JP4861872B2 - Fluidized bed boiler - Google Patents

Description

  The present invention relates to a fluidized bed boiler provided with a fluidized bed type combustion furnace.

Conventionally, as a technique in such a field, a waste treatment apparatus described in Patent Document 1 below is known. This apparatus is an apparatus for treating chlorine-containing plastic waste, and includes a circulating fluidized bed combustor for combusting the waste and a pyrolysis furnace for pretreating the waste introduced into the combustor. A heating medium made of heated sand or heated gas is put into the pyrolysis furnace, mixed with waste, and conveyed. Then, the waste is thermally decomposed by the heat of the heating medium to remove chlorine in the waste in advance.
JP 2000-44726 A

  As described above, particularly in recent years, a combustion furnace using waste plastic or the like as a fuel has been demanded, but many waste plastics contain chlorine. And, when the fuel containing chlorine is burned by the combustor, the corrosion of the boiler tube for recovering the heat of the exhaust gas is advanced and the life is shortened, so it is necessary to reduce chlorine from the fuel. In order to suppress the generation of pollutants due to combustion, it is important to reduce chlorine from fuel. Here, in the above-mentioned apparatus, since a high-temperature heating medium is input in the chlorine removing process, a large amount of energy is required for heating the heating medium. In this type of apparatus, it is necessary for operation. It is desirable to save as much energy as possible.

  Accordingly, an object of the present invention is to provide a fluidized bed boiler that can save energy for operation.

  A fluidized bed type boiler of the present invention includes a fluidized bed type combustion furnace that burns fuel that is input, a circulation line that circulates solids discharged from the bottom of the combustion furnace and returns them to the combustion furnace, and a circulation line A separation / removal unit that is provided on the circulation line for separating and removing unsuitable substances that are inappropriate for combustion from the solid matter circulating in the circulation line, and heat of the solid matter that is provided on the circulation line and circulates in the circulation line A heat recovery unit that recovers to a medium, and a fuel heat treatment unit that performs pretreatment of fuel that is input to the combustion furnace by heat treatment using heat of the heat medium obtained by the heat recovery unit. .

  In this fluidized bed boiler, the solid matter discharged from the bottom of the combustion furnace is circulated so as to be returned to the combustion furnace again through the circulation line, and inappropriate substances contained in the solid matter are selected during the circulation. Removed. Further, in the heat recovery section on the circulation line, the heat of the solid is transferred to the heat medium. In the fuel heat treatment unit, heat treatment of the fuel is performed using the heat of the heat medium. In this way, the heat that would otherwise be discarded is effectively used as the heat used for fuel pretreatment, so that the energy required for boiler operation as a whole can be saved.

  Moreover, the fuel processed in the fuel heat treatment unit may be introduced into the circulation line. In this case, the fuel is heat-treated in the fuel heat treatment section, and then charged into the combustion furnace together with the solid matter returned in the circulation line.

  The fluidized bed boiler of the present invention further includes a gas processing unit that processes gas generated by heat treatment of the fuel in the fuel heat processing unit, and the gas processing unit sucks and discharges gas from the fuel heat processing unit. And a gas dissolving part that dissolves the gas discharged by the gas suction part into a liquid.

  According to this configuration, by removing the gas generated by the heat treatment of the fuel from the fuel heat treatment section and dissolving it in the liquid, it is possible to recover the gas in a form that facilitates subsequent processing. Further, since the generated gas is sucked and discharged in the fuel heat treatment section, the heat treatment accompanied with gas generation can be promoted in the fuel heat treatment section. Specifically, the gas suction unit may include a liquid ejector that ejects liquid.

  According to the fluidized bed boiler of the present invention, it is possible to save energy for operation.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a fluidized bed boiler according to the present invention will be described in detail with reference to the drawings.

  An external circulation type fluidized bed type (Circulating Fluidized Bed type) boiler 1 shown in FIG. 1 is a boiler using waste plastic and RPF as fuel, and includes a fluidized bed type combustion furnace 3 having a vertically long cylindrical shape. . A fuel inlet 3a for introducing fuel is provided in the middle part of the combustion furnace 3, and a gas outlet 3b for discharging combustion gas is provided in the upper part. A cyclone 7 that functions as a solid-gas separator is connected to the gas outlet 3b. The discharge port 7a of the cyclone 7 is connected to a downstream gas processing system via a gas line. 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 intermediate side surface of the combustion furnace 3.

  In the combustion furnace 3, the solid material containing the fuel introduced from the inlet 3a flows by the combustion / flowing air introduced from the lower air supply line 3c, and the fuel flows about 800 to 900 while flowing. Burn at ℃. The combustion gas generated in the combustion furnace 3 is introduced into the cyclone 7 with accompanying solid particles. The cyclone 7 separates solid particles and gas by a centrifugal separation action, returns the separated solid particles to the combustion furnace 3 through the return line 9, and sends the combustion gas from which the solid particles have been removed from the discharge port 7 a through the gas line. It is sent to the gas processing system at the subsequent stage.

  In this combustion furnace 3, a solid substance called “in-furnace bed material” is generated and collected at the bottom, and the bed material is sintered and melted and solidified by the concentration of impurities (low melting point materials, etc.) in the in-furnace bed material. Alternatively, it is necessary to suppress malfunctions caused by incombustibles. For this reason, in the combustion furnace 3, the in-furnace bed material is periodically discharged from the bottom discharge port 3 d to the outside. The discharged bed material is returned to the combustion furnace 3 through the circulation line 23 again. In addition, waste plastics used as fuel for the boiler 1 often contain unsuitable materials such as metals that are unsuitable for combustion, and it is necessary to remove these unsuitable materials from the combustion furnace 3.

  For this reason, a sorting device 25 having a sieve and a magnetic separation device is provided on the circulation line 23. In this sorting device 25, a metal, a metal, a soot, or the like that is unsuitable for combustion is selected from the circulating bed materials. And unsuitables such as rubble, rubble, and clinker are selected and removed. By such circulation and sorting of the bed material, unsuitable substances are removed from the combustion furnace 3 by the sorting device 25, so that the fluidity of the combustion substances in the combustion furnace 3 is ensured and good combustion is performed. At the same time, flow defects in the combustion furnace 3, the cyclone 7, and the return line 9 are suppressed.

  The gas treatment system includes a gas heat exchanger 13 connected to the gas outlet 7a of the cyclone 7 via a gas line, and a bug connected to the outlet 13a of the gas heat exchanger 13 via a gas line. And a filter (dust collector) 15. The gas heat exchanger 13 is provided with a boiler tube 13b that allows water to flow across the exhaust gas flow path. When the high-temperature exhaust gas sent from the cyclone 24 comes into contact with the boiler tube 13b, the heat of the exhaust gas is recovered in the water in the tube, and the generated high-temperature steam is sent to the power generation turbine through the boiler tube 13b. The bag filter 15 removes fine particles such as fly ash that are still accompanying the combustible gas. The clean gas discharged from the discharge port 15a of the bag filter 15 is discharged from the chimney 19 via the gas line and the pump 17 to the outside.

  As described above, in the boiler 1, waste plastic or RPF is used as fuel. Since such fuel contains chlorine and heavy metal, when the fuel is burned, exhaust gas containing chlorine and heavy metal is generated, and such exhaust gas advances corrosion of the boiler tube 13a and shortens its life. Therefore, it is preferable to reform such raw fuel before introducing it into the combustion furnace 3 and remove chlorine and heavy metals from the raw fuel as much as possible.

  In view of this, the boiler 1 has a fuel reforming function for reforming the raw fuel before being charged into the combustion furnace 3, and a function for selectively removing unsuitable substances by circulating the bed material through the above-described bed material circulation line 23. A reformed fuel generator 20 is provided which has the function of joining the reformed fuel to the circulating bed material and putting it into the combustion furnace 3 together.

  The reformed fuel generator 20 includes a screw conveyor type bed material cooling device 31 connected to the bottom discharge port 3d of the combustion furnace 3, and a screw transfer device 33 provided in the subsequent stage. The outlet 31c provided at the downstream end of the bed material cooling device 31 and the upstream end of the screw conveyance device 33 are connected via a bed material conveyance line 23a and are conveyed onto the bed material conveyance line 23a. The above-described sorting device 25 is provided to sort and remove unsuitable combustion materials from the bed material. Further, the outlet at the downstream end of the screw transfer device 33 is connected to the fuel input port 3a of the combustion furnace 3 via the bed material transfer line 23b. By such connection, the bed material cooling device 31, the bed material conveyance line 23a, the screw conveyance device 33, and the bed material conveyance line 23b constitute the above-described circulation line 23 for circulating the bed material. In FIG. 1, the “a” mark on the bed material transfer line 23 b immediately after the screw transfer device 33 means that it is connected to the “a” mark immediately before the fuel inlet 3 a of the fuel furnace 3. ing.

  The bed material cooling device 31 is provided with a cylindrical jacket on the outer side of the outer cylinder defining the bed material conveyance path, and a heat medium that flows and circulates the heat medium between the outer cylinder and the jacket. A flow path 31a is formed. The bed material of about 800 ° C. discharged from the bottom discharge port 3d moves the heat to the heat medium while being screw-conveyed in the conveyance path of the bed material cooling device 31, so that the high-temperature bed material is efficiently cooled. The Since the bed material cooled to an appropriate temperature that can be handled by the sorting device 25 is sent to the sorting device 25, the function of the sorting device 25 is not hindered at a high temperature, and efficient magnetic sorting is performed. On the other hand, the heat medium having a high temperature is sent to the shaft furnace 35 through the heat medium circulation line 41 as will be described later. For example, oil is used as the heat medium.

  Furthermore, the reformed fuel generation unit 20 includes a vertically long cylindrical shaft furnace (fuel heat treatment unit) 35 for removing chlorine and heavy metals from raw fuel such as waste plastic and RPF to be introduced. The shaft furnace 35 is provided with a cylindrical jacket surrounding an outer cylinder that defines a raw fuel transport path, and a heat medium that allows a high-temperature heat medium to flow and circulate between the outer cylinder and the jacket. A flow path 35a is formed. The heat medium flow path 35 a is connected to the heat medium flow path 31 at of the bed material cooling device 31 via the heat medium circulation line 41, and the heat medium flows through the heat medium circulation line 41. And the heat medium flow path 35a.

  Further, on the heat medium circulation line 41, pumps p1 and p2 for smoothly flowing the heat medium, a heat medium tank 43 for storing the circulating heat medium, and a heater for further heating the heat medium in the tank 43. 45. When the temperature of the heat medium in the bed material cooling device 31 is not sufficient, the heat medium is further heated by the heater 45, and the temperature usable for the heat treatment in the shaft furnace 35 can be set. A heater for heating the inside of the shaft furnace 35 may be directly provided in the shaft furnace 35.

  Above the shaft furnace 35, there is provided a raw fuel input part 39 for feeding the raw fuel introduced from the fuel introduction port 39a into the shaft furnace 35 by the screw conveyor 39b. The lower end of the shaft furnace 35 is connected to the screw conveying device 33. Thus, the shaft furnace 35 is sealed by the screw conveying mechanism at both the upper and lower ends, and the inside of the shaft furnace 35 is connected to the decompression device 37 and decompressed.

  Based on such a configuration, the raw fuel input from the upper end of the shaft furnace 35 by the raw fuel input unit 39 moves downward in the shaft furnace 35 while being heated to about 400 to 600 ° C. by the heat of the heat medium. And by heating and decompression, the chlorine contained in the raw fuel, the contained heavy metals (Pb, etc.), and some tar components are vaporized and removed from the raw fuel. The vaporized contained chlorine and the like are discharged through the suction line 37 a and drawn into the decompression device 37. The reformed fuel reaches the lower end of the shaft furnace 35 and is conveyed while being mixed with the bed material by the screw conveying device 33. Thereafter, the fuel is fed into the combustion furnace 3 from the fuel inlet 3a together with the bed material through the bed material transfer line 23b. Further, in this case, even if tar that has not been vaporized in the shaft furnace 35 adheres to the fuel, the sticking property of the tar is reduced by the mixed bed material, and the occurrence of trouble in conveyance in the circulation line 23 is suppressed. .

  In this way, the raw fuel introduced into the boiler 1 is reformed while passing through the shaft furnace 35 to reduce the contained chlorine and the contained heavy metals, and then merges with the bed material circulating through the circulation line 23. It is put into the combustion furnace 3 together with the material. And the chlorine and heavy metal in the exhaust gas which generate | occur | produce in the combustion furnace 3 are reduced because the fuel thrown into the combustion furnace 3 is reformed in advance. As a result, corrosion of the boiler tube 13b can be suppressed, and the life of the boiler 1 can be extended. In addition, since chlorine and heavy metals in the fuel are reduced, it is possible to reduce the amount of dioxins in the exhaust gas and ash residue, and to expand the application range of ash residue to civil engineering materials and cement raw materials. Can do. Although it is a secondary effect, since the moisture in the fuel is reduced in the shaft furnace 35, the steam specification boiler 1 equivalent to the conventional boiler can be manufactured in a small size.

  Here, since the heat medium circulates between the bed material cooling device 31 and the shaft furnace 35, the heat of the high-temperature bed material from the bottom discharge port 3 d of the combustion furnace 3 is changed by the bed material cooling device 31. The heat medium recovered to the heat medium by the cooling process and having a high temperature moves to the shaft furnace 35, and the heat of the heat medium is used for the heat treatment of the raw fuel. In other words, the heat that would otherwise be discarded outside the boiler 1 system after the cooling of the bed material is effectively used as the heat used for fuel reforming in the shaft furnace 35, so that it is necessary for the operation of the boiler 1 as a whole. Can save a lot of energy.

  In order to make effective use of energy, a method of performing heat treatment of the raw fuel by bringing the raw fuel into contact with the circulation medium circulating through the combustion furnace 3 and the cyclone 7 can be considered. However, in such a method, the circulating medium itself is highly fixed, and the tar content generated by the heat treatment adheres to the circulating medium, which may cause problems in the flow and conveyance of the circulating medium. In addition, the process control of the entire boiler is complicated. Compared to such a method, in the boiler 1, the heat treatment in the shaft furnace 35 is performed using a heat medium separated from the circulation medium. There is little influence.

  Further, since the inside of the shaft furnace 35 is decompressed by the decompression device 37, vaporization of chlorine and heavy metals from the raw fuel is promoted. As a result, in this type of conventional shaft furnace, the fuel is dechlorinated by heating at 400 ° C. or higher. In this shaft furnace 35, not only the dechlorination of the fuel but also the heavy metal treatment can be performed. Therefore, the corrosion of the boiler tube 13b is further suppressed by the heavy metal treatment of the fuel. In addition, there is an effect of suppressing the leakage of chlorine / heavy metal gas to the outside by making the inside of the shaft furnace 35 have a negative pressure by the decompression device 37. Hereinafter, a specific configuration of the decompression device 37 will be described.

  The decompression device 37 includes a water tank 51 in which water is stored, and a water ejector (gas suction unit) 53 is attached to the upper part of the water tank 51. The water ejector 53 jets water collected from the lower part of the water tank 51 downward toward the water surface. The water ejector 53 is connected to the above-described suction line 37a. The water ejector 53 generates a suction force by the water injection, and the chlorine / heavy metal gas in the shaft furnace 35 is sucked into the suction line. Pull through 37a. The drawn-in gas collides with the water surface of the water tank (gas dissolving part) 51 together with the jetted water, thereby being dissolved in water. Thus, since the ejector 53 is used as the gas suction means, the operation of drawing the gas and the operation of feeding the drawn gas into the water in the water tank 51 are performed simultaneously. Further, a drainage line 55a for discharging water in which gas is dissolved out of the system and a water supply line 55b for replenishing water are also provided at the lower part of the water tank 51.

  According to the configuration of the decompression device 37, the difficult-to-handle high-temperature chlorine / heavy metal gas generated by the fuel reforming process in the shaft furnace 35 is dissolved in water and easily recovered from the drain line 55a. Processing at a later stage can be performed. In this manner, the decompression device 37 also has a function as a gas processing unit that processes the gas generated in the fuel reforming process. In addition, when the gas is drawn in by a decompression device using a fan, the decompression device is likely to corrode and has a short life. However, if the decompression device 37 is used, corrosion due to the gas is small and the life is long.

  The present invention is not limited to the embodiment described above. For example, the boiler 1 of the embodiment is of an external circulation type fluidized bed type, but the present invention is an internal circulation type fluidized bed type boiler, a bubble type fluidized bed boiler (Bubbling Bed type boiler) or a turbulent flow. It can also be applied to type fluidized bed boilers (Turbulent Bed type boilers).

It is a figure showing one embodiment of a fluidized bed type boiler concerning the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fluidized bed type boiler, 3 ... Combustion furnace, 3d ... Bottom discharge port, 23 ... Bed material circulation line, 25 ... Magnetic sorting apparatus (sorting process part), 31 ... Bed material cooling device (heat recovery part), 35 ... Shaft furnace (fuel heat treatment part), 37 ... Depressurization device (gas treatment part), 51 ... Water tank (gas dissolution part), 53 ... Water ejector (gas suction part).

Claims (4)

A fluidized bed type combustion furnace that combusts the input fuel;
A circulation line for circulating the solid matter discharged from the bottom of the combustion furnace to return it to the combustion furnace again;
A sorting and removing unit that is provided on the circulation line and sorts and removes unsuitable substances unsuitable for combustion from the solids circulating in the circulation line;
A heat recovery unit provided on the circulation line and recovering heat of the solid material circulating through the circulation line to a heat medium;
A fluidized bed boiler, comprising: a fuel heat treatment section that performs a pretreatment of the fuel introduced into the combustion furnace by a heat treatment using heat of the heat medium obtained in the heat recovery section.   The fluidized bed boiler according to claim 1, wherein the fuel processed in the fuel heat treatment section is introduced into the circulation line. A gas treatment unit for treating a gas generated by the heat treatment of the fuel in the fuel heat treatment unit;
The gas processing unit includes a gas suction unit that sucks and discharges gas from the fuel heat treatment unit, and a gas dissolution unit that dissolves the gas discharged by the gas suction unit in a liquid. Item 3. The fluidized bed boiler according to Item 1 or 2. The fluidized bed boiler according to claim 3, wherein the gas suction unit includes a liquid ejector that ejects the liquid.

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