Hiroyuki SUZUKI*
Eiji NAKAYAMA*
Kiyoyuki SAKURAI*
*
Ebara Environmental Plant Co., Ltd.
At the end of March 2017, EBARA reconstructed the Funabashi Hokubu Incineration Plant in Funabashi City, Chiba Prefecture, and also completed the construction of (1) a high-efficiency waste-to-energy facility (Funabashi Meguru Plant) that consists of incineration equipment with a capacity of 381 t/d and bulky waste crushing equipment with a capacity of 15 tons per 5 hours, and (2) a waste heat utilization facility (Funabashi Meguru Spa). The high-efficiency waste-to-energy facility is characterized by a reduced environmental burden, and it can achieve low CO and low NOx by adopting EBARA’s latest stoker-type incineration system, HPCC21, and an exhaust gas recirculation system and by running stable, constant high-temperature combustion at a low air ratio. The facility is expected to contribute to waste treatment services, which will facilitate the establishment of a recycling-based society and which is rooted in the local community, through waste-to-energy conversion as well as the utilization of green energy, such as the supply of hot water to the waste heat utilization facility by utilizing waste heat from the waste-to-energy facility.
Keywords: Municipal solid waste, Incineration plant, Low air ratio combustion, Carbon monoxide, Nitrogen oxides, Environmental enlightenment, Waste heat utilization facility, High-efficiency waste-to-energy plant
Due to the aging of the existing incineration plant (capacity: 435 tons/day), which began operation in 1992, Ebara constructed a new stoker-type incineration plant with a capacity of 381 tons/day (127 tons/day×3 units) on the neighboring site (Figure 1).
With its cutting-edge technology, the stoker-type incineration plant has not only a greatly enhanced power generation capability but also stricter emission control values in consideration of the local environment.
Along with the construction work of the new incineration plant, a waste heat utilization facility (Funabashi Meguru Spa) was constructed on the adjoining site to improve the health of the local inhabitants. The aging incineration plant was demolished, and the site is currently used as a multipurpose ground and green space in preparation for the future construction of a new plant (Figure 2).
Fig. 1 Funabashi Hokubu Incineration Plant
Fig. 2 Overall layout of Funabashi Hokubu Incineration Plant
The incineration plant is a state-of-the-art facility with cutting-edge stoker technology and a lower environmental burden. The generated electric power is used within the plant and the waste heat utilization facility, and the majority of the electric power is sold to the electric power company. Heat is also supplied to facilities that can utilize waste heat, such as for public baths and heated indoor swimming pools. The plant was constructed with careful consideration for the surrounding environment and economy and is community-friendly; all wastewater produced inside the plant is recycled, and it uses a wastewater closed system designed to prevent wastewater from being discharged outside of the plant and other environmental conservation equipment.
The flow of the units of the incineration plant is shown in Figure 3. The collected household refuse (general waste) is temporarily stored in the waste pit, then loaded into the charging hopper by the waste crane, and fed into the incinerator by the refuse feeder. The refuse is then incinerated in the incinerator at a high temperature of 850 ℃ or over, and the bottom ash is humidified and cooled in the ash extractor. After that, the iron is separated from the bottom ash by the magnetic separator and the bottom ash is transferred to the ash pit, where it is stored.
The exhaust gas is cooled to 170 ℃ in the boiler and the flue gas cooler. Then, activated carbon and slaked lime are injected, and the dust, acid gases, and dioxins are adsorbed and removed by the bag filter. Nitrogen oxides are decomposed at a high temperature and are removed by injecting ammonia water into the hot portion of the boiler. Selective catalytic reduction unit is installed to remove even more nitrogen oxide.
Stable combustion is maintained even at low air ratios with an exhaust gas recirculation system, which branches the exhaust gas from the outlet of the bag filter and blows it into the incinerator as agitation air.
The steam produced from the boiler is fed to the steam turbine and used for power generation (Figure 4). The steam turbine it uses is a two-stage condensing extraction turbine, and the bleed steam in the first stage is fed to the low-pressure steam receiver and used for processes inside the plant, such as deaerator heating, or to supply heat to the adjacent indoor heated swimming pool. The bleed steam in the second stage is fed to the feed water heater and used to heat the feed water in the boiler. The adoption of the two-stage condensing extraction turbine increases the amount of steam to be used for power generation and maximizes power generation efficiency.
The specifications of the major units of the Funabashi Hokubu Incineration Plant are shown in Table 1.
Fig. 3 Flow of units
Fig. 4 Flow of steam system
| Receiving and supply equipment | |
| Waste pit | Capacity: 10000 m3 |
| Waste pit crane | Fully automatic crane×2 |
| Combustion equipment | |
| Incinerator | Full continuous type stoker incinerator |
| Treatment capacity: 127 t/d × 3 incinerators | |
| Combustion gas cooling equipment | |
| Boiler | Natural circulation type water tube boiler |
| Evaporation amount: 21.8 t/h×3 boiler units | |
| Steam condition: 4 MPaG×400℃ | |
| Flue gas treatment equipment | |
| Flue gas cooling method | Water injection method |
| Dust collection method | Bag filter |
| Denitration method | Selective non-catalytic reduction and selective catalytic reduction units |
| HCI/SOx removal method | Dry method (slaked lime injection) |
| Measure against dioxins and mercury | Activated carbon blow-in method |
| Equipment utilizing waste heat | |
| Steam turbine | Two-stage condensing extraction type |
| Power generator | Three-phase alternating current synchronous power generator 8800 kW |
| Ash unloading equipment | |
| Bottom ash | Magnetic separation treatment after humidification and cooling Carrying out by pit and crane |
| Fly ash | Chemical treatment, carrying out by pit and crane |
| Wastewater treatment equipment | |
| Plant wastewater | Inorganic wastewater: Recycled inside the plant after coagulating sedimentation + sand filtration treatment |
| Organic wastewater: Treated by the inorganic wastewater process after biological treatment | |
| Domestic wastewater | Discharged into the river after treatment by a combined type private sewage treatment system |
| Bulky waste treatment equipment | |
| Crushing | Combustible: Biaxial shredding type |
| Incombustible: Vertical type high-speed crusher | |
| Separator | Electromagnetic type magnetic separator, aluminum separator, particle size separator |
The exhaust gas concentrations measured in the performance test are shown in Table 2. All exhaust gas concentrations are below the guaranteed values, proving that the units have satisfactory performance.
The incineration plant combusts waste at a low air ratio and high temperature through the exhaust gas recirculation system. If the air ratio is decreased to incinerate municipal solid waste with uneven properties, the peak of carbon monoxide (CO) generation is likely to occur. In contrast, the production of nitrogen oxides (NOx) can be decreased by reducing the air ratio. Maintaining low concentrations of both CO and NOx requires an optimum air ratio, mixing and agitation in the secondary combustion chamber, and stable internal temperature in the incinerator. The incineration plant meets these conditions through the exhaust gas recirculation system and further reduces the concentration of NOx by using a selective non-catalytic reduction process in combination with the system.
As shown in Figure 5, the incineration plant operates at an oxygen concentration of approximately 3.5 % (air ratio: 1.25) at the outlet of the boiler, while the average concentration of CO is kept at 5 ppm, and the occurrence of its peak is also controlled. To deal with NOx, ammonia water is only injected into the boiler, and the concentration of NOx is controlled to an average of 35 ppm without injecting ammonia water into the selective catalytic reduction tower.
| Regulated substance | Guaranteed value | Performance test result | |||
| No. 1 | No. 2 | No. 3 | |||
| Dust | g/m3（NTP）*1 | 0.007 | <0.0006 | <0.0006 | <0.0006 |
| Hydrogen chloride | ppm*1 | 20 | 9.5 | 13 | 9.5 |
| Sulfur oxides | ppm*1 | 15 | 7 | 7.9 | 4.6 |
| Nitrogen oxides | ppm*1 | 45 | 30 | 28 | 31 |
| Carbon monoxide | ppm*1*2 | 15 | 10 | 8 | 5 |
| Dioxins | ngTEQ/m3（NTP）*1 | 0.05 | 0.00024 | 0.00035 | 0.00013 |
| Mercury | mg/m3（NTP） | 0.05 | <0.0006 | 0.0017 | <0.0007 |
Fig. 5 NOx and CO concentrations during operation
The incineration plant produces high-temperature water with the combustion waste heat generated by waste, and supplies heat to the adjacent waste heat utilization facility as the heat source for the public baths, indoor heated swimming pool, floor heating, and air conditioning. All electric power consumed inside the waste heat utilization facility is also provided by wasteto-energy power generation.
It is estimated that the waste heat utilization facility receives 110000 visitors a year. It contains two large public baths, two open-air baths, a heated swimming pool used as a walking exercise pool, and hot tubs. It also has areas for light exercise (i.e., yoga space, exercise machines), for light meals, and for selling local vegetables. The waste heat utilization facility stimulates the local citizens to interact and improve their health. (Figure 6 and Figure 7).
Fig. 6 Waste heat utilization facility
Fig. 7 Heated swimming pool
The incineration plant expects more than 4000 visitors a year, including students from Funabashi City elementary schools and nearby citizens. There are explanations installed on the visitor’s walkway that explain the units of the incineration plant and their operating states so that visitors can easily understand. Visitors can view the actual operating state of the plant not only through the plant tour windows but also from the data displayed on the monitor in real time (Figure 8). Later on in the tour course, visitors are given a quiz (Figure 9) centered on environmental issues to improve their awareness of these issues. The quiz system has a face recognition function so multiple visitors can participate freely.Visitors can take quizzes on sorting garbage or reviewing what they learned in the tour, and the system rewards those who gave the correct answers by displaying their faces on the monitor. We expect that children will actively participate in the quizzes.
Fig. 8 Explanation item (explanation of how waste is carried in)
Fig. 9 Explanation item (quiz section)
During the construction work, we were considerate of how not to change the surrounding environment or the habitats of local animals and plants. For example, a nesting box is installed on the premises of the new plant for the common kestrels (Falco tinnunculus) that nested on the premises of the existing plant to be demolished. In addition, an attempt was made to transplant the rootstocks of the deforested tall trees into the square of the waste heat utilization facility.
The common kestrels had already begun to make a nest during the construction work period and are currently incubating eggs (Figure 10). The transplanted rootstocks have budded.
Fig. 10 A common kestrel nesting (photographed in the nest box installed on the stack)
The construction of the stoker-type incineration plant was completed in April 2017, and it has been in good operation since, contributing to Funabashi City’s waste disposal services. It also supports the realization of a low-carbon society by making full use of the greatly enhanced power generation capability to supply electric power to the areas outside of the plant.
In conclusion, we would like to sincerely thank to the people of Funabashi City for all their advice and guidance, and all who cooperated in the construction of the incineration plant and the waste heat utilization facility.
1) Akiyasu Okamoto et al.: For the Oyama Wide-Region Health and Hygiene Union - Construction of the energy recovery promotion facility “Chuo Incineration Center 70-Ton Incinerator, ” Ebara Engineering Review, No. 253, pp. 39-43 (April 2017).
2) Takashi Imaizumi et al.: Basic Improvement Work of the “Kameda Incineration Center” in Niigata City, Niigata Prefecture, Ebara Engineering Review, No. 253, pp. 34-38 (April 2017).
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