Sustainability, Vol. 11, Pages 6433: Towards Circular Economy Solutions for The Management of Rice Processing Residues to Bioenergy via Gasification (Sustainability)

A techno-economic assessment of two circular economy scenarios related to fluidized bed gasification-based systems for combined heat and power (CHP) generation, fueled with rice processing wastes, was conducted. In the first scenario, a gasification unit with 42,700 t/y rice husks capacity provided a waste management industrial symbiosis solution for five small rice-processing companies (SMEs), located at the same area. In the second scenario, a unit of 18,300 t/y rice husks capacity provided a waste management solution to only one rice processing company at the place of waste generation, as a custom-made solution. The first scenario of a cooperative industrial symbiosis approach is the most economically viable, with an annual revenue of 168 €/(t*y) of treated rice husks, a very good payout time (POT = 1.05), and return in investment (ROI = 0.72). The techno-economic assessment was based on experiments performed at a laboratory-scale gasification rig, and on technological configurations of the SMARt-CHP system, a decentralized bioenergy generation system developed at Aristotle University, Greece. The experimental proof of concept of rice husks gasification was studied at a temperature range of 700 to 900 °C, under an under-stoichiometric ratio of O2/N2 (10/90 v/v) as the gasification agent. Producer gas’s Lower Heating Value (LHV) maximized at 800 °C (10.9 MJ/Nm3), while the char’s Brunauer Emmet Teller (BET) surface reached a max of 146 m2/g at 900 °C. Recommendations were provided for a pretreatment of rice husks in order to minimize de-fluidization problems of the gasification system due to Si-rich ash. With the application of this model, simultaneous utilization and processing of waste flows from various rice value chain can be achieved towards improving environmental performance of the companies and producing energy and fertilizer by using waste as a fuel and resource with value.