Engineering

Coal–Fired Boilers

The principal pollutants from coal-fired boilers, which have been targeted by local and federal regulatory agencies, are SO2, NOX, and PM 10 particulates. The particular pollution control equipment for a given installation is dependent on the combustion system, the chemistry of the fuel being burned, and the applicable regulations.

SO2 Removal (Flue Gas Desulfurization)

Sulfur dioxide removal is known in the industry as flue gas desulfurization (FGD). The most commonly used FGD equipment for utility boilers are wet scrubbers and spray dryers.

Wet Scrubbers

  • Efficiencies between 90% and 98% over a range of low and high sulfur coals
  • Low initial cost and power consumption
  • Major drawback: converts air pollution to water pollution
  • Wet sludge must be dewatered and converted to usable product or safe landfill material

Spray Dryers

  • Alkaline slurry sprayed onto flue gas
  • Water vaporizes and SO2 reacts with solids, leaving dry powder
  • Vapor and fugitive particulates conveyed to the dust collector
  • Advantages: low cost construction, dry product, no wastewater, lower water usage
  • Usual reagent: slaked lime (Ca(OH)2)
  • Normal efficiency on low-sulfur coal: 70%-90%
  • Calcium to sulfur ratio: 1.1 to 1.6 (less efficient than wet scrubbers)
  • Generally used on coals with <1.5% sulfur where economically advantageous

NOX Removal Technologies

Nitrogen oxides (NOX) in flue gas are reduced to N2 and H2O through selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR).

Selective Catalytic Reduction (SCR)

  • Ammonia sprayed into flue gas reacts with nitrogen oxides over a catalyst
  • Different catalysts have different operating temperatures
  • Operating temperature ranges: 450°F (platinum) to 840°F (zeolite)

Selective Non-Catalytic Reduction (SNCR)

  • Reducing agent injected in furnace to react with nitrogen oxides at high temperature
  • Reaction occurs between 1600°F and 2000°F
  • Lower capital cost than SCR (no catalyst needed)

Dust Collection Solutions

Electrostatic precipitators (ESPs) were the most commonly used dust collection equipment in coal-fired power plants and are now being replaced or retrofitted with fabric filter dust collectors/baghouses.

Advantage of Baghouses: Baghouses are significantly more efficient than ESPs. Baghouses are also cheaper and require less maintenance than ESPs.

BCE Innovation: BCE has a proven system that allows us to use our baghouses in coal-fired boilers. Our system eliminates the risk of fires starting in the baghouse plenums. The result is that we provide the best solution available.