Emissions MONITORING?
15 Jan 2000
For the moment at least, notwithstanding developments in combustion analysis (see main text), continuous emissions monitoring (CEM) remains a prerequsite for the operation of many industrial processes, writes Mike Spear. Increasingly stringent environmental regulations in many countries now demand in situ CEM analysers that are fully verifiable and provide a continuous log of emissions such as NOx, SOx, CO2 and CO.
To meet these changing regulatory requirements which, for example, have seen NO limits for power generation plant come down from 800ppm in the mid 1980s for a coal-fired station, to an anticipated level this year of less than 20ppm for CCGT gas plants Procal Analytics has introduced a new range of CEM analysers and control units that will enable lower levels of pollutants to be monitored.
Procal's instruments are generally used to monitor stack emissions from applications such as power stations, incinerators, cement kilns and refineries. They operate on photometric principles mainly infrared, some ultra-violet using fixed wavelengths to determine the concentrations of specific compounds. The latest Procal 5000 analyser, however, is a full spectrum, high sensitivity UV analyser that goes beyond the traditional approach of having separate filters for each relevant wavelength.
Instead of, typically, eight fixed wavelengths, the 5000 monitors over several hundred very narrow wavelengths. Procal has developed methods of calibration and calculation that take advantage of the large amounts of data available in the full UV spectrum. These allow accurate measurements of mixed gases even when the signals in the UV spectrum overlap.
The 5000 also has all the features of the current Procal range such as 24-hour long term operation in severe environments. The main gases measured are NO, NO2 and SO2 all with strong and distinct UV spectra. In addition, NH3, H2S, organic sulphides, ozone, chlorine and aromatics can all be measured. In fact, there is no restriction on the number of gases that can be measured simultaneously except that of signal strength. Water vapour and CO2 are not UV absorbers and thus have no effect.
All measurements with the 5000 are stable thanks to the instrument's calibration and built-in autozero system. They can be verified with calibration gases automatically and manually, using the same in situ cell. Temperature and pressure of the stack gases are also measured.
Having a reliable, easily maintained measurement system is only half the environmental battle, however. Delivering those measurements in a form acceptable to the environmental authorities is just as important. To address this half of the equation Procal has also launched its ACU (analyser control unit) for Windows. This is a PC software package, under Windows NT, that provides control, display and data logging for up to eight Procal optical head units.
The ACU can produce automatic environmental authority reporting, formatted to suit local requirements, and is easy to adapt for future changes in legislation. There are three levels of display and access for operators, supervisors and service engineers.
Crucially, though, no action by operator, supervisor or service engineer can change readings already in the data log an essential feature to preserve the credibility of the results.
The first major order for ACU is soon to go into a 1 million tpa cement plant in Bilbao, Spain. Measurements here include NOx, SO2, CO, CO2, H2O, O2, dust and temperature.
