CFB offers superior fuel flexibility together with high efficiency and low emissions due to a moderate combustion temperature suitable for low NOx emissions and in-furnace sulphur reduction.
The nature of CFB combustion offers a use of wide range of fuels from different types of coal to biomass and even waste-derived fuels. The high fuel flexibility gives economic advantages and provides the possibility of reducing CO2 in co-combustion of coal together with biomass.
VTT has a unique CFB pilot plant to study in-furnace combustion phenomena experimentally. In-furnace measurements of temperature and pressure together with on-line sampling of gas and solid matters make it possible for a comprehensive understanding of fuel combustion behaviour under CFB conditions. This combined with process modelling tools developed for pilot-scale and bench-scale CFB plants enables a systematic approach to the development of the CFB combustion process.
Our R&D strenghts toward development of supercritical CFB’s
Our strength is to combine experimental results obtained from CFB pilot- and bench-scale devices into modelling tools that have been developed so as to understand combustion phenomena in CFB combustion. The key issues to understand are materials behaviour inside the furnace, heat transfer phenomena, ash chemistry, emission formation, etc. We have also developed a dynamic combustion process simulation based on the Apros simulator. Dynamic simulation enables us to study fuel specific affects on process dynamics. Recently we have started a new approach still to decrease CO2 emissions in power generation aiming to integrate concentrated solar power into CFB boiler. Our target is to achieve an emission limit below 500 g/kWh electricity in coal combustion.
VTT’s unique research facilities to serve industrial development
We have unique experimental facilities; CFB and BFB pilot plants with a fuel capacity of 50-100 kW and 20-30 kW respectively. We have developed 1D process models to our pilot plans to develop our understanding of process behaviour and to scale-up the results to large-scale fluidized bed boilers. A smaller bench-scale BFB/CFB device is used to produce the parameters to process models from combustion sub-phenomena related to sulphur capture, NOx chemistry, material behaviour, etc.
Development of CFB combustion has been done in a wide international network under several EU-funded projects – HIPE CFB, CLEFCO, CFB800, FlexiBurn, O2GEN. There has been very strong industrial participation in the development to serve the needs of utility power generation operators as well as boiler suppliers.