Waste Management 34 (2014) 2505–2519

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Trace element partitioning in ashes from boilers firing pure wood or mixtures of solid waste with respect to fuel composition, chlorine content and temperature Naeem Saqib, Mattias Bäckström ⇑ Department of Science and Technology, Man-Technology Environment Research Center, Örebro University, SE-701 82 Örebro, Sweden

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Article history: Received 24 February 2014 Accepted 28 August 2014 Available online 26 September 2014 Keywords: Incineration residue Trace element partitioning Ash Solid waste management

a b s t r a c t Trace element partitioning in solid waste (household waste, industrial waste, waste wood chips and waste mixtures) incineration residues was investigated. Samples of fly ash and bottom ash were collected from six incineration facilities across Sweden including two grate fired and four fluidized bed incinerators, to have a variation in the input fuel composition (from pure biofuel to mixture of waste) and different temperature boiler conditions. As trace element concentrations in the input waste at the same facilities have already been analyzed, the present study focuses on the concentration of trace elements in the waste fuel, their distribution in the incineration residues with respect to chlorine content of waste and combustion temperature. Results indicate that Zn, Cu and Pb are dominating trace elements in the waste fuel. Highly volatile elements mercury and cadmium are mainly found in fly ash in all cases; 2/3 of lead also end up in fly ash while Zn, As and Sb show a large variation in distribution with most of them residing in the fly ash. Lithophilic elements such as copper and chromium are mainly found in bottom ash from grate fired facilities while partition mostly into fly ash from fluidized bed incinerators, especially for plants fuelled by waste wood or ordinary wood chips. There is no specific correlation between input concentration of an element in the waste fuel and fraction partitioned to fly ash. Temperature and chlorine content have significant effects on partitioning characteristics by increasing the formation and vaporization of highly volatile metal chlorides. Zinc and cadmium concentrations in fly ash increase with the incineration temperature. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Incineration processes for solid waste has the unique benefit of about 90% volume and 60–75% mass reduction, energy recovery and nearly complete destruction of organic material giving an answer to the many problems of sustainable waste management and increased disposal cost (De Boom and Degrez, 2012; Chimenos and Segarra, 1999; Hjelmar, 1996). Bottom ash, fly ash and air pollution control (APC) residues are by-products of waste incineration. Fly ash and APC residues are often considered together to have a unique output from incineration plants. Both these residues are often considered hazardous waste due to the content of toxic trace elements such as Cd and Pb with increased levels of chlorides and soluble salts also observed that can pose a serious threat to human health and the environment (Pan et al., ⇑ Corresponding author. Tel.: +46 19 30 39 65 (office), +46 727 21 57 02 (mobile). E-mail addresses: [email protected] (N. Saqib), [email protected] (M. Bäckström). http://dx.doi.org/10.1016/j.wasman.2014.08.025 0956-053X/Ó 2014 Elsevier Ltd. All rights reserved.

2013; Okkenhaug et al., 2013; Chang et al., 2000). Therefore possible understanding of the formation of these residues and distribution of trace elements in them are imperative for their further use and to select appropriate waste management strategies to make inroads towards a sustainable future. In Sweden, total ash production including all types of ashes has increased by 20% (1.2–1.5 million tons) dry substance, from 2006 to 2010 (Lövström, 2010) which shows an increase in the use of incineration technology for solid waste management. A study by Swedish Waste Management (2011) has found that, in 2010, total production of bottom ash, fly ash, mixed ash and flue gas purification products were 0.6, 0.4, 0.06 and 0.02 million tons respectively. 60% of total produced bottom ash is being utilized as construction material at landfills while 8% in road construction and surfacing applications (SEPA, 1996b) whereas the rest of the bottom ash has found uses in soil improvement, capping of mine waste, forest fertilization and some unspecified uses. Fly ash and other mixed ashes are detoxified and are either landfilled or sent for treatment to other enterprises (Swedish Waste Management, 2011).

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During incineration, generally highly volatile mercury and cadmium are found completely in flue gas or fly ash and elements with medium volatility like lead and zinc are distributed equally among both residues or more to fly ash while others having low vapor pressure and high boiling point like copper and iron mainly stays in the bottom ash (Arena and Gregorio, 2013; Shi et al., 2004; Wang et al., 1999). Recent research (Zhang et al., 2008, 2012; Chang et al., 2009; Astrup et al., 2011) have suggested that the fate of trace elements might be a function of several factors such as incineration temperature, complex waste composition, feed chlorine content, oxygen concentration, flue gas treatment process, physico-chemical properties of trace elements, their compounds and reaction affinity of trace elements with non-metals like chlorine. Since incineration of unsorted MSW (containing PVC and food waste), industrial waste and other type of waste can significantly enhance the formation of volatile element chlorides, promoting the emission of harmful trace elements. So in order to minimize such risks and to make the better use of residues it is essential to attain deep understanding about factors affecting the transfer characteristics of trace elements during incineration. A study similar to our work by Rendek et al. (2007) was conducted to investigate the influence of waste fuel and incineration technology on bottom ash properties. It was reported that addition of industrial and demolishing waste increase sulfur content while plastic waste added significant amount of chlorine. Both these components are water soluble and also affect the fate of trace elements, so part of these wastes in total amount must be addressed to predict the partitioning and leaching behavior of trace elements. Volatility of trace elements and presence of chlorine in the waste are responsible factors for the formation of metallic chlorides. In unsorted MSW (Municipal Solid Waste), plastic (PVC) and food (NaCl) waste can add significant amounts of organic and inorganic chlorine, respectively, which will affect the distribution of trace elements (Shi et al., 2004). In another study by Pedersen et al. (2009), different types of waste fractions were fired during normal operation to examine their effect on trace element partitioning during waste incineration and it was reported that the firing of chlorine rich waste (PVC, salt) and shoes increased volatilization of lead and an increased recovery was observed in fly ash and aerosol fractions. Also, organically bound chlorine was vaporized as HCl(g) whereas inorganically bound chlorine was recovered in bottom ash as alkali metal chlorides thus making chlorine a critical element not only for partitioning but also for corrosion and deposition problems. Forest waste (bark, sawdust, stem chips, logging residues) contains comparatively lower concentrations of chlorine (0.01–0.03 wt.%) (Alakangas, VTT, 2005). Use of waste wood and virgin wood as fuel is also an increasing trend in Sweden and waste wood often contains high contents of Zn, Pb, As, Cu and S compared to virgin wood (Krook et al., 2006). Apart from chlorine, zinc also evaporates from the combustion chamber and forms deposits especially in grate fired conditions (Åmande et al., 2006). In previous studies, thermodynamic calculations have shown that the presence of chlorine compounds like HCl and a reducing atmosphere usually increase the rate of volatilization especially for Pb, Cu, Cd and Zn, therefore increasing enrichment of these elements in fly ash (Zhang et al., 2008; Wang et al., 1999). Influence of chlorine on trace element partitioning has also been reported to be temperature dependent (Chiang et al., 1997). The effect of moisture and chlorine on element partitioning in a laboratory tubular furnace was investigated by Li et al. (2010) and it was observed that chlorine has higher impact on the volatilization rate of elements at 800 °C than at 600 °C especially for Pb, Cu, Ni, Cr and Cd whereas Hg is volatile even at low temperatures. Temperature has a pronounced impact on vapor pressure of trace elements and hence on partitioning, it usually increases with temperature. It has been reported that during waste incineration Hg is

most likely to vaporize, followed by Cd, Pb, and Zn, while Cr and Ni are least likely to evaporate (Jianxin et al., 2007). Impact of temperature on trace element partitioning has been subject to some studies (Abanades et al., 2002; Zhang and Kasai, 2004; Asthana et al., 2010). Various incineration facilities can have different trace elements partitioning behavior in the final residues. Jung et al. (2004) reported high concentration of some elements (Cu, Cr, Al) in fly ash for fluidized bed boiler compared to grate furnaces. Temperature, turbulence and residence time are crucial factors affecting the distribution of trace elements. Grate furnaces are the most commonly employed incinerators for MSW combustion where fuel is fed onto a moving grate with supply of excess air and there is a minimal need for pre-sorting and fine size reduction (Blasiak et al., 2006). In Europe, about 90% of the installations are using different types of grates for MSW treatment (European Commission, 2006). Normally residence time for the waste on the grate is not more than 60 min and for the flue gases it is about P2 s to have enough time for trace elements distribution between phases to reach equilibrium (European Commission, 2006). Typical reaction conditions for oxidative combustion process are a temperature in the range of 800–1450 °C under pressure of 1 bar (European Commission, 2006). In bubbling or circulating fluidized bed (BFB or CFB) boilers, a bed of inert material like quartz sand is used to distribute the heat evenly to water tubes in order to maintain low temperature to minimize the overall NOx production as nitrogen supply will be reduced (Bontoux, 1999). The difference in temperatures and oxygen concentrations in both sorts of combustion systems will definitely affect the fate of trace elements. The present study focuses on the discussion of trace element partitioning in different ashes resulting from the combustion of various waste fuels including household, industrial, forest chips, waste wood and mixture of different wastes, being treated in Swedish waste incineration facilities. Waste materials contain varying contents of chlorine and trace elements. The influence of combustion temperature on the rate of volatilization of trace elements is discussed here with the guidance of literature and previous research. Six incineration facilities across Sweden including two grate fired, three circulating fluidized bed boilers (CFB) and one bubbling fluidized boiler (BFB) have been considered to have a broad overview of trace elements behavior in various boiler types and variable incineration conditions like temperature. This study will help to further explore the impact of various factors affecting the fate of trace elements during incineration such as type of waste fuel, input chlorine content and incineration technology.

2. Materials and methods 2.1. Sampling and characterization of waste fuels Waste fuels sampling for analysis is complicated process due to the uncertainty of being able to ensure a representative sample from a relatively heterogeneous mixture. Heterogeneity is the single largest cause of sampling error. A sample, with a mass of only a few grams, to be used for the chemical analysis, is intended faithfully to represent the composition of the materials in a bulk waste body. A sample can be used if sampling has been correctly performed and in a representative manner, but with the reservation that it represents only one particular body of waste and its unique composition at the time of taking the sample. According to theory of sampling by Gy (1976) it is always a compromise between cost and accuracy during sampling. To minimize cost and effort it is to keep in mind that all parts of bulk sample must be accessible and should have an equal chance of inclusion in the sample and hence final sample must be representative of whole population. However

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several types of error have been reported to affect the accuracy of sampling process. Fundamental error caused by material inherent variability like variation in size and particles density is never zero unless population is homogeneous or that the entire population is included in the analysis. Other types of error are due to segmentation and grouping of particles, spatial and periodic variation and handling of samples. A better picture of the fuel composition is gradually built up by taking repeated samples over a longer period of time. The complexity of sampling is considerably affected by pretreatment of fuel whether it has been pre-treated by crushing or not before it is burnt. 2.1.1. Sampling at grate facilities Waste fuel sampling is critical in case of grate facilities since waste goes untreated to the incineration process. Fuel analysis was not performed as a part of this study; data have been collected partly from the facilities and partly from previous studies about fuel sampling at the same incineration plants (Blomqvist and Jones, 2012). At Umeå and Söderenergi waste incineration plants (grate fired based boilers), sampling was done according to a segmentation method based on CEN/TS15442 (Rylander and Wiqvist, 2008). A schematic overview of the segmentation process is shown in Fig. 1. The method involves mixing of waste before collecting 5–7 tons of sample. The sample is crushed and mixed twice to reduce the large pieces into a few centimeters in size. The mixed fuel sample is then spread on a clean surface (10  10 m) and split into 2 halves, one half is removed and the other is spread again in the same manner (Fig. 1) and the process is repeated until the thickness of height of the fuel is 20 cm. This thick layer is than divided into small squares of about one square meter and from every square one sample is collected with a spade to get a total of 30 kg to ensure a representative sample. The goal is to ensure that sample composition is representative from the bottom to the top of pile. Fuel samples were analyzed for its metal contents at Swedish National Testing and Research Institute (SP). Prior to analysis fuel samples are homogenized by grinding using a knife mill, then samples are dried in an oven at 40 °C and finally samples are sieved and fraction smaller than 2 mm is divided into two parts to enable representative sub sample for analysis. Further details are given elsewhere (SGI, 2006). 2.1.2. Sampling at fluidized bed facilities Due to the fuel pre-treatment, where fuel is shredded and mixed, fuel sampling at a fluidized bed facility is a relatively simple

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process. A hatch in the vicinity of the fuel feed to the fluidized bed is used for sampling directly from the falling stream of waste. The sample is taken by repeatedly inserting a spade in the falling fuel stream until a sample of about 30 kg has been attained. Samples are analyzed according to criteria set by Swedish National Testing and Research Institute (Arm et al., 2006).

2.2. Sampling of ashes Six participating facilities were chosen to represent various types of fuels being incinerated in both combustion systems (fluidized bed and grate fired boilers) as mentioned in Table 1. An amount of 1 kg for each ash was sampled by staff members on all facilities at four different occasions during two days to have as representative samples as possible. So for each ash sample there are four sub-samples. The sample jars were filled up to the rim and closed with tight lids to avoid any contact with air to prevent further oxidation and carbonation. The four sub-samples of ashes were thoroughly mixed to get a homogenized sample and one part was taken out for total content analysis. About 100 g of each ash was sent to an external laboratory (ALS Scandinavia AB) for chemical characterization. During the sampling period, operation was stable and operating with the normal fuel mixture as reported in Table 1 at all facilities. Flue gas treatment systems are presented in Table 2. All bottom ash samples were collected from the ash pit after water quenching and samples of fly ash were collected from bag filters in the case of Umeå, Nynäshamn and Händelö P14 plants. For Händelö P13 and Söderenergi plants, fly ash samples were collected from the electrostatic precipitators and in the case of the Sundsvall facility, fly ash was collected as a mixed sample from both the bag filters and the electrostatic precipitator. Bottom ash samples were dried at 40 °C and coarse ashes were crushed to a size of Cu > Pb. Same order for trace elements was reported for household waste from two other Swedish cities Stockholm and Högdalen in a recent study by Rylander and Wiqvist (2008). In a similar study by Åslund (2000), for Uppsala city, the order was reported as Cu > Zn > Pb. Household waste is a complex heterogeneous mix that might vary from one location to another. The composition of various fractions differs between sub-urban and downtown areas, and regions of lower income and education characteristics (Miafodzyeva and Brandt, 2011). Overall, each Swedish resident produces about 480 kg of household waste per year in which the biggest fraction (48%) is organic waste (mainly food waste) so a high concentration of inorganic chlorine (from NaCl) is expected (Bernstad et al., 2013). Other fractions in household waste include newspapers, plastics, glass and packaging of metals (Åslund, 2000). In Sweden, 48.4% of total household waste is treated through incineration, 49.2% is recovered by recycling or biological treatment while the rest is landfilled (Miafodzyeva and Brandt, 2011).  Händelö P14 has treated a mixture of household and industrial waste and concentrations of trace elements followed the order Zn > Cu > Pb > Cr. Söderenergi plant is treating a mixture of fuel pellets and industrial waste; and an order of Cu > Zn > Pb > Cr is observed. Industrial waste in Sweden includes waste mainly from manufacturing industries e.g. pulp and paper, wood and wood products industry as well as steel and metal works. Around 40% of industrial waste is incinerated while the rest is either treated biologically for recycling or landfilled (SEPA, 2005).  Facilities at Nynäshamn and Händelö P13 have burned waste wood and ordinary virgin wood chips, respectively, and the order of trace elements concentrations are Zn > Cr > Cu > Pb and Zn > Cu > Cr, respectively. Waste wood originates from construction, demolition and industrial activities. As shown in Table 1, it contains higher concentrations of all trace elements compared to ordinary wood chips that might be due to any surface treatment or wood treatment using Cu, Cr and As (CCA impregnation). Similar results have been reported earlier by Krook et al. (2004) about elevated concentration of trace elements in Swedish waste wood. In Sweden, 70–80% of all construction and demolition recovered waste wood is incinerated at biofuel boilers while 5–10% is utilized as fuel at MSW incinerators (SEPA, 1996b). Nynäshamn facility has permission to incinerate recovered waste wood. Sweden also imports waste wood from Germany and the Netherlands. Concentrations of As, Cu and Cr are higher in Swedish waste wood compared to imported waste wood (Krook et al., 2004). CreosoteÒ is a typical wood preservative that has been widely used in Sweden for a long time especially in the building sector. Several restrictions have already been employed since 1992 on the use of surface treated wood in Sweden. From 2002, the wood that has been treated using Cu, Cr and As (CCA) or only creosote is classified as hazardous waste in Sweden (Krook et al., 2006). Common pre-treatment processes for waste wood in Sweden include crushing of wood pieces down to wood chips, use of magnetic separators to remove ferrous metals and then screening to

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remove the fine fractions produced during wood processing. Resulting wood product is sold to district heating plants (Andersson and Tullin, 1999).  Both chlorine and sulfur are critical elements in the waste fuel with respect to element speciation, partitioning to various combustion fractions and corrosion in the boilers (Sorell, 1997; Luan et al., 2013). Speciation of trace elements is believed to be influenced by the type of chlorine bond because organic chlorine (PVC, C2Cl4) is expected to be released as HCl in gas phase and reacts more eagerly with trace elements in comparison to inorganic (NaCl, KCl) chlorine (Pedersen et al., 2009). Alkali metal chlorides have ionic bonding and have higher lattice energy compared to molecular bonded organic chlorine (PVC, C2Cl4). Chlorine provided by organic compounds in the waste is more easily accessible compared to inorganics (Wang et al., 1999). Therefore the availability of hydrogen, trace elements and Cl might boost the formation of trace element chlorides. Pedersen et al. (2009) reported that high input of chlorine increases the volatilization of lead and might also increase the volatility of zinc as well and forms chlorine rich deposits by enhancing the vaporization of trace elements. In another study Wang et al. (1999) also concluded that the increase in input organic chlorine is responsible for increased partitioning to fly ash for cadmium and zinc with a slight increase for copper and chromium as well. Other aspects of higher input of chlorine concentration are corrosion and fouling problems due to increased deposition fluxes. According to a study by Sorell (1997), almost all input chlorine compounds are converted to HCl during combustion; its content in the flue gases from a refuse incinerator is about 400–1500 ppm based on the rule of thumb that every 0.1% of chlorine in the input waste produces about 80 ppm of HCl. Deposition generally occurs as a result of vapor condensation, reaction of gaseous products with already formed deposit and physical deposition of fly ash (Schofield, 2012). Due to reducing local conditions in the lower area of the furnace, deposits are rich in chlorides while in the higher area of the furnace or in the convection part, deposits are enriched with sulfates which are more stable under oxidizing conditions than chlorides. Therefore oxidation–chlorination processes govern the corrosion in combustion environments (Kassman et al., 2011). Sulfur has been reported to inhibit corrosion (Krause and Rothman, 1985). This is because sufficient amount of SO2 in the combustion environment would convert highly corrosive metal chlorides to less corrosive sulfates. Therefore a lower concentration of chlorine in the input waste fuel is favorable for longevity of the equipment (Vainio et al., 2013).  In this study chlorine and sulfur contents are highest (2.14% and 0.99%, respectively) for Söderenergi mixed waste and lowest for Händelö P13 wood chips (0.005% and 0.002%, respectively) as shown in Table 1. It is reported by Berg et al. (2005) that corrosion and deposit formation generally increase with waste wood combustion compared to ordinary wood due to high concentrations of Zn, Pb and Cl in the input waste. In this study, zinc concentration is highest for waste wood. Household waste from Umeå contains almost 3 times more chlorine and double sulfur content than household waste from Sundsvall. Similarly, other facilities provide a good platform for comparison of trace elements and chlorine partitioning between bottom and fly ash. An increased input concentration of trace elements can boost corrosion problems. Fig. 2 indicates relationship between trace element contents in the waste and fraction partitioned to fly ash. 3.2. Trace element distribution in bottom and fly ashes Concentration of trace elements in the incineration residues are reported in Table 4. A comparison of facilities using the same type

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of fuel but different sort of combustion system is presented here for a better picture of the results. Incineration facilities at Umeå and Sundsvall both are treating household waste but in different kind of boilers as reported in Table 2. Similarly, Söderenergi and Händelö P14 treat mixed waste, while Nynäshamn and Händelö P13 have been coupled for biofuel incineration. For the ease of explanation and discussion of results, all ten trace element of interest are divided with respect to their volatility into three subgroups, low volatile (Ni, Co, Cr, and Cu), medium volatile (Pb, Zn, As and Sb) and highly volatile trace elements (Hg, Cd) (Alcock et al., 1984). General distribution behavior of elements in the combustion residues is discussed in this section with respect to composition of waste fuels and used incineration process. A brief overview of chlorine and temperature effect will be discussed in the next sections. 3.2.1. Umeå (grate fired boiler) and Sundsvall (CFB) treating household waste Household waste is a heterogeneous fuel and contains several specific waste fractions with different physical and chemical properties. Rylander and Wiqvist (2008) performed sorting analysis on household waste from 3 Swedish cities and reported about 19 subfractions.  During waste incineration, highly volatile elements were mainly found in fly ash for both facilities (Table 4). Due to the high vapor pressure, most of the mercury is evaporated. Highest percentage of mercury and cadmium was present in fly ash from both facilities; only about 9% of the total cadmium was present in the bottom ash for Sundsvall bottom ash. These values are in accordance with already published results (Brunner and Mönch, 1986; Jung et al., 2004; Zhang et al., 2008, 2012). Major sources for mercury in Swedish household waste are batteries, switches, light sources (lamps), measuring and control equipment while stabilizers, pigments and Ni–Cd batteries are the main sources for cadmium (Holm et al., 2002). However, mercury consumption has decreased in Sweden from 9 tons/ year in 1991 to 2 tons/year in 1997 and has been phased out in many applications (Holm et al., 2002). At lower incineration temperatures different mercury compounds in the waste are decomposed to elemental mercury which can react with chlorine at higher temperatures to form mercury chlorides. Elemental mercury and its chlorides are dominant species at high temperature (Velzen et al., 2002). Similarly, cadmium is a quite volatile element and formation of cadmium chloride is likely and will mainly be found in the flue gas. When lowering the temperature of the flue gases, the volatile cadmium will adsorb to smaller ash particles and therefore the flue gas cleaning system is a vital feature to control its emission (Benestad et al., 1995). A combination of electrostatic precipitator (ESP) and bag filter at Sundsvall whereas only bag filter at Umeå is employed for flue gas treatment. A better removal of small particles and trace elements might therefore be expected at the Sundsvall facility.  Elements with medium volatility showed mixed behavior. Zinc was distributed 55% and 52% in fly ash for Umeå and Sundsvall facilities, respectively (Fig. 3). Similar results for zinc partitioning have been reported earlier (Brunner and Mönch, 1986; Morf et al., 2000). Zinc in the Swedish household waste is contributed by various sources like textile/rubber/leather (32–17 640 mg/ kg), plastics (15–10 000 mg/kg), glass ( Pb, in waste wood Zn > Cr > Cu, in virgin wood Zn > Cu > Cr, while in mixed waste it is Cu > Zn > Pb.  Firing household or mixed waste in fluidized boilers caused high transfer into fly ash as compared to grate boilers for Pb and low volatiles Cr, Cu and Ni. The reason might be high combustion efficiency and turbulence in fluidized boilers.  Firing of waste wood in fluidized boilers caused increased transfer to fly ash for As and Cr compared to firing virgin wood probably due to increased input of these elements in waste wood.  Generally, mercury and cadmium were partitioned mostly in the fly ash in all cases during incineration, most probably because of vaporization, condensation on fly ash particles and adsorption mechanisms. While 2/3 of lead was transferred to fly ash but As, Zn and Sb showed high variations, with most of antimony and zinc distributing to fly ash. Arsenic showed a mixed behavior. Low volatiles stayed in the bottom ash for grate facilities but showed surprisingly high transfer to fly ash for fluidized bed incinerators especially in cases where waste wood was used as fuel. A likely reason could be solid particle entrainment to fly ash for fluidized boilers.  Waste fuel chlorine content and incineration temperature are very crucial factors affecting the partitioning of trace elements and corrosion of equipment. Increased chlorine in the fuel feed decreased the trace element transfer to bottom ash by forming metal chlorides that are highly volatile. Temperature has a significant impact especially on elements with low boiling points. Zinc and cadmium concentrations increased in fly ash with increased combustion temperature.  An increased input concentration of certain trace elements, like zinc when firing waste wood and chlorine while firing industrial waste, caused increased concentration in fly ash. It might also boost the deposition and corrosion problems. So it is suggested to keep input metal and chlorine concentrations as low as possible.  Generally, fluidized boilers accommodates most of low volatile trace elements into fly ash in this study The difference in partitioning might be due to different residence times for fuels and ash particles, temperatures and fluid dynamics factors like superficial velocities.

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Trace element partitioning in ashes from boilers firing pure wood or mixtures of solid waste with respect to fuel composition, chlorine content and temperature.

Trace element partitioning in solid waste (household waste, industrial waste, waste wood chips and waste mixtures) incineration residues was investiga...
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