Hydrogen-rich gas production by steam gasification of hydrochar derived from sewage sludge

Abstract

Steam Alkali catalyst Hydrogen Hydrothermal carbonization a b s t r a c tHydrothermal carbonization is an effective pretreatment for further thermal conversion of high moisture biomass without a high cost of a dehydration process. The current paper concerns the properties of hydrochar derived from hydrothermal carbonization of sewage sludge, and the feasibility of steam gasification of hydrochar for hydrogen-rich gas production was investigated. Sewage sludge derived hydrochar was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and inductively coupled plasma atomic emission spectroscopy to evaluate its feasibility for gasification application. The effect of reaction temperature, steam to biomass mass ratio, and addition of alkali catalysts on steam gasification characteristics of raw sewage sludge and corresponding hydrochar were evaluated, in terms of major composition of the produced gas, gas yield, gasification efficiency and energy density. The results showed that sewage sludge derived hydrochar was rich in hydrophilic functional groups and increased Fe, Ni, alkali and alkaline earth metals (i.e. K, Na, Ca, Mg), resulting in a higher hydrogen yield and energy efficiency than direct steam gasification of sewage sludge under identical conditions. In addition, hydrogen-rich gas production was also favored with the presence of alkali catalysts, especially for the hydrochar. The present study demonstrates that hydrothermal carbonization provides an effective pretreatment of sewage sludge for production of hydrogen-rich gas via steam gasification.

Gasification characteristics of hydrochar and pyrochar derived from sewage sludge

“…Steam gasification of the pyrochar and hydrochar was carried out in a laboratory-scale fixed-bed reactor system [15]. It is mainly composed of a quartz tubular reactor, steam generation kit, N 2 line, and a gas purification unit.…”

“…Argon was adopted as the carrier gas, and standard gas mixtures were applied for quantitative calibration. Gasification characteristics of the pyrochar and hydrochar were evaluated in terms of hydrogen yield, lower heating value (LHV) of the product gas and gasification efficiency [15,21]. Besides, an index of energy recovery efficiency (ERE) [22] was used in this work to evaluate the effect of two different pretreatments on the entire energy balance, which is calculated as:…”

“…Therefore, different gasification behavior of hydrochar derived from sewage sludge is expected to that of the hydrochar from lignocellulosic biomass. Our previous study [15] investigated the gasification behavior of the hydrochar derived from sewage sludge by hydrothermal carbonization. It was observed that compared to the raw material, the hydrothermally treated sewage sludge had improved gasification characteristics in terms of hydrogen-rich syngas production.…”

Renewable hydrogen for the chemical industry

“…43 This can be done by pyrolysis and/or gasification (Table 2). 44,45 Gasification is a welldeveloped process where hydrogen-rich fuel gas (CO, H 2 , and CH 4 ) is produced at 700-1200°C using gasification agents (O 2 , CO 2 , steam, and air). 16,20 Gasification with air produces a low-quality gas (4-7 MJ/m 3 HHV), whereas higher quality gas (∼10-18 MJ/m 3 HHV) can be obtained under more oxidative conditions, i.e., pure O 2 .…”

Obtenção de hydrochar a partir de carbonização hidrotérmica de cascas do fruto de Magonia pubescens A. St. Hil. Sapindaceae: Caracterização e avaliação em processo de adsorção

“…Os difratogramas das amostras são apresentados na Figura 5, por meio dos quais observa-se na casca in natura um pico definido em valores de 2θ: 22°-23°, o qual representam a fração de celulose cristalina [61,62]. Há ainda uma banda larga e discreta em ≈16°, que corresponde à fração amorfa de celulose, hemicelulose e lignina.…”