Prevent Electrostatic Precipitator and Baghouse Hopper Blockage with Hopper Heaters

Coal-fired power plants in the U.S. require the use of electrostatic precipitators or bag houses to filter out very fine fly ash particles incorporated into flow gas. The ash is collected while the flue gas passes through filter bags or large electrodes and then falls into hoppers. As the hot fly ash cools, it may condense on the hopper walls. The mixture of dry, sulfur-rich fly ash and water is very problematic, so it is very important that there is no condensation in the collection hoppers.

The mixture of water and fly ash can cause the hopper to block up (or "pluggage "), and most importantly, residual sulfur in the flue gas will combine with condensate to form sulfuric acid. The sulfuric acid attacks the inside of the hopper walls, causing corrosion, weakening walls and generating significant (and costly) maintenance problems over time.

Efficient and continuous removal of fly ash is essential for all coal-fired power plants. Collection hoppers are an integral part of the removal process. Plugging or inoperable hoppers are a known problem for engineers and maintenance crews. Constant maintenance and excess downtime seriously prevent a plant's ability to manage the production rate of fly ash. Slower fly ash production means a reduction in energy production and efficiency. The power generation of a power station is directly proportional to its rate of combustion of coal, which in turn directly affects the production of fly ash. The maintenance personnel usually attempt to remedy ash system failures in real time by disabling the affected hopper, while continually generating electricity and ash. In some situations (to prevent shutdowns of boilers), ash will be dumped on the floor, requiring costly cleaning.

Evacuation and management of fly ash is much easier if the ash is kept warm. One of the most common ways of maintaining high fly ash and hopper temperatures is by connecting electric hopper heaters to the outside hopper walls. Hopper heaters play a very important role in removing the fly ash from precipitators and bag filter walls by keeping the hopper temperatures over the flue gas acid dew point. The only function of the hopper heater is to preheat the hopper and the internal environment to prevent the formation of moisture, fly ash clumping and the development of sulphuric acid.

Hopper heaters are designed for a dirty, high-vibration power plant environment. They provide the optimum watt density for proper thermal transfer through the hopper wall and uniform heating. They are available in square, rectangular and trapezoidal shapes for any hopper design. For poke tubes, man-ways and cylindrical throats, ancillary flexible heating cloths are available. The use of electric hopper heaters in electrostatic precipitator and bag house fly ash collection systems is an effective time-tested way to prevent condensation and the resulting clumping and corrosive acids in hopper products, thus providing better opportunities for continuous production of fly ash.

Hazardous Area Heater Control Systems for Coal Hoppers and Conveyors

Explosion proof control system.

A major hazard in coal burning utilities is the transfer and storage of coal due to the presence of highly combustible coal dust. Mitigating the risks of combustible dusts eliminate the potential for dust explosions. It is critically important that any coal handling or coal storage facility have access to experienced application engineers who understand the specific requirements when handling coal and managing coal dust.

Electric heat is very often used to prevent coal freeze-ups in hoppers and conveyors. The most common electric heaters used are are exterior mounted panel heaters with carefully calculated watt densities to keep sheath temperatures low. A less preferred solution is the use of tubular heating elements that may have higher sheath temperatures. Tubular heaters are usually clamped or stud-welded to the exterior of the coal hopper or conveyor chute.  In either case, a control system must be employed to maintain operating temperatures and to safely limit temperatures below dust ignition temperatures.  Since the presence of coal dust in the atmosphere is considered normal, the use of explosion proof housings, conduit, and wiring practices is required for these control systems.

Internal view.

Hotfoil, a New Jersey manufacturer of electric hopper and coal handling heating systems,  designs, engineers, and fabricates custom control systems specifically for these applications. 

With decades of experience in hopper, conveyor, and tank heating systems they provide their customers with a single-source, turn-key, electrical heating and control system solutions provider. All products are 100% quality tested prior to leaving the facility, and an added plus is that they provide on-site start-up assistance.

Electric Heating and Control Solutions for Power Generation

Hotfoil-EHS specializes in electric surface heating systems in power plants for fly ash hoppers on electrostatic precipitators or baghouses, coal and material handling systems, tanks, and pipes.

For more information, visit http://www.hotfoilehs.com.

Freeze Protection for Coal Handling Systems

Coal stored outdoors on the stockpile or delivered by unit train or barges picks up moisture from rain and snow. When this wet or frozen coal is conveyed, it inevitably comes into contact with the plate steel of the various hoppers and chutes within the coal handling system. During winter, this plate steel is below freezing for extended periods.

When wet or frozen coal encounters steel at sub freezing temperatures an instantaneous bond is formed. This bond causes immediate and often catastrophic blockage of the hopper and chutes. The bond and resultant blockage is so severe that pneumatic drilling equipment and explosives are often required to free up the system.

This problem, known as FLASH FREEZING, is extremely inconvenient and very costly. Several cases are documented where utility and industrial boilers have been shut down due to blocked conveying systems.

The document below describes effective electric heating systems for coal handling freeze protection.

Freeze Protection for Coal Handling Systems from Hotfoil EHS, Inc.