Steelmaking — Bessemer converter operation During a Bessemer converter blow, the appearance of brown smoke (brown fumes) indicates which stage of oxidation inside the converter?

Introduction / Context:
The Bessemer converter refines pig iron into steel by blowing air through the molten bath. The sequence of oxidation reactions can be judged, historically, by flame and fume color. Recognizing these visual cues is part of traditional process control and remains a useful learning tool for steelmaking history and fundamentals.

Given Data / Assumptions:

• Initial bath composition typical of pig iron: high C, and notable Si and Mn.
• Air is blown through tuyeres at the converter bottom.
• Visual observation of fumes and flame color relates to which elements are oxidizing.

Concept / Approach:
Oxidation proceeds preferentially for elements with higher oxygen affinity at the prevailing temperature. Silicon and manganese oxidize early, producing oxides and characteristic brownish smoke in the early stage. Carbon oxidation becomes dominant later, seen as a bright, voluminous flame due to carbon monoxide burning at the mouth. Understanding this order helps interpret the converter’s progress without modern instrumentation.

Step-by-Step Solution:
At blow start: strong oxidation of Si and Mn occurs first.Their oxides and accompanying particulates create a brown smoke/fume—visual indicator of early refining.As Si and Mn diminish, carbon oxidation (to CO/CO2) becomes dominant, altering flame character and intensity.Therefore brown smoke indicates the stage where air is burning out silicon and manganese.

Verification / Alternative check:
Classical metallurgical texts describe the “brown fumes” at the start of the blow and a later “carbon period” marked by a roaring flame. This aligns with the selected option.

Why Other Options Are Wrong:
Option (b) shifts to the carbon period, which is later. (c) is an operational instruction not tied to the fume color; tapping occurs at the proper endpoint. (d) contradicts historical practice. (e) deoxidation is a finishing step using additions, not an air-blow stage.

Common Pitfalls:
Assuming carbon oxidizes first because it is abundant; oxygen affinity and kinetics dictate the real order under converter conditions.

Final Answer:
Air is burning out silicon and manganese