Power Plant Engineering

(B) TWO STATE CONTINUOUS TYPE BIOGAS PLANT
In such a plant the Phase-I (acid formation) and Phase-II (methane formation) take place in
separate chambers. The plant produces more biogas in the given time than the single stage plant. How-
ever, the process is complex and the plant is costlier, difficult to operate and maintain. Two stage plant
is preferred for larger biogas plant systems.

---

NON-CONVENTIONAL ENERGY RESOURCES AND UTILISATION
57
BATCH TYPE BIOGAS PLANT
The infeed biomass is fed in batches with large time interval between two consecutive batches.
One batch of biomass infeed is given sufficient retention time in the digester (30 to 50 days). After
completion of the digestion, the residue is emptied and the fresh charge is fed. The fresh biomass
charge may be subjected to aeration or nitrogenation after feeding and then the digester covers are
closed for the digestion process. Thereafter, the Biogas is derived from the digester after 10 to 15 days.
Fermentation continues for 30 to 50 days.
Salient Features:
1. Batch type biogas plant delivers gas intermittently and dis-continuously.
2. Batch type biogas plant may have several digesters (reacters) which are fed in a sequential
manner and discharged in a sequential manner to obtain the output biogas continuously.
3. Batch type biogas plants have longer digestion time and are therefore more suitable for
materials which are difficult for anaerobic digestion (e.g. harder, fibrous biomass).
4. Batch type biogas plant needs initial seeding to start the anaerobic fermentation.
5. Batch type biogas plant needs larger volume of the digester to accommodate large volume of
the batch. Hence initial cost is higher.
6. Operation and maintenance is relatively more complex. Batch type biomass plants need well
organised and planned feeding. Such plants are preferred by European farmers. Such plants
are not yet popular in India.