Innovative CHP Technologies

The utilisation of new biomass fuels and the development of next generation combustion systems should provide the basis for more cost efficient heat as well as combined heat and power production from biomass in the future. However, the CHP technologies presently available on the market are restricted to the large (steam cycles for plants >2 MWel) and medium (ORC processes for plants between 400 and 2,000 kWel) capacity ranges, while no appropriate technologies exist for the small capacity range, which is of special interest for decentralised CHP applications. In previous projects undertaken by BEST, a strong focus was placed on the development of a biomass CHP technology based on a Stirling engine. These R&D efforts have helped to bring this technology, which has the potential to cover a capacity range between 35 and 100 kWel, to the demonstration stage. The actual research strategy of BEST focuses for instance on the development of technologies, which can be applied in the capacity range between approximately 100 and 400 kWel, a capacity range which is not covered at present. In this capacity range, the application of micro gas turbines is currently the most promising approach, which also provides a high potential for new process developments. There is a considerable need for R&D on indirectly fired gas turbines, especially in the crucial step of high temperature heat exchange, in order to increase the inlet temperatures of the turbine and thereby increase the efficiency of the whole process. Since gas turbines typically show high exhaust gas temperatures (600°C and higher), combined cycles (e.g. coupling with an ORC process) provide options to significantly increase the electric efficiency of the process. Moreover, combinations of biogas fired micro gas turbines with biomass combustion plants offer a great potential for achieving high electrical and overall efficiencies.

In the larger capacity range, steam cycles have been commercially available for many years and show reliable performance, high availability and acceptable efficiencies. However, the application of new biomass fuels will require additional research in this field. R&D mainly focuses on the interface between the combustion part and the steam cycle, i.e. the boiler section. With respect to the characteristics of new biomass fuels, methods must be determined to optimise steam parameters without running into severe problems with deposit formation, corrosion and thus plant availability. A previous project dealt with the optimisation of steam parameters with respect to fuel properties, with a special emphasis placed on wood fuels. In the future, this research is to be extended to new biomass fuels. Moreover, an internally financed strategic research project at BEST dedicated to boiler tube corrosion will provide important information, strengthening the knowledge base in this field.