CHAPTER 7FLOW RATE MONITORS

Flow rate monitors were not widely applied in the United States until after 1993 when the acid rain program mandated their installation for the calculation of SO2 allowances. The allowance is an emission rate, expressed in units of tons of a pollutant emitted per year, which is calculated from hourly emissions data. As discussed in Chapter 2, these allowances are allocated, banked, sold, and traded, or, otherwise, have commercial value. The U.S. EPA considered that flow monitors would be the most accurate means of determining allowances for coal‐fired units since, for these sources, analyzers can be certified, calibrated, and audited more uniformly. Although engineering calculations based on heat rate or process operations may also be used to determine flue gas flow rates, evaluation of the accuracy of these methods is more difficult, particularly where the fuel composition is variable. The U.S. EPA requirements for determining SO2 mass emission rates using flow monitors led to the installation of over 1000 flow monitors at coal‐fired electric utility facilities in the early 1990s.

Emission standards that specify the continuous monitoring of pollutant mass emission rates imply that flow monitors are to be part of CEM systems. This can be seen by examining the following relation:

and

(7‐2)

where

  • pmrs = pollutant mass rate (kilograms per hour, ...

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