Fuel-Flexible, Efficient and Sustainable Low Temperature Gasification

The project aims at testing the low temperature circulating fluidised bed (LT-CFB) gasification technology as a promising platform for improved utilisation of a variety of low-value and difficult biomass fuels from different sectors of society, with the goal of producing electricity and heat with a high efficiency to increase security of the national energy supply. Concurrently, the ash fraction extracted from the process will be developed into a product of high fertilizer value, thus significantly improving the technology’s economic feasibility and sustainability.
The thermal gasification technologies developed so far have all been limited to the use of slow growing biomass with low ash content, e.g. wood, but gasification of high-alkali biomass fractions has never before been a success. However, wood resources are scarce; therefore platforms converting a broad variety of biomass types to energy are desirable. The LT-CFB gasification technology is such a platform. The temperature is kept below the melting point of the ash components, i.e. max process temperatures around 700-750 °C. In this way, sintering of the ash and subsequent fouling (from e.g. potassium) or corrosion (from e.g. chlorine) of the plant unit operations are avoided, as these compounds will leave the process in solid form, deposited on ash particles. On the 500 kWthermal unit at DTU, hot gas efficiencies of 87-93% were achieved on various fuels. Based on these results, it is expected that the plant efficiency can reach >95% in full scale
Ashes from combustion of biomass are the oldest mineral fertilisers in the world. However, in industrialized societies, the places where nutrients are excreted and the places where they are required are no longer the same, the largest part ending up in domestic waste or excreta. Recirculation of nutrients to agricultural soils is especially important for those produced from essentially non-renewable resources such as phosphorous (P), where global commercially available stocks will eventually become scarce and are possibly depleted already in 50-100 years. Depletion is also likely to increase phosphate production costs by a factor 3 to 5 in this century. These challenges may be beyond comparison, because - unlike for fossil-fuel energy - there is no biological or technological substitute for P.