Optimization of a biomass briquette fuel system based on grey relational analysis and analytic hierarchy process: A study using cornstalks in China

Biomass, such as agricultural straw, can be converted into briquette fuel using technology to expand the possible applications of biomass and improve biomass utilization efficiency. The major machines required in a briquette fuel system, such as those used for drying, chopping, briquetting, and cooling, have become more efficient. However, a biomass briquetting fuel system requires special machines to reach a high character index, and all units in the system must match and be combined to produce an optimum system that satisfies multiple objectives, such as economy, environmental protection, stability, and large-scale operation. In this paper, a mathematical model for a synthesized evaluation was established according to theories of grey relational analysis (GRA) and the analytic hierarchy process (AHP). This model was used to select a biomass briquette fuel (BBF) system scheme considering hierarchies of economy, cleanliness and environmental protection, production capacity, product quality, and production stability, along with 20 other indices, including capital investment, dust content, drying capability, briquette rate, and the machine repair cycle. The most significant factors influencing each hierarchy were analyzed using a sensitivity analysis. Based on the GRA and AHP theories, an optimal scheme was selected for a fully operational 2 × 104 t/a cornstalk briquette fuel plant in China. The optimum scheme included six sets of briquetting machines with a capacity of 2 t/h + three sets of chopping machines with a capacity of 5 t/h + six sets of drying machines with a capability of 2 t/h + 1 set of cooling machines with a capacity of 12 t/h. The evaluated indices and weight coefficients were chosen objectively, and the comprehensive and technical performances of the selected BBF system scheme improved. These results provide a reference for the scheme selection and operation of large-scale BBF systems.