Manuel Martínez

Effect of coal weathering on some geochemical parameters

The effect of coal weathering on some geochemical parameters was studied. Seven pairs of fresh and altered samples were selected from different Venezuelan coal deposits. The following analyses were performed: water and ash percent, heating value, bitumen content and composition, infrared spectroscopy, n-alkane distribution and humic substances concentration (HS). As weathering proceeds, there is a corresponding change in HS concentration. Most geochemical parameters show small changes with HS concentrations below 15%. For intense weathering, all parameters measured show important modifications. Such changes are due to the breaking of the coals macrostructure.

Trace elements of Paleocene Táchira coals, southwestern Venezuela: a geochemical study

Abstract The concentration and distribution of 35 elements in 78 coal samples from the Tachira State coal fields belonging to Los Cuervos Formation (Paleocene) of western Venezuela were obtained using atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission (ICP-AES). The aim of this work was to determine, through a multivariate statistical approach (factor analysis), if there is a correlation between the trace element content in coal beds and the provenance rocks at the time of peat deposition. Comparison with world averages and geometric means for trace element concentrations in coal-bed samples shows that B, Ba, La, V, Mn, Zn, and Pb are depleted. However, Tachira coal samples show a perceptible enrichment in Bi, Sb, As, Cd, and Mo, and they are highly enriched in Ag and Co. Nicholls plot suggests that only B and Co show a distinctive organic affinity. Enriched elements (Ni, Ag, Cd, Mo, Co) are both statistically and genetically related, and we attribute their origin to a volcaniclastic Jurassic unit. Other statistical factors (Th–V–P and Ca–Mg–Mn) reveal a different provenance, indicating a felsic plutonic source and a sedimentary limestone, respectively. A fourth factor (K–Mo–Th–S) is composed mainly of clay minerals and authigenic sulfides.

Organic Geochemical Investigation and Coal-bed Methane Characteristics of the Guasare Coals (Paso Diablo Mine, Western Venezuela)

Abstract The aim of this work was to carry out a geochemical study of channel samples collected from six coal beds in the Marcelina Formation (Zulia State, western Venezuela) and to determine experimentally the gas content of the coals from the Paso Diablo mine. Organic geochemical analyses by gas chromatography-mass spectrometry and isotopic analyses on-line in coalbed gas samples were performed. The results suggest that the Guasare coals were deposited in a continental environment under highly dysoxic and low salinity conditions. The non-detection of 18α(H)-oleanane does not preclude that the organic facies that gave rise to the coals were dominated by angiosperms. In addition, the presence of the sesquiterpenoid cadalene may indicate the subordinate contribution of gymnosperms (conifers) in the Paleocene Guasare mire. The average coalbed gas content obtained was 0.6 cm3/g. δ13C and δD values indicate that thermogenic gas is prevalent in the studied coals.

Ti/Zr ratio as a geochemical tool for the correlation of weathered coals from geological formations in two Latin American sedimentary basins

ABSTRACT Major and trace element concentrations in fresh and altered coals in outcrops and coalfields from Táchira and Mérida states (Venezuela), as well as from Napo and Pastaza provinces (Ecuador), have been determined to establish inorganic parameters not dependent of weathering effects. Noteworthy is that the Ti/Zr ratio is approximately constant in each sedimentary basin even for great distances (>100 km). Worldwide data of trace elements analysis in coal samples support the stated Ti/Zr ratio constancy in different basins for fresh and weathered ones. Therefore, Ti/Zr ratio can be considered a rapid tool to easily identify coal seam correlations.

A new displacement-based approach to calculate stress intensity factors with the boundary element method

The analysis of cracked brittle mechanical components considering linear elastic fracture mechanics is usually reduced to the evaluation of stress intensity factors (SIFs). The SIF calculation can be carried out experimentally, theoretically or numerically. Each methodology has its own advantages but the use of numerical methods has become very popular. Several schemes for numerical SIF calculations have been developed, the J-integral method being one of the most widely used because of its energy-like formulation. Additionally, some variations of the J-integral method, such as displacement-based methods, are also becoming popular due to their simplicity. In this work, a simple displacement-based scheme is proposed to calculate SIFs, and its performance is compared with contour integrals. These schemes are all implemented with the Boundary Element Method (BEM) in order to exploit its advantages in crack growth modelling. Some simple examples are solved with the BEM and the calculated SIF values are compared against available solutions, showing good agreement between the different schemes.

Thermo-Mechanical Numerical Analysis in Steel Plates Butt Welded

In this work, 2D and 3D Finite Element models to simulate the temperature distribution and residual stress in butt-welded steel plates with the aid of computer simulation, using the commercial software Abaqus®, are developed. The work is carried out in two stages: 1) An analysis of heat transfer in transient state regardless of the structural part is performed, and 2) Thermal and structural responses are sequentially coupled in a thermo-mechanical process simulation in order to determine the final residual stresses induced during progressive heating and subsequent cooling. The results show that for 2D and 3D models the residual stress distribution for relatively thick plate welding can be characterized by a state of stresses plane, dominated by longitudinal stresses. The main difference between both models occurs for transverse stress σY where the values for 3D are significantly greater than for 2D.Copyright

Characterization of Physicochemically Abnormal Coals in the Matarere Formation (Cerro Saroche National Park, Venezuela)

Proximate and ultimate analyses, % Rm , vitrinite anisotropy, Rock-Eval T max, and biomarkers have been studied on several coal samples collected at two outcrops in the Cerro Saroche National Park (Venezuela) in order to determine their geochemical characteristics. The results indicate that these coals were deposited in a transitional paleoenvironment under weakly reducing conditions (Palaeogene Matatere Formation), and were derived from mixed organic matter input. Carbon content and other data (%Rm and anisotropy) suggest high levels of maturity (matagenesis to metamorphism) of these coals. However, this does not correspond to the low-volatile bituminous stage (late catagenesis) according to the ASTM classification by rank. These coals might have reached overmaturity as a result of heating by Neogene igneous events.

Bend Flexibility Factors of Piping Elbows and Piping Elbows With Trunnion Attachments Using the Boundary Element Method

Flexibility Factor is an important parameter for the design of piping system related to oil, gas and power industry. Elbows give a great flexibility to piping system, but where a trunnion is attached to an elbow in order to support vertical pipe sections, the piping flexibility is affected. Generally, determination of elbow flexibility factors has been performed by engineering codes such as ASME B31.3 or ASME B31.8, or using the Finite Element Method (FEM) and Finite Difference Method (FDM). In this work, bend flexibility factors for 3D models of piping elbows and piping elbows with trunnion attachments using the Boundary Element Method (BEM) are calculated. The BEM is a relatively new numerical method for this kind of analysis, for which only the surface of the problem needs to be discretized into elements reducing the dimensionality of the problem. This paper shows the simulation of 9 elbows with commercially available geometries and 29 geometries of elbows with trunnion attachments, 10 of them using commercial elbow dimensions, with applied in-plane and out-of-plane bending moments. Structured meshes are used for all surfaces, except the contact surface of elbow-trunnion joints, and no welded joints are simulated. The results show smaller values of flexibility factors of elbow and elbow–trunnion attachments in all loading cases if are compared to ASME B31.3 or correlations obtained from other works. The results also indicate that flexibility factor for elbow-trunnion attachment subjected to in-plane bending moment is greater than flexibility factor for out-of plane bending moment. Accuracy of BEM’s results were not good when flexibility characteristic values are lesser than 0.300, which confirm the problems of this numerical method with very thin-walled structures. The method of limit element could be used as tool of alternative analysis for the design of made high-pitched system, when the problem with very thin-walled structures is fixed.© 2009 ASME