Coal-Fired Boilers in Dust Collector Manufacturing and Dust Collector Design
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
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 have yielded efficiencies between 90% and 98% over a range of low and high sulfur coals. In addition to the high efficiency, the initial cost and power consumption for this equipment is low. The major drawback is that an air pollution problem has become a water pollution problem, where wet sludge must be dewatered and converted to either a usable product or safe landfill material.
In a spray dryer, alkaline slurry is sprayed onto the flue gas. The water is vaporized and the SO2 reacts with the solids, leaving a dry powder. The vapor and fugitive particulates are then conveyed to a dust collector. Advantages of a spray dryer are low cost construction, dry product with no waste water and lower water usage than a wet scrubber. The usual reagent used is slaked lime (Ca(OH)2) and the normal efficiency on low-sulfur coal is 70%-90%. The ratio of calcium reagent to sulfur is between 1.1 and 1.6, which is less efficient than with a wet scrubber. Spray dryers are generally used on coals with <1.5% sulfur where it is the more economical choice, offsetting the disadvantages of higher reagent use and lower efficiency.
NOX Removal
Nitrogen oxides (NOX) in flue gas are reduced to N2 and H2O through selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). In SCR, ammonia is sprayed into the flue gas and reacts with nitrogen oxides in the gas when the stream passes over a catalyst. Different catalysts have different operating temperatures. The normal operating temperature ranges from about 450° (platinum) to 840° (zeolite).
With SNCR, a reducing agent is injected in the furnace to react with the nitrogen oxides at high temperature, the reaction occurring between 1600° and 2000°. The capital cost is lower than for SCR because no catalyst is needed.
Dust Collection
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. Baghouses are significantly more efficient than ESPs. Baghouses are also cheaper and require less maintenance than ESPs.
BCE has a proven system that allows us to use our baghouses in coal-fired boilers. Our system completely and totally eliminates the risk of fires starting in the baghouse plenums. The result is that we provide the best solution available.