Koji KOBAYASHI*
Binglai ZHAO*
Zhang JIANDONG*
Liu JINRONG*
Zhu MINGLEI*
Cong PENGFEI*
*
EBARA QINGDAO CO., LTD.
In October 2020, the EBARA Group delivered a grate-type incineration system for the Xiamen East Phase II waste incineration facility in Xiamen City, Fujian Province, China (Figure 1).
Fig. 1 Xiamen City east waste incineration plant II
The nominal capacity of this facility is 750 t/d (750 tons/day/furnace), but it has a treatment capacity of 900 t/d since continuous operation at 120% load is required by agreement.
This is the third facility we have delivered an incineration system to in Xiamen City, with a treatment capacity that is three times that of the Xiamen East Phase I Facility (nominal capacity: 300 t/d) which was delivered first, and roughly 1.4 times that of the Xiamen West Phase II Facility (nominal capacity: 625 t/d) which was delivered next. Table 1 shows an outline of the Xiamen East Phase I and Xiamen West Phase II facilities to which systems have been delivered.
Table 1 Xiamen East I & Xiamen West II plant summary
In China, waste materials are characterized by high moisture content and extremely high ash content. The EBARA Group has applied its past experience and achievements to establish design technology for grate-type incinerators suited to handle this characteristic composition of waste in China, and has gradually accumulated successful results in facility upsizing.
The Xiamen East Phase II Facility is one of the largest capacity incineration systems among the projects undertaken by the EBARA Group. We have achieved large-scale, stable operation of the facility through design ideas and improvements for upsizing its incineration furnaces.
Xiamen City, Fujian Province, is one of the five special economic zones in China, and is a central city in southeastern China designated as a sub-provincial city. Furthermore, Xiamen has an important trading port and is known as “the garden on the sea” for its beautiful natural environment.
The city covers 1 700 km2 in area and has a population of roughly 5.16 million. It is located in the south subtropical oceanic monsoon climate zone with an annual average temperature of 21°C, and it has a particularly rainy season from March to September in which approximately 80% of the annual precipitation falls. It also often suffers natural disasters such as thunderstorms and typhoons. Figure 2 shows the location of Xiamen City in mainland China.
Fig. 2 Location of Xiamen City, Fujian in mainland China
Table 2 shows the design values for the lower calorific value and composition of waste at the Xiamen East Phase II Facility.
| Item | Low-calorific value refuse | Design refuse | High-calorific value refuse |
| Lower calorific value | 4 600 kJ/kg | 8 000 kJ/kg | 10 000 kJ/kg |
| Water content | 50.7 wt% | 40.3 wt% | 33.5 wt% |
| Combustible content | 28.3 wt% | 40.7 wt% | 48.4 wt% |
| Ash content | 21.0 wt% | 19.0 wt% | 18.1 wt% |
The main equipment specifications of the Xiamen East Phase II Waste Incineration Facility are shown below. Note that equipment items (2) to (5) are scope of the customer.
(1) Incineration furnace
Type: Grate-type incinerators
Rated treatment capacity: 1,500 t/d (750 t/d x 2 furnaces)
Maximum treatment capacity: 1 800 t/d (900 t/d x 2 furnaces)
(2) Boilers
(3) Steam turbine power generation equipment
(4) Exhaust gas treatment equipment
Exhaust gas treatment system: SNCR + semi-dry type harmful gas treatment (slaked lime slurry spray) + dry type harmful gas treatment (slaked lime) + activated carbon spray + bag filter + wet type harmful gas treatment + SCR
(5) Stack
(6) Pollution control standard values [standard values of exhaust gas at stack outlet]
Table 3 shows the pollution control standard values for reference, although they are not the EBARA Group’ scope of guarantee.
| Item | Unit | Regulation value | Remarks |
| Dust*1 | mg/m3（NTP） mg/m3（NTP） |
5 or less 4.5 or less |
O211% converted value O212% converted value |
| SOx*1 | mg/m3（NTP） ppm |
10 or less 3.1 or less |
O211% converted value O212% converted value |
| NOx*1 | mg/m3（NTP） ppm |
50 or less 22 or less |
O211% converted value O212% converted value |
| HCl*1 | mg/m3（NTP） ppm |
5 or less 2.76 or less |
O211% converted value O212% converted value |
| CO*1 | mg/m3（NTP） ppm |
50 or less 36 or less |
O211% converted value O212% converted value |
| Dioxins*1 | ng-TEQ/m3（NTP） ng-TEQ/m3（NTP） |
0.1 or less 0.09 or less |
O211% converted value O212% converted value |
*1: The second line for each pollution control standard value indicates the value converted to standard oxygen concentration, which is the unit used in Japan.
Figure 3 shows the process flow diagram of this facility.
Fig. 3 Process flow diagram of the facility
Collected household waste is stored in a waste bunker, and then dried by moisture separation and a temperature rise resulting from fermentation, causing the calorific value to increase. The waste is then loaded into a waste hopper by a waste crane, sent to incineration furnaces via waste feeder, and incinerated at high temperatures of 850°C or more.
The high-temperature exhaust gas generated by the incineration furnaces is heat-recovered in a boiler and its temperature is lowered to 190°C. It is then cooled down to 155°C in a semi-dry reactor, while acidic substances are removed at the same time using slaked lime slurry. Next, the exhaust gas is mixed with slaked lime and activated carbon sprayed in the flue gas duct, as the acid gas is neutralized and heavy metals and dioxins are adsorbed. After that, fly ash, salts produced by the neutralization, and the heavy metals and dioxins adsorbed by the activated carbon are separated and removed using a dust collection filter. The exhaust gas after dust has been removed, the exhaust gas is further treated by a wet harmful gas removal device to remove acidic gas, and subsequently denitrated by catalytic reactions in a catalytic reaction tower. It is then discharged into the atmosphere from the stack by an induced draft fan.
The bottom ash discharged from the incineration furnace is cooled by a bottom ash discharger and then transferred to an ash pit for temporary storage. Following that, the bottom ash is loaded onto ash transportation vehicles by an ash crane and transported outside of the facility.
The fly ash captured by the dust collection filter and other components is sent to an ash silo on a conveyor and temporarily stored there. After that, it is mixed with water, cement, and a chelating agent in a fly ash treatment device and then transferred to a disposal site by fly ash transportation vehicles.
Unlike facilities for Japan, the construction of waste incineration facilities in China is performed by a SPC*
2 which undertakes the waste treatment business, and the incineration plant manufacturer delivers the incineration furnaces and other main equipment.
The scope of the EBARA Group’s delivery for the Xiamen East Phase II Waste Incineration Facility covers the basic design of the incineration system (including some detailed design), the delivery of main equipment (grate-type incinerators, hydraulic equipment, burners, fans, conveyors, ACC, waste hopper level meters), and the dispatch of supervisors.
*2: Abbreviation for “Special Purpose Company,” referring to a company with a specific purpose who is responsible for management of waste incineration facility.
In August 2017, the EBARA Group concluded a formal agreement with the SPC for the Xiamen East Phase II Facility, and in October 2020, completed a 72 + 24-hour test*
3 and delivery of the equipment.
Table 4 shows the detailed construction schedule.
Table 4 Construction schedule
After the conclusion of the agreement, the design works was promptly started, and the installation of the equipment delivered by the EBARA Group was completed in July 2020. Figure 4 shows the installation status of the stokers, and Figure 5 shows the installation status of the waste feeder .
Fig. 4 Stoker installation
Fig. 5 Waste feeder installation
No-load commissioning of the entire facility was carried out from June to the end of August 2020, and waste feeding began from September 2020 to start load commissioning. A “72 + 24-hour test” was commenced on October 2, 2020 and completed on October 6, 2020.
*3: A 72 + 24-hour test is a test verification method for thermal power plants unique to China, in which a plant performs rated treatment operation for 72 + 24 consecutive hours.
The incineration system delivered to this facility was the first unit, which has a treatment capacity of 900 t/d. This is the largest in the world among incineration systems delivered by the EBARA Group, improved from the conventional design in order to accommodate upsizing.
The EBARA Group’s large grate-type incinerators use a structure combining multiple units in the width direction according to the treatment capacity. By installing original thermal expansion absorption mechanisms at the joints of the unit to address thermal expansion during operation, upsizing of the incineration furnaces has been made possible.
The facility adopts a four-row (four-run) type grate incinerator combining four units in the width direction. Each row (run) is divided into a dry stoker, a combustion stoker I, a combustion stoker II, and a post-combustion stoker, in the traveling direction of waste. Each stoker is independently driven, and the frequency of their operation can be set individually.
Although the EBARA Group has already delivered multiple four-run type grate-type incinerators for incineration facilities in China, for this facility we have implemented several special steps to improve the combustion efficiency, in order to support the properties of waste in China which is characterized by high moisture content and extremely high ash content.
To facilitate the transportation of waste, inclined type stokers were adopted for the dry stoker and the combustion stoker I. Furthermore, horizontal stokers were adopted for the combustion stoker II and post-combustion stoker, to ensure complete combustion of waste and reduce the ignition loss of ash, while the total length of the stokers has been increased from conventional types.
In addition, in order to accommodate waste in China which is difficult to burn, steps intended to disentangle waste and promote combustion have been located at the outlet of the dry stoker and the outlet of combustion stoker I.
Figure 6 shows the structures of the stokers in this facility.
Fig. 6 The structure of 4-row Slope Attached Long type grate-type incinerator
Air necessary for the combustion of waste is supplied from under-furnace chutes in the lower areas of the stokers, while the amount of air to each chute can be individually changed. By adjusting the frequency of operation of each stoker and the combustion air capacity of each chute according to changes in the properties of waste and the treatment capacity, it will be possible to achieve stable combustion in response to a wide range of waste properties.
During load commissioning, waste transported into the waste bunker was stored for five to seven days, and after the calorific value of the waste was raised, it was fed into the incineration furnaces.
The lower calorific value (analysis value in the 72 + 24 hour rated treatment commissioning) of the waste fed into the incineration furnaces was roughly 7 500 kJ/kg on average (6 800 to 8 600 kJ/kg), which was close to the design waste property of 8 000 kJ/kg. The composition of waste consisted of roughly 17% ash, roughly 52% moisture, and roughly 31% combustible content by weight ratio.
In the load commissioning procedure which was continued for approximately one month, it was confirmed that there were no problems with the mechanical functions of the grate-type incinerators and that their operation was stable.
The status of combustion in the furnaces was also good, and it was possible to maintain a uniform combustion completion point on the stokers which were roughly 12 m in width. It was also confirmed that the outlet temperatures of the furnaces were kept to an optimal high temperature of 950 to 1 050°C, and that the retention time of high-temperature gas exceeded the design conditions.
Figure 7 shows the status of combustion in this facility, and Figure 8 shows the outlet temperatures of the incineration furnaces and the amounts of steam generation, during load commissioning.
Fig. 7 Situation of combustion
Fig. 8 Trend of furnace outlet temperature and steam generation
This facility is required to operate under a 120% load for 24 hours a day at its rated treatment capacity of 750 t/d. The actual scale of the facility is 900 t/d, which is the maximum treatment capacity.
The data actually obtained during the one-month period of load commissioning shows that the number of days of operation exceeding the maximum treatment capacity of 900 t/d was approximately one-fourth of the period. Also, the average treatment capacity was 869 t/d (116% load of the rated treatment capacity), and the maximum treatment capacity was 1 118 t/d (149% load of the rated treatment capacity, and 124% load of the maximum treatment capacity). (In China, no statutory control is imposed on overload operation, and continuous overload operation is allowed as long as the safety of the equipment is ensured) The ignition loss of the main ash was also low, and its actual average and maximum values for a period of one month were 1.31% and 2.5%, respectively.
Figure 9 shows the actual incineration amounts during load commissioning.
Fig. 9 The waste incineration amount in 1 month
The 72 + 24-hour test of the facility was completed in October 2020, and it has continued to operate smoothly since then.
The incineration furnaces delivered to the facility were the first large grate-type incinerator with a maximum treatment capacity of 900 t/d/furnace for the EBARA Group. The facility has been satisfactorily adapted to waste in China and has achieved stable operation. It has allowed us to obtain knowledge, findings, and practical experience for upsizing that exceeds 1 000 t/d/furnace.
In China, the construction of waste incineration facilities has begun to spread from large cities in coastal areas to medium and small-sized cities in inland areas, so high-performance incineration systems compatible with various facility sizes are being required.
The EBARA Group is determined to respond to the demands of the Chinese market through ongoing technological improvements based on the experience we have accumulated in the past.
Finally, we would like to express our deepest gratitude to all those involved in this project for their cooperation.
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