Understanding Coal Power Station Pollution

Coal-based thermal power stations are a significant source of air pollution. When coal is burned to generate electricity, it releases various substances into the atmosphere. These substances are byproducts of the combustion process and the composition of the coal itself.

Major Pollutants from Coal Combustion

The combustion of coal in power plants releases a mix of pollutants that affect air quality. The primary pollutants include:

• Nitrogen Oxides ($\text{NO}_\text{x}$): Formed at high temperatures during combustion when nitrogen in the air and coal reacts with oxygen.
• Sulfur Dioxide ($\text{SO}_2$): Produced from the sulfur content present in the coal.
• Suspended Particulate Matter (SPM): Fine solid particles, including fly ash and soot, that are released during burning.
• Carbon Monoxide ($\text{CO}$): An incomplete combustion product, formed when there isn't enough oxygen for coal to burn completely into carbon dioxide ($\text{CO}_2$).

Let's look at how these pollutants are generated:

• Nitrogen Oxides ($\text{NO}_\text{x}$): High temperatures in the boiler cause atmospheric nitrogen ($\text{N}_2$) and nitrogen compounds in the coal to react with oxygen ($\text{O}_2$), forming nitric oxide ($\text{NO}$) and nitrogen dioxide ($\text{NO}_2$), collectively known as $\text{NO}_\text{x}$.
• Sulfur Dioxide ($\text{SO}_2$): Coal contains varying amounts of sulfur. During combustion, this sulfur oxidizes, primarily forming sulfur dioxide ($\text{SO}_2$).
• Suspended Particulate Matter (SPM): Coal contains non-combustible mineral matter. When coal burns, this mineral matter forms ash. Some of this ash, called fly ash, is carried up with the flue gases as tiny particles, contributing to SPM. Soot is also formed due to incomplete combustion.
• Carbon Monoxide ($\text{CO}$): Ideal combustion turns carbon in coal into carbon dioxide ($\text{CO}_2$). However, if the oxygen supply is insufficient or the temperature is too low, incomplete combustion occurs, producing carbon monoxide ($\text{CO}$), a toxic gas.

Analysing the Options

The question asks about the pollutants added to the atmosphere by coal-based thermal power stations. Based on our understanding, these stations release Nitrogen Oxides ($\text{NO}_\text{x}$), Sulfur Dioxide ($\text{SO}_2$), Suspended Particulate Matter (SPM), and Carbon Monoxide ($\text{CO}$).

Let's evaluate the given options:

• Option 1: Only lists $\text{NO}_\text{x}$ and $\text{SO}_2$. This is incomplete as SPM and $\text{CO}$ are also significant pollutants.
• Option 2: Lists $\text{NO}_\text{x}$, $\text{SO}_2$, and SPM. This is better but misses $\text{CO}$.
• Option 3: Lists $\text{NO}_\text{x}$, SPM, and $\text{CO}$. This is also incomplete as it misses $\text{SO}_2$.
• Option 4: Lists $\text{NO}_\text{x}$, $\text{SO}_2$, SPM, and $\text{CO}$. This option includes all the major pollutants discussed.

Therefore, the option that correctly lists the pollutants from coal-based thermal power stations is the one mentioning $\text{NO}_\text{x}$, $\text{SO}_2$, SPM, and $\text{CO}$.

Revision Table: Coal Power Station Pollutants

Additional Information on Thermal Power Pollution

Beyond the criteria pollutants like $\text{NO}_\text{x}$, $\text{SO}_2$, SPM, and $\text{CO}$, coal-based thermal power stations also release other substances:

• Carbon Dioxide ($\text{CO}_2$): While a natural product of complete combustion and essential for life, $\text{CO}_2$ is a major greenhouse gas contributing to climate change. Coal combustion is a large source of anthropogenic $\text{CO}_2$ emissions.
• Heavy Metals: Coal contains trace amounts of heavy metals like mercury, arsenic, lead, and cadmium. These are released into the atmosphere as vapor or attached to fly ash during combustion.
• Radioactive Elements: Coal also contains trace amounts of naturally occurring radioactive elements, such as uranium and thorium, which can be concentrated in ash and released.

Modern coal power plants employ various pollution control technologies such as electrostatic precipitators or baghouses for SPM removal, flue gas desulfurization (FGD) or scrubbers for $\text{SO}_2$ removal, and low $\text{NO}_\text{x}$ burners or selective catalytic reduction (SCR) for $\text{NO}_\text{x}$ control. Reducing $\text{CO}$ requires optimizing combustion efficiency.