Wolfgang Krumm

Mathematical modelling and simulation of bubbling fluidised bed gasifiers

A mathematical model for simulation of gasification processes of solid fuels in atmospheric or pressurised bubbling fluidised beds incorporating bed and freeboard hydrodynamics, fuel drying and devolatilization, and chemical reaction kinetics is presented. The model has been used to simulate four bubbling fluidised bed gasifiers, described in literature, of different scales from atmospheric laboratory scale up to pressurised commercial scale, processing brown coal, peat and sawdust. The gasifiers have been operated within a wide range of parameters using air, air/steam or oxygen/steam as gasification agent, operating with or without recirculation of fines at operating pressures up to 2.5 MPa. The simulation results for overall carbon conversion, temperature and concentrations of gaseous species agree sufficiently well with published experimental data.

Reduction of the energy demand for seawater RO with the pressure exchange systems PES

Abstract Nearly all reverse osmosis plants operated for the desalination of sea water in order to produce drinking water in industrial scale are equipped with an energy recovery system based on turbines. These are activated by the concentrate (brine) leaving the plant and transfer the energy contained in the high pressure of this concentrate usually mechanically to the high-pressure pump. In the pressure exchange system PES the energy contained in the brine is transferred hydraulically and with an efficiency of approximately 98% to the feed. This reduces the energy demand for the desalination process significantly and thus the operating costs. At the same time this advanced technological approach allows for reducing the size of the high-pressure pump to an amount of feed water equivalent to the amount of permeate produced, saving investment costs. The installation of PES in existing installations with a permeate production of more than 2,000m3/d allows for short amortisation times. The concept of the pressure exchange system PES and the operating data of the demonstration plant installed in the reverse osmosis unit INALSA I on Lanzarote, Spain with a permeate production of 5,000m3/d are presented.

Optimization of the energy demand of reverse osmosis with a pressure-exchange system

Abstract Energy recovery systems based on turbines activated by concentrate leaving the plant have been in operation in many reverse osmosis (RO) plants for many years. Other design approaches for RO plants save energy by reducing the energy demand for the desalination process itself. One of them is the pressure-exchange system (PES) which is able to achieve considerably lower energy requirements in comparison to the conventional systems. The PES is suited for plants with a permeate production of more than 2000 m 3 /d. It enables a simple, variable adaptation of discharge volume and has, due to its design and direct transmission of high pressure from the brine to the feed, an efficiency of approximately 98%, with economic energy utilization and short amortization times. This proven system has ben used in the field of mining for more than 20 years, and with volume flows of up to 1400 m 3 /h and pressures of up to 16 MPa. On one of the Canary islands, a PES is presently under construction in a RO plant for seawater desalination with a permeate capacity of 5000 m 3 /d for demonstration purposes.

Highly efficient nanoarchitectured Ni5TiO7 catalyst for biomass gasification.

We report the synthesis of needle-shaped nanocrystals of Ni(5)TiO(7) utilizing a solid-phase reaction of NiO with a porous and rough TiO(2) surface produced by plasma electrolytic oxidation. The single crystalline orthorhombic nanocrystals are grown along the [010] axis, featuring a length of ∼10 μm and diameters varying from several tens of nanometers up to 200 nm. The resulted novel Ni(5)TiO(7)/TiO(2)/Ti nanoarchitectured compound composite has been proven outstandingly active as a catalyst and appears most suitable for high-temperature operation in biomass gasification. The findings may pave the way to an improved and environmentally friendly technology of energy generation.

Empirical Modeling of Iron Oxide Dissolution in Sulphuric and Hydrochloric Acid

A new approach is presented to an empirical modeling of chemical pickling processes, based on the activation energy of oxide dissolution in hydrochloric acid (HCl) and sulfuric acid (H2SO4). The model allows us to calculate pickling times as a function of definite parameters. The main oxide layers on hot-rolled materials are magnetite (Fe3O4), hematite (Fe2O3), and wustite (FeO). On the laboratory scale, the activation energy of each oxide has been determined. FeO is a metastable oxide and has been produced based on magnetite powder in a H2/H2O atmosphere. The oxide powders used for the experimental procedure have been analyzed by X-ray powder diffraction to insure the proper stoichiometry and composition. The model allows us to calculate the time of oxide dissolution based on the parameters temperature, acid concentration, and the composition of the oxide layer. Calculated values are verified by surface potential measurement on industrial oxide layers. The hot-rolled material used for verification is low carbon steel. A comparison between calculated pickling times and experimental data will be presented.

THEORETICAL AND EXPERIMENTAL INVESTIGATION OF HOAR-FROST GENERATION AND THAW OFF PROCESS ON A COMPACT ENERGY-ABSORBER

ABSTRACT A mathematical model is presented which describes the hoar-frost generation and the thaw off process on a compact energy-absorber. Simulation results which show the influence of a hoar-frost layer on the energy gain are discussed. The simulation results also show the dependence of the energy gain and the energy demand of the thaw off process under different operation and weather conditions. Finally suggestions are given for the optimum operation of an energy absorber.

Upgrading of automobile shredder residue via innovative granulation process ‘ReGran’

Stricter regulatory requirements concerning end-of-life vehicles and rising disposal costs necessitate new ways for automobile shredder residue utilisation. The shredder granulate and fibres, produced by the VW-SICON-Process, have a high energy content of more than 20 MJ kg−1, which makes energy recovery an interesting possibility. Shredder fibres have a low bulk density of 60 kg m−3, which prevents efficient storing and utilisation as a refuse-derived fuel. By mixing fibres with plastic-rich shredder granulate and heating the mixture, defined granules can be produced. With this ‘ReGran’ process, the bulk density can be enhanced by a factor of seven by embedding shredder fibres in the partially melted plastic mass. A minimum of 26–33 wt% granulate is necessary to create enough melted plastic. The process temperature should be between 240 °C and 250 °C to assure fast melting while preventing extensive outgassing. A rotational frequency of the mixing tool of 1000 r min−1 during heating and mixing ensures a homogenous composition of the granules. During cooling, lower rotational frequencies generate bigger granules with particles sizes of up to 60 mm at 300 r min−1. To keep outgassing to a minimum, it is suggested to melt shredder granulate first and then add shredder fibres. Adding coal, wood or tyre fluff as a third component reduces chlorine levels to less than 1 wt%. The best results can be achieved with tyre fluff. In combination with the VW-SICON-Process, ReGran produces a solid recovered fuel or ‘design fuel’ tailored to the requirements of specific thermal processes.

THEORETICAL AND EXPERIMENTAL ANALYSIS OF DESIGN AND OPERATION OF MULTI-ENERGY SOURCE HEATING SYSTEMS

ABSTRACT Comparison of simulation results with experimental results for a multi-energy source heating system are presented. The heating system consists of a compact energy-absorber-heat pump system with an integrated cold water storage. A laboratory building acts as heat load. This first intermediate report shows that the simulation results agree well with experimental data. The aim of this project is to develop a mathematical model of a multienergy heating system in order to determine the optimum layout and operational mode.

MATHEMATICAL MODELING OF PERFORMANCE AND OPERATIONAL MODE OF ENERGY-ABSORBERS

ABSTRACT A mathematical model is presented which describes the operational mode and the performance characteristics of energy-absorbers. The simulation of different types of energy-absorbers shows the dependence of the daily and annual average value of specific energy gain and its composition due to different energy sources from the environment. Furthermore the annual average value of the specific energy gain as a function of the temperature difference between environmental and working fluid and as a function of the working fluid flow rate is shown for different types of energy-absorbers. The climatic input values for the calculation are generated by a weather model. Finally suggestions are given for the optimum operation of energy absorbers.