Deutsche Vereinigung für Verbrennungsforschung (DVV) – IFRF’s German National Committee – is a member of the German Federation of Industrial Research Associations (AiF), the leading national organisation promoting applied research and development benefiting Germany’s small and medium-sized businesses.  AiF provides public funds for research projects, with DVV carrying out such projects through its university and research organisation members.  DVV’s industry members provide consultancy to the projects throughout their duration.

New projects

1. Intensification of drying in drum-shaped convective dryers by optimising the influence of fixtures using the example of model materials and woody biomass

 Overview:

The thermal drying process often represents the most energy-intensive step in the use of moist biomass.  Therefore, the choice of process has a decisive influence on the achievable product quality.  In this sense, convective drum dryers have established themselves as versatile devices for drying moist biomass.  To achieve this, they are equipped with internal cross fittings and/or lifting shovels which cause the material to be dried to trickle down and spread.  This increases the heat and mass transfer and is often decisive for the overall performance of the drying apparatus and the achievable product quality in industrial practice.

In industry, convective drum dryers are usually designed purely empirically on the basis of existing designs and accrued experience – this is especially true for SMEs.  The design process often lacks a detailed understanding of the interrelationships relevant to heat and material transport and a quantitative assessment of the mechanical behaviour of the drying material under interaction with fixtures.  This makes it difficult to design convective drum dryers – particularly with regard to new products – which brings significant disadvantages to SMEs in particular.

In this context, this project aims to investigate the relationship between the mechanical behaviour at the cross fittings and the drying progress.  A numerical approach will be  developed and verified experimentally, which enables a reliable description of the movement behaviour and the drying progress.  This will create the basis for a predictively usable numerical approach that will allow the distribution of the material to be dried over the drum cross-section to be assessed and adjusted within an industrial context and, based on this, to effect optimal drying progress.  It is intended that the resulting tool can be used across industries in industrial applications for process optimisation of convective drying processes in drum systems, especially in SMEs.

Project contacts:

Technische Universität Berlin
Chair of Mechanical Process Engineering and Solids Processing (MVTA)
Prof. Dr.-Ing. Harald Kruggel-Emden
Ernst-Reuter Platz 1, Sekr. BH 11, 10587 Berlin, Germany

Otto-von-Guericke-Universität Magdeburg
Prof. Dr.-Ing. Eckehard Specht
Chair of Thermodynamics and Combustion (LTV)
Universitätsplatz 2, 39106 Magdeburg, Germany

2. Reduction of nitrogen oxide formation in the oscillating combustion of ammonia (AmOszi)

 Overview:

With climate change and the need for decarbonisation as central challenges of the 21^st century, many industries are looking for alternative options to provide heat at various temperature levels without emitting greenhouse gases (GHG) in a sustainable manner.  While ‘green’ electricity or hydrogen are being discussed as energy carriers for a wide spectrum of applications across all sectors, ammonia (NH₃) may also offer benefits for some applications, since it is easier to store and transport over long distances than hydrogen.  This makes ammonia particularly interesting for off-grid installations which cannot directly be supplied with hydrogen by pipeline yet still require a combustion process.

These advantages have to be balanced with the inherent conversion losses from hydrogen to ammonia when assessing the overall efficiency and economic viability of ammonia as an energy carrier or a fuel.  Another challenge is the potentially high emissions of nitrogen oxides (NO_X) if ammonia is burned directly.  Also, emissions of nitrous oxide (N₂O), also a potent greenhouse gas, are of concern.

These aspects are the focus of the ‘AmOszi’ project” in which Gas- und Wärme-Institut Essen e.V. (GWI) and the Institute for Technical Chemistry (ITC) at the Karlsruhe Institute of Technology (KIT) will investigate the potential benefits of the oscillating combustion approach to reduce NO_X formation when burning ammonia in furnace and steam generator applications, also in comparison to other primary measures for NO_X reduction.  For most technically relevant gaseous fuels, NO_X formation by the thermal formation mechanism is the most dominant formation pathway.  With ammonia, however, NO_X formation via fuel-bound nitrogen is expected to be the main route for NO_X formation, which may require different primary NO_X reduction methods than more conventional gaseous fuels.  Oscillating combustion is one potentially interesting approach to address this issue.

In the oscillating combustion processes, the flow rates of fuel, oxidiser (or both) are modulated in a regular pattern in order to generate fuel-rich and fuel-lean regions in the combustion chamber.  This should help reduce NO_X formation, similar to conventional staging.  Previous studies with the oscillating combustion of both natural gas and coal showed a reduced NO_X formation.  This may indicate that oscillating combustion could also be a way to reduce NO_X emissions from ammonia combustion to below the legal limits, despite the presence of fuel-bound nitrogen.

The project will start with detailed investigation of the chemical kinetics of ammonia – air combustion, both to analyse the impact of the very different fuel characteristics of ammonia (compared to natural gas), and as a prerequisite step for CFD simulations in order to identify suitable reduced reaction mechanisms for time-efficient modelling.  Kinetic investigation also serves to determine relevant time-scales and to estimate NO_X and N₂O emissions in qualitative terms, compared to methane combustion.

Based on these fundamental investigations, CFD simulations of the oscillating combustion of ammonia with air are to be carried out, both to help with the adaptations of burner systems for the test rigs, but also to provide a better understanding of the combustion, heat transfer and pollutant formation mechanisms, and determine suitable operational parameters, e.g. frequencies or swirl intensity.

Experimental investigations will be carried out, using GWI’s semi-industrial burner test rigs to recreate the situations in both, a thermal processing furnace and a boiler application respectively.  The performance of established primary NO_X reduction methods will be compared to that of oscillating combustion.  The project will be finalised by CFD simulations transferring the findings of the investigations on a semi-industrial scale to industrial scale applications.

Project contacts:

Gas- und Wärme-Institut Essen e.V.
Hafenstrasse 101, 45356 Essen, Germany
Dr.-Ing. Tim Nowakowski (tim.nowakowski@gwi-essen.de)

Karlsruher Institut für Technologie
Institut für technische Chemie
P.O. Box 3640, 76021 Karlsruhe, Germany

3. Development of flexible canal burner systems to integrate process gases and hydrogen within energy intensive industrial processes (EffiH2)

Overview:

In order to reach the current climate targets, the consumption of fossil fuels along with the emission of anthropogenic carbon dioxide (CO₂) needs to be reduced significantly.  This can only be achieved by using energy from renewable sources such as wind and solar energy or biomass.  One possibility is to produce hydrogen (H₂) via electrolysis using renewable electrical energy, e.g. from solar or wind power.  Afterwards, the hydrogen can be fed into the natural gas grid.

This scenario will lead to increasing hydrogen fractions in the natural gas grid, which will fluctuate regionally due to the highly volatile nature of the renewable energy sources.  These dynamical gas compositions will pose a huge challenge for technical combustion systems.  Especially for duct burners, the increasing and highly fluctuating hydrogen fractions add to the already demanding technical challenges.

The combustion of hydrogen provides significantly different characteristics than usual carbon-hydrates.  While the enrichment of smaller amounts of hydrogen in natural gas has only minor impacts on combustion behaviour and emissions formation, the operation with higher and more variable hydrogen fractions can pose a huge challenge.  The temperature of hydrogen/air flames is considerably higher than comparable natural gas flames, therefore hydrogen combustion leans to a higher thermal nitrogen oxide (NO_X) formation, while common approaches to reduce the NO_X formation can lead to thermal diffusive instabilities.  Safety aspects, such as the risk of flame flashbacks, also need to be considered, since hydrogen, depending on the equivalence ratio, provides an up to five times higher laminar flame speed than natural gas.  These effects of hydrogen enrichment make the design of fuel flexible burner systems a highly complex and demanding task.

Therefore, the target of this research project is the development of numerical and geometrical models and approaches for the design of duct burners.  The numerical combustion models should be able to reproduce the essential characteristics of the combustion and emissions formation at varying gas compositions.  By investigating generic and duct burners experimentally, the combustion models will be adjusted to feature critical design and operation parameters of duct burners at a specified range of gas compositions.  Based on the new numerical models, a geometrical approach for a flexible burner module will be designed, which can then be used as a base design for the combustion of hydrogen and process gases in duct burners.  Based on these results, specific and directly available guidance for SMEs will be established.

Project contacts:

Gas- und Wärme-Institut Essen e.V.
Hafenstrasse 101, 45356 Essen, Germany
M.Sc. Tim Schneider (tim.schneider@gwi-essen.de)

RWTH Aachen
Institut für Technische Verbrennung
Templergraben 64, 52056 Aachen, Germany