M.V. Navarro

Spatial and temporal PAH concentrations in Zaragoza, Spain

The concentration of seven polycyclic aromatic hydrocarbons (PAH) associated with the atmospheric solid phase was measured in the Zaragoza (North-East of Spain) atmosphere using fluorescence spectroscopy in the synchronous mode (FS). The PAH results were reported for four different urban and suburban places, located within the city and during the period October 1999-September 2001. The PAH data obtained indicated the importance of local sources generated from urban/industrial areas. Although the PAH total concentration was quite similar in all the sampling sites, the main differences were due to Benzo[a]pyrene (BaP) and Coronene (Cor) concentrations, reaching the highest values in the sites associated with heavy traffic (trucks, lorries, etc.). The temporal evolution of atmospheric solid phase PAH concentrations indicated a seasonal trend. Higher PAH concentrations were found during colder seasons for the four sampling sites. The influence of environmental parameters such as temperature, rain, relative humidity, wind speed and direction on the PAH emissions was analyzed observing a positive correlation between the total PAH concentration and the relative humidity and a negative one with the temperature. With regard to the wind direction, higher PAH emissions were detected when wind was coming from an east and north-east direction. Wind from a north-westerly direction showed lower PAH emissions associated with the cierzo wind which provided cleaner air.

Valorisation of waste tyre by pyrolysis in a moving bed reactor

The aim of this work is to assess the behaviour of a moving bed reactor, based on a screw transporter design, in waste tyre pyrolysis under several experimental conditions. Waste tyre represents a significant problem in developed countries and it is necessary to develop new technology that could easily process big amounts of this potentially raw material. In this work, the influence of the main pyrolysis process variables (temperature, solid residence time, mass flow rate and inert gas flow) has been studied by a thorough analysis of product yields and properties. It has been found that regardless the process operational parameters, a total waste tyre devolatilisation is achieved, producing a pyrolytic carbon black with a volatile matter content under 5 wt.%. In addition, it has been proven that, in the range studied, the most influencing process variables are temperature and solid mass flow rate, mainly because both variables modify the gas residence time inside the reactor. In addition, it has been found that the modification of these variables affects to the chemical properties of the products. This fact is mainly associated to the different cracking reaction of the primary pyrolysis products.

Catalytic pyrolysis of wood biomass in an auger reactor using calcium-based catalysts

Wood catalytic pyrolysis using calcium-based materials was studied in an auger reactor at 450°C. Two different catalysts, CaO and CaO·MgO were evaluated and upgraded bio-oils were obtained in both cases. Whilst acidity and oxygen content remarkable decrease, both pH and calorific value increase with respect to the non-catalytic test. Upgrading process was linked to the fact that calcium-based materials could not only fix the CO2-like compounds but also promoted the dehydration reactions. In addition, process simulation demonstrated that the addition of these catalysts, especially CaO, could favour the energetic integration since a lowest circulation of heat carrier between combustor and auger reactor should be needed. An energy self-sustained system was obtained where thermal energy required for biomass drying and for pyrolysis reaction was supplied by non-condensable gas and char combustion, respectively.

Valorisation of forestry waste by pyrolysis in an auger reactor.

Pyrolysis of forestry waste has been carried out in an auger reactor to study the influence of operational variables on the reactor performance and the properties of the related products. Pine woodchips were used for the first time as raw material and fed continuously into the reactor. Ten experiments were carried out under inert atmosphere at: (i) different reaction temperature (1073, 973, 873, 823 and 773 K); (ii) different solid residence time (5, 3, 2 and 1.5 min); and (iii) different biomass flow rate (3.9, 4.8 and 6.9 kg/h). Results show that the greatest yields for liquid production (59%) and optimum product characterisation were obtained at the lowest temperature studied (773 K) and applying solid residence times longer than 2 min. Regarding bio-oil properties, GC/MS qualitative identification show that the most abundant compounds are volatile polar compounds, phenols and benzenediols; and very few differences can be observed among the samples regardless of the pyrolysis operating conditions. On the whole, experimental results demonstrate that complete reaction of forest woodchips can be achieved in an auger reactor in most of the experimental conditions tested. Moreover, this study presents the initial steps for the future scaling up of the auger reactor with the aim of converting it into a mobile plant which will be able to remotely process biomass such as energy crops, forestry and agricultural wastes to obtain bio-oil that, in turn, can be used as energy vector to avoid high transport costs.

Critical review on atmospheric PAH. Assessment of reported data in the Mediterranean basin

Polycyclic aromatic hydrocarbons (PAH) are a special group of atmospheric contaminants included in the persistent toxic substances (PTS) and also in the volatile organic compounds (VOC) groups. PAH are present in the atmosphere and its origin can be due to anthropogenic and/or biogenic activities. Their specific characteristics, high volatility, mutagenic and/or carcinogenic power, easily transportable for long distances with the wind undergoing photodecomposition processes, which imply reactions with solar light, NOx and O3, make them important contaminants despite of the fact that they are present at very low concentrations. These characteristics make some of the PAH to be listed by the Environmental Protection Agency (EPA) as priority pollutants with negative environmental impact due to their toxicity and they can affect very negatively the living being due to their carcinogenic/mutagenic character. Because of atmospheric PAH properties, it is not worth to study them in small areas because they do not know about natural or political borders and they can affect to a huge population. The growing use of transport and energy consumption, PAH have mainly anthropogenic origin, joined the growing cancer incident, must be the alarm to take these toxic organic contaminants into account and under control. This paper is a revision on the reported data on atmospheric PAH in the Mediterranean basin and was shown at the Workshop of the United Nations Environmental Protection (UNEP), meeting held in Athens, February 2002.

Study of the viability of the process for hydrogen recovery from old tyre oils

In this paper, an approach to the production of hydrogen from waste rubber is proposed. The process consists in performing the pyrolysis of waste rubber to produce the raw material (oils) that will be used in a gasification process with oxygen to obtain hydrogen. Tyre pyrolysis runs were experimentally performed to study the influence of temperature and reaction time on oils production, concluding that tyre pyrolysis requires low-severity process variables because at severe conditions, no improvements in conversion are obtained and a slight decrease in oils production is observed. In addition, thermodynamic calculations were performed to know the energy requirements for the oils gasification process. The equilibrium constants in terms of process pressure and temperature were calculated observing that all the processes are spontaneous and clearly lead to conversion products. The hydrogen recovery is calculated and from overall data, it is concluded that the production of hydrogen from old tyre seems to be a feasible process and a way of obtaining a clean energy for the future from a non-biodegradable waste material.

Sorbent characteristics influence on the adsorption of PAC: I. PAH adsorption with the same number of rings

Abstract The aim of this paper is to study the abatement of three-ring polycyclic aromatic hydrocarbons (PAHs) from hot gas emissions during energy generation in coal combustion. The three-ring PAHs are one of the most abundant PAH groups emitted during coal combustion. Four of them—Acenaphthene (Ac), Phenanthrene (Phe), Fluorene (Fu) and Anthracene (An)—have been listed by US EPA as priority pollutants. The three-ring PAH adsorption capacities are related to the textural properties of the 16 sorbents used in this work. Single and multiple linear regressions —principal component regression (PCR)—were applied in this study. The main conclusions reached are two: (1) the micropore volume is the most determinant parameter for these PAH removal; (2) the adsorption of three-ring PAH by sorbents from waste hot gas emissions is inversely proportional to their volatility: the lower the PAH volatility, the higher the adsorbent adsorption capacity. The adsorption isotherms show that Phe and An, both examples of PAHs with three aromatic rings, behave similarly. However, their behaviour differs from that of Ac and Fu, compounds where only two of their three rings exhibit an aromatic nature.

Improvement of liquids from coal–tire co-thermolysis. Characterization of the obtained oils

Abstract Liquids from coal–tire hydrothermolysis, obtained in a swept fixed bed reactor (SFB), have been improved. The upgraded process was carried out keeping constant the residence time (30 min) and hydrogen pressure (10 MPa) at two different temperatures (400°C and 450°C) with three different catalysts: Red Mud, Ni/Mo, supported on alumina, and Mo salt, supported on carbon black (CB). The upgraded oils have been characterised by GC-MS and by their hydrocarbon components by TLC-FID. Their Naphtha, Kerosene, Gas Oil, Heavy Gas Oil and Vacuum Residue percentages are quantified by simulated distillation. Some inferences on catalyst mechanisms during the upgrading processes, as a function of the analytical data obtained in the characterisation of the upgraded oils, are commented.

Influence of sorbent characteristics on the adsorption of PAC: II. Adsorption of PAH with different numbers of rings

Abstract The aim of this work was to relate sorbent textural characteristics with the adsorption capacities of two-, three- and four-ring polyaromatic hydrocarbons at the conditions emitted during energy generation. The sorbent textural parameters, total micropore volume, V N 2 , narrow micropore volume, V CO 2 , mesopore volume, V BJH , and the free active sites were analysed trying to correlate them with their Np, Phe and Py adsorption capacities. To get this aim, single- and multiple-lineal regressions (MLR) were applied to the three studied polycyclic aromatic hydrocarbons (PAH). A principal component analysis was performed to generate new and uncorrelated variables. The relations between the textural parameters were analysed using a principal components regression (PCR). The PCR analysis had a good statistical quality, but it did not allow differentiating free active site types nor V N 2 and V CO 2 . The correlations were, thus, set up applying a multiple-linear regression to the original variables (MLR). The regression statistical quality was similar to the PCR analysis and it could give an easier explanation of the parameters that affected the adsorption. In the Np adsorption, the 60% data variance was explained and the adsorption was positively correlated to V CO 2 and the micropore mean diameter ( L ). In the Phe regression, the 86% variance was explained and its adsorption was positively correlated to V N 2 and the micropore distribution, n . In the Py adsorption, the 88% data variance was explained and this adsorption was positively correlated to V N 2 and V BJH . These dependencies were according to the molecular parameters of these compounds, molecular diameter and volatility because the higher the aromatic cycles containing compounds, the more favoured the adsorbate–adsorbate interactions. Besides, the higher the mean diameter micropores, the lower the diffusion problems showed by Np, Phe and Py.

Waste tyre pyrolysis: modelling of a moving bed reactor.

This paper describes the development of a new model for waste tyre pyrolysis in a moving bed reactor. This model comprises three different sub-models: a kinetic sub-model that predicts solid conversion in terms of reaction time and temperature, a heat transfer sub-model that calculates the temperature profile inside the particle and the energy flux from the surroundings to the tyre particles and, finally, a hydrodynamic model that predicts the solid flow pattern inside the reactor. These three sub-models have been integrated in order to develop a comprehensive reactor model. Experimental results were obtained in a continuous moving bed reactor and used to validate model predictions, with good approximation achieved between the experimental and simulated results. In addition, a parametric study of the model was carried out, which showed that tyre particle heating is clearly faster than average particle residence time inside the reactor. Therefore, this fast particle heating together with fast reaction kinetics enables total solid conversion to be achieved in this system in accordance with the predictive model.