María Cuesta

Thermal behaviour during the pyrolysis of low rank perhydrous coals

Abstract Perhydrous coals are characterised by high H/C atomic ratios and so their chemical structure is substantially modified with respect to that of conventional coals. As a result, perhydrous coals show different physico-chemical properties to common coals (i.e. higher volatile matter content, enhancement of oil/tar potential, relatively lower porosity and higher fluidity during carbonisation). However, there is little information about thermal behaviour during the pyrolysis of this type of coal. In this work, six perhydrous coals (H/C ratio between 0.83 and 1.07) were pyrolysed and analysed by simultaneous thermogravimetry/mass spectrometry. The results of this work have revealed the influence of high H/C values on the thermal behaviour of the coals studied. During pyrolysis the perhydrous coals exhibit very well defined, symmetrical peaks in the mass loss rate profiles, while normal coals usually show a broader peak. The shape of such curves suggests that in perhydrous coals fragmentation processes prevailed over condensation reactions. The high hydrogen content of perhydrous coals may stabilise the free radicals formed during heat treatment, increasing the production of light components.

Press archives as temporal records of landslides in the North of Spain : relationships between rainfall and instability slope events

This paper evaluates the usefulness of press archives as temporal records of landslides in Asturias, northern Spain. It also shows the potential for this kind of information in the establishment of relationships between slope instability events and climatic parameters. In this way, a search has been made of Asturian regional newspaper archives, including data from the period between January 1980 and June 1995 (5290 newspapers reviewed). The methodology developed shows some limitations, due to the low frequency of news items relating to landslides and the lack of scientific data collected by correspondents. Moreover, there is a bias towards instability events concerning people, infrastructures and other human resources. Statistical analysis of 209 news items relating to slope instability is useful to establish the geological and spatial location of landslides. Fifty-one point two percent of them are situated in the Central Coal Basin, with a sedimentary siliceous bedrock. Temporal data are accurate in 83.2% of the cases. A comparison between climatic and slope instability events reveals that 79% of the landslides developed during rainfall events, associated with the monthly 24-h rainfall maximum values. Highest landslide frequencies are reached in years with more than 1000 mm rainfall, mainly in December and April.

Control of the chemical structure of perhydrous coals; FTIR and Py-GC/MS investigation

Abstract This work analyses a set of perhydrous coals (mainly composed of huminite/vitrinite maceral group) in order to determine the inter-relations between the hydrogen content and the modifications in the coal structure at a molecular level. The study involves the direct solid state characterisation of the coal combined with the analysis of representative fragments of the coal network obtained through flash-pyrolysis. The perhydrous character of the coals is not reflected either in the aliphatic hydrogen concentration (from FTIR data) or by the presence of straight-chain aliphatic moieties in the pyrolysates. This structural study shows that perhydrous coals contain mainly aromatic structures with 1–2 rings and a very small concentration of aromatic rings of large size. In agreement with this, phenol and alkyl phenols are the most prominent degradation products whereas other aromatic compounds (mainly benzene and naphthalene derivatives) are minor and probably evaporative compounds. The major structural elements in the samples studied are simple phenols with a preponderance of substituted para alkyl. The results obtained show that the processes of hydrogen enrichment affect the reactions of aromatisation and condensation. During the natural evolution of the perhydrous coals the transformations of the oxygenated functionalities in the lignin precursor seem to have taken place without the parallel structural reorganisation of the lignin framework responsible for the formation of polycyclic aromatic systems. As a result, the chemical structure of perhydrous vitrinites in coals is substantially modified with respect to that described in ‘normal’ coals. The results obtained also indicate that the source of hydrogen content and the effect that it has during the subsequent evolution process of the coals, affects the chemical structure of the perhydrous vitrinite and hence its properties and behaviour.

Hybrid passive–active absorption using microperforated panels

A theoretical and experimental study of a proposed hybrid passive–active plane-wave system to provide broadband acoustic absorption is presented. The passive absorber consists of a microperforated panel (MPP), used in place of conventional fibrous materials, in front of an air layer. The active system uses an active transducer (a loudspeaker), an error sensor (a microphone), and an adaptive controller. MPPs are thinner than fibrous materials and provide a better solution in hygienic environments. For two such systems, the dependence of performance on MPP parameters is studied for two control strategies: impedance matching and pressure release. The first condition is found to be better for cases where the acoustic impedance of the system approaches that of air. Otherwise, the pressure-release condition is better, and a wideband solution is the implementation of the active control system up to a frequency where the natural band of the passive system provides higher absorption. Therefore, the use of a low-pa...

Structure of tars derived from low-temperature pyrolysis of pure vitrinites: influence of rank and composition of vitrinites

Abstract In this paper, a gas chromatography (GC)/mass spectrometry (MS) analysis of the volatile fraction of low temperature tars obtained at 550°C by means of the Gray–King pyrolysis of four Stephanian (Carboniferous) monomaceralic coals (pure vitrinites) and a structural study of the whole material by means of nuclear magnetic resonance (NMR, 1H and 13C) are undertaken. Furthermore, a precise assignment of the different spectral regions is achieved through 13C editing of the protonated carbons, identification of quaternary carbon atoms and 2D proton detected 1H, 13C correlation experiments. The study gives valuable information about chemical variability within the vitrinite maceral group. Apart from variation with rank, the results show the effect of factors such as the nature of the precursors, degree of gelification and preservation of the structure, and depositional environment. This effect is not very well understood and it is not always reflected in the conventional bulk characterisation parameters. However, there is no doubt that it affects the thermal behaviour of the material and, therefore, has an indirect effect on its conversion processes. The low-temperature tars are made up mainly of mono- and di-aromatic structures with a preponderance of phenolic compounds. All of the above mentioned factors (rank, nature of precursors, degree of gelification, preservation of the structure, depositional environment) affect the internal distribution of phenols in a complicated manner. Nevertheless, the higher proportion of telinite and initially structured macerals in the raw vitrinite and its precursors is clearly reflected in the amount of 2,4-dimethyl phenol and 4-ethyl phenol. Vitrinites made up of more gelified and homogeneous material give rise to tars with a higher amount of aromatic hydrogen and a higher quantity of condensed aromatic systems. Variation in the maceral composition within the vitrinite maceral group leads to differences in the amount of aliphatic carbon and in the distribution of the aliphatic moieties. Such variations seem to be closely related to the relative amounts of telinite and collotelinite and the proportion of collodetrinite present in the raw materials.

Pseudomonas guariconensis sp. nov., isolated from rhizospheric soil.

We isolated a bacterial strain designated PCAVU11(T) in the course of a study of phosphate-solubilizing bacteria occurring in rhizospheric soil of Vigna unguiculata (L.) Walp. in Guárico state, Venezuela. The 16S rRNA gene sequence had 99.2 % sequence similarity with respect to the most closely related species, Pseudomonas taiwanensis, and 99.1 % with respect to Pseudomonas entomophila, Pseudomonas plecoglossicida and Pseudomonas monteilii, on the basis of which PCAVU11(T) was classified as representing a member of the genus Pseudomonas. Analysis of the housekeeping genes rpoB, rpoD and gyrB confirmed the phylogenetic affiliation and showed sequence similarities lower than 95 % in all cases with respect to the above-mentioned closest relatives. Strain PCAVU11(T) showed two polar flagella. The respiratory quinone was Q9. The major fatty acids were 16 : 0 (25.7 %), 18 : 1ω7c (20.4 %), 17 : 0 cyclo (11.5 %) and 16 : 1ω7c/15 : 0 iso 2-OH in summed feature 3 (10.8 %). The strain was oxidase-, catalase- and urease-positive, the arginine dihydrolase system was present but nitrate reduction, β-galactosidase production and aesculin hydrolysis were negative. Strain PCAVU11(T) grew at 44 °C and at pH 10. The DNA G+C content was 61.5 mol%. DNA-DNA hybridization results showed values lower than 56 % relatedness with respect to the type strains of the four most closely related species. Therefore, the results of genotypic, phenotypic and chemotaxonomic analyses support the classification of strain PCAVU11(T) as representing a novel species of the genus Pseudomonas, which we propose to name Pseudomonas guariconensis sp. nov. The type strain is PCAVU11(T) ( = LMG 27394(T) = CECT 8262(T)).

Active control of the exhaust noise radiated by an enclosed generator

Abstract The aim of this work was to design and implement a hybrid passive/active system to control the noise radiated by a small generator. Passive control is afforded by enclosing the generator with a close-fitting, leaky, rectangular box. The measured Insertion Loss is higher than 20 dB above 500 Hz. Special attention is paid to technical aspects such as air refreshing and temperature inside the enclosure. Low frequency noise escapes from the enclosure through air intake and gas exhaust openings. A single-input single-output (SISO) feedforward active noise control (ANC) system, implemented in a commercially available device, is used to reduce the radiated exhaust noise below 500 Hz. The reference signal to the SISO ANC system is supplied by an accelerometer located on the air filter case of the generator. The error signal is provided by an electret microphone along the exhaust pipe. The control source consists of a high temperature loudspeaker, positioned in a side-branch configuration to avoid direct contact with the exhaust gas. Some harmonics were attenuated more than 30 dB.

Pseudomonas helmanticensis sp. nov., isolated from forest soil.

A bacterial strain, OHA11(T), was isolated during the course of a study of phosphate-solubilizing bacteria occurring in a forest soil from Salamanca, Spain. The 16S rRNA gene sequence of strain OHA11(T) shared 99.1% similarity with respect to Pseudomonas baetica a390(T), and 98.9% similarity with the type strains of Pseudomonas jessenii, Pseudomonas moorei, Pseudomonas umsongensis, Pseudomonas mohnii and Pseudomonas koreensis. The analysis of housekeeping genes rpoB, rpoD and gyrB confirmed its phylogenetic affiliation to the genus Pseudomonas and showed similarities lower than 95% in almost all cases with respect to the above species. Cells possessed two polar flagella. The respiratory quinone was Q9. The major fatty acids were C16 : 0, C18 : 1ω7c and summed feature 3 (C16 : 1ω7c/iso-C15 : 0 2-OH). The strain was oxidase-, catalase- and urease-positive, positive for arginine dihydrolase but negative for nitrate reduction, β-galactosidase production and aesculin hydrolysis. It was able to grow at 31 °C and at pH 11. The DNA G+C content was 58.1 mol%. DNA-DNA hybridization results showed values lower than 49% relatedness with respect to the type strains of the seven closest related species. Therefore, the combined genotypic, phenotypic and chemotaxonomic data support the classification of strain OHA11(T) to a novel species of the genus Pseudomonas, for which the name Pseudomonas helmanticensis sp. nov. is proposed. The type strain is OHA11(T) ( = LMG 28168(T) = CECT 8548(T)).

The influence of impregnation by hydrocarbons on coal structure during its thermal evolution

The present work analyses the changes in the chemical structure of a perhydrous coal during its thermal evolution at different temperatures in an open-medium pyrolysis system. The results obtained were compared with those described for non-perhydrous coals in order to establish the effect of the substances assimilated by the coal structure (hydrocarbon/oil-like substances) on the thermal evolution of the coal. The transformation ratio at each stage of thermal treatment was determined and the chemical-structural characterisation of the resultant products was performed. Changes in textural and microtextural properties associated with structural modifications during the evolution were also tested. The results obtained show that this perhydrous coal develops a specific evolution pathway different from that followed by non-perhydrous coals with a normal H/C ratio. The substances assimilated by the perhydrous coal cannot be easily and totally released from its structure so that they can be only partially removed after thermal treatment. Thus, the treatment debilitates the interactions between the substances and the coal matrix in addition to weakening and cracking the matrix during the thermal process. The increase in temperature also leads to the conversion of some of the heavy assimilated substances into lighter compounds. However, the assimilated substances are present even at high temperatures of the thermal process, providing hydrogen which has the effect of stabilising the radicals originated during the pyrolysis and improving the fluidity properties in the reacting medium.

Optimisation of an active control system to reduce the exhaust noise radiated by a small generator

Abstract In a previous paper (Cuesta M, Cobo P. Active control of the exhaust noise radiated by an enclosed generator. Applied Acoustics 2000;61(1):83–94) the authors reported a passive/active system to control the exhaust noise radiated by a small generator. Passive control was afforded by a steel rectangular enclosure lined with a layer of absorbing material. The enclosure, designed to provide the higher Insertion Loss, supplied attenuation higher than 20 dB above 500 Hz. To reduce the noise below 400 Hz, an active control system was designed with one reference, one error input and one control output. Whilst many harmonics in this frequency band were attenuated, the ANC system was unable to reduce some of them. The aim of this paper is to identify the origin of this lack of attenuation and to alleviate it. An exhaustive analysis of both the transfer function between the secondary source and the error sensor (the plant) and the reference signal has been carried out. A new ANC system with improved performance is described which controls all the harmonics until 300 Hz.