Subtopic: Bio-fuels and their use in farm mechanization
Question Statement:
A farmer constructed a 2 m³ 40 days HRT Deenbandhu biogas plant used solely for cooking, burner efficiency 45%. Gas density 0.94 kg m⁻³, heating value 21 MJ kg⁻¹. Total effective energy available per day in MJ will be
Options:
(A) 17.77
(B) 18.91
(C) 24.47
(D) 39.48
Official Answer Key:
A
Step-by-Step Solution & Explanation
Daily gas output of a steady-state digester of this size is taken as its full working volume, 2 m³/day. Mass of gas/day = 2 × 0.94 = 1.88 kg. Gross energy = 1.88 × 21 = 39.48 MJ. Applying the 45% burner (utilisation) efficiency: Effective energy = 39.48 × 0.45 = 17.77 MJ/day. (D) 39.48 is the un-corrected gross energy — a common trap for skipping the efficiency step.
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