Numerical Simulation of the Diffusion Characteristics of Odor Pollutants of Waste Bunkers in Waste Incineration Plant

Abstract

This paper utilizes the waste bunker of a waste incineration plant as the analysis model. It analyzes the airflow characteristics under various unloading door opening states and the air flow velocity through CFD simulation. The simulation analysis results show that when one unloading door is opened, it is recommended to adjust the opening amplitude or set an air outlet to optimize the airflow distribution. If two unloading doors are opened, it is advised to prioritize the two middle unloading doors (M4, M5) or the two rightmost doors (M7, M8). Furthermore, the exhaust port located relatively far from the unloading door should be closed to reduce the turbulence of the airflow. When all unloading doors are opened, the air flow velocity at the unloading door needs to be increased to achieve an efficient exhaust effect and prevent negative pressure problems at low speed. The results offer theoretical support for odor control technologies and provide valuable design recommendations for air outlets and unloading doors in municipal waste incineration plants. Additionally, this study proposes optimization strategies and effective solutions for addressing odor pollutant diffusion in waste incineration facilities.

1. Introduction

The generation of municipal solid waste (MSW) has become a significant challenge for the environmental field due to the growing global population, accelerating economic development, and urbanization [1,2]. In China, MSW is primarily managed through three methods: incineration, landfill, and composting [3,4]. According to the 2023 National Bureau of Statistics, China’s annual municipal solid waste output reached 244 million tons. Incineration, the leading method, accounted for 51.7% of waste treatment and achieved an environmentally safe treatment rate of 99.2%. This indicates that incineration is increasingly becoming the dominant method for municipal solid waste management, reflecting China’s advancements in waste treatment technology and policies, and a growing focus on environmental protection and resource recycling.

Incineration offers significant advantages as a waste management method [5]. It can reduce the volume of municipal solid waste by up to 90%, leading to substantial waste volume reduction [6]. The high-temperature incineration process ensures the complete decomposition of harmful substances and the elimination of pathogens, including carcinogens, viruses, and highly toxic organic matter [7]. Compared to traditional landfill methods, incineration significantly reduces the concentration of pollutants in landfills and the emissions of flammable and odorous gases. The heat energy produced during incineration can be recovered and converted into steam for heating or power generation, thereby promoting resource recycling [8,9]. In addition, waste incineration plants usually occupy a small area and are well-suited for construction in suburban areas. This reduces land use and waste transportation costs, improves treatment efficiency, and positively impacts urban economic development [10]. However, one of the critical issues associated with waste incineration plants is the emission of odor pollutants. The incineration processes releases odorous gases during the unloading, storage, and feeding phases, which can have significant impacts on the surrounding environment and the quality of life of nearby residents [11]. Therefore, it is crucial to control odor pollution from the waste bunkers in waste incineration plants. These gases mainly consist of hydrogen sulfide (H₂S) and ammonia (NH₃) [12]. In addition, they also contain a variety of volatile organic compounds (VOCs), which are not only diverse but may have a significant impact on air quality at certain concentrations [13,14]. These pollutants can disperse through the air, causing nuisance odors and, in some cases, potential health risks. Accurately predicting and controlling the dispersion of these pollutants is essential for the effective management of odor impacts. Odor pollution associated with waste incineration is a global environmental issue that affects the quality of life of surrounding residents and may also have adverse effects on human health [15]. Lee et al. [16] studied the air flow distribution and odor diffusion in the waste bunker through numerical simulation and found that when the incinerator is running, fresh air can effectively prevent the spread of odor, while when the incinerator is stopped, the odor is easily spread to the waste bunker area.

In recent years, the acceleration of urbanization has led to an increase in municipal solid waste output. Consequently, the issue of odor pollution from waste incineration has garnered significant attention from scholars both domestically and internationally [17]. Research worldwide indicates a growing focus on odor pollution monitoring technology and management strategies. For example, several developed countries have implemented intelligent monitoring and management of odor pollution during waste incineration using Internet of Things technology, incineration status diagnostic systems, online pollutant monitoring, and artificial intelligence algorithms [18]. Low-cost sensors are used to monitor urban air pollution. In a coastal town in southern Italy [19], three sensors and a diffusion model were used to analyze dust (10 μm) distribution and simulate the movement of pollutants under the influence of weather. Domestic research mainly focuses on the emission characteristics of pollutants and their pollution evaluation [20]. Based on the current research status domestically and internationally, odor pollution monitoring and control technology has become a primary research focus. With advancements in technology and increasing public demands for environmental quality, research on odor pollution from waste incineration is expected to deepen, particularly in intelligent monitoring and management, with anticipated breakthroughs.

Studying the diffusion mechanism of odor pollutants is crucial for waste incineration plants. This research will help develop more effective monitoring and control technologies and improve pollutant removal efficiency. A comprehensive understanding of the diffusion characteristics of these pollutants and their influencing mechanisms is essential for the government to formulate effective environmental protection policies and management strategies. This study is vital for guiding the sustainable development of the waste incineration industry and ensuring that the environment and public health are protected from adverse impacts. Various factors, including air flow velocity, terrain, and temperature, influence the diffusion of odor pollutants. By deeply studying the diffusion mechanism of odor pollutants, we can provide a scientific basis for optimizing monitoring and control technologies at waste incineration plants and promote technological progress and innovation. This approach will improve the incineration process, optimize emission system design, increase pollutant removal efficiency, and offer essential references for government departments to formulate environmental protection policies and management measures, thereby safeguarding the environment and public health.

2. Materials and Methods

2.1. Numerical Simulation Method

Ansys was selected as the simulation software, focusing on the waste bunker within the waste incineration process in this study. A 1:1 computational model was developed based on field investigations and measurements. As shown in Figure 1, the waste bunker measures 78.95 m in length, 40 m in width, and 47.50 m in height. The waste bunker has eight unloading doors, labeled M1 to M8, each 4.5 m wide and 6 m high. Each waste bunker also has three primary air suction ports (labeled a1, a2, a3) for drying and preheating the MSW and three secondary air suction ports (labeled b1, b2, b3) to enhance combustion and pyrolysis. The primary air suction ports measure 1.81 m by 1.81 m, while the secondary air suction ports are circular with a diameter of 1.31 m. A specialized negative pressure-regulating suction port, measuring 1.4 m by 1.4 m, is located at the bottom of the left wall of the waste bunker to adjust the negative pressure and maintain an optimal combustion environment.

Under the initial working conditions, we set the unit size of the grid to 1 m, permitting expansion within a certain range with a maximum size limit of 2 m. In areas with significant curvature, we established a minimum grid size of 20 mm, with a growth rate of 1.2 and a transition ratio of 0.272, to ensure that the grid smoothly transitions from fine to coarse. Consequently, the maximum step size of the entire grid is limited to 2 m, and the total number of cells is approximately 1.5 million, consisting of roughly 62,000 grid nodes. Subsequently, error warnings were identified in certain regions of the grid, prompting us to refine these localized areas and conduct further inspections, ultimately maintaining the skewness within the range of 0 to 1, with a maximum skewness of approximately 0.9 and an average skewness of around 0.69. These measures aim to enhance grid quality and ensure the reliability of simulation results.

During the simulation, we did not consider the negative pressure effect of the external wind speed on the waste bunker when the unloading door was opened, and only used the negative pressure generated by the incinerator when it sucked air as the only driving factor for the airflow at the unloading door. During the simulation, the external temperature was set to a constant 30 °C, and the state of the unloading door was directly set to open or closed. To improve the accuracy and realism of the simulation, we obtained the specific odor pollutant data in the waste bunker through field surveys. The survey results show that the waste bunker mainly contains the odor pollutants shown in Table S1, among which those with higher concentrations are dimethyl disulfide, methyl sulfide, and ethanol. Therefore, during the modeling process, we added these three main pollutants to the natural air for mixing to more realistically simulate the gas environment in the waste bunker. Boundary conditions were applied as follows:

(1)

A pressure inlet boundary condition was specified at the air intake, with the inlet temperature set to the outdoor ambient temperature of 30 °C. The turbulence intensity and hydraulic diameter were defined, and the vertical boundary method was used to determine the inlet direction accurately.

(2)

A velocity inlet boundary condition was applied at the unloading door, with its direction opposite the vertical boundary. The air flow velocity was set at 3.5 m/s, and turbulence characteristics were detailed by specifying turbulence intensity and hydraulic diameter.

(3)

The operating pressure was set to standard atmospheric pressure (101,325 Pa). Gravity acceleration was set to g = −9.8 m/s², opposite the Z-axis, to account for its effect on fluid flow. These settings ensure the authenticity and accuracy of the simulation environment.

2.2. Simulation Conditions

According to the on-site investigation and the discharge door’s opening conditions during actual operations, several standard unloading doors’ opening methods were selected for simulation analysis and comprehensive comparison to reflect operational scenarios accurately. Thus, we selected various opening and closing methods, including single-leaf, double-leaf, and full-opening, for comparative analysis. The conditions are named based on the following principle: Condition A (M1, 3.5) indicates that the M1 unloading door is activated, with an air flow velocity set to 3.5 m/s. Specific conditions include:

(1)

For a single unloading door, conditions A (M1, 3.5) and B (M1, 4.5) represent simulations with the M1 unloading door open at air flow velocity of 3.5 m/s and 4.5 m/s, respectively.

(2)

For both unloading doors opened simultaneously, conditions C (M1M2, 3.5), C (M4M5, 3.5), and C (M7M8, 3.5) represent simulations with various combinations of unloading doors (M1M2, M4M5, M7M8) at a fixed air flow velocity of 3.5 m/s.

(3)

For all unloading doors fully opened, condition D (fully open, 3.5) represents the simulation scenario with all unloading doors open at an air flow velocity of 3.5 m/s.

3. Results and Discussion

3.1. Single Unloading Door Opening

3.1.1. Condition A (M1, 3.5 m/s)

Figure 2 shows the velocity flow lines in three-dimensional space, highlighting variations in airflow speed and direction across different regions. The flow lines in the right region are more complex and denser, indicating significant changes in airflow direction and velocity compared to the left region, where the airflow is smoother and slower. Vortex formation is also depicted, particularly in the right region, indicating rotational airflow that may enhance mixing but could also lead to uneven distribution. The centralized airflow region in the middle section suggests it functions as a primary airflow channel, efficiently directing exhaust gases from the waste bunker. The color illustrations represent pressure gradient magnitudes, with more pronounced acceleration or deceleration of airflow in areas with higher pressure gradients. Overall, the airflow distribution is complex, requiring careful consideration in the design and operation phases to optimize airflow organization and ensure uniform and effective exhaust gas discharge.

Figure 3a shows that at X = 10 m, the pressure distribution exhibits significant inhomogeneity, as indicated by the color gradient. The large color variation suggests strong pressure fluctuations in this flow region. Figure 3b indicates that at X = 30 m, the pressure distribution is more uniform, with a lower overall pressure value. The reduced pressure gradient leads to smoother flow and less pressure variation. Figure 3c reveals a clear pressure difference at Y = 10 m, with a distinct gradient between the low-pressure area on the left and the high-pressure area on the right, likely due to the influence of buildings or obstacles. Figure 3d at Y = 30 m shows a relatively uniform pressure distribution with localized fluctuations. The pressure within the waste bunker remains relatively constant, and the gradient is less pronounced and more stable. Figure 3e, at Z = 10 m demonstrates significant vertical pressure variation, with lower pressures at the top and higher pressures at the bottom. Figure 3f at Z = 30 m shows a uniform pressure distribution, with pressure values concentrated in the lower zone, indicating a more consistent stress distribution at this height.

Figure 4a shows that the velocity distribution at X = 10 m is complex, with multiple velocity peaks and vortices. To manage airflow and reduce vortices, consider increasing the deflector plate or adjusting the position and size of the air outlet. Figure 4b indicates that at X = 30 m, the velocity distribution is relatively uniform with fewer vortices. Increasing the number of monitoring points or adjusting the combustion strategy could help optimize the uniform velocity distribution in this area. Figure 4c shows that at Y = 10 m, the velocity distribution is more significantly influenced by the primary wind, which is uniformly distributed at this air flow velocity. In Figure 4d, the section at Y = 30 m, deeper in the waste bunker, displays a velocity distribution affected by secondary wind and combustion processes, leading to higher speeds and a velocity red zone. It is recommended that detection points or adjust the air outlet adjusted. Figure 4e depicts the section at Z = 10 m, located in the middle to upper part of the waste bunker, where velocity distribution is uneven due to secondary wind and combustion processes. Figure 4f shows that at Z = 30 m, the velocity distribution is relatively uniform, with fewer vortices.

3.1.2. Condition B (M1, 4.5 m/s)

Figure 5 shows the velocity flow path at an air flow velocity of 4.5 m/s. Compared with the velocity flow path at an air flow velocity of 3.5 m/s, the velocity flow lines at 4.5 m/s show a more complex and dense distribution. Like the velocity flow line at 3.5 m/s, the velocity flow lines on the right show more complicated and dense characteristics at both air flow velocity while the velocity flow lines on the left appear relatively flat and have a slower flow rate.

Figure 6a shows that at X = 10 m, near unloading door M8, there are significant pressure fluctuations. Figure 6b indicates a more stable pressure distribution at X = 30 m. Figure 6c reveals that at Y = 10 m, the unloading door M8 causes uneven pressure and pressure build-up. It is advisable to adjust the waste bunker bottom design or enhance the auxiliary ventilation system. Figure 6d reflects the overall pressure distribution trend at Y = 30 m, crucial for evaluating pressure balance across the waste bunker width.

Figure 6e shows that at Z = 10 m, the pressure is influenced by the unloading door’s operation and can be optimized by adjusting the ventilation strategy. Figure 6f demonstrates a more uniform pressure distribution at Z = 30 m, suggesting a need to change the combustion strategy or ventilation system. The pressure distribution along the X-axis shows instability, with high pressure on the sides and low pressure in the center, potentially leading to odor gas accumulation and inefficient contaminant discharge. In the Y-axis direction, the upper right corner may have turbulent flow retention, possibly causing gas reflux and stagnation. Installing an air outlet in this area is recommended.

Figure 7 shows that the velocity exhibits a stagnation zone in the Y-axis direction, which could lead to turbulent flow areas. When the unloading doors are opened in the Z-axis direction, airflow from the negative pressure adjustment port diffuses outward, potentially allowing contaminated gases to escape through gaps in other unloading doors, leading to air leakage. To address this issue, it is recommended that the negative pressure adjustment port be closed and the suction of the air outlet increased. Adjusting the negative pressure at the air outlet can effectively control air flow velocity and odor concentration at the unloading door, reducing air leakage and pollutant escape. Optimizing the air outlet layout and adjusting its negative pressure can enhance pollutant control and energy efficiency, improving overall system efficiency and safety.

3.2. Double Unloading Door Opening

3.2.1. Condition C (M1M2, 3.5 m/s)

According to the simulation results in Figure 8, the flow field distribution of the negative pressure adjustment port significantly affected the flow field distribution when the two left unloading doors were opened. This caused considerable turbulence near these doors, adversely impacting the effective discharge of polluted gases. Significant backflow was also observed at the air outlet, likely due to suboptimal design or operational conditions. This backflow impaired overall ventilation efficiency. To resolve these issues, it is recommended that the extraction air outlet be reevaluated repositioned as far from the unloading doors as possible to minimize backflow and optimize airflow distribution. Implementing deflector elements to guide airflow away from the unloading doors and reduce turbulence at the openings is also advised. Furthermore, adopting more efficient negative pressure adjustment techniques will ensure better absorption and discharge of contaminated gases, thereby improving environmental protection and reducing health risks.

Figure 9 shows that the pressure distribution near the air outlet exhibits more uniform diffusion and a pronounced gradient from high to low pressure in this opening and closing mode. This pattern allows for a smooth transition from low to high pressure. Compared to the higher pressure in the surrounding area, the lower pressure at the air outlet is crucial for effectively discharging contaminated gases from the waste bunker, thus improving decontamination. Overall, this pressure distribution configuration is optimal for the unloading process.

Figure 10 reveals that velocities are predominantly concentrated near the air outlet and the two open unloading doors. The airflow velocity near the negative pressure adjustment port at the unloading door increases significantly to 6.0 m/s, leading to airflow accumulation in this region and hindering its effective diffusion towards the air outlet. Two improvement measures are proposed to address this issue: First, increase the air outlet’s power by augmenting the extractor fan’s pumping force to enhance airflow suction and better extract accumulated airflow. Second, close or redesign the negative pressure adjustment port to direct airflow upwards, preventing unwanted accumulation at the unloading door. Optimizing the extraction system by increasing the air outlet flow rate or enhancing its operational efficiency can significantly improve production efficiency and reduce energy consumption. Additionally, adjusting the negative pressure adjustment port can effectively control pollutant diffusion, thus enhancing overall environmental quality.

3.2.2. Condition C (M4M5, 3.5 m/s)

Figure 11 shows that when the middle two unloading doors are open, the velocity streamlines display a relatively straight pattern with minimal stagnation or turbulence zones. This indicates that, under these conditions, the fluid flow in the waste bunker is relatively uniform, with no significant blockages or instability. However, turbulence was observed at several extractor locations farther from the open unloading doors, likely due to suboptimal design or positioning of the air outlet, which causes turbulent flow as the fluid encounters obstructions in these areas.

To address this issue, increasing the pumping power at air outlets exhibiting turbulence and backflow is recommended to optimize fluid flow conditions. Additionally, closing certain air outlets away from the unloading doors can help mitigate fluid separation and re-aggregation, thereby reducing turbulent flow. Adjusting the air outlet size can further streamline and improve fluid flow in the waste bunker. In regions with more uniform flow, pressure distribution should be analyzed further, and adjustments should be made based on monitoring results. Specifically, in areas with abnormally high pressure, it may be necessary to increase ventilation or adjust the air outlet to prevent equipment damage or safety hazards due to excessive pressure, ensuring efficient system operation and safety.

Figure 12 shows a relatively uniform pressure distribution along the X-axis and Y-axis directions, indicating adequate ventilation for controlling and regulating pressure, and reducing dust and pollutant accumulation. However, slight pressure diffusion towards the air outlet was observed in the unloading area at the lower right side of the wall, likely due to increased localized airflow demand from material handling activities.

Figure 12e,f reveals a significant positive pressure region near the air outlet along the Z-axis, characterized by a pronounced pressure gradient. This suggests that the design or placement of the extractor opening may not adequately address the need for efficient extraction of contaminated gases, leading to delays in extraction. The pressure phenomenon could also be related to the overall design of the extraction system, including factors like the size and shape of the air outlet and its distance from the working surface.

To improve this situation, consider the following measures: First, increase the intensity of air extraction by adjusting the air outlet’s parameters (e.g., aperture, deflection angle) to enhance airflow regulation and more efficiently extract accumulated pollutants. Second, explore solutions from other studies, such as incorporating a parallel-flow air supply device to improve airflow homogeneity and enhance the exhaust hood’s efficiency in capturing flue gases. Implementing these measures could improve pressure distribution along the Z-axis and enhance the overall performance of the ventilation system.

Figure 13 shows that at the X-axis position in the upper left corner of the waste bunker, the flow rate is higher, indicating more active gas flow in this region. From the Z-axis direction, gas discharged from the middle two unloading doors exhibits an upward flow trend, with no accumulation or retention in the lower region. This behavior may be due to the design characteristics of the unloading doors; their shape and location may facilitate upward gas flow. Additionally, the gas moves gradually towards the air outlet, which is extracted more efficiently. By adjusting the negative pressure at the air outlet, air velocity and odor concentration at the unloading doors can be controlled more effectively, optimizing the system’s overall efficiency. Thus, opening the middle two unloading doors proves to be an effective strategy for efficiently extracting contaminated gas.

3.2.3. Condition C (M7M8, 3.5 m/s)

In Figure 14, when the right two unloading doors are open, airflow is shown as relatively straight streamlines, like when the middle two unloading doors are open, indicating smooth flow with minimal stagnation or turbulence. However, turbulence was observed at the air outlet further from the open unloading doors, likely due to airflow obstruction or diversion in these areas. Closing some air outlets reduces turbulence and backflow, optimizing overall airflow efficiency, reducing energy consumption, and improving system performance. Additionally, the minimal impact of the negative pressure adjustment port makes airflow more uniform in other areas, enhancing system stability. Proper configuration and adjustment of the air outlet help control and optimize airflow paths, reduce stagnation and turbulence, and improve operational efficiency and system stability. This optimization strategy applies to the current scenario and serves as a valuable reference for designing and optimizing similar systems.

In Figure 15a,b, the overall pressure distribution shows a clear downward trend along the X-axis, gradually decreasing pressure from the discharge port to the pumping port. This trend is consistent with axial stagnation or reflux of airflow, which is induced by the central low-pressure region within the cyclone unloader. The vortex structure effectively models the internal flow under continuous conditions, particularly in high-vacuum direct-exhaust atmospheric dry pumps. The performance of these pumps can be optimized by adjusting parameters such as rotational speed and temperature.

In Figure 15c,d, the pressure distribution along the Y-axis is lower and more uniform, likely because the unloading door on the left side is closed. This observation aligns with the impact of side-wall pumping on the flow field in a binary wind tunnel, which alters the thickness of the attached surface layer displacement and indirectly influences potential flow. Conversely, the high-pressure region around the open unloading door experiences reduced pressure and improved flow. This finding is similar to studies on controlling flow separation in the impeller of a highly loaded pressurized compressor using non-constant pulsating suction, which has proven effective in improving aerodynamic performance by controlling flow separation.

In Figure 15e,f, the pressure distribution along the Z-axis is centrally located at the open unloading door and the negative pressure-regulating port, with slight pressure gradient changes. This observation is consistent with numerical studies on the effects of axial compressor pumping on downstream leaf discharge flow fields, where pumping affects the velocity and pressure distribution on the downstream leaf surface and the blade surface. The pressure near the air outlet, elevated from the ground, is uniformly distributed, with extraction outlet pressures ranging from 1000 Pa to 28,000 Pa in negative pressure, and the gradient changes more rapidly, facilitating faster extraction. These findings align with studies on the flow field in a binary wind tunnel with side-wall extraction, where the optimal extraction state allows for uninterrupted flow free from side-wall interference.

In summary, the analysis of Figure 15 reveals pressure distribution characteristics across various directions and the underlying physical mechanisms, which align with existing studies. These findings are crucial references for optimizing the design and improving the performance of pneumatic conveying devices.

The analysis of the velocity distribution in Figure 16 shows that velocity is primarily concentrated on the right side of the cavity, while it is comparatively lower on the left side. Compared to previous conditions, the velocity distribution along the right side of the Z-axis is more uniform and stable, with a smoother transition. Observations from the Z-axis direction reveal no significant stagnation areas at the air outlet, facilitating effective gas discharge. Additionally, the velocity gradient remains stable without any prominent high-flow regions. Based on these observations, performing the unloading operation under these conditions is advisable.

3.3. All Unloading Door Opening

3.3.1. Condition F (All, 3.5 m/s)

Figure 17 shows that with all unloading doors open, the velocity flow lines are relatively straight, with minimal stagnation or turbulence, and only slight turbulence is observed near the left-side air outlet. To address this, increasing the pumping force at these extractor ports is recommended to reduce localized turbulence. The flow conditions in other areas are more uniform and should be analyzed further based on pressure and velocity distributions to optimize overall fluid dynamics.

Figure 18 indicates that when all discharge ports are open, the interior of the waste bunker is in a slightly negative pressure state, which suggests low stability. Although the overall pressure distribution shows a uniform diffusion trend, the pressure gradient is minimal, posing a risk of low-pressure backflow and leakage. Under these micro-negative pressure conditions, the storage material tends to flow from higher to lower pressure areas, leading to instability and potential backflow or leakage. This instability may result from gravity and additional factors such as gas exchange and temperature changes. Therefore, opening all unloading doors under these conditions could exacerbate instability and should be cautiously approached.

Figure 19 shows that fluid diffusion becomes more complex when all unloading doors are opened. As illustrated in Figure 19a, the fluid exhibits turbulent flow, likely due to low velocity, which prevents the fluid from effectively rising to the air outlet and instead causes it to diffuse toward the center. This issue is further highlighted in the side view of Figure 19d, where insufficient velocity hinders direct flow from the unloading door to the air outlet, leading to fluid spread and backflow within the waste bunker. This suggests that gas discharge is inefficient under these conditions. It is necessary to adjust the gas flow rate and pressure to enhance pressure distribution and prevent low-pressure backflow and leakage to improve gas discharge efficiency.

3.3.2. Condition F (All, 4.5 m/s)

Figure 20 reveals that when all unloading doors are open and the air flow velocity is 4.5 m/s, the flow lines become more complex than an air flow velocity of 3.5 m/s, resulting in increased turbulence and recirculation areas. While this may enhance gas mixing, it also causes accumulation in turbulent zones. A detailed analysis of pressure and velocity distributions is needed to optimize gas flow and discharge effectiveness.

According to the analysis of Figure 21, adjusting the flow rate results in a more uniform pressure distribution. Although red pressure zones are present, they are diffusely distributed along the walls, indicating the effect of wall diffusion. Figure 21a,b show that lower pressure areas are primarily concentrated at the center of the waste bunker. From there, the pressure diffuses outward, creating a trend of concentrated diffusion towards the walls. This condition promotes uniform pressure distribution and prevents pressure buildup. Figure 21c,d illustrate that after adjusting the speed, a red pressure zone appears on the wall opposite the unloading door and diffuses upward. The pressure at the exhaust port remains relatively low, which creates a pressure gradient that facilitates effective gas discharge through the air outlet. In other areas of the waste bunker, the pressure distribution is relatively uniform, with no significant pressure turbulence zones observed. Figure 21e shows higher pressure around the air outlet, creating a negative pressure area at the outlet, which enhances the efficiently discharging of gas. In summary, this operational configuration supports the efficient discharge of polluted gases while maintaining uniform pressure within the waste bunker, avoiding complex flow areas.

According to the analysis presented in Figure 22, adjusting the air flow velocity significantly enhances velocity diffusion in the waste bunker. Under a substantial pressure gradient distribution, the velocity distribution becomes uniform and effective, expanding efficiently to the air outlet. Figure 22a,b show that the velocity at the center of the unloading door has not reached its maximum value, with diffusion mainly focused above each air outlet. In Figure 22c, the velocity diffusion is more pronounced, effectively spreading from the unloading door to the air outlet without causing accumulation or turbulence. Figure 22d indicates that although there is a high-speed area (marked in red), the rapid diffusion prevents accumulation on the opposite wall, ensuring effective dispersion. Adjusting the air flow velocity significantly improves the velocity diffusion effect within the waste bunker. Therefore, it is recommended that all unloading doors be opened when operating under high-speed air flow conditions.

4. Conclusions and Recommendations

This paper utilizes CFD simulation to explore the characteristics of the pressure and velocity fields of a waste bunker in a waste incineration plant under different working conditions. The results show that the configuration of the unloading door significantly affects pressure and airflow patterns, which in turn affects the control of odorous gases and the overall efficiency of the waste treatment process. This leads to the following main conclusions:

(1)

Single Unloading Door: A stable negative pressure environment can be maintained. Excessive negative pressure in certain areas may cause local turbulence and accumulation. To optimize airflow distribution, adjust the number of unloading doors or set an air outlet in the accumulation area.

(2)

Double Unloading Doors: Negative pressure can be effectively stabilized and diffused by opening the M1 and M2 unloading doors to prevent gas leakage. For better gas discharge and stable diffusion, operate with the open M4, M5 or M7, M8 unloading doors open, and adjust the pressure gradient.

(3)

All Unloading Doors Fully Open: The waste bunker can maintain a slightly negative pressure state under low air flow velocity. This condition may lead to leakage and turbulence. To reduce odorous gas leakage and improve airflow, fully open the unloading doors during air flow velocity to achieve efficient gas diffusion and uniform pressure distribution.

In summary, CFD simulations and analyses of the pressure and velocity fields in the waste bunker, along with rational adjustments to the number and positions of the unloading doors and the setting of air outlets, are effective methods to optimize the negative pressure environment. These measures prevent air leakage and turbulence, improve operating efficiency, reduce environmental pollution, and significantly enhance the safety and health of the surrounding environment. It can lay a foundation for the subsequent research on the prevention and control technology of odor pollutants in the clean incineration of waste, and provide a reference for designing the exhaust vents and unloading doors of the waste bunker of municipal solid waste incineration plants.

In subsequent research, we will use experimental data for verification, conduct physical experiments to confirm the validity of the CFD simulation results, and evaluate the accuracy of the model under actual conditions. In addition, we will also study the impact of external environmental factors on the results, such as external temperature and air flow velocity.