Hydrothermal liquefaction process of food waste in batch and continuous lab scale reactors

Due to the energy burden that represents the drying step, wet biomass is often underexploited for energy purpose. Indeed, this step represents one of the most energy consuming step in a thermochemical process and is often economically prohibitive. During hydrothermal liquefaction, conversion of biomass takes place at temperatures between 250 and 374 °C and at pressures above the saturation pressure to ensure that water remains in the liquid phase, typically above 100 bars, avoiding enthalpy energy penalties [1]. To avoid competitive use of land for food supply and excessive cost of entrance biomass, blackcurrant pomace and brewery’s spent grains have been selected and tested on liquefaction as food residues. Experiments have been carried out in a 600 mL batch reactor (PARR), allowing maximum temperature of 320°C and maximum pressure of 130 bars. Effects of operating parameters such as temperature and holding time, biomass pretreatment and reactor configuration are investigated on mass yields, aqueous phase composition and energy balance. Results obtained in the batch reactor constitute the reference of this study, in the comprehension of the mechanism of the liquefaction of food residues. Also, these results form the basis for a model to scale up the process, and are confronted to the results on a continuous lab scale plant. Please click Additional Files below to see the full abstract

Heat of reaction of hydrothermal liquefaction reactions

Wet waste streams include a wide variety of products such as food processing residues, sewage sludge but also the organic fraction of municipal solid waste. Humidity typically varies from 50 to above 90 %. Dewatering and drying is possible for most feedstocks but at a significant cost. Hydrothermal liquefaction produces a biocrude that can be further upgraded into biofuels. The conversion takes place at temperatures between 250 and 400 °C and at pressures above the saturation pressure to ensure that water remains in the liquid phase, typically above 100 bar [1]. Even though the basic principles of hydrothermal liquefaction are well known, there are still some significant scientific questions and technical issues. One of the important questions that remain is the heat of reaction and the heat balance of the reaction. Please click Additional Files below to see the full abstract

Kinetic Modelling for Hydrothermal Conversion of Food Wastes

A kinetic model was developed for the prediction of HTL product yields based on a chemical mechanism. The model was developed after experimental studies on food wastes and food processing wastes. The model parameters were determined by training the model on experimental data on HTL of food wastes. Two other models from the literature were also tested. The calculated yields were compared with a large range of experimental data from the literature. Yields of bio-oil and char can be predicted from the process conditions, temperature, holding time, dry matter content, and the biochemical composition of the resource. Differences in the experimental recovery procedure and polarity of the extraction solvent are taken into account. This study shows that a kinetic model based on compositions allows a more detailed representation of the hydrothermal reactions than models purely based on resources and products. The precision of any model remains, however, largely dependent on the quality of the input data

Bio-oil production from biogenic wastes, the hydrothermal conversion step [version 2; peer review: 2 approved]

Background: Food wastes are an abundant resource that can be effectively valorised by hydrothermal liquefaction to produce bio-fuels. The objective of the European project WASTE2ROAD is to demonstrate the complete value chain from waste collection to engine tests. The principle of hydrothermal liquefaction is well known but there are still many factors that make the science very empirical. Most experiments in the literature are performed on batch reactors. Comparison of results from batch reactors with experiments with continuous reactors are rare in the literature. Methods: Various food wastes were transformed by hydrothermal liquefaction. The resources used and the products from the experiments have been extensively analysed. Two different experimental reactors have been used, a batch reactor and a continuous reactor. This paper presents a dataset of fully documented experiments performed in this project, on food wastes with different compositions, conditions and solvents. The data set is extended with data from the literature. The data was analysed using machine learning analysis and regression techniques. Results: This paper presents experimental results on various food wastes as well as modelling and analysis with machine learning algorithms. The experimental results were used to attempt to establish a link between batch and continuous experiments. The molecular weight of bio-oil from continuous experiments appear higher than that of batch experiments. This may be due to the configuration of our reactor. Conclusions: This paper shows how the use of regression models help with understanding the results, and the importance of process variables and resource composition.  A novel data analysis technique gives an insight on the accuracy that can be obtained from these models

Process Integration of Lignocellulosic Biomass Pre-treatment in the Thermo-Chemical Production of F-T Fuels. Centralised Versus Decentralised Scenarios

The purpose of this study is to evaluate, in terms of process integration, the centralised and decentralised pre-treatment of lignocellulosic biomass for its thermo-chemical conversion into liquid fuels through gasification and Fischer-Tropsch (F-T) synthesis (biomass to liquids, BtL). The aim is to quantify the process integration benefits of a centralised configuration in comparison to the energy savings obtained through the transportation of a higher energy density fuel, in this case torrefied biomass instead of raw biomass. The analysis is carried out through the detailed energy and mass balances, and the pinch analysis of the centralised and decentralised configurations

Development of a kinetic model for HTL conversion of waste biomass

International audienceThe objective of this work is to develop a simulation tool in order to predict the HTL product distribution in term of aqueous phase, gas phase, bio-oil and bio-char for an organic waste based on it biochemical composition and the conversion conditions (temperature and residence time). A reaction scheme was proposed after compositional analysis of the resources and the reaction products. The kinetic parameter of this mechanism were optimized by minimizing the differences with the experimental yields of gas, aqueous phase, bio-oil and bio-char for 24 experimental points. Each point was produced from 2 to 4 experiments.The model is able to reproduce the evolution of the different product fraction with time except at the beginning between 0 and 20 min this is during the heat up time were the temperature is always changing leading to a non-stationery situation. This tool can be used for a process simulation in the prediction of product yields and. To obtain a more precise model, a work is ongoing in the laboratory with quantification of intermediate species in an objective of developing a comprehensive and predictive model of intermediate species or intermediate family of species.

Evaluation of the Heat Produced by the Hydrothermal Liquefaction of Wet Food Processing Residues and Model Compounds

Hydrothermal liquefaction has proven itself as a promising pathway to the valorisation of low-value wet food residues. The chemistry is complex and many questions remain about the underlying mechanism of the transformation. Little is known about the heat of reaction, or even the thermal effects, of the hydrothermal liquefaction of real biomass and its constituents. This paper explores different methods to evaluate the heat released during the liquefaction of blackcurrant pomace and brewers’ spent grains. Some model compounds have also been evaluated, such as lignin, cellulose and glutamic acid. Exothermic behaviour was observed for blackcurrant pomace and brewers’ spent grains. Results obtained in a continuous reactor are similar to those obtained in a batch reactor. The heat release has been estimated between 1 MJ/kg and 3 MJ/kg for blackcurrant pomace and brewers’ spent grains, respectively. Liquefaction of cellulose and glucose also exhibit exothermic behaviour, while the transformation of lignin and glutamic acid present a slightly endothermic behaviour

Thermo-economic analysis and multi-objective optimisation of lignocellulosic biomass conversion to Fischer-Tropsch fuels

This paper addresses the techno-economic evaluation and optimisation of processes converting lignocellulosic biomass into liquid fuels, through the development of a suitable framework and the modelling and design of Biomass to Liquids (BTL) processes. In particular, the focus is on the production of drop-in fuels through gasification and Fischer-Tropsch (FT) synthesis. Several conversion technologies are presented and evaluated in the literature, but the comparison of different options is hazardous because of the different assumptions and methodologies adopted in each study. A systematic and consistent approach is therefore developed to explore the trade-offs of alternative process configurations and of the operating conditions. The comparison presented in this study explores the trade-offs of different technological options in terms of competing economic and thermodynamic objectives. Results show that for 200 MWth biomass input plant capacities, production costs are in the range of 1.0-1.4 €/l for technologies producing up to about 0.5 kJFT/kJth and close to being neutral in terms of electricity balance. For technologies using electrolysis the conversion can increase to 0.8 kJFT/kJth with production costs of 1.8 €/l. The electricity storage capacity, in this case, is of 0.5 kJe/kJFT, corresponding to a net electricity requirement of about 0.4 kJ e/kJth

Development of a kinetic model for HTL conversion of waste biomass

International audienceThe objective of this work is to develop a simulation tool in order to predict the HTL product distribution in term of aqueous phase, gas phase, bio-oil and bio-char for an organic waste based on it biochemical composition and the conversion conditions (temperature and residence time). A reaction scheme was proposed after compositional analysis of the resources and the reaction products. The kinetic parameter of this mechanism were optimized by minimizing the differences with the experimental yields of gas, aqueous phase, bio-oil and bio-char for 24 experimental points. Each point was produced from 2 to 4 experiments.The model is able to reproduce the evolution of the different product fraction with time except at the beginning between 0 and 20 min this is during the heat up time were the temperature is always changing leading to a non-stationery situation. This tool can be used for a process simulation in the prediction of product yields and. To obtain a more precise model, a work is ongoing in the laboratory with quantification of intermediate species in an objective of developing a comprehensive and predictive model of intermediate species or intermediate family of species.

Analysis of Physicochemical Properties of Bio-Oil from Hydrothermal Liquefaction of Blackcurrant Pomace

International audienceBio-oils obtained from hydrothermal liquefaction of biomass are black viscous fuels with good heating values. This paper presents results of physical and chemical characterization of bio-oils produced by hydrothermal liquefaction of blackcurrant pomace. The oils are analyzed with standard normalized tests and compared to specifications required by commercialized biofuels and conventional fuels. Iodine value and total acid number are determined, showing relatively high values. GC/MS analysis demonstrates that bio-oil recovery by solvent extraction followed by subsequent evaporation of the solvent leads to the loss of some volatile compounds in the bio-oil. Thermogravimetric analysis are performed to study the volatility of HTL bio-oils, as well as to evaluate the carbon residue after evaporation. The viscosity of a bio-oil recovered by ethyl-acetate extraction was measured with a rotational viscometer at 25 degrees C, leading to a viscosity of 1.7 Pa.s. The results show furthermore that adding sodium hydroxide to the reaction medium has a limited influence on the properties of bio-oils. The choice of extraction solvent has conversely a significant influence on the quality of the produced oil. We demonstrate in this paper how standardized tests can be applied to hydrothermal bio-oils, to compare them with commercial fuels and evaluate the need for upgrading