Issue No. 252〔Delivered Products & Systems〕

Report on Delivery and Operational Condition of Grate-type
(Stoker-type) Incinerator with Advanced Flue Gas Treatment System in China
-Nanjing City, Jiangsu Province-

Author

Kazushige KUROSAWA*

Zhibao
ZHANG**

Zhengbing
WANG**

*

Ebara Environmental Plant Co., Ltd.

**

Ebara Qingdao Co., Ltd.

Ebara’s grate-type incinerators with a treatment capacity of 2 000 t/d (500 t/24 h×4 lines) were delivered to Nanjing City, Jiangsu China, and their performance test was completed in March 2016. Ebara Environmental Plant Co., Ltd. and Ebara Qingdao Co., Ltd, have already delivered incinerators to seven facilities in China: fluidized-bed incinerators to two facilities and grate-type incinerators to five. Three of them have been reported in past issues of the Ebara Engineering Review. This paper reports on the delivery of incinerators to the eighth facility in China, the plant capacity of which is the largest among the eight facilitie
In China, there is a need for ever-more-sophisticated waste incineration technology; in 2014, the relevant national standard of China was revised, and more stringent emission regulation of waste incineration plants were imposed. This paper reports the operating conditions, performance test results, etc., of the sophisticated flue gas treatment facility to meet the more stringent emission regulation.

Keywords: China, Nanjing, Municipal solid waste, Grate-type incinerator, EGR, SCR, Sodium bicarbonate injection

1. Introduction

On March, 2016, The Ebara group delivered grate-type incinerators to a Waste-to-Energy (WTE) Plant in Nanjing City, Jiangsu Province, China, where we conducted a performance test and turned them over. (Figure 1).

This is the second WTE plant in Nanjing. The plant was constructed by Nanjing Waste to Energy Co., Ltd., a special purpose company (SPC) established by Shanghai Environmental group Co., Ltd., which undertook the project from the Nanjing government. The scope of Ebara’s contribution to the project included the basic design of the incineration system (from the waste bunker to the stack) and the supply of the main equipment of the incineration plants. Our past experience allowed us to take into proper consideration China-specific waste characteristics - high moisture and ash content. Thus, we adopted refinements and improvements for the scale-up design of the incinerator.

Fig. 1　Nanjing Waste-to-Energy Plant

2. Overview of Nanjing

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

3. Overview and characteristics of the plant

Table 1 shows the lower calorific values and composition of the waste in Nanjing; Table 2 shows the specifications of the equipment; Figure 3 shows the process flow in the plant; Table 3 shows the emission criteria of the stack outlet flue gas. O211% equivalent is the value according to Chinese standard, O212% equivalent is the value converted to the standard oxygen concentration used in Japan.

Table 1　Lower calorific value of waste and waste composition
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

Table 2　Equipment specification
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：

S N C R：Selective Non Catalytic Reduction
S C R ：Selective Catalytic Reduction

※3：

Ebara’s scope of work: Basic design
SPC’s scope of work: Detail design, Purchase and Construction

※4：

SPC scope: Design, Purchase and Construction

Table 3　The emission value of the stack outlet flue gas
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）

4. Scope of supply, performance warranty and construction schedule

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.

Table 4　Guaranteed values
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%
Table 5　Construction schedule
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

5. Characteristics of the plant

5.1 Adoption of dry type sodium bicarbonate injection

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

5.2 Exhaust gas recirculation (EGR) as NOx Inhibition system and SCR as NOx removal system

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.

6. Performance test results

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.

Table 6　Results of performance test (100% Load)
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

※ 1: Because of some specifications from the SPC, the EGR (exhaust gas recirculation) of Line 3 and Line 4 has not achieved the design result and the result was treated as inapplicable.
※ 2: The SCR was installed only in Line 3 before the performance test.

Fig. 6　Trend of NOx of SCR inlet and outlet

7. Conclusion

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.

References

1) Kazushige Kurosawa, Wang ZhengBing, et al, “Report on the Establishment of the Thermal Disposal Technology for Large-scale Grate-type Incinerators in China and on Stable Operation of Them (second report)”, Collected Papers Associated with the 37th waste Management Research Symposium, (January 2016).
2) Koji KOBAYASHI, Kazushige KUROSAWA, Motoshi ARIHARA, Wenjie YANG, Zhibao ZHANG, and Binglai ZHAO “Report on Delivery and Operational Condition of Large-scale Grate-type (Stoker-type) Incinerator in Nanchang City, Jiangxi, China”, Ebara Engineering Review No.251 (April 2016), pp.32-38.

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