Biological service ensures high gas yield from waste plant

The tanks are constructed in duplex grades 1.4062, 1.4162 and 1.4462.
The tanks are constructed in duplex grades 1.4062, 1.4162 and 1.4462.

A biogas plant with a large duplex stainless steel tank recently went live in Saitama Prefecture, 40 km north of Tokyo.

Text & images by Weltec Biopower

Produced by Weltec Biogas, the facility – which is equipped with a 450-kW cogeneration power plant – is the fourth project to be rolled out by the German manufacturer in Japan. In terms of substrates, the operator makes use of organic leftovers from the vicinity. Since the raw material mix varies, Weltec ensures a steady biogas output with its biological service. This special service of the biogas specialist also comprises another plant of the same customer.

Renewable energy growing

Even after the reactor accident in Fukushima back in 2011, Japan continues to use nuclear power. However, renewable energies are consistently expanded and already account for a fifth of the power generated. Above all, organic waste is the preferred substrate in Japan. The biogas plant in Saitama, too, digests some 12,000 t of organic waste into energy. The substrate mix consists of organic waste and cattle manure from a nearby farm that belongs to the operator. The largely liquid organics are introduced to the digester by means of a central pump.
Solid feedstocks are transported by a dosing feeder with a capacity of 27 m³.

Stainless & duplex equipment

Pump parts are usually made of highly abrasion-resistant special alloys
Pump parts are usually made of highly abrasion-resistant special alloys

To ensure efficient digestion of this mixture, Weltec Biopower has set up a stainless-steel digester with a capacity of 2,823 m³. Its diameter measures 25.34 m, and its height is 6.3 m. The upstream substrate storage tank, which is made of stainless steel, has a capacity of 336 m³, a diameter of 9.31 m and a height of 5.03 m. The 525-m³ digestate storage tank (diameter 11.64 m, height 5.03 m), too, is made of high-quality stainless steel. The tanks are produced of duplex stainless steel 1.4062 or 1.4162 in the lower rings, and duplex 1.4462 for the top rings which are in contact with the biogas.
Pump parts are usually made of highly abrasion-resistant special alloys, often with additional coatings such as chrome plating.

Residual compost

The digestate is separated and the solid phase is dried with special technology in order to further reduce the volume. Most of this residue is used as compost, and some of it as fertiliser.
“The Japanese appreciate the custom plant design and the benefits of our modular approach, especially because the plant structure with stainless-steel modules facilitates the consideration of the special risks in areas that experience a lot of seismic activity“, explains Vladimir Bogatov, who is responsible for sales.
All in all, Weltec provided the customer with an all-inclusive package in “made in Germany” quality along with individual after-sales service. Subsequently, the Japanese operator also entrusted Weltec with the biological supervision of its other biogas plant, which had been set up by a different provider in 2017.
As this plant‘s yield was above average, the biology experts of WELTEC had the substrate mix of the old plant carefully analysed by a Japanese lab. Based on the results, the raw material mix and the retention time have been optimised. Due to the constantly changing composition of the waste, WELTEC will continue to supervise the two plants biologically to maximise the gas yield.

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