Low-temperature carbonisation — Which statement best describes the products and aims of low-temperature carbonisation of coal (about 500–700 °C)?
-
AIt is mainly used to produce smokeless domestic coke (semi-coke) with significant tar by-product
-
BIt is intended for producing metallurgical coke for blast furnaces
-
CIt produces a higher gas yield than high-temperature carbonisation
-
DIt produces less tar than high-temperature carbonisation
-
EIt yields little or no condensable by-products
Answer
Correct Answer: It is mainly used to produce smokeless domestic coke (semi-coke) with significant tar by-product
Explanation
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