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TERMS AND DEFINITIONS
(Updated 10/14/98)
- Bottom Ash -
- The coarse, solid, non-combustible particulate matter that results from the combustion
of ground or powdered coal and falls to the bottom of the boiler, but have not melted.
Bottom ash has a similar chemical composition to fly ash but is produced in gradations
ranging from fine sand to small aggregate (3/8"). Bottom ash is typically grey to
black in color, angular, and has a porous surface texture.Bottom ash is usually a small
portion of the total ash produced by the boiler.It may be vitrified or clinkered, but is
friable. It will often show metals in the leachate and may tend to be acid producing.
- Boiler Slag -
- Larger particles of coal ash that have settled to the bottom of the boiler and have
completely melted. A vitreous material which is normally the major portion of residues
produced at the bottom of cyclone boilers. Since slag has been fused, there is very little
chemical activity and leachate is not normally contaminated.
- Coal Ash, Coal Combustion
Ash, Coal Combustion Material, Coal Combustion Residue -
- All are equivalent collective terms referring to any materials or residues produced from
the combustion of coal.
- Coal Combustion By-Products (CCB)
-
- A collective term referring to any large volume material or residue produced from the
combustion of coal or cleaning of stack gasses regardless of ultimate commercial
application or disposal. Specifically, it includes fly ash, bottom ash, boiler slag,
fluidized bed combustion ash, and flue gas desulfurization material.
- Coal Combustion Products (CCP) -
- A collective term for materials or residues produced from the combustion of coal or
cleaning of stack gasses for which there is a commercial market and are reprocessed, sold,
or stored for commercial use.
- Coal Combustion Wastes (CCW)
-
- A collective term for materials or residues produced from the combustion of coal or
cleaning of stack gasses for which there are no commercial markets and they are disposed
of as a solid waste.
- Flue Gas Desulfurization (FGD)
Material -
- The solid stabilized by-product material that results from the flue gas desulfurization
scrubber system also referred to as scrubber sludge. It is produced when the stack gasses
are sent through pulverized limestone to remove sulfur dioxide. The resulting material
consists of calcium sulfate/sulfite and is commonly combined with fly ash to dry and
stabilize the material. Usually a thixotropic material unless stabilized with fly ash or
other dry materials. Some utilities produce an "oxidized" material which is
primarily calcium sulfate or synthetic gypsum. The scubber sludge may be dry, but is
commonly delivered as filter cake. It is normally high in calcium sulfites and sulfates.
The filter cake may be very difficult to remove from dump trucks or hopper cars. Filter
cake is not difficult to handle after dumping, but is soft and usually to wet to compact.
- Fluidized Bed Combustion (FBC) Ash
-
- A fly ash or spent sorbent from the flue gas produced from the combustion of coal in a
fluidized bed combustion boiler. It resembles conventional fly ash, but
contains spent sorbent and is produced at lower temperatures. It is normally highly
alkaline. The high alkalinity tends to minimize metals in the leachate. Unconditioned FBC
fly ash will usually contain considerable dust, much of which may have a particle size
under 10 microns.
- Fly Ash -
- The finely divided residue that results from the combustion of ground or powdered coal
and is removed from the stack gasses with various types of air quality control equipment.
Fly ash is a pozzolan: a siliceous material which, in the presence of water, will
chemically combine with lime (calcium oxide) to produce a cementitious material with
excellent structural properties. Some fly ashes contain sufficient calcium compounds to be
self- hardening, while others require the addition of calcium (usually in the form of
cement or lime) to harden. There are two main types of fly ash: Class F (low lime) and
Class C (high lime). Class F fly ash is typically associated with eastern and midwestern
U.S. coals and Class C is associated with western U.S. coals. High quality conventional
fly ash will contain very little sulfate compounds or unburned carbon.
- Fossil Fuel Combustion
(FFC) Waste Streams -
- A collective term utilized by EPA for materials or residues produced from the combustion
of coal or cleaning of stack gasses.
- Pozzolans -
- Siliceous or siliceous and aluminous materials that in themselves possess little or no
cementitious value but will, in finely divided form and in the presence of water,
chemically react with calcium hydroxide at ordinary temperatures to form compounds
possessing cementitious properties.
- Scrubber Sludge -
- Another name for FGD material.
- Thixotrophy -
- The property of a material that enables it to stiffen in a relatively short time on
standing, but, upon agitation or manipulation, can change to a very soft consistency or to
a fluid of high viscosity, the process being completely reversible.
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