M.S. Callén

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.

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.

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.

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.

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.

Assessment of PAH emissions as a function of coal combustion variables in fluidised bed. 2. Air excess percentage

Abstract A low rank coal combustion was carried out in a fluidised bed combustion pilot plant at laboratory scale, with the aim of studying the influence of the air excess percentage on the PAH formation and emission. The experiments were performed at 850°C with a constant air total flow of 860 L h −1 , varying the coal feeding rate and therefore the air excess percentages. In each experiment, five samples have been collected from two cyclones, bubbling system, nylon filter, and adsorption system. The PAH contained in these five samples have been analysed by FS (fluorescence spectroscopy in mode synchronous) after extraction by sonication with dimethyl-formamide (DMF) The analyses show that the total PAH amount keeps a close relationship with the air excess percentage: the higher the air excess, the lower the total PAH amount emitted.

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.