Coke oven gas cooling and scrubbing:\nIn by-product recovery at an integrated steel plant, the circulating flushing liquor used to cool and wash the hot coke oven gas is primarily composed of what?

Introduction / Context:
When coal is carbonized in coke ovens, the evolved raw gas exits hot and laden with tars, ammonia, hydrogen sulfide, and other components. Immediate cooling and initial scrubbing are done using a recirculating liquid called flushing liquor to condense tars and absorb soluble components. Understanding its composition is central to by-product recovery operations and environmental control.

Given Data / Assumptions:

• Industrial coke oven gas (COG) cooling and washing system considered.
• By-product recovery includes tar separation and ammonia removal.
• Standard practice in integrated steel plants.

Concept / Approach:
The circulating liquor becomes ammoniacal as it absorbs ammonia and other nitrogenous bases from the raw gas. This ammoniacal liquor is deliberately recycled through the primary coolers and scrubbers (often called the flushing liquor circuit) to enhance removal of tars and soluble gases. Downstream units then process this liquor to recover ammonia (often converted to ammonium sulfate) and to manage wastewater. Acid solutions like sulfuric or hydrochloric acid are used in specific neutralization steps elsewhere, not as the main flushing medium in the hot-gas coolers.

Step-by-Step Solution:

Verification / Alternative check:
Process descriptions from coke oven by-product units consistently reference the ammoniacal liquor circulation loop for primary cooling and tar removal.

Why Other Options Are Wrong:

• K2CO3 solution is used for CO2 scrubbing in some gas-treatment systems, not for primary flushing.
• Dilute acids are used in specific neutralization/absorption steps, not as the primary cooler liquor.
• Pure water alone is less effective and quickly becomes ammoniacal in service.

Common Pitfalls:
Assuming any water-based fluid is equivalent; the chemistry of the circulating liquor influences tar handling, corrosion, and subsequent by-product recovery.

Final Answer:
Ammoniacal liquor (aqueous ammonia solution from gas washing).