Annex_VIII_CaseStudy1502_Taki_Japan.pdf

IEA Hydropower Implementing Agreement Annex VIII -

Hydropower Good Practices: Environmental Mitigation Measures and Benefits

Case Study 15-02: Others – Use of Driftwood in Reservoir – Taki Dam, Japan

Key Issue:

15-Other

Climate Zone:

Cf: Temperate humid climate

Subject:

- Processing and Effective Use of Driftwood

in the Reservoir

Effects:

- Effective Use of Construction Byproducts

Entire View of the Taki Power Plant

and the Taki Dam

Project Name:

Taki Dam

Country:

Fukushima Pref., Japan (Asia)

Implementing Party & Period

- Project: Electric Power Development Co. Ltd. (J-POWER)

1961 (Commencement of operation) -

- Good Practice: Electric Power Development Co. Ltd. (J-POWER)

1990 -

Keywords:

Driftwood, Recycling, Charring

Abstract:

Taki Dam is located in an area of heavy snowfall, and a large amount of driftwood

flows into the reservoir annually during periods of high run-off due to thaw and rainfall.

The removal of this driftwood requires much labor and cost. Moreover, its final

disposal often encounters problems. As a result, studies were carried out on the

beneficial use of driftwood, and technologies were developed for its recycling into

charcoal, wood vinegar and craftwork. In 1993, this Good Practice was commended

by the Ministry of International Trade and Industry for its contribution to the promotion

of waste recycling.

1. Outline of the Project

The Taki Dam in the Tadami River, which belongs to the Agano River system, is located in

Kanayama-machi, Oonuma-gun, Fukushima Prefecture. This gravity overflow concrete dam,

exclusively used for power generation, has a 264 m long crest, 46 m elevation, effective

storage of 10,300,000 m 3 and catchment area of 1978.8 km 2 .

With the attraction of the rich hydropower resource of the Tadami River that runs through the

project site, the investigation of the midstream and upstream of the river started long time

back in the end of the Taisho Period (1912 to 1926), along with the development of the main

Agano River in the downstream. With a rapid rise in electric power demand after WWII, the

development of the midstream area progressed concurrently with a second investigation of the

entire watershed. This led to the consistently planned development of the Tadami River

System, with a goal of constructing facilities with a generating capacity of 2,000 MW. The

plan included the construction of large upstream reservoirs in Okutadami and Tagokura and a

group of midstream balancing reservoirs. Later on, the 10 th meeting of the Adjustment Council

of Electric Power Development Co. Ltd. in July 1953 agreed on the general development plan

for the Tadami and the Kuromata River and reached the decision to construct the Taki Power

Plant as the afterbay reservoir of the Tagokura Power Plant.

The construction, preceded by the investigation and survey of the power plant site in 1958,

started in July 1959. In July 1961, the reservoirs were filled and on August 15 of the same

year, power generation started. Table 1 shows the specifications of the Taki Power Plant and

the Taki Dam.

Table 1 Specifications of the Taki Power Plant and the Taki Dam

Item

Specification

Name

Taki Power Plant

Source of water

Tadami River, which belongs to the Agano River system

Maximum output

920,000 MW

Power

Plant

300 m 3 /sec

Maximum discharge

Effective head

35.82 m

Number of generators

Waterwheel type

Single vertical axis spiral Kaplan

Name

Taki Dam/Taki balancing reservoir

Type

Concrete gravity

Dam height

46 m

Crest length

264 m

Dam and

Reservoir

120,343 m 3

Dam volume

1978.8 km 2

Catchment area

Total reservoir

capacity

27,000,000 m 3

Available depth

5.0 m

2. Features of the Project Area

The Tadami River, which runs through the

Taki Dam point, originates in Lake Oze and

flows into the Sea of Japan. The river, which

runs a total distance of approx. 260 km and

has a catchment area of approx. 8,400 km2,

is blessed with a rich water resource thanks

to heavy snowfall during the winter period

and an available head of as high as 1,400 m,

and has been a site for hydropower

development since before the war. As the

Fukushima Pref.

Taki Dam

Fig. 1 Location Map of the Taki Dam

site is located in a narrow place between mountains in an area of high snowfall, a large

amount of driftwood flows into balancing reservoirs whenever flooding occurs due to snow

melting and rainfall, and therefore the removal of driftwood is an annual event.

3. Benefits

3.1 Background of Effective Use of Driftwood

Dam reservoirs have an inflow of a large

amount of driftwood and other forms of

debris during typhoons and heavy rainfalls

(Photo 1). These driftwood and other forms

of debris not only cause problems to water

intake for power generation but also damage

the landscape of dam reservoirs. It is,

therefore, one of important hydropower

maintenance responsibilities to routinely

remove them from reservoirs for disposal.

However, the removal requires large

facilities and much labor and cost, and final disposal of removed driftwood and other forms of

debris have often presented considerable problems. Although depending on the severity of

floods that occur each year, the amount of driftwood and other forms of debris processed

annually is an average of over 30,000 m 3 , which, however, does not include the large amount

of intact, submerged driftwood. This example shows a driftwood recycling effort, for example,

by charring it, to ensure their effective use.

Photo 1 Driftwood in the Dam Lake

3.2 Recycling through Charring

Driftwood is so diverse in conditions, for example, regarding the tree type and age, length,

thickness, shape (straight or curved), and degree of damage and staining. In consideration of

these conditions, dam site conditions, characteristics of recycled products and social demand

among other factors, Electric Power Development Co. Ltd. decided on an effort to recycle

driftwood by charring it.

The advantages of carbonization worthy of note include:

1) Thermal decomposition of fur, staining, mold and other impurities produces stable

carbides.

2) Since carbides are free of corrosion or chemical changes, they have no adverse effects on

the environment when left unused.

3) Carbon fixation helps reduce carbon dioxide emissions from driftwood burning.

4) Since carbonization reduces the weight by about 20% and the volume by about 60%,

transportation becomes easy.

5) Since the masses of charcoal can easily be crushed, this increases transportation options.

6) Carbonated materials have many applications including fuels and charcoals.

The charcoal manufacturing process is as shown in the flow chart in Fig. 2. Fig. 3 shows an

example of the traditional Japanese charcoal kiln made of clay and rocks used as the test kiln

around the Taki Dam. The charcoal manufacturing test succeeded for the first time in

September 1990. The attempt was unprecedented in the world, and the product was called

driftwood charcoal. About 2% of the several thousand cubic meters of driftwood removed

each year is charred for their effective use.

1. Removal of driftwood from reservoirs

2. Sorting of driftwood

3. Storing and drying of driftwood

4. Production of charcoal

5. Vertical laying of driftwood in the kiln

6. Increasing of kiln temperature

7. Carbonization (Collection of wood vinegar)

Charcoal manufacturing cycle

11-

8. Refining

9. Sealing and cooling of the kiln (Black charcoal)

10. Opening of the kiln

11. Processing and shipping

10-

Fig. 2 Driftwood Charring Process

Plan

flue

blowhole

Section

clay (gravel mix)

clay

Fig. 3 Test Kiln for Driftwood

Table 2 shows a quality comparison between the driftwood charcoal and the charcoal

manufactured from ordinary wood. The driftwood charcoal, characterized by such properties

as a small ash content and a large calorific value, found an application as a clean fuel. Since it

also has aerating, particle capturing, water cleaning, humidity control and deodorizing

capacities associated with its porous surface, it is used in various products including humidity

control construction materials (for example, sheets), water cleaners and pillow and mattress

stuffing, which are commercially available through the affiliates of Electric Power

Development Co. Ltd.

Table 2 Quality Comparison between Charcoal Manufactured

from Ordinary Wood and Driftwood Charcoal

Charcoal manufactured

from ordinary wood

(Japanese beech)

Driftwood charcoal

(Japanese beech)

Item

Calorific value (kcal/kg)

7.040

7.590

Ash content (%)

7.0

3.0

Carbon (%)

85.5

86.3

Hydrogen (%)

1.2

2.2

Elementary analysis

Nitrogen (%)

0.4

0.3

Oxygen (%)

5.9

8.2

True specific gravity

1.76

1.55

Unit weight (g/cm 3 )

0.57

0.37

Water absorption (%)

124

136

Hardness

12.0

3.0

Effluent pH

8.8

7.5

3.3Use of Wood Vinegar

Collecting and cooling the gases discharged from the smokestack during the charcoal

manufacturing process produces condensed liquid with pungent smell. This liquid, which is

thermally decomposed tree fibers of cellulose and lignin, is separated by gravity into three

layers when left standing: the upper layer comprising lightweight crude oil, the intermediate

layer comprising wood vinegar and the bottom layer comprising tar. The wood vinegar is

strongly acid (pH2 to 3) transparent liquid with a yellowish or brownish tint, and contains

acetic acid as the main component, and reportedly, over 200 types of other organic compounds.

This wood vinegar, like charcoal, has proven to have a number of effects that reflect the

working of natural chemical components, and thus has attracted increasing research interest.

Wood vinegar is commercially available today for gardening applications and for applications

similar to those of the driftwood charcoal.

3.4 Use of Driftwood in Craftwork

Driftwood has a corroded and softened surface thus giving the first glance impression of

being rotten. However, it often has a solid interior. The interior of quality driftwood with

attractive grain patterns is used to produce woodwork, which is sold at a shop in the dam.

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