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Presented paper identifies the possible corrosion problems related to animal waste incineration since it is a key issue for their use in the power sector. Cow dung as an example of animal-origin biomass is examined in terms of high-temperature corrosion and slagging hazards in comparison with commonly used mixed straw. Results of the laboratory-scale corrosion studies of pure ash deposits on two steel alloys: 16Mo3 and 10CrMo9–10 are reported. Selected steel types are commonly used in boiler construction for superheaters and waterwalls – parts of a boiler that are most exposed to the high-temperature corrosion risk. The corrosion experiments were carried out under oxidizing conditions at 460 °C, 510 °C and 560 °C for 168 h. To determine the corrosion rate the mass of steel samples was measured after 24, 72 and 168 h. For a better understanding of the corrosion process, a detailed chemical analysis of ashes was conducted together with SEM-EDS analysis of the corrosion products. Ash melting and deposition behavior of both ashes were predicted according to 11 indices. It was found that cow dung and mixed straw ash differ significantly in terms of quantitative chemical compositions and ash melting characteristics. Cow dung ash is characterized by a high concentration of alkali compounds (2.57 wt% Cl, 30.6 wt% CaO, 5.56 wt% K2O) together with high phosphorus content typical for animal manure. The presence of alkali chlorides in the cow dung ash deposits led to a build-up of chlorides on the steel surface, which caused accelerated corrosion. At 560 °C the corrosion rate was over 3 times higher for cow dung ash than for mixed straw ash. The corrosion occurred due to the formation of low-melting FeCl2 mixtures since chlorine- and iron-rich particles were found in the crevices and cracks within deposits. The results clearly demonstrated the high corrosive potential of animal-origin biomass and therefore indicate the potential problems related to its thermal conversion process. These adverse effects can be reduced by ash removal and maintaining the temperature of the heating surfaces below 560 °C.

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).

Artificial neural networks were used for the prediction of three biomass ash fusion temperatures: initial deformation temperature IDT, hemispherical temperature HT and flow temperature FT based on chemical composition of the ash. Applicability of 400 neural network configurations (of linear, MLP, RBF and GRNN types) was verified statistically. Multilayer perceptron with 12 inputs representing fractions of the ash compounds, 11 hidden neurons and three outputs (IDT, HT, FT) proved to be the optimal neural model configuration. Statistical analysis suggested also, that considering intrinsic dispersion within the raw experimental data (literature data supplemented with the authors’ own results describing the halloysite addition effect), quality of the resulting 3-output IDT-HT-FT model (IDT prediction with R2 0.615, HT with R2 0.756 and FT with R2 0.729) could be regarded satisfactory for the identification and generalization of the discussed relationships. Analysis of the neural model sensitivity in respect to the input variables demonstrated, that the most important factors affecting all ash transition temperatures in the 3-output IDT-HT-FT model were: K2O, SiO2, CaO and Al2O3 fractions. Moreover, individual sensitivity in respect to IDT, HT and FT temperatures slightly varied (characteristics provided by independently established 1-output networks – IDT model, HT model and FT model, respectively). Statistically verified neural network working as the 3-output IDT-HT-FT model can be applied in various computational tasks in biofuels energy sector required by Industry 4.0 principles, as well as in the selected Circular Economy problems.

A new, innovative approach in the search for an effective and cheap carbon dioxide sorbent, in line with the circular economy and sustainable development principles, directs the attention of researchers to various types of waste ashes generated as a result of biomass combustion. In addition to the use of environmentally safe materials that have been experimentally identified, and that, in some way, have adjustable sorption capacity, it is also possible to rationally develop a widely applicable, simple, and inexpensive technology based on large amounts of this type of post-industrial waste, which is also an equally important issue for the natural environment (reducing the need for ash storage and accumulation). Even the lower sorption capacity can be successfully compensated for by their common availability and very low cost. Thus, the CO2 adsorption capability of the ashes from the combustion of straw biomass was experimentally investigated with the use of a high-pressure adsorption stand. The presented original technological concept has been positively verified on a laboratory scale, thus a functionalization-based approach to the combustion of substrate mixtures with nano-structural additives (raw, dried, calcined halloysite, kaolinite), introduced to improve the performance of straw biomass combustion and bottom ash formation in power boilers, clearly increased the CO2 adsorption capacity of the modified ashes. This allows for an advantageous synergy effect in the extra side-production of useful adsorbents in the closed-loop “cascade” scheme of the CE process. The addition of 4 wt.% kaolinite to straw biomass caused an over 2.5-fold increase in the CO2 adsorption capacity in relation to ash from the combustion of pure straw biomass (with a CO2 adsorption capacity of 0.132 mmol/g). In the case of addition of 4 wt.% nano-structured species to the straw combustion process, the best effects (ash adsorption capacity) were obtained in the following order: kaolinite (0.321 mmol/g), raw halloysite (0.310 mmol/g), calcined halloysite (0.298 mmol/g), and dried halloysite (0.288 mmol/g). Increasing the dose (in relation to all four tested substances) of the straw biomass additive from 2 to 4 wt.%, not only increase the adsorption capacity of the obtained ash, thus enriched with nano-structural additives, but also a showed a significant reduction in the differences between the maximum adsorption capacity of each ash is observed. The experimental results were analyzed using five models of adsorption isotherms: Freundlich, Langmuir, Jovanović, Temkin, and Hill. Moreover, selected samples of each ash were subjected to porosimetry tests and identification of the surface morphology (SEM). The obtained results can be used in the design of PSA processes or as permanent CO2 adsorbents, based on the environmentally beneficial option of using ashes from biomass combustion with appropriately selected additives.

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 MWth capacity. A unique nozzle design for injecting powdery sorbents into the combustion zone was implemented. The base NOx 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 NOx 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 NOx 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 main objective of the research was to develop a method of biomass grindability determination (Biomass Grindability Index), which would allow for a clear classification of different types of solid biofuels in terms of their milling properties. The objective of the research included also the assessment of the possibility of adaptation of the existing coal grindability determination methods for evaluation of biomass milling. In the course of research, the biomass grindability determination method was modified to obtain the highest possible reliability of the developed index. The scope of laboratory tests being focused on influence of circumferential speed of test mill beaters, particle size distribution of sample, test time, mass and volume of sample. The results of laboratory and industrial tests have shown that the grindability index based on mean particle sizes of feed and product is unreliable. Grindability of different types of biomass, comminuted in beater mills, can be clearly determined by the index expressed as the ratio of energy consumption during the test to the amount of specified product size fraction. During the study laboratory test results obtained for proposed grindability index were compared to other grindability indices determined for utilized in research types of biomass.

Up to now, a few studies on the efficiency of heavy metal(-oid)s capture by a sorbent directly mixed with fuel, have been performed. For this reason, the main objective of the study is to determine whether or not such a solution is effective when RDF is incinerated. The paper presents a two-step analysis of the impact of three sorbents (ammonium sulphate, kaolinite and halloysite) in three dosages (2, 4 and 8 wt%) on heavy metal(-oid)s retention in the bottom ash. 12 heavy metal(-oid)s were taken into consideration - As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, V and Zn. Samples were incinerated in a lab-scale tubular reactor at two temperatures - 900 °C and 1100 °C. The first step of investigation constitutes ICP analysis of heavy metal(-oid)s content in the bottom ash, coupled with SEM/EDS analysis. Afterwards, the second step was to determine the stability of formed additive-heavy metal(-oid)s complexes via leachability tests in neutral and acid environments. The performed research has shown that ammonium sulphate is effective in Cr, Cu and Hg capture, halloysite – in Cd, Co, V and Mn capture, whereas kaolinite – in Pb capture.

The paper presents results of the investigation of an innovative biomass and alternative fuel low-temperature gasification method before co-firing in industrial or power plant boilers. Before running industrial-size installation, laboratory tests were carried out to determine usability of alternative fuels to low-temperature gasification process. Tests were conducted in a laboratory reactor designed and constructed specifically for this purpose. The experimental stand enables recording of the weight loss of a sample and syngas composition. The process occurs for a fuel sample of a constant weight and known granulation and with a flue gas of known composition used as a gasifying agent. The aim of the laboratory research was to determine the usability of selected biomass fuel for indirect co-firing in power boilers and to build a knowledge base for industrial-size process by defining the process kinetics (time for fuel to remain in the reactor), recommended fuel granulation and process temperature. Presented industrial-size gasification unit has been successfully built in Marcel power plant in Radlin town, Poland. It consist an innovative rotary gasification reactor. Gasification process takes place with use of flue gas from coal and coke-oven fired boiler as a gasifying agent with recirculation of resulting gas (syngas) with combustible components: CO, H 2 , CH 4 . C n H m to the boiler’s combustion chamber. The construction of the reactor allows the use of a wide range of fuels (biomass, industrial waste and municipal waste). This paper presents the results of the reactor tests using coniferous wood pellets as a fuel. Presented tests confirmed a possibility of continuous low-temperature gasification in a rotary gasification reactor with combustion of a process’ products in boiler’s combustion chamber.

The paper presents results of the investigation of an innovative biomass and alternative fuel low-temperature gasification method before co-firing in industrial or power plant boilers. Gasification process takes place with use of flue gas as a gasifying agent with recirculation of resulting gas (syngas) to the boiler's combustion chamber. Industrial-size rotary gasification reactor using flue gas as a gasifying agent has been designed and successfully built in Marcel power plant in Radlin town, Poland. The construction of the reactor allows the use of a wide range of alternative fuels (biomass, industrial waste and municipal waste). The paper presents the results of the reactor tests using coniferous wood pellets as a fuel. The flue gas from coal and coke-oven gas co-firing were used as the gasifying agent. The measuring system ensures online measurements of syngas composition: CO, CO2, H2, CH4. As a result of presented gasification process a syngas with combustible components has been obtained and recirculated to the boiler's combustion chamber. Before running industrial-size installation, laboratory tests were carried out to determine usability of selected fuels to gasification process. Tests were conducted in a laboratory stand, equipped with a gasification reactor designed and constructed specifically for this purpose. The experimental stand enables the weight loss of a sample and syngas composition to be recorded. The aim of the laboratory research was to determine the usability of selected alternative fuel for indirect co-firing in power boilers and to build a knowledge base for industrial-size process.

The paper presents results of investigations on KCl interaction with halloysite under high temperature conditions. Halloysite is an aluminosilicate that can be used as a fuel additive to prevent chlorine corrosion and formation of low melting corrosive deposits during combustion of biomass. It is claimed that an increase of the emission of gaseous chlorine as HCl(g) and decrease of chlorine share in the ash as result of KCl and halloysite interaction should be expected. During presented tests the mixtures of KCl and halloysite with different ratios were thermally decomposed in a muffle furnace at high temperatures of 900°C and 1100°C. Then, the analyses of potassium and chlorine contents in the formed solid residues were determined. Besides, it has been proved that halloysite addition changes the ash deposit structure as well as increases the ash fusion temperatures. This was supported by performing phase equilibrium calculations for the investigated different halloysite/KCl mixtures. The positive effects of halloysite on potassium capture while reducing chlorine content in solid residue to prevent formation of corrosive deposits have been confirmed.

The prediction of phase transformation of biomass ashes is challenging due to the highly variable composition of these fuels as well as the complex processes accompanying phase transformations. The AFT (Ash Fusion Temperature) model was performed in Statistica 13.1 software. This model was divided into three separate submodels, which were designed to predict the characteristic ash melting temperatures for raw and modified biomass. It is based on the chemical composition of fuel and ash as obtained using ash analysis standards. For the discussed models, several coefficients describing multiple regression parameters are presented. The AFT model discussed in this article is suitable for predicting ash fusion temperatures for biomass and allows for the prediction of the temperature with an average error of

The motivation of this paper is new NOx emission regulations according to IED Directive 2010/75/EU of EU which introduce the BAT’s conclusions as binding. The paper presents the methodology and results of research on the effectiveness of SCR catalysts during combustion of pulverised coal in a model furnace installed at the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology (IPET). The aim of the research was to search for catalysts that could be placed in a regenerative rotary air heater - RAH-SCR. Two catalysts were tested: a commercial plate-type based on V2O5 and a prototype ceramic based on platinum. Presented results of investigation demonstrate a potentially high efficiency of RAH-SCR installations which can meet new environmental regulations of NOx emission. The highest NOx reduction efficiency (92.87%) was obtained for an industrial catalyst at 329°C, from about 436.3 to 31.1 mg/m3 as NO2 @ 6%O2 to 31,1. At lower temperature, 260°C maximum efficiency of NOx reduction does not exceed 60%, from 440,0 to 169,6 mg/m3. The placement of the catalyst in the RAH can also be a support for SNCR installations due to the increase in DeNOx efficiency and reduction of NH3 slip.

The subject of the CFD analysis presented in this paper is the process of biomass indirect co-firing carried out in a system composed of a stoker-fired furnace coupled with a gasification reactor. The installation is characterised by its compact structure, which makes it possible to minimise heat losses to the environment and enhance the physical enthalpy of the oxidising agent – flue gases – having a favourable chemical composition with oxygen and water vapour. The test results provided tools for modelling of biomass thermal processing using a non-standard oxidiser in the form of flue gases. The obtained models were used to optimise the indirect co-combustion process to reduce emissions. An overall effect of co-combustion of gas from biomass gasification in the stoker furnace is the substantial reduction in NO emissions by about 22%.

The paper presents slagging and fouling properties of ashes when hard coal was fired in a pulverized coal-fired boiler (230 t/h capacity) and the change of fouling indices of resulting fly ash when halloysite fireside additive was used. During reported full-scale study the pulverized coal-fired boiler was fired with hard coal with the addition of pulverized halloysite injected directly into furnace through the designed spray-nozzles in the upper part of boiler furnace. Chemical analysis of fuel properties and collected from the ESP (electrostatic precipitator) fly ash samples was carried out to obtain the following information: • determine chemical properties of coal and its ash produced during combustion in order to determine its propensity for slagging versus reference study conducted without the use of additive • identify the slagging and fouling indicators when halloysite additive was used. The tests results are intended to determine the effectiveness of the pulverized halloysite injection to the furnace in terms of reducing slagging and fouling of heating surfaces, in particular the evaporator and convective section of the boiler. The required halloysite feeding is determined by comparing the change in chemical composition (ash modification effectiveness) between fly ashes produced in the reference and test case so as it is corrected according to the fuel slagging properties (fuel slagging index).

Ambitious EU environmental policy decreasing CO2 emissions from combustion of fossil fuels impact on whole EU economy. Utilization of biomass as carbon neutral fuel helps to address these challenges Combustion and co-combustion of biomass, especially agriculture residue biomass, is associated with many technical problems such us: bed agglomeration, slagging and fouling, chlorine corrosion, decreased boiler efficiency which do not occur in conventional fossil fuels combustion. In this study six fuels were investigated on their deposition ability (2 types of straw, Miscanthus and herbaceous pellets, RDF—Refuse-Derived Fuel and reference coal). Biomasses were selected as the most commonly used in Polish and German power industry. Analysis comprised chlorine and sulphur contents of the fuel, ash oxides analysis and ash fusion temperatures. The main objectives of this work were to predict ash deposition tendency of chosen fuels using ash deposition indices and compare it with reference fuel. Next weaknesses of selected indicators are pointed out.

Clanek prezentuje analýzu zplyňovani alternativniho paliva s využitim spalin jako zplyňovaciho prostředku. Jako výsledek zplynovaciho procesu “syngas” byly definovany hořlave složky (CO, H2, CH4, CnHm). Byly provedeny laboratorni testy pro urceni použitelnosti vybraneho alternativniho paliva pro proces zplyňovani při nizkých teplotach. Testy byly provaděny v laboratornim reaktoru, který umožnil zplyňovat vzorek paliva o hmotnosti cca. 1 g. Experimentalni zařizeni umožňuje zaznamenat ubytek hmotnosti vzorku a jeho složeni. Proces probiha u vzorků paliva s konstantni hmotnosti a s různou granulometrii a se stanoveným složenim spalin použitým jako zplyňovaci medium. Cilem laboratorniho výzkumu bylo zjistit použitelnost paliva RDF pro nepřime spolu-spalovani v energetických kotlich a vytvořit znalostni zakladnu pro realný průmyslový proces definovanim parametrů procesu: kinetiky (doby setrvani paliva v reaktoru), doporucena granulometrie paliva a teploty procesu.

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/...

Deposits in power boilers are formed during combustion of practically all solid fuels. The source of deposit formation in boilers is the presence of mineral substance in the fuel. A mineral substance undergoes a series of physical and chemical processes. They produce particles of ash and volatiles which mix with the flue gas. Ash particles floating in the flue gas strike heat exchange surfaces. Steam superheater tubes in power boilers are covered either with powdery deposits, loosely staying on the surface, or bonded ones, stuck firmly onto the surface. The spacing of boiler tubes influences the velocity field of the flue gas and trajectories of ash patricles. Orlowski (1972) summerised, for Polish boilers, the tube arrangements of convective in-line superheaters as s1/D=1.5-2 and s2/D =1.5-3, and radiant ones as s1=350-1500 mm, and s2/D =1.05-1.1, where s1, s2 - describe tube spacing, and D is a tube diameter. Particles of ash have a size distribution of a few microns up to 200 µm. Typical range of flow velocity within superheater bundles is 5-15 m/s. Typical temperature of flue gas in this area is between 500 and 1000C. As can be seen, the spacing of tubes and particle size produce quite different conditions resulting in the various history of deposit formation. In two of the latest publications Weber et al. (2013) described prediction of ash particle trajectories using contemporary Computational Fluid Dynamics software. They studied what conditions must be provided in order to predict impaction of ash particles using Reynolds Averaged Navier-Stokes (RANSs) approach. They pointed out that although

The article presents analysis of the particle size distribution inside pellets and the influence of moisture content before pelletization process on final product mechanical strength. The following types of biomass were used without and with the content of additive (halloysite): Polish wheat straw – (SP-K), miscanthus (DM), cereal straw (DS) and herbaceous pellets (BZ). Particles inside pellets were characterized by a grain size smaller than 3 mm and the cumulative weight percent passing through the sieve with mesh screen 1 mm for each sample was higher than 70 %. The moisture content before pelletization process for tested materials was in the range of 25% - 30% depending on the material which was used, while values of mechanical strength of pellets were within the range of 77.7% - 96.2% (depending on the type of material and moisture content before the pelletization process).

The main source of ammonia in ash are residues from an unreacted NH3 from the denitrification process, either from SCR or SNCR systems. The paper discusses the standards of NH3 content in fly ash and presents the most commonly used methods of removing excess ammonia from fly ash. In the next part of the work the results of laboratory tests on NH3 desorption are presented. Desorption was performed on samples of fly ash taken from the electrostatic precipitator of real PC boiler. Removal of NH3 from the ash was carried out in a heating chamber at 130°C and 150°C and detected by an analyser equipped with a NDIR sensor. Additionally, at the temperature of 130°C, the NDIR and analytical methods were compared (in accordance with the BN-750541-05 procedure) and the measurement uncertainty of both methods was estimated.

This paper presents a comparison of the degree of fouling in a hot water stoker-fired boiler after it has been fired with two types of coal with different characteristics for an extended period of time. The extent at which indices that characterise the tendency to cause slagging and fouling on boiler heating surfaces found in the literature correspond to the actual state of ash deposits in the boiler is discussed. New ranges of fouling indices values are proposed that correspond to the results from observing fouling in the boiler.

One of the methods of obtaining energy from renewable sources is the technology of indirect cofiring of biomass. It consists in the gasification of secondary fuel and combustion of the generated gas in the boiler together with its primary fuel. The paper presents a thermodynamic analysis of the use of the boiler flue gases as the converting medium in the process of indirect co-firing - a technology which is being developed at the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology. The basis of the analysis are the data resulting from variant calculations conducted with the use of the Gaseq program. The calculations were made for various compositions of gasified fuel and the converting medium, variable fuel/oxidiser ratios and variable gasification temperatures. As a result, the equilibrium composition and the calorific value of the generated gas were obtained. The main optimisation objective adopted here was the nondimensional efficiency coefficient, which is the ratio of the chemical energy of products to the chemical energy of the process reactants.

Particulate fouling of convective heat-transfer surfaces is usually assessed by empirical correlations. Nevertheless, constant progress in numerical calculation methods allows for prediction of deposition. This paper presents results of 2D modeling of powdery, medium-temperature deposit formation on superheater tubes. In contrast to other studies, presented approach results in shape prediction of deposits versus time of boiler operation. The mechanism includes the force of gravity, elastic rebound and adhesion forces acting at the moment of ash particle impaction. The forces determine if the particle bounces off the surface or stays onto it building up the deposit. Two practical cases are considered - an upward flue gas flow and a downward flow in the boiler. The results of simulations are compared with measurements in real boilers published earlier. The full-scale results are reproduced well. The simulations are carried out with use of Fluent code by means of User Defined Files. The described mechanism is implemented in Define_DPM_Erosion, and shape prediction is mirrored using Define_Grid_Motion functions of the Fluent code.

The paper presents results of investigations on using halloysite as an additive in biomass-fired boilers. It has been shown that in the case of a few different agricultural biomasses the halloysite addition increased the ash sintering temperature to the values noted for coals. This is an effect of bonding sodium and potassium in the form of chlorides and other compounds. In practical terms the halloysite additive may reduce slagging and fouling of boiler heating surfaces as well as deteriorate the agglomeration processes in fluidized beds. Moreover, addition of halloysite reduces the amount of KCl and NaCl present in ash (and therefore in ash deposits) thus decreasing the rate of high temperature corrosion.

Interconnected and dual fluidized bed (FB) systems with various regimes of gas-solids flow are commonly studied with the aim to find and ensure suitable circulation of solids and control of flow between two chambers/reactors with different reacting gases. Dual separated fluidized beds or fluidized and transporting bed systems are convenient for cleaning of gases with regeneration of a solid sorbent or for gasification of solid fuels and production of fuel gas practically free of nitrogen. The paper concentrates on the development, comparison and checking of three simplified models for solid particle velocity, pressure drop and mass flux in a pneumatic transport reactor (riser). The simplified models have been used in a more general model for flow of solids via orifices between a FB near the incipient fluidization and a tube with vertical pneumatic transport (PT) of solids and recirculation to the FB. The model predictions have been compared with experimental data and validated in a limited range of operating conditions: for lower solids fluxes of sand particles ( d p = 0.3 mm, mass fluxes below 40 kg/m 2 /s) at gas velocities higher than the terminal velocity U T of solids and for relatively high solid fluxes (over 160 kg/m 2 /s) and gas velocities higher and lower than U T . Predictions from the models were used to estimate effects of particle size, gas velocity in the pneumatic transport column and height of the FB on circulating mass flux of solids. Comparison of the model-computed and experimental mass fluxes of solids with a theoretical forecast for the saturation carrying capacity of gas in pneumatic transport and a forecast of “choking” as computed by use of the Yang correlation has indicated possible problems and instabilities of solids flow in regimes with higher solids mass fluxes and/or lower gas velocities in the riser (PT-column). To control the circulation rate of a given particulate material in the dual FB-PT systems three main, practically important parameters should be considered: the superficial gas velocity in the riser (PT-column), height of the FB and cross sectional area of the orifices.

The paper deals with waste gasification as a technology allowing for indirect co-firing of large quantities of biodegradable wastes in coal-fired power boilers. In contrast to common landfilling and direct co-firing, gasification of wastes presents a number of advantages. Problematic species in original feedstocks can be partly safely incinerated in the furnace and partly retained in the gasification residues. The paper focuses on the impact of indirect co-firing on basic boiler parameters and performance. The work carried out was in the form of a case study for co-firing LCV gas in a 230 t/h dual fuel pulverized coal-gas fired boiler. Thermal shares of 10, 20 and 40% have been investigated for two extreme LCV gas qualities represented in the calculations by its calorific value of 2.0 and 8.5 MJ/m3n respectively, thus six calculation cases are given. The results of the study reveal that even high thermal shares of LCV gas may be achieved for co-firing of better quality gas without significant effects on boiler operation. For lower quality gas, even a 10% thermal share influenced boiler operation to a great extent. This paper also gives consideration in relation to avoided CO2 emissions accomplished via indirect co-firing.

The paper presents novel experimental results for the combustion of liquid bio-fuels in an internal circulating fluidized bed (ICFB). A 20 kW experimental facility equipped with an air-assisted injector has been used. Reliable operation, high combustion efficiency and limited temperature increase along the combustion riser tube have been attained at different operating conditions. However, CO emission has been rather higher than expected. A form of micro-explosive behaviour of the fuel has been experienced at relatively low bed temperatures (710–730 °C), but this behaviour was significantly less intense than in bubbling fluidized beds. A mathematical model of the combustion of liquid fuels has been adapted to ICFB conditions. The comparison between model and experimental results demonstrates that the efficiency of fuel-air mixing has a crucial role on combustion behaviour. Poor contact between air and fuel in the bottom half of the riser is responsible for high CO levels measured during the experiments. On the whole, the research demonstrates that the proposed liquid injection process could be suitable for application in co-gasification or for incineration of liquid wastes.

In this work, the high temperature air/steam gasification (HTAG) technique has been tested for a fuel in pellet form made from waste material of woody and plastic origin. The feedstock was gasified ...

In the paper the results of comparative investigations on heat transfer performance of boiler convective bundle and its additional surface, i.e. membrane water wall are presented. For this purpose the non-uniform flow field was modelled in an isothermal test stand operated in self-modeling mode. Then the heat transfer characteristics of such arrangement were estimated by means of naphthalene heat/mass transfer analogy technique. The bundle samples in the shape of round bars (rods) were cast with naphthalene and placed in 27 locations in the bundle while water-wall-modeling samples were coated with naphthalene by painting. Both types of samples were exposed to cold air flow. The results were then compared to the mean heat transfer performance of the same bundle exposed to uniform flow field. The differences of approximately 10% were noticed. Moreover, the heat transfer coefficients for additional surface were even three times lower than those of the bundle. In view of results obtained in the work, the commonly made assumption of equality of heat transfer coefficients for both the bundle and its additional surface may lead to certain errors in heat transfer calculations and discrepancies between the calculated values of heating surfaces area and later operational needs of steam generator.

The article deals with results of full-scale investigations on fouling in convective bundles of chosen types of coal-fired boilers. The boilers tested were: conventional pulverized-coal fired two-pass boilers (two types), a single-pass subcritical (a tower shape) boiler and CFB boiler. Mechanisms of deposit formation and basics of deposit modeling are shortly discussed. An own approach to predict build-up of loose powdery sediments was developed on the basis of the results of full-scale measurements. The correlation for maximum fouling time was obtained by statistical processing of measurement data and is applied in optimization of sootblower system operation. The obtained correlation depends on the following variables: geometric properties of the bundle, fly ash size distribution and basic parameters of the flue gases-all of them are easily accessible in boiler operation.

The paper presents the results of an investigation concerning heat transfer and pressure loss in air crossflow of diagonally shaped membrane heating surfaces. The heat and mass transfer analogy by means of naphthalene sublimation technique is used in order to evaluate mean Nusselt number values in such tube banks. The effect of tube bank arrangement on heat transfer coefficients and flow resistance is discussed. Convective heat transfer and pressure loss characteristics of diagonally shaped membrane tube banks, plain tube banks and ordinary membrane tube banks are compared.

Gasification and pyrolysis are very promising technologies for clean energy production especially from low rank fuels. Biomass and wastes with high chlorine, alkali and even heavy metals content are fuels preferential for thermal utilization. However, several problems during combustion in conventional steam boilers occurs e.g. slagging, fouling, chlorine corrosion, boiler efficiency deterioration. New efficient and cost effective technologies are needed, even in small-scale applications. The main objective of this work was to compare the thermochemical behaviour and process parameters effects of different biomass under air gasification and pyrolysis conditions. Three important fuels for European power industry were selected: woody biomass and two residual biomass, such as oat straw and dried citrus wastes. In order to evaluate the possibility to use different feedstocks or to combine and/or integrate them in thermochemical processes, a comparison among typical and untypical feedstocks is needed. Tests performed on small scale fixed bed reactor show the gas yield, its composition and LHV parameter. The results were performed in Royal Institute of Technology (KTH) in Sweden during BRISK program (Biofuels Research Infrastructure for Sharing Knowledge).

The paper addresses the combined gasification of biomass and brown coal in an internal circulating fluidized bed (ICFB) for generating a valuable producer gas. A primary method for tar abatement and gas improving was adopted, consisting in a Ni-based catalyst in the bed together with sand. The hydrogen concentration in the producer gas was high (up to 35% in the best case, > 20% typically) demonstrating the validity of the ICFB process for co-gasification of coal with biomass. Higher H 2 and CO contents and lower tar yields were obtained with greater coal loadings. The tar was reduced by up to three times when changing from inert to a partly catalytic bed, under steam gasification conditions. However, this good figure is contrasted by a rather fast decay in catalytic activity, and a rather low carbon conversion even in presence of the catalyst. A mathematical model based on thermodynamic computations predicts the trend and values of the measured gas concentrations at different steam/fuel ratios, providing useful indications for its optimal choice. The findings of the research reinforce the idea that dual bed gasification is suitable even when a relatively low reactivity fuel is used, such as the brown coal in this study.