Dioxin formation and control in a gasification-melting plant

Area of Science:

• Environmental Science
• Chemical Engineering
• Waste Management

Background:

• Thermal waste treatment plants using gasification and melting are common in Japan.
• Understanding dioxin formation and removal is crucial for environmental protection.

Purpose of the Study:

• Investigate dioxin formation and removal in a commercial thermal waste treatment plant.
• Assess the impact of municipal solid waste (MSW) composition, particularly plastic content.
• Evaluate the effectiveness of catalytic decomposition for dioxin removal.
• Determine the suitability of dioxin surrogate compounds for plant monitoring.

Main Methods:

• Analysis of dioxin levels in flue gas at various stages of a gasification and melting plant.
• Controlled variation of MSW input, focusing on plastic content.
• Utilizing bag filter equipment with catalytic filters for dioxin removal.
• Mass balance analysis of dioxins and fly ash.
• Evaluation of organohalogen compounds as dioxin surrogates.

Main Results:

• Increased dioxin content in flue gas observed when plastic waste exceeded plant capacity.
• Catalytic bag filters reduced gaseous dioxin levels below 0.1 ng toxic equivalency (TEQ)/m³ N.
• Dioxin mass balance and fly ash analysis confirmed decomposition and adsorption.
• Dioxin surrogate compounds correlated well with actual dioxin levels.

Conclusions:

• Disturbances in combustion due to excessive plastic waste significantly increase dioxin formation.
• Catalytic filters are effective in reducing dioxin emissions to meet stringent environmental standards.
• Dioxin surrogate monitoring provides a reliable method for assessing plant performance and compliance.