• Energy Research
• Restricted close
• DE close
• MediaTUM close

In this paper, the performances of two iron-based syngas-fueled chemical looping (SCL) systems for hydrogen (H2) and electricity production, with carbon dioxide (CO2) capture, using different reactor configurations were evaluated and compared. The first investigated system was based on a moving bed reactor configuration (SCL-MB) while the second used a fluidized bed reactor configuration (SCL-FB). Two modes of operation of the SCL systems were considered, namely, the H2 production mode, when H2 was the desired product from the system, and the combustion mode, when only electricity was produced. The SCL systems were modeled and simulated using Aspen Plus software. The results showed that the SCL system based on a moving bed reactor configuration is more efficient than the looping system with a fluidized bed reactor configuration. The H2 production efficiency of the SCL-MB system was 11 % points higher than that achieved in the SCL-FB system (55.1 % compared to 44.0 %). When configured to produce only electricity, the net electrical efficiency of the SCL-MB system was 1.4 % points higher than that of the SCL-FB system (39.9 % compared to 38.5 %). Further, the results showed that the two chemical looping systems could achieve >99 % carbon capture efficiency and emit ~2 kg CO2/MWh, which is significantly lower than the emission rate of conventional coal gasification-based plants for H2 and/or electricity generation with CO2 capture.

In the course of the “Energiewende,” the German electricity market is undergoing major changes. The state-aided priority of renewable generation has led to a significant decline in electricity prices. This reduces the profit margin of cogeneration units and increases the necessity of flexible operation to avoid electricity production when spot prices drop below marginal costs. In this work, a 100 MWel combined-cycle (CC) power plant supplying heat and power to a paper mill is investigated. Currently, the plant is operated heat-controlled and is therefore unable to react to changing electricity spot prices. With the integration of heat storage, the plant is enabled to switch to power-controlled mode. To evaluate the technical impact of the storage, the plant and a thermochemical MgO/Mg(OH)2 storage are modeled using the stationary process simulation tool ebsilon professional. Different operation modes are investigated and results are used to derive a mixed integer linear programming (MILP) model to optimize the operation of the plant/storage system. Using this method, the overall economic impact of the storage on the plant operation is quantified.

AbstractAlumosilicate minerals are suitable sorbents at high temperatures for removing alkalis in syngas. Thermogravimetric investigations of these sorbents usually focus on the reaction mechanisms. Herein, a crucible arrangement is described that allows evaporation of the alkali source and sorption of gaseous alkali components in one temperature zone. With this experimental setup, kinetic investigations of alkali sorption are possible in a conventional thermobalance. Experiments were performed with sodium chloride as the alkali source and kaolin as the getter material. The reaction rate increased with alkali concentration and showed an exponential dependence on temperature. Thus, the Arrhenius model approach and power law model were selected for mathematical description.

This paper presents the results of a thermodynamic and economic evaluation of a novel hybrid combination of a compressed air energy storage and a combined cycle power plant. The new cycle is modeled on basis of a GE LM6000 gas turbine model, an adiabatic compressor model, an air expander and a conventional dual pressure HRSG configuration. Furthermore, a detailed design of the recuperator is presented. With the simulated components, a storage efficiency of 60% is reached. In CHP configuration the total efficiency of the plant reaches up to 86.2%. The thermodynamic and economic performance is compared to a conventional LM6000 combined cycle. For the economic evaluation the German electricity day-ahead prices and average gas price of the year 2014 are used. Overall it is found that the CAES/CCPP concept exhibits far more operation hours per year and a higher profit margin than the compared CCPP. Taking into account the investment and operational costs, especially with steam extraction the net present value of the novel cycle is higher than that of the combined cycle, despite the challenging market environment for storage technologies in Germany.

Gas–solid fluidized bed reactors play an important role in many industrial applications. Nevertheless, there is a lack of knowledge of the processes occurring inside the bed, which impedes proper design and upscaling. In this work, numerical approaches in the Eulerian and the Lagrangian framework are compared and applied in order to investigate internal fluidized bed phenomena. The considered system uses steam/air/nitrogen as fluidization gas, entering the three-dimensional geometry through a Tuyere nozzle distributor, and calcium oxide/corundum/calcium carbonate as solid bed material. In the two-fluid model (TFM) and the multifluid model (MFM), both gas and powder are modeled as Eulerian phases. The size distribution of the particles is approximated by one or more granular phases with corresponding mean diameters and a sphericity factor accounting for their nonspherical shape. The solid–solid and fluid–solid interactions are considered by incorporating the kinetic theory of granular flow (KTGF) and a drag model, which is modified by the aforementioned sphericity factor. The dense discrete phase model (DDPM) can be interpreted as a hybrid model, where the interactions are also modeled using the KTGF; however, the particles are clustered to parcels and tracked in a Lagrangian way, resulting in a more accurate and computational affordable resolution of the size distribution. In the computational fluid dynamics–discrete element method (CFD–DEM) approach, particle collisions are calculated using the DEM. Thereby, more detailed interparticulate phenomena (e.g., cohesion) can be assessed. The three approaches (TFM, DDPM, CFD–DEM) are evaluated in terms of grid- and time-independency as well as computational demand. The TFM and CFD–DEM models show qualitative accordance and are therefore applied for further investigations. The MFM (as a variation of the TFM) is applied in order to simulate hydrodynamics and heat transfer to immersed objects in a small-scale experimental test rig because the MFM can handle the required small computational cells. Corundum is used as a nearly monodisperse powder, being more suitable for Eulerian models, and air is used as fluidization gas. Simulation results are compared to experimental data in order to validate the approach. The CFD–DEM model is applied in order to predict mixing behavior and cohesion effects of a polydisperse calcium carbonate powder in a larger scale energy storage reactor.

Due to the high conversion rates and the low tar amounts in the product gas, entrained flow gasification of biomass can be an alternative process to state of the art gasification technologies, e.g., fluidized-bed gasifiers. Feedstock treatment is mandatory for entrained flow gasification (EFG). However, it has the potential of making residuals available for energetic use. In this study, the feasibility of EFG of solid biomass in an industrial-like test rig with a state of the art pneumatic dense-phase coal feeding system is shown. Four biomasses—torrefied wood (TW), beech wood (B), hydrothermal carbonized green waste (HCG), and corn cobs (CoC)—were used and compared to Rhenish lignite (RL). Especially, the gasification behavior of hydrothermal carbonized biomass is rarely known from the literature. The study includes a comparison of the fuels regarding feeding behavior, conversion rate, achievable gas composition, and cold gas efficiency (CGE) as well as tar formation. The oxygen stoichiometric ratio λ wa...

A thermodynamic Aspen Plus simulation model for a reversible solid oxide fuel cell (RSOFC) is presented and evaluated. It is composed of an electrolysis and a fuel cell module. The latter is based on an existing non reversible SOFC model. The electrolysis model simulates water electrolysis as well as catalytic reactions of inlet gases. The model has been validated using data from literature. It has been found that the support layer on fuel electrode supported cells has to be treated differently in terms of diffusion than the active layer. Simulation results show that for the investigated cell parameters, the positive effect of adding CO2 to the steam feed on the electrolysis process is due to wateregas-shift reactions and not CO2 electrolysis. An analysis of outlet gas compositions in electrolysis mode showed that the assumption of the cell as an equilibrium reactor was justified. A parameter study has been conducted, showing that increasing the operation temperature and pressure can improve the overall performance, while changing the inlet gas compositions in general improves either fuel cell or electrolysis mode and deteriorates performance for the other mode.

A new generation of refrigerants, the hydrofluoroolefines, has been introduced within the last years. These fluids have a significantly smaller Global Warming Potential compared to the state-of-the-art fluids, which are within the class of hydrofluorocarbons. The hydrofluoroolefines are unsaturated molecules consisting of double-bonded carbon atoms. Especially, compared to hydrofluorocarbons, which are saturated molecules, the interaction with polymers might differ. Therefore, this study investigates the compatibility between polymers and refrigerants, which are commonly used as working fluids in Organic Rankine Cycles or refrigeration units. The compatibility is evaluated due to a theoretical analysis of the relevant mechanisms of the fluid-polymer interaction and an experimental study. The investigated refrigerants are two state-of-the-art fluids, namely R245fa and R134a, as well as three next-generation refrigerants R1233zd-E, R1234yf and R1234ze-E. In addition, two blends, namely R450a and R513a, as well as a lubricant polyolester are investigated. The polymers comprise six elastomers and two thermoplastics, more specifically, two different compositions of ethylene-propylene-diene rubber, two compositions of fluororubber, chlorobutadiene rubber, nitrile-butadiene rubber, polytetrafluoroethylene and polypropylene. The material compatibility is evaluated by changes in volume, weight, Shore hardness as well as in small load hardness. Summing up, 64 different fluid-polymer combinations are tested at two different temperature levels.

Abstract Predicting conversion rates of solid fuels in entrained flow gasifiers, operating at increased temperatures and pressures, and better understanding the underlying reaction kinetics are of major interest for all industrial gasification applications. Numerical simulations in combination with experiments in lab- and pilot-scale entrained flow reactors help to understand the occuring reaction processes and can be used for gasifier optimization. The presented model is based on the software Ansys Fluent 16.0 and is validated for a bituminous coal with focus on the impact of total pressure. An nth order effectiveness factor approach with measured intrinsic reaction kinetics is applied in order to take diffusion limitations into account, and a thermal annealing model is included in order to account for the influence of decreased reactivities of the char surface due to deactivation, both being relevant at increased operating temperatures. The required model input parameters are derived from pyrolysis experiments and laboratory analyses. The simulation results are in good agreement with experimental data obtained from a pressurized entrained flow reactor operated at the Technische Universitat Munchen. The validation experiments are carried out at an operating temperature of 1200 °C, at total pressures of 0.5 MPa, 1.0 MPa and 2.0 MPa, and with a constant molar O / C ratio of one.