The limit values for NOx emissions are being lowered further and further by statutory provisions and licensing requirements. Furthermore, pressure is increasing on the operators of thermal waste incineration plants to reduce operating costs. At the same time efforts are made to increase the efficiency of the furnace and to minimize the wear of the furnace wall. For all optimization options, the correct measurement of the temperature in the combustion chamber represents a crucial measure. Nitrogen oxides arise from the nitrogen content in the waste and the high combustion temperatures, which are necessary for the destruction of the organic pollutants. With the aid of ammonia water as a reducing agent in the temperature range of 850 to 1050 °C the nitrogen oxides are converted to nitrogen (N₂) and water (H₂O).

Temperature is measured by means of thermocouples near the wall. However, it does not correspond to the furnace internal temperature, especially if the walls are equipped with heat exchangers. The inertia of the thermocouples causes a wide range of process control fluctuations. Furthermore, thermocouples present the physical problem of aging, that is to say a slowly increasing measurement uncertainty. They need to be replaced regularly, so consumption costs constantly arise. Therefore, the use of wear-free pyrometers which determine the temperature in milliseconds from the infrared radiation of the measurement object is considered advisable for this measurement task. Since the combustion process is very complex, an appropriate pyrometer must be chosen for it. Different devices are used, depending on the measuring point. They differ in their spectral sensitivity and measuring method.

CellaTemp PK 51 / CellaTemp PX 13 / CellaPort PT 113
These devices were developed especially for temperature measurements in flame heated furnaces. Thanks to the selective spectral range of 3.9 µm, water vapour and CO₂ existing in the pyrometer´s field of vision have no effect on the measuring results, even when measuring from large distances. This allows precise measurements through flames and combustion gases.

CellaCombustion PK 62 / CellaCombustion PX 47 / CellaCombustion PT 147
Special pyrometers are used for non-contact temperature measurement of sooty flames in coal-fired power stations and incineration plants. The measurement and signal processing, both based on the two-colour method, detect the heat radiation of the soot emitting particles of the flame in the near infrared range at two wavelengths. In order to correct the influence of the wavelength-dependent radiation properties of the soot particles and the optical density of flames, a special algorithm is used during the temperature determination. The flame temperature can be used to optimize burnout in the furnace operation, reduce pollutant emissions and minimize slagging of the combustion chamber and heat exchangers.

CellaCombustion PK 73 / PX 18 / PT 118
In order to keep the pollutant emission below the permissible limit values, the minimum temperature of the exhaust gas, after feeding combustion air, must be between 850 – 1,100 °C , depending on its composition.

CellaCombustion PK 68
To ensure the efficiency of the heat exchanger of the firing system, the pipes of the heat exchanger are continuously monitored for their temperature. If the temperature exceeds a certain level due to increasing encrustation of the tubes, they must be cleaned. Pyrometers that work according to the two-colour measurement method are used to measure the temperature. This method provides reliable measured values even under extreme conditions in the boiler with strongly changing particle content. In addition, modern two-colour pyrometers have a function that monitors whether a safe measurement is still possible or whether the protective screen needs to be cleaned.