Gasification and smelting system using oxygen blowing for plastic waste including polyvinyl chloride

A new type of waste gasification and smelting system using oxygen blowing based on high-temperature metallurgy, was developed by Sumitomo Metals, Japan. This system can steadily gasify and melt not only municipal waste, but also plastic waste and polyvinyl chloride (PVC) waste by using a top-blow oxygen lance together with sideways-blow oxygen lances. As a result of gasification in the high-temperature reducing atmosphere and rapid gas cooling, dioxin-free, high-calorie purified gas was produced. Ash components in the wastes were smelted in a high-temperature reducing atmosphere, and high-quality slag free of heavy metals was produced. Most of the chlorine in the wastes was converted into hydrogen chloride in the off gas. The hydrogen chloride can be recovered as hydrochloric acid or chlorine, which are recyclable to PVC manufacturing.     

Development of a catalytic dehalogenation (Cl,Br) process for municipal waste plastic-derived oil

Dehalogenation is a key technology in the feedstock recycling of mixed halogenated waste plastics. In this study, two different methods were used to clarify the effectiveness of our proposed catalytic dehalogenation process using various carbon composites of iron oxides and calcium carbonate as the catalyst/sorbent. The first approach (a two-step process) was to develop a process for the thermal degradation of mixed halogenated waste plastics, and also develop dehalogenation catalysts for the catalytic dehydrochlorination of organic chlorine compounds from mixed plastic-derived oil containing polyvinyl chloride (PVC) using a fixed-bed flow-type reactor. The second approach (a single-step process) was the simultaneous degradation and dehalogenation of chlorinated (PVC) and brominated (plastic containing brominated flame retardant, HIPS–Br) mixed plastics into halogen-free liquid products. We report on a catalytic dehalogenation process for the chlorinated and brominated organic compounds formed by the pyrolysis of PVC and brominated flame retardant (HIPS–Br) mixed waste plastics [(polyethylene (PE), polypropylene (PP), and polystyrene (PS)], and also other plastics. During dehydrohalogenation, the iron- and calcium-based catalysts were transformed into their corresponding halides, which are also very active in the dehydrohalogenation of organic halogenated compounds. The halogen-free plastic-derived oil (PDO) can be used as a fuel oil or feedstock in refineries.     

Upgrading of poly(vinyl chloride) by chemical modifications using sodium sulfide

The recycling of poly(vinyl chloride) (PVC) is one of the most important issues in the treatment of waste plastics. To improve PVC recycling, it is necessary to develop new recycling techniques, including new techniques for the dechlorination of chlorine-containing polymers. It has been established that wet dechlorination of PVC in NaOH/ethylene glycol solution is more effective than dry dechlorination. In this study, the wet process was used, and the chemical modification of PVC by nucleophilic substitution was considered for upgrading waste PVC. Chlorine was substituted in solution by several nucleophilic reagents, thus changing the properties of PVC. The reaction of PVC in Na2S/ethylene glycol solution at 170°C resulted in the formation of a mixture comprising 32% elimination and 26% substitution products. The scanning electron microscopy/energy dispersive X-ray spectroscopy mappings and elementary analysis of PVC indicated that this chlorine-substitution process led to cross-linking by sulfur.     

Decreased PCDD/F formation when co-firing a waste fuel and biomass in a CFB boiler by addition of sulphates or municipal sewage sludge

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are formed during waste incineration and in waste-to-energy boilers. Incomplete combustion, too short residence times at low combustion temperatures (<700 °C), incineration of electronic waste and plastic waste containing chlorine are all factors influencing the formation of PCDD/Fs in boilers. The impact of chlorine and catalysing metals (such as copper and iron) in the fuel on PCDD/F formation was studied in a 12 MW_th circulating fluidised bed (CFB) boiler. The PCDD/F concentrations in the raw gas after the convection pass of the boiler and in the fly ashes were compared. The fuel types were a so-called clean biomass with low content of chlorine, biomass with enhanced content of chlorine from supply of PVC, and solid recovered fuel (SRF) which is a waste fuel containing higher concentrations of both chlorine, and catalysing metals. The PCDD/F formation increased for the biomass with enhanced chlorine content and it was significantly reduced in the raw gas as well as in the fly ashes by injection of ammonium sulphate. A link, the alkali chloride track, is demonstrated between the level of alkali chlorides in the gas phase, the chlorine content in the deposits in the convection pass and finally the PCDD/F formation. The formation of PCDD/Fs was also significantly reduced during co-combustion of SRF with municipal sewage sludge (MSS) compared to when SRF was fired without MSS as additional fuel.     

Determination of total chlorine and bromine in solid wastes by sintering and inductively coupled plasma-sector field mass spectrometry

A sample preparation method based on sintering, followed by analysis by inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) for the simultaneous determination of chloride and bromide in diverse and mixed solid wastes, has been evaluated. Samples and reference materials of known composition were mixed with a sintering agent containing Na₂CO₃ and ZnO and placed in an oven at 560 °C for 1 h. After cooling, the residues were leached with water prior to a cation-exchange assisted clean-up. Alternatively, a simple microwave-assisted digestion using only nitric acid was applied for comparison. Thereafter the samples were prepared for quantitative analysis by ICP-SFMS. The sintering method was evaluated by analysis of certified reference materials (CRMs) and by comparison with US EPA Method 5050 and ion chromatography with good agreement. Median RSDs for the sintering method were determined to 10% for both chlorine and bromine, and median recovery to 96% and 97%, respectively. Limits of detection (LODs) were 200 mg/kg for chlorine and 20 mg/kg for bromine. It was concluded that the sintering method is suitable for chlorine and bromine determination in several matrices like sewage sludge, plastics, and edible waste, as well as for waste mixtures. The sintering method was also applied for determination of other elements present in anionic forms, such as sulfur, arsenic, selenium and iodine.     

Simultaneous treatment of PVC and oyster-shell wastes by mechanochemical means

This work presents a new process for dechlorinating poly-vinyl chloride (PVC) by the use of oyster-shell waste. The process consists of milling of PVC waste with oyster-shell waste, followed by washing the milled sample with water. The milling of PVC and oyster-shell mixture results in size reduction and rupture in bonds, leading to mechanically induced reactions between the two to form CaCl2 and hydrocarbon with C=C bonds. Washing the milled mixtures with water at room temperature allows complete removal of chlorine from the milled sample. More than 95% of chlorine in PVC was removed when 2h grinding is conducted for the mixture. The present process could offer a potential route to the handling and disposal of oyster-shell and PVC wastes.     

Studies on the dechlorination and oil-production technology of waste plastics

 Recycle technology for waste plastics containing polyvinyl chloride (PVC) has been developed in the Hokkaido National Industrial Research Institute for the production of solid and liquid fuel, and has established a recycling process which includes a dechlorination process for PVC plastics, and a two-stage catalytic pyrolysis process for plastics using zeolite catalysts. The dechlorination equipment consists of a two-axis screw extruder with a heating element, which can remove chlorine up to 99.9 wt. % from PVC containing plastics as hydrogen chloride. The product had about 44 000 kJ/kg calorific value and was fed into the next oil production process, although it could also be used as a solid fuel. Natural and synthetic zeolite were used as catalysts for the two-stage catalytic process, which produced a light oil with a boiling point which was between those of kerosene and gasoline. The yield of this oil reached 82 wt. %. The chemical type was analyzed using liquid chromatography, and was found to have many aromatic compounds. These technologies make it possible to produce a nonpolluting, high-calorie solid fuel and a liquid fuel very efficiently. Received: July 19, 2000 / Accepted: September 21, 2000     

Examination of the influence of dissolved halite (NaCl) on the leaching of lead (Pb) from cement-based solidified wastes

The leaching of lead from cement-based solidified waste forms mixed at different water/cement ratios was studied by conducting equilibrium and semi-dynamic leaching tests using deionized water and sodium chloride solutions. The results suggest that leaching of the primary constituents of the cement (calcium, silicon and sulfate) is controlled by solubility equilibria, with increased leaching into chloride solutions due to ionic strength effects. The original porosity of the waste forms increased with water/cement ratio and chloride solutions further increased it as a result of decalcification. Lead leaching was generally low, and appears to be a transport-controlled process, such that leaching correlates positively with porosity.     

Study on dechlorination technology for municipal waste plastics containing polyvinyl chloride and polyethylene terephthalate

It is necessary to remove chlorine efficiently from municipal waste plastics (MWP) that contain polyvinyl chloride (PVC) and other plastics containing chlorine. In this article we consider thermal degradation liquefaction technology. In Japan, the chlorine content of reclamation oil products must be kept below 100 ppm owing to the quality standard for pyrolysis oil. Liquefaction dechlorination technology for MWP is still an important issue to study. The twin-screw extruder that has been developed as dechlorination technology for blast furnaces and coke ovens has a shorter residence time for dechlorination than other dechlorination technologies. In this article, we used a single-screw extruder for the dechlorination process because it also has a short residence time. Experiments on the dechlorination process were carried out by using a single-screw extruder to assess its dechlorination performance. Practical use of the single-screw was demonstrated by the operation of a commercial oil reclamation plant operated by Sapporo Plastic Recycle Co., Ltd. (SPR). Moreover, an investigation of cascade recycling was carried out in 2008 in which material recycle wastes were mixed with MWP and processed by chemical recycling (liquefaction). It was demonstrated that cascade recycling is an efficient recycling combination and contributes to local feedstock recycling. However, it was shown that MR wastes affect the quality of the reclamation oil when they make up more than 40% of the feed mix. If the quantity of MR wastes is kept below 40%, the reclamation oil is able to meet the quality standard. The SPR plant can be operated safely and in a stable manner.     

Waste plastics recycling by an entrained-flow gasifier

We studied an entrained-flow gasification process which efficiently converts waste plastics to energy at a high energy recovery rate. Waste plastics, after being shredded to <8 mm or <14 mm, were fed into an entrained-flow gasifier with air and oxygen. In the gasifier, organic substances were pyrolyzed, partially combusted, and then converted into synthetic gas (CO, H₂) at a high temperature (over 1600 K). The clarified gasification characteristics were that the lower heat value (LHV) of the product gas was over 4.2 MJ/Nm³ and the cold gas efficiency was approximately 60%. Other inert substances in the wastes such as ashes and metals were melted into slag and condensed on bag filters. The bag filters and a water scrubber removed impurities such as dusts, heavy metals, and hydrogen halides from the product gases. Solid hydrocarbons, which include char and soot, were removed at a hot cyclone and on the bag filters. Received: July 19, 2000 / Accepted: October 3, 2000     

Kinetics of thermal de-chlorination of PVC under pyrolytic conditions

Although PVC-containing wastes are an important potential source of energy they are frequently disposed in landfill. In thermal treatment processes such as pyrolysis and gasification, the presence of poly(vinyl chloride) (PVC), a compound with 56.7% of chlorine, may cause problems concerned with environmental protection, as consequence of the formation of hydrochloric acid, chlorine gas and dioxins, as well as corrosion phenomena of the reactor/equipment materials. Thus, a possible solution may involve a previous removal of the chlorine from PVC containing waste through a pyrolysis process at low temperatures before the material being submitted to a subsequent thermal treatment, for energetic valorization. In this work, a kinetic model for the thermal decomposition of PVC has been developed, in view of its de-chlorination. DTA/TGA testing at different temperatures indicated a first order reaction and an activation energy of 133,800J/mol. An almost completed de-chlorination reaction was obtained at 340°C under an inert atmosphere. The resulted material is a C(n)H(n) type polymer with potential to be used in an energy recovery process. Validation test performed at laboratory scale indicate that the temperature of 340°C enables the removal of ～99.9% of the chlorine present in PVC. The chloride can be fixed in the form of an aqueous solution of HCl or calcium chloride, driving to an alternative full process with environmental benefits and reduction of the costs associated to the PCV - containing materials/wastes management.     

Bio-drying and size sorting of municipal solid waste with high water content for improving energy recovery

Bio-drying can enhance the sortability and heating value of municipal solid waste (MSW), consequently improving energy recovery. Bio-drying followed by size sorting was adopted for MSW with high water content to improve its combustibility and reduce potential environmental pollution during the follow-up incineration. The effects of bio-drying and waste particle size on heating values, acid gas and heavy metal emission potential were investigated. The results show that, the water content of MSW decreased from 73.0% to 48.3% after bio-drying, whereas its lower heating value (LHV) increased by 157%. The heavy metal concentrations increased by around 60% due to the loss of dry materials mainly resulting from biodegradation of food residues. The bio-dried waste fractions with particle size higher than 45 mm were mainly composed of plastics and papers, and were preferable for the production of refuse derived fuel (RDF) in view of higher LHV as well as lower heavy metal concentration and emission. However, due to the higher chlorine content and HCl emission potential, attention should be paid to acid gas and dioxin pollution control. Although LHVs of the waste fractions with size <45 mm increased by around 2× after bio-drying, they were still below the quality standards for RDF and much higher heavy metal pollution potential was observed. Different incineration strategies could be adopted for different particle size fractions of MSW, regarding to their combustibility and pollution property.     

Production of high quality syngas from argon/water plasma gasification of biomass and waste

Extremely hot thermal plasma was used for the gasification of biomass (spruce sawdust, wood pellets) and waste (waste plastics, pyrolysis oil). The plasma was produced by a plasma torch with DC electric arc using unique hybrid stabilization. The torch input power of 100–110 kW and the mass flow rate of the gasified materials of tens kg/h was set up during experiments. Produced synthetic gas featured very high content of hydrogen and carbon monoxide (together approximately 90%) that is in a good agreement with theory. High quality of the produced gas is given by extreme parameters of used plasma – composition, very high temperature and low mass flow rate.     

Influence of bromine on metal volatilization in waste combustion

Co-combustion tests of municipal solid waste and bromine-containing waste plastics have been performed in the TAMARA test incinerator in order to investigate the fate of bromine in waste combustion. HBr is the main bromine combustion product. Approximately 50% of the bromine inventory stays in the grate ashes, which is much more than is found for chlorine. The percentage of bromine transferred into the fly ash also exceeds that of chlorine. There is a strong indication that bromine has a promoting effect upon the volatility of most of the heavy metals that are typically mobilized by chlorine. Received: February 2, 2000 / Accepted: March 3, 2000     

Two-stage Sequential Electrochemical Treatment of Nitrate Brine Wastes

Nitrates in concentrated brines can be electrochemically reduced in the cathodic chamber of a split-cell electrochemical reactor with formation of ammonium (and small amounts of nitrite). Fortunately, ammonium may be electrochemically oxidized to nitrogen gas in the anodic reaction chamber if a coupled sequential process is used. The presence of chloride in the brine waste is an important consideration in oxidative electrochemical processes, however, because it cycles through oxidized and reduced states at the electrode surfaces and in the bulk solution. Electrochemical oxidation converts chloride ions to “active chlorine” species with additional oxidizing capability (chlorine, hypochlorous acid and hypochlorite – essentially bleach), as well as to chlorates, depending on the reaction conditions. The production of these active species improves treatment performance in the ammonium oxidation phase since oxidation is no longer limited to the electrode surface. However, the process must be engineered to minimize loss of process efficiency due to parasitic side reactions (chloramines and chlorate). In this study, two-stage batch electrolysis was conducted using a three-electrode (copper anode, platinum-coated titanium cathode, silver/silver chloride reference) electrochemical cell, with the anodic and cathodic chambers separated by a Nafion 117 membrane. Treatment of nitrate and ammonium was tested with and without the presence of chloride in the waste. No significant difference was observed in cathodic nitrate reduction with chloride present or absent. However, the presence of chloride in the solution favored overall soluble nitrogen elimination upon oxidation. Increasing applied current increased production of undesirable byproducts (especially chlorate).     

Waste plastics recycling process using coke ovens

The Japan Iron and Steel Federation (JISF), as its voluntary energy-saving action plan, proposed a 10% energy reduction by 2010 with 1990 as the basis. Further, it has suggested an additional 1.5% energy saving by the use of waste plastics as a metallurgical raw material. The amount of processing of waste plastics which corresponds to this amount of energy conversion is about 1 million t scale during 1 year. Conventional known methods for recycle-processing of waste plastics include, for example, the method of injection into a blast furnace to use waste plastics as an iron-ore reducing agent instead of coal. On the other hand, the coking process is considered to be suitable as a waste plastic recycling facility because the process involves coal carbonization in a high-temperature and reducing atmosphere. Carbonization tests with mixed waste plastics were conducted with laboratory equipment and in actual coke ovens. As a result, it was confirmed that the waste plastics recycling process using coke ovens is feasible. Therefore, a waste plastics recycling process using coke ovens was started as a chemical recycling technology at Nippon Steel.     

Influence of poly(bisphenol A carbonate) and poly(ethylene terephthalate) on poly(vinyl chloride) dehydrochlorination

Recycling of poly(vinyl chloride) (PVC) waste is a serious problem because of its high chlorine content. Dehydrochlorination of PVC-containing polymer waste produces solid residue char, for which conversion to pyrolysis oil in a petrochemical plant seems to be an attractive way of recycling PVC waste. Unfortunately, some polymer admixtures react with HCl and cause formation of chloroorganic compounds in a char. This article describes the influence of polycarbonates and poly(ethylene terephthalate) on thermal feedstock recycling of PVC wastes using a two-stage method. It was found that the presence of polycarbonate causes the formation of small amounts of benzyl chloride and other chloroaryl or chloroalkylaryl compounds. Poly(ethylene terephthalate) interacts with HCl forming significant amounts of various chlorocompounds – mainly chloroethyl esters of terephthalic and benzoic acids, but derivatives possessing chlorine directly connected to the aromatic ring are also formed.     

Surface ozonation of polyvinyl chloride for its separation from waste plastic mixture by froth floatation

Selective surface modification of polyvinyl chloride (PVC) by ozonation was evaluated to facilitate the separation of PVC from other heavy plastics with almost the same density as PVC, especially polyethylene terephthalate (PET), by the froth flotation process. The optimum froth flotation conditions were investigated, and it was found that at 40°C, 90% of PVC and PET plastics floated. The bubble size became larger and the area covered with bubbles on the plastic surface was reduced with increasing temperature. Optimum PVC separation was achieved with the flotation solution at 40°C and mixing at 180–200 rpm, even for sheet samples 10 mm in size. Combined treatment by ozonation and froth flotation is a simple, effective, and inexpensive method for PVC separation from waste plastics.     

氯气泄漏扩散过程及后果评价的研究现状分析

综述了氯气泄漏扩散过程及后果评价的研究成果。从现场试验、实验室模拟和数学模拟三方面分析了氯气泄漏扩散各研究方法的优势和局限性。强调了氯气泄漏扩散后果评价的必要性。指出:必须针对中国特有的一些重气扩散建立专属知识产权的数学模型;不同层次数学模型的精度皆有待于进一步提高;需加强基于特定数学模型的全过程统一界面模拟程序的开发。     

Improved quartz furnace method for chlorine and sulfur determination in municipal solid waste

 A method of determining the chlorine (Cl) and sulfur (S) in municipal solid waste (MSW) was studied. The quartz furnace method was improved in two ways: recovery from ash by hot extraction with dilute nitric acid, and avoidance of the volatilization of alkali (earth) metal chlorides by setting the sample combustion temperature at 600°C. In a comparison with the bomb method, using nine sets of kitchen garbage and waste plastics, the bomb method yielded a 15%–25% lower value than the improved quartz furnace method. Combustion in the bomb was frequently incomplete, resulting in recovery losses of Cl and S. The average kitchen garbage involved 5.2 mg Cl/g, of which at least 24.1% would be converted to HCl. Plastics contained 23 mg Cl/g generating 88.1% HCl on average. In the same way, kitchen garbage contained 3.0 mg S/g, generating 52.3% SO _x , whereas plastics contained 1.1 mg S/g with 55.1% SO _x formation. Received: March 20, 2002 / Accepted: October 13, 2002