Converting Minerals to Metals - Mining and the Environment: From Ore to Metal - page 285

Direct Measurements

Direct measurement is one of the more accurate techniques but is only applicable to existing
and active operations. Measurements should take into account standard and non-standard
operating conditions. Direct measurement data allow calculation of actual loads to the envi-
ronment, by multiplying concentration times emission volume. For hot gaseous emissions it
is necessary to account for temperature differences. It is also essential that sampling proce-
dures conform to established measurement protocols. Collection and analysis of samples is
expensive and complicated, especially where various substances are emitted, and emission
sources are fugitive in nature. Sampling may not be representative for the entire process,
and may provide only one example of actual emissions.

Measurements should take into
account standard and non-
standard operating conditions.

Mass Balances

Mass balances identify the quantity of a substance going in and out of the control volume,
which may be a process, a piece of equipment, or a facility as such as a smelter (see Figure
2.6 as one example). While common practice, the validity of a stationary mass balance that
does not account for accumulation or depletion of the substance within the control vol-
ume, cannot be assumed. There will always be errors inherent in the estimation of inputs
and losses from the control volume, and in the fates of the substance under consideration,
increasing the error bands of the mass balance, especially for minor emissions streams. A
rigid inventory of chemical use and emissions is essential to establish accurate mass bal-
ances. Any mass balance should consider chemical or biological degradation that may
occur during process or treatment. It is also important to realize that even small errors in
any one step of the mass flow can significantly skew emission estimates. While there may
be many variables in a mass balance, errors may be minimized through continued devel-
opment and refinement of the mass balance equation.

A rigid inventory of chemical
use and emissions is essential to
establish accurate mass balances.

Engineering Calculations

Engineering calculations may be used to estimate emissions subject to rigid controls, when
there is a thorough understanding of the substance's fate in relation to process conditions
and chemistry. Engineering calculations commonly use standard physical and chemi-
cal laws and constants to allow estimate emissions. They are based on known perform-
ance standards of processes and equipments, and of the physical and chemicals properties
and reactions of the substance under consideration. Engineering calculations may be very
simple (such as a simple black box model) or extremely complex with factors for weather
influences, chemical speciation, and the many site specific factors. As in all calculations the
old rule applies: 'garbage in garbage out'. The complexity of a calculation will influence
the accuracy of the emission estimate. Whenever possible, the calculations should be veri-
fied by direct measurements.

As in all calculations the old rule
applies: 'garbage in garbage out'.

Emission Factors

Emission factors are tools used to estimate emissions to the environment based on
standard formulae or experience derived from similar operations. They are useful tools