Industrial air emissions: Which type of chemical process plant is classically associated with large sulfur dioxide (SO2) emissions if controls are inadequate or during upsets?

Introduction / Context:
Sulfur dioxide is a key air pollutant linked to acid rain and respiratory irritation. Identifying its major industrial sources is essential for emission control strategies and environmental compliance.

Given Data / Assumptions:

• Plant types represent common heavy industries.
• We consider typical process off-gases and the consequences of poor control.
• Focus is on SO2, not NOx, CO, or particulates.

Concept / Approach:
In the contact process for sulfuric acid, sulfur or sulfide ores are burned to produce SO2, which is then catalytically converted to SO3 and absorbed to form H2SO4. If conversion/absorption is incomplete or during startup, shutdown, or upset, substantial SO2 can be released. Iron and steel operations may emit SO2 from sulfur in coke, but sulfuric acid plants are directly centered on SO2-rich process streams, making them emblematic sources when uncontrolled.

Step-by-Step Solution:
Identify process chemistry: sulfur oxidation → SO2 generation.Recognize control points: catalyst beds and absorber; bypass or inefficiency → SO2 slip.Select the plant inherently handling high SO2: sulfuric acid plant.

Verification / Alternative check:
Emission inventories often highlight sulfuric acid units as significant SO2 sources in the absence of tail-gas treatments (e.g., wet gas scrubbing or double absorption).

Why Other Options Are Wrong:
Nitric acid: primarily NOx issues.Chlor-alkali: chlorine, brine aerosols, mercury (legacy), not SO2 centered.Iron and steel: can emit SO2, but less directly process-intrinsic than H2SO4 manufacture.Cement: mainly dust and NOx/SO2 depending on fuels, but not the classic SO2 process stream.

Common Pitfalls:
Confusing by-product SO2 from fuel combustion with processes where SO2 is the primary intermediate.

Final Answer:
Sulfuric acid plant