An efficient small-scale biomass cogeneration plant with silicon tetrachloride as working fluid: Techno-economic analysis

Biomass-fired Organic Rankine Cycles are a well-established solution for combined heat and power.. However, unlike other renewable technologies, the cost of generation from biomass has not decreased over time, because of high capital requirements and persistent biomass prices. To address this issue, Silicon Tetrachloride (SiCl 4 ) has been recently proposed as an innovative working fluid in high-temperature Rankine cycles, offering significant efficiency gains due to outstanding thermal stability, compared to typical organic fluids. This work explores the techno-economic feasibility of coupling a 1 MW gross electric SiCl 4 cycle with a biomass boiler. By utilizing commercial molten salts as the heat carrier, instead of conventional thermal oil, the system operates at a turbine inlet temperature of 525°C. The annual performance of the proposed CHP plant is assessed under both baseload and load-following scenarios within an existing district heating network. The cycle's off-design behaviour is analysed at part-load and full-electric conditions. With a condensing temperature of 100°C, the gross cycle efficiency reaches 32.3% at nominal power. While state-of-the-art ORC is economically viable only when they exceed 5’000 hours equivalent annual operating hours, the SiCl 4 plant is beneficial in contexts with limited cogeneration hours (mild climates) and significant heat rejection during the non-heating season.