Pollution Prevention Guidelines to provide technical advice and guidance to staff and consultants involved in pollution-related projects. The guidelines represent state-of-the-art thinking on how to reduce pollution emissions from the production process. In many cases, the guidelines provide numerical targets for reducing pollution, as well as maximum emissions levels that are normally achievable through a combination of cleaner production and end-of-pipe treatment. The guidelines are designed to protect human health; reduce mass loadings to the environment; draw on commercially proven technologies; be cost-effective; follow current regulatory trends; and promote good industrial practices, which offer greater productivity and increased energy efficiency.
Table of Contents
- Industry Description and Practices
- Waste Characteristics
- Pollution Prevention and Control
- Target Pollution Loads
- Treatment Technologies
- Emissions Guidelines
- Monitoring and Reporting
- Key Issues
Industry Description and Practices
Coal is one of the world’s most plentiful energy resources, and its use is likely to quadruple by 2020. Coal occurs in a wide range of forms and qualities; but there are two broad categories: (a) hard coal, which includes coking coal, used to produce steel, and other bituminous and anthracite coals used for steam and power generation, and (b) brown coal (subbituminous and lignite), which is used mostly as onsite fuel. Coal has a wide range of moisture content (2–40%), sulfur content (0.2–8%), and ash content (5–40%). These can affect the value of the coal as a fuel and cause environmental problems in its use.
The depth, thickness, and configuration of the
coal seams determine the mode of extraction.
Shallow, flat coal deposits are mined by surface
processes, which are generally less costly per ton
of coal mined than underground mines of similar
capacity. Strip mining is one of the most economical
surface processes. Here removal of
overburden and coal extraction proceed in parallel
strips along the face of the coal deposit, with
the spoil being deposited behind the operation
in the previously mined areas. In open pit mining,
thick seams (tens of meters) are mined by
traditional quarrying techniques. Underground
mining is used for deep seams. Underground mining methods vary according to the site conditions, but all involve the removal of seams followed by more or less controlled subsidence of the overlying strata.
Raw coal may be sold as mined or may be processed in a beneficiation/washing plant to remove noncombustible materials (up to 45% reduction in ash content) and inorganic sulfur (up to 25% reduction). Coal beneficiation is based on wet physical processes such as gravity separation and flotation. Beneficiation produces two waste streams: fine materials that are discharged as a slurry to a tailings impoundment, and coarse material (typically greater than 0.5 millimeters) that is hauled away as a solid waste.
The main impacts of surface mining are, in general, massive disturbances of large areas of land and possible disruption of surface and groundwater patterns. In some surface mines, the generation of acid mine drainage (AMD) is a major problem. Other significant impacts include fugitive dust and disposal of overburden and waste rock.
In underground mines, the surface disturbance
is less obvious, but the extent of subsidence can
be very large. Methane generation and release can
also be a problem under certain geological conditions.
If groundwater systems are disturbed, the possibility of serious pollution from highly saline or highly acidic water exists. Impacts may continue long after mining ceases. Table 1 presents the levels of liquid effluents, solid waste, and dust generated by the major mining techniques. Beneficiation plants produce large volumes of tailings and solid wastes. Storage and handling of coal generates dust at rates of as much as 3 kilograms per metric ton (kg/t) of coal mined, with the ambient dust concentration ranging from 10 to 300 micrograms per cubic meter (μg/ m3) above the background level at the mine site.