Recently, biomass application as a renewable energy source is increasing worldwide. However, its availability differs in dependence on the location and climate, therefore, agricultural residues as cow dung (CD) are being considered to supply heat and/or power installation. This paper aims at a wide evaluation of CD fuel properties and its prospect to apply in the form of pellets to direct combustion installations. Therefore, the proximate, ultimate composition and calorific value were analyzed, then pelletization and combustion tests were performed, and the ash characteristics were tested. It was found that CD is a promising source of bioenergy in terms of LHV (16.34 MJ·kg⁻¹), carbon (44.24%), and fixed carbon (18.33%) content. During pelletization, CD showed high compaction properties and at a moisture content of 18%,and the received pellets’ bulk density reached ca. 470 kg·m⁻³ with kinetic durability of 98.7%. While combustion, in a fixed grate 25 kW boiler, high emissions of CO, SO₂, NO, and HCl were observed. The future energy sector might be based on biomass and this work shows a novel approach of CD pellets as a potential source of renewable energy available wherever cattle production is located.

The aim of the presented research was to determine the suitability of cherry stones as a solid fuel. Mixtures of cherry stones with the addition of 10%, 15%, and 20% rye bran as a binder were subjected to the pressure agglomeration process in a rotary matrix working system (170, 220, and 270 rpm). The density of pellets, their kinetic durability, and power demand of the granulator’s device for each mix were determined. The highest quality was characterized by pellets containing 20% rye bran, which were combusted in a 25 kW boiler with a retort grate. The concentration of CO, CO₂, NO, SO₂, HCl, and O₂ in the exhaust gas was tested. On the basis of the results of combustion, high heating value (HHV), low heating value (LHV), and elemental analysis, it was found that pellets from cherry stones with the addition of rye bran can serve as a substitute for wood pellets in low-power installations.

Agri-food waste is generated at various food cycle stages and is considered to be a valuable feedstock in energy systems and chemical syntheses. This research identifies the potential and suitability of a representative agri-food waste sample (i.e., plum stones) as a solid fuel. Ground plum stones containing 10, 15, and 20 wt.% of rye bran were subjected to pelletization. The pelletizer was operated at 170, 220, and 270 rpm, and its power demand for the mixture containing 20 wt.% of rye bran was 1.81, 1.89, and 2.21 kW, respectively. Such pellets had the highest quality in terms of their density (814.6 kg·m⁻³), kinetic durability (87.8%), lower heating value (20.04 MJ·kg⁻¹), and elemental composition (C: 54.1 wt.%; H: 6.4 wt.%; N: 0.73 wt.%; S: 0.103 wt.%; Cl: 0.002 wt.%; O: 38.2 wt.%). Whole plum stones and pellets were subjected to combustion in a 25 kW retort grate boiler in order to determine the changes in the concentrations of NO, SO₂, CO, CO₂, HCl, and O₂ in the post-combustion flue gas. Collected results indicate that plum stone–rye bran pellets can serve as effective substitutes for wood pellets in prosumer installations, meeting the Ecodesign Directive requirements for CO and NO.

The aim of the described research was to assess the suitability of onion husk waste as a material for the production of solid fuels in the form of granules (pellets). Due to the low susceptibility to thickening of onion husks, the addition of a binder in the form of potato pulp was used (waste with a high starch content). Both wastes were subjected to elemental analysis determining the content of C, H, N, S, Cl, and their HHV (High Heating Value) and LHV (Low Heating Value). Mixtures containing the addition of 10%, 15%, and 20% potato pulp to onion husks were subjected to granulation in a “flat matrix–thickening rollers” operating system at three rotational speeds of the granulator matrix a 170, 220, and 270 rpm. The influence of the potato pulp addition and matrix rotational speed on the quality of the obtained pellet was determined. The highest quality product was combusted in a low-power boiler with a retort grate, and the content of CO, CO₂, SO₂, NO, and HCl in the exhaust gas was determined. The highest quality granulate was obtained from a mixture containing 10% potato pulp, which was compacted at 170 rpm matrix, where the kinetic strength was 99.50% and the density was about 650 kg·m⁻³. The results of the combustion emissions from onion husk granules exceed the requirements of the EcoDesign Directive with the greatest being the case of CO.

The paper presents the results of the pelletization (agglomeration) tests of post-harvest tobacco waste as a feedstock for fuel pellet production. The experiment was conducted on a prototype pelleting–briquetting device with a flat matrix. The influence of the tobacco waste moisture content (17, 21 and 25wt.%) and the rotational speed of the agglomerating rolls (120, 170 and 220 rpm) on the power demand and on the pellet’s kinetic durability and density were determined. It was found that the moisture content has a significant impact on the pellet’s density but slightly affects its kinetic durability. The obtained pellets were characterized by a high density above 1000 kg·m⁻³ and kinetic durability above 97%. In order to examine the exhaust composition, the obtained pellets were combusted in a 25 kW fixed great boiler. High amounts of CO, SOx, NO and HCl were obtained, which suggests that the selection of a different technology for tobacco waste pellet combustion should be made.