Optimization of a straw ring-die briquetting process combined analytic hierarchy process and grey correlation analysis method

•The method combining analytic hierarchy process and grey correlation analysis was proposed to optimize the straw ring-die briquetting process.•The priority weight of briquetting variables to optimization goal were obtained through analytic hierarchy process analysis.•The influences of each straw briquetting parameter to optimization objects were studied.

Briquetting of biomass is an attractive option to mitigate the energy crisis and environmental problems. A device to make this transformation is called ring-die briquetting system. In this research, a study on the optimization of a rice straw ring-die briquetting process combined analytic hierarchy process and grey correlation analysis was presented. Optimization variables include moisture content, particle size of the raw material, temperature, and the gap between the roller and ring-die while the average energy consumption, productivity, density and the rate of qualified biofuels were optimization objects. Results showed that moisture content and clearance between die and roller influenced productivity, energy consumption and product density significantly. The optimum process condition was obtained around moisture content of 20%, with a clearance between die and roller of 2.5 mm, die temperature of 120 °C and particle size between 20–35 mm. Experimental verification results indicated that this combination of factors produced a better overall pelleted fuel.