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The problems of reducing the slagging ability and corrosiveness of coal with a high content of low-melting salts (the so-called salty coal (SC) in the processes of its combustion) are considered. Salty coal is considered to be the coal, the ash of which contains Na2O>2%. The object of study is the salty coal of Donbass and ways of solving the problems of its use. The influence of low-melting salts on the formation of ash deposits and the development of corrosion of the metal surface during the combustion of salty coal from different fields was determined. A noticeable decrease in the slagging ability and corrosiveness of the test coal was noted during the removal of salts by water extraction. The composition of corrosive compounds (oxides Fe2O3,Fe3O4and iron sulfide FeS) has been determined, formed during the combustion of native coal, and their absence in the case of desalinated coal. Artificial fuel mixtures produced from more reactive salty and conventional low reactive coal have been studied. To create a mixed fuel, long-flame salty coal (low stage of metamorphism) from the Northern Donbas and unsalty lean coal (high stage of metamorphism) from Kuzbas were used. A significant deviation (to 9%) was noted for the release of ash during the combustion of mixtures from the additivity, indicating a chemical interaction between the mineral components of the mixture. The formation of new refractory mineral phases of ash (nepheline, ultramarine, combeite) during the combustion of composite fuel from coals of different metamorphism and salinity was established. The obtained results will be useful in the development of recommendations for the preparation of model fuel mixtures and their accident-free combustion in industrial boiler units. Experimental data on the determination of new mineral compounds in the case of composite fuels can be used to create a general theory of slagging in the combustion of salty coal of different origins

Two interconnected mathematical models have been developed to describe slagging of a steam boiler furnace at the macro and micro levels. The macro-level model is implemented in Ansys Fluent. Using the fuel characteristics and temperature in the furnace, this model can predict the characteristics of ash formation on heat exchanger tubes when the melting temperature of the mineral part of solid fossil fuel is exceeded. The obtained values of slagging rates are used as initial data in the software implementation of the original Matlab microlevel model. Under conditions of dynamic change in the thickness of the slag layer, this model can evaluate the heat transfer characteristics in the hot gas/slag layer/tube wall/water coolant system. The results showed that switching a coal-fired boiler from a solid fossil fuel to a fuel slurry will improve stability and uninterrupted boiler operation due to a lower slagging rate. The combustion of coal water slurries with petrochemicals compared with coal–water fuel is characterized by higher maximum temperatures in the furnace (13–38% higher) and a lower average growth rate of slag deposits (5% lower), which reduces losses during heat transfer from flue gases to water coolant by 2%.

Different streams of low-grade biomass of different origins (road side grass, miscanthus, wheat straw and spruce bark) were upgraded to reasonable quality commodity fuels by significantly reducing the alkali and chlorine content, through washing with water in a first step and torrefaction in a second. The aim was to produce a cleaner fuel with a higher energy content for further densification. The final goal was to demonstrate the improvements attained by the upgrading process during combustion using the lab-scale combustion simulator facility of ECN part of TNO. Analyses of the original, washed and washed/torrefied samples showed that approximately 90% of Cl and up to 60–80% of K can be removed by this upgrading route; during the torrefaction step Cl and S are removed from the solids; during torrefaction K and Na are not significantly altered; the pre-wash step is crucial for the removal of K. Si and Ca remain largely in the solid fraction; post-wash seems to be a viable route to upgrade dry-type of biomasses; “straw” like material requires more time for washing than “grass” type. The combustion results showed that: NOx emissions are generally decreased after upgrading; High temperature chlorine corrosion can be effectively mitigated; Fine particulate matter (submicron/aerosols) formation is strongly reduced, effectively reducing the risk of alkali induced fouling. However, slagging tests revealed that pre-washing and torrefaction has minor impact on the slagging propensity of the fuel. Only, slightly reduced slagging is observable and therefore the use of mineral combustion additives, or smart blending with other fuels in order to further mitigate the slagging risks is strongly recommended.

Biomass is a clean alternative fuel to coal in terms of carbon, NOx, and SO2 emissions in the power generation sector. However, ash deposition problems have been a concern with biomass fuels due to the high alkali and residual sulphur contents in the ash forming particles. In this study, the influence of oxy-fuel firing conditions of wood pellets combustion on ash partitioning and deposit formation, were investigated experimentally on a 250-kW pilot scale pulverized furnace and theoretically through chemical equilibrium modelling using the FactSage program. Oxy-fuel combustion case was compared with air-fuel case in this assessment. The results of this study showed that wood pellets had a low tendency for radiation zone slagging, but, had a high fouling tendency in the convective passes. It is possible that oxy-fuel combustion inhibited the release of volatile elements to the gas phase in the initial stages of the combustion, thus reducing the alkali sulphates slagging, increasing however, the alkali sulphate fouling tendencies on the convective passes. Moreover, the effect of the oxy-fuel environment on the ash formation was significant. The chemical equilibrium modelling showed reasonable predictions of the ash behaviour of wood pellets in terms of alkali behaviour and explained to some extent the influence of the oxy environment on ash deposit formation.

The paper deals with the issues related to the effect of slagging within the steam boilers furnaces and shows the determination results on peat ash fusibility of Kirov region deposits. Fusibility properties of peat ash (temperatures of deformation, sphere, hemisphere and flow) from the four industrial areas (Dymny, Pishchalsky, Karinsky, Gorokhovsky) depending on its chemical composition are presented. Melting temperature of the mineral part of the peat, determined by GOST, is averaged and does not reflect the actual melting temperature of the individual particles in fly ash. The existence of such separate particles having a melting temperature below the average melting temperature of the ash makes it difficult to find the operating temperature of the torch to reach the minimum of the furnace slagging during peat combustion. The comparison of melting characteristics of peat ash with the reference literature data is performed. The initial slagging temperature is calculated depending on the ratio of the acidic and basic oxides in peat ash.

The tendency of ash particles to stick under high temperatures is dictated by the ash chemistry, particle physical properties, deposit surface properties and furnace operation conditions. A model has been developed in order to predict the particle sticking efficiency for fly ash deposition at high temperatures. The model incorporates the particle properties relevant to the ash chemistry, particle kinetic energy and furnace operation conditions and takes into consideration the partial sticking behaviour and the deposit layer. To test the model, the sticking behaviours of synthetic ash in a drop tube furnace are evaluated and the slagging formation from coal combustion in a down-fired furnace is modelled. Compared with the measurements, the proposed model presents reasonable prediction performance on the particle sticking behaviour and the ash deposition formation. Through a sensitivity analysis, furnace operation conditions (velocity and temperature), contact angle and particle size have been found to be the significant factors in controlling the sticking behaviours for the synthetic ash particles. The ash chemistry and furnace temperature dictate the wetting potential of the ash particles and the melting ability of the deposit surface; particle size and density not only control the particle kinetic energy, but also affect the particle temperature. The furnace velocity condition has been identified as being able to influence the selective deposition behaviour, where the maximum deposition efficiency moves to smaller particles when increasing the gas velocity. In addition, the thermophoresis effect on the arrival rate of the particles reduces with increasing the gas velocity. Further, increasing the melting degree of the deposit layer could greatly enhance the predicted deposition formation, in particular for the high furnace velocity condition.

Paper presents short review of research problems, applied methods for solving problems and main results obtained by the researchers in Laboratory for Thermal Engineering and Energy (LTE) of the "Vinča" Institute of Nuclear Sciences, Belgrade, Serbia dealing with pulverized coal combustion processes and technologies for reduction of pollutions problems at thermal power plants in a period since 2000. The presented results were published in numerous studies realized for different users, Ph. D., Masters, and Specialist thesis, in international and domestic scientific journals and monographs, presented at numerous international and domestic scientific conferences, etc. Presented research projects and results of applied research projects realized at pulverized coal combustion thermal power plants clearly show that LTE team was involved in key activities of rehabilitation and modernization, including implementation of best available technologies for pollution reduction at thermal power plants, in the region of South East Europe. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III42010, Grant no. III42011, Grant no. TR33050 and Grant no. TR33042]

Combustion of coals and biomass in boiler furnaces leads to formation of fireside deposits on irradiated and convective surfaces. This problem is not a new one, but it became one of the main operational problems in boilers using low rank coal and some sort of biomass. In the paper presented are the results of research of ash deposit processes in laboratory conditions. An experimental furnace was used for these purposes. The experiments were performed on a tubular experimental furnace which ensures appropriate temperature and mass transfer conditions for physical and chemical transformations of the mineral matter of fuel as in real conditions. The main working parameters can be varied in wide ranges. The influence of grinding fineness, excess air and wall surface temperature was analysed. Also, an ash related problems during coal and biomass combustion was considered. Key empirical correlations for slagging and fouling were tested. Two types of Serbian coals (Kolubara and Kosovo) and several biomasses were analysed. It was shown that many sorts of biomass and Kosovo coal have a great propensity to slagging and fouling. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III42011: Development and improvement of technologies for energy efficient and environmentally sound use of several types of agricultural and forest biomass and possible utilization for cogeneration]

Calculation and experimental investigations were carried out to determine the parameters of the impulse air jet created by the pneumatic generator of the air-impact system of the cleaning of tubular heat exchangers in boilers. Two configurations (lengthwise and checkerboard) of the arrangement of tubular heat exchangers located at distances from 1.0 m to 2.5 m of nozzle exit were experimentally investigated and the forces acting on them were determined. Numerical modeling of the impulse jet impact on heat exchange tubes was carried out. It was shown that an increase in the pressure of the generated impulse jet to 2.35 MPa makes it possible to significantly increase the acting force from 78 N to 1881 N at a large distance from the exhaust nozzle. The results obtained can be used in the development of specific systems for air impact cleaning systems of boiler units with other sizes and configurations of the heat exchange tubes.

Ash fusion characteristics of biomass have significant effect on slagging. In this work, the effects of ash fusion characteristics on slagging have been studied by ash fusion experiments and computational fluid dynamics modelling. Based on the basic ash composition of biomass, the mixture of silicon dioxide, calcium oxide, potassium oxide and aluminium oxide have been selected as simulated ashes for ash fusion characteristics investigation. The results indicate that deformation temperature decreases with increased potassium oxide. High content of calcium oxide and silicon dioxide increase deformation temperature for the skeleton effect, respectively. The reactions of potassium oxide, calcium oxide and silicon dioxide lead to low melting products and decrease deformation temperature. Aluminium oxide increases deformation temperature by forming Si-Al-K compounds while K content is high and decreases deformation temperature while Ca or Si content is high due to the Si- Al-Ca compounds. On basis of the experimental results, an ash particle adhesion model has been developed using the corresponding characteristic temperatures of adhesion. Combined with the deposition model of inertial impaction, a computational fluid dynamics modelling study of ash deposition on heating surface has been performed. For a kind of cotton straw ash with low melting temperature, the modelling results indicate that adhesion of molten ash plays a major role during slagging. The accretion rate of molten ash adhesion accounts for 85% of the total accretion rate. For a kind of corn straw ash with high melting temperature, the proportion is only 37%. Compared with the actual slagging during biomass combustion, the modelling results can reflect a similar slagging situation on the surface of tube.

The aim of this paper is to investigate the mechanical properties of coal and biomass ash during the sintering process. For this study, bituminous coal, lignite, wheat straw, barley straw, and rye straw were selected. The proximate, ultimate, and oxide analyses were performed. The ash from these fuels was prepared in a special way that ensured the physicochemical invariability of the initial state of the mineral matter of coal and biomass. The purpose of this selection was to obtain widely available and clearly diversified materials. Based on the results of ash composition and ultimate analysis the most common ash deposition, indices were determined. Certain conflict of index indications was observed. Then, the mechanical test and pressure drop test were performed. During the mechanical test, the fracture stress as a function of sintering temperature was measured. During the pressure drop test, the pressure before and behind the sample was measured as a function of sintering temperature. Both tests showed that the characteristic changes (the occurrence of a maximum on the pressure drop curve and the inflection point at the mechanical curve) dependencies were at nearly the same temperatures. These results were compared with the initial deformation temperature (IDT) from the standard Leitz method. A linear relationship between sintering temperatures determined by the mechanical test, pressure drop test, and IDT Leitz test was obtained. The obtained results are promising in terms of the application of the mechanical methods (fracture stress test and pressure drop test) as methods of the early stage prediction of slagging/fouling risks.

The application of excessive amounts of manure to soil prompted interest in using alternative approaches for treating slurry. One promising technology is hydrothermal carbonisation (HTC) which can recover nutrients such as phosphorus and nitrogen while simultaneously making a solid fuel. Processing manure under acidic conditions can facilitate nutrient recovery; however, very few studies considered the implications of operating at low pH on the combustion properties of the resulting bio-coal. In this work, swine manure was hydrothermally treated at temperatures ranging from 120 to 250 ◦C in either water alone or reagents including 0.1 M NaOH, 0.1 M H2SO4, and finally 0.1 M organic acid (CH3COOH and HCOOH). The influence of pH on the HTC process and the combustion properties of the resulting bio-coals was assessed. The results indicate that pH has a strong influence on ash chemistry, with decreasing pH resulting in an increased removal of ash. The reduction in mineral matter influences the volatile content of the bio-coal and its energy content. As the ash content in the final bio-coal reduces, the energy density increases. Treatment at 250 ◦C results in a more “coal like” bio-coal with fuel properties similar to that of lignite coal and a higher heating value (HHV) ranging between 21 and 23 MJ/kg depending on pH. Processing at low pH results in favourable ash chemistry in terms of slagging and fouling. Operating at low pH also appears to influence the level of dehydration during HTC. The level of dehydration increases with decreasing pH, although this effect is reduced at higher temperatures. At higher-temperature processing (250 ◦C), operating at lower pH increases the yield of bio-coal; however, at lower temperatures (below 200 ◦C), the reverse is true. The lower yields obtained below 200 ◦C in the presence of acid may be due to acid hydrolysis of carbohydrate in the manure, whereas, at the higher temperatures, it may be due to the acid promoting polymerisation.

To meet combustion quality requirements, Miscanthus is conventionally harvested in late winter/early spring after senescence due to a lowering of fuel nitrogen, chlorine and ash content. This can overcome combustion issues such as slagging, fouling and corrosion however there is a significant reduction in dry matter yields compared to early harvesting in the autumn. In this study, Miscanthus × giganteus harvested conventionally (after senescence) and early (green) have been pre-treated by hydrothermal carbonisation (HTC) at 200 °C and 250 °C. HTC at 200 °C improves the grindability of the biomass but results in limited energy densification. HTC at 250 °C results in increased energy densification producing a bio-coal with a HHV ranging from 27 to 28 MJ/kg for early and 25 to 26 MJ/kg for conventional harvesting; the Hardgrove Grindability Index (HGI) increases from 0 to 150. At higher HTC temperatures, the combustion profile of the bio-coal exhibits a ‘coal like’ single stage combustion profile. HTC results in a significant reduction in alkali metal content, increases safe combustion temperatures and reduces the theoretical propensity of the derived fuel to slag, foul and corrode. The results indicate that HTC can valorise both conventional and early harvested Miscanthus without producing any adverse effect on the yields and quality of the bio-coal. The challenges associated with early harvesting of Miscanthus appear to be largely overcome by HTC resulting in increased yields of up to 40% per hectare due to reduction in dry matter loss.

The work objective is to study the effect of the temperature lime burning conditions in a rotary kiln on the quality indices of the industrial lime used in the steelmaking. The methodology for studying the heat transfer conditions and the temperature behavior of the bulk material under the heat passage and temperature-waves propagation in the semibounded space of a rotary kiln is offered. It is shown that a system of equations describing boundary conditions of the limestone heating by the radiant heat flux becomes increasingly complicated in the case of the parallel convective heat transfer. To simplify the calculations, it is suggested to reduce the combined radiant and convective heat transfer to the convective one (in form) using the known criterial dependences. The investigation results of the heat transfer in the ‘flame - limestone’ system with testing apparent and optimum temperatures in the burning zone are presented. The thermal effect in the rotary kiln on the lime quality indices is specified experimentally under the laboratory and plant conditions. Conditioning of the slag adjustment by the lime consumption during the steel electrosmelting in an arc furnace is defined. Conclusions on the effect of the furnace thermal performance on the principle processes of the carbonate raw materials kilning in the industrial lime manufacturing are formulated. The optimal furnace temperature conditions for manufacturing quality lime with more than 90% CaO are specified.

The slagging and fouling characteristics of the heat recovery steam generator (HRSG) for ferrosilicon electric furnaces are discussed in this paper. Three ash samples were taken from the HRSG of a ferrosilicon furnace in Ningxia Province, China, which suffered from serious slagging and fouling. X-ray fluorescence (XRF), X-ray powder diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the ash samples. The results show that low melting point salt Na 2 SO 4 and composite salts Na (AlSi 3 O 8 ) and 3K 2 SO 4 ·CaSO 4 deposit on the superheater tube walls in aerosol form and solidify to form the initial slag layer. With the continuous deposition of the low melting point compounds, more and more ash particles in the flue gas adhere to the slag surface to form a thicker slag. Low melting point composite salt NaO·Al 2 O 3 ·SiO 2 is absorbed on the evaporator tube walls in aerosol form. With the deposition of NaO·Al 2 O 3 ·SiO 2 , more and more ash particles are absorbed to form the fouling. Since there is less space between pin-finned tubes, the large iron-rich slag particles are easily deposited on tube walls and fin surfaces, which is advantageous to the fouling process. There are large quantities of superfine ash particles in the flue gas that easily adhere to other particles or tube walls, which facilitates the slagging and fouling process.

Preliminary lab-scale investigations were conducted on slagging abatement in biomass-firing by fuel mixing. Three agriculture biomass fuels and olive cake were used in the experiments. Polish lignites and bituminous coals were examined as anti-sintering additives. The effects of chlorine release, potassium retention and ash sintering were examined by heating samples of biomass fuels and additives in the muffle oven and, next, firing them in the laboratory down-fired furnace at the temperature in the range of 800-1150ºC. The obtained slag samples were analysed on: chlorine and potassium content, sintering tendency and crystalline components. Among the examined coals lignite from Turów mine and bituminous coal from Bolesław Śmiały mine appeared to be the most effective in potassium retention in aluminosilicate and chlorine release from slag. Possibly the major factor of these coals which reduced ash sintering was relatively high content of kaolinite

This experimental study focusses on the viability of three low-grade biofuels in small-scale biomass units of 7&ndash, 12 kW The tested materials were homemade grass pellets (gp1 and gp2) and a mixture of leaves and woody pellets (lp50) that were made without binders and completely characterized in terms of their chemical and physical properties (proximate analysis, elementary composition, ash content, flowability, etc.). The results obtained with the non-commercial fuels were compared with commercial wood pellets (wp). The viability study comprised the operational parameter influences, such as primary and secondary airflow, fuel consumption, etc., together with the impact of those parameters on the main problems in combustion (concentration and particle distribution, fouling and slagging). The results revealed that the biomass whose behavior during combustion induced fewer particulate emissions and deposits was the mixed fuel, made of 50% leaf + 50% wood pellet (lp50). Contrary to the grass-based pellets, lp50 has the possibility of being used in commercial devices with the incorporation of processes during the manufacturing that improve their properties.

8 Figures, 4 Tables.-- Work presented at the 8th European Conference on Coal Research and Its Applications, Leeds (UK) from 6-8th September 2010., Oxyfuel combustion is envisaged as one of the main options for power production from fossil fuels in a carbon constrained scenery. There are still certain aspects of oxycombustion still on research stage, one of those is the issue of boiler materials resistance to corrosion due to solid deposits formed as a consequence of slagging in CO2 rich flue gases. The novel approach to the issue is the simulation of realistic slagging by pyrite projection through an oxyacetylene spray gun, flying along a controlled flame and impacting onto metallic surfaces of selected composition for fireside waterwall construction (F22, P91, 409, 347, 304H and I800HT). Metallic surface temperature was kept at 400, 500, 600 and 700ºC, and after deposition, metallic coupons were aged for long periods (150 and 1500 hours) at the selected conditions (O2/N2, CO2/N2). The characterization of deposits was performed with XRD, SEMEDX and carburization tests. The first finding is that the oxidation scale progression is different when partially transformed pyrite covers metallic surfaces: chromium oxide grows as a response to oxidation between the steel and the deposit, less dense and partially interrupted, and no iron oxide scale is generated. There is a clear presence of chromium sulphides in competence with the chromium oxide. On the other hand, comparison of scales in CO2 vs. air indicates same chemical composition but different morphology: in air combustion, corrosion layers are thicker and cracked. These results can improve the prediction of operational problems in coal oxyfuel combustion.

Over the last decades, several indices based on ash chemistry and ash fusibility have been used to predict the ash behaviour during coal combustion, namely, its tendency for slagging and fouling. However, due to the physical–chemical differences between coals and biomass, in this work only the applicability of an ash fusibility index (AFI) to the combustion and co-combustion of three types of biomass (straw pellets, olive cake and wood pellets) with coals was evaluated. The AFI values were compared with the behaviour of ash during combustion in a pilot fluidized bed and a close agreement was observed between them. For a better understanding of the mechanisms associated with bed ash sintering, they were evaluated by SEM/EDS and the elements present on the melted ash were identified. Evidences of different sintering mechanisms were found out for the fruit biomass and herbaceous biomass tested, depending on the relative proportions of problematic elements. The particles deposited on a fouling probe inserted in the FBC were analyzed by XRD and the differences between the compounds identified allowed concluding that the studied biomasses present different tendencies for fouling. Identification of KCl and K 2 SO 4 in the deposits confirmed the higher tendency for fouling of fruit biomass tested rather than wood pellets.

This paper presents the findings of research into cofiring two Bosnian cola types, brown coal and lignite, with woody biomass, in this case spruce sawdust. The aim of the research was to find the optimal blend of coal and sawdust that may be substituted for 100% coal in large coal-fired power stations in Bosnia and Herzegovina. Two groups of experimental tests were performed in this study: laboratory testing of co-firing and trial runs on a large-scale plant based on the laboratory research results. A laboratory experiment was carried out in an electrically heated and entrained pulverized-fuel flow furnace. Coal-sawdust blends of 93:7% by weight and 80:20% by weight were tested. Co-firing trials were conducted over a range of the following process variables: process temperature, excess air ratio and air distribution. Neither of the two coal-sawdust blends used produced any significant ash-related problems provided the blend volume was 7% by weight sawdust and the process temperature did not exceed 1250oC. It was observed that in addition to the nitrogen content in the co-fired blend, the volatile content and particle size distribution of the mixture also influenced the level of NOx emissions. The brown coal-sawdust blend generated a further reduction of SO2 due to the higher sulphur capture rate than for coal alone. Based on and following the laboratory research findings, a trial run was carried out in a large-scale utility - the Kakanj power station, Unit 5 (110 MWe), using two mixtures; one in which 5%/wt and one in which 7%/wt of brown coal was replaced with sawdust. Compared to a reference firing process with 100% coal, these co-firing trials produced a more intensive redistribution of the alkaline components in the slag in the melting chamber, with a consequential beneficial effect on the deposition of ash on the superheater surfaces of the boiler. The outcome of the tests confirms the feasibility of using 7%wt of sawdust in combination with coal without risk to the efficiency of the unit, its combustion process and with the benefits of emissions reductions. Furthermore, they show that no modification to the existing coal transport system and boiler equipment is necessary to achieve this outcome.

An experimental study of counter-current annular two-phase flow of high-viscosity liquid and air in a large diameter pipe was carried out to investigate the inception criterion for entrainment of molten slag droplet in an entrained flow coal gasifier. Liquid film thickness was measured using a high-speed camera for 4 types of liquid with various viscosities and surface tensions. It was clearly shown that the measured average wave amplitude had a good correlation with the gas Reynolds number, and that the predicted critical gas velocity for droplet inception using new formula of wave amplitude had a good agreement with the experimental results under the condition of very low fluid Reynolds number( Ref ≤10). The critical Weber number Wec =1.73 was obtained as inception criterion of droplet entrainment.

This experimental work aims to study the viability of making use of agricultural and forest residues as an alternative to produce biofuels for commercial devices. It focuses on the feasibility of three non-commercial biomass fuels in an underfed biomass pilot combustor with a power range of 7-12 kW(th) (500-800 kW/m(2)). To carry out the investigation, the repeatability of the facility was studied using fuel with a high ash content. The relative deviations in the main parameters considered (combustion rate, gaseous emissions and particulate matter emissions) were below 10%. A feasibility analysis was performed by comparing the result obtained with a barley and leaf pellet with that obtained with a commercial wood pellet as a reference. The parameters used in this study were the operational parameters of the plant as well as the particle concentration and distribution, fouling and slagging. Comparing the results of the different fuels, it was determined that 25% leaf + 75% wood pellet (lp25) could be used as a commercial pellet with the incorporation of an additive. However, the two other fuels presented undesirable behavior characterized by high particle concentrations and notable amounts of slag. Web of Science 9 10 art. no. 1823

In this work, the thermal behavior of rice husk, sewage sludge, and their blends during combustion processes was investigated by means of thermogravimetric analysis (TGA), and the slagging characteristics were studied through X-ray fluorescence (XRF) and melting temperature. The effects of the proportion of rice husk and sewage sludge blends on the combustion process, ignition and burnout characteristics were also studied. The blends had rice husk percentages of 30, 50, 70 and 100%. The results indicate that there are four main stages of the material burning processes: dehydration, volatile oxidation, and decomposition/oxidation. The reactivity of the blends improved with increasing amounts of rice husk and the results suggest synergistic interactions between rice husk and sewage sludge during the co-combustion process. All co-combustion ashes showed a lower slagging potential owing to their high amorphous SiO2 content. On the basis of combustion properties and slagging characteristics of ash, the ratio of sewage sludge in the blends should not exceed 30%.

Given the increasing demand for energy consumption, biomass has been more and more important as a new type of clean renewable energy source. Biomass direct firing is the most mature and promising utilization method to date, while it allows a timely solution to slagging problems. Alkali metal elements in the biomass fuel and the ash fusion behavior, as the two major origins contributing to slagging during biomass combustion, are analyzed in this paper. The slag presents various layered structures affected by the different compositions of ash particles. Besides, the high-temperature molten material which provides a supporting effect on the skeletal structure in biomass ash was proposed to evaluate the ash fusion characteristics. In addition, numerous solutions to biomass slagging, such as additives, fuel pretreatment and biomass co-firing, were also discussed.

In Italy, the accumulation of driftwood along the shore is a significant issue, especially for the coastal municipalities of the Central and Northern regions. The purpose of this study was to evaluate the distribution and availability of the coastal driftwood in Italy and its impacts, as well as analyzing its chemical–physical properties to evaluate possible employment in combustion applications. On the basis of a data gathering campaign for the period 2010–2014, about 60,000 tons of driftwood are reported to accumulate along the Italian shores every year. The two regions hardest-hit were Liguria and Veneto, with about 15,000 tons and 12,000 tons, respectively. Three sites were selected for driftwood sampling. The main issue deriving from chemical characterization was the high chlorine content (up to 2% on dry basis) and metal oxides in the ashes. Driftwood samples were then subjected to a natural washing cycle for 1 month; results revealed a significant drop in chlorine and metal oxides contents (up to 80%) and a low decrease of the lower heating value (about 20%). Furthermore, the percolated water was analyzed in terms of chemical oxygen demand (COD), showing values (up to 1100 mg O2/L) above the Italian limits for discharges into surface waters.

The behavior of quartz, kaolinite and calcite, as main components of coal mineral matter, has a direct impact on slags formations and development in pulverized coal combustion. The mineral transformations along temperature can be followed by differential scanning calorimetry (DSC), provided that the formation and crystallization of mullite (3Al2O3·2SiO2) are exothermic phenomena. Peak heights and areas allow to quantify the occurrence and extent of those mineral transformations for pure kaolinite and its mixture with calcite as fluxing agent. On the other hand, sinterization time at temperatures bellow mullite formation has a clear impact on the onset and the shape of the peaks. In this way, it is demonstrated that mineral transformations at solid state have a direct effect on the final structure of mineral species generated by slagging., Authors acknowledge the European Commission for the financial support by contract no. ECSC 7220-PR/048. M.C.M. and M.T.I. are thankful to the Ministry of Science and Technology.