Page 271 - Advances In Productive, Safe, and Responsible Coal Mining

250 Advances in Productive, Safe, and Responsible Coal Mining

13.1.3.3 Coal combustion residuals

First-generation coal-fired power plants spewed coal ash and other hazardous pol-
lutants into the atmosphere until environmental regulations began requiring emis-
sion control systems. Bag houses, scrubbers, electrostatic precipitators, and other
technology were added on at tremendous cost and electricity generating companies
then hadtodealwithwhere to storeCCRsthatwerenow beingcaptured. Storage
in lagoons, landfills, or silos has long been the norm for coal ash management in
most countries, but that is changing around the world as storage space becomes
limited and as environmentally acceptable and competently engineered means of
reusing CCRs are proven. For example, according to the European Coal Combus-
tion Products Association, 13.8 of the 48 million tons of coal ash produced in
15 EU countries in 2010 were reused. Countries like the Netherlands and Germany
that no longer allow landfill storage saw 100% and 97% reuse, respectively. The
UK Quality Ash Association and the American Coal Ash Association (ACAA)
reported 50% and 43% reuse, respectively, in 2013 [12]. In China, the recycling
rate is about 30% despite a 2005 government challenge to achieve 75% [13].In
the United States, of the 53 million tons of coal ash generated in 2013, 23 million
tons were reused with the remainder stored in landfills (36%) and wet storage facil-
ities (21%) [14].
The chief benefit of reusing CCRs is to stabilize or encapsulate components that
may be environmentally harmful such as arsenic, lead, mercury, selenium, and
dioxins. Common reuses for the previously described CCR groups are as follows [14]:
l Fly ash is most commonly used as a high-performance substitute for Portland cement and in
blended cements such as asphaltic concrete. Fly ash also serves as a filler in wood and plastic
products, paints, and metal castings. Building material applications range from grouts and
masonry products to cellular concrete and roofing tiles. Geotechnical applications include
soil stabilization and structural fill for road base and embankments.
l Bottom ash and boiler slag is most commonly used for skid control on icy roads. These mate-
rials are also suitable for geotechnical applications such as structural fills and land reclama-
tion. The physical characteristics of bottom ash and boiler slag lend themselves as
replacements for aggregate in flowable fill and in concrete masonry products. Boiler slag
is also used for roofing granules and as blasting grit.
l FGD material is most commonly used as synthetic gypsum in wallboard and as spray dryer
absorbent. FGD gypsum is used in almost 30% of gypsum panel products manufactured in
the United States. It is also used in agricultural applications to treat undesirable soil condi-
tions and to improve crop performance.
Despite trends toward reuse, storage remains the primary waste disposal avenue for
CCRs largely because it is generally both the easiest and the cheapest option, espe-
cially when there is an available disposal site near a power plant. According to the
ACAA, if coal ash can be piped to a nearby storage site rather than trucked, costs
are $3–5 per ton; however, when the disposal site is further away and a more complex
transport solution is needed due to either higher moisture content or larger volume, the
cost could rise to $20–40 per ton [14].