Valorization of sugarcane biorefinery residues using supercritical water gasification: A case study and perspectives

The present study evaluates the use of supercritical fluid technology, particularly supercritical water gasification (SCWG), to add value to residues from a sugarcane biorefinery that produces first and second generation ethanol. This case study aims at elucidating how process system engineering tools such as thermal process integration, life cycle analysis, economic evaluation and multi-objective optimization can contribute to minimizing some future challenges of the industrial implementation of supercritical fluid-based technologies, which were discussed in the Workshop on Supercritical Fluids and Energy - SFE'13. In addition, this case study exposes future perspectives in terms of the requirements to further develop this field. The optimized solutions of the evaluated case showed that the SCWG process increases the overall efficiency of the process in terms of energy and carbon fixation. It decreases the CO2 equivalent emissions and it leads to a thermally self-sufficient process. The economic analysis showed a high investment cost but a feasibility of using the current market prices for the produced fuels and electricity. © 2014 Elsevier B.V. All rights reserved.

François Maréchal, Alberto Mian, Adriano Viana Ensinas

The present study evaluates the use of supercritical fluid technology, particularly supercritical water gasification (SCWG), to add value to residues from a sugarcane biorefinery that produces first and second generation ethanol. This case study aims at elucidating how process system engineering tools such as thermal process integration, life cycle analysis, economic evaluation and multi-objective optimization can contribute to minimizing some future challenges of the industrial implementation of supercritical fluid- based technologies, which were discussed in the Workshop on Supercritical Fluids and Energy – SFE’13. In addition, this case study exposes future perspectives in terms of the requirements to further develop this field. The optimized solutions of the evaluated case showed that the SCWG process increases the overall efficiency of the process in terms of energy and carbon fixation. It decreases the CO2 equivalent emissions and it leads to a thermally self-sufficient process. The economic analysis showed a high investment cost but a feasibility of using the current market prices for the produced fuels and electricity.

2015

Optimal design methods applied to solar-assisted hydrothermal gasification plants

Alberto Mian

The gasification of highly watered waste residues may help to reduce fossil fuels consumption, as well as emissions, all the while improving efficiency. The integration of supercritical gasification with solar energy may improve the performances of both new and existing plants. The design and optimization of such kinds of energy conversion plants requires to take into account the following aspects: renewable sources are intermittent, prices of fuels and materials are continuously fluctuating and are uncertain, the energy efficiency should be maximized and the capital and opeating costs should be minimized. The main goal of this thesis is to develop mathematical programming frameworks in order to solve the design, the scheduling and the Heat Exchanger Network Synthesis (HENS) of any industrial plant. In particular, the final goal is to apply the proposed methods to the design of a solar-assisted supercritical gasification plant. The methods are developed in order to propose strategies to account for uncertainty, sizing constraints, scheduling options and multi-period HENS. In order to apply the frameworks elaborated in this dissertation, a set of mathematical models is suggested. The goal is to describe the thermodynamics of the considered process units: supercritical water gasification, gas separation, solar energy conversion technologies and storage utilities are studied. The pre-design problem is first tackled by coupling an energy targeting model with a Global Sensitivity Analysis (GSA) method and a Monte Carlo (MC) simulation. Given a set of energy conversion options, the most promising energy conversion paths with respect to a set of uncertain parameters are identified while applying energy integration principles. The design problem is then tackled and the design, the scheduling, as well as HENS for multi-period operations are investigated. The result is a sequential mathematical programming algorithm for solving the problem. A decomposition approach is applied using a bi-level optimization strategy, where derivative-free optimization algorithms are coupled with derivative based, mixed integer linear and non linear models. The framework is tested on a literature example and on a large scale example in order to prove its effectiveness. The integration of thermal storage options is included in order to highlight the improvements that can be achieved with process heat recovery. The computation time problem is addressed and an alternative strategy to solve the same problem is put forward. Finally, the developed methods are coupled with a Multi-Objective Optimization algorithm and the multi-period design problem for designing a solar-assisted super-critical gasification plant is solved. It is thus demonstrated how the proposed methods can be successfully applied to industrial-scale problems. It remains that computational issues are problem-dependent and sensitive to the problem definition.

EPFL2016

Comparison of extraction techniques for product diversification in a supercritical water gasification-based sugarcane-wet microalgae biorefinery: Thermoeconomic and environmental analysis

François Maréchal, Adriano Viana Ensinas

This study presents a thermoeconomic and environmental assessment of the extraction of lipids and proteins from wet microalgal biomass in a 3G biorefinery by two different technologies: supercritical fluid extraction (SFE) and low-pressure solvent extraction (LPSE). Simulation tools were used to study a sugarcane biorefinery producing ethanol from sugarcane juice (1G) and bagasse (2G); the microalgal growth in an open pond; and the processing of microalgal biomass into lipids, proteins and synthetic natural gas (SNG). Supercritical water gasification (SONG) of microalgal biomass enables an increase in biofuel production of 10.2% MJ when no extraction process is considered and of 1.9% MJ when LPSE is considered. The heat demand of the proposed biorefinery with LPSE was increased by 87.8% compared with the demand of the sugarcane biorefinery without microalgal growth and processing. When the SFE process is considered, the heat demand of the overall process increased 3.2 times. SFE for wet microalgae processing is not economically attractive, as it increases the total investment by 71%. The CO2 flow used in the SFE process demonstrated to be a key factor in the thermoeconomic viability of the process. Regarding the wet processing of microalgae prior to SCWG, the best alternative studied was the use of LPSE technology. (C) 2018 Elsevier Ltd. All rights reserved.

ELSEVIER SCI LTD2018

Optimal design methods applied to solar-assisted hydrothermal gasification plants

Alberto Mian

EPFL2016