Coal Fired Boiler Dust Collectors

AEROPULSE Series CFB reverse pulse baghouse provide a safe, efficient and economical means of controlling particulate emissions from industrial and utility coal-fired boilers. They are custom engineered specifically from the temperature, chemistry, gas flow and particulate fineness conditions of such boilers.

Experience based on more than 2,000 baghouses and over fifty coal-fired boiler applications installed and operating has allowed AEROPULSE to design two key factors into the CFB Series: Reliability of operation and low maintenance requirements.

HIGH FULL SIDE INLET
• Unique full side baffle

• Diffuser distributes flue gas evenly, lower upward air velocity, lowers bag abrasion, lower pressure drop, longer life.

MICROPROCESSOR CONTROL
• Affords protection against both high and low temperature excursions, permanent graphic
display is generated for easy reference and quick diagnosis.

BYPASS SYSTEM
• Internal bypass system eliminates need for external ducting, valving and controls.

• Optional multi-module design permits servicing while collector is operating if shutdown or by-pass is not feasible.

Baghouse Dust Collectors for Air Pollution
Control in the Boiler Industry

Up until recently, the most common equipment used to collect flue gas from boilers has been a reverse-air baghouse. Now, however, AeroPulse pulse-jet collectors have demonstrated a number of advantages in new systems and retrofit installations within the boiler industry.

Reverse-air vs. Pulse–jet collectors

Reverse-air collectors in high temperature applications typically use woven fiberglass bags. Dust-laden gas enters from the inside of the bag and clean gas exits through the bag wall. However, the woven glass bag, by itself, is relatively inefficient as a filtration media. In practice, the bag simply serves as a mechanical structure for the build-up of a dust layer, or cake, which provides the actual filtration. Periodically, the bags are cleaned by passing a reverse flow of air through them, a process which requires shutting down a portion of the baghouse. This means that in order to maintain a continuous output from a reverse-air baghouse, one extra compartment must be provided. Individual compartments are then taken off-line, in rotation, for periodic cleaning. In addition, these units cannot be over cleaned because they rely on the cake to provide filtration. They also operate on relatively low grain loadings as well as very low air-to-cloth ratios. When used as a baghouse in a boiler application, these reverse- air units typically run at 1.1 to 1.3 cfm of gas to each square foot of filter.

In contrast, pulse-jet collectors use felted bags where the bag itself provides filtration. These bags are supported on metal cages and the dust-laden gas enters from the outside, with clean gas exiting from the inside. To clean the bag, a short burst of gas is injected into the inside of the bag. This pulse consists of about 20-25% compressed air and 75-80% gas which has just been cleaned. The combination of compressed air and induced gas creates a wave which mechanically shakes the dust from the outside of the bag. In addition, the flow of air is reversed through the bag, removing fine particles trapped between fibers, and providing thorough cleaning. Pulse jet baghouse can operate at high grain loadings, with air-to-cloth ratios that are typically three times higher than reverse-air units. For coal fired boilers P.P.S. felted bags are used. They are resistant to SO3 attack.

Pulse-jet advantages

Because of these fundamental differences in operating principles, pulse-jet collectors offer several significant advantages in boiler applications including:

• constant, high-volume production throughout the life of the bags.
• simpler systems, with less operating valves to maintain.
• less susceptibility to corrosion.
• smaller units that require less space to install.

Because woven bags cannot be thoroughly cleaned, the pressure drop across the bag typically "creeps" up over the operating life of the bag. As pressure increases, the fan is able to move less gas through the collector and production decreases. Felted bags maintain a uniform pressure drop that translates into a constant production rate.

In addition, the need for a modular design usually results in a four-compartment collector. Pulse-jet units eliminate the need for the cyclone and its associated airlock valve, plus the dampers required to segregate different modules. A typical four-compartment reverse-air system has five airlocks and eight dampers. A pulse jet system requires a single airlock. With the very corrosive environment present in boiler installations, this represents a significant reduction in maintenance.

Gas velocity through woven bag collectors is significantly lower than with felted filters. And, the reverse-air design presents larger metal surfaces because of its multiple compartments. These factors, plus the temperature drop in the cyclone contribute to greater cooling of the gas inside the collector. When this cooling is sufficient to drop the gas below the dew point, major corrosion problems can result.

Because they provide higher air-to-cloth ratios and don’t require multiple housings, pulse-jet units are more compact than comparable reverse-air systems. This means they require less space and can be retrofitted quite easily into existing reverse air installations.

AeroPulse Advantages

With almost 35 years of dust collection experience behind them, AeroPulse baghouses are designed to provide long life and reliable service in even the most difficult applications.

Less energy for cleaning

AeroPulse baghouses use 4 1/2 inch diameter bags mounted on 7-inch centers, as opposed to most pulse-jet designs which use 6-inch bags on 8-inch centers. The 70 to 90 psi air and induced gas used to clean the bags results in a pressure of 14 to 18 inches of water at the wall of the 4 1/2 inch bags. With 6-inch bags, less cleaning energy is produced at the bag wall. (Typically 10 x 12 inches of water). Therefore, more compressed air is required for the same cleaning efficiency.

Better collection efficiency

The smaller AeroPulse bag design results in greater open space between bags. Therefore, for the same gas flow through the baghouse, the upward gas velocity is lower in an AeroPulse unit. This means less dust is re-entrained during the cleaning cycle. In addition, AeroPulse has pioneered the successful use of high-side inlet connections, which also serve to reduce upward gas velocity. The combination of these two factors means an AeroPulse collector performs significantly better in applications involving small, light-weight particulate such as the flue gas from a coal fired boiler.

Easier bag removal

An AeroPulse baghouse features true top bag removal. The bag assembly, consisting of bag, cage and venturi, is smaller in diameter than the tubesheet hole. This design eliminates two major problems frequently encountered when trying to remove snap-in bags. Because bags can shrink tightly around the cage, it is often necessary to cut a snap-in bag from its cage before the cage can be removed. Or, a hole in a snap-in bag can cause the bag to fill with dust so that it is bigger than the tubesheet opening through which it must be removed. In either case, the AeroPulse design allows the assembly to be removed easily. If it is necessary to change a bag, the process is accomplished outside of the collector, then the assembly is simply reinstalled.

Longer bag life

The design of the AeroPulse venturi incorporates lugs under the tubesheet. These lugs serve to provide lateral stability, preventing bags from moving in the gas stream which can cause wear. Cages are fabricated of either 304 or 316 SS to minimize corrosion. In addition, the method used for mounting
bags to cages assures a snug fit at the bottom of the cage despite variations in bag length. Without this snug fit, bags wear at the bottom of the cage, as proven by the number of bags which do fail at this point.

AeroPulse pulse-jet baghouses are at work right now in over fifty boiler iinstallations. They can provide you with a lower installed cost and better operating efficiencies.

Wood fired boiler systems

In these applications SO3 is not a problem. Therefore Nomex bags can be used in Place of P.P.S. bags.

One problem with wood fired boilers is a carryover of sparks into the baghouse. This has caused many baghouse fires.

AeroPulse is in the process of getting a patent on a system to eliminate the possibility of these fires. We can discuss this system upon the signing of an Confidentiality Agreement.

Oil fired boilers

Though on a small scale AeroPulse has successfully put in units handling the Effluent from oil fired boilers. This requires the addition of lime.

Please contact us for a quote on this application.