Geopolymers can be treated as an environmentally friendly alternative for concrete and enables utilization of various wastes. This paper focuses on the possibility of application of discarded cathode ray tube (CRT) glass inside a metakaolin-based geopolymer in the form of an aggregate, providing an ecological method of recycling of this hazardous material. The main goal of this paper was to develop an optimal composition of a new geopolymer and to describe its behavior under varying curing conditions. A geopolymer made of different mixtures was subjected to flexural and compressive strength tests. The density, mass loss, temperature changes, and metals leaching were determined as well. The results demonstrated that neither the content of CRT glass nor the curing regime has a significant influence on the mechanical behavior. However, the strength of the geopolymer containing 50% CRT glass by mass increased with time in contrast to a geopolymer with a higher CRT glass content. The development of temperature inside the mixture was dependent on the amount of metakaolin. The concentration of toxic metals in an aqueous extract decreased considerably after the encapsulation of CRT glass inside the geopolymer. The presented results indicate that discarded CRT glass can be considered an aggregate for a metakaolin-based geopolymer. The new material shows high strength and makes the CRT glass safe for the environment.

The neutralization of wastewater treatment residues is an issue for many countries. The European Union (EU) legal regulations have limited the use of the residues in agriculture and implemented a ban for their disposal. Therefore, urgent action should be taken to find solutions for the safe disposal of sewage sludge. The problem refers in particular to the new EU member countries, including Poland, where one can now observe an intensive development of sewage system networks and new sewage treatment plants. At the same time, these countries have few installations for thermal sewage sludge utilization (e.g., there is only one installation of that type in Poland). Simultaneously, there are many coal-fired mechanical stoker-fired boilers in some of these countries. This paper presents suggestions for the production of granulated fuel from sewage sludge and coal slime. Additionally, among others, lime was added to the fuel to decrease the sulfur compounds emission. Results are presented of research on fuel with two average grain diameters (∼15 and 35 mm). The fuel with such diameters is adapted to the requirements of the combustion process taking place in a stokerfired boiler. The research was aimed at identifying the behavior of the burning fuel, with special attention paid to its emission properties (e.g., to the emissions of oxides of nitrogen [NO_x], sulfur dioxide [SO₂], and carbon mon-oxide [CO], among others). The concentration and emission values were compared with similar results obtained while burning hard coal. The combustion process was carried out in a laboratory stand where realization of the large-scale tests is possible. The laboratory stand used made simulation possible for a wide range of burning processes in mechanical stoker-fired boilers.

One of the ways used to reduce the emission of carbon dioxide and other harmful substances is the implementation of biomass co-firing processes with coals. Such processes have been implemented for many years throughout many countries of the world, and have included using existing high-power coal boilers. Despite numerous experiments, there are still no analyses in the literature allowing for their generalization. The purpose of this paper is to determine the generalized energy and ecological characteristics of dust steam boilers co-firing hard coal with biomass. The energy characteristics determined in the paper are the dependence of the gross energy efficiency of boilers on such decision parameters as their efficiency and the share of biomass chemical energy in fuel. However, the ecological characteristics are the dependence of emission streams: CO, NO_x, SO₂, and dust on the same decision parameters. From a mathematical point of view, the characteristics are approximation functions between the efficiency values obtained from the measurements and the emission streams of the analysed harmful substances and the corresponding values of the decision parameters. Second-degree polynomials are assumed in this paper as approximation functions. Therefore, determining the characteristics came down to determining the constant coefficients occurring in these polynomials, the so-called structural parameters. The fit of the determined characteristics was assessed based on the coefficients of random variation and the test of estimated significance of structural parameters. Boiler characteristics can be used when forecasting the impact of changes in operating conditions on the effects achieved in existing, modernized, and designed boilers. The generalization of the characteristics was obtained from the measurement results presented in 10 independent sources used to determine them.

When burning fuel in grate furnaces, supplying the right amount of air to them is as important as the method of air supply. In a furnace with a fixed grate, the supply method of primary air is determined by the distribution of the supplied air stream over time, and in a furnace with a movable grate, the said method involves the distribution of the stream along the active length of the grate. The need to account for air distribution is attributable to complex processes that occur during the combustion process. The paper describes experimental studies aimed at determining the influence of the distribution of the supplied primary air on the emission of CO₂, CO, SO₂, NO_x, and on the content of combustible parts in the slag. In all cases, the total amount of primary air supplied to the process as well as other process control parameters was identical, and only the distribution of primary air was different. The paper proposes the use of a generalized function to describe the distribution of air, defined by its total demand and the relative time R that fuel remains on the grate until the maximum air stream is obtained. The quantity R was accepted at the value ranging from 1/6 to 2/3. With the rise of R, the emissions of CO₂, CO, and SO₂ increased by 53%, 125%, and 27%, respectively, and the emissions of NO_x and the share of combustibles in the slag decreased by 12% and 79%, respectively.