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Combustion processes

​Developing fluidized bed and grate combustion processes

Fluidized bed combustion offers superior fuel flexibility together with high efficiency and low emissions due to its moderate combustion temperature suitable for low NOx emissions and in-furnace sulphur reduction.

The nature of CFB combustion offers the use of a wide range of fuels from different types of coal to biomass and even waste-derived fuels. The high fuel flexibility gives economic advantages and gives a possibility to decrease CO2 in the co-combustion of coal and biomass. Grate combustion offers a medium-scale solution to utilise biomass fuels for local energy production. VTT offers pilot-scale experimental facilities and processes modelling services for boiler suppliers, power companies and investors to ensure the success of fuel portfolio changes and investments. 

VTT has unique pilot-scale fluidized bed and grate firing plants to study in-furnace combustion phenomena experimentally. A comprehensive process diagnostic of temperature and pressure together with on-line sampling of gas and solid matters makes it possible for study fuel combustion behaviour at pilot-scale. This, combined with process modelling tools developed for pilot scale and bench scale plants, enables systematic approach for the development of fluidized bed and grate combustion processes.

Our strenght is to combine experimental work, modelling and simulation tools

Our strength is to combine experimental results obtained from pilot- and bench-scale devices into modelling tools that have been developed to understand combustion phenomena in fluidized bed and grate combustion. The key issues to understand are materials behaviour inside the furnace, heat transfer phenomena, ash chemistry, emission formation, etc. We have also developed dynamic combustion process simulation based on the Apros simulator. Dynamic simulation enables us to study fuel-specific effects on process dynamics.

Recently we have started a new approach to further reduce CO2 emissions in power generation, aiming to integrate concentrated solar power into a CFB boiler. Our target is to achieve an emission limit below 500 g/kWh electricity in coal combustion.

Role of VTT’s experimental facilities fluidized bed process development

We have unique experimental facilities; CFB and BFB pilot plants with a fuel capacity of 50–100 kW and 20–30 kW respectively and grate firing pilot plant with fuel capacity 100 kW. We have developed 1D process models for our pilot plans to develop our understanding of process behaviour and to scale-up the results to large-scale boilers. A smaller bench-scale BFB/CFB device is used to produce parameters to process models from combustion sub-phenomena related to sulphur capture, NOx chemistry, material behaviour, etc.

Development of CFB combustion has been carried out in a wide international network under several EU-funded projects – HIPE CFB, CLEFCO, CFB800, FlexiBurn, O2GEN, On-Cord. There has been very strong industrial participation in the development to serve the needs of utility power generation operators as well as boiler suppliers.