• Energy Research

AbstractThe performance of a draft‐tube conical spouted bed for drying fine particles under batch operating conditions has been assessed at several temperatures using nonporous and open‐sided draft tubes, and the results have been compared with those obtained when operating without a draft tube. In order to ascertain the influence of temperature on drying, experimental runs have been carried out in the 25–300 °C temperature range. The open‐sided draft tube provides the best performance due to the excellent gas‐solid contact attained with this device, which enables shorter drying times. A maximum air temperature of 200 °C is recommended for energy optimization. An open‐sided tube protruding above the stagnant bed by at least 2/3 of the latter's height produces much lower and denser fountains than a tube flush with the upper surface of the bed.

Abstract Continuous pyrolysis of scrap tyres has been carried out in a conical spouted bed reactor and the results (yields, composition of the volatile fraction and carbon black properties) have been compared with those obtained operating in batch mode in a previous study. Continuous operation in the 425–600 °C range gives way to a yield of 1.8–6.8 wt.% of gases, 44.5–55.0 wt.% of liquid fraction (C5–C10 range hydrocarbons, with a maximum yield of limonene of 19.3 wt.% at 425 °C), 9.2–11.5 wt.% of tar C 11 + and 33.9–35.8 wt.% of char. The main differences between the continuous and batch processes are in the yield of light aromatics, which is higher in the continuous process, and in that of the heavy liquid fraction or tar, which is higher in the batch process. These are the advantages of the continuous process, although hydrogenation of the liquid fraction is required even in this case in order to use it as fuel. The high yield of limonene, the flexibility in the operating conditions and the capacity for a continuous removal of the residual carbon black from the reactor are the advantages of conical spouted bed technology. The excellent performance of the conical spouted bed reactor for the tyre pyrolysis process is due to the solid cyclic movement, the good contact between phases, the high heating rate and the reduced residence time of the volatile products.

Abstract The thermal pyrolysis of three different polyolefin plastics (HDPE, LDPE and PP) has been carried out in a conical spouted bed reactor. This technology is especially interesting because of the high selectivity to waxes due to the low residence times and high heating rates that reduce secondary reactions and increase the yield of primary pyrolysis products (waxes). These have been obtained operating at 450, 500 and 600 °C and a complete characterization has been carried out using different techniques, such as gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectrophotometry, simulated distillation and the measurement of heating value and melting point. Operating conditions and feed type have been observed to have a significant effect on the properties of the different waxes. The characterization has been carried out bearing in mind the potential use of waste plastic-derived waxes as a feedstock for cracking units.

This study investigates the effect the pyrolysis reactor and the condensing system type have on the tyre derived oil (TDO) and DL-limonene yield, as well as benzothiazole concentration in the TDO. All the experiments were performed at 475 °C and three technologies were investigated, fixed bed reactor (FBR), bubbling fluidised bed reactor (BFBR) and conical spouted bed reactor (CSBR), with the latter being the reactor that provided the highest TDO yield (58.2 wt.%). Furthermore, the CSBR enhances DL-limonene production due to its excellent features (low residence time of volatiles and high heat and mass transfer rates), which minimize secondary cracking reactions. Moreover, in order to maximize the TDO retention efficiency and selectively reduce the concentration of certain heteroaromatic species, two types of condensation systems were evaluated: tube-andshell condenser (indirect contact) and quenching condenser (direct contact). The quenching condenser not only promoted the condensation efficiency for DL-limonene, but also reduced the concentration of benzothiazole in the collected TDO. Indeed, the direct contact between water (fed into the quencher) and the hot volatile stream favours the dissolution of some polar heteroaromatic species, thus reducing the nitrogen and sulphur content in the TDO and increasing the applicability of TDO as fuel. This research was supported by the Recycling and Economic Development Initiative of South Africa (REDISA) and the National Research Foundation (NRF). It was also financed by the Ministry of Economy and Competitiveness (CTQ2016-75535-R) and the Ministry of Science, Innovation and Universities of the Spanish Government (RTI2018-101678-B-I00), the European Regional Development Fund (ERDF), the European Commission (HORIZON H2020-MSCA RISE- 2018. Contract No. 823745), the Basque Government (IT1218-19) and the University of the Basque Country (UFI 11/39). The authors acknowledge that any opinions, findings, conclusions or recommendations expressed in this material are the authors' own, and the sponsorscannot accept any liability whatsoever in this regard.

Abstract The current review provides an assessment of the main waste plastics valorization routes to produce syngas and H2, thus covering different gasification strategies and other novel alternative processes, such as pyrolysis and in-line catalytic steam reforming. The studies dealing with plastics gasification are in general scarce. However, due to the knowledge acquired on biomass and coal gasification, the state of development of plastic gasification technologies is considerable and, in fact, several gasification studies have been performed at pilot scale units. Air gasification is the most studied and developed strategy and pursues the production of a syngas for energy purposes. In spite of the higher H2 content and heating value of the gas produced by steam gasification, this alternative faces significant challenges, such as the energy requirements of the process and the tar content in the syngas. Moreover, the co-gasification of plastics with coal and biomass appears to be a promising valorization route due to the positive impact on process performance and greater process flexibility. Other promising alternative is the pyrolysis and in-line reforming, which allows producing a syngas with high hydrogen content and totally free of tar.

Abstract The steam gasification of sawdust was carried out in a bench scale plant fitted with a fountain confined conical spouted bed reactor and a nonporous draft tube, and using olivine as primary catalyst. The effect temperature (in the 800–900 °C range) had on product distribution (gas, tar and char) and composition was studied. Not only did temperature have a positive effect on the gas yield and carbon conversion, but it also played a crucial role in tar removal, as its concentration fell from 49.2 g Nm−3 (on a dry basis) at 800 °C to 6.7 g Nm−3 operating at 900 °C. Moreover, temperature also enhanced the hydrogen yield of the gas, recording a value of 7.28 wt% at 900 °C. Regarding tar formation and its evolution pathway, as gasification temperature was increased the tar composition (analyzed by GC/MS, FTIR and simulated distillation techniques) evolved to more stable aromatic compounds (of higher molecular weight), such as naphthalene or fluoranthene, with heterocyclic or light aromatic compounds being almost absent at 900 °C.

Abstract Scrap car tyres have been pyrolysed in a conical spouted bed reactor at 425, 500, 550 and 610 ∘ C in batch operation. The pyrolysis products have been analysed on-line in a gas chromatograph. Temperature has a great influence on the product distribution of gas, liquid, aromatics and tar fraction. The gas and aromatic fractions increase with temperature, whereas liquid and tar fractions decrease. A detailed identification of the composition of the fractions has been carried out.

Abstract Particle entrainment is a serious problem in spouted bed contactors when operation is carried out using beds made up of ultrafine particles, irregular ones and fine and coarse particle mixtures. Accordingly, the conventional conical spouted bed has been modified by inserting a fountain confiner in the contactor, and a study has been carried out on the efficiency of the confinement device to avoid fine particle entrainment. Furthermore, the influence of the geometry of the device on the hydrodynamics of conical spouted beds has been studied. The results show that the fountain confiner largely avoids fine particle entrainment, i.e., 60–70% reduction depending on the type of draft tube used. Furthermore, the fountain confiner reduces the operating bed pressure drop and the maximum cycle time of the particles in the contactor, but has no effect on the minimum spouting velocity. Nevertheless, the greatest advantage of the fountain confiner lies in the stabilization of the fountain and the homogenisation of the solid circulation in the bed, which leads to a significant increase in the gas-solid contact in the fountain.

Abstract An original pyrolysis pilot plant provided with a conical spouted bed reactor has been designed and built for treating 25 kg/h of biomass. The scale-up of the process has been based on the previous knowledge acquired in both hydrodynamics and pyrolysis studies carried out at laboratory scale, as well as on the research conducted on 1:1 scale reactor made of methacrylate and operating at ambient conditions. The main components of the pyrolysis pilot plant are described and their performance is tested and assessed. Furthermore, preliminary results obtained by pyrolysing pinewood sawdust are presented. The pyrolysis plant operates in continuous mode for long periods without major operation problems. The excellent features of the spouted bed reactor (high heat transfer rates, short residence times, continuous char removal, etc.) allow obtaining high bio-oil yields. Thus, the maximum bio-oil yield is obtained at 480 °C, reaching a value of 65.8%, with the yields of gas and char being 18.8% and 15.4%, respectively. The bio-oil obtained has suitable features for its subsequent valorization.