ES2647667T3 - Procedure for optimizing the complete combustion of exhaust gases from an incinerator plant - Google Patents

Abstract

Procedure for the optimization of the complete combustion of exhaust gases from an incinerator plant, which comprises the following steps the solid material (2) to be incinerated is introduced through an inlet (6) in a combustion chamber (8) that defines a primary combustion space (12), the solid material (2) is incinerated in the primary combustion space (12) in the form of a combustion bed (14) transported above a combustion grill (16) with feed of primary air and the incinerated solid material is discharged from the primary combustion space (12) through an outlet (18) arranged in front of the inlet (6) seen in the transport direction (F), the primary combustion gases that are they release during combustion of the solid material (2) they are burned by feeding secondary air in a post-combustion chamber (28) that defines a secondary combustion space (27) and which is arranged under the chamber flue (8) seen in the direction of flow of said primary combustion gases, the exhaust gases containing the primary combustion gases being homogenized before entering the secondary combustion space (27) in a mixing zone (26 ) by means of a fluid introduced by a nozzle (24a, 24b, 24c), the mixing zone (26) being arranged in the direction of flow of the exhaust gases at least approximately directly following the combustion bed (14), characterized because the fluid outlet speed of the nozzle (24a, 24b, 24c) is 40 to 120 m / s and because the nozzle (24a, 24b, 24c) is oriented at an angle of -10º to + 10º with respect to the inclination of the combustion grill (16).

Description

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DESCRIPTION

Procedure for optimizing the complete combustion of exhaust gases from an incinerator plant

The present invention relates to a process for the optimization of the complete combustion of exhaust gases of an incinerator plant according to the preamble of claim 1. Such a method is described, eg in EP-A- 1508745 The expert knows well incinerator plants for the combustion of solid combustible materials, such as municipal waste, substitute fuels, biomass and other materials. Plants of this type comprise a combustion chamber, in which solids are incinerated by feeding primary air, which is called primary combustion. From the entrance in the combustion chamber to the exit, the solid material goes through different partial processes, which can be divided approximately in drying, ignition, combustion and complete combustion of the ashes.

In each of these partial processes, exhaust gases of different compositions are generated. While in the drying phase, the primary air absorbs only moisture from the solid material to be incinerated, in the ignition phase pyrolytic decomposition products are produced. Unlike the drying phase, the oxygen fed in the ignition phase reacts in many cases completely, so that the exhaust gas stream generated in this phase has very little or no oxygen. In the combustion phase, exhaust gases with typical compositions of CO, CO2, O2, H2O and N2 are generated, while practically unconsumed air is finally presented above the complete combustion of the ashes.

As a general rule, these different exhaust gas streams arrive after a primary combustion into a post-combustion chamber arranged downstream seen in the flow direction, where they undergo complete combustion by feeding secondary air, which is called secondary combustion.

A process comprising a combustion of the solid material and a post-combustion of the components not completely burned from the exhaust gases is known for example from WO 2007/090510, whose objective is to decompose the primary nitrogen compounds NH3 and HCN, to minimize the formation of nitrogen oxides (NOx) in the post-combustion chamber.

EP-A-1077077 refers to a procedure similar to that of WO 2007/090510, the SNCR method being used for the removal of nitrogen oxides from the flue gases, in which no catalyst is used by injecting on the contrary a reducing agent in smoke gases. SNCR procedures of this type work at temperatures of 850 to 1000 ° C and require sophisticated regulation.

Also WO 99/58902 refers to the reduction of nitrogen oxides. According to the procedure described therein, the gases leaving the combustion chamber are homogenized by adding a medium without oxygen or with little oxygen in a mixing stage, following which the stream of homogenized exhaust gases passes through an area at rest, in which the nitrogen oxides already formed must be reduced. Depending on the operating conditions it may happen that the amount of gas from the pyrolysis is so large that the amount of locally available secondary air is not sufficient for complete combustion. This leads to the release of unburned gases from the post-combustion chamber, which is manifested, for example, in CO points in the chimney.

As a result of the different combustion zones, an imbalance of temperatures results in addition to differences in the composition of the exhaust gas streams. In the ignition and combustion zone there is a substantially higher temperature than for example in the complete combustion zone of the ashes. This imbalance is further reinforced in the post-combustion chamber, since the exhaust gases generated in the ignition and combustion zone have a greater part of primary combustion gases than the exhaust gases generated in the complete combustion zone of the ashes and the combustion of these combustible gases further increases the temperature.

Precisely in the area of the entrance side, the peripheral wall that surrounds the combustion chamber or the post-combustion chamber can suffer, on the one hand, damage due to the existing high temperatures. On the other hand, in this area, incrustations or coking can occur due to high temperatures, which must be eliminated in costly maintenance work.

The problem of reducing the amount of unburned substances and in particular CO is attempted to solve for example with the procedures 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 causes a turbulent flow of the gases that leave the combustion chamber. In addition, a special nozzle arrangement for the introduction of the fluid is described, for example, in EP-A-1081434, by means of which a rotary current is generated in the flow channel in an injection plane disposed in the roof area of calls. However, in particular the procedure described in US-B-5313895 only solves the problem of temperature imbalance in the combustion chamber only unsatisfactorily. According to said document, in the combustion chamber the temperature in the area of the inlet side must be reduced by injection of water droplets or water vapor. However, this is not favorable in view of the energy recovery balance. The objective of the present invention is therefore to make available a process for combustion optimization.

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complete with exhaust gas from an incinerator plant, which guarantees, on the one hand, great safety in operation and allows, on the other hand, to obtain a great recovery of combustion energy.

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

The process according to the invention therefore comprises the steps of introducing the solid material to be incinerated through an entry into a combustion chamber that defines a primary combustion space, if the solid material is incinerated in the primary combustion space in form of a combustion bed transported above a combustion grill by feeding primary air and the incinerated solid material being discharged from the primary combustion space through an outlet arranged in front of the inlet seen in the direction of transport.

The primary combustion gases that are released during the combustion of the solid material are incinerated by feeding secondary air into a post-combustion chamber that defines a secondary combustion space and which is disposed downstream seen in the flow direction of said primary combustion gases, that is, as a rule above the combustion chamber.

Before entering the secondary combustion space, that is, upstream seen in the direction of flow and, therefore, as a rule below it, the exhaust gases containing the primary combustion gases are homogenized in a mixing zone This is done by a fluid introduced by a nozzle.

In this context, "a" (nozzle) has to be understood as an indefinite article; therefore, the term refers to both a single nozzle and several nozzles.

By homogenization it is understood in this context that the exhaust gases or the different exhaust gas streams of different compositions are mixed in such a way that a gas mixture is obtained as homogeneous as possible. According to the invention, the mixing zone is arranged at least approximately directly after the combustion bed seen in the direction of flow of the exhaust gases. As a rule and in other words, it is arranged at least approximately directly above the combustion bed. This makes it possible to mix very hot exhaust gas streams, such as can be formed, for example, in the ignition or combustion zone, practically directly above the combustion bed with the coldest exhaust gas streams in the drying and combustion zone. full of ashes and therefore compensate or reduce temperature points in time. The procedure allows at the same time that the energy recovery balance is not impaired, as would be the case, for example, in case of cooling by means of a cooling agent.

Moreover, thanks to the homogenization of the exhaust gas streams generated in the different combustion zones, a gas mixture is obtained, which is optimally conditioned for post-combustion in the secondary combustion space. The result is that the present invention allows, even in the case of low (secondary) excess air, to guarantee optimum complete combustion of the exhaust gases; therefore, the emission of harmful substances, such as CO or unburned hydrocarbons, can be kept very low, even in the case of small quantities of secondary fed air.

In addition, it has been found that the mixture of reduced nitrogen-containing combustion gases (nitrogen oxide precursor substances) generated in the combustion zone with oxygen that occurs above the drying or complete combustion zone does not It leads to an increase in nitrogen oxides. This can be explained because during the mixing of the exhaust gas stream of the combustion zone with the oxygen-rich exhaust gas streams that occur in the drying and complete combustion zone, the temperature of the combustion is reduced at the same time. same, which prevents the formation of thermal NOx.

As explained above, the fluid is introduced according to the invention by one or several nozzles.

According to the invention, the fluid outlet speed of the nozzle is approx. 40 to approx. 120 m / s, the nozzle being oriented in the direction of the present invention at an angle of -10 ° to + 10 ° with respect to the inclination of the combustion grill.

In addition to the nozzles defined above there may be other nozzles, which are not oriented at the angle defined above with respect to the inclination of the combustion grill.

The inclination of the combustion grill means in this context the total inclination of the grill (and not the orientation of individual grill levels, if applicable).

Thanks to the orientation of the nozzle according to the invention, it is ensured that, in the case of the arrangement according to the invention of the mixing zone directly above the combustion bed, excessive swirling of solid materials of the solid material is also avoided. grill.

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Also the fluid injection rate according to the invention of approx. 40 to approx. 120 m / s helps prevent the formation of swirls of solid materials.

The combination found of the arrangement of nozzles according to the invention and the injection speed therefore allows, in summary, to connect the mixing zone at least approximately directly following the combustion bed seen in the direction of gas flow Exhaust, without excessive formation of unwanted eddies of the solid materials of the combustion grill.

The fact that a good homogenization with the injection rate according to the invention of approx. 40 to approx. 120 m / s is even more surprising in view that substantially higher values are indicated in the state of the art. In EP-A-1508745, for example, an output speed of at least MACH 1 is disclosed. A MACH number of 1 is equivalent to the speed of sound, which for air at 20 ° C is generally indicated by 343 m / s and that at higher temperatures, as they occur in homes, adopts even higher values. The distance between the mixing zone and the combustion bed can be a maximum of 1.5 meters, preferably a maximum of 0.8 meters. This distance therefore refers to the maximum distance between the upper limit of the combustion bed and the beginning of the mixing zone seen in the direction of flow of the exhaust gases. In view of the usual dimensions of an incinerator plant, said maximum distance still enters the concept "approximately above the combustion bed". Since the upper limit of the combustion bed is usually arranged approx. 0.3 to 1 m above the surface of the combustion grill, the mixing zone is arranged at a corresponding distance from the combustion grill. In addition, the mixing zone can extend at most up to a distance of 2 meters measured from the combustion bed. Seen in the direction of flow of the exhaust gases, the mixing zone therefore ends after a maximum of 2 meters and, therefore, still at a sufficient distance in front of the secondary air injection. In the mixing zone, which according to the invention is arranged at least approximately directly after the combustion bed, said upper limit is sufficient to obtain the desired homogenization of the exhaust gases.

Especially good homogenization is achieved if, according to a preferred embodiment, the fluid outlet speed of the nozzle is approx. 90 m / s

The exit velocity refers here to the velocity that the fluid presents when exiting the opening of the nozzle. The nozzles used as standard have, as a rule, a circular cross-section of nozzle from 60 mm to 200 mm. It is conceivable that the cross section of the nozzle is continuously narrowed in the direction of the mouth of the nozzle, so that the diameter of the outlet opening of the nozzle is 60 mm to 90 mm.

To minimize the formation of a swirl of solid materials caused by the introduction of the fluid, the corresponding nozzle is preferably oriented at an angle of -10 ° to + 5 °, more preferably from -5 ° to + 5 ° with respect to the inclination of the combustion grill. The corresponding nozzle can be oriented at an angle of -10 ° to 0 ° with respect to the inclination of the combustion grill. According to another preferred embodiment, the fluid comprises a smoke gas that has been returned from an area disposed downstream following the secondary combustion space. In conventionally configured garbage incinerator plants, the return is preferably made from an area between the steam generator and the chimney. As a general rule, the amount of smoke gas introduced corresponds to approx. between 5 and 35% of the amount of primary air fed, preferably at approx. 20% Alternatively or in addition to the smoke gas, any conceivable fluid, in particular air, an inert gas, such as nitrogen, water vapor or mixtures thereof can be used.

Since the highest temperatures generally occur in the area of the inlet side of the combustion chamber, the injection of the fluid is carried out according to a preferable embodiment by means of a nozzle or row of nozzles arranged in this area. Therefore, a marked imbalance of temperatures and, therefore, damage or dirt in the peripheral wall that surrounds the combustion space can be effectively prevented.

In particular, when a flue gas that has been returned is used as a fluid, the corresponding nozzle preferably has an outer tube and an inner tube that extends in the axial direction of the outer tube and is wrapped by it, the inner tube for the conduction of smoke gas and the outer tube for the conduction of air. The inner diameter of the inner tube is preferably approx. 70 mm, while the inner diameter of the outer tube, that is, the outer diameter of the annular passage between the inner tube and the outer tube is approx. 110 mm

The air stream serves in this embodiment as protection, which protects the nozzle against the adhesion of impurities entrained in the smoke gas. Precisely at the temperatures that occur in the entrance area, these adhesions can easily lead to fouling, which in an extreme case can lead to the failure of the nozzle. According to the described embodiment, this is effectively prevented.

It has proved advantageous that at least 1 nozzle per meter of the width of the combustion chamber is provided. The introduction of the fluid is preferably carried out by means of at least two nozzles, even more preferably by means of at least six nozzles. This guarantees as complete a homogenization as possible with a relatively small amount of injected fluid. A combustion chamber of an incinerator plant to perform the procedure may comprise a peripheral wall that surrounds a primary combustion space, an input for the introduction of the solid material to be incinerated in the primary combustion space, a combustion grill to incinerate the material solid, an exit arranged in front of the entrance seen in the direction of

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transport of the solid material to discharge the incinerated solid material from the primary combustion space and a nozzle for the homogenization of the exhaust gases that are released in the combustion and that contain the primary combustion gases. The nozzle is arranged in an area of at least 3 meters, preferably 0.5 meters to 3 meters, or more preferably 0.5 to 2 meters above the combustion grill.

As a general rule, the nozzle is arranged in the peripheral wall of the combustion chamber, preferably in the area of the inlet or outlet.

To prevent homogenization from being linked to a swirling of the solid material present in the combustion bed, the nozzle is oriented at an angle of -10 ° to + 10 °, preferably from -10 ° to + 5 °, so more preferable from -5 ° to + 5 ° with respect to the inclination of the combustion grill. In addition, the corresponding nozzle may be oriented at an angle of -10 ° to 0 ° with respect to the inclination of the combustion grill. The invention will be illustrated with the aid of the attached Figures. These show:

Figure 1 a schematic representation of a combustion chamber and a post-combustion chamber represented in part to perform the process according to the present invention.

Figure 2 a graphical representation of the concentration of O2 (in% in vol.) Or of the concentration of CO (in mg / m3 in the normal state) measured over time in an exhaust gas stream generated in the combustion zone, the nozzles being connected or disconnected at different time intervals.

As shown in Figure 1, the solid material 2 to be incinerated is introduced into a loading hopper 4 and is generally introduced by means of a metering pusher through an inlet 6 in the combustion chamber 8. The combustion 8 comprises a peripheral wall 10, which envelops a primary combustion space 12 that narrows upwards.

The solid material 2 is transported in the form of a combustion bed 14 above a combustion (feed) grill 16 through which primary air flows and is incinerated during this process. In the transport direction F, a drying zone, an ignition zone, a combustion zone and a complete ash combustion zone are arranged one after the other, before the incinerated solid material is discharged through an outlet 18 disposed opposite the entrance 6 then feeding through a desscoriador to a transport of slags. The distribution of the primary air is carried out in the embodiment shown by chambers below the individual grill 20a, 20b, 20c, 20d, which are fed by separate primary air pipes 22a, 22b, 22c, 22d.

Nozzles 24a, 24b, 24c indicated in Figure 1 are arranged on the peripheral wall 10 of the combustion chamber by means of arrows, through which a fluid is introduced into the combustion chamber 8.

The nozzles are configured here such that the fluid outlet speed of the nozzles is 40 to 120 m / s.

In the embodiment shown, a nozzle 24a is disposed in the area of the inlet side 8 'of the combustion chamber 8, specifically in a part 10' of the peripheral wall 10 facing the inlet, which extends obliquely. upwards. Two nozzles 24b, 24c are arranged in the area of the outlet side 8 ", a nozzle 24b being arranged in the part 10" of the peripheral wall, which extends upwardly inclined and one in the part 10 "'of the peripheral wall, which defines the front side 25 and which extends in the vertical direction. Any other number and arrangement of the nozzles that are suitable for the purposes of the present invention is also conceivable.

By means of the nozzles 24a, 24b, 24c, the exhaust gases containing the combustion gases that are released during combustion are homogenized in a mixing zone 26 which is arranged at least approximately directly after the combustion bed 14 seen in the direction of flow of these flue gases. This homogenization is indicated in the Figure by the broken arrows, schematically designating the area with a relatively high temperature and a relatively high concentration of primary flue gases and B the area with a lower temperature and a lower concentration of primary combustion gases. After homogenization, that is, in the Figure above the areas designated with A and B, the exhaust gases are presented in the form of a homogeneous mixture of gases.

It enters a post-combustion chamber 28 arranged next to the combustion chamber 8 and which defines a secondary combustion space 27, in which the exhaust gases are burned by feeding secondary air. For this, other nozzles 32a, 32b for the introduction of secondary air are provided in the peripheral wall 30 of the post-combustion chamber 28.

As shown in Figure 2, the introduction of the fluid when the nozzle is actuated in the ON position causes the concentration of O2 measured locally in the exhaust gas stream generated in the combustion zone (shown in thick solid lines ) corresponds roughly to the global O2 concentration, that is, that which is presented together in the exhaust gases generated in the combustion chamber (shown in fine lines of broken lines). On the contrary, when the nozzle is not actuated in the OFF position, the locally measured O2 concentration is substantially more

lower than what is measured globally.

Regarding the 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 activated, which also indicates the homogenization of the exhaust gases by the introduction of the fluid.

Claims (6)

1. Procedure for optimizing the complete combustion of exhaust gases from an incinerator plant, which comprises the following stages The solid material (2) to be incinerated is introduced through an inlet (6) into a combustion chamber (8) that defines a primary combustion space (12), the solid material (2) is incinerated in the primary combustion space (12) in the form of a combustion bed (14) transported above a combustion grill (16) with primary air supply and the incinerated solid material is discharged of the primary combustion space (12) through an outlet (18) arranged in front of the inlet (6) seen in the transport direction (F), 10 The primary combustion gases that are released during the combustion of the solid material (2) are burned by feeding secondary air into a post-combustion chamber (28) that defines a secondary combustion space (27) and that current is disposed under the chamber of combustion (8) seen in the direction of flow of said primary combustion gases, the exhaust gases containing the primary combustion gases being homogenized before entering the secondary combustion space (27) in a mixing zone (26) by means of a fluid introduced by a nozzle (24a, 24b, 24c), being arranged the mixing zone (26) in the direction of flow of the exhaust gases at least approximately directly after the combustion bed (14), characterized in that the fluid outlet speed of 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 ° with respect to to the inclination of the 20 combustion grill (16). 2. Method according to one of the preceding claims, characterized in that the outlet speed 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 ° with respect to the inclination of the combustion grill (16). Method according to one of the preceding claims, characterized in that the fluid comprises a smoke gas that has been returned from an area disposed downstream following the secondary combustion space (27). 5. Method according to claim 4, characterized in that the amount of smoke gas introduced corresponds to between 5% and 35%, preferably approx. 20% of the amount of primary air fed. Method according to one of the preceding claims, characterized in that the injection of the fluid is made by a nozzle (24a) disposed in the area of the inlet side of the combustion chamber (8). Method according to one of claims 4 or 5, characterized in that the nozzle (24a, 24b, 24c) has an outer tube and an inner tube that extends in the axial direction of the outer tube and is wrapped by it, the inner tube for the conduction of the smoke gas and the outer tube for the conduction being provided 35 air Method according to one of the preceding claims, characterized in that the introduction of the fluid is carried out by means of at least two nozzles (24a, 24b, 24c), preferably by means of at least six nozzles (24a, 24b, 24c).