REP Bioenergy and Waste-to-Energy 4 — Questions and Answers
Question 1: Under the U.S. Renewable Fuel Standard (RFS), which biofuel pathway requires at least a 60% lifecycle greenhouse gas reduction compared to the petroleum baseline?
- Conventional biofuel (corn ethanol)
- Advanced biofuel
- Cellulosic biofuel (Correct answer)
- Biomass-based diesel
Correct answer: Cellulosic biofuel
Cellulosic biofuel under RFS requires a minimum 60% lifecycle GHG reduction, the highest threshold among RFS fuel categories.
Question 2: Which emission control technology is specifically designed to reduce dioxin and furan emissions from municipal solid waste incinerators?
- Selective catalytic reduction (SCR)
- Activated carbon injection upstream of fabric filters (Correct answer)
- Electrostatic precipitators alone
- Wet scrubbers removing SO2 only
Correct answer: Activated carbon injection upstream of fabric filters
Activated carbon injection adsorbs dioxins and furans before they are captured in fabric filter baghouses, achieving over 99% removal efficiency.
Question 3: What is the primary purpose of the tipping floor in a mass-burn waste-to-energy facility?
- Final ash cooling and disposal
- Receiving, inspecting, and blending incoming waste before combustion (Correct answer)
- Biogas upgrading to pipeline quality
- Residue metal recovery after combustion
Correct answer: Receiving, inspecting, and blending incoming waste before combustion
The tipping floor is where waste trucks deposit loads, operators inspect for prohibited materials, and waste is blended to maintain consistent fuel quality.
Question 4: Which economic incentive mechanism allows biomass electricity generators in the U.S. to sell renewable energy certificates separate from the electricity itself?
- Production Tax Credit (PTC) only
- Renewable Portfolio Standards (RPS) creating REC markets (Correct answer)
- Carbon capture credits under Section 45Q
- Investment Tax Credit (ITC) monetization
Correct answer: Renewable Portfolio Standards (RPS) creating REC markets
State RPS programs create demand for renewable energy certificates (RECs), allowing biomass generators to monetize the renewable attribute separately from electricity sales.
Question 5: Torrefaction of biomass produces a product with improved properties primarily due to which chemical change?
- Complete carbonization into charcoal
- Partial decomposition of hemicellulose increasing energy density and hydrophobicity (Correct answer)
- Full gasification into syngas
- Enzymatic breakdown of lignin
Correct answer: Partial decomposition of hemicellulose increasing energy density and hydrophobicity
Torrefaction at 200–300°C decomposes hemicellulose, increasing energy density, reducing moisture uptake, and improving grindability for pellet and co-firing applications.
Question 6: In a landfill gas-to-energy (LFGE) project, what is the typical range of landfill gas methane concentration?
- 5–15%
- 20–35%
- 45–60% (Correct answer)
- 70–85%
Correct answer: 45–60%
Mature landfill gas typically contains 45–60% methane, generated by anaerobic decomposition of organic waste within the landfill mass.
Question 7: What does 'bottom ash' refer to in a waste-to-energy combustion facility, and what is its typical management pathway in the US?
- Fly ash collected in air pollution control devices, landfilled as hazardous waste
- Residue falling from the grate after combustion, often processed for metal recovery and beneficial reuse (Correct answer)
- Biochar produced from pyrolysis, applied to soil
- Activated carbon waste from dioxin control systems
Correct answer: Residue falling from the grate after combustion, often processed for metal recovery and beneficial reuse
Bottom ash is the coarse residue from the grate (~20% of waste weight), typically processed to recover ferrous and non-ferrous metals before aggregate reuse.
REP Bioenergy and Waste-to-Energy 4
Under the U.S.
Renewable Fuel Standard (RFS), which biofuel pathway requires at least a 60% lifecycle greenhouse gas reduction compared to the petroleum baseline?