Waste incineration power generation – using the residual heat of life to complete the energy cycle

Foshan Nanhai Green Power Renewable Energy Co., Ltd. (hereinafter referred to as Nanhai Green Power), a wholly-owned subsidiary of Hanlan Environmental Protection Co., Ltd., is an urban solid waste treatment company mainly engaged in municipal solid waste incineration power generation, municipal solid waste compression and transfer, sludge treatment, and kitchen waste treatment. The company currently owns one municipal solid waste incineration power plant (Nanhai Waste Incineration Power Plant No. 2, put into operation in 2011) with a daily processing capacity of 1,500 tons. This plant uses a Siemens DCS system to monitor and manage the power plant's production process. Faced with the increasing volume of municipal solid waste, in 2013, the company decided to expand by building a waste incineration power plant of the same scale.
Overcoming the Garbage Siege
Garbage siege has become a global problem, and in China, it is even more urgent. China generates approximately 200 million tons of garbage annually, with an average annual output of 440 kilograms per person, and this figure is increasing at a rate of about 5% per year. Cities across the country have already landfilled or dumped approximately 8 billion tons of various types of garbage, accumulating waste that occupies 500 million square meters of land. Two-thirds of cities are already surrounded by garbage. Currently, Guangdong Province alone generates approximately 88,000 tons of household waste daily, and this figure may even exceed 100,000 tons by 2020. The annual amount of garbage piled up would be roughly equivalent to 2.5 Yuexiu Mountains.
Waste-to-energy incineration transforms waste into valuable resources, using the residual heat of life to complete the waste cycle, becoming a new way out for waste. It has gained attention from Nordic countries, Japan, Singapore, and other countries, and the technology is constantly maturing. However, the widespread adoption of waste-to-energy incineration in my country still needs time.
Nanhai Green Power Company attaches great importance to the construction and operation of municipal solid waste incineration power plants, striving to become the best municipal solid waste incineration power company in China and the world, and making outstanding contributions to China's waste incineration power industry. Currently, the Nanhai Municipal Solid Waste Incineration Power Plant II (completed in 2011) has been rated as a 3A-level waste incineration power plant by the Ministry of Housing and Urban-Rural Development of China (one of only five such plants in China at present).
Located within the Nanhai University Town, Nanhai Green Power Company is surrounded by numerous universities, businesses, and residents. The company's management believes in transparency and openness to the government, community, and the public; striving to be a good steward of the city, a good neighbor to the community, and a good role model in the industry. Therefore, Nanhai Green Power Company works diligently in all aspects of construction and operation, employing the best design, the most advanced equipment, and implementing superior management. The Nanhai Municipal Solid Waste Incineration Power Plant II has already adopted Siemens' DCS, achieving excellent results after three years of use. Based on past successful cooperation, Nanhai Green Power Company has again chosen Siemens as its partner for new waste-to-energy projects, specifically adopting Siemens' latest and most advanced design solution—the Totally Integrated Automation (TIA) solution. This solution not only provides the entire plant's DCS control system, namely the PCS 7 system, including 8 redundant controllers (one for each of the 3 incinerators and 2 engines, two for the common areas, and one for the flue gas purification system), but also includes hardware such as power supplies, switches, communication cards, high and low voltage power distribution, motors, high and low voltage frequency converters, soft starters, and intelligent motor control cabinets. In addition, it has been comprehensively optimized based on its own and Nanhai Green Power Company's many years of professional experience in waste incineration, providing full life-cycle services from design and programming, supply and installation, production commissioning to after-sales service.
Although waste-to-energy incineration operates on the same principle as traditional coal-fired power generation—converting combustion heat into electricity via a steam turbine generator—the raw material supply for waste-to-energy incineration differs significantly. Coal-fired power generation uses pulverized coal as its sole raw material, resulting in a simple supply chain and a mature, streamlined process. In contrast, waste-to-energy incineration involves processes such as screening, sorting, deodorization, and drying. Some waste may also contain flammable and explosive ammonia, necessitating explosion-proof controls. This process is far more complex than coal-fired power generation, involving more automated control points and requiring engineers to be familiar not only with the control standards of the coal-fired power generation industry but also with the specific requirements of waste-to-energy incineration.
The most concerning and challenging aspect of waste-to-energy incineration is the treatment of dioxins. These organic compounds are highly toxic, stable, and easily accumulate in organisms. However, through scientific waste incineration, dioxins can be completely decomposed. The "3Ts" are the nemesis of dioxins: temperature, time, and turbulence. Specifically, the furnace temperature must be maintained above 850℃; the flue gas must remain in the furnace at this temperature for more than 2 seconds; and thorough mixing is essential to ensure complete combustion of the waste.
At the Nanhai Green Power Incineration Plant, the upper part of the incinerator typically reaches a temperature of around 950℃, while the bottom combustion zone can exceed 1000℃, ensuring optimal combustion temperatures. Furthermore, the waste remains in the incinerator for at least 40 minutes, continuously agitated and circulated with air to ensure complete combustion. Internally, frequency converters regulate the airflow of the blowers and exhaust fans, achieving both energy savings and maintaining a negative pressure environment within the furnace to prevent flue gas leakage. The entire plant operates on a fully enclosed, automated production system: waste is sent to a transfer station—compressed and sealed in standard containers before being transported to the incineration plant—fully fermented in the waste pit—transferred to the furnace for complete combustion—dioxins are treated and controlled below safe standards—fly ash is treated and chelated into cement blocks—wastewater and exhaust gases are purified. After multiple treatments, only about one-tenth of the original volume of chelated cement blocks and purified gas are ultimately released, resulting in virtually no unpleasant or unusual odors throughout the plant.
TIA becomes an environmental guardian
Siemens, possessing automation and drive technologies, introduced the concept of Totally Integrated Automation (TIA). The goal of TIA is to move industrial automation from partial to integrated, seamlessly connecting automated equipment and systems through a unified data management, communication, configuration, and programming environment. This reduces engineering time, increases production efficiency, and consequently lowers equipment operation and maintenance costs. PCS 7 is seamlessly integrated into TIA, applicable to the full range of products, systems, and solutions at all levels of industrial automation, from enterprise management to control levels, all the way to the field level, enabling unified and customizable automation systems for all mixed-process industries.
To achieve all this, process design is crucial. Siemens engineers fully leveraged Nanhai Green Power Company's operational experience in waste-to-energy incineration, customizing a DCS platform and providing a full lifecycle service from planning and design, supply, installation, commissioning to after-sales support, and even system upgrades. During project execution, a senior engineer with extensive industry experience led the team. Hardware engineers integrated 26 cabinets, 25 bus integration boxes, and all hardware, including power and network components, according to design specifications and industry standard databases. Simultaneously, software engineers programmed the entire process, translating process requirements into simplified operations. After hardware and software integration, Siemens conducted internal testing followed by testing at the user's factory. After these tests, the system underwent 168 hours of safe and trouble-free operation before being safely delivered for use. Based on the Totally Integrated Automation (TIA) solution, all third-party control systems and on-site hardware equipment in the waste-to-energy incineration process are integrated into a unified system with global data, achieving data interoperability and eliminating information silos. The entire plant's production process is seamlessly integrated and centrally managed. Operators only need to use a single platform to control the entire production process, monitor the waste incineration status and data in real time, and significantly reduce personnel operating costs. At the same time, the centralized and transparent data is also the foundation for future digital production. Siemens has also reserved an interface for the MES system, which can easily connect the plant's production data with the MES system to achieve comprehensive integrated management from upper-level assets to on-site equipment, completing the leap to digital manufacturing.
This project utilizes the CPU 410-5H, a powerful and rugged process industry controller from the SIMATIC family. This high-performance controller boasts high-speed computing capabilities to meet the demanding requirements of the process industry. Designed for all-weather applications, the CPU 410-5H can operate in harsh environments with varying temperatures, vibrations, and shocks, and complies with various EMC requirements.
The emerging information revolution is gaining momentum, profoundly impacting various industries such as waste-to-energy and the power sector. In the latest round of large-scale engineering projects, companies across the power industry have unanimously proposed a new concept—the digital power plant. The purpose of building a digital power plant is to maximize the efficiency of power generation enterprises. The structural model of a digital power plant can be divided into three levels: plant level, unit (workshop) level, and field monitoring equipment level. Currently, my country's power plants at the plant and unit (workshop) levels have achieved digitization, but the vast majority of the field control equipment level has not yet been digitized. Fieldbus system (FCS) technology holds promise for solving this problem.
Fieldbus systems (FCS) are crucial for data interoperability. Traditional solutions link controllers to field devices via hard contacts to I/O modules, requiring extensive cabling and limiting data acquisition. With the increasing prevalence of digital manufacturing and preventative maintenance, field instruments require more parameters, highlighting the advantages of Profibus. In this project, field process instruments are connected via Profibus-PA bus, with a single node in the system using DP/PA-LINK to convert PA to DP. Controllers and field devices are connected via dual-redundant Profibus-DP bus; controllers and servers are connected via a dual-ring network and Ethernet, while servers and clients are connected via industrial Ethernet. Twenty-five IP65-rated, all-stainless steel bus junction boxes are strategically placed near the field instruments to minimize cabling.
The bus collects data from all devices throughout their entire lifecycle, including data from third-party subsystems and even on-site weighbridge data, and enables online monitoring through PDM management software. While monitoring status and understanding detailed equipment information, it also proactively predicts equipment lifecycles, providing effective support for the company's asset management system and equipment maintenance. Users can anticipate which components require maintenance and repair, extending their lifespan, rather than passively waiting for problems to occur before attempting repairs and troubleshooting.
The Nanhai Waste-to-Energy Plant No. 2 has been operating efficiently for three years. The new waste-to-energy plant project is currently in the commissioning stage and is scheduled to be completed in 2015. After it is put into operation, Nanhai Green Power will be able to process 3,000 tons of waste per day, which can completely digest the current 2,800 tons of domestic waste in Nanhai District, and ultimately completely solve the problem of harmless treatment of domestic waste in Nanhai District.
Nanhai Green Power Company, in partnership with Siemens and with the help of TIA solutions, fully utilizes the residual heat of waste, allowing it to complete its energy cycle and restoring a clean environment to nature.