Search Results (7)

The correct design of effective SNCR (Selective Non-Catalytic Reduction) requires solving several technological challenges. For this purpose, CFD modeling and bench tests were used. This study investigated various parameters affecting the NOx reduction rate in a WR-25 stoker boiler. The first parameter analyzed was the NSR (normalized stoichiometric ratio), with a constant urea concentration of 12.5% in the solution injected into the boiler. CFD modeling indicated that increasing the NSR significantly enhances reduction efficiency, especially between NSR 1 and 2, where the efficiency more than doubles. Bench tests confirmed this trend across all boiler power levels, showing deeper reagent penetration in the chamber at higher NSR levels. However, further doubling of NSR did not yield significant efficiency improvements, likely due to limitations in chemical mixing under reagent excess conditions. Further, it was revealed that NOx reduction efficiency decreases as boiler power increases, probably due to reduced reagent residence time at the required thermodynamic conditions. Additionally, different nozzle tip designs were tested, with multi-hole nozzles (two-hole and three-hole), showing better NOx reduction than single-hole nozzles due to improved reagent distribution. Finally, a lower urea concentration in the reagent (12%) led to better NOx reduction compared to a 32.5% concentration, likely due to improved droplet penetration and mixing with flue gases. Full article

The simultaneous firing characteristics of woodchips and spent mushroom substrates (SMS) were studied in a stoker-type industrial boiler. The type of spent substrate intended for combustion consisted of oyster mushrooms. SMS from mushroom farms generally have a high water content. Dryers are therefore used for combustion. The moisture content of SMS was reduced to achieve low moisture to combust sufficiently at about 20%. First, the basic characteristics of the boiler were confirmed by conducting a woodchip combustion test under various operating loads of 30, 50, 70, and 100%. Thereafter, a simultaneous combustion test of woodchips and SMS was performed. During the experiment, exhaust gas concentrations in the boiler combustion chamber were measured, such as the temperature of oxygen (O₂), carbon monoxide (CO), and nitrogen oxides (NOx). In addition, industrial and basic analyses were performed on woodchips and SMS. The main differences in the fuel analysis results between woodchips and SMS were ash, nitrogen, sulfur content and net calorific value. According to the analysis, the nitrogen content of SMS was 2.6%, which was 8.7 times higher than that of woodchips, and the ash content was also 14.8%, which was 18.5 times that of woodchips. As a result of the combustion experiment, the woodchip experiment revealed that the values of O₂ and CO decreased and the combustion chamber temperature increased as the amount of fuel increased. Due to higher combustion temperature, thermal NOx also increased. When comparing this combustion test with the co-firing test, there was no significant difference in O₂, CO, and combustion chamber temperature. However, with regard to the NOx value, the results showed a sharp increase from 64 ppm to 135 ppm. Although the NOx value increased, SMS had enough heat to be burned as fuel. Therefore, the utility of various agricultural byproducts as fuel has prospects for achieving an effective approach to energy cost reduction. Full article

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. Full article

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. Full article

In this study, the features of fly ashes originating from industrial-scale high volatile bituminous coal combustion and co-combustion of coal with 10% admixture of alternative fuel SRF (solid recovered fuel) are presented, with emphasis on the organic petrographical characteristics. The organic petrographical and mineralogical data are co-evaluated with geochemical data, with the aim to provide a full classification of the studied fly ashes, as well as base information toward any potential application of this waste material, according to the recycling economy principles. By applying organic petrographical methods, the assignment of the carbon-rich residuals to the respective feed fuel, either coal or SRF, can be achieved. The obtained quantitative evaluation provides useful information regarding the combustion conditions in the stoker boiler. The analyzed fly ashes contain significant C-residuals, mostly in the form of fused, dense, and anisotropic particles, while the enrichment in sooty particles is caused due to the addition of SRF fuel. In conjunction with the moderate-low content of potential hazardous elements, the features of the contained C-residual phases suggest that these fly ashes could possibly be the subject of further studies for their applicability as soil improvements. Full article

The paper assesses the impact of combustion of biofuels produced based on municipal sewage sludge in stoker-fired boilers on the amount of pollutant emissions and examines the tendency of ash deposition of biofuels formed during the combustion process. The combustion tests were performed in a laboratory system enabling simulation of a combustion process present in stoker-fired boilers. The study was conducted for three types of biofuels; i.e., fuel from sewage sludge and coal slime (PBS fuel), sewage sludge and meat and bone meal (PBM fuel) and fuel based on sewage sludge and sawdust (PBT) with particle size of 35 mm and 15 mm. This paper describes and compares the combustion process of biofuels with different granulation and composition and presents the results of changes in emission values of NO_x, SO₂, CO, and CO₂. The emission results were compared with the corresponding results obtained during combustion of hard coal. The results showed that biofuels with lower particle sizes were ignited faster and the shortest ignition time is achieved for fuel based on sewage sludge and coal slime-PBS fuel. Also, the highest NO and SO₂ emissions were obtained for PBS fuel. During the combustion of fuel based on sewage sludge and meat and bone meal (PBM), on the other hand, the highest CO₂ emissions were observed for both granulations. Biofuels from sludge show a combustion process that is different compared to the one for hard coal. The problems of ash fouling, slagging, and deposition during biofuels combustion were also identified. The tendency for ash slagging and fouling is observed, especially for fuel from sewage sludge and meat and bone meal (PBM) and fuel based on sewage sludge and sawdust (PBT) ashes which consist of meat and bone meal and sawdust which is typical for biomass combustion. Full article

This study investigates the feasibility of co-firing fly ashes from different boilers, circulating fluidized beds (CFB) or stokers as a sustainable material in alkali activators for ground granulated blast-furnace slag (GGBS). The mixture ratio of GGBS and co-firing fly ashes is 1:1 by weight. The results indicate that only CF fly ash of CFB boilers can effectively stimulate the potential characteristics of GGBS and provide strength as an alkali activator. CF fly ash consists of CaO₃ (48.5%), SiO₂ (21.1%), Al₂O₃ (13.8%), SO₃ (10.06%), Fe₂O₃ (2.25%) and others (4.29%). SA fly ash consists of Al₂O₃ (19.7%), SiO₂ (36.3%), Fe2O3 (28.4%) and others (15.6%). SB fly ash consists of Al₂O₃ (15%), SiO₂ (25.4%), Zn (20.6%), SO₃ (10.9%), Fe₂O₃ (8.78%) and others (19.32%). The mixtures of SA fly ash and SB fly ash with GGBS, respectively, were damaged in the compressive strength test during seven days of curing. However, the built up strength of the CF fly ash and GGBS mixture can only be maintained for 7–14 days, and the compressive strength achieves 70% of that of a controlled group (cement in hardening cement paste). The strength of blended CF fly ash and GGBS started to decrease after 28 days, and the phenomenon of ettrigite was investigated due to the high levels of sulfur content. The CaO content in sustainable co-firing fly ashes must be higher than a certain percentage in reacting GGBS to ensure the strength of blended cements. Full article