REP Bioenergy and Waste-to-Energy 2 — Questions and Answers
Question 1: Which gasification agent produces the highest heating value syngas but is too costly for most commercial waste-to-energy applications?
- Steam
- Air
- Pure oxygen (Correct answer)
- Carbon dioxide
Correct answer: Pure oxygen
Pure oxygen gasification produces high-quality syngas with minimal nitrogen dilution but is economically prohibitive for most commercial WtE projects.
Question 2: The Fischer-Tropsch process converts syngas into liquid fuels primarily through which reaction type?
- Fermentation
- Catalytic hydrogenation of CO and H2 (Correct answer)
- Pyrolytic cracking
- Anaerobic oxidation
Correct answer: Catalytic hydrogenation of CO and H2
Fischer-Tropsch synthesis uses catalysts to polymerize CO and H2 into liquid hydrocarbons ranging from diesel to waxes.
Question 3: In a biomass integrated gasification combined cycle (BIGCC) plant, what is the primary efficiency advantage over conventional steam-only biomass power?
- Lower feedstock moisture tolerance
- Use of gas turbine topping cycle before steam recovery (Correct answer)
- Elimination of all emissions
- Direct methane injection to grid
Correct answer: Use of gas turbine topping cycle before steam recovery
BIGCC achieves higher electrical efficiency by extracting work from a gas turbine first, then recovering exhaust heat in a steam cycle.
Question 4: Which municipal solid waste fraction typically has the highest energy content on a dry weight basis?
- Food waste
- Glass and ceramics
- Plastics (Correct answer)
- Ferrous metals
Correct answer: Plastics
Plastics have a high calorific value (~35–45 MJ/kg dry) derived from their hydrocarbon polymer chains, exceeding most other MSW components.
Question 5: What does the term 'refuse-derived fuel (RDF)' specifically refer to?
- Raw unprocessed municipal solid waste burned directly
- Processed and shredded MSW with non-combustibles removed for fuel use (Correct answer)
- Landfill gas captured after waste decomposition
- Sewage sludge pellets used in boilers
Correct answer: Processed and shredded MSW with non-combustibles removed for fuel use
RDF is MSW that has been mechanically processed—shredded, screened, and separated—to remove non-combustibles and improve fuel consistency.
Question 6: Hydrothermal liquefaction (HTL) is particularly advantageous for which feedstock characteristic compared to conventional pyrolysis?
- Very dry lignocellulosic wood chips
- High-moisture content algae and wet biomass (Correct answer)
- Pre-dried agricultural residues
- Low-ash coal blends
Correct answer: High-moisture content algae and wet biomass
HTL processes wet biomass in supercritical or near-critical water, avoiding the energy cost of drying that makes conventional pyrolysis inefficient for wet feedstocks.
Question 7: Which metric is used to quantify how much electrical energy a waste-to-energy plant generates per tonne of waste processed?
- Capacity factor
- Specific electricity output (kWh/tonne) (Correct answer)
- Net heating value ratio
- Combustion efficiency index
Correct answer: Specific electricity output (kWh/tonne)
Specific electricity output (kWh per tonne of waste) measures the electrical generation efficiency of a WtE facility relative to waste throughput.
REP Bioenergy and Waste-to-Energy 2
Which gasification agent produces the highest heating value syngas but is too costly for most commercial waste-to-energy applications?