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Waterwheel-driven Trash Removal Screen for Irrigation Canals

by the CADDET Japanese National Team

INTRODUCTION

Recently in Japan, residues and waste entering into irrigation canals in various parts of the country have been increasing. As rural areas become more urbanised and farming methods more sophisticated, more municipal and agricultural waste is produced. Such trash clogs screens installed at siphons and pumping stations and division works, causing inundation and difficulty in taking in water, thus creating problems for canal management.

Although major canal facilities have auto-screens powered by electric motor or internal combustion engine, the equipment and the operating and maintenance costs are expensive. Manual trash removal used in many other canal facilities also puts a burden on all concerned. Hence, the Laboratory of Regional Energy Resources at the National Research Institute of Agricultural Engineering has developed a waterwheel-driven trash removal screen which clears waste and residues from canals by utilising the energy in the water current. Field tests have confirmed that the screen works effectively in practical use.

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A waterwheel-driven trash removal screen viewed from downstream

OUTLINE OF THE SYSTEM

The new trash removal system consists of an undershot wheel, a gear box, a screen unit and an eject conveyor. The energy in the water current flowing in a canal is converted into rotational power of the wheel, which drives the screen rakes and the eject conveyor.
The waterwheel is 1.3 m in diameter, 1.1 m in width, and has twelve 0.2 m wide blades. It is equipped with a torque limiter, which automatically cuts power transmission to the gear box to prevent the chain from breaking if the wheel becomes overloaded. This can happen when the screen rakes and/or the conveyor stop running because they are blocked by trash. The gear box houses a reduction gear to cut the rotation speeds transmitted from the wheel, and a sprocket wheel for speed reduction. In addition, a torque limiter is fitted to a device which transmits power to the screen unit and the eject conveyor. This torque limiter is an automatic reset type, which restarts the power transmission when the overload is gone.

The screen unit comprises a bar screen made of twenty-four iron bars at an angle of 30 , each 6 mm thick, 0.15 m wide and 2.8 m long, together with rakes, chains and a screen lift. The eject conveyor is a chain conveyor with 4 rakes, which gather trash from the screen and deposit it onto the canal bank.

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Schematic of the system

FIELD TEST

Field tests have been conducted on the waterwheel-driven auto-screen installed in an irrigation canal flowing through Misato-mura, near Matsumoto City in Nagano. The 1.2 m wide waterway has 0.6 m high side-walls and a slope of 1/500. It is placed 12 km from the water intake point at a discharge rate of 0.4 m3/sec and a velocity of 1 m/sec through rice fields, orchards and built-up areas to the location of the screen. The canal therefore collects not only agricultural residues and waste such as mowed grass, vegetables, fruits and plastic sheeting but also considerable amounts of municipal waste such as garbage, empty cans and bottles and polystyrene trays. The screen removes as much as 2 light truck loads of trash per day.

Experience during the period July 1995 to June 1996 led to several improvements to the design, such as:

  • increasing the number of screen rakes to eight to improve the clearing of trash from the screen unit;
  • fitting guides to stop trash from getting between the chains and gears;
  • installing an auxilliary screen between the bottom of the canal and the screen;
  • fitting a sound-insulation box covering the waterwheel to reduce noise nuisance caused by the blades slapping the water.

Further improvements, particularly noise-reduction measures, have been identified and will be the subject of further study.

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Eject Conveyor (view from the right bank)

ECONOMICS

The equipment costs of the waterwheel-driven trash removal screen tested in the field were some JPY 5 million (where JPY is the Japanese yen). However, this is because the screen was a trial model; from now on it will cost only JPY 2 million or less to manufacture a similar system. In comparison, the equipment costs of a motor or engine driven auto-screen of the same scale are at least JPY 5 million.

With no imported energy, the waterwheel-driven auto-screen has few running costs; it only requires some lubrication of the bearing parts. A similar-sized motor-driven auto-screen uses a 3 kW motor and costs about JPY 170,000 in power expenses, plus maintenance costs, to run continuously for a year.

CONCLUSION

The field test satisfactorily demonstrated that the waterwheel-driven trash removal system could work effectively and efficiently in practical use.

The total length of main irrigation canals in Japan, serving farms of 100 ha or more, was about 28,000 km in 1988. The energy of water current flowing these canals has seldom been utilised until now. The waterwheel-driven auto-screen is an appropriate way to utilise dispersed energy sources in rural areas such as water current in canals.

This technology is applicable to the removal of trash from small rivers and from the intakes for hydraulic power plants. Its simple structure and low initial costs make it possible for developing countries to easily manufacture these auto-screens by themselves and use them widely.

For more information contact the CADDET Japanese National Team in Tokyo.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.