Low-temperature carbonisation — Which statement best describes the products and aims of low-temperature carbonisation of coal (about 500–700 °C)?

Introduction:
Carbonisation temperature controls coke properties and by-product distribution. Low-temperature carbonisation (LTC) differs substantially from high-temperature carbonisation (HTC) used in metallurgical coke making.

Given Data / Assumptions:

• LTC temperature range roughly 500–700 °C; HTC about 900–1200 °C.
• Focus on dominant product purpose and relative yields of gas and tar.

Concept / Approach:
LTC yields a porous, smokeless “semi-coke” suited for domestic or industrial heating (not metallurgy). Because reactions are milder, LTC typically generates relatively high tar yields and a modest gas volume. HTC is required for strong metallurgical coke and gives higher gas volumes but lower tar yields.

Step-by-Step Solution:
Identify the objective: LTC → smokeless fuel, not BF coke.Compare by-products: LTC → more tar, less gas; HTC → more gas, less tar.Select the statement that aligns with these trends: option (a).

Verification / Alternative check:
Typical data: gas yield LTC ≈ 120–200 Nm³/ton (lower); HTC can be several hundred Nm³/ton (higher). Tar yield LTC ≈ 10–14% vs. HTC ≈ 2–5%.

Why Other Options Are Wrong:

• (b) Metallurgical coke requires HTC for strength and low volatiles.
• (c) and (d) invert gas/tar trends.
• (e) Incorrect; LTC intentionally recovers valuable tar and other condensables.

Common Pitfalls:
Assuming all carbonisation is for metallurgical coke; mixing yield trends between LTC and HTC.

Final Answer:
It is mainly used to produce smokeless domestic coke (semi-coke) with significant tar by-product