Subject:- Renewable Energy Sources

Topic:- Wind Energy

Difficulty:- medium

Biogas plants are built indifferent sizes & shapes depending on the process carried out. These plants are mainly classified as.

• Continuous or batch type
• Dome & drum type.

Continuous OR Batch type biogas plants.:-

• In the continuous type of biogas plant the biomass is fed regularly to the digester & it delivers the biogas continuously.

Continuous type biogas plants are of two types .

1. Single stage continuous type biogas plant.
2. Two stage continuous type biogas plant.

1) Single stage continuous type biogas plants:-

In this type of plants the entire process of conversion of biomass into biogas are carried out in the single chamber or digester without barrier construction of plant is simple in construction easy to operate & control. It does not need any skilled workers.

2) Two stage continuous type biogas plant :-

These plant have two chambers for digestion of biomass. In the first chamber the biomass is fed in which the

Stage 1. of acid formation takes place. Then the diluted acids are only fed into the second chamber where the

Stage 2. of methane formation is carried out. So produced is collected from the second chamber. Various factors affecting the production of biogas.

Following are the Imp. Factors of the rate of production of biogas.

• Temperature & pressure :- The process of anaerobic fermentation & methane forming bacteria work best in the temperature range of 250 C- 550 C & pressure of about (1.1-1.2) bar absolute. The rate of biogas production increases with the increase in temperature but the percentage of methane reduces. It is found that temperatures $350^o C – 380^o C$ are best for methane production.
• Solid concentration & loading Rate:- The cow dung water & various organic residues from agricultural waste are supplied as feed to the digester. The proportions recommended are. Cow Dung + Solid sast;1 by weight & forming to about 10% of solid content& 90% of water. The amount of feed supply per day to the digester is called Loading Rate.
• Retention Period :- The Longer Retention Period needs larger size digester & it allows more complete digestion of feed.
• PH value or Hydrogen ion concentration :- PH value indicates the degree of acidity OR alkalinity of a solution the PH value is represented as the logarithm of the reciprocal of hydrogen ion concentration In gm equivalent per liter of solution.
• Nutrients Concentration :- The major nutrients required by the bacteria in the digester are $N_2 ,P ,S , C ,H_2 , O_2$, to accelerate the anaerobic rate. Thus it is necessary that the major nutrients are supplied in correct chemical from & concentrations.
• Toxic Substances :- The presence of ammonia , pesticides detergents, heavy metals are considered as toxic substance to micro- organisms since their presence reduces the fermentation rate.
• Digester Size & Shape :- It is found that the biogas production per unit volume of digester is high when its diameter to depth ratio ranges between 0.66 to 1.
• Stirring OR agitation of the content of digester :- Since bacteria in the digester has very limited reach to their food , it is necessary that the slurry is property mixed & bacteria get their food supply.