the rotation speed of the screw conveyor 25. The amount of bottom ash extracted is increased (S115).

  In this way, when the temperature of the furnace 3 exceeds the predetermined upper limit temperature, the amount of bottom ash extracted is increased, so that the bottom ash processed by the magnetic separator 27, the filter 29, and the crusher 31 increases, and the line L4 , Sand and ash reintroduced into the furnace 3 through L3. That is, the amount of the bottom ash with a coarse particle size increases, and the circulating material (sand and ash) introduced into the furnace 3 after the particle size adjustment is increased, so that the fluidity of the circulating material in the furnace 3 is increased. improves. Therefore, heat transfer to the water pipe using the circulating material as a medium is improved, so that the combustion temperature of the furnace 3 is lowered, and an excessive increase in the temperature of the furnace 3 is suppressed.

  During the operation of the boiler 1, the above-described processes S <b> 101 to S <b> 115 are repeatedly performed by the extraction amount control unit 33. According to the control of the extraction amount control unit 33, the temperature control of the furnace 3 can be performed by appropriately maintaining the particle size distribution of the circulating material.

  Further, in the boiler 1, the bottom ash is extracted from the furnace 3, and the sand and ash whose particle sizes are adjusted are reintroduced into the furnace 3 through the above-described processes. Thus, not only the sand introduced into the furnace 3 is reused, but also the entire bottom ash is reused after removing foreign substances and valuables. That is, since not only the sand introduced but also the ash generated by the combustion of fuel is reused, the amount of new sand supplied from the sand reservoir 21 can be reduced. As a result, the consumption of sand in the boiler 1 can be reduced, the cost of the sand to be prepared and the processing cost of the used sand can be reduced, and the operating cost can be reduced.

  For example, depending on the nature of the fuel, a sufficient amount of ash may be generated by combustion. In this case, it is necessary to introduce the sand from the sand storage unit 21 into the furnace 3 as a circulating material at the beginning of the operation. Thereafter, the ash generated from the fuel is circulated to the lines L4 and L3 to store the sand. It is also possible to dispense with the supply of sand from the section 21.

  The present invention is not limited to the embodiment described above. For example, in the embodiment, the extraction amount of the bottom ash is controlled based on the temperature of the lower portion of the furnace 3 by the thermometer 35, but even if the extraction amount is controlled based on the temperature of the other part of the furnace 3. Good. In the embodiment, the extraction amount is increased when the temperature of the furnace 3 exceeds a predetermined upper limit temperature (threshold). For example, when the gradient of the temperature rise of the furnace 3 exceeds a predetermined threshold Alternatively, control may be performed to increase the extraction amount. Further, the determination of the increase / decrease of the extraction amount in the processes S105, S109, and S115 is not limited to the automatic process. Further, the present invention is not limited to application to a circulating fluidized bed boiler, but can also be applied to processing of circulating material in other types of combustion furnaces. For example, the present invention can be applied to an incinerator that does not generate power by heat exchange of exhaust gas.

  DESCRIPTION OF SYMBOLS 1 ... CFB boiler (fluidized bed combustion furnace), 3 ... Fire furnace, 3c ... Bottom ash discharge port, 25 ... Screw conveyor (extraction amount control means), 31 ... Crusher (ash return means), 33 ... Extraction amount control Part (extraction amount control means), L4, L3... Circulating material line (ash return means).

Claims (3)

A furnace that burns fuel;
A bottom ash discharge port for extracting the bottom ash from the furnace,
An extraction amount control means for controlling the extraction amount of the bottom ash from the bottom ash discharge port based on the temperature of the furnace;
Of the bottom ash extracted from the furnace, ash return means for adjusting the particle size of at least the ash contained in the bottom ash and returning it to the furnace,
A fluidized bed combustion furnace comprising: The extraction amount control means includes:
2. The fluidized bed combustion furnace according to claim 1, wherein when the temperature of the furnace exceeds a predetermined threshold, the amount of the bottom ash extracted is increased. A furnace that burns fuel;
In a fluidized bed combustion furnace comprising a bottom ash discharge port for extracting bottom ash from the furnace,
An extraction amount control step for controlling the extraction amount of the bottom ash from the bottom ash discharge port based on the temperature of the furnace,
Of the bottom ash extracted from the furnace, at least an ash return step of adjusting the particle size of the ash contained in the bottom ash and returning it to the furnace,
A method for operating a fluidized bed combustion furnace, comprising:

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