Introduction to the advantages and application fields of flue gas ...

Advantages and Applications of Flue Gas Desulfurization Nozzles

The components of flue gas desulfurization (FGD) nozzles are segmented into individual parts, enhancing the strategic use of materials. High wear-resistant materials such as silicon carbide and metal alloys are utilized in critical areas like the guiding fluid, pre-swirl chamber, and nozzle hole, ensuring durability. Meanwhile, in less critical connection points, materials with excellent mechanical strength like plastic, fiberglass-reinforced plastics, or metal alloys, are employed. This approach maximizes both functionality and economic efficiency, boosting the performance and cost-effectiveness of FGD nozzles.

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Additionally, FGD nozzles are designed for easy installation and improved impact resistance. If a particular part is damaged, only that part needs to be replaced, which reduces maintenance costs compared to replacing the entire nozzle. The variety in material composition allows FGD nozzles to be used in various conditions such as clear liquid, slurry, strong corrosion, and high wear environments.

Introduction to Flue-Gas Desulfurization

The technology of flue-gas desulfurization (FGD) is vital for removing sulfur dioxide (SO2) from the exhaust of fossil-fuel power plants and industries like waste incineration, refineries, and cement and lime kilns.

Methods of FGD

Stringent environmental regulations require the removal of SO2, with methods that can remove up to 90% of SO2 from flue gases. Common methods include both wet and dry scrubbing techniques.

History of FGD

Studies on removing sulfur dioxide date back to over 150 years, with significant developments in the 1920s in England. The first major FGD units were installed during the 1930s, halting during World War II and resuming thereafter with more robust implementations emerging in the 1970s.

FGD on Ships

The International Maritime Organization (IMO) mandates the use of exhaust gas scrubbers on ships to ensure compliance with MARPOL Annex VI sulfur regulations. These systems must be approved by flag States and can be inspected by port States.

Sulfuric Acid Mist Formation in FGD

Fossil fuels contain sulfur, which converts primarily into SO2 and sometimes SO3 under high temperatures and excess oxygen. SO3 forms sulfuric acid mist, which is difficult to remove and often addressed with wet electrostatic precipitators.

FGD Chemistry

Basic Principles

FGD systems typically have stages for fly ash and SO2 removal, with wet systems usually involving an initial fly ash removal stage followed by SO2-absorber. In dry systems, lime reacts with SO2 before particulate control.

Scrubbing with Alkali

Common alkali scrubbing agents like calcium carbonate or sodium hydroxide react with SO2 to form various sulfites. Advanced systems can further oxidize these into saleable gypsum.

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Types of Wet Scrubbers

Various designs like spray towers and packed beds promote gas-liquid interaction to maximize SO2 removal, with considerations for pressure drop and scaling issues.

Venturi Scrubbers

Venturi scrubbers accelerate gas streams, facilitating efficient SO2 and fly ash removal, but require careful management of pressure drops and scrubbing media.

Packed Bed Scrubbers

Packed bed scrubbers offer higher SO2 removal efficiency with lower pressure drops, but they risk plugging from particulate matter.

Spray Towers

Simpler in design, spray towers efficiently circulate slurries for SO2 absorption, though requiring higher liquid-to-gas ratios compared to other methods.

Regenerative and Emerging FGD Methods

Regenerative Scrubbing

Sodium sulfite solutions can regenerate by reversing reactions with temperature changes, enabling cost-effective and continuous operation.

Ammonia Gas-phase Oxidation

Emerging technologies using electron beams and ammonia convert SO2 into ammonium sulfate, which serves as fertilizer. This method, implemented successfully in plants like Chendu and Pomorzany, offers both sulfur and nitrogen oxide removal.

Statistics and Costs

FGD units, ranging from 5 MW to 1,500 MW in capacity, employ wet scrubbers predominantly in the US. Costs vary significantly based on system type and plant size, with wet scrubbers generally more expensive than dry variants.

Alternative Methods

Methods like hydrodesulfurization treat fuels before or during combustion, adding substances such as lime to form sulfates in the ash, offering an alternative to post-combustion sulfur removal.

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