Kazushige KUROSAWA*
Zhibao ZHANG**
Zhengbing WANG**
*
Ebara Environmental Plant Co., Ltd.
**
Ebara Qingdao Co., Ltd.
Fig. 1 Nanjing Waste-to-Energy Plant
Nanjing City, the capital of Jiangsu Province, China, is the center of politics, the economy and culture, as well as a strate gic point in the traffic patterns for Jiangsu. The city has an area of 6 597 km2 with a population of approximately 8.18 million. Nanjing, the ancient capital of the Six Dynasties, well known as a historical and cultural city built about 2600 years ago, has been a major city in the region of the Yangtze River basin in South China.
Nanjing, with its warm and humid climate, is very hot and humid in summer. Nanjing, Chongqing and Wuhan are famous for being the hottest cities in China and are colloquially referred to as “The Three Furnaces”.
Figure 2 shows the location of Nanjing in China.
Fig. 2 Location of Nanjing, Jiangsu, in China
| Item | Low-calorific Value waste |
Design waste |
High-calorific Value waste |
| Lower calorific value | 4187 kJ/kg | 6699 kJ/kg | 8374 kJ/kg |
| Moisture content | 56.1% | 48.4% | 43.2% |
| Combustible content | 25.2% | 33.4% | 38.9% |
| Ash content | 18.5% | 18.1% | 17.8% |
Fig. 3 Flow sheet of plant
| Item | Specification |
| Incinerator | Model HPCC from Ebara※ 1
Grate-type Incinerator |
| Capacity: 2 000 t/d (500 t/24 h×4 lines) | |
| Boiler※3 | Type: Natural-circulation water tube boiler with superheaters |
| Steam capacity: 47.0 t/h (Max. 51.7 t/h)×4 units | |
| Steam condition: 400 ℃× 4.0 MPaG (at the outlet of the superheater) | |
| Steam turbine generator※4 | Steam turbine (condensing type) + generator |
| Steam turbine: 18 MW × 2 units | |
| Generator: 20 MW × 2 units | |
| Flue-gas treatment facility※3 | Dust collector type: Bag filter |
| Removal method of HCl・SOx: Semi-dry type system (slaked-lime slurry rotary atomizing injection) + dry type system (sodium bicarbonate injection) |
|
| De-NOx method: SNCR※ 2+ SCR※ 2 | |
| Removal method of dioxins・Hg compounds: activated carbon injection |
|
| Stack※3 | External wall: Reinforced concrete structure Internal stack: Carbon steel |
| Height: 80 m |
※1：
HPCC: High Pressure Combustion Control
※2：
※3：
※4：
SPC scope: Design, Purchase and Construction
| Item | O211% equiv. | O212% equiv. |
| Dust | ≦8.0 mg/m3（NTP） | ≦7.2 mg/m3（NTP） |
| Sulfur oxides (SOx) | ≦50 mg/m3（NTP） | ≦15.8 ppm |
| Nitrogen oxide (NOx) | ≦80 mg/m3（NTP） | ≦35.1 ppm |
| Hydrogen chloride (HCl) | ≦10 mg/m3（NTP） | ≦5.5 ppm |
| Carbon monoxide (CO) | ≦50 mg/m3（NTP） | ≦36.0 ppm |
| Hydrogen fluoride (HF) | ≦1 mg/m3（NTP） | ≦1.0 ppm |
| Dioxins | ≦0.1 ng-TEQ/m3（NTP） | ≦0.09 ng-TEQ/m3（NTP） |
In China, differently from Japan, construction of WTE plants is often undertaken by the SPC itself which conducts the project. Consequently, we are responsible for the basic design (from the waste bunker to the stack, including part of the detailed design) of the incineration system, the delivery of main equipment (grates, hydraulic drive units, burners, the ACC system, and waste hopper level sensors), and dispatching supervisors. Guaranteed values are shown in Table 4.
Table 5 shows the Construction schedule.
It took 3 years and 2 months from the signing of the contract to hand-over.
| Item | Guaranteed value |
| Annual total operation time | 8 000 hours or longer |
| Operating load range (incineration load) |
60% to 110% 110% within 2 h/d |
| The temperature of furnace outlet | 850 ℃ or higher at 2 seconds or longer |
| Ash ignition loss | 3％ or less |
| Boiler efficiency | 80％ or higher |
| Grate replacement ratio | Operation time 8 000 hours less than 4% 16 000 hours less than 11% 24 000 hours less than 15% 32 000 hours less than 18% |
| Mile stone | Schedule |
| Contract | January 2013 |
| Equipment installation | July 2013 to September 2014 |
| Commissioning (Waste incineration) | January 2015 to March 2016 |
| Hand-over | March 2016 |
Nanjing city is near the border of Anhui Province; to restrain hazardous gas diffusion to other provinces, very strict emission standards are in place. To meet the hydrogen chloride emission criterion of less than 10 mg/m3 (NTP), a wet scrubber system is most effective, but, because of its large water supply requirement, the discharge of drainage, and decreases in power generation, it was not adopted by the SPC.
To ensure meeting the strict emission criteria, based on the semi-dry reactor chosen by the SPC, we suggested at the basic design stage using sodium bicarbonate as dry injection to fulfill the emission criteria; this suggestion was ultimately adopted.
For the concentration of HCl at the inlet of the flue gas treatment facility and the outlet of the stack, see Figure 4; for the SOx concentration, see Figure 5. The guaranteed value of HCl is 10 mg/m3 (NTP) and the real average emission value is about 5 mg/m3 (NTP); the removal rate is as high as 98.5%. In addition, the guaranteed value of SOx is 50 mg/m3 (NTP) and the real average emission value is about 3 mg/m3 (NTP); the removal rate is as high as 91%.
Fig. 4 Trend of HCl for the inlet of flue gas treatment facility and the outlet of stack
Fig. 5 Trend of SOx for the inlet of flue gas treatment facility and the outlet of stack
GB18485-2014 (municipal waste incineration pollution control standards) was revised in 2014, and the new NOx emission criteria for municipal solid waste incineration plants was 250 mg/m3 (NTP) at O211% equivalent (about 110 ppm at O212％ equivalent).
However, because of the customer requirements and site conditions of the plant, sometimes the plant emission criteria are more strict than national standards, so it is necessary to adopt appropriate technology to meet such requirements.
The NOx emission criteria for the plant is below 80mg/m3 (NTP) at O211% equivalent (about 35 ppm at O212％ equivalent), which is more strict than the NOx emission criteria in Japan in most cases. So in the basic design stage, EGR with low air ratio operation was suggested by Ebara to reduce NOx generation. In addition to SNCR, SCR were also suggested to meet the strict emission value. As a result, the customer decided to adopt SCR only for Line 3 incinerator.
The principle of SCR is that ammonia and NOx are under chemical reaction by catalysts to convert NOx into N2 and H2O.
SCR is common in Japan waste incineration plants but was newly introduced in China, with this plant.
Except for some untested items because of some specifications from the SPC, all the items met the guaranteed values in the performance test. For the results of the performance test, see Table 6.
The detailed effects of EGR have been reported in the latest journal2); here, the operation data with SCR are shown in Figure 6.
SCR was installed only in Line 3; therefore, the figure 6 refers to the data of Line 3. Because it was not able to perform the designed effect of EGR in Line 3 because of some specifications from the SPC, the measurement was about 100 mg/m3 (NTP) of NOx concentration at the inlet of the SCR (at the outlet of boiler), which was a little higher than the original design. On the other hand, the NOx concentration at the outlet of the SCR was decreased to less than 50 mg/m3 (NTP), so the removal ratio of the SCR was more than 50%. This result demonstrates the capacity of the SCR system, when the NOx regulation level becomes more severe in future.
| NO. | Test item | Unit | Guaranteed value | Line 1 | Line 2 | Line 3 | Line 4 | Conclusion |
| 1 | Steam temperature at the outlet of Boiler | ℃ | 400 (+5, -10) |
398.6 | 398.1 | 401.4 | 400 | Qualified |
| 2 | Boiler efficiency | % | ≧80 | 82.56 | 81.58 | 82.88 | 81.29 | Qualified |
| 3 | Retention time of flue gas of 850 ℃ or higher | s | ≧2 | 3 | 3.2 | 3.3 | 3.2 | Qualified |
| 4 | NOx（NTP，dry，O211%） | |||||||
| NOx at boiler outlet with SNCR | mg/m3（NTP） | ≦80 | 78.2 | 72.5 | −※1 | −※1 | −※1 | |
| NOx at SCR outlet | mg/m3（NTP） | ≦80 | − | − | 46.7※2 | − | −※1 | |
| 5 | Flue gas at stack outlet (NTP, dry, O211%) | |||||||
| DUST | mg/m3（NTP） | ≦8 | 4 | 3.3 | 4.1 | 4.1 | Qualified | |
| HCl | mg/m3（NTP） | ≦10 | 7.2 | 3.6 | 7.4 | 6.5 | Qualified | |
| HF | mg/m3（NTP） | ≦1 | 0.7 | 0.6 | 0.8 | 0.7 | Qualified | |
| SOx | mg/m3（NTP） | ≦50 | 8.9 | 1.7 | 1.6 | 0.1 | Qualified | |
| CO | mg/m3（NTP） | ≦50 | 6.6 | 24.2 | 4.4 | 15.3 | Qualified | |
| TOC | mg/m3（NTP） | ≦10 | 2 | 1.7 | 4.4 | 1.4 | Qualified | |
| Hg and compounds | mg/m3（NTP） | ≦0.05 | ＜0.0003 | ＜0.0003 | ＜0.0003 | ＜0.0003 | Qualified | |
| Cd and compounds | mg/m3（NTP） | ≦0.05 | ＜0.008 | ＜0.008 | ＜0.008 | ＜0.008 | Qualified | |
| Pb+Cr and other heavy metals | mg/m3（NTP） | ≦0.5 | 0.31 | 0.1 | 0.29 | 0.18 | Qualified | |
| Black degree of flue gas | Ringelman | ≦1 | ＜1 | ＜1 | ＜1 | ＜1 | Qualified | |
| Dioxins | ng-TEQ/m3（NTP） | ≦0.1 | 0.088 | 0.075 | 0.075 | 0.063 | Qualified | |
| 6 | Incineration capacity | t/d | 500 | 535.56 | 561.44 | 536.19 | 550.78 | Qualified |
| 7 | Ash ignition loss. (wet ash) | % (weight) | ≦3 | 2.06 | 2.78 | 2.88 | 2.64 | Qualified |
Fig. 6 Trend of NOx of SCR inlet and outlet
In the large cities in China, many large-scale waste incineration plants have been constructed and the emission regulations have become equivalent to or stricter than those in developed countries in recent years.
We are looking forward to contributing to the demand of waste incineration plants in China and the environmental protection causes based on our technological improvements and experience.
Finally, we would like to express our grateful thanks to all the people who cooperated to this project.
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