The results of industrial research on co-combustion of solid recovered fuel (SRF) with hard coal in a stoker boiler type WR-25 has been presented. The share of SRF in the fuel mixture was 10%. During the co-combustion of SRF, no technological disturbances or significant reduction in energy efficiency of the boiler were noted. Obtained SO₂, NO_x and CO emissions were comparable with coal combustion but dust emissions increased. During combustion of the coal mixture with a 10% share of SRF in the test boiler WR-25, the emission standards established for the combustion of the dedicated fuel were met. However, comparison of obtained emission results with the emission standards established for co-incineration of waste, revealed the exceedance of permissible levels of HCl, dust, heavy metals, dioxins and furans. Additionally, the residence time of flue gases in over 850°C conditions for the test boiler WR-25 was too short (1.3 seconds) in refer to the legislative requirements (2 seconds) for the thermal conversion of waste.

The idea of combustion of suspended fuels was developed in the 1980s. The largest producer and user of slurry fuels (Coal Water Slurry, CWS) is China [3]. Despite of several decades of CWS research history, investigations are still carried out to improve the parameters of disperse fuels and to improve the combustion of these fuels. The close relationship between the properties of slurry fuels and number of parameters (mainly the type and properties of the coal feedstock) generates the necessity of CWS receipts and determines for what purposes the fuel may be destined. In the case of the use of coal sludge, the resulting slurry allows for the combustion / "disposal" of coal slurry in pulverized boilers. In the case of using better quality fine coal fractions in CWS production, a slurry will be created allowing for achieving the crucial technological goal such as operation of power units with a reduced technical minimum.

Liquid biofuels are of special interest due to the possibility of their application as a substitute for fossil liquid fuels. The necessary step is to investigate the possibility of bio-fuel application in terms of its properties and similarities to fossil liquid fuels (e.g., crude oil, heavy fuel oil, diesel). The properties and combustion performance of heavy fuel oil (HFO) and products of the fatty acids distillation residues (FADR) were analyzed in this study. The application of animal-fat-delivered fuels is fully suggested in the literature. Nevertheless, the investigations focused on the raw materials or their transformation into diesel. The novelty of this paper is the utilization of FADR as a substitute for HFO. The utilization of FADR allows the use of this material as a feedstock to obtain valuable products (fuel) and avoids generating waste after animal fat processing. The experimental investigations were carried out using a technical-scale 150 kW_th combustion chamber. FADR can be recognized as a substitute for HFO due to its beneficial calorific properties and viscosity. Other beneficial effects are the significantly lower emission of SO₂ (lower than 1 ppm) and PAHs (i.e., 355 µg/m³_n) during the combustion of FADR. Finally, the application of FADR requires less energy demand for fuel heating and pressurization.