SPECIALIZED AIR DISTRIBUTION SYSTEM AND AIR DISTRIBUTION METHOD FOR A WASTE INCINERATOR WITH SLUDGE CO-INCINERATION

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application No. PCT/CN2025/098517 with a filing date of May 30, 2025, designating the United States, now pending, and further claims priority to Chinese Patent Application No. 202410974328.7 with a filing date of Jul. 19, 2024. The content of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference.

TECHNICAL FIELD

The disclosure belongs to the field of incineration technologies, and more specifically, to a specialized air distribution system and air distribution method for a waste incinerator with sludge co-incineration.

BACKGROUND ART

Currently, the primary effective method for sludge hazard-free treatment is incineration. However, this requires reducing the moisture content of sludge to less than 25%. The moisture content of sludge, after mechanical dewatering at sewage treatment plants, however, can only be reduced to 65% at most, resulting in very low calorific value, making ignition and complete incineration difficult. Consequently, improvements must be made, by a doubly effective approach, to the incineration structure of traditional waste incinerators to facilitate full co-incineration of sludge with waste, realizing sludge hazard-free treatment while addressing waste disposal needs.

In the Chinese Utility Model Patent No. CN219656083U, a mixed incineration system for sludge and solid waste is disclosed, which includes a waste incinerator, a high-temperature air pre-heater, a low-temperature air pre-heater, a deaerator, a biomass gasifier, a vacuum dryer and an ejector. The biomass gas outlet of the biomass gasifier is connected to the fuel inlet of an auxiliary burner installed on the waste incinerator. The flue gas outlet of the waste incinerator is connected to the first inlet of a mixer through a second fan, while a branch from the outlet of the low-temperature air pre-heater is connected to the second inlet of the mixer. The outlet of the mixer is connected to the biomass gasifier. The beneficial effects of this technical solution are as follows: it effectively reduces the energy consumption of the vacuum drying system, ensures stable incineration of low-calorific-value household waste and sludge, and produces flue gas with extremely low levels of dust and nitrogen oxides.

However, the aforementioned patent employs a biomass gasifier, which incurs high costs and poses challenges for widespread adoption. Without incorporating a biomass gasifier, sludge itself has high moisture content and low calorific value, making incineration challenging. When simply fed dewatered sludge into a waste incinerator, its low calorific value makes incineration difficult. Thus, modifications to the incineration structure of the waste incinerator are essential to meet stable incineration requirements.

To address the above technical issues, there is an urgent need to develop an incineration structure modification technology for the traditional waste incinerator (without requiring an additional biomass gasifier). This solution would effectively incinerate the mixture of sludge and domestic waste, and fully utilize the energy potential of sludge, transforming biomass and municipal sludge from waste into valuable resources. Such innovation would simultaneously achieve enhanced economic benefits and environmental protection, demonstrating significant potential for widespread application.

SUMMARY

The purpose of the present disclosure is to address the deficiencies of the existing technology mentioned above by providing a specialized air distribution system for a waste incinerator with sludge co-incineration, aimed at improving the incineration structure of existing waste incinerators. By optimizing the flow rate, velocity, and injection angle of the secondary air, the present disclosure alters the flow conditions and pathways of the gas within the furnace, that is, changing the gas flow route from an L-shape to an α-shape. This forces high-temperature flue gas flow to form a large recirculation zone in the front part of the furnace, facilitating the ignition and complete burnout of low-calorific-value fuels.

The second purpose of the present disclosure is to provide a specialized air distribution method for a waste incinerator with sludge co-incineration.

The technical solution adopted by the present disclosure is as follows: A specialized air distribution system for a waste incinerator with sludge co-incineration includes a furnace 1, a primary air circulation cycle system, and a secondary air circulation cycle system. The primary air circulation cycle system includes a first ejector 6, a primary air fan 5, and a primary air main pipe 7. A circulating flue gas suction port is provided on a side wall of the upper part of the furnace and connected to the first ejector 6. The primary air fan 5 is connected to the first ejector 6. An outlet of the first ejector 6 is connected to the primary air main pipe 7. The primary air main pipe 7 is connected to multiple primary air inlets at the lower part of the furnace 1 through multiple output ports. The secondary air circulation cycle system includes a second ejector 3, a steam drum 2, and a secondary air fan 4. The steam drum 2 arranged above the furnace 1 is connected to the second ejector 3 through a high-pressure steam pipe. An outlet of the second ejector 3 is connected to a secondary air inlet on the side wall of the rear arch outlet of the furnace 1. And the secondary air fan 4 is connected to the second ejector 3.

The high-temperature flue gas below the front arch area within the furnace forms an α-shaped flow

Preferably, the angle of inclination β of the rear arch of the furnace is ≥26°, and the angle of inclination α of the front arch is ≥35°.

The geometric parameters of the front arch of the furnace should satisfy the following requirements: the angle δ between momentum I of the synthesized gas flow and the front arch is ≥120°, and its momentum synthesis angle γ is ≤30°.

The secondary air nozzles are circular, numbering 8-10, with a diameter of 110 mm.

A specialized air distribution method for a waste incinerator with sludge co-incineration is provided. Based on the specialized air distribution system for a waste incinerator with sludge co-incineration, it adjusts the rear arch inclination angle β and the front arch inclination angle α, and confirms the flow rate, injection velocity, and downward injection angle of the secondary air, so that high-temperature flue gas below the front arch area within the furnace forms an α-shaped flow.

When forming the α-shaped flue gas flow below the front arch area within the furnace of the incinerator: the rear arch inclination angle β is required ≥26°, the front arch inclination angle α is required ≥35°, the injection velocity of the secondary air is required greater than or equal to 50 m/s, the flow rate of the secondary air is 10%-15% of the total air volume (with air accounting for 10% and steam for 5%), and the downward injection θ is required ≥5°.

The momentum synthesis angle of the synthesized gas flow Y is required ≤30°, and the angle δ between the momentum I of the synthesized gas flow and the front arch is required ≥120°.

This application proposes retrofitting traditional waste incinerator with high-velocity injected secondary air to achieve an α-shaped flue gas pathway flame incinerator. The formation of α-shaped flames significantly increases the residence time of flue gas in the furnace arch area, ensuring complete fuel burnout. Simultaneously, due to the α-shaped flow of flue gas, larger unburned fuel particles in the flue gas can be redropped onto the fuel layer by centrifugal force for continued incineration, further improving incineration efficiency and reducing dust emissions. Existing literature primarily focuses on modifying the furnace arches structure of waste incinerator to form an α-shaped high-temperature flue gas path, which recirculates within the furnace to repeatedly heat the burning material, utilizing waste heat for more thorough incineration. However, such modifications involve enormous workload, very high costs, and require prolonged furnace shutdowns, making large-scale implementation difficult. In contrast, the secondary air retrofit method proposed in this application could achieve the same objectives with substantially reduced workload and costs, facilitating widespread adoption.

In summary, compared to existing technologies, the beneficial effects of the present disclosure are as follows: in terms of economic benefits, it can significantly improve the processing efficiency of solid waste disposal enterprises, reduce their investment costs, and thereby enhance the resource recycling and utilization capacity of the region; in terms of social benefits, it can significantly reduce pollutant emissions and minimize damage to the health of the surrounding public; it can be promoted and applied to the entire industry, promote scientific and technological progress, and contribute to the development of efficient solid waste treatment technology.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS

To provide a clearer explanation of the specific embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the accompanying drawings required for describing the specific embodiments or the prior art. Obviously, the drawings in the following description illustrate some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings may be obtained from these accompanying drawings without creative effort.

FIG. 1 is a diagram of an L-shaped flow flame in the prior art;

FIG. 2 illustrates the α-shaped flow flame formed after improvement according to the present disclosure;

FIG. 3 is a schematic diagram of the system structure of the present disclosure;

FIG. 4 is a definition diagram of design parameters for a flame incinerator based on the momentum flux method;

FIG. 5 is a schematic diagram of momentum synthesis;

FIG. 6 shows the original design of a 750 tons/day waste incinerator;

FIG. 7 is an arrangement diagram of measuring points for hot-state test;

FIG. 8 shows the flue gas temperature distribution at the measuring points.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following embodiments will clearly and comprehensively describe the technical solutions of the present disclosure. It is evident that the described embodiments represent only a portion of the embodiments of the disclosure, not all embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort shall fall within the scope of protection of the present disclosure.

In the description of the present disclosure, it should be understood that terms such as “center”, “longitudinal”, “transverse”, “length”, “width”, “thickness”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, “clockwise”, and “counterclockwise” indicate orientations or positional relationships based on those shown in the accompanying drawings. These terms are used solely for facilitating the description of the disclosure and simplifying the explanation, not to indicate or imply that the referenced apparatus or elements must have specific orientations or be constructed and operated in specific orientations. Thus, they should not be construed as limiting the disclosure.

Furthermore, terms such as “first” and “second” are used for descriptive purposes only and should not be interpreted as indicating relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined as “first” or “second” may explicitly or implicitly include one or more such features. In the description of the present disclosure, “a plurality” means two or more, unless otherwise explicitly defined. Additionally, terms such as “mounted” “connected” and “coupled” should be interpreted broadly. For example, connections may be fixed or detachable, or integrally formed; they may be mechanical, electrical, or direct connections, or indirect connections through intermediate media, or internal communications between two components. Those of ordinary skill in the art may understand the specific meanings of these terms in the context of the present disclosure based on specific circumstances.

A specialized air distribution system for a waste incinerator with sludge co-incineration is shown in FIG. 3, including a furnace 1, a primary air circulation cycle, and a secondary air circulation cycle. The primary air circulation cycle includes a first ejector 6, a primary air fan 5, and a primary air main pipe 7. A flue gas suction port is provided on the side wall of the upper part of the furnace and connected to the low-pressure inlet of the first ejector 6 through a pipeline. The primary air fan 5 is connected to the high-pressure inlet of the first ejector 6 through a pipeline. The outlet of the first ejector 6 is connected to the primary air main pipe 7. The primary air main pipe 7 is connected to multiple primary air inlets at the lower part of the furnace 1 through multiple output ports arranged on the primary air main pipe 7. The secondary air circulation cycle includes a second ejector 3, a steam drum 2, and a secondary air fan 4. The steam drum 2 arranged above the furnace 1 is connected to the high-pressure inlet of the second ejector 3 through a high-pressure steam pipe. The outlet of the second ejector 3 is connected to the secondary air inlet on the rear arch outlet of the furnace 1. The secondary air fan 4 is connected to the low-pressure inlet of the second ejector 3. Multiple holes on the primary air main pipe 7 form the output ports, which are connected to the primary air inlets through pipelines.

This application fully utilizes the thermal energy of high-temperature flue gas in the furnace, simultaneously enhancing ignition and burnout performance while reducing nitrogen oxide emissions in the exhaust flue gas, which achieves dual benefits. Specifically, the primary air fan 5 employs a high-pressure blower to extract 1000° C. high-temperature flue gas (accounting for 15% by mass) from the furnace through the first ejector 6. This flue gas mixes with cold air (accounting for 85% by mass) in the first ejector 6 to form hot gas above 160° C., which then enters the primary air main pipe 7 again (eliminating the need for being heated by high-pressure steam and conserving energy). This process improves the ignition and burnout performance of waste. Simultaneously, due to flue gas recirculation, the oxygen content decreases, significantly reducing nitrogen oxide emissions and enhancing environmental performance.

The steam drum 2 is installed in the upper part of the furnace (1). High-pressure steam (accounting for ⅓ by the mass of mixture) with a pressure of 40 kgf/cm² and a temperature of 300 degrees Celsius is drawn from the steam drum 2 via a high-pressure steam pipe and introduced into the second ejector 3. The cold air (accounting for ⅔ by mass of mixture) provided by the secondary fan 4 is extracted. And the mixture forms 100° C. high-velocity hot air in the second ejector 3, serving as secondary air for the waste incinerator. This high-velocity stream is injected into the furnace at high speed to establish an α-shaped flow flame.

The key of the present disclosure is to change the air distribution mode of the waste incinerator by adding the secondary air ejected at high speed into the furnace 1, and to modify the traditional L-shaped flue gas path (as shown in FIG. 1) of the waste incinerator to an α-shaped path (as shown in FIG. 2) through momentum synthesis. The resulting novel incinerator design is better suited for burning mixtures of low-calorific-value dewatered sludge and municipal waste (MSW). The key advantages of employing an α-shaped flue gas path in MSW flame incinerators are:

• • 1. Sludge entering the incinerator has significantly higher moisture content than other solid waste. The mixture requires preheating and drying for effective ignition. With the formation of the α-shaped path, high-temperature flue gas is forced to turn downwards below the front arch, forming a recirculation zone. This intensifies heat exchange between the flue gas and the waste fuel and strengthens thermal radiation of the high-temperature flue gas onto the solid waste fuel, facilitating ignition.
  • 2. By flowing in the α-shaped path, the combustible gases and hot carbon particles in the flue gas are forced to mix thoroughly with air, which enhances incineration efficiency.
  • 3. Adopting the α-shaped path: i) lengthens the flue gas travel path, ii) increases the residence time of high-temperature gas in the furnace, iii) reduces fly ash content in the flue gas, and iv) increases the burnout rate of the solid waste fuel.

The α-shaped flow flame is achieved by increasing the injection momentum of the secondary air. Raising the injection velocity of the secondary air boosts its momentum, enabling the formation of the α-shaped flue gas channel within the furnace.

To establish the α-shaped flue gas channel in the flame incinerator, to establish the α-shaped flue gas path in the flame incinerator, the geometric parameters of the front arch of the furnace 1 must satisfy the following requirements: the angle δ between the momentum I of the synthesized gas flow and the front arch is ≥120°, and its momentum synthesis angle Y is required ≤30°

Specifically, the method to achieve the α-shaped flow flame can be obtained through the following data model and calculation steps.

S1: Defining Key Parameters for Momentum-Based Design Method of the Waste Incinerator

As shown in FIG. 4: A is the cross-sectional area (m²), w is the flue gas velocity (m/s), h is the section height (m), I is the momentum flux (N). The width of the incinerator is B.

S1-1 Defining Flue Gas Velocity and Momentum Flow Rate at the Rear Arch Outlet

The momentum flow rate method is based on momentum vector synthesis theory. The flue gas velocity at the rear arch outlet is w₃, and its direction aligns with the rear arch inclination angle (β). Therefore, w₃ is calculated based on the cross-sectional area A₃=h₃*B at the rear arch outlet (the definition of h₃ is shown in FIG. 1):

w 3 = K 3 ⁢ V Y ⁢ B j ⁢ Q Y + C A 3 ⁢ C ( 1 )

Where K₃=0.4, C=273, As is the cross-sectional area at the rear arch outlet (m²), w₃ is the flue gas velocity at the rear arch outlet (m/s), Bis the width of the incinerator, h₃ is the height of the rear arch outlet (as shown in FIG. 1). Q_y is the flue gas temperature at the rear arch outlet (° C.), V_y is the total flue gas volume generated by fuel per unit mass, B_j is the fuel consumption rate of the waste incinerator (kg/h).

The flue gas momentum flow rate (I₃) at the rear arch outlet is calculated as follows:

I 3 = ρ Y ⁢ w 3 ⁢ V Y ⁢ B j ⁢ Q Y + C C ( 2 )

Where,

ρ Y = 1 . 2 ⁢ 9 ⁢ C C + Q Y ,

C=273, other definitions are the same as in equation (1).

S1-2. Defining Flue Gas Velocity and Momentum Flow Rate at the Front Arch Outlet

The flue gas velocity at the front arch outlet (w₁) is parallel to the front arch inclination angle (α), as shown in FIG. 1. Considering the formation of the recirculation zone below the front arch, the flue gas flow cross-sectional area at the front arch outlet is A₁=h1*B. The flue gas velocity (w₁) is calculated as follows:

w 1 = K 1 ⁢ V Y ⁢ B j ⁢ Q Y + C CA 1 ( 3 )

Where: K₁=0.2, C=273, A₁ is the cross-sectional area at the front arch outlet (m²), w₁ is the flue gas velocity at the front arch outlet (m/s), B is the width of the incinerator, h₁ is the height of the front arch outlet (as shown in FIG. 1). Here, Q_y is the flue gas temperature at the front arch outlet (° C.), V_y is the total flue gas volume generated by fuel per unit mass, B_j is the fuel consumption of the waste incinerator.

The flue gas momentum flow rate (I₁) at the front arch outlet is calculated as follows:

I 1 = ρ Y ⁢ w 1 ⁢ V Y ⁢ B j ⁢ Q Y + C C ( 4 )

Where: C=273, other definitions are consistent with equation (3).

S1-3. Defining Flue Gas Velocity and Momentum Flow Rate in the Uncovered Areas of Arches

The cross-sectional area at the outlet of the uncovered area in the furnace is: A₂=h₂*B. The flue gas velocity (w₂) in this area is vertically upward and can be calculated as follows:

w 2 = K 2 ⁢ V Y ⁢ B j ⁢ Q Y + C CA 2 ( 5 )

Where: K₂=0.4; A₂ is the cross-sectional area at the front arch outlet (m²), w₂ is the flue gas velocity at the outlet of the uncovered area (m/s), B is the width of the incinerator, h₂ is the outlet length of the uncovered area. Here, Q_y is the flue gas temperature at the front arch outlet (° C.), V_y is the total flue gas volume generated by fuel per unit mass, B_j is the fuel consumption of the waste incinerator.

The flue gas momentum flux (I₂) in the uncovered furnace arch area is calculated as follows:

I 2 = ρ Y ⁢ w 2 ⁢ V Y ⁢ B j ⁢ Q Y + C C ( 6 )

Where: C=273, and other definitions are consistent with equation (5).

S1-4. Defining the Momentum Flow Rate of Secondary Air

Secondary air injected at high velocity from the rear arch outlet can penetrate deep into the front arch region to supply oxygen for enhancing the incineration of waste fuel. When secondary air is injected at high speed, it possesses significant momentum, which is crucial for forming the α-shaped flue gas flow path. In this application, the secondary air is injected at ambient temperature. The momentum flow rate (I₄) of the secondary air is calculated as follows:

I 4 = P 0 × V 0 × W 0 ( 7 )

Where: W₀ is the injection velocity of the secondary air; P₀=1.29×(273+100)/273 kg/m³, approximately regarded as the density of hot air; V₀ is the volume of the injected secondary air (m³/s).

S1-5 Principle of Momentum Synthesis

As shown in FIG. 4, the momentum flow rates I₁ to I₄ are orthogonally decomposed. In the X-direction, taking leftward as positive:

I 1 ⁢ x = I 3 × cos ⁢ β + I 4 × cos ⁢ θ - I 1 × cos ⁢ α

In the Y-direction, taking upward as positive:

I 1 = I 1 × sin ⁢ α + I 2 + I 3 × sin ⁢ β - I 4 × sin ⁢ θ

Orthogonal synthesis is performed on I_1x and I₁:

Synthesized ⁢ momentum ⁢ I = I 1 ⁢ x 2 + I 1 ⁢ y 2

The direction angle γ of the synthesized momentum I is defined as follows:

Synthesized ⁢ momentum ⁢ angle ⁢ γ = t s - 1 ⁢ I y I x

The angle between the extension line of the momentum I of the synthetic gas flow along the Y angle and the front arch is δ. The point where the synthesized gas flow momentum I intersects the front arch is designated as K.

S1-6 Conditions for Forming the α-Shaped Flue Gas Flow Path

Experimental results indicate that to achieve an α-shaped flue gas path in the flame incinerator, the geometric parameters of the front arch must satisfy the following requirements: the angle δ between momentum I of the synthesized gas flow and the front arch is ≥120°, and its momentum synthesis angle γ is required ≤30°.

S1-7 Prerequisites for Forming the α-Shaped Flue Gas Path Through Secondary Air Proposed in this Patent

The following conditions must be met: rear arch inclination angle β ≥26°; front arch inclination angle α≥35°; secondary air injection velocity ≥50 m/s; secondary gas flow volume accounts for 15% of the total air volume (with air accounting for 10% and steam for 5%); downward injection angle θ≥5 degrees; secondary air nozzles are circular, numbering 8-10, with a diameter of 110 mm.

Under these conditions: the momentum synthesis angle γ of the synthesized gas flow is required ≤30°, and the angle δ between momentum I and the front arch is required ≥120°, which satisfies the requirements for forming the α-shaped flue gas flow path through secondary air injection. Verification Case Study

This disclosure selected a conventional incinerator with a waste treatment capacity of 750 tons/day for analysis.

(1) Conventional Design

The original incinerator design is shown in FIG. 5 (without secondary air addition). The effective length of the grate (L_p) is 16.2 m, the grate width (B) is 10.8 m, the coverage length of the front arch (L_Q) is 3.3 m, the coverage length of the rear arch (L_H) is 7.2 m, the middle uncovered section has a coverage length (L_HK) of 5.7 m, the front arch inclination angle (α) is 40°, the rear arch inclination angle (β) is 28°, and the rear arch height is 2.121 m.

Calculation Results:

TABLE 1
Momentum flux parameters of the conventional waste incinerator.

	I1y	I2y	I3y	Iy
	7.24	41.31	12.66	61.21

	I1x	I2x	I3x	Ix
	8.62	0	−23.82	−15.19

As can be seen from calculation results by using the momentum flux method for the conventional waste incinerator, the flue gas flow rate within the incinerator cannot meet the requirements for forming an α-type flue gas path. According to the momentum flux method discussed in Section 2.7, the momentum synthesis angle (δ) is 64°, which is much smaller than the recommended value of 120°.

(2) Improved Design

Based on the above design, this disclosure installed 8 circular nozzles at the rear arch outlet, with a downward inclination angle of 5° and a diameter of 110 mm. The secondary air flow volume accounts for 15% of the total air volume (with air flow volume accounting for 10% and steam flow volume accounting for 5%), and the secondary air velocity is 50 m/s.

Calculation Results:

TABLE 2
Momentum flux parameters of the new waste incinerator.

I1y	I2y	I3y	I4y	Iy
7.24	41.31	12.66	−21.55	39.66

I1x	I2x	I3x	I4x	Ix
8.62	0	−23.82	−246.31	−261.51
γ = −arctan
(Iy/Ix) = 8.62°

The corrected momentum synthesis angle (δ) is 131°, and the angle between the combined momentum flow rate direction and the horizontal direction (γ) is −8.62°. This satisfies the requirement that the angle (δ) between momentum I of the synthesized gas flow and the front arch is ≥120°, and the momentum synthesis angle (Y) is ≤30°, thus enabling the formation of an α-type flame.

Experimental Verification

To validate the design results, a hot-state test was conducted on the waste incinerator with the treatment capacity of 750 tons/day. The analysis data of the municipal solid waste recently entering the incineration plant is shown in Tables 3˜4.

TABLE 3
Industrial Analysis of the Waste Sample

	M (%)	V (%)	FC (%)	A (%)
	47.20	27.07	4.36	21.37

TABLE 3
Industrial Analysis of the Waste Sample

	M (%)	V (%)	FC (%)	A (%)

	47.20	27.07	4.36	21.37

Due to being stored in the waste pit for approximately one week before incineration, the moisture content decreased from 47.2% to 30%, resulting in a 32% increase in the mass of the municipal solid waste ((1-30%)÷(1-47.2%)=1.32)). The calorific value of the waste upon entering the furnace was 6730 KJ/kg (1610 kcal/kg)×1.32=8888.68 (2123 kcal/kg).

The measurement point arrangement is shown in FIG. 6. The layout of measurement points for the hot-state test is depicted in FIG. 7, and the flue gas temperature distribution at these points is shown in FIG. 8.

To form an α-type flame, the flue gas is forced to flow downward in a swirling manner blow the front arch to enhance incineration, and then rises towards the incinerator furnace chamber outlet, thus forming an α-shaped flow. Consequently, the temperature within the α-shaped flue gas circuit, i. e., at measurement positions 6, 7, 9, 2, and 8, is expected to be significantly higher than those at other measurement positions. This is clearly visible in FIG. 5. Therefore, it can be confidently concluded that the method developed in this study, based on the momentum flux method, successfully generates an α-shaped flue gas path within the waste incinerator to enhance incineration.

Furthermore, analysis of local temperatures in the new α-type flue gas path waste incinerator indicates that the MSW fuel was not fully ignited at measurement position 1, where the temperature should be around 200° C. The reason why the temperature at position 1 is 477° C. is due to the α-shaped flue gas path, which causes the flue gas temperature to be higher and passes through the area below the front arch. This temperature rise is highly beneficial for the successful ignition of low-calorific-value MSW fuel. The higher temperature at measurement position 2 is because the waste fuel here is already ignited and burning completely. Additionally, the high-temperature flue gas flows through this area, causing a sharp temperature increase. The lower temperatures at measurement positions 3, 4, and 5 are due to their location in the burnout zone of the incinerator, where the waste fuel does not release significant heat. Temperatures at measurement positions 6, 7, 8, and 9 are very high because these positions are within the intense combustion zone, and the fuel releases considerable heat.

From the above results, it is evident that the temperature values in the annular region below the front arch and the uncovered zone are higher than those in other areas, signifying the formation of the desired α-shaped flue path, which aligns with the design results. Therefore, the new α-type flue gas path waste incinerator is both effective and efficient in burning MSW with high moisture content and relatively poor burn-through characteristics, especially in the case of sewage sludge.

This application proposes using the method of adding secondary air to induce α-shaped flow of the flue gas. This approach does not require altering the furnace structure of the waste incinerator, has low cost, and facilitates widespread implementation. As shown in FIG. 7 and FIG. 8, the so-called secondary air refers to several strong airflows that are rapidly sprayed into the furnace from above the fire bed, which have a significant effect on disturbing the airflow condition inside the furnace and enhancing the mixing between them. It can improve the thermal efficiency of the waste incinerator without increasing the total incineration air volume. Simultaneously, the high-velocity, high-momentum secondary air flows can also entrain the flue gas within the furnace, organizing it into the intended furnace flow pattern to prolong the path of flue gas and fly ash, and change the degree to which the gas flow fills the furnace and the position of the incineration center. When appropriately arranged, a curtain of secondary air can even be formed within the furnace, trapping fly ash particles in the flue gas. This can not only change the ignition conditions of the fuel but also further reduce various types of incomplete incineration losses within the furnace, improving the incineration efficiency of the waste.

To fully utilize the mixing and disturbance effects of secondary air, it must possess a certain initial velocity (or a certain penetration distance). However, when the incinerator operates under thermal conditions, the furnace is at a very high temperature. At this point, the viscosity of the flue gas increases substantially, making secondary air penetration difficult. Consequently, the penetration distance calculated using the traditional free jet decay formula often deviates from reality, sometimes significantly, preventing the secondary air from achieving the intended effect. Based on past engineering experience, the penetration depth of secondary air under thermal conditions is not solely related to velocity, but also to the density and flow rate of the secondary air, i. e., to the single-jet momentum flux rate of the secondary air. The greater the single-jet momentum flux rate, the greater the disturbance to the flue gas and the deeper the penetration. Furthermore, it is also related to the ratio of the momentum flux rate of the secondary air to that of the flue gas rising from the grate surface. When this ratio increases, both the disturbance and mixing effects are enhanced. Reasonable values for these two physical quantities enable the secondary air to achieve optimal practical results. However, determining the optimal values for these two quantities is a relatively complex problem. Therefore, one objective of this paper is to derive practical calculation formulas based on the momentum design method. Using these formulas, the optimal ratio of the momentum flux rate of secondary air to that of the flue gas rising from the grate can be calculated. This allows for changing the flow conditions and path of the flue gas within the furnace, specifically transforming the L-shaped flow path of flue gas into an α-shaped flow path. This forces high-temperature gas to form a large recirculation zone at the front area of the furnace, which is beneficial for the ignition and burnout of low-calorific-value fuel.

The above embodiments are merely used to illustrate the technical solutions of the present disclosure and are not intended to limit it. Although the present disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or equivalently replace some or all of the technical features. Such modifications or replacements do not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present disclosure.