Question

Which of the following are thermochemical conversion processes for biomass
(A). Gasification
(B). Anaerobic digestion
(C). Fermentation
(D). Liquification
Choose the correct answer from the options given below:

• (A) and (B) only.
• (C) and (D) only.
• (A) and (D) only.
• (B) and (C) only.

Hint:

Thermochemical processes are faster (seconds to hours) and better suited for low-moisture woody biomass, whereas biochemical processes are slower (days to weeks) and ideal for wet organic waste.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Biomass conversion technologies are broadly classified into thermochemical conversion processes (which use thermal energy to drive chemical transformations) and biochemical conversion processes (which utilize microorganisms and enzymes).

Step 2: Detailed Explanation:
Let us classify each given process.
1.Gasification (A): Involves heating biomass in a high-temperature ($700^{\circ}\text{C}$ to $1000^{\circ}\text{C}$), oxygen-starved environment to produce a gaseous fuel mixture (syngas or producer gas).
This is a classic thermochemical process.
2.Anaerobic Digestion (B): Converts organic waste into biogas using anaerobic microbes at low temperatures ($35^{\circ}\text{C}$ to $55^{\circ}\text{C}$).
This is a biochemical process.
3.Fermentation (C): Uses yeasts or bacteria to convert sugars in biomass into ethanol.
This is a biochemical process.
4.Liquification/Liquefaction (D): Thermochemical liquefaction converts high-moisture biomass into bio-crude oil under high pressures ($5$ to $20\text{ MPa}$) and moderate temperatures ($250^{\circ}\text{C}$ to $350^{\circ}\text{C}$).
This is a thermochemical process.
Thus, only (A) Gasification and (D) Liquification are thermochemical processes.

Step 3: Final Answer:
The processes (A) and (D) are thermochemical, whereas (B) and (C) are biochemical.