Background to the project
Small to medium scale combustion plants are destined to grow in importance
Small (<500 kWth) to medium scale (0.5-10 MWth) combustion plants are destined to grow in importance in a future decentralised, sustainable European energy supply scenario. The flexible utilisation of new, “difficult” biomass fuels in these plants is one of the major challenges for the coming years.
Challenging in terms of combustion behaviour and emissions
While large-scale plants have become individually tailored to cheaper, low-grade fuels, small-scale applications today rely on chemically untreated stem wood fuels (log wood, wood chips, wood pellets) and medium-scale applications additionally on selected cheaper assortments such as forest residues as well as waste wood. Other resource efficient fuels like wood from short rotation forestry (SRF – e.g. poplar and willow), herbaceous fuels (e.g. straw) as well as residues from agriculture and industry (shells, kernels, sludges etc.) will, however, inevitably become important also for these applications. However, due to their chemical composition, these fuels are challenging in terms of combustion behaviour and emissions. Increased S, Cl and N contents lead to increased gaseous HCl, SOx and NOx emissions. Elevated ash contents with high levels of e.g. K, Si and P cause problems with slagging, deposit formation and fine particulate emissions. Especially the latter is growing in relevance with the EU-Ecodesign directive (relevant for small-scale plants) and the Medium Combustion Plant (MCP) directive.
The development of cost efficient and general primary concepts for increased fuel flexibility is urged
However, in small-scale combustion, individually tailored solutions and expensive secondary measures for emission reduction are economically not viable and for medium-scale plants limited knowledge regarding the problems associated to the utilisation of “difficult” biomass fuels so far held back the development of flexi-fuel combustion systems, leaving the market sector almost unexploited. Therefore, the development of cost efficient and general primary concepts for increased fuel flexibility is urged in order to boost the innovation, enlarge market potential and deliver clean and efficient technology solutions.
The overall objective of BIOFLEX! is to increase fuel flexibility and innovation potential for the use of more difficult solid biomass fuels that do not compete with food production, in the small to medium-scale heat and power production sector.
- To further develop and implement fuel design and combustion system design related measures making the clean and efficient utilisation of bio-residues, by-products and other resource efficient energy crops, such as straw, grass, salix, horse manure beddings and sludges, possible in small-to-medium scale applications, at low emissions, high efficiencies and high availabilities, comparable to the Ecodesign and MCP directives.
- To develop guidelines for the design of appropriate low emission combustion technologies and for appropriate fuel design of the identified fuels.
- To perform testing of these measures in appropriately adapted testing plants in cooperation with furnace and boiler manufacturers.
To widely introduce new challenging biomass fuels into the small to medium-scale combustion market, further comprehensive R&D work on primary design concepts on fuels and combustion technology is needed. This project will take such actions by expanding the level of fundamental understanding of conversion of the new feedstocks, as well as developing and applying the ideas in practice.
Major R&D pathways
- To improve the understanding of ash transformation issues in combustion, by fundamental ash transformation research and by connecting ash transformation with the combustion.
- To investigate the application of additives and fuel blending in order to make new problematic feedstock better applicable in small to medium-scale biomass combustion systems.
- The further development of combustion technologies for the small (<500 kWth) as well as the medium (0.5 – 10 MWth) capacity range by means of primary measures such as
- New grate furnace and pulverised fuel burner technologies for ash rich difficult biomass fuels
- CFD optimised combustion chamber and advanced air staging concepts
- Improved control systems tailored to the demand of fuel flexibility
Progress beyond state-of-the-art
The progress beyond state-of-the-art of BIOFLEX! will be significant. Today, when utilising bio-residues, by-products and other resource efficient energy crops in state-of-the-art small and medium-scale biomass combustion plants, usually severe problems with slagging and deposit formation lead to unacceptably low plant availabilities, increased maintenance efforts as well as increased gaseous and PM emissions.
Within BIOFLEX! for the first time, solutions and technologies will be developed which make an application of these fuels in small and medium-scale plants possible
R&D on improved understanding of ash transformation and fuel blending/additivation
Will be performed to activate the great potential of fuel blending and additivation as a flexible fuel design measure to enable utilization of a broader range of biomass feedstocks. In the precedent ERA-NET Bioenergy project FutureBioTec, it was shown that fuel blending as well as the use of additives (e.g. clay minerals such as kaolin) in principle significantly decrease the alkali related fine PM emissions as well as slagging problems. Within BIOFLEX!, these measures will be analysed in depth for a broader fuel spectrum, and appropriate new concepts for fuel blending, additive selection as well as fuel/additive mixing ratios will result from the Project.
Ash transformation concepts will for the first time be implemented into realistic, combustion-related modelling
The ash chemistry will be coupled with combustion modelling, to investigate the fundamental ash transformation concepts derived and to enable predictions of slagging and alkaline release during combustion. The concept could serve as powerful tools in the pre-diction of the behaviour of the ash components in a fuel bed (a worldwide novelty).
New, beyond state-of-the-art combustion technologies
New, beyond state-of-the-art combustion technologies will be developed for a fuel-flexible combustion of conventional and new biomass fuels. At low emissions as well as efficiencies and plant availabilities comparable with present wood combustion systems. Moreover, within the project, present fixed-bed and pulverised fuel combustion concepts shall be further developed and optimised for the utilisation of the fuel assortments mentioned by applying novel and innovative CFD simulation tools as well as by test runs at appropriately adapted testing plants. Based on accompanying techno-economic analyses it shall also be shown that the resulting furnace concepts are economically affordable and commercially competitive in comparison with conventional wood combustion systems as well as with fossil fuel fired systems.