The formulae used for calculation in the Predictive Emission Monitoring Systems are constantly updated through a series of online stack measurements. Any emissions that tend to affect the set parameters are measured by the DVN GL and DCS witnesses and values for tests verified. The measurements done are used to come up with a conclusive formula that is used for PEMS calculations. The quality of PEMS has to be analyzed from time through annual audits performed by licensing authorities. The system has been adopted perfectly in the US and is also widely used in Europe for detection of Nitrogen-Oxygen emissions.
Unlike other emission monitoring systems, Predictive Emission Monitoring Systems do not require any gas analysers. The input conditions used by an industry are used to predict the emissions to be produced on the other end. Some of the factors that are used to determine the emissions include fuel used, boiler settings, turbine setting, temperature data, load, environmental conditions, pressure and flow rate. A basic model is created and used to determine emissions on the actual plant. The system ensures that the emissions produced are compliant with state laws. Most companies have replaced Continuous Monitoring Emission Systems with the PEMS.
The United States EPA has tested the Predictive Emission Monitoring Systems and come up with positive results. For this reason, the government has recommended most plants to replace their CEMS with PEMS to save on operational and maintenance cost. Gas analysers may sometimes produce faulty results and this makes it necessary for companies to adopt better monitoring systems. Companies that have employed PEMS systems conduct research programs to check whether the system is compliant with licensing authorities. The results are usually tabulated and presented to the authorities for inspection. Some of the gases that can be monitored by PEMS include SO2, CO2, NOx, O2 and CO among others.