Ash Handling Plant

ASH HANDLING PLANT

What is Ash Handling?

Ash handling refers to the method of collection, conveying, interim storage and load out of various types of ash residue left over from solid fuel combustion processes.

The most common types of ash include bottom ash, bed ash, fly ash and ash clinkers resulting from the combustion of coal, wood and other solid fuels.

Ash handling systems may employ pneumatic ash conveying or mechanical ash conveyors.

A typical pneumatic ash handling system will employ vacuum pneumatic ash collection and ash conveying from several ash pick up stations-with delivery to an ash storage silo for interim holding prior to load out and transport. Pressurized pneumatic ash conveying may also be employed.

Coarse ash material such as bottom ash is most often crushed in clinker grinders (crushers) prior to being transported in the ash conveyor system.

Very finely sized fly ash often accounts for the major portion of the material conveyed in an ash handling system. It is collected from Baghouse type dust collectors, electrostatic precipitators and other apparatus in the flue gas processing stream.

Ash mixers (conditioners) and dry dustless telescopic devices are used to prepare ash for transfer from the ash storage silo to transport vehicles.

ASH HANDLING CAPABILITIES

Diverse range of applications

Founded in 1933, National Conveyors Company has been furnishing ash handling systems for over 7 decades. Their diverse range of customers includes:

·  Utility Generators

·  Industrial Power Plants

·  Independent Power Producers

·  Cogeneration Plants

·  Institutional Power Plants

·  Waste to Energy Producers

·  Steam Heating Plants

·  Process Steam Plants

Many fuels and furnace designs

Most of the Ash Handling Systems are used today at plants fired with the following fuels:

·  Bituminous Coal

·  Anthracite Coal

·  Lignite

·  Culm (gob)

·  Sub-Bituminous Coal

·  Bagasse

·  Wood

·  Oil

·  RDF

·  Tires

·  Mixed Fuels

·  Coke

National Systems are installed serving chain grate, stoker fired, cyclone; pulverized coal fired and fluidized bed design furnaces.

National systems handle all ash products

Extensive experience includes the design and supply of complete systems for handling:

·  Bottom Ash

·  Bed Ash

·  Sifting Ash

·  Mill rejects

·  Economizer Ash

·  Air Heater Ash

·  Ash Clinkers

·  Rear Pass

·  Baghouse Ash

·  Precipitator Ash

·  Pyrites

·  Superheater Ash

·  Stack Ash

·  Slag

Pneumatic or mechanical systems

There are different types of ash handling systems. These include:

·  Vacuum pneumatic

·  Pressure pneumatic

·  Vacuum & Pressure pneumatic

·  Dry mechanical conveyor systems

·  Submerged mechanical conveyor systems

TYPICAL NATIONAL ASH HANDLING SYSTEM INSTALLATION

National ash handling system at mid-west power plant. Ash storage silo can be seen at left. A vacuum pneumatic ash collection/ash conveying system is used.

VACUUM PNEUMATIC ASH HANDLING SYSTEMS

Vacuum pneumatic ash collection & ash conveying system consists of:-

1.  Air Intake

2.  Fully Enclosed, Quick Acting, Swing Disc valve

3.  Pipe Fittings with Replaceable, Reversible, Interchangeable Wear backs (550 BHN)

4.  Paddle Type Ash Conditioning Unit

5.  Abrasion Resistant centrifugally Cast Conveyor Pipe

6.  Silo Vent Filter

7.  Centrifugal Receiver/Separator

8.  Pulse Jet Bag Type Dust Collector

9.  Continuous Ash Collecting Double Dump Gates

10.  Silo Relief Valve

11.  Ash Storage Silo

12.  Air Pipe

13.  Fugitive Dust Filter

14.  Telescopic Dry Unloader

15.  Vacuum Breaker

16.  Guard Filter

17.  Mechanical Exhausters

System Operation

Ash which has accumulated in various collection hoppers is pneumatically conveyed to a centrifugal receiver atop the ash storage silo. Vacuum forces providing the conveyance air flow are created by a blower (exhauster) located near the silo.

Coarser ash particulates collecting at the bottom of the receiver are transferred to the silo via a double dump gate air lock assembly (see description on following page). Finer ash particles and the induced conveying air flow report through the "vortex finder" pipe at the top of the centrifugal receiver to a pulse jet, bag type dust collector located nearby. Ash particulates released by periodic blow down of the bags collect below, where this material is transferred to the silo via a double dump gate air lock assembly. Overall solids recovery typically exceeds 99.9% for 2 micron and larger particulates.

PRESSURE PNEUMATIC ASH HANDLING SYSTEMS

Schematic - Pressure Pneumatic Ash Collection/Ash Conveying System

Pressurized pneumatic ash handling systems are most often used for conveying ash over long distances. Such systems are also usefully applied when ash is to be delivered to multiple interim storage or load out stations.

An upstream mechanical blower creates a flow of conveying air. Ash is transferred from collection hoppers to the conveying pipeline on a programmed cycle with the use of rotary airlock feeders or double dump gate airlock valves.

At the end of the ash conveying pipeline ash is received in a highly abrasion resistant silo mounted target box from which it falls by gravity into the storage silo.

Ash conveying air is normally exhausted to the atmosphere through a silo vent filter or it can be recycled to other dust collection equipment.

COMBINATION VACUUM/PRESSURE ASH HANDLING CONVEYING SYSTEMS

Combination vacuum/pressure pneumatic ash conveying systems can be beneficially applied to take advantage of the simplicity of a vacuum system for the collection and delivery of ash to a transfer hopper from which it is reclaimed through an air lock feeding device for pressurized pneumatic conveyance to a remote location silo for subsequent load out.

ASH SYSTEM COMPONENTS

·  Disc Type Ash Intake Valves

·  Abrasion Resistant Pipe & Fittings

·  Ash Receivers

·  Pulse Jet Type Dust Collectors

·  Rotary Airlock Feeders

·  Double Dump Gate Airlock Feeder

·  Exhauster Units (Vacuum Pneumatic Systems)

·  Blower Units (Pressure Pneumatic Systems)

·  Clinker Grinders

·  Bottom Ash Hopper/Vertical Lifting Doors

·  Ash Storage Silos

·  Ash Conditioners

·  Dry Unloaders

·  Ash System Computerized HMI Controls

DISC TYPE ASH INTAKE VALVE

National type "D" (Disc Type) fly ash intake valve used at ash pick up stations in a vacuum pneumatic ash collection system.

ASH CONVEYOR PIPE & FITTINGS

National "Wear back" Abrasion Resistant Ash Conveying Pipeline Fittings

Completely cast of Ni-Hard, having a minimum hardness of BHN 550. These fittings provide significantly longer life than those employing other metallurgy.

Note the bolted, interchangeable, replaceable and reversible "WEARBACK" sections and inspection ports.

Ash Receivers

The photograph above shows a centrifugal ash receiver mounted above a National double dump gate airlock valve.

The centrifugal ash receiver has an important role in ash handling systems. Normally positioned on top of a silo or storage hopper, it performs the principal separation between ash particulates and the ash conveying air flow by means of cyclonic action (forces). The majority of ash particulates report to the lower apex cone of the receiver from which they can be directly discharged to the storage silo or in the case of a vacuum ash conveying system, this transfer is performed using a double dump gate airlock valve as shown at the right. The airflow overflowing to the top of the receiver reports to a companion pulse jet type dust collector for final particulate removal from the conveying air stream.

National provides a variety of highly efficient, abrasion resistant centrifugal ash receivers. For ease of replacement, these are of segmented. Bolted design with all sections cast in NI-HARD having a minimum hardness of BHN 550 for maximum abrasion resistance.

Pulse Jet Dust Collectors

Pulse Jet Bag Type Dust Collector as used in National ash conveying systems.

In vacuum pneumatic ash conveying systems the pulse jet bag type dust collector is used together with a centrifugal ash receiver to reclaim ash particulates from the conveying air stream and deposit such ash in the ash storage silo. The pulse jet collector receives the overflow airstream from the ash receiver (the dirty air), collecting ash particulates on the surface of multiple fiber bags which are subsequently "blow down", and causing accumulated ash to fall to the bottom discharge opening and into the ash storage silo below. Clean (filtered) air overflows the top of the dust collector, passing to the atmosphere or other processing.

Rotary Airlock Feeder

National Rotary Airlock Feeder for Ash Handling

3 sizes are available. Capacities 150 cu. ft. to 800 cu. ft. /hr (4.25 cu m./hr to 22.6 cu. m./hr). Replaceable abrasion resistant liner. Outboard bearings. Online replacement of internals. Shipped fully assembled with or without drive.

Double Dump Gate Airlock Valve

National Double Dump Gate Airlock Valve

A dependable system for transfer of material in both vacuum pneumatic and pressure pneumatic ash conveying systems. National offers a range of sizes to suit your needs.

See the above page for a photo and cross sectional drawing.

Exhausters (Vacuum Pneumatic System)

National exhauster unit supplied for a vacuum pneumatic ash conveying system.

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Blowers (Pressure Pneumatic System)

Blower Unit

National blower unit supplied for a pressure pneumatic ash conveying system.

Clinker Grinder

A clinker grinder is a useful component in those ash conveying systems where coarse bottom ash or other coarsely sized material must be reduced in size so as to be suitable for pneumatic conveyance or other means of ash handling.

Bottom Ash Hoppers & Vertical Lifting Doors

National custom designed bottom ash hoppers with vertical lifting doors.

Photograph above shows National lifting doors installed in a bottom ash hopper.

Drawing at right shows typical cross section view. Note refractory lining.

Clinker grinder reduces (crushes) bottom ash material to a size suitable for pneumatic ash conveying. Note offset intake tee for introduction of crushed bottom ash to the pneumatic ash conveying pipeline.

Ash Storage Silos

Custom designed ash storage silos are a National Conveyors specialty.

Paddle Type Ash Conditioner

Paddle type ash conditioner as supplied for National ash handling systems.

The twin shaft paddle mixer conditions ash and unloads same to transport vehicles. Ash feed rate from the ash storage silo is precisely controlled. Water spray feed rate is adjusted by control valves. The conveying action provided by the rotating paddles provides continuous flow of uniformly mixed ash with no excess water or dusting.

Dry Ash Unloaders

Telescopic Unloading Chute

Computerized (HMI) Controls

National ash collection and ash conveying systems are provided with state of the art computerized HMI controls. Graphical color touch screen interface (HMI) allows the operator to monitor ash system operation, select all system functions and identify and troubleshoot malfunctions.

THE ULTIMATE IN-ASH COLLECTION & ASH CONVEYING CONTROL

Typical National Conveyors HMI Control Screens for a State-Of-The-Art Ash System

ADDITIONAL INFORMATION:

Lime Handling System - Typical

A typical National Conveyors Lime Handling System employing vacuum pneumatic lime unloading with pressurized pneumatic conveyance to a remote lime storage silo.