**3.1 Flue gas elements**

Sampling of flue gas elements from the entire boiler can be divided into three groups:


Co-Combustion of Coal and Alternative Fuels 71

chamber. The results of O2 concentration measurements for 60 % and 90 % nominal output (350 t/h steam) are illustrated in Fig. 7. The results of CO and NOX concentration

The measurment results suggest that there is intensive suppression of NOX formed increases in areas of secondary and tertiary air supply. CO concentration has developed as expected.

To determine the solid particle concentration in air flow, the Czech standard ČSN ISO 9096 needs to be observed. It is gravimetric determination of concentrations based on isokinetic sampling of solid particles from air flow. In the case of fluidized bed chambers the aim is to determine the solid particle concentration in the lower part of the fluidized bed layer and in the boiler furnace. For a bigger or smaller particle separation, the fluidized layer density varies depending on furnace height as well. The density in the lower part is in the range of 500 – 800 kg.m-3, in the upper part of the furnace with the circulating layer the range is 0.1- 0.5 kg.m-3. Pressure in the fluidized layer is always measured for various height levels. The

Fig. 7. Results of O2 concentration measurements by water-cooled sampling probe in relation to height at 60 % and 90 % nominal output during co-combustion tests in power

The concentration decreases if the secondary air supply is gradual.

**3.2 Solid particle concentration measurements** 

station Tisová.

measurements for 60 % nominal output are illustrated in Fig. 8.

To monitor the fluidized bed boiler operation process O2, CO, CO2, NOX, and SO2 measurements can be taken. Other elements are usually monitored up to the exit from the separator of solid particles in front of the chimney. Fig. 5. illustrates a cooled sampling probe that might be used to take flue gases samples. The probe has an identical construction to that used for temperature measuring. During exhaustion gas is rapidly cooled down (from 800 oC to approx. 30 oC in cooled probe) so that there is no reaction with any other flammable waste gases. Gas is then sampled to be analyzed in the mobile laboratory. It is always recommended that a cooled probe is used to take samples from the furnace, cyclone and cyclone linking channels – Fig. 6. Sampling of flue gases from the second pass of the boiler occurs at temperatures safely below 800 oC. Thanks to that temperature a larger part of the gaseous sample is not able to oxidize quickly and thus it is possible to use a sampling tube made of stainless steel or sintered corundum, Al2O3. To set concentration (e.g., SO2), sampling channels must be heated up during the sampling operation so that no reaction with water occurs.

Fig. 5. Probe for flue gas sampling from fluid layer

Fig. 6. illustrates a sampling probe used in the detailed net measuring of O2 concentration in the boiler combustion chamber with a steam output 125 t/h. (15 % biofuels and 90 % lignite coal).

Fig. 6. Probe for flue gas sampling from furnace of boiler

A grid method of measuring O2 , CO and NOX concentration was used. Measurements were taken using instrumentation openings in the middle of the side walls of the combustion

To monitor the fluidized bed boiler operation process O2, CO, CO2, NOX, and SO2 measurements can be taken. Other elements are usually monitored up to the exit from the separator of solid particles in front of the chimney. Fig. 5. illustrates a cooled sampling probe that might be used to take flue gases samples. The probe has an identical construction to that used for temperature measuring. During exhaustion gas is rapidly cooled down (from 800 oC to approx. 30 oC in cooled probe) so that there is no reaction with any other flammable waste gases. Gas is then sampled to be analyzed in the mobile laboratory. It is always recommended that a cooled probe is used to take samples from the furnace, cyclone and cyclone linking channels – Fig. 6. Sampling of flue gases from the second pass of the boiler occurs at temperatures safely below 800 oC. Thanks to that temperature a larger part of the gaseous sample is not able to oxidize quickly and thus it is possible to use a sampling tube made of stainless steel or sintered corundum, Al2O3. To set concentration (e.g., SO2), sampling channels must be heated up during the sampling operation so that no reaction

Fig. 6. illustrates a sampling probe used in the detailed net measuring of O2 concentration in the boiler combustion chamber with a steam output 125 t/h. (15 % biofuels and 90 % lignite

A grid method of measuring O2 , CO and NOX concentration was used. Measurements were taken using instrumentation openings in the middle of the side walls of the combustion

with water occurs.

coal).

Fig. 5. Probe for flue gas sampling from fluid layer

Fig. 6. Probe for flue gas sampling from furnace of boiler

chamber. The results of O2 concentration measurements for 60 % and 90 % nominal output (350 t/h steam) are illustrated in Fig. 7. The results of CO and NOX concentration measurements for 60 % nominal output are illustrated in Fig. 8.

Fig. 7. Results of O2 concentration measurements by water-cooled sampling probe in relation to height at 60 % and 90 % nominal output during co-combustion tests in power station Tisová.

The measurment results suggest that there is intensive suppression of NOX formed increases in areas of secondary and tertiary air supply. CO concentration has developed as expected. The concentration decreases if the secondary air supply is gradual.
