Characterization of products obtained from pyrolysis and steam gasification of wood waste,RDF, and RPF

Pyrolysis and steam gasification of woody biomass chip (WBC) obtained from construction and demolition wastes, refuse-derived fuel (RDF), and refuse paper and plastic fuel (RPF) were performed at various temperatures using a lab-scale instrument. The gas, liquid, and solid products were examined to determine their generation amounts, properties, and the carbon balance between raw material and products.The amount of product gas and its hydrogen concentration showed a considerable difference depending on pyrolysis and steam gasification at higher temperature. The reaction of steam and solid product, char, contributed to an increase in gas amount and hydrogen concentration. The amount of liquid products generated greatly depended on temperature rather than pyrolysis or steam gasification. The compositions of liquid product varied relying on raw materials used at 500 °C but the polycyclic aromatic hydrocarbons became the major compounds at 900 °C irrespective of the raw materials used. Almost fixed carbon (FC) of raw materials remained as solid products under pyrolysis condition whereas FC started to decompose at 700 °C under steam gasification condition.For WBC, both char utilization by pyrolysis at low temperature (500 °C) and syngas recovery by steam gasification at higher temperature (900 °C) might be practical options. From the results of carbon balance of RDF and RPF, it was confirmed that the carbon conversion to liquid products conspicuously increased as the amount of plastic increased in the raw material. To recover feedstock from RPF, pyrolysis for oil recovery at low temperature (500 °C) might be one of viable options. Steam gasification at 900 °C could be an option but the method of tar reforming (e.g. catalyst utilization) should be considered.     

Production of gaseous fuel from refuse plastic fuel via co-pyrolysis using low-quality coal and catalytic steam gasification

In this study, refuse plastic fuel (RPF) was copyrolyzed with low-quality coal and was gasified in the presence of a metal catalyst and steam. Some metal catalysts, such as Ni, NiO, and Mg, and mixtures of these with base promoters such as Al₂O₃ and Fe₂O₃ were employed in the pyrolysis and gasification processes to convert the synthesis gas into more valuable fuel gas. The operating temperatures for the pyrolysis and gasification were between 700° and 1000°C. The experimental parameters were the operating temperature, catalyst type, basic promoter type, and steam injection amount. Solid fuel samples (5 g) were fed into a semibatch-type quartz tube reactor when the reactor reached the designated temperature. The synthesis gas was analyzed by gas chromatography. The use of low-quality coal as fuel in co-pyrolysis with RPF was explored. For the co-pyrolysis of RPF and low-quality coal, the effectiveness of the catalysts for fuel gas production followed the order Mg > NiO > Ni. In catalytic gasification of RPF, the addition of Al₂O₃ seemed to reduce the activity of the corresponding catalysts Ni and Mg. The maximum fuel gas yield (92.6%) was attained when Mg/Fe₂O₃ was used in steam gasification at 1000°C.     

Hydrogen-rich fuel gas production from refuse plastic fuel pyrolysis and steam gasification

In this study, experimental conditions were optimized to maximize the production of hydrogen gas from refuse plastic fuel (RPF) by pyrolysis and steam gasification processes conducted in a laboratory-scale reactor. We carried out gasification using 10-g RPF samples at different temperatures (700°-1000°C) with and without steam. The effect of the amount of steam (0–0.25 g/min) for RPF steam gasification was also studied. The effect of K₂CO₃ as a catalyst on these processes was also investigated. Experimental results showed that the hydrogen gas yield increased with temperature; with respect to the gas composition, the hydrogen content increased mainly at the expense of other gaseous compounds, which highlights the major extension of secondary cracking reactions in the gaseous fraction at higher temperatures.     

Co-gasification of wood and polyethylene with the aim of CO and H2 production

This article describes the gasification of polyethylene–wood mixtures to form syngas (H₂ and CO) with the aim of feedstock recycling via direct fermentation of syngas to ethanol. The aim was to determine the effects of four process parameters on process properties that give insight into the efficiency of gasification in general, and particularly into the optimum gasification conditions for the production of ethanol by fermentation of producer gas. Gasification experiments (fluidized bed, 800°–950°C) were done under different conditions to optimize the composition of syngas suitable for fermentation purposes. The data obtained were used for statistical analysis and modeling. In this way, the effect of each parameter on the process properties was determined and the model was used to predict the optimum gasification conditions. The parameters varied during the experiment were gasification temperature, equivalence ratio, the ratio of plastic to wood in the feed, and the amount of steam added to the process. The response models obtained proved to be statistically significant in the experimental domain. The optimum gasification conditions for maximization of carbon monoxide and hydrogen production were identified. The conditions are: temperature 900°C, equivalence ratio 0.15, amount of plastic in the feed 0.11 g/g feed, and amount of steam added 0.42 g/g feed. These optimum conditions are at the edge of the present experimental domain. The maximum combined CO and H₂ efficiency was 42%, and for the maximum yield of CO and H₂ it is necessary to minimize the polyethylene content, minimize the added steam and the equivalence ratio, and maximize temperature.     

Gasification of waste plastics by steam reforming in a fluidized bed

The process of producing synthetic gas from waste plastics by steam reforming was investigated. To evaluate this process, the steam reforming of the oils derived from low-density polyethylene and polystyrene were carried out using a laboratory-scale fluidized bed of Ni-Al₂O₃ catalysts. The performance of gasification in terms of carbon conversion, gas yield, and gas compositions was examined. Although oils derived from plastics contain many kinds of heavy hydrocarbons and aromatics, they were well gasified at temperatures above 1023 K with a steam/carbon ratio of 3.5 and a weight hourly space velocity of 1 h⁻¹. The hydrogen content of the product gas was very high at approximately 72 vol% for polyethylene-derived oil and 68 vol% for polystyrene-derived oil. These compositions agreed well with the values calculated from chemical equilibrium.     

Steam gasification of epoxy circuit board in the presence of carbonates

To recover useful metals from end-of-life electronic devices and to convert plastic components from these devices into clean fuel gas, steam gasification of epoxy board samples was carried out at 600–700?°C and 0.1?MPa pressure in the presence of a ternary eutectic carbonate (lithium carbonate, sodium carbonate, and potassium carbonate). Hydrogen and carbon dioxide were the main products, and methane and carbon monoxide were detected as minor products. The gasification proceeded in two steps: an initial rapid pyrolysis followed by secondary steam gasification of char produced from the pyrolysis. The ternary eutectic carbonate accelerated not only the latter steam gasification but also the initial rapid pyrolysis. The activation energy for the steam gasification of epoxy board samples in the presence of the carbonate was 122?kJ/mol.     

Catalytic gasification of tars from a dumping site

The work deals with catalytic gasification, pyrolysis and non-catalytic gasification of tar from an industrial dumping site. All experiments were carried out in a vertical stainless steel gasification reactor at 800 °C. Crushed calcined dolomite was used as the gasification catalyst. Parameters such as addition of water and air, and the influence of the catalyst in regard to the composition of the process gas were investigated. The catalytic gasification experiment in the steady state produced process gas with the composition: 56 % of H₂, 9 % of CO, 11 % of CH₄ and 12 % of CO₂ (mol.%). Concentration of the C₂ fraction was lower than 1 mol.%. Volume flow of air was later changed from 120 to 230 ml min^?1 reducing the amount of hydrogen to 51 mol.% and that of methane to 10 mol.%. Process gas created in a non-catalytic gasification process contained 26–30 mol.% of methane, 13–15 mol.% of carbon monoxide and 15–17 mol.% of the C₂ fraction and lower amounts of hydrogen (20 mol.%) and carbon dioxide (2–3 mol.%). The highest apparent conversion of tar was reached in the catalytic gasification processes. A higher rate of catalyst deactivation can be observed when water or air is not added.     

Production of hydrogen by steam gasification of dehydrochlorinated poly(vinyl chloride) or activated carbon in the presence of various alkali compounds

Steam gasification of dehydrochlorinated poly(vinyl chloride) (PVC) or activated carbon was carried out in the presence of various alkali compounds at 3.0 MPa and 560°C–660°C in a batch reactor or in a semi-batch reactor with a flow of nitrogen and steam. Hydrogen and sodium carbonate were the main products, and methane and carbon dioxide were the minor products. Yields of hydrogen were high in the presence of sodium hydroxide and potassium hydroxide. The acceleration effect of the alkali compounds on the gasification reaction was as follows: KOH > NaOH > Ca(OH)₂ > Na₂CO₃. The rate of gasification increased with increasing partial steam pressure and NaOH/C molar ratio. However, the rate became saturated at a molar ratio of NaOH/C greater than 2.0.     

钙基固定剂对制氢和污染性气体减排的影响

在未来相当长的一段时间内,煤气化仍是大规模制取氢气的主要途径。目前,常规煤气化过程得到的是H2、CO和CO2为主的混合气,需要通过净化、变换和分离工艺才能得到洁净的氢气,工艺过程复杂。采用连续式超临界水反应装置,以质量分数为20%的水煤浆为反应原料,考察了Ca/C摩尔比和温度对褐煤制氢系统的影响。试验结果表明：Ca（OH）2不仅可以很好地固定气相中的CO2和硫化物,而且对煤气化过程也表现出较好的催化作用。反应温度600℃,压力为25MPa的条件下,与未加Ca（OH）2相比,Ca/C摩尔比为0.45时,气体中CO2的体积分数由50.7%降至1.0%,趋于完全固定;硫化物浓度由10 878mg/m3降至807mg/m3;H2的体积分数由32.4%增至73.3%。Ca（OH）2对煤气化的催化作用在高温下更加明显。     

Catalyst durability in steam reforming of thermally decomposed waste wood

Thermal gasification and reforming technologies applicable over a wide temperature range were investigated for high efficiency and for the calorific value of the gas evolved from organic waste such as woody debris. The durability of the reforming catalyst and the availability of catalyst regeneration were investigated using laboratory-scale catalytic reformers and a gasifier. Commercial Ni-based catalyst and calcined limestone (CaO) were applied to the reforming reaction. The results of woody waste gasification and reforming revealed the hydrogen concentration produced to be sustained at a high catalyst temperature of 1123 K, which prevented the catalyst from deactivating. The results also indicated that catalyst regeneration by air oxidation at the same temperature would be effective for enhancing catalytic activity.     

Influence of mixed molten carbonate composition on hydrogen formation by steam gasification

Steam gasification in the presence of carbonate compounds is an effective method to recover useful materials from electronic waste streams by converting plastics into gaseous products that can be used for energy production and avoiding the expensive manual disassembly process. We investigated steam gasification of activated carbon in the presence of various mixtures of lithium carbonate, sodium carbonate, and potassium carbonate. The activated carbon was almost completely converted into hydrogen and carbon dioxide at 700°C under 0.1 MPa pressure in the presence of carbonate mixtures. Carbon dioxide was also derived from partial decomposition of lithium carbonate. Steam gasification was accelerated in the presence of various carbonate mixtures and at increasing steam partial pressures. These experimental results show that fluidity of carbonates, the potassium content of the carbonate, and the steam partial pressure are important factors in accelerating steam gasification.     

Energy recovery from solid waste fuels using advanced gasification technology

Since the mid-1980s, TPS Termiska Processer AB has been working on the development of an atmospheric-pressure gasification process. A major aim at the start of this work was the generation of fuel gas from indigenous fuels to Sweden (i.e. biomass). As the economic climate changed and awareness of the damage to the environment caused by the use of fossil fuels in power generation equipment increased, the aim of the development work at TPS was changed to applying the process to heat and power generation from feedstocks such as biomass and solid wastes. Compared with modern waste incineration with heat recovery, the gasification process will permit an increase in electricity output of up to 50%. The gasification process being developed is based on an atmospheric-pressure circulating fluidised bed gasifier coupled to a tar-cracking vessel. The gas produced from this process is then cooled and cleaned in conventional equipment. The energy-rich gas produced is clean enough to be fired in a gas boiler (and, in the longer term, in an engine or gas turbine) without requiring extensive flue gas cleaning, as is normally required in conventional waste incineration plants. Producing clean fuel gas in this manner, which facilitates the use of efficient gas-fired boilers, means that overall plant electrical efficiencies of close to 30% can be achieved. TPS has performed a considerable amount of pilot plant testing on waste fuels in their gasification/gas cleaning pilot plant in Sweden. Two gasifiers of TPS design have been in operation in Grève-in-Chianti, Italy since 1992. This plant processes 200 tonnes of RDF (refuse-derived fuel) per day. It is planned that the complete TPS gasification process (including the complete fuel gas cleaning system) be demonstrated in several gas turbine-based biomass-fuelled power generating plants in different parts of the world. It is the aim of TPS to prove, at commercial scale, the technical feasibility and economic advantages of the gasification process when it is applied to solid waste fuels. This aim shall be achieved, in the short-term, by employing the cold clean product gas in a gas boiler and, in the longer-term, by firing the gas in engines and gas turbines. A study for a 90 MWth waste-fuelled co-generation plant in Sweden has shown that, already today, gasification of solid waste can compete economically with conventional incineration technologies.     

Steam gasification of waste tyre: Influence of process temperature on yield and product composition

An experimental survey of waste tyre gasification with steam as oxidizing agent has been conducted in a continuous bench scale reactor, with the aim of studying the influence of the process temperature on the yield and the composition of the products; the tests have been performed at three different temperatures, in the range of 850–1000 °C, holding all the other operational parameters (pressure, carrier gas flow, solid residence time). The experimental results show that the process seems promising in view of obtaining a good quality syngas, indicating that a higher temperature results in a higher syngas production (86 wt%) and a lower char yield, due to an enhancement of the solid–gas phase reactions with the temperature. Higher temperatures clearly result in higher hydrogen concentrations: the hydrogen content rapidly increases, attaining values higher than 65% v/v, while methane and ethylene gradually decrease over the range of the temperatures; carbon monoxide and dioxide instead, after an initial increase, show a nearly constant concentration at 1000 °C. Furthermore, in regards to the elemental composition of the synthesis gas, as the temperature increases, the carbon content continuously decreases, while the oxygen content increases; the hydrogen, being the main component of the gas fraction and having a small atomic weight, is responsible for the progressive reduction of the gas density at higher temperature.     

The potential of SO2 for reducing corrosion in WtE plants

Due to the high-temperature boiler corrosion induced by chloride-rich fly ash deposits, steam generation in today’s Waste-to-Energy (WtE) plants is typically designed only for 40 bar/400 °C as an economic compromise between acceptable corrosion rate and maximum power generation. The high-corrosive metal chlorides in the fly ash can react with SO₂ forming low-corrosive sulfates. The sulfation efficiency is enhanced by high SO₂ levels and sufficient residence time of the flue gas at high-temperatures (700–900 °C). The fly ash sulfation was tested in full scale in a Swedish WtE plant by applying the economic sulfur recirculation method. Probes of several alloys (16Mo3, Inconel 625, Sanicro 28) were exposed for 1000 h at controlled material temperatures in the superheater position, at normal and during sulfating operation respectively. Analyses of the fly ash showed that the molar Cl/S was decreased to values well below 1 and the corresponding corrosion rates of the individual material samples were less than half when sulfur recirculation was in operation. These positive findings demonstrate that the sulfur recirculation process has high potential for low-corrosive high-temperature steam generation (T ≈ 500 °C) and improved electricity production. Further steam superheating can be realized by staged superheating using small amounts of secondary fuel.     

Reduction of tar using cheap catalysts during sewage sludge gasification

Solid-fuel conversion or gasification study of sewage sludge and energy recovery has become increasingly important because energy recovery and climate change are emerging issues. Various types of catalysts, such as dolomite, steel slag and calcium oxide, were tested for tar reduction during the sewage sludge gasification process. For the experiments on sewage sludge gasification reactions and tar reduction using the catalysts, a fixed bed of laboratory-scale experimental apparatus was set up. The reactor was made of quartz glass using an electric muffle furnace. The sewage sludge samples used had moisture contents less than 6%. The experimental conditions were as follows: sample weight was 20 g and reaction time was 10 min, gasification reaction temperature was from 600 to 800°C, and the equivalence ratio was 0.2. The quantity of catalysts was 2–6 g, and temperatures of catalyst layers were 500–700°C. As the reaction temperature increased up to 800°C, the yields of gaseous products and liquid products increased, whereas char and tar products decreased, showing effects on gas product compositions. These results were considered to be due to the increase of the water-gas reaction and Boudouard reaction. In the case of experiments with catalysts, dolomite (4 g), steel slag (6 g) and calcium oxide (6 g) were used. When the temperature of catalysts increased, the weight of the tar produced decreased with different cracking performances by different catalysts. Reforming reactions were considered to occur on the surface of dolomite, steel slag and calcium oxide, causing cracking of the hydrocarbon structure, which eventually showed reduced tar generation.     

Gasification characteristics of sewage sludge combined with wood biomass

The gas products from gasification processes have been considered to have some limitations in gas composition and heating value from the previous studies. Gasification characteristics of sewage sludge and wood mixture were investigated using different mixing ratios with the purpose of better quality of gas product suitable for energy/power generation. The gasification experiment was performed by an indirectly heated fluidized bed reactor. As reaction temperature increased from 600 to 900 °C, the yield of gas product increased with higher generation of CO, H₂ and CH₄ by more activated gas conversion reactions. As the equivalence ratio increased from 0.2 to 0.4, composition ratio of CO₂ increased while CO, CH₄, H₂ decreased as expected. Several operating variables including mixing ratio of wood with dried sludge were also tested. From this initial stage of experiment, optimal operating conditions for the bubbling fluidized bed gasifier, could be considered 900 °C in temperature; 0.2 in equivalence ratio and 40 % in wood mixing ratio within test variables range. These results will be more thoroughly investigated for the application to the larger scale pilot system.     

Gasification and reforming of biomass and waste samples by means of a novel catalyst

This study conducted gasification and catalytic reforming experiments with the expectation of obtaining new advantages on energy recovery and aimed for the development of an effective catalyst. Initially, the use of thermal gasification technology for waste treatment in line with waste-to-energy strategies was reviewed. Technological systems which have gasification were classified and their current status was discussed. Then, the results of gasification and reforming experiments showed that product gas with 50 % H₂ or more was obtained using a Ni catalyst on a mesoporous silica–based SBA-15 support (NiO/SBA-15), which we newly developed. Experiments using wood feedstock revealed that H₂ production by the catalyst was better when the NiO content was 20 % (W/W) or more than when another catalyst or the Ni catalyst with a lower Ni loading was used. Tar formation as a by-product was also well controlled by the catalyst, and use of a catalyst with 40 % NiO reduced the tar concentration to less than 0.2 g/\( {\text{m}}^{3}_{\text{N}} \). Experiments using a mixed feedstock of wood and RPF resulted in an increase in hydrocarbon concentration because of insufficient reforming. This finding suggests that future work is required to find a better solution to wood and RPF co-gasification.     

Gasification and its emission characteristics for dried sewage sludge utilizing a fluidized bed gasifier

Various research has attempted to determine the proper treatment of sewage sludge, including thermal technologies. Efficient thermal technologies have been focused on because of their energy saving/energy recovery. Gasification technology can be considered one of these approaches. In this study, the characteristics of gasification reactions were investigated with the aim of finding fundamental data for utilizing sewage sludge as an energy source. For the experiments on sewage sludge gasification reaction characteristics, a laboratory-scale experimental apparatus was set up with a fluidizing bed reactor of 70-mm inner diameter and 600-mm total height using an electric muffle furnace. The experimental materials were prepared from a sewage treatment plant located in Seoul. The reaction temperature was varied from 630 to 860°C, and the equivalence ratio from 0.1 to 0.3. The gas yields, compositions of product gas, and cold gas efficiencies of product gas were analyzed by GC/TCD and GC/FID installed with a carboxen-1000 column. The experimental results indicated that 800°C, ER 0.2 was an optimum condition for sewage sludge gasification. The maximum yield of product gas was about 44%. Producer gas from experiments was mainly composed of hydrogen, carbon monoxide, carbon dioxide, and methane. The cold gas efficiency of sewage sludge gasification was about 68%. The H₂/CO ratio and CO/CO₂ ratio were about 1.1 and 1.4, respectively, in optimum reaction conditions. Gaseous pollutants such as SO₂, HCl, NH₃, H₂S, and NO₂ were also analyzed at various gasification/combustion conditions, and their gaseous products were compared, showing significantly different oxidized product distributions.     

Gasification of refuse derived fuel in a fixed bed reactor for syngas production

Steam gasification of two different refuse derived fuels (RDFs), differing slightly in composition as well as thermal stability, was carried out in a fixed-bed reactor at atmospheric pressure. The proximate and ultimate analyses reveal that carbon and hydrogen are the major components in RDFs. The thermal analysis indicates the presence of cellulose and plastic based materials in RDFs. H2 and CO are found to be the major products, along with CO2 and hydrocarbons resulting from gasification of RDFs. The effect of gasification temperature on H2 and CO selectivities was studied, and the optimum temperature for better H2 and CO selectivity was determined to be 725 degrees C. The calorific value of product gas produced at lower gasification temperature is significantly higher than that of gas produced at higher process temperature. Also, the composition of RDF plays an important role in distribution of products gas. The RDF with more C and H content is found to produce more amounts of CO and H2 under similar experimental conditions. The steam/waste ratio showed a notable effect on the selectivity of syngas as well as calorific value of the resulting product gas. The flow rate of carrier gas did not show any significant effect on products yield or their distribution.     

Removal of H2S using molten carbonate at high temperature

Gasification is considered to be an effective process for energy conversion from various sources such as coal, biomass, and waste. Cleanup of the hot syngas produced by such a process may improve the thermal efficiency of the overall gasification system. Therefore, the cleanup of hot syngas from biomass gasification using molten carbonate is investigated in bench-scale tests. Molten carbonate acts as an absorbent during desulfurization and dechlorination and as a thermal catalyst for tar cracking. In this study, the performance of molten carbonate for removing H₂S was evaluated. The temperature of the molten carbonate was set within the range from 800 to 1000 °C. It is found that the removal of H₂S is significantly affected by the concentration of CO₂ in the syngas. When only a small percentage of CO₂ is present, desulfurization using molten carbonate is inadequate. However, when carbon elements, such as char and tar, are continuously supplied, H₂S removal can be maintained at a high level.To confirm the performance of the molten carbonate gas-cleaning system, purified biogas was used as a fuel in power generation tests with a molten carbonate fuel cell (MCFC). The fuel cell is a high-performance sensor for detecting gaseous impurities. When purified gas from a gas-cleaning reactor was continuously supplied to the fuel cell, the cell voltage remained stable. Thus, the molten carbonate gas-cleaning reactor was found to afford good gas-cleaning performance.