Micro-scale digesters in practice

Micro-scale digesters produce biogas using only own (waste) biomass resources from farms, where livestock manure is the main substrate. Biogas is produced as a result of a fermentation process – the organic material in the substrates is reduced and converted to biogas by micro-organisms.

The biogas is mostly utilised for energy generation – heat (produced in boilers) or heat and power (generated in combined heat and power (CHP) installations). There are several different ways of biogas usage. One of them is upgrading to biomethane, which can be used as transport fuel or fed into the natural gas grid.

Digested manure is used as a fertilizer spread on farmland. It has many advantages over raw manure (i.a. unpleasant odours are reduced). Micro-scale digesters are renewable energy sources, which contributes to reduction of greenhouse gas emissions and decrease of fossil fuels use.

Figure: Estimated number of operating agricultural micro-scale digesters identified in selected countries according to a survey by BioEnergy Farm 2 project partners.

Figure: Estimated number of operating agricultural micro-scale digesters identified in selected countries according to a survey by BioEnergy Farm 2 project partners.

How does MSD work?

Manure digesting – scheme. Source: NAPE.

Figure: Manure digesting – scheme. Source: NAPE. 

The chain utilizing of the manure starts from the livestock house. The manure is temporarily stored in a reception tank, and then fed to the digester. During the fermentation process in the digester biogas is produced. When the retention time in the digester (post digester) has elapsed, the digestate is pumped into a storage tank, and then utilized on the farmland as fertilizer.

Biogas can be utilized in a number of ways but generally it is used to generate heat and power in micro combined heat and power generators (CHP) or only for producing heat in a boiler. The produced electricity and heat is used by farmers for household and agricultural purposes. Because the production is small, sufficient heat demand should be found on the farm and in the neighbourhood. Eventual electricity surplus can be fed to the grid.

 

If there is no heat demand in the near area of CHP installation, the biogas, instead of heat and electricity production, could be upgraded to transport fuel or grid gas standards. However, it requires additional support in legal frameworks (a.i. regulations and injection criteria).

To summarize, the most feasible solution of biogas utilization depends on specific local conditions, but usually biogas is used for producing heat or combined heat and power…

How does a MSD look like?

Language

Host Microferm. Location: Well, the Netherlands

Substrate: 6 000 – 8 000 t/year – liquid pig and cattle manure

Amount of biogas: 200 000 – 260 000 m3/year

Biogas utilization: combined heat and power

Electric power: 65 kW

Thermal power: 95 kW

Electric energy: 550 000 kWh

Heat utilization: process heating and milk processing

Location: Well, the Netherlands. Source: HoSt.

Biolectric digester. Location Oelegem, Belgium

Substrate: 2 900 t/year  – liquid cattle manure

Amount of biogas: 69 600 m3/year

Biogas utilization: combined heat and power

Electric power: 19.4 kW

Electric energy: 155 200 kWh

Thermal energy: 335 000 kWh

Heat utilization: process heating and in the farmhouse

Micro-biogas plant on slurry (mono-digester). Location: Oelegem, Belgium. Source: Bioelectric.

NQ Anlagentechnik, Location Balve, Duitsland

Substrate: 6 800 t/year – liquid cattle manure + 780 t/year of cattle dung

Amount of biogas: 321 000 m3/year

Biogas utilization: combined heat and power

Electric power: 75 kW

Electric energy: 630 000 kWh

Thermal energy: 749 400 kWh

Heat utilization: process heating, in the residential house and in the milking parlour

Wet fermentation. Location: Balve, Germany. Source: NQ Anlagentechnik.

Gosmer Biogas. Location: Aarhus, Denmark

Substrate: 9 100 t/year  -liquid pig manure

Amount of biogas:  120 000 m3/year

Biogas utilization:  combined heat and power + heat (in boiler)

Electric power: 30 kW

Electric energy: 150 000 kWh

Thermal energy: 360 000 kWh + 130 000 kWh (boiler)

Heat utilization: in Sow stables and in the farmhouse

Manure-based with a simple separation. Location: Aarhus, Denmark. Source: Gosmer Biogas.

 

DynaHeat-HPE. Location: Birkenhof, Germany

Substrate: 2 200 t/year – liquid cattle manure

Amount of biogas: 80 000 m3/year

Biogas utilization: combined heat and power

Electric power: 7 – 12 kW

Electric energy: 90 000 kWh

Thermal energy: 180 000 kWh

Heat utilization: process heating and in the residential house

Containerized wet digestion plant. Location: Birkenhof, Germany. Source: DynaHeat-HPE.

Biovec. Location: Zaragoza, Spain.

Substrate: 2 000 t/year  –  pig slurry

Amount of biogas: 150 000 m3/year

Biogas utilization:  heat (in boiler)

Thermal power: 170 kW

Thermal energy: 900 000 kWh

Heat utilization:  process heating  and in the farmhouse

Manure and slurry based with mixer in pre-treatment tank. Location: Undués de Lerda (Zaragoza), Spain. Source: Biovec.

Evalor. Location: Saint Lambert la Potherie, France.

Substrate: 4 000 t/year – liquid pig manure  + 50 t/year of leftovers  + 100 t/year of grass silage

Amount of biogas:  100 000 m3/year

Biogas utilization: heat (in boiler)

Thermal power: 110 kW

Heat utilization: process heating & in the livestock building

Small scale liquid manure plant. Location: Saint Lambert la Potherie, France. Source: Evalor.

Fermtech Systems. Location: Hengelo (GLD), the Netherlands

Substrate: 3 000 t/year – liquid cattle manure+ 100 t/year of glycerin

Amount of biogas:  150 000 m3/year

Biogas utilization:  combined heat and power

Electric power: 35 kW

Thermal power: 45 kW

Electric energy: 280 000 kWh

Heat utilization: process heating  and in the future for manure treatment

Tower digester, combined with hydrolysis. Location: Hengelo, the Netherlands. Source: Fermtechsystems.

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