Abstract
Abstract
The combined heat and power generation (CHP), based on the use of renewable energy sources, is an essential aspect of currently developing energy systems. Among the other renewable sources, biomass is characterized by high caloric value, wide availability, and low prices. This paper shows the operational aspects of the prototypical micro-scale CHP system powered by a straw-fired batch boiler and works according to the modified Rankine cycle. Based on the previously conducted studies, a dedicated construction of a 100-kW straw-fired batch boiler was designed and implemented. Thermal oil heated in the boiler is transferred respectively to the evaporator, superheater, and additional oil/water heat exchanger. The control of the system operation is realized using a dedicated automation system based on the programmable logic controller (PLC). Presented results include the impact of various fuel inputs on the thermal oil heating process. The average power transferred from the boiler to the thermal oil in the case of a single combustion process was ca. 69 MJ/h (consequently the amount of transferred energy was ca. 121 MJ). During the continuous combustion process, the average power was ca. 169 MJ/h and energy transferred from the boiler to the oil was ca. 542 MJ. The power generated in the power generator resulted mainly from three parameters: the actual steam pressure and steam flow as well as from the actual set of electric load. The maximum power in the case of operation without maximum power tracking was 825 W, while the maximum power obtained when maximum power tracking was used was ca. 1,150 W. Such a low value of electricity generation was a consequence of the system’s limitations (resulting e.g. in a significant drop in steam temperature and pressure in the steam bus). Finally, a list of possible modifications was given.