Wavelength (д. т) (a)
In the pulp and paper industry, the main gas emissions are from the pulp production. The main sources of emission are in the soda recovery boiler, lime kiln, evaporation plant, and bark combustion boiler.
FIGURE 13.56 (a) The emission spectrum of an LED.45 The 4.3-|xm LED spectrum shows a dip at
Around 4.3 (xm, which corresponds to background carbon dioxide absorption typically present at concentrations of the order of 300 ppmv. (fa) IR gas sensor configuration utilizing several LED chips,50,51 I, IR LEDs; 2. microreflector; 3. thermosensor; 4. TO-3 header; S. thermoelectric cooler; 6. reference photodetector; 7. sample photodetector; 8. sapphire window; 9. protection window; 10. spherical mirror; 11, gas chamber.
The gases normally monitored include: oxides of sulfur and nitrogen (S02, NO*),
Malodorous (reduced) sulfur compounds, generally expressed as TRS, particulates (PM), and
Carbon monoxide (CO) and carbon dioxide (C02).
Continuous monitoring of emission gases is necessary to ascertain that the emissions from a production unit remain within the limit values.52 The limit value for S02 in Finland is 4 kg or less per tonne of puip produced. The authorities often require plants to continuously monitor the main emissions. Information on the environmental load generated by a production unit is available to customers upon request. This information is also used for the environmental management of the plant.
Special conditions in the paper pulp industry require reliable monitoring. Emission gases, including corrosive gases and particulates, are generally moisture laden. Fouling and blocking of the sampling system is a major problem in continuous monitoring. It is noted that stationary monitoring systems frequently show low values, even though the service and calibration have been properly performed.52 This is due to partial blocking of the sampling line by moisture, leakages, etc.
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