Study On Thermodynamic-economic-environment Evaluation Of Supercritical Water Treatment Of Papermaking Black Liquor

Black liquor is a kind of waste water produced in the process of papermaking,which poses a great threat to the environment and human health due to its high pH value,high COD concentration and pungent odor.As the main component of black liquor is lignin,it is essentially a kind of available biomass resources,so the recycling and harmless treatment of black liquor in papermaking is of great significance.The technology of supercritical water gasification and supercritical water oxidation is suitable for the treatment of black liquor with high water content without drying the material.The two technologies can respectively convert the black liquor into hydrogen-rich gas or heat energy to realize the green recycling of resources and the harmless treatment of waste.Based on the key research and development project of Hunan Province[2018SK2019],this study conducted research and evaluation on the black liquor supercritical water treatment process from the aspects of thermodynamics,economy and environment.The main innovations and research work are as follows:(1)The process model of black liquor supercritical water gasification and supercritical water oxidation system was established by Aspen Plus V11 software,and the influence of different operating parameters on the reaction characteristics and thermodynamic properties of the system was explored.The results show that when the gasification temperature increase from600°C to 800°C,the hydrogen yields,energy efficiency and exergy efficiency of the black liquor supercritical water gasification system have a large increase,while the increase range of energy efficiency and exergic efficiency of the black liquid supercritical water oxidation system is relatively small.(2)The techno-economic analysis of black liquor supercritical water gasification and black liquor supercritical water oxidation system was carried out by the total annual revenue requirement method,economic indicators such as the average annual output value and annual income of the system under the working condition of 600-800? were calculated.The results show that in the two systems,the lowest treatment cost of black liquor is 398.78 RMB/t,and the economic benefit of the black liquor supercritical water gasification system is much higher than that of the supercritical water oxidation system.(3)The life cycle assessment was used to evaluate the environmental impact of forestry subsystem,pulp and papermaking subsystem and black liquor supercritical water treatment subsystem,which were involved in the process of black liquor from generation to treatment.The environmental burdens of the subsystems were determined at 600-800? reaction temperature.The results show that with the increase of reaction temperature,the system to the environment comprehensive effect lowering,forestry subsystem is the whole life cycle of black liquor system is the main source of environmental burden.The forestry subsystem is the main source of environmental burden in the whole life cycle of black liquor system,followed by the pulp and paper subsystem,the black liquor supercritical water treatment subsystem impact is minimized.Meanwhile,supercritical water gasification system is better than that of supercritical water oxidation system of environmental benefits.