Influences of chlorine content on emission of HCl and organic compounds in waste incineration using fluidized beds

Factors affecting the durability of dimethyl dithiocarbamate-stabilized air pollution control (APC) residues derived from municipal solid waste incineration

Sodium dimethyl dithiocarbamate (SDD) is widely used for stabilizing heavy metals to minimize pollution from air pollution control (APC) residues derived from municipal solid waste incineration. However, the effect of environmental conditions on heavy metal leaching from SDD-stabilized APC residues remains unknown. Therefore, this study aimed to evaluate the durability of SDD-stabilized APC residues and determine the relationship between heavy metal leaching and environmental factors, including pH, temperature, and oxygen. The results revealed that accelerated SDD decomposition and the decline in durability of SDD-stabilized APC residues were caused by acidic and aerated conditions and temperatures above 40 °C. A decrease in pH from 12.25 to 4.69 increased the Cd and Pb concentrations in SDD-stabilized APC residue leachate from below detection (0.002 mg/L) to 1.32 mg/L and 0.04 mg/L to 3.79 mg/L, respectively. Heating at 100 °C for 2 d increased the Cd and Pb concentrations from below detection (0.002 mg/L and 0.01 mg/L) to 2.96 mg/L and 0.47 mg/L, respectively. Aeration for 5 d increased the Cd and Pb concentrations from below detection to 0.09 mg/L and 0.49 mg/L, respectively. The decline in durability was attributed to acid hydrolysis, thermal decomposition, and oxidative damage of SDD, resulting in breakage of the chelated sulfur-metal bond, which was confirmed by the decrease in the oxidizable fraction of heavy metals and the SDD content. This study improves the understanding of the factors contributing to the decline in durability of heavy metals in SDD-stabilized APC residues, which is important for ensuring the long-term stabilization and environmental safety of these residues.

Acid gas emission and ash fusion characteristics of multi-component leather solid waste incineration in bubbling fluidized bed

The tanning sludge (TS) and other tanning solid wastes are produced in significant quantities by the leather industry. To evaluate the combustion properties, acid gaseous pollutant conversion, and ash management, co-firing of TS with various wastes was investigated in a bubbling fluidized bed. TG-FTIR test indicated that tanning solid wastes had superior combustion properties and include more gaseous pollutants than TS. The leather mixed solid waste (LMSW) formed by mixing had better fuel characteristics than TS. The conversion rates of SO2 and HCl of LMSW incineration were 67% and 40%, respectively. The co-combustion of TS and solid wastes reduces the conversion rate of acid gas. Increasing the proportion of high-inorganic chlorine raw material could further reduce the conversion rate and increase the ash fusion temperature appropriately. Because ash and slag were primarily composed of Ca and Fe elements, the addition of calcium carbonate (CaCO3) can increase ash melting point while reducing acid gas emissions. When CaCO3 was added at a calcium to sulfur (Ca/S) ratio of 2, the acid gas emission was reduced by more than 80% and the softening temperature was raised by 90 °C. When Ca/S is greater than 2, the economics of adding CaCO3 decreased.

Mechanochemical Degradation of Poly(vinyl chloride) into Nontoxic Water-Soluble Products via Sequential Dechlorination, Heterolytic Oxirane Ring-Opening, and Hydrolysis

As one of the most widely used commodity plastics, poly(vinyl chloride) (PVC) is extensively used worldwide, yet is difficult to recycle and is often discarded immediately after use. Its end-of-life treatment often generates toxic hydrogen chloride and dioxins that pose a critical threat to ecosystems. To address this challenge, the mechanochemical degradation of PVC into water-soluble biocompatible products is presented herein. Oxirane mechanophores are strategically introduced into the polymeric backbone via sequential dechlorination followed by epoxidation. The oxirane mechanophore in the polymer backbone undergoes a force-induced heterolytic ring-opening to carbonyl ylide intermediates, which eventually generates acetals during the course of the reaction. The subsequent hydrolysis of the backbone acetals affords the scission of the polymeric chain into water-soluble low-molecular-weight fragments. Combined with its low cytotoxicity and phytotoxicity, this solvent-free mechanochemical degradation process offers a green alternative for the degradation of PVC.

Bottom slag-to-flue gas controls on S and Cl from co-combustion of textile dyeing sludge and waste biochar: Their interactions with temperature, atmosphere, and blend ratio

S and Cl distribution patterns and their evolution pathways were quantified during the co-combustions of textile dyeing sludge (TDS) and waste biochar (BC). S in the flue gas rose from 10.60% at 700 °C to 45.09% at 1000 °C for the mono-combustion of TDS in the air atmosphere. At 1000 °C, S in the bottom slag and flue gas grew by 2.65% and fell by 2.11%, respectively, for the TDS mono-combustion in the 30%O₂/70%CO₂ atmosphere. The 40% BC addition increased the S retention in the bottom slag by 30.39% and decreased its release to the flue gas by 34.50% by changing the evolution of CaSO₄ and enabling more K to fix S as K₂SO₄. The decomposition of inorganic Cl was the main source of the Cl-containing gases. The 20%O₂/80%CO₂ atmosphere (36.29%) and 40% BC addition (27.26%) had higher Cl in the bottom slag than did TDS mono-combusted at 1000 °C (25.60%) by inhibiting the decomposition of organic Cl. Our study provides insights into the co-combustion of TDS and BC and controls on S and Cl for a cleaner production. Future research remains to conducted to verify scale-up experiments.

Do FeCl3 and FeCl3/CaO conditioners change pyrolysis and incineration performances, emissions, and elemental fates of textile dyeing sludge?

The pyrolysis and incineration performances of sulfur-rich textile dyeing sludge (TDSS) were determined in response to the additions of FeCl₃ or FeCl₃ + CaO. The emissions of eight air pollutants from the incineration and pyrolysis were systematically identified. The 3-to-8% FeCl₃ additions increased the comprehensive combustibility index by 2.14 and 1.62 times, respectively, as opposed to the 5-to-10% FeCl₃ + 8-to-15% CaO additions. The CaO addition inhibited the TDSS incineration, while the FeCl₃ addition increased HCl emission. NO_x, SO₂, and H₂S emissions decreased initially and increased between 600 and 950 °C. SO₂ and NO_x emissions rose with FeCl₃ but FeCl₃ + CaO. FeCl₃ catalyzed NO_x, while CaO retained SO₂. The main pyrolysis gas/liquid products were alkane, alkenes, nitrile, heterocyclic compounds, benzene, and its derivatives. Benzene and its derivatives accounted for 55.33% of the control group and 42.25-57.23% of the treatment groups. The FeCl₃ and FeCl₃ + CaO additions did not significantly influence the pyrolysis products. The measured versus thermodynamically simulated SO_x and HCl emissions were consistent. Neural network-based simultaneous optimizations of the non-linear dynamics of eight kinds of gases pointed to 50% and 14.4% reductions in the emissions and the pyrolytic temperature, respectively, with the 3% FeCl₃, relative to the control.

Occurrence, profiles, and control of unintentional POPs in the steelmaking industry: A review

The steelmaking industry is an important source of unintentionally produced persistent organic pollutants (UP-POPs). This review summarizes the emission levels, characteristics, and formation mechanisms of UP-POPs, including halogenated dioxins, polychlorinated biphenyls, polychlorinated naphthalenes, and penta- and hexa- chlorobenzenes in the steelmaking industry to improve our understanding of the emissions of UP-POPs from the steelmaking industry. The factors influencing UP-POP formation during the iron ore sintering (IOS) process are also reviewed. The raw materials and temperature during the steelmaking process are important factors influencing UP-POP generation. Raw materials containing plastics, paints, cutting oil, rubber, and iron from electronic waste recycling can contribute to high emissions of UP-POPs during steelmaking processes. Electrostatic precipitator dust contains chlorine, carbon, and metals, which are usually recycled as a component of the raw material, and could also promote dioxin formation and emissions from IOS. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are easily formed in high concentrations at temperatures in the range of 200 °C-650 °C. This review also provides a comprehensive summary of the UP-POP emission limits in the steel industry worldwide and the best available techniques and environmental practices for UP-POP emission reduction. The information in this review will be useful for the reduction of UP-POPs in the steelmaking process.

Combustion performance and emissions from torrefied and water washed biomass using a kg-scale burner

This study investigates wastes and biomass as alternative fuels in a kg-scale burner in terms of combustion characteristics and emissions. Water washing, torrefaction, and their combination are used to improve the properties of the wastes and biomass. The air pollutants in the exhaust of the burner are also analyzed. It could be concluded that the reactivity and average heat supply from the pretreatment are improved significantly. The improvement ratio of average heat supply can be up to 103.5 %, stemming from water-soluble ash removal during water washing. Torrefaction can lift the average heat supply due to the increment of fixed carbon content in the fuels, but it reduces the reactivity owing to the decrement of volatile matters. Most of the raw or pretreated materials can be directly combusted, as a result of lower regulated air pollutants (e.g., NO_x, SO₂, CO) from them than from coal. Water washing can successfully remove chlorine in the wastes by dissolution since most of the chlorine in the wastes are in salt form. The chlorine reduction significantly reduces the HCl concentration (55-58 % reduction efficiency) and the toxicity concentration of polychlorinated dibenzo-p-dioxins and dibenzofurans (78-84 %), while torrefaction increases the toxicity concentration owing to the de novo synthesis.

Practical dechlorination of polyvinyl chloride wastes in NaOH/ethylene glycol using an up-scale ball mill reactor and validation by discrete element method simulations

To avoid the formation of undesired Cl compounds during polyvinyl chloride (PVC) wastes treatment and facilitate the recycling of valuable NaCl and dechlorinated hydrocarbons as feedstocks, advanced dechlorination (de-Cl) process should be developed. Here, an up-scale ball mill reactor was established for the de-Cl of real PVC wastes, including sealing strips from waste refrigerators and crushed cable coverings from waste cables. The effects of NaOH on de-Cl were validated with lab-scale studies and the influences of mechanical conditions were innovatively investigated. A maximum de-Cl degree of 99% was obtained with 1 M NaOH in ethylene glycol for sealing strips, whereas a maximum de-Cl degree of 92% was obtained with Φ1.27 cm stainless steel balls at a moderate rotation speed for cable coverings. The remaining Cl content in the sample residues was small and decreased with decreasing residue size, resulting in minimum contents of 0.49% and 0.61% for sealing strips and cable coverings, respectively. The de-Cl behavior was consistent with a shrinking-core model and the meaning of kinetic parameters was illustrated. The ball milling process was simulated by discrete element method (DEM). A positive correlation was observed between the apparent rate constant of the experimental de-Cl process and the specific impact energy calculated using DEM simulations. The combined experimental and simulation approach suggested that the surface of PVC is first dechlorinated and then crushed into fine particles by ball milling to expose the inner unreacted surface. For industrial application, the balance of chemical and mechanical conditions should be optimized.

Seasonal characterization and dosimetry-assisted risk assessment of indoor particulate matter (PM10-2.5, PM2.5-0.25, and PM0.25) collected in different schools

Inhalation of particulate matter (PM) has been linked to serious adverse health effects, such as asthma, cardiovascular diseases and lung cancer. In the present study, coarse (PM_10-2.5), accumulation mode (PM_2.5-0.25), and quasi-ultrafine (PM_0.25) particulates were collected inside twelve educative centers of Tarragona County (Catalonia, Spain) during two seasons (cold and warm). Chemical characterization of PM, as well as risk assessment were subsequently conducted in order to evaluate respiratory and digestive risks during school time for children. Levels and chemical composition of PM were very different among the 12 centers. Average PM levels were higher during the cold season, as well as the concentrations of most toxic metals. In most schools, PM levels were below the daily PM₁₀ threshold established in the regulation (50 μg/m³), with the exception of school number 1 during the cold season. On average, and regardless of season, coarse PM was highly influenced by mineral matter, while organic matter and elemental carbon were prevalent in quasi-ultrafine PM. The concentrations of the toxic elements considered by the legislation (As, Cd, Pb, and Ni) were below their correspondent regulatory annual limits. Calculated risks were below the safety thresholds, being fine fractions (PM_2.5-0.25 and PM_0.25) the main contributors to both digestive and respiratory risks.

Separation mechanism of polyvinyl chloride and copper components from swollen electric cables by mechanical agitation

In this study, a high-accuracy separation process is proposed for recycling pure polyvinyl chloride (PVC) and Cu from the thin electric cables of electrical, electronic, and automotive wastes by PVC swelling and mechanical agitation in hydrophobic organic solvent mixed with water. The high stirring speed and low blade height combined with proper blade type and reactor tank shape ensure a separation rate of over 98%. By conducting computational fluid dynamic and discrete element model simulations, quantitative force, fluid velocity, and data visualization analyses were performed. The obtained separation rate exhibited strong positive correlations with the resultant, drag, and centripetal forces at various stirring speeds and blade heights. Using the experimental and simulation data, a plausible separation mechanism was suggested. It was found that Cu pieces could slip out from swollen PVC covers under the action of external forces, while the stirring speed should be high enough to apply sufficient external forces to cables via either blade-to-cable collisions or fluid drag. Furthermore, the vertical motion of cables induced by the low blade height was essential because the rotation in the bottom reactor part inhibited the slipping of Cu pieces.

Estimating source strengths of HCl and SO2 emissions in the flue gas from waste incineration

HCl and SO₂ emission is one of the major concerns related to municipal solid waste incinerator (MSWI). In this study, a material flow analysis model was developed to estimate the HCl and SO₂ concentrations in the MSWI flue gases (FGs), and their concentrations in the full-scale MSWI were monitored. The calculated concentrations of HCl and SO₂ in the FG were 770-1300 mg/Nm³ and 150-640 mg/Nm³, respectively, in close agreement with the monitored values. More than 99% of Cl and 92% of S from the FG were captured into solid residues by the air pollution control (APC) systems. Moreover, since only 48.4%-67.5% of Cl and 21.3%-53.4% of S were transferred to the FG from the municipal solid waste (MSW), it was more reliable to estimate the source strengths and release amounts of HCl and SO₂ in the FG based on the amounts of Cl and S in the APC residues (AR) and exhaust gas rather than in the MSW. This simple method is easily applicable and the estimated results could provide scientific basis for the appropriate design and operation of the APC systems as well as corrosion control of heat recovery systems.

The impact of hydrochloric acid on the catalytic destruction behavior of 1,2-dichlorbenzene and PCDD/Fs in the presence of VWTi catalysts

Catalytic oxidation is regarded an effective technique to control the emissions of chlorinated benzenes (CBzs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from waste incinerators. Among the numerous factors affecting the degradation efficiency of CBzs and PCDD/Fs, limited attention has been paid to the impact of hydrochloric acid (HCl) present in the flue gas. This study investigates how HCl affects the catalytic degradation of 1,2-dichlorbenzene (1,2-DCBz) at different reaction times and temperature regimes. The results showed that the removal efficiency of 1,2-DCBz, which was achieved by the V₂O₅/WO₃-TiO₂ (VWTi) catalyst, decreased the largest by 10% in the presence of HCl. Furthermore, it was found that the increasing concentration of water vapor hindered the degradation efficiency of 1,2-DCBz. No relationship between the process temperature and the destruction efficiency of PCDD/Fs was observed in the presence of HCl. Potential increasing of the removal efficiency of 1,2-DCBz was confirmed by adding different amount of activated carbon (AC) in the presence of HCl.

Status and perspectives of municipal solid waste incineration in China: A comparison with developed regions

With the rapid expansion of municipal solid waste (MSW) incineration, the applicability, technical status, and future improvement of MSW incineration attract much attention in China. This paper aims to be a sensible response, with the aid of a comparison between China and some representative developed regions including the EU, the U.S., Japan, South Korea, and Taiwan area. A large number of up-to-date data and information are collected to quantitatively and impartially support the comparison, which covers a wider range of key points including spatial distribution, temporal evolution, technologies, emissions, and perspectives. Analysis results show that MSW incineration is not an outdated choice; however, policy making should prevent the potentially insufficient utilization of MSW incinerators. The structure of MSW incineration technologies is changing in China. The ratio of plants using fluidized bed is decreasing due to various realistic reasons. Decision-makers would select suitable combustion technologies by comprehensive assessments, rather than just by costs. Air pollution control systems are improved with the implementation of China's new emission standard. However, MSW incineration in China is currently blamed for substandard emissions. The reasons include the particular elemental compositions of Chinese MSW, the lack of operating experience, deficient fund for compliance with the emission standard, and the lack of reliable supervisory measures. Some perspectives and suggestions from both technical and managerial aspects are given for the compliance with the emission standard. This paper can provide strategic enlightenments for MSW management in China and other developing countries.

HCl removal performance of Mg-stabilized carbide slag from carbonation/calcination cycles for CO2 capture

Synthetic MgO/CaO sorbent prepared by industrial waste (carbide slag) experiencing various CO₂ capture cycles can effectively capture HCl.

Potential PM2.5 impacts of festival-related burning and other inputs on air quality in an urban area of southern Taiwan

The Mid-Autumn Festival (MAF), or Moon Festival, is a harvest festival in Taiwan, celebrated by families across the island with evening barbecues outside. This study investigated the potential impact of these activities on the air quality in Tainan, a city in southern Taiwan. Fine particulate matter (PM2.5) was examined in the period leading up to the MAF (pre-MAF), during the Festival (MAF), after the Festival (post-MAF), and in the period after this (a period of moderate air quality: MAQ). Gaseous pollutants in PM2.5 were, from highest to lowest mean concentration, NH3, SO2, HCl, HNO3, HNO2, and oxalic acid, while inorganic salts were mainly in the form of the photochemical products SO4(2-), NH4(+), and NO3(-). These inorganic salts accounted for 37.6%-44.5% of the PM2.5 mass concentration, while a further 26.3%-42.8% of the PM2.5 mass was total carbon (TC). TC was mostly composed of organic carbon (OC) produced by photochemical reactions. Of this, 9.8%-14.9% was carboxylates, of which oxalate was the most abundant compound, accounting for 22.8%-31.9% of carboxylates. The presence of phthalates in the PM2.5 indicated emissions from the plastics industry. Although a noticeable amount of aerosol was produced by festival activities and burning of softwood and hardwood, onshore air currents during the festival prevented potential high aerosol loading. During the moderate air quality period following post-MAF, the concentration of total carbohydrates was 1.44-2.64 times the amount during the festival. Levoglucosan and myo-inositol accounted for 81.7%-89.6% of the total carbohydrate concentration. The average Levo/Manno ratio was 18.64 ± 5.24. The concentration of levoglucosan was closely related to that of PO4(3-), erythritol, and galactose. Backward trajectories indicated that biomass burning in China affected the air quality of Tainan City.

HCl and PCDD/Fs emission characteristics from incineration of source-classified combustible solid waste in fluidized bed

Adding different quantities of CaO in combustible solid waste can inhibit the production of PCDD/Fs during incineration.

Behavior of TiO₂ nanoparticles during incineration of solid paint waste: a lab-scale test

In order to assess the potential impacts posed by products containing engineered nanoparticles, it is essential to generate more data about the release of these particles from products' life cycle. Although first studies were performed to investigate the release of nanoparticles from use phase, very few data are available on the potential release from recycling or disposal of nano-enhanced products. In this work, we investigated the behavior of TiO2 nanoparticles from incineration of solid paint waste containing these particles. Solid paint debris with and without TiO2 nanoparticles were treated in a lab scale incineration plant at 950°C (combustion temperature) and in oxidizing atmosphere. The obtained ashes were also vitrified with additives and the release of Ti was finally evaluated by leaching test. From our incineration lab-scale experiment, we did not observe a release of TiO2 nanoparticles into the atmosphere, and Ti was attached to the surface of obtained solid residues (i.e. ashes). The characterization of ashes showed that TiO2 nanoparticles reacted during the incineration to give calcium titanate. Finally, a very low release of Ti was measured, less 1 mg/kg, during the leaching test of ashes vitrified with glass cullet and feldspathic inert. Our work suggests that TiO2 nanoparticles added in paints may undergo to physicochemical transformation during the incineration, and that Ti found in ashes may be strongly immobilized in glass matrix. Since this conclusion is based on lab-scale experiment, further research is required to identify which nanoparticles will be emitted to the environment from a real-word-incineration system of household hazardous waste.

Optimization for municipal solid waste treatment based on energy consumption and contaminant emission

This paper analyzes the characterization of energy consumption and contaminant emissions from a municipal solid waste (MSW) treatment system that comprises transfer station, landfill site, combustion plant, composting plant, dejecta treatment station, and an integrated MSW treatment plant. The consumed energy and energy medium materials were integrated under comprehensive energy consumption (CEC) for comparison. Among typical MSW disposal methods such as combustion, composting, and landfilling, landfilling has the minimum CEC value. Installing an integrated treatment plant is the recommended MSW management method because of its lower CEC. Furthermore, this method is used to ensure process centralization. In landfill sites, a positive linear correlation was observed between the CEC and contaminant removal ratios when emitted pollutants have a certain weight coefficient. The process should utilize the minimum CEC value of 5.3702 kgce/t MSW and consider energy consumption, energy recovery, MSW components, and the equivalent of carbon dioxide emissions.

The reduction of dioxin emissions from the processes of heat and power generation

The first reports that it is possible to emit dioxins from the heat and power generation sector are from the beginning of the 1980s. Detailed research proved that the emission of dioxins might occur during combustion of hard coal, brown coal, and furnace oil as well as coke-oven gas. The emission of dioxins occurs in wood incineration; wood that is clean and understood as biomass; or, in particular, wood waste (polluted). This paper thoroughly discusses the mechanism of dioxin formation in thermal processes, first and foremost in combustion processes. The parameters influencing the quantity of dioxins formed and the dependence of their quantity on the conditions of combustion are highlighted. Furthermore, the methods of reducing dioxin emissions from combustion processes (primary and secondary) are discussed. The most efficacious methods that may find application in the heat and power generation sector are proposed; this is relevant from the point of view of the implementation of the Stockholm Convention resolutions in Poland with regard to persistent organic pollutants.

Emission characteristics of dioxins, furans and polycyclic aromatic hydrocarbons during fluidized-bed combustion of sewage sludge

Pre-dried sewage sludge with high sulfur content was combusted in an electrically heated lab-scale fluidized-bed incinerator. The emission characteristics of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polycyclic aromatic hydrocarbons (PAHs) were studied. Coal and calcium oxide (CaO) were added during the sewage sludge combustion tests to optimize combustion conditions and control SO2 emission. The results indicated that the flue gases emitted during mono-combustion of sewage sludge were characterized by relatively high concentrations of SO2, NOx and organic pollutants, due to the high sulfur, nitrogen, and volatile matter content of sewage sludge. The total 16 USEPA priority PAHs and 2,3,7,8-substituted PCDD/Fs produced from sewage sludge combustion were found to be 106.14 microg/m3 and 8955.93 pg/m3 in the flue gas, respectively. In the case of co-combustion with coal (m(sludge)/m(coal) = 1:1), the 16 PAHs and 2,3,7,8-substituted PCDD/Fs concentrations were markedly lower than those found during mono-combustion of sewage sludge. During co-combustion, a suppressant effect of CaO on PCDD/Fs formation was observed.

The prospect and development of incinerators for municipal solid waste treatment and characteristics of their pollutants in Taiwan

Taiwan is a small, densely populated island with unique experiences in the construction and operation of incinerators. In such a small area, Taiwan has built 22 incinerators over a short span of time, combusting large amount of municipal solid waste as much as 23,250 tons per day. This study focuses on the history of construction and development of incinerators in Taiwan as well as the characteristics of pollutants, such as heavy metals (Pb, Cd, and Hg), acid gases (NO _x , SO _x , CO, and HCl), and dioxins emitted from the incinerators. Furthermore, the study also covers the generation and composition of municipal solid waste (MSW), and the production of energy in Taiwan. According to Taiwan's data on pollutant emissions, the emission level of pollutants is under control and meets the stringent regulations of Taiwan Environmental Protection Administration (TEPA). Researches have shown that using air pollution control devices (APCDs) in the operation of incinerators provides effective measures for air pollutant control in Taiwan. The main advantage of using incinerators is the generation of electricity (waste-to-energy) during the incineration of municipal solid waste, producing energy that can be consumed by the general public and the industry. Taiwan's extensive experience in incinerator construction and operation may serve as an example for developing countries in devising waste treatment technology, energy recovery, and the control of contagious viral diseases.