JP2015134996A - Asphalt mixture manufacturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an asphalt mixture manufacturing device capable of controlling condensation that causes corrosion and other defects, when introducing outside air as a part of exhaust gas circulated and supplied for burner combustion.SOLUTION: An asphalt mixture manufacturing device has an outside air introduction duct 17 for adjusting the oxygen density at midway along a circulation duct 13 that supplies a part of exhaust gas for combusting a burner 5. The outside air introduction duct 17 is disposed along the periphery of a throat 19 at an edge of the burner 5, so as to prevent condensation of the combustion air when the outside air taken in by the duct 17 is preheated by thermal exchange at the surface of the throat 19 of the burner 5 and introduced into the circulation duct 13.

Description

  The present invention relates to an asphalt mixture manufacturing apparatus provided with a dryer that heat-drys a new aggregate or waste material that is a material of an asphalt mixture that is a road pavement material.

  In the asphalt mixture production equipment that produces the asphalt mixture that is road pavement material, heat is consumed when the aggregate is heated and dried with a dryer. Is planned. For example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2013-83126), a circulation duct is branched from an exhaust duct for exhaust gas discharge of a dryer, and the other end of the circulation duct is used as a dryer. Some of them are connected to a combustion air supply fan of a burner provided to circulate and supply a part of high-temperature exhaust gas as combustion air for the burner to recover heat.

  The oxygen concentration in the exhaust gas derived from the dryer is slightly increased by the outside air flowing from the gap such as the end of the drum, but is insufficient for use as combustion air for the burner. In the apparatus described in the above, the outside air introduction duct is provided in the middle of the circulation duct, the oxygen concentration meter for detecting the oxygen concentration in the circulation duct is provided, and the oxygen concentration value in the circulation duct detected by the oxygen concentration meter. Based on this, the amount of outside air introduced from the outside air introduction duct into the circulation duct is controlled so that the oxygen concentration in the combustion air to the burner can be properly combusted while utilizing as much heat as possible from the high temperature exhaust gas. It is adjusted to increase.

JP2013-83126A

  However, since the high-temperature exhaust gas that is circulated and supplied to the burner as combustion air contains a large amount of water evaporated by heat drying of the aggregate, introduction of room temperature outside air for oxygen concentration adjustment If the exhaust gas temperature drops significantly with this, in some cases, the dew point temperature will be lowered, and condensate will be generated in the circulation duct, which may lead to problems such as corrosion and non-ignition of the burner. .

  In view of the above points, the present invention provides an asphalt mixture that can suppress the generation of condensed water that causes problems such as corrosion when introducing outside air to exhaust gas that is circulated and supplied to a burner as combustion air. It is an object to provide a manufacturing apparatus.

  In order to solve the above-mentioned problems, the present inventors have conducted extensive research. As a result, if the outside air introduced into the exhaust gas, which is combustion air, is preheated, the decrease in the exhaust gas temperature at the time of introduction is suppressed. I thought that the generation of condensed water could be effectively suppressed. As a means for preheating the outside air, it may be possible to install a heat source such as a heater separately. However, the present inventors have found that the throat attached to the hot air supply burner tip is red hot depending on the burner combustion amount. For example, if the outside air is preheated by exchanging heat with the throat surface of the burner, it is not necessary to prepare a separate heat source and the heat load on the throat is also increased. It is considered that the generation of condensed water in the duct can be effectively suppressed while reducing, and the present invention has been achieved.

  That is, in the asphalt mixture manufacturing apparatus according to the first aspect of the present invention, a hot air supply burner is provided at one end of a cylindrical drum that is rotatably and tiltably supported, while an exhaust gas derivation is provided at the other end of the drum. The exhaust duct is connected to a combustion air supply fan for the burner and a part of the exhaust gas discharged from the exhaust duct is circulated and supplied as combustion air for the burner. And an asphalt mixture manufacturing apparatus comprising an outside air introduction duct for adjusting the oxygen concentration of combustion air in the duct to a concentration required for burner combustion in the middle of the circulation duct, wherein the outside air introduction duct is connected to the tip of the burner. Around the outer periphery of the throat of the section, circulating the outside air sucked from the outside air introduction duct by preheating by heat exchange with the throat surface of the burner Combustion air when were introduced into the transfected is characterized by being configured so as not to condense.

  Moreover, in the asphalt mixture manufacturing apparatus according to claim 2, a plurality of protruding pieces are provided on the outer periphery of the throat, and the turbulent flow is generated by the protruding pieces in the outside air flowing along the outer periphery of the throat so that heat exchange efficiency is achieved. It is characterized by being configured to enhance

  According to the asphalt mixture manufacturing apparatus of the first aspect of the present invention, an outside air introduction duct for adjusting the oxygen concentration is provided in the middle of a circulation duct for supplying a part of the exhaust gas as combustion air for the burner, and the outside air introduction duct. Is placed along the outer periphery of the throat at the tip of the burner, and when the outside air sucked from the outside air introduction duct is preheated by heat exchange with the throat surface of the burner and introduced into the circulation duct, Since it is configured not to condense, the generation of condensed water due to the introduction of outside air can be effectively suppressed, and problems such as corrosion and burner non-ignition caused by condensed water can be prevented, and the cooling effect of the burner throat is also expected. It is possible to reduce the heat load on the throat.

  Further, according to the asphalt mixture manufacturing apparatus of claim 2, a plurality of projecting pieces are provided on the outer periphery of the throat, and heat is exchanged by generating turbulent flow in the outside air flowing along the outer periphery of the throat. Therefore, the outside air can be preheated efficiently, and the generation of condensed water when introducing the outside air can be more effectively suppressed.

It is a schematic explanatory drawing which shows one Example of the asphalt mixture manufacturing apparatus which concerns on this invention. FIG. 3 is a partially omitted cross-sectional view of an outside air introduction duct provided around the throat outer periphery of the burner. It is a partially cutaway perspective view of an outside air introduction duct provided around the throat outer periphery of the burner.

  In the asphalt mixture manufacturing apparatus according to the present invention, an outside air introduction duct for adjusting oxygen concentration is provided in the middle of a circulation duct that circulates and supplies a part of exhaust gas as combustion air for a burner, and the outside air introduction duct. Around the throat outer periphery of the burner tip, by circulating the outside air sucked in from the outside air introduction duct along the throat outer periphery, while preheating by exchanging heat with the hot throat surface The exhaust gas, which is the combustion air in the duct, is prevented from dropping below the dew point temperature when introduced into the circulation duct, so that condensation does not occur in the duct. In addition, a plurality of projecting pieces are provided on the outer peripheral surface of the throat whose outer periphery is surrounded by the outside air introduction duct to prevent the flow of the surrounding air and generate turbulent flow. It is intended to increase the efficiency of heat exchange with the throat surface by generating turbulence and stirring appropriately.

  When the aggregate is heated and dried by the asphalt mixture manufacturing apparatus having the above-described configuration, a part of the exhaust gas derived from the exhaust duct downstream of the dryer is circulated and supplied to the combustion air supply fan of the burner through the circulation duct. On the other hand, an appropriate amount of outside air is introduced into the circulation duct from the outside air introduction duct to compensate for the oxygen concentration that is insufficient as combustion air. At this time, since the high-temperature exhaust gas discharged from the dryer with the heat drying treatment of the aggregate contains a large amount of moisture evaporated from the aggregate, the exhaust gas temperature increases with the introduction of ambient air. If it drops significantly, in some cases, it will be below the dew point temperature, and a large amount of condensed water will be generated in the circulation duct, which may cause problems such as corrosion of the duct and non-ignition of the burner. In the present invention, since the outside air for adjusting the oxygen concentration is introduced after being preheated to some extent by exchanging heat with the surface of the hot burner throat, the decrease in the exhaust gas temperature in the duct is suppressed and condensed. It is possible to effectively suppress the occurrence of defects such as duct corrosion caused by condensed water.

  Thus, according to the asphalt mixture manufacturing apparatus of the present invention, when a part of the exhaust gas is circulated and supplied to the burner as combustion air, the outside air to be introduced for oxygen concentration adjustment is introduced after being preheated to some extent. Therefore, it is possible to effectively suppress the generation of condensed water which causes problems such as corrosion of ducts and non-ignition of burners, which is preferable for maintenance. In addition, since heat generated from the throat surface of the existing burner is used as a heat source for preheating the outside air, there is no need to prepare a separate heat source such as a heater, and red heat is generated depending on the burner combustion amount, etc. The heat load on the throat, which can be as high as possible, can be expected to be reduced, and part of the heat dissipated from the throat surface can be effectively recovered as thermal energy, which is suitable.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  In the figure, reference numeral 1 denotes an asphalt mixture manufacturing apparatus according to the present invention, which mainly includes a dryer 2 which is an aggregate heating and drying apparatus. The dryer 2 rotatably supports a cylindrical drum 3 having a large number of scraping blades (not shown) on the inner periphery thereof on a machine base (not shown) to drive a motor (see FIG. The hot air is supplied into the drum 3 from the burner 5 provided in the hot hopper 4 on one end side of the drum 3 and is connected to the cold hopper 6 on the other end side of the drum 3. The high-temperature gas flow that passes through the drum 3 is maintained by suction with the exhaust fan 8 interposed downstream of the exhaust duct 7.

  An aggregate hopper (not shown) for storing aggregates of various particle sizes is installed in the vicinity of the dryer 2, and aggregates discharged from the aggregate hopper are put into the drum 3 via the belt conveyor 9. While the aggregate is rolling down in the drum 3, the aggregate is brought into contact with the high-temperature gas stream, heated and dried to a desired temperature, and sequentially discharged from the discharge port below the hot hopper 4. A dust collector 10 such as a bag filter that collects dust in the exhaust gas is provided downstream of the exhaust duct 7, and the downstream end of the dust duct 10 is connected to the chimney 12 via the air volume adjusting damper 11 and the exhaust fan 8. The exhaust gas purified by the dust collector 10 is discharged from the chimney 12 to the atmosphere.

  Reference numeral 13 in the figure denotes a circulation duct that is branched from the downstream side of the dust collector 10 of the exhaust duct 7. The other end of the circulation duct 13 is connected to the combustion air supply fan 14 of the burner 5 of the dryer 2. A part of the high-temperature exhaust gas derived from the dryer 2 can be circulated and supplied as combustion air for the burner 5, and the air flow adjusting damper 15 and the circulation duct 13 flow down in the middle of the circulation duct 13. And an oxygen concentration meter 16 for detecting the oxygen concentration in the exhaust gas.

  Reference numeral 17 in the figure denotes an outside air introduction duct for introducing outside air into the circulation duct 13, and an outside air introduction damper 18 for adjusting the outside air introduction amount is provided in the middle of the outside air introduction duct 17. The amount of outside air introduced into the circulation duct 13 is adjusted by controlling the opening degree of the outside air introduction damper 18 based on the oxygen concentration value in the circulation duct 13 detected at, and uses as much of the high-temperature exhaust gas heat as possible. However, the oxygen concentration in the combustion air (exhaust gas) to the burner 5 is increased to such an extent that proper combustion can be maintained (for example, about 18 to 19%).

  Further, the outside air introduction duct 17 is formed in a substantially annular shape so as to be along the outer periphery of the throat 19 at the tip of the burner 5, and a part of the flow path is blocked by the partition plate 20, As shown by the alternate long and short dash line in FIGS. 2 and 3, the outside air A sucked from the outside air inlet 21 circulates along the outer periphery of the throat 19 and is then introduced into the downstream circulation duct 13. . At this time, the outside air A, which has been at room temperature at the time of suction, is preheated through heat exchange by being in contact with the surface of the high temperature throat 19 for a certain period of time, so that the exhaust gas temperature in the duct when introduced into the circulation duct 13 The reduction width can be suppressed, and the generation of condensed water in the duct can be reduced.

  Reference numeral 22 in FIG. 3 denotes a turbulent flow generating piece, which is approximately when the outside air A sucked from the outside air introduction port 21 circulates and passes through the annular outside air introduction duct 17 formed on the outer periphery of the throat 19. A plurality of projecting pieces 22 arranged in a staggered manner obstruct the flow and generate a turbulent flow, so that heat exchange between the outside air A and the surface of the hot throat 19 can be performed more efficiently. ing. It should be noted that the shape, size, number of installations, and arrangement of the protruding pieces 22 are not limited to those shown in the figure, and may be appropriately selected and adjusted according to actual heat exchange efficiency and the like. . Moreover, you may make it project on the throat 19 side not on the outer peripheral surface of the throat 19 but on the inner peripheral surface of the annular outside air introduction duct 17. Further, the outside air introduction duct 17 may be provided in a substantially spiral shape so as to circulate a plurality of times along the outer peripheral surface of the throat 19. In this case, the contact time between the outside air A and the throat 19 surface is extended to perform heat exchange. It is possible to further increase the efficiency of.

  When the aggregate that is the material of the asphalt mixture is heat-dried in the asphalt mixture manufacturing apparatus 1 having the above configuration, a part of the exhaust gas led out from the exhaust duct 7 downstream of the dryer 2 is burned through the circulation duct 13. The opening degree of the outside air introduction damper 18 is controlled based on the oxygen concentration value of the combustion air (exhaust gas) in the circulation duct 13 detected by the oxygen concentration meter 16 while being circulated and supplied to the combustion air supply fan 14. Then, an appropriate amount of outside air A is introduced into the circulation duct 13 from the outside air introduction duct 17, and the burner 5 is adjusted so as to maintain an oxygen concentration that allows proper combustion.

  At this time, since the high-temperature exhaust gas discharged from the exhaust duct 7 by the heat drying process of the aggregate in the dryer 2 contains a large amount of moisture evaporated from the aggregate, normal temperature outside air is supplied to the circulation duct 13. If the temperature of the combustion air (exhaust gas) in the duct is greatly reduced when it is introduced, the dew point temperature may be lowered in some cases, and condensed water may be generated in the circulation duct 13. In the example, since the outside air introduction duct 17 is provided along the outer periphery of the throat 19 of the burner 5 that is at a high temperature, the outside air A before introduction of the duct is preheated to some extent by exchanging heat with the surface of the throat 19. The temperature of combustion air (exhaust gas) can be suppressed when the circulation duct 13 is introduced, and the generation of condensed water that causes problems such as duct corrosion and burner 5 non-ignition can be effectively suppressed. It is.

  In addition, if the outside air A introduced into the circulation duct 13 can be preheated even a little, a decrease in the temperature of combustion air (exhaust gas) can be suppressed, which contributes to a reduction in the generation of condensed water in the duct. However, according to the test data conducted by the present inventors, for example, the combustion air (exhaust gas: temperature approximately 100 ° C., humidity approximately 30%) before the introduction of the outside air is not heated to the outside air (temperature approximately 15 ° C.). ) Is introduced as it is, the temperature of the combustion air becomes approximately 23 ° C. and falls below the dew point temperature (approximately 28 ° C.), but condensation occurs, but preheated outside air (temperature approximately 50-60 ° C.) is introduced. As a result, the combustion air temperature was kept at about 60 to 70 ° C., and condensation could be avoided without falling below the dew point temperature.

  Further, the surface temperature of the throat 19 that becomes hot (approximately 500 ° C.) depending on the amount of combustion of the burner 5 is reduced by approximately 100 ° C. due to heat exchange with the outside air A flowing through the outside air introduction duct 17. It can be reduced by about 50 ° C. as the heat exchange efficiency is improved by adding the projecting piece 22, and it is possible to prevent the occurrence of red heat and confirm the effect of reducing the heat load on the throat 19. It was done.

DESCRIPTION OF SYMBOLS 1 ... Asphalt mixture manufacturing apparatus 2 ... Dryer 3 ... Drum 5 ... Burner 7 ... Exhaust duct 13 ... Circulation duct 14 ... Combustion air supply fan (burner) 17 ... Outside air introduction duct 19 ... Throat (burner) 22 ... Projection piece

Claims (2)

  One end of a cylindrical drum rotatably supported by an inclination is provided with a burner for supplying hot air, while the other end of the drum is provided with an exhaust duct for exhaust gas discharge, and is branched from the middle of the exhaust duct. A circulation duct is connected to the combustion air supply fan of the burner, and a part of the exhaust gas discharged from the exhaust duct is circulated and supplied as combustion air for the burner, and the combustion air in the duct is placed in the middle of the circulation duct. An asphalt mixture manufacturing apparatus provided with an outside air introduction duct for adjusting the oxygen concentration to a concentration necessary for burner combustion, wherein the outside air introduction duct is arranged so as to be along the outer periphery of the throat at the tip of the burner, and the outside air introduction duct The configuration is such that combustion air does not condense when the outside air to be sucked in is preheated by heat exchange with the throat surface of the burner and introduced into the circulation duct. Asphalt mixture manufacturing apparatus characterized.   A plurality of projecting pieces projecting from the outer periphery of the throat, and turbulent flow is generated by the projecting pieces in the outside air flowing along the outer periphery of the throat so as to increase the efficiency of heat exchange. The asphalt mixture manufacturing apparatus according to 1.

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