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Item type:Publication, Access status: without files , Biomass pellet fueled chemical looping gasification: Reaction kinetics study with a fluidized bed - thermogravimetric analysisBiomass pellets show the advantages of higher energy density, lower transportation and storage costs compared to powder biomass, making them attractive for future industrial applications. In this work, a fluidized bed-thermogravimetric analysis (FB-TGA) is developed. The gas-solid process for gram-scale biomass pellets under fluidization state at high temperature is characterized. The effects of gasification agents, bed material components and operating conditions on devolatilization and char gasification are investigated. The devolatilization is revealed to be a rapid phase transition process of volatiles, of which the rate is mainly affected by the intense heat and mass transfer with increasing temperature. While the char gasification is significantly slower, taking more than 600 s for all conditions, therefore be considered as the rate-control step. The hematite oxygen carrier can effectively promote the char gasification by breaking the concentration balance of gas components near the char surface. The char reaction kinetics is fitted based on the isothermal differential method. Results show that the cylindrical geometrical contraction model exhibits an excellent linear correlation. With a mass ratio of oxygen carrier/quartz sand of 1:9, the average activation energies of 130.58 kJ/mol and 104.17 kJ/mol are obtained when CO₂ and steam as gasifying agents.Publicationtype: Journal Article14 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Modeling and simulation of the start-up process of coal fired power plants with post-combustion CO₂ captureA detailed model of a post-combustion CO₂ capture plant (pcc-plant) is developed in the Modelica ® language which allows the simulation of start-up and shutdown processes. The model of the pcc-plant is coupled to a simplified model of a coal fired power plant to investigate the coupled process. To guarantee a stable and automatic operation, a sequential control for start-up and shutdown procedures is implemented in both plants. Two case studies, focussing on the pcc-plant, are subsequently performed in this contribution. In the first case study, the influence of different parameters and input variables on the start-up time is investigated in order to analyze the start-up process of the pcc-plant. The varied variables are the steam flow rate to the reboiler, the solvent flow rate and the total amount of solvent in the pcc-plant. In the second case study two different start-up control structures for the carbon capture plant are proposed and their performances are presented and compared.Publicationtype: Journal ArticleScopus© Citations 24 351 429 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Improvements on the liquefaction of a pipeline CO₂ stream for ship transport(2018-05); Ship transport and pipeline transport of CO₂ are considered to be viable options for large scale CCS. While pipeline transport is usually recommended for shorter distances, ship transport might also be considered for these distances in the early stage of CCS due to its high flexibility and low capital expenses. Ship transport is usually carried out in liquefied state at a temperature around −50 °C and low pressures. Thus, an efficient liquefaction process is required. Unlike other works on CO₂ liquefaction, it is assumed that the CO₂ has been transported by pipeline before it is transported by ship. Consequently, the CO₂ is expanded instead of being compressed and purification is not necessary as it has already been carried out before pipeline transport. Basic 1-stage, 2-stage and 3-stage closed cycle liquefaction processes are modelled, showing that a significant reduction of the minimum specific energy demand can be obtained by employing a multi-stage cascade design. The energy demand for the 2-stage base process is approximately 39% lower than for the 1-stage process. The energy demand can be further reduced by approximately 13% with a 3-stage process. Four measures of optimisation have been analysed: For the CO₂ stream, energy recovery with a liquid expander and a two phase expander are investigated. For the refrigeration cycle, the use of an aftercooler and the replacement of the cascade heat exchanger by a phase separator is studied. It can be seen that the energy demand can be reduced by approximately 30%–40% with respect to the base process if those four measures are implemented. The impact of the optimisations is influenced by the impurity concentrations of the CO₂ stream. Besides liquefaction, the specific electrical and thermal energy demands for the injection of CO₂ have been calculated. The electrical energy demand is proportional to the wellhead pressure and was found to be between 1.9 kWh/t CO₂ and 7.8 kWh/t CO₂. The thermal energy demand is between 21.0 kWh/t CO₂ and 30.5 kWh/t CO₂ , increasing for higher wellhead pressures and impurity concentrations.Publicationtype: Journal Article187 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dynamic flowsheet simulation for chemical looping combustion of methane(2018-05); ; ; Werther, JoachimIn a Chemical Looping Combustion system, the fuel and air reactors are strongly coupled because of chemical reactions in both and the circulation of solid oxygen carrier between them. To capture the effects inside the system, a novel dynamic flowsheet simulation environment for solids processes is applied to Chemical Looping Combustion of methane. Flowsheet simulation is a tool for process analysis and optimization covering multiple process units and flows in a system. An experimental 25 kWth pilot plant is operated, and all of its process units are modeled. The modeling comprises three fluidized bed reactors, two operating in bubbling fluidized bed condition and one as a circulating fluidized bed riser. A cyclone is used for gas-solid separation after the air reactor. The loop seals ensure gas sealing between the reactors. Fluid mechanics inside the systems are modeled with empirical and semi-empirical correlations, to enable fast calculations. This approach becomes handy when long-term dynamic effects like abrasion, start-up, or shut-down procedures as well as load changes are to be modeled. Chemical reactions for a gaseous fuel and their implications on gas flows were implemented. In addition, oxidation and reduction of the solid oxygen carrier in the three reactors were part of the simulation. To validate the simulation results, the pilot plant was operated with methane as fuel. Gas measurements were taken after both stages of the fuel reactor. Additionally, solid samples were drawn from the hot facility to examine the oxidation state of the carrier, when fuel is introduced. A transient simulation of plant operation over a total runtime of 40 min reveals that the solids inventories of the fluidized bed reactors in the system need only 30 s in the present case to reach a new steady state after a load change. If the oxidation and reduction reactions of the oxygen carrier are taken into account, however, this response time extends dramatically to several hundreds of seconds, which can also be seen in the experimental campaigns. The simulation of such a system behavior requires a powerful simulation tool for flowsheeting, which has been found here in the dynamic simulation framework.Publicationtype: Journal Article138 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Chemical looping combustion of high sodium lignite in the fluidized bed: Combustion performance and sodium transfer(2018-03); ; ; ; Werther, JoachimThe Zhundong coalfield in Xinjiang, China, is the largest integrated coal basin newly found. The present work concentrates on the application of chemical looping combustion (CLC) with a Zhundong lignite, which is characterized by high sodium content. Some experiments in a laboratory scale fluidized bed facility with an active iron ore oxygen carrier, were performed using the lignite as fuel and CO2 as gasifying agent at a temperature of 900 °C, with the objective of investigating its combustion performance and sodium transfer behavior in CLC. Results indicate that the gasification reactivity of the three coals follows the order of German lignite > Zhundong lignite > American bituminous coal in the current experimental conditions. During reducing stage, the unique product of sodium transfer from coal to the fly ash is albite (NaAlSi3O8) due to the reactions between sodium and other coal ash. The sodium deposition on the oxygen carrier particles was not found. 40 reducing-oxidizing cycles were performed, and sodium accumulation in the bed materials with cycles was found due to some ash staying in the bed. However, the growth of bed particles due to the sodium accumulation was not observed by determining the particle size distributions of bed materials. This indicates that burning the high sodium Zhundong coal in the present conditions have no influence on the particle agglomeration. Finally, a literature survey was made and results indicate that the main sodium in the Xinjiang coal basin of China is water soluble with an average value of 64%. The pure salt of NaCl, as one common water soluble sodium phase in Zhundong coals, was introduced to a bed of iron ore particles at 900 °C with regard to investigate the influence of NaCl on fluidization stability. Based on the measurements of pressure drop, bed temperature and SEM-EDS, it was found that NaCl does not react with the iron ore but in fact only acts as glue between iron ore particles. Further, the sodium transfer routes in CLC of Zhundong coal with iron ore based oxygen carrier are given and some discussions are made with regard to practical operation. The corrosion problems on the heating surface in the air reactor can be significantly reduced compared to a conventional Zhundong coal fueled furnace, since most of sodium will release and be converted in the fuel reactor.Publicationtype: Journal Article222 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Pilot scale testing and modeling of enzymatic reactive absorption in packed columns for CO₂captureEfficient processes for carbon dioxide (CO2) capture from post-combustion flue gases are required to combat global climate change. A key stage in post-combustion capture is selective CO2 separation from the flue gas stream. Separation of CO2 from mixed gases using countercurrent gas–liquid absorption in packed columns is a well-established technology for treatment of industrial gas streams. This approach can be adapted to remove CO2 from post-combustion flue gas, however, process improvements are needed to minimize the corresponding capital costs and energy requirements. Special challenges for CO2 recovery from flue gas arise from the very large volumes of gas to be processed, the need to operate the process with an inlet flue gas stream at atmospheric pressure, and the high amount of energy required to regenerate the absorption liquid. Aqueous solutions of the tertiary amine N-methyldiethanolamine (MDEA) are commercially used for high pressure CO2 separation due to high loading capacity for CO2, relatively good chemical and thermal stability and low volatility. Application of MDEA-based solutions to ambient pressure separations, such as CO2 capture from flue gases, is challenging since high reaction rates are required. High reaction rates for the MDEA system are achievable at high temperatures, which is conflicting with the preference of low temperatures to exploit high absorption capacity. This conflict can be overcome with the addition of a rate enhancing catalyst that enables high reaction rates at low temperatures. To put this innovative breakthrough technology closer to industrial application CO2 absorption in 30–50 wt.% aqueous solutions of MDEA in absence and presence of the CO2 absorption enhancing enzyme carbonic anhydrase (CA) was evaluated in pilot scale. The pilot scale investigation employed a packed column for parametric testing. Test variables included the liquid phase composition (30–50 wt.% MDEA), the column liquid load (8–24 m3 m−2 h−1), the absorber temperature (20–40 °C), and the application of CA in a dissolved or immobilized form. The CO2 absorption mass transfer enhancement provided by CA was measured. In the presence of dissolved CA, 30 wt.% aqueous MDEA showed superior performance in terms of absorption rates compared to operation using 50 wt.% MDEA(aq). No significant change in the CO2 absorption rate was observed for operation at given loads between 20 °C and 40 °C with dissolved CA present. At 20 °C with 30 wt.% MDEA the absorption rate with dissolved CA increased by more than 9 times compared to the absorption rate without enzyme. These results broaden the operation window for efficient CO2 absorption using MDEA solutions and allow for the exploitation of new process regimes, wherein high equilibrium loadings are achievable by applying lower absorption temperatures. Based on the experimental results obtained with dissolved CA, a simplified rate-based model of enzymatic reactive absorption (ERA), accounting for enzyme accelerated reaction kinetics, was developed which was capable of accurately predicting CO2 absorption rate when compared with experimental data. Implemented in a process simulator the model allows for the detailed investigation of the process behavior and the complex interactions of ab- and desorption operations in the presence of the CA. The validated model is intended to guide future experimental work as well as further performance optimization. In addition to the work exploiting the catalyst in its free form, the utilization of CA immobilized in a granular form and held in the pockets of Katapak-SP packing was successfully demonstrated.Publicationtype: Journal Article61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Towards an optimization of the CO₂ stream composition—A whole-chain approach(2016-11-01); ; ; ; CO2 streams captured from power stations or industrial plants may contain impurities that impact the consecutive steps of the CO2 capture and storage (CCS) chain. As the basis for an optimization of CO2 purity over the whole CCS chain, impacts of different impurities were investigated at key steps including studies on (i) corrosion of metallic materials in CO2 streams and brine, (ii) fluid and interfacial properties as a function of pressure, temperature and CO2 stream composition and their implications for CO2 transport, injection and geological storage, (iii) costs of different pipeline design options, (iv) geochemical alterations at typical reservoir conditions and their implications for geomechanical rock properties. Major findings are synthesized for two exemplary single source-single sink CCS chain scenarios involving CO2 stream compositions typical for pre-combustion capture and oxyfuel combustion. Recommendations for material selection for compression, transport and injection were derived for various CO2 stream compositions. To reliably control corrosion, a limitation of water contents to 50 ppmv is recommended for pipeline transportation of all CO2 streams. At geological storage conditions, the presence of either O2, NOx or SO2 only weakly affected fluid-mineral/rock interactions that still impacted geomechanical rock properties.Publicationtype: Journal Article101 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Optimizing integrated reference cases in the OCTAVIUS projectAdding a carbon capture plant to a power plant reduces the efficiency of said power plant. In order to keep this drop in efficiency as small as possible, several optimisation studies are performed in the OCTAVIUS project. Based on the work of the European Benchmarking Task Force-EBTF within the CESAR, CAESAR, and DECARBit projects, two reference power plants are modelled in Ebsilon®Professional. The first is an 800 MWe coal case, the second a 430 MWe natural gas combined cycle (NGCC) case. For each power plant two separate capture plants are considered: one using 30 wt% MEA as solvent system, the other with CESAR1, a mixture of AMP and PZ as solvent system. This results in four different reference cases which are optimized by varying different process parameters and evaluating process modifications. In a second step, the integration of the capture plant into the power plant is evaluated. This is important especially for the coal fired power plant, where integration of waste heat from the capture plant or the CO2 compressor intercoolers can lead to a significant increase in overall efficiency. The configuration of intercoolers for the CO2 compressor is adapted to achieve the highest overall efficiency. For the natural gas combined cycle plant, integration is not that beneficial, since there is no heat sink available in the water steam cycle. In the end, the cost of electricity and cost of CO2 avoided is calculated for all four cases. While the CESAR1 solvent system in a conventional absorber-stripper scheme is less costly (almost 17%) than the MEA solvent system in a process with Lean Vapour Compression for the coal cases, the result is the opposite for the two NGCC cases though the difference is not substantial.Publicationtype: Journal Article157 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Oxyfuel combustion for CO2 capture in power plants(Elsevier, 2015-08-04); ; ; ; Oxyfuel combustion is one of the leading technologies considered for capturing CO from power plants with CCS. This involves the process of burning the fuel with nearly pure oxygen instead of air. In order to control the flame temperature, some part of the flue gas are recycled back into the furnace/boiler. Since the publication of the Special Report on CO Capture and Storage by the International Panel for Climate Change (IPCC, 2005), the development of oxyfuel combustion technology has progressed significantly and could be considered at par in terms of technology maturity as compared to other leading CO capture technologies. This paper presents an overview to the current state-of-the-art technology on the development of oxyfuel combustion applied to (a) PC and CFB coal fired power plants and (b) gas turbine based power plant. It should be noted that it is not the intention of this paper to provide a comprehensive review but to present what have been achieved in the past 10 years of RD&D efforts. For coal fired power plant using oxyfuel combustion, this paper primarily presents the different development aspects of the burners and boilers (combustion and heat transfer), emissions, operation of the plant (i.e. start-up and turndown) and its integration to the ASU and CPU. For gas turbine based power plant using oxyfuel combustion, the different GT cycles are described, looking at the different aspects in combustion, emissions, cycle efficiency and development of the turbomachineries. Also presented in this paper is a snapshot to what we have learned from the operation of the different large-scale pilot plants and development of large scale demonstration projects worldwide. The paper concludes by presenting the potential of this technology and highlighting the importance of realizing large scale demonstration plant as a necessary step to achieve its ultimate goal of technology commercialization. 2 2 2Publicationtype: Journal Article232 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Assessment of the different parameters affecting the CO2 purity from coal fired oxyfuel processThe oxyfuel process is one of the most promising options to capture CO2 from coal fired power plants. The combustion takes place in an atmosphere of almost pure oxygen, delivered from an air separation unit (ASU), and recirculated flue gas. This provides a flue gas containing 80-90vol% CO2 on a dry basis. Impurities are caused by the purity of the oxygen from the ASU, the combustion process and air ingress. Via liquefaction a CO2 stream with purity in the range from 85 to 99.5vol% can be separated and stored geologically. Impurities like O2, NOX, SOX, and CO may negatively influence the transport infrastructure or the geological storage site by causing geochemical reactions. Therefore the maximum acceptable concentrations of the impurities in the separated CO2 stream must be defined regarding the requirements from transportation and storage. The main objective of the research project COORAL therefore is to define the required CO2 purity for capture and storage.Publicationtype: Journal Article14