The HiEff-BioPower technology consists of highly interlinked system components, which have been developed, improved and combined in a technologically and economically efficient way. Therefore, the project demanded for an appropriately interlinked approach. A stepwise development procedure has been followed. Thereby, the main plant components (gasifier, gas cleaning unit, SOFC system) and the whole system were developed in parallel.
During the first two project periods, the work focused (i) on the development of the overall system approach, (ii) the definition of the framework conditions and interfaces regarding the single plant units, (iii) the development, design and manufacturing of the components, (iv) the assembly of a first testing plant consisting of a 400 kW gasifier, a full stream GCU and a 6 kW SOFC system operating in a product gas side stream extracted from downstream the GCU as well as on (v) test runs with this testing plant. As a basis for the system design two design fuels have been defined, namely a moist biomass fuel with about 30 wt% w.b. moisture content and a dry biomass fuel with about 5-10 wt% w.b. moisture content.
Regarding the fixed-bed updraft gasifier, R&D mainly focused on the development of measures to make it more fuel flexible and to adapt it for the integration into the whole system. To enhance fuel flexibility, a new fuel feeding system, a water cooled grate and primary air humidification as a measure for fuel bed temperature control have been implemented. Moreover, a new primary gas treatment zone based on partial oxidation (POX) has been developed and integrated directly on top of the gasifier fuel bed. In this zone the tar content of the product gas, which typically amounts about 100 g/Nm³ at fuel bed exit, could be reduced by more than 95% at operation temperatures of the POX zone of 850°C.
The core of the final GCU concept developed is a particle filtration unit based on high-temperature ceramic candle filters operating at 600°C and equipped with a reverse pulse cleaning system. Upstream of the filter an entrained flow sorption process is located, where NaHCO3 in a mixture with dolomite is applied for HCl removal. Downstream the filtration a fixed-bed dry sorption reactor utilising ZnO und CuO as sorbents has been implemented for H2S removal. This reactor operates at temperatures of 350 to 400°C. Lab-scale tests as well as test runs at the testing plant have been performed in order to investigate different options regarding tar reforming upstream the SOFC. It turned out that the application of a reformer based on catalytically coated wire meshes downstream the H2S removal reactor provides the best results. This reformer has been operated at about 650 to 700°C. To provide the anticipated temperature levels in the different reactors, the GCU also includes product gas cooling and heating steps. Within the final system design it has been possible to integrate these heat exchangers in a way that all off-heat can be utilised in a heat recovery system and that all heating energy needed is provided from process internal heat sources. With this gas cleaning concept is has finally been possible to achieve during comprehensive test runs the product gas quality needed for SOFC operation, which means HCl contents below 5 ppm, H2S contents below 1 ppm, dust contents below 1 mg/Nm³ and tar contents below 100 ppm.
Regarding the SOFC, two generations of stack modules have been developed and integrated in a SOFC system which has also been further developed and improved during the project. With this SOFC system it has been possible to produce more than 6 kWel at the test stand and 5.2 kWel at the testing plant. The results of the test runs performed however showed a rather fast degradation of the stacks leading to lower electricity output. Since the product gas quality has been on target, the reason for this degradation must be related to the SOFC system itself or to harmful components in the product gas that have not been identified yet. Further R&D will be needed to investigate this issue in detail.
Besides these technical tasks, also a strong focus was put on economic, environmental and market related issues. The compilation of a comprehensive market study regarding the market potentials and future trends for biomass CHP systems in Europe has been performed in order to identify the most relevant future markets for the new technology. Techno-economic analyses have been performed in order to check the economic viability of the new technology and to define cost targets for the single plant components. Moreover, environmental, economic and societal assessments have been performed which confirmed especially the environmental advantages of the HiEff-BioPower technology compared to other CHP systems.
