[biogasRENEWABLEenergy]12.02.2007 Class

BIOGAS DESIGN & PERFORMANCE (TECHNOLOGY)

Capacity of BIOGAS PLANT = 100ft^3.
BIOGAS is used to run the engine-generator setting to produce electricity:
#Thermal efficiency of engine = 40%;
#Electro Mechanical Efficiency of Generator = 75%;
#1ft^3 of biogas containing 55% Methane (CH4) provides 550 Btu of heat;
#40% of fuel energy is tranferable to cooling water;
#1kWh=3411Btu;
#10 lb of Dung plus Water is need to prepare Slurry which occupies a volume of 2/7 ft^3. (equivalent to 1.8 litre of Slurry per kg of Dung);
#Digester is expected to operated at 95oF (=35oC);
#Village needs 125 kWh of Electricity per day.
FIND:
[1]. Biogass (CH4, CO2, H2S, H2) Requirement for Biogass Equipment in m3/day.
[2]. Estimation of Manure Requirement.
[3]. Estimation Digester Capacity (Cylinder). Additional information: 4308 lb (1955kg) is feed to digester daily & should remain inside for 50days for Anaerobic Fermentation.
[4]. Estimation of Gas Holder Size.
[5]. Estimation of heat requirement in Joule (from 68oF to 95oF).

Solution:
[1]. ok

[2]. ok

[3]. ok

[4]. ok

[5]. This Assignment...
Amount of dung / day = 4,308 lb;
Amount of water / day = Amount of dung / day = 4,308 lb;
So, Total mass that need to heat is = 4,308 + 4,308 = 8,616 lb=3908.2176 kg (1 lb=0.4536kg);
95oF= 52.725oC (1 oF = 0.555 oC) and
68oF= 37.74oC.

Assumption: dung+water is well-mixed so, therfore: Cp of Dung=Cp of Water.
Definition of kcal: "The kcal is the heat needed to raise 1 kg of water by 1 oC" [2005. Pearson Education, Inc., Upper Saddle River, NJ. "Answer to Question of Chapter 14: Heat, p.340]
By this definition we can find the heat needed, as below:

Q = 3908.2176 (kg) x (52.725 - 37.74) (oC) x [1 kcal / (1 kg)(1oC)] x [4186 J / 1 kcal] = ...Joule
Q = 3908.2176 x 14.985 x 4186 (Joule)
Q = 245,151,586.120896 J.
Q = 245.1516 MJ/day

Q = 245.1516 x 1055.1 MBtu/day
Q = 258,659.4385 MBtu/day
(because: 1 Btu/s = 1055.1 W; 1 W = 1 J/s; there fore: 1Btu/s=1055.1J/s)

Lasman Parulian Purba, ST (mr)
SN: 4910120113
Master Degree Student in
Mechanical Engineering
Faculty of Engineering
Prince of Songkla University,
HatYai Campus,
THAILAND

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