A.M. Mastral

Assessment of PAH emissions as a function of coal combustion variables

The influence of fluidized bed combustion (FBC) temperature and coal rank on polycyclic aromatic hydrocarbon (PAH) emissions was assessed. A low-rank coal and a high-rank coal were burnt in a fluidized bed reactor (FBR) on a laboratory scale. An outlet gas sample was passed through a capture system provided with three traps: nylon filter, Teflon filter and XAD-2 resin. The PAH captured were analysed by fluorescence spectroscopy (FS) after sonic extraction with dimethylformamide (DMF). The results show that the total PAH emission depends mainly on the pyrolytic process and to a lesser degree on the combustion efficiency. Although the total amount of PAH emitted follows a specific trend as a function of the combustion temperature, the amount of each PAH emitted seems to be consequence of a random distribution due to PAH interconversion and association. Under all conditions of combustion, the amount of PAH emitted in the gas phase is higher than that collected in two cyclones preceding the gas sampling location.

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.

Comparison of receptor models for source apportionment of the PM10 in Zaragoza (Spain)

Receptor models are useful to understand the chemical and physical characteristics of air pollutants by identifying their sources and by estimating contributions of each source to receptor concentrations. In this work, three receptor models based on principal component analysis with absolute principal component scores (PCA-APCS), Unmix and positive matrix factorization (PMF) were applied to study for the first time the apportionment of the airborne particulate matter less or equal than 10microm (PM10) in Zaragoza, Spain, during 1year sampling campaign (2003-2004). The PM10 samples were characterized regarding their concentrations in inorganic components: trace elements and ions and also organic components: polycyclic aromatic hydrocarbons (PAH) not only in the solid phase but also in the gas phase. A comparison of the three receptor models was carried out in order to do a more robust characterization of the PM10. The three models predicted that the major sources of PM10 in Zaragoza were related to natural sources (60%, 75% and 47%, respectively, for PCA-APCS, Unmix and PMF) although anthropogenic sources also contributed to PM10 (28%, 25% and 39%). With regard to the anthropogenic sources, while PCA and PMF allowed high discrimination in the sources identification associated with different combustion sources such as traffic and industry, fossil fuel, biomass and fuel-oil combustion, heavy traffic and evaporative emissions, the Unmix model only allowed the identification of industry and traffic emissions, evaporative emissions and heavy-duty vehicles. The three models provided good correlations between the experimental and modelled PM10 concentrations with major precision and the closest agreement between the PMF and PCA models.

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.

Toxic organic emissions from coal combustion

Atmospheric fluidized bed combustion (AFBC) is considered to be an environmentally favorable combustion technology where the control of emissions can be integrated into the combustion system. FBC operates at low temperatures, 800–900°C, to prevent thermal NO formation and to favor the sulfur removal by the sorbent, but it has not been taken into account that when coal is burnt, not only NOx, SOx and COx are emitted. In addition, volatile organic pollutants (VOCs) are emitted. From these VOCs, the polycyclic aromatic hydrocarbons (PAHs) constitute one of the most dangerous compounds because of the possibility of interacting with biological nucleophiles. It is expected that new legislation about the regulation on PAH emissions will be very restrictive. In this work, PAH emissions from coal AFBC as a function of the coal combustion variables (combustion temperature, gas flow and percentage of excess oxygen) are reported. In addition, the effect of bed nature on PAH emissions is also assessed. Polyaromatic hydrocarbon emissions at the standard conditions used at the AFBC power stations are assessed by the study carried out in an AFBC laboratory pilot plant. The PAHs listed by the US EPA as priority pollutants are analyzed by fluorescence spectroscopy (FS) at the synchronous mode.

Some inferences on the mechanism of atmospheric gas/particle partitioning of polycyclic aromatic hydrocarbons (PAH) at Zaragoza (Spain)

Gas/particle partitioning of pollutants is an important mechanism determining atmospheric processing and its impact to environmental and human health. In this paper, the gas-particle partitioning of polycyclic aromatic hydrocarbons (PAH) has been studied with the aim of determining the main mechanism of PAH partitioning in Zaragoza (Spain) aerosols. To reach this goal, the ambient concentrations of PAH (gas and particle phase) collected in this city for one year period (2003-2004) have been analyzed. The partitioning between the particle and gas phases was studied according to three different models: the Junge adsorption model, the absorption into the organic matter model using the octanol-air (K(OA)) partition coefficient and the absorption into the organic matter plus the adsorption onto the soot carbon model using the soot-air (K(SA)) partition coefficients. Experimental gas/particle partition coefficients (K(P)) correlated well with the subcooled liquid vapour pressures (P(L)(0)) of PAH but with slopes higher than the expected value of -1. Experimental K(p) values were well fit to the modelled ones when, in addition to absorption into organic matter, adsorption onto the soot carbon was considered. It could be concluded that the main partition mechanism in Zaragoza aerosols was explained by adsorption onto the soot carbon. However, K(p) modelled values were affected by the different thermodynamic parameters related to soot types. The influence of the organic matter and elemental carbon fractions on the K(p) modelling was also studied. The different particle characteristics, local factors, the presence of non-exchangeable fraction and non-equilibrium were considered like main keys to explain deviations of the experimental K(p) values from predictions according to models.

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.

Deep oxidation of pollutants using gold deposited on a high surface area cobalt oxide prepared by a nanocasting route

Gold deposited on a cobalt oxide with high surface area (138 m(2)g(-1)), obtained through a nanocasting route using a siliceous KIT-6 mesoporous material as a hard template, has demonstrated high activity for the total oxidation of propane and toluene, and ambient temperature CO oxidation. The addition of gold promotes the activity when compared to a gold-free Co(3)O(4) catalyst prepared using the same nanocasting technique. The enhanced catalytic activity when gold is present has been explained for the deep oxidation of propane and toluene in terms of the improved reducibility of cobalt oxide when gold is added, rather than to the intrinsic activity of metallic gold particles. The improved behaviour for CO oxidation has been linked to the simultaneous presence of Au(δ+) and Au°.

Optimisation of scrap automotive tyres recycling into valuable liquid fuels

The recycling of rubber from old tyres by batch hydrogenation has been performed using tubing bomb reactors. Important process variables like temperature, reaction time, initial hydrogen pressure and nature of gas used have been studied. In all the runs the maximum total conversion was achieved. Conversion products are comprised of oils and gases, being the asphaltene yield lower than 1% in all conditions tested. The most valuable conversion products, oils, have been systematically analysed by TLC-FID1 and the influence of the process variables in oils composition has been assessed. From the obtained results, it can be deduced that the conversion of rubber in oils is a fast thermal process, which is neither affected by initial pressure nor the nature of gas used. But on the other hand, the nature of obtained oils and gases is a function of process variables.