**3.2 Solid particle concentration measurements**

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

Co-Combustion of Coal and Alternative Fuels 73

Thermocouple 2. Digital thermometer 3. Cylindrical probe 4. Digital pressure sensor 5. Disposable probe for isokinetic sampling 6. Separator 7. Steam condenser 8. Cooling water inlet and outlet 9. Bottle

**Boiler output 40 % 70 % 100 %** 

Medium concentration of solid particles – left side 841.9 3 308.5 4,427 [ g.m-3N ] Medium concentration of solid particles – right side 670.1 1,165.7 1,827 [ g.m-3N ] Mass flow of solid particles – left side 31.21 173.6 234.9 [ kg.s-1 ] Mass flow of solid particles – right side 20.14 65.91 100.12 [ kg.s-1 ] Total mass flow of solid particles 51.35 239.51 335.02 [ kg.s-1 ] Lower heating value 11,860 11,950 11,870 [ kg.s-1 ] Fuel consumption 10.041 16.72 23.283 [ kg.s-1 ] Volume of ash and limestone supply to boiler 2.447 5.677 6.995 [ kg.s-1 ] Circulation number of solid phase – left side 42 81 77 [ 1 ] Circulation number of solid phase – right side 27 31 32 [ 1 ] Circulation number of solid phase through cyclone 34.5 56 54,5 [ 1 ] Distribution of bed ash and light ash 40:60 25:75 13:87 [ %]

Table 5. Determination of the circulation number at different boiler outputs

Fig. 9. Diagram of measurement unit for solid particle isokinetic sampling.

10. Measuring equipment 11. U tube manometer 12. Air pump

Fig. 10. Sampling water-cooled probe

acquired pressure data are continuously monitored by operation measuring instruments. To determine the solid particles concentration in flue gases, the gravimetric method with solid particles isokinetic sampling can be used. Fig. 9. illustrates the measurement unit for solid particle isokinetic sampling.

Fig. 8. Average CO and NOX concentration distribution along the height of the combustion chamber of the boiler at 60 % nominal output in Power station Tisová.

To determine the concentration at the measuring points, a disposable sampling probe is used. Another option would be a sampling probe with cooled support as illustrated in Fig. 10. This probe was developed to measure solid particles through an opening in the membrane wall flag. The sampling device touches the cooled parts only with smaller part to prevent gases from cooling below the dew point during the sampling process. The results of measurement of the solid particle concentration are illustrated in Table 5. for the 100 %, 70 % and 40 % nominal outputs for 15 % biofuel and 90 % lignite. (Power station Tisová 350 t/h steam, 9,42 MPa/ 505 oC). The circulation number is quite high but it corresponds with the very low content of combustible particles measured in chutes under the cyclones. The results of cyclone efficiency measurements for various boiler outputs are from 96,5 % to 98,7 % for right and left cyclone. Generally we can say that hot cyclones of fluidized bed boilers have high separation ability.

acquired pressure data are continuously monitored by operation measuring instruments. To determine the solid particles concentration in flue gases, the gravimetric method with solid particles isokinetic sampling can be used. Fig. 9. illustrates the measurement unit for solid

Fig. 8. Average CO and NOX concentration distribution along the height of the combustion

To determine the concentration at the measuring points, a disposable sampling probe is used. Another option would be a sampling probe with cooled support as illustrated in Fig. 10. This probe was developed to measure solid particles through an opening in the membrane wall flag. The sampling device touches the cooled parts only with smaller part to prevent gases from cooling below the dew point during the sampling process. The results of measurement of the solid particle concentration are illustrated in Table 5. for the 100 %, 70 % and 40 % nominal outputs for 15 % biofuel and 90 % lignite. (Power station Tisová 350 t/h steam, 9,42 MPa/ 505 oC). The circulation number is quite high but it corresponds with the very low content of combustible particles measured in chutes under the cyclones. The results of cyclone efficiency measurements for various boiler outputs are from 96,5 % to 98,7 % for right and left cyclone. Generally we can say that hot cyclones of fluidized bed boilers have high separation ability.

chamber of the boiler at 60 % nominal output in Power station Tisová.

particle isokinetic sampling.

Thermocouple 2. Digital thermometer 3. Cylindrical probe 4. Digital pressure sensor 5. Disposable probe for isokinetic sampling 6. Separator 7. Steam condenser 8. Cooling water inlet and outlet 9. Bottle 10. Measuring equipment 11. U tube manometer 12. Air pump

Fig. 9. Diagram of measurement unit for solid particle isokinetic sampling.

Fig. 10. Sampling water-cooled probe


Table 5. Determination of the circulation number at different boiler outputs

Co-Combustion of Coal and Alternative Fuels 75

lime or anatase. The comparison of the diffraction patterns revealed nearly the same mineral composition obtained for both unburned carbons – the dominant mineral phase in both samples was quartz and minor occurrence of anatase was identified as well. The both bottom ashes showed the similar mineral composition as well – it was lime there that was the most abundant mineral phase and also minor amount of quartz, anhydrite and anatase was identified in these samples. The similar mineral composition was obtained also for both fly ashes where quartz was the most dominant mineral and where the occurrence of lime, anhydrite, anatase and calcite was of minor significance. Hence, it can be concluded that the addition of solid waste fuel to coal during the combustion did not change the mineral composition of both unburned carbon and the ash samples.

Fig. 11. X-ray diffraction patterns of fly ash (C). Q-quartz, L-lime, Cal – calcite, A – anhydrite, Mag – magnetite, C3A – tricalcium aluminate, Ch - calcium hydroxide, M -

By means of X-ray fluorescence spectrometry the contents of major, minor and trace elements were determined in coal (C), unburned carbon (UC), bottom ash (BA), fly ash (FA) and waste alternative fuel (WF). These results as well as the ash contents in these materials are given in Table 6. The porosity of the coal and bottom ash is rather low, whereas unburned carbon shows highly-developed system of ruptures, pores and cavities leading to high porosity of this material. That is why unburned carbon is being studied in relation to

(Bartoňová at al., 2009).

mullite T – anatase

**4.2 Chemical analyses** 

its adsorption properties.
