Influence of temperature on product distribution and biochar properties by municipal sludge pyrolysis

Biochar has the potential to amend degraded soil and improve crop yield. An experiment involving municipal sludge pyrolysis was carried out in a horizontal quartz reactor over the temperature range of 300–700 °C. The aim of this work was to investigate the influence of pyrolysis temperature on product distribution and biochar properties required for agronomic applications. Results of the experiment showed that yield and energy conversion efficiency of biochar decreased as pyrolysis temperatures rose, while bio-oil and syngas increased gradually. Biochar aromaticity barely changed, while polarity gradually decreased and specific surface area increased with a rise in pyrolysis temperature. Nutritive elements showed different enriching characteristics in the sludge pyrolysis process: nitrogen failed to enrich in biochars, whereas both phosphorus and potassium were enriched. Heavy metals showed good stability in the pyrolysis process except chromium; the contents of all metals used in the biochar conformed to Chinese control standards for agronomic application.     

Catalytic co-pyrolysis of <Emphasis Type="Italic">Pterospermum acerifolium</Emphasis> and plastic waste

The continuous increase in generation of solid wastes and gradual declining of fossil fuels necessities the development of sustainable conversion technologies. Recent studies have shown that the addition of biomass with hydrogen-rich co-reactants (plastics) altogether enhances the quality of bio-fuels using pyrolysis process. It was observed that red mud (which is produced as by-product in Bayer process) was used as a catalyst in few conversion process. In this study, pyrolysis of biomass (Pterospermum acerifolium) and waste plastic mixture with activated red-mud catalyst was investigated using thermo-gravimetric analysis. The kinetic parameters (activation energy and pre-exponential factor) of this process were determined using distributed activation energy model (DAEM). The DAEM was effectively applied to decide the activation energy (E) and pre-exponential factor (A) for each sample at various conversions during the catalytic co-pyrolysis. The biomass, plastic, biomass–plastic, and biomass–plastic–catalyst exhibited activation energies in the ranges of 78–268, 172–218, 67–307, and 202–292 kJ/mol, respectively.     

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.     

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.     

Clay-sewage sludge co-pyrolysis. A TG-MS and Py-GC study on potential advantages afforded by the presence of clay in the pyrolysis of wastewater sewage sludge

Wastewater sewage sludge was co-pyrolyzed with a well characterized clay sample, in order to evaluate possible advantages in the thermal disposal process of solid waste. Characterization of the co-pyrolysis process was carried out both by thermogravimetric-mass spectrometric (TG-MS) analysis, and by reactor tests, using a lab-scale batch reactor equipped with a gas chromatograph for analysis of the evolved gas phase (Py-GC).Due to the presence of clay, two main effects were observed in the instrumental characterization of the process. Firstly, the clay surface catalyzed the pyrolysis reaction of the sludge, and secondly, the release of water from the clay, at temperatures of approx. 450-500 °C, enhanced gasification of part of carbon residue of the organic component of sludge following pyrolysis.Moreover, the solid residue remaining after pyrolysis process, composed of the inorganic component of sludge blended with clay, is characterized by good features for possible disposal by vitrification, yielding a vitreous matrix that immobilizes the hazardous heavy metals present in the sludge.     

Pyrolysis of jute dust: effect of reaction parameters and analysis of products

Biowastes are becoming potential feedstocks for direct utilization or conversion to solid, liquid and gaseous fuels via various thermochemical routes. In this regard, jute dust which is a major agro-industrial waste in jute mills was pyrolysed in a fixed-bed reactor with an aim to study the product distribution and their characterization and to identify the optimum condition for bio-oil yield. The investigated process variables were temperature (400–700 °C), heating rate (10 and 40 °C/min) and nitrogen gas flow rate (50–250 ml/min). The yield of bio-oil is found to be maximum at 500 °C with a heating rate of 40 °C/min. However, further increase in temperature leads to decrease in bio-oil yield. Chemical compositions of the bio-oils were investigated using chromatographic and spectroscopic techniques such as ¹H NMR, FTIR and GC–MS. The heating value of the bio-oil is 26.71 MJ/kg. The study shows that jute dust have potential for conversion to bio-oil through the process of pyrolysis to supplement the petro-derived liquid fuel for heating and transportation applications after upgrading. The biochar produced as a co-product of jute dust pyrolysis can be a potential soil amendment with multiple benefits including increased soil fertility and C-sequestration.     

Characteristic of heavy metals in biochar derived from sewage sludge

This study investigates the characteristic of heavy metals (Pb, Zn, Cu, Cd, Cr, Ni and As) in biochar derived from sewage sludge at different pyrolysis temperatures (300, 400, 500, 600 and 700 °C). The heavy metal concentrations, chemical speciation distribution, leaching toxicity, and bio-available contents were investigated using ICP-OES after microwave digestion, a sequential extraction procedure recommended by the Community Bureau of Reference (BCR), an improved nitric acid–sulphuric acid method, and diethylenetriamine pentaacetic acid (DTPA) extraction method, respectively. The results showed that a great percentage of the heavy metals remained in biochar, the concentrations of heavy metals in biochar (except Cd in B7) were higher than that in sludge, and the enrichment of the heavy metals in biochar enhanced with the pyrolysis temperature. Although the effect of pyrolysis temperature on the chemical speciation distribution, the leaching toxicity and the bio-available contents of heavy metals in biochar was inconsistent, the potential risk of biochar on soil and groundwater contamination was lower than sewage sludge.     

Pyrolysis of polyolefins for increasing the yield of monomers' recovery

Pyrolysis of plastic waste is an alternative way of plastic recovery and could be a potential solution for the increasing stream of solid waste. The objective of this work was to increase the yield the gaseous olefins (monomers) as feedstock for polymerization process and to test the applicability of a commercial Ziegler-Natta (Z-N): TiCl(4)/MgCl(2) for cracking a mixture of polyolefins consisted of 46%wt. of low density polyethylene (LDPE), 30%wt. of high density polyethylene (HDPE) and 24%wt. of polypropylene (PP). Two sets of experiments have been carried out at 500 and 650°C via catalytic pyrolysis (1% of Z-N catalyst) and at 650 and 730°C via only-thermal pyrolysis. These experiments have been conducted in a lab-scale, fluidized quartz-bed reactor of a capacity of 1-3kg/h at Hamburg University. The results revealed a strong influence of temperature and presence of catalyst on the product distribution. The ratios of gas/liquid/solid mass fractions via thermal pyrolysis were: 36.9/48.4/15.7%wt. and 42.4/44.7/13.9%wt. at 650 and 730°C while via catalytic pyrolysis were: 6.5/89.0/4.5%wt. and 54.3/41.9/3.8%wt. at 500 and 650°C, respectively. At 650°C the monomer generation increased by 55% up to 23.6%wt. of total pyrolysis products distribution while the catalyst was added. Obtained yields of olefins were compared with the naphtha steam cracking process and other potentially attractive processes for feedstock generation. The concept of closed cycle material flow for polyolefins has been discussed, showing the potential benefits of feedstock recycling in a plastic waste management.     

Feedstock recycling from plastic and thermoset fractions of used computers (I): pyrolysis

The increasing production of computers, the progress in their performance, and the shorter time between innovation and production has led to increasing numbers of obsolete products. It has thus become necessary to recover some materials from old computers and to protect the environment from a new type of pollution. Such recycling is difficult because of the diversity of polymeric materials used, e.g., thermoplastics (polystyrene or acrylonitrile-butadiene-styrene) and thermosets (epoxy resins), and the relatively high levels of flame retardants (halogen- and nitrogen-containing compounds) added during production. Pyrolysis seems to be a suitable way to recover materials and energy from such waste without component separation if an efficient method for reducing toxic compounds can be applied. In this study, the pyrolysis of plastic and thermoset fractions (keyboards, casings, printed circuit boards, and mixtures thereof) of used computers was studied by thermogravimetry and batch reactor pyrolysis. The degradation products were separated into three fractions, solid, liquid, and gaseous, each of them being characterized by suitable methods such as gas chromatography (GC-MSD, gas chromatography-mass spectrometry detection; GC-AED, gas chromatography-atomic emission detection), infrared (FT-IR) and 1H-NMR (nuclear magnetic resonanace) spectroscopy, and elemental analysis. It has been established that most of the halogens, nitrogen, and sulfur is concentrated in the residue. However, the elimination of hazardous toxic compounds, mainly those containing bromine, is necessary before being able to safely use the pyrolysis oils as fuels or in refinery or petrochemical industry flows.     

生物炭修复Cd,Pb污染土壤的研究进展

随着矿产开采、冶炼等工业活动以及污水灌溉、施用污泥和劣质化肥等农业活动的进行，Cd，Pb等有害重金属不断进入农业环境中，对农田、菜地等造成污染。生物炭作为重要的土壤改良剂，在对Cd，Pb污染土壤的修复中表现出巨大的潜力。从生物炭的特性及制备、修复效果及其影响因素、修复机理等方面，对近年来国内外有关生物炭修复Cd，Pb污染土壤的研究成果和现状进行了总结，并对生物炭修复Cd，Pb污染土壤的发展前景和未来研究方向进行了展望。     

Sludge as dioxins suppressant in hospital waste incineration

Nitrogen containing compounds such as ammonia, urea and amines can effectively inhibit the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Sewage sludge accumulates both sulfur and nitrogen during wastewater treatment so it could be used to reduce PCDD/Fs formation. Indeed, it is observed in this study that the gas evolving from the sludge drying process can significantly suppress chlorobenzene (CBz) and PCDD/Fs formation from fly ash collected from a hospital waste incinerator. For instance, the reduction of hexachlorobenzene (HxCBz) and PCDD/Fs amount was 92.1% and 78.7%, respectively, when the drying gas evolving from 2g sludge flew through 2g fly ash. These tests were conducted in the frame of projects devoted to hospital waste incineration. The disposal technology for hospital waste (HW), developed in this institute, features rotary kiln pyrolysis combined with post-combustion followed by flue gas cleaning. Hence, some preliminary tests were devoted to investigate dioxins suppression by co-pyrolysis and co-combustion of polyvinyl chloride (PVC) and sludge in lab scale. More experimental research will be conducted to appropriately assess these effects of sludge on PCDD/Fs emissions during co-pyrolysis/combustion of HW and sludge.     

Characteristics of products and PCDD/DF emissions from a pyrolysis process of urethane/styrofoam waste from electrical home appliances

A plastic fraction consisting mainly of polyurethane/styrofoam waste is generated after separating valuable spare parts and metals from used electrical home appliances. In Korea, such waste is currently incinerated in cement kilns or is landfilled. However, owing to its high volatile matter content, conversion into gaseous or liquid pyrolysis products is a preferable alternative. A pyrolysis process of polyurethane and styrofoam waste from electrical home appliances was evaluated by characterizing the products generated at 500°–800°C. The para meters determined were the yields of gas, oil, and char; the characteristics of the remaining char; and the con centration of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzo-furans in the product gas. As expected, the char yield decreased at higher temperatures, whereas gas and oil yields showed increasing tendency. The oil products could be used as storable fuels with a calorific value of 6000–8000 kcal/kg. Fine pores were observed in the char. The adsorption and decolorizing ability of the char were almost the same as those of activated carbon, so that pyrolysis char has potential for use as a sorbent. Further feasibility studies will be needed before utilizing pyrolysis technology to recover either fuels or usable products from polyurethane/styrofoam waste.     

Reaction Kinetic Model For Optimal Pyrolysis Of Plastic Waste Mixtures

Reaction kinetics at various temperatures for pyrolysis of mixtures of plastic waste [polyethylene(PE) and polystyrene(PS)] are modelled in terms of five types of pyrolysis reaction. The model development is based on the assumption that as plastic wastes are heated in a non-reactive environment they are decomposed homogeneously to various products of gas, oil and char by a first-order rate, irreversible reaction and isothermal condition. Among the five models, the type II model in which the activated polymer exists as an intermediate product is the most accurate in predicting the pyrolysis products of pure PE or pure PS. Also, for mixtures of plastics both type II and IV models can be used to explain the composition of pyrolysis products. Furthermore, from the analysis of variance (ANOVA), the mixing ratio and temperature are shown to be the parameters that have the greatest effect on the pyrolysis reaction of polymer waste mixture. The pyrolysis reaction time for the maximum oil production from PE-PS mixtures is shorter than for PE alone and approaches that of PS alone. Oil production increases with increase of PS content. The optimal temperature for maximum oil production is 600°C for the pyrolysis of 2:8, 5:5 and 1:0 mixtures (w/w) of PE and PS. Oil production for PS alone is constant when the pyrolysis is above 600°C.     

污泥热解催化剂的研究进展

污泥热解处理技术具有较好的应用价值和发展前景,催化剂的加入可提高反应效率,降低处理成本,提高目标产物品质。本文综述了添加不同种类污泥热解催化剂对反应条件、反应过程、反应产物的影响,分析了不同种类催化剂的优势与不足,并对该领域未来的研究方向提出了建议。指出:应深入探究催化剂的作用机理,开发高效、环保型催化剂;重点研发废弃物制备催化剂,实现废物资源化利用;开展污泥与其他废弃物共热解的研究。     

Total recycling of CCA treated wood waste by low-temperature pyrolysis

A system to turn a potentially harmful stream of solid waste into a set of substreams with either commercial value or highly concentrated residual streams is presented. The waste which is considered is metal impregnated (in particular Chromated Copper Arsenate (CCA) treated) wood waste and timber, such as telephone poles, railway sleepers, timber from landscape and cooling towers, wooden silos, hop-poles, cable drums and wooden playground equipment. These waste streams sum up to several 100,000 tons of material per year currently to be dumped in every major country of the European Community (EC). Technologies need to be developed to reduce this CCA treated wood waste, such that all of the metals are contained in a marketable product stream, and the pyrolysis gases and/or pyrolysis liquid are used to their maximum potential with respect to energy recuperation. Pyrolysing the CCA treated wood waste may be a good solution to the growing disposal problem since low temperatures and no oxidising agents are used, which result in lower loss of metals compared to combustion. An experimental labscale pyrolysis system has been developed to study the influence of the pyrolysis temperature and the duration of the pyrolysis process on the release of metals and the mass reduction. The macrodistribution and microdistribution of the metals in the solid pyrolysis residue is studied using Inductively Coupled Plasma Mass Spectrometry (ICP–MS) and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Analysis (SEM–EDXA). Furthermore, a complete mass balance is calculated over the pyrolysis system. Based on these results a semi-industrial pyrolysis system (pilot plant scale) has been developed consisting of three stages: grinding, packed bed pyrolysis and metal separation. Special types of equipment have been developed to carry out the three stages. A new grinding system has been developed, based on a crushing mechanism rather than a cutting mechanism. The crushed wood is introduced by means of a screw feeding system into a reaction column. In this pyrolysis reactor the wood is heated by subjecting it to a flow of hot gases. This causes an adiabatic pyrolysis, which results in volatilisation of the volatile compounds whereas the mineral compounds (containing the metals) remain entrapped in a coal-type residue which is very rich in carbon. The condensable compounds in the pyrolysis gas condense while leaving the reaction zone due to the inverse temperature gradient. The pyrolysis gas leaving the reactor is used as fuel for the hot gas generator. The charcoal which is extracted at the bottom of the reactor, is cooled, compressed, removed and stored, ready to feed the subsequent stage. A specially developed grinder is used to remove the metal particles from the charcoal and the separation between metal and charcoal particles is accomplished in a pneumatic centrifuge as a result of the difference in density. Using this system the ultimate waste is less than 3% of the initial wood mass. Results obtained with a semi-industrial scale prototype confirm the effectiveness of the process.     

Tar-free fuel gas production from high temperature pyrolysis of sewage sludge

Pyrolysis of sewage sludge was studied in a free-fall reactor at 1000–1400 °C. The results showed that the volatile matter in the sludge could be completely released to gaseous product at 1300 °C. The high temperature was in favor of H₂ and CO in the produced gas. However, the low heating value (LHV) of the gas decreased from 15.68 MJ/N m³ to 9.10 MJ/N m³ with temperature increasing from 1000 °C to 1400 °C. The obtained residual solid was characterized by high ash content. The energy balance indicated that the most heating value in the sludge was in the gaseous product.     

Characterization of human manure-derived biochar and energy-balance analysis of slow pyrolysis process

Biochars have received increasing attention in recent years because of their soil improvement potential, contaminant immobilization properties, and ability to function as carbon sinks. This study adopted a pyrolytic process to prepare a series of biochars from dried human manure at varying temperatures. The thermal analysis of human manure and physicochemical properties of the resulting biochars illustrated that human manure can be a favorable feedstock for biochar production. In particular, the porous texture and nutrient-rich properties of biochars produced from human manure and may significantly enhance soil fertility when used as used soil additives. A temperature range of 500–600 °C was optimal for human manure biochar production. Significantly, when the moisture content of the feedstock is lower than 57%, the system could not only harvest manure-derived biochar but also have a net energy output, which can be provide heat source for nearby users.     

Effect of some environmentally degradable materials on the pyrolysis of plastics II: influence of cellulose and lignin on the pyrolysis of complex mixtures

Pyrolysis of polymer mixtures with a composition similar to that of municipal plastic waste containing polyvinyl chloride (PVC) and of municipal plastic waste free of PVC was performed in the presence of components of biomass, namely lignin, cellulose, or both. The pyrolysis products were characterized by standard methods utilized in the petrochemical industry, i.e., paraffins-isoparaffinsolefins-naphthenes-aromatics analysis, proton nuclear magnetic resonance and infrared spectroscopy, and gas chromatography-mass spectrometry. Up to 3 wt% lignin, cellulose, or both in mixed polymers changed the material balance of pyrolysis by decreasing the amount of waxy products. The presence of both PVC and biomass components significantly changed the material balance by decreasing the waxy product yield and increasing the gas and coke yield. The composition of all pyrolysis products was also modified with the addition of PVC, components of biomass, or both.     

Pyrolysis and gasification of meat-and-bone-meal: Energy balance and GHG accounting

Meat-and-bone-meal (MBM) produced from animal waste has become an increasingly important residual fraction needing management. As biodegradable waste is routed away from landfills, thermo-chemical treatments of MBM are considered promising solution for the future. Pyrolysis and gasification of MBM were assessed based on data from three experimental lab and pilot-scale plants. Energy balances were established for the three technologies, providing different outcomes for energy recovery: bio-oil was the main product for the pyrolysis system, while syngas and a solid fraction of biochar were the main products in the gasification system. These products can be used – eventually after upgrading – for energy production, thereby offsetting energy production elsewhere in the system. Greenhouse gases (GHG) accounting of the technologies showed that all three options provided overall GHG savings in the order of 600–1000 kg CO₂-eq. per Mg of MBM treated, mainly as a consequence of avoided fossil fuel consumption in the energy sector. Local conditions influencing the environmental performance of the three systems were identified, together with critical factors to be considered during decision-making regarding MBM management.     

Low energy comsumption management of agricultural residues

In this paper, a mechanical filtering system to treat pig slurry is proposed. The filter was made from the aerobic decomposition product of the organic fraction of municipal wastes and wheat straw was used as the support.Using a pilot plant to treat 2100 liters of swine slurry, an adequate reduction in BOD₅; COD, and other parameters was obtained. The organic matter content of the material trapped in the filter was similar to that of compost and farmyard manure, but the nitrogen and phosphorous levels and the C/N ratio were more similar to farmyard manure. After passing through a filtering system, the treated liquid can be used for fertirrigation and as a feed for algae ponds. After a period of stabilization, the solid material can be mixed to produce manure. Although wheat straw was used as the support in this experiment, other agricultural wastes such as rice straw, corn stalks, millet stems, banana, cotton, and coconut trash can be used. Rather than municipal solid waste compost, other kinds of compost obtained from agricultural wastes such as leaves, bark, husks, etc., can be used as the filter.