Thermochemical methods for the treatment of municipal sludge

Gasification has been increasingly seen as a method to convert solid fuel into combustible syngas. However, these applications require syngas with strict requirements and raw syngas often does not meet these requirements. Therefore, a form of syngas upgrading needs to be applied. One of the most common form of syngas upgrading is removal of CO2, which is often present in large concentrations in raw syngas. The currently existing CO2 removal technologies were either designed not with syngas in mind or for large scale industries, which makes them somewhat inefficient for application with gasification syngas. This calls for more research into efficient removal of CO2, from syngas. In this review, the application of deep eutectic solvent (DES) as one of the potential new absorbent for CO2 removal from gas streams and more specifically from syngas are discussed. DES has garnered attention due to its high CO2 absorption performance, process friendliness, and environmental friendliness. At present, most studies on DES are still limited to basic absorption behavior of the absorbent. This review aims to provide not just a clear picture of the current research situation for DES as CO2 removal absorbent, but also detail the possible research directions that might be taken for the development of DES as CO2 absorbent from syngas. To that end, this paper shall discuss the specific situation of gasification development, syngas utilization, and the current DES research situation including: its advantages compared to conventional absorbents, its current research situation, challenges, and possible future research directions.

Recent developments of deep eutectic solvent as absorbent for CO2 removal from syngas produced from gasification: Current status, challenges, and further research

Comprehensive experimental study on energy conversion of household kitchen waste via integrated hydrothermal carbonization and supercritical water gasification

Conversion of food waste to energy: A focus on sustainability and life cycle assessment

Metal-organic frameworks(MOFs) have attracted much attention as adsorbents for the separation of CO2 from flue gas or natural gas. Here,a typical metal-organic framework HKUST-1(also named Cu-BTC or MOF-199) was chemically reduced by doping it with alkali metals(Li, Na and K) and they were further used to investigate their CO2 adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction(XRD), thermo-gravimetric analysis(TGA)and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO2 storage capacity of HKUST-1 doped with moderate quantities of Li+, Na+and K+, individually, was greater than that of unmodified HKUST-1. The highest CO2 adsorption uptake of 8.64mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST-1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO2 than those of N2. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO2 after 10 cycles.

Alkali metal cation doping of metal-organic framework for enhancing carbon dioxide adsorption capacity

Hydrothermal carbonization of food waste after oil extraction pre-treatment: Study on hydrochar fuel characteristics, combustion behavior, and removal behavior of sodium and potassium.

Hazardous waste incineration fly ash (HFA) is high risk for the environment due to heavy metals leaching and other pollutants. Sintering treatment potentially reduces the mass and volume of HFA and immobilizes heavy metals in ceramic-like bodies. However, HFA contains a large amount of heavy metals, thus sintering at too high a temperature will lead to the volatilization of heavy metals. The low-temperature sintering behavior of HFA at different temperature (450 °C, 670 °C and 900 °C) and different atmospheres (21% O2, 47.3% O2, 60.5% O2 and 100% O2) was investigated in this study. The mass loss, morphology, bulk density, elemental composition, heavy metal leaching rate, and mineral phase transformation of sintered ash were experimentally tested. With increasing sintering temperature, more mass of HFA was lost and the leaching rate of heavy metals decreased. For instance, sintered at 450 °C, 670 °C and 900 °C under air, the mass losses were 4.30%, 6.58%, and 17.96%, the leaching rate of Pb were 19.37%, 2.74%, and 0.65%, respectively. Sintered ash became denser and formed ceramic-like particle due to thermal agglomeration and chemical reactions. The bulk density significantly increased, which was favorable to reduce space occupancy for fly ash landfill. Oxygen-rich atmosphere could make the fly ash denser and inhibit the volatilization and leaching of Pb. The obtained findings are beneficial for deep understanding of the sintering behavior of HFA at low-temperature.

Low-temperature sintering behavior of fly ash from hazardous waste incinerator: Effect of temperature and oxygen on ash properties

In order to study the transformation and distribution of sulfur element during supercritical water gasification (SCWG) of sewage sludge, sulfur contained products in different phase were detected in batch reactor. The XPS analysis showed that organic sulfur was the main part of sulfur compounds in sewage sludge. On the other hand, inorganic sulfur was dominated by SiS2, and SiS2 was subsequently converted into SiO2 and H2S during SCWG. The increase of temperature promoted H2S and SO2 yield but reduced their concentration. The addition of KOH could reduce the yield and concentration of H2S and SO2. The minimum concentration of H2S and SO2 was observed at 450 °C with KOH addition, which was 1313.94 ppm and 698.03 ppm, respectively. Sulfur compound in liquid was mainly found in the form of sulfate and its concentration decreased with increasing temperature.

Sulfur conversion and distribution during supercritical water gasification of sewage sludge

A two-step process for energy-efficient conversion of food waste via supercritical water gasification: Process design, products analysis, and electricity evaluation.

In this study, the effect of absorption pressure and temperature towards the CO2 absorption capacity and rate of choline chloride - monoethanol amine deep eutectic solvent (ChCl-MEA DES) was evaluated. Water mixing into ChCl-MEA DES was also examined as a method to improve CO2 absorption behavior. Equilibrium experiments were done in a batch reactor and the data was analyzed using response surface methodology (RSM). Results suggested that the dominant mode of CO2 absorption by ChCl-MEA DES was physical absorption. The maximum capacity of CO2 absorption obtained in this study was 0.379 mol-CO2/mol-DES from absorption at (10 bar, 40 °C) using DES with 50 %v water. Water mixing up to 50 %v was found to nearly double the CO2 absorption capacity of ChCl-MEA DES compared to neat DES. Study into CO2 absorption rate by ChCl-MEA DES found that it is mainly influenced positively by pressure and water content, while not significantly influenced by temperature. CO2 absorption rate of ChCl-MEA DES with 50 %v water was found to be on average twice of that of neat DES. It was also found that water content up to 50 %v does not change the mechanism of CO2 absorption by ChCl-MEA DES.

Study on the effect of operating parameters towards CO2 absorption behavior of choline chloride – Monoethanolamine deep eutectic solvent and its aqueous solutions

Caimeng Yu

Papers

Hydrothermal carbonization of food waste after oil extraction pre-treatment: Study on hydrochar fuel characteristics, combustion behavior, and removal behavior of sodium and potassium.

Low-temperature sintering behavior of fly ash from hazardous waste incinerator: Effect of temperature and oxygen on ash properties

Sulfur conversion and distribution during supercritical water gasification of sewage sludge

A two-step process for energy-efficient conversion of food waste via supercritical water gasification: Process design, products analysis, and electricity evaluation.

Study on the effect of operating parameters towards CO2 absorption behavior of choline chloride – Monoethanolamine deep eutectic solvent and its aqueous solutions