The integrated gasification combined cycle (IGCC) is the most environmentally friendly coal-fired power generation technology that offers near zero green house gas emissions. This technology has higher thermal efficiency compared to conventional coal-fired power generation plants and uses up to 50% less water. This work involves the optimization of IGCC power plants by applying process integration techniques to maximize the use of energy available within the plant. The basis of this project was the theoretical investigations which showed that optimally designed and operated IGCC plants can achieve overall thermal efficiencies in the regions of 60%. None of the current operating IGCC plants approach this overall thermal efficiency, with the largest capacity plant attaining 47%. A common characteristic in most of these IGCC plants is that an appreciable amount of energy available within the system is lost to the environment through cold utility, and through plant irreversibility to a smaller extent. This work focuses on the recovery of energy, that is traditionally lost as cold utility, through application of proven process integration techniques. The methodology developed comprises of two primary energy optimization techniques, i.e. pinch analysis and the contact economizer system. The idea behind using pinch analysis was to target for the maximum steam flowrate, which will in turn improve the power output of the steam turbine. An increase in the steam turbine power output should result in an increase in the overall thermal efficiency of the plant. The contact economizer system is responsible for the recovery of low potential heat from the gas turbine exhaust en route to the stack to heat up the boiler feed water (BFW). It was proven in this work that a higher BFW enthalpy results in a higher overall efficiency of the plant. A case study on the Elcogas plant illustrated that the developed method is capable of increasing the gross efficiency from 47% to 55%. This increase in efficiency, however, comes at an expense of increased heat exchange area required to exchange the extra heat that was not utilized in the preliminary design. / Dissertation (MEng)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

Im Rahmen dieser Arbeit werden Konzepte für Gasaufbereitung in Kombikraftwerken mit integrierter Wirbelschichtvergasung und CO2-Abtrennung untersucht (IGCC-CCS). Dabei stehen die Konvertierung von Kohlenmonoxid (CO-Shift) und die Einbindung dieses Prozeß-schrittes in ein IGCC-CCS-Kraftwerk im Mittelpunkt. Ziel der Arbeit ist die energetische und wirtschaftliche Bewertung von Konzepten zur CO2-Abtrennung für ein ab 2015 baubares, grundlastfähiges IGCC-CCS-Kraftwerk der 800-MW-Klasse. Dazu werden neben den bekannten konventionellen, mehrstufigen Konzepten der Rohgas- und Reingas-Shift weitere alternative Ansätze zur Steigerung des Anlagenwirkungsgrades sowie zur Senkung der spezifischen CO2-Emission verfolgt. Die Ergebnisse der mit Hilfe von ASPEN Plus und EBSILON Professional durchgeführten Prozesssimulationen werden im Vergleich zu Dampfkraftwerken neuester Bauart wirtschaftlich bewertet.

Im Rahmen dieser Arbeit werden Konzepte für Gasaufbereitung in Kombikraftwerken mit integrierter Wirbelschichtvergasung und CO2-Abtrennung untersucht (IGCC-CCS). Dabei stehen die Konvertierung von Kohlenmonoxid (CO-Shift) und die Einbindung dieses Prozeß-schrittes in ein IGCC-CCS-Kraftwerk im Mittelpunkt. Ziel der Arbeit ist die energetische und wirtschaftliche Bewertung von Konzepten zur CO2-Abtrennung für ein ab 2015 baubares, grundlastfähiges IGCC-CCS-Kraftwerk der 800-MW-Klasse. Dazu werden neben den bekannten konventionellen, mehrstufigen Konzepten der Rohgas- und Reingas-Shift weitere alternative Ansätze zur Steigerung des Anlagenwirkungsgrades sowie zur Senkung der spezifischen CO2-Emission verfolgt. Die Ergebnisse der mit Hilfe von ASPEN Plus und EBSILON Professional durchgeführten Prozesssimulationen werden im Vergleich zu Dampfkraftwerken neuester Bauart wirtschaftlich bewertet.

Approximately 10% of all energy consumed in the United States is derived from high temperature gas turbine engines. As a result, a 1% increase in engine efficiency would yield enough energy to satisfy the demands of approximately 1 million homes and savings of over $800 million in fuel costs per year. Efficiency of gas turbine engines can be improved by increasing the combustor temperature. Modern engines now operate at temperatures that far exceed the material limitations of the metals they are comprised of in the pursuit of increased thermal efficiency. Various techniques to thermally protect the turbine components are used to allow for safe operation of the engines despite the extreme environments: film cooling, internal convective cooling, and thermal barrier coatings. Historically, these thermal protection techniques have been studied separately without account for any conjugate effects. The end goal of this work is to provide a greater understanding of how the conjugate effects might alter the predictions of thermal behavior and consequently improve engine designs to pursue increased efficiency. The primary focus of this study was to complete the first open literature, high resolution experiments of a modeled first stage turbine vane with both active film cooling and a simulated thermal barrier coating (TBC). This was accomplished by scaling the thermal behavior of a real engine component to the model vane using the matched Biot number method. Various film cooling configurations were tested on both the suction and pressure side of the model vane including: round holes, craters, traditional trenches and a novel modified trench. IR thermography and ribbon thermocouples were used to measure the surface temperature of the TBC and the temperature at the interface of the TBC and vane wall, respectively. This work found that the presence of a TBC significantly dampens the effect of altering film cooling conditions when measuring the TBC interface temperature. This work also found that in certain conditions adiabatic effectiveness does not provide an accurate assessment of how a film cooling design may perform in a real engine. An additional focus of this work was to understand how contaminant deposition alters the cooling performance of a vane with a TBC. This work focused on quantifying the detrimental effects of active deposition by seeding the mainstream flow of the test facility with simulated molten coal ash. It was found that in most cases, except for round holes operating at relatively high blowing ratios, the performance of film cooling was negatively altered by the presence of contaminant deposition. However, the cooling performance at the interface of the TBC and vane wall actually improved with deposition due to the additional thermal resistance that was added to the exterior surface of the model vane. / text

Die vorliegende Arbeit befasst sich mit Untersuchungen zur Trockenentschwefelung von Brenngasen durch Partialoxidation von H2S an Herdofenkoks. Hierzu wurden Versuche in der Technikumsanlage VTE 2004 mit einem simulierten PHTW Gas durchgeführt. Es zeigte sich, dass der COS-Abbau nicht wie bisher angenommen durch die COS-Partialoxidation sondern durch die COS-Hydrolyse erfolgt. Die COS-Hydrolyse gewinnt dabei mit abnehmender Raumbelastung an Bedeutung. Der Entschwefelungsgrad erhöht sich mit steigendem Sauerstofffaktor und abnehmender Raumbelastung. Sauerstofffaktoren >4 sind aufgrund des vollständigen H2S-Umsatzes und der nicht ablaufenden COS-Partialoxidation nicht sinnvoll. Die Gewinnung des abgeschiedenen Schwefels auf dem Herdofenkoks konnte nachgewiesen werden. Abschließende Berechnungen ergaben, dass sich mit den erreichten Schwefelkonzentrationen im Reingas das Verfahren im aktuellen Entwicklungsstand für die Vorentschwefelung im IGCC-Kraftwerk eignet.

A comprehensive process intensification analysis was performed for the integration of the Pd-based membrane reactor technology into IGCC power plants by designing effective process control strategies as well as identifying and optimally characterizing inherently safe operational conditions to achieve the most favorable economic outcomes. Experimental results indicated that Pd-based composite membranes supported on porous stainless steel tubes, fabricated with H2 permeance values as high as ~50 m3/[m2.h.atm0.5] at 450°C were capable of extra purity H2 production (≥99.99%). Two illustrative process control and performance monitoring cases namely, process regulation and servo mechanism, were considered and quite satisfactory process control was attained by maintaining CO conversion at levels higher than 95% so that the retentate stream could become suitable for high pressure CO2 sequestration. From a process safety standpoint, process parameters and operating conditions were identified and optimized to achieve the target performance level of 98% CO conversion and 95% H2 recovery and at the same time to prevent conditions which could potentially induce hazards and thus compromise process system safety. Furthermore, the average total product cost of a water-gas shift membrane reactor module including manufacturing costs and general expenses was carefully estimated by taking into account the full cost structure and found to be 1464 $/ft2. Moreover, a comprehensive economic assessment was performed for composite Pd/Alloy membrane reactor technology options integrated into IGCC power plants in the presence of market and regulatory uncertainty (possible regulatory action on CO2 emissions) as well as technology risks with the aid of Monte-Carlo simulation techniques. Within such a context, it was demonstrated that an IGCC plant with embedded Pd-based membrane reactors and a stream of revenues coming from electricity and H2 selling (IGCC co-production mode), represented an economically attractive and advantageous option when comparatively assessed against its main competitors namely, an IGCC plant with shift reactors and double stage Selexol units as well as the more traditional supercritical pulverized coal power plant option with an Econamine unit installed for CO2 capture purposes.

Coal is a very prominent energy source in the world, but it is environmentally unattractive due to its high sulfur and ash content as well as its alleged contribution towards climate change, but it is affordable, abundant, and has high energy content. Thus, utilizing coal in a cleaner and more efficient way has become necessary. One promising clean coal technology involves fully gasifying coal into synthesis gas, cleaning it, and feeding it into a high-efficiency combined cycle, such as an Integrated Gasification Combined Cycle (IGCC). Inspired by the recent success of warn gas cleanup (WGCU), mild and partial gasification are proposed as less energy intensive options. This Integrated Mild/Partial Gasification Combined Cycle (IMPGC) could significantly save energy and improve efficiency. The objective of this study is to investigate the capabilities of IMPGC as both a new plant and a retrofit option for traditional coal power plants with and without carbon capture. I MPGC relies on the principles of mild and partial gasification and the recently available WGGU technology with the following benefits: a.) completely negate the need for syngas cooling; b.) significantly reduce the energy needed to fully thermally crack the volatiles and completely gasify the char as in the IGCC system; c.) preserve the high chemical energy hydro-carbon bonds within the feedstock to allow more efficient combustion in the gas turbine; d.) reduce the size of gasifier and piping to reduce the costs; and e.) enable retrofitting of an old coal power plant by preserving the existing equipment. The software used (Thermoflex®) was first validated with established cases from the U.S. Department of Energy. For new plants, the results show that IMPGC’s efficiency is 8 percentage points (20%) higher than IGCC, 8 points higher than a modern subcritical Rankine cycle, and 3-4 points higher than an ultra-supercritical (USC) cycle. When retrofitting older plants, a minimum improvement of over 4 points is predicted. When carbon capture is involved, IMPGC’s efficiency becomes 10 points better than a subcritical plant and 8 points better than a USC plant. Emissions wise, IMPGC is better than IGCC and much better than Rankine cycle plants.

DE LA TESISEs una contribución al desarrollo de un nuevo método de purificación de gas de síntesis en plantas IGCC, que posibilita un incremento de la eficiencia energética de las plantas de obtención de energía, a partir de combustible fósil, y con ello reducir la emisión de gas de efecto invernadero a la atmósfera. Se estudia un proceso nuevo por absorción regenerativa en óxidos metálicos, capaz de eliminar los contaminantes del gas a alta temperatura, aprovechando con ello el contenido energético asociado al intervalo térmico, que los procesos actuales pierden en la purificación por vía húmeda. Se enumeran a continuación los objetivos concretos alcanzados, con las fases del trabajo desarrollado:1- Estudio de la cinética de la reacción de purificación del gas de síntesis, siguiendo las reacciones de absorción no catalíticas, con deposición de sólido, realizando un estudio exhaustivo, para conseguir unos modelos de reacción gas-sólido que contemplen el mayor número de posibilidades. Se ha pretendido crear una herramienta de simulación con el menor número de restricciones a la hora de aplicarlo a cualquier reacción que involucre cambio en la estructura del sólido con la conversión del mismo, para de este modo no tener un modelo cautivo de un determinado tipo de sorbente.2- Se han obtenido los parámetros cinéticos experimentalmente, mediante análisis termogravimétrico, aplicables a los modelos desarrollados, para el caso concreto del sorbente disponible.3- Se han modelizado matemáticamente los posibles reactores que pueden emplearse en la eliminación del compuesto H2S de este gas de gasificación, especialmente los reactores de lecho fluidizado de burbujeo, ya que poseen muy buenas cualidades de homogeneidad de temperatura y concentraciones. Se ha realizado el estudio de sensibilidad a las variaciones de los parámetros de funcionamiento. 4- Se ha construido una planta experimental a pequeña escala que ha permitido probar el sorbente con garantías en los resultados, para lo que se la ha dotado de los elementos de control y análisis de gas necesarios. 5- Se han realizado un número de experimentos suficiente para estudiar el comportamiento del sorbente en estudio, y para la obtención de datos experimentales que han permitido la validación de los diferentes modelos desarrollados.6- Se han obtenido las siguientes conclusiones resumidas:6.1 Se ha obtenido la cinética propia de la reacción gas-sólido no catalítica del sistema estudiado, viendo la influencia de la composición del gas en la velocidad de reacción. La cinética de primer orden describe adecuadamente los procesos de absorción y regeneración, habiéndose obtenido los parámetros cinéticos correspondientes. 6.2 Utilizando los modelos cinéticos desarrollados se proponen los valores de las características estructurales que optimizarían el comportamiento del sólido, en cuanto a su capacidad de retención de contaminante sulfurado: Porosidad no superior al 30% y área superficial de alrededor de 25 m2/g (frente a los valores actuales del 50%y 8,93 m2/g).6.3 El análisis termogravimétrico ha permitido identificar y cuantificar los valores de los diferentes parámetros que intervienen en la reacción gas-sólido: el coeficiente de reacción intrínseca superficial, la difusividad del gas en la capa de sólido formado, y el coeficiente de transferencia de masa gas-sólido. Asimismo las pruebas experimentales realizadas han puesto de manifiesto la influencia de la composición del gas en la cinética de reacción. 6.4 El equipo piloto de reacción experimental a pequeña escala, capaz de operar a alta temperatura y presión, ha permitido la validación de los modelos desarrollados del sistema de desulfurización, demostrándose que son una herramienta adecuada para su estudio, tanto para diseño, como en operación y control avanzado. Como posible continuación se presentan las siguientes posibilidades en la tarea de modelización: Estudiar modelos más precisos basados en ecuaciones de continuidad multifásicas, para su aplicación en sistemas de computación de alto rendimiento, o bien desarrollar modelos basados en reglas lógicas. En cuanto al desarrollo del sorbente, se pone de manifiesto la necesidad de continuar en su desarrollo para alcanzar los valores de las características señaladas. / OF THE THESISThis thesis is a contribution to the development of a new method of synthesis gas purification in IGCC plants, that make possible a further increase of the energy efficiency, and with this to reduce the emission of greenhouse gas to the atmosphere. It is studied a regenerative absorption in metallic oxides, capable of the elimination of the pollutants from the high-temperature gas, but taking advantage of the energy contents associated with the high temperature process streams, which is lost in the purification by wet route. The objectives and conclusions reached in the development of the thesis work are summarized below:1- The study of the kinetics of the purification reactions of the synthesis gas, non catalytic absorption reactions, with solid deposition. An exhaustive study has been carried out, to obtain some gas-solid reaction models that envisage a great number of possibilities. It has been created a simulation tool with a reduced number of restrictions that makes possible its use with any reaction that involves changes in the structure of the solid thus ensuring generality and independence of a given type of sorbent.2- The kinetic parameters have been obtained by thermogravimetric analysis for the concrete case of the available sorbent to be used in the testing of the developed models. 3- Appropriated type of reactors that can be employed in the elimination of the H2S compound of the gas contemplated have been identified and modeled. Special attention has been given to the bubbling fluidized bed reactors, since they possess very good properties of temperature and concentrations homogeneity. It has been accomplished the sensibility study to the variations of the operation parameters.4- An experimental bubbling fluidized bed reactor plant at bench-scale has been built that has permitted to extract the data from the selected sorbent with guarantees in the results.5- A sufficient number of experiments to study the behaviour of the selected sorbent under study have been accomplished successfully, and the experimental data obtained have permitted the validation of the different developed models.6- The specific conclusions reached are: 6.1. The study of the no-catalytic gas-solid reaction of the system studied shows that kinetics of first order describe adequately the absorption and regeneration processes.6.2. The accomplished experimental tests have shown the influence of the composition of the gas in the kinetics mechanism. The kinetic parameters are very dependent of the composition of the gas, not only of the reactive species, specially of the components that determine the reducing power.6.3. The thermogravimetric analysis has permitted to identify the values of the different parameters that appear in the gas reaction-solid: the coefficient of superficial intrinsic reaction, the diffusivity of the gas in the formed solid layer, and the gas-solid mass transfer coefficient.6.4. Using the developed kinetic models, the values of the structural characteristics that would optimise the behaviour of the solid are proposed, concerning its capacity of retention of sulfured pollutant: Porosity not superior to 30% and superficial area of about 25 m2 / g (as compared to the current values of the 50% and 8,93 m2 / g).6.5. The experimental small scale BFB pilot plant, capable of operating at high-temperature and pressure, has permitted the validation of the developed models for the desulphurisation system. The models developed have demonstrated that they are an adequate tool for the study, design, as well as the operation and advanced control of the system under study. As possible continuation of this thesis work in the modelization task the following is indicated: To study more accurate models based on fundamental multiphasic continuity equations, or else to develop models based on logic rules. With respect to development of the sorbent, the need of continuing in its development to reach the values of the indicated characteristics is shown.

Im Rahmen der vorliegenden Arbeit werden dynamische Modelle eines IGCC-Kraftwerkes mit CO2-Abtrennung unter Verwendung des Modellierungstools Modelica/Dymola entwickelt. Dabei liegt der Schwerpunkt auf dem Gaspfad der Gasreinigung. Es ist vorteilhaft, für verschiedene Aufgaben, Modelle mit unterschiedlicher Tiefe zu verwenden. Mit den detaillierten Modellen werden Simulationen der Teilprozesse durchgeführt. Für den Aufbau eines Gesamtsystems werden vereinfachte Modelle verwendet. Anhand des Gesamtsystems werden drei Regelkonzepte (Gleitdruckregelung, Leistungsregelung der Gasturbine, Leistungsregelung des Vergasers) untersucht und bewertet. Des Weiteren werden drei Störfallszenarien (Ausfall des Sättigers im Brennstoffsystem, Betriebsstörung in der Vergaserinsel, Unterbrechung der Stickstoffzumischung im Brennstoffsystem) getestet.

The objective of this thesis is to provide an extensive description of the correlations in some of the most crucial sub-processes for hard coal fired IGCC with carbon capture (CC-IGCC). For this purpose, process simulation models are developed for four industrial gasification processes, the CO-shift cycle, the acid gas removal unit, the sulfur recovery process, the gas turbine, the water-/steam cycle and the air separation unit (ASU). Process simulations clarify the influence of certain boundary conditions on plant operation, performance and economics. Based on that, a comparative benchmark of CC-IGCC concepts is conducted. Furthermore, the influence of integration between the gas turbine and the ASU is analyzed in detail. The generated findings are used to develop an advanced plant configuration with improved economics. Nevertheless, IGCC power plants with carbon capture are not found to be an economically efficient power generation technology at present day boundary conditions.