Question

Pyrolysis of biomass at a relatively low temperature produces

• A. Mixture of combustible gases having low calorific value
• B. Combustible gas and carbon char
• C. Carbonaceous char
• D. Liquid fuel of very high calorific value

Hint:

Recall how traditional charcoal is made, slow heating at low temperature in absence of air.

Answer 1

The Correct Option is C

Step 1: Pyrolysis is the thermochemical breakdown of biomass in the absence of oxygen, and what comes out of it, mostly char, mostly liquid or mostly gas, depends heavily on the temperature and the heating rate used.

Step 2: At relatively low temperature with slow heating and long residence time, the process is called carbonization or slow pyrolysis. This is the same basic idea used in traditional charcoal kilns. The slow, low heat breaks the biomass down gently and most of the solid carbon skeleton is left behind as charcoal, that is, carbonaceous char.

Step 3: As the temperature and heating rate go up (fast pyrolysis, around 450 to 550 degree C with very short vapour residence time), the vapours are condensed quickly before they can crack further, and the major product shifts to liquid bio-oil.

Step 4: At still higher temperature with longer residence time (gasification conditions), the char and heavy vapours keep breaking down further and the major product becomes combustible gas.

Step 5: So a relatively low pyrolysis temperature favors char formation, not gas and not high calorific liquid fuel, making carbonaceous char the correct answer.