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Item type:Publication, Access status: with files , Assessment tool for the hybridisation of minigrids - Case study in NigerMinigrids are a great electrification strategy for developing countries. [1] Formerly operated only by diesel generators, they could be equipped with renewable energy and storage systems to become more reliable and competitive. Since resources are limited, it is not possible to hybridise all minigrids at the same time. An MS-EXCEL-based multi-criteria decision analysis (MCDA) tool offers a rational and impartial way of decision-making presenting the most eligible minigrids for a hybridisation. For the demonstration purposes, it is applied to the electricity sector of Niger.Publicationtype: Conference PaperScopus© Citations 2 259 393 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Conditioning of a pipeline CO₂ stream for ship transport from various CO₂ sourcesIn this work, the closed-cycle and open-cycle process design for the conditioning of a CO₂-stream for ship transport are compared in terms of the minimum specific energy demand. In contrast to other works, a high-pressure pipeline CO₂-stream is assumed as an input stream rather than a low pressure CO₂-stream from a capture plant. An output temperature of -50 °C is selected, which corresponds to an output pressure of 6.75 bar for pure CO₂ and output pressures of less than 25 bar for typical Post-Combustion and Oxyfuel CO₂-streams. It is shown that the minimum specific energy demand for closed-cycle refrigeration processes can be significantly reduced by a 2-stage or 3-stage temperature cascade. With approximately 46 kJ/kgCO₂, the minimum energy demand of the 3-stage open-cycle process is almost the same as for the 3-stage closed-cycle process. It is shown that the open-cycle process design cannot be used for CO₂-streams with impurities, unless the stream is purified in the refrigeration process. The results for typical Post-Combustion and Oxyfuel CO₂-streams show that the minimum specific energy demand slightly increases with an increasing impurity concentration. For the 1-stage closed-cycle process, it rises from 82.1 kJ/kgCO₂ for pure CO₂ to 83.4 kJ/kgCO₂ for an Oxyfuel stream with 98% CO₂ purity. That increase is smaller for the 2-stage closed-cycle and even smaller for the 3-stage process.Publicationtype: Conference PaperScopus© Citations 4 291 365 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Benchmarking of the DMX™ CO₂ capture processThis paper presents the main results of Task 13.4 of the OCTAVIUS project dedicated to the benchmarking of DMX versus MEA 30 wt. % CO2 capture processes. In the introduction are given the main objectives of the FP7 Project OCTAVIUS, which ended in June 2016. In this first part are also presented the main characteristics of the DMX process developed by IFP Energies nouvelles (IFPEN) and licensed by PROSERNAT, which uses a phase change solvent. The benchmarking study takes into account the design and the optimal integration of the CO2 capture process within the power plant and the CO2 compression at 110 bara. The thermal integration has been realised by TUHH. The design and evaluation of the capture processes were carried out by IFPEN based on the results of mini-pilots experimentation within OCTAVIUS and of previous works. The comparison has been performed for a reference power plant (805 MWe coal power station) using criteria defined jointly with the industrial partners of the OCTAVIUS project. This techno-economic study confirms that the DMXTM process is very promising as it allows a reduction in energy penalty compared to the MEA reference process without Lean Vapour Compression by approximately 2% points. As a consequence, it gives lower Cost of Electricity and lower avoided CO2 cost: 42.6 €/tCO2 (56.5 €/tCO2 for the MEA reference process). The DMX process needs now to be demonstrated in an industrial scale pilot plant.Publicationtype: Conference PaperScopus© Citations 18 542 382 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Enzyme Carbonic Anhydrase Accelerated CO₂ Absorption in Membrane ContactorMembrane contactors offer a promising alternative to conventional CO2 absorption processes using columns. In a membrane contactor the advantages of absorption technology and membrane technology are combined as direct contact of the solution and gas feed stream is avoided by membrane barrier. In this study, the possibility of employing the enzyme carbonic anhydrase (CA) for the acceleration of CO2 reaction in MDEA and MEA solution in combination with the use of a membrane contactor was investigated in a lab scale module. The membranes employed in this study were microporous and specifically chosen to have both hydrophobic (bulk) and hydrophilic (surface) properties in order to avoid wetting of solution and reduce fouling by the enzymes simultaneously. By adding the enzyme carbonic anhydrase (CA), a significant improvement of CO2 absorption rate was observed in MDEA solution while a negative effect was observed in MEA solution. Meanwhile the porous hydrophobic membranes were coated with a highly selective poly(ionic liquids) layer increasing the affinity of CO2 towards the interfacial area and hence also the driving force. The concept may initially appear counter intuitive, as the dense membrane layer introduces an added resistance, however the active membrane material gave promising results and was observed to accelerate CO2 transport in MDEA solution. The combination of both enzyme and PILs resulted in synergies, which significantly improved CO2 absorption in MDEA solution.Publicationtype: Conference Paper77 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Automated classification and identification procedure for prediction of energy consumption in multi-mode buildingsWith an increasing share of renewable energy sources, largely decentralized, energy hubs are gaining relevance in the energy landscape as promising solutions because they match local production with consumption. To efficiently control an energy hub a prediction of the energy consumption of the buildings in the hub is required. This work proposes an on-line identification scheme to identify the closed-loop behavior of buildings as they are usually under unknown local lower-level control. Since buildings are typically controlled in different modes depending on the time of day (night setback), an identification of a switched system is proposed, combining a classification step to identify the switching times followed by the identification of a piecewise linear model for each mode. As a test case an operational Swiss office building is considered.Publicationtype: Conference Paper15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Optimal use of energy storage potentials in a renewable energy system with district heatingGrowing shares of intermittent renewable energy sources in power systems lead to temporal imbalances between electricity supply and demand. Technologies which help to balance the electric grid such as energy storages, demand response or flexible coge-neration concepts are therefore gaining on importance. However, the investigation of these potentials from a system perspective requires a simulation approach that takes into account the interactions between supply and demand side as well as power system stability. While most prior studies utilize either linear optimization models to investigate storage options on a system level, or nonlinear simulation models for power system analysis, the present work utilizes a combination of both approaches.Publicationtype: Conference PaperScopus© Citations 5 393 604 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Enzyme Accelerated Carbon Capture in different Contacting Equipment - A Comparative Study(Elsevier, 2016-11); ; ; ; CO2 capture is an essential step for providing a sustainable and ecological solution to cope with increasing energy supply burning fossil fuels. However, industrial application of current CO2 capture technologies is limited due to the significant energy penalty. In order to reduce this energy penalty two different approaches of process intensification are examined in this study. The first approach aims at the intensification of mass transfer to compensate for low absorption rates of solvents with high capacity that would allow for more energy-efficient CO2 capture. Here the tertiary amine methyldiethanolamine (MDEA) is combined with a highly efficient biocatalyst, the enzyme Carbonic Anhydrase (CA), for which significant enhancement of absorption performance was demonstrated in literature. In addition to the intensification of the solvent system, the contacting of gas and liquid streams in ab- and desorption can be improved in intensified contacting devices (ICD). Here especially membrane contactors (MC) and rotating packed beds (RPB) are promising alternatives to classical packed columns. MC provide a well-defined interfacial area that is orders of magnitude higher than for conventional equipment and introduces additional operational flexibility, expressed by the independent flow ratio between liquid and gas phase. In a RPB centrifugal forces are exploited to increase acceleration of the liquid and improve turbulence and mass transfer. The rotational speed of the rotating packing introduces an additional degree of freedom compared to common static equipment. Both ICDs offer a very compact design. While both, ICD and the improved solvent system with CA, can significantly intensify the CO2 capture process, research on the combination of both is scarce. In order to evaluate the potential benefit of a joint implementation, a first step of imminent importance is to characterize the operating windows of such an intensified process. Based on prior results concerning the energy requirements for solvent regeneration, an aqueous amine solution with 30 wt.-% MDEA is investigated in this study without and with dissolved CA. In order to evaluate the potential improvement of a joint application of the ICD and the application of CA absorption experiments in a packed column and in the two ICDs are performed. While all three devices show similar absorption performance without CA added, the RPB offers the advantage to handle exceptionally high gas loads while the MC can be operated over a much wider range of liquid loads. When CA is added to the solvent system the packed column and the RPB show superior performance compared to the MC. While none of the combinations is generally superior, the different means for process intensification extent the operating window and facilitate improved absorption performances.Publicationtype: Conference Paper35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Different Strategies for Accelerated CO₂ Absorption in Packed Columns by Application of the Biocatalyst Carbonic AnhydraseWithin this work, the combination of an energetically favorable aqueous N-Methyldiethanolamine (MDEA) solution and the enzyme carbonic anhydrase is investigated in a packed column pilot plant. The use of aqueous MDEA solution for CO2 separation is already known from natural gas applications, for which an increased driving force due to the higher partial pressures of CO2 overcompensates reaction kinetic limitations. The objective of the addition of carbonic anhydrase is to countervail the loss of separation efficiency caused by the lower driving force in CO2 capture from power plant flue gases. Hence, carbonic anhydrase acts as a key to harness the energetic advantage of these solvent systems. However, application of the enzyme also poses restrictions on the process. Especially compliance with the enzyme stability limits is challenging for desorption, which is generally performed at high temperatures. In order to determine an optimal implementation of the enzyme into the process the current work presents different strategies how to apply CA as a biocatalyst in reactive absorption processes and shows how absorption efficiency is influenced. For introducing the enzyme to a packed column two approaches are investigated in this study. The simplest way of application is to dissolve the enzyme in the solvent. This allows the enzyme to work exactly where the reaction kinetic limitation can be found, in the liquid boundary layer. However, due to the temperature sensitivity of the enzyme an additional enzyme recovery step prior to the desorber might be necessary if desorption is to be performed at high temperatures. The immobilization of the enzyme inside the absorption column presents an alternative to prevent this additional separation, but may cause additional mass transfer limitations at the solid particles in which the enzyme is immobilized. The immobilization and the necessity of a suitable packing in which the enzyme particles can be filled, also makes this strategy more complicated but allows placing the enzyme at a location of most suitable process conditions in the column. But most importantly it completely avoids that the enzymes experience high temperature in the desorber. Systematic investigations of the influence of specific liquid load, liquid inlet temperature, MDEA-concentration and enzyme immobilization on absorption performance are conducted. Dissolved enzyme showed a nearly three times higher absorption performance than the immobilized enzyme under equivalent operating conditions, however the immobilized enzyme concentration used was effectively 50 times lower, meaning the result is actually quite promising for immobilized CA. From the investigated operating conditions, a liquid inlet temperature of 20 °C, a MDEA concentration of 30 wt.-% and a liquid flow rate of 24 m3 m-2 h-1 showed the best absorption performance with the dissolved enzyme. The measured absorption rate was 7.57 times higher than without enzyme added.Publicationtype: Conference Paper99 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Comparison of natural gas combined cycle power plants with post combustion and oxyfuel technology at different CO₂ capture ratesWithin this work a natural gas-fired combined cycle plant is investigated with post-combustion CO₂ capture (PCC) and as a semi-closed oxyfuel combustion combined cycle (SCOC-CC) using process simulation tools. In most studies the CO₂ capture rate of PCC units is set to 90% while the SCOC-CC is often considered for zero emission plants. To allow a comparison between the processes the capture rate needs to be taken into account. If a certain CO₂ emission value is required a different capture rate may be economically attractive. The effect of the capture rate is investigated from 60% to 97.5% for PCC and from 75% to 100% for the SCOC-CC. For PCC the capture rate has a strong influence on the efficiency penalty. For a broad range of capture rates the specific heat duty is found to be approx. constant. However, for very high capture rates the heat duty strongly increases. The efficiency penalty of the SCOC-CC is much less affected by the chosen capture rate, because the duty of the air separation unit (ASU) is independent on the capture rate. However to achieve a sufficient CO₂ purity a reduced capture rate can be necessary. The processes are compared regarding the loss of electrical energy per kg CO₂ captured. PCC has a significantly lower specific loss for low capture rates of approx. 0.38 kWhel/kg CO₂ compared to the SCOC-CC with more than 0.48 kWhel/kg CO₂. For capture rates of > 90% the losses of both processes approach each other. With high purity oxygen the SCOC-CC can achieve a capture rate of 100% as well as a CO₂ purity of >96 vol.-% at a specific loss of 0.49 kWhel/kg CO₂.Publicationtype: Conference PaperScopus© Citations 38 486 455 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Optimisation potentials for the heat recovery in a semi-closed oxyfuel-combustion combined cycle with a reheat gas turbineSemi-closed oxyfuel-combustion combined cycle plants are one possibility to realise CCS technologies with natural gas-fired power plants. Due to the recirculation of exhaust gas the working fluid in the gas turbine consists mainly of CO2. This leads to the necessity for an increased pressure ratio to achieve the efficiency and the exhaust gas temperatures of conventional gas turbines. In this work a conventional natural gas-fired combined cycle plant with a reheat gas turbine modified for oxyfuel operation will be presented. As it is assumed that the necessary pressure ratio is not realisable with axial compressors two different scenarios are considered. On the one hand the pressure ratio is the same as in the conventional process and on the other hand the pressure ratio is set to an assumed maximum of 60. The exhaust gas temperature lies significantly above the values of the conventional plant. Generally the higher pressure ratio results in a higher net efficiency of the plant. An unchanged heat recovery process results in a loss of efficiency of at least 9.3 to 10.8 %-pts. depending on the pressure ratio. Increasing the steam parameters can achieve a reduction of this loss ranging from 0.5 %-pts for the high pressure ratio to 1.0 %-pts for the low pressure ratio. An alternative approach for the heat recovery is the application of an internal recuperator in the gas turbine. When the achievable pressure ratio is far from the optimum value, as in the low pressure ratio case, this approach can lead to significantly lower losses of 9.1 %-pts. With a higher pressure ratio the effects of the optimisation options are similar.Publicationtype: Conference PaperScopus© Citations 9 316 234