Christoph Pfeifer

Fluid-Dynamic Investigations in a Scaled Cold Model for a Dual Fluidized Bed Biomass Steam Gasification Process: Solid Flux Measurements and Optimization of the Cyclone

Gasification of biomass is an attractive technology for combined heat and power (CHP) production. A dual fluidized bed steam gasifier is in commercial operation at the biomass CHP plant in Guessing/Austria since 2002. For circulating fluidized bed applications the bed material consumption is economically crucial. Thus, cyclones for circulating fluidized beds need to be designed properly. Some erosion and caking in the cyclone of the gasifier could be observed with increasing hours of operation. The influences of these effects as well as the influence of the solid circulation rate between the two units on the separation efficiency were investigated by fluid-dynamic investigations using a scaled cold model. The results show that due to erosion and caking elutriation rates are increased, especially for smaller particles. However, the cyclone achieves fractional separation efficiencies of more than 99.9%.

Synergetic utilization of biomass and fossil fuels: influence of temperature in dual fluidized bed steam co-gasification of coal and wood.

Gasification of biomass and coal is an attractive technology for combined heat and power production, as well as for synthesis processes such as the production of liquid and gaseous biofuels. The allothermal steam blown gasification process yields a high calorific product gas, practically free of nitrogen. Originally, the system was designed for biogeneous fuels and residues but it can also handle a large number of other fuels such as several types of coal. To demonstrate the influence on the system performance of hard coal as an example of a solid fossil fuel a fuel blend of wood pellets and hard coal was fed into the DFB gasifier. The fuel blend ratio was 20 % coal in terms of energy. The DFB pilot plant was operated at a fuel power of 78 kW and a steam to fuel ratio of 1.0 kg/kgdb during the investigations. The system was operated at gasification temperatures between 830 and 870 °C. This paper points out the influence of the temperature on the system in terms of product performance, syngas quality as well as process efficiency.

Application of CaO-Based Bed Material for Dual Fluidized Bed Steam Biomass Gasification

Gasification of biomass is a suitable option for decentralized energy supply based on renewable sources in the range of up to 50 MW fuel input. The paper presents the dual fluidized bed (DFB) steam gasification process, which is applied to generate high quality and nitrogen-free product gas. Essential part of the DFB process is the bed material used in the fluidized reactors, which has significant impact on the product gas quality. By the use of catalytically active bed materials the performance of the overall process is increased, since the bed material favors reactions of the steam gasification. In particular, tar reforming reactions are favored. Within the paper, the pilot plant based on the DFB process with 100kW fuel input at Vienna University of Technology, Austria is presented. Actual investigations with focus on CaO-based bed materials (limestone) as well as with natural olivine as bed material were carried out at the pilot plant. The application of CaO-based bed material shows mainly decreased tar content in the product gas in contrast to experiments with olivine as bed material. The paper presents the results of steam gasification experiments with limestone and olivine, whereby the product gas composition as well as the tar content and the tar composition are outlined.

Circulating fluidized bed combustion reactor: Computational Particle Fluid Dynamic model validation and gas feed position optimization

Abstract A 3D Computational Particle Fluid Dynamic (CPFD) model is validated against experimental measurements in a lab-scale cold flow model of a Circulating Fluidized Bed (CFB). The model prediction of pressure along the riser, downcomer and siphon as well as bed material circulation rates agree well with experimental measurements. Primary and secondary air feed positions were simulated by varying the positions along the height of the reactor to get optimum bed material circulation rate. The optimal ratio of the height of primary and secondary air feed positions to the total height of the riser are 0.125 and 0.375 respectively. The model is simulated for high-temperature conditions and for reacting flow including combustion reactions. At the high temperature and reaction conditions, the bed material circulation rate is decreased with the corresponding decrease in pressure drop throughout the CFB for the given air feed rate.

Bed Material and Parameter Variation for a Pressurized Biomass Fluidized Bed Process

A pressurized gas at high temperatures with low impurities often is a basic requirement for applications for biomass gasification. Therefore, the Vienna University of Technology, in cooperation with the Austrian Bioenergy Centre, operates a pressurized gasification pilot plant in order to investigate thepressurized gasification process and estimate its potential. Within the scope of this paper this test facility as well as its operation behavioris described. Furthermore the parameters pressure, gasification temperature, lambda value and gasification agent have been investigated regarding to their influenceon the producer gas composition and arepresented and discussed in the following.

Thermogravimetric analysis and kinetic study of marine plastic litter

This paper deals with marine plastic debris and its collection and recycling methods as one possible answer to the rising amount of plastic in marine environments. A novel approach is to use energy recovery, for example pyrolysis of marine plastic debris into high-energy products. Compared to other thermal processes, pyrolysis requires less technical effort and the end products can be stored or directly reused. In order to design such an onboard pyrolysis reactor, it is necessary to know more facts about the feedstock, especially the thermochemical behaviour and kinetic parameters. Therefore, a thermogravimetric analysis was carried out for three selected plastic sizes with a temperature range of 34-1000 °C. The results obtained from TGA showed the same curve shape for all samples: single stage degradation in the temperature region of 700-780 K with most of the total weight loss (95%). Small microplastics had an average activation energy of 320-325 kJ/mol.