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

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

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 wood and bark combustion.

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