A domestic waste incinerator applying compound high-efficiency low-NO x combustion and its combustion method

Abstract

The present invention relates to a composite domestic waste incinerator and a method for burning and treating domestic waste. The incinerator includes a furnace chamber (I) and a chimney (II) located at the top of the furnace chamber (I), which are interconnected; a plurality of primary air nozzles (11) for forming a coke layer are provided in the furnace chamber (I), a recirculating flue gas jet nozzle for promoting the mixing of NH3 and NOx, and a secondary air nozzle for realizing the step-by-step reduction of NOx in the furnace chamber (I). For the method for burning and treating domestic waste, the method realizes the efficient removal of NOx by coupling and regulating the precipitation of N element in the solid phase bed layer and the migration of N during the furnace combustion process, and through the synergistic effect of the bed coke, the recirculating flue gas jet and the deeply staged secondary air. Compared with the prior art, the present invention has the advantages of high efficiency and low cost, and can realize the efficient removal of NOx without using SNCR and SCR, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of domestic waste incineration, and in particular to a domestic waste incinerator and a combustion method using a composite high-efficiency and low-NOx combustion method. Background Art

[0002] The incineration of municipal solid waste has the advantages of small land occupation, high reduction degree, and energy recovery. In the application and promotion of incineration technology, the issue of pollutant emissions has received widespread attention. NOx is a major pollutant in the process of waste incineration, of which "fuel-type NOx" accounts for the vast majority, and its generation is promoted by high temperature and high oxygen.

[0003] In order to meet the increasingly stringent emission standards, incinerators need to use flue gas purification measures such as SNCR (selective non-catalytic reduction) and SCR (selective catalytic reduction) to control NOx emissions during actual operation. SNCR technology is to spray reducing agents such as ammonia and urea into the furnace within the temperature window of 850-1100℃, and convert NH3 into N2 through the reaction of NOx. SCR technology uses NH3 to reduce NOx to N2 at a low temperature of 290-400℃ with the help of catalysts. Although emission standards can be met after the application of these technologies, the investment and operating costs are significantly increased due to the need to configure additional equipment and consume reducing agents and catalysts. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a high-efficiency, low-cost domestic waste incinerator and combustion method that can achieve efficient removal of NOx without using SNCR and SCR.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The present invention combines the bed combustion characteristics and the furnace flow characteristics, and provides a high-efficiency and low-cost NOx coordinated control method for a domestic waste incinerator through composite regulation of N precipitation during bed combustion and N migration during furnace combustion.

[0007] Specifically, the inventors first realized that due to the high volatile content of domestic waste, the design of incinerators often adopts a large-space furnace structure. The horizontal partitioning of gas products in the grate and bed layer easily forms a "chimney flow" in the furnace, and the mixing of combustible components and oxygen is poor. In order to burn out, a higher excess air coefficient will be used, which will lead to a higher NOx concentration in the flue gas.

[0008] Further analyzing from the principle, during the incineration process, there are already substances such as NH3 with the ability to reduce NOx in the released form of N element. At the same time, there is a reaction environment with appropriate temperature during the combustion process. Therefore, the purpose of NOx removal should also be achieved through the regulation of the combustion process itself. The removal of NOx depends on the form of N element during the combustion process, and the form of N is closely related to the combustion state of the bed layer and the flow characteristics of the furnace.

[0009] In the present invention, methods such as air staging and flue gas recirculation are tried to reduce the NOx emissions of domestic waste incinerators. Considering comprehensively from the combustion characteristics of the bed layer and the flow characteristics of the furnace, the NOx removal effect can be guaranteed, and the technical reproducibility is also good. The specific scheme is as follows:

[0010] A domestic waste incinerator applying compound high-efficiency low-NOx combustion, which includes a furnace connected to each other and a chimney located at the top of the furnace;

[0011] In the furnace, there are multiple primary air nozzles for forming a coke layer, recirculation flue gas jet nozzles for promoting the mixing of NH3 and NOx, and secondary air nozzles for realizing the step-by-step reduction of NOx in the furnace.

[0012] Furthermore, the furnace includes a grate for stacking the solid bed layer generated during the incineration of domestic waste, a front arch and a rear arch respectively arranged on both sides of the chimney, and a tail arch connected to the rear arch;

[0013] The primary air nozzles are used to spray air for bed layer combustion and are arranged in an array on the grate;

[0014] The recirculation flue gas jet nozzles are used to spray the flue gas extracted from the incinerator and include a main circulation nozzle located on the tail arch;

[0015] The secondary air nozzles are used to spray air to help the combustible components in the gas phase burn out and include a primary nozzle located on the front arch.

[0016] Furthermore, the recirculation flue gas jet direction of the main circulation nozzle is perpendicular to the gas rising direction in the incinerator.

[0017] Furthermore, the recirculation flue gas jet nozzles also include a secondary circulation nozzle located on the rear arch.

[0018] Furthermore, the secondary air nozzles also include at least a pair of secondary nozzles separately arranged in pairs at the lower part of the chimney.

[0019] Furthermore, the secondary air nozzles also include a flute-shaped pipe for ensuring the complete combustion of the combustible components in the gas phase, and the flute-shaped pipe is separately arranged in pairs at the upper part of the chimney.

[0020] A combustion method for a domestic waste incinerator using the above-mentioned compound high-efficiency low-NOx combustion. This method realizes the efficient removal of NOx by coupling and regulating the precipitation of N element in the solid-phase bed layer and the migration of N during the furnace combustion process, and through the synergistic effect of bed coke, recycled flue gas jet and deeply staged secondary air.

[0021] Further, this method includes the following steps:

[0022] (1) Heterogeneous reduction of NOx: For the precipitation of N element during the combustion of domestic waste, regulate the air flow rate ejected by the primary air nozzle (11), that is, the primary air, to form a coke layer under a reducing atmosphere in the solid-phase bed layer, and realize the heterogeneous reduction of NOx;

[0023] The said coke layer is the solid-phase bed layer mainly composed of coke above the flame front during the combustion of domestic waste. Specifically, during the combustion of domestic waste, under the radiation of the furnace, the bed layer starts to catch fire from the surface to form a flame front. The heat of the flame front is transmitted to the lower-layer raw materials, causing them to heat up, dry, pyrolyze, and then catch fire, making the flame front propagate downward, as Figure 1 shown. During the propagation of the flame front, it is necessary to control the supply amount of primary air within a suitable range, so that oxygen is exhausted in the combustion reaction of the flame front, and a coke layer under a reducing atmosphere is formed above it.

[0024] The heterogeneous reduction of NOx is the heterogeneous reaction between the coke layer under the above-mentioned reducing atmosphere and the NOx generated by the reaction of the flame front. Specifically, it includes three steps: adsorption, dissociation, and desorption, as Figure 2 shown. In the adsorption stage, NO is adsorbed on the coke surface to generate X(NO) and X(NNO); subsequently, under the action of adjacent active sites, these two substances will undergo a dissociation reaction, in which the N-O bond is broken, and the O atom transfers to the adjacent active site, generating X(N), X(NN), and C(O) or oxidized alkali metals; finally, X(N) may directly transform into X(NN), or may adsorb NO to generate X(NNO), and be transformed into X(NN) in subsequent reactions. X(NN) spontaneously reacts to desorb N2, thus completing the conversion of NOx to N2.

[0025] (2) Homogeneous reduction of NOx: For the NOx in the gas phase above the solid-phase bed layer, use the recycled flue gas jet from the recycled flue gas jet nozzle on the rear arch (3) and the tail arch to guide the mixing of NH3 and NOx on the bed layer surface, and adjust the gas phase temperature and oxygen content to promote the "self-generated SNCR" reaction and realize the homogeneous reduction of NOx;

[0026] The so-called "self-generated SNCR" means using the recirculating flue gas jet to guide the mixing of gas-phase products above the bed layer, and using the NH3 generated by the fuel itself to reduce NOx to N2. Specifically, during the grate combustion process, the gas products above the bed layer have the characteristic of horizontal zoning according to different conversion stages of the raw materials. In the oxygen-rich area, NOx is mainly generated, while in the fuel-rich area, N elements are mainly released in the form of NH3. By using the momentum of the flue gas jet from the tail arch, the mixing of these gas products can be promoted, and the temperature and oxygen concentration of the reaction environment can be adjusted to promote the reduction reaction of NH3 to NOx. In addition, according to actual needs, flue gas jets arranged at the rear arch can be added to further assist in adjusting the temperature and oxygen concentration in this area and optimizing the flow field.

[0027] (3) Deep reduction of NOx: For the migration of N during the furnace combustion process, the air ejected by the secondary air nozzles at multiple levels and multiple angles, that is, the secondary air, is used to form a strongly swirling combustion with a stable flow field and uniform temperature, so as to achieve deep reduction of NOx in the furnace and ensure the complete combustion of combustible components in the gas phase.

[0028] Moreover, the secondary air can further form a flute tube jet through the flute tube to strengthen the mixing and uniform temperature field, or can enhance the reaction activity by carrying water. The so-called flute tube jet is to inject the secondary air or other auxiliary media into the furnace in the form of a flute tube. Through the design of the number, position, angle and flow rate of the nozzles, the effects of strengthening the mixing and uniform temperature field can be achieved, which can further improve the NOx reduction efficiency and promote the complete combustion of combustible components. Carrying water to enhance the reaction activity means adding water to the secondary air or recirculating flue gas. Through the generation of highly reactive free radicals such as H, OH, and HO2 by water during the reaction process, the reduction reaction of NOx and the oxidation reaction of combustible components are strengthened.

[0029] The so-called strongly swirling combustion is to form a uniform and stable strongly swirling flow field in the furnace by using the secondary air with deep staging through the design of the injection speed, angle and position of the secondary air. Experimental studies have shown that the strongly swirling flow field can strengthen the turbulent pulsation, extend the residence time, adjust the temperature level in the furnace, and improve the combustion efficiency and intensity. Based on these characteristics, by adjusting the secondary air, a suitable temperature for the reduction of NOx by NH3 can be created, and the rate of oxidation of precursors such as NH3 to generate NOx can be controlled under oxygen-limited conditions. According to the mechanism of NOx generation and reduction, as Figure 5 shown, NOx can be reduced step by step, so as to promote more N elements to exist in the form of N2. At the same time, due to the increase in combustion intensity caused by strong swirling, the complete combustion of combustible components in the gas phase can be ensured.

[0030] Further, in step (1), the combustion temperature is 900 - 1200 °C, and the excess air coefficient is 1.1 - 1.2; in step (2), 20 - 30% of the flue gas at the tail of the incinerator is taken as the recycled flue gas, the gas phase temperature is 25 - 30 °C, and the oxygen volume concentration is 7 - 10%, which is specifically determined by the overall excess air coefficient of the incinerator; in step (3), the secondary air nozzles can be arranged above the throat of the furnace, and the specific position is determined according to the size and structure of the furnace. The secondary air nozzles are sprayed in from all around the furnace wall. The injection angle of the secondary air nozzles is 0 - 30°, and the inlet velocity is 80 - 100 m / s, which specifically needs to be determined according to the actual gas flow situation in the furnace to ensure the generation of a strong swirling flow field, so that the secondary air is fully mixed with the combustible components, ensuring the complete combustion of the combustible gas. The secondary air excess coefficient is 0.3 - 0.4.

[0031] Further, the secondary air nozzles and / or the recycled flue gas jet nozzles can also spray water to enhance the reaction activity; the proportion of water added to the recycled flue gas and / or should be determined according to the furnace temperature to ensure that the gas phase temperature in the furnace (I) is within the range of 850 - 1100 °C suitable for "self - generating SNCR".

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] (1) By controlling the supply amount of primary air within a suitable range, the present invention enables oxygen to be completely consumed in the combustion reaction at the flame front, and a coke layer is formed above it under a reducing atmosphere, which has a significant reducing effect on NOx;

[0034] (2) By utilizing the momentum of the tail flue gas jet, the present invention can promote the mixing of these gas products, and adjust the temperature and oxygen concentration of the reaction environment to promote the reduction reaction of NH3 to NOx;

[0035] (3) By adjusting the secondary air, the present invention forms a strong swirling combustion with a stable flow field and uniform temperature, which can strengthen the turbulent pulsation, extend the residence time, adjust the temperature level in the furnace, and improve the combustion efficiency and intensity, ensuring the complete combustion of the gas - phase combustible components. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the distribution of the reaction layer in the solid - phase bed layer on the grate of the present invention;

[0037] Figure 2 It is a schematic diagram of the heterogeneous reduction reaction process of NOx by the coke layer of the present invention;

[0038] Figure 3 It is the verification experimental result of the heterogeneous reduction of NOx by the coke layer in Example 1;

[0039] Figure 4For the promoting effect of the recycled flue gas jet on the horizontal mixing of NH3 and NO above the bed layer in Example 1;

[0040] Figure 5 This is the step-by-step reduction reaction path diagram of NOx under the action of the deep-stage staged secondary air of the present invention;

[0041] Figure 6 This is the structural schematic diagram of the composite domestic waste incinerator in Example 1;

[0042] Figure 7 This is the working principle diagram of the composite domestic waste incinerator in Example 1;

[0043] As shown by the labels in the figure: furnace I, chimney II, grate 1, primary air nozzle 11, tail arch 2, main circulation nozzle 21, rear arch 3, secondary circulation nozzle 31, front arch 4, primary nozzle 41, secondary nozzle 42, and flute tube 5. Specific embodiments

[0044] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Example 1

[0046] A domestic waste incinerator applying composite high-efficiency low-NOx combustion, such as Figures 6-7 , the incinerator includes a furnace I communicating with each other and a chimney II located at the top of the furnace I;

[0047] In the furnace I, there are provided a plurality of primary air nozzles 11 for forming a coke layer, recycled flue gas jet nozzles for promoting the mixing of NH3 and NOx, and secondary air nozzles for realizing the step-by-step reduction of NOx in the furnace I.

[0048] Specifically, the furnace I includes a grate 1 for stacking the solid-phase bed layer generated during the incineration of domestic waste, a front arch 4 and a rear arch 3 respectively disposed on both sides of the chimney II, and a tail arch 2 connected to the rear arch 3; the primary air nozzles 11 for ejecting the air for bed combustion and arranged in an array on the grate 1; the recycled flue gas jet nozzles for ejecting the flue gas extracted from the incinerator, including the main circulation nozzle 21 located on the tail arch 2; the secondary air nozzles for ejecting the air to help the combustible components in the gas phase burn out, including the primary nozzle 41 located on the front arch 4.

[0049] The recycled flue gas jet nozzles further include a secondary circulation nozzle 31 located on the rear arch 3. The secondary air nozzles further include three pairs of secondary nozzles 42 separately arranged in pairs at the lower part of the chimney II. The secondary air nozzles further include a flute tube 5 for ensuring the complete combustion of the combustible components in the gas phase, and the flute tube 5 is separately arranged in pairs at the upper part of the chimney II.

[0050] The recirculating flue gas jet direction of the primary circulation nozzle 21 is perpendicular to the rising direction of the gas in the incinerator. The secondary air nozzle and / or the recirculating flue gas jet nozzle can also spray water to enhance the reaction activity.

[0051] A combustion method using the domestic waste incinerator using the composite high-efficiency and low-NOx combustion as described above, the method achieves efficient removal of NOx by coupling and regulating the precipitation of N elements in the solid phase bed and the migration of N in the furnace combustion process, and by the synergistic effect of the bed coke, the recirculating flue gas jet and the deep classification secondary air, specifically comprising the following steps:

[0052] (1) Heterogeneous reduction of NOx: In view of the precipitation of N element during the combustion of domestic waste, the air flow rate sprayed from the primary air nozzle 11, i.e., the primary air, is regulated to form a coke layer under a reducing atmosphere in the solid phase bed layer, thereby achieving heterogeneous reduction of NOx; wherein, the combustion temperature is about 1050°C, the air excess coefficient is 1.1, and the flow rate is distributed in the range of 0.10-0.36 m / s according to the different positions of the grate 1;

[0053] The coke layer is a solid bed layer with coke as the main component above the flame front during the combustion of domestic waste. Specifically, during the combustion of domestic waste, under the radiation of the furnace, the bed layer starts to ignite from the surface to form a flame front. The heat of the flame front is transferred to the lower raw materials, causing them to heat up, dry, pyrolyze, and then ignite, causing the flame front to spread downward. Figure 1 As shown. During the propagation of the flame front, the primary air supply must be controlled within an appropriate range so that the oxygen is consumed in the combustion reaction of the flame front and a coke layer is formed above it in a reducing atmosphere.

[0054] In this embodiment, the NO concentration at different heights of the bed was tested, such as Figure 3 As shown, when the flame front propagates to the lower part of the bed, although the NO concentration at the flame front position exceeds 1300ppm, as shown by the triangle, the NO concentration on the bed surface at this moment is only about 200ppm, as shown by the square, which confirms that the coke layer has a significant reducing effect on NOx.

[0055] (2) Homogeneous reduction of NOx: For NOx in the gas phase above the solid phase bed, the recirculating flue gas jets of the recirculating flue gas jet nozzles on the rear arch 3 and the tail arch 2 are used to guide the mixing of NH3 and NOx on the bed surface, and the gas phase temperature and oxygen content are adjusted to promote the "self-generated SNCR" reaction and achieve homogeneous reduction of NOx; wherein, the flow rate of the recirculating flue gas jet is 20% of the tail flue gas, in this example, the jet flow rate is 18 m / s, the gas phase temperature is 25°C, and the oxygen volume concentration is 7.87%;

[0056] The numerical simulation results of flue gas recirculation show that, for details, seeFigure 4 , after arranging the recirculating flue gas jet, the NOx concentration of the flue gas in the embodiment decreased from 322 mg / Nm 3 to 194 mg / Nm 3 , and at the same time, the CO emission also decreased from 10 mg / Nm 3 to 0.44 mg / Nm 3 . Not only effectively inhibits the generation of NOx through "autogenous SNCR", but also promotes the burnout of gaseous combustible components by strengthening the mixing.

[0057] (3) Deep reduction of NOx: Aiming at the migration of N during the furnace combustion process, the air ejected from the four-stage and multi-angle secondary air nozzles, that is, the secondary air, forms a strongly swirling combustion with a stable flow field and uniform temperature. And the secondary air further forms a flute tube jet through two flute tubes 5 to strengthen the mixing and uniform temperature field, and enhances the reaction activity by carrying water, realizing the deep reduction of NOx in the furnace I and ensuring the burnout of combustible components in the gas phase; among them, the secondary air nozzle is arranged 9 - 11 meters above the furnace throat, horizontally sprayed into the front wall of the incinerator, with an inlet velocity of 80 - 100 m / s, so that the secondary air is fully mixed with the unburned flue gas in the furnace to ensure the burnout of combustible gases. The excess air coefficient of the secondary air is 0.35, and the proportion of water added to the recirculating flue gas is 2%.

[0058] A numerical simulation calculation and analysis was carried out for the arrangement of the secondary air. After applying the strongly swirling combustion, the NOx flue gas concentration in the calculation case further decreased from 194 mg / Nm 3 to 113 mg / Nm 3 , and at the same time, the CO emission also further decreased to 0.1 mg / Nm 3 or less.

[0059] The above is only a preferred embodiment of the present invention, and it is not a limitation to the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A combustion method for a domestic waste incinerator applying compound high-efficiency and low-NOx combustion, characterized in that, The domestic waste incinerator applying compound high-efficiency low-NOx combustion includes a furnace chamber (I) and a chimney (II) located at the top of the furnace chamber (I) which are interconnected; In the furnace chamber (I), a plurality of primary air nozzles (11) for forming a coke layer are provided, a recirculating flue gas jet nozzle for promoting the mixing of NH3 and NOx, and a secondary air nozzle for realizing the step-by-step reduction of NOx in the furnace chamber (I); The furnace chamber (I) includes a grate (1) for stacking the solid-phase bed layer generated during the incineration of domestic waste, a front arch (4) and a rear arch (3) respectively arranged on both sides of the chimney (II), and a tail arch (2) connected to the rear arch (3); The primary air nozzles (11) are used to eject the air for bed combustion and are arranged in an array on the grate (1); The recirculating flue gas jet nozzle is used to eject the flue gas extracted from the incinerator, including a main circulation nozzle (21), and the main circulation nozzle (21) is located on the tail arch (2); The secondary air nozzle is used to eject the air to help the combustible components in the gas phase burn out, including a primary nozzle (41), and the primary nozzle (41) is located on the front arch (4); This method realizes the efficient removal of NOx by coupling and regulating the precipitation of N element in the solid-phase bed layer and the migration of N during the furnace combustion process, and through the synergistic effect of bed coke, recirculating flue gas jet and deeply staged secondary air. This method includes the following steps: (1) Heterogeneous reduction of NOx: Aiming at the precipitation of N element during the combustion of domestic waste, the air flow rate ejected by the primary air nozzles (11) is regulated to form a coke layer in a reducing atmosphere in the solid-phase bed layer, realizing the heterogeneous reduction of NOx; (2) Homogeneous reduction of NOx: Aiming at the NOx in the gas phase above the solid-phase bed layer, the recirculating flue gas jet of the recirculating flue gas jet nozzles on the rear arch (3) and the tail arch (2) is used to guide the mixing of NH3 and NOx on the bed surface, and the gas phase temperature and oxygen content are adjusted to promote the "self-generated SNCR" reaction, realizing the homogeneous reduction of NOx; (3) Deep reduction of NOx: Aiming at the migration of N during the furnace combustion process, the air ejected by the secondary air nozzles is used to form a strongly swirling combustion with a stable flow field and uniform temperature, realizing the deep reduction of NOx in the furnace chamber (I) and ensuring the complete combustion of the combustible components in the gas phase.

2. The combustion method according to claim 1, wherein In step (1), the combustion temperature is 900 - 1200 °C, and the excess air coefficient is 1.1 - 1.2; In step (2), 20 - 30% of the flue gas at the tail of the incinerator is taken as the recirculating flue gas, the gas phase temperature is 25 - 30 °C, and the volume concentration of oxygen is 7 - 10%; In step (3), the injection angle of the secondary air nozzle is 0 - 30°, the inlet velocity is 80 - 100 m / s, and the excess air coefficient of the secondary air is 0.3 - 0.

4.

3. The combustion method according to claim 1, wherein The secondary air nozzle and / or the recirculating flue gas jet nozzle also eject water to enhance the reaction activity, ensuring that the gas phase temperature in the furnace chamber (I) is within the range of 850 - 1100 °C.

4. The combustion method according to claim 1, wherein The recirculating flue gas jet direction of the main circulation nozzle (21) is perpendicular to the upward direction of the gas in the incinerator.

5. The combustion method according to claim 1, characterized in that, The recirculated flue gas jet nozzle further includes a secondary recirculation nozzle (31), and the secondary recirculation nozzle (31) is located on the rear arch (3).

6. The combustion method according to claim 1, characterized in that, The secondary air nozzle further includes at least a pair of secondary nozzles (42), and the secondary nozzles (42) are separately arranged in pairs at the lower part of the chimney (II).

7. The combustion method according to claim 1, characterized in that, The secondary air nozzle further includes a strengthening nozzle (5) for ensuring the complete combustion of combustible components in the gas phase, and the strengthening nozzle (5) is separately arranged in pairs at the upper part of the chimney (II).

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