using thermon heat trace cables & modules
FLY ASH – Removing Fly Ash From Precipitators & Baghouse Hoppers
Fly ash is a by-product of coal combustion composed of fine particles expelled from the coal combustion chamber (boiler) with flue gases – in modern coal-fired power plants, fly ash is generally captured by emission controls and particle filtration equipment, such as electrostatic precipitators (ESP’s), “baghouses” and scrubbers before the flue gases reach the chimney stacks.
The precipitators and baghouses have multiple pyramidal hoppers located at the bottom, in which the fly ash is gathered by gravity and then transferred to a storage silo.
- Baghouse: a baghouse (BH, B/H), bag filter (BF) or fabric filter (FF) is an air pollution control device removing particulates out of air or gas released from industrial processes or combustion for electricity generation.
- Electrostatic precipitator : a device for removing suspended dust and filtering fine particles from a gas or exhaust by applying a high voltage electrostatic charge and collecting the particles on charged plates.
According to ACAA, more than 100 million tons of fly ash is produced in the United States every year; most coming from the combustion of coal in power plants.
THERMON ELECTRIC SURFACE HEATING
Hopper heating systems can utilise Thermon RSX type trace heating cables or HT heating modules. Constant wattage heat tracing cable and MI (mineral-insulated) heating cables up to 500°C can be installed on a wire mesh to function as a hopper heater.
Ash Fly Flow Obstruction In Hoppers & Storage Silo’s – Ratholing
“No-flow” ash fly situations are caused by arching (also known as bridging) or ratholing. Arching occurs when an obstruction in the shape of an arch or a bridge forms over the outlet as a result of the fly ashes cohesive strength. When fly ash forms a stable arch above the outlet, discharge is prevented and a no-flow condition results.
Ratholing occurs when material empties out through a flow channel above an outlet. As the level of fly ash in the flow channel drops, a resistance to further flow into this channel occurs due to the material’s cohesive strength. No further material discharge occurs from the outlet, resulting in a no-flow condition.
The pyramidal shape of typical ESP or baghouse hoppers makes potential arching and ratholing problems, hence the requirement for powerful and reliable hopper heating systems in the coal-fired power generation industry.
THERMON HT Hopper Heating Modules
caking & clogging prevention
Thermon HT hopper heating module is a rugged, self-contained high performance heater system designed for reliable operation on surfaces prone to vibration. The hopper heater module is specified to provide heat outputs up to 4650 watts per square metre depending on the application distributing heat evenly over the entire panel surface. To ensure optimal performance, each system is engineered by T&D and Thermon based on the heating requirements of the specific application.
A parallel circuit design, based on a stamped high temperature Inconel® heating element, provides the Thermon HT heating module with multiple flow paths for electrical current to pass. This design eliminates the burnout potential common with series heating cable and wire-based designs. Protection of the heating element from vibration is achieved with a cushion layer of insulation that also directs the flow of heat from the module to the surface being heated.
The rugged construction of the module includes a tough .9 mm thick aluminised steel shell providing mechanical protection during handling, installation and operation. Weld splatter, rust or oil will not affect the integrity or performance of the heater – low profile design of the panel permits rapid, trouble-free installation.
- Supply Voltages: 120 – 600 VAC
- Maximum Maintenance Temperature: 423°C
Thermon HT Hopper Heating Module Construction
- Fluoropolymer insulated high temperature 1.3 mm² lead wires (with stress relief at connection)
- Parallel circuit high temperature alloy heating element
- Temperature-rated insulation (directs energy towards surface to be heated)
- Aluminized steel protective enclosure and cover (.9 mm thick)
- Aluminized steel reinforced attachment channel (1.9 mm thick)
- 6.3 mm hole cut-outs for optional earth connection
1. Assemble hopper heating mounting components in correct order. i) place reinforcing channel and module over channel and studs. ii) place washer on each stud iii) secure with one nut per stud iv) add second nut to each stud and tighten v) carefully route hopper heater lead wires to junction box and connect to the terminal strip.
2. Typical wiring schematic for hopper heating modules.
3. Hopper heating system designs are based on the transfer of heat into the hopper via convection and conduction in the air spaces between each stiffener to provide an “oven” effect to ensure even heat distribution
COAL FIRED POWER STATIONS
Despite global environmental pressures to reduce dependence on coal-fired power generation the amount of coal-generated power remains stable. Coal-generated power currently makes up 40% of the U.S. energy mix, (The U.S. Coal Combustion Products Market: A Historical Market Analysis, American Coal Ash Association (2015). Taichung Power Plant is a coal-fired power plant in Longjing, Taichung, Taiwan – with an installed coal-fired generation capacity of 5,500 MW, it is the largest coal-fired power station in the world.
➡ Vega sensors and transmitters provide accurate, reliable level measurement for liquids, slurries and bulk solids.