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The structural property of soot particles released during the pellet combustion of different municipal solid waste (MSW) was comparatively investigated through high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and X-Ray diffraction (XRD). The results showed under the same combustion condition, soot particles generated from different waste components have the same typical core-shell shape. But soot mass and aggregate morphology were strongly dependent on waste component material. When plastic (textiles) waste was burned, the soot obtained featured a much higher mass and more compact morphology with larger particle size compared to that from burning biomass and kitchen waste. Nanostructural characterization results revealed that paper and kitchen waste possessed the highest graphitization degree in soot, followed by wood waste, textiles, and plastic. Additionally, with the increasing addition of plastic in the mixed waste, the flame temperature was slightly reduced. And the soot was formed a lot and became more disordered in the nanostructure with shorter, more tortuous fringes and larger separation distances, which suggested a higher oxidation tendency. The A D1 /A G ratio had a linear relationship with the fringe separation distance and fringe tortuosity, with R2 values of 0.824 and 0.847, respectively. • Soot from burning municipal solid waste was comparatively studied. • Morphology and nanostructure varied largely among the soot samples. • Biomass fraction formed soot particles with well graphitic nanostructure. • Fringe characteristics play an important role in reactivity. • Plastic in mixed MSW enhanced the soot reactivity. [ABSTRACT FROM AUTHOR]

As second part of an extensive study on the relation of co-combustion of biomass and fly ash quality, co-combustion fly ashes were investigated from full-scale co-combustion experiments in the Netherlands using agricultural biomass, meat and bone meal, paper sludge and municipal sewage sludge as secondary fuel. The fly ash was investigated in relation to its performance for use in concrete. It was shown that the quality of co-combustion fly ash can be explained from the characteristics of the fuel and the combustion process. Further, it was shown that also fly ash obtained from high co-combustion percentages is able to meet the basic requirements of the European standard for fly ash in concrete (EN 450). Whether an individual co-combustion fly ash does so, depends on the nature of the co-fired fuel and especially on the amount and nature of its inorganic matter. [ABSTRACT FROM AUTHOR]

The volatilization characteristics of three MSW-derived materials (FO, RT and FL) produced by local waste-management companies were investigated as potential solid recovered fuels (SRFs). FL was prepared from sorted domestic waste and consisted of non-recyclable plastics, refuse paper and biomass. RT and FO were obtained through active hygienization of unsorted MSW and refuse materials from selective waste-collection streams. RT was rich in plastics and had low biomass, whereas FO was mainly biomass and refuse paper. The rate of energy release during volatilization depended on the content of biomass and plastic, especially at a low conversion. Major contaminants had different rates of volatilization. Nitrogen and sulfur tended to accumulate in the charred solid, and were released as SO2 and nitrous oxides during both the volatilization–combustion stage and the char burning stage. Chlorine release was faster for the fuels rich in plastic waste. According to their ash melting characteristics and slagging indexes (Fs: 1188°C for FO, 1192°C for RT and 1234°C for FL) the three fuels were equivalent to commercial SRFs. The three fuels showed potential as standardized SRF, although it would be desirable to reduce their chlorine content and, in the case of FO, to increase it’s heating value. [ABSTRACT FROM AUTHOR]

Abstract: The present paper analyzes the nitrogen monoxide generation and reduction during co-combustion of biomass (sawdust) in a power plant fired with pulverized coal. The physical and mathematical models highlight the nitrogen monoxide generation and reduction of its concentration by the air staging and combination of various primary methods. The paper analyzes the influence of the primary air excess coefficient, of the initial diameter of equivalent fuel particles and of the gravimetric participation of the sawdust to the mixture. The internal recirculation of combustion gases at the burning inlet, the recirculation of the combustion gases at the furnace end-part, the value of the air excess coefficient and the introduction time of the secondary air are considered constant. The mathematical model is validated through tests on real pilot installation (2MWt). [Copyright &y& Elsevier]

Ash content, and the problematic related to it are currently the most important drawbacks of biomass combustion. The present work carries out the modelling and simulation of an innovative CHP system composed of an updraft gasifier, an external combustion chamber and Organic Rankine Cycle (ORC) generator for the energetic valorization of olive leaves: a free and abundant by-product of the olive oil industry. The CHP system can produce 93.8 kW of net electrical power and approximately 412 kW of available thermal power for the heating necessities of a medium-sized olive oil mill. The CHP efficiency achieved is 58.41% and the net electrical efficiency 10.82% together with a biomass consumption of 240 kg/h. Based on the simulation results, the producer gas reaches a suitable lower heating value (4.60 MJ/kg) and a gasification efficiency of 88.10%. At the gasifier operating conditions, the producer gas presents the following mole composition: 12.8% H 2 , 19.2% CO, 2.6% CH 4 , 8.3% CO 2 , 11.8% H 2 O, 42.1% N 2 , 1.7% Tar and the rest Ar, O 2 , H 2 S, dust and particulates. The results from ORC simulations show a very good efficiency (18.7%) at 25 bar of working pressure and 300 °C of turbine inlet temperature. Toluene has been selected as suitable organic fluid for high temperature heat sources (> 900 °C). In this paper, an innovative energy recovery system for high ash content biomass has been theoretically developed, representing a good opportunity to promote distributed generation systems. [ABSTRACT FROM AUTHOR]

Fuel drying is an energetically and economically expensive pretreatment process, which may not be worth the investment in the case of small-scale generation plants. This paper presents an investigation on the air dryer feasibility to enhance the operation of biomass steam boiler. In the proposed approach, the external drying technology using preheated air and the biomass steam production system is modelled in terms of energy and an economical analysis. A focus is given to the system size influence on the dryer economic suitability: the smallest size of the biomass combustion system for which fuel drying is a suitable solution, from the economic point of view, is computed. In the computations, the heat used for drying is assumed to be part of the cost for operating the dryer and the thermal balance of the system is assumed to be previously verified. According to the model results, if the steam production plant operational time is above 8000 h/y, wood chips drying is feasible if the system size is larger than 1.78 t daf / h of fuel processed. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an experimental and numerical study on co-firing olive waste (0, 10%, 20% on mass basis) with two coals in an entrained flow reactor under three oxy-fuel conditions (21%O2/79%CO2, 30%O2/70%CO2 and 35%O2/65%CO2) and air–fuel condition. Co-firing biomass with coal was found to have favourable synergy effects in all the cases: it significantly improves the burnout and remarkably lowers NOx emissions. The reduced peak temperatures during co-firing can also help to mitigate deposition formation in real furnaces. Co-firing CO2-neutral biomass with coals under oxy-fuel conditions can achieve a below-zero CO2 emission if the released CO2 is captured and sequestered. The model-predicted burnout and gaseous emissions were compared against the experimental results. A very good agreement was observed, the differences in a range of ±5–10% of the experimental values, which indicates the model can be used to aid in design and optimization of large-scale biomass co-firing under oxy-fuel conditions. [Copyright &y& Elsevier]

Abstract: Thermodynamic modeling is used as a tool to predict the chemistry of ash-forming elements in biomass and waste combustion for corrosion- or deposition-related issues. One major limitation is the lack of comprehensive databases that contain the thermodynamic data of ash compounds and phases formed during combustion. The present paper is a review of the state-of-the-art of the thermodynamic models and databases for ashes of biomass and waste combustion, future developments and the coupling of thermodynamic modeling with modeling of physical properties of molten ash. Recent developments have improved the accuracy for predicting the phase equilibria of alkali salt mixtures. The databases are being expanded by taking into account Ca, Pb, and Zn in the salt mixtures. Chromates have also been included to predict the stabilities of the corrosion products on boiler heat exchanger materials. The thermodynamic data for silicate systems still lack data for critical subsystems for biomass ashes. The K2O–CaO–SiO2 system which is important for slagging and agglomeration in biomass combustion still needs experimental investigations to make accurate modeling possible. The thermodynamic data of phosphates are discussed and a new modeling approach for molten phosphates is shown for the K2O–P2O5 system. Models for predicting physical properties coupled with the thermodynamic functions of molten silicates and salts are reviewed. Examples of advanced thermodynamic modeling to study ash-related issues in biomass combustion are also shown. [Copyright &y& Elsevier]

Abstract: Ash transformation processes have been studied during co-firing of wheat straw and pine stem wood and softwood bark. Pilot-scale trials in a 150kW pulverised-fuel-fired burner were performed. Thermodynamic equilibrium calculations were made to support the interpretation of the results. The results show that reactions involving condensed phases are kinetically limited compared to reactions between gaseous ash compounds. Accordingly, the conditions promote gas phase reactions resulting in the formation of chlorides, sulphates and carbonates whereas reactions involving condensed reactants are suppressed. Both the slagging and fouling propensities of all co-firing mixes were reduced compared to that for pure straw. For the wood/straw mixes this was mainly due to a dilution of the ash forming elements of straw whereas for straw/bark, an additional effect from interaction between the fuel ash components was observed to reduce slagging. In general it can be concluded that under powder combustion conditions equilibrium is approached selectively and that the ash matter is strongly fractionated. The general results in this paper are useful for straw-fired power stations looking for alternative co-firing fuels. [Copyright &y& Elsevier]

Abstract: The use of challenging, heterogeneous fuels and multi-fuel combustion is characteristic for modern-day circulating fluidized bed (CFB) combustion. This increases the need for monitoring the performance of the process. However, long-term online measurement of different phenomena in CFB boilers is a challenging task, and the lack of measurements complicates direct monitoring of the process. For this reason there is a need for new methods like soft sensors, which could be used to support or compensate the direct measurements of bed diagnostics. This paper demonstrates an adaptive soft sensor that utilizes process data to estimate the quality of the bed by predicting the grain size distribution in the bottom ash of circulating fluidized bed boilers. The grain size fractions from the sieving of bottom ash are used as reference values for bed quality. Either linear or nonlinear regression can be used to train the model. Adaptive variable selection is performed before constructing the dynamic model, which utilizes the selected variables to estimate the different grain size fractions online. The new approach has been tested using process data and grain size distributions measured from three individual CFB boilers fired by biomass, and the results show that the adaptive approach provides a useful tool for bed diagnostics. [Copyright &y& Elsevier]

Abstract: Simultaneous combustion of biomass (wood or straw) with coal represents an alternative energy source with economic potential and smaller pollutant emission. Under the current environmental legislation, biomass is seen as a zero emitter of carbon dioxide emissions. The paper analyses the potential corrosion and the formation of adherent deposits in the coal–biomass co-combustion process at two pilot installations. Three types of experiments with a mixture of coal, straw and wood are conducted. For the slagging phenomena, two installations pilot (grate-fired furnace) were used: one of 55kW thermal power and other of 2MW. As a control sample, different types of steels were used. The results can lead to the implementation of measures to reduce the effects of corrosion. The final aim is to increase the boilers efficiency and life duration. Furthermore, the ash analyses allow their use as fertilizer in agriculture. [Copyright &y& Elsevier]

Abstract: Potassium and sodium are well-known catalysts in the thermal reactions of biomass. This paper develops a modified Langmuir-Hinshelwood expression linking the rate of thermal degradation of a biomass to its potassium or sodium content. Willow samples impregnated with different potassium or sodium concentrations were studied for their pyrolysis behaviour by thermogravimetric analysis, and apparent first order kinetics derived. The developed relation yields a maximum reaction rate constant and a metal saturation constant that can predict the rate of willow pyrolysis based on temperature and concentration of potassium or sodium. The apparent first-order reaction rate reaches a limit at ca. 3.5 wt.% (Na) and 4 wt.% (K); this is attributed to maximum active site availability. Ab initio modelling of possible chelated structures indicates that the metal ions form multiple interactions with hydroxyl and ether groups in the cellulose structure. Metal ions chelated at the C6 position in the ring, have interactions with four oxygen atoms, while metal ions at the C2 position have interactions with only two oxygens. Structures are more stable when the metals can coordinate to more oxygen groups. It is speculated that changes in geometry upon chelation favours certain ring conformations, which might enhance reactivity to cracking reactions. [Copyright &y& Elsevier]

Abstract: One of the main advantages of biodiesel fuels is that almost eliminate carbon dioxide emissions based on the CO2 consumption during plant growth. However it is accepted for most researchers that when burned in diesel engines there is an increase of the NOx emissions when these are compared to the NOx emissions produced by mineral diesel fuel. HCCI with diesel fuel is being considered as an alternative combustion process in the internal combustion engine, mainly because of the huge potential for simultaneous reduction of NOx and soot emissions while fuel conversion efficiency is not compromised, in fact, it is usually increased. The HCCI combustion process can accept a variety of fuel types, like biodiesel and mixtures with mineral diesel fuel. The main reason for burning biodiesel fuel in HCCI combustion mode is that it enables the simultaneous reduction of NOx and soot emissions to current standard requirements, as well as the elimination of CO2. This paper shows a methodology for HCCI combustion mode of biodiesel mixtures based on a high swirl ratio and EGR rate combined with late injection where HRR, NOx, CO, HC and soot emissions have been analyzed. This strategy has reduced fuel wall impingement encountered when early injection is used. Bowl in piston geometry has been designed with a dedicated swirling flow model and a NOx emission of biodiesel fuel has been reduced. [Copyright &y& Elsevier]

Abstract: The use of gasified fuels for electricity generation is gaining interest as an alternative to traditional fuels especially in regions with abundant biomass or coal resources. However their use in some of the most extended power generation technologies like gas turbines and combined cycles is not straightforward. The authors have studied the use of gasified fuels in the gas turbine and combined cycle technologies within a four year research project funded by the Spanish Government (SPHERA project). The main goals of the research were to identify the components and processes that limit the use of the syngas fuels (bottle-necks) and suggest the necessary modifications to be implemented in standard combined cycle power plants, selecting them according to their technical feasibility and economic viability. To this purpose, the research was divided in six tasks, each one was aimed at analysing the effects of syngas fuels on the performance of a particular component within the power plant or at assessing the impact of fuel composition at a particular level (from component level through system level and up to plant level). These tasks were focused essentially on the following topics: technology review, combustion system, turbine expansion and plant performance both for standard and redesigned equipment. This paper provides a global overview of the main steps and outcomes of this research showing the main results and conclusions obtained in each task. It is intended to show, from a global point of view and in a single document, a roadmap to adapt the existing combined cycle technology to syngas operation. It is therefore out of the scope of this project to provide a deep insight into particular issues or into models that have been covered in detail in other publications by the authors. [Copyright &y& Elsevier]

Abstract: The scope of this paper includes the development of a modelling approach to predict the ash release behaviour and chemical composition of inorganics during co-firing of coal and biomass. In the present work, an advanced analytical method was developed and introduced to determine the speciation of biomass using pH extraction analysis. Biomass samples considered for the study include wood chips, wood bark and straw. The speciation data was used as an input to the chemical speciation model to predict the behaviour and release of ash. It was found that the main gaseous species formed during the combustion of biomass are KCl, NaCl, K2SO4 and Na2SO4. Calculations of gas-to-particle formation were also carried out to determine the chemical composition of coal and biomass during cooling which takes place in the boiler. It was found that the heterogeneous condensation occurring on heat exchange surfaces of boilers is much more than homogeneous condensation. Preliminary studies of interaction between coal and biomass during ash formation process showed that Al, Si and S elements in coal may have a ‘buffering’ effect on biomass alkali metals, thus reducing the release of alkali–gases which act as precursors to ash deposition and corrosion during co-firing. The results obtained in this work are considered to be valuable and form the basis for accurately determining the ash deposition during co-firing. [Copyright &y& Elsevier]

Abstract: The performance of a small-scale two-staged gasification system is reported. In this system wood chips are gasified with a fixed bed gasifier and then tar in the produced gas is reformed in a non-catalytic reformer, finally the production gas is used to generate electricity. In this system, the gasifying agents are high temperature air and steam supplied into the gasifier and the reformer. This paper reports on optimum gasification air ratio (defined as the ratio of the oxygen mole supplied into the gasifier to the oxygen mole required for complete combustion of biomass), reforming air ratio (defined as the ratio of the oxygen mole supplied in the reformer to the oxygen mole required for the complete combustion of biomass) and steam ratio (defined as the ratio of the steam mole supplied into the gasifier to the carbon mole in biomass supplied into the gasifier) for producing required gas supplied into a dual-fueled diesel engine. The results showed that, under optimum conditions, the higher heating value of the reformed gas was 3.9 MJ/m3 N; the cold gas efficiency (defined as the ratio of HHV reformed gas×reformed gas flow rate to HHV biomass×biomass feed rate) of the gasification system was 66%, and the gross thermal efficiency of the overall system was 27%. [Copyright &y& Elsevier]

Circulating fluidized bed combustion has proven to be an effective way of converting biomass wastes into clean energy. This paper introduces the experiment study on rice husk combustion in a circulating fluidized bed. Experiments on a cold model show that rice husk is difficult to be fluidized, and adding silicon sand and coal improves the fluidization condition. Effects of sand diameter, gas velocity and mass fraction on rice husk mixing were tested. The rice husk can mix well with 0.3–0.8 mm sand at gas velocity 0.8–2 m/s. Experiments on 1 MW thermal test facility show that rice husk ignition temperature is only 340 °C, much lower than coal. The gas velocity and air split have great effect on rice husk combustion. At proper operation condition, the rice husk combustion efficiency reaches 97%, and the carbon content in fly ash is between 3% and 8%, whereas CO emissions varies from 200 to 800 ppm, SO2 ranges from 50 to 100 ppm and NOx ranges from 150 to 220 ppm. [Copyright &y& Elsevier]

This paper systematically reviews the PM sampling and measurement methods, formation mechanisms, distribution, inorganic composition and the factors influencing PM emission during combustion of coal/biomass/MSW. Particle sampling and measurement methods are developing rapidly utilizing various techniques, however, the direct sampling techniques for particle in the high temperature flue gas is still lacking. Particle is generated by a series of physical processes (evaporation, condensation, fragmentation etc.) and chemical reaction processes of inorganic mineral components and organically bound metal compounds in the solid fuels. The available literature data shows that the emission of coarse particles from coal combustion is generally higher than that from biomass, while the emission of ultrafine and fine particle from biomass combustion is higher than that of coal. Particle emission is related to a variety of influencing factors such as solid fuels particle size, inherent ash content, mineral properties, binding form of inorganic elements, combustion parameters (temperature, pressure, residence time, oxygen concentration etc.) and ash chemical composition. The content of Na, K, S, Cl, Si and Al plays a decisive role in PM 10 emissions, the (Na 2 O + K 2 O)/(SiO 2 + Al 2 O 3) ratio of ash can be used as an index to predict the yield of PM 0.3 in coal and biomass combustion. Unlabelled Image • The direct sampling techniques for PM in the high temperature flue gas is lacking. • PM chemical composition generated from coal, biomass and MSW combustion was different. • Ultrafine particles yields follows: Biomass> Coal, Forest biomass> Agricultural biomass. • The (Na 2 O + K 2 O)/(SiO 2 + Al 2 O 3) mass ratio of ash can be used as an index to predict PM 0.3 yields. [ABSTRACT FROM AUTHOR]

Laboratory combustion experiments were conducted to clarify some implications of co-firing coal with hog fuel and sludge in a power boiler. Combustion tests in a fixed bed stainless steel reactor at four temperatures (675, 725, 775, and 825 °C) under conditions simulating different moisture contents of hog-sludge blends indicated no problems with ignition. Burn-out of the coal reached 88–99%. However, the burn-out was very sensitive to the excess air, especially when co-firing wet hog fuel. Co-firing with coal will lead to higher sulfur dioxide emissions. Sulfation experiments were conducted in a fixed bed quartz reactor for five limestone particle size ranges (90–150 μm, 212–300 μm, 425–595 μm, 850–1000 μm, 2.0–3.4 mm) at the same temperatures as the combustion tests, with steam added to simulate the variation in the moisture content of the fuel mixture. The tests showed that the capacity of limestone to capture sulfur depends on temperature and particle size. The highest Ca utilization of the limestone was 51% (for the smallest particle size, at 825 °C). At 825 and 775 °C, the sulfur capture capacity of the limestone decreased significantly with increasing particle size, whereas at lower temperatures (725 and 675 °C), the Ca utilization was much less dependent on particle size. The sulfur capture capacity of the limestone was unaffected by the moisture content of the hog-sludge fuel. Calcium contained in the sand used as an inert in the power boiler may be capable of capturing small amounts of sulfur. [Copyright &y& Elsevier]