Hans Joachim Krautz

Drying of Lignite in a Pressurized Steam Fluidized Bed—Theory and Experiments

The present article describes the basic principles of drying of lignite in a pressurized steam fluidized bed and a test facility of the Chair of Power Plant Technology as well as results achieved during experiments. At first the water binding of lignite, the heat transfer, and the influence of pressure and particle size are explained. A description of the two facilities available at the Chair of Power Plant Technology—cold and hot models—and a presentation of the experiments done and results obtained follows. The construction of a 10 tons/h pilot plant is briefly reported.

A comparative study of different CFD-codes for numerical simulation of gas–solid fluidized bed hydrodynamics

Abstract The hydrodynamics of a gas–solid fluidized bed reactor were studied numerically. Computational two-dimensional results from open source software packages MFIX and OpenFOAM , and those obtained from the commercial software package Fluent were discussed and compared with numerical and experimental data existing in the literature. The gas–solid flow was simulated applying the multifluid Eulerian–Eulerian model, where the solid phase is treated as a continuum. The solid-phase properties were calculated by using the kinetic theory of granular flow. Momentum exchange coefficients were calculated using the Gidaspow and Syamlal–O’Brien drag functions. Pressure drop and bed expansion ratio predicted by the simulations were in relatively close agreement with benchmark numerical and experimental data sets in the bubbling regime. Contrary to the OpenFOAM predictions, computations with MFIX and Fluent predicted instantaneous and time-average local voidage and velocity profiles which are comparable with results from the literature.

Numerical Simulation of Dense Gas-Solid Multiphase Flows Using Eulerian-Eulerian Two-Fluid Model

Gas-solid fluidized beds are widely applied in chemical processes such as drying, combustion, synthesis of fuels, granulation, polymerization etc. They have several advantageous properties including; excellent heat and mass transfer, nearly isothermal conditions due to intense gas-solid mixing, large gas-solid surface area, smooth transport of solids, uniform solid product in batch processes, and possibility of continuous and largescale operations. On the other hand, these reactors have several drawbacks that provide a strong motivation for further studies and developments. These include; difficulty in scalingup and design, erosion of vessel and internals, formation of agglomerates, non-uniform products due to non-uniform solids residence time during continuous operation, and high particle entrainment. These drawbacks are bottlenecks for practitioners to reliably design and scale-up commercial fluidized bed reactors. The main reason for this is that the gassolid multiphase flow dynamics coupled with heat and mass transfer and chemical reactions that occur in these systems are very complex and not yet fully understood. In bubbling gas-solid fluidized beds, bubble characteristics such as size, shape, velocity, distribution have a vital influence on the hydrodynamics of bed and hence on its performance as a chemical reactor and/or a heat exchange unit. The extent of gas-solid mixing and segregation, heat and mass transfer as well as reaction conversion are governed by the number, size and motion of bubbles passing through the bed (Kunii & Levenspiel, 1991). Therefore, fundamental understanding of the hydrodynamics of fluidized beds thereafter their heat and mass transfer as well as chemical conversion come only after a sound understanding of bubbling behaviour is achieved. However, prediction of bubble characteristics is extremely complex as bubbles can grow, coalesce, split or even disappear as they move from the distributor where they are formed to the top of the bed where they finally erupt. Moreover, bubble characteristics vary with geometric construction of the bed and operating conditions. In many applications, heat exchanger tubes are inserted to enhance the rate of heat and mass transfer and chemical conversion, control the operating temperature, promote good mixing and reduce gulf circulation of solids. In these systems, the bubbling behaviour is also strongly influenced by the geometry and arrangement of the internals (Yates et al., 1990; Hull et al., 1999; Asegehegn et al., 2011a). Therefore,

Lignite-Fired Combined Cycle Power Plant With ACPFBC: Concept and Thermodynamic Calculations

A 200 kWth test plant was constructed by BTU Cottbus for the purpose of developing a special variant of coal conversion based on 2nd generation PFBC. This concept, primarily to be used for generating power from lignite, employs a circulating type fluidized bed and is characterized by a design that combines the two air-blown steps “partial gasification” and “residual char combustion” in a single component. The subject of this paper is to develop an overall power plant concept based on this process, and to perform the associated thermodynamic calculations. In addition to the base concept with one large heavy-duty Siemens gas turbine V94.3A fired with Lausitz dried lignite (19% H2O), further versions with variation of Siemens gas turbine model (V94.3A and V64.3A), the water content of the fuel fired (raw lignite with more than 52% H2O or dried lignite) as well as the method of drying the coal were investigated. Common assumptions for all versions were ISO conditions for the ambient air and a condenser pressure of 0.05 bar. As expected, the calculations yielded very attractive net efficiencies of almost 50% (LHV based) for a variant with the small V64.3A gas turbine and up to more than 55% for the large plants with the V94.3A gas turbine. It was further demonstrated that thermodynamic integration of an advanced, innovative coal drying process (e.g. fluidized-bed drying with waste heat utilization) causes an additional gain in net efficiency of about three percentage points compared with the variant of firing lignite that was first dried externally. In addition to the basic function of the coal conversion system, it was necessary to also assume preconditions such as complete carbon conversion, reliable hot gas cleaning facilities and fuel gas properties that are acceptable for combustion in the gas turbine. Put abstract text here.Copyright

Einsatzsimulation zur Erbringung von Primärregelleistung mit Batteriespeichern

Die Verbundpartner Energiequelle GmbH, 50Hertz Transmission GmbH und die BTU Cottbus – Senftenberg / Lehrstuhl Kraftwerkstechnik befassen sich im FuE-Vorhaben „Systemdienstleistungen und Energiespeicherung mittels Grosbatterien zur Stabilisierung von Netzen mit hohen EE-Anteilen – Konzeption und Demonstration“ (kurz: SDLBatt) mit der Weiterentwicklung eines hocheffizienten Batteriespeichers zum Regelkraftwerk. Die Erbringung von Regelleistung und weiteren Systemdienstleistungen sowie die hierfur notwendigen Entwicklungen und Erprobungen werden auf Basis eines innovativen 10-MW-Li-Ion-Batteriesystems, welches durch den Projektpartner Energiequelle GmbH in Feldheim errichtet und betrieben wird, betrachtet. Betriebsdaten, energetische Bilanzierung, rechtlichregulatorische Randbedingungen und Simulation verschiedener Betriebsstrategien stehen im Vordergrund der Untersuchungen.

Comparative Analysis of Brazilian Residual Biomass for Pellet Production

Brazil is an important producer and the largest exporter of sugar, ethanol, coffee, orange juice, and tobacco. The countrys availability of land, water and labour has allowed for increased production and exports. Continuing the trade expansion and diversification of markets and products remain at the core of Brazil’s agricultural growth strategy (Valdez et al. 2006). The increase in crops generates a biomass residue surplus. It is known that approximately 30% of the sugar cane production is bagasse (Rosillo-Calle et al. 2007) and 22% of rice is constituted of husks (Eriksson and Prior 1990). This residual biomass can be transformed into a valuable fuel, becoming an important local energy source. There are several conversion technologies for biomass, based on the type, available residues and the market demand. Pressing of residues increases storage and transport efficiency. Pellets, briquettes, or any other pressed form can be used as a fuel. Recent research shows different combustion technologies for biomass: gasification, pyrolysis and combined heat and power (Rosillo-Calle et al. 2007).