Energy analysis of a micro-scale biomass cogeneration system

Highlights: • Biomass-fired straw batch boiler was investigated dynamically. • Experiments were performed on the micro combined heat and power system. • A parametric study of the system was presented. • Simple Pay Back Time of the installation was between 1 and 15 years. • It is possible to obtain about 2 times higher electrical efficiency. Microscale heating devices are mandatory for users located in areas lacking of heating networks, especially in the rural ones. An interesting option for schools, farms, houses, and other users is to increase the functionality of heating devices with the power generation option. Such systems may operate on the basis of a simple Rankine Cycle fired by biomass. In this paper, the energy and economic parameters of a prototype micro-cogeneration system based on a 100 kW_th straw-fired boiler with a thermal oil jacket and a 14.8 kW steam engine were investigated. During the experimental tests, the power at a level of 1.1 kW_el was obtained by the prototype installation when steam pressure was equal to 4.3 bars and steam mass flow was about 105 kg/h. The relatively low electric power resulted from a limited heat exchange surface of the evaporator and, undersized nominal power of electricity generator and piping heat and pressure losses. On the other hand, the maximum measured pressure was 10 bars, when steam temperature was ca. 200 °C, pointing out that the installation has a significant potential of improvement from the power generation point of view. A dynamic simulation model was developed using TRNSYS software in order to investigate the system capabilities. This model was calibrated using experimental investigations, and further technical improvements of the installation were analyzed from energy and economic points of view. The possibility of integrating an absorption chiller in the system was also considered. As a result, the operation of the existing micro-cogeneration system was simulated and the operation parameters of the proposed micro trigeneration system were analyzed.