Analysis of critical process optimization in the black liquor gasification system

Abstract

The energy balance of the black liquor gasification (BLG) system, which is the core part in the Pulp-Syngas-Heat and Electricity combined cycle system, was analysed in this paper. Based on existing engineering parameters, we compared the energy consumption, conversion efficiency and energy cost of the BLG system under the different process conditions, in particular the air separation and concentration sections. Comparative analysis of these critical processes would facilitate the optimization of energy conversion efficiency and energy cost, as well as ascertain the influence of electricity and heat price on them. Results showed the drive combination of mechanical vapour recompression concentrating black liquor and electric driven preparation of oxygen (MVR-Motor) had the highest energy conversion efficiency of 73.18% but maximal energy cost. The drive combination of multi-effect evaporation concentrating black liquor and back pressure steam turbine preparation of oxygen (MEE-BPST) had the lowest energy cost, despite its energy conversion efficiency a little lower than MVR-Motor. For the drive combination of MVR-Motor, BLG system can get 224.32 kgce net energy output per 1000 kg straw pulp. Selection of reasonable process technology would promote the commercialization of BLG and the links to paper industry, biomass energy industry, and chemical industry, which benefits the control of black liquor pollution.