Biomethane

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AIMAG has implemented a door-to-door waste collection system. This system is also applied to organic waste and, in general, it shows an increasing quality of collected waste.

After collection, the organic fraction is transported to one of the two composting plants managed by AIMAG which have a total capacity of 110.000 tons/year and where 30.000 tons of compost are produced every year.

In Massa Finalese, the composting plant was integrated with a semi-dry anaerobic digestion section and an upgrading section for the refining of the biogas and the production of biomethane, which is then sent to the distribution network.

The anaerobic digestion section is fed with urban organic waste.

SOME NUMBERS

  • 50.000 tons/year of treated organic waste
  • 3.080.000 mc of produced biomethane
  • 17.000 tons/year of compost produced for organic agriculture

PROCESS

1

WASTE PRETREATMENT

The pretreatment section allows the separation of the non-degradable waste fraction (plastic, wood, metal and inert waste), which could eventually be found in the organic waste transported to the plant, in order to avoid problems in the following anaerobic digestion phase and ensure the highest efficiency of the plant.

Pre-treated organic waste is then stored in a walking-floor feeding bunker through which it is transported to the digestor.

2

ANAEROBIC DIGESTOR

The digestor is continuosly fed. It designed as a horizontal piston flow reactor and it is equipped with eight paddle stirrers and a heating system with the possibility of operating in mesophilic (37 ° C) or in thermophilic (50 – 55 ° C) conditions.

3

DIGESTATE

The extracted digestate has a high water content so it is mixed with the green fraction, which is able to absorb water and give structure to the material: it is then sent to the composting phase.

A wheel loader deposits the green fraction in an external hopper of adequate capacity, able to automatically dose the material according to the quantity of digestate to be mixed.

4

UPGRADING

The refining of the biogas is done through a PSA technology system with chemical absorption of H2S and removal of CO2, N2, O2.

The PSA system allows a high efficiency of the treatment.

5

FEED-IN

The resulting biomethane is sent to the cabin of connection to the gas distribution network, which is composed by an analysis and measurement section, a filtration and pressure reduction section and an odorization system.

In the “fiscal measurement” part of the cabin, there are the gas analysis and fiscal flow measurement instruments and the valves for the deviation of the gas in the flare in case of overpressure or in case the gas doesn’t respect the specifications.

The filters, the pressure regulation section, the non-fiscal gas flow measurement and finally the odorization system are instead located in the “non-fiscal measurement and regulation” part of the cabin.

ADVANTAGES AND BENEFITS

The main benefit is the environmental one: the plant produces a green fuel from renewable resources, reducing the consumption of fossil fuels and the climate-changing emissions.

There are also two important advantages for the producing process: the compost obtained by predigestate organic material presents better qualities than the one obtained by the only aerobic process. Thanks to the new part of the plant, a reduction of odorous emissions will be reached.

There are also economic advantages thanks to the incentives provided by the Ministerial Decree.

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