Rudarsko-geološko-naftni zbornik

Torrefaction of rice husk as preparation of coal-biomass co-firing and its propensity on ash deposition

2024-06-28T12:46:56+02:00

The most extensive use of coal in Indonesia is for electricity generation. Due to increasing concerns about climate change and the need to reduce emissions caused by burning coal, biomass-based fuels are becoming more competitive. The biomass carbonization process, or torrefaction, to produce solid fuel has been introduced elsewhere. This research uses sub-bituminous coal and rice husks, considering Indonesia's large potential for both. The primary objective of this research was to determine the optimal temperature and residence time for the rice husk torrefaction process, intending to reduce the alkali oxide content that led to ash deposition. This was necessary due to the limited information available, particularly for local rice husks from Indonesia. We carried out the rice husk torrefaction at 300, 350, and 400°C temperatures for 30, 60, and 90 minutes. The results show that a temperature of 350°C and a residence time of 60 minutes were the optimal conditions. In these conditions, the potassium and sodium oxides decreased, and the calorific value increased. To get a coal-rice husk blending with a calorific value greater than 5,000 cal/g (ADB), the proportion of coal to rice husk should be 90 and 10%, respectively. The rice husk torrefaction process did not have much influence on the occurrence of ash deposition. However, the torrefaction process increased the calorific value, reduced transportation costs due to the lower moisture content, and improved grindability so that it was easy to blend with coal.

Numerical analyses to observe the performance of a monumental building at the University of Bengkulu, Indonesia

2024-05-25T14:44:44+02:00

The Integrated Laboratory Building of Political and Social Science Faculty, located in a seismic-prone area, has been the subject of a comprehensive study of its performance using seismic response analysis. This research has yielded significant findings, gathering crucial secondary data, such as soil layers, bedrock depth, building structure, and earthquake wave information. The seismic response analysis, conducted by referencing the synthetic earthquake wave from the Bengkulu–Mentawai earthquake in 2007, with a magnitude of M_w 8.6, has provided a comprehensive overview of the earthquake waves at the foundation soil layers. The data, analysed using the finite element method to understand the structural response, revealed that the Peak Ground Acceleration (PGA) and amplification factor at the surface soil layer are 0.220g and 1.429, respectively. The most critical PGA and amplification factors at the foundation soil layer are 0.147g and 0.955. Structural analysis has revealed internal forces and beam elements experiencing over-strength, necessitating retrofitting the affected structural elements to reduce the impact. One practical and highly effective method of retrofitting involves increasing the beam dimensions by 53.12%. With retrofitting, the impact of structural deformation can be minimised, enhancing the building's resilience in case of an earthquake of equal or greater magnitude. These findings underscore the importance of our research and highlight the significant role of engineers, architects, and researchers in ensuring the safety and longevity of structures in seismic-prone areas.

Computational Simulation of Sediment Motion Stability Process on Bridge Abutment Due to Crib Placement (Case Study: Harapan River, Jayapura Regency)

2024-06-02T22:38:45+02:00

Erosion occurs when the flow of velocity in a channel exceeds the threshold velocity that causes the bed material to move. This phenomenon is observed in the Harapan River, resulting in significant impacts, such as riverbed lowering and narrowing due to the presence of water structures (bridge abutments) spanning across the river. The objective of this study is to investigate the sediment motion stability around bridge abutments before and after the installation of cribs in order to prevent structural failures. Sediment sampling was conducted at six points around the bridge abutments, using the Pebble Count method along zigzag paths. The grain size of the bed material was classified according to the Sturgess classification standard, and the material dispersion process was analysed using the Hjustorm curve. Design rainfall was transformed into design flood discharge, which was then simulated using the Two-Dimensional Hydrodynamic, comparing the river conditions before and after crib installation. In abutments without cribs, erosion occurred in direct contact with the abutment on the right side for each sediment grain diameter. However, in abutments with cribs, erosion still occurred, but it did not directly contact either abutment despite the presence of a crib. The crib prevented and protected the abutments from being eroded by the riverbed.

Investigating relationships between intrinsic properties, preparation parameters of coal and coke quality: A Systematic Literature Review

2024-06-18T18:50:50+02:00

The purpose of this study is to review some of the key research concepts related to metallurgical coke. As the research landscape for coke metallurgy is evolving, researchers are increasingly interested in the effects of the intrinsic properties of coal, coal preparation parameters, and the technological conditions of coke production on the quality of metallurgical coke. As part of this review, a specific protocol, content analysis and thematic coding of cases of the “Preferred Reporting Items for Systematic Review and Meta-Analyses” method were used to investigate the simultaneous effect of these two parameters on the quality of coke in selected journal articles. A review of 118 articles was conducted, including their abstract, introduction, methodology, and results. According to the results of this study, coal blends and coal particle sizes have a direct effect on the three sections of coke mechanical properties, coke texture, and coke reactive properties. Reviewing various articles has shown that the presence of fatty coals in smaller size distribution, combined with larger-sized weak coals, leads to the formation of a stronger structure in the produced coke. However, this does not guarantee an improvement in the coke reactivity parameters. On the other hand, increasing the blending ratio of coking coals in the final mixture for producing normal-sized coke (dimensions smaller than 3 millimetres) improves the coke reactivity parameters. Studies investigating coke structure have demonstrated that a cohesive mosaic structure in high-quality cokes results from well-distributed maceral blends of coking coals with optimal size distribution among other coals.

Assessing and Improving Compressed Air Systems in Underground Mines (A Case Study in Iran)

2024-06-03T10:22:48+02:00

Compressed air is one of the most common methods of energy transfer in industrial and mining systems. Compressed air has numerous applications in underground mines to ensure safety (ventilation fans), carry out extraction operations (compressed air equipment and machines), and manage technical services like dewatering and the operating of spare equipment. Therefore, it is necessary to investigate the compressed air supply systems in mines to assess the sufficiency of compressed air, reduce energy consumption, and lower operating costs. Considering the significance of utilizing compressed air in underground mines, it is essential to verify the adequacy of the flow rate and permissible pressure of compressed air for all mine air consumers. This requires proper design and adjustment of the compressed air distribution network. In this paper, the compressed air network in the main compressor house of the Qaleh-Zari copper mine in Iran was investigated. To achieve this goal, the compressed air consumption in various mining operation conditions was investigated and discussed after surveying the airflow transmission lines. The pressure drops in each line were estimated as well. Regarding the results, the airflow consumption in regular mining operations is about 36 cubic meters per second. The drop in air pressure within the network lines is below the permissible limit, but the overall pressure drop is significant. In this approach, practical adjustments such as changing the diameter of the pipes, increasing the airflow pressure, and utilizing local compressors near consumers' locations were proposed and investigated.

Andesite Slope Stability Analysis Using Rock Mass Rating (RMR) and Slope Mass Rating (SMR) in Gunung Batu and Graha Puspa Areas, West Bandung Regency, West Java, Indonesia

2024-07-02T10:14:59+02:00

The susceptibility of West Java to landslides, coupled with its high population density, prompts research into landslide potential in the region. Notably, Gunung Batu and Graha Puspa in West Bandung Regency feature substantial andesite slopes situated along the Lembang fault and serve as tourist attractions. This study aims to assess the stability of these slopes using rock mass rating (RMR) and slope mass rating (SMR). The analysis integrates methods like rock mass classification (RMR), kinematics analysis, and empirical slope stability analysis (SMR), drawing on data obtained from uniaxial compressive strength (UCS) tests and scanline surveys. The andesite slopes exhibit RMR values ranging from 74 to 81, indicating good to very good rock mass quality. Design parameters and engineering properties are identified, including rock mass cohesion and internal friction angle, suggesting safe cut slope angles. Specific slopes are found susceptible to toppling or wedge failures. SMR values range from 72 to 96, categorizing the slopes as class I-II, indicating stability and a low probability of failure. Minor reinforcement options like scaling, toe ditch, fence, and spot bolting are proposed. Considering West Java's seismic and rainfall risks, the study recommends further modelling to incorporate variations in seismic acceleration and water content. The method would yield safety factors and cut-off values under different slope conditions, enhancing the understanding and management of landslide risks in the region.

Investigating Absorption Effects on Oil Droplets in Enhanced Oil Recovery: A Force Analysis Approach

2024-05-20T14:22:19+02:00

This research aims to analyze the forces that affect oil droplets to illustrate that augmenting the mass of an oil droplet fosters favorable conditions for interaction between displaced and displacing fluids. This, in turn, impedes the bypassing of the displacing fluid around the oil droplets. In this investigation, the concept of augmenting the mass of an oil droplet is realized through absorption phenomena, employing coated spinel oxide (cobalt ferrite oxide) nanoparticles (CFO NPs). The synthesis of CFO NPs was successfully carried out in the laboratory using a sol-gel technique, followed by coating with a surfactant and lauric acid. The coated spinel oxide NPs underwent characterization using IR, XRD, and XRF techniques. The procedures started with the calculation of capillary force restrictions for small and large oil droplets. Furthermore, practical experiments involving oil droplets on glass plates at a 30° angle were conducted for different scenarios: without water injection, with water injection, and during the "absorption effect" of CFO NPs. The findings revealed that a large oil droplet exhibits lower capillary pressure restrictions compared to a small oil droplet, with a disparity of 0.02 m/s². Consequently, it is comparatively easier for large oil droplets to become free than small ones. Moreover, a large oil droplet exhibits faster movement than small oil droplets due to gravitational effects in the absence of any injections. During the water injection scenario, the water droplets were unable to displace the oil droplet; instead, they passed through the passage beside and above the oil droplet consistently with an increase in the amount of water droplets. However, in the coated CFO NPs scenario, absorption of the coated CFO NPs onto the oil droplet was observed. This resulted in the aggregation of oil molecules, augmenting the gravity of the oil droplet and creating favourable conditions for its displacement. Notably, no water bypass beside the oil droplet was observed in this scenario, unlike the water scenario. Additionally, the aggregation of oil molecules induced corner flow, providing conducive conditions for microemulsion formation, altering wettability, modifying residual oil saturation, and enhancing injection performance. Euler's equation was employed to analyse corner flow, indicating that the level of oil deformation increases with the rising rotation velocity, potentially leading to an increased recovery factor.

Pressure build-up test analyses of a hydraulically fractured well with reduced half-length

2024-06-21T16:30:11+02:00

When the oil production of the hydraulically fractured well A-1 began to decline, a refracturing of the well was planned, as a reduction in the fracture size was assumed after a long production period. Several possibilities of the pressure build-up test analyses were performed to determine the best evaluation of the reduced fracture half-length. Although the objectives of these tests are to determine the reservoir properties, such as rock permeability and skin factor, as well as fracture conductivity, the Saphir programme is also used to model the fracture half-length. This is the most important parameter required for the design of the new fracturing process and for the creation of a new production model. For this purpose, the methods of the pressure build-up test analysis are first described theoretically. Based on different analyses of the same pressure build-up test, the one that best matches the analytical model of a fractured well with the measured pressure curve and the derivative curve is selected. It is found that the most accurate result for fracture half-length is obtained from the fractured well model with multiphase flow.

Selection of the optimal technology to prevent sand production, taking into account rock deconsolidation in the bottomhole formation zone

2024-06-05T13:05:56+02:00

This article presents studies on the selection of the best sand control option, technologically based on the application of the method of fixing the bottomhole part of the well system with polymerized proppant, which will prevent the destruction of the formation zone of the wells and facilitate the development of the Kumkol field in the future. During the development of the Kumkol field, the main and most complicating factor in the operation of wells is sand production, leading to long downtime and repairs. The aim of the study is to scientifically substantiate and improve the technological methods of fixing the bottomhole zone of the well system to exclude or limit sand production with the well production of the Kumkol field, taking into account the current state of the reservoir rocks. The work applied a set of research methods, including: analysis of the experience of combating sand ingress at the Kumkol field; the use of the theoretical foundations of the relationship between the methods of anti-sand filtration and the properties of reservoir rocks; mathematical experiments on the constructed geological and mathematical model of the current state of the rocks of the decompacted zone. The scientific novelty of the work lies in the establishment of patterns that relate the impact of the destruction of reservoir rocks with a weakly cemented property in a production well on the degree of formation of deconsolidation zones at the bottom of wells that reveal a weakly cemented rock formation.

Flow Pattern Prediction in Horizontal and Inclined Pipes using Tree-Based Automated Machine Learning

2024-06-05T13:01:58+02:00

In the oil and gas industry, understanding two-phase (gas-liquid) flow is pivotal, as it directly influences equipment design, quality control, and operational efficiency. Flow pattern determination is thus fundamental to industrial engineering and management. This study utilizes the Tree-based Pipeline Optimization Tool (TPOT), an Automated Machine Learning (AutoML) framework that employs genetic programming, in obtaining the best machine learning model for a provided dataset. This paper presents the design of flow pattern prediction models using the TPOT. The TPOT was applied to predict flow patterns in 2.5 cm and 5.1 cm diameter pipes, using datasets from existing literature. The datasets went through handling of imbalanced data, standardization, and one-hot encoding as data preparation techniques before being fed into TPOT. The models designed for the 2.5 cm and 5.1 cm datasets were named as FPTL_TPOT_2.5 and FPTL_TPOT_5.1, respectively. A comparative analysis of these models alongside other standard supervised machine learning models and similar state-of-the-art similar two-phase flow prediction models was carried out and the insights on the performance of these TPOT designed models were discussed. The results demonstrated that models designed with TPOT achieve remarkable accuracy, scoring 97.66% and 98.09%, for the 2.5 cm and 5.1 cm datasets respectively. Furthermore, the FPTL_TPOT_2.5 and FPTL_TPOT_5.1 models outperformed other counterpart machine learning models in terms of performance, underscoring TPOT's effectiveness in designing machine learning models for flow pattern prediction. The findings of this research carry significant implications for enhancing efficiency and optimizing industrial processes in the oil and gas sector.

Sedimentology of the Paleogene Volcaniclastic Gravity Flow Deposit of the Ulukışla Formation, South Central Türkiye

2024-05-22T12:37:07+02:00

The sedimentological study of volcaniclastic successions is essential for gaining insight into the intricate geological history of the Ulukışla Basin in south Central Anatolia. This study, based on a comprehensive facies analysis of two representative stratigraphic sections, attempts to reconstruct the depositional conditions associated with volcaniclastic sedimentation within the Ulukışla Formation. Facies assemblages dominated by debris-flow deposits and turbidites provide clear evidence for deposition under deep-water conditions related to the proximal environment. Sedimentary characteristics of these deposits made up of volcanogenic conglomerates with basaltic to andesitic clasts of variable size, sandstones, and subordinate mudstone are suggestive of derivation from the nearby Ulukışla volcanic rocks. Almost all the lithofacies display a high tuff content indicative of possible sediment contributions from sub-aerial volcanic sources. The main controlling factors responsible for deposition include submarine gravity flow processes thought to have been triggered by slope instability or the collapse of a volcanic edifice. Thus, the resulting volcaniclastic accumulations are interpreted to be linked to volcanic apron deposits. In the realm of prospective research, the acquisition of geochemical and geochronological data stands as a promising avenue, offering crucial insight into the temporal aspects and tectonic setting of deposition of the Ulukışla volcaniclastic sequence.

Insight into rock thermal conductivities in the North Croatian Basin through in situ measurements

2024-06-04T17:38:50+02:00

The thermal conductivity of rocks represents one of the significant variables when investigating geothermal potential of an area on a local scale as well as regionally when performing basin analysis with the aim of estimating hydrocarbon potential. While steady-state methods of measuring thermal conductivity are presumed to yield more reliable results, transient methods allow for in situ measurements, thereby considerably simplifying and reducing measurement costs. This study was performed with the goal to expand the understanding of thermal conductivity of rocks typical for the North Croatian Basin (NCB) infill, as well as the underlying basement rocks. The measured values reveal distinct ranges across various lithologies. The thermal conductivity values measured in crystalline rocks are quite consistent, showing narrow ranges of values for each lithotype: for granite the measured values are between 2.317 and 2.486 W m^-1 K^-1, the value range for gneiss is between 3.332 and 3.565 W m^-1 K^-1 and the thermal conductivity of amphibolite is in the range between 1.549 and 1.623 W m^-1 K^-1. In contrast, the thermal conductivity values of sedimentary rocks vary within broader ranges – the values in sandstones range between 1.778 and 2.433 W m^-1 K^-1, for marlstones the registered range is between 0.917 and 2.323 W m^-1 K^-1, the values measured in shales range between 0.894 and 2.304 W m^-1 K^-1 and biocalcarenites show values of thermal conductivity between 0.990 and 2.023 W m^-1 K^-1. The greater variability in values measured for sedimentary rocks is attributed to the variability in porosity and fluid saturation, as well as the greater variability of mineral composition. Further research is needed to determine which factor has the greatest influence on the variability of thermal conductivity values, i.e. to establish to which extent each of the factors contributes to the measured values.