Economizer Ash

Handling economizer ash presents several challenges due to a combination of ash characteristics that are prone to forming clinkers, including high calcium oxide content, high unburned carbon content, and/or coarse particles. UCC understands how material reacts during collection and transportation, enabling us to provide solutions in both wet and dry applications downstream to a final disposal point.

Mechanical Systems

A mechanical system requires no water and much less horsepower than a hydraulic or pneumatic system of comparable capacity. The Dry Flight Conveyor (DFC) also known as a drag chain conveyor is a mechanical chain and flight conveyor that continuously transports high temperature, dry or moist abrasive material. The DFC is commonly considered for applications where a pneumatic system is undesirable due to combustibles present in the material conveyed. Typical applications include economizer systems, selective catalytic reduction (SCR) units, atmospheric fluidized bed boiler (AFBC) units, and cement discharge from the kiln.

Its modular construction provides maximum flexibility in routing the Dry Flight Conveyor (DFC) or drag chain conveyor to the equipment it will serve and can be configured from horizontal to vertical arrangements. In addition, the conveyor’s low profile design allows it to be adapted to installations where headroom is limited. Multiple configurations are available to match capacity, size and performance to your specific needs.

The DFC is a completely closed trough with motor-driven chain and flights. Ash from the hopper drops through the return flights and onto the bottom of the conveyor. The chain/flight assembly moves the material to the discharge chute. The chute can lead to a storage tank or bottom ash system, such as the Submerged Flight Conveyor (SFC).

Pneumatic Systems

A vacuum system is often the best choice for conveying economizer ash when existing pneumatic systems are in place or where constraints do not permit the use of dry flight conveyor (mechanical) systems. To minimize clinkering in economizer hoppers, UCC recommends continuous removal of the hot ash from the hopper and storage in a dry tank to cool. Large chunks of economizer ash are caught by a sizing grid or reduced by a specially designed economizer ash crusher.

A pressure system is often the best choice for conveying economizer ash where long distance conveying is needed. A positive displacement blower furnishes conveying air which transports ash to the silo under positive pressure.

DFC™ Dry Flight Conveyor System:

  • Continuous ash removal minimizes clinkering in hoppers. The DFC is highly recommended when calcium oxide content of the ash is 15% or greater.
  • The enclosed trough can maintain economizer vacuum to reduce clinkering with the use of airlock dump gates on the discharge.
  • Accommodates a variety of ash types and particle sizes, including lumps
  • Several standard modules allow for horizontal, inclined and vertical motion. Accommodates installations with minimum headroom.
  • Designed to withstand high temperature material (up to 800° F) without damage to conveyor
  • Premium construction for highly reliable 24/7 performance
    • Bottom plate of ½” thick abrasion resistant steel and 3/8” thick abrasion resistant side liners minimize wear.
    • Chain links are drop forged from high chrome/magnesium steel with a core hardness of 300-400 BHN. The entire link is then case hardened to 500-650 BHN for wear resistance.
    • Drive shaft runs in self-aligning double-row roller bearings designed for long life. Chain sprockets on the drive shaft are induction hardened to 560 BHN to maximize life.
  • Modular construction reduces cost and design time, improves installation accuracy, and minimizes spare part requirements
  • Low maintenance as a result of low speed operation and wear-resistant components
  • Low horsepower drive assembly minimizes power consumption

NUVEYOR® Vacuum System:

  • Ability to stop and restart due to low ash-to-air ratios
  • Low headroom requirements below the fly ash collection hoppers
  • Capable of handling a wide range of ash types
  • Full load/no load control allow system to achieve rated capacity more efficiently
  • Wear sections follow each change in pipeline direction
  • Low maintenance at precipitator and economizer areas
  • Single pneumatic valve under each hopper
  • Single air intake per row
  • One I/O per hopper valve
  • No plugging
  • Proven temperature tolerant design for large particle economizer ash

Performance Specs:

Max Distance: 1500 ft (4500 m)
Maximum Capacity: 80 TPH
Mass Ratio ash : air: 5-22
Air Velocity: 3000 – 5200 ft/min (16-27 m/sec)
Maximum Conveyor Line Pressure: 20 in Hg (530 mm Hg)
Maximum Prime Over Pressure: 22 in Hg (560 mm Hg)

  1. What are the advantages of using a mechanical system vs. pneumatic (pressure or vacuum) system when conveying economizer ash? Is one more preferable over the other? [+]
    A mechanical system would be our first recommendation because it provides continuous removal of ash
  2. Is there a system to continually remove economizer ash? [+]
    Yes. UCC offers Dry Flight Conveyor (DFC) that provides the continuous ash removal of economizer ash.
  3. Can you dispose of the economizer ash with the bottom ash?[+]
    If the plant has a SFC or other mechanical system, you can have a mechanical DFC discharge the economizer ash directly into the bottom ash.
  4. Is the economizer part of fly ash or bottom ash?[+]
    Making the economizer ash part of a fly ash system is more economical, however, if you are planning to resell the fly ash, then it should be part of the bottom ash system.
  5. Can DFC’s be configured vertically for some material?[+]

    Yes, DFC’s can be run vertically for some material with chain and flight.

  6. What is used to isolate the DFC’s from the hoppers above?[+]

    For DFC economizer systems that discharge into an SFC, an airlock between two DFCs is most common, but rotary vane feeders have also been used just below the hopper flanges.

  7. What determines the use of a single vs. double strand chain?[+]

    Double strand chains are typically used when particle size is too big to convey with a single chain.

  8. What is the maximum temperature that a DFC can stand without damage to the conveyor?[+]

    The DFC is designed to withstand temperatures up to 800°F (427°C).

NUVA FEEDER Dilute Phase Pressure System

The NUVA FEEDER® pressure system is optimal where conveying capacity requirements exceed the limits of a vacuum system. 

Vacuum Systems

The NUVEYOR® Vacuum System is an industry standard for efficient, reliable ash removal and is capable of conveying up to 80 TPH and distances of 1500 ft (450m).

Recirculation

Ideal for converting wet sluice systems into a “dry” ash system without change to the existing bottom ash hoppers.

 

DFC

Mechanical chain and flight conveyor that continuously transports high temperature, dry or moist abrasive material.

 

Silo Unloading

United Conveyor Corporation Silo Unloading systems are designed to store and unload ash efficiently and cost effectively with the capability of transferring ash in either a dry or damp condition to trucks or rail cars.