WO2012130446A1

WO2012130446A1 - Method for optimising the burnout of exhaust gases of an incinerator

Info

Publication number: WO2012130446A1
Application number: PCT/EP2012/001361
Authority: WO
Inventors: Maurice Henri WALDNER
Original assignee: Hitachi Zosen Inova Ag
Priority date: 2011-03-29
Filing date: 2012-03-28
Publication date: 2012-10-04
Also published as: EP2691701A1; ES2647667T3; EP2691701B1; EP2505919A1; US20140182492A1; EP2691701B2; NO2691701T3; JP2014513786A; RS56483B1; PL2691701T3; RS56483B2; FI2691701T4

Abstract

The present invention relates to a method for optimising the burnout of exhaust gases of an incinerator, in which the solids (2) to be combusted are introduced via an inlet (6) into a combustion chamber (8) defining a primary combustion space (12), the solids (2) in the primary combustion space (12), in the form of a combustion bed (14) conveyed over a combustion grate (16), are combusted with the admission of primary air and the combusted solids are discharged from the primary combustion space (12) via an outlet (18) disposed opposite the inlet in the conveying direction (F). The primary combustion gases released during the combustion of the solids (2) are combusted, with the admission of secondary air, in a secondary combustion chamber (28) defining a secondary combustion space (27) and arranged downstream of the combustion chamber (8) in the flow direction of the combustion gases. Before entering the secondary combustion space (27), the exhaust gases containing the primary combustion gases are homogenised in a mixing zone (26) by means of a fluid introduced via a nozzle (24a, 24b, 24c). The invention is characterised in that the mixing zone (26) at least approximately directly adjoins the combustion bed (14) in the flow direction of the exhaust gases, the exit speed of the fluid from the nozzle (24a, 24b, 24c) is from 40 to 120 m/s, and the nozzle (24a, 24b, 24c) is aligned at an angle of -10° to +10° relative to the inclination of the combustion grate.

Description

Method for optimizing the burnout of exhaust gases of an incinerator

The present invention relates to a method for optimizing the combustion of exhaust gases of a combustion plant according to the preamble of claim 1 and a combustion chamber for carrying out the method and a waste incineration plant comprising such a combustion chamber.

Incinerators for burning solid fuels such as municipal waste, refuse derived fuels, biomass and other materials are well known to those skilled in the art. Such plants include a combustion chamber in which the solid is burned with supply of primary air, which is referred to as primary combustion. The solid from the inlet into the combustion chamber to the outlet through various sub-processes, which can be roughly subdivided into drying, ignition, combustion and ash burning.

In each of these sub-processes, exhaust gases of different composition are generated. While in the drying phase, the primary air only absorbs moisture from the solid to be burned, can be found in the ignition phase pyrolytic decomposition products. In contrast to the drying phase, the oxygen supplied in the ignition phase is often completely converted, so that the exhaust gas flow generated in this phase has very little or no oxygen. In the combustion phase, exhaust gases with typical compositions of CO, C0 ₂ , 0 ₂ ,

CONFIRMATION COPY H ₂ 0 and 2, while finally over the ash ash practically unused air is present.

As a rule, after the primary combustion, these different exhaust gas streams pass into a secondary combustion chamber arranged downstream in the direction of flow, where they are burnt out with the supply of secondary air, which is referred to as secondary combustion.

A method comprising a combustion of the solid and an afterburning of the incompletely burned exhaust components is known, for example, from WO 2007/090510, which aims to break down the primary nitrogen compounds NH ₃ and HCN in order to prevent the formation of nitrogen oxides (NO _x ) in the Minimize afterburning chamber. EP-A-1077077 relates to a similar process to that of WO 2007/090510, wherein the SNCR process is used for denitrification of the flue gases, in which no catalyst is used, but a reducing agent is injected into the flue gases. Such SNCR processes operate at temperatures of 850 to 1000 ° C and require sophisticated control.

The reduction of nitrogen oxides is also discussed in WO 99/58902. According to the method described therein, the gases emerging from the combustion chamber are homogenized with the addition of an oxygen-free or oxygen-poor medium in a mixing stage, after which the homogenized exhaust gas flow passes through a steady zone in which the already formed nitrogen oxides are to be reduced. Depending on the operating conditions, it may happen that the amount of accumulating pyrolysis gas is so large that the locally available secondary air quantity is insufficient for complete burnout. This causes unburned gases to escape from the post-combustion chamber, resulting in, for example, CO peaks in the chimney.

As a result of the various combustion zones, apart from the differences in the composition of the exhaust gas flows, a temperature shift results as well. Thus, a much higher temperature is present in the ignition zone and the combustion zone than in the ash combustion zone, for example. This shift is exacerbated in the post-combustion chamber because the exhaust gases generated in the ignition and combustion zones have a higher proportion of combustible primary combustion gases than the exhaust generated in the ash combustion zone, and the combustion of these combustible gases further increases the temperature.

Especially in the inlet-side region, the peripheral wall surrounding the combustion chamber or the afterburning chamber can be damaged on the one hand by the prevailing high temperatures. On the other hand, because of the high temperatures, caking or coking may occur in this area, which must be removed in time-consuming maintenance work.

The problem of reducing the amount of unburned substances and in particular CO, for example, attempts to overcome the processes described in EP-A-1081434, EP-A-1382906 and US-B-5313895. For example, according to US-B-5313895 a mixed fluid is introduced, which separates the gases leaving the combustion chamber into a Eddy current offset. In addition, for example, EP-A-1081434 describes a special nozzle arrangement for introducing the fluid, by means of which a rotating flow in the flow channel is produced in a jet plane lying in the region of the flame ceiling. However, in particular, the method described in US Pat. No. 5,313,895 only takes account of the problem of the temperature gradient in the combustion chamber in an unsatisfactory manner. Thus, according to said document in the combustion chamber, the temperature in the inlet-side region should be reduced by means of injection of water droplets or water vapor. But this is in terms of

Energy recovery balance disadvantageous. The aim of the present invention is thus to provide a method for optimizing the burnout of exhaust gases of a combustion plant, which on the one hand ensures a high degree of operational reliability and which, on the other hand, allows a high energy recovery from the combustion to be obtained.

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

Thus, the method according to the invention comprises the steps of introducing the solid to be combusted via an inlet into a combustion chamber defining a primary combustion chamber, combusting the solid in the primary combustion chamber in the form of a combustion bed conveyed via a combustion grate by supplying primary air and the combusted solid via a combustion chamber in the conveying direction the inlet opposite outlet is discharged from the primary combustion chamber.

The primary combustion gases liberated upon combustion of the solid become downstream in the flow direction, i. usually arranged above the combustion chamber, a secondary combustion chamber defining afterburner chamber burned under supply of secondary air.

Before entering the secondary combustion chamber, i. upstream of, and thus typically below, the exhaust gases containing the primary combustion gases are homogenized in a mixing zone. This is done by means of a fluid introduced via a nozzle. In this context, "a" (nozzle) is to be understood as an indefinite article, meaning that the term encompasses both a single nozzle and a plurality of nozzles.

Homogenization is understood in this context to mean that the exhaust gases or the individual exhaust gas streams of different composition are mixed in such a way that the most homogeneous possible gas mixture is obtained. According to the invention, the mixing zone now at least approximately immediately adjoins the combustion bed in the flow direction of the exhaust gases. As a rule, it is thus arranged in other words at least approximately directly above the combustion bed. This allows very hot exhaust gas streams, such as may occur in the ignition or combustion zone, practically immediately above the combustion bed with the cooler exhaust gas streams from the drying and ash combustion zone to mix and thus compensate for temperature peaks early or lower. At the same time, the method allows the energy recovery balance to be unaffected, as would be the case with cooling by means of a cooling medium.

Incidentally, the homogenization of the exhaust gas streams generated in the individual combustion zones results in a gas mixture which is optimally preconditioned for afterburning in the secondary combustion chamber. As a result, the present invention thus allows to ensure an optimal combustion of the exhaust gases even at low (secondary) excess air; the emission of pollutants, such as CO or unburned hydrocarbons, can thus be kept very low even with small amounts of supplied secondary air.

It has also been found that the mixture of the reduced nitrogenous combustion gases (nitrogen oxide precursor substances) generated in the combustion zone with the oxygen present above the drying zone or the burnout zone does not result in an increase in nitrogen oxides. This can be explained by the fact that in the course of the mixture of the exhaust gas flow from the combustion zone with the resulting in the drying and Ausbrandzone oxygen-rich exhaust gas streams at the same time its temperature is lowered, which prevents the formation of thermal NO _x .

As stated above, according to the invention, the fluid is introduced via one or more nozzles. According to the invention, the exit velocity of the fluid from the nozzle is about 40 to about 120 m / s, wherein the nozzle is aligned in the sense of the present invention at an angle of -10 ° to + 10 ° relative to the inclination of the combustion grate.

In addition to the nozzles defined above, further

No nozzles are present that are not in the above defined

Angle are aligned relative to the inclination of the combustion grate. Inclination of the combustion grate in this context is understood to mean the total inclination of the grate (and not the orientation of possibly existing individual grate steps).

The inventive alignment of the nozzle ensures that even with the inventive arrangement of the mixing zone immediately above the fuel bed excessive swirling of solids is avoided by the rust.

To prevent fluidization of solids, the inventive injection rate of the fluid also contributes from about 40 to about 120 m / s.

The found combination of nozzle arrangement according to the invention and injection rate thus makes it possible in total to connect the mixing zone in the direction of flow of the exhaust gases at least approximately directly to the combustion bed, without resulting in excessive unwanted swirling of the solids from the combustion grid. That already with the inventive

Eindüsgeschwindigkeit of about 40 to about 120 m / s, a good homogenization can be obtained, is all the more surprising, since much higher values are taught in the prior art. For example, in EP-A-1508745 an exit velocity of at least 1 MACH is disclosed. A MACH number of 1 is equivalent to the speed of sound, which is usually 343 m / s for air at 20 ° C, and is even higher at higher temperatures found in combustion chambers.

According to a preferred embodiment, the distance between the mixing zone and the fuel bed is at most 1.5 meters, preferably at most 0.8 meters. This distance thus refers to the maximum distance between the upper limit of the fuel bed and the beginning of the mixing zone viewed in the direction of flow of the exhaust gases. Said maximum distance still falls within the concept of "approximately above the fuel bed" in view of the usual dimensions of an incinerator. Since the upper limit of the fuel bed is typically about 0.3 to 1 meter above the surface of the combustion grate, the mixing zone is corresponding to the combustion grate spaced.

According to a further preferred embodiment, the mixing zone extends at most up to a distance of 2 meters measured from the fuel bed. When viewed in the direction of flow of the exhaust gases, the mixing zone according to this embodiment thus ends after a maximum of 2 meters and thus still at a sufficient distance before the secondary air injection. In the invention At least approximately immediately adjacent to the combustion bed subsequent mixing zone, said upper limit is sufficient to obtain the desired homogenization of the exhaust gases. A particularly good homogenization is achieved if, according to a preferred embodiment, the exit velocity of the fluid from the nozzle is about 90 m / s.

The exit velocity refers to the velocity that the fluid has on exit from the nozzle opening. The nozzles used as standard usually have a circular nozzle cross-section of 60 mm to 200 mm. It is conceivable that the nozzle cross-section continuously tapers in the direction of the nozzle orifice so that the diameter of the outlet opening of the nozzle is 60 mm to 90 mm.

In order to minimize swirling of the solids caused by the introduction of the fluid, the respective nozzle is preferably oriented at an angle of -10 ° to + 5 °, more preferably -5 ° to + 5 °, relative to the inclination of the combustion grate. According to a further preferred embodiment, the respective nozzle is aligned at an angle of -10 ° to 0 ° relative to the inclination of the combustion grate.

According to a further preferred embodiment, the fluid comprises a flue gas returned from a downstream zone of the secondary combustion chamber. In conventionally configured waste incineration plants, the recirculation preferably takes place from one zone between the steam generator and the fireplace. In general, the amount of introduced flue gas is about 5 to 35% of the amount of primary air supplied, preferably about 20%. Alternatively or in addition to the flue gas, any other conceivable fluid can be used, in particular air, an inert gas, such as nitrogen, water vapor or mixtures thereof.

Since the highest temperatures are generally present in the inlet-side region of the combustion chamber, according to a preferred embodiment, the injection of the fluid takes place via a nozzle or nozzle row arranged in this region. Thus, a very pronounced temperature shift and thus damage or contamination of the peripheral wall surrounding the combustion chamber can be effectively prevented.

In particular, if a recirculated flue gas is used as the fluid, the respective nozzle preferably has an outer tube and an inner tube extending in the axial direction of the outer tube and enclosed by the inner tube, wherein the inner tube is intended for guiding the flue gas and the outer tube for guiding air , Preferably, the inner diameter of the inner tube is about 70 mm, while the inner diameter of the outer tube, i. the outer diameter of the present between the inner tube and outer tube annular gap, about 110 mm.

The air flow in this embodiment serves as a shield which protects the nozzle from the accumulation of contaminants entrained in the flue gas. Especially in the inlet side area Temperatures such deposits could easily lead to caking, which can lead to failure of the nozzle in extreme cases; This is effectively prevented according to the described embodiment. It has proven to be advantageous if at least 1 nozzle per meter of the combustion chamber width is provided. Preferably, the introduction of the fluid via at least two nozzles, more preferably at least six nozzles. This ensures as complete as possible homogenization with a relatively small amount of injected fluid.

In addition to the described method, the present invention further relates to a combustion chamber for carrying out the method. It comprises a peripheral wall enclosing a primary combustion space, an inlet for introducing the solid to be combusted into the primary combustion space, a combustion grate for combustion of the solid, an outlet opposite the inlet in the conveying direction of the solid for discharging the burnt solid from the primary combustion space and a nozzle for homogenizing the exhaust gases containing the combustion gases released during the combustion. The nozzle according to the invention is arranged in a range of at most 3 meters, preferably 0.5 meters to 3 meters, most preferably 0.5 to 2 meters above the combustion grate.

In general, the nozzle is arranged in the peripheral wall of the combustion chamber, preferably in the region of the inlet or the outlet. In order to avoid that the homogenization is associated with a Aufwirbelung present in the fuel bed solid, the nozzle according to the invention at an angle of -10 ° to + 10 °, preferably from -10 ° to + 5 °, more preferably from -5 ° to + 5 °, oriented relative to the inclination of the combustion grate. According to a further preferred embodiment, the respective nozzle is aligned at an angle of -10 ° to 0 ° relative to the inclination of the combustion grate. In addition to the described method and the combustion chamber described, the present invention also comprises a waste incineration plant comprising a combustion chamber as described.

The invention is illustrated by the attached figures. Of these shows

Fig. 1 is a schematic representation of a

Combustion chamber and a partially shown Nachbrennkammer for carrying out the method according to the present invention; and

Fig. 2 is a graphical representation of the measured

0 ₂ concentration (in% by volume) or CO concentration (in mg / m ³ in the standard state) over time in an exhaust gas stream generated in the combustion zone, the nozzles on or off at individual time intervals. are turned off.

As shown in Fig. 1, the solid to be burned 2 is filled in a hopper 4 and of this usually introduced by means of a Dosierstössels via an inlet 6 into the combustion chamber 8. The combustion chamber 8 comprises a peripheral wall 10, which encloses an upwardly tapering, primary combustion chamber 12.

The solid 2 is in the form of a fuel bed 14 through a flow of primary air

Promoted (advancing) combustion grate 16 and thereby burned. In the conveying direction F are successively a drying zone, a

Ignition zone, a combustion zone and an ash combustion zone before the burnt solid discharged via an inlet 6 opposite the outlet 18 and is subsequently fed via a slag conveyor slag promotion. The distribution of the primary air takes place in the embodiment shown via individual sub-wind chambers 20a, 20b, 20c, 20d, which are fed via separate primary air lines 22a, 22b, 22c, 22d. In the peripheral wall 10 of the combustion chamber are indicated in Fig. 1 indicated by arrows nozzles 24a, 24b, 24c, via which a fluid is introduced into the combustion chamber 8.

The nozzles are designed such that the exit velocity of the fluid from the nozzles is 40 to 120 m / s.

In the embodiment shown, a nozzle 24a is disposed in the inlet side region 8 'of the combustion chamber 8, specifically in an inlet facing, obliquely upwardly extending portion 10' of the peripheral wall 10. Two nozzles 24b, 24c are shown in FIG outlet side region 8 '', wherein a nozzle 24b in the obliquely upwardly extending portion 10 '' and in which the end face 25 defining, vertically extending portion 10 '''of the peripheral wall is arranged. However, any other number and arrangement of nozzles suitable for the purposes of the present invention is also conceivable.

By means of the nozzles 24a, 24b, 24c, the exhaust gases, which contain the combustion gases liberated during the combustion, are homogenized in a mixing zone 26 which adjoins the combustion bed 14 in the flow direction at least approximately directly. This homogenization is indicated in the figure by dashed arrows, where A schematically denotes the region of relatively high temperature and relatively high concentration of primary combustion gases, and B denotes the region of lower temperature and lower concentration of primary combustion gases. After homogenization, ie in the figure above the areas designated A and B, the exhaust gases are in the form of a homogeneous gas mixture.

This flows into an afterburner chamber 28, which is connected downstream of the combustion chamber 8 and defines a secondary combustion chamber 27, in which the exhaust gases are burned while supplying secondary air. For this purpose, in the peripheral wall 30 of the afterburner chamber 28 further nozzles 32a, 32b are provided for introducing the secondary air. As illustrated in FIG. 2, the introduction of the fluid when the nozzle is in the ON position results in that The O ₂ concentration measured locally in the exhaust gas flow generated in the combustion zone (shown in thick solid lines) corresponds approximately to the global, ie the total, present in the combustion chamber-generated exhaust gas 0 ₂ concentration (shown in thin dashed lines) , In contrast, when the nozzle is not actuated in the OFF position, the locally measured 0 ₂ concentration is much lower than that measured globally.

Concerning CO concentration, a relatively low, approximately constant value is obtained when the nozzle is actuated, while relatively high and strongly divergent values are obtained when the nozzle is not actuated, which further illustrates the homogenization of the exhaust gases by the introduction of the fluid.

Claims

claims

A method for optimizing the combustion of exhaust gases of a combustion plant, comprising the steps of the solid to be incinerated (2) via a

Inlet (6) into a one primary

Combustion chamber (12) defining the combustion chamber (8) is introduced, the solid in the primary combustion chamber (12) in the form of a combustion grate promoted

Burned fuel bed (14) is burned under supply of primary air and the burnt solid via a in the conveying direction (F) the inlet opposite outlet arranged (18) from the primary combustion chamber (12) is discharged, and in the combustion of the solid (2) freed primary combustion gases arranged in a flow direction downstream of the combustion chamber (8) defining a secondary combustion chamber (27)

Afterburning chamber (28) are burned with the supply of secondary air, wherein the exhaust gases containing the primary combustion gases before entering the secondary combustion chamber (27) are homogenized in a mixing zone (26) by means of a fluid introduced via a nozzle (24a, 24b, 24c), characterized in that the mixing zone (26) in the flow direction of the exhaust gases at least approximately directly to the fuel bed (14), the exit velocity of the fluid from the nozzle (24a, 24b, 24c) is 40 to 120 m / s, and that the nozzle (24a, 24b, 24c) is oriented at an angle of -10 ° to + 10 ° relative to the inclination of the combustion grate.

A method according to claim 1, characterized in that the distance between the mixing zone (26) and the fuel bed (14) is at most 1.5 meters, preferably at most 0.8 meters.

Method according to one of the preceding claims, characterized in that the mixing zone (26) extends at most up to a distance of 2 meters measured from the fuel bed (14).

Method according to one of the preceding claims, characterized in that the exit velocity of the fluid from the nozzle (24a, 24b, 24c) is 90 m / s.

Method according to one of the preceding claims, characterized in that the nozzle (24a, 24b, 24c) is oriented at an angle of -5 ° to + 5 ° relative to the inclination of the combustion grate.

Method according to one of the preceding claims, characterized in that the fluid is from a downstream of the secondary Combustion chamber (27) downstream zone comprises recycled flue gas.

A method according to claim 6, characterized in that the amount of introduced flue gas is 5% to 35%, preferably about 20% of the amount of primary air supplied.

Method according to one of the preceding claims, characterized in that the injection of the fluid takes place via a nozzle (24a) arranged in the inlet-side region of the combustion chamber (8).

Method according to one of the preceding claims, characterized in that the nozzle has an outer tube and an inner tube extending in the axial direction of the outer tube and enclosed by this, wherein the inner tube for guiding the flue gas is determined and the outer tube for guiding air.

Method according to one of the preceding claims, characterized in that the introduction of the fluid via at least two nozzles, preferably at least six nozzles takes place.

Combustion chamber for carrying out the method according to one of the preceding claims, comprising a peripheral wall (10) enclosing a primary combustion space (12), an inlet (6) for introducing the solid to be combusted into the primary combustion space (12), a combustion grate (16) for combustion of the solid, an outlet (18) opposite the inlet (6) in the conveying direction (F) of the solid for discharging the burnt solid from the primary combustion chamber (12) and a nozzle (24a, 24b, 24c ) for homogenizing the waste gases containing the combustion-released primary combustion gases, characterized in that the nozzle in a range of at most 3 meters, preferably 0.5 meters to 3 meters, most preferably 0.5 meters to 2 meters, above the combustion grate (16) is arranged, and that the nozzle at an angle of -10 ° to + 10 ° relative to the inclination of

Combustion grate (16) is aligned.

Combustion chamber according to claim 11, characterized in that the nozzle is arranged in the peripheral wall (10) of the combustion chamber (8).

Combustion chamber according to claim 11 or 12, characterized in that the nozzle (24a) is arranged in the region of the inlet (6).

Combustion chamber according to one of claims 10 to 13, characterized in that the nozzle (24a, 24b, 24c) is oriented at an angle of -5 ° to + 5 ° relative to the inclination of the combustion grate (16).

Waste incineration plant comprising a combustion chamber (8) according to one of claims 11 to 14.