**1. Introduction**

62 Fossil Fuel and the Environment

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Energy utilization of alternative fuels including biofuels is one of the main tasks for development of recoverable sources in the world. The research consists of combustion tests in the large CFB boilers and measuring data inside the combustor. Since 1995, 29 large CFB boilers of different designs and power outputs have been in operation in the Czech Republic - as shown in the Table 4. Construction of the boilers, technical documentation, licensing and engineering has been based on foreign experience. Every large power project is always preceded by trial measurements and tests on smaller pilot, trial or if need be model equipment. Due to the great difference in scale, some unexpected measuring equipment behavior or problems must be taken into consideration for cocombustion of coal and alternative fuels.

The present research aiming at characterising the co-combustion under-atmospheric fluidized bed conditions by different physical and chemical characteristics has the following objectives:

