• Energy Research

The addition of plastics to the steam pyrolysis/gasification of wood sawdust with and without a Ni/AlO catalyst was investigated in order to increase the production of hydrogen in the gaseous stream. To study the influence of the biomass/plastic ratio in the initial feedstock, 5, 10 and 20 wt.% of polypropylene was introduced with the wood in the pyrolysis reactor. To investigate the effect of plastic type, a blend of 80 wt.% of biomass and 20 wt.% of either polypropylene, high density polyethylene, polystyrene or a mixture of real world plastics was fed into the reactor. The results showed that a higher gas yield (56.9 wt.%) and a higher hydrogen concentration and production (36.1 vol.% and 10.98 mmol H g sample, respectively) were obtained in the gaseous fraction when 20 wt.% of polypropylene was mixed with the biomass. This significant improvement in gas and hydrogen yield was attributed to synergetic effects between intermediate species generated via co-pyrolysis. The Ni/Al O catalyst dramatically improved the gas yield as well as the hydrogen concentration and production due to the enhancement of water gas shift and steam reforming reactions. Very low amounts of coke (less than 1 wt.% in all cases) were formed on the catalyst during reaction, with the deposited carbonaceous material being of the filamentous type. The Ni/AlO catalyst was shown to be effective for hydrogen production in the co-pyrolysis/gasification process of wood sawdust and plastics.

The effect of the operating conditions (base angle, air inlet diameter, stagnant bed height, particle diameter, and air velocity) on the fountain geometry (height and amplitude) has been studied. Likewise, particle ascending and descending zones in the fountain have been delimited. These studies have been carried out by means of an optical fiber and by an image treatment system. An equation has been proposed for the calculation of the fountain height from the vertical component of the particle velocity in the axis at the base of the fountain. The contactor base angle has a major incidence on the fountain geometry. The external diameter of the fountain and that of the core are conditioned by the diameter of the spout at the base of the fountain. The diameter of the core (or ascending zone) decreases with the fountain level for all experimental conditions.

Abstract This study pursues the development and characterization of a fountain enhanced spouting regime. This novel gas solid-contact method combines the advantages of fountain confined conical spouted beds with those of draft tube conical spouted beds. The aim of confining the fountain, and therefore attaining a clearly differentiated regime, is to progress towards a highly efficient conical spouted bed reactor for biomass gasification. Accordingly, and in order to delve into the knowledge of the regimes attained in this contact method, a study has been conducted by analyzing the influence operating parameters (temperature, gas flow rate, particle size and bed mass) and draft tube geometry (tube diameter and entrainment zone height) have on hydrodynamics. Fountain confinement allows greatly enlarging the fountain region, especially the height, which improves the contact between reacting gases and the catalyst. Moreover, the residence time distribution, and therefore the average residence time, may be optimized by confining and enlarging the fountain zone. These features promote tar cracking and so increase biomass conversion efficiency, which are highly relevant facts for use of conical spouted bed reactors in gasification.

Abstract The 7·106 t of waste tires that are generated yearly represent for a potential source of fuels considering its composition, rich in C and H, and its chemical features. Waste tires can be recycled through several processes aiming for either material, energy, or chemical product recovery. In this work we review the current status of these valorization pathways, with a particular focus on pyrolysis, its main products and their characteristics. Despite the extended reviews on the pyrolysis of tires, scarce material is available regarding the possibilities that scrap tires pyrolysis oil (STPO) offers and its limitations. STPO is both the most economically and energetically attractive product, and its composition (as obtained by different authors) is analyzed in this work, finding that the main barriers to solve for its direct implementation are (i) high sulfur content, (ii) high content of aromatics and (iii) high proportion of heavy molecules (>350 °C). From an industrial perspective, a sequential 2-stage hydrotreating–hydrocracking strategy has been proposed for STPO upgrading in order to simultaneously overcoming all these limitations and produce high quality fuels.

The influence the support has on the performance of Ni catalysts used in the reforming of biomass fast pyrolysis volatiles has been assessed. Accordingly, five catalysts have been prepared by wet impregnation method, namely Ni/Al2O3, Ni/SiO2, Ni/MgO, Ni/TiO2 and Ni/ZrO2. These catalysts have been characterized by nitrogen adsorption/desorption, X-ray fluorescence spectroscopy, temperature programmed reduction and X-ray diffraction techniques. The pyrolysis-reforming runs have been performed in a bench scale unit operating in continuous regime. The biomass (pine wood sawdust) pyrolysis step has been carried out in a conical spouted bed reactor at 500 ºC, with the volatiles produced (a mixture of gases and bio-oil) being reformed in-line on the prepared catalysts in a fluidized bed reactor at 600 ºC. Remarkable differences have been observed amongst the catalyst prepared, with Ni/Al2O3, Ni/MgO and Ni/ZrO2 being those leading to the most encouraging results, whereas Ni/TiO2 and, especially Ni/SiO2, showed a limited reforming activity. The performance of each catalyst has been related to its properties determined in the characterization. This work was carried out with financial support from the Ministry of Economy and Competitiveness of the Spanish Government (CTQ2016-75535-R (AEI/FEDER, UE) and CTQ2015-69436-R (MINECO/FEDER, UE)) and the Basque Government (IT748-13).

The steam gasification of pinewood sawdust derived char has been studied in a conical spouted bed reactor. The effect temperature (in the 800–900 °C range), steam partial pressure (from 0.2 to 1) and sawdust particle size (0.3–1, 1–2 and 2–4 mm ranges) have on the char gasification kinetics has been determined. The pyrolysis step was performed in situ prior to the gasification step, at the same temperature as that in gasification. Four models have been proposed for the fitting of experimental results, i.e., homogeneous, shrinking core, nth order and random pore models, with the latter providing the best results. The activation energy obtained from the fitting is 190 kJ mol−1 and the reaction order with respect to steam partial pressure (α) is 0.344.

Abstract This paper describes the hydrodynamic and heat transfer performance of a pilot-plant scale conical spouted bed reactor designed for the pyrolysis of biomass wastes. The spouted bed reactor is the core of a fast pyrolysis pilot plant with continuous biomass feed of up to 25 kg/h, located at the Ikerlan-IK4 facilities. The aim of this paper is to obtain a deeper understanding of the spouted bed reactor performance at pyrolysis temperatures, in order to operate under stable conditions, improve the heat transfer rate in the reactor and minimize energy requirements. The influence of temperature on conical spouted bed hydrodynamics has been studied and wall-to-bed and bed-to-surface heat transfer coefficients have been determined.

Scrap tyre pyrolysis under vacuum is attractive because it allows easier product condensation and control of composition (gas, liquid and solid). With the aim of determining the effect of vacuum on the pyrolysis kinetics, a study has been carried out in thermobalance. Two data analysis methods have been used in the kinetic study: (i) the treatment of experimental data of weight loss and (ii) the deconvolution of DTG (differential thermogravimetry) curve. The former allows for distinguishing the pyrolysis of the three main components (volatile components, natural rubber and styrene-butadiene rubber) according to three successive steps. The latter method identifies the kinetics for the pyrolysis of individual components by means of DTG curve deconvolution. The effect of vacuum in the process is significant. The values of activation energy for the pyrolysis of individual components of easier devolatilization (volatiles and NR) are lower for pyrolysis under vacuum with a reduction of 12K in the reaction starting temperature. The kinetic constant at 503K for devolatilization of volatile additives at 0.25atm is 1.7 times higher than that at 1atm, and that corresponding to styrene-butadiene rubber at 723K is 2.8 times higher. Vacuum enhances the volatilization and internal diffusion of products in the pyrolysis process, which contributes to attenuating the secondary reactions of the repolymerization and carbonization of these products on the surface of the char (carbon black). The higher quality of carbon black is interesting for process viability. The large-scale implementation of this process in continuous mode requires a comparison to be made between the economic advantages of using a vacuum and the energy costs, which will be lower when the technologies used for pyrolysis require a lower ratio between reactor volume and scrap tyre flow rate.

Abstract The minimum spouting velocity, Ums, is a critical topic, and an exact prediction of this parameter certainly can be useful in design and scale-up of the conical spouted beds. In the present study, a number of intelligence methods was applied to predict Ums in conical spouted beds equipped with non-porous draft tube. Six dimensionless moduli comprising the essential operating and geometric parameters, namely, the gas density, the gas viscosity, the particle diameter, the particle density, the cone angle, the nozzle diameter, the static bed height, the length of the tube, the entrainment height, and the tube diameter were taken as models inputs. The total number of data samples is 1004 that includes 572 data points to train the smart models and 432 data points to test those models. The self-organizing map (SOM) was used to examine the effect of inputs correlation on the performance of the chosen smart models. Among the different models, a multi-layer perceptron (MLP) trained by Bayesian Regulation (BR) incorporating SOM i.e. (MLP-BR-SOM) predicted the best results with mean relative error of 9.71 and 12.45% for train and test data, respectively. In addition, sensitivity analysis (SA) of the proposed model was performed and it was shown the Ar, DT/D0, and H0/D0 have most influential parameters in prediction of Ums.