Subject:- Renewable Energy Sources

Topic:- Wind Energy

Difficulty:- High

The following data is given for a family biogas digester suitable for the output of 10 cows, the retention time is 30 days, temperature $300^oC$ dry matter consumed per day is 2kg/day/cow & biogas yield is $0.24m^3$ per kg. The efficiency of burner is 60%, methane proportion is 0.8, Heat of combustion of methane is $28mJ/m^3$, calculate the volume of digester & the power available from the digester. Assume density of dry material in the fluid is $50 kg/m^3$.

dry matter Consumed
Mo = 2Kg/day/ cow & no. of cows = 10

. Total dry mass input, MD= Mo X no. of cows

= 2 X 10

=20 Kg/ Day

Density of dry mass $P= 50 Kg/m^3$ (given)

fluid volume . $Vf = MD /Pm = 20/50=0.4m^3 /day$

Find Digester Volume Vd =

Vd= fluid Volume (Vf) X Retention Time(tr)

= 0.4 x 30

$=12m^3$

Energy Available ; E in KW :-

Given :-

Biogas yield / Kg
Cb $= 0.24m^3/ Kg$ of dry Input

Volume of biogas Production, Vb=Cb x mass of dry Input

= 0.24x20

$=4.8m^3/ day$

Methane in biogas, Vm= Vb x methane Proportion

= 4.8x0.8 $=3.84m^3/day$

Heat energy in methane

∆H = Vm x heat of combustion /m3 of methane

$= 3.84(m^3/day)x28(MJ/m^3)$

= 3.84x28x1000KJ/day

= 107520KJ/day

Power Available from digester .

E=∆H x "η" burner= 107520x0.6 KJ/day

=107520x0.6/(24 x 3600) Kw

=0.74667 KW