Simulation of a CFB Boiler Integrated With a Thermal Energy Storage System During Transient Operation

In the current work, a transient/dynamic 1-dimensional model has been developed in the commercial software APROS for the pilot 1 MWth CFB boiler of the Technical University of Darmstadt. Experiments have been performed with the same unit, the data of which are utilized for the model validation. The examined conditions correspond to the steady-state operation of the boiler at 100, 80, and 60% heat loads, as well as for transient conditions for the load changes from 80 to 60% and back to 80%. Fair agreement is observed between the simulations and the experiments regarding the temperature profiles in the riser, the heat extracted by the cooling lances, as well as the concentration of the main species in the flue gases; a small deviation is observed for the pressure drop, which, however, is close to the results of a CFD simulation run. The validated model is extended with the use of a thermal energy storage (TES) system, which utilizes a bubbling fluidized bed to store/return the particles during ramp up/down operation. Simulations are performed both with and without the use of TES for the load path 100–80–60–80–100%, and the results showed that the TES concept proved to be superior in terms of changing load flexibility, since the ramp up and down times proved to be much faster, and lower temperature drops between the loads are observed in this case

NUMERICAL COMPUTATION OF HYDRODYNAMIC BEHAVIOR OF BIOMASS PARTICLES IN CIRCULATING FLUIDIZED BEDS

A model using a particle based approach is developed to accurately predict the hydrodynamic behavior of biomass particles in CFBs. Generally, the change in the pressure gradient with height in CFB riser is small. Numerical results are in good agreement with experiments, both in form and magnitude

Dynamics of large-scale fluidized bed combustion plants

Fluidized bed combustion (FBC) plants are widely used in energy systems across the world for the thermochemical conversion of solid fuels, and are especially suitable for low-rank fuels (a category to which renewable solid fuels belong). FBC plants are traditionally operated for base-load electricity production and for heat production, both of which processes are characterized by steady and stable operation. As the share of variable renewable electricity (VRE) sources is expected to increase dramatically, FBC plants will have to adapt their operations to the new flexibility requirements related to the inherent variability of VRE sources. By enhancing their operational and product flexibilities, FBC plants can remain financially attractive and offer services to support the balancing of the grid. As tools for assessing the operational flexibility of thermal power plants, dynamic modeling and simulation are gaining attention from both researchers and plant operators. However, it is a common practice to assume that the dynamics of the gas side are much faster than those of the water-steam side, i.e., not accounting for the in-furnace dynamic mechanisms.This thesis aims to characterize the dynamic behaviors of commercial-scale FBC plants, accounting for both the gas and water-steam sides of bubbling and circulating fluidized bed (BFB and CFB) units. For this purpose, a dynamic semiempirical model of the gas side of FBC plants is developed and integrated into a process model of the water-steam side. The models are validated against steady-state and transient operational data measured at two commercial-scale industrial units. The model is then used to analyze the inherent dynamics of the gas and water-steam sides, to compare the transient behaviors of BFB and CFB units, and to assess the dynamic performances of FBC plants when operated under different control structures. The results of the dynamic analysis show that the stabilization times of the temperatures across the furnace differ, largely based on the local heat capacity of the region in the furnace, i.e., the amount of bulk solids. The work includes an assessment of the impact of the characteristic times of the in-furnace mechanisms (i.e., fluid dynamics, fuel conversion and heat transfer) on the computed stabilization times of key in-furnace variables at plant level, and suggests some simple mathematical relationships for predicting these times. When accounting for the water-steam side, the results show that the inherent dynamics of variables such as live steam pressure, flow and power production are in the same order of magnitude as the dynamics of the gas side, particularly for the CFB case. This highlights the importance of accounting for the gas side when attempting to model accurately the dynamics of FBC plants. Furthermore, FBC plants are found to be able to provide fast load changes when operated under control structures that manipulate the live steam valve, although this is found to trigger operational issues, such as pressure overshoots.The results of this thesis are of particular importance in terms of assessing the transient capabilities of FBC plants to operate in electricity-driven markets where fast operation is required, and they can be used to identify opportunities and challenges. Furthermore, knowledge about the transient operation of large-scale FB reactors will be crucial for the development of FB applications other than combustion, such as polygeneration or thermochemical energy storage

Fluidized bed plants for heat and power production in future energy systems

Fluidized bed (FB) plants are used for heat and power production in several energy systems around the world, with particular importance in systems using large shares of renewable solid fuel, e.g., biomass. These FB plants are traditionally operated for base-load electricity production or for heat production, and thus characterized by relatively small and slow load changes. In parallel, as the transition towards energy systems with net-zero emissions increases the share of variable renewable energy (VRE) sources, the need for implementing variation management strategies at various timescales arises – giving heat and power plants the possibility to adapt their operations to accommodate the inherent variability of VRE sources. Following this, FB technology is envisioned for a wide range of novel applications expected to play significant roles in the decarbonization of energy systems, such as thermochemical energy storage and carbon capture and storage. In this context, research efforts are needed to investigate the technical and economic features of FB plants in energy systems with high levels of VRE.The aim of this thesis is to elucidate the capabilities of FB plants for heat and power production in net-zero emissions energy systems. For this purpose, two main pathways are explored: i) transient operation as fuel-fed plants, and ii) the potential conversion into decarbonized plants, i.e., into VRE-fed layouts providing dispatchable outputs.For fuel-fed FB plants, a dynamic model of biomass-fired FB plants has been developed, considering the two types of FB boilers (BFB and CFB) and including validation against steady-state and transient operational data collected from two commercial plants. As a novelty of this work the model describes both the gas (in-furnace) and water-steam sides such that the interactions between the two can be assessed. The results of the simulations show that i) the characteristic times for the gas side are shorter in BFB furnaces than in CFBs, albeit these times are for both furnace types not longer than those for the water-steam side; ii) the computed timescales for the dynamics of FB plants fall well within those required for offering complementing services to the grid; and iii) the use of control and operational strategies for the water-steam side can confer capabilities superior to fuel-feeding control in terms of avoiding undesirable unburnt emissions and providing temporary overload operation. The retrofit of fuel-fed FB plants into poly-generation facilities cogenerating a combustible biogenic gas is also assessed, revealing that partial combustion of this gas can be used to provide faster inherent dynamics than the original configuration.For VRE-fed FB layouts, techno-economic process modeling has been carried out for large-scale deployment of solar- and electricity-charging processes based on three different chemical systems: i) carbonation/calcination (calcium); ii) thermally reduced redox (cobalt oxides); and iii) chemically reduced redox (iron oxides). One attractive aspect of these layouts is the possibility to build part of them by retrofitting current fuel-fed FB plants. While the technical assessment for solar applications indicates that cobalt-based layouts offer the highest levels of efficiency and dispatchability, calcium-based processes present better economics owing to the use of inexpensive calcium material. The results also show that electricity-charged layouts such as iron looping can play an important role in the system providing variation management strategies to the grid while avoiding costly H2 storage. Further, the economic performances of VRE-fed FB layouts are benefitted by the generation of additional services and products (e.g., carbon capture and on-demand production of H2), and by scenarios with high volatility of the electricity prices

Heat transfer in oxy-fuel fluidized bed boilers

In spite of the stabilization of coal demand in developed countries, the role of coal in the next decades energy mix is still essential. Particularly relevant will be in the great developing economies, such as India or China, where this fuel is abundant and avoid external energy dependences. In parallel, the international community needs to drive its efforts towards politics that commit fossil fuels energetic companies to drop their CO2 emissions drastically for 2015. In this regard, great advances have been made towards gaining plant efficiency and therefore, reducing the tones of CO2 per produced kWh. Still, emissions need a more drastic reduction if we want to avoid an increment of atmosphere temperature higher than 2ºC. Here, the CO2 capture and storage (CCS) technologies will have the potential of reducing up to 25% of CO2 from stationary sources as soon as they will be commercially available. Among the CO2 capture technologies, grouped in pre-combustion, post-combustion and oxy-fuel combustion, this last one is receiving outstanding support by the national and European authorities. The possibility of implementing oxy-fuel combustion into circulating fluidized bed technology, contributes to approaching the concept of clean-coal technology. Fluidized bed combustors have the outstanding feature of offering the possibility of burning a wide variety of fuels They have the possibility to capture SO2 emissions, adding in-bed limestone. Their working temperature is lower than in pulverized fuel boilers, which avoids thermal NOx formation. Additionally to these characteristics, already exploited under air-firing, applying oxy-fuel combustion technology and being able to capture the CO2 emissions from the coal combustion, or even from blends of coal and other fuels, makes oxy-fuel combustion in fluidized bed a great opportunity to turn the coal sustainable in the future power plant designs. About the implications derived of applying oxy-fuel technology to a commercial scale CFB boiler, scarce literature exits, especially when considering high O2 concentrations at inlet. A one dimensional model has been developed. The overall modeling strategy, in which the model has been based on, is explained in the first part of Chapter 2. It is based on the already known and validated air-firing semi-empirical expressions. The model has been divided into three sub-models interacting with each other: fluid-dynamics, combustion and energy balance of plant. For attributing reliability to the developed model, the scarce public experimental measurements of real air-firing boilers have been compared with the model results. Additionally, three studies regarding the modeling of large oxy-fuel CFB boilers have also been used for comparing the model predictions. In spite of having insufficient information about the published models details, the model developed in this work fairly fits the predictions in the literature. This has allowed making the sensibility analysis, trying to draw the main consequences of oxy-fuel deployment in CFB boilers. For retrofitting purposes, i.e. with no changes on an air-firing boiler configuration, the adequate O2 proportion of oxygen at entrance should be around 30%. Higher O2 concentrations lead to smaller cross sectional areas of the boiler. For a given fuel power required in a boiler, feeding 45% O2 in the comburent, would reduce the cross sectional area down to 54% of the original one. This involves a reduction of heat transfer surface along the boiler walls of 23% approximately. The immediate consequence is the need of resorting to external heat transfer surfaces, i.e., external heat exchangers (EHE). This device would need to remove almost 50% of the total heat of combustion in the case of feeding comburent with 60% O2 content. The importance of the EHE resides not only in compensating the reduction of heat transfer surface in the riser, but in managing higher amount of elutriated solids. The simulations have shown that higher solids densities in the boiler will enhance heat transfer coefficients to the riser walls. For certain boiler geometry, if increasing boiler load, higher recycled solids rate will be required. Feeding 60% of O2 at inlet, fuel input can be increased from 600 to 800 MW if elutriated solids increase from 25 to 40 kg/m2s. This refers us again to the higher solids crossing the EHE. An increase of 10% of heat removal will be required in this device for said changing load. Applying EHEs to conventional boilers was not essential during air-firing operation. But for oxy-fuel combustion it was here demonstrated to be crucial for accomplishing the boiler energy balance. However, several operational and design uncertainties will need to be solved, before deploying first demonstration oxy-CFB boiler. The design of the future EHE will imply two relevant distinguishing features of oxy-firing operation: the influence of gas composition on the determination of the heat transfer coefficients and the greater amount of elutriated solids, cooled down in the EHE. The CIRCE bubbling fluidized bed pilot plant presents the adequate bubbling working regime to obtain results of heat transfer coefficient for a wide range of oxy-fuel conditions and extracting further conclusions on possible effects of gas composition on heat transfer coefficients. The range of O2 concentration at inlet reached values as high as 60%. Such a high concentration was scarcely achieved in pilot plants due, in most cases, to the limiting bed cooling capacity. Measurements of heat transfer coefficients were taken when cooling was needed to control the combustion temperature. Water could circulate through one or more of the four cooling jackets, depending on the cooling requirements. Heat transfer coefficients were indirectly measured by energy balance with the water mass flow and temperatures. There are no previous results on heat transfer measurements under oxy-fuel combustion, up to date. The pilot plant is characterized by two important performance parameters: the fluidizing velocity and the bed temperature. These two parameters are common for all the fluidized bed plants working on combustion. Particularly for characterizing oxy-fuel combustion, the composition of the oxidant gas is the other key parameter in the plant operation. These three factors have been analyzed and their influence on heat transfer was examined. The three of them are, however, interrelated. O2 concentration and bed temperature varied the gas density and thus, the fluidizing velocity. At the same time, the fluidizing velocity will affect the heat transfer coefficients and consequently, bed temperature would be influenced. For accounting for this kind of dependences, non-dimensional numbers have been used for comparison. It was detected no dominant effect of non-dimensional numbers on the heat transfer. This is mainly offset by the different fluidization velocities in AF and OF operation. In the former, uf was kept over 1 m/s, whereas OF required lower velocities, around 0.9 m/s. It was then determined the adequate semi-empirical correlations for the effective thermal conductivity and the residence time of particles at the heat transfer surface. Hence, a semi-empirical mechanistic approach is recommended for a good agreement with the experimental heat transfer coefficients obtained during oxy-fuel operation. It was demonstrated the relevance of the gaseous film resistance in the oxy-fuel tests, and a new empirical coefficient was deduced for both modes. As examined in Chapter 3, section 3.5, the recommended expressions to predict heat transfer coefficients during oxy-fuel combustion modified the thermal film resistance, fitting the empirical parameter M with experimental data. Where: M=6.51 for oxy-firing and M=11.33 for air-firing The larger amount of solids arriving at the EHE will influence the values and distribution of the average and local heat transfer coefficients, respectively. A review of the difficulties associated with the estimation of heat transfer to the tubes of a heat exchanger has been examined. By the use of a scaled-down EHE, it was possible to experimentally confirm the influence of heat transfer coefficients when horizontal movement of solids took place. The increase of solids rate stressed the inequalities of the local heat transfer coefficient, whereas the longer residence time taken by particles to travel through the EHE allows higher average heat transfer coefficient. The contribution of this parameter to the average heat transfer coefficient was correlated by means of a new expression, as developed in Chapter 4, section 4.4. This expression allows modifying the heat transfer coefficient previously deduced for stationary conditions, and therefore, accounting for the enhancement of heat transfer when recirculation of solids takes place. A real design of an EHE was then simulated and integrated in the existing CFB model previously developed. This is the first time that such a model is developed to predict the heat transfer area required in oxy-fuel operation. The EHE sub-model must fulfill the energy balance requirements previously set for the CFB model. The temperature, at which solids must be recycled back into the boiler, in order to keep the desired boiler temperature, is accomplished with this sub-model. The expressions for the heat transfer coefficient and the enhancement due to recycled mass flow of solids were included in the EHE sub-model. Hence, it was possible to determine the increase on the heat transfer surface, for different O2 concentration in the oxidant stream, and two ranges of boiler temperature required. It was then recognized that, in spite of doubling the heat transfer surface requirements, when O2 concentration increased 10%, the heat transfer surface increases less than expected if solids flow influence were not included in the heat transfer evaluation. This thesis demonstrates that heat transfer surface design, arrangement and allocation, will differ in future oxy-fuel CFB boilers. Particularly, the heat transfer in the EHE will need address the influence of fluidizing gas composition and recycled solids, for an adequate and efficient heat exchanger configuration

Computationsl modelling of dimethyl ether separation and steam reforming in fluidized bed reactors

This study presents a computational fluid dynamic (CFD) study of Dimethyl Ether (DME) gas adsorptive separation and steam reforming (DME-SR) in a large scale Circulating Fluidized Bed (CFB) reactor. The CFD model is based on Eulerian-Eulerian dispersed flow and solved using commercial software (ANSYS FLUENT). Hydrogen is currently receiving increasing interest as an alternative source of clean energy and has high potential applications, including the transportation sector and power generation. Computational fluid dynamic (CFD) modelling has attracted considerable recognition in the engineering sector consequently leading to using it as a tool for process design and optimisation in many industrial processes. In most cases, these processes are difficult or expensive to conduct in lab scale experiments. The CFD provides a cost effective methodology to gain detailed information up to the microscopic level. The main objectives in this project are to: (i) develop a predictive model using ANSYS FLUENT (CFD) commercial code to simulate the flow hydrodynamics, mass transfer, reactions and heat transfer in a large scale dual fluidized bed system for combined gas separation and steam reforming processes (ii) implement a suitable adsorption models in the CFD code, through a user defined function, to predict selective separation of a gas from a mixture (iii) develop a model for dimethyl ether steam reforming (DME-SR) to predict hydrogen production (iv) carry out detailed parametric analysis in order to establish ideal operating conditions for future industrial application. The project has originated from a real industrial case problem in collaboration with the industrial partner Dow Corning (UK) and jointly funded by the Engineering and Physical Research Council (UK) and Dow Corning. The research examined gas separation by adsorption in a bubbling bed, as part of a dual fluidized bed system. The adsorption process was simulated based on the kinetics derived from the experimental data produced as part of a separate PhD project completed under the same fund. The kinetic model was incorporated in FLUENT CFD tool as a pseudo-first order rate equation; some of the parameters for the pseudo-first order kinetics were obtained using MATLAB. The modelling of the DME adsorption in the designed bubbling bed was performed for the first time in this project and highlights the novelty in the investigations. The simulation results were analysed to provide understanding of the flow hydrodynamic, reactor design and optimum operating condition for efficient separation. Bubbling bed validation by estimation of bed expansion and the solid and gas distribution from simulation agreed well with trends seen in the literatures. Parametric analysis on the adsorption process demonstrated that increasing fluidizing velocity reduced adsorption of DME. This is as a result of reduction in the gas residence time which appears to have much effect compared to the solid residence time. The removal efficiency of DME from the bed was found to be more than 88%. Simulation of the DME-SR in FLUENT CFD was conducted using selected kinetics from literature and implemented in the model using an in-house developed user defined function. The validation of the kinetics was achieved by simulating a case to replicate an experimental study of a laboratory scale bubbling bed by Vicente et al [1]. Good agreement was achieved for the validation of the models, which was then applied in the DME-SR in the large scale riser section of the dual fluidized bed system. This is the first study to use the selected DME-SR kinetics in a circulating fluidized bed (CFB) system and for the geometry size proposed for the project. As a result, the simulation produced the first detailed data on the spatial variation and final gas product in such an industrial scale fluidized bed system. The simulation results provided insight in the flow hydrodynamic, reactor design and optimum operating condition. The solid and gas distribution in the CFB was observed to show good agreement with literatures. The parametric analysis showed that the increase in temperature and steam to DME molar ratio increased the production of hydrogen due to the increased DME conversions, whereas the increase in the space velocity has been found to have an adverse effect. Increasing temperature between 200 oC to 350 oC increased DME conversion from 47% to 99% while hydrogen yield increased substantially from 11% to 100%. The CO2 selectivity decreased from 100% to 91% due to the water gas shift reaction favouring CO at higher temperatures. The higher conversions observed as the temperature increased was reflected on the quantity of unreacted DME and methanol concentrations in the product gas, where both decreased to very low values of 0.27 mol% and 0.46 mol% respectively at 350 °C. Increasing the steam to DME molar ratio from 4 to 7.68 increased the DME conversion from 69% to 87%, while the hydrogen yield increased from 40% to 59%. The CO2 selectivity decreased from 100% to 97%. The decrease in the space velocity from 37104 ml/g/h to 15394 ml/g/h increased the DME conversion from 87% to 100% while increasing the hydrogen yield from 59% to 87%. The parametric analysis suggests an operating condition for maximum hydrogen yield is in the region of 300 oC temperatures and Steam/DME molar ratio of 5. The analysis of the industrial sponsor’s case for the given flow and composition of the gas to be treated suggests that 88% of DME can be adsorbed from the bubbling and consequently producing 224.4t/y of hydrogen in the riser section of the dual fluidized bed system. The process also produces 1458.4t/y of CO2 and 127.9t/y of CO as part of the product gas. The developed models and parametric analysis carried out in this study provided essential guideline for future design of DME-SR at industrial level and in particular this work has been of tremendous importance for the industrial collaborator in order to draw conclusions and plan for future potential implementation of the process at an industrial scale

Emprego da minimização da energia de Gibbs para predizer a composição dos gases de exaustão oriundos de uma caldeira que utiliza como combustíveis subprodutos gerados na indústria siderúrgica

Nos processos para produção de aço em uma usina siderúrgica são produzidos gases que normalmente podem ser aproveitados como combustíveis pela própria planta. Os gases de alto forno, de coqueria, de aciaria e o alcatrão compõem frequentemente a mistura de combustíveis alimentados nas caldeiras de diversas usinas siderúrgicas. A combustão de diferentes misturas (mix) de combustíveis na caldeira pode gerar altos níveis de gases não oxidados, especialmente o CO. Altas concentrações destes gases acarretam problemas ambientais, o que não é desejado. Como tentativa de solução do problema, significativos níveis de excesso de ar são inseridos no sistema. Entretanto, o excesso de ar pode acarretar na redução da eficiência energética do processo e pode não solucionar o problema. Neste contexto, os objetivos deste trabalho são: (i) Testar diferentes composições para a alimentação de uma caldeira em operação em uma indústria siderurgia e calcular a composição da saída dos gases de exaustão; (ii) Investigar o efeito do aumento do excesso de ar na composição dos gases de exaustão e na eficiência energética do processo. Para isto é proposta a utilização da técnica de minimização da energia livre de Gibbs. Esta metodologia é frequentemente utilizada para se calcular a composição química de um sistema fechado em equilíbrio químico com uma ou mais fases. Portanto é possível afirmar que a energia livre de Gibbs é mínima quando o sistema atinge o estado de equilíbrio químico. Para a obtenção da composição química do sistema, um problema de otimização restrito deve ser resolvido. As variáveis a serem ajustadas representam a composição de equilíbrio do sistema. Assim, com o desenvolvimento deste estudo espera-se ser possível predizer quais a condições operacionais maximizam a eficiência energética do processo e minimizam a emissão de gases não oxidados.The development of the steel industry has increased energy demand, exerting strong influence on the use of energy resources. The utilization energetic is extremely important because it enables the steel industry greatly reduce their costs. In the steelmaking process, they are produced four by-products with high capacity for energy generation. The produced by-products are directed to thermoelectric plants and used as fuel for the generation of electricity. In this work it proposed a modeling for the prediction of the equilibrium concentration of the chemical species present in the furnace of a steel boiler installed in a thermoelectric plant. The employed technique consists of the minimization of the Gibbs energy of the reaction medium present in the furnace of steel boiler equipment on the thermoelectric central plant. The optimization problem was proposed, by defining thus the objective function and restrictions to be resolved employing the commercial software Matlab® . The solution of the optimization problem resultant provides the description of composition output of the exhaust gases. This work it was possible to evaluate the impact of changes in air feed flow rate and operating temperature of the composition of the exhaust gases. The applied methodology is able to reproduce satisfactorily the information provided by industry and obtained in the literature, that describe the combustion of the byproducts on the steel industry by-products.CAPE

Untersuchungen zur Erhöhung der Flexibilität zirkulierender Wirbelschichtkraftwerke zur Integration erneuerbarer Energien

Die Integration volatiler erneuerbaren Energiequellen in den Strommarkt erfordert Ausgleichstechnologien, die Versorgungssicherheit gewährleisten können. Solche Technologien müssen schnelle Lastwechsel über einen großen Lastbereich durchführen können und möglichst niedrige Treibhausgasemissionen aufweisen. In der vorliegenden Arbeit wird vorgeschlagen, existierende zirkulierende Wirbelschichtkraftwerke mit Kohlefeuerung für die Co-Verbrennung von Kohle, Biomasse und Ersatzbrennstoff umzurüsten. Der Ansatz ermöglicht eine sehr schnelle und kostengünstige technische Umsetzung bei gleichzeitig hohem CO2-Einsparpotential. Bestehende Großkraftwerke sind meist auf Nennlast und für einen bestimmten Brennstoff ausgelegt. Daher besteht Forschungsbedarf, die Brennstoffflexibilität und die Lastflexibilität von zirkulierenden Wirbelschichtfeuerungen besser zu verstehen und Wege zu finden, diese zu erhöhen. Ein Fokus dieser Dissertation ist die experimentelle Untersuchung der Bedingungen im Brennraum bei der Co-Verbrennung im Lastwechselbetrieb. Dazu wurden stationäre und dynamische Versuche in einer 1 MWth Versuchsanlage zur Co-Verbrennung von Braunkohle, Strohpellets und Refuse Derived Fuel durchgeführt. Für den Co-Verbrennungsbetrieb unter transienten Bedingungen müssen insbesondere die Temperaturen und der Wärmeübergang im Brennraum beherrscht werden. Die Versuchsergebnisse zeigen die große Bedeutung der hydrodynamischen Bedingungen für den Gesamtprozess. Der Temperaturverlauf, der Ort der Verbrennung, die Wärmeübertragung in der Wirbelschicht und andere Parameter wurden durch die komplexe Gas-Partikelströmung der zirkulierenden Wirbelschicht bestimmt. In der Arbeit wird gezeigt, welche Parameter die Hydrodynamik beeinflussen. Zur Erhöhung der Lastflexibilität wurden Lastwechselversuche auf die Betriebsparameter hin untersucht, die den stärksten Einfluss auf den Wärmeübergang zur Wasser-Dampfseite haben. Die Erkenntnisse wurden genutzt, um Konzepte für die Beschleunigung von Lastwechseln zu erarbeiten. Eines dieser Konzepte wurde erfolgreich in der Versuchsanlage getestet. Die experimentellen Daten wurden genutzt, um ein Modell der zirkulierenden Wirbelschichtverbrennung mit der dynamischen Prozesssimulationssoftware APROS zu entwickeln. Die Zielstellung der Prozesssimulation war die Untersuchung des dynamischen Betriebs der Co-Verbrennung. Die Übereinstimmung der Simulationsergebnisse mit den experimentellen Daten ist hoch und das Modell kann zukünftig zum Beispiel für die Bewertung neuer Lastwechselkonzepte genutzt werden. Die Dissertation liefert eine umfassende Bewertung der Flexibilität von zirkulierenden Wirbelschichtkraftwerken im Hinblick auf die Co-Verbrennung erneuerbarer Festbrennstoffe unter Lastwechselbedingungen. Maßnahmen und Konzepte werden vorgestellt, um diese Flexibilität weiter zu erhöhen