Hydro makes the most of driftwood15 May 2001
Takahisa Shinjo explains how a power company in Japan is reaping unexpected benefits from its hydro reservoirs. Accumulated driftwood is being used to produce a number of products ranging from fertilisers to face creams
apan’s Electric Power Development Company (EPDC) owns and operates 58 hydro power stations which have a maximum generating capacity of 8260MW. EPDC controls 40 reservoirs for hydro power production, several of which are also used for flood control and irrigation. In addition, an unexpected benefit is emerging from these reservoirs in the form of driftwood.
In 1999, 20,500m3 of driftwood, trash and garbage was extracted from EPDC’s reservoirs. Standard practice in Japan means that forest is usually cleared from a reservoir before it is filled. This accumulated driftwood is not due to wood already in the reservoir but to forest and social development upstream and around the reservoir, the spread of disposable products as well as illegal dumping.
Driftwood, trash and garbage disturb power generation and can damage recreational river facilities. They can also have a detrimental effect on scenery and disturb inflow and fisheries, especially during floods. Consequently electric enterprise companies have extracted this waste material, not only to ensure a stable electricity supply, but to improve the river and reservoir environment.
In the past extracted driftwood was incinerated but a new processing system was required that was more economical and minimised environmental loading. Carbonisation or chipping were considered the most feasible options. The income from the sale of end-products (charcoal, wood vinegar and chips) helps to reduce the cost of these processes, making it almost equal to the cost of incineration. Carbonisation and chipping also minimise the production of carbon dioxide whereas incineration adds to the production of this greenhouse gas. As a result, EPDC decided to install carbonisation systems and chipping systems at several dams.
In 1991 EPDC installed kilns for carbonisation at five of its sites: Tagokura, Outadami, Ikehara, Kazaya and Yanase.
The advantages of carbonising driftwood are:
• All impurities are disintegrated by heat and then stabilised by carbonisation.
• Carbonised substances will not rot or change chemically, so they can be kept for a long period of time without increasing environmental loading.
• Fixation of carbon minimises the production of carbon dioxide.
• Products are easy to handle, since carbonisation reduces weight by up to 20% and volume by up to 60%.
• A multitude of transportation methods are possible since the carbonised products are easily crushed.
• Products can be used in a number of ways, eg as a fuel.
At Tagokura and Okutadami, where an old Japanese-style cement kiln is used, the carbonisation process takes one to two weeks from setting up to extraction at the sites. Steel kilns are used at Ikehara, Kazaya and Yanase, where it only takes five days for the whole process.
Driftwood charcoal is highly porous and has a larger exposed surface than other charcoals. This means that aside from fuel use, it can be used for absorption, water cleaning, water storage, humidity control, deodourisation and snow melting by heat storage. In addition, since it is strongly alkaline with a pH of 13 and contains calcium, silicon, potassium and magnesium, it can be used for soil improvement and as a fertiliser.
Pulverised charcoal is manufactured and sold as deodourant for drinking water, humidity control sheets for houses and bedclothes. The Japanese have used charcoal for heating since ancient times. Although electricity, gas and oil have been used since the 1900s, charcoal is still a favoured fuel because of its nature and warmth.
The liquid produced by the carbonisation process is composed of disintegrated cellulose and lignin. The liquid can be separated into light oil, wood vinegar and wood tar by density. The wood vinegar, (pH2 to 3) is yellow brown to dark brown in colour and composed of more than 200 kinds of materials, including acetic acid. This has been used as a preservative, deodourant and medicine, and more recently in insecticides, sterilisation, soil improvement and promoting plant growth. As a result, the wood vinegar is drawing attention in the fields of animal husbandry, gardening and agriculture.
Furthermore, EPDC has refined the wood vinegar, which contains mainly vegetable polyphenol and indispensable unsaturated multi-valued fatty acids, and has removed substances which are harmful to humans, such as formaldehyde and methanol. EPDC has also developed cosmetics, cleansing creams and face creams, taking advantage of the antiseptic characteristics of the wood vinegar.
Charcoal and wood vinegar will be sold to the Development Project Company (DPC) to help reduce the cost of driftwood processing. The carbonisation of driftwood and the production of wood vinegar and cosmetics will be continued by DPC. A company called EPURE will market the products.
There is a lot of driftwood available at the Sakuma reservoir. EPDC has chipped this since 1995 as there is no land available for a wood vinegar and charcoal processing plant. In addition chipping products are used by local people.
Chips are sold to a plywood manufacturer to reduce the cost of driftwood processing. Chips unsuitable for plywood are used as bed wood material for a black mushroom plantations.
Recently, the discharge of driftwood has been fairly stable because a predicted flood event did not occur. As a result, the driftwood tends to be small and the number of larger diameter woods that can be chipped for plywood has reduced year by year, whereas the share of small woods and manmade garbage has increased. A small wood processing unit has been introduced to chip small wood for the production of organic fertiliser which has been sold to local farmers since 1999.
EPDC had incinerated driftwood at the Kazaya, Futatsuno, Ikehara, Nanairo, Komori and Kutisubo plants in Kinki district. However the incinerators need to be remodelled according to a review of Waste Processing Laws and as a result, EPDC has decided to introduce a mobile chipping machine for organic fertiliser instead.
Driftwood is chipped for organic fertiliser by the machine which has a productivity of 10t/hour. EPDC transports this machine by lorry for chipping at the above dams. Chips will be sold to local stock farmers who will manufacture the organic fertiliser to reduce the cost of driftwood processing. EPDC is planning to transport and operate this machine at Ynase in Shikoku district to chip its driftwood in the future.