ENERGY OPTIMIZATION OF STEAM GASIFICATION IN A FLUIDIZED BED REACTOR BY ASPEN PLUS

Abstract

The gasification process is considered as an effective combustible gas production from municipal solid waste or biomass. Chemical reactions of this process can be separated into three reaction zones as pyrolysis zone, volatile combustion zone, and char gasification zone. The aim of this study was to optimize the required energy used in a steam gasification process by considering three operating parameters (gasification temperature, equivalence ratio, and steam-to-biomass ratio) in order to achieve an energy self-sufficient condition under the criteria that the carbon conversion efficiency must be more than 70 percentages, and carbon dioxide oxide gas is lower than 20 volumatic percentages. The simulation model of steam gasification process was done and validated with the experimental data according to the research by Nikoo & Mahinpey (2008). The series of RYIELD reactor, RGIBBS reactor, and RCSTR reactor represented all chemical reactions which occurred in fluidized bed gasifier. Forty-eight batches of simulation test run were set in order to perform energy optimization with several sets of operating parameters. Equivalence ratio was varied from 0 to 0.31, and steam-to-biomass ratio was varied from 0 to 4.49. Then, gasification temperature was properly selected in range of 600 – 1000 oC to obtain the energy self-sufficient condition. Finally, the optimum point of simulation test run is at gasification temperature is 911 oC, equivalence ratio is 0.18, and steam-to-biomass ratio is 1.78. This operating point gives the maximum of carbon conversion efficiency at 91.03 percentages, and carbon dioxide oxide gas is still in criteria at 15.18 volumatic percentages.