ICAR AIEEA-PG — Agricultural Engineering & Technology (Major Subject Group 10) · India · National Testing Agency for ICAR
Original practice questions written to the published syllabus · not past papersTurning crop residues, dung and oils into fuel: briquettes, gasifiers, biogas plants and liquid biofuels, and auditing farm energy.
In the exams: ICAR AIEEA-PG Unit V; ICAR AICE subject 42 Units 1–3 and 8; ICAR AICE subject 39 Unit 9; GATE AG biogas sizing (2 of 8 papers)
ICAR AIEEA-PG — Agricultural Engineering & Technology
Unit V renewable energy: definitions and principles of proximate and ultimate analysis, calorific value, briquetting, updraft vs downdraft gasifiers, producer gas composition, dual-fuel engines, anaerobic digestion stages and conditions, KVIC vs fixed-dome plants, ethanol and biodiesel basics, with short calculations.
How our questions for ICAR AIEEA-PG spread across the units of Bio-energy Systems: Design & Applications. Difficulty: 32 easy, 44 medium, 3 hard.
| Gasification: updraft and downdraft gasifiers | 8 | |
| Biogas plant sizing and gas yield | 8 | |
| Biomass characterisation: proximate and ultimate analysis | 7 | |
| Biodiesel and transesterification | 7 | |
| Calorific value | 6 | |
| Combustion of biomass | 6 | |
| Anaerobic digestion stages | 6 | |
| Bio-ethanol | 6 | |
| Energy audit and energy ratio in agriculture | 6 | |
| Briquetting and pelleting | 5 | |
| Pyrolysis | 5 | |
| Producer gas and dual-fuel engines | 5 | |
| Biogas plant types: floating drum and fixed dome | 4 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A sample of crop residue has, on an as-received basis, moisture 12%, volatile matter 62% and ash 8%. Its ash content on a dry basis is closest to:
C. 9.09%
Dry-basis value = as-received value ÷ (1 − moisture fraction) = 8 ÷ (1 − 0.12) = 9.09%. Leaving the 8% unchanged ignores the basis; dividing by (1 − moisture − ash) = 0.80 (10.00%) is the dry ash-free conversion, which cannot be applied to ash itself. Multiplying by (1 + M), 8 × 1.12 = 8.96%, is a common but wrong shortcut.
Freshly cut wood contains 40% moisture on a wet basis. Its moisture content on a dry basis is:
C. 66.7%
Take 100 kg of wet wood: 40 kg water and 60 kg dry matter. Dry basis = water ÷ dry matter = 40 ÷ 60 × 100 = 66.7%. The dry-basis figure is always larger than the wet-basis figure for the same wood. 28.6% divides the water by wet mass plus water, 40 ÷ 140.
A dry biomass has a higher heating value of 18.5 MJ/kg and contains 6% hydrogen (dry basis). Taking the latent heat of water as 2.442 MJ/kg, its lower heating value (dry basis) is:
D. 17.18 MJ/kg
Water formed = 9 × H = 9 × 0.06 = 0.54 kg per kg fuel. LHV = HHV − 2.442 × 0.54 = 18.5 − 1.32 = 17.18 MJ/kg. Forgetting the factor 9 (1 kg H2 forms 9 kg H2O) gives 18.35 MJ/kg; adding instead of subtracting (19.82 MJ/kg) reverses the definition; 8.51 MJ/kg multiplies the HHV by (1 − 9H) = 0.46 instead of subtracting the latent heat.
A fast-pyrolysis unit converts dry biomass (HHV 19 MJ/kg) to bio-oil at a yield of 65% by mass; the bio-oil HHV is 17 MJ/kg. The fraction of feed energy recovered in the bio-oil is:
B. 58.2%
Energy recovery = 0.65 × 17 ÷ 19 = 58.2%. Bio-oil has a lower HHV than the dry feed largely because it carries 15–30% water and is rich in oxygen, so energy recovery is below the mass yield. 65.0% is the mass yield; 72.6% inverts the heating-value ratio (0.65 × 19 ÷ 17); 89.5% is the heating-value ratio alone (17 ÷ 19).
A downdraft gasifier consumes 50 kg/h of wood chips and 75 kg/h of air. The stoichiometric air–fuel ratio of the wood is 6 kg/kg. The equivalence ratio is:
B. 0.25
Actual A/F = 75 ÷ 50 = 1.50 kg/kg. ER = actual ÷ stoichiometric = 1.50 ÷ 6 = 0.25, within the usual gasification range of about 0.2–0.4. 1.50 is the actual air–fuel ratio, not the ER; 4.00 is its inverse. 0.67 is the fuel–air ratio (50 ÷ 75).
The optimum pH range for methanogenic digestion is about:
D. 6.8–7.2
Methanogens are the most pH-sensitive group; methane production is best near neutral pH, roughly 6.8–7.2, and falls sharply below about 6.5. A falling pH signals accumulating volatile fatty acids (souring), usually from overloading. pH 4–5 suits yeast fermentation to ethanol, not methanogenesis. pH 8.5–9.5 raises free-ammonia toxicity, and pH 2–3 stops methanogens entirely.
The chamber of a fixed-dome biogas plant into which slurry is pushed as gas accumulates, and from which digested slurry overflows, is called the:
D. Outlet (displacement) chamber
As gas collects under the dome it pushes slurry down in the digester and up into the outlet chamber; the level difference between the two is the gas pressure. When gas is used, slurry flows back. The mixing tank is at the inlet, the guide frame belongs to floating-drum plants, and the water trap removes condensate from the gas pipe.
For a family biogas plant, the hydraulic retention time chosen at the design stage should be:
A. Longer in cold climates and seasons, because gas production per day falls as temperature drops
Microbial activity slows sharply with temperature, so unheated plants in cooler regions need longer HRT (bigger digesters) for the same degradation. National programmes therefore specify longer HRTs for hill and cold regions than for warm plains. Very short HRTs risk washout of slow-growing methanogens, which is the opposite problem.
Ordinary distillation of a fermented ethanol–water mash cannot yield anhydrous ethanol because:
C. Ethanol and water form an azeotrope at about 95.6% ethanol by mass
At the azeotropic composition the vapour and liquid have the same composition, so further distillation cannot concentrate the ethanol. Fuel ethanol for blending must be nearly water-free, so the rectified spirit is dehydrated, most commonly with molecular sieves (or by azeotropic distillation with an entrainer). Ethanol boils at about 78 °C, below water.
A wheat crop has a total energy input of 15000 MJ/ha and an energy output (grain + straw) of 90000 MJ/ha. The energy ratio and the net energy are:
D. 6.0 and 75000 MJ/ha
Energy ratio = 90000 ÷ 15000 = 6.0. Net energy = 90000 − 15000 = 75000 MJ/ha. The inverse (0.17) is input per unit output.
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