The flue gas composition is often measured using a combination of techniques that differ in terms of both physical operation principle and type of output. Gas analyzers, FTIR spectrometers, and mass spectrometers are the most popular tools used for this purpose. In this research, we study the composition of the flue gas from the combustion of fuel slurries and dry composite fuels based on industrial and agricultural waste. It has been established that the use of slurry fuels makes the anthropogenic emissions 2–4 times lower than from the combustion of coal slime. For example, the CO2 emissions from the combustion of dry coal slime were 2.5–3.7 times higher than from the combustion of slurry fuels. In addition, the combustion of slurry fuels made it possible to cut down the nitrogen oxide emissions by 1.3–1.5 times and sulfur oxide emissions by 1.3–2.7 times. A comparison of the results obtained using different measurement techniques has shown that differences between the CO and CO2 content in the combustion products measured by a gas analyzer and an FTIR spectrometer did not exceed 20%. The use of FTIR spectroscopy provided new knowledge on the concentrations of hydrocarbons from the combustion of fuels based on promising industrial wastes.