Process simulation for rice husk staging pyrolysis and gasification with steam

Biomass staging pyrolysis and gasification process can increase carbon conversion rate and reduce tar content by rising up temperature. This process uses part of the product gas for combustion in an external burner to generate high temperature anaerobic flue gas and provide heat for pyrolysis and gasification. This paper selected rice husk as the gasification material, and used Aspen Plus software to simulate the process of rice husk staging pyrolysis and gasification with steam. Heat recovery and utilization, and the recycling of part of the product gas were considered in the simulation model. The influence of the gasification temperature and the steam-to-biomass ratio on product gas component yield, the carbon conversion rate and low heat value of product gas were analyzed by simulation. Results show that: Heat self-sufficient of the staging pyrolysis and gasification process can be achieved by using 15.4%-20.5% of the total product gas for combustion. The amount of H₂ and CO in product gas and the carbon conversion rate increase with gasification temperature. Low heat value of the product gas reaches the minimum when the gasification temperature is 700°C, followed by gradually increase. Increasing the amount of steam intake will increase the amount of H₂ and CO₂ as well as the carbon conversion rate, but reduce the low heat value of the product gas. When gasification temperature ranges from 800°C to 1000°C, and w(H₂O)/w(B)>0.15(mass ratio of steam and biomass), the amount of CO decreases as the steam intake increases, meanwhile the carbon conversion rate is close to 100%.