Scaling-up a biomass fired micro-CHP ORC for better performance towards commercialization

Microcogeneration utilizing Organic Rankine cycle technology is seen as a technology of vast potential, but commercialization attempts of many systems have shown how challenging it is to transform laboratory results into competitive products. Throughout the development, the authors’ collective focus on cogeneration from biomass, including very low grade one, for which organic Rankine cycle power systems appear as a suitable choice. In the past, at the Czech Technical University, the authors developed a 50 kWth 2 kWe unit that has undergone an on-site pilot installation. The economic parameters were however for many other applications prohibitive, especially with respect to the new legal requirements for biomass combustion. Therefore, in order to improve the economic performance, the system has been scaled up to 120 kWth and 6.2 kWe. This manuscript discusses the process of scaling up, designing, assembling and operating the upscaled combined heat and power unit. It includes modifications of previously applied technologies, especially regarding the boiler, an in house designed rotary vane expander and the overall system configuration. Furthermore, the authors present a comparison of the operational parameters of the new 6.2 kWe unit with the previous smaller 2 kWe unit, as well as a comparison of the implemented rotary vane expanders as a specific feature of the design. The comparison is performed on several thousand hours of experimental data for both units. From the total net combined heat and power production efficiency standpoint, the larger unit exceeds the former one by five percentage points, reaching 89%, even though the expander performance is slightly poorer with a nominal isentropic efficiency of 56%. However, the economic performance of the upscaled unit excels in comparison with the smaller one. Economic evaluation with a reference 120 kW biomass boiler concludes that an increase of the capital cost of the boiler by one third justifies the investment into the ORC CHP module     «

Microcogeneration utilizing Organic Rankine cycle technology is seen as a technology of vast potential, but commercialization attempts of many systems have shown how challenging it is to transform laboratory results into competitive products. Throughout the development, the authors’ collective focus on cogeneration from biomass, including very low grade one, for which organic Rankine cycle power systems appear as a suitable choice. In the past, at the Czech Technical University, the authors deve...     »