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Environmental Impact of Energy Recovery from Waste Tyres
Abstract
Accumulation of millions of worn automotive tyres poses a considerable environmental problem. As an important part of the solid waste stream in today’s society, worn tyres have traditionally been discarded in landfills or stored in stockpiles. Over the past several decades, however, innovative alternatives to disposal have been developed, partly as a result of high tipping fees charged by landfill operators. Because of their high heat content and their low levels of moisture and nitrogen compared to coal, tyres are ideally suited for energy recovery through combustion. Utilization of waste tyres as supplemental or alternate fuel in various industrial combustion facilities, thus, has become one of the most important alternatives to disposal. Combustion processes, however, generate gaseous pollutants and solid waste materials, which must be disposed of or re-used as secondary raw materials. It is therefore important to characterize these combustion products in order to assess the environmental impacts of energy recovery from scrap tyres. Studies have shown that substantial reductions of some environmental pollutants can be achieved by partially replacing conventional fuels with waste tyres. On the other hand, using tyres as fuel may lead to considerable increases in the levels of other pollutants. Most notable among the effects of tyre combustion are, relative to conventional fuels, a pronounced decrease in the emission of nitrogen oxides into the atmosphere, and a generally significant increase in atmospheric zinc emissions as well as in the zinc contents of the solid combustion products. The geochemical effects on solid and gaseous combustion products are more or less pronounced depending on fuel composition, conditions of combustion, type of facility, and effectiveness of air pollution control devices. Thus, the use of tyre fuel has environmental impacts that must be weighed against the benefits of reducing the large volume of waste tyres in the global waste stream.
... Accumulation of millions of worn automotive tires poses a considerable environmental problem. On average, approximately one scrap tire per person per year accumulates in industrialized countries (see discussion in [1]). As an important part of the solid waste stream in today's society, worn tires have traditionally been discarded in landfills or stored in stockpiles. ...
... Because of their high heat content and their low levels of moisture and nitrogen compared to coal, tires are ideally suited for energy recovery through combustion. Consequently combustion of waste tires as supplemental or alternate fuel in various industrial combustion facilities has become the most important alternative to dis-posal [1]. In 2001, for example, 41% of all tires discarded in the US were used as fuel [2], and in Germany [3] the percentage was even higher (Fig. 1). ...
... Because combustion processes generate gaseous pollutants and solid waste materials, which must be disposed of or reused as secondary raw materials, it is important to characterize these combustion products in order to assess the environmental impacts of energy recovery from scrap tires. Several laboratory studies focused on the emissions resulting from combustion of pure tire fuel and of blends of coal plus waste tires (see [1] for discussion and references). The results of these studies revealed that, compared to coal combustion, burning of pure tires or coal + tire blends under the same conditions generally leads to a decrease in atmospheric emissions of nitrogen oxides (NO x ), but produces higher emissions of carbon monoxide (CO), polycyclic aromatic hydrocarbons (PAH), and submicrometer-sized particulate matter (PM). ...
Medium-sulfur bituminous coal and a mixture of 95 wt.% coal plus 5 wt.% tire-derived fuel (TDF) in the form of shredded automotive tires were combusted in a stoker boiler under the same conditions. This paper presents quantitative chemical compositions of the fuels and of the gaseous and particulate emissions. The coal + TDF mixture is considerably richer in Zn than the pure coal as a result of the high Zn content of the shredded tires (∼1 wt.% Zn). Atmospheric emissions of Zn increased from 15 g/h to nearly 2.4 kg/h when coal + TDF was combusted. Similarly, emissions of most other metals and metalloids, as well as those of HCl increased when TDF (∼3000 ppm Cl) was added. The enhanced metal emissions might be due to formation of gaseous metal chloride species in the stack gases. On the other hand, emissions of CO decreased slightly, whereas those of NOx, SO2, and total particulate matter remained virtually unchanged. These results help in assessing the environmental impact of energy recovery from scrap tires in stoker boilers.
... Atmospheric Zn contamination is derived in part from the burning of hydrocarbon-based fuels such as coal and tires (1,2). The isotopic ratios of Zn, reported in parts per thousand relative to the Johnson Matthey Catalysts (JMC) Zn metal standard batch 3-0749 L (δ 66 Zn), have recently been used in an attempt to "fingerprint" and track atmospheric contaminant sources (e.g., refs 3-7). ...
... The coal was a high-volatile C bituminous coal from southern Indiana, USA, and the TDF was shredded tire material obtained from Entech, Inc. (Michigan, USA). The sizes, moisture, and ash contents, and bulk chemical compositions of these materials were presented previously (2,15). The Zn concentrations of the digested fuel separates specific to this investigation are presented in Table 1. ...
... Sample Preparation. Bulk chemical analyses of the coal, TDF, coal+5%TDF, and most of the PM samples have been reported previously (2,15); however, for this study it was necessary to digest new sample splits and to analyze them for their bulk chemical concentrations prior to isotopic analysis. Because these samples are highly refractory, we evaluated the effectiveness of multiple digestion methodologies and their impact on the measured δ 66 Zn of the samples. ...
Atmospheric Zn emissions from the burning of coal and tire-derived fuel (TDF) for power generation can be considerable. In an effort to lay the foundation for tracking these contributions, we evaluated the Zn isotopes of coal, a mixture of 95 wt % coal + 5 wt % TDF, and the particulate matter (PM) derived from their combustion in a power-generating plant. The average Zn concentrations and δ(66)Zn were 36 mg/kg and 183 mg/kg and +0.24‰ and +0.13‰ for the coal and coal + TDF, respectively. The δ(66)Zn of the PM sequestered in the cyclone-type mechanical separator was the lightest measured, -0.48‰ for coal and -0.81‰ for coal+TDF. The δ(66)Zn of the PM from the electrostatic precipitator showed a slight enrichment in the heavier Zn isotopes relative to the starting material. PM collected from the stack had the heaviest δ(66)Zn in the system, +0.63‰ and +0.50‰ for the coal and coal + TDF, respectively. Initial fractionation during the generation of a Zn-rich vapor is followed by temperature-dependent fractionation as Zn condenses onto the PM. The isotopic changes of the two fuel types are similar, suggesting that their inherent chemical differences have only a secondary impact on the isotopic fractionation process.
... To determine tire wear we rely on generalized specifications from the literature. The treads of tire consist of five components to yield a combination of durability, flexibility, and grip (Camatini et al., 2001;Gieré et al., 2004;Kocher et al., 2010;Apeagyei et al., 2011;Gunawardana et al., 2012;Wu, 2016). Since the production of tires is a well-kept secret of the manufacturers, especially as far as the composition of the additives is concerned, the following figures are approximate values for these components: ...
... Even though bitumen is not easily detected by SEM-EDX, it can be identified on the basis of its sulfur content when occurring in agglomerates of different minerals glued together (according to the manufacturer's information, asphalt contains 2-8 mass% bitumen with 2-6 mass% S) ( Fig. 6(a)). It must be stated, however, that sulfur is not an unequivocal marker element for bitumen because it also appears in tire wear in similar concentrations (see Gieré et al., 2004). ...
... To determine tire wear we rely on generalized specifications from the literature. The treads of tire consist of five components to yield a combination of durability, flexibility, and grip (Camatini et al., 2001;Gieré et al., 2004;Kocher et al., 2010;Apeagyei et al., 2011;Gunawardana et al., 2012;Wu, 2016). Since the production of tires is a well-kept secret of the manufacturers, especially as far as the composition of the additives is concerned, the following figures are approximate values for these components: ...
... Even though bitumen is not easily detected by SEM-EDX, it can be identified on the basis of its sulfur content when occurring in agglomerates of different minerals glued together (according to the manufacturer's information, asphalt contains 2-8 mass% bitumen with 2-6 mass% S) ( Fig. 6(a)). It must be stated, however, that sulfur is not an unequivocal marker element for bitumen because it also appears in tire wear in similar concentrations (see Gieré et al., 2004). ...
Traffic-related non-exhaust particulate matter mainly consists of tire wear, brake wear, and road wear. For this study, passive-samplers were placed near highly frequented roads in industrial, agricultural, and urban environments with the aim of collecting and characterizing super-coarse (> 10 µm) airborne particles. Single-particle analysis using SEM-EDX was conducted on more than 500 particles with nearly 1500 spectra to determine their size, shape, volume, and chemical composition. The ambient aerosol near all studied roads is dominated by traffic-related abrasion particles, amounting to approximately 90 vol%. The majority of the particles were composites of tire-, road-, and brake-abrasion material. The particle assemblages differed in size distribution, composition, and structure depending on driving speed, traffic flow, and traffic fleet. Our study documents that tire wear significantly contributes to the flux of microplastics into the environment. A decrease in the release of this abrasion material, however, is unlikely in the near future.
... Used tires create a challenging disposal issue since they are generated in large quantities (i.e., nearly 300 million used tires per year in the U.S.) and have limited end of life options via current technologies (Collins et al., 1995;Giere et al., 2004Giere et al., , 2006. For instance, they can be treated and reused or coarsely ground and used as filler for artificial turf or civil engineering projects (Gawel and Slusarski, 1999). ...
... Thermal treatment of used tires could be an attractive option because of general compositional properties of tires (e.g., the low levels of moisture, nitrogen, and mineral matter) compared to coal (Giere et al., 2004(Giere et al., , 2006. The pyrolytic oil from tire waste can be used directly as a fuel or blended with petrochemical feedstock (Kim et al., 1994). ...
... Disposal of waste tire rubbers has recently been considered as an environmental challenge worldwide (Giere et al., 2004). More than 1000 million scrap tires are produced annually throughout the world (Dhir et al., 2001). ...
... Discarding scrap tires in landfills is an environmental concern becoming legally prohibited in several countries. Therefore innovative methods of recycling tire rubber are in great demand (Giere et al., 2004). There are some safe technologies for recycling waste tires. ...
Disposal of rubber tires is an environmental challenge in many countries. Recently we introduced a new technology to use rubber as a source of zinc (Zn) for crops. According to the previous results, rubber particles size is a key factor determining the rate of nutrient release from the rubber wastes. In this study, nano-particles were prepared from waste tire rubber by applying different treatments. The suitable approach for the preparation of nano-particles from waste tire rubber was milling them inside ball mill for 5 h in the presence of silicon wastes. The efficiency of rubber nano-particles as Zn source for cucumber in nutrient solution culture was compared with a commercial Zn-sulfate fertilizer. In hydroponic experiment, ground tire rubber and nano-particles of tire rubber and rubber ash were used. The cucumber seedlings grown in the nutrient solution containing nano-particles of tire rubber and rubber ash had greater shoot and fruit yield and also accumulated higher amounts of Zn in their tissues as compared with those grown in Zn sulfate-containing nutrient solution. Thus, nano-particles synthesized from waste tire rubber and rubber ash offer a strong value as Zn fertilizer for cucumber grown in the nutrient solution culture.
... However, transforming ST into an energy source, is a double palliative for countries, especially small islands, aiming for sustainable development, but with economies based on fossil fuel importation, inconsistencies in the handling and disposal of this material, and where stealthy dumping is rampant [35], as in Puerto Rico [15] and other Latin American countries [34,57]. To mitigate the adverse economic, environmental and public health effects of the mishandling and disposal of ST, it is crucial to apply the most cost effective techniques headed to recover the energy from this resource [18,58,59]. ...
... Therefore, if Puerto Rico has the capacity to produce TDF, it ought to expand the ST market in order to consider this material as an alternate fuel as done by USA and Germany, two countries with very strict air quality standards, but supporters of the cogeneration of energy using TDF [29]. Despite TDF reduces the cost of energy production [60,61], thermoelectric power plants prefer to use whole ST, since producing TDF can be up to five times more expensive than pulverizing coal [58], while its making consumes large amounts of energy [62]. However, TDF can be used to feed thermal processes in many other industries, for instance metallurgical, cement, pharmaceutical and recycling, or to provide electricity to run the operations of those industries, via energy recovery by pyrolysis, the most recommended method [39,40]. ...
Puerto Rico generates and disposes nearly five million/year scrap tires (ST), of which 4.2% is recycled and 80% is exported. The Island has one of the world highest electrical service tariff ($0.28 kWh), because of its dependency on fossil fuels for power generation. The Government has not considered ST for electricity production, despite more than 13,000 ST are generated daily, and paradoxically exported for that purpose. Theoretically, if ST recycling increases to 10% and assuming that the caloric value of ST be 33 MJ/kg, it was estimated that scrap tires processed with pyrolysis can supply annually about 379 MWh, a potential value that shall not be unnoticed. This paper is a literature review to describe the legal, technical, and economic framework for the viability of ST for power generation in Puerto Rico using pyrolysis, the most recommended process for ST energy recovery. Data of ST from Puerto Rico was used to model the potential of ST for pyrolytic energy conversion. The herein article is intended to invite other insular countries and territories, to join efforts with the academic and scientific community, and with the energy generation sector, to validate ST as a sustainable option for energy generation.
... Disposal of rubber tires is a considerable environmental problem in many countries (Giere et al. 2004). It is estimated that about 1000 million scrap tires are produced annually throughout the world (Dhir et al. 2001). ...
... On the other hand landfilling of scrap tires is an environmental concern and becoming legally prohibited in different countries. Therefore innovative methods of recycling tire rubber are in great demand (Giere et al. 2004). There are some safe technologies for recycling waste tires. ...
Background and Aims
We tested the utility of some biological treatments to hasten degradation of waste tire rubber in soil and thus the release of zinc and sulfur for plant uptake.
Methods
Three rates of ground tire rubber (0, 150, and 300 mg kg−1) were incorporated into a Zn-deficient calcareous soil. Before addition to the soil, ground rubber was given four microbial treatments including no inoculation, inoculation with Rhodococcus erythropolis, inoculation with R. erythropolis+Escherichia coli, and inoculation with R. erythropolis+E. coli+Acinobacter calcoaceticus. In the pot experiment, corn (Zea mays L. Hybrid Single Cross 500) and sunflower (Helianthus annuus L. cv. Record) plants were exposed to three rates of ground rubber (0, 150, and 300 mg kg−1) or 3 mg zinc kg−1 as ZnSO4. Before addition to the soil, ground rubber and ZnSO4 were inoculated or non-inoculated with R. erythropolis+E. coli+A. calcoaceticus.
Results
Ground rubber and microbial inoculation treatments reduced soil pH and the magnitude of this reduction increased over time. Ground rubber in combination with microbial inoculation increased DTPA-extractable soil Zn and Fe. The amount of DTPA-extractable Zn and Fe of rubber-amended soils increased over time so that the highest concentration of available Zn and Fe was found at week 10. Application of microbial inoculated ground tire rubber significantly increased shoot Zn concentration of each plant species.
Conclusions
Bacterial inoculation of ground rubber was effective in hastening increase in DTPA-extractable Zn in the studied calcareous soil and in enhancing Zn uptake by plants.
... Worn automotive tire accumulation is a considerable environmental problem in many countries (Giere, et al., 2004). It is estimated that about 1000 million scrap tires are produced annually throughout the world, rep- resenting a significant treatment and disposal problem ( Dhir et al., 2001). ...
... As an important part of the solid waste stream in today's society, worn tires have traditionally been discarded in landfills or stored in stockpiles. Over the past several decades, however, innovative alternatives to disposal have been developed, partly as a result of high tipping fees charged by landfill operators (Giere, et al., 2004). ...
‘Cerasiforne’ tomato (Lycopersicon esculentum Mill.) was grown in soilless potting media contained different substrate formulas including 25:25:50 volume ratio of acid-washed (AWR) or non-washed shredded rubber (NAWR):vermiculite or zeolite:perlite. Additionally, plants were grown in a peat:perlite substrate. Plants grown in media containing AWR had greater root and shoot dry weight and fruit production than those grown in the NAWR media or the peat:perlite substrate. Fruit zinc (Zn) and iron (Fe) concentration of plants grown in AWR-containing media was significantly lower than those grown in NAWR-containing media. Plants grown in the presence of waste rubber accumulated greater Zn in their shoots compared to those grown in the peat: perlite media. Acid washing of rubber significantly reduced shoot Zn concentration. Shredded waste rubber might be used as a component of container media in production of hydroponically-grown tomato; however, acid-washing of rubber is required to prevent potential Zn toxicity for plant.
... Disposal of rubber tires is a considerable environmental problem in many countries (Giere et al. 2004). It is estimated that about 1000 million scrap tires are produced annually throughout the world (Dhir et al. 2001). ...
... On the other hand landfilling of scrap tires is an environmental concern and becoming legally prohibited in different countries. Therefore innovative methods of recycling tire rubber are in great demand (Giere et al. 2004). There are some safe technologies for recycling waste tires. ...
Ground rubber contains 15–20g Zn kg−1 but very low levels of Cd and could serve as an inexpensive byproduct Zn fertilizer. The aim of this investigation was to
test Zn release in a soil treated with ground tire rubber and rubber ash compared with commercial Zn fertilizer and a laboratory
grade zinc sulfate. A Zn-deficient soil was chosen from wheat fields in Isfahan province, central Iran, and the ground rubber,
rubber ash and fertilizer-Zn and laboratory ZnSO4 were added at 0.5 and 2mg Zn kg−1; 0.5kgha−1 would usually correct Zn deficiency in such pot tests. The soil DTPA-extractable Zn was then measured with time and the results
were described examining first order, Elovich, power function and parabolic diffusion kinetics models. In the pot experiment,
corn (Zea mays L.) plants were exposed to three rates of Zn (0, 20, 40mg Zn kg−1) from two different sources (ZnSO4 and ground rubber). Ground rubber was applied as 2–3mm and <1mm diameter particles. Zinc treatments were mixed with the
soils before planting. At harvest, concentrations of Zn, Pb, and Cd in roots and shoots of corn were measured. Results showed
that ground rubber and rubber ash significantly increased the concentration of DTPA-Zn in the soil and this increase was higher
than achieved with the commercial Zn fertilizer. At the lower Zn application rate, Zn release followed parabolic diffusion,
while at the higher rate the kinetics of release followed power function and Elovich models. There was an increase in Zn concentration
of corn shoot and roots by adding of Zn regardless the source of applied Zn. With increase in the rate of rubber used, the
shoot Zn uptake increased. The Pb concentration of shoot and Cd concentrations of shoot and roots were low (less than 0.02mgkg−1) in all treatments. The results showed that the soil DTPA Zn decreases over time if the soil is amended with a soluble form
of Zn whereas the reverse was observed if the Zn is added as ground rubber which only gradually transforms. Thus ground rubber
and rubber ash offer strong value as Zn fertilizer for Zn deficient soils.
KeywordsWaste tire rubber–Calcareous soil–Zn fertilizer–Release kinetics
... There is a similar lack of detailed studies of primary PM emitted from power plants, which combust blends of coal and waste tires. Combustion of tires has become the most important alternative to disposal and stockpiling (25). Tires make good fuel because, compared to coal, they have high heat contents but are low in both moisture and nitrogen. ...
... Tires make good fuel because, compared to coal, they have high heat contents but are low in both moisture and nitrogen. Partial replacement of conventional fuels with whole or shredded tires (known as tire-derived fuel or TDF) can lead to substantial reductions of some environmental pollutants and considerable increases in others (25). Thus, the use of tire fuel has environmental impacts that must be weighed against the benefits of reducing the large volume of tires in the global waste stream. ...
The research presented here was conducted within the scope of an experiment investigating technical feasibility and environmental impacts of tire combustion in a coal-fired power station. Previous work has shown that combustion of a coal+tire blend rather than pure coal increased bulk emissions of various elements (e.g., Zn, As, Sb, Pb). The aim of this study is to characterize the chemical and structural properties of emitted single particles with dimensions <2.5 microm (PM2.5). This transmission electron microscope (TEM)-based study revealed that, in addition to phases typical of coal fly ash (e.g., aluminum-silicate glass, mullite), the emitted PM2.5 contains amorphous selenium particles and three types of crystalline metal sulfates never reported before from stack emissions. Anglesite, PbSO4, is ubiquitous in the PM2.5 derived from both fuels and contains nearly all Pb present in the PM. Gunningite, ZnSO4-H2O, is the main host for Zn and only occurs in the PM derived from the coal+tire blend, whereas yavapaiite, KFe3+(SO4)2, is present only when pure coal was combusted. We conclude that these metal sulfates precipitated from the flue gas, may be globally abundant aerosols, and have, through hydration or dissolution, a major environmental and health impact.
... Some of the Al and Si could be from clay minerals. The Cl and S could be from tire particles (e.g., Gieré et al., 2004). The origin of the remaining elements was uncertain and is interpreted to be from surrounding particles in the sample. ...
A multi-analytical geochemical investigation of Pb-contaminated collocated road dust and soils, at two size fractions, was performed in Fishtown, Philadelphia, PA, USA. The combinations of methods employed in this case study were chosen to better characterize the contamination, enhance identification of pollution sources, improve understanding of the impact of former Pb smelters, and to study the relationships between two media and between two size fractions. High concentrations of Cu and Sn were observed in both bulk and finer road dust, whereas large concentrations of Zn and Pb were found in both bulk and finer soil samples, implying pollution. There were no obvious associations between Pb soil concentrations and former smelter locations. Therefore, the primary source of the high mean Pb content in bulk (595 ppm) and fine soils (687 ppm) was likely legacy lead paint and/or leaded-gasoline products. Using electron microscopy, we found that Pb particles were mainly 0.1–10 µm in diameter and were ubiquitous in both soil and dust samples. Two-way analysis of variance tests revealed that, for most chemical elements explored here, there were statistically significant differences in concentrations based on media and size fractions, with finer sizes being more polluted than the bulk. The mineralogical composition and the sources of several pollutant elements (Cr, Cu, Zn, Pb), however, were similar for both soil and dust, pointing to material exchange between the two media. We suggest that future investigations of collocated road dust and soils in urban environments use the methodologies applied in this study to obtain detailed insights into sources of roadside pollution and the relationships between neighboring media.
... Boonyatumanond et al. (2007) reported high correlations of Pyr and BghiP with tire residues, which are likely derived from extender oils used to make tires, whereas Atal et al. (1997) detected petrogenic PAHs > 178 g mol -1 (Phe, Ant, Flt, Pyr, BaP, among others) in constituents of waste tires, but due to their complicated extraction with a high uncertainty they were not quantified; however, these researchers reported that parent PAH survivability is a minor path for PAH emissions at fuel-rich conditions as is the case of adobe kilns. Waste tires are attractive products to be recycled as fuel, due to their high calorific power of 29-39 MJ kg −1 (Giere et al., 2004) which is greater compared with the 27 MJ kg −1 of carbon (Pirnie, 1991). Nevertheless, combustion processes, utility boilers and kilns using this kind of fuel should be designed and optimized in order to avoid air pollution problems (Barlaz et al., 1993;Caponero et al., 2003Caponero et al., , 2005. ...
Artisanal pottery in Mexico is largely manufactured in handmade adobe kilns using scrap tires as main fuel in rural and periurban areas, making this activity one of the main sources of atmospheric pollutants. An intensive sampling campaign was conducted in a Mexican small town in order to characterize the toxic species emitted by more than 400 adobe kilns working in two scenarios: low and normal activity, as well as to determine their carcinogenic potential. PM10 concentrations ranged 50-80 μg m−3 and 77-290 μg m−3 during low and normal activity periods, while PM2.5 concentrations were 33-57 μg m−3 and 37-177 μg m−3 in the same periods. Organic carbon and elemental carbon presented concentrations around four and seven times greater, respectively, during a normal activity period than during a low activity period in both particle sizes. Quantified polycyclic aromatic hydrocarbons were twice greater during the normal activity period than during the low activity period. Carcinogenic PAHs accounted for 53-59% of total PAHs in all cases and the carcinogenic potential (B[a]Peq) in PM10 during the normal activity was 25 times higher than the European Commission recommendation, proving thereby the high risk that nearby population faces to those emissions.
... Accumulation of waste tyre rubber is a considerable environmental challenge in many countries (Adhikari et al. 2000;Gieré et al. 2004). These solid wastes contain sulfur, zinc oxide (ZnO), stearic acid, carbon black, proprietary additives and bead wires (Steudel and Steudel 2006). ...
Previous research has shown that ground rubber from tyres can be used to supply fertiliser zinc (Zn) for prevention of Zn-deficiency in crops, and that inoculation of the ground rubber with several bacterial species hastens the release of Zn to the soil. We evaluated the ability of several microbial combinations to speed the release of Zn from ground rubber and to decrease soil pH to favour phytoavailability of Zn to crops. In a batch experiment, treatment combinations of two rates of ground crumb rubber (nil or 300 mg kg⁻¹, equal to 0 or 3.4 mg Zn kg⁻¹) and 24 bacterial inoculants were incorporated into a Zn-deficient calcareous soil. In a pot experiment, two wheat cultivars were grown on the soil without or with ground rubber amendment or with equivalent Zn from ZnSO4 (15 mg kg⁻¹) in combination with two selected microbial treatments. All microbial treatments significantly decreased soil pH at week 3, most notably the inoculant comprising Rhodococcus erythropolis and Acinetobacter calcoaceticus (RA) + Pseudomonas putida P41 (P1) + mixed Thiobacillus spp. (Mt). In the presence of tyre rubber, soil pH at week 10 was still significantly lower than the initial value, and soil DTPA-extractable Zn concentration increased until week 6 and then remained unchanged or slightly reduced at week 10. The greatest increase in DTPA-Zn concentration occurred with the RA inoculation. Microbial inoculation treatments were classified by cluster analysis into eight groups based on soil pH and concentrations of iron (Fe) and Zn. Group 8 produced the lowest pH and highest concentrations of DTPA-Fe (average 6.92 mg kg⁻¹) and DTPA-Zn (average 2.67 mg kg⁻¹). Inoculations with RA and with RA + P1 + T. thioparus were the most effective in hastening an increase in DTPA-extractable Zn and significantly enhanced Zn uptake by wheat plants, whereas inoculations with P. putida P168 and with RA + P2 + Mt were most effective in decreasing soil pH and increasing plant Fe concentration.
... A lot of studies dealt with the co-incineration/combustion of waste tyre with coal. Combustion of a mixture of waste tyre and coal has many advantages (Atal and Levendis 1995;Gieré et al. 2004;Xiang-guo et al. 2006) such as the thermal destruction of toxic organic compounds and pathogens, and energy recovery. Singh et al. (2009) studied, in a pilot scale, the co-combustion of tyre rubber and pulverized coal and found that NO emissions were reduced in comparison with the combustion of coal. ...
A review of the energy recovery from waste tyres is presented and focuses on the three thermochemical processes used to valorise waste tyres: pyrolysis, gasification, and combustion/incineration. After recalling the chemical composition of tyres, the thermogravimetric behaviours of tyres or their components under different atmospheres are described. Different kinetic studies on the thermochemical processes are treated. Then, the three processes were investigated, with a particular attention given to the gasification, due to the information unavailability on this process. Pyrolysis is a thermochemical conversion to produce a hydrocarbon rich gas mixture, condensable liquids or tars, and a carbon-rich solid residue. Gasification is a form of pyrolysis, carried out at higher temperatures and under given atmosphere (air, steam, oxygen, carbon dioxide, etc.) in order to yield mainly low molecular weight gaseous products. Combustion is a process that needs a fuel and an oxidizer with an ignition system to produce heat and/or steam. The effects of various process parameters such as temperature, heating rate, residence time, catalyst addition, etc. on the energy efficiency and the products yields and characteristics are mainly reviewed. These thermochemical processes are considered to be the more attractive and practicable methods for recovering energy and material from waste tyres. For the future, they are the main promising issue to treat and valorise used tyres. However, efforts should be done in developing more efficient technical systems.
... Active management programs in the USA remarket used tires as fuel (37.7%), ground rubber (24.6%), civil engineering materials (18.0%), exports (8.0%), and for other purposes (3.4%), while the remaining tires are landfilled (13%), baled with no market (0.9%), or unaccounted for (4.6%) (RMA, 2013). Tires are an attractive chemical commodity, construction material, and solid fuel, due to their high energy density of 29e37 MJ kg À1 (Giere et al., 2004). The storage and reuse of tires requires attention to their potential environmental impact, including leaching and open-air burning. ...
In summer 2012, a landfill liner comprising an estimated 1.3 million shredded tires burned in Iowa City, Iowa. During the fire, continuous monitoring and laboratory measurements were used to characterize the gaseous and particulate emissions and to provide new insights into the qualitative nature of the smoke and the quantity of pollutants emitted. Significant enrichments in ambient concentrations of CO, CO2, SO2, particle number (PN), fine particulate (PM2.5) mass, elemental carbon (EC), and polycyclic aromatic hydrocarbons (PAH) were observed. For the first time, PM2.5 from tire combustion was shown to contain PAH with nitrogen heteroatoms (a.k.a. azaarenes) and picene, a compound previously suggested to be unique to coal-burning. Despite prior laboratory studies' findings, metals used in manufacturing tires (i.e. Zn, Pb, Fe) were not detected in coarse particulate matter (PM10) at a distance of 4.2 km downwind. Ambient measurements were used to derive the first in situ fuel-based emission factors (EF) for the uncontrolled open burning of tires, revealing substantial emissions of SO2 (7.1 g kg(-1)), particle number (3.5×10(16) kg(-1)), PM2.5 (5.3 g kg(-1)), EC (2.37 g kg(-1)), and 19 individual PAH (totaling 56 mg kg(-1)). A large degree of variability was observed in day-to-day EF, reflecting a range of flaming and smoldering conditions of the large-scale fire, for which the modified combustion efficiency ranged from 0.85-0.98. Recommendations for future research on this under-characterized source are also provided.
... While people are enjoying the benefits, wastes of them have generated significant environmental issues, e.g. toxicity, land occupation and groundwater contamination [1,2]. To alleviate the situation, aged plastic and scrape tire rubber are applied in asphalt production and proved to be able to modify the properties of base asphalt in certain aspects. ...
... Tires are composed of a polymer mixture, 9,10 which are mainly natural rubber (NR) 11 called as polyisoprene (IR) 12,13 and styrene butadiene rubber (SBR). 14 In addition, black carbon, fiber, extender, and vulcanizing agents are added during the manufacturing, which leads to the complex thermal degradation behavior. ...
The thermal degradation of tires under various oxygen concentrations (7-30%/Bal. N2) was investigated thermo-gravimetrically at 10˚C min-1 heating rate over a temperature range from ambient to 1000˚C. Significant mass loss (~55%) was observed at the temperature of 300-500˚C, where the thermal degradation rate was almost identical and independent on oxygen concentrations due to simultaneous volatilization and oxidation. A series of Gas Chromatography/ Mass Spectroscopy (GC/MS) measurements taken from the effluent of a thermo-gravimetric analysis (TGA) unit at temperature of 300-5000˚C leads to the overall thermal degradation mechanisms of waste tires and some insights for understanding evolution steps of air pollutants including volatile organic carbons (VOCs) and polycyclic aromatic hydrocarbons (PAHs). In order to describe the fundamental mechanistic behavior on tire combustion, the main constituents of tires, styrene butadiene rubber (SBR) and polyisoprene (IR), has been investigated in the same experimental conditions. The thermal degradation of SBR and IR suggests the reaction mechanisms including bond scissions followed by hydrogenation, gas phase addition reaction, and/or partial oxidation.
The present study was conducted to investigate the potential of Zn-solubilizing Pseudomonas strains to release Zn from tire waste powder (TWP) in a liquid medium and soil. A pot experiment was also conducted to investigate the effects of TWP (as a Zn source) at four rates of 0, 9, 18 and 27 g TWP kg⁻¹ soil and Pseudomonas strains (Ctrl: without bacterial inoculation, or inoculated with B1: A5, B2: K5, B3: A2, B4: A11 or B5: D12 strain) on growth and Zn nutrition of maize. Fourteen bacterial strains were grown in liquid Pikovskayas (PVK) medium supplemented with TWP, and ten superior Pseudomonas strains with high Zn solubilization activities were selected for the subsequent Zn kinetics study. In the TWP-treated soil, the concentrations of DTPA-extractable Zn were significantly higher in inoculated treatments than those in the control treatment in all incubation times. Individual application of Pseudomonas strains or TWP treatments significantly increased the shoot biomass of maize plants. Furthermore, the combined application of Pseudomonas strains and TWP led to higher shoot Zn concentration of plants as compared to the individual applications. The highest shoot Zn concentration was observed with the use of 18 g TWP kg⁻¹ soil in treatment inoculated with B4 strain, which was 16.5-fold higher than that in the control. These findings indicate that co-application of effective Pseudomonas strains with TWP in soils can lead to higher Zn bioavailability for plants, i.e. indicating the potential of TWP as a slow-release Zn fertilizer for crops.
The aim of this research is to develop magnetically recoverable Heteropoly acid (HPA) based catalyst (Rubber-Fe3O4@SiO2@H3PMo12O40) for biodiesel production. Magnetic Rubber powder with high dispensability, porosity and magnetism were prepared by co-precipitation method and covered by silica using TEOS to form Rubber-Fe3O4@SiO2. Finally, nanostructured catalyst was prepared by impregnation of phosphomolybdic acid (PMA). The proposed catalyst was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) equipped with Dispersive Energy X-ray spectroscopy (EDS), Thermogravimetric analysis (TGA), The Brunauer-Emmett-Teller (BET) surface area analysis and vibrating sample magnetometer (VSM). The results showed the Keggin structure of the catalyst. The performance of the proposed core-shell nanocomposite to catalyze transesterification reaction was evaluated and optimized by response surface methodology (RSM). According to the results, 3 w/w %, 3 h, 12:1 and 69 °C were found as optimum values for catalyst dosage, reaction time, molar ratio of methanol to oil and reaction temperature, respectively. The production yield was higher than 85% for four runs. At the fifth try, the catalyst performance was decreased slightly to 78.87%.
Waste ground tire rubber and its ash were washed using different ratios of HNO3, H2SO4, andH2Oand the resultant solutionswere analyzed for Zn, Pb, Cd, Fe. The extracted solution with the highest Zn content was then used as a source of Zn for hydroponics-grown tomato. The highest recovery of Zn from rubber and its ash was obtained using 4 M HNO3. Two levels of Zn supplied by the ash leachate increased the plant Zn concentration compared with the control. The results showed the possibility of using acid-washing leachate of ground tire rubber and its ash as a suitable Zn source in hydroponics solutions.
Solid waste combustion and gasification has a potential for use as an alternative fuel to be used in distributed power applications. Due to the heterogeneity of the fuel it is imperative that a full understanding of the mechanism of degradation is obtained. This will ensure proper combustion and gasification design yielding the highest efficiency with the least emissions. While the major reaction sequences have been studied and identified, there is nearly no understanding of how soot precursors, such as PAH, form and react during the decomposition processes. The waste focused on for this research effort is tires. Experimental work has been carried out to characterize the thermal decomposition of the major constituents of tires and actual tire filings using Thermo-Gravimetric Analysis (TGA) in various atmospheres; 100% N 2, air, and oxygen-lean and rich air. It can be shown that the structure of the material plays a role in the amounts and types of PAHs formed. A quantitative mechanism is developed to describe the evolution of PAH in the different atmospheres during decomposition. The identities and absolute concentrations of 60 major and minor species have been established. In addition, a catalyst has been used not only to mitigate the generation of pollutants, but also to find a suitable catalyst and optimal operation condition for the prevention of air pollutants. These measurements supply information on the identities and levels of hazardous air pollutants, and provide useful data for the development and validation of detailed reaction mechanisms describing their origin and fate.
This investigation has been initiated to characterize the thermal decomposition of waste tires with Thermo-Gravimetric Analysis (TGA) in various atmospheres ranging in oxygen content; 100% N2 , 7%, 21% (air) and 30% O2 . Chemical analysis focusing on light hydrocarbons, substituted aromatics, and polycyclic aromatic hydrocarbon has been done qualitatively and quantitatively to understand the mechanism of thermal degradation of scrap tires and hazardous air pollutants such as PAH. The release of chemicals from scrap tires has been determined experimentally using Gas Chromatography/Mass Spectroscopy (GC/MS) coupled to TGA unit. The identities and absolute concentrations of over 50 major and minor species have been established. Significant volatile organic carbons (VOC) including substituted aromatics and PAH were observed between 300°C and 500°C. In addition, significant black carbon residual was observed in most environments except air and oxygen enhanced atmospheres and suggested not only the potential recovery of black carbon out of feedstock, but also the possibility of combined thermal treatment between combustion and gasification. These measurements supply information on the identities and levels of hazardous air pollutants, and provide useful new data for the development and validation of detailed reaction mechanisms describing their origin and fate. Finally, while high contents of VOC show significant potential to be utilized as an unconventional solid fuel, they also tend to generate hazardous pollutants.
The CO(2) cofeed impact on the pyrolysis of styrene butadiene rubber (SBR) was investigated using thermogravimetric analysis (TGA) coupled to online gas chromatography/mass spectroscopy (GC/MS). The direct comparison of the chemical species evolved from the thermal degradation of SBR in N(2) and CO(2) led to a preliminary mechanistic understanding of the formation and relationship of light hydrocarbons (C(1-4)), aromatic derivatives, and polycyclic aromatic hydrocarbons (PAHs), clarifying the role of CO(2) in the thermal degradation of SBR. The identification and quantification of over 50 major and minor chemical species from hydrogen and benzo[ghi]perylene were carried out experimentally in the temperature regime between 300 and 500 °C in N(2) and CO(2). The significant amounts of benzene derivatives from the direct bond dissociation of the backbone of SBR, induced by thermal degradation, provided favorable conditions for PAHs by the gas-phase addition reaction at a relatively low temperature compared to that with conventional fuels such as coal and petroleum-derived fuels. However, the formation of PAHs in a CO(2) atmosphere was decreased considerably (i.e., ∼50%) by the enhanced thermal cracking behavior, and the ultimate fates of these species were determined by different pathways in CO(2) and N(2) atmospheres. Consequently, this work has provided a new approach to mitigate PAHs by utilizing CO(2) as a reaction medium in thermochemical processes.
In fluidized bed, low-grade and waste materials are used for combustion. These fuels have high alkali, sulphur and toxic elements which on combustion produces deposition and corrosion in the system. The major problem associated with fluidized bed system is agglomeration. Fuel, ash and bed particles stick together to form bulk mass which reduces fluidization and finally shutdown the system. In this study discussion made on factors affects fluidization, combustion efficiency and emission. Identification and control techniques of agglomeration and difficulties involved in bed sulphur capture are also analyzed.
Discarded automobile tires have become a concern to the general public, largely because the growing number of stockpile fires has focused attention on the potentially harmful combustion products as well as products of incomplete combustion (PICs) emitted into the atmosphere from uncontrolled burning of scrap tires. This paper describes a small-scale combustion study that was designed to collect, identify, and quantify the products emitted during the simulated open combustion of scrap tires. During the study, it was found that total estimated emissions of semivolatile organics ranged from 10 to 50 g/kg of tire material burned. Alkyl-substituted mono- and polyaromatic hydrocarbons were the predominant emission products identified. Elevated levels of zinc and lead were also measured.
Including car, truck, bus, and airplane tires, 266 million tires were scrapped in the US in 1996 (Scrap Tire Management Council (STMC), 1997.). More than three-quarters of these tires were used as fuel, recycled for material applications, or exported. The remainder accumulates in junkyards or landfills where they pose a fire hazard and provide a breeding ground for disease carrying rodents and insects. Using information on scrap tire composition and the current markets using them, we examine the technologies used to recover their value either for energy or as rubber. As the majority of scrap tires are used as fuel, we calculate their life cycle energy budget considering both the energy consumed for tire production and the energy recovered from their use as fuel. Based on our findings, we draw some preliminary conclusions on how to maximize value recovery from this ubiquitous artifact of industrial societies.
Tire-derived fuel (TDF) was tested in a small-scale (44 kW or 150,000 Btu/hr) combustor to determine its feasibility as a fuel for use in reburning for control of nitrogen oxide (NO). TDF was gravity-fed into upward flowing combustion gases from a primary natural gas flame doped with ammonia to simulate a high NO combustion process. Emissions of NO, oxygen, carbon dioxide, carbon monoxide, and particulate matter were measured. The tests varied the nominal primary NO level from 600 to 1,200 ppm and the primary stoichiometry from 1.1 to 1.2, and used both natural gas and TDF as reburn fuels. The reburn injection rate was varied to achieve 8-20% of the total heat input from the reburn fuel. NO emissions reductions ranged between 20 and 63% when using TDF, depending upon the rate of TDF injection, primary NO, and primary stoichiometry. NO emission reductions when using natural gas as the reburn fuel were consistently higher than those when using TDF. While additional work remains to optimize the process and evaluate costs, TDF has been shown to have the potential to be a technically viable reburning fuel.
The total generation of scrap car tires throughout the world is estimated at 1000 million pieces per year which presents economic, environmental treatment and disposal problems. In the European Union, the estimated generation of scrap car tires is about 180 million per year of which 65% should be recycled by the member states. In Fnnand, the recovery percentage is about 90. There are many ways scrap car tires can be reused and these may include heat and power production, road construction, landfills, protection of sea shores from waves and so on. A cement production plant at the south-west coast of Finland has replaced traditional fossil fuel (coal and petcoke) by 10% scrap car tires. Car tires contain heavy metals. This study focuses on how toxic elements Hg and Tl can be captured as particulates in presence of Mn and Cr oxides. The shifting of gaseous phases of metals to particulate forms is more beneficial for the ecosystem because metal-containing particulates are more easily seperatable from the gas stream by the emission control equipments.
New York State Electric & Gas Corp. (NYSEG), the first utility in the state to burn scrap tires, has in the last three years burned more than 1.3 million tires to generate power. This alternate fuel saved more than 16,000 tons of coal -- close to a month's normal consumption -- at NYSEG's Jennison plant in upstate New York. Disposing of old tires is a well-known problem. NYSEG's solution was to process these tires into fuel and burn them with coal to produce electricity. The tires, when chipped into 2-in. by 2-in. chips, make a manageable and efficient fuel. With a heat value of 13,200 Btu/lb, the average 20-pound passenger car tire contains energy equal to that generated by 30 lb of coal. Besides mitigating obvious environmental problems, the bottom ash from the coal-tire mix is used as a road traction agent and the flyash is used in making cement. Burning tires as fuel saves coal and lowers fuel costs, and consequently decreases customers' energy bills.
Each year in the United States, we dispose of nearly 240 million used tires. The tires are made of oil, carbon, and steel---three valuable commodities. The possibility of using tires as a fossil-fuel supplement in stoker boilers was first explored during the worldwide oil crisis of the early 1970s TDF was initially tested in paper mills in the Pacific Northwest. Since that time, TDF has been used by paper mills and cement kilns all across North America. Inherent high heat value and low moisture content make TDF a suitable fuel to burn along with wood waste. With a volatile-to-fixed-carbon ratio of more than 2 to 1, TDF provides quick heat release to help offset the 40--55% moisture in wood waste. During the past 15 years, paper mills across the country have used TDF as a wood-waste supplement to stabilize operation of combination-fuel boilers. This paper demonstrates and quantifies the benefits of TDF as a supplementary fuel in a combination-fuel boiler.
Coal combustion byproducts (CCBs) are high-volume wastes produced by the electrical power industry and typically disposed of in landfills and lagoon impoundments. In the disposal environment, meteoric water or groundwater may percolate through and interact with the ash materials, producing leachate that contains elevated levels of many trace elements. Various geochemical reactions control the release of solutes and the formation of secondary minerals in CCB disposal facilities during weathering. Concern about the potential release of trace elements into the environment has motivated a large number of studies aimed at predicting the maximum concentrations of elements in leachate solutions. Secondary minerals formed during weathering of CCBs have the potential to limit the mobility of trace elements in an ash disposal facility. Geochemical modelling has been used by many investigators to predict the equilibrium concentrations of solutes in CCB leachate, solutions and the stable secondary minerals that will form in weathered ash. Unfortunately, basic kinetic, thermodynamic and adsorption data are lacking for many solid phases, particularly those that may contain trace elements. In addition, secondary solid phases are very difficult to identify by direct analytical methods due to their low abundances and/or amorphous character, so it is often not possible to directly determine the identity and compositions of secondary phases in ash disposal environments. Despite these difficulties, numerous secondary solid phases have been directly observed and/or predicted to form via weathering reactions in CCBs. A tabulation of all secondary phases that have formed or have the potential to form in the CCB disposal environment is given, along with the relevant references. The potential for secondary phases to sequester trace elements via precipitation, adsorption and co-precipitation is discussed. Secondary phases with the greatest potential to limit the mobility of trace elements are amorphous Fe-oxyhydroxide and amorphous aluminosilicate phases, which are metastable precursors to Fe-oxide and clay minerals, respectively.
The combustion of coal around the world for power generation produces huge volumes of fly ash. In Europe alone this amounted to about 40 Mt in 2000 of which less than 50% was utilized. The waste ends in lagoons, ash mounds, and landfill sites. Coal ashes have high concentrations of many trace elements, some of which are of environmental concern. Although the origin of elements in coals is not considered in this chapter, other aspects of the geochemistry are, and in particular the location of elements within the coal as this influences the behaviour of elements during combustion. During combustion many elements are volatile and are concentrated on the surfaces of the ash particles. Analyses of input coal and combustion residues from Eggborough power station (UK) demonstrate retention of the majority of elements in the solid combustion products, and analyses of size-fractionated fly ash have enabled the percentage surface association to be calculated, which for elements such as As and Mo is considerable. A consideration of the general leaching behaviour leads to the conclusion that it is the surface-associated elements that are most susceptible to leaching in the aqueous environment. The pH is an important control on trace element mobility in water, and in leachates from fly ash ranges from 3.3 to 12.3. High-sulphur coals generate acidic leachates, but not exclusively as the laboratory and field data demonstrate in case studies on UK coals. Batch and column leaching tests on fly ashes are reviewed and data presented for fresh fly ash and weathered fly ashes from two UK mounds dating back 17 and 40 years. The weathered ashes do have lower leachate concentrations than the fresh ash, but in spite of their ages they would not be considered to be inert. The batch leaching tests are of value in simulating high liquid-to-solid ratios encountered in ash lagoons, whereas the column leaching tests relate more closely to ash mounds. Finally, the results of field studies are reviewed and data presented for samples from boreholes in the two ash mounds. Analyses of the ash and extracted porewaters demonstrate depth-related changes due to reaction of the ash with the infiltrating water and whether or not equilibrium was established. Calculations demonstrate that the porewaters achieve saturation with respect to gypsum at depth in the boreholes. Infiltration over the years has led to detectable changes in the concentrations of some of the major elements in the bulk ash, such as Ca, and this enables realistic infiltration rates to be calculated. However, there are not comparable changes in the concentrations of the trace elements in the ash because the rate at which elements are being removed in solution is not sufficiently great.
The generation of electricity by thermal conversion of coal results in significant volumes of solid waste. Most of these materials are disposed of in surface impoundments near coal-fired power plants or in active coal mines. Disposal rates vary from country to country. In the USA, 60-70 wt% of these materials are disposed. Although these materials rarely meet the definition of hazardous, leachate tests on some coal ash have shown them capable of producing elevated concentrations of some regulated metals. As a result of the well-documented environmental concerns posed by coal combustion, and the disposal of coal combustion products (CCPs), a large body of research has focused on characterizing the mechanisms of mobilization and attenuation of trace elements in coal and its ash. However, groups opposed to coal combustion or unregulated disposal of ash overlook the value of these materials as well-proven replacements for aggregate, cement, or soil in numerous engineering and agricultural applications. An extensive body of knowledge has been gathered describing the variability and versatility of these materials. It has been shown that proper utilization or management of ash requires a good understanding of its chemical, physical, and mineralogical properties. This chapter is intended to provide a broad overview of the chemistry and mineralogy of coal, and the combustion products that are formed when coal is burned.
The study of the impact of the use of scrap tires as a fuel substitute with respect to gaseous emissions was conducted at a cement plant which produces one million tons of cement per year. This study was conducted through the modeling of the atmospheric dispersion of contaminants emitted, with the use of the ISC-ST2 software put forth by the United States' Environmental Protection Agency. The entry data required by this Gaussian model were the meteorological data, the characteristics of the source and the pollutants, the data relating to the buildings downwash effects and the location of the receptors. The simulation of the atmospheric dispersion of pollutants allows for the evaluation of daily and annual maximum concentrations as well as the localisation of the latter, which is done just as easily at a cement kiln operating with coal only or with a combination of coal and scrap tires. The analysis of the results obtained shows whether the incorporation of tires leads to an increase or a decrease in the concentration of pollutants (particulate matter, non-condensable gases, metals, hydrogen chloride, and semi-volatile compounds). Finally, it is possible to determine if the energy recovery of scrap tires used by a cement kiln meets environmental standards.
The objective of this paper is to evaluate the recycling potential of waste tires as an energy source and for use in road pavement. North Carolina, U.S.A., is used as a case study. Scrap tires may be burned for supplemental fuel in pulp and paper mill boilers and cement kilns. Five pulp and paper mill boilers in North Carolina could consume over 90% of the 6 million tires generated annually in the state. Cement kilns located within 400 km of North Carolina population centers could consume about 6.6 million tires annually. Based on the quantity of pavement laid in North Carolina, non-proprietary and proprietary versions of asphalt rubber concrete have the potential to consume 1.8 and 7.2 million tires, respectively. Rubber modified asphalt concrete has the potential to consume up to 16.5 million tires. However, technological and economic limitations suggest that large scale implementation is unlikely for the short term. Environmental considerations pertaining to each alternative are discussed. Estimates of this nature are critical as planning regions formulate solid waste management plans which include recycling.
Experimental and modeling investigations have been performed on the co-combustion of a traditional fossil fuel and a tire residue. The experimental runs have been carried out using a pilot-scale vertical furnace (0.5 MW) with a burner for pulverized solid fuels. Different conditions have been set up for the co-combustion of a medium volatile bituminous coal and a tire residue. The scope was to test the feasibility of burning secondary fuels (biomasses and residues) with coals using a low NO x burner developed for pulverized coal in the ENEL Research Centre. A co-combustion model was developed for interpreting the results and extrapolating kinetic parameters to practical conditions. It considers the effect of the particle size distribution, the different reactivity, and, in general, the different combustion behavior of each fuel fed to the furnace. The kinetic scheme adopted is simple and the introduced assumptions allow easy coupling with computational reactive fluid dynamic codes. Fuel conversion, oxygen concentration and carbon-in-ash profiles have been computed and compared with the experimental results. Quite good agreement has been obtained, allowing kinetic information to be used in more comprehensive descriptions of full-scale systems.
The trace metal loading of used car and truck tires and the fractions of the metals volatilized upon incineration of the tire were determined. INAA was chosen due to its multielement analysis capability and its low detection limit for many elements. A high purity planar germanium detector was used. Among the elements measured were, Al (4–150 g/g), Ti (41–730 g/g), V (0.04–0.4g/g), Mg (>80–580 g/g), Zn (1–2.2%) as typical concentrations; also some amounts of antimony, bromine and arsenic have been found. Major differences in elemental concentrations have been observed between the tread and the wall of a tire, and also between different brands.
What happens to car tires after they`ve exhausted their life on the road? Whether they are handed over to a tire dealer or tossed into the trash, many tires get a second life, reincarnated into products like doormats, park benches, and playground equipment. But the biggest single market for scrap tires is fuel; fuel that supplements the feedstock of paper mills, cement kilns, and even electric utility boilers. As well as offering a higher heating value than coal, tires can lower utilities` fuel costs and reduce polutant like nitrogen oxides and ash. But it`s the rare utility boiler that is amenable to burning tires successfully. 5 refs., 9 figs.
This work examined the combustion behavior (flame characteristics and temperatures) and the emissions (SO2, NO, NO2, CO, CO2, polynuclear aromatic hydrocarbons (PAH), soot and ash) from blends of a pulverized bituminous coal and ground waste automobile tires. The following fuel feed compositions were examined: 100% coal, 75–25% and 50–50% coal and tire blends, as well as 100% tire. Coal and tire particles were in the size ranges of 63–75 and 180–212 μm, respectively. Combustion of cylindrical streams of particles look place under steady flow conditions, in an electrically-heated drop-tube furnace in air, at a gas temperature of 1150°C and a particle heating rate of ≈105°C/s, The bulk equivalence ratio, φ, in the furnace was varied in the range of 0.5 to 2, by varying the particle mass loading. Combustion observations on burning clouds of particles were conducted with simultaneous pyrometry and cinematography. Interparticle flame interactions were visually observed mostly in the near-stoichiometric and fuel-rich regions. Volatile flame interactions were apparent at a lower φ for tire crumb particles than for coal particles and became progressively more intense with increasing φ until, at sufficiently high φs large group flames formed for tire particles. As particle flame interactions increased, average maximum temperatures in the flame decreased. Coal particles resisted the formation of group flames, even at high φs. Such observations correlated with the trends observed for the PAH emissions of the two fuels, those of tire crumb being much higher than those of coal and commencing at a lower φ. A certain degree of stratification in the combustion of blends of particles of the two fuels was observed. This kept the PAH emissions at levels much lower than those expected based on the weighted average emissions of the two fuels. NOx emissions from tires were much lower than those of coal, while those of the blends were close to the weighted average emissions. Combustion or fuel blends in the two aforementioned particle size cuts, generated the lowest NOx emissions when the small coal particles were combined with either the small or the large tire particles. SO2 emissions from the blends were found to be close to the weighted average emissions of the two fuels. Blending coal with tire reduced the CO2 emissions of coal but increasedtheCO emissions. CO emissions were significant only in the fuelrich region. Tire ash was of similar size and shape as the parent tire particles themselves. To the contrary, the ash of coal was polydisperse, including large cenospheres and tiny particle fragments. Particulate emissions (soot and ash), measured in the range of 0.4 to Sum, increased with φ. Generally, tire produced more mass of submicron particulates than coal. Particulate emissions of blends of the two fuels were close to those expected based on weighted average of the two.fuels,
The present work outlines the main results of a full-scale study conducted on the utilization of waste tires as auxiliary fuel in cement production. Experimental tests were conducted for determining the influence of shredded tires on combustion conditions, emissions produced, and the characteristics of clinker obtained, for feeding ratios over 35% in terms of total heat input. The addition of tire chips did not lead to any appreciable modification in either the whole process or the quality of clinker produced; gaseous emissions were mostly unaffected, with significant improvements related to the reductions obtained in nitrogen and sulfur oxides concentrations. Experimental findings from tests conducted with tire chips exposed to kiln combustion flue gases compare favorably with the typical burnout times derived from theoretical approaches. These experimental data and calculations to estimate particle trajectories beyond the injection point, through proper theoretical analysis of the kinetic behavior, result in important indications for the shredding operation and for optimum injection modes.
The objective of this work is the characterization of the solid conversion product from coal−tire copyrolysis because, nowadays, any new process should be faced without resolving the problem of the subproducts generated. A low-rank coal and a nonspecific mixture of scrap automotive tires, 50/50 w/w, have been coprocessed at 400 °C for 30 min at different H2 pressures and atmospheres. Once the most valuable conversion products, the liquids, were recovered by tetrahydrofuran extraction, a complementary battery of analytical techniques was applied to characterize the solids or chars, looking for their possible use. 13C nuclear magnetic resonance, infrared, immediate and ultimate analyses, ASA, and scanning electron microscopy−energy-dispersive X-ray spectrometry were performed on them. By X-ray diffractometry the presence of sphalerite, pyrrhotite, and anhydrite was detected. Thermogravimetric studies demonstrated that the combustion induction temperature is 400 °C. Char combustion tests at 900 °C with discussion of NOx, SOx, and polycyclic aromatic hydrocarbon emissions are included. Mineral matter behaves as if only coal is processed with the Zn exception, from ZnO in the tire, which is converted into ZnS. It is shown that the char organic component has a higher aromaticity than the one from coal.
Waste tire combustion in an atmospheric fluidized-bed (AFB) reactor (7 cm i.d., 76 cm height) has been performed in a laboratory plant with the aim of studying the polycyclic aromatic hydrocarbon (PAH) emissions as a function of combustion temperature. The main aim has been to compare these organic emissions with the ones obtained when coal is burned at the same combustion conditions. PAH emissions have been analyzed in solids collected in two cyclons at the exit of the reactor and in a trap system formed by a condenser, a filter (20 μm), and an adsorbent. After PAH extraction with dimethylformamide (DMF) by sonication, fluorescence spectroscopy in the synchronous mode (FS) has been used as an analytical technique to quantify the PAHs emitted. It could be concluded that higher PAH emissions are generated when this waste material is burnt at the same conditions used for coal atmospheric fluidized-bed combustion (AFBC).
Results are presented on the correlation of the emissions of carbon monoxide (CO) and polynuclear aromatic hydrocarbons (PAH) from the combustion of pulverized bituminous coal and tire-derived fuel. The particle size cuts of coal and tire crumb were 63−75 and 180−212 μm, respectively. Combustion experiments were conducted in laboratory-scale facilities under controlled conditions. The relation between CO and PAH species in the combustion effluent was investigated at drop-tube furnace gas temperatures, in the range of 1000−1300 °C, and several fuel mass loadings in the furnace, expressed in terms of bulk equivalence ratios in the range of 0.7−2.4. Up to 60 two−seven ring PAH compounds were detected by capillary gas chromatography−mass spectrometry (GC−MS) techniques. Results showed that both CO and PAH emission yields increased with increasing bulk equivalence ratio (in the aforementioned range) at a fixed gas temperature. The CO and especially the PAH yields from tire-derived fuel were much higher than those from coal, but the relative amounts of individual PAH components were remarkably similar in the combustion effluent of the two fuels. At fixed bulk equivalence ratios, however, as the furnace gas temperature increased the PAH yields from both fuels decreased drastically, while the CO yields increased. At the highest temperature tested herein (1300 °C), the effluent of the combustion of both fuels was practically devoid of PAHs [at a detection limit of 0.7 μg of a PAH component/g of fuel burnt]. Reasons for the observed increase in CO with temperature are discussed. CO2 and NOx emission yields were also monitored, and the results are reported herein.
Comparative results are presented on the combustion and toxic emissions (SO2, NOx, CO, and PAHs) from a pulverized bituminous coal and ground waste automobile tires. The combustion behavior of single particles in the range of 60−212 μm was monitored pyrometricaly and cinematographically, at a gas tem perature of 1150 °C and a heating rate of ≈105 °C/s. Tire particles burned faster (by a factor of 2−3) than similar size coal. Coal particles experienced distinct devolatilization and char combustion stages. Upon intense volatile combustion, the chars of tire particles burned accompanied by secondary devolatilization that aided the burnout of their carbon black residue. No soot appeared to escape the volatile flame envelope. The SO2 emissions from the combustion of steady-flow clouds (aerosols) of tire and coal particles were comparable (within a factor of 2), the NOx emissions of tires were lower than those of coal by a factor of 3−4, reflecting their lower fuel nitrogen content. Insignificant amounts of CO were detected in the effluent of both fuels at fuel-lean or stoichiometric conditions. CO sharply increased in fuel-rich combustion, while NOx emissions decreased. No polynuclear aromatic hydrocarbon (PAH) emissions were detected in the effluent of fuel-lean and stoichiometric combustion of clouds of coal particles at a furnace gas residence time of 0.75 s. Even at mildly fuel-rich conditions, 1.0 < φ < 1.8, only small amounts of PAHs were detected in the effluent of burning coal particles. At higher equivalence ratios, φ, PAH emissions increased sharply. Combustion of clouds of tire particles produced no detectable PAHs at φ < 0.6, but as stoichiometry was approached or exceeded, the PAH emissions increased substantially. Thus, the onset of detectable PAH emissions occurred at lower φ for tires than for coal. Beyond that point, the PAH emissions of both fuels increased exponentially in fuel-rich combustion, asymptotically reaching the pyrolytic gas-phase PAH emissions in N2. Individual gas-phase PAH emissions of tires were 1.5−2 times higher than those of coal at comparable fuel-rich φ and were 1.5−10 times higher under pyrolytic conditions, where maximum amounts were recorded. Similar trends were observed in the condensed-phase PAH emissions of both fuels; however, the highest yield was obtained under oxygen-starved oxidative environments. Differences in the PAH emission tendencies of the two fuels were amplified when combustion took place in fixed beds. Coal burned relatively clean, while tire crumb emitted copious amounts of smoke and PAHs, with individual compounds dramatically exceeding (by 10−100 times) those from burning pulverized coal.
A comparative study on FBC of coal and waste tire was performed from an environmental point of view. A sub-bituminous coal and a nonspecific waste tire blend were used, respectively, as fossil and nonfossil fuels in a fluidized bed combustion (FBC) experimental laboratory installation. The same FBC conditions were carried out keeping constant the air total flow (860 L/h), the percentage of excess oxygen (20%), and varying the combustion temperature (650, 750, 850, and 950 °C). The main objective was to establish the influence of the fuel used in PAH formation and emission. Regarding the PAH formation and emission in FBC, this is the first time that emissions from coal and waste tire combustion are compared. The PAH were collected in different traps and extracted with dimethylformamide (DMF). PAH analysis and quantification were determined by fluorescence spectroscopy in the synchronous mode (FS). Data on polycyclic aromatic hydrocarbons (PAH) are reported and the results obtained show the following: (1) Independently of the combustion temperature, a drastic increase in PAH emissions is obtained when tire is used instead of coal at the same conditions. In this case, the PAH formation and emission seem to be promoted. (2) The pyrolytic process and the interaction between radicals in the mechanisms implied in PAH formation are highly important. (3) The combustion temperature influence is more remarkable in tire combustion than in coal combustion. In the first one, the lowest PAH emissions are obtained at low combustion temperatures (750 °C) while for coal, the highest PAH emissions appear in the range of 750−850 °C.
As a fuel, scrap tires are an economically viable choice to supplement existing sources. In addition, policies promoting the use of scrap tires as a fuel can reduce their potential for creating environmental hazards. For example, when in stockpiles, scrap tires cause emissions of toxic compounds from arson-caused fires, and can be a breeding ground for disease-carrying insects. The growing number of industrial applications where scrap tires can serve as a supplemental fuel includes cement kilns, the pulp and paper industry, and utility boilers.
Over the past decade, there have been a number of emissions studies on scrap tire and tire-derived fuel (TDF) supplemented combustion. In many cases, co-combustion with TDF has been shown to decrease emissions. This paper summarizes how supplementing combustion with TDF affects emissions of different pollutants.
Scrap tire and TDF combustion are not currently regulated by a specific New Source Performance Standards (NSPS) or Most Achievable Control Technology (MACT) standard because they typically regulate an emission unit, not a fuel type. The United States Environmental Protection Agency (EPA) is currently debating how to regulate facilities that supplement their combustion with scrap tires. This paper discusses some of those options.
This is a laboratory study on the combustion emissions from pulverized solid fuels: NOx (NO and NO2), SO2, CO and CO2. Coal, waste tire crumb and waste plastics, such as poly(styrene), poly(ethylene), poly(methyl methacrylate), poly(propylene) and poly(vinyl chloride) (PVC), were burned in an electrically heated drop-tube furnace at high particle heating rates (104-105 K s−1) and elevated gas temperatures (1300–1600 K). The fuel to air bulk equivalence ratio, φ, was varied in the range of 0.4–1.8. Air or a nitrogen-free mixture of O2CO2Ar were used as oxidizing gases. Results showed that fuels which contain nitrogen generated the highest NOx emissions. Combustion of coal generated four times more NOx than combustion of tire crumb, in proportion to their nitrogen content, and ten times more NOx than that of the nitrogen-free plastics. The specific NOx emissions decreased dramatically (3–6 times) with increasing bulk equivalence ratio for all fuels. However, the NO2/NO ratio increased with the equivalence ratio in the fuel-rich region. Increasing the gas temperature, in the range 1300–1600 K, resulted in 10–25% more NOx, depending on the fuel. Atmospheric nitrogen contributed 20% of the total NOx emissions for coal, 30% for tires and 100% for the plastics. SO2 emissions of the particular coal and tire crumb tested were comparable. While absolute SO2 emissions of coal and tire increased with the equivalence ratio, specific emissions exhibited a mild downward trend. SO2 emissions were higher in the absence of atmospheric nitrogen, especially at fuel-rich conditions. Mild emissions of CO were encountered in the fuel-lean regions, but they increased exponentially in the fuel-rich region accounting for as much as 10% of the carbon at φ = 2. Overall, the CO2 emissions were proportional to the carbon content of the fuels.
Approximately 70,000 tons of slags, containing a high concentration of fine-grained carbon and heavy metals were accumulated in the town of Belovo (Kemerovo region, Russia) as a result of Zn-smelting between 1950 and 1994. Spontaneous ignition of fine-grained carbonaceous material and the subsequent burning of the waste heaps produced a zoning pattern which is characterized by three types of altered waste material: burned (or pyrometamorphic) waste, metamorphosed waste, and weakly altered waste. The self-combustion process is the reason for a redistribution of various elements. Leaching tests were carried out to understand the behavior of soluble (extracted by distilled water) and mobile (extracted by 1N HCl) metal forms; water analyses were performed using atomic absorption spectroscopy. The mobile metal species were accumulated close to the combustion center, in the burned and metamorphosed waste. In contrast to this, the soluble species were precipitated further away from the combustion center, on the surface of the waste heaps near active fumaroles, which provide evidence for ongoing combustion in the interior parts of the heaps. These observations are confirmed by mineralogical studies using routine mineralogical techniques: elementary copper and newly formed zincite and willemite are found in the burned and thermally metamorphosed waste, whereas soluble sulfates of Cu, Zn and Fe were deposited in the weakly altered zones near the surface of the waste heaps. The relative ability of the studied elements to migrate, determined as the proportion of the mobile or soluble to total metal concentrations, decreases in the order Cd>Zn>Cu>Pb>Fe for both the soluble and mobile forms. Primary metal-bearing waste material appears to be more resistant to weathering than the secondary phases formed as a result of combustion. Every hour, drainage waters remove about 3 kg Zn and 2 kg Cu from the waste heaps.
Comparative combustion studies were performed on particles obtained from pulverized bituminous coal and waste automobile tyres (rubber). Particle size cuts of 75–90 and 180–212 μm were burned in a thermogravimetric analyser, at low heating rates, and in an electrically heated drop-tube furnace, at high heating rates. The combustion of individual particles in the drop-tube furnace was observed with three-colour pyrometry, to obtain time-temperature histories and with high-speed cinematography to record flame particle size histories. Combustion was conducted at a gas temperature of 1450 K, in air. Upon pyrolysis, the phenomena of melting, swelling and formation of large blowholes were observed only in the case of the coal particles. The tyre particles formed chars with rough surfaces and smaller blowholes. Separate volatile and char combustion phases were detected for the coal particles studied. Tyre particles experienced an intense primary volatile combustion phase, followed by a phase of simultaneous secondary volatile combustion, of lesser intensity, and char combustion. During the initial volatile phase combustion, the peak flame temperatures were comparable for both materials, in the range 2200–2400 K. The secondary volatile/char combustion phase, observed for the type particles, was cooler, i.e. 2000–2100 K. The coal chars burned with temperatures of 1850–2000 K. Combustion was diffusionally controlled (regime III) for coal chars of both sizes and for tyre chars of the larger size cut only. Char burnout times were considerably shorter for tyre particles than coal, which can be attributed to the secondary devolatilization and the lower density of the former.
Discarded tires have been a disposal problem and continue to accumulate throughout the world today. In the United States, in particular, over 279 million discarded tires are being added to an estimated 2 billion tires currently stockpiled around the country. The stockpiled tires provide breeding sites for mosquitoes which can spread diseases and often constitute fire hazards. Utilization of discarded tires would minimize environmental impact and maximize conservation of natural resources. Current practice includes retreading, recycling as crumb rubber, and combustion for thermal energy. A literature review was made to compare the discarded tire recycling practices in the United States, Japan and Korea.
A western Kentucky power plant conducted a series of test burns with coal+tire-derived fuel (tdf) and coal+tire-derived fuel+petroleum coke blends. Collections of fuel, fly ash, and bottom ash/slag were made from the cyclone-fired unit under four fuel combinations: coal, coal+ca. 1% tdf, coal+ca. 3% tdf, and coal+ca. 3% tdf+petroleum coke. Fly ash carbons derived from the three fuel types can be distinguished, allowing an assessment of the impact of co-combustion on fly ash quality. While certain aspects of the ash chemistry are distinctive, Zn increasing in tdf-derived fly ash and Ni and V increasing in petroleum coke-derived fly ash, changes in the coal source between sampling dates complicate the assessment of the chemistry.
The nature and causes of the scrap tire problem are examined from the viewpoint of the discipline of economics rather than a technological perspective. State governmental responses to the problem and commonly proposed remedies are briefly reviewed and the nature of the tire market's failure to prevent the scrap tire problem is examined in order to gain insight into effective and efficient corrections, without involving direct governmental participation in funding of recycling, market development and technology selection. Those functions remain in the private sector. The role of government suggested is the traditional one: that of setting the market “rules of the game”. A completely market-based mechanism involving a tire disposal fee that remains wholly in the private sector is developed for dealing with new scrappage and a method is suggested by which to calculate a cost-effective disposal fee. This article will be of interest to state and local environmental officials concerned with the tire problem and who wish an understanding of the fundamental causes of the problem.
Shredded scrap automotive tyres were pyrolysed in a static batch reactor in a stream of nitrogen. The products were passed directly to a second heated reactor, where secondary reactions of the pyrolysis vapours occurred. The condensed tyre pyrolysis oil, after secondary reaction, was analysed for the content of polycyclic aromatic hydrocarbons (PAH). The concentration of PAH in the oil was high, reaching over 10% of the total mass of derived oil. Individual PAH of known carcinogenic or mutagenic activity, for example benzo[a]pyrene, benzo[e]pyrene, chrysene and fluoranthene, were present in significant concentrations. The concentration of PAH were found to increase with increasing secondary reaction temperature, the formation of PAH occurring via a Diels-Alder type reaction involving the aromatization of olefinic compounds. The derived tyre pyrolysis oil represents a significant health hazard.
Tire debris contains significant quantities of zinc (Zn), and there is concern about the diffuse Zn contamination of soils from tire wear. An experiment was set up to quantify the fate and effect of Zn from tire debris in soil. Two different soils were mixed with the <100-microm fraction of car and truck tire debris (25 g kg(-1) soil) or zinc sulfate (ZnSO4) as a reference. Soils were transferred to soil columns with free drainage and placed outdoors for 11 months. Leachates of the tire debris amended soils did not contain significantly (P>0.05) more Zn than control soils except for a 3-fold increase in one soil amended with cartire debris. The increase in Zn leaching due to tire debris was only 3% of the corresponding increase in the ZnSO4 treatment at the same total Zn in soil. Tire debris application increased the soil nitrification potential, whereas ZnSO4 application, at corresponding or smaller total Zn concentration, decreased nitrification potential. An increase in soil pH was observed in all soils treated with tire debris and explains the increased nitrification potential. About 10-40% of the Zn from tire debris was isotopically exchangeable in soil sampled after 1 year weathering. It is concluded that a significant fraction of Zn is released from the rubber matrix within 1 year, but the parallel increase in soil pH limits the mobilization of Zn in soil.
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