A flue gas cleaning system, also known as a flue gas treatment system or flue gas desulfurization (FGD) system, is a set of equipment and technologies used to remove pollutants from flue gases generated by industrial processes, power plants, and other combustion sources. The purpose of a flue gas cleaning system is to reduce the emissions of harmful pollutants and comply with environmental regulations. Here are some details about flue gas cleaning systems:
1. Pollutant Removal
- 1. Sulfur Dioxide (SO2) Removal: Flue gas cleaning systems primarily focus on removing sulfur dioxide, a major pollutant emitted from fossil fuel combustion. Various methods, such as wet scrubbing with limestone slurry (wet FGD) or dry sorbent injection (dry FGD), are used to remove SO2.
- 2. Particulate Matter Removal: Flue gas cleaning systems also target the removal of particulate matter, including fly ash, dust, and other solid particles, to reduce air pollution. Devices like electrostatic precipitators (ESPs) or fabric filters (baghouses) are commonly used for this purpose.
- 3. Nitrogen Oxides (NOx) and Mercury Removal: Some advanced flue gas cleaning systems also incorporate technologies to reduce nitrogen oxides and mercury emissions. Selective catalytic reduction (SCR) systems and activated carbon injection (ACI) are commonly used for NOx and mercury removal, respectively.
2. Flue Gas Desulfurization (FGD):
- 1. Wet FGD Systems: Wet FGD systems use a chemical reaction between flue gas and a scrubbing medium, usually limestone slurry (calcium carbonate), to remove sulfur dioxide. The reaction forms calcium sulfite or calcium sulfate, which is then collected and disposed of.
- 2. Dry FGD Systems: Dry FGD systems involve the injection of dry sorbent materials, such as lime or sodium bicarbonate, into the flue gas stream. The sorbent reacts with sulfur dioxide to form solid byproducts that are collected and removed from the system.
3. Particulate Matter Control:
- 1. Electrostatic Precipitators (ESPs): ESPs use an electrical charge to attract and collect particulate matter from flue gases. The charged particles are then collected on collecting plates or electrodes and removed from the system.
- 2. Fabric Filters (Baghouses): Baghouses consist of fabric filter bags that capture and collect particulate matter as flue gases pass through them. The collected particles are periodically removed from the bags for disposal.
4. Other Flue Gas Cleaning Technologies
- 1. Selective Catalytic Reduction (SCR): SCR systems use a catalyst and inject a reducing agent, such as ammonia or urea, into the flue gas stream. The catalyst facilitates a chemical reaction that converts nitrogen oxides (NOx) into nitrogen and water vapor.
- 2. Activated Carbon Injection (ACI): ACI involves injecting activated carbon into the flue gas to adsorb and remove mercury and other toxic air pollutants.
- 3. Wet Electrostatic Precipitators (WESPs): WESPs are similar to ESPs but operate in a wet environment. They are used for removing fine particulate matter and acid mists from flue gases.
5. Monitoring and Control Systems:
- 1. Flue gas cleaning systems incorporate monitoring and control systems to optimize performance and ensure compliance with emission standards. These systems continuously monitor various parameters, such as gas flow, temperature, and pollutant concentrations, and adjust the operation of the equipment accordingly.
Flue gas cleaning systems play a vital role in reducing air pollution and minimizing the environmental impact of combustion processes. The selection and design of the appropriate flue gas cleaning system depend on factors such as the type of pollutants, the size and capacity of the facility, and regulatory requirements.