**4.1 Mineral analyses**

The X-ray diffraction patterns were obtained for the samples of unburned carbon (UC), bottom ash (BA) and fly ash (FA) Fig. 11. With the aid of elemental analyses of unburned carbon and ash samples the major mineral phases were established in the diffraction patterns and are marked with abbreviations explained in the figure caption. Coal has already been given in indicating the dominant occurrence of quartz and kaolinite. Diffuse area observed in the unburned carbon diffraction pattern (approximately from 25 to 31) corresponds with semi-crystalline carbon phases. Somewhat lower crystallinity (broadened peaks) is evident also in case of magnetite and calcium hydroxide. Conversely, high-degree crystalline levels are represented e.g. by sharp peaks of quartz,

Substitution of conventional fossil fuels (like bituminous coal or lignite) by low-carbon fuels for the energetic use is an efficient and cost-effective means of meeting the Kyoto Protocol establishing greenhouse emission targets for each of the participating developed countries (related to their 1990 emission levels). Considerable reductions of CO2 emissions can be achieved by combustion of waste; therefore combustion of waste materials of various origins (industrial, agricultural etc.) or their co-combustion with fossil fuels in fluidized bed boilers became a legitimate alternative to conventional coal combustion. Another reason why particular attention is paid to energetic utilization of wastes is also elimination of waste

But there are still challenges to be solved such as behaviour of the mineral matter during the wastes' combustion. Although the elemental behaviour during coal combustion has been studied and described in detail, the works dealing with redistribution of elements during waste combustion are quite rare, nevertheless, the conclusions described in these works are rather analogous – the application of the results obtained for the coal combustion on the combustion of wastes is not possible since the character of these materials is quite different. (Bartoňová at al., 2008). Another problem is that even if the waste materials differ from one another in their characteristics and content of toxic elements, most works only focus on

This chapter intends to shed more light on the spectrum of alternative fuels used for energy production focusing on the evaluation of the effect of co-combustion of waste fuel and coal on the environment. In the circulating fluidized bed power station in Tisová - 350 t/h – Table 4., the waste alternative fuel (WF) containing plastics (1-20 %), fabric and carpets (45- 75 %), rubber (5-15 %), paper (1-10 %) and wood (1-10 %) was co-combusted with the coal and the limestone. The samples of coal, limestone, bottom ash and fly ash were collected at regular time intervals and unburned carbon particles were separated from bottom ash by hand. Analysis of major, minor and trace elements was performed by X-ray fluorescence spectrometry (SPECTRO XEPOS) and mineral analysis was carried out using X-ray diffraction analysis (BRUKER D8 ADVANCE). Ash content of the samples was determined at 815C. The distribution of macro pores was determined by means of mercury porozimetry (Micromeritics – AUTOPORE IV); SORPTOMATIC 1990 (Thermo Finnigan) equipment was used for the determination of specific surface area and mezopore-size distribution. Scanning

The X-ray diffraction patterns were obtained for the samples of unburned carbon (UC), bottom ash (BA) and fly ash (FA) Fig. 11. With the aid of elemental analyses of unburned carbon and ash samples the major mineral phases were established in the diffraction patterns and are marked with abbreviations explained in the figure caption. Coal has already been given in indicating the dominant occurrence of quartz and kaolinite. Diffuse area observed in the unburned carbon diffraction pattern (approximately from 25 to 31) corresponds with semi-crystalline carbon phases. Somewhat lower crystallinity (broadened peaks) is evident also in case of magnetite and calcium hydroxide. Conversely, high-degree crystalline levels are represented e.g. by sharp peaks of quartz,

**4. Co-combustion of coal and solid waste fuels** 

and minimizing costs of waste deposition. (Loo & Kopperjan 2008).

electron microscope micrographs were taken by SEM PHILIPS XL – 30.

wood and bark combustion.

**4.1 Mineral analyses** 

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. (Bartoňová at al., 2009).

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 mullite T – anatase

#### **4.2 Chemical analyses**

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 its adsorption properties.

Co-Combustion of Coal and Alternative Fuels 77

coal with waste fuel the specific surface area of unburned carbon reached 297 m2/g, which is significantly higher value. This work was focused on the comparison of minor and trace elements behaviour during the co-combustion of coal and waste alternative fuels with the previous results regarding the combustion of the same pure coal in the same power station but without the added waste fuel. Elemental behaviour exactly in the combustion chamber did not change noticeably when waste alternative fuel was co-combusted with the coal. Even the most abundant elements in waste alternative fuel (related to coal) - Zn, Cl and Br - showed nearly the same behaviour. This observation can be explained through similar high volatility of these

**Measured contents wi**

**Ash (%) 23.4 67.7 98.0 98.8 5.6**  Na2O (%) < 0.2 < 0.2 < 0.3 < 0.3 < 0.1 MgO (%) < 0.1 < 0.1 0.3 0.6 < 0.02 Al2O3 (%) 5.9 21.4 11.6 17.6 0.6 SiO2 (%) 11.8 37.3 21.0 30.9 3.9 P2O5 (%) 0.1 0.3 0.16 0.3 0.08 K2O (%) 0.1 0.4 0.5 0.4 0.07 CaO (%) 0.7 1.5 44.0 29.8 2.4 TiO2 (%) 1.5 5.0 3.0 4.9 0.14 MnO (%) 0.02 0.04 0.10 0.04 0.003 Fe2O3 (%) 1.5 4.2 6.1 5.4 0.1 S (%) 1.1 0.7 3.1 2.7 0.1 V (ppm) 62.4 270.0 72.0 233.0 < 6.4 Cl (ppm) 41.5 72.8 87.4 411.0 121.4 Ni (ppm) 12.5 33.0 23.2 75.5 26.4 Cu (ppm) 67.0 176.8 82.2 185.0 25.0 Zn (ppm) 26.6 43.1 111.0 370.3 1717.0 Ga (ppm) 14.4 30.0 21.7 40.1 < 1.0 Ge (ppm) 5.4 11.4 7.4 15.9 1.1 As (ppm) 39.0 27.0 66.0 97.8 < 0.7 Se (ppm) 1.2 2.1 1.6 8.3 0.5 Br (ppm) 1.8 1.2 2.1 12.2 49.1 Rb (ppm) 11.4 39.9 35.2 30.1 < 0.6 W (ppm) 19.1 52.5 21.8 60.2 < 8.1 Pb (ppm) 6.9 22.2 18.2 36.0 1.46 Th (ppm) 5.7 14.4 8.9 17.4 < 1.0

Table 6. Ash contents and concentrations of elements in coal (C), unburned carbon (UC),

bottom ash (BA), fly ash (FA) and waste fuel (WF)

**C UC BA FA WF** 

elements both in the coal and in the waste materials. (Bartoňová at al., 2009).

**Element Sample** 
