Flue Gas Conditioning

AIR POLLUTION CONTROL Flue Gas Conditioning

Flyash precipitators will not operate effectively if a sufficient amount of Sulfur trioxide (SO₃) is not present in the flue gas. By injecting SO₃ and, in some cases, ammonia into the flue gas downstream of the air preheater, performance of Electrostatic Precipitators (ESPs) can be achieved. All of the SO₃ attaches to the flyash and does not increase SOx emissions.

To produce the desired conditioning gas in the FGC process, elemental sulfur is burned in a furnace which produces SO; SO₂ is converted to SO₃ with a catalyst and injected into the flue gas normally at levels less than 20 ppm.

Technology Benefits

Injection of SO₃ and ammonia into flue gas to improve operation of Electrostatic Precipitators (ESPs)
Reduces flyash resistivity and improves ESP capture of fine particulate for reduced opacity and emissions
Technology proven on over 500 applications worldwide
Cost effective alternative to expensive ESP re-builds or modifications

Sulfur Based Systems

There are two sulfur options: molten sulfur and pelletized dry sulfur (DSI^™ Technology). Ammonia systems can be operated independently or added to SO₃ for dual flue gas conditioning. The solution is unique based on a unit's capacity and flyash conditioning needs, as well as the type of coal burned.

Molten Sulfur

Molten sulfur is the most economical and common feedstock in U.S., widely available in bulk shipments. It is non-hazardous and allows complete combustion within sulfur burner. It is reliably and accurately metered and transferred to burner; as well as, heated to temperature with plant steam or via small, electric steam boiler.

Equipment Sequence for Molten Sulfur:

Molten Tank
Metering Pumps
SO₃ Production
- Air Blower
- Air Heater
- Sulfur Burner
- SO₂/SO₃ Converter
Injection Probes

Pelletized Sulfur (DSI^™ Technology)

Pelletized Sulfur or Dry Sulfur Interface Technology (DSI^™ Technology) provides substantial benefits, especially for smaller capacity units. It eliminates unloading of hot molten sulfur from a tanker truck and reduces steam usage and amount of jacketed interconnecting process piping. Dry Sulfur is shipped on pallets or in silo and can be stored indefinitely without need for steam heating. It has more flexibility in sulfur storage location and equipment layout and is widely available in one-ton super-sacks or bulk deliveries. As with molten sulfur, it is also non-hazardous.

Equipment Sequence for DSI^™ Technology:

Dry Unloading
Dry Silo w/Conveyor
Sulfur Melter
Metering Pumps
SO₃ Production
- Air Blower
- Air Heater
- Sulfur Burner
- SO₂/SO₃ Converter
Injection Probes

Ammonia Systems

Ammonia systems are available using anhydrous or aqueous ammonia. NH₃ is effective alone in certain precipitator enhancement applications, or also in conjunction with SO₃ creating a "dual" conditioning process.

Wide range of system size availability.
When Dual System is installed, some SO₃ equipment (such as the air blower & PLC) can be shared with NH₃ dilution.
Option for using urea based system where reagent safety is a concern
Dual FGC required for high ash coals and flyash where SO₃ alone is not sufficient
Works well on high ash coals (China and India)

Fly Ash Resistivity vs. Flue Gas Temperature

Cold side ESP’s are located downstream of the air heater. Typical flue gas temperatures at the ESP inlet are in the range of 120-204°C (250-400°F), which is in the temperature range where flyash may have high resistivity, depending on the coal and ash characteristics. The Fuel Tech system modifies the resistivity to improve the collection efficiency of the ESP.

Modeling

ESP modeling services are available to evaluate the performance improvement of FGC compared to ESP modifications. This option can be a valuable service to evaluate particulate control options.

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