Takahiro YAMAUCHI*
Zhibao ZHANG*
Zhengbing WANG*
Binglai ZHAO*
Wenyuan ZHANG*
Jianjie CHANG*
*Ebara Qingdao Co.,Ltd.
In recent years, the amount of solid waste generated in China has been on the increase, and so controls of appropriate treatment for solid waste have been tightened. Here, we report on the upsizing of facilities in response to market demand for solid waste treatment in China, the stable treatment of solid waste according to the quality and characteristics of local waste, and the improvement of energy recovery technology.
Keywords: China, Municipal solid waste, Waste incinerator, Grate-type incineration system, Fluidized-bed incineration system, Combustion control
At present, the amount of solid waste generated in China is about 600 000 tons or more/day, and it is said that about half of the waste is incinerated and processed for power generation at about 300 facilities. Around 2010, the incineration processing capacity per incinerator was about 300 to 400 t/d, but nowadays, incinerators tend to have a higher incineration processing capacity, around 600 t/d/incinerator. It is anticipated that the amount of solid waste generated in China will continue to increase and demand for solid waste incineration processing facilities will remain firm (Figure 1).
Figure 1. Change in cumulative number and cumulative capacity of solid waste processing facilities in China Source: ACI International Solid Waste Management Summit 2019
In addition, the Chinese government issued the revised version of the Standard for Pollution Control on Municipal Solid Waste Incineration (GB18485-2014), which also applies to sludge produced by water treatment facilities and equipment in addition to municipal waste covered by the conventional Standard for Pollution Control on Municipal Solid Waste Incineration. Under these circumstances, demand for appropriate treatment of sludge is expected to increase at solid waste processing facilities in China in the future.
EBARA Qingdao Co., Ltd. (hereinafter referred to as “EQC”) was founded in Qingdao City, China, in 1992 as an Ebara group company (Figure 2). At present, EQC manufactures boilers, incinerators, and other products for solid waste processing facilities for Japan. Since 2009, it has been engaged in design, procurement, and manufacture of incineration core technology products, such as waste feeding devices and incinerators for solid waste processing for China, and guidance in installation and commissioning of manufactured equipment (EP + SV: Engineering Procurement + SuperVisor) in collaboration with Ebara Environmental Plant Co., Ltd. (hereinafter referred to as “EEP”).
Figure 2. Exterior photo of the EBARA Qingdao Co., Ltd. plant
The Ebara group’s large grate-type incineration systems adopt a structure that combines multiple units in the widthwise direction. This structure enables us to set an appropriate incinera tion capacity by increasing or decreasing the number of units according to the scale of the customer’s solid waste processing facility.
Ebara provides an original thermal expansion absorption mechanism in the joint between units. Based on our experience and findings accumulated through three lanes, which represents the largest number of units in Japan, in 2007 EQC (as the Ebara group) received an order for an grate-type incineration system (300 t/d/incinerator × two incinerators), which was the first grate-type incineration system in China, from Xiamen City (Xiamen East Phase 1), Fujian Province. Then, in 2011, EQC received another order for a grate-type incineration system with an incineration processing capacity exceeding 500 t/d/incinerator (525 t/d/incinerator × two incinerators) for Zhangzhou City1), Fujian Province.
In 2013, EQC (as the Ebara group) received an order for a four-lanes grate-type incineration system (600 t/d/incinerator × two incinerators), which was the first four-lanes incineration system in China, for Nanchang City,2) Jiangxi Province. An internal structural diagram of the four-lanes grate-type incineration system is shown below (Figure 3).
Figure 3. Internal structural diagram of the four-lanes, grate-type incineration system
The grate-type incineration system (750 t/d/incinerator × two incinerators) for Xiamen City, Fujian Province, which was ordered in 2017, has the highest processing capacity per incinerator among four-lanes, grate-type incineration systems. (The system is scheduled to be completed in 2020.)
With the recent trend toward upsizing of solid waste processing facilities in China, EQC has seen an increase from 12% to 29% in the percentage of orders it receives for solid waste processing facilities with an incineration processing capacity of 600 tons or more/day/incinerator (Table 1).
In addition, as the incineration processing capacity per incinerator increases, it is also necessary to upsize waste feeding devices, which feed waste to incinerators. For these, we have adopted a structure that combines multiple units in the widthwise direction, as with grate-type incinerators. The increase in the number of units and the effect of waste quality specific to China (waste quality that is high in bulk density and requires more thrust for waste feeding than waste in Japan) caused meandering of waste feeding devices in early commissioning. This problem was resolved by installing a guide mechanism exclusively to prevent meandering.
As the per-incinerator incineration capacity of grate-type incineration systems increases, combustion stability has become quite important.
EQC has introduced EEP’s original automatic combustion control (ACC) to ensure not only compliance with the regulation values of hazardous substances in exhaust gas, but also stable control of the amount of evaporation that greatly affects the amount of electric power generated (Figure 4).
Figure 4. Control of amount of evaporation by ACC in the case of a four-lanes, grate-type incineration system
ACC has achieved a probability of occurrence of 99.9% or more with a variation range of within ±10% relative to the set value of the amount of evaporation, proving an excellent state of combustion.
Moreover, the width of the four-lanes, grate-type incinerator is about 10 meters, and uniform combustion completion points can be maintained along the overall width. This fact confirms that the state of combustion is good visually (Figure 5).
Figure 5. State of combustion inside a four-lanes, grate-type incinerator
In China, the system for assessing solid waste processing facilities (CJJT137 – Standard for assessment of municipal solid waste incineration plants) defines the introduction of ACC as AAA, which is the highest rank of assessment.
At many solid waste processing facilities in China, however, incinerators are operated manually by supervisors of central control rooms, and there are few facilities that have actually introduced and are making full-scale use of ACC.
EQC is working to improve both combustion stability and customer satisfaction through the utilization of ACC for large grate-type incineration systems.
Of the various kinds of solid waste produced in China, general waste generates a smaller amount of heat compared to Japan. For this reason, to thoroughly combust low-quality waste with a low amount of heat generated, EQC adopts the structural design shown below (Figure 6) for the hardware of the grate-type incinerator body, in addition to ACC, or software.
Figure 6. Features of the grate-type combustion system structure for low-quality waste in China
(1) Using radiation heat
The rear internal wall (goose neck portion) of the grate-type incinerator is designed to drop inside to further facilitate the transmission of radiation heat from the rear internal wall to the combustion stokers and the burn-out stoker.
(2) Improving stirrability
A step is formed between the drying stoker and the Combustion I and II stokers and the burn-out stoker inside the grate-type incinerator to improve turnaround and stirrability of waste.
(3) Securing a sufficient retention time
The distance from the drying stoker to the burn-out stoker inside the grate-type incinerator is designed to be longer than that of grate-type incinerators for use in Japan in order to ensure a sufficient retention time inside the incinerator.
EQC does business mainly in China through EP + SV of incineration core technology products. Recently, modification projects (S&S: Service and Support) in the operation phase of facilities delivered by EQC have been on the increase as well.
In particular, changes in collected waste (reduced kitchen garbage, increased cardboard due to increased door-to-door delivery services, etc.) are speeding up the quality improvement of electric power generated from waste (standard quality: 6 700 to 7 500 kJ/kg) compared with what was anticipated at the time of the design of the delivered facility. This causes a problem where the amount of waste to be processed must be reduced to control the rise of the internal temperature of the incinerator.
Thus, EQC carried out modification work of additionally installing a heat recovery water pipe called a water wall inside the grate-type incinerator to increase the heat transfer area. This significantly enhanced the amount of heat recovery evaporation and also increased the amount of electric power generated by about 18 288 000 kWh a year (Table 2).
Such S&S cases are not yet popular in China, but we will offer problem-solving proposals based on the design capabilities that EQC has accumulated through EP + SV and EEP’s experience in cases of life extension works in the phase of facility operation.
Moreover, China is imposing stricter guidance on the appropriate processing of industrial waste, such as sludge and hazardous waste based on the revised version of the Standard for Pollution Control on Municipal Solid Waste Incineration (GB18485-2014) and the Pollution Control Standard for Hazardous Waste Incineration (GB18484-2001).
In line with this, there is an ongoing extreme diversification of the kinds of waste that are required to be incineration-processed in China, including sludge and hazardous waste.
As a solution to this situation, EQC proposes the fluidized-bed incinerator system, which is one of the Ebara group's optimal incinerator types (models), and it has received an increasing number of orders (number of incinerators) (Table 3).
The fluidized-bed incinerator system4), thanks to the uniformity of temperature inside the fluidized bed achieved by its distinguished heat transfer characteristic, features the capability to perform mixed combustion processing of substances with a single incinerator, from processed substances generating a small amount of heat, such as sludge, to processed substances generating a large amount of heat, such as waste oils and waste plastics. We will utilize the findings and experience we have gained in Japan to further introduce the Ebara group's optimal incinerator types (models) to China as the main market (Figure 7).
Figure 7. Examples of the Ebara group's incineration technologies (schematic diagram of Grate-type incineration system and Fluidized-bed incineration system)
EQC initially delivered solid waste processing facilities only within China, where it is located, and mostly to coastal cities, with a relatively large amount of solid waste generated.
In recent years, however, it has delivered facilities also to inland regions of China as well as overseas (Singapore) in response to the expansion of the regions in which its customers operate the solid waste processing business.
The solid waste processing facility delivered to Singapore has a processing capacity of 143 t/d/incinerator × four incinerators. It processes industrial waste, mainly wet sludge (amount of heat generated: 2 900 kJ/kg), and adopts a fluidized-bed incinerator system. The facility is scheduled to be completed this year (2019), and we report on its incineration characteristics, performance test results, etc. in another article in this Engineering Review.
EQC is determined to further commit to technical improvements in response to market needs for solid waste processing facilities, and to contribute to the establishment of a sustainable society, which is a common issue not only in China but also around the globe, through the stable processing of solid waste, energy recovery, and other areas.
To conclude, we would like to express our deep gratitude to all those who cooperated in EQC’s individual projects of solid waste processing facilities.
1) Kurosawa, Kobayashi, Tian, Wang, Shan, Report on Delivery and Operational Condition of Large-Scale Grate-Type (Stoker-Type) Incinerators in Zhangzhou City, Fujian, China, EBARA Engineering Review, No. 250, pp.76-83 (January 2016).
2) Kobayashi, Kurosawa, Arihara, et al., Report on Delivery and Operational Condition of Large-Scale Grate-Type (Stoker-Type) Incinerators in Nanchang City, Jiangxi, China, EBARA Engineering Review, No. 251, pp.32-38 (April 2016).
3) Kurosawa, Saku, Sato, Tian, Wang, Report on Delivery and Operation Condition of Large-Scale Grate-Type Incinerators in Weihai City, Shandong, China, EBARA Engineering Review, No. 235, pp.23-28 (April 2012).
4) Matsuoka, Imaizumi, Performance of Fluidized-Bed Incineration Facilities and Their Potential, EBARA Engineering Review, No. 253, pp.64-68 (April 2017).
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