CHAPTER C14
ASH HANDLING
PIPING SYSTEMS
Vincent C. Ionita
Senior Engineering Specialist
Bechtel Power Corporation
Frederick, Maryland
Joel H. Aschenbrand
James S. Merritt Company
Montgomeryville, Pennsylvania
INTRODUCTION TO ASH HANDLING SYSTEMS
Automatic ash handling systems developed as the size of coal-fired boilers increased
beyond the sizes permitting manual handling of the quantity of ash. To remove
ash from the boiler vicinity to a remote disposal location, conveying systems utilizing
pipe offered the greatest flexibility for routing. The ash falling to the bottom of
the boiler furnace for removal is known as bottom ash. The particulate carried in
the flue gas stream to economizer, air heater, or other downstream hoppers is
called fly ash. As environmental standards have evolved, more complete removal
of particulate from the flue gas stream has necessitated increasing emphasis on fly
ash collection and conveying systems. In ash-handling systems, the pipe utilized for
conveying ash is termed the conveyor or conveyor line.
TYPES OF SYSTEMS
Ash is conveyed manually, mechanically, pneumatically, and hydraulically. Only
pneumatic and hydraulic systems utilize pipe and are discussed here. Pneumatic
systems may be positive or negative pressure, as described later. Hydraulic systems
are also known as sluice systems and may be used independently or in combination
with pneumatic systems. Mechanical systems typically include submerged or dry-
flight conveyors, screw conveyors, or belt conveyors.
C.727
C.728
PIPING SYSTEMS
Negative-Pressure Dilute-Phase
In negative-pressure dilute-phase systems (vacuum systems), a vacuum pump (me-
chanical exhauster) or steam or water exhauster is used to create a vacuum, inducing
air to flow through the conveyor line. Ash is admitted to the moving airstream and
conveyed to the disposal point (Fig. C14.1). In systems using water exhausters, the
ash is sometimes mixed with the water and sluiced to the disposal location. The
pressures in these systems range from 16 in Hg (40 cm Hg) to