DESIGN OF BIO-GAS FOR RURAL AREA

5.1         DESIGN PROPOSAL [BIO-GAS PLANT]:

Bio gas plant is one of the plant for renewable energy sources. It transforms rural village in to clean village and also provide gas as energy source and gives fertilizer at end.

BASIC THINGS:

Total numbers of animals in village = 3000

As per standard data assume per day dung of animal=10.5 Kg.

So total per day dung = 3000 * 10.5 =31500 Kg. /day

DESIGN OF DIGESTER:

Assume retention period (RT) = 70 days.

Assume mixing proportion of solid and water is 1:2.

Now total amount of slurry per day (Sd) = Total per day dung + Water amount

                                                                =  31500 + (2*31500)

                                                       =  94500 Kg. /day

                                                                =   94500 Lit. /day

                                                                =   94.5 m3 / day

Digester volume (Vd) = Sd * RT

                                 =  94.500 * 70

                                 =  6615 m3

                            

Assume cylinder shaped bio gas plant.

Provide total 6 numbers of units in different areas , so digester volume becomes for one unit= 6615 ÷ 6 =1102 m3

So provide= 1100 m3

Total digester volume (Vd) = π r2 h

                                   1100 = π r2 (h = 10 m)

So dimensions of digester are h=10 m

                                                     R= 6 m

DESIGN OF GAS HOLDER:

Assume digester temperature= 26-28 ˚C

Now from following fig find Gd by taking RT=70 days

FIGURE  : GD VS RT CHAR

Specific gas production Gd = 37 Lit. / Kg. / day

Daily gas production G = Gd × Feed volume

                                      = 37 × 31500

                                      =1165500 Lit.

                                =1165.5 m3

Now assume gas holder capacity = 60 %

Gas holder volume = Daily gas production × Capacity of holder

                               = 1165.5 × 0.60

                               =699.3 m3

So take Gas holder volume = 700 m3

Now for 6 units provide volume of holder of each unit = 700 ÷ 6

                                                                                     = 116.66

                                                                          Take it =120 m3

Provide cylinder shaped holder; so…

Volume =  π r2 h

      120 = π r2 (h = 1 m)

So dimensions of Gas holder are H = 1 m

                                  

                                                          R = 6 m

 DESIGN OF INLET & OUTLET :

Total volume of slurry mix per unit = 94.50 ÷ 6 = 15.75 m3 / day

Assume two time filling operation in plant; so take total volume of slurry = 15.75 ÷ 2

                                                                                                                   = 7.87 m3 / day

                                                                                                        Take it = 8 m3 / day

Provide rectangular tank…

So..    Total volume for one time mixing of slurry =  L × B × H

                                                                          8 =  L × B × (H=1m)

Dimension of inlet are  L = 3 m

                                       B = 3m

                                       H = 1 m

Here 8 m3 / day required < 9  m3 / day provided.

Hence ok

Provide same size for outlet tank also.

[References taken from biogas book by LUDWIG SASSE, & WWW.BIOTEC-ASIA.COM & WWW.TANAU.AC.IN]