Issue No. 252〔Delivered Products & Systems〕

Construction of Municipal Waste Treatment Plant
“Clean Plaza Yokote”

Author

Keisuke
TSUKAMOTO*

Kenichi
NISHIYAMA*

Minoru
SASAKI*

Minoru
KANAZAWA*

Koichi
SATO*

Yoichi
HIRAKAWA*

*

Ebara Environmental Plant Co., Ltd.

On March 30, 2016, the Clean Plaza Yokote, a new integrated waste treatment plant, which we delivered in Yokote in Akita Prefecture, was completed. This plant consists of a heat recovery facility and a recycle center. The heat recovery facility uses our latest and proven system, EBARA HPCC21 stoker, to allow operation at a low air ratio of 1.3 or less, and the boiler steam conditions with high-temperature and high-pressure (4 MPa × 400 °C), which is the highest level for facilities of this scale in Japan. As a result, the gross power generation efficiency has been significantly improved to reach to as high as approximately 20%. We confirmed that the recycle center can recover iron and aluminum at high purity of over 98%. The plant also uses natural energy proactively with a solar power system, and a snow storage chamber that stores snow in winter and uses it for air conditioning in summer. Another important feature of the plant is that it stores necessary stockpiles and secures sufficient space so that it can work as a logistic support center during disasters.

Keywords: Municipal waste, Grate-type incinerator, Incineration plant, Environment, Recycle, Low air ratio combustion, Dioxins, Gross power generation efficiency

1. Introduction

At the end of March 2016, we delivered Clean Plaza Yokote to Yokote City, Akita Prefecture (Figure 1). Clean Plaza Yokote is a new waste treatment plant constructed as an integration of the three aged waste treatment plants in the city. This plant consists of a heat recovery facility capable of processing 95 tons of combustible waste a day using two state-of-the-art, grate-type incinerators and a recycle center capable of treating 9 tons of incombustible and bulk wastes and 21 tons of recyclables per day.

Clean Plaza Yokote is the first waste treatment plant in Akita Prefecture that is built based on the design/ build/operate (DBO) approach (under a 20-year comprehensive contract covering design, building, and operation). For this project Ebara Environmental Plant Co., Ltd., as a representative company, formed a consortium with two local construction companies, Itoken Corporation and Yokote Construction, for design, material procurement, and construction of the plant. Since the plant started operation, a SPC (special purpose company) capitalized by Ebara has undertaken to manage and operate the plant as well as management of recycle waste over the next 20 years.

Fig. 1 Clean Plaza Yokote

2. Overview of the plant

Figure 2 shows the entire plant.

Fig. 2 Overview of the facility

2.1 Waste receiving system

In the old waste treatment plants in Yokote City many citizens brought their waste in private cars, sometimes forming a line of waiting cars extending even outside the premises. Under the circumstances, the Clean Plaza Yokote has introduced an IC card system into the weighing system for bringing-in and -out of waste, to achieve shorter time for weighing, aiming to prevent the plant from being crowded with garbage trucks and private cars bringing in waste. In addition, for safety and convenience of private citizens bringing in waste, the plant provides a one-stop service that allows all brought-in mixed waste to be received at a single dedicated location inside the recycle center.

2.2 Heat recovery facility

Figure 3 and Table 1 show the process flow at the heat recovery facility and the overview of its main systems, respectively. Table 2 shows the emission criteria.

Fig. 3 Process flow at the heat recovery facility

Table 1 Overview of the systems at the heat recovery facility
Receiving and feeding equipment
Waste bunker Two-stage bunker consisting of input bunker and storage bunker
Waste crane Two full automatic cranes
Incineration equipment
Incinerator Full continuous-combustion, grate-type incinerator (Model HPCC21 from Ebara)
Capacity: 95 t/d (47.5 t/d x 2 units)
Combustion-gas cooling equipment
Boiler Natural-circulation water tube boiler with superheaters
Evaporation: max. 6.4 t/h x 2 units
Steam conditions: 4.0 MPa x 400 ℃ (at the outlet of the superheater)
Generating equipment
Steam turbine One-extraction 9-stage impact type condensing turbine
Generator Three-phase synchronous generator with a capacity of 1 670 kW
Flue gas treatment equipment
Method of cooling flue gas Water injection
Dust collection method Bag filter
NOx reduction method Selective non-catalytic reduction based on urea solution
HCl and Sox removal method Dry (slaked-lime blowing)
Measures against dioxins and mercury Activated carbon blowing
Waste-heat utilization equipment
Major usage of waste heat Road heating by using turbine exhaust
Ash-removal and -treatment equipment
Incinerated ash Carried out using ash bunker and crane to be recycled as raw material for cement at the Ofunato factory of Taiheiyo Cement Corporation
Fly ash Chelated and then carried out using ash bunker and crane
Wastewater treatment equipment
Plant waste water Coagulated and sand-filtered, and then reused within the premises, without being discharged
Domestic waste water Treated in a combined septic tank, and then discharged
Refuse sewage Circulated inside the bunker
Table 2 Emission criteria
Restricted substance Criteria value
Dust g/m3（NTP）※1 0.007 or less
Hydrogen chloride ppm※1 50 or less
Sulfur oxides ppm※2 30 or less
Nitrogen oxides ppm※1 80 or less
Carbon monoxide ppm※1(average per 4 hours)
　　　　(average per hour)
20 or less
80 or less
Dioxins ng-TEQ/m3（NTP）※1 0.04 or less
※1　Value for 12% of O2 under dry condition
※2　Unconverted value under dry condition

2.3 Recycle center

Figure 4 and Table 3 show the process flow at the recycle center and an overview of its systems.

Fig. 4 Process flow at the recycle center

Table 3 Overview of the systems at the recycle center
Line for incombustible waste and bulk waste
Capacity 1.8 t/h
Crushing method Low-speed, biaxial shearing + high-speed vertical rotation
Screening and recovery method
　1）Iron Separated with a magnetic separator for use as recyclables
　2）Aluminum Separated with an aluminum separator for use as recyclables
　3）Residua combustible and incombustible waste
Incinerated at the heat recovery facility
Line for cans
Capacity 0.38 t/h
Screening and recovery method
　1）Iron Separated with a magnetic separator and compacted with a compacting machine for reuse as pressed steel cans
　2）Aluminum Separated with an aluminum separator and compacted with a compacting machine for reuse as pressed aluminum cans
　3） Inappropriate waste
Manually separated and crushed
Line for bottles
Capacity 1.14 t/h
Screening and recovery method
　1）Returnable bottles
Manually separated and collected in special
containers as recyclables
　2）Clear bottles Manually separated and recycled as cullet
　3）Brown bottles Manually separated and recycled as cullet
　4）Other color bottles Manually separated and recycled as cullet
　5）Inappropriate waste Manually separated and then crushed
Line for waste paper
Capacity 2.58 t/h
Recovery method
　1）Newspaper Compression baled for use as recyclables
　2）Magazines Compression baled for use as recyclables
　3）Corrugated cardboard Compression baled for use as recyclables
Other recyclables
　1）Metals Stored and recovered for use as recyclables
　2）Dry batteries Stored and recovered
　3）Small home appliances Stored and recovered for use as recyclables
　4）Glass and ceramic products Stored and recovered for use as recyclables
　5）Clothes Stored and recovered for use as recyclables
　6）Fluorescent tube Stored and recovered

3. Construction schedule

Table 4 shows construction milestones.

Table 4 Construction schedule
Contract conclusion Jun-2013
Start of land creation Aug-2013
Start of building construction Mar-2014
Start of plant installation Jul-2014
Initial power receiving Aug-2015
Start of comissioning Nov-2015
Performance test Feb-2016
Completion End of March 2016

4. Features of the plant

4.1 Adoption of the grate-type incinerator HPCC21

Clean Plaza Yokote uses the EBARA incinerator model HPCC211), a state-of-the-art, grate-type incinerator. This provides stable operation with an air ratio between 1.2 and 1.3, greatly contributing to improved boiler efficiency, and further to improved power generation efficiency.

4.2 High efficiency power generation using steam condition of 4 MPa x 400 °C

With top priority placed on safe, stable waste treatment, the plant was designed to improve power generation efficiency with the goal of acting as a regional energy center. For improving power generation efficiency, the most critical thing is to increase the steam temperature and pressure of the boilers. Based on our past accomplishments, we designed the steam conditions with 4 MPa x 400 °C, the highest level for boilers with the same scale as in this plant in Japan, as well as increasing the vacuum degree of the condensers. As a result, we obtained the gross power generation efficiency of 19.6% as a design value. In Figure 5 we added the value for Clean Plaza Yokote (shown as a star mark) in the Reference Fig. 1-2: Actual and Calculated Power Generation Efficiencies at Waste Incineration Plants from Reference Material #1 in Manual for Maintaining Facilities for Efficient Power Generation by Refuse Incineration 2) issued by the Ministry of the Environment. Compared with the past actual values and the calculated values for 4 MPa x 400 °C, the generating efficiency of ca. 20% achieved at Clean Plaza Yokote is proven very high for plants with a capacity of 100 t/d.

Fig. 5 Power generation efficiency at Clean Plaza Yokote

4.3 Function as a logistics support center during disasters

Clean Plaza Yokote is positioned by Yokote City as a wide-area logistics support center during disasters. For this reason, prepared for unexpected disasters, the plant is designed with the following points taken into consideration:

（1）Earthquake-resistant design

The most important point for the logistics support center is to be highly earthquake-resistant. To this end, the buildings are structurally designed so that they can be safely used even after a large earthquake and can store and treat disaster waste generated by earthquakes in a prompt manner.

（2）Waste treatment during disasters

The plant has a waste bunker with a capacity of 3600 m3 to store as much disaster waste as possible, corresponding to a capacity for 15 days.

In addition, the plant is designed to allow an incinerator and a boiler to be started with an emergency diesel generator so that waste can be treated even if power from the electrical grid is lost during a disaster. Once activated, the incinerator and the boiler can start up the regular steam-turbine generator, allowing the second incinerator to be operated.

Furthermore, the plant is equipped with a well-water pumping system and a pretreatment system that allow continuous operation of the incinerators by supplying well-water as plant water even if the waterworks is lost.

（3）Logistics support center

Functioning as a logistics support center during a disaster, the administrative building in the plant provides a space where up to 140 people can live for three days with drinking water, food, blankets, pharmaceuticals, and others stockpiled and maintained.

4.4 Active introduction of natural energies

The plant actively introduces natural energies mainly to enlighten the local community people. The main facilities utilizing natural energies are as follows:

（1）Snow storage chamber (Figure 6)

A snow-based air conditioning system is introduced that stores snow in an independent building (snow storage chamber) during the winter months to make effective use of the chilliness of the snow in the summer months. This system is partially responsible for air conditioning on the first floor of the administrative building.

Fig. 6 Snow storage chamber

（2）Solar power generation system (Figure 7)

A solar power generation system is introduced with a generation capacity of 10 kW. In general, snowfall areas are not suitable for solar power generation because snow covers the panels. With a steeper slope to prevent snow from staying on the panels, the system is capable of generating power even in the winter months.

Fig. 7 Solar power generation system

5. Plant operating condition

5.1 Heat recovery facility

The heat recovery facility officially started to receive waste at the end of October 2015 and started the hot commissioning in November. The pre-use self inspection defined by METI for thermal power plant was completed before the end of December, followed by the preliminary performance test in mid-January 2016 and the acceptance performance test in mid-February.

Table 5 shows the results of the load tests conducted as part of the pre-use self inspection. The boilers were tested-approximately with a maximum continuous rating of 6.4 t/h and the steam-turbine generator was tested with the rated output of 1 670 kW. Table 5 shows the main-steam flow rates, temperatures, pressures, generator outputs, and other conditions observed in the tests. Approximately 2 t/h of the main steam were surplus, which were made to bypass the turbine. The gross power generation efficiency is, by calculation, 16.6%. If the main steam surplus is factored in, the efficiency becomes 20%, which satisfies the design value of 19.6%. Table 6 shows the measurement results on the flue gas during the acceptance performance testing.

With an oxygen concentration at boiler-outlet of 2.7%, the plant demonstrated stable operation with a very low air ratio of approximately 1.2. The average concentrations of CO and NOx were 10 ppm (for #1) and 5 ppm (for #2), and 58 ppm (for #1) and 47 ppm (for #2), respectively, proving to be sufficiently lower than the criteria values. The measured values for dioxins and other restricted substances also sufficiently satisfied the emission criteria.

Table 5 Load test results
Measured item Unit Result
Boiler main-steam flow rate (#1 and #2) Z1/Z2 t/h 6.15/6.13
Boiler main-steam temperature (#1 and #2) ― ℃ 400/401
Boiler main-steam pressure (# 1 and #2) ― MPa 3.94/3.95
Main-steam flow rate at turbine inlet ― t/h 9.82
Turbine-bypassing steam amount Zb t/h 2.10
Generator output Pg kW 1670
Amount of waste treated (#1) B1 t/h 2.01
Amount of waste treated (#2) B2 t/h 2.04
Waste calorific value (calculated value) H kJ/kg 8940
Gross power generation efficiency※1
Gross power generation efficiency※2　
with turbine-bypassing amount factored in		 η
η’		 ％ 16.6%
20.0%
Table 6 Acceptance performance test results
Measured item Unit Judgement criteria Result Judge
#1 #2
Incineration capacity ％ ≧100%
(≧47.5 t/d each)		 ≧100% ≧100% Pass
Ignition loss ％ ≦5 ＜0.1％ ≦0.9％ Pass
Dust concentration g/m3（NTP） ≦0.007 ＜0.002 ＜0.002 Pass
Sulfur oxides ppm ≦30 22 17 Pass
Nitrogen oxides ppm ≦80 58 47 Pass
Hydrogen chloride ppm ≦50 29 24 Pass
Carbon monoxide ppm(average per 4 hours) ≦20 10 5 Pass
Dioxins ng-TEQ/m3（NTP） ≦0.04 0.00054 0.0039 Pass
0.00016 0.0081 Pass
Ammonia mg/m3（NTP） ― 1.1 1.7 ―
Mercury mg/m3（NTP） ― ＜0.01 ＜0.01 ―
Boiler outlet oxygen ％（wet） ― 2.5 2.9 ―
Air ratio ― ―
(with 25% water content in exhaust gas)		 1.2 1.2 ―

5.2 Recycle Center

The recycle center started to experimentally accept waste and recyclables in late December 2015 and started to accept from the whole area of Yokote City in February 2016. The center conducted the preliminary performance test in late January 2016 and acceptance performance test in late February. Table 7 shows the purity of recyclables measured in the acceptance performance test. All these values demonstrate that the center is capable of recovering resources with high purity.

Table 7 Purity of recyclables
Crushed iron 98.3% Clear bottles 100.0%
Crushed Aluminum 98.1% Brown bottles 100.0%
Steel cans 99.6% Other bottles 100.0%
Aluminum cans 100.0%

6. Remote Monitoring

In June 2016, we opened a remote support center inside the Fujisawa District of Ebara Corporation (Figure 8). At this center skilled operators monitor operating conditions of incineration plants all across the nation to accurately and promptly respond to unexpected events. At this center, operation data and conditions, and ITV images in Clean Plaza Yokote are remotely monitored to support stable operation of the plant.

Fig. 8 Remote support center

7. Conclusion

Clean Plaza Yokote, a waste treatment plant, was completed on March 30, 2016. Both the heat recovery facility and recycle center in the plant have been successfully running. With operational support based on the remote monitoring that started in June 2016, we are determined to smoothly operate and maintain the plant for a long period over the next 20 years to help build a sustainable society.

Finally, we would like to express our deep gratitude to the people in Yokote City and all those concerned who provided great guidance and assistance for the construction of the plant.

References

1) Naoto AKIBA and Tetsuji IGUCHI, “Stoker-Type Waste Incineration Plant for Iwamizawa, Hokkaido Construction and Delivery of Iwamizawa Environmental Clean Plaza,” Ebara Engineering Review No. 249 (October 2015): 14-20.
2) Manual for Maintaining Facilities for Efficient Power Generation by Refuse Incineration (revised March 2010) from Waste Measures Section, Waste & Recycling Measures Department, Minister’s Secretariat, Ministry of the Environment.

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