The paper presents the combustion profile of selected fuels as a result of thermogravimetric analysis. The main purpose of this study was to investigate a mixture of different types of fuel and the influence of the use of a fuel additive on the combustion process profile. As a fuel additive, halloysite was used to investigate the thermogravimetric profiles. It was confirmed that the main combustion parameters such as ignition temperature, burnout temperature, and maximum peak temperature correlated accordingly with different combustibility indices such as the ignition index, the burnout index, and the combustion indices. Furthermore, the present study provided a comparison of selected methods for analyzing non-isothermal solid-state kinetic data and investigated the kinetics of thermal decomposition to describe the ongoing process. Two non-isothermal model methods (Kissinger and Ozawa) were used to calculate the Arrhenius parameters. The effect of heating rate and the addition of halloysite as a fuel additive on decomposition were studied.

In the presented paper, two types of animal-origin biomass, cow dung and chicken litter, are characterized in terms of combustion-related problems and ash properties. It was found that these parameters strongly depend on the farming style. Whether it is cow dung or chicken litter, free-range raw materials are characterized by higher ash contents than industrial farming ones. Free-range samples contain chlorine at lower levels, while industrial farming samples are chlorine rich. Free-range samples are characterized by the predominant content of silica in the ash: 75.60% in cow dung and 57.11% in chicken litter, while industrial farming samples contain more calcium. Samples were classified by 11 “slagging indices” based on the ash and fuel composition to evaluate their tendencies for slagging, fouling, ash deposition and bed agglomeration. Furthermore, an assessment was made against the current EU law regulations, whether the ashes can be component materials for fertilizers. The phosphorus concentration in the investigated ashes corresponds to 4.09–23.73 wt% P₂O₅ and is significantly higher in industrial chicken litter samples. The concentrations of Hg, Cu, As, Ni, Cd and Pb in all samples are below the limits of the UE regulations. However, concentrations of Cr in all samples and Zn in industrial chicken litter exceed these standards.

An innovative dry SNCR method realized by a sorbent injection applied to a stoker furnace is presented. The process is based on urea powder admixed with halloysite, an aluminosilicate clay mineral. Field tests were performed at an industrial stoker hot water boiler of 30 MW_th capacity. A unique nozzle design for injecting powdery sorbents into the combustion zone was implemented. The base NO_x emission without SNCR was determined to be 365 mg/Nm³. During the reference test, the emission was reduced to avg. 175 mg/Nm³, which produces a NO_x reduction of 52%. NH₃ slip in the flue gas was stable and did not exceed 2 ppm. Combining urea and halloysite powders leads to a number of positive effects; not only is NO_x emission reduced to values typical for wet SNCR, but also a significant, over ten-fold increase in the concentration of adsorbed mercury in fly ash was observed. When confronted with wet SNCR, dry SNCR has no adverse effect on boiler efficiency because it does not increase the stack heat loss. The presented method can be used in any small- or medium-scale furnace, including waste-to-energy units or medical and hazardous waste incineration units.

The application of secondary NO_x control methods in medium to low-capacity furnaces is a relatively new topic on the energy market and thus requires further research. In this paper, the results of full-scale research of SNCR and hybrid SNCR + SCR methods applied into a 29 MW_th solid fuel fired stoker boiler is presented. The tests were performed for a full range of boiler loads, from 33% (12 MW_th) to 103% (30 MW_th) of nominal load. A novel SNCR + SCR hybrid process was demonstrated based on an enhanced in-furnace SNCR installation coupled with TiO₂-WO₃-V₂O₅ catalyst, which provides extra NO_x reduction and works as an excess NH₃ “catcher” as well. The performance of a brand-new catalyst was evaluated in comparison to a recovered one. The emission of NO_x was reduced below 180 mg NO_x/Nm³ at 6% O₂, with ammonia slip in flue gas below 10 mg/Nm³. Special attention was paid to the analysis of ammonia slip in combustion products: flue gas and fly ash. An innovative and cost-effective method of ammonia removal from fly ash was presented and tested. The main idea of this method is fly ash recirculation onto the grate. As a result, ammonia content in fly ash was reduced to a level below 6.1 mg/kg.

This paper presents a study of the fouling properties of solid fuels based on analyses of ashes from hard coal, forestry biomass, and agricultural biomass, ash deposits collected directly from the boiler surfaces, and ash deposits collected from a deposition probe. All samples were collected in the area of the steam superheater/reheater of a OP 380 pulverized-coal boiler co-firing forestry and agricultural biomass. In addition, the study concerns mitigation of unwanted fouling through application of a silica-based fireside additive. An analysis was carried out to obtain the following information: physical and chemical properties of ash produced during co-firing of a biomass mixture (50 wt.% forestry/50 wt.% agricultural biomass) and coal in order to determine its propensity for fouling and slagging without the use of a fireside additive; slagging/fouling indices during co-firing of a biomass mixture (50 wt.% forestry/50 wt.% agricultural biomass) and coal with the use of a fireside additive; and slagging/fouling indices during co-firing of pure agricultural biomass (sunflower husk) and coal with the use of a fireside additive. The mass flow of co-fired biomass fuel supplied to the boiler during reference measurements and mass flow when the additive was fed were the same and amounted to 33 wt.% of the total fuel mass flow. Finally, the effectiveness of fouling mitigation is determined by comparing the results of the deposition rate obtained with the use of a deposition probe for all three cases of co-firing.

This paper presents a new, innovative technological approach, in line with Circular Economy principles, to the effective management of sludge generated during municipal wastewater treatment processes and subsequently used for biogas production. This approach allows for optimal, functional, and controlled cascade-type biotechnological thermal conversion of carbon compounds present in sewage sludge, later in solid digestate residues (after biogas production), and finally in the ash structure (after incineration, purposefully dosed nanostructural additives make the production of a useful solid product possible, especially for cyclic adsorption and slow release of nutrients (N, P, K) in the soil). The idea is generally targeted at achieving an innovative conversion cycle under a Circular Economy framework. In particular, it is based on an energy carrier (methane biogas) and direct energy production. The functionalized combustion by-products can be advantageous in agriculture. The use of ashes with nanostructural additives (halloysite, kaolinite) from combustion of sewage sludge after the anaerobic fermentation as an adsorbent of selected nutrients important in agriculture (Na⁺, K⁺, NO₃⁻, SO₄²⁻, PO₄³⁻, Cl⁻) was verified at laboratory scale. The tests were carried out both for pure ash and for the ash derived from combustion with the purposeful addition of kaolinite or halloysite. The equilibrium conditions for nitrate, potassium, sodium, phosphate(V), sulphate(VI), and chloride ions from aqueous solutions with the use of the three adsorbent structures were determined. The obtained innovative results were interpreted theoretically with adsorption isotherm models (Langmuir, Freundlich, Temkin, Jovanović). The most spectacular and clearly favorable results related to the influence of nanostructural additives in the process of sludge combustion, and formation of sorption surfaces under high temperature conditions were identified in the case of sorption-based separation of phosphate(V) ions (an increase from 1.13% to 61.24% with the addition of kaolinite, and even up to 76.19% with addition of halloysite).