Thomas Nussbaumer

Sampling and analysis of particles and tars from biomass gasifiers

Abstract Particles and tars are considered as harmful components in internal combustion engine applications of biomass derived producer gas. Since state-of-the-art cocurrent gasifiers or gas cleaning devices can reach distinctively lower particle and tar levels than previous units, long duration sampling periods are needed for the determination of the producer gas contaminants. A new sampling method which uses several classes of “tar” components and allows long duration sampling has been developed and thoroughly tested. Up to date, the method has been used at eight different gasifier installations and seven gas cleaning systems within Europe.

Measurements and particle resolved modelling of heat-up and drying of a packed bed

The objective of this study is to measure the heat-up and the drying of a packed bed consisting of large wood particles as encountered in furnaces and to compare the predictions of a particle resolved approach to measurements. Within the experiments both single particle and packed bed measurements for the drying of wood were carried out. For both cases the samples as single particles and as a packed bed were exposed to a gas stream its temperature ranging from T = 443 to 743 K. The temperatures and the mass loss due to drying were recorded during the experiments and the heat transfer properties were correlated with earlier 7ndings. Within the present contribution a packed bed is considered as an ensemble of a 7nite number of particles. The heat-up and drying process of each particle is described by one-dimensional and transient conservation equations for mass and energy. Applying this model to all particles of a packed bed forms the entire packed bed process as a sum of individual particle processes. The arrangement of particles within the bed de7nes a solid phase and a void space between the particles. The :ow through the void space of a packed bed is modelled as a :ow through a porous media taking into account interaction between the solid and the gaseous phase by heat and mass transfer. A comparison between measurements and predictions of drying models yielded satisfactory agreement only for the constant evaporation temperature model. Furthermore, the results show, that a particle resolved approach is better suited than a continuum mechanic approach to describe packed bed processes since this approach omits additional empirical correlations for a packed bed. ? 2002 Published by Elsevier Science Ltd.

Time-resolved characterization of primary emissions from residential wood combustion appliances

Primary emissions from a log wood burner and a pellet boiler were characterized by online measurements of the organic aerosol (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and of black carbon (BC). The OA and BC concentrations measured during the burning cycle of the log wood burner, batch wise fueled with wood logs, were highly variable and generally dominated by BC. The emissions of the pellet burner had, besides inorganic material, a high fraction of OA and a minor contribution of BC. However, during artificially induced poor burning BC was the dominating species with ∼80% of the measured mass. The elemental O:C ratio of the OA was generally found in the range of 0.2-0.5 during the startup phase or after reloading of the log wood burner. During the burnout or smoldering phase, O:C ratios increased up to 1.6-1.7, which is similar to the ratios found for the pellet boiler during stable burning conditions and higher than the O:C ratios observed for highly aged ambient OA. The organic emissions of both burners have a very similar H:C ratio at a given O:C ratio and therefore fall on the same line in the Van Krevelen diagram.

A new method for an economic assessment of heat and power plants using dimensionless numbers

Abstract A comparison of economic data for different technologies and fuels is difficult due to the number of parameters that can alter the profitability of heat and power production. In addition, the variation of currency exchange rates considerably reduces the possibility of comparing plants in different countries. In the present study, a new method based on dimensionless costs is proposed to overcome these difficulties. Dimensionless capital costs C (including maintenance) and dimensionless fuel costs F are introduced by dividing the costs by the price for heat or electricity. In a diagram of C versus F the economy of different technologies can be compared. The diagram is divided into a profitable and an unprofitable area. The orientation of the data from one specific plant shows immediately whether the plant can be operated economically or not. Furthermore it can be seen by which factor either the fuel costs have to be reduced, or the price for electricity or heat has to be increased, or the capital and maintenance costs have to be reduced to reach the profitable area. The dimensionless diagram is independent from currency exchange rates. To demonstrate the application of the method, data from an economic assessment study of power production plants from biomass using pyrolysis, gasification and combustion technologies are presented.