Pollution Emission and Treatment from Diesel Generator Sets

Diesel generator sets are widely used for power supply, but the pollutants they emit during operation have raised significant concerns. When fuel is burned inefficiently, it releases harmful substances, including smoke and noise, which can lead to environmental pollution, such as electromagnetic radiation. The main pollutants from diesel generator engines are nitrogen oxides (NOx) and particulate matter (PM). These pollutants pose varying degrees of harm to human health, ecosystems, and produced goods. The severity of these pollutants' impact is closely related to their toxicity, concentration in the air, and the duration of exposure, making it crucial to address this issue.

Main Pollutants and Their Effects

During the operation of diesel generator sets, the primary pollutants generated include nitrogen oxides (NOx), particulate matter (PM), and hydrocarbons (HC). These pollutants not only negatively impact the environment but also pose serious threats to human health and ecosystems. Understanding the characteristics and hazards of these pollutants is essential for developing effective control measures.

1. Nitrogen Oxides (NOx)

Composition and Nature: NOx mainly consists of nitric oxide (NO) and nitrogen dioxide (NO2). NO is a colorless gas with slight irritant properties. Although it has little effect on human health at low concentrations, high levels can lead to central nervous system disorders, impacting cognitive and motor functions.
Environmental Impact: NOx affects air quality and can react with other substances to form ozone, further harming the ecosystem and human health.

2. Particulate Matter (PM)

Source and Harm: Particulate matter refers to solid substances collected from the air after dilution and cooling to 52°C. The harm caused by PM depends on its size and composition, especially affecting the lungs and bronchi. Smaller particles (PM2.5) can penetrate deep into the lungs and even enter the bloodstream, leading to respiratory and cardiovascular diseases and other health issues.
Classification of Particulate Matter: Particulate matter is categorized into primary and secondary particles. Primary particles are directly produced during combustion, while secondary particles arise from gas transformations and are generally more difficult to control and remove.

3. Hydrocarbons (HC)

Composition and Impact: Hydrocarbons include unburned fuel, lubricating oil, and their breakdown products along with some oxides. Long-term inhalation of excessive hydrocarbons can impair blood production, leading to anemia, neuromuscular disorders, and reduced lung resistance to infections.

Waste Gas Treatment Methods

To address the pollutant emissions from diesel generator sets, several waste gas treatment methods have been developed, including:

1. Wet Water Treatment

This method involves filtering waste gas directly with water. While it can remove some pollutants, its effectiveness is limited and may not meet strict emission standards.

2. Dry Smoke Removal Treatment

This method uses dry purification devices to eliminate smoke, but it is less effective for removing other harmful substances.

3. Dry Harmful Substance Treatment

This approach filters harmful substances such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and sulfur dioxide (SO2) from the waste gas, meeting national emission standards.

Control Strategies for NOx and Particulate Matter

Controlling NOx and particulate matter produced during combustion in diesel generator sets is a complex technical challenge. Research indicates that NOx formation requires combustion temperatures above 2000°C with sufficient in-cylinder oxygen, while particulate matter forms at temperatures exceeding 1000°C under oxygen-deficient conditions.

Control During Pre-combustion Phase: Reducing the amount of combustible mixture can lower combustion temperatures, effectively reducing NOx emissions.
Control During Diffusion Combustion Phase: Maintaining a good mixture of fuel and air at high combustion temperatures helps lower particulate matter generation.
Modern diesel generators commonly employ advanced technologies like high-pressure injection, guided injection, electronic control injection, exhaust gas recirculation, and direct water injection to effectively control NOx and particulate matter.

Exhaust After-treatment Technologies

Exhaust after-treatment aims to prevent waste gas from being directly emitted into the atmosphere. Common methods include:

1. Particulate Matter Capture

Particulate matter capture devices are typically installed at the exhaust end of diesel generators, commonly using ceramic particulate filters and disposable paper filters.
Ceramic Filters: These use a honeycomb structure to effectively capture carbon particles from the exhaust, achieving over 90% filtration efficiency. However, they require regular cleaning to avoid increased exhaust back pressure, which can affect generator performance.

2. Catalytic Conversion

Catalytic conversion uses ammonia or urea as a reducing agent to convert NOx in the waste gas into nitrogen (N2) and oxygen (O2) at temperatures between 300 and 400°C. This method can reduce NOx emissions by 95%, making it one of the most effective ways to control NOx emissions. However, it has high equipment costs, is large in size, and requires significant maintenance.

Conclusion

In summary, diesel generator sets produce various pollutants during operation that threaten the environment and human health. Through scientific control and effective waste gas treatment technologies, emissions of these pollutants can be significantly reduced, minimizing their impact on ecosystems and health. As technology continues to advance, the environmental performance of diesel generator sets is expected to improve further, contributing to sustainable development.