Optimización de la metodología de contratación de carbones térmicos con destino a la generación eléctrica

En los últimos quince años se ha producido una liberalización de los mercados eléctricos en los distintos países de ámbito occidental que ha ido acompañado de un incremento por la preocupación por la incidencia de las distintas tecnologías de generación en el entorno medioambiental. Ello se ha traducido en la aparición de un marco regulatorio más restrictivo sobre las tecnologías de generación fósiles, con mayor incidencia en las derivadas de productos petrolíferos y carbón. A nivel mundial han ido apareciendo cambios normativos relativos a las emisiones de distintos elementos contaminantes (CO2, SO2, NOx…), que hacen que en particular las centrales térmicas de carbón vean muy afectadas su rentabilidad y funcionamiento. Esta situación ha supuesto que la tecnología de generación eléctrica con carbón haya avanzado considerablemente en los últimos años (calderas supercríticas, sistemas de desulfuración, gasificación del carbón…). No obstante, el desarrollo de la generación con energías renovables, la generación con gas mediante centrales de ciclo combinado y la opinión social relativa a la generación con carbón, principalmente en Europa, suponen un serio obstáculo a la generación con carbón. Por consiguiente, se hace necesario buscar vías para optimizar la competitividad de las centrales de carbón y el camino más razonable es mejorar el margen esperado de estas plantas y en particular el coste de adquisición del carbón. Ello se hace aún más importante por el hecho de existir numerosas centrales de carbón y un elevado número de nuevos proyectos constructivos de centrales de carbón en países asiáticos. Por consiguiente, el objeto de la presente tesis doctoral se centra en definir una metodología para optimizar la compra de carbón, desde el punto de vista económico y técnico, con destino a su consumo en una central térmica, con ello reducir el coste del carbón consumido y mejorar su competitividad. También se enfoca a determinar que herramientas pueden ser utilizadas para optimizar la gestión del carbón después de su compra y con ello abrir la posibilidad de obtener márgenes adicionales para dicho carbón. De acuerdo con este objetivo, el autor de la presente Tesis Doctoral realiza tres aportaciones novedosas en el ámbito de la contratación de carbón térmico y su optimización posterior: - Evaluación de carbones para su adquisición considerando el efecto de la calidad del carbón en el coste de generación asociado a cada carbón ofertado. - Creación, desarrollo, implantación y utilización de una potente herramienta de planificación de Combustibles. Esta herramienta, está diseñada con el objeto de determinar la solución económica óptima de aprovisionamientos, consumos y niveles de existencias para un parque de generación con centrales de carbón y fuelóleo. - La extensión de una metodología contractual habitual en el mercado spot de Gas Natural Licuado, a la contratación spot de Carbón de Importación. Esta se basa en el desarrollo de Acuerdos Marcos de Compra/Venta de carbón, que por su flexibilidad permitan obtener resultados económicos adicionales después de la compra de un carbón. Abstract In the last fifteen years, a liberalization of the electrical markets has occurred in the western countries. This process has been accompanied by an increasing concern of the impact of the different generation technologies towards the environment. This has motivated a regulated framework restricting the use of fossil fuels, impacting a great deal in coal and oil based products. Worldwide, new legal changes have been arising related to the emissions of the different pollutants (CO2, SO2, NOx…). These changes have had a deep impact in the feasibility, profit and running of coal fired power plants. This situation has motivated the coal electrical generation technologies to move forward in an important way in the last few years (supercritical furnaces, desulphuration plants, coal gasification…). Nevertheless, the development of the renewable generation, the gas combined cycle generation and the social opinion related to the coal electrical generation, mainly in Europe, have created a serious obstacle to the generation of electricity by coal. Therefore it is necessary to look for new paths in order to optimize the competitiveness of the coal fired power plants and the most reasonable way is to improve the expected margin of these plants and particularly the coal purchase cost. All of the above needs to be taken into context with the large number of existing coal fired power plants and an important number of new projects in Asian countries. Therefore, the goal of the current doctoral dissertation is focused to define a methodology to be considered in order to optimize the coal purchase, from an economical and a technical point of view. This coal, destined for power plant consumption, permits the reduction of consumption coal cost and improves the plant’s competitiveness. This document is also focused to define what tools we can use to optimize the coal management after deal closing and therefore open the possibility to get further margins. According to this goal, the author of this doctoral dissertation provides three important new ideas in the ambit of contracting steam coal and the posterior optimization: - Evaluation of coal purchases, considering the effect of coal quality on the cost of generation associated with each type of coal offered. - The creation, development, deployment and use of a strong planning tool of fuels. This tool is designed for the purpose of determining the optimal economic solution of fuel supply, consumption and stock levels for a power generation portfolio using coal and fuel oil fired power plants. - The application of a common contractual methodology in the spot market of Liquid Natural Gas, for the contracting spot imported coal. This is based on the development of Framework Agreements for the Purchasing / Sale of coal, which because of its flexibility allows for the gain of additional financial results after the purchase of coal.

Gasification technology assessment of sterile coal to clean electrical power generation.

Sterile coal is a low-value residue associated to the coal extraction and mining activity. According to the type and origin of the coal bed configuration, sterile coal production can mainly vary on quantity, calorific value and presence of sulphur compounds. In addition, the potential availability of sterile coal within Spain is apparently high and its contribution to the local power generation would be of interest playing a significant role. The proposed study evaluates the availability and deployment of gasification technologies to drive clean electricity generation from waste coal and sterile rock coal, incorporating greenhouse gas emission mitigation systems, like CO2, H2S and NOx removal systems. It establishes the target facility and its conceptual basic design proposal. The syngas obtained after the gasification of sterile coal is processed through specific conditioning units before entering into the combustion chamber of a gas turbine. Flue gas leaving the gas turbine is ducted to a heat recovery steam generation boiler; the steam produced within the boilerdrives a steam turbine. The target facility resembles a singular Integrated Gasification in Combined Cycle (IGCC) power station. The evaluation of the conceptual basic design according to the power output set for a maximum sterile contribution, established that rates over 95% H2S and 90% CO2 removal can be achieved. Noticeable decrease of NOx compounds can be also achieved by the use of commercial technology. A techno-economic approach of the conceptual basic design is made evaluating the integration of potential unitsand their implementation within the target facility aiming toachieve clean power generation. The criterion to be compliant with the most restrictive regulation regarding environmental emissions is setting to carry out this analysis.

Application of protection means against explosions in underground mines

Underground coal mines explosions generally arise from the inflammation of a methane/air mixture. This explosion can also generate a subsequent coal dust explosion. Traditionally such explosions have being fought eliminating one or several of the factors needed by the explosion to take place. Although several preventive measures are taken to prevent explosions, other measures should be considered to reduce the effects or even to extinguish the flame front. Unlike other protection methods that remove one or two of the explosion triangle elements, namely; the ignition source, the oxidizing agent and the fuel, explosion barriers removes all of them: reduces the quantity of coal in suspension, cools the flame front and the steam generated by vaporization removes the oxygen present in the flame. The present paper is essentially based on the comprehensive state-of–the-art of Protective Systems in underground coal mines, and particularly on the application of Explosion Barriers to improve safety level in Spanish coal mining industry. After an exhaustive study of series EN 14591 standards covering explosion prevention and protection in underground mines, authors have proven explosion barriers effectiveness in underground galleries by Full Scale Tests performed in Polish Barbara experimental mine, showing that the barriers can reduce the effects of methane and/or flammable coal dust explosions to a satisfactory safety level.

Numerical simulation of group combustion of pulverized coal

A mathematical model for the group combustion of pulverized coal particles was developed in a previous work. It includes the Lagrangian description of the dehumidification, devolatilization and char gasification reactions of the coal particles in the homogenized gaseous environment resulting from the three fuels, CO, H2 and volatiles, supplied by the gasification of the particles and their simultaneous group combustion by the gas phase oxidation reactions, which are considered to be very fast. This model is complemented here with an analysis of the particle dynamics, determined principally by the effects of aerodynamic drag and gravity, and its dispersion based on a stochastic model. It is also extended to include two other simpler models for the gasification of the particles: the first one for particles small enough to extinguish the surrounding diffusion flames, and a second one for particles with small ash content when the porous shell of ashes remaining after gasification of the char, non structurally stable, is disrupted. As an example of the applicability of the models, they are used in the numerical simulation of an experiment of a non-swirling pulverized coal jet with a nearly stagnant air at ambient temperature, with an initial region of interaction with a small annular methane flame. Computational algorithms for solving the different stages undergone by a coal particle during its combustion are proposed. For the partial differential equations modeling the gas phase, a second order finite element method combined with a semi-Lagrangian characteristics method are used. The results obtained with the three versions of the model are compared among them and show how the first of the simpler models fits better the experimental results.

Comparison of CO2 From Coal Capture Processes and Valorisation Technologies

Coal is the most plentiful and evenly distributed fossil fuel worldwide. Based on current production, it is estimated that the reserves will last approximately 130 years. Its use worldwide has been increasing, mainly due to consumption by emerging countries. CO2 emissions generated by combustion and the repercussions of such on climate change support the view that it could no longer be used. CO2 capture may be the solution to continue using it, which would cater for the growing energy demand worldwide. The aim of this study is to compare different processes concerning CO2 capture that may be economically viable, ultimately showing that coal, a fossil energy source widely distributed around the world, can, as a result of using different CO2 capture processes, be used as a clean source of electricity. Hence, in places where geological hurdles may render the costs of CO2 storage considerably higher, since it might have to travel far, coal may be used for other purposes, thus valorising CO2 within the industrial sector. This research is focused on the technical and economic comparison of the most relevant CO2 capture projects designed in Spain using different existing technologies. The oxyfuel project in Ciuden (Leon, Spain), the IGCC Elcogas, precombustion CO2-capture project (Puertollano, Spain) and the postcombustion project in Carboneras (Almeria, Spain) will be analyzed in order to assess the options available to valorise captured CO2. Valorising captured CO2 may be an adequate solution in areas where, although CO2 capture is still possible, storage is not equally so, thus generating a further benefit. The possible uses of CO2 will be assessed in vegetable growing greenhouses, harnessing CO2 in vegetable life cycles. This will also be used in growing algae for subsequent biodiesel production. Both CO2 capture and valorising will eventually lead to the clean use of coal, which will thus enhance the level of self-supply, aiding the development of electric vehicles, which require large amounts of electricity, as well as improve the level of energy autonomy in countries around the world. Another type of fuel, biodiesel, will also be obtained, without this affecting international food prices.

Behaviour of dolomite, olivine and alumina as primary catalysts in air-steam gasification of sewage sludge

Sewage sludge gasification assays were performed in an atmospheric fluidised bed reactor using air and air–steam mixtures as the gasifying agents. Dolomite, olivine and alumina are three well known tar removal catalysts used in biomass gasification processing. However, little information is available regarding their performance in sewage sludge gasification. The aim of the current study was to learn about the influence of these three catalysts in the product distribution and tar production during sewage sludge gasification. To this end, a set of assays was performed in which the temperature (750–850 °C), the in-bed catalyst content (0, 10 and 15 wt.%) and the steam–biomass ratio (SB) in the range of 0–1 were varied with a constant equivalence ratio (ER) of 0.3. The results were compared to the results from gasification without a catalyst. We show that dolomite has the highest activity in tar elimination, followed by alumina and olivine. In addition to improving tar removal, the presence of water vapour and the catalysts increased the content of H2 in the gases by nearly 60%.

Air-steam gasification of sewage sludge in a bubbling bed reactor: Effect of alumina as a primary catalyst

Numerous references can be found in scientific literature regarding biomass gasification. However, there are few works related to sludge gasification. A study of sewage sludge gasification process in a bubbling fluidised bed gasifier on a laboratory scale is here reported. The aim was to find the optimum conditions for reducing the production of tars and gain more information on the influx of different operating variables in the products resulting from the gasification of this waste. The variables studied were the equivalence ratio (ER), the steam-biomass ratio (SB) and temperature. Specifically, the ER was varied from 0.2 to 0.4, the SB from 0 to 1 and the temperature from 750 °C (1023 K) to 850 °C (1123 K). Although it was observed that tar production could be considerably reduced (up to 72%) by optimising the gasification conditions, the effect of using alumina (aluminium oxide, of proven efficacy in destroying the tar produced in biomass gasification) as primary catalyst in air and air-steam mixture tests was also verified. The results show that by adding small quantities of alumina to the bed (10% by weight of fed sludge) considerable reductions in tar production can be obtained (up to 42%) improving, at the same time, the lower heating value (LHV) of the gas and carbon conversion.

Full scale test for explosion water barriers in small cross-section galleries

Underground coal mines explosions generally arise from the inflammation of a methane/air mixture. This explosion can also generate a subsequent coal dust explosion. Traditionally such explosions have being fought eliminating one or several of the factors needed by the explosion to take place. Although several preventive measures are taken to prevent explosions, other measures should be considered to reduce the effects or even to extinguish the flame front. Unlike other protection methods that remove one or two of the explosion triangle elements, namely; the ignition source, the oxidizing agent and the fuel, explosion barriers removes all of them: reduces the quantity of coal in suspension, cools the flame front and the steam generated by vaporization removes the oxygen present in the flame. Passive water barriers are autonomous protection systems against explosions that reduce to a satisfactory safety level the effects of methane and/or flammable dust explosions. The barriers are activated by the pressure wave provoked in the explosion destroying the barrier troughs and producing a uniform dispersion of the extinguishing agent throughout the gallery section in quantity enough to extinguish the explosion flame. Full scale tests have been carried out in Polish Barbara experimental mine at GIG Central Mining Institute in order to determine the requirements and the optimal installation conditions of these devices for small sections galleries which are very frequent in the Spanish coal mines. Full scale tests results have been analyzed to understand the explosion timing and development, in order to assess on the use of water barriers in the typical small crosssection Spanish galleries. Several arrangements of water barriers have been designed and tested to verify the effectiveness of the explosion suppression in each case. The results obtained demonstrate the efficiency of the water barriers in stopping the flame front even with smaller amounts of water than those established by the European standard. According to the tests realized, water barriers activation times are between 0.52 s and 0.78 s and the flame propagation speed are between 75 m/s and 80 m/s. The maximum pressures (Pmax) obtained in the full scale tests have varied between 0.2 bar and 1.8 bar. Passive barriers protect effectively against the spread of the flame but cannot be used as a safeguard of the gallery between the ignition source and the first row of water troughs or bags, or even after them, as the pressure could remain high after them even if the flame front has been extinguished.

Clean Coal Technologies Scenario and Evaluation of Present CO2 Dwindling Initiatives to Approach Zero Emission Power Stations By Coal Combustion. Deployment Situation and Evaluation Study

In the present uncertain global context of reaching an equal social stability and steady thriving economy, power demand expected to grow and global electricity generation could nearly double from 2005 to 2030. Fossil fuels will remain a significant contribution on this energy mix up to 2050, with an expected part of around 70% of global and ca. 60% of European electricity generation. Coal will remain a key player. Hence, a direct effect on the considered CO2 emissions business-as-usual scenario is expected, forecasting three times the present CO2 concentration values up to 1,200ppm by the end of this century. Kyoto protocol was the first approach to take global responsibility onto CO2 emissions monitoring and cap targets by 2012 with reference to 1990. Some of principal CO2emitters did not ratify the reduction targets. Although USA and China spur are taking its own actions and parallel reduction measures. More efficient combustion processes comprising less fuel consuming, a significant contribution from the electricity generation sector to a CO2 dwindling concentration levels, might not be sufficient. Carbon Capture and Storage (CCS) technologies have started to gain more importance from the beginning of the decade, with research and funds coming out to drive its come in useful. After first researching projects and initial scale testing, three principal capture processes came out available today with first figures showing up to 90% CO2 removal by its standard applications in coal fired power stations. Regarding last part of CO2 reduction chain, two options could be considered worthy, reusing (EOR & EGR) and storage. The study evaluates the state of the CO2 capture technology development, availability and investment cost of the different technologies, with few operation cost analysis possible at the time. Main findings and the abatement potential for coal applications are presented. DOE, NETL, MIT, European universities and research institutions, key technology enterprises and utilities, and key technology suppliers are the main sources of this study. A vision of the technology deployment is presented.

Comparison of Chemical Absorbents Used for CO2 Capture in Coal-Fired Power Plants.

Climate change conference was hold in Copenhagen in 2009, global warming became the worldwide focus once again. China as a developing country has paid more attention for this environmental problem. In China, a large part of carbon dioxide is emitted to the atmosphere from combustion of fossil fuels in power plants. How to control emission of the greenhouse gas into atmosphere is becoming an urgent concern. Among numerous methods, CO2 capture is the hope to limit the amount of CO2 emitted into the air. The well-established method for CO2 capture is to remove CO2 by absorption into solutions in conventional equipment. Absorbents used for CO2 and H2S capture are important choice for CO2 capture technology. It is related to the cost and efficiency of plant directly and is essential to investigate the proposed CO2 and H2S absorbents.

Safety assessment of underground vehicles passing over highly resilient straight tracks in the presence of a broken rail

In this paper, vehicle-track interaction for a new slab track design, conceived to reduce noise and vibration levels has been analyzed, assessing the derailment risk for trains running on curved track when encountering a broken rail. Two different types of rail fastening systems with different elasticities have been analysed and compared. Numerical methods were used in order to simulate the dynamic behaviour of the train-track interaction. Multibody system (MBS) modelling techniques were combined with techniques based on the finite element method (FEM). MBS modelling was used for modelling the vehicle and FEM for simulating the elastic track. The simulation model was validated by comparing simulated results to experimental data obtained in field testing. During the simulations various safety indices, characteristic of derailment risk, were analysed. The simulations realised at the maximum running velocity of 110 km/h showed a similar behaviour for several track types. When reducing the running speed, the safety indices worsened for both cases. Although the worst behaviour was observed for the track with a greater elasticity, in none of the simulations did a derailment occur when running over the broken rail.

Safety assessment of underground vehicles passing over highly resilient curved tracks in the presence of a broken rail

Vehicle–track interaction for a new resilient slab track designed to reduce noise and vibration levels was analysed, in order to assess the derailment risk on a curved track when encountering a broken rail. Sensitivity of the rail support spacing of the relative position of the rail breakage between two adjacent rail supports and of running speed were analysed for two different elasticities of the rail fastening system. In none of the cases analysed was observed an appreciable difference between either of the elastic systems. As was expected, the most unfavourable situations were those with greater rail support spacing and those with greater distance from the breakage to the nearest rail support, although in none of the simulations performed did a derailment occur when running over the broken rail. When varying the running speed, the most favourable condition was obtained for an intermediate speed, due to the superposition of two antagonistic effects.

Improved design of an overhead rail current conductor for application in underground lines

Overhead rail current collector systems for railway traction offer certain features, such as low installation height and reduced maintenance, which make them predominantly suitable for use in underground train infrastructures. Due to the increased demands of modern catenary systems and higher running speeds of new vehicles, a more capable design of the conductor rail is needed. A new overhead conductor rail has been developed and its design has been patented [13]. Modern simulation and modelling techniques were used in the development approach. The new conductor rail profile has a dynamic behaviour superior to that of the system currently in use. Its innovative design permits either an increase of catenary support spacing or a higher vehicle running speed. Both options ensure savings in installation or operating costs. The simulation model used to optimise the existing conductor rail profile included both a finite element model of the catenary and a three-dimensional multi-body system model of the pantograph. The contact force that appears between pantograph and catenary was obtained in simulation. A sensitivity analysis of the key parameters that influence in catenary dynamics was carried out, finally leading to the improved design.

Comparison of vibration and rolling noise emission of resilient and solid monobloc railway wheels in underground lines

Flat or worn wheels rolling on rough or corrugated tracks can provoke airborne noise and ground-borne vibration, which can be a serious concern for nearby neighbours of urban rail transit lines. Among the various treatments used to reduce vibration and noise, resilient wheels play an important role. In conventional resilient wheels, a slightly prestressed V­shaped rubber ring is mounted between the steel wheel centre and tyre. The elastic layer enhances rolling noise and vibration suppression, as well as impact reduction on the track. In this paper the effectiveness of resilient wheels in underground lines, in comparison to monobloc ones, is assessed. The analysed resilient wheel is able to carry greater loads than standard resilient wheels used for light vehicles. It also presents a greater radial resiliency and a higher axial stiffness than conventional V­wheels. The finite element method was used in this study. A quarter car model was defined, in which the wheelset was modelled as an elastic body. Several simulations were performed in order to assess the vibrational behaviour of elastic wheels, including modal, harmonic and random vibration analysis, the latter allowing the introduction of realistic vertical track irregularities, as well as the influence of the running speed. Due to numerical problems some simplifications were needed. Parametric variations were also performed, in which the sensitivity of the whole system to variations of rubber prestress and Poisson’s ratio of the elastic material was assessed.Results are presented in the frequency domain, showing a better performance of the resilient wheels for frequencies over 200 Hz. This result reveals the ability of the analyzed design to mitigate rolling noise, but not structural vibrations, which are primarily found in the lower frequency range.

Comparison of CO2 from coal captureprocesses and valorisation technologies

Coal is the most plentiful and evenly distributed fossil fuel worldwide. Based on current production, it is estimated that the reserves will last approximately 130 years. Its use worldwide has been increasing, mainly due to consumption by emerging countries. CO2 emissions generated by combustion and the repercussions of such on climate change support the view that it could no longer be used. CO2 capture may be the solution to continue using it, which would cater for the growing energy demand worldwide. The aim of this study is to compare different processes concerning CO2 capture that may be economically viable, ultimately showing that coal, a fossil energy source widely distributed around the world, can, as a result of using different CO2 capture processes, be used as a clean source of electricity. Hence, in places where geological hurdles may render the costs of CO2 storage considerably higher, since it might have to travel far, coal may be used for other purposes, thus valorizing CO2 within the industrial sector. This research is focused on the technical and economic comparison of the most relevant CO2 capture projects designed in Spain using different existing technologies. The oxyfuel project in Ciuden (Leon, Spain), the IGCC Elcogas, precombustion CO2-capture project (Puertollano, Spain) and the postcombustion project in Carboneras (Almeria, Spain) will be analyzed in order to assess the options available to valorizecaptured CO2. Valorizing captured CO2 may be an adequate solution in areas where, although CO2 capture is still possible, storage is not equally so, thus generating a further benefit. The possible uses of CO2 will be assessed in vegetable growing greenhouses, harnessing CO2 in vegetable life cycles. This will also be used in growing algae for subsequent biodiesel production. Both CO2capture and valorizing will eventually lead to the clean use of coal, which will thus enhance the level of self-supply, aiding the development of electric vehicles, which require large amounts of electricity, as well as improve the level of energy autonomy in countries around the world. Another type of fuel, biodiesel, will also be obtained, without this affecting international food prices.