DESIGN AND SIZING OF A DIGESTER COUPLED TO AN AIR SOLAR COLLECTOR - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 150

The Sizing

Digestion enclosure: diameter = 3 m height = 2 m capacity = 11.77 m 3
Dome: central height = 1 m.
Evacuation and storing reservoirs: 2 m 3
Piping diameter: 30 cm
The digester enclosure maximum load is of 8240 kg substrate of digestion. For a
residence time fixed to 90 days, the daily provisioning of the digester is about 130 liters/day.

Table 1. Sizing of the digester

Diameter
(m)

Length
(m)

Volume (m 3 ) Digester units

Top Dome 3 1 - - 3.63

Enclosure Center Cylindrical 3 1.5 - -

1.77

Bottom V shape 3 0.5 - -

Storage tank and ponds Rectangular - 1 2 1 2

Low Temperature Solar System

Operating Principle

The heating up to a temperature reaching 40 °C improves the production of biogas. In
order to keep a positive energy balance, we use renewable energy for the heating of the
family digester: an air static solar collector at low temperature (figure 2). A depression causes
a circulation of hot air through a stones bed surrounding the digester. Due to heat transfer
from air to the stones bed, a thermal seasonal storage is carried out. This system ensures the
restitution of the heat stored throughout the cold periods for the heating of the digester.

Solar collect

Hot air

Air exit

Air inlet

Ground leve

Digestion
enclosure

Heat storage
in stones bed

Heat transfer
air-stones

Figure 2. Heating system.