Air pollution control context: Among common industrial sources, which plant does not typically emit an appreciable amount of sulphur dioxide (SO2) to the atmosphere under normal operation?

Introduction:
Industrial sources release different primary air pollutants depending on feed, process chemistry, and control equipment. Sulphur dioxide, abbreviated as SO2, is a classic pollutant from the oxidation of sulphur present in fuels and certain ores. The question asks which listed plant does not normally emit appreciable SO2, which requires recalling the dominant chemistry and fuels used by each industry.

Given Data / Assumptions:

• We consider routine, well operated plants.
• Fuel sulphur content and process gas composition define SO2 tendency.
• The options reflect typical large point sources.

Concept / Approach:
SO2 forms when sulphur oxidizes during combustion or is released from sulphide ores. Thermal power plants and petroleum refineries burn sulphur bearing fuels, so SO2 appears in flue gas unless desulphurised. Sulphuric acid manufacture begins with sulphur or sulphide oxidation to SO2 as an intermediate, so unmanaged streams may contain SO2. In contrast, nitric acid production centers on oxidizing ammonia to NO and NO2, yielding oxides of nitrogen rather than sulphur compounds, so appreciable SO2 is not characteristic of that stack.

Step-by-Step Solution:
Identify SO2 prone sectors: high sulphur fuels or sulphur feedstocks.Thermal power: coal and heavy oils contain sulphur, generating SO2.Refineries: process heaters and FCC regenerators burn sulphur bearing fuel gas and coke, forming SO2.Sulphuric acid plant: SO2 is a process intermediate to H2SO4, so leaks or tail gas can contain SO2.Nitric acid plant: core pollutant is NOx, not SO2, so SO2 emissions are not appreciable.

Verification / Alternative check:
Pollution control focus confirms this pattern: FGD targets SO2 at power plants; refineries implement sulphur recovery units; sulphuric plants use tail gas cleanup; nitric acid units install NOx abatement such as selective catalytic reduction, which addresses NO and NO2, not SO2.

Why Other Options Are Wrong:
Thermal power plant: burns sulphur containing fuel and forms SO2. Petroleum refinery: combustion and catalyst regeneration emit SO2. Sulphuric acid plant: SO2 is inherent to the process. Cement kiln: may emit SO2 from raw materials and fuel sulphur, though variable.

Common Pitfalls:
Assuming all large stacks behave similarly. Emissions mirror process chemistry. A plant focused on nitrogen oxidation will not inherently emit sulphur oxides.

Final Answer:
Nitric acid plant