JP2014513786A - How to optimize the complete combustion of incinerator exhaust gas - Google Patents

Abstract

The present invention relates to a method for optimizing the complete combustion of exhaust gas from an incinerator. In this method, a solid substance (2) to be combusted is introduced into a combustion chamber (8) forming a primary combustion space (12) through an intake port (6), and primary air is sucked into the primary chamber. The stage in which the solid material forming the combustion bed (14) carried on the combustion grate in the combustion space (12) is burned and the burned solid material is the inlet with respect to the carrying direction (F). The primary combustion gas discharged from the stage where it is discharged from the primary combustion space (12) through the outlet (18) arranged on the opposite side and the secondary air is sucked and burned of the solid substance (2) Is disposed downstream of the combustion chamber with respect to the flow direction of the combustion gas and burned in the secondary combustion chamber (28) forming the secondary combustion space (27). Here, the exhaust gas containing the primary combustion gas is homogenized by the fluid introduced through the nozzles (24a, 24b, 24c) in the mixing zone (26) before entering the secondary combustion space (27). . In the present invention, the mixing zone (26) is at least approximately directly adjacent to the combustion bed (14) with respect to the flow direction of the exhaust gas, and the injection speed of the fluid injected from the nozzles (24a, 24b, 24c) is 40 m / s to 120 m / s, characterized in that the nozzles (24a, 24b, 24c) are oriented at an angle of −10 ° to + 10 ° with respect to the inclination of the combustion grate (FIG. 1).

Description

  The present invention relates to a method for optimizing the complete combustion of an incinerator exhaust gas as described in the preceding paragraph of claim 1 and comprising a combustion chamber for carrying out the method and such a combustion chamber Also related to waste incinerators.

  Incinerators for burning solid fuels such as municipal waste, alternative fuels, biomass, and other materials are well known to those skilled in the art. Such equipment has a combustion chamber in which primary air is sucked and solid material is burned. Such combustion is called primary combustion. Here, the solid substance is subjected to various partial treatments while entering the combustion chamber from the intake and exiting from the intake. Such partial treatment is largely classified into drying, ignition, combustion, and ash combustion.

In each of these partial treatments, exhaust gases having different compositions are generated. In the drying stage, the primary air simply absorbs moisture from the burned solid material, while in the ignition stage, pyrolysis products are generated. The oxygen supplied in the ignition stage is usually completely converted, unlike the drying stage, and the exhaust gas stream generated in this stage contains little or no oxygen. In the combustion stage, exhaust gas containing CO, CO ₂ , O ₂ , H ₂ O and N ₂ as typical components is generated, while in the ash combustion stage, air is hardly consumed until the end.

  After the primary combustion, these various exhaust gas streams reach a secondary combustion chamber arranged downstream in the flow direction, and the secondary air is sucked and burned. This combustion is called secondary combustion.

A method including combustion of solid substances and secondary combustion of exhaust gas components of incomplete combustion is disclosed in, for example, International Publication No. 2007/090510 (Patent Document 1). In Patent Document 1, in order to minimize the formation of nitrogen oxides in the secondary combustion chamber (NO _X), which is intended to degrade NH ₃ and HCN is a primary nitrogen compounds .

European Patent Application No. 1077077 (Patent Document 2) describes a method similar to the method disclosed in Patent Document 1. In Patent Document 2, the SNCR method is used to remove NO _X from the flue gas. In the SNCR method, no catalyst is used, and instead a reducing agent is injected into the flue gas. The SNCR method is performed at a temperature of 850 ° C. to 1000 ° C., and complicated control is required.

  The reduction of nitrogen oxide is further described in International Publication No. 99/58902 (Patent Document 3). In the invention described in Patent Document 3, a medium that does not contain oxygen or has a low oxygen concentration is added to the gas discharged from the combustion chamber in the mixing stage and homogenized. Thereafter, the homogenized exhaust gas stream passes through a steady state zone where the nitrogen oxides already produced are reduced. In this method, depending on the operating conditions, the accumulated amount of pyrolysis gas becomes large, and a sufficient amount of secondary air for complete combustion may not be used locally. As a result, unburned gas leaks from the secondary combustion chamber, for example, CO peaks occur in the flue gas.

  The presence of the various combustion treatment zones results in temperature imbalances in addition to the different components of each exhaust gas stream. The temperatures of the ignition zone and the combustion zone are very high compared to, for example, the ash combustion zone. This imbalance is even more pronounced in the secondary combustion chamber. The proportion of combustible primary combustion gas in the exhaust gas generated in the ignition zone and combustion zone is higher than that in the ash combustion zone, and the temperature rises further due to the combustion of these combustible gases. is there.

  In particular, in the region on the intake side, the side wall surrounding the combustion chamber or the secondary combustion chamber may be damaged by the influence of high temperature. In addition, high temperature caking or coking can occur in this area, which must be removed using complex maintenance procedures.

  For example, it was described in European Patent Application Publication No. 1081434 (Patent Document 4), European Patent Application Publication No. 1382906 (Patent Document 5), and US Pat. No. 5,133,895 (Patent Document 6). The method seeks to overcome the problem of reducing the amount of unburned material (especially CO). For example, Patent Document 6 describes that a mixed fluid is introduced so that a gas exiting a combustion chamber is swirled in a spiral flow. In addition, for example, Patent Document 4 describes a special nozzle configuration for introducing such a fluid, which allows rotation within an injection plane arranged in the area of the flameproof cover of the flow path. A flow is formed.

  However, particularly in the method described in Patent Document 6, the problem of temperature imbalance existing in the combustion chamber is not sufficient. This method lowers the temperature of the region on the intake side of the combustion chamber by injecting water droplets or water vapor, which is disadvantageous from the viewpoint of energy recovery balance.

International Publication No. 2007/090510 European Patent Application No. 1077077 International Publication No. 99/58902 European Patent Application No. 1081434 European Patent Application Publication No. 1382906 US Pat. No. 5,313,895

  It is an object of the present invention to provide a method for optimizing the complete combustion of exhaust gas from an incinerator that has high operational reliability and can recover energy from the combustion process with high efficiency.

  The above object is achieved by a method according to claim 1. Preferred embodiments of the invention are described in detail in the respective dependent claims.

  The method according to the invention comprises introducing a combusted solid substance into a combustion chamber forming a primary combustion space via an intake, and sucking primary air and being transported on a combustion grate in the primary combustion space. Each step of burning the solid material forming the combustion bed and discharging the combusted solid material from the primary combustion space via an outlet located opposite to the inlet with respect to the transport direction Is included.

  The primary combustion gas released during the combustion of the solid material is sucked in the secondary air and burned in the secondary combustion chamber forming the secondary combustion space. The secondary combustion chamber is disposed downstream of the combustion chamber with respect to the flow direction of the combustion gas (in other words, above the combustion chamber).

  The exhaust gas containing the primary combustion gas is homogenized in the mixing zone before entering the secondary combustion space (in other words upstream in the flow direction and hence below this combustion space). This homogenization is caused by the fluid introduced through the nozzle.

  Here, the nozzle may be a single nozzle or a plurality of nozzles. The homogenization mentioned above also means that the exhaust gas or the individual exhaust gas streams of different components are mixed so that a gas mixture that is as homogeneous as possible is obtained.

  In the present invention, the mixing zone is adjacent to the combustion bed at least approximately directly with respect to the flow direction of the exhaust gas. In other words, the mixing zone is located at least approximately immediately above the combustion bed. This makes it possible, for example, to mix a very hot exhaust gas stream generated in the ignition zone or combustion zone with a relatively cool exhaust gas stream from the drying or ash combustion zone, almost directly above the combustion bed, and thus The temperature peak can be canceled or reduced at an early stage. At the same time, this method avoids the deterioration of the energy recovery balance, which occurs for example in the case of cooling with a cooling medium.

  In addition, the gas mixture is obtained as a result of the homogenization of the exhaust gas stream generated in the individual combustion treatment zones and is adjusted to be optimized for secondary combustion in the secondary combustion space. As a result, according to the present invention, even if the (secondary) air surplus is reduced, it is possible to reliably perform the optimized complete combustion of the exhaust gas. As a result, even if the intake amount of the secondary air is reduced, the release of harmful substances such as CO or unburned hydrocarbons can be suppressed to a very low level.

In addition, even if reduced nitrogen-containing combustion gas (nitrogen oxide precursor) generated in the combustion zone and oxygen present on the drying zone or ash combustion zone are mixed, the increase in nitrogen oxide does not occur as a result. I understand. This is because when the exhaust gas stream from the combustion zone and the exhaust gas stream rich in oxygen that accumulates in the drying and ash combustion zones are mixed, the temperature of these gas streams decreases at the same time, thereby reducing the thermal NO _x. This can be explained by the fact that the generation of is suppressed.

  As mentioned above, according to the present invention, fluid is introduced through one or more nozzles. Also, according to the present invention, the ejection speed of the fluid ejected from the nozzle is about 40 m / s to about 120 m / s, and the nozzle is oriented at an angle of −10 ° to 10 ° with respect to the inclination of the combustion grate It is attached.

  In addition to the nozzles defined as described above, it is also possible to further provide nozzles that are not aligned with the above angle with respect to the inclination of the combustion grate.

  Here, the inclination of the combustion grate means the average of the inclination of the entire combustion grate (it is not the orientation of any of the existing grate steps).

  The orientation of the nozzle according to the invention ensures that the solid material is not excessively wound up from the combustion grate even if the mixing zone is arranged directly above the combustion bed according to the invention. In accordance with the present invention, a fluid ejection speed of about 40 m / s to about 120 m / s is also useful to avoid rolling up solid material.

  The combination of the new nozzle arrangement according to the invention and the injection speed makes the mixing zone at least approximately with respect to the flow direction of the exhaust gas without causing excessive unwinding of solid matter from the combustion grate. It can be directly adjacent to the combustion bed.

  It is even more surprising in view of the fact that very large values are taught in the prior art that a good homogenization can be achieved as early as an injection speed of about 40 m / s to about 120 m / s according to the present invention. That is. For example, EP-A-1508745 discloses that the injection speed is at least a Mach number of 1. The speed of Mach number 1 is synonymous with the speed of sound, and is specifically about 343 m / s in the case of air at 20 ° C. And at high temperatures such as those found in incinerators, this speed is even greater.

  According to a preferred embodiment of the invention, the distance between the mixing zone and the combustion bed is at most 1.5 m, preferably at most 0.8 m. This distance is the maximum distance between the upper boundary position of the combustion bed and the start position of the mixing zone when considered along the exhaust gas flow direction. This maximum distance is within the scope of the expression “approximately directly above the combustion bed” in view of the normal dimensions of the incinerator. Since the upper boundary position of the combustion bed is typically about 0.3 m to about 1 m above the combustion grate, there is a suitable distance between the mixing zone and the combustion grate.

  According to a preferred embodiment of the invention, the mixing zone extends up to a distance of 2 m as measured from the combustion bed. Therefore, the mixing zone according to this embodiment ends at a maximum position of 2 m when considered along the flow direction of the exhaust gas. Even in this case, a sufficient distance is taken until the secondary air is injected. In accordance with the present invention, if the mixing zone is at least approximately directly adjacent to the combustion bed, the upper boundary position described above is sufficient to achieve the desired homogenization of the exhaust gas.

  According to a preferred embodiment of the present invention, particularly good homogenization is achieved by setting the ejection speed of the fluid ejected from the nozzle to about 90 m / s.

  Here, the ejection speed is a speed that the fluid has when ejected from the nozzle opening. Standardly used nozzles typically have a circular nozzle cross-section of 60 mm to 200 mm. The cross section of the nozzle may be formed so as to continuously taper along the direction of the nozzle opening so that the diameter of the injection opening of the nozzle is 60 mm to 90 mm.

  Each nozzle is preferably oriented at an angle of −10 ° to + 5 ° with respect to the inclination of the combustion grate, more preferably to minimize roll-up of the solid material due to the introduction of fluid. It is oriented at an angle of -5 ° to + 5 °. Also, in a further preferred embodiment of the invention, each nozzle is oriented at an angle of -10 ° to 0 ° with respect to the inclination of the combustion grate.

  In a further preferred embodiment of the present invention, the fluid comprises flue gas recirculated from a subsequent zone downstream of the secondary combustion space. In typical waste incinerator configurations, flue gas recirculation is preferably performed from the zone between the steam generator and the flue. The amount of flue gas introduced is about 5% to about 35%, preferably about 20%, of the amount of primary air taken in. Apart from or in addition to flue gas, any suitable other fluids can be used, in particular inert gases such as air, nitrogen, water vapor, or mixed gases thereof.

  Usually, the highest temperature is in the region on the intake side of the combustion chamber, so according to a preferred embodiment of the invention, the fluid is a single nozzle located in the region on the intake side of the combustion chamber, or Injected through a plurality of nozzle rows. This effectively avoids a very significant temperature imbalance in the side wall surrounding the combustion chamber and the resulting damage or contamination.

  In particular, when refluxed flue gas is used as such a fluid, each nozzle preferably has an outer tube and an inner tube that extends along the axial direction of the outer tube and is surrounded by the outer tube. . Here, the inner pipe is for transmitting smoke, and the outer pipe is for transmitting air. The inner diameter of the inner tube is preferably about 70 mm, and the inner diameter of the outer tube (in other words, the outer diameter of the annular gap existing between the inner tube and the outer tube) is about 110 mm.

  In this embodiment, the air flow is used as a protective wall that protects the nozzle against the deposition of impurities contained in the flue gas. In particular, at the temperature in the region on the intake side, caking is likely to occur due to such adhesion, and in extreme cases, it may cause damage to the nozzle. In this embodiment, such a problem can be effectively prevented.

  It has proved advantageous to provide at least one nozzle per meter of combustion chamber width. The fluid is preferably introduced from at least 2 nozzles, more preferably from at least 6 nozzles. This allows as complete homogenization as possible using a relatively small amount of injection fluid.

  In addition to the method described above, the present invention also provides a combustion chamber for performing the method. The combustion chamber has a side wall surrounding the primary combustion space, an intake for introducing the solid material to be burned into the primary combustion space, a combustion grate for burning the solid material, and the direction of transport of the solid material. An outlet disposed on the opposite side of the inlet for discharging the burned solid material from the primary combustion space; and a nozzle for homogenizing the exhaust gas containing the primary combustion gas discharged during the combustion process; , Including. Here, the nozzles are arranged according to the invention in the range above the combustion grate up to 3 mm, preferably 0.5 m to 3 m, most preferably 0.5 m to 2 m.

  The nozzle is generally arranged on the side wall of the combustion chamber, preferably in the region on the intake side or the region on the outlet side.

  In order to avoid the rolling up of the solid material present in the combustion bed with the homogenization process, the nozzle is in accordance with the invention an angle of −10 ° to + 10 ° with respect to the inclination of the combustion grate, Preferably, it is oriented at an angle of −10 ° to + 5 °, more preferably an angle of −5 ° to + 5 °. In a further preferred embodiment of the invention, each nozzle is oriented at an angle of −10 ° to 0 ° with respect to the inclination of the combustion grate.

  In addition to the method and combustion chamber described above, the present invention also provides a waste incinerator that includes the combustion chamber described above.

  The present invention will be described with reference to the accompanying drawings.

FIG. 1 is a diagram schematically showing a part of a combustion chamber and a secondary combustion chamber for performing the method according to the present invention. FIG. 2 shows the result of measuring the O ₂ concentration (vol% unit) and CO concentration (mg / m ³ unit in the standard atmospheric state) of the exhaust gas flow generated in the combustion zone while switching the nozzle operation period and the stop period. It is a graph which shows with respect to time.

  As shown in FIG. 1, the solid material 2 to be combusted is injected into the supply hopper 2 and introduced into the combustion chamber 8 through the intake 6. For this introduction, generally, a dosing tappet is used. The combustion chamber 8 includes a side wall 10, and the side wall 10 surrounds a primary combustion space 12 formed so as to taper upward.

  The solid material 2 forms a combustion bed 14 (feed) and is transported on the combustion grate 16. Primary air flows through the combustion grate and the solid material is burned during this process. At this time, the drying zone, the ignition zone, the combustion zone, and the ash combustion zone are continuously provided along the transport direction F. Thereafter, the combusted solid material is discharged from an outlet 18 disposed on the opposite side of the inlet 16 and then sent through a slag remover of the slag transporter. In the illustrated embodiment, primary air is distributed through individual lower hot air chambers 20a, 20b, 20c, 20d, and each of the lower hot air chambers has a separate primary air line 22a, 22b, 22c, 22d. Supplied through.

  Nozzles 24 a, 24 b, 24 c (indicated by arrows in FIG. 1) are arranged on the combustion chamber side wall 10 and are used to introduce fluid into the combustion chamber 8. These nozzles are configured such that the ejection speed of fluid from the nozzles is 40 m / s to 120 m / s.

  In the illustrated embodiment, the nozzle 24 a is arranged in the region 8 ′ on the intake side of the combustion chamber 8, in particular in the portion 10 ′ of the side wall 10 facing the intake, inclined and extending upward. Has been. Further, the nozzles 24b and 24c are arranged in the region 8 '' on the outlet side. In this case, one nozzle 24b is disposed on the inclined portion 10 ″ of the side wall and extending upward, and one nozzle is disposed on the portion 10 ′ ″ that forms the end face 25 and extends vertically. . However, any other number and arrangement of nozzles that meet the objectives of the present invention may be used.

  The exhaust gas containing the combustion gas released during the combustion process is homogenized in the mixing zone 26 by using the nozzles 24a, 24b, 24c, 24d. The mixing zone is at least approximately directly adjacent to the combustion bed 14 with respect to the flow direction of the exhaust gas. In FIG. 1, this homogenization is indicated by dashed arrows. Here, the symbol A schematically shows a region where the temperature is high and the concentration of the primary combustion gas is high, and the symbol B is a low temperature compared to the region indicated by the symbol A and the primary combustion gas. The area | region where the density | concentration of low is shown typically. After homogenization, in other words, above the regions indicated by the symbols A and B in FIG. 1, the exhaust gas exists in a homogeneous gas mixture.

  The exhaust gas follows the combustion chamber 8 and flows into the secondary combustion chamber 28 forming the secondary combustion space 27. And secondary air is inhaled and exhaust gas is burned in a secondary combustion chamber. Therefore, nozzles 32 a and 32 b for introducing secondary air are provided on the side wall 30 of the secondary combustion chamber 28.

As shown in FIG. 2, when the fluid is introduced by operating with the nozzle turned on, the O ₂ concentration measured locally in the exhaust gas flow generated in the combustion zone (O _{2, local} : thick in the figure). The solid O ₂ concentration (O _{2, global} : indicated by a thin broken line in the figure), that is, the overall O ₂ concentration existing in the exhaust gas flow generated in the combustion chamber substantially matches the O ₂ concentration throughout the region. On the other hand, when the nozzle in the OFF position to stop the measurement value of the local O ₂ concentration than the measurement value of the entire specific O ₂ concentration significantly lower.

  As for the CO concentration, when the nozzle is operated, a relatively low and almost constant value is obtained, whereas when the nozzle is stopped, a relatively high and very various value is obtained. . This result also shows that the exhaust gas is homogenized by the introduction of fluid.

Claims (15)

A method for optimizing the complete combustion of exhaust gas from an incinerator,
A stage in which a solid substance (2) to be burned is introduced into a combustion chamber (8) forming a primary combustion space (12) via an intake port (6)
Primary air is aspirated and the solid material forming a combustion bed (14) carried on a combustion grate in the primary combustion space (12) is combusted;
The combusted solid material is discharged from the primary combustion space (12) via an outlet (18) disposed on the opposite side of the inlet with respect to the transport direction (F);
The primary combustion gas that is sucked in the secondary air and released during the combustion of the solid substance (2) is arranged downstream of the combustion chamber with respect to the flow direction of the combustion gas to form a secondary combustion space (27). Combusting in the secondary combustion chamber (28),
The exhaust gas containing the primary combustion gas is homogenized by the fluid introduced through the nozzles (24a, 24b, 24c) in the mixing zone (26) before entering the secondary combustion space (27),
The mixing zone (26) is adjacent to the combustion bed (14) at least approximately directly with respect to the flow direction of the exhaust gas, and the injection speed of the fluid injected from the nozzles (24a, 24b, 24c) is 40 m / s to 120 m / s, and the nozzles (24a, 24b, 24c) are oriented at an angle of −10 ° to + 10 ° with respect to the inclination of the combustion grate, how to.   Method according to claim 1, characterized in that the distance between the mixing zone (26) and the combustion bed (14) is at most 1.5 m, preferably at most 0.8 m. .   3. Method according to claim 1 or 2, characterized in that the mixing zone (26) extends up to a distance of 2 m as measured from the combustion bed (14).   The method according to any one of claims 1 to 3, wherein an ejection speed of the fluid ejected from the nozzle (24a, 24b, 24c) is 90 m / s.   The nozzle (24a, 24b, 24c) is oriented at an angle of -5 ° to + 5 ° with respect to the inclination of the combustion grate, according to any one of claims 1 to 4. The method described.   6. A method according to any one of the preceding claims, wherein the fluid comprises flue gas recirculated from a zone following downstream of the combustion chamber (27).   The method according to claim 6, characterized in that the amount of flue gas introduced is 5% to 35%, preferably about 20%, of the amount of primary air taken in.   The method according to any one of claims 1 to 7, characterized in that the fluid is ejected via a nozzle (24a) arranged in an inlet side region of the combustion chamber (8).   The nozzle includes an outer tube and an inner tube that extends along the axial direction of the outer tube and is surrounded by the outer tube. The inner tube is for transmitting flue gas. 9. A method according to any one of claims 1 to 8, characterized in that the tube is for transmitting air.   10. A method according to any one of the preceding claims, wherein the fluid is introduced from at least two nozzles, preferably from at least six nozzles. A combustion chamber for carrying out the method according to any one of claims 1 to 10,
A side wall (10) surrounding the primary combustion space (12);
An inlet (6) for introducing solid material to be burned into the primary combustion space (12);
A combustion grate (16) for burning the solid material;
An outlet (18) disposed on the opposite side of the inlet (6) with respect to the conveying direction (F) of the solid substance, and for discharging the burned solid substance from the primary combustion space (12);
Nozzles (24a, 24b, 24c) for homogenizing exhaust gas containing primary combustion gas discharged during the combustion process,
The nozzle is arranged above the combustion grate (16) in a range of at most 3 mm, preferably 0.5 m to 3 m, most preferably 0.5 m to 2 m, and the combustion grate (16) A combustion chamber characterized by being oriented at an angle of −10 ° to + 10 ° with respect to the inclination of the combustion chamber.   12. Combustion chamber according to claim 11, characterized in that the nozzle is arranged on the side wall (10) of the combustion chamber (8).   The combustion chamber according to claim 11 or 12, wherein the nozzle (24a) is disposed in a region on the intake port (6) side.   The nozzle (24a, 24b, 24c) is oriented at an angle of -5 ° to + 5 ° with respect to the inclination of the combustion grate (16). The combustion chamber according to Item 1.   A waste incinerator including the combustion chamber according to any one of claims 11 to 14.

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