Treatment Technologies and Optimization of Waste Pits in Municipal Solid Waste Incineration Power Plants.
1 Current Situation of Municipal Solid Waste Incineration Power Plants
1.1 Difficulties in Waste Stacking Operations
A single waste collection pit is typically divided into four management zones: one storage area, two fermentation areas, and one feeding area. Zone rotation is carried out based on the fermentation status in the storage area and the feeding requirements in the feeding area. During zone rotation, all waste accumulated at the bottom of the storage area must be transferred to another zone for thorough processing. This approach facilitates direct monitoring and management of the waste volume in the storage area. Improper control of the waste pit capacity can easily lead to localized accumulation, adversely affecting waste fermentation. This may result in frequent operational issues such as low calorific value or incomplete combustion, ultimately compromising the environmental quality of the composting process.
1.2 Frequent Malfunctions of Equipment Accessories
The garbage crane is currently the most widely used machinery in domestic waste-to-energy power plants. Its main functions include grabbing, transporting, and feeding waste. The garbage crane contains multiple electrical components, and its internal parts must work in close coordination. During operation, improper handling, inadequate maintenance, or inherent quality issues can easily lead to system failures, resulting in a complete shutdown of production.
1.3 High Leachate Production
During the fermentation process of waste, a specific type of leachate is generated. Every summer, the increase in fruit and vegetable waste, combined with higher rainfall, mixes into the leachate, resulting in a larger volume—commonly referred to as the "wet season." To ensure smooth drainage and treatment of leachate, cleaning efforts for the drainage system at the bottom of leachate wells and the reflux channels should be intensified during this period. If the drainage system of the sewage collection network and leachate pathways are not cleared promptly, blockages can occur in the leachate channels of the wastewater treatment plant. This may lead to increased leachate concentration, cause sewage flotation, and adversely affect the efficiency of waste incineration for power generation.
1.4 Insufficient Waste Fermentation
In northern regions of China, low winter temperatures significantly slow down the waste accumulation and decomposition process. The fermentation cycle during winter is considerably longer compared to summer, which requires only 3–5 days. This extended fermentation period results in lower calorific value of the waste during combustion, substantially reducing the power generation efficiency of waste incineration.
2 Waste Pool Treatment Technology in Municipal Solid Waste Incineration Power Plants
2.1 Waste Crane and Hydraulic Grab Technology
The mechanical equipment involved in waste crane operations has high operational frequency and a high failure rate. Therefore, it must be operated in strict compliance with specifications and maintained adequately. The grabbing load of the grab should be lower than the rated capacity. During grabbing, movements should be gentle, lifting should be slow, and operations should ensure smooth start-up, operation, and stopping. The grab must remain above the waste pile during movement to prevent collisions with the waste, which could cause rolling, avoid impacts with the walls, and prevent vehicle collisions. When retrieving debris from the walls, movements should be slow to minimize impact force. Ensure that limit switches and anti-sway functions are stable, and that the crane’s performance is automatically reduced within the specified limits.
2.2 Odor Control Technology
Waste incineration plants must not only withstand high temperatures but also control odors. During daily operations, a certain level of negative pressure should be maintained. The waste chute must be well-sealed, and the odor removal system should operate smoothly during shutdowns. Roll-up shutters are installed on the trestle and unloading platform to ensure they remain closed during vehicle entry and exit, preventing more than two unloading valves from being open simultaneously. By adjusting the suction force of the primary air, the optimal negative pressure level is maintained between –100 Pa and –50 Pa to prevent odor dispersion.
2.3 Unloading Door Technology
Conventional unloading doors struggle to prevent odor emissions from the waste pool. The existing two-piece swing-type drainage valves, while functional, have drawbacks such as large mass and high complexity. Through structural analysis, a solution involving the use of two side-mounted upper cover shutters to form the unloading doors has been proposed. The upper part of the chute is designed as a lightweight cover structure, which fits tightly against the outer wall of the chute. It is operated hydraulically or electrically for opening and closing. An electromagnetic seal is installed along the edge of the cover to effectively prevent odors from the waste pool from spreading into the working area.
2.4 Fermentation Technology
During the waste fermentation process, parameters such as moisture content, organic matter content, and carbon‑to‑nitrogen ratio are predetermined. Maintaining a composting temperature above 55°C and an oxygen concentration greater than 10% can improve the fermentation efficiency. In winter, the ambient temperature in waste storage pits in northern regions often remains below 15°C for extended periods, which is significantly lower than the minimum required fermentation temperature. Even with extended fermentation time, this leads to issues such as uneven fermentation, incomplete decomposition, and inadequate drainage of leachate. When such under-fermented waste is fed into the incinerator, it adversely affects combustion conditions, resulting in incomplete burning, slag discharge, fluctuations in furnace temperature, and instability in flue gas indicators. To address these challenges in cold climates, it is essential to enhance waste heating and maintain the ambient temperature within the range of 25–30°C.
2.5 Biochemical Treatment Technology
The recycled waste contains a high concentration of both organic and inorganic matter, a significant portion of which is biodegradable. When treating such leachate using the UASB anaerobic process, the COD utilization rate exceeds 70%. This process achieves a COD loading rate of 10 kg/m³·d without external energy consumption, saving space and reducing the operational energy demand of the reactor.For the aerobic treatment stage, the SBR (Sequencing Batch Reactor) process is employed. The SBR process is a time-based intermittent reaction system where operations such as water intake, mixing, aeration, sedimentation, and drainage are performed independently. This process exhibits strong resistance to shock loads and allows flexible adjustment of operational parameters in response to complex and variable conditions. When combined with anaerobic treatment, it effectively enhances both treatment efficiency and effluent quality.
Domestic waste is first weighed by garbage trucks before being transported to the unloading platform and then transferred into the waste storage pool. After composting and fermentation, the resulting leachate is discharged through the grate opening and flows into the leachate collection sump. It is then pumped via sewer lines to the leachate treatment plant for further processing.An intake for the primary air fan of the incineration plant is installed on one side of the waste pool wall. This system extracts odorous air from the waste pool and uses it as combustion air, thereby maintaining negative pressure inside the pool. This prevents the spread of foul odors and the accumulation of biogas.Additionally, an exhaust system is installed at the top of the waste pool. During incinerator shutdowns, this system extracts odorous gases from the upper section of the pool. The extracted gases are treated through deodorizing and purification equipment to prevent the escape of unpleasant odors.
3 Optimization Research on Municipal Solid Waste Incineration Power Plants
3.1 Main Factors Affecting Municipal Solid Waste in Incineration Power Plants
Municipal solid waste (MSW) refers to garbage generated by urban residents in their daily lives, including recyclables, kitchen waste, hazardous waste, and other categories. According to statistics, the annual amount of kitchen waste in China reaches approximately 30 million tons, accounting for about 70% of the total municipal solid waste. With the acceleration of urbanization, the production of municipal solid waste shows a year-on-year increasing trend. Currently, the annual volume of recyclable waste in China is estimated at around 40 million tons.In daily life, however, inadequate attention to this issue often leads to resource wastage and environmental pollution. Since municipal solid waste contains significant amounts of organic matter, inorganic substances, heavy metals, and other pollutants, it poses risks to human health and increases the concentration of harmful gases in the air, thereby complicating subsequent treatment processes.
According to a survey conducted by the China Urban Construction Institute, the main factors affecting the treatment efficiency of municipal solid waste incineration power projects include combustion temperature, calorific value, combustion duration, and leachate treatment. Among these, the control of heat loss in the incinerator and the management of leachate have a significant impact. Through continuous technological improvements and innovations, heat loss during incinerator operation has been minimized and is generally controlled within 5%.As a result, current incineration technology demonstrates high treatment efficiency for municipal solid waste power generation projects. Key performance indicators include:
·High furnace temperature (850–900°C);
·High incinerator thermal efficiency (averaging 88%–91%);
·An waste heat recovery system that ensures effective heat recovery and steam parameters meeting turbine design requirements;
·Low concentration of leachate discharges.
3.2 Optimization Measures for Waste Incineration Power Plants
With the increasing volume of waste, environmental pollution issues have become more severe, among which the most critical concern is the generation of large quantities of dioxins. These toxic substances pose significant threats to human health once they enter the body. Optimization measures are as follows:First, adopt appropriate methods to effectively treat the harmful substances produced during the incineration power generation process. Second, utilize high-temperature combustors in waste incineration power plants to enhance the energy efficiency and overall performance of the equipment, ensuring that operations remain unaffected by hazardous materials. Finally, employ advanced technologies to thoroughly treat various toxic pollutants generated during waste incineration before they are released into the atmosphere, and implement scientific and rational methods to ensure the safe and continuous operation of both personnel and equipment.
3.3 Economic Viability of Municipal Solid Waste Incineration for Power Generation
The economic viability of waste-to-energy incineration projects is generally evaluated based on factors such as the investment payback period (or return on investment), operating costs (or operating profit margin), and net present value (NPV). The investment payback period refers to the time required for a project to recoup its initial investment, spanning from the start of construction to the commencement of commercial operation. This period includes costs related to construction, production, and recovery.A positive NPV indicates that the investment has been fully recovered. During the construction phase and initial operation, the NPV and annual return rate of a municipal solid waste incineration power system are often low or even negative, suggesting that the project is not yet profitable. In contrast, a higher NPV during later stages of operation signifies that the project has become economically profitable.
3.4 Optimization Suggestions for Municipal Solid Waste Incineration Power Plants
The primary methods for treating municipal solid waste are landfilling and incineration, with incineration accounting for over 90% of waste treatment. However, certain issues persist during its processing and operation. To enhance the technology, operational efficiency, and emission standards of waste incineration power generation, the following measures are recommended:First, increase capital investment to improve the configuration and maintenance of facilities and equipment. Based on the characteristics and needs of different cities and regions, select appropriate levels of technical equipment, process routes, and operational methods. Optimize facility management and operational procedures, and enhance training for operational personnel to raise safety awareness and improve operational skills.Second, strengthen the monitoring and data collection of operating conditions for relevant equipment. Use the collected data to optimize the control of combustion temperature within the incinerator, and implement real-time monitoring and adjustment of combustion efficiency to ensure the incinerator operates under optimal conditions.
4 Conclusion
Municipal solid waste incineration power plants play a crucial role in urban development. However, numerous challenges persist during their actual operation, including issues related to waste pit management, difficulties in leachate collection, and insufficient monitoring of incinerator performance.To address these problems, this paper has discussed key treatment technologies for the waste pits in such facilities. By optimizing equipment and operational management, among other aspects, it is possible to enhance the overall efficiency and environmental performance of waste treatment processes.
Source:https://mp.weixin.qq.com/s/LhHWxKyJEZLa5IB9Ewz7pQ